Surface treated structure, surface treated sheet, and propeller fan

Abstract

This surface-machined structure is provided with a plurality of blocks, which are three-dimensional objects arranged on a target surface, being a surface of a target object. The plurality of blocks are arranged spaced apart from one another in a second direction. Each of the plurality of blocks includes a plurality of fine grooves on an upper surface of the block. The plurality of fine grooves are arranged spaced apart from one another in the second direction, and extend from an upstream side toward a downstream side in a first direction. The width, in the second direction, of each of the plurality of fine grooves is less than the width, in the second direction, of a gap between the blocks. Two end portions, in the second direction, of the upper surface are higher than bottom portions of the plurality of fine grooves in a cross section through the block extending along a plane perpendicular to the first direction.

Description

[Technical Field]

[0001] This disclosure relates to a surface-treated structure, a surface-treated sheet, and a propeller fan. This application claims priority to Japanese Patent Application No. 2021-69498 filed on April 16, 2021, and Japanese Patent Application No. 2022-18395 filed on February 9, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, attention has been focused on biomimetics, a technology that mimics and utilizes the diverse functions of living organisms. Nature Technology (registered trademark) is known as an example of a manufacturing company that uses biomimetic technology in electrical products and other products.

[0003] Dimple processing is known as a method for processing the surface of rotatable blades. In devices that use blades that rotate due to fluids such as wind or running water, such as the generator exemplified in Patent Document 1, providing dimples on the rotating blades increases the surface area of ​​the blades and strengthens wind resistance, thereby increasing the rotation speed of the blades. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-3945 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in devices that move fluid by rotating blades powered by a motor, such as blowers and fans, providing dimples on the rotating blades may result in inefficient fluid movement. Specifically, the dimples increase the surface area of ​​the blades, increasing fluid resistance, which increases the rotational load on the blades and may hinder smooth rotation of the blades. Furthermore, the dimples may generate turbulence on the blade surface as the blades rotate, which may hinder the movement of fluid in a specific direction.

[0006] An object of one aspect of the present disclosure is to provide a surface-treated structure, a surface-treated sheet, and a propeller fan that allow efficient fluid movement. Note that this aspect of the present disclosure relates to biomimetics because it includes a technical idea that focuses on the structure of butterfly scales and fish scales. [Means for solving the problem]

[0007] A surface-processed structure according to one aspect of the present disclosure comprises a plurality of blocks, which are three-dimensional objects, arranged on a target surface, which is the surface of an object, the target surface extending in a first direction and a second direction perpendicular to each other, the plurality of blocks arranged in the second direction at intervals from each other, the upper surface of each of the plurality of blocks including a plurality of fine grooves, the plurality of fine grooves arranged in the second direction at intervals from each other and extending from the upstream side to the downstream side in the first direction, a groove-shaped block gap extending in the first direction is formed between two adjacent blocks among the plurality of blocks, the width in the second direction of each of the plurality of fine grooves is less than the width in the second direction of the block gap, and both ends in the second direction of the upper surface are above the bottoms of the plurality of fine grooves in a cross section of the block extending along a plane perpendicular to the first direction.

[0008] In a surface-treated sheet according to one aspect of the present disclosure, the surface-treated structure is provided on a substrate that can be placed on the target surface.

[0009] A propeller fan according to one aspect of the present disclosure comprises a rotating shaft and blades extending outward from the rotating shaft, the surface-treated structure is provided on the surface of the blade, and the first direction is a direction from the leading edge side to the trailing edge side of the blade. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a partially exploded side view of an electric fan equipped with a propeller fan. [Figure 2] FIG. 2 is a perspective view of the propeller fan as seen from the front side. [Figure 3] FIG. [Figure 4A] FIG. 4 is a cross-sectional view taken along the line BB in FIG. 3. [Figure 4B] This is a partially enlarged view of the front of the wing. [Figure 5] FIG. 2 is a partially enlarged perspective view of the surface-treated sheet. [Figure 6] FIG. 6 is a partially enlarged perspective view of the area enclosed by the dashed line in FIG. 5. [Figure 7A] FIG. 1 is an enlarged perspective view of one block. [Figure 7B] FIG. 7 is a partially enlarged perspective view of the area enclosed by the dashed line in FIG. 6. [Figure 8] FIG. 2 is a partially enlarged schematic plan view of the surface-treated sheet. [Figure 9A] FIG. 9 is a schematic front view of the surface-treated sheet shown in FIG. 8. [Figure 9B] FIG. 9 is a schematic side view of the surface-treated sheet shown in FIG. 8. [Figure 10A] FIG. 1 is a perspective view of a surface-treated sheet according to a first embodiment. [Figure 10B] 1 is a table showing the relationship between the surface-treated sheet and the target flow in Example 1. [Figure 10C] 1 is a table showing dimensions of the surface-treated sheet according to Example 1. [Figure 10D] FIG. 1 is a front view of a surface-treated sheet according to a first embodiment. [Figure 10E] FIG. 2 is a side view of the surface-treated sheet according to the first embodiment. [Figure 11A] FIG. 10 is a perspective view of a surface-treated sheet according to a second embodiment. [Figure 11B] 10 is a table showing the relationship between the surface-treated sheet and the target flow in Examples 2 and 3. [Figure 11C] 10 is a table showing dimensions of surface-treated sheets according to Examples 2 and 3. [Figure 12A] FIG. 10 is a perspective view of a surface-treated sheet according to a third embodiment. [Figure 12B] FIG. 10 is a front view of a surface-treated sheet according to a third embodiment. [Figure 12C] FIG. 11 is an enlarged perspective view of the block of the third embodiment as viewed from the downstream side. [Figure 13A] FIG. 10 is a schematic side view of a surface-treated sheet according to a first modified example. [Figure 13B] FIG. 10 is a schematic side view of a surface-treated sheet according to a second modified example. [Figure 13C] FIG. 10 is a schematic side view of a surface-treated sheet according to a third modified example. [Figure 13D] FIG. 10 is a schematic side view of a surface-treated sheet according to a fourth modified example. [Figure 13E] FIG. 10 is a schematic side view of a surface-treated sheet according to a fifth modified example. [Figure 13F] FIG. 10 is a schematic side view of a surface-treated sheet according to a sixth modified example. [Figure 14A] FIG. 13 is a schematic plan view of a surface-treated sheet according to a seventh modified example. [Figure 14B] FIG. 13 is a schematic plan view of a surface-treated sheet according to an eighth modified example. [Figure 14C] FIG. 13 is a schematic plan view of a surface-treated sheet according to a ninth modified example. [Figure 14D] FIG. 10 is a schematic plan view of a surface-treated sheet according to a tenth modified example. [Figure 15A] FIG. 23 is a schematic plan view of a surface-treated sheet according to an eleventh modified example. [Figure 15B] FIG. 23 is a schematic front view of a surface-treated sheet according to an eleventh modified example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0012] [Fan 1] The electric fan 1 will now be described. FIG. 1 is a partially exploded side view of the electric fan 1 equipped with a propeller fan 100. As shown in FIG. 1, the electric fan 1 includes a front guard 2, a rear guard 3, a main body 4, a stand 5, and the propeller fan 100. The main body 4 is supported by the stand 5 and houses a drive motor (not shown) inside. A rotating shaft 4A of the drive motor is provided on the front of the main body 4. A rotating shaft 110 of the propeller fan 100 (see FIG. 2, etc.) is fixed to the rotating shaft 4A using a screw cap 6.

[0013] The front guard 2 and rear guard 3 are provided to surround the propeller fan 100 fixed to the main body 4. The rear guard 3 is fixed to the main body 4 so as to cover the back side (negative pressure side) of the propeller fan 100. The front guard 2 is fixed to the rear guard 3 so as to cover the front side (positive pressure side) of the propeller fan 100. The stand 5 is provided for placing the electric fan 1 on a floor or the like, and supports the main body 4. An operating unit (not shown) is provided at a predetermined position on the stand 5 for turning the electric fan 1 on and off, switching the operating state, etc. The stand 5 may have a function for oscillating the electric fan 1 and a function for adjusting its height.

[0014] [Propeller Fan 100] The propeller fan 100 will now be described. FIG. 2 is a perspective view of the propeller fan 100 as seen from the front side. FIG. 3 is a front view of the propeller fan 100. As shown in FIGS. 2 and 3, the propeller fan 100 has a rotating shaft 110 and a plurality of blades 120. The rotating shaft 110 is a boss hub of the propeller fan 100 and has a generally cylindrical shape with a bottom. Each of the plurality of blades 120 has a smoothly curved plate shape. The plurality of blades 120 protrude radially outward from the outer circumferential surface of the rotating shaft 110. The plurality of blades 120 are arranged at equal intervals along the circumferential direction of the rotating shaft 110 and have the same shape. The propeller fan 100 of this example has seven blades 120.

[0015] Propeller fan 100 is driven by the drive motor described above and rotates in rotation direction A, which is counterclockwise when viewed from the front, around the axis of rotating shaft 110. That is, multiple blades 120 rotate in rotation direction A. As a result, air flows from the suction side, which is the rear side of propeller fan 100, toward the outlet side, which is the front side of propeller fan 100, and is blown toward the front of electric fan 1.

[0016] The detailed structure of the multiple wings 120 will now be described. Fig. 4A is a cross-sectional view taken along the arrow BB in Fig. 3. Fig. 4B is a partially enlarged view of the front surface 125 of the wing 120. In this example, the multiple wings 120 have the same shape, so only one wing 120 will be described. As shown in Figs. 2 to 4A, the wing 120 includes a leading edge 121, a trailing edge 122, and a peripheral edge 123.

[0017] The leading edge 121 is an edge portion of the blade 120 located on the downstream side in the rotation direction A. The leading edge 121 is curved so that its radially intermediate portion protrudes upstream in the rotation direction A. The trailing edge 122 is an edge portion of the blade 120 located on the upstream side in the rotation direction A. The trailing edge 122 is curved so that its radially intermediate portion protrudes upstream in the rotation direction A. The peripheral edge 123 is an edge portion of the blade 120 extending along the rotation direction A. The peripheral edge 123 connects the radially outer end of the leading edge 121 and the radially outer end of the trailing edge 122. As a whole, the distance between the leading edge 121 and the trailing edge 122 increases radially outward in the blade 120.

[0018] As propeller fan 100 rotates in rotation direction A, air flows from leading edge 121 to trailing edge 122 on blade 120. Front surface 125 of blade 120 is a concavely curved positive pressure surface. Back surface 126 of blade 120 is a convexly curved negative pressure surface. In the above configuration, when propeller fan 100 rotates, air flowing from leading edge 121 onto the blade surface of blade 120 flows from leading edge 121 in a generally circumferential direction and flows out from trailing edge 122.

[0019] In the propeller fan 100, a surface treated sheet 200 is installed on the front surface 125 and the rear surface 126, which are the blade surfaces of the blade 120. In this example, the surface treated sheet 200 is attached to almost the entire surface of the front surface 125 and almost the entire surface of the rear surface 126. Alternatively, the surface treated sheet 200 may be installed on one of the front surface 125 and the rear surface 126. The surface treated sheet 200 may be installed on a part of the front surface 125 or on a part of the rear surface 126.

[0020] 4B, the surface-treated sheet 200 is attached so as to be in surface contact with the front surface 125 of the blade 120 and extends along the front surface 125. In this example, the direction from the leading edge 121 toward the trailing edge 122, i.e., the direction in which air flows relative to the rotating blade 120, corresponds to a first direction described below. The radial direction of the blade 120 corresponds to a second direction described below.

[0021] [Surface Treatment Sheet 200] The surface-treated sheet 200 will now be described. FIG. 5 is a partially enlarged perspective view of the surface-treated sheet 200. FIG. 6 is a partially enlarged perspective view of the dashed-line frame shown in FIG. 5. Hereinafter, the upper side, lower side, lower left side, upper right side, upper left side, and lower right side in FIG. 5 are defined as the upper side, lower side, front side, rear side, left side, and right side of the surface-treated sheet 200, respectively. The example in FIG. 5 is a portion of the surface-treated sheet 200, measuring 2 mm in the front-to-back direction and 2 mm in the left-to-right direction. In FIG. 6, of the multiple blocks 500, only one block 500 on the front left side is shown with a fine groove 520.

[0022] 5 and 6, in the surface-treated sheet 200, a surface-treated structure 201 is provided on a substrate 202 that can be placed on a target surface, which is the surface of an object. In the following, to describe the surface-treated sheet 200 that is placed on the front surface 125 of the wing 120, the wing 120 is the target object and the front surface 125 is the target surface.

[0023] The surface-treated sheet 200 of this example is a thin, lightweight, flexible sheet. Specifically, the thickness of the surface-treated sheet 200 is less than 2000 μm, for example, approximately 100 μm. The substrate 202 may be formed of a material that can be fixed to a target surface by adhesion or welding, and includes, for example, at least one material selected from the group consisting of resin, rubber, and metal. The resin includes, for example, at least one material selected from the group consisting of polypropylene (PP), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), acrylonitrile butadiene styrene (ABS), and urethane. The rubber includes, for example, silicone rubber. The metal includes, for example, at least one material selected from the group consisting of aluminum and stainless steel. The substrate 202 is flexible enough to deform to fit the surface shape of the target surface, allowing for seamless surface contact with the target surface.

[0024] The surface-treated structure 201 has a plurality of blocks 500. The plurality of blocks 500 are three-dimensional objects arranged on a target surface, which is the surface of the target object, and are aligned in a first direction parallel to the target surface. The first direction may be a straight or curved direction. In this example, the surface-treated structure 201 is formed on a substrate 202. The plurality of blocks 500 are arranged on the target surface via the substrate 202. The front-rear and left-right directions of the surface-treated sheet 200 are approximately parallel to the surface direction of the target surface. The upper side of the surface-treated sheet 200 faces away from the target surface. The lower side of the surface-treated sheet 200 faces the target surface.

[0025] The multiple blocks 500 form multiple block rows 501. Each of the multiple block rows 501 consists of two or more blocks 500 lined up in a first direction. The multiple block rows 501 are arranged side by side in a second direction perpendicular to the first direction. The second direction may be a straight direction or a curved direction. Therefore, the multiple blocks 500 are two-dimensionally arranged side by side in the first direction and the second direction on the substrate 202.

[0026] In the propeller fan 100, the surface treated sheet 200 is attached to the front surface 125 of the blade 120 so that the front side of the surface treated sheet 200 faces the leading edge 121 and the rear side of the surface treated sheet 200 faces the leading edge 121. Therefore, as shown in Fig. 5, the rear direction of the surface treated sheet 200 is parallel to the first direction (see Fig. 4B). The left-right direction of the surface treated sheet 200 is parallel to the second direction.

[0027] As shown in Figure 4A, the blade surface of the blade 120 of this example curves from the leading edge 121 side to the trailing edge 122 side toward the front side of the blade 120. Therefore, as shown in Figures 4B and 5, the upward and downward directions of the surface treated sheet 200 are inclined relative to the front and rear directions of the blade 120, respectively. Specifically, the upward direction of the surface treated sheet 200 is inclined upstream in the first direction relative to the front direction of the blade 120.

[0028] 6, each of the multiple blocks 500 has an inclined surface 510 that extends from the upstream side to the downstream side in the first direction so that the distance from the target surface gradually increases. The inclined surface 510 is at least a part of the surface of the block 500 that faces upward. In this example, the entire top surface of the block 500 forms the inclined surface 510 that slopes upward toward the rear.

[0029] The inclined surfaces 510 of the blocks 500 are aligned on a single line V extending in the first direction. Specifically, in each of the block rows 501, the single line V extending in the first direction passes through the inclined surfaces 510 of all of the blocks 500 that make up the block row 501 in a planar view. The line V is an imaginary straight line or curve that extends parallel to the first direction. In the example of FIG. 6, the line V extending linearly backward passes through all of the blocks 500 in the block row 501 in a planar view.

[0030] The detailed structure of the plurality of blocks 500 will be described. Fig. 7A is an enlarged perspective view of one block 500. Fig. 7B is an enlarged perspective view of a part of the area enclosed by the dashed line in Fig. 6. In Fig. 7A, the fine grooves 520 provided in the block 500 are not shown.

[0031] The multiple blocks 500 may be made of any material that can be formed on the substrate 202, and may be made of the same material as the substrate 202 or a different material from the substrate 202. The multiple blocks 500 may be made by molding such as injection molding, or by removal processing such as milling, laser processing, or etching. In this example, multiple blocks 500 having the same shape are made by performing micro-processing by etching on the top surface of the substrate 202. Below, one block 500 will be described.

[0032] The inclined surface 510 functions to generate an airflow that flows in a first direction by coming into contact with the air that flows into the front surface 125 when the blade 120 rotates. In the example of Fig. 7A, the block 500 has a rectangular parallelepiped shape that is long in the first direction so that the inclined surface 510 can guide the air in the first direction over a longer distance. The inclined surface 510 is a flat surface that slopes upward toward the downstream side in the first direction.

[0033] The inclined surfaces 510 have a relatively large area so as to be in sufficient contact with the air flowing into the front surface 125. When the surface-treated sheet 200 is viewed in a plan view, the total area of ​​the multiple inclined surfaces 510 in the surface-treated sheet 200 is, for example, 60% or more of the total area. In this example, the length of the inclined surfaces 510 in the first direction is equal to the depth D, which is the length of the block 500 in the first direction. The length of the inclined surfaces 510 in the second direction is equal to the length of the block 500 in the second direction. The length of the block 500 in the second direction is equal to the groove spacing G2 of the block gaps 550 described below. The groove spacing G2 is the distance between two adjacent block gaps 550.

[0034] 7A , the inclined surface 510 is a plane that slopes linearly from the upstream end 511 at the front end of the inclined surface 510 to the downstream end 512 at the rear end of the inclined surface 510. Therefore, the height H2 of the inclined surface 510 is a minimum value Hmin at the upstream end 511 and a maximum value Hmax at the downstream end 512. In other words, the distance from the target surface to the inclined surface 510 is minimum at the upstream end 511 and maximum at the downstream end 512.

[0035] Height H2 of inclined surface 510 is equal to the height of block 500. The smaller height H2 of upstream end 511, the smaller the contact area between air flowing into block 500 from the upstream side in the first direction and front surface 521 of block 500. In this example, height H2 of upstream end 511 is the minimum value Hmin, so this contact area is suppressed and air can move smoothly over inclined surface 510.

[0036] In block 500, the inclination angle α of inclined surface 510 relative to the target surface is determined by the height difference and depth D of inclined surface 510. The larger the inclination angle α, the more air moving on inclined surface 510 can be moved to a position higher and farther from the target surface, but the contact pressure between the air and inclined surface 510 increases, which may result in a decrease in the air flow rate. The smaller the inclination angle α, the more effectively the decrease in the flow rate of air moving on inclined surface 510 can be suppressed, but the air may not be able to be moved to a position higher and farther from the target surface. From this perspective, the inclination angle α is within the range of 6 degrees to 27 degrees.

[0037] The size and shape of the inclined surface 510 are not limited to the above example. For example, the inclination angle α is not limited to the above range of 6 degrees to 27 degrees, but may be at least greater than 0 degrees and less than 45 degrees.

[0038] As shown in FIG. 7B , each of the multiple blocks 500 has multiple microgrooves 520 formed on the inclined surface 510. In other words, the upper surface of each block 500 includes multiple microgrooves 520. The multiple microgrooves 520 are aligned at intervals in a second direction perpendicular to the first direction and extend from the upstream side to the downstream side in the first direction. The multiple microgrooves 520 function to form an air layer within the microgroove 520 due to a relatively slow airflow. As a result, air passing near the top of the microgroove 520 can glide along the surface of the air layer formed within the microgroove 520. In other words, the multiple microgrooves 520 are provided to reduce the contact area between the air flowing along the inclined surface 510 and the inclined surface 510, thereby reducing the contact resistance to the airflow on the inclined surface 510 and allowing the airflow to flow smoothly.

[0039] In this example, the multiple microgrooves 520 extend to the same depth from the upstream end 511 to the downstream end 512 in the first direction on the inclined surface 510. Between two adjacent microgrooves 520 among the multiple microgrooves 520, rail-shaped convex portions 530 extending in the first direction are formed. In other words, the upper surface of each block 500 includes multiple convex portions 530 provided between two adjacent microgrooves 520 among the multiple microgrooves 520. Therefore, on the inclined surface 510, the multiple convex portions 530 and the multiple microgrooves 520 are alternately arranged. Air flowing into the inclined surface 510 flows in the first direction along the upper surfaces of the multiple convex portions 530. In this example, the multiple microgrooves 520 have the same shape, so only one microgroove 520 will be described.

[0040] The length of the microgroove 520 in the second direction is the groove width W1. As the groove width W1 becomes smaller, it becomes easier to form an air layer inside the microgroove 520, but it becomes more difficult to accurately fabricate the microgroove 520, and the contact area between the air and the inclined surface 510 becomes larger. As the groove width W1 becomes larger, it becomes easier to accurately fabricate the microgroove 520, but it becomes more difficult to form an air layer inside the microgroove 520, and air passing near the upper part of the microgroove 520 becomes more likely to flow in. When air flows into the microgroove 520, frictional resistance corresponding to the contact area between the air and the microgroove 520 is generated. From this perspective, the groove width W1 of the microgroove 520 is within a range of 0.5 μm to 600 μm.

[0041] The vertical length of the microgroove 520 is the height H1. The smaller the height H1, the easier it is to accurately fabricate the microgroove 520, while air passing near the top of the microgroove 520 more easily flows into the microgroove 520. The larger the height H1, the deeper the air layer in the microgroove 520, making it easier to form an air layer. However, if the height H1 is too deep, the air layer is formed at a deep position, causing resistance at the top of the microgroove 520 and making it difficult to accurately fabricate the microgroove 520. Furthermore, if the height H1 is large, the height of the protrusion 530 relative to its width increases, which may reduce the rigidity of the protrusion 530 and make it more likely to bend. If the protrusion 530 bends, the air layer in the microgroove 520 may be destroyed. From this perspective, the height H1 of the microgroove 520 is within a range of 0.5 μm to 300 μm.

[0042] The groove interval G1 is the distance between two adjacent microgrooves 520 and is equal to the length of the convex portion 530 in the second direction. As the groove interval G1 increases, it becomes easier to accurately form the multiple microgrooves 520, but the number of microgrooves 520 that can be formed on the inclined surface 510 decreases, resulting in a higher contact resistance to the airflow on the inclined surface 510. As the groove interval G1 decreases, the number of microgrooves 520 that can be formed on the inclined surface 510 increases, resulting in a lower contact resistance to the airflow on the inclined surface 510, but it becomes more difficult to accurately form the multiple microgrooves 520. From this perspective, the groove interval G1 of the microgrooves 520 is within a range of 1 μm to 800 μm.

[0043] The number of microgrooves 520, the groove width W1, the height H1, and the groove interval G1 are not limited to the above examples and may be values ​​different from the above ranges. The multiple microgrooves 520 are not limited to extending in the first direction over the entire inclined surface 510, and may extend in the first direction in a portion between the upstream end 511 and the downstream end 512.

[0044] The arrangement of multiple blocks 500 will be described. Fig. 8 is a schematic plan view partially enlarged of the surface-treated sheet 200. Fig. 9A is a schematic front view of the surface-treated sheet 200 shown in Fig. 8. Fig. 9B is a schematic side view of the surface-treated sheet 200 shown in Fig. 8. In the example of Fig. 8, four block rows 501 are arranged in the second direction, and in each block row 501, four blocks 500 are arranged in the first direction.

[0045] In each of the plurality of blocks 500, the entire inclined surface 510 is exposed on the upstream side of the block 500 in the first direction. Specifically, in the examples of FIGS. 8 and 9B , two blocks 500 adjacent to each other in the first direction among the plurality of blocks 500 are an upstream block 500A and a downstream block 500B located downstream of the upstream block 500A. When viewed from the rear surface 522 of the upstream block 500A, the entire inclined surface 510 of the downstream block 500B is exposed without being obstructed by other members.

[0046] Furthermore, the downstream end 512 of the inclined surface 510 in the first direction is the farthest from the target surface in the block 500. In other words, the downstream end 512 of the inclined surface 510 is at the highest position in the block 500.

[0047] Furthermore, upstream end 511 of inclined surface 510 in downstream block 500B in the first direction is closer to the target surface than downstream end 512 in the first direction of upstream block 500A. In other words, upstream end 511 of downstream block 500B is located lower than downstream end 512 of upstream block 500A.

[0048] In each of the plurality of block rows 501, a groove-shaped gap 540 extending in a direction intersecting the first direction is formed between two adjacent blocks 500 in the first direction among the plurality of blocks 500. In the examples of Figures 8 and 9B, a gap 540 extending in the second direction is formed between two adjacent blocks 500 in the front-to-rear direction in each block row 501.

[0049] A groove-shaped block gap 550 extending in a direction intersecting the second direction is formed between two adjacent blocks 500 among the plurality of blocks 500. In the example of Figures 8 and 9A, in two adjacent block rows 501, a block gap 550 extending in the first direction is formed between a block 500 in the left block row 501 and a block 500 in the right block row 501.

[0050] In this manner, among the plurality of blocks 500, two adjacent blocks 500 in the first direction are arranged side by side with a gap 540 therebetween, and two adjacent blocks 500 in the second direction are arranged side by side with a block gap 550 therebetween. Because the plurality of blocks 500 are spaced apart from one another in this manner, the plurality of blocks 500 can be produced more accurately and easily on the substrate 202 than, for example, producing the plurality of blocks 500 so that they are connected to one another.

[0051] 9A, the length of the block gap 550 in the second direction is the groove width W2. The block gap 550 has the function of forming an air layer between two blocks 500 adjacent to each other in the second direction. As a result, air passing near the top of the block gap 550 can glide along the surface of the air layer formed in the block gap 550. In other words, the block gap 550 is provided to reduce the contact area between the air passing near the top of the block gap 550 and the surface-treated sheet 200, thereby reducing the contact resistance to the airflow above the block gap 550 and allowing the airflow to flow smoothly.

[0052] The smaller the groove width W2, the easier it is to form an air layer in the block gap 550, but it becomes more difficult to accurately form the gap 550 and to line up multiple blocks 500 in the second direction. The larger the groove width W2, the easier it is to accurately form the block gap 550 and to line up multiple blocks 500 in the second direction, but it becomes more difficult to form an air layer in the block gap 550, and air passing near the top of the block gap 550 tends to flow in. When air flows into the block gap 550, frictional resistance occurs according to the contact area between the air and the block gap 550. From this perspective, the groove width W2 of the block gap 550 is within a range of 10 μm to 600 μm.

[0053] The groove width W1 in the second direction of each of the aforementioned multiple microgrooves 520 is smaller than the groove width W2 in the second direction of the block gap 550. Here, the flow velocity of the air flowing into the surface-treated sheet 200 varies depending on, for example, the rotation speed of the propeller fan 100. In grooves such as the microgrooves 520 and the block gap 550, the relationship between the flow velocity of the air toward the groove and the groove width affects whether an air layer can be effectively formed therein. If an air layer cannot be effectively formed inside the groove, air may flow into the groove, causing the groove to act as a resistance that impedes the air flow.

[0054] For example, suppose the flow speed range of the air flowing into the surface-treated sheet 200 is divided into three ranges: low speed, medium speed, and high speed. When the flow speed of the air flowing in is in the low speed range, the relatively wide block gaps 550 can form an air layer more effectively than the relatively narrow microgrooves 520. When the flow speed of the air flowing in is in the medium speed range, both the block gaps 550 and the microgrooves 520 can form an air layer more effectively. When the flow speed of the air flowing in is in the high speed range, the microgrooves 520 can form an air layer more effectively than the block gaps 550. In other words, regardless of the speed range of the air flowing in the surface-treated sheet 200, at least one of the block gaps 550 and the microgrooves 520 can effectively form an air layer. This surface-treated structure 201 can exhibit a friction-reducing effect over a wide range of flow speeds of the air flowing in.

[0055] The ratio of the height H1 to the groove width W1 of the microgroove 520 is referred to as the aspect ratio of the microgroove 520. The ratio of the height H2 to the groove width W2 of the block gap 550 is referred to as the aspect ratio of the block gap 550. The aspect ratio of the block gap 550 effective in the low-speed range may be smaller than the aspect ratio of the microgroove 520 effective in the high-speed range. In this case, the surface area of ​​the block gap 550 can be made smaller relative to the surface area of ​​the microgroove 520. Therefore, even if an air layer is not effectively formed in the block gap 550 in the high-speed range, the contact area with the air flowing into the block gap 550 can be reduced, thereby suppressing frictional resistance when the block gap 550 becomes a resistance.

[0056] In this example, the multiple blocks 500 are arranged so as to form multiple block gaps 550 that are continuously aligned in the first direction. The multiple block gaps 550 form a single fluid flow path extending in the first direction. Specifically, as shown in FIGS. 5 and 8, the multiple blocks 500 are two-dimensionally arranged in a lattice pattern on the substrate 202. Therefore, between two adjacent block rows 501, a fluid flow path is formed in which multiple block gaps 550 are continuously aligned in the first direction. The multiple microgrooves 520 provided on the upper surface of the blocks 500 and the fluid flow path are alternately aligned along the second direction. Air flowing through this fluid flow path flows smoothly in the first direction without meandering.

[0057] As shown in FIG. 9B, the length of the gap 540 in the first direction is the groove width W3. As will be described later, air flowing into the surface-processed sheet 200 from the upstream side in the first direction flows continuously along the inclined surfaces 510 of the multiple blocks 500 lined up in the first direction. The larger the groove width W3, the easier it is to line up multiple blocks 500 in the first direction. However, when air flows from the inclined surface 510 of the upstream block 500A to the inclined surface 510 of the downstream block 500B, some of the air may flow into the gap 540, reducing the volume of the airflow.

[0058] On the other hand, the smaller the groove width W3, the higher the possibility that adjacent blocks 500 will be connected in the first direction when manufacturing multiple blocks 500. However, even if adjacent blocks 500 are connected in the first direction, the function of flowing air in the first direction is not significantly impaired. From this perspective, the groove width W3 of the gap 540 is within a range of 300 μm or less.

[0059] The air flow in the surface-treated sheet 200 will now be described. As described above, when the propeller fan 100 rotates in the rotation direction A, air moving relative to the rotating blades 120 flows onto the blade surfaces of the blades 120. At this time, the air flows from the leading edge 121, which is downstream in the rotation direction A, to the front face 125 and the rear face 126. Below, the air flow in the front face 125 will be described, but the air flow in the rear face 126 is similar.

[0060] As shown in Fig. 8, as the blades 120 rotate, the surface-treated sheet 200 also rotates in the rotation direction A. In this example, as described above, the upward direction of the surface-treated sheet 200 is inclined toward the front side, which is the upstream side in the first direction, with respect to the front direction of the blades 120. Therefore, as shown in Fig. 9B, the surface-treated sheet 200 rotating in the rotation direction A moves toward the upper front side. Therefore, the air flowing into the front surface 125 moves relatively to the surface-treated sheet 200 so as to approach it from the upper front side.

[0061] In this case, air moves from the upstream side to the downstream side in the first direction in the surface-treated sheet 200 as follows. As shown in FIG. 8, in the surface-treated sheet 200, air flowing toward the surface-treated sheet 200 is branched into multiple main streams ST1 and multiple substreams ST2. In the multiple main streams ST1, most of the air flowing into the surface-treated sheet 200 flows above the multiple blocks 500 that occupy most of the surface-treated sheet 200 in a planar view. In the multiple substreams ST2, the remaining air flowing into the surface-treated sheet 200 flows on both the left and right sides of the multiple blocks 500 in a planar view. Therefore, above the surface-treated sheet 200, the flowing-in air flows in the first direction so that the main streams ST1 and the substreams ST2 alternate and line up on the left and right.

[0062] 8 and 9B, the multiple main streams ST1 are airflows formed corresponding to the multiple block rows 501, respectively. In each of the multiple main streams ST1, air flows from the upstream side to the downstream side in the first direction along the inclined surfaces 510 of two or more blocks 500 that make up the corresponding block row 501. Specifically, when the air flows along the inclined surface 510 of the upstream block 500A, it moves upward from the front surface 125 of the blade 120 as it moves downstream from the upstream end 511.

[0063] The inclined surface 510 of each block 500 is provided with the plurality of fine grooves 520 described above. The area of ​​the outer surface of the inclined surface 510 is small due to the presence of the plurality of fine grooves 520. The outer surface of the inclined surface 510 is substantially formed by the upper end surfaces of the plurality of convex portions 530. As described above, the groove width W1 of the plurality of fine grooves 520 is extremely narrow, so an air layer is formed therein that makes it difficult for air to penetrate. Therefore, the air flowing over the inclined surface 510 substantially comes into contact only with the outer surface of the inclined surface 510, thereby reducing the contact area between the inclined surface 510 and the air. The contact resistance applied to the airflow over the inclined surface 510 is reduced, thereby suppressing a decrease in the flow velocity of the main stream ST1.

[0064] The air then flows downstream, passing over downstream end 512 of upstream block 500A, and moves onto inclined surface 510 of downstream block 500B. In this example, the entire inclined surface 510 of downstream block 500B is exposed to the upstream block 500A, and downstream end 512 is the highest part of the upstream block 500A. The airflow continuously flowing above the upstream block 500A and downstream block 500B generates an air vortex E near the upper side of upstream end 511 of downstream block 500B due to the difference in elevation between downstream end 512 of upstream block 500A and upstream end 511 of downstream block 500B.

[0065] As a result, when main stream ST1 flowing along inclined surface 510 of upstream block 500A passes downstream end 512 of upstream block 500A, it slides over airflow vortex E and moves to inclined surface 510 of downstream block 500B. That is, airflow vortex E prevents main stream ST1 from flowing into gap 540 between upstream block 500A and downstream block 500B, thereby reducing the contact resistance applied to main stream ST1.

[0066] Furthermore, in this example, the upstream end 511 of the downstream block 500B is closer to the target surface than the downstream end 512 of the upstream block 500A. Therefore, the air flowing out from the downstream end 512 of the upstream block 500A can easily move to the inclined surface 510 of the downstream block 500B without interfering with the upstream end 511 of the downstream block 500B. Furthermore, because the gap 540 between the upstream block 500A and the downstream block 500B is extremely narrow, the air flowing from the upstream block 500A to the downstream block 500B is prevented from flowing into the gap 540.

[0067] In each block row 501, the air repeats the above-described movement, thereby continuously moving in a bouncing manner along the inclined surfaces 510 of two or more blocks 500 lined up in the first direction. On each inclined surface 510, the air does not move from the upstream end 511 to the downstream end 512, but moves from a position downstream of the upstream end 511 to the downstream end 512. This reduces the distance that the air moves in the first direction on each inclined surface 510, further reducing the contact resistance applied to the airflow on the inclined surface 510.

[0068] In this way, in each block row 501, the contact resistance applied to the airflow on the inclined surface 510 is relatively small, so that the main stream ST1 flows smoothly in the first direction. When the main stream ST1 flows from the upstream block 500A to the downstream block 500B, a decrease in flow velocity is suppressed by the influence of the airflow vortex E. The multiple main streams ST1 flow smoothly and stably while being suppressed from deviating from the first direction.

[0069] As shown in FIGS. 8 and 9A, the multiple substreams ST2 are airflows formed between the multiple block rows 501 in a plan view. In each of the multiple substreams ST2, air flows from the upstream side to the downstream side in the first direction along a fluid flow path formed near the top of the multiple block gaps 550 aligned in the first direction. The substream ST2 is sandwiched between two main streams ST1 flowing on both sides of the substream ST2. As described above, the block gaps 550 are wider than the microgrooves 520, and no airflow vortex E occurs in the block gaps 550. This causes a difference in flow velocity between the substream ST2 and the main stream ST1. In other words, the flow velocity of the substream ST2 differs from that of the main streams ST1 on both sides of the substream ST2, which prevents the substream ST2 from deviating from the first direction.

[0070] As a result, in the surface-treated sheet 200, air flows in a first direction due to multiple main flows ST1 and subflows ST2, and a different flow velocity distribution occurs in the second direction, which is the span direction. In other words, flow velocity stripes of relatively low-speed and high-speed layers alternate in the laminar boundary layer above the surface-treated sheet 200. The momentum of the airflow flowing in the first direction above the surface-treated sheet 200 is diffused in the span direction. This can slow the growth of turbulent regions compared to when a uniform flow flows above the surface-treated sheet 200.

[0071] As described above, the surface-treated sheet 200 having the above-described surface-treated structure 201 allows the plurality of main streams ST1 and substreams ST2 to move smoothly and stably in the first direction. By providing the surface-treated sheet 200 on the plurality of blades 120, the propeller fan 100 is able to rotate smoothly with reduced air resistance during rotation, and is also able to accurately blow air at higher speeds in the first direction.

[0072] An example of a method for designing the above-mentioned surface processed structure 201 will be described. In the following example, of the flows of fluids and flow velocities that may occur in the environment or product to which the surface processed structure 201 is applied, the flows that are the main target of the surface processed structure 201 are referred to as target flows. The surface processed structure 201 is designed with two flows of multiple flows with different flow velocities as target flows.

[0073] Since the surface-treated structure 201 of this example is applied to the blades 120 of the electric fan 1, multiple airflows with different flow speeds can be generated in the electric fan 1 depending on the operating mode. For example, the operating modes of the electric fan 1 include "strong fan" where the wind speed is high (e.g., 15 m / s), "medium fan" where the wind speed is medium (e.g., 10 m / s), and "weak fan" where the wind speed is low (e.g., 4 m / s). The surface-treated structure 201 is designed to suit two target flows corresponding to two of these operating modes.

[0074] The surface-engineered structure 201 has two types of grooves for controlling airflow: microgrooves 520 and block gaps 550. The microgrooves 520 are designed to match the faster of the two target flows. The block gaps 550 are designed to match the slower of the two target flows. This allows the surface-engineered structure 201 to smoothly deliver airflow, similar to the above embodiment, regardless of which of the two operating modes the electric fan 1 is in.

[0075] Example 1 An example design of the surface-treated structure 201 in Example 1 will be described. FIG. 10A is a perspective view of the surface-treated sheet 200 in Example 1. FIG. 10B is a table showing the relationship between the surface-treated sheet 200 in Example 1 and the target flow. FIG. 10C is a table showing the dimensions of the surface-treated sheet 200 in Example 1. FIG. 10D is a front view of the surface-treated sheet 200 in Example 1. FIG. 10E is a side view of the surface-treated sheet 200 in Example 1.

[0076] As shown in Fig. 10A, the surface-processed structure 201 of Example 1 has the same basic structure as the above-described embodiment. As shown in Fig. 10B, the surface-processed structure 201 of this example is designed in the following procedure, with the target flows being the airflow (flow velocity 15 m / s) in the "electric fan high" mode and the airflow (flow velocity 4 m / s) in the "electric fan low" mode of operation of the electric fan 1.

[0077] First step (determining the target value of pitch P corresponding to the fast target flow) A target value for the pitch P of the grooves is determined based on which of the two target flows has the faster flow velocity. In this example, a target value for the pitch P1 of the fine grooves 520 is determined based on the airflow of "electric fan high." As shown in FIG. 12D, the pitch P1 is equal to the combined length of the groove width W1 of one fine groove 520 and the length of one convex portion 530 in the second direction (i.e., the groove interval G1).

[0078] As an example, the target value of the pitch P can be calculated using the following (Equation 1) based on the relationship with the target flow. P=P´*v / u ··· (Number 1) In (Equation 1), P' is a dimensionless value of the pitch P, and in this example, P'=15 to 30. v is the kinematic viscosity coefficient, which in this example is the kinematic viscosity coefficient of air at 20°C (15.01 x 10 -6 (m / s)). u is the friction velocity of the target flow in the surface treated structure 201, which in this example is the flow velocity of 15 (m / s) at "high fan speed." As shown in FIG. 10B, in this example, based on (Equation 1), the target value of the pitch P1 of the fine grooves 520 is calculated to be in the range of 15 to 30 (μm).

[0079] Second step (determining the target value of pitch P corresponding to the slow target flow) A target value for the pitch P for forming grooves is determined based on the target flow with the slower flow velocity of the two target flows. In this example, a target value for the pitch P2 of the block gaps 550 is determined based on the airflow of "weak fan." As shown in FIG. 12D , the pitch P2 is equal to the combined length of the groove width W2 of one block gap 550 and the length of one block 500 in the second direction (i.e., the groove interval G2).

[0080] In this example, the target value of the pitch P2 of the block gaps 550 is calculated based on (Equation 1). In this case, u is the flow velocity of 4 (m / s) for "weak fan." As a result, as shown in FIG. 10B, the target value of the pitch P2 of the block gaps 550 is calculated to be in the range of 56 to 112 (μm).

[0081] Third step (determining the number of microgrooves 520) The number of microgrooves 520 to be provided in each block 500 is determined. The number of microgrooves 520 to be provided in each block 500 is at least three, and more preferably five or more. As shown in Fig. 10D, in this example, five microgrooves 520 are provided in each block 500.

[0082] Fourth step (determining the size of the fine groove 520) The groove width W1 of each microgroove 520 is determined. As shown in FIG. 10D , one microgroove 520 and one convex portion 530 are arranged side by side in the second direction at one pitch P1. Here, when the groove width W1 is relatively large and the groove interval G1 is relatively small, the proportion of the microgrooves 520 on the inclined surface 510 of the block 500 increases, making it easier to suppress frictional resistance to the flow of fluid. From this perspective, the groove width W1 is larger than the groove interval G1. In other words, the width in the second direction of each of the multiple microgrooves 520 is larger than the width in the second direction of each of the multiple convex portions 530.

[0083] The multiple protrusions 530 provided on each block 500 include two first protrusions that form both end portions 513 of the upper surface of the block 500 in the second direction, and multiple second protrusions that are different from the two first protrusions. In other words, the multiple second protrusions are arranged between the two first protrusions. Above each first protrusion, a boundary region BR is formed between the main stream ST1 and the substream ST2. The boundary region BR is a region where the flow velocity changes along the second direction so that the main stream ST1 and the substream ST2 switch. The boundary region BR suppresses mutual interference between the main stream ST1 and the substream ST2, stabilizing the overall airflow.

[0084] Here, it is preferable to generate momentum diffusion of each airflow so that the main stream ST1 and the substream ST2 flow stably without meandering. To efficiently generate this momentum diffusion, it is preferable that the flow velocity between the main stream ST1 and the substream ST2 change abruptly in the boundary region BR, so it is preferable that the boundary region BR is narrow. The size of the boundary region BR depends on the wall width G10, which is the length of each first convex portion in the second direction. From this perspective, the wall width G10 is less than the groove width W1 of the fine groove 520.

[0085] On the other hand, because the first convex portions are part of the wall portions that form the microgrooves 520, if the thickness of the first convex portions is too small, durability may be impaired or accurate manufacturing of the first convex portions may become difficult. From this perspective, the wall width G10 is equal to or greater than the thickness of the second convex portions (groove spacing G1). In other words, the width in the second direction of each of the two first convex portions is equal to or greater than the width in the second direction of each of the plurality of second convex portions.

[0086] In this example, the pitch P1 is set to 15 (ms) within the range of 15 to 30 (μm), which is the target value for the pitch P1 determined in the first step. Based on this, the groove width W1 is set to 10 (ms) and the groove spacing G1 is set to 5 (ms). The wall width G10 is also set to 5 (ms), the same as the groove spacing G1.

[0087] Here, in order to suppress the frictional resistance to the airflow, it is necessary to suitably design the aspect ratio of the groove (i.e., the ratio of height H to groove width W). The grooves to be designed in this example are fine grooves 520 and block gaps 550. Height H can be calculated using the following (Equation 2). H=H´*v / u ··· (Number 2) In (Equation 2), H' is a dimensionless version of the height H. v and u are the dynamic viscosity coefficient and friction velocity, as in (Equation 1). The aspect ratio of the grooves (ie, height H / groove width W) is in the range of 0.5 to 0.7 from the viewpoint of reducing fluid resistance.

[0088] In this example, the groove shape, which is the shape of the vertical cross section of the microgroove 520, is a square shape that forms a rectangle when viewed from the first direction. As shown in Fig. 10C, in order to suppress the frictional resistance of the airflow flowing along the microgroove 520, the aspect ratio of the microgroove 520 (i.e., height H1 / groove width W1) is set to 0.5. Once the groove width W1 of the microgroove 520 is determined, the height H1 of the microgroove 520 can be calculated by multiplying the groove width W1 by 0.5. Since the groove width W1 is 10 (ms), the height H1 is set to 5 (ms).

[0089] Fifth step (determining the size of the block gap 550) Once the number of microgrooves 520, groove width W1, groove interval G1, and wall width G10 are determined as described above, it is possible to calculate the length of block 500 in the second direction (i.e., groove interval G2). As shown in Fig. 10C, in this example, the groove interval G2 is determined to be 80 (µm) corresponding to the five microgrooves 520 and six protrusions 530 provided in block 500.

[0090] Furthermore, within the range of 56 to 112 (μm), which is the target value of the pitch P2 determined in the second step, a value that satisfies the following first and second conditions is determined as the pitch P2.

[0091] The first condition will be explained. The pitch P2 is a value that satisfies the condition that "the groove width W2 of the block gap 550 is larger than the groove width W1 of the fine groove 520." This condition is synonymous with the width of each of the plurality of fine grooves 520 in the second direction being smaller than the width of the block gap 550 in the second direction. The groove width W2 corresponds to the difference between the pitch P2 and the groove interval G2. In other words, the pitch P2 should be a value that is larger than the sum of the groove interval G2 and the groove width W1.

[0092] When the pitch P2 satisfies the first condition, a flow velocity difference is likely to occur between the main flow ST1 caused by the fine grooves 520 and the secondary flow ST2 caused by the block gaps 550. In this example, since the groove spacing G2 of the block gaps 550 is 80 (μm) and the groove width W1 of the fine grooves 520 is 10 (ms), the pitch P2 needs to be greater than 90 (μm).

[0093] The second condition will now be explained. The pitch P2 is a value that satisfies the condition that "the groove width W2 of the block gap 550 is smaller than the sum of the groove widths W1 of the multiple microgrooves 520 provided in one block 500." This condition is synonymous with the width of the block gap 550 in the second direction being less than the sum of the widths of the multiple microgrooves 520 in the second direction. In other words, the pitch P2 needs to be less than the sum of the groove interval G2 and the sum of the groove widths W1 of the microgrooves 520 in one block 500.

[0094] By satisfying the second condition, the width of the main flow ST1 can be made wider than the width of the side flow ST2, resulting in a surface-finished structure 201 that is effective overall in high-speed ranges. In this example, there are five microgrooves 520, and the groove width W1 is 10 ms, so the sum of the groove widths W1 of the microgrooves 520 is 50 ms. The pitch P2 should be less than 130 μm, which is the sum of the groove widths W1 plus the groove spacing G2 of 80 μm.

[0095] Therefore, in this example, the range of the target value of the pitch P2 that satisfies the first and second conditions is 90 to 112 μm. The pitch P2 may be determined within this range, but as shown in FIG. 10C, the pitch P2 is assumed to be determined to be 112 μm. In this case, the groove width W2 of the block gap 550 is 32 μm.

[0096] · Sixth step (determining the aspect ratio of the block gap 550) As described above, the aspect ratio of block gap 550 (i.e., height H2 / groove width W2) may be 0.5 to 0.7 from the viewpoint of reducing fluid resistance. Here, as shown in FIG. 10E, since the upper surface of block 500 is inclined surface 510, height H2 of block 500 increases in the first direction. Accordingly, the aspect ratio of block gap 550 also gradually increases from the upstream side to the downstream side in the first direction. In other words, unlike microgroove 520, the aspect ratio of block gap 550 changes in the first direction.

[0097] To suppress the frictional resistance of the block gap 550, the aspect ratio of the block gap 550 at the upstream end should be 0.5 or less and the aspect ratio of the block gap 550 at the downstream end should be 0.7 or more. In other words, the aspect ratio of the block gap 550 should increase in the first direction so as to straddle the range of 0.5 to 0.7. The height H2 of the block 500 should be determined so as to satisfy this condition.

[0098] In this example, the aspect ratio of the upstream end of the block gap 550 is determined by the groove width W2 (32 μm) and the height H2 (i.e., minimum value Hmin) of the upstream end 511 of the block 500. The minimum value Hmin of the block 500 needs to be 16 μm or less so that this aspect ratio is 0.5 or less. On the other hand, the aspect ratio of the downstream end of the block gap 550 is determined by the groove width W2 (32 μm) and the height H2 (i.e., maximum value Hmax) of the downstream end 512 of the block 500. The maximum value Hmax of the block 500 needs to be 22.4 μm or more so that this aspect ratio is 0.7 or more.

[0099] However, if the aspect ratio of the block gap 550 is excessively large or small, the function of the block gap 550 may not be fully realized. Therefore, the aspect ratio of the block gap 550 may have a lower limit of 0.3 and an upper limit of 2.5. In this example, the minimum value Hmin of the block 500 is set to 10 μm so that the aspect ratio at the upstream end of the block gap 550 is approximately 0.3. The maximum value Hmax of the block 500 is set to 60 μm so that the aspect ratio at the downstream end of the block gap 550 is approximately 1.85. As a result, as shown in FIG. 10C , the aspect ratio of the block gap 550 increases from approximately 0.3 to approximately 1.85 in the first direction.

[0100] In the above-described block 500, the height difference S of the inclined surface 510 is the difference between the maximum value Hmax and the minimum value Hmin, i.e., 50 μm. As described above, the inclination angle α of the inclined surface 510 is determined by the height difference S and the depth D of the inclined surface 510. That is, the depth D of the inclined surface 510 may be determined by the height difference S and the inclination angle α of the inclined surface 510. The inclination angle α may be determined within a range of 6 degrees to 27 degrees, but in this example, the inclination angle α is set to 14 degrees and the depth D is set to 100 μm. In this case, since the depth D is greater than the height H2 and the groove spacing G2, the block 500 is elongated in the first direction in which the airflow flows. Note that the height difference S of the inclined surface 510 and the aspect ratio of the block gap 550 may be suitably designed by adjusting the inclination angle α and / or the depth D.

[0101] Seventh step (determining the size of the gap 540) 10E, a groove-like gap 540 extending in the second direction is formed between two adjacent blocks 500 in the first direction among the plurality of blocks 500. The gap 540 is provided between two adjacent blocks 500 in the first direction. When the groove width W3 of the gap 540 and the height difference S of the inclined surface 510 are approximately equal, an air vortex E (see FIG. 9B) is likely to be generated effectively. For example, when the groove width W3 is in the range of 0.75 to 1.25 times the height difference S, the groove width W3 and the height difference S are approximately equal.

[0102] 10C, the groove width W3 is set to 40 (μm), which is approximately equal to the height difference S (50 μm). In other words, the height difference S of the block 500 that is upstream in the first direction of the two blocks 500 is approximately equal to the width of the groove-shaped gap 540 in the first direction.

[0103] -Example of creation and use of surface processing structure 201 Based on the design values ​​determined in the first to seventh steps (see FIG. 10C ), a surface-processed structure 201 is fabricated in which a plurality of blocks 500 are arranged two-dimensionally. In the surface-processed structure 201 fabricated in this manner, a plurality of microgrooves 520 are arranged on the upper surface of the blocks 500 at a first pitch corresponding to a first flow velocity that is relatively faster of two different flow velocities. A plurality of block gaps 550 are arranged on the upper surface of the blocks 500 at a second pitch corresponding to a second flow velocity that is relatively slower of the two different flow velocities. In this example, the first pitch corresponding to the first flow velocity is pitch P1, which corresponds to the high-speed airflow of "electric fan high." The second pitch corresponding to the second flow velocity is pitch P2, which corresponds to the low-speed airflow of "electric fan low."

[0104] By attaching the surface-treated sheet 200 having the above-described surface-treated structure 201 to, for example, the blades 120 of the electric fan 1, the following effects are achieved. When the operation mode of the electric fan 1 is "high fan", a high-speed target flow flows along the surface-treated structure 201. Because each microgroove 520 is designed to match the high-speed target flow, an air layer is effectively formed by each microgroove 520, significantly reducing contact resistance with the main stream ST1. On the other hand, when the operation mode of the electric fan 1 is "low fan", a low-speed target flow flows along the surface-treated structure 201. Because each block gap 550 is designed to match the low-speed target flow, an air layer is effectively formed by each block gap 550, significantly reducing contact resistance with the secondary stream ST2.

[0105] In this way, the surface-treated structure 201 is designed to match the two operating modes of the electric fan 1, and therefore, in either the "electric fan high" or "electric fan low" operating mode, the contact resistance with at least one of the main stream ST1 and the side stream ST2 is significantly reduced. As a result, the airflow including the main stream ST1 and the side stream ST2 flows smoothly along the surface-treated structure 201 as a whole. Therefore, the surface-treated structure 201 can exert a friction-reducing effect over a wide range of flow speeds of the air flowing in.

[0106] Block 500 end design As described above, it is preferable to generate momentum diffusion of each airflow to stabilize the main flow ST1 and the subflow ST2. To generate this momentum diffusion, it is preferable to have a large flow velocity difference between the main flow ST1 and the subflow ST2. To achieve this, the height difference between the top surfaces of adjacent blocks 500 and the bottom surfaces of the block gaps 550 may be increased. In particular, because the block gaps 550 and the blocks 500 are aligned in the second direction, the height difference between the top surfaces of the blocks 500 and the bottom surfaces of the block gaps 550 may be increased at the boundary between the adjacent blocks 500 and the block gaps 550.

[0107] From this perspective, both end portions 513 in the second direction on the upper surface of block 500 are located higher than the bottoms of the plurality of microgrooves 520 in a cross section of block 500 extending along a plane perpendicular to the first direction. In other words, in a longitudinal cross section of block 500 cut perpendicular to the first direction, both end portions 513 are located higher than the bottoms of the plurality of microgrooves 520. Both end portions 513 are bank-like structures that separate microgrooves 520 and block gaps 550 on the upper surface of block 500.

[0108] If the two first convex portions described above were not provided on the upper surface of the block 500, the height of each of the end portions 513 would be equal to or lower than the bottom of the microgroove 520. In this case, the difference in height at the boundary between the block 500 and the block gap 550 would be smaller than when each of the end portions 513 is located higher than the bottom of the microgroove 520. In other words, the effect of increasing the flow velocity difference between the main stream ST1 and the substream ST2 may be weakened.

[0109] In this example, the upper end surfaces of the multiple protrusions 530 form the outer surface of the block 500. The outer surface of the block 500 is an imaginary surface that extends along the highest part of the upper surface of the block 500. Both end portions 513 of the upper surface of the block 500 in the second direction are at the same height as this outer surface. In other words, each end portion 513 is included in the upper end surfaces of the first protrusions at both ends of the block 500 in the second direction. This allows the main stream ST1 to flow smoothly along the flat outer surface of the block 500 while increasing the difference in height at the boundary between the block 500 and the block gap 550.

[0110] The upper surfaces of the blocks 500 are inclined surfaces 510, which can improve the flow velocity of the main stream ST1 and increase the difference in flow velocity between the main stream ST1 and the substream ST2. Alternatively, the upper surfaces of the blocks 500 may be flat surfaces extending in the first and second directions. Even in this case, the same effect as described above can be achieved by providing a plurality of fine grooves 520 on the upper surface of each block 500 and providing a block gap 550 between two adjacent blocks 500.

[0111] Example 2 A design example of the surface-treated structure 201 in Example 2 will be described. FIG. 11A is a perspective view of the surface-treated sheet 200 according to Example 2. FIG. 11B is a table showing the relationship between the surface-treated sheet 200 and the target flow in Examples 2 and 3. FIG. 11C is a table showing the dimensions of the surface-treated sheet 200 according to Examples 2 and 3. Below, differences from Example 1 will be described.

[0112] As shown in Fig. 11A, the surface-processed structure 201 of Example 2 has the same basic structure as the above embodiment. As shown in Fig. 11B, the surface-processed structure 201 of this example is designed using the same procedure as in Example 1, with the target flows being the airflow (flow velocity 15 m / s) in "electric fan high" and the airflow (flow velocity 10 m / s) in "electric fan medium" of the operating modes of the electric fan 1.

[0113] First step (determining the target value of pitch P corresponding to the fast target flow) Similar to the first embodiment, the target value of the pitch P1 of the fine grooves 520 is calculated to be in the range of 15 to 30 (μm) in accordance with the airflow of "electric fan high".

[0114] Second step (determining the target value of pitch P corresponding to the slow target flow) In this example, the target value of the pitch P2 of the block gaps 550 is determined according to the airflow in the "electric fan mode." In this case, u in (Equation 1) is the flow velocity of 10 (m / s) in the "electric fan mode." As a result, as shown in FIG. 11B, the target value of the pitch P2 is calculated to be in the range of 22 to 45 (μm).

[0115] Third step (determining the number of microgrooves 520) As in the first embodiment, five microgrooves 520 are provided in each block 500 .

[0116] Fourth step (determining the size of the fine groove 520) The number of fine grooves 520, groove width W1, groove interval G1, and wall width G10 are determined in the same manner as in Example 1 (see FIG. 11C). The groove shape of fine grooves 520 is rectangular, as in Example 1.

[0117] Fifth step (determining the size of the block gap 550) As in Example 1, the groove spacing G2 is determined to be 80 μm corresponding to the five microgrooves 520 and six protrusions 530 provided in the block 500. However, this groove spacing G2 is larger than the target value of the pitch P2, which is 22 to 45 μm. When the flow velocity difference between the two target flows is relatively small, the groove spacing G2 (i.e., the size of the block 500) exceeds the target value of the pitch P2, and the block gap 550 may not be positioned within the target value of the pitch P2.

[0118] In this case, the groove width W2 of the block gap 550 is determined by multiplying the groove width W1 of the microgroove 520 by a predetermined factor. The predetermined factor is, for example, in the range of 1 to 5 (excluding 1). As shown in FIG. 11C, in this example, the groove spacing G2 is determined to be 20 μm, which is twice the groove width W1. As a result, the pitch P2 is determined to be 100 μm, which is the sum of the groove spacing G2 and the groove width W2.

[0119] · Sixth step (determining the aspect ratio of the block gap 550) As in the first embodiment, the height H2 of the block 500 may be determined so that the aspect ratio of the block gap 550 increases in the first direction and falls within the range of 0.5 to 0.7.

[0120] In this example, it is assumed that the minimum value Hmin of the block 500 is determined to be 10 μm so that the aspect ratio at the upstream end of the block gap 550 is approximately 0.5. It is assumed that the maximum value Hmax of the block 500 is determined to be 45 μm so that the aspect ratio at the downstream end of the block gap 550 is approximately 2.2. As a result, as shown in FIG. 11C , the aspect ratio of the block gap 550 increases from approximately 0.5 to approximately 2.2 in the first direction.

[0121] In the above block 500, the height difference S of the inclined surface 510 is the difference between the maximum value Hmax and the minimum value Hmin, that is, 35 (μm). In this example, it is assumed that the inclination angle α is set to 10 degrees and the depth D is set to 200 (μm).

[0122] Seventh step (determining the size of the gap 540) In this example, the groove width W3 is determined to be 30 (μm), which is approximately equal to the height difference S (35 μm).

[0123] -Example of creation and use of surface processing structure 201 Based on the design values ​​determined in the first to seventh steps (see FIG. 11C), a surface-finished structure 201 is fabricated in which multiple blocks 500 are arranged two-dimensionally. In the surface-finished structure 201 of this example, multiple microgrooves 520 are arranged at a first pitch corresponding to a first flow velocity, and multiple block gaps 550 are arranged at a second pitch corresponding to a second flow velocity. The first pitch corresponding to the first flow velocity is pitch P1 corresponding to the high-speed airflow of "electric fan high." The second pitch corresponding to the second flow velocity is pitch P2 corresponding to the medium-speed airflow of "electric fan medium." In this case, the surface-finished structure 201 can exhibit a friction-reducing effect over a wide range of flow velocities of the incoming air, similar to Example 1. The end design of the blocks 500 is the same as Example 1.

[0124] Example 3 A design example of the surface-treated structure 201 in Example 3 will be described. Fig. 12A is a perspective view of the surface-treated sheet 200 according to Example 3. Fig. 12B is a front view of the surface-treated sheet 200 according to Example 3. Fig. 12C is an enlarged perspective view of the block 500 of Example 3 as viewed from the downstream side. Differences from Example 1 will be described below.

[0125] As shown in FIG. 12A, the surface-processed structure 201 of Example 3 has the same basic structure as the above-described embodiment, but differs in that the groove shape of the microgrooves 520 is V-shaped. In the V-shaped microgrooves 520, the groove width W1 gradually decreases downward. As with Example 2, the surface-processed structure 201 of this example is designed using the same procedure as Example 2, with the target flows being the airflow (flow velocity 15 m / s) in the "Fan High" operating mode of the electric fan 1 and the airflow (flow velocity 10 m / s) in the "Fan Medium" operating mode (see FIG. 11B). As a result, the same design values ​​as Example 2 are determined (see FIG. 11C). As with Example 2, the surface-processed structure 201 can exhibit friction reduction effects over a wide range of flow velocities of the incoming air.

[0126] In this example, as in the above embodiment, the upper surface of the block 500 is an inclined surface 510, so the height H2 increases in the first direction. Both end portions 513 of the block 500 are at the same height as the outer surface of the block 500 and are included in the upper end surfaces of the convex portions 530 at both ends in the second direction. However, the block 500 of this example differs from the above embodiment in the following respects.

[0127] As in the above embodiment, the microgrooves 520 extend in the first direction on the inclined surfaces 510 with a constant groove width W1. Unlike the above embodiment, the block 500 has a trapezoidal shape with an upper side shorter than a lower side when viewed from the first direction. Both side surfaces of the block 500 in the second direction extend diagonally downward from both end portions 513 of the upper surface of the block 500. Furthermore, the inclination angle of both side surfaces of the block 500 in the second direction relative to the substrate 202 increases toward the first direction. In other words, the inclination of both side surfaces of the block 500 becomes steeper toward the first direction, approaching a vertical plane.

[0128] Specifically, as shown in Fig. 12B, on front surface 521 facing the upstream side of block 500, the inclination angle of the side surfaces extending diagonally downward from both end portions 513 is approximately 45 degrees. On the other hand, as shown in Fig. 12C, on rear surface 522 facing the downstream side of block 500, the inclination angle of the side surfaces extending diagonally downward from both end portions 513 is approximately 80 degrees. The inclination angle of both side surfaces of block 500 gradually increases from front surface 521 to rear surface 522 of block 500.

[0129] According to the above structure, even if the height H2 of the block 500 increases in the first direction, the length in the second direction of the block 500 (i.e., the groove interval G2) is constant. Therefore, in a plan view, the block 500 has a rectangular shape that extends with a constant width in the first direction, similar to the above embodiment.

[0130] If the slope of both side surfaces of the block 500 in the second direction is constant, the length of the block 500 in the second direction increases as the height H2 of the block 500 increases in the first direction. In this case, the block 500 has a trapezoidal shape that widens in the first direction in plan view. As a result, the distance between two adjacent blocks 500 in the second direction (i.e., the groove width W2) narrows in the first direction, which may cause the side surfaces of the blocks 500 to connect. In this case, the bottom surface of the block gap 550 bulges upward at the location where the two blocks 500 connect, potentially reducing the height difference between the top surface of the block 500 and the bottom surface of the block gap 550.

[0131] In contrast, in this example, as described above, the slope of both side surfaces of the block 500 becomes steeper in the first direction, so the interval between two adjacent blocks 500 in the second direction is constant. Therefore, the connection between two adjacent blocks 500 is suppressed, and the difference in height between the top surface of the block 500 and the bottom surface of the block gap 550 can be increased, thereby increasing the flow velocity difference between the main flow ST1 and the secondary flow ST2.

[0132] [remarks] The present disclosure is not limited to the above-described embodiments and modifications, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0133] In the above embodiment, the surface-treated sheet 200 is provided on the propeller fan 100 of the electric fan 1, but the surface-treated sheet 200 may be provided on any surface of an object that comes into contact with a fluid, such as a gas or liquid. For example, providing the surface-treated sheet 200 on the outdoor fan of an air conditioner can efficiently blow air in a power-saving, quiet manner. Furthermore, providing the surface-treated sheet 200 on the inner surface of a drainage or exhaust hose can allow the fluid flowing through the hose to flow smoothly in the desired direction.

[0134] In the above embodiment, an example has been given in which the surface-treated structure 201 can be easily and accurately provided on the target object by placing the surface-treated sheet 200 on the target surface. Alternatively, the surface-treated structure 201 may be formed directly on the surface of the target object, such as the propeller fan 100. At least one of the plurality of blocks 500 may not have the plurality of microgrooves 520 formed on the inclined surface 510.

[0135] The surface-treated structure 201 can be applied in various forms. For example, the shape and arrangement of the multiple blocks 500 can be modified in various ways as follows. Figs. 13A to 13F are schematic side views of the surface-treated sheet 200 according to first to sixth modified examples, respectively. Figs. 14A to 14D are schematic plan views of the surface-treated sheet 200 according to seventh to tenth modified examples, respectively. Fig. 15A is a schematic plan view of the surface-treated sheet 200 according to an eleventh modified example. Fig. 15B is a schematic front view of the surface-treated sheet 200 according to the eleventh modified example.

[0136] As shown in a first modified example in Fig. 13A, two or more blocks 500 lined up in the first direction in each block row 501 may be connected to each other. As shown in a second modified example in Fig. 13B, each of the multiple blocks 500 may have an upstream end 511 provided on the substrate 202 so as to form a triangular shape in side view. As shown in a third modified example in Fig. 13C, two or more blocks 500 lined up in the first direction in each block row 501 may have a mountain shape that is connected in the first direction in side view.

[0137] As shown in a fourth modified example in Fig. 13D, each of the plurality of blocks 500 may have a plate shape extending obliquely upward along the first direction from on the base material 202. As shown in a fifth modified example in Fig. 13E, each of the plurality of blocks 500 may have a shape that protrudes in an arc-like or parabolic shape in side view from the base material 202. As shown in a sixth modified example in Fig. 13F, in each of the plurality of blocks 500, the inclined surface 510 may be curved in an arc-like or parabolic shape in side view.

[0138] In the third to fifth modified examples (see FIGS. 13C to 13E), an inclined or curved surface extending from an upstream end 511 at the front end of the block 500 to a downstream end 512 at the top end of the block 500 functions as the inclined surface 510. In this case, the inclined or curved surface extending from the downstream end 512 to the rear end of the block 500 forms the rear surface 522 of the block 500.

[0139] As shown in the seventh modified example in Fig. 14A, the multiple blocks 500 may be arranged in a staggered pattern. In this example, the multiple blocks 500 constitute multiple block rows 502. Each of the multiple block rows 502 consists of two or more blocks 500 lined up in the second direction. The multiple block rows 502 are arranged side by side in the first direction. Of two multiple block rows 502 adjacent to each other in the first direction, one block row 502 is shifted in the second direction by half a block 500 from the other block row 502.

[0140] Similar to the above embodiment, the inclined surfaces 510 of the blocks 500 are aligned on a single line V extending in the first direction. Specifically, as shown in Fig. 14A , the line V passing through the left or right portion of one block 500 passes through the right or left portion of the blocks 500 included in each block row 502 in all block rows 502 in plan view. That is, the line V passes through the inclined surfaces 510 of the blocks 500 in all block rows 502 in plan view.

[0141] The air heading toward the surface-treated sheet 200 is branched into multiple main streams ST1 and multiple substreams ST2 as follows: The air heading toward the left or right portion of each block 500 flows in a first direction along the corresponding line V. At this time, the air flows continuously along the multiple inclined surfaces 510, forming multiple main streams ST1. Meanwhile, the remaining air flows in the first direction alternately through the center of the inclined surfaces 510 and the block gaps 550. As described above, the block gaps 550 are wider than the microgrooves 520, and no air vortex E occurs in the block gaps 550, so multiple substreams ST2 with a different flow velocity from the main stream ST1 are formed.

[0142] In the seventh modified example (see FIG. 14A), similarly to the above embodiment, multiple main streams ST1 and multiple substreams ST2 are alternately arranged in the second direction, so that the momentum of the airflow flowing in the first direction on the surface-treated sheet 200 is diffused in the span direction. Therefore, the multiple main streams ST1 and substreams ST2 can move smoothly and stably in the first direction, and faster air can be accurately blown in the first direction.

[0143] As shown in the eighth modified example in Figure 14B, the multiple blocks 500 may have different shapes in multiple patterns, or may be arranged randomly. In this case, in the surface-treated sheet 200, the number and range of blocks 500 through which the line V passes vary depending on the position in the second direction. When air flows along the line V, if the number and range of blocks 500 through which the line V passes are large, the air flows smoothly and forms a main stream ST1. On the other hand, when air flows along the line V, if the number and range of blocks 500 through which the line V passes are small, a substream ST2 with a flow velocity different from that of the main stream ST1 is formed.

[0144] As described above, when the shape patterns of the blocks 500 are different or the blocks 500 are randomly arranged, multiple main streams ST1 and multiple substreams ST2 are formed, and the formation positions of the main streams ST1 and the substreams ST2 vary in the second direction. Therefore, in the eighth modified example (see FIG. 14B ), similar to the above embodiment, the multiple main streams ST1 and the substreams ST2 can move smoothly and stably in the first direction, and a faster airflow can be accurately blown in the first direction.

[0145] As shown in the ninth modified example in Fig. 14C, a plurality of blocks 500 that are long in the second direction may be aligned in the first direction to form a single block row 501. In this case, the air flowing toward the surface-treated sheet 200 flows continuously along the inclined surfaces 510 of the plurality of blocks 500 that make up the block row 501, thereby forming a main flow ST1 as a whole. Therefore, in the ninth modified example (see Fig. 14C), as in the above embodiment, a faster airflow can be accurately blown in the first direction.

[0146] As shown in the tenth modified example in Figure 14D, the first direction in which two or more blocks 500 constituting each block row 501 are arranged may extend in a curved line. That is, in each block row 501, two or more blocks 500 may be arranged continuously in a curved line in a plan view. In this case, each block 500 may be arranged so that its front side faces the upstream side in the first direction and its rear side faces the downstream side in the first direction. As a result, in each block 500, the inclined surface 510 extends so as to be inclined upward in the first direction, and the multiple fine grooves 520 extend substantially parallel to the first direction and linearly.

[0147] In the tenth modified example (see FIG. 14D), the air flowing toward the surface-treated sheet 200 is also divided into multiple main streams ST1 and multiple substreams ST2 and flows in the first direction, thereby achieving the same effect as the above embodiment. In this example, since the first direction is curved, the multiple main streams ST1 and multiple substreams ST2 also flow in curved shapes. In this way, by utilizing the function of the surface-treated structure 201 to direct air in a fixed direction, air can be easily blown in a desired direction.

[0148] 15A, each of the plurality of blocks 500 may be diamond-shaped in plan view, and these diamond-shaped blocks 500 may be arranged in a lattice pattern. A gap 560 is formed between two adjacent blocks 500, extending at an angle relative to the first and second directions.

[0149] In this case, the number of blocks 500 through which the line V passes varies depending on the position in the second direction in the surface-treated sheet 200. When air flows along the line V, the number of blocks 500 through which the air passes is greater when the line V passes through the left or right portion of the block 500 than when the line V passes through the center portion of the block 500.

[0150] Here, when air flows over a certain distance, the greater the number of blocks 500 through which the air passes, the greater the air flow velocity for the following reason. The greater the number of blocks 500 over a certain distance through which the air flows, the greater the number of gaps 560 within that certain distance. When the air flows through the gaps 560, contact resistance is less likely to occur in the air. In other words, the air flowing through the gaps 560 can easily move without reducing its flow velocity.

[0151] In the eleventh modified example (see FIG. 15A ), multiple main streams ST1 are formed by air flowing through the left or right portion of the block 500, and multiple substreams ST2 are formed by air flowing through the center portion of the block 500. As in the above embodiment, the multiple main streams ST1 and the multiple substreams ST2 are arranged alternately in the second direction. This allows the multiple main streams ST1 and the multiple substreams ST2 to move smoothly and stably in the first direction, and allows faster air to be blown accurately in the first direction.

[0152] As shown in FIG. 15B, on the inclined surface 510 of the block 500, the multiple microgrooves 520 may extend in a downward curved manner in a front view, and may have a shape that narrows toward the bottom. The multiple protrusions 530 may extend in an upward curved manner in a front view, and may have a shape that narrows toward the top. The multiple protrusions 530 may protrude upward to a greater height the closer they are to the center in the second direction. Each of the multiple protrusions 530 may have a shape that increases in height toward the downstream side in the first direction. Even when the inclined surface 510 is configured in this manner, it can exhibit the same function as the inclined surface 510 in the above embodiment.

[0153] 15B, the tops of the plurality of convex portions 530 have a relatively small surface roughness. The bottoms of the plurality of microgrooves 520 have a relatively large surface roughness. This allows air flowing into the inclined surface 510 to flow easily over the convex portions 530 and to flow less easily within the microgrooves 520. Note that in the above embodiment and other modified examples as well, the surface roughness of the convex portions 530 may be made relatively small, or the surface roughness of the microgrooves 520 may be made relatively large.

[0154] In the above embodiment, the microgrooves 520 are provided on the inclined surface 510 of the block 500. Alternatively, the block 500 may not have the inclined surface 510. The microgrooves 520 may not be provided on the block 500. For example, the surface-finished structure 201 may include a plurality of first grooves aligned in the second direction and a second groove extending parallel to the first grooves and narrower and shallower than the first grooves. A plurality of second grooves may be aligned between adjacent first grooves. In this case, as in the above embodiment, the first grooves function similarly to the block gaps 550, and the second grooves function similarly to the microgrooves 520, thereby achieving a friction-reducing effect over a wide range of flow velocities of the flowing air.

[0155] According to the present disclosure, it is possible to provide the following surface-treated structure, surface-treated sheet, and propeller fan. (1) A surface-processed structure according to one embodiment of the present disclosure includes: a three-dimensional object disposed on a target surface, the three-dimensional object comprising a plurality of blocks arranged in a first direction parallel to the target surface; each of the plurality of blocks has an inclined surface that extends so that the distance from the target surface gradually increases from the upstream side to the downstream side in the first direction; The inclined surfaces of the blocks are aligned on a line extending in the first direction.

[0156] (2) In the surface-treated structure, the entire inclined surface is exposed to the upstream side of the block in the first direction, The downstream end of the inclined surface in the first direction is the farthest from the target surface among the blocks.

[0157] (3) In the surface-treated structure, two blocks adjacent to each other in the first direction among the plurality of blocks are an upstream block and a downstream block located downstream of the upstream block, The upstream end of the inclined surface of the downstream block in the first direction is closer to the target surface than the downstream end of the inclined surface of the upstream block in the first direction.

[0158] (4) In the surface-treated structure, Each of the plurality of blocks has a plurality of fine grooves provided on the inclined surface, The plurality of fine grooves are aligned at intervals in a second direction perpendicular to the first direction, and extend from the upstream side to the downstream side in the first direction.

[0159] (5) In the surface-treated structure, The plurality of fine grooves extend from an upstream end to a downstream end of the inclined surface in the first direction.

[0160] (6) In the surface-treated structure, the plurality of blocks are two-dimensionally arranged side by side in the first direction and the second direction, A groove-shaped block gap extending in a direction intersecting the second direction is formed between two blocks adjacent to each other in the second direction among the plurality of blocks, The width of each of the plurality of microgrooves in the second direction is smaller than the width of the gap in the second direction.

[0161] (7) In the surface-treated structure, the plurality of blocks are arranged so as to form a plurality of gaps that are successively arranged in the first direction, The plurality of gaps form one fluid flow path extending in the first direction.

[0162] (8) A surface-processed structure according to one embodiment of the present disclosure includes: a plurality of first grooves aligned in a second direction; a second groove extending parallel to the first groove and narrower and shallower than the first groove; Equipped with A plurality of the second grooves are aligned between adjacent ones of the first grooves.

[0163] (9) In the surface-treated structure, The aspect ratio of the first groove is smaller than the aspect ratio of the second groove.

[0164] (10) A surface-treated sheet according to one embodiment of the present disclosure includes: The surface texture is provided on a substrate that is mountable on the target surface.

[0165] (11) A propeller fan according to one aspect of the present disclosure includes: a rotating shaft portion and a blade extending outward from the rotating shaft portion, the surface structure is provided on a surface of the wing; The first direction is a direction from the leading edge side to the trailing edge side of the wing.

Claims

1. a plurality of blocks that are three-dimensional objects arranged on a target surface that is a surface of the target object; the target surface extends in a first direction and a second direction that are orthogonal to each other; the plurality of blocks are arranged in the second direction at intervals from one another, In each of the plurality of blocks, an upper surface of the block includes a plurality of microgrooves; The plurality of microgrooves are aligned in the second direction at intervals from one another and extend from the upstream side to the downstream side in the first direction, A groove-shaped block gap extending in the first direction is formed between two of the blocks adjacent to each other in the second direction, a width in the second direction of each of the plurality of fine grooves is less than a width in the second direction of the block gap; both end portions of the upper surface in the second direction are located above bottoms of the plurality of microgrooves in a cross section of the block extending along a plane perpendicular to the first direction, The upper surface includes a plurality of protrusions, and each of the plurality of microgrooves is provided between two adjacent protrusions among the plurality of protrusions, upper end surfaces of the plurality of protrusions form an outer surface of the block; both ends of the upper surface in the second direction are at the same height as the outer surface, a width in the second direction of each of the plurality of microgrooves is larger than a width in the second direction of each of the plurality of protrusions, the plurality of convex portions include two first convex portions that constitute both end portions of the upper surface in the second direction, and a plurality of second convex portions different from the two first convex portions, Both side surfaces of each of the plurality of blocks in the second direction are flush with each other and extend in the first direction from the target surface to upper ends of the two first protrusions. Surface treatment structure.

2. The width in the second direction of each of the two first convex portions is equal to or greater than the width in the second direction of each of the plurality of second convex portions. The surface-treated structure according to claim 1 .

3. The width of the block gap in the second direction is less than the sum of the widths of the plurality of fine grooves in the second direction. The surface-processed structure according to claim 1 or 2.

4. the plurality of microgrooves are arranged on the upper surface at a first pitch corresponding to a first flow velocity that is relatively faster among the two different flow velocities; The plurality of block gaps are arranged on the upper surface at a second pitch corresponding to a second flow velocity that is relatively slower than the two different flow velocities. The surface-treated structure according to any one of claims 1 to 3.

5. A plurality of blocks that are three-dimensional objects arranged on a target surface that is the surface of an object, the target surface extends in a first direction and a second direction that are orthogonal to each other; the plurality of blocks are arranged in the second direction at intervals from one another, In each of the plurality of blocks, an upper surface of the block includes a plurality of microgrooves; The plurality of microgrooves are aligned in the second direction at intervals from one another and extend from the upstream side to the downstream side in the first direction, A groove-shaped block gap extending in the first direction is formed between two of the blocks adjacent to each other in the second direction, a width in the second direction of each of the plurality of fine grooves is less than a width in the second direction of the block gap; both end portions of the upper surface in the second direction are located above bottoms of the plurality of microgrooves in a cross section of the block extending along a plane perpendicular to the first direction, the upper surface is an inclined surface that extends such that the distance from the target surface gradually increases from the upstream side toward the downstream side in the first direction, The plurality of microgrooves extend to the same depth from an upstream end to a downstream end in the first direction on the upper surface. Surface treatment structure.

6. A plurality of blocks that are three-dimensional objects arranged on a target surface that is the surface of an object, the target surface extends in a first direction and a second direction that are orthogonal to each other; the plurality of blocks are arranged in the second direction at intervals from one another, In each of the plurality of blocks, an upper surface of the block includes a plurality of microgrooves; The plurality of microgrooves are aligned in the second direction at intervals from one another and extend from the upstream side to the downstream side in the first direction, A groove-shaped block gap extending in the first direction is formed between two of the blocks adjacent to each other in the second direction, a width in the second direction of each of the plurality of fine grooves is less than a width in the second direction of the block gap; both end portions of the upper surface in the second direction are located above bottoms of the plurality of microgrooves in a cross section of the block extending along a plane perpendicular to the first direction, an aspect ratio indicating a ratio of a depth to a width in the second direction in the block gap gradually increases from an upstream side to a downstream side in the first direction, the aspect ratio at the upstream end of the block gap is 0.5 or less, The aspect ratio at the downstream end of the block gap is 0.7 or more. Surface treatment structure.

7. the plurality of blocks are two-dimensionally arranged side by side in the first direction and the second direction, and are arranged such that the plurality of block gaps form one fluid flow path extending in the first direction; The plurality of microgrooves provided on the upper surface and the fluid flow paths are alternately arranged along the second direction. The surface-processed structure according to any one of claims 1 to 6.

8. A plurality of blocks that are three-dimensional objects arranged on a target surface that is the surface of an object, the target surface extends in a first direction and a second direction that are orthogonal to each other; the plurality of blocks are arranged in the second direction at intervals from one another, In each of the plurality of blocks, an upper surface of the block includes a plurality of microgrooves; The plurality of microgrooves are aligned in the second direction at intervals from one another and extend from the upstream side to the downstream side in the first direction, A groove-shaped block gap extending in the first direction is formed between two of the blocks adjacent to each other in the second direction, a width in the second direction of each of the plurality of fine grooves is less than a width in the second direction of the block gap; both end portions of the upper surface in the second direction are located above bottoms of the plurality of microgrooves in a cross section of the block extending along a plane perpendicular to the first direction, A groove-shaped gap extending in the second direction is formed between two of the blocks adjacent to each other in the first direction, a height difference between the upper surfaces of the block located upstream in the first direction out of the two blocks is equal to a width of the groove-shaped gap in the first direction; Surface treatment structure.

9. A surface-treated sheet comprising a substrate that can be placed on the target surface and that has the surface-treated structure according to any one of claims 1 to 8 provided thereon.

10. a rotating shaft portion and a blade extending outward from the rotating shaft portion, The surface processed structure according to any one of claims 1 to 8 is provided on the surface of the blade, The first direction is parallel to a direction from a leading edge side to a trailing edge side of the wing. Propeller fan.

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