Turbofan

Abstract

The present application aims to provide a turbofan capable of reducing noise. A plurality of blades (4) of a turbofan (1) have a thick wall portion (10), a thin wall portion (11), and a step portion (12). The thick wall portion (10) is a portion where the plate thickness is thicker on the leading edge (8) side. The thin wall portion (11) is a portion where the plate thickness is thinner than the thick wall portion (10) and is provided on the trailing edge (9) side. The step portion (12) is a portion provided between the thick wall portion (10) and the thin wall portion (11) and where the plate thickness decreases toward the positive pressure surface side from the thick wall portion (10) side toward the thin wall portion (11) side. Furthermore, in a cross-sectional view perpendicular to the rotation axis (Ax) of the blade (4), a circular arc-shaped second curved surface (111) of the negative pressure surface forming the thin wall portion (11) is located on the positive pressure surface side with respect to a circular arc-shaped first curved surface (101) of the negative pressure surface forming the thick wall portion (10), and the first curved surface (101) and the second curved surface (111) are connected by a negative pressure surface (121) of the step portion (12).

Description

[0001] Cross-reference of related applications

[0002] This application is based on Japanese Patent Application No. 2020-120669, filed on July 14, 2020, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to turbo fans. Background Technology

[0004] Turbine fans have been known for use in blowers. Generally, turbine fans are characterized by low losses and high efficiency. However, turbine fans suffer from the following problem: airflow stripping occurs on the negative pressure surface slightly upstream of the trailing edge of the blades. The vortices with large velocity gradients generated by this stripping interfere with the trailing edge of the blades, producing noise.

[0005] The turbine fan described in Patent Document 1 has blades with the following shape: the blade thickness is relatively thin at the leading edge, gradually increases towards the center, and then gradually decreases towards the trailing edge. Furthermore, in the portion of the blade where the thickness gradually increases from the leading edge towards the center, stepped portions are provided on both the positive and negative pressure sides. Therefore, the blade is formed such that the thickness of the portion downstream of the stepped portion is greater than the thickness of the portion upstream of the stepped portion. That is, the stepped portion can also be referred to as a thickness-increasing portion where the thickness increases from the upstream side to the downstream side.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 6071394

[0009] According to the inventors' research, in the structure of the turbofan described in Patent Document 1, the airflow along the negative pressure surface of the blades is stripped at the stepped section, forming a vortex with a large velocity gradient. Moreover, there is a problem that this vortex interferes with the stepped section (i.e., the section with increased plate thickness), generating noise.

[0010] In addition, the structure of the turbofan described in Patent Document 1 does not solve the following problem: airflow stripping occurs on the negative pressure surface slightly upstream of the trailing edge of the blade, and the vortex with a large velocity gradient generated by this stripping interferes with the trailing edge of the blade, generating noise. Summary of the Invention

[0011] The purpose of this invention is to provide a turbine fan that can reduce noise.

[0012] According to one aspect of the present invention, a turbofan is provided, comprising: a shroud having an air intake; a main board disposed in the direction of rotation axis of the shroud; and a plurality of blades disposed about the rotation axis between the shroud and the main board. The plurality of blades of the turbofan have a thick-walled portion, a thin-walled portion, and a stepped portion. The thick-walled portion is a portion formed on the leading edge side with a thicker plate thickness. The thin-walled portion is a portion disposed on the trailing edge side with a thinner plate thickness than the thick-walled portion. The stepped portion is a portion disposed between the thick-walled portion and the thin-walled portion, with the plate thickness decreasing from the thick-walled portion side towards the thin-walled portion side towards the positive pressure surface side. Furthermore, in a cross-sectional view perpendicular to the rotation axis of the blades, relative to the arcuate first curved surface of the negative pressure surface forming the thick-walled portion, the arcuate second curved surface of the negative pressure surface forming the thin-walled portion is located on the positive pressure surface side, and the first and second curved surfaces are connected by the negative pressure surface of the stepped portion.

[0013] Therefore, the velocity boundary layer generated in the airflow along the negative pressure surface of the blade can be disturbed starting from the boundary between the thick-walled section and the stepped section, and a turbulent boundary layer can be generated with this boundary as the stripping point of the airflow, causing the mainstream to move away from the negative pressure surface of the thin-walled section and away from the rearward side in the direction of rotation. Therefore, compared with a conventional turbine fan without a stepped section, this turbine fan shifts the location of the stripping of the airflow along the negative pressure surface of the blade forward and reduces the velocity gradient of the airflow colliding with the negative pressure surface at the trailing edge of the blade, thereby reducing noise.

[0014] Furthermore, since the stepped section located in the middle of the blade has a shape where the plate thickness decreases from the upstream side to the downstream side and towards the positive pressure surface, the interference distance between the vortex with a large velocity gradient generated at the boundary between the thick-walled section and the stepped section (i.e., the airflow separation point) and the negative pressure surface of the stepped section can be increased. Therefore, the noise generated at the boundary between the thick-walled section and the stepped section (i.e., the airflow separation point) can be reduced.

[0015] Furthermore, the parenthesized reference symbols attached to each constituent element, etc., indicate an example of the correspondence between that constituent element, etc., and the specific constituent elements, etc., described in the embodiments described later. Attached Figure Description

[0016] Figure 1 It is a cross-sectional view along the rotation axis of the turbine fan involved in the first embodiment.

[0017] Figure 2 yes Figure 1 A sectional view along line II-II.

[0018] Figure 3 yes Figure 2 An enlarged view of Part III.

[0019] Figure 4This is an explanatory diagram illustrating the airflow generated by the turbine fan according to the first embodiment.

[0020] Figure 5 This is an explanatory diagram used to illustrate the airflow generated by the turbofan of the comparative example.

[0021] Figure 6 This is a graph comparing the noise of the turbine fan according to the first embodiment with the noise of the turbine fan of the comparative example.

[0022] Figure 7 This is a graph showing the relationship between the reduction ratio of plate thickness and the low noise effect in the turbine fan according to the first embodiment.

[0023] Figure 8 This is a cross-sectional view along the rotation axis of the turbine fan involved in the second embodiment.

[0024] Figure 9 This is a cross-sectional view along the rotation axis of the turbine fan involved in the third embodiment.

[0025] Figure 10 This is an enlarged view showing the stepped portion of the blades and the vicinity of the turbofan according to the fourth embodiment. Detailed Implementation

[0026] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, in the following embodiments, the same or equivalent parts are labeled with the same reference numerals, and their descriptions are omitted. Additionally, regarding the drawings referenced in each embodiment, the shapes of the various structures of the turbine fan are illustrated schematically to facilitate understanding and are not intended to limit the present invention.

[0027] (First Implementation)

[0028] The first embodiment will be described with reference to the accompanying drawings. The turbine fan of this embodiment is, for example, a blower used in air conditioning units or ventilation units.

[0029] like Figure 1 and Figure 2 As shown, the turbine fan 1 includes a shroud 2, a main plate 3, and multiple blades 4. The shroud 2 is formed in a ring shape, with an intake 5 for drawing in air at its center. The shroud 2 extends radially outward from the intake 5, gradually approaching the main plate 3, and along the main plate 3. Furthermore, in... Figure 2 In the diagram, the inner diameter D1 of the suction port 5 of the shield 2 is represented by a dashed line with the symbol D1.

[0030] The motherboard 3 is formed in a disk shape and is positioned along the rotation axis of the shroud 2. The motherboard 3 is positioned opposite the shroud 2. The motherboard 3 is formed approximately perpendicular to the rotation axis Ax of the turbine fan 1. Furthermore, the motherboard 3 is not limited to… Figure 1 The shape can be planar as shown, or it can be a shape in which the central part protrudes towards the suction port 5. The main board 3 is fixed to the shaft 7 of the motor 6 and rotates about the rotation axis Ax by the drive of the motor 6.

[0031] Multiple blades 4 are arranged about a rotation axis Ax between the main plate 3 and the shield 2. The multiple blades 4 are arranged at predetermined intervals in the rotation direction. The multiple blades 4 extend rearward in the rotation direction from the leading edge 8 toward the trailing edge 9. Furthermore, the leading edge 8 of the blades 4 is located radially inward compared to the inner diameter D1 of the suction port 5 of the shield 2.

[0032] The turbine fan 1 in this embodiment is a closed fan formed by the main board 3, the shield 2, and multiple blades 4. Specifically, one side of the rotation axis Ax of the multiple blades 4 is connected to the main board 3, and the other side of the rotation axis Ax is connected to the shield 2.

[0033] The turbine fan 1 rotates together with the shaft 7 driven by the electric motor 6. When the turbine fan 1 rotates, the air drawn in from the intake port 5 flows through the flow path between the multiple blades 4 at the leading edge 8 of the blades 4 (hereinafter referred to as the "inter-blade flow path"), and is blown out radially outward from the air outlet formed between the trailing edge 9 of the blades 4, the shroud 2 and the main plate 3.

[0034] Next, refer to Figures 1-3 The multiple blades 4 of the turbofan 1 are described in detail. Furthermore, in Figure 3 In the diagram, the shading lines representing the cross-section of blade 4 have been omitted for easier observation.

[0035] like Figures 1-3 As shown, the multiple blades 4 have a thick-walled portion 10, a thin-walled portion 11, and a stepped portion 12.

[0036] The thick-walled portion 10 is the thicker section of the blade 4 formed on the leading edge 8 side. In a cross-sectional view perpendicular to the rotation axis Ax of the blade 4, the negative pressure surface of the thick-walled portion 10 is formed as an arc-shaped curved surface convex toward the positive pressure surface. In the following description, the curved surface of the negative pressure surface of the thick-walled portion 10 will be referred to as the first curved surface 101.

[0037] The thickness T1 of the thick-walled portion 10 is preferably set to, for example, 3 mm or more. In addition, when viewed in cross-section perpendicular to the rotation axis Ax of the blade 4, the radius of curvature of both the positive pressure side and the negative pressure side of the leading edge 8 of the blade 4 is preferably set to 1.5 mm or more.

[0038] The thin-walled portion 11 is a part of the blade 4 that is located downstream of the thick-walled portion 10 (i.e., on the side closer to the trailing edge 9 than the thick-walled portion 10) and is thinner than the thick-walled portion 10. For example... Figure 2 As shown, in a cross-sectional view perpendicular to the rotation axis Ax of the blade 4, the negative pressure surface of the thin-walled portion 11 is also formed as an arc-shaped curved surface convex toward the positive pressure surface side. In the following description, the curved surface of the negative pressure surface of the thin-walled portion 11 will be referred to as the second curved surface 111. Relative to the first curved surface 101 of the thick-walled portion 10 described above, the second curved surface 111 of the thin-walled portion 11 is located on the positive pressure surface side.

[0039] The thickness T2 of the thin-walled portion 11 is preferably set to be, for example, 75% or less relative to the thickness T1 of the thick-walled portion 10. The reasons for this will be explained later.

[0040] The stepped portion 12 is a portion provided between the thick-walled portion 10 and the thin-walled portion 11, where the plate thickness decreases from the thick-walled portion 10 side toward the thin-walled portion 11 side toward the positive pressure surface side. That is, the stepped portion 12 can also be referred to as a plate thickness reduction portion where the plate thickness decreases from the upstream side to the downstream side.

[0041] exist Figure 3 In the diagram, a single-dotted line A represents the boundary between the thick-walled portion 10 and the stepped portion 12, and a single-dotted line B represents the boundary between the stepped portion 12 and the thin-walled portion 11. However, these boundary lines are for illustrative purposes only; in reality, the thick-walled portion 10, the stepped portion 12, and the thin-walled portion 11 are formed as a single unit.

[0042] The negative pressure surface 121 of the stepped portion 12 connects the first curved surface 101 of the thick-walled portion 10 and the second curved surface 111 of the thin-walled portion 11 with a smooth curved shape. That is, the negative pressure surface at the boundary between the stepped portion 12 and the thick-walled portion 10 is formed with a smooth curved shape. In addition, the negative pressure surface at the boundary between the stepped portion 12 and the thin-walled portion 11 is also formed with a smooth curved shape. Moreover, in the first embodiment, when viewed in cross-section perpendicular to the rotation axis Ax of the blade 4, the negative pressure surface 121 of the stepped portion 12 is formed with a curved shape that bulges toward the positive pressure surface side.

[0043] like Figure 3 As shown, in a cross-sectional view perpendicular to the rotation axis Ax of the blade 4, the tangent at the center of the negative pressure surface 121 of the stepped portion 12 is referred to as the first tangent L1. Furthermore, the tangent at the portion on the stepped portion 12 side of the negative pressure surface of the thick-walled portion 10 is referred to as the second tangent L2. In the first embodiment, the angle θ1 formed by the first tangent L1 and the second tangent L2 is set to an acute angle. Specifically, the angle θ1 formed by the first tangent L1 and the second tangent L2 is, for example, set to a range of 20° to 70°.

[0044] exist Figure 1For ease of explanation, the location of the stepped portion 12 on the negative pressure surface of the blade 4 is indicated by crosshairs. The stepped portion 12 is located radially outward compared to the inner diameter D1 of the suction port 5 of the shield 2.

[0045] In addition, Figure 2 In the diagram, double-dotted lines C and D represent the lines that divide the blade length into three equal parts. Furthermore, the blade length refers to the length along the mid-arc line of the blade 4. The stepped portion 12 is only provided in the central region when the blade length is divided into three equal parts. Moreover, in the first embodiment, the stepped portion 12 is only provided in the region between the boundary line C on the leading edge 8 side when the blade length is divided into three equal parts and the boundary line E when the blade length is divided into two equal parts.

[0046] Next, refer to Figure 4 The airflow when the turbine fan 1 of this embodiment rotates and the resulting effects will be explained.

[0047] When the turbine fan 1 rotates, the air drawn in from the intake 5 flows from the leading edge 8 of the blade 4 into the inter-blade flow path. At this time, as... Figure 4 As indicated by arrows F1 and F2, the air flowing near the leading edge 8 of blade 4 flows along the positive or negative pressure surface of blade 4 in the inter-blade flow path due to the wall adhesion effect. Here, as described above, in this embodiment, the inter-blade flow path expands sharply from the step portion 12 located in the middle of blade 4. Therefore, the velocity boundary layer generated in the airflow along the negative pressure surface of blade 4 is disturbed starting from the boundary between the thick-walled portion 10 and the step portion 12. Moreover, a turbulent boundary layer is generated downstream with this boundary as the stripping point. Therefore, from the stripping point towards the downstream side, the distance between the negative pressure surface of the thin-walled portion 11 (i.e., the second curved surface 111) and the mainstream F3 gradually increases. Therefore, the velocity gradient of the airflow F4 colliding with the negative pressure surface of the trailing edge 9 of blade 4 is small, thus reducing noise.

[0048] Furthermore, in this embodiment, the stepped portion 12 has a structure in which the plate thickness decreases from the thick-walled portion 10 side toward the thin-walled portion 11 side toward the positive pressure surface side. Therefore, the vortex V1 with a large velocity gradient generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the airflow separation point) flows downstream in the inter-blade flow path with almost no interference from the negative pressure surface 121 of the stepped portion 12. Therefore, the noise generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the airflow separation point) is small.

[0049] Furthermore, in this embodiment, on the negative pressure surface of the blade 4, the boundary between the stepped portion 12 and the thick-walled portion 10 is connected by a smooth curved surface, and the boundary between the stepped portion 12 and the thin-walled portion 11 is also connected by a smooth curved surface. Moreover, the negative pressure surface 121 of the stepped portion 12 is formed as a curved surface bulging towards the positive pressure surface. Therefore, even if the vortex V1 generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the airflow separation point) interferes with the negative pressure surface 121 of the stepped portion 12, the noise generated therein is small.

[0050] Next, in order to compare with the turbo fan 1 of this embodiment, the airflow and the resulting effects when the turbo fan 100 of the comparative example rotates will be explained.

[0051] like Figure 5 As shown, the comparative example turbine fan 100 has the following structure: no step portion 12 is provided on the blade 4, and the negative pressure surface of the blade 4 is formed by an arc-shaped curved surface from the leading edge 8 to the trailing edge 9.

[0052] In the comparative example, when the turbine fan 100 rotates, the air drawn in from the intake 5 also flows from the leading edge 8 of the blade 4 into the inter-blade flow path. At this time, as shown by arrows F1 and F2, the air flowing near the leading edge 8 of the blade 4 flows along the positive or negative pressure surface of the blade 4 in the inter-blade flow path due to the wall adhesion effect. Moreover, in the comparative example, since the step portion 12 is not provided, as shown by arrow F3, the mainstream flowing in the inter-blade flow path flows along the positive or negative pressure surface of the blade 4 towards the trailing edge 9 in the inter-blade flow path. Furthermore, airflow stripping occurs on the negative pressure surface slightly upstream of the trailing edge 9, and vortices V3 with large velocity gradients are generated due to this stripping. These vortices V3 with large velocity gradients interfere with the trailing edge 9 of the blade 4, thereby generating noise.

[0053] Here, in Figure 6 Experimental results comparing the noise levels of the turbo fan 1 according to the first embodiment and the turbo fan 100 of the comparative example are shown.

[0054] In this experiment, the turbofan 1 of the first embodiment and the turbofan 100 of the comparative example were rotated at the same speed, and the noise was compared.

[0055] like Figure 6 As shown in the chart, according to the experiment, the turbo fan 1 of the first embodiment can reduce noise by 1.5 dB compared to the turbo fan 100 of the comparative example.

[0056] In addition, Figure 7 The results of an experiment show the relationship between the reduction ratio of the blade 4 thickness in the structure of the turbofan 1 in the first embodiment and the low noise effect.

[0057] Furthermore, the reduction ratio of plate thickness refers to the ratio by which the plate thickness T2 of the thin-walled portion 11 is reduced relative to the plate thickness T1 of the thick-walled portion 10.

[0058] In this experiment, multiple turbine fans 1 with different plate thickness reduction ratios were prepared, and the low-noise effect was measured when these multiple turbine fans 1 were rotated at a specified speed. In this experiment, the speed of the turbine fan 1 was set to 3200 rpm, and the air volume was set to 535 m³ / h. 3 / min. Furthermore, in Figure 7 In the chart, the structure of the turbine fan 100 with a plate thickness reduction ratio of 1 is equivalent to the comparative example without the step portion 12.

[0059] from Figure 7 The chart reads the following: When the thickness reduction ratio is set to 75% or less, the low noise effect becomes extremely significant. Additionally, it reads the following: If the thickness reduction ratio is set to 60% or less, the low noise effect is greater than 1.5dB.

[0060] The turbine fan 1 of this embodiment described above has the following effects.

[0061] (1) In this embodiment, a stepped portion 12 is provided between the thick-walled portion 10 and the thin-walled portion 11 of the blade 4 to rapidly expand the flow path between the blades. This allows the velocity boundary layer generated in the airflow along the negative pressure surface of the thick-walled portion 10 to be disturbed starting from the boundary between the thick-walled portion 10 and the stepped portion 12, and a turbulent boundary layer to be generated at this boundary as the point of airflow stripping, causing the main flow F3 to move away from the negative pressure surface of the thin-walled portion 11 in the direction of rotation. Therefore, compared to the turbine fan 100 of the comparative example described above, this turbine fan 1 shifts the point of airflow stripping along the negative pressure surface of the blade 4 forward, reduces the velocity gradient of the airflow F4 colliding with the negative pressure surface of the trailing edge 9 of the blade 4, and thereby reduces noise.

[0062] Furthermore, since the stepped portion 12 has a shape in which the plate thickness decreases from the upstream side to the downstream side and towards the positive pressure surface side, the interference distance between the vortex V1 with a large velocity gradient generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the airflow separation point) and the negative pressure surface 121 of the stepped portion 12 can be increased. Therefore, the noise generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the airflow separation point) can be reduced.

[0063] (2) In this embodiment, the step portion 12 is provided in the central region when the blade length is divided into three equal parts.

[0064] Here, the region on the leading edge 8 side when the blade length is divided into three equal parts (hereinafter referred to as the "front region") has the function of allowing the airflow flowing in from the inlet of the blade 4 to flow along the wall of the blade 4 and improving the robustness to the inflow angle of the airflow, so the step portion 12 is not preferably provided.

[0065] On the other hand, assuming that a step portion 12 is provided in the region on the trailing edge 9 side when the blade length is divided into three equal parts (hereinafter referred to as the "tail region"), a vortex with a large velocity gradient generated from this point will collide with the negative pressure surface of the trailing edge 9 of the blade 4, thus making it difficult to reduce noise.

[0066] In contrast, in this embodiment, since the step portion 12 is not provided in the front region, robustness to the inflow angle of the airflow can be improved. Furthermore, the step portion 12 provided in the central region can disrupt the airflow flowing along the negative pressure surface of the thick-walled portion 10, and a turbulent boundary layer is generated at this step portion as the airflow stripping point, causing the mainstream F3 to move away from the negative pressure surface of the thin-walled portion 11 in the direction of rotation. Therefore, the turbofan 1 of this embodiment can reduce noise by reducing the velocity gradient of the airflow F4 colliding with the negative pressure surface of the trailing edge 9 of the blade 4.

[0067] (3) In this embodiment, the step portion 12 is positioned radially outward compared to the inner diameter D1 of the suction port 5 of the shield 2.

[0068] Here, assuming that the step portion 12 is provided at a position radially inward compared to the inner diameter D1 of the inlet 5 of the shield 2, it is difficult to make the airflow flowing in from the inlet of the blade 4 flow from the leading edge 8 of the blade 4 along the wall surface of the thick-walled portion 10 to the inter-blade flow path.

[0069] In contrast, in this embodiment, since the stepped portion 12 is not provided at a position radially inward compared to the inner diameter D1 of the inlet 5 of the shield 2, the airflow flowing in from the inlet of the blade 4 can flow from the leading edge 8 of the blade 4 along the wall surface of the thick-walled portion 10 to the inter-blade flow path. Therefore, robustness to the inflow angle of the airflow can be improved.

[0070] (4) In this embodiment, the negative pressure surface at the boundary between the stepped portion 12 and the thick-walled portion 10 is formed into a smooth curved shape.

[0071] Here, assuming that a corner is formed on the negative pressure surface at the boundary between the stepped portion 12 and the thick-walled portion 10, the vortex V1 with a large velocity gradient generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the point where the airflow is separated) may interfere with the corner and generate noise.

[0072] In contrast, in this embodiment, no corner is formed on the negative pressure surface at the boundary between the stepped portion 12 and the thick-walled portion 10. Therefore, even if a vortex V1 is generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the point where the airflow separates), the noise generated there can be reduced.

[0073] (5) In this embodiment, it is preferable to set the thickness T2 of the thin-walled portion 11 to 75% or less relative to the thickness T1 of the thick-walled portion 10.

[0074] Therefore, based on the above experimental results, by setting the thickness T2 of the thin-walled portion 11 to 75% or less relative to the thickness T1 of the thick-walled portion 10, the low-noise effect can be greatly improved. According to the above experimental results, the noise can be reduced by more than 1.5 dB.

[0075] (6) In this embodiment, when viewed in cross section perpendicular to the rotation axis Ax of the blade 4, the negative pressure surface 121 of the step portion 12 is a curved surface that bulges toward the positive pressure surface.

[0076] As a result, the distance between the vortex generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the point where the airflow is separated) and the negative pressure surface 121 of the stepped portion 12 becomes greater, thus reducing the noise generated therein.

[0077] (7) In this embodiment, when viewed in cross section perpendicular to the rotation axis Ax of the blade 4, the angle θ1 formed by the first tangent L1 in the central part of the negative pressure surface 121 of the step portion 12 and the second tangent L2 in the negative pressure surface of the thick wall portion 10 on the side of the step portion 12 is an acute angle.

[0078] Therefore, no corner is formed on the negative pressure surface at the boundary between the stepped portion 12 and the thick-walled portion 10, so that even if vortices are generated at the boundary between the thick-walled portion 10 and the stepped portion 12 (i.e., the point where the airflow separates), the noise generated there can be reduced.

[0079] (8) In this embodiment, when viewed in cross-section perpendicular to the rotation axis Ax of the blade 4, the radius of curvature of both the positive pressure side and the negative pressure side of the leading edge 8 of the blade 4 is preferably set to 1.5 mm or more. Furthermore, the plate thickness T1 of the leading edge 8 of the blade 4 is preferably set to 3 mm or more.

[0080] Therefore, by increasing the thickness T1 of the leading edge 8, the airflow entering from the inlet of the blade 4 can flow along the wall surface from the leading edge 8 of the blade 4 to the inter-blade flow path. Thus, robustness to the inflow angle of the airflow can be improved.

[0081] (Second Implementation)

[0082] Reference Figure 8 The second embodiment will be described. The second embodiment differs from the first embodiment in that the structure of the stepped portion 12 of the blade 4 is changed, but otherwise it is the same as the first embodiment. Therefore, only the parts that are different from the first embodiment will be described.

[0083] exist Figure 8For ease of explanation, the location of the stepped portion 12 on the negative pressure surface of the blade 4 is also shown by crosshairs. In addition, a dashed line is used to represent the imaginary line H that includes the tangent point P between the trailing edge 9 of the blade 4 and the shield 2 and is perpendicular to the rotation axis Ax.

[0084] like Figure 8 As shown, in the second embodiment, the step portion 12 is formed within the height range of the trailing edge 9 of the blade 4. That is, the step portion 12 is formed between the aforementioned imaginary line H and the main board 3. According to this structure, the mainstream can be moved away from the negative pressure surface of the trailing edge 9 of the blade 4 in the rotational direction within the height range of the trailing edge 9 of the blade 4. Therefore, the noise generated at the trailing edge 9 of the blade 4 can be reduced.

[0085] (Third Implementation)

[0086] Reference Figure 9 The third embodiment will be described. The third embodiment also changes the structure of the step portion 12 compared to the first embodiment, etc., but is otherwise the same as the first embodiment, etc. Therefore, only the parts that are different from the first embodiment, etc. will be described.

[0087] exist Figure 9 For ease of explanation, the location of the stepped portion 12 on the negative pressure surface of blade 4 is indicated by crosshairs. For example... Figure 9 As shown, in the third embodiment, the stepped portion 12 is formed to extend radially inward from the side of the shield 2 toward the side of the main board 3. According to this structure, in order to cope with the rapid airflow on the side of the main board 3, by stripping the rapid airflow on the side of the main board 3 away from the trailing edge 9, the mainstream airflow can be further moved away from the negative pressure surface of the trailing edge 9 of the blade 4 in the direction of rotation. Therefore, the velocity gradient of the airflow colliding with the negative pressure surface of the trailing edge 9 of the blade 4 can be reduced, thus reducing noise.

[0088] (Fourth Implementation)

[0089] Reference Figure 10 The fourth embodiment will be described. The fourth embodiment differs from the first embodiment in that the structure of the step portion 12 is changed, but the rest is the same as the first embodiment. Therefore, only the parts that are different from the first embodiment will be described.

[0090] like Figure 10As shown, in the fourth embodiment, in a cross-sectional view perpendicular to the rotation axis Ax of the blade 4, the angle θ2 formed by the first tangent L1 at the center of the negative pressure surface 121 of the stepped portion 12 and the second tangent L2 at the stepped portion 12 side of the negative pressure surface of the thick-walled portion 10 is set to approximately 90°. In this structure, the velocity boundary layer generated in the airflow along the negative pressure surface of the thick-walled portion 10 can be disturbed starting from the boundary between the thick-walled portion 10 and the stepped portion 12, and a turbulent boundary layer can be generated with this boundary as the stripping point of the airflow, causing the mainstream to move away from the negative pressure surface of the thin-walled portion 11 in the rotational direction. Therefore, in the fourth embodiment, noise can be reduced by shifting the stripping point of the airflow along the negative pressure surface of the blade 4 forward and reducing the velocity gradient of the airflow colliding with the negative pressure surface of the trailing edge 9 of the blade 4.

[0091] (Other implementation methods)

[0092] (1) In the above embodiments, the turbine fan 1 is described as a closed fan consisting of a main board 3, a shield 2 and multiple blades 4 as a single unit, but it is not limited thereto. The turbine fan 1 may also be an open fan consisting of a main board 3 and multiple blades 4 as a single unit, while the multiple blades 4 and the shield 2 are composed of different components.

[0093] (2) In the first embodiment described above, the step portion 12 is described as being provided only in the region between the boundary line C on the leading edge 8 side when the blade length is divided into three equal parts and the boundary line E when the blade length is divided into two equal parts, but it is not limited thereto. The step portion 12 may be provided only in the region between the boundary line C on the leading edge 8 side when the blade length is divided into three equal parts and the boundary line D on the trailing edge 9 side when the blade length is divided into three equal parts.

[0094] (3) In the first embodiment described above, it is explained that the plate thickness T1 of the thick-walled portion 10 is preferably set to, for example, 3 mm or more, and the radius of curvature of both the positive pressure side and the negative pressure side of the leading edge 8 of the blade 4 is preferably set to 1.5 mm or more, but is not limited thereto. The plate thickness T1 of the thick-walled portion 10 and the radius of curvature of the leading edge 8 in a cross-sectional view perpendicular to the rotation axis Ax can be arbitrarily set.

[0095] This invention is not limited to the embodiments described above and can be appropriately modified. Furthermore, the various embodiments described above are not unrelated to each other; except for cases where they are explicitly incompatible, they can be appropriately combined. Additionally, in each of the above embodiments, the elements constituting the embodiment are not necessarily essential, except where they are specifically stated to be necessary or are explicitly considered necessary in principle. Furthermore, in each of the above embodiments, when referring to the number, value, quantity, range, etc., of the constituent elements of the embodiment, the number is not limited to that specific number, except where it is specifically stated to be necessary or is explicitly limited to a specific number in principle. Furthermore, in each of the above embodiments, when referring to the shape, positional relationship, etc., of the constituent elements, the shape, positional relationship, etc., is not limited to that shape, positional relationship, etc., except where it is specifically stated or is limited to a specific shape, positional relationship in principle.

[0096] (Summarize)

[0097] According to a first viewpoint shown in part or all of the above embodiments, a turbofan includes: a shroud having an air intake, a main plate disposed in the direction of the rotation axis of the shroud, and a plurality of blades disposed about the rotation axis between the shroud and the main plate. The plurality of blades of the turbofan have a thick-walled portion, a thin-walled portion, and a stepped portion. The thick-walled portion is a portion formed on the leading edge side with a thicker plate. The thin-walled portion is a portion disposed on the trailing edge side with a thinner plate than the thick-walled portion. The stepped portion is a portion disposed between the thick-walled portion and the thin-walled portion, where the plate thickness decreases from the thick-walled portion side toward the thin-walled portion side toward the positive pressure surface side. Furthermore, in a cross-sectional view perpendicular to the rotation axis of the blades, relative to the arcuate first curved surface of the negative pressure surface forming the thick-walled portion, the arcuate second curved surface of the negative pressure surface forming the thin-walled portion is located on the positive pressure surface side, and the first and second curved surfaces are connected by the negative pressure surface of the stepped portion.

[0098] According to the second viewpoint, the stepped section is located in the central area when the blade length is divided into three equal parts.

[0099] Therefore, since no step is provided in the front region, robustness to the inflow angle of the airflow can be improved. Furthermore, the step provided in the central region can disrupt the airflow flowing along the negative pressure surface of the thick-walled section, and generate a turbulent boundary layer by using this step as an airflow stripping point, causing the mainstream to move away from the negative pressure surface in the direction of rotation. Therefore, noise can be reduced by decreasing the velocity gradient of the airflow colliding with the negative pressure surface at the trailing edge of the blade.

[0100] According to the third viewpoint, the leading edge of the blade is located radially inward compared to the inner diameter of the shroud's inlet. Furthermore, the stepped portion is positioned radially outward compared to the inner diameter of the shroud's inlet.

[0101] Therefore, since no step is provided radially inward compared to the inner diameter of the shroud's inlet, the airflow entering from the blade inlet can flow from the leading edge of the blade along the wall of the thick-walled portion to the inter-blade flow path. This improves robustness to the airflow inflow angle.

[0102] According to the fourth viewpoint, the negative pressure surface at the boundary between the stepped portion and the thick-walled portion forms a smooth curved shape.

[0103] As a result, no corner is formed on the negative pressure surface at the boundary between the stepped section and the thick-walled section, thus reducing the noise generated thereeven if vortices are generated at the boundary between the thick-walled section and the stepped section (i.e., the point where the airflow separates).

[0104] According to the fifth point of view, the thickness of the thin-walled section is less than 75% of the thickness of the thick-walled section.

[0105] Therefore, according to the inventors' experiments, when the thickness of the thin-walled section is set to be less than 75% of the thickness of the thick-walled section, the noise reduction effect becomes extremely significant. Experiments show that noise can be reduced by more than 1.5 dB.

[0106] According to the sixth point of view, when viewed in cross-section perpendicular to the rotation axis of the blade, the negative pressure surface of the step is a curved surface that bulges toward the positive pressure surface.

[0107] As a result, the distance between the vortex generated at the boundary between the thick-walled section and the stepped section (i.e., the point where the airflow is separated) and the negative pressure surface of the stepped section becomes greater, thus reducing the noise generated there.

[0108] According to the seventh point of view, when viewed in a cross-section perpendicular to the rotation axis of the blade, the angle formed by the tangent in the central part of the negative pressure surface of the stepped portion and the tangent in the stepped side of the negative pressure surface of the thick-walled portion is an acute angle.

[0109] As a result, no corner is formed on the negative pressure surface at the boundary between the stepped section and the thick-walled section, thus reducing the noise generated thereeven if vortices are generated at the boundary between the thick-walled section and the stepped section (i.e., the point where the airflow separates).

[0110] According to the eighth point of view, under cross-sectional observation perpendicular to the blade's rotation axis, the radius of curvature of both the positive and negative pressure sides of the blade's leading edge is 1.5 mm or more, and the thickness of the blade's leading edge is 3 mm or more.

[0111] Therefore, by increasing the thickness of the leading edge plate, the airflow entering from the blade inlet can flow along the wall from the leading edge of the blade to the flow path between the blades. This improves robustness to the inflow angle of the airflow.

[0112] According to the ninth point of view, the step is formed at least within the height range of the trailing edge of the blade.

[0113] Therefore, at least within the height range of the trailing edge of the blade, the mainstream can be moved away from the negative pressure surface of the trailing edge of the blade in the direction of rotation, thereby reducing the noise generated at the trailing edge of the blade.

[0114] According to the tenth viewpoint, the stepped portion is formed to extend radially inward from the shield side toward the main board side.

[0115] Therefore, to cope with the rapid airflow on the mainboard side, the rapid airflow on the mainboard side is separated at a position away from the trailing edge, thereby increasing the distance between the negative pressure surface at the trailing edge of the blade and the mainstream flow. This reduces the velocity gradient of the airflow colliding with the negative pressure surface at the trailing edge of the blade, thus lowering noise.

Claims

1. A turbo fan comprising: a shroud having an air intake; a main board disposed along a rotation axis of the shroud; and a plurality of blades disposed about a rotation axis between the shroud and the main board, characterized in that... The plurality of said blades have: A thick-walled portion is formed on the leading edge side and has a relatively thick plate; A thin-walled portion, which is disposed on the trailing edge side compared to the thick-walled portion, and whose plate thickness is thinner than that of the thick-walled portion; and A stepped portion is provided between the thick-walled portion and the thin-walled portion, and the plate thickness decreases from the thick-walled portion side toward the thin-walled portion side toward the positive pressure surface side. In a cross-sectional view perpendicular to the rotation axis of the blade, the arc-shaped second curved surface forming the negative pressure surface of the thin-walled portion is located on the positive pressure surface side, relative to the first arc-shaped curved surface forming the negative pressure surface of the thick-walled portion. Furthermore, the first and second curved surfaces are connected by the negative pressure surface of the stepped portion. In a structure where the leading edge of the blade is located radially inward compared to the inner diameter of the inlet of the shroud, the stepped portion is only provided in the central region when the blade length is divided into three equal parts. The negative pressure surface of the stepped portion is a curved surface that bulges toward the positive pressure surface. The second curved surface, which forms the negative pressure surface of the thin-walled portion, protrudes from the positive pressure surface side. The stepped portion generates a turbulent boundary layer by stripping the airflow along the first curved surface of the thick-walled portion at the boundary with the thick-walled portion, causing the main flow to move away from the second curved surface of the thin-walled portion in the direction of rotation.

2. The turbine fan according to claim 1, characterized in that, The stepped portion is positioned radially outward compared to the inner diameter of the inlet of the shield.

3. The turbine fan according to claim 1, characterized in that, The negative pressure surface at the boundary between the stepped portion and the thick-walled portion is formed into a smooth curved shape.

4. The turbine fan according to claim 1, characterized in that, The thickness of the thin-walled portion is less than 75% of the thickness of the thick-walled portion.

5. The turbine fan according to any one of claims 1 to 4, characterized in that, When viewed in cross-section perpendicular to the rotation axis of the blade, the angle formed by the tangent at the center of the negative pressure surface of the stepped portion and the tangent at the stepped side of the negative pressure surface of the thick-walled portion is an acute angle.

6. The turbine fan according to any one of claims 1 to 4, characterized in that, When viewed in cross-section perpendicular to the rotation axis of the blade, the radius of curvature of both the positive pressure side and the negative pressure side of the leading edge of the blade is 1.5 mm or more, and the thickness of the leading edge of the blade is 3 mm or more.

7. The turbine fan according to any one of claims 1 to 4, characterized in that, The stepped portion is formed at least within the height range of the trailing edge of the blade.

8. The turbine fan according to any one of claims 1 to 4, characterized in that, The stepped portion is formed to extend radially inward from the shield side toward the main board side.

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