Propeller fans and axial flow fans

Abstract

The outer peripheral part of a rotary blade (1) has a shape that is bent toward the upstream side of an airflow. A protrusion (20) extending parallel to a blade trailing edge (1b) of the rotary blade (1) is provided on a negative-pressure surface (1f) side of the blade trailing edge (1b). The protrusion (20) has a first inclined part (20a) that gradually increases in height from a blade leading edge side toward the apex of the protrusion (20), and a second inclined part (20b) that gradually decreases in height from the apex of the protrusion (20) toward the blade trailing edge (1b). A first angle, which is the angle of the first inclined part (20a), is steeper than a second angle, which is the angle of the second inclined part (20b).

Description

[Technical Field]

[0001] The present disclosure relates to a propeller fan and an axial flow fan used in a ventilation fan, an air conditioner, or the like. [Background technology]

[0002] In order to reduce noise, the rotor blades of the propeller fan of an axial flow blower have been designed to be forward-moving in the direction of rotation and tilted toward the upstream side of the airflow. In recent years, in order to further reduce noise, it has been proposed to bend the outer periphery of the rotor blade toward the upstream side of the airflow, thereby reducing interference caused by tip vortices that occur on the outer periphery of the blade.

[0003] Separation vortices are also formed near the leading edge of the blade, and airflow in a turbulent boundary layer is generated on the suction surface side of the rotor. The larger the separation vortex generated near the leading edge of the blade, the larger the blade trailing vortex generated behind the trailing edge, as the airflow on the suction surface becomes turbulent as it flows toward the trailing edge. In axial flow fans, noise is generated due to the interference of the blade tip vortex, separation vortex, and blade trailing vortex with adjacent rotors, bellmouths, etc. The larger the blade tip vortex, separation vortex, and blade trailing vortex, and the greater the turbulence of the airflow generated on the suction surface, the worse the noise characteristics become.

[0004] In Patent Document 1, a roughly triangular ridge is provided on the edge of the blade on the rear side in the rotation direction on the negative pressure side, roughly along the extension direction of the blade, to suppress noise caused by airflow on the negative pressure side. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-19335 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, the generally triangular ridge has a larger inclination angle on the leading edge side than on the trailing edge side, which makes it difficult to efficiently reduce the wake vortex generated behind the trailing edge of the blade, resulting in little noise reduction effect.

[0007] The present disclosure has been made in consideration of the above, and aims to provide a propeller fan that further reduces noise generated by blade wake vortices that occur behind the blade trailing edge. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the propeller fan of the present disclosure includes a boss portion that is driven to rotate, and a plurality of rotor blades that are attached to the boss portion in a radial pattern and generate an airflow in the direction of the rotation axis. The outer periphery of the rotor blade has a shape that is bent toward the upstream side of the airflow. A blade trailing edge of the rotor blade has a suction surface on the suction surface side. Along The protrusions are provided so as to extend continuously in parallel to each other. The protrusions have a first inclined portion whose height gradually increases from the leading edge of the blade to the apex of the protrusion, and a second inclined portion whose height gradually decreases from the apex of the protrusion to the trailing edge of the blade, and the first angle, which is the angle of the first inclined portion, is steeper than the second angle, which is the angle of the second inclined portion. If the height of the protrusion is tr and the thickness of the rotor blade is tk, then 0.04≦tr / tk≦0.56 holds. [Effects of the Invention]

[0009] The propeller fan according to the present disclosure has the effect of further reducing noise generated by blade wake vortices generated behind the blade trailing edges. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing a configuration of an axial flow fan according to an embodiment; [Figure 2] FIG. 1 is a perspective view showing a configuration of a propeller fan according to an embodiment; [Figure 3] FIG. 1 is a perspective view showing the generation of a blade tip vortex in a rotor of a propeller fan according to an embodiment; [Figure 4]1 is a plan view showing a rotor blade of a propeller fan according to an embodiment; [Figure 5] 1 is a partial cross-sectional view of a propeller fan according to an embodiment taken along a radial direction; [Figure 6] FIG. 1 is a perspective view showing a rotor blade of a propeller fan according to an embodiment; [Figure 7] 1 is a cross-sectional development view of an inner peripheral edge portion of a blade of a propeller fan according to an embodiment of the present invention; [Figure 8] 1 is a cross-sectional development view of a blade outer peripheral edge portion of a propeller fan according to an embodiment; [Figure 9] 1 is a cross-sectional development view of a middle portion between an inner peripheral edge portion and an outer peripheral edge portion of a blade of a propeller fan according to an embodiment; [Figure 10] 1 is a partially sectional development view showing a protrusion of a rotor blade of a propeller fan according to an embodiment of the present invention; [Figure 11] 1 is an enlarged cross-sectional view showing a protrusion of a rotor blade of a propeller fan according to an embodiment of the present invention; [Figure 12] FIG. 10 is a diagram showing a change in the inclination of a tangent to a negative pressure surface of a rotor blade of a propeller fan according to an embodiment. [Figure 13] Cross-sectional development showing the vortex behind the blade that occurs in a comparative example without protrusions [Figure 14] FIG. 1 is a cross-sectional development view showing blade wake vortices generated in the rotor blades of a propeller fan according to an embodiment having protrusions. [Figure 15] FIG. 10 is a diagram showing the relationship between the height of the protrusions on the blades of the propeller fan according to the embodiment and the specific noise reduction. [Figure 16] FIG. 10 is a diagram showing the relationship between the distance of the protrusion from the trailing edge of the blade of the propeller fan according to the embodiment and the specific noise reduction rate. [Figure 17] FIG. 10 is a plan view showing a modified example of the propeller fan according to the embodiment; [Figure 18] FIG. 10 is a plan view showing another modified example of the propeller fan according to the embodiment; [Figure 19] FIG. 1 is a plan view showing a propeller fan according to an embodiment; [Figure 20]12 is an enlarged cross-sectional development of the propeller fan according to the embodiment shown in FIG. 11 rotated so that the Z-axis direction is the up-down direction. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a propeller fan and an axial flow fan according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0012] Embodiment FIG. 1 is a perspective view showing the configuration of an axial flow fan 100 according to an embodiment. The axial flow fan 100 includes a propeller fan 10, a main body 21, a bell mouth 30 serving as an air tunnel, a motor (not shown), and a motor fixing member (not shown). The propeller fan 10 and the motor are disposed inside the bell mouth 30. The propeller fan 10 includes a cylindrical boss 2 and multiple rotor blades 1 having the same three-dimensional shape. The boss 2 is driven by the motor and rotates in the direction of arrow W around a rotation axis 3. The rotor blades 1 are attached radially to the outer periphery of the boss 2. As the propeller fan 10 rotates, the rotor blades 1 generate airflow in the direction of arrow A. The bell mouth 30 gradually narrows in diameter from the large-diameter inlet side toward the outlet side.

[0013] FIG. 2 is a perspective view showing the configuration of propeller fan 10 according to the embodiment. FIG. 3 is a perspective view showing the generation of a blade tip vortex in rotor 1 of propeller fan 10 according to the embodiment. FIG. 4 is a plan view showing rotor 1 of propeller fan 10 according to the embodiment. FIG. 5 is a partial cross-sectional view of propeller fan 10 according to the embodiment, cut along the radial direction. Rotor 1 has blade leading edge 1a, which is the end at the front in the direction of rotation indicated by arrow W, blade trailing edge 1b, which is the end at the rear in the direction of rotation indicated by arrow W, blade inner peripheral edge 1c, which is the end on the inner peripheral side (boss portion 2 side), and blade outer peripheral edge 1d, which is the end on the outer peripheral side. FIG. 1 shows five rotor blades 1, and FIG. 2 shows three rotor blades 1. Other numbers of rotor blades 1 may be used.

[0014] When the rotation of the propeller fan 10 generates airflow in the direction of arrow A, the flow on the inner periphery is advected in the centrifugal direction, creating a pressure difference between the pressure surface 1g and the suction surface 1f of the rotor 1. As a result, a leakage vortex is generated on the outer periphery of the rotor 1, from the high-pressure pressure surface 1g to the low-pressure suction surface 1f, as shown in FIG. 3. This is called a blade tip vortex 5. This blade tip vortex 5 causes noise due to interference between a separation vortex generated near the blade leading edge 1a and a blade wake vortex generated behind the blade trailing edge 1b, as will be described later. As shown in FIG. 5, with respect to the airflow direction indicated by arrow A, the blade surface upstream is the low-pressure suction surface 1f, and the blade surface downstream is the high-pressure pressure surface 1g. FIG. 4 shows the chord centerline g, which connects the midpoints between the blade leading edge 1a and the blade trailing edge 1b at each radial position around the coordinate center O, from the blade inner periphery 1c to the blade outer periphery 1d. 3 and 4, the Z axis corresponding to the rotation axis 3, the X axis and the Y axis which are two axes perpendicular to the Z axis, and the coordinate center O of the X axis, the Y axis and the Z axis are shown.

[0015] As shown in Fig. 5, propeller fan 10 has a shape in the direction connecting the inner circumferential portion and the outer circumferential portion, in which the outer circumferential portion is bent toward the upstream side of the airflow as indicated by arrow A. This reduces interference due to blade tip vortices 5 described above. In Fig. 4, the shape is an S-shape in which the inner circumferential portion is convex with respect to the airflow and the outer circumferential portion is concave with respect to the airflow, but the shape is not limited to this and may be any shape in which the outer circumferential portion is bent toward the upstream side of the airflow.

[0016] FIG. 6 is a perspective view showing rotor blade 1 of propeller fan 10 according to the embodiment. FIG. 7 is a developed cross-sectional view of blade inner peripheral portion 1c of propeller fan 10 according to the embodiment. FIG. 7 is a developed cross-sectional view obtained by cutting propeller fan 10 along a cylindrical plane of radius D1-D1' in FIG. 4 and developing the cross-section into a two-dimensional plane. FIG. 8 is a developed cross-sectional view of blade outer peripheral portion 1d of propeller fan 10 according to the embodiment. FIG. 8 is a developed cross-sectional view obtained by cutting propeller fan 10 along a cylindrical plane of radius D2-D2' in FIG. 4 and developing the cross-section into a two-dimensional plane. FIG. 9 is a developed cross-sectional view of an intermediate portion between blade inner peripheral portion 1c and blade outer peripheral portion 1d of propeller fan 10 according to the embodiment. FIG. 9 is a developed cross-sectional view obtained by cutting propeller fan 10 along a cylindrical plane of radius D3-D3' in FIG. 4 and developing the cross-section into a two-dimensional plane. Fig. 10 is a partial cross-sectional development showing protrusion 20 of rotor 1 of propeller fan 10 according to the embodiment. Fig. 11 is an enlarged cross-sectional development showing protrusion 20 of rotor 1 of propeller fan 10 according to the embodiment. Fig. 12 is a diagram showing changes in the slope of the tangent to the suction surface 1f of rotor 1 of propeller fan 10 according to the embodiment. Fig. 13 is a cross-sectional development showing blade wake vortices 14 and the like generated in a comparative example without protrusion 20. Fig. 14 is a cross-sectional development showing blade wake vortices 14 and the like generated in rotor 1 of propeller fan 10 according to the embodiment with protrusion 20.

[0017] As shown in Figures 7 to 9, the blade 1 has a shape that is convex upstream from the blade leading edge 1a to the blade trailing edge 1b. Therefore, near the blade trailing edge 1b, the blade 1 is inclined downstream (toward the negative side in the ZL direction) as it progresses toward the blade trailing edge 1b. Furthermore, the blade leading edge 1a is thicker than the blade trailing edge 1b. As can be seen from Figures 7 to 9, the blade 1 gradually becomes thinner from the blade inner peripheral edge 1c toward the blade outer peripheral edge 1d. Furthermore, the blade leading edge 1a has an R-shape to prevent airflow separation. The blade trailing edge 1b also has an R-shape to prevent airflow separation. At the blade trailing edge 1b, the curvature of the R-shape on the suction surface 1f side is greater than the curvature of the R-shape on the pressure surface 1g side.

[0018] As shown in Figures 2, 3, 4, 6, and 9, a protrusion 20 for suppressing the release of blade wake vortices 14 shown in Figure 14 is provided near the blade trailing edge 1b on the suction surface 1f side of the rotor 1. The protrusion 20 extends parallel to the blade trailing edge 1b. It is desirable that the protrusion 20 be provided continuously over at least one-third of the length of the blade trailing edge 1b. It is desirable that the protrusion 20 be provided continuously from a radial position Rrib near the blade inner peripheral edge 1c to a radial position Rrib' near the blade outer peripheral edge 1d, as shown in Figure 4.

[0019] As shown in FIGS. 10 and 11 , the protrusion 20 has a first inclined portion 20a whose height gradually increases from the protrusion end (point PB in FIG. 11 ) on the blade leading edge 1a side toward the apex of the protrusion 20 (point PD in FIG. 11 ), and a second inclined portion 20b whose height gradually decreases from the apex (point PD in FIG. 11 ) of the protrusion 20 toward the protrusion end (point PF in FIG. 11 ) on the blade trailing edge 1b side. The first angle of the first inclined portion 20a is steeper than the second angle of the second inclined portion 20b. In other words, the protrusion 20 has a shape in which the inclination θ1 with respect to the blade surface on the upstream side (the blade leading edge 1a side) is greater than the inclination θ2 with respect to the blade surface on the downstream side (the blade trailing edge 1b side). It is desirable for the protrusion 20 to have the same cross-sectional shape in the direction along the blade trailing edge 1b.

[0020] 9, the blade chord length L is defined as the longest distance between two parallel lines LW1 and LW2 when the blade is sandwiched between them in the cylindrical cross section of the rotor 1. The direction parallel to the blade chord length L from the blade leading edge 1a to the blade trailing edge 1b is defined as the XL direction, and the direction perpendicular to the blade chord length L, parallel to the lines LW1 and LW2, from downstream to upstream is defined as the ZL direction.

[0021] In Figure 11, the curved surface connecting points PA and PB is the curved surface on the blade leading edge 1a side of the blade surface adjacent to the protrusion 20. The arc connection connecting points PB and PC is the portion connecting the portion of the protrusion 20 on the blade leading edge 1a side to the blade surface. The curved surface connecting point PC and the vertex point PD is the curved surface on the blade leading edge 1a side of the protrusion 20. The curved surface connecting points PD and PE is the curved surface on the blade trailing edge 1b side of the protrusion 20. The arc connection connecting points PE and PF is the portion connecting the portion of the protrusion 20 on the blade trailing edge 1b side to the blade surface. The curved surface connecting points PF and PG is the curved surface on the blade trailing edge 1b side of the blade surface adjacent to the protrusion 20. Point PG is a point included in the blade trailing edge 1b.

[0022] The curved surface connecting points PA and PB and the curved surface connecting points PF and PG are part of the suction surface 1f, which is the upstream surface of the rotor 1. The curved surface connecting points PC and PD and the curved surface connecting points PD and PE form the protrusion 20. The curved surface connecting points PA and PB and the curved surface connecting points PF and PG are convex surfaces facing upstream. The curved surface connecting points PC and PD and the curved surface connecting points PD and PE are convex surfaces facing upstream, and have a greater curvature than the curved surface connecting points PA and PB and the curved surface connecting points PF and PG. In other words, the protrusion 20 is a curved surface with a greater curvature than the suction surface 1f of the rotor 1.

[0023] The suction surface 1f and the protrusion 20 are smoothly connected in an arc shape by an arc connection portion connecting points PB and PC and an arc connection portion connecting points PE and PF. The curved surface connecting points PA and PB and the curved surface connecting points PC and PD are continuously and smoothly connected by an arc connection portion connecting points PB and PC so that the slopes at the connection portions are equal. The arc connection portion connecting points PB and PC is convex toward the downstream side. The curved surface connecting points PD and PE and the curved surface connecting points PF and PG are continuously and smoothly connected by an arc connection portion connecting points PE and PF so that the slopes at the connection portions are equal. The arc connection portion connecting points PE and PF is convex toward the downstream side. The curved surface connecting points PD and PE, which is the curved surface of the protrusion 20 on the blade trailing edge 1b side, is formed with a smaller curvature than the curved surface connecting points PC and PD, which is the curved surface of the protrusion 20 on the blade leading edge 1a side.

[0024] FIG. 12 shows the change in the XL direction of the tangent slope dZL / dXL of the suction surface 1f of the rotor blade 1 of the propeller fan 10. As shown in FIGS. 11 and 12, the curved surface connecting points PA and PB is convex toward the upstream side, and the arc connection portion connecting points PB and PC is convex toward the downstream side. Therefore, the tangent slope dZL / dXL is maximum at point PB between points PA and PC. Line LPB is a line tangent to the blade surface at point PB. The slope of the blade surface portion adjacent to the protrusion 20 on the blade leading edge 1a side is defined by line LPB. In other words, the slope of the blade surface portion adjacent to the protrusion 20 on the blade leading edge 1a side is the slope at point PB, which is closer to the blade leading edge 1a than point PD, the apex of the protrusion 20, and where the tangent slope is at its maximum downstream slope.

[0025] The curved surface connecting points PC and PD that make up the protrusion 20 is a curved surface that is convex toward the upstream side and that protrudes more upstream as it approaches the blade trailing edge 1b. The arc-shaped connecting portion connecting points PB and PC is a curved surface that is convex toward the downstream side, so the slope of the tangent to the XL axis on the blade leading edge 1a side of the protrusion 20 is greatest at point PC. Line LPC is a line that is tangent to the blade surface at point PC. The slope of the protrusion 20 on the blade leading edge 1a side is defined by line LPC. In other words, the slope of the protrusion 20 on the blade leading edge 1a side is the slope of point PC, which is the position on the blade leading edge 1a side of point PD, the apex of the protrusion 20, where the slope of the tangent is at its greatest upstream slope.

[0026] The curved surface connecting points PD and PE that make up the protrusion 20 is a curved surface that is convex toward the upstream side and that protrudes more upstream as it approaches the blade leading edge 1a. The arc-shaped connection connecting points PE and PF is a curved surface that is convex toward the downstream side, so the slope of the tangent to the protrusion 20 on the blade trailing edge 1b side with respect to the XL axis is maximum at point PE. Line LPE is a line that is tangent to the blade surface at point PE. The slope of the protrusion 20 on the blade trailing edge 1b side is defined by line LPE. In other words, the slope of the protrusion 20 on the blade trailing edge 1b side is the slope at point PE, near the connection between the protrusion 20 and the blade trailing edge 1b, where the slope of the tangent is at its maximum downstream slope. Line LPB2 is a line that passes through point PE and is parallel to line LPB.

[0027] The inclination θ1 of the protrusion 20 on the blade leading edge 1a side is defined as the angle between the lines LPB and LPC. The inclination θ2 of the protrusion 20 on the blade trailing edge 1b side is defined as the angle between the lines LPB2 and LPE.

[0028] The height tr of the protrusion 20 and the thickness tk of the rotor blade 1 are defined as follows: The vertex of the protrusion 20 in the ZL direction is defined as point PD. The height tr of the protrusion 20 and the thickness tk of the blade portion are defined by the height in the ZL direction at the position of point PD. A straight line LPB is defined as the imaginary blade surface. Point Pt is a point that passes through the vertex of the protrusion 20 indicated by point PD, on a line extending in the ZL direction, and intersects with line LPB. The height from point Pt to point PD, the vertex of the protrusion 20, is defined as the height tr of the protrusion 20. Point Pk is a point that passes through the vertex of the protrusion 20 indicated by point PD, on a line extending in the ZL direction, and intersects with the blade surface of the pressure surface 1g. The width from point Pt to point Pk is defined as the thickness tk of the blade portion.

[0029] The width tw of the protrusion 20 and the distance B of the protrusion 20 from the blade trailing edge 1b are defined as follows: The width tw of the protrusion 20 is the distance in the XL direction from point PC, which is the leading edge of the protrusion 20, to point PE, which is the trailing edge of the protrusion 20. The distance in the XL direction from point PE, which is the trailing edge of the protrusion 20, to point PG on the blade trailing edge 1b of the rotor 1 is the distance B of the protrusion 20 from the blade trailing edge 1b.

[0030] As shown in Figures 13 and 14, airflow from the front and the side flows into the blade leading edge 1a, forming a separation vortex 31 near the blade leading edge 1a. An airflow 32 in the turbulent boundary layer is generated on the suction surface 1f side of the rotor 1. The larger the separation vortex 31 generated near the blade leading edge 1a, the larger the blade trailing vortex 14 generated behind the blade trailing edge 1b, as the airflow 32 becomes more turbulent as it flows toward the blade trailing edge 1b. As shown in Figure 13, without the protrusion 20, the flow of the airflow 32 toward the blade trailing edge 1b cannot be impeded, and a relatively large blade trailing vortex 14, which is a Karman vortex, is generated behind the blade trailing edge 1b. In contrast, as shown in Figure 14, if the rotor 1 is provided with the protrusion 20, the flow of the airflow 32 toward the blade trailing edge 1b can be impeded, and the blade trailing vortex 14 generated behind the blade trailing edge 1b can be reduced.

[0031] In this embodiment, the inclination θ2 of the protrusion 20 on the blade trailing edge 1b side is set larger than the inclination θ1 of the protrusion 20 on the blade leading edge 1a side. In other words, the first angle, which is the angle of the first inclined portion 20a, is set steeper than the second angle, which is the angle of the second inclined portion 20b. This makes it possible to more effectively impede the flow of airflow 32 toward the blade trailing edge 1b than the protrusion in Patent Document 1, and further reduce the blade wake vortex 14 generated behind the blade trailing edge 1b. This makes it possible to further reduce noise.

[0032] That is, in Patent Document 1, when the flow point changes and the angle of the flow entering the rotor 1 changes, the shape of the protrusions can cause excessive separation, potentially resulting in increased noise. Furthermore, dust and other particles tend to accumulate at the apex of the protrusions, and when dust accumulates, the shape of the protrusions changes, potentially resulting in a change in the flow, excessive separation, and increased noise. In contrast, the protrusions 20 of the present embodiment have a curved shape on the upstream side of the flow and a sharp point on the downstream side, with the thick apex being closer to the upstream side of the flow. This prevents excessive flow separation and stabilizes the flow. Therefore, even if the flow point changes and the flow angle changes, the impact is small, and the effects of the protrusions 20 can be stably achieved. Furthermore, because the shape of the protrusions changes continuously, there are no corners, making it difficult for dust and other particles to accumulate. This makes it difficult for the shape of the protrusions to change, and the effects of the protrusions 20 can be stably achieved.

[0033] Furthermore, it is desirable that θ1 be greater than 90°. By making θ1 greater than 90°, it is possible to weaken the turbulence caused by the blade wake vortex 14. In other words, it is desirable that the angle of the protrusion 20 satisfy the relationship 90°<θ1<θ2.

[0034] 15 is a diagram showing the relationship between the height of the protrusions 20 on the blades of the propeller fan 10 according to the embodiment and the specific noise reduction. In FIG. 15, the horizontal axis represents the ratio of the height tr of the protrusions 20 to the plate thickness tk, and the specific noise reduction rate ΔK T As shown in FIG. 15, the relationship between the height tr of the protrusion 20 and the specific noise reduction ratio ΔK T There is an optimum point for this. It can be seen that in order to obtain an effective noise reduction effect, an effect of -1 (dB) or more in terms of specific noise can be obtained in the range of 0.04≦tr / tk≦0.56.

[0035] Specific noise K T is the calculated value as follows: K T =SPL A -10Log(Q·P T 2.5 ) Q is the air volume [m 3 / min] and PT is the total pressure [Pa], and SPL A is the noise characteristic [dB] after A-weighting correction.

[0036] It is desirable that the width tw of the protrusion 20 be in the range of 1 time the height tr of the protrusion 20 to 4 times the height tr of the protrusion 20, as shown in the following formula. 1×tr≦tw≦4×tr

[0037] The shape of the protrusion 20 is a smooth curved shape that is higher in the center and lower in the periphery. The curved shape may be, for example, a parabola or a quadratic curve.

[0038] FIG. 16 shows the relationship between the distance of the protrusion 20 from the blade trailing edge 1b of the propeller fan 10 according to the embodiment and the specific noise reduction ratio ΔK T 16 shows the relationship between the specific noise reduction rate ΔK and the ratio of the distance B of the protrusion 20 from the trailing edge 1b of the blade to the chord length L. T As shown in Fig. 16, if the position of the protrusion 20 is too far from the blade trailing edge 1b, the noise reduction effect is small, so in order to obtain an effect of -1 (db) or more, it is desirable to provide the protrusion 20 in the range of 0.01 ≦ B / L ≦ 0.08.

[0039] Fig. 17 is a plan view showing a modified example of propeller fan 10 according to the embodiment. Fig. 18 is a plan view showing another modified example of propeller fan 10 according to the embodiment. In Fig. 17, protrusions 20 are provided on the outer periphery side from the center position in the radial direction. In Fig. 18, protrusions 20 are provided on the inner periphery side from the center position in the radial direction.

[0040] With the propeller fan 10 according to the embodiment, noise reduction is possible regardless of the pattern of the protrusions 20, and it has been experimentally confirmed that a specific noise reduction effect of -1.8 (dB) can be achieved. Even when it is not possible to arrange the protrusions 20 over the entire blade trailing edge 1b due to manufacturing reasons, a certain degree of effect can be achieved. These series of evaluation results were obtained by evaluating a rotor 1 with a diameter of 220 mm at a constant rotation speed of 1400 / min. It is to be noted that the length of the protrusions 20 is preferably parallel to the blade trailing edge 1b and is at least one-third of the length of the blade trailing edge 1b.

[0041] Next, a description will be given of a shape related to a molding method of propeller fan 10. Fig. 19 is a plan view showing propeller fan 10 according to an embodiment. As shown in Figs. 1, 2, and 9, in propeller fan 10 according to the embodiment, when viewed from the direction of rotation shaft 3 (Z-axis direction), multiple rotor blades 1 are evenly arranged in the circumferential direction around rotation shaft 3 so as not to overlap. With this configuration, propeller fan 10 can be molded from resin using a mold that is divided into two halves, upper and lower, in the Z-axis direction.

[0042] Here, in this embodiment, protrusion 20 also has a shape that can be molded in two parts. FIG. 20 is an enlarged cross-sectional development view of propeller fan 10 according to the embodiment shown in FIG. 11 , rotated so that the Z-axis direction is the vertical direction. Resin molding is performed using a mold that is divided into two parts in the vertical direction of FIG. 20 , i.e., the positive and negative directions of the Z-axis. To enable this molding, protrusion 20 may have a cylindrical cross section with rotation axis 3 extending in the Z-axis direction as its axis, the cross section being wider from the upstream side to the downstream side. Specifically, the slope of straight line LPC may be such that it slopes upward from blade leading edge 1a toward blade trailing edge 1b as it progresses from downstream (Z-axis negative side) to upstream (Z-axis positive side), and the slope of straight line LPE may be such that it slopes upward from blade trailing edge 1b toward blade leading edge 1a as it progresses from downstream (Z-axis negative side) to upstream (Z-axis positive side).

[0043] This shape prevents undercuts during molding, makes it possible to use a mold with a simple upper and lower configuration, and does not incur a significant increase in cost for implementation. In addition, this shape eliminates corners, preventing dust from adhering, and allows the noise reduction effect to be maintained for a long period of time even when no cleaning work is required.

[0044] The configurations shown in the above embodiments are examples of the contents of the present disclosure, and may be combined with other known technologies, and parts of the configurations may be omitted or modified within the scope of the gist of the present disclosure. [Explanation of symbols]

[0045] 1 rotor, 1a blade leading edge, 1b blade trailing edge, 1c blade inner peripheral edge, 1d blade outer peripheral edge, 1f suction surface, 1g pressure surface, 2 boss portion, 3 rotor shaft, 5 blade tip vortex, 10 propeller fan, 14 blade wake vortex, 20 protrusion portion, 20a first inclined portion, 20b second inclined portion, 21 main body, 30 bell mouth, 31 separation vortex, 32 airflow, 100 axial flow fan, g blade chord centerline, L blade chord length, O coordinate center.

Claims

1. A propeller fan comprising: a boss portion that is driven to rotate; and a plurality of rotor blades that are attached radially to the boss portion and generate an airflow in the direction of a rotation axis, an outer periphery of the rotor has a shape that is bent toward the upstream side of the airflow, a protrusion extending continuously and parallel to the trailing edge of the blade is provided on a suction surface side of the trailing edge of the blade, the protrusion has a first inclined portion whose height gradually increases from the blade leading edge side toward the apex of the protrusion, and a second inclined portion whose height gradually decreases from the apex of the protrusion toward the blade trailing edge side, and a first angle which is an angle of the first inclined portion is steeper than a second angle which is an angle of the second inclined portion, When the height of the protrusion is tr and the plate thickness of the rotor is tk, 0.04≦tr / tk≦0.56 holds true A propeller fan characterized by:

2. The propeller fan according to claim 1 , wherein the first inclined portion and the second inclined portion are curved surfaces that are convex toward the upstream side.

3. The propeller fan according to claim 1 , wherein a cross section of the protrusion, taken along a cylindrical surface having an axis on the rotation axis, has a shape that widens from the upstream side to the downstream side.

4. Let B be the distance between the end of the protrusion on the blade trailing edge side and the blade trailing edge of the rotor, and let L be the blade chord length which is the distance between the blade leading edge and the blade trailing edge of the rotor, 0.01≦B / L≦0.08 2. The propeller fan according to claim 1, wherein the following holds true:

5. The curved surface of the protrusion on the blade trailing edge side is formed with a smaller curvature than the curved surface of the protrusion on the blade leading edge side.

2. The propeller fan according to claim 1 .

6. The length of the protrusion along the trailing edge of the wing is at least one-third of the length of the trailing edge of the wing.

2. The propeller fan according to claim 1 .

7. The propeller fan according to any one of claims 1 to 6, a motor that rotates the boss portion of the propeller fan; a main body including a bell mouth disposed around the propeller fan; An axial flow fan comprising:

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