A backward centrifugal fan based on circumferential uneven perforated noise reduction blade

Abstract

The application aims to provide a backward centrifugal fan based on a circumferential non-uniform perforated noise reduction blade, comprising a volute and an impeller, the impeller comprising circular-arc-shaped blades, the circular-arc-shaped blades comprising a suction surface, a pressure surface, a circular-arc-shaped leading edge and a trailing edge, one side of the circular-arc-shaped leading edge of the circular-arc-shaped blades being provided with a row of perforations, the perforations being inclined from the pressure surface to the suction surface along the airflow direction, and one side of the trailing edge of the circular-arc-shaped blades being provided with three rows of perforations, the perforations being inclined from the suction surface to the pressure surface along the airflow direction; the circular-arc-shaped blades comprise circumferentially arranged first to tenth blades, and the circumferential profiles of the perforations corresponding to the first to tenth blades are helical lines. The non-uniform perforation design of the circumferential blades makes the flow conditions of the surfaces of each blade different, and the blade wake strengths different, which not only changes the phases of sound sources on the surfaces of different blades, but also changes the phases of interference sound sources of different blades and volute tongues, so that the sound intensity superposition of all circumferential blade surfaces and volute sound sources in the far field is reduced, and the fan noise in the far field is directly reduced.

Description

Technical Field

[0001] The present invention relates to a centrifugal fan, specifically a centrifugal fan based on perforated noise-reducing blades. Background Technology

[0002] Centrifugal fans, as a type of ventilation equipment, are widely used in industrial and civil fields and are closely related to people's living environment. The periodic interference between the centrifugal fan impeller and the volute generates periodic and random unsteady forces on the solid wall surface, which in turn causes the fan blades to vibrate and radiate high-intensity noise, affecting people's physical and mental health.

[0003] Currently, common methods for reducing aerodynamic noise in wind turbines include: wavy leading-edge blade design, serrated trailing-edge blades, and blade perforations. A wavy leading-edge design breaks up large vortices on the blade surface, reducing pressure pulsation at the leading edge and thus lowering the noise source intensity. Serrated trailing-edge blades disrupt smaller vortices on the non-working surfaces, reducing the jet-wake effect near the trailing edge and thus lowering aerodynamic noise. Blade perforations, with multiple rows of perforations at the leading or trailing edge, suppress flow separation on the blade surface, causing the separation point to shift backward, weakening turbulence intensity, and thus reducing noise radiation intensity.

[0004] However, for centrifugal fans, due to the presence of the volute, the pressure distribution on the surface of each blade is not uniform, i.e., the circumferential pressure is uneven. Furthermore, a uniform perforation design for each blade cannot maximize the reduction of centrifugal fan noise. For example... Figure 1 As shown, blade 1 is closest to the volute tongue 11, and its trailing edge 14 is closest to the volute 12, resulting in the smallest space for fluid compression and a larger high-pressure region. As the blade number increases, the distance between the blade trailing edge and the volute wall increases, the flow area increases, the fluid pressure decreases, and the high-pressure region shrinks significantly. Therefore, blades with lower numbers have a larger vortex separation area at the trailing edge, and the separation point is closer to the blade leading edge 13. Thus, a perforated design for every blade is not the optimal solution for reducing centrifugal fan noise. Summary of the Invention

[0005] The purpose of this invention is to provide a backward centrifugal fan based on circumferentially non-uniformly perforated noise-reducing blades that can further reduce aerodynamic noise.

[0006] The objective of this invention is achieved as follows:

[0007] This invention discloses a backward centrifugal fan based on circumferentially non-uniformly perforated noise-reducing blades, characterized in that: it includes a volute and an impeller, the impeller including arc-shaped blades, the arc-shaped blades including a suction surface, a pressure surface, an arc-shaped leading edge, and a trailing edge, a row of perforations is provided on one side of the arc-shaped blade leading edge, inclined from the pressure surface to the suction surface in the direction of airflow, and three rows of perforations are provided on one side of the arc-shaped blade trailing edge, inclined from the suction surface to the pressure surface in the direction of airflow; the arc-shaped blades include circumferentially arranged first to tenth blades, and the corresponding circumferential perforation profile of the first to tenth blades is a spiral.

[0008] The present invention may also include:

[0009] 1. The position of the perforation at the leading edge of the arc is determined by the circumferential profile of the perforation at the leading edge, and the position of the perforation at the trailing edge is determined by the circumferential profile of the perforation at the trailing edge. With the impeller center as the origin of the x and y axes and the center of the circle, the expressions for the circumferential profiles of the leading and trailing edge perforations are:

[0010]

[0011] In the formula, R is the distance from the leading edge to the center of the circle, C is the blade chord length, t is a variable with a value of 0-1, and a and b are variable parameters. For the circumferential profile of the leading edge perforation, a is 0.20-0.24 and b is 0.68-0.86; for the circumferential profile of the first row of perforations on the trailing edge, a is 0.65-0.75 and b is 0.05-0.19.

[0012] 2. The perforation area is 1%-2% of the original blade area, and the diameter of the perforation at the leading edge is the same as that at the trailing edge.

[0013] 3. The distance L1 between the leading edge of the perforation row and the leading edge of the arc is 3%-7% of the blade chord length C. The perforation position is located before the flow separation point. The spacing l1 between the perforations is 1 / 6 of the blade height h1 at the corresponding perforation position. The distance between the perforations located at the edge of the arc-shaped blade and the edge of the arc-shaped blade is 1 / 2 of the perforation spacing.

[0014] 4. The distance L2 from the first row of perforations on the trailing edge to the leading edge of the arc is 60%-70% of the blade chord length C. The spacing D between the three rows of perforations is 8%-10% of the blade chord length C. The perforation position on the trailing edge is located before the generation of vortices on the pressure surface. The spacing l2, l3 and l4 between the perforations is taken as 1 / 6 of the blade height h2, h3 and h4 at the corresponding perforation positions. The distance between the perforations located at the blade edge and the blade edge is 1 / 2 of the perforation spacing.

[0015] 5. The deflection angle α of the leading edge perforation is less than the deflection angle β of the trailing edge perforation, and the deflection angle range is 30°-60°.

[0016] The advantages of this invention are:

[0017] Simultaneous perforation at both the leading and trailing edges of the blade effectively suppresses flow separation on the blade surface, including flow separation between the suction surface at the leading edge and the pressure surface at the trailing edge. Suppressing the former breaks down the small vortex separation structure on the blade surface, reducing pressure pulsation at the leading edge and thus lowering the noise source intensity. Reducing the intensity of the latter disrupts large separation vortices on the blade surface, reducing the jet-wake effect near the trailing edge and thus lowering blade aerodynamic noise.

[0018] The non-uniform perforation design of the circumferential blades results in different flow conditions on each blade surface and different blade wake intensities. This not only changes the sound source phase of different blade surfaces, but also changes the interference sound source phase of different blades and volute tongues. As a result, the superposition of sound intensity of all circumferential blade surfaces and volute tongues in the far field is reduced, directly reducing the wind turbine noise in the far field. Attached Figure Description

[0019] Figure 1 This is a schematic diagram showing the uneven circumferential pressure distribution in a backward centrifugal fan.

[0020] Figure 2 This is an illustration of the effect of circumferentially uneven perforation.

[0021] Figure 3 Schematic diagram of the circumferential profile of the blade perforation;

[0022] Figure 4 This is a schematic diagram showing the location of the perforation on blade 10;

[0023] Figure 5 A schematic diagram of the perforation angle of the blade;

[0024] Figure 6 This is a schematic diagram of the perforation spacing at the leading edge of the blade (10).

[0025] Figure 7 This is a schematic diagram of the spacing between the 10 trailing edge perforations on the blade. Detailed Implementation

[0026] The invention will now be described in more detail with reference to the accompanying drawings:

[0027] Combination Figures 1-7 This invention relates to a circumferentially non-uniformly perforated centrifugal fan blade, comprising a volute 12, an impeller, and a main structure of the circumferentially non-uniformly perforated centrifugal fan formed by the circumferential profile of the perforated blades. The impeller consists of arc-shaped blades formed by a suction surface 19, a pressure surface 20, perforations, an arc-shaped leading edge 13, and a trailing edge 14. The arc-shaped blades include different blades numbered 1-10. One row of perforations is provided on one side of the leading edge 13, extending from the pressure surface 20 along the airflow direction to the suction surface. Three rows of perforations are provided on one side of the trailing edge 14, extending from the high-pressure suction surface 19 along the airflow direction to the pressure surface. The circumferential profile of the perforated blades numbered 1-10 is a spiral.

[0028] The perforation pattern of the blades is the same at different circumferential positions; only the perforation location differs. Figures 4-7 The perforation pattern of the blade 10 is described in detail, characterized by including a leading edge 13, a trailing edge 14, a suction surface 19, a pressure surface 20, a row of perforations at the leading edge, and three rows of perforations at the trailing edge.

[0029] The position of the perforation at the leading edge 13 of the blade is determined by the circumferential profile 15 of the leading edge perforation, and the position of the perforation at the trailing edge 14 of the blade is determined by the circumferential profiles 16-18 of the trailing edge perforation. The expression for the circumferential profile of the blade perforation is as follows:

[0030]

[0031] In the formula, R is the distance from the leading edge of the centrifugal fan blade to the center, C is the blade chord length, t is a system variable with a value of 0-1, and a and b are variable parameters. For the circumferential profile 15 of the leading edge perforation of the blade, a is 0.20-0.24 and b is 0.68-0.86; for the circumferential profile 16 of the first row of perforations on the trailing edge of the blade, a is 0.65-0.75 and b is 0.05-0.19.

[0032] The position and diameter of the perforations at the leading and trailing edges of the blades need to be standardized. If the perforation diameter is too large, a large amount of airflow will flow from the working surface of the blade to the non-working surface, and the aerodynamic characteristics of the fan cannot be guaranteed. If the perforation diameter is too small, the airflow passing through the hole will not be sufficient to suppress flow separation. Therefore, the perforation area of ​​this invention is 1%-2% of the original blade area, and the diameter of the perforation at the leading edge of the blade is the same as that at the trailing edge, which is 2-4 mm.

[0033] Combination Figure 1 Near the leading edge 13 of the blade, there is a small separation flow on the suction surface 19, and the static pressure on the pressure surface 20 is greater than that on the suction surface 19. Near the trailing edge 14, there is a large separation vortex on the pressure surface, and the static pressure on the pressure surface 20 is less than that on the suction surface 19. The principle of blade perforation is to penetrate from the high-pressure area to the low-pressure area along the main flow direction inside the fan. Considering the operating characteristics of a backward centrifugal fan, a row of perforations is designed at the leading edge to suppress the small separation flow at the leading edge, with the direction from the pressure surface 20 to the suction surface 19. Three rows of perforations are designed at the trailing edge to break the large separation vortex at the trailing edge, with the direction from the suction surface 19 to the pressure surface 20. Therefore, the deflection angle of the trailing edge perforations is opposite to that of the leading edge perforations; the deflection angle α of the leading edge perforations is less than the deflection angle β of the trailing edge perforations, and the deflection angle range is 30°-60°.

[0034] Combination Figure 1 , 4For blade 6, the distance L1 between the perforation positions on the leading edge of blade 10 and the blade leading edge is 3%-7% of the blade chord length C. The perforation positions are located before the flow separation point to suppress flow separation on the suction surface of the blade leading edge, forcing the flow separation point to move axially backward. This not only reduces flow losses caused by flow separation but also breaks up large vortices at the blade leading edge, reducing pressure pulsation amplitude and thus reducing the intensity of the sound source at the blade leading edge. The spacing l1 between the perforations is taken as 1 / 6 of the blade height h1 at the corresponding perforation position, and the distance from the perforation located at the blade edge to the blade edge is 1 / 2 of the perforation spacing.

[0035] Combination Figure 1 , 4 The distance L2 between the first row of perforations on the trailing edge of blade 10 and the leading edge of the blade is 60%-70% of the blade chord length C. The spacing D between the three rows of perforations is 8%-10% of the blade chord length C. The perforations on the trailing edge are located before the generation of vortices on the pressure surface to suppress large-scale vortices on the pressure surface of the blade trailing edge. The trailing edge perforations can directly guide the high-pressure airflow from the suction surface of the blade to the pressure surface. In addition to suppressing large separation flow on the trailing edge of the non-working surface of the blade, it can also reduce the wake-volute interference effect and reduce the wake turbulence intensity, thereby reducing the interference between the moving blade wake and the volute. This reduces the sound source intensity near the blade trailing edge and also reduces the sound source intensity near the most important sound source area of ​​the centrifugal fan—the volute tongue 11. The spacing l2, l3, and l4 between the perforations are taken as 1 / 6 of the blade height h2, h3, and h4 at the corresponding perforation positions. The distance between the perforations located at the blade edge and the blade edge is 1 / 2 of the perforation spacing.

Claims

1. A backward centrifugal fan based on circumferentially non-uniformly perforated noise-reducing blades, characterized in that: The system includes a volute and an impeller. The impeller includes arc-shaped blades, each with a suction surface, a pressure surface, an arc-shaped leading edge, and a trailing edge. A row of perforations is provided on one side of the arc-shaped leading edge, extending from the pressure surface towards the suction surface along the airflow direction. Three rows of perforations are provided on one side of the arc-shaped trailing edge, extending from the suction surface towards the pressure surface along the airflow direction. The arc-shaped blades include circumferentially arranged first to tenth blades, with the corresponding circumferential profile of the perforations on the first to tenth blades being a spiral. The position of the perforation at the leading edge of the arc is determined by the circumferential profile of the perforation at the leading edge, and the position of the perforation at the trailing edge is determined by the circumferential profile of the perforation at the trailing edge. With the impeller center as the origin of the x and y axes and the center of the circle, the expressions for the circumferential profiles of the leading and trailing edge perforations are: In the formula, R is the distance from the leading edge to the center of the circle, C is the blade chord length, t is a variable with a value of 0-1, and a and b are variable parameters. For the circumferential profile of the leading edge perforation, a is 0.20-0.24 and b is 0.68-0.86; for the circumferential profile of the first row of perforations on the trailing edge, a is 0.65-0.75 and b is 0.05-0.

19.

2. A backward centrifugal fan based on circumferentially non-uniformly perforated noise-reducing blades according to claim 1, characterized in that: The perforation area is 1%-2% of the original blade area, and the diameter of the perforation at the leading edge is the same as that at the trailing edge.

3. A backward centrifugal fan based on circumferentially non-uniformly perforated noise-reducing blades according to claim 1, characterized in that: The distance L1 between the leading edge of the perforation row and the leading edge of the arc is 3%-7% of the blade chord length C. The perforation position is located before the flow separation point. The spacing l1 between the perforations is 1 / 6 of the blade height h1 at the corresponding perforation position. The distance between the perforations located at the edge of the arc-shaped blade and the edge of the arc-shaped blade is 1 / 2 of the perforation spacing.

4. A backward centrifugal fan based on circumferentially non-uniformly perforated noise-reducing blades according to claim 1, characterized in that: The distance L2 from the first row of perforations on the trailing edge to the leading edge of the arc is 60%-70% of the blade chord length C. The spacing D between the three rows of perforations is 8%-10% of the blade chord length C. The trailing edge perforations are located before the pressure surface vortex is generated, and the spacing between the perforations... , and Take the leaf height at the corresponding perforation position , and 1 / 6 of the blade edge, the distance between the perforation and the blade edge is 1 / 2 of the perforation spacing.

5. A backward centrifugal fan based on circumferentially non-uniformly perforated noise-reducing blades according to claim 1, characterized in that: The deflection angle α of the leading edge perforation is less than the deflection angle β of the trailing edge perforation, and the deflection angle ranges from 30° to 60°.

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