Blade trailing edge design method for reducing centrifugal fan noise

Abstract

This invention discloses a blade trailing edge design method for reducing centrifugal fan noise, comprising an upper cover plate, blades, and a lower cover plate. The specific process is as follows: the intersection line of the upper cover plate and the blade is defined as blade profile A when the relative blade height is 0; the intersection line of the lower cover plate and the blade is defined as blade profile B when the relative blade height is 1; the blade profiles at 1 / 4 and 3 / 4 of the relative blade height are defined as blade profile C and blade profile D, respectively; using the leading edge points of blade profiles B, C, and D as origins, blade profiles B, C, and D are rotated respectively; connecting the rotated trailing edges yields an inclined S-shaped trailing edge blade. This invention solves the problem of excessive noise during the operation of existing fans.

Description

Technical Field

[0001] This invention belongs to the field of wind turbine technology and relates to a blade trailing edge design method for reducing noise in centrifugal fans. Background Technology

[0002] A blower is a fluid machine that increases gas pressure and discharges gas by inputting mechanical energy. It is widely used in industries such as metallurgy, steelmaking, energy, and defense. Centrifugal fans are a common type of blower, utilizing a high-speed rotating impeller to change the speed and direction of gas flow, converting kinetic energy into potential energy. As my country has basically entered industrialization, related energy-consuming industries are undergoing energy conservation, emission reduction, and industrial upgrading. Centrifugal fans, as a major power machinery equipment in the energy industry, are widely used in various sectors of society. However, centrifugal fans are also high-energy-consuming equipment, consuming approximately one-tenth of the country's total electricity generation. In recent decades, my country's centrifugal fan industry has developed rapidly, but in terms of certain high-end energy-saving technologies, there is still a gap compared to developed countries, with problems such as low fan efficiency and high noise levels. How to reduce fan noise and vibration while ensuring centrifugal fan performance and maximizing fan efficiency is an important task in current centrifugal fan research. Summary of the Invention

[0003] The purpose of this invention is to provide a blade trailing edge design method to reduce the noise of centrifugal fans and solve the problem of excessive noise during the operation of existing fans.

[0004] The technical solution adopted in this invention is a blade trailing edge design method for reducing centrifugal fan noise, including an upper cover plate, blades, and a lower cover plate. The specific process is as follows: the intersection line of the upper cover plate and the blade is defined as blade profile A when the relative blade height is 0, the intersection line of the lower cover plate and the blade is defined as blade profile B when the relative blade height is 1, the blade profiles at 1 / 4 relative blade height and 3 / 4 relative blade height are defined as blade profile C and blade profile D, respectively, and the leading edge points of blade profile B, blade profile C, and blade profile D are taken as origins, respectively, and blade profile B, blade profile C, and blade profile D are rotated, and the rotated trailing edges are connected to obtain an inclined S-shaped trailing edge blade.

[0005] The invention is further characterized in that,

[0006] The specific steps are as follows:

[0007] Step 1: Define the intersection line of the upper cover plate and the blade as blade profile A when the relative blade height is 0, and define the intersection line of the lower cover plate and the blade as blade profile B when the relative blade height is 1.

[0008] Step 2: Define the endpoint of blade profile A that is closer to the center of the centrifugal fan impeller as the leading edge point, and define the endpoint of blade profile A that is farther away from the center of the centrifugal fan impeller as the trailing edge.

[0009] Define the endpoint of blade profile B that is closer to the center of the centrifugal fan impeller as the leading edge point A, and define the endpoint of blade profile B that is farther away from the center of the centrifugal fan impeller as the trailing edge A;

[0010] Step 3: Keep the upper cover plate and blade profile A unchanged, take the leading edge point A as the origin, rotate the blade profile B counterclockwise, and connect the trailing edge to the trailing edge A to obtain an inclined trailing edge blade.

[0011] Step 4: Divide the inclined trailing edge blade obtained in Step 3 into four equal parts along the height direction using a plane parallel to the lower cover plate. The blade profile C, which is closer to blade profile A, is 1 / 4 of the blade height relative to the blade profile, and the blade profile D, which is closer to blade profile B, is 3 / 4 of the blade height relative to the blade profile.

[0012] Step 5: Define the endpoint of the blade profile C closest to the center of the centrifugal fan impeller as the leading edge point B, and with the leading edge point B as the origin, rotate the blade profile C counterclockwise. Define the endpoint of the rotated blade profile C furthest from the center of the centrifugal fan impeller as the trailing edge B.

[0013] Define the endpoint of the blade profile D closest to the center of the centrifugal fan impeller as the leading edge point C, and take the leading edge point C as the origin. Rotate the blade profile D clockwise, and define the endpoint of the rotated blade profile D furthest from the center of the centrifugal fan impeller as the trailing edge C.

[0014] Step 6: Connect the trailing edge to trailing edge B, trailing edge B to trailing edge C, and trailing edge C to trailing edge A smoothly using spline curves to obtain an inclined S-shaped trailing edge blade.

[0015] In step 3, the rotation angle of blade profile B is 5°.

[0016] In step 5, the rotation angle of the blade profile C is 2.5°.

[0017] In step 5, the rotation angle of the blade profile D is 2.5°.

[0018] The beneficial effects of this invention are: the blade trailing edge design method of this invention for reducing centrifugal fan noise, without affecting the fluid flow area, designs the blade as an inclined S-shaped trailing edge blade, which improves the undesirable flow state such as flow separation and backflow on the blade surface, makes the fluid flow in the impeller more stable, suppresses the separation vortex of the blade trailing edge, and reduces the turbulent kinetic energy of the blade trailing edge, effectively reducing the noise during the operation of the fan. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the centrifugal fan impeller structure obtained by the blade trailing edge design method for reducing centrifugal fan noise according to the present invention.

[0020] Figure 2 This is a schematic diagram of the structure of an existing centrifugal fan impeller;

[0021] Figure 3 This is a schematic diagram of the blade trailing edge design method for reducing centrifugal fan noise according to the present invention.

[0022] Figure 4 These are the aerodynamic noise monitoring points during the numerical simulation of the centrifugal fan impeller obtained by the method of this invention;

[0023] Figure 5 This is a comparison chart of the radiated noise of existing centrifugal fans and centrifugal fans with blades obtained using the method of this invention;

[0024] Figure 6 This is a comparison chart of the aerodynamic noise at monitoring points of existing centrifugal fans and centrifugal fans with blades obtained using the method of this invention.

[0025] In the figure, 1. upper cover plate, 2. blade, 3. lower cover plate, 4. blade profile A, 5. blade profile B, 6. blade profile C, 7. blade profile D, 8. leading edge point A, 9. leading edge point B, 10. leading edge point C. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0027] This invention provides a method for designing the trailing edge of a centrifugal fan blade to reduce noise. The specific process is as follows: the intersection line of the upper cover plate 1 and the blade 2 is defined as the blade profile A4 when the relative blade height is 0; the intersection line of the lower cover plate 3 and the blade 2 is defined as the blade profile B5 when the relative blade height is 1; the blade profiles at 1 / 4 and 3 / 4 of the relative blade height are defined as blade profile C6 and blade profile D7, respectively; using the leading edge points of blade profiles B5, C6, and D7 as origins, blade profiles B5, C6, and D7 are rotated respectively; the rotated trailing edges are then connected to obtain an inclined S-shaped trailing edge blade. The resulting centrifugal fan impeller structure is as follows. Figure 1 As shown, an inclined S-shaped trailing edge blade 2 obtained by the method of the present invention is disposed between the upper cover plate 1 and the lower cover plate 3.

[0028] The structure of existing centrifugal fan impellers is as follows: Figure 2 As shown, it includes an upper cover plate 1 and a lower cover plate 3, with a blade 2 disposed between the upper cover plate 1 and the lower cover plate 3.

[0029] like Figure 3 As shown, please follow these steps:

[0030] Step 1: Define the intersection line of the upper cover plate 1 and the blade 2 as the blade profile A4 when the relative blade height is 0, and define the intersection line of the lower cover plate 3 and the blade 2 as the blade profile B5 when the relative blade height is 1.

[0031] Step 2: Define the endpoint of blade profile A4 that is closer to the center of the centrifugal fan impeller as the leading edge point, and define the endpoint of blade profile A4 that is farther away from the center of the centrifugal fan impeller as the trailing edge.

[0032] Define the endpoint of blade profile B5 that is closer to the center of centrifugal fan impeller as leading edge point A8; define the endpoint of blade profile B5 that is farther from the center of centrifugal fan impeller as trailing edge A.

[0033] Step 3: Keep the upper cover plate 1 and the blade profile A4 unchanged. Using the leading edge point A8 as the origin, rotate the blade profile B5 counterclockwise by 5°. After rotation, connect the trailing edge to the trailing edge A to obtain an inclined trailing edge blade.

[0034] Step 4: Divide the inclined trailing edge blade obtained in Step 3 into four equal parts along the height direction using a plane parallel to the lower cover plate 3. The blade profile C6, which is closer to the blade profile A4, is 1 / 4 of the blade height, and the blade profile D7, which is closer to the blade profile B5, is 3 / 4 of the blade height.

[0035] Step 5: Define the endpoint of the blade profile C6 closest to the center of the centrifugal fan impeller as the leading edge point B9, and with the leading edge point B9 as the origin, rotate the blade profile C6 counterclockwise by 2.5°, and define the endpoint of the rotated blade profile C6 furthest from the center of the centrifugal fan impeller as the trailing edge B.

[0036] Define the endpoint of blade profile D7 closest to the center of centrifugal fan impeller as leading edge point C10, and take leading edge point C10 as origin. Rotate blade profile D7 clockwise by 2.5°, and define the endpoint of blade profile D7 furthest from the center of centrifugal fan impeller as trailing edge C.

[0037] Step 6: Connect the trailing edge to trailing edge B, trailing edge B to trailing edge C, and trailing edge C to trailing edge A smoothly using spline curves to obtain an inclined S-shaped trailing edge blade.

[0038] The design method of this invention firstly reduces the rotational noise of the fan (caused by the unsteady flow of the fluid) by rotating the blade profile B5 to form an inclined trailing edge and creating a phase difference. The larger the inclination angle, the greater the reduction in the sound pressure level of the rotational noise. However, in order to ensure the flow area of ​​the fan, the blade profile B5 is rotated counterclockwise by 5°. Secondly, when the fluid passes through the edge of the blade trailing edge, it will produce shedding and backflow phenomena. The inclined S-shaped trailing edge blade obtained by the method of this invention can decompose and disperse the shedding vortices, reduce the intensity of the airflow, make the velocity distribution in the flow channel more uniform, and reduce the vortex shedding noise caused by laminar boundary layer separation. At low Mach numbers, the flow-induced noise can be considered to mainly come from vortices. Furthermore, the turbulent kinetic energy generated by the inclined S-shaped trailing edge blade obtained by the method of this invention is smaller than that of the original blade, thereby reducing the broadband noise of the fan.

[0039] The method of this invention rotates the blade profile at different relative blade heights without causing blade distortion. The resulting inclined S-shaped trailing edge blade can break the large-scale vortex in the blade wake region into small-scale vortices, reducing velocity loss, effectively reducing turbulent kinetic energy, and thus reducing the radiated noise of the blade.

[0040] To verify the feasibility of the blade trailing edge design method for reducing centrifugal fan noise according to the present invention, a centrifugal fan with inclined S-shaped trailing edge blades obtained by the method of the present invention was compared with an existing centrifugal fan. The same parameters were set as follows: design speed of 1200 r / min and design flow rate of 12.056 kg / s. During fan operation, due to the periodic rotation of the blades, the fluid continuously impacts the volute tongue, resulting in significant noise in the volute tongue region. Therefore, the monitoring point was placed at the volute tongue position. Figure 4 As shown.

[0041] The calculation results are as follows Figure 5 As shown, the acoustic directivity curves at a radius of 4m with the wind turbine center point as the origin show little difference in radiated noise at the first harmonic frequency, while at the second harmonic, the radiated noise of the wind turbine using blades obtained by the method of this invention is significantly reduced; as Figure 6 As shown, within the 0-4800Hz range, the noise at the trailing edge of the blade obtained by the method of this invention is significantly lower than that of the existing technology model. The inclined S-shaped trailing edge blade obtained by the method of this invention effectively reduces the vorticity and turbulent kinetic energy at the trailing edge of the blade, thereby reducing the noise of the centrifugal fan.

Claims

1. A method for designing the trailing edge of blades to reduce noise in a centrifugal fan, comprising an upper cover plate (1), blades (2), and a lower cover plate (3), characterized in that, The specific process is as follows: the intersection line of the upper cover plate (1) and the blade (2) is defined as the blade profile line A (4) when the relative blade height is 0, the intersection line of the lower cover plate (3) and the blade (2) is defined as the blade profile line B (5) when the relative blade height is 1, the blade profile lines at 1 / 4 relative blade height and 3 / 4 relative blade height are defined as blade profile lines C (6) and blade profile lines D (7) respectively, the leading edge points of blade profile lines B (5), blade profile lines C (6) and blade profile lines D (7) are taken as the origin, and the blade profile lines B (5), blade profile lines C (6) and blade profile lines D (7) are rotated respectively, and the rotating trailing edges are connected to obtain the inclined S-shaped trailing edge blade; The specific steps are as follows: Step 1: Define the line of intersection between the upper cover plate (1) and the blade (2) as the blade profile A (4) when the relative blade height is 0, and define the line of intersection between the lower cover plate (3) and the blade (2) as the blade profile B (5) when the relative blade height is 1. Step 2: Define the endpoint of the blade profile A (4) that is close to the center of the centrifugal fan impeller as the leading edge point, and define the endpoint of the blade profile A (4) that is far from the center of the centrifugal fan impeller as the trailing edge point; The endpoint of the blade profile B (5) closest to the center of the centrifugal fan impeller is defined as the leading edge point A (8), and the endpoint of the blade profile B (5) furthest from the center of the centrifugal fan impeller is defined as the trailing edge A; Step 3: Keep the upper cover plate (1) and blade profile A (4) unchanged, take the leading edge point A (8) as the origin, rotate the blade profile B (5) counterclockwise, and connect the trailing edge with the trailing edge A after rotation to obtain the inclined trailing edge blade. In step 3, the rotation angle of blade profile B (5) is 5°; Step 4: Divide the inclined trailing edge blade obtained in step 3 into four equal parts along the height direction using a plane parallel to the lower cover plate (3). The blade profile C (6) which is closer to the blade profile A (4) is 1 / 4 of the blade height, and the blade profile D (7) which is closer to the blade profile B (5) is 3 / 4 of the blade height. Step 5: Define the endpoint of the blade profile C (6) that is close to the center of the centrifugal fan impeller as the leading edge point B (9), and take the leading edge point B (9) as the origin. Rotate the blade profile C (6) counterclockwise, and define the endpoint of the rotated blade profile C (6) that is far from the center of the centrifugal fan impeller as the trailing edge B. Define the endpoint of the blade profile D (7) that is close to the center of the centrifugal fan impeller as the leading edge point C (10), and take the leading edge point C (10) as the origin. Rotate the blade profile D (7) clockwise, and define the endpoint of the blade profile D (7) that is far from the center of the centrifugal fan impeller as the trailing edge C. In step 5, the rotation angle of the blade profile C(6) is 2.5°; In step 5, the rotation angle of the blade profile D(7) is 2.5°; Step 6: Connect the trailing edge to trailing edge B, trailing edge B to trailing edge C, and trailing edge C to trailing edge A smoothly using spline curves to obtain an inclined S-shaped trailing edge blade.

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