A centrifugal fan with a front edge unevenly distributed tapering diverging type blade

Abstract

The centrifugal fan with the front edge uneven distribution tapering and expanding type blade comprises a perforated blade, an upper end cover, a lower end cover, the upper end cover and the lower end cover are installed together to form an impeller shell, and the perforated blade is installed in the impeller shell; the perforated blade comprises a suction surface, a pressure surface, a circular arc front edge and a tail edge, a front edge perforated column is arranged beside the circular arc front edge, and a tail edge perforated column is arranged beside the tail edge; the front edge perforated column is in a tapering form, and the tail edge perforated column is in a expanding form. The present application can uniformly control the pressure pulsation of the blade suction surface and the pressure surface. The deflection of the perforation angle can ensure the directionality of the airflow flow and reduce the jet effect caused by the perforation, aiming at the different effects to be achieved by the front edge and the tail edge perforation. Through the design of the tapering front edge perforation and the expanding tail edge perforation, the uniformity of the nearby pressure pulsation can be more accurately controlled, the noise source is reduced, and the target of further reducing the vortex noise caused by the blade is achieved.

Description

Technical Field

[0001] The present invention relates to a centrifugal fan, specifically a centrifugal fan comprising perforated blades. Background Technology

[0002] Centrifugal fans, as a type of ventilation equipment, are characterized by their small size, simple structure, good ventilation effect, and economic efficiency. They are widely used in factories, mines, tunnels, cooling towers, vehicles, ships, and buildings for ventilation, dust removal, and cooling, and are closely related to people's living environment. During operation, the blades of a centrifugal fan periodically beat the air, creating uneven pressure pulsations around the blades, thus generating aerodynamic noise, which is the main noise component of centrifugal fans. Related studies have shown that leading-edge noise and trailing-edge noise are the main noise sources of centrifugal fans.

[0003] Currently, centrifugal fan noise reduction design schemes focus on optimizing either the leading-edge or trailing-edge noise of the blades. Leading-edge noise reduction is primarily driven by biomimetic-inspired wave-shaped leading-edge designs. Numerous studies have shown that wave-shaped leading-edge blades can improve post-stall dynamic characteristics, delay stall occurrence, and significantly reduce broadband turbulence interference noise. However, this design also increases the complexity of leading-edge turbulence, making it difficult to guarantee the centrifugal fan's aerodynamic performance. Trailing-edge noise reduction often employs serrated structures to disrupt vortices on the blade surface, thereby reducing the jet-wake effect. However, the serrated design scheme, its principles, and its role in leading-edge interference are difficult to study in isolation. Therefore, a more targeted approach is needed to modify the blade structure while simultaneously reducing both leading and trailing-edge noise, thus achieving optimized blade noise reduction. Summary of the Invention

[0004] The purpose of this invention is to provide a centrifugal fan with blades of gradually converging and expanding with uneven leading edge distribution that achieves noise reduction without affecting the performance of the centrifugal fan.

[0005] The objective of this invention is achieved as follows:

[0006] This invention discloses a centrifugal fan with blades of gradually converging and expanding with unevenly distributed leading edges. The fan comprises perforated blades, an upper end cover, and a lower end cover. The upper and lower end covers are assembled together to form an impeller housing. The perforated blades are installed inside the impeller housing. Each perforated blade includes a suction surface, a pressure surface, an arc-shaped leading edge, and a trailing edge. A row of leading edge perforations is provided beside the arc-shaped leading edge, and a row of trailing edge perforations is provided beside the trailing edge. The leading edge perforation row is in a gradually converging form, and the trailing edge perforation row is in a gradually expanding form.

[0007] The present invention may also include:

[0008] 1. The leading edge perforation row is a single row of leading edge perforations, and the spacing between the leading edge perforations gradually increases from the direction of the lower end cap to the direction of the upper end cap; the trailing edge perforation row is two rows of trailing edge perforations, and the trailing edge perforations in each row are evenly distributed.

[0009] 2. The leading edge perforation is set at a distance L1 from the leading edge of the blade, which is 7%-9% of the blade chord length C. The diameter of the leading edge perforation on the suction surface 5 of the blade is 50%-60% of that on the pressure surface 6. The shortest distance l1 between the leading edge perforations is 1 / 5 of the corresponding blade height h1. The distance d1 between the perforation located at the blade edge and the blade edge is the shortest perforation distance l. 1min 1 / 2 of.

[0010] 3. The distances L2 and L3 from the leading edge of the two rows of trailing edge perforations are 70%-72% and 80%-82% of the blade chord length C, respectively. The diameter of the trailing edge perforations gradually increases by 50%-60% from the pressure surface 5 to the suction surface 6. The spacing l2 between the trailing edge perforations is evenly distributed. Take 1 / 5 of the blade height h2 at the corresponding perforation position. The distances d2 and d3 between the perforations located at the blade edge and the blade edge are 1 / 2 of the perforation spacing.

[0011] 4. The angle between the leading edge perforation and the perforated blade is 50°-70°, and the angle between the trailing edge perforation and the perforated blade is 40°-50°.

[0012] The advantages of this invention are:

[0013] 1. The simultaneous perforation design near the leading and trailing edges of the blade can evenly distribute the pressure pulsation on the suction and pressure surfaces of the blade.

[0014] 2. Since the effects to be achieved by perforating the leading edge and trailing edge are different, deflecting the perforation angle can ensure the directionality of airflow and reduce the jet effect caused by perforation.

[0015] 3. By designing the perforations near the leading and trailing edges with gradual narrowing and widening, the areas requiring pressure increase or decrease can be precisely controlled by varying the orifice diameter, achieving a quantitative design effect. Ultimately, the design of the gradually narrowing leading edge perforation and the gradually widening trailing edge perforation allows for more precise control of the uniformity of nearby pressure pulsations, thereby reducing noise sources and further minimizing eddy noise caused by the blades. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the impeller structure;

[0017] Figure 2 This is a schematic diagram of the perforated blade structure;

[0018] Figure 3a This is a top view of the perforated blade. Figure 3b A schematic diagram showing the perforations at the leading and trailing edges of the perforated blade;

[0019] Figure 4 This is a schematic diagram of the deflection angle of the perforated blade;

[0020] Figure 5 This is a schematic diagram of the leading edge perforation;

[0021] Figure 6 This is a schematic diagram of the tail edge perforation;

[0022] Figure 7 A schematic diagram showing the distribution dimensions of the leading edge perforation and the trailing edge perforation;

[0023] Figure 8 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0024] The invention will now be described in more detail with reference to the accompanying drawings:

[0025] Combination Figure 1-8 This invention discloses a centrifugal fan blade with a non-uniformly arranged perforated design at the leading edge, exhibiting the characteristics of a tapered and expanding nozzle. Its features include: a suction surface 5, a pressure surface 6, an arc-shaped leading edge 3 and a trailing edge 4, a perforated row 7 near the leading edge, and two rows of perforated rows 8 near the trailing edge. The final overall centrifugal impeller is composed of an upper end cover 1, a lower end cover 2, and 10 perforated blades. Figure 1 Integral centrifugal fan impeller.

[0026] The perforations on the leading and trailing edges of the blades are intended to achieve different effects, therefore their location and diameter need further standardization. Firstly, regarding the diameter, if the perforation diameter is too large, under the pressure of the rotating blade surface, a large amount of fluid will flow through the hole, causing leakage and compromising the aerodynamic characteristics of the fan. Conversely, if the diameter is too small, it will cause blockage, leading to pressure turbulence on the blade surface and failing to achieve noise reduction. Therefore, the perforation diameter D should be 2%-5% of the blade's spanwise length.

[0027] Noise reduction can be further achieved by gradually reducing and expanding the pipe diameter. Figure 3b A schematic diagram showing the location of the blade perforations is provided. To address the reverse flow problem at the leading edge, the perforations are positioned at a distance L1 from the blade's leading edge, representing 7%-9% of the blade chord length C. The perforations are designed to taper, further accelerating the airflow and thus disrupting the reverse flow on the suction surface at the blade's leading edge. Figure 5This is a schematic diagram showing the dimensions of the perforation row 7 near the leading edge of the blade. The diameter of the perforation on the suction surface 5 is 50%-60% of that on the pressure surface 6, meaning the diameter D1 of the perforation row 7 on the pressure surface is 5-7 mm, and the diameter D2 of the perforation on the suction surface is 2-4 mm. The shortest distance between the perforations, l1, is 1 / 5 of the corresponding blade height h1. Furthermore, due to the significant curvature change in the leading edge region of the upper end cap 1, the perforations in the leading edge section are arranged in an arithmetic progression from dense to sparse from the lower end cap 2 to the upper end cap 1. The distance d1 between the perforations located at the blade edge and the blade edge is the shortest perforation spacing l. 1min Half of it. This is to ensure that backflow and compression do not occur in small areas.

[0028] Figure 3b The diagram shows the location of the perforation row 8 near the trailing edge. The distances L2 and L3 from the two rows of perforations 8 at the trailing edge to the leading edge of the blade are 70%-72% and 80%-82% of the blade chord length C, respectively. Figure 6 This is a schematic diagram of the dimensions of the perforation at the trailing edge. The change in the perforation diameter at the trailing edge follows the opposite pattern to that at the leading edge. The diameter of the perforation at the trailing edge gradually increases by 50%-60% from the pressure surface 5 to the suction surface 6. That is, the perforation diameter D3 of the pressure surface 5 is 2-4 mm, and the perforation diameter D4 of the suction surface 6 is 5-7 mm. Figure 7 The spacing l2 between the perforations at the middle and tail edges is evenly distributed. The perforation height h2 at the corresponding perforation position is taken as 1 / 5. The distance d2 and d3 between the perforation located at the edge of the blade is 1 / 2 of the perforation spacing. This is similar to the design of the perforations near the leading edge.

[0029] Figure 4 The deflection angle of the blade perforations is shown. The angle α between the leading edge perforation row 7 and the blade is 50°-70°, and the angle θ between the trailing edge perforation row 8 and the blade is 40°-50°. The trailing edge perforations ensure that the flow is in the same direction as the airflow and minimize the jet effect caused by the trailing edge perforations.

[0030] This invention implements a perforation design with varying orifice diameters on the blade surface, with a total of three rows of perforations. The perforations are located near the leading edge of the blade, positioned before the reverse flow, to suppress flow separation on the non-working surface of the leading edge, forcing the flow separation point to move axially backward. Simultaneously, by varying the orifice diameter, it draws analogy to a converging nozzle design. According to the continuity equation, the rate of change of the pipe cross-sectional area is:

[0031]

[0032] Where A is the perforation area, v is the specific volume, and c f The velocity inside the pipe is denoted as .

[0033] As shown in the above equation, in subsonic flow, the cross-sectional area is inversely proportional to the flow velocity inside the pipe. As the cross-sectional area decreases, the flow velocity inside the pipe increases further. Bernoulli's equation shows that the flow velocity inside the pipe is inversely proportional to the pressure in subsonic conditions. Therefore, the positive pressure on the non-working surface near the perforations is increased. This can be achieved by controlling the degree of tapering of the orifice to more specifically and quantitatively increase the pressure at the blade's leading edge, thereby reducing the counter-current vortex at the leading edge and lowering the reverse pressure gradient, thus improving the sound source intensity at the blade's leading edge. Furthermore, based on the different pressure gradient changes at the upper and lower end caps of the blade, an unequal perforation arrangement in the blade height direction allows for a more targeted and denser perforation arrangement at locations with stronger reverse pressure gradients, all within the same number of perforations. The combined effect of these two designs makes the pressure change around the blade more uniform. Simultaneously, the tapering orifice design can control the pressure change near the orifice within a certain range. Compared to straight pipes, this design achieves a more targeted and uniform pressure effect, making noise reduction easier to achieve.

[0034] Two rows of blade perforations are designed near the blade trailing edge, with the perforations located before the recirculation at the working surface to reduce the flow velocity on the non-working surface of the blade trailing edge. The perforations gradually widen radially towards the non-working surface, utilizing an effect opposite to that of a converging nozzle to further reduce the flow velocity. This pressurizes and guides the high-speed airflow from the working surface of the blade to the non-working surface, which not only suppresses large separation flow at the trailing edge of the non-working surface but also reduces the wake-volute interference effect. This reduces the sound source intensity near the blade trailing edge and also reduces the sound source intensity caused by interference between the blade and the volute tongue 9.

[0035] This invention features three rows of perforations on the blade surface: one row at the leading edge, two rows at the trailing edge, and no perforations in the middle section. The perforation diameter is adjusted according to pressure pulsation and flow characteristics. Firstly, perforations are only made at the leading and trailing edges, ensuring that the basic aerodynamic performance of the fan remains largely unchanged. Secondly, the variable perforation diameter based on the flow characteristics at the leading and trailing edges is analogous to the effect of a converging nozzle, allowing for more targeted localized pressurization or acceleration within specific pressure and velocity ranges. This results in more uniform pressure fluctuations around the blade, better suppressing flow separation and jet wake phenomena, and ultimately reducing fan noise.

Claims

1. A centrifugal fan with blades of gradually converging and expanding with unevenly distributed leading edges, characterized in that: It includes perforated blades, an upper end cover, and a lower end cover. The upper end cover and the lower end cover are installed together to form the impeller housing, and the perforated blades are installed inside the impeller housing. The perforated blade includes a suction surface, a pressure surface, a curved leading edge, and a trailing edge. A row of leading edge perforations is provided next to the curved leading edge, and a row of trailing edge perforations is provided next to the trailing edge. The row of leading edge perforations is tapered, and the row of trailing edge perforations is expanded. The diameter of the perforations on the leading edge pressure surface is 5-7 mm, and the diameter of the perforations on the leading edge suction surface is 2-4 mm. The diameter of the perforations on the trailing edge pressure surface is 2-4 mm, and the diameter of the perforations on the trailing edge suction surface is 5-7 mm. The leading edge perforation row consists of one row of leading edge perforations, with the spacing between the leading edge perforations gradually increasing from the direction of the lower end cap to the direction of the upper end cap; the trailing edge perforation row consists of two rows of trailing edge perforations, with each row of trailing edge perforations being evenly distributed.

2. A centrifugal fan with progressively narrowing and expanding blades with unevenly distributed leading edges according to claim 1, characterized in that: The leading edge perforation is set at a distance from the leading edge of the blade. At this location, the diameter of the perforation at the leading edge is 7%-9% of the chord length C of the blade. The diameter of the perforation at the leading edge is 50%-60% of the diameter of the suction surface. The shortest distance between the perforations at the leading edge, l1, is the corresponding blade height. 1 / 5 of the distance between the perforation and the blade edge. For the shortest perforation spacing 1 / 2 of.

3. A centrifugal fan with progressively narrowing and expanding blades with unevenly distributed leading edges according to claim 1, characterized in that: The distance between the two rows of trailing edge perforations and the leading edge of the blade and These represent 70%-72% and 80%-82% of the blade chord length C, respectively; the diameter of the trailing edge perforation gradually increases by 50%-60% from the pressure side to the suction side; and the spacing between the trailing edge perforations... Arrange evenly, and take the leaf height at the corresponding perforation position. 1 / 5 of the distance between the perforation located at the blade edge and the blade edge , It is 1 / 2 of the perforation spacing.

4. A centrifugal fan with progressively contracting and expanding blades with unevenly distributed leading edges according to claim 1, characterized in that: The angle between the leading edge perforation and the perforated blade is 50°-70°, and the angle between the trailing edge perforation and the perforated blade is 40°-50°.

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