A bionic centrifugal fan with front-swept blades
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI POWERFUL ELECTRIC CO LTD
- Filing Date
- 2026-04-16
- Publication Date
- 2026-07-21
Smart Images
Figure CN122040665B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of wind turbine technology, and in particular to a biomimetic centrifugal fan with a low-noise forward-swept blade. Background Technology
[0002] Centrifugal fans, as core fluid transport equipment, are widely used in key sectors of the national economy such as HVAC, rail transportation, power and chemical industries, and residential ventilation. With the continuous advancement of dual-carbon goals and the ever-increasing demands for low-noise and high-efficiency equipment in both civil and industrial settings, the aerodynamic performance, wideband noise control level, and structural reliability of centrifugal fans have become core technological competition points in the industry. Among these, the fan blades, as the core working component of the impeller, directly determine the fan's total pressure efficiency, operating noise, and service life through their spanwise aerodynamic layout and profile design, making them a core focus of centrifugal fan technology optimization.
[0003] Existing centrifugal fan blades suffer from core technical defects: unreasonable spanwise sweep layout, with full forward sweep, full backward sweep, and equal sweep angle schemes failing to simultaneously control the flow field across the entire span, making it difficult to balance aerodynamic efficiency and noise reduction; simple leading-edge noise reduction structure, with serrated structures having narrow noise reduction bandwidth and high wind resistance, accompanied by severe aerodynamic performance degradation, and prone to fouling and failure; poor compatibility between blade surface guiding and drag reduction structures, with straight ribs easily inducing secondary flow and insufficient long-term operational stability; and weak trailing-edge structure noise reduction capability, with straight trailing-edge vortex shedding noise being high, and conventional bifurcated trailing-edge having poor spanwise compatibility and limited broadband noise floor suppression effect. Summary of the Invention
[0004] This invention overcomes the shortcomings of the prior art and provides a biomimetic centrifugal fan with a low-noise forward-swept blade.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a biomimetic centrifugal fan low-noise forward-swept blade, comprising a blade body, wherein the blade body is divided into a blade root section, a transition section and a blade tip section along the spanwise direction, and is divided into a blade leading edge, a blade body and a blade trailing edge along the chordwise direction, wherein the blade leading edge is connected to the chordwise front end of the blade body, and the blade trailing edge is connected to the chordwise rear end of the blade body, wherein the blade body has a suction surface and a pressure surface arranged opposite to each other;
[0006] The leading edge of the blade is provided with a three-dimensional composite biomimetic leading edge structure, which includes: a wave-shaped substrate extending along the span of the leading edge of the blade, a gradient serrated unit integrally formed on the windward side of the wave-shaped substrate, and a textured surface covering the wave-shaped substrate and the gradient serrated unit.
[0007] The suction and pressure surfaces of the blade body are integrally formed with guide ribs, which extend along the chord direction and their extension direction matches the sweep angle of the gradually changing sweep layout of the blade body in the spanwise direction; the suction and pressure surfaces of the blade body are also fully covered with drag-reducing microstructures.
[0008] The trailing edge of the blade is provided with a gradually bifurcated trailing edge structure, which is arranged along the entire span of the blade.
[0009] The blade body is provided with a gradient thickness structure along the span, and the thickness of the gradient thickness structure decreases linearly from the root section to the tip section.
[0010] In a preferred embodiment of the present invention, the blade body adopts a spanwise gradient sweeping layout, wherein the blade root segment is located at 0% to 30% spanwise of the blade body and is configured as a forward sweeping structure, the transition segment is located at 30% to 70% spanwise of the blade body and is configured as a linear gradient sweeping structure, the blade tip segment is located at 70% to 100% spanwise of the blade body and is configured as a backward sweeping structure, and the two ends of the transition segment are smoothly connected to the blade root segment and the blade tip segment, respectively;
[0011] The forward sweep angle of the leaf root segment is 15° to 22°, the backward sweep angle of the leaf tip segment is -5° to -12°, and the sweep angle of the transition segment gradually changes linearly along the span from the forward sweep angle of the leaf root segment to the backward sweep angle of the leaf tip segment in an S-shaped curve.
[0012] In a preferred embodiment of the present invention, the amplitude of the wavy substrate is 0.3-0.7 mm and the wavelength is 1.5-2.5 mm; the height of the gradient sawtooth unit linearly changes from 0.1-0.3 mm at the leaf root to 0.4-0.6 mm at the leaf tip; and the size of the uneven microtexture is 10-50 μm.
[0013] In a preferred embodiment of the present invention, the guide ribs are of three levels, with their height linearly varying from 0.4 to 0.6 mm at the blade root to 1.4 to 1.6 mm at the blade tip, and their pitch being 0.8 to 1.2 mm. The extension direction matches the tangential velocity of the flow field corresponding to the spanwise sweep layout of the blade body.
[0014] In a preferred embodiment of the present invention, the drag-reducing microstructure includes microscale units, a nano-hydrophobic layer disposed on the surface of the microscale units, and boundary layer induction grooves disposed on the surface of the blade body; the size of the microscale units is 40-60 μm, and the arrangement density is 1800-2200 units / cm²; the nano-hydrophobic layer has micropores with a pore size of 80-120 nm and a water contact angle greater than 150°; the depth of the boundary layer induction grooves is 15-25 μm, and the groove spacing is 0.4-0.6 mm.
[0015] In a preferred embodiment of the present invention, the bifurcation angle of the gradually bifurcated trailing edge structure linearly changes from 10° to 14° at the leaf root segment to 14° to 18° at the leaf tip segment.
[0016] In a preferred embodiment of the present invention, in the gradient variable thickness structure, the maximum thickness of the leaf root segment is 14% to 16% of the chord length of the corresponding position of the leaf, the minimum thickness of the leaf tip segment is 7% to 9% of the chord length of the corresponding position of the leaf, and the thickness of the leaf body decreases linearly from the leaf root segment to the leaf tip segment along the spanwise direction.
[0017] In a preferred embodiment of the present invention, the suction surface and the pressure surface are respectively disposed on the front and back sides of the blade body. The rib height of the guide rib is positively correlated with the sweep angle at the corresponding spanwise position. The larger the forward sweep angle of the blade root section, the higher the rib height at the corresponding position. The larger the absolute value of the backward sweep angle of the blade tip section, the lower the rib height at the corresponding position.
[0018] This invention addresses the shortcomings of the prior art and has the following beneficial effects:
[0019] The blade body of this invention consists of a root section, a transition section, and a tip section along its span. This spanwise gradually sweeping layout alters the incident angle of the leading edge of the root section to reduce the positive angle of attack. Simultaneously, the swept-back structure reduces the fluid impact intensity at the leading edge of the tip and alters the flow path of the leakage flow at the tip gap. This effectively suppresses boundary layer separation in the root region and increases the load proportion in that region, thereby weakening the peak load at the tip section and curbing the generation and development of tip leakage vortices. Compared to existing technologies where full-span forward sweeping easily leads to premature root boundary layer separation, full-span backward sweeping exacerbates tip vortices, and the constant sweep angle layout cannot simultaneously address the inherent defects of the full-span flow field characteristics, this invention eliminates secondary flows induced by abrupt changes in the spanwise pressure gradient, significantly reducing the wind turbine's broadband noise floor from the source while ensuring the uniformity of the flow field across the entire span of the blade.
[0020] The blade leading edge of this invention features a three-dimensional composite biomimetic leading edge structure comprising a wave-shaped substrate, a gradient sawtooth unit integrally formed on the windward side, and a surface textured micro-texture. Furthermore, both the suction and pressure surfaces of the blade body are integrally formed with guide ribs matching the corresponding sweep angle, fully covering the drag-reducing microstructure. By utilizing the wave-shaped profile and gradient sawtooth array, the large-scale concentrated leading-edge vortex street is forcibly decomposed into a dispersed micro-vortex structure. The guide ribs actively guide the boundary layer fluid along the mainstream surface direction, disrupting the vortex shedding periodicity and promoting laminar flow within the boundary layer. The state is prematurely transitioned to turbulence due to the disturbance of the uneven microtexture, thereby efficiently transporting low-energy fluid to the trailing edge to delay boundary layer separation. Compared with the limitations of existing technologies where single wave or sawtooth structures are prone to increasing wind resistance and thus damaging aerodynamic efficiency, and single surface drag reduction structures are prone to fouling and thus degrading performance, this composite structure achieves the reduction of frictional resistance and the suppression of lateral secondary flow at the multi-scale micro level. While broadening the noise reduction frequency range under all operating conditions, it also compensates for the blade's work loss, achieving a two-way gain of aerodynamic noise suppression and total pressure efficiency improvement.
[0021] This invention couples the macroscopic flow field reshaping mechanism of the gradually sweeping layout with the microscopic vortex control mechanism of the three-dimensional composite biomimetic leading edge structure, guide ribs and gradually bifurcated trailing edge structure, and supplements it with a gradient variable thickness structure that linearly decreases from the blade root to the blade tip. This enables the fan to form a closed-loop aerodynamic optimization link from the fine cutting of the incident flow at the leading edge, the smooth guidance of the main boundary layer and the discretization of the trailing edge wake during operation. This strengthens the work-capacity of the macroscopic curved surface. The combination of these two technologies effectively overcomes the problem of the contradiction between structural strength and aerodynamic performance caused by the uniform thickness or conventional straight trailing edge of traditional blades. This endows the centrifugal fan with excellent structural fatigue resistance, wide-band noise suppression and excellent overall hydrodynamic efficiency under complex high-speed conditions. Attached Figure Description
[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0023] Fig. 1 This is a perspective structural diagram of a preferred embodiment of the present invention;
[0024] Fig. 2 This is a top view of a preferred embodiment of the present invention;
[0025] Fig. 3 This is a side view of a preferred embodiment of the present invention;
[0026] In the figure: 1. Blade body; 2. Blade root section; 3. Transition section; 4. Blade tip section; 5. Wavy base; 6. Gradient serrated unit; 7. Guide ribs; 8. Gradient bifurcation trailing edge structure. Detailed Implementation
[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.
[0029] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.
[0030] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.
[0031] Example 1: As Figs. 1-3As shown, the biomimetic centrifugal fan low-noise forward-swept blade in this embodiment includes a blade body 1. The blade body 1 is the core working component of the centrifugal fan impeller and is suitable for various mainstream centrifugal fan models such as forward centrifugal fans and backward centrifugal fans. It is especially suitable for centrifugal fan scenarios with high requirements for low noise and high efficiency, such as household fresh air systems, commercial air conditioning units, and industrial ventilation equipment.
[0032] The blade body 1 is divided into a root segment 2, a transition segment 3 and a tip segment 4 along the spanwise direction, and into a leading edge, a main body and a trailing edge along the tangential direction. The leading edge is connected to the tangential front end of the main body, and the trailing edge is connected to the tangential rear end of the main body. The main body has a suction surface and a pressure surface that are arranged opposite to each other.
[0033] It should be clarified that in this embodiment, the spanwise segments of the blade body 1 are continuous integrated structures without splicing, welding or other split connection structures. Preferably, the blade body 1 can be obtained by 3D printing integrated molding or by precision casting, five-axis linkage CNC milling or other machining methods to ensure smooth connection between each segment structure and avoid additional flow separation and noise sources caused by structural abrupt changes.
[0034] Among them, blade root section 2 is the connection section between blade body 1 and wind turbine hub. It is the main load-bearing structure of blade body 1 and must meet the structural strength and fatigue life requirements during wind turbine operation. Blade tip section 4 is the outermost radial end of blade body 1, forming a blade tip gap with wind turbine volute. It is the main generation area of blade tip leakage flow and blade tip vortex, and also one of the core sources of wideband noise floor of wind turbine. Transition section 3 is the connection section between blade root section 2 and blade tip section 4. It plays a core role in load transfer and smooth flow field transition, avoiding flow field turbulence caused by structural abrupt changes between blade root section 2 and blade tip section 4.
[0035] In this embodiment, the blade body 1 adopts a spanwise gradient sweeping layout, wherein the blade root segment 2 is located at 10% to 30% spanwise of the blade body and is configured as a forward sweeping structure, the transition segment 3 is located at 30% to 70% spanwise of the blade body and is configured as a linear gradient sweeping structure, and the blade tip segment 4 is located at 170% to 100% spanwise of the blade body and is configured as a backward sweeping structure. The two ends of the transition segment 3 are smoothly connected to the blade root segment 2 and the blade tip segment 4, respectively.
[0036] Specifically, this study addresses the shortcomings of the commonly used equal-sweep angle layout, full-span forward-swept, or backward-swept layouts for centrifugal fan blades. In existing technologies, while full-span forward-swept blades can suppress tip vortices to some extent, they can lead to excessive loads on the blade root section 2 and premature boundary layer separation, resulting in flow losses and noise in the blade root region. While full-span backward-swept blades can optimize the flow state of the blade root section 2, they can exacerbate tip leakage and tip vortices, leading to a significant increase in the fan's broadband noise floor. Furthermore, the equal-sweep angle layout cannot adapt to the flow field characteristics at different positions along the blade span and cannot simultaneously optimize the flow across the entire span of the blade root, mid-blade, and tip.
[0037] In this embodiment, the blade root section 2 at 0%–30% spanwise position adopts a forward-swept structure. By changing the incident angle of the leading edge of the blade root section 2 through the forward-swept structure, the positive angle of attack of the blade root section 2 is reduced, the boundary layer separation in the blade root region is suppressed, and the load ratio of the blade root section 2 is increased, while the peak load of the blade tip section 4 is reduced, thereby reducing the intensity of the blade tip vortex from the source. The transition section 3 at 30%–70% spanwise position adopts a linear gradient structure with a sweep angle, realizing a smooth transition from the forward-swept structure of the blade root section 2 to the backward-swept structure of the blade tip section 4, avoiding the abrupt change in the spanwise pressure gradient caused by the abrupt change in the sweep angle, preventing secondary flow of fluid along the spanwise direction, and ensuring the uniformity of the flow field in the spanwise direction of the blade. The blade tip section 4 at 70%–100% spanwise position adopts a backward-swept structure. By reducing the fluid impact intensity at the leading edge of the blade tip through the backward-swept structure, the flow path of the leakage flow in the blade tip gap is changed, the generation and development of the leakage vortex in the blade tip is suppressed, and the broadband noise floor generated in the blade tip region is significantly reduced.
[0038] It should be added that, in this embodiment, the smooth connection between transition section 3 and blade root section 2 and blade tip section 4 means that the sweep angle values at both ends of transition section 3 are completely consistent with the sweep angle values at the end of blade root section 2 and the beginning of blade tip section 4, respectively. In addition, the first derivative of the leading edge profile of transition section 3 is continuous along the span, without inflection points or bends, ensuring a smooth transition of the blade leading edge profile along the entire span, and avoiding additional flow noise and aerodynamic losses caused by abrupt changes in the profile.
[0039] In this embodiment, the leading edge of the blade is provided with a three-dimensional composite biomimetic leading edge structure, which includes: a wave-shaped substrate 5 extending along the spanwise direction of the leading edge of the blade, a gradient serrated unit 6 integrally formed on the windward side of the wave-shaped substrate 5, and a textured surface covering the wave-shaped substrate 5 and the gradient serrated unit 6.
[0040] Among them, the three-dimensional composite biomimetic leading edge structure systematically optimizes the shortcomings of existing single biomimetic leading edge structures, such as narrow noise reduction bandwidth, limited noise reduction effect, and aerodynamic efficiency loss. In existing technologies, a single wavy leading edge can only suppress eddy noise at a specific frequency, and its suppression effect on broadband noise floor is limited; a single serrated leading edge can broaden the noise reduction bandwidth, but it will lead to increased flow drag at the blade leading edge, resulting in a decrease in aerodynamic efficiency; while a smooth leading edge surface cannot suppress boundary layer disturbances at the microscale, and cannot achieve full-scale flow noise suppression.
[0041] In this embodiment, the wave-shaped substrate 5 extends continuously along the entire span of the blade's leading edge, serving as the basic carrier of the three-dimensional composite biomimetic leading edge structure. Its function is to decompose the large-scale incident vortex at the blade's leading edge into multiple small-scale vortices through the wave-shaped leading edge profile, while simultaneously altering the pressure distribution at the leading edge, suppressing the generation and shedding of leading-edge separation vortices, and fundamentally reducing the intensity of vortex noise. The gradient sawtooth unit 6 is integrally formed on the windward side of the wave-shaped substrate 5, i.e., the side of the blade's leading edge facing the fluid injection direction. The tips of the sawtooth unit face the fluid injection direction, and its function is to decompose the concentrated vortex street at the leading edge through the sawtooth structure. The solution is a dispersed micro-vortex structure, which disrupts the periodicity of vortex shedding and significantly widens the noise reduction frequency range, achieving effective suppression of wide-frequency noise floor across all operating conditions of the fan. The concave-convex micro-texture fully covers the surface of the wave-shaped substrate 5 and the gradient sawtooth unit 6, which is a micro-scale biomimetic drag reduction and noise reduction structure. Its function is to change the boundary layer structure of the leading edge surface through the concave-convex micro-texture, transforming the laminar state in the boundary layer into a turbulent state in advance, suppressing the occurrence of laminar separation, and reducing the frictional resistance between the fluid and the leading edge surface. While achieving noise reduction, it avoids the loss of aerodynamic efficiency and even improves the total pressure efficiency of the fan.
[0042] It should be clarified that in this embodiment, the wave-shaped base 5, the gradient sawtooth unit 6 and the blade body 1 are integrally formed structures without separate bonding, welding or other connecting structures, thus avoiding problems such as reduced surface accuracy and structural detachment caused by connecting structures; the concave and convex micro-texture can be obtained by laser surface texturing or directly prepared during the 3D printing integral forming process, ensuring the dimensional accuracy and surface consistency of the micro-texture.
[0043] In this embodiment, both the suction surface and the pressure surface of the blade body are integrally formed with guide ribs 7. The guide ribs 7 extend along the chord direction and their extension direction matches the sweep angle of the spanwise gradually curved sweep layout of the blade body 1. The suction surface and the pressure surface of the blade body are also fully covered with drag-reducing microstructures.
[0044] Among them, the guide ribs 7 are extended protruding rib structures that extend along the chord direction of the blade and are evenly spaced along the span. They are symmetrically arranged on the suction and pressure surfaces of the blade body, or they can be asymmetrically arranged according to the flow field difference between the suction and pressure surfaces. In the prior art, the guide structure on the blade surface mostly adopts a straight rib structure, which can only achieve unidirectional flow guidance and cannot adapt to the complex three-dimensional flow field on the surface of centrifugal fan blades. This can easily lead to the generation of secondary vortices on both sides of the ribs, which will aggravate flow losses and noise.
[0045] In this embodiment, the extension direction of the guide ribs 7 matches the sweep angle of the spanwise gradually curved sweep layout of the blade body 1. The extension angle of the ribs is adjusted according to the sweep angle changes at different positions along the span of the blade body 1, ensuring that the direction of the ribs perfectly matches the mainstream flow direction of the fluid on the surface of the blade body 1. This actively guides the boundary layer fluid on the surface of the blade body 1, suppressing lateral secondary flow within the boundary layer. Simultaneously, it transports the low-energy fluid within the boundary layer to the trailing edge of the blade, delaying boundary layer separation and significantly reducing eddy noise and flow losses caused by boundary layer separation. Furthermore, the guide ribs 7 also strengthen the blade structure, increase the blade's natural frequency, prevent resonance during wind turbine operation, and reduce blade vibration noise, achieving simultaneous suppression of aerodynamic and structural noise.
[0046] In this embodiment, the guide rib 7 and the blade body are integrally formed. The root of the guide rib 7 and the blade surface are smoothly transitioned without any structural abrupt changes such as right angles or sharp angles, thus avoiding flow separation and eddies at the root of the guide rib 7. The starting end of the guide rib 7 along the chord direction is located at 10% of the chord direction of the blade body, and the ending end is located at 90% of the chord direction of the blade body. This ensures the flow guidance effect in the entire chord direction and avoids the flow impact and eddy shedding caused by the guide rib 7 extending to the leading and trailing edges of the blade.
[0047] In this embodiment, the drag-reducing microstructure fully covers the entire suction and pressure surfaces of the blade body, including the surface of the guide ribs 7. It is a microscopic drag-reducing and noise-reducing structure covering the entire surface of the blade body. In the prior art, the drag-reducing microstructures on the blade surface mostly adopt a single sharkskin microstructure, which can only achieve drag reduction effect, has limited effect on inhibiting boundary layer separation, and cannot take into account hydrophobic and antifouling performance. During long-term operation, dust and oil stains easily accumulate in the microstructure, resulting in a rapid decay of drag-reducing and noise-reducing effect.
[0048] The drag-reducing microstructure in this embodiment is a multi-scale, multi-level composite biomimetic structure that simultaneously possesses multiple functions such as drag reduction, noise reduction, hydrophobicity, and antifouling. By altering the boundary layer characteristics of the blade surface through microstructure, it reduces the frictional resistance between the fluid and the blade surface, while suppressing micro-eddies within the boundary layer, further reducing broadband noise floor. At the same time, the hydrophobic structure enhances the antifouling and anti-corrosion performance of the blade surface, ensuring the stability of the wind turbine's performance during long-term operation.
[0049] In this embodiment, the trailing edge of the blade is provided with a gradually bifurcated trailing edge structure 8, which is arranged along the entire span of the blade.
[0050] This paper addresses the shortcomings of existing technologies, such as high vortex shedding noise and strong wake interference, caused by the straight trailing edge of the blade. In existing technologies, the straight trailing edge of centrifugal fan blades generates periodic vortex shedding, resulting in strong discrete noise and broadband noise. At the same time, the vortices shed from the trailing edge strongly interfere with the downstream volute, further amplifying the overall noise of the fan. Furthermore, a single, uniformly sized bifurcated trailing edge can only adapt to the flow field at a specific spanwise position and cannot achieve vortex shedding suppression across the entire spanwise direction, resulting in limited noise reduction bandwidth.
[0051] In this embodiment, the gradually bifurcated trailing edge structure 8 is arranged along the entire span of the blade. The bifurcated structure decomposes the large-scale concentrated vortex shedding at the trailing edge of the blade into multiple small-scale dispersed vortices, thereby disrupting the periodicity of vortex shedding and significantly reducing the noise generated by trailing edge vortex shedding. It also weakens the intensity of the trailing edge wake and reduces the interference noise between the wake and the volute, achieving full-link suppression of aerodynamic noise of the wind turbine. At the same time, the gradually bifurcated structure can adapt to the flow field characteristics at different positions along the blade span, ensuring the vortex shedding suppression effect across the entire span, widening the noise reduction frequency range, and achieving effective suppression of wideband noise floor under all operating conditions.
[0052] In this embodiment, the gradient bifurcation trailing edge structure 8 and the blade body are integrally formed. The root of the bifurcation structure and the trailing edge of the blade are smoothly transitioned without structural abrupt changes, avoiding additional flow separation and noise at the bifurcation root. The tooth tips of the bifurcation structure face the wake direction of the blade, that is, the downstream direction of the chord, to ensure the dismantling effect of the trailing edge vortex.
[0053] In this embodiment, the blade body 1 is provided with a gradient thickness structure along the span, and the thickness of the gradient thickness structure decreases linearly from the root segment 2 to the tip segment 4.
[0054] The gradient variable thickness structure design takes into account both the structural strength and aerodynamic performance of the blade, and optimizes the existing technology of blades with uniform thickness that cannot balance structural strength and aerodynamic performance. In the existing technology, if the blade root section 2 is to be structurally strong, a larger thickness is required, which will result in an excessively large airfoil thickness in the blade tip section 4, increasing aerodynamic drag and flow loss. If a thinner thickness is used to ensure the aerodynamic performance of the blade tip section 4, the structural strength of the blade root section 2 will be insufficient, which will not meet the safety requirements of wind turbine operation.
[0055] In this embodiment, the thickness of the gradient variable thickness structure decreases linearly from the blade root section 2 to the blade tip section 4. The blade root section 2, as the main load-bearing structure, adopts a larger thickness to ensure the structural strength, stiffness, and fatigue life of the blade, meeting the mechanical performance requirements during high-speed operation of the wind turbine. The blade tip section 4 adopts a smaller thickness to optimize the airfoil aerodynamic performance of the blade tip section 4, reduce flow resistance and flow loss, and at the same time reduce the overall weight of the blade, reduce the rotational inertia of the impeller, and reduce the start-up power consumption and operating energy consumption of the wind turbine. The linearly decreasing thickness change ensures a smooth transition of the airfoil of each section in the spanwise direction of the blade, avoiding flow field turbulence and aerodynamic losses caused by abrupt changes in thickness, and achieving a perfect balance between structural strength and aerodynamic performance.
[0056] In this embodiment, the gradient variable thickness structure of the blade body 1 refers to the maximum thickness of the airfoil in the same spanwise section decreasing linearly along the spanwise direction. The airfoil profiles of each spanwise section maintain geometric similarity, and the thickness is adjusted only proportionally to ensure the aerodynamic performance consistency of the airfoil across the entire spanwise direction of the blade and avoid the non-uniform spanwise flow field caused by changes in the airfoil profile.
[0057] Example 2: This example is a further optimization and limitation based on Example 1, which clarifies the specific implementation of the gradual change in the sweep angle of the leaf root segment 2, the sweep angle of the leaf tip segment 4, and the sweep angle of the transition segment 3.
[0058] In this embodiment, the forward sweep angle of the leaf root segment 2 is 15° to 22°, the backward sweep angle of the leaf tip segment 4 is -5° to -12°, and the sweep angle of the transition segment 3 gradually changes linearly along the span from the forward sweep angle of the leaf root segment 2 to the backward sweep angle of the leaf tip segment 4 in an S-shaped curve.
[0059] The values of the forward and backward sweep angles are based on the optimal parameter range obtained from a large number of numerical simulations, wind tunnel tests, and prototype performance tests. For centrifugal fan models with different power and speed, targeted adjustments can be made within this range to ensure the best noise reduction and efficiency improvement effects.
[0060] It should be clarified that the forward sweep angle of blade root segment 2 refers to the angle between the tangent of the leading edge of the blade and the radial reference line of the impeller within the blade root segment 2. Within the span of 20% to 30% of the blade root segment, the forward sweep angle can remain constant or can be gradually varied in the range of 15° to 22° to ensure the forward sweep effect of blade root segment 2.
[0061] When the sweep angle of the blade root section 2 is less than 15°, the sweep structure is not effective enough in suppressing boundary layer separation of the blade root section 2, and cannot effectively increase the load ratio of the blade root section 2. The load peak of the blade tip section 4 cannot be effectively reduced, and the noise reduction effect is limited. When the sweep angle of the blade root section 2 is greater than 22°, it will lead to an excessive reduction in the angle of attack of the blade root section 2, a significant decrease in the lift coefficient of the blade root section 2, insufficient overall work capacity of the blade, and a significant decrease in the total pressure and efficiency of the wind turbine. At the same time, excessive sweep will lead to the deterioration of the structural stress of the blade root section 2, a significant increase in the bending stress of the blade, and a risk of structural failure.
[0062] In this embodiment, the sweep angle of the blade tip segment 4 is -5° to -12°, where the negative sign indicates that the direction of the sweep angle is tilted towards the positive direction of impeller rotation. The larger the absolute value of the sweep angle, the greater the degree of sweep of the blade tip segment 4. Within the spanwise range of 70% to 100% of the blade tip segment 4, the sweep angle can remain constant or undergo small gradual changes within the range of -5° to -12° to ensure the sweep effect of the blade tip segment 4.
[0063] When the absolute value of the sweep angle of the blade tip section 4 is less than 5°, the sweep structure is not effective enough in suppressing the leakage flow and vortex at the blade tip, and cannot effectively reduce the broadband noise floor in the blade tip region, and the noise reduction effect does not meet expectations. When the absolute value of the sweep angle of the blade tip section 4 is greater than 12°, it will cause the leading edge of the blade tip section 4 to be excessively tilted, the aerodynamic load of the blade tip section 4 to be excessively reduced, the overall work capacity of the blade to decrease, and the total pressure performance of the wind turbine to be significantly degraded. At the same time, excessive sweeping will cause the structural stiffness of the blade tip section 4 to decrease, making it easy for flutter to occur during wind turbine operation, causing additional vibration noise and structural fatigue risks.
[0064] In this embodiment, the sweep angle of the transition segment 3 gradually changes linearly along the span from the forward sweep angle of the blade root segment 2 to the backward sweep angle of the blade tip segment 4 using an S-shaped curve. The S-shaped linear change means that within the spanwise range of 30% to 70% of the transition segment 3, the rate of change of the sweep angle follows an S-shaped distribution. Specifically, the sweep angle at the beginning of the transition segment 3 is the same as the sweep angle at the end of the blade root segment 2, with a rate of change of 0; the rate of change reaches its maximum value in the middle of the transition segment 3; and at the end of the transition segment 3, the sweep angle is the same as the sweep angle at the beginning of the blade tip segment 4, with the rate of change returning to 0. This achieves a smooth and continuous gradual change in the sweep angle, ensuring the continuity of the second derivative of the blade leading edge profile along the spanwise direction, without any inflection points or angles.
[0065] In existing technologies, the sweep angle of transition section 3 is mostly changed by a linear gradient, that is, the sweep angle changes at a uniform speed along the span. This gradient method will cause a sudden change in the rate of change of the sweep angle at both ends of transition section 3, which will cause a sudden change in the pressure gradient along the blade span, resulting in secondary flow of fluid along the span, which will aggravate flow loss and noise. However, the S-shaped curve linear gradient method used in this embodiment perfectly solves this defect. Through the S-shaped sweep angle change rate distribution, a smooth transition of the sweep angle from blade root section 2 to blade tip section 4 without abrupt changes is achieved, avoiding abrupt changes in the span pressure gradient, effectively suppressing secondary flow of fluid along the span, ensuring the uniformity and stability of the flow field across the entire span of the blade, and further improving the aerodynamic efficiency of the fan while achieving noise reduction.
[0066] Preferably, in this embodiment, for a small centrifugal fan used in a household fresh air system, the rated speed is 1200 r / min and the impeller diameter is 250 mm. The optimal parameters are set as follows: the forward sweep angle of the blade root section 2 is 18°, the backward sweep angle of the blade tip section 4 is -8°, and the sweep angle of the transition section 3 is gradually changed by the S-curve fitted by the above-mentioned fifth-order polynomial. Under these parameters, the A-weighted sound power level of the fan can be reduced by 3.2 dB(A), the total pressure efficiency can be increased by 4.5%, and the noise reduction and efficiency improvement effects are significant.
[0067] Preferably, in this embodiment, for a medium-sized centrifugal fan used in a commercial air conditioning unit, the rated speed is 1800 r / min and the impeller diameter is 400 mm. The optimal parameters are set as follows: the forward sweep angle of the blade root section 2 is 20°, the backward sweep angle of the blade tip section 4 is -10°, and the sweep angle of the transition section 3 is gradually changed by the S-curve fitted by the above-mentioned fifth-order polynomial. Under these parameters, the A-weighted sound power level of the fan can be reduced by 4.5 dB(A), the total pressure efficiency can be increased by 5.2%, and the structural strength requirements for long-term operation of the fan can be met.
[0068] Example 3: This example is a further optimization and limitation based on Example 1, which clarifies the specific implementation methods and optimal parameter ranges for each structure.
[0069] In this embodiment, the wave-shaped substrate 5 has an amplitude of 0.3–0.7 mm and a wavelength of 1.5–2.5 mm; the height of the gradient sawtooth unit 6 linearly changes from 0.1–0.3 mm at the leaf root segment 2 to 0.4–0.6 mm at the leaf tip segment 4; and the size of the uneven microtexture is 10–50 μm.
[0070] In this embodiment, the amplitude of the wavy substrate 5 refers to the vertical distance between the crests and troughs of the wavy substrate 5, which is also the height of the undulation of the wavy profile; the wavelength refers to the spanwise distance between two adjacent crests of the wavy substrate 5, and is the core parameter that determines the noise reduction effect of the wavy substrate 5. In this embodiment, the amplitude and wavelength parameters of the wavy substrate 5 are designed based on the characteristic scale of the leading-edge vortex during wind turbine operation. By matching with the characteristic scale of the vortex, the optimal disintegration effect of the leading-edge separated vortex is achieved.
[0071] When the amplitude of the wavy base 5 is less than 0.3 mm, the undulation height of the wavy profile is insufficient, which cannot effectively dismantle the large-scale leading-edge separation vortex and has a limited effect on suppressing vortex noise. When the amplitude of the wavy base 5 is greater than 0.7 mm, the undulation height of the wavy profile is too large, which will lead to a significant increase in the windward area of the blade leading edge, a significant increase in flow resistance, and a decrease in the aerodynamic efficiency of the fan. At the same time, the excessive amplitude will lead to excessive abrupt changes in the leading-edge profile, which will generate new flow separation at the trough position and cause additional noise.
[0072] When the wavelength of the wave-shaped substrate 5 is less than 1.5 mm, the number of wave crests in the wave-shaped structure is too large and the leading edge profile is too dense, which will lead to a significant increase in frictional resistance at the leading edge and an increase in aerodynamic losses. When the wavelength of the wave-shaped substrate 5 is greater than 2.5 mm, the number of wave crests in the wave-shaped structure is too small, which cannot effectively disassemble the separation vortex in the entire span of the leading edge, resulting in a noise reduction blind zone and insufficient suppression effect of broadband background noise.
[0073] Preferably, in this embodiment, the amplitude and wavelength of the corrugated substrate 5 are set in a fixed ratio, with the optimal ratio being amplitude:wavelength = 1:3.5. At this ratio, the corrugated substrate 5 achieves optimal dismantling of the leading-edge separation vortex while minimizing the increase in flow resistance, thus maximizing noise reduction while ensuring that the aerodynamic efficiency of the fan does not decrease. For example, when the amplitude of the corrugated substrate 5 is 0.5mm, the corresponding optimal wavelength is 1.75mm. This parameter is suitable for most small and medium-sized centrifugal fan models, exhibiting excellent versatility and adaptability.
[0074] In this embodiment, the height of the gradient sawtooth unit 6 refers to the vertical distance from the tooth root to the tooth tip of the sawtooth unit. The height of the sawtooth unit increases linearly along the blade span from the blade root segment 2 to the blade tip segment 4, that is, the sawtooth height is the smallest at the blade root segment 2 and the sawtooth height is the largest at the blade tip segment 4, forming a gradient sawtooth structure. The core logic of this gradient design is that there are significant differences in the incoming flow velocity and vortex scale at different positions along the blade span. The incoming flow velocity at the blade root segment 2 is lower and the vortex scale is smaller, so a smaller sawtooth height is used to meet the dismantling requirements of small-scale vortices; the incoming flow velocity at the blade tip segment 4 is higher and the vortex scale is larger, so a larger sawtooth height is used to meet the dismantling requirements of large-scale vortices, thereby achieving the optimal noise reduction effect across the entire span.
[0075] When the height of the gradually tapered sawtooth unit 6 in the blade root section 2 is less than 0.1 mm, the sawtooth height is insufficient and cannot effectively disintegrate the leading edge eddy current of the blade root section 2, resulting in limited noise reduction effect. When the height of the blade root section 2 is greater than 0.3 mm, the sawtooth height is too large, which will cause the flow resistance at the leading edge of the blade root section 2 to increase significantly, and at the same time cause flow separation in the blade root section 2, which will aggravate flow loss and noise.
[0076] When the height of the gradient sawtooth unit 6 at the blade tip section 4 is less than 0.4 mm, the sawtooth height is insufficient and cannot effectively dissipate the large-scale leading edge vortex of the blade tip section 4, thus failing to achieve the expected suppression effect on broadband background noise in the blade tip region. When the height of the blade tip section 4 is greater than 0.6 mm, the sawtooth height is too large, which will lead to a significant increase in the windward area of the leading edge of the blade tip section 4, a significant increase in flow resistance, and a decrease in the structural stiffness of the sawtooth, making it easy for the fan to vibrate during operation and causing additional structural noise.
[0077] It should be added that, in this embodiment, the tooth tip angle of the gradient sawtooth unit 6 is 30° to 60°. The tooth tip angle is the angle between the two tooth surfaces of the sawtooth unit, and the preferred tooth tip angle is 45°. At this angle, the sawtooth unit has the best disintegration effect on the leading-edge vortex, while minimizing flow resistance. The arrangement of the sawtooth units along the spanwise direction corresponds to the crests and troughs of the wavy substrate 5.
[0078] Preferably, the tooth tip of the sawtooth unit corresponds to the crest position of the wave-shaped substrate 5, and the tooth root of the sawtooth unit corresponds to the trough position of the wave-shaped substrate 5, forming a wave-sawtooth composite structure, which further improves the dismantling effect of the leading edge eddy current and broadens the noise reduction bandwidth.
[0079] In this embodiment, the size of the microtexture is 10–50 μm, meaning the height difference between the protrusions and depressions of the microtexture is 10–50 μm, i.e., the undulation height of the microtexture. The microtexture is a uniformly distributed pit or protrusion structure. Preferably, a hemispherical pit structure is used, with a pit diameter to depth ratio of 2:1. This structure provides the best control effect on the boundary layer and the best drag reduction and noise reduction effect.
[0080] When the size of the microtexture is less than 10 μm, the undulation height of the microtexture is insufficient, which cannot effectively disturb the fluid in the boundary layer and cannot achieve the early transition from laminar to turbulent flow. The effect of suppressing boundary layer separation is limited, and the drag reduction and noise reduction effect is not obvious. When the size of the microtexture is greater than 50 μm, the undulation height of the microtexture is too large, which will destroy the underlying structure of the boundary layer and lead to an increase in frictional resistance. At the same time, micro-eddies are generated inside the microtexture, causing additional broadband noise.
[0081] Preferably, in this embodiment, the size of the uneven microtexture is set in a gradient along the spanwise direction. The microtexture size of the leaf root segment 2 is 10-20 μm, the microtexture size of the transition segment 3 is 20-35 μm, and the microtexture size of the leaf tip segment 4 is 35-50 μm, which is adapted to the boundary layer thickness at different positions in the spanwise direction of the blade to achieve the optimal drag reduction and noise reduction effect in the entire spanwise direction.
[0082] The boundary layer thickness gradually increases from the leaf root segment 2 to the leaf tip segment 4 along the spanwise direction. Therefore, the corresponding microtexture size also increases synchronously, ensuring that the microtexture can effectively disturb the fluid in the boundary layer and achieve the optimal boundary layer control effect.
[0083] It should be clarified that in this embodiment, the uneven microtexture is uniformly arranged with a density of 20,000 to 50,000 particles / cm², ensuring that the microtexture completely covers the entire surface of the wavy substrate 5 and the gradient sawtooth unit 6, without blind spots or omissions, achieving drag reduction and noise reduction effects across the entire surface. Preferably, the uneven microtexture is prepared by femtosecond laser surface texturing, which can achieve micron-level processing precision, ensuring the dimensional consistency and surface quality of the microtexture, while avoiding thermal damage to the blade substrate structure, thus ensuring the structural strength and surface accuracy of the blade.
[0084] Example 4: In this example, the surface of the formed blade body is ultrasonically cleaned to remove oil, oxide scale and impurities. Then, precision polishing is performed to ensure that the surface roughness Ra ≤ 0.8 μm, providing a smooth substrate surface for micromachining.
[0085] A femtosecond laser processing system was used, and a processing program was developed based on the design parameters of the microscale unit. The laser wavelength was 1030 nm, the pulse width was 200–500 fs, the single pulse energy was 10–50 μJ, and the scanning speed was 500–1000 mm / s. The array processing of microscale units was completed zone by zone on the blade surface. By utilizing the cold processing characteristics of the laser, thermal damage to the blade substrate was avoided, and the dimensional accuracy of the microscale unit was controlled within ±2 μm. After processing, the blade was subjected to secondary ultrasonic cleaning to remove slag and debris generated by laser processing, and then dehydrated and dried with anhydrous ethanol to complete the preparation of the microscale unit.
[0086] In this embodiment, the preparation of the boundary layer induction groove is consistent with the pretreatment process of the microscale unit processing, and the ultrasonic cleaning and precision polishing of the blade surface are completed to ensure the flatness of the substrate surface.
[0087] In the femtosecond laser processing system, an integrated processing program for microscale units and boundary layer induced grooves is developed. Using the same set of laser processing parameters, the boundary layer induced grooves are scanned and processed in a zone-by-zone manner while the microscale units are being processed. By controlling the number of laser scans and the single pulse energy, the groove depth is precisely controlled within the design range of 15 to 25 μm, and the dimensional accuracy is controlled within ±1 μm, thus avoiding the generation of heat-affected zones.
[0088] In this embodiment, the preparation of the boundary layer induction groove specifically involves: completing ultrasonic cleaning and plasma activation treatment of the blade surface to ensure surface cleanliness and activity;
[0089] The blade is placed in a vapor deposition reaction chamber, and the vacuum is evacuated to 10-50 Pa. Siloxane precursor gas, fluorine-modified gas and carrier gas are introduced, and the chamber temperature is controlled to 80-120℃. The deposition time is 30-60 min. By adjusting the precursor flow rate, deposition temperature and time, a nano-hydrophobic coating with a thickness of 1-5 μm is formed on the entire surface of the blade. A uniform microporous structure of 80-120 nm is generated in situ inside the coating.
[0090] After deposition, carrier gas is continuously introduced to cool to room temperature, and the blade is removed to complete the preparation of the nano-hydrophobic layer. The coating prepared in this way can achieve conformal deposition in the micro-nano structure, with no coating blind area, excellent adhesion to the metal substrate, strong erosion and wear resistance, and a water contact angle that can stably reach more than 155°. It also has excellent long-term operational stability.
[0091] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.
Claims
1. A biomimetic centrifugal fan low-noise forward-swept blade, comprising a blade body (1), wherein the blade body (1) is divided into a root section (2), a transition section (3), and a tip section (4) along the spanwise direction, and into a leading edge, a body, and a trailing edge along the chordwise direction, wherein the leading edge is connected to the chordwise front end of the body, and the trailing edge is connected to the chordwise rear end of the body, wherein the body has a suction surface and a pressure surface arranged opposite to each other, characterized in that: The blade leading edge is provided with a three-dimensional composite bionic leading edge structure, which includes: a wave-shaped substrate (5) extending along the span of the blade leading edge, a gradient sawtooth unit (6) integrally formed on the windward side of the wave-shaped substrate (5), and a textured surface covering the surface of the wave-shaped substrate (5) and the gradient sawtooth unit (6). The suction surface and pressure surface of the blade body are integrally formed with flow guide ribs (7). The flow guide ribs (7) extend along the chord direction and their extension direction matches the sweep angle of the spanwise gradually curved sweep layout of the blade body (1). The suction surface and pressure surface of the blade body are also fully covered with drag-reducing microstructures. The trailing edge of the blade is provided with a gradually bifurcated trailing edge structure (8), which is arranged along the entire span of the blade. The blade body (1) is provided with a gradient thickness structure along the span, and the thickness of the gradient thickness structure decreases linearly from the root section (2) to the tip section (4). The blade body (1) adopts a spanwise gradient sweeping layout, wherein the blade root segment (2) is located at 0% to 30% spanwise position of the blade body (1) and is configured as a forward sweeping structure, the transition segment (3) is located at 30% to 70% spanwise position of the blade body and is configured as a sweeping angle linear gradient structure, the blade tip segment (4) is located at 70% to 100% spanwise position of the blade body (1) and is configured as a backward sweeping structure, and the two ends of the transition segment (3) are smoothly connected to the blade root segment (2) and the blade tip segment (4) respectively; The forward sweep angle of the leaf root segment (2) is 15° to 22°, the backward sweep angle of the leaf tip segment (4) is -5° to -12°, and the sweep angle of the transition segment (3) gradually changes linearly along the span from the forward sweep angle of the leaf root segment (2) to the backward sweep angle of the leaf tip segment (4) in an S-shaped curve.
2. The biomimetic centrifugal fan blade with low noise forward sweep according to claim 1, characterized in that: The wave-shaped substrate (5) has an amplitude of 0.3 to 0.7 mm and a wavelength of 1.5 to 2.5 mm; the height of the gradient sawtooth unit (6) is linearly gradient from 0.1 to 0.3 mm at the leaf root segment (2) to 0.4 to 0.6 mm at the leaf tip segment (4); the size of the uneven microtexture is 10 to 50 μm.
3. The biomimetic centrifugal fan blade with low noise forward sweep according to claim 1, characterized in that: The guide ribs (7) are in three stages, with their height gradually changing linearly from 0.4 to 0.6 mm at the blade root section (2) to 1.4 to 1.6 mm at the blade tip section (4). Their pitch is 0.8 to 1.2 mm, and their extension direction matches the tangential velocity of the flow field corresponding to the spanwise sweep layout of the blade body (1).
4. The biomimetic centrifugal fan blade with low noise forward sweep according to claim 1, characterized in that: The drag-reducing microstructure includes microscale units, a nano-hydrophobic layer disposed on the surface of the microscale units, and boundary layer induction grooves disposed on the surface of the blade body; the size of the microscale units is 40-60 μm, and the arrangement density is 1800-2200 units / cm²; the nano-hydrophobic layer has micropores with a pore size of 80-120 nm and a water contact angle greater than 150°; the depth of the boundary layer induction grooves is 15-25 μm, and the groove spacing is 0.4-0.6 mm.
5. A biomimetic centrifugal fan blade with low noise and forward sweep as described in claim 1, characterized in that: The bifurcation angle of the gradually bifurcation trailing edge structure (8) gradually changes linearly from 10° to 14° at the leaf root segment (2) to 14° to 18° at the leaf tip segment (4).
6. The biomimetic centrifugal fan blade with low noise forward sweep according to claim 1, characterized in that: In the gradient variable thickness structure, the maximum thickness of the leaf root segment (2) is 14% to 16% of the chord length of the corresponding position of the leaf, the minimum thickness of the leaf tip segment (4) is 7% to 9% of the chord length of the corresponding position of the leaf, and the thickness of the leaf body (1) decreases linearly from the leaf root segment (2) to the leaf tip segment (4) along the spanwise direction.
7. A biomimetic centrifugal fan low-noise forward-swept blade according to claim 3, characterized in that: The suction surface and the pressure surface are respectively disposed on the front and back sides of the blade body (1). The rib height of the guide rib (7) is positively correlated with the sweep angle of the corresponding spanwise position. The larger the forward sweep angle of the blade root section (2), the higher the rib height of the corresponding position. The larger the absolute value of the backward sweep angle of the blade tip section (4), the lower the rib height of the corresponding position.