An asymmetric diffuser volute of a centrifugal fan based on a gradually changing cross section

Abstract

The present application relates to centrifugal fan technical field, especially to a kind of asymmetric diffuser volute of centrifugal fan based on gradual change section, including volute body and its inside volute flow passage;The outer flow passage streamline of volute flow passage extends along Archimedes spiral with the center O' of volute body, the inner flow passage streamline of volute flow passage extends along the radius of impeller with the center O' of volute body, and the starting point of Archimedes spiral is located on inner flow passage streamline;Volute flow passage is provided with multiple control sections along the development direction of Archimedes spiral, and the section reference point of each control section is located at the corresponding position of Archimedes spiral, control section is all controlled using egg-shaped curve, and adjacent control section is continuously expanded volute flow passage wall by boundary smooth mixing between the formation.The present application realizes flexible diffuser by egg-shaped gradual change section, reduces flow separation and backflow, improves static pressure recovery capability and flow field uniformity, improves centrifugal fan aerodynamic performance.

Description

Technical Field

[0001] This invention relates to the field of centrifugal fan technology, and in particular to an asymmetric diffuser casing for centrifugal fans based on a gradually changing cross section. Background Technology

[0002] Low-pressure centrifugal fans are simple to manufacture and have a compact structure, making them widely used in ventilation, air exchange, and dust removal applications such as air conditioners, range hoods, and air purifiers. However, traditional low-pressure centrifugal fan casings mostly adopt rectangular or rounded rectangular cross-sections. Traditional rectangular cross-section casings are prone to boundary layer separation, secondary flow, and local backflow in the volute tongue and diffusion regions, leading to decreased static pressure recovery capacity, poor flow field uniformity, and increased operating noise. Especially under low-pressure, high-flow conditions, the discontinuous change in the flow channel cross-section during diffusion in rectangular casings easily leads to increased local velocity gradients and flow field distortion, further reducing the fan's aerodynamic and acoustic performance. Therefore, a new type of casing structure that can achieve flexible diffusion, reduce flow separation, and improve static pressure recovery capacity is urgently needed. Summary of the Invention

[0003] The purpose of this invention is to overcome the defects of boundary layer separation, secondary flow and local backflow in the existing rectangular cross-section volute. It proposes an asymmetric diffuser volute for centrifugal fans based on a gradually expanding cross-section. By adopting a control cross-section that continuously expands along the Archimedean spiral, flexible diffusion is achieved, flow separation is reduced, and static pressure recovery capability and flow field uniformity are improved.

[0004] To achieve this objective, the present invention adopts the following technical solution: A centrifugal fan asymmetric diffuser volute based on a gradually changing cross section includes a volute body, wherein a volute flow channel is formed within the volute body for collecting and diffusering the impeller outlet airflow located inside it. The outer flow channel streamline of the volute flow channel extends along the Archimedean spiral from the center O' of the volute body, and the inner flow channel streamline of the volute flow channel extends along the radius of the impeller from the center O' of the volute body, with the starting point of the Archimedean spiral located on the inner flow channel streamline. The volute flow channel is provided with multiple control sections along the unfolding direction of the Archimedean spiral. The reference point of each control section is located at the corresponding position of the Archimedean spiral. All control sections are controlled by an egg-shaped curve. Adjacent control sections are connected by a smooth boundary mixing to form a continuously expanding volute flow channel wall.

[0005] Preferably, a two-dimensional rectangular coordinate system ZO'V is established for the volute body: with the center O' of the volute body as the origin O', the V-axis is established with the direction of the straight line connecting the starting point of the Archimedean spiral and the center O', and the Z-axis is established with the straight line perpendicular to the direction of the straight line connecting the starting point of the Archimedean spiral and the center O'. With the positive direction of the Z-axis as the expansion reference for the volute flow channel expansion angle θ, the volute flow channel is provided with four control sections at the volute flow channel expansion angles θ=0°, 90°, 180° and 270° along the expansion direction of the Archimedes spiral in the two-dimensional rectangular coordinate system ZO'V.

[0006] Preferably, the four control sections defined at the volute flow channel expansion angles θ=0°, 90°, 180° and 270° are the volute initiation section, the first control section, the second control section and the volute outlet section, respectively. The volute initiation section is the section of the volute flow channel located at the volute tongue of the volute body in the two-dimensional rectangular coordinate system ZO'V, and the volute outlet section is the section of the volute flow channel located at the starting point of the Archimedean spiral in the two-dimensional rectangular coordinate system ZO'V. The control section is formed by a closed connection of a large-end egg-shaped curve and a small-end egg-shaped curve, and the large-end egg-shaped curve and the small-end egg-shaped curve transition smoothly at the connection point; Define the major semi-axis of the large-end egg-shaped curve as A, the minor semi-axis of the small-end egg-shaped curve as a, and the common minor semi-axis of the large-end egg-shaped curve and the small-end egg-shaped curve as b, satisfying A≥a>b>0.

[0007] Preferably, the exit section of the volute is taken as the polar angle of the Archimedean spiral. Based on the unfolding reference, obtain the polar angle of the Archimedean spiral at any Archimedean spiral angle. The opening of the volute at the location And it satisfies the series expansion: Where R is the impeller radius, and m is the volute expansion coefficient, with 0.02 ≤ m ≤ 0.15. This is the polar angle of the Archimedean spiral, expressed in degrees, with the unit being °. when When ≤0.5, the first three terms of the series expansion are used for calculation; when When the value is greater than 0.5, higher-order terms are retained for calculation.

[0008] Preferably, the initial cross-section of the volute is used as the expansion reference for the volute flow channel expansion angle θ, and the volute expansion coefficient m is based on the volute width B and the circumferential component of the absolute velocity of the airflow at the impeller outlet. And the transition from the initial section of the volute to the polar angle of the Archimedean spiral. Cumulative flow at the location Sure: Assuming the airflow flows uniformly along the volute channel, the distance from the initial cross-section of the volute to the polar angle of the Archimedean spiral is... Cumulative flow at the location With polar angle Proportional, satisfying: ; Where Q is the total flow rate of the centrifugal fan. From the initial cross section of the volute to the polar angle The cumulative flow at that location.

[0009] Preferably, a local two-dimensional rectangular coordinate system XOY is established for the control section: with the center of the control section as the origin O, an X-axis is established along the common minor axis of the control section, and a Y-axis is established along the common major axis of the control section. The positive direction of the Y-axis points to the large-end egg-shaped curve, and the negative direction of the Y-axis points to the small-end egg-shaped curve. The large-endian and small-endian egg-shaped curves are parameterized using the coefficient of variation k of the egg-shaped curve, and their curve equations are as follows: Where k is the coefficient of variation of the egg-shaped curve, and satisfies 0≤k≤1.5.

[0010] Preferably, taking the initial cross-section of the volute as the development reference for the volute flow channel development angle θ, the egg-shapedness E(θ) of the control cross-section located at the volute development angle θ is defined as the ratio of the large-end semi-axis A(θ) to the small-end semi-axis a(θ) of the control cross-section, that is: ; Where E(θ) is the oval shape of the control section located at the volute unfolding angle θ, A(θ) is the major semi-axis of the control section at the large end at the volute unfolding angle θ, and a(θ) is the minor semi-axis of the control section at the small end at the volute unfolding angle θ. When E=1, the control section degenerates into a near-circular or near-elliptical section. As E increases, the asymmetric characteristics of the control section gradually increase.

[0011] Preferably, taking the initial cross-section of the volute as the expansion reference for the volute flow channel expansion angle θ, the egg-shapedness E gradually expands along the volute flow channel expansion angle θ, satisfying the following: ; Where E(θ) is the egg-shapedness of the control section located at the volute expansion angle θ, and E(0)=1. ; The final egg shape increment and 0.8 ≤ ≤4, where n is the expanding exponent and 1.5≤n≤3, The maximum volute flow channel expansion angle and 330° ≤ ≤360°.

[0012] Preferably, the coefficient of variation k of the egg-shaped curve varies with the egg-shapedness E(θ) of the control section at the volute flow channel expansion angle θ, satisfying: ; Where k(θ) is the coefficient of variation of the egg-shaped curve of the control section at the volute unfolding angle θ, and 0 ≤ k(θ) ≤ 1.5. The coefficient of variation of the initial egg-shaped curve with respect to the starting cross section of the volute is 0 ≤ ≤0.3, The egg-shaped coupling coefficient is 0.5 ≤ ≤1.2, E(θ) is the egg-shapedness of the control section located at the volute unfolding angle θ.

[0013] Preferably, the ratio of the large end semi-axis A to the small end semi-axis a satisfies: 1≤A / a≤5.0; The ratio of the common short semi-axis b to the small-end long semi-axis a satisfies: 0.5 ≤ b / a < 1.0; Wherein, A / a=1 corresponds to the egg shape of the initial cross section of the volute; apart from the initial cross section of the volute, as the expansion angle of the volute flow channel increases, A / a>1.0.

[0014] One of the above technical solutions has the following beneficial effects: 1. The volute cross section adopts an egg-shaped gradual cross section design. Near the volute tongue, the egg shape degree is close to 1, and the cross section is close to a circle or ellipse, which can effectively reduce the jet impact and local backflow phenomenon at the impeller outlet. As the expansion angle increases, the egg shape degree gradually increases, and the large end gradually extends towards the diffuser side, forming a continuously changing asymmetric diffuser channel, which improves the static pressure recovery capability of the middle and rear sections of the volute.

[0015] 2. A smoother diffusion process is achieved through continuously varying curvature, allowing the fluid to maintain good adhesion and flow along the volute wall, reducing local flow separation and backflow phenomena, and improving streamline continuity and velocity field uniformity. When the control section reaches its maximum size, the radius of curvature at the large end is the largest, forming a flexible diffusion structure, which allows all accumulated flow to be smoothly discharged from the volute, thus improving the overall aerodynamic performance of the centrifugal fan. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an asymmetric diffuser volute for a centrifugal fan based on a gradually changing cross section according to the present invention; Figure 2 This is a schematic diagram of the flow channel in the asymmetric diffuser volute of a centrifugal fan based on a gradually changing cross section according to the present invention. Figure 3 This is a schematic diagram of the geometric parameters of the control section in the asymmetric diffuser casing of a centrifugal fan based on a gradually changing cross section, according to the present invention. Figure 4 This is a schematic diagram illustrating the control of cross-sectional changes at different volute flow channel expansion angles in an asymmetric diffuser volute based on a gradually varying cross-section according to the present invention. Figure 5 This is a schematic diagram comparing the velocity streamlines of an asymmetric diffuser casing for a centrifugal fan based on a gradually changing cross section with those of a traditional rectangular cross section casing, according to the present invention. Detailed Implementation

[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" 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.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] like Figure 1As shown, an asymmetric diffuser volute for a centrifugal fan based on a gradually changing cross section includes a volute body 1, wherein a volute flow channel 2 is formed inside the volute body 1 for collecting and diffusering the airflow from the outlet of the impeller 3 located inside it. The outer flow channel streamline of the volute flow channel 2 extends along the Archimedean spiral with the center O' of the volute body 1, and the inner flow channel streamline of the volute flow channel 2 extends along the radius R of the impeller 3 with the center O' of the volute body 1, and the starting point of the Archimedean spiral is located on the inner flow channel streamline. The volute flow channel 2 is provided with multiple control sections along the unfolding direction of the Archimedean spiral. The reference point of each control section is located at the corresponding position of the Archimedean spiral. Each control section is controlled by an egg-shaped curve. Adjacent control sections are connected by smooth boundary mixing to form a continuously expanding volute flow channel wall.

[0022] To further explain, a two-dimensional rectangular coordinate system ZO'V is established for the volute body 1: with the center O' of the volute body 1 as the origin O', the V-axis is established with the direction of the straight line connecting the starting point of the Archimedean spiral and the center O', and the Z-axis is established with the direction of the straight line perpendicular to the straight line connecting the starting point of the Archimedean spiral and the center O'. With the positive direction of the Z-axis as the expansion reference for the volute flow channel expansion angle θ, the volute flow channel 2 is provided with four control sections at the volute flow channel expansion angles θ=0°, 90°, 180° and 270° along the expansion direction of the Archimedes spiral in the two-dimensional rectangular coordinate system ZO'V.

[0023] like Figure 1 As shown, the outlet airflow of the centrifugal impeller 3 continuously enters the volute flow channel 2 of the volute body 1 along the circumferential direction. The flow rate inside the volute body 1 continuously accumulates along the flow direction. By designing the streamline of the outer flow channel 2 of the volute flow channel as an Archimedean spiral, as shown... Figure 2 As shown by the yellow dashed line, the inner flow channel streamline of the volute flow channel 2 extends along the radius R of the impeller 3 from the center O' of the volute body 1, and the starting point P of the Archimedean spiral is located on the inner flow channel streamline. This ensures the width and angle design of the volute flow channel 2 between the inner flow channel streamline and the Archimedean spiral, reducing airflow deflection and secondary flow generation. To further optimize the design of the volute flow channel 2, multiple control sections are set along the unfolding direction of the Archimedean spiral. The reference point of each control section is located at the corresponding position of the Archimedean spiral. All control sections are controlled by an egg-shaped curve, and adjacent control sections are connected by a smooth boundary mixing to form a continuously expanding volute flow channel wall.

[0024] In a preferred embodiment, four control sections are set at the volute flow channel 2 at the unfolding angles θ=0°, 90°, 180° and 270° along the unfolding direction of the Archimedean spiral in a two-dimensional rectangular coordinate system ZO'V. Figure 4 As shown, control sections are established at four locations: I, F, G, and H, and each is controlled by an egg-shaped curve. Finally, a continuous volute flow channel wall is formed by smooth mixing at the boundary, which avoids the problem of discontinuous changes in the cross-sectional area of ​​the flow channel in the traditional rectangular cross-section volute. This allows the fluid to maintain good adhesion and flow along the volute wall, reduces local flow separation and backflow, and improves streamline continuity and velocity field uniformity.

[0025] It should be noted that the volute body 1 is a one-piece injection-molded plastic volute. The control sections are continuously arranged along the Archimedean spiral. The egg-shaped curve is mainly controlled and modified using four control sections. A continuous and smooth flow channel wall is formed through boundary mixing to meet the injection molding process requirements of the centrifugal fan.

[0026] To further explain, the four control sections defined at the volute flow channel expansion angles θ=0°, 90°, 180° and 270° are the volute initiation section, the first control section, the second control section and the volute outlet section, respectively. The volute initiation section is the section of the volute flow channel 2 located at the volute tongue of the volute body 1 in the two-dimensional rectangular coordinate system ZO'V. The volute outlet section is the section of the volute flow channel 2 located at the starting point of the Archimedean spiral in the two-dimensional rectangular coordinate system ZO'V. The control section is formed by a closed connection of a large-end egg-shaped curve and a small-end egg-shaped curve, and the large-end egg-shaped curve and the small-end egg-shaped curve transition smoothly at the connection point; Define the major semi-axis of the large-end egg-shaped curve as A, the minor semi-axis of the small-end egg-shaped curve as a, and the common minor semi-axis of the large-end egg-shaped curve and the small-end egg-shaped curve as b, satisfying A≥a>b>0.

[0027] Furthermore, the control section is formed by a closed connection of a large-end egg-shaped curve and a small-end egg-shaped curve, with a smooth transition between the large-end and small-end egg-shaped curves at the connection point, such as... Figure 3 As shown by the red and blue curves, the major semi-axis of the large-end egg-shaped curve is defined as A, the minor semi-axis of the small-end egg-shaped curve as a, and the common minor semi-axis of the large-end and small-end egg-shaped curves as b, satisfying A≥a>b>0. By using an asymmetric control section instead of the traditional rectangular section, and utilizing the dimensional difference between its large and small ends to form an asymmetric diffusion structure, the velocity gradient change of the airflow during diffusion is made more gradual, thereby improving the static pressure recovery capability of the volute.

[0028] To further explain, the exit section of the volute is taken as the polar angle of the Archimedean spiral. Based on the unfolding reference, obtain the polar angle of the Archimedean spiral at any Archimedean spiral angle. The opening of the volute at the location And it satisfies the series expansion:

[0029] Where R is the radius of impeller 3, and m is the volute expansion coefficient, with 0.02 ≤ m ≤ 0.15. This is the polar angle of the Archimedean spiral, expressed in degrees, with the unit being °. when When ≤0.5, the first three terms of the series expansion are used for calculation; when When the value is greater than 0.5, higher-order terms are retained for calculation.

[0030] Known volute opening The radial dimension of the flow channel at any expansion angle is determined by a series expansion formula rather than a simple linear relationship. This allows for a more precise description of the gradual expansion pattern of the volute flow channel, ensuring a better match between changes in the channel cross-sectional area and changes in cumulative flow rate, and guaranteeing that the average flow velocity within the channel remains relatively stable. When When ≤0.5, the calculation using the first three terms of the series expansion is sufficient to meet the engineering design accuracy requirements; when When the value is greater than 0.5, higher-order terms are retained in the calculation to ensure the accuracy of the volute opening at large expansion angles. By precisely controlling the variation of the volute opening along the expansion angle, flow losses caused by excessively high or low local velocities are avoided, diffusion efficiency is improved, and precise mathematical basis is provided for the parametric modeling and manufacturing of the volute.

[0031] To further explain, taking the initial cross-section of the volute as the expansion reference for the volute flow channel expansion angle θ, the volute expansion coefficient m is based on the volute width B and the circumferential component of the absolute velocity of the airflow at the impeller outlet. And the transition from the initial section of the volute to the polar angle of the Archimedean spiral. Cumulative flow at the location Sure: Assuming the airflow flows uniformly along the volute channel, the distance from the initial cross-section of the volute to the polar angle of the Archimedean spiral is... Cumulative flow at the location With polar angle Proportional, satisfying: ; Where Q is the total flow rate of the centrifugal fan. From the initial cross section of the volute to the polar angle The cumulative flow at that location.

[0032] The volute development coefficient *m* is a key dimensionless parameter relating the volute's geometry to its aerodynamic parameters. Its value is determined by comprehensively considering the volute width *B* and the impeller outlet circumferential velocity component. The influence of total flow rate Q is considered. By limiting the value of m to 0.02 ≤ m ≤ 0.15, the rate of change of the volute opening along the development angle is ensured to be within a reasonable range: too small a value of m will result in insufficient volute opening and excessively high flow velocity in the flow channel; too large a value of m will result in excessively rapid volute opening, excessively low flow velocity in the flow channel, and insufficient diffusion. By determining the volute development coefficient m based on aerodynamic parameters, the volute geometry is matched with the aerodynamic performance of the fan, ensuring the stability of the average flow velocity along the flow channel and reducing flow losses and noise caused by sudden changes in flow velocity.

[0033] To further explain, a local two-dimensional rectangular coordinate system XOY is established for the control section: with the center of the control section as the origin O, an X-axis is established along the common minor axis of the control section, and a Y-axis is established along the common major axis of the control section. The positive direction of the Y-axis points to the large-end egg-shaped curve, and the negative direction of the Y-axis points to the small-end egg-shaped curve. The large-endian and small-endian egg-shaped curves are parameterized using the coefficient of variation k of the egg-shaped curve, and their curve equations are as follows:

[0034] Where k is the coefficient of variation of the egg-shaped curve, and satisfies 0≤k≤1.5.

[0035] like Figure 3 As shown, a local two-dimensional rectangular coordinate system XOY is established within the control section. The origin O is the centroid of the control section. An X-axis is established along the common minor axis of the control section, and a Y-axis is established along the common major axis. The positive direction of the Y-axis points to the large-end oval curve, and the negative direction points to the small-end oval curve. All sections use the same local coordinate definition and are continuously arranged along the Archimedean spiral normal to ensure consistency in the parametric modeling of the volute section.

[0036] Both the large-end and small-end egg-shaped curves are elliptical curves, and the control section satisfies the curve equation in the local two-dimensional rectangular coordinate system XOY: Where A and a are the major and minor semi-axises of the control section, respectively, b is the common minor semi-axis, and k is the coefficient of variation of the egg-shaped curve, with A ≥ a > b > 0. The coefficient of variation k is used to adjust the contour shape of the egg-shaped curve, and its value range is 0 ≤ k ≤ 1.5. When k = 0, the effective major semi-axis of the curve is a; as k increases, the effective major semi-axis of the curve gradually increases according to (Aa)k + a, and reaches A when k = 1. Therefore, by adjusting k, the effective major semi-axis of the curve can be continuously changed within the range determined by a and A, thereby realizing the parametric adjustment of the egg-shaped curve contour. Since this embodiment limits k to 0 ≤ k ≤ 1.5, (Aa)k + a ≥ a > 0, thus ensuring that the denominator of the curve equation is always non-zero, avoiding the situation where the curve equation is undefined due to the degradation of the effective major semi-axis.

[0037] Specifically, the two ends of the large-end and small-end egg-shaped curves intersect the y-axis at two points, M and Q, respectively, where |OM|=A and |OQ|=a. The lengths of the two endpoints are L=|MQ|=|OM|+|OQ|=A+a. The two ends of the large-end and small-end egg-shaped curves intersect the x-axis at two points, N and P, respectively. The length of the common minor axis at the widest point of the ellipses at both ends is 2b=|PN|, and the semi-minor axes of the ellipses at both ends are b=|OP|=|ON|. That is, 2b and b are also the diameter 2d and radius d of the largest circle formed by the horizontal plane when the egg is placed vertically, which is max(2d)=2b.

[0038] To ensure that the control section has stable asymmetric diffusion characteristics and meets the processing and manufacturing requirements of centrifugal fans, the parameters satisfy: A≥a>b>0; 1.0≤A / a≤5.0, preferably 1.2≤A / a≤3.0; 0.5≤b / a<1.0, preferably 0.7≤b / a≤0.9; the coefficient of variation k of the egg-shaped curve satisfies 0≤k≤1.5, preferably 0.2≤k≤1.0.

[0039] At the initial section of the volute, the egg-shapedness E=1, corresponding to A=a. As the volute unfolding angle θ increases, the egg-shapedness E gradually increases, and the semi-major axis A of the large end gradually becomes greater than the semi-major axis a of the small end, i.e., A>a, thereby gradually increasing the asymmetry of the control section.

[0040] The A / a ratio determines the dimensional difference between the large and small ends of the control section. When A / a = 1, the semi-major axis of the large end is equal to that of the small end, resulting in the lowest degree of asymmetry in the control section. As A / a increases, the dimensional difference between the large and small ends gradually increases, and the asymmetric characteristics of the control section gradually intensify. If A / a is too large, the large end will be too large, which can easily lead to excessively low flow velocity and flow separation in the large end region. The preferred A / a is 1.2 to 3.0 to balance asymmetric diffusion effect and flow stability.

[0041] The b / a ratio determines the flatness of the control section. If b / a is too small, the section will be too flat and the flow channel height will be insufficient. If b / a is too large, the section will be close to a circle and the asymmetry will be weakened. The preferred b / a is 0.7 to 0.9 to ensure that the flow channel has a reasonable height-to-width ratio.

[0042] The coefficient of variation k of the egg-shaped curve controls the degree of asymmetry of the curve profile. If k is too small, the egg-shaped curve will be close to an ellipse and the asymmetric characteristics will be insufficient. If k is too large, the curve profile will change drastically and the curvature will easily change abruptly. The preferred value of k is 0.2 to 1, which ensures that the cross-sectional profile is continuous and smooth and has stable asymmetric diffusion characteristics.

[0043] To further explain, taking the initial cross-section of the volute as the development reference for the volute flow channel development angle θ, the egg-shapedness E(θ) of the control section located at the volute development angle θ is defined as the ratio of the large-end semi-axis A(θ) to the small-end semi-axis a(θ) of the control section, that is: ; Where E(θ) is the oval shape of the control section located at the volute unfolding angle θ, A(θ) is the major semi-axis of the control section at the large end at the volute unfolding angle θ, and a(θ) is the minor semi-axis of the control section at the small end at the volute unfolding angle θ. When E=1, the control section degenerates into a near-circular or near-elliptical section. As E increases, the asymmetric characteristics of the control section gradually increase.

[0044] Egg-shapedness E is a core parameter characterizing the degree of asymmetry in the control cross-section. This reflects the ratio of the large-end semi-axis A(θ) to the small-end semi-axis a(θ). At the starting position of the volute tongue, since the airflow from the impeller outlet has just entered the volute, the flow rate is small and the velocity is high. The egg-shapedness E is designed to be close to 1, making the cross-section nearly circular or elliptical, which can reduce the impact of the impeller outlet jet on the volute tongue and the local backflow phenomenon. Taking the initial cross-section of the volute at the starting position of the volute tongue as the reference cross-section for the development angle, the development angle of the volute flow channel at this position is defined as θ=0. As the development angle of the volute flow channel increases, the cumulative flow rate in the volute gradually increases. The continuous gradual expansion of the egg-shapedness E causes the large end to gradually extend towards the diffuser side, forming a continuously changing asymmetric diffuser flow channel to adapt to the increasing cumulative flow rate. Through the continuous gradual expansion of the egg-shapedness E along the development direction, a smooth transition of the volute flow channel 2 from the near-circular cross-section near the volute tongue to the asymmetric control cross-section at the outlet is achieved. This reduces the flow impact and backflow in the volute tongue region and improves the static pressure recovery capability of the middle and rear sections of the volute, taking into account both low noise and high efficiency requirements.

[0045] To further explain, taking the initial cross-section of the volute as the expansion reference for the volute flow channel expansion angle θ, the egg-shapedness E gradually expands along the volute flow channel expansion angle θ, satisfying the following: ; Where E(θ) is the egg-shapedness of the control section located at the volute expansion angle θ, and E(0)=1. ; The final egg shape increment and 0.8 ≤ ≤4, where n is the expanding exponent and 1.5≤n≤3, The maximum volute flow channel expansion angle and 330° ≤ ≤360°.

[0046] The gradual expansion law of the egg-shapedness E adopts a power function form. The egg-shapedness E(θ) is 1 at the initial position of the volute tongue, i.e., θ=0°; and 1+ΔE at the volute exit position, i.e., θ=θmax. Therefore, ΔE represents the total increment of the egg-shapedness from the initial section of the volute to the exit section. The gradual expansion index n is used to adjust the rate of change of the egg-shapedness along the volute expansion angle. The larger n is, the slower the increase of the egg-shapedness in the initial stage and the faster the increase in the later stage. The termination development angle is used to determine the gradual expansion law of egg shape. This is achieved by adjusting ΔE, n, and... It can control the final increment, expansion rate, and expansion range of egg shape respectively.

[0047] To further clarify, the coefficient of variation k of the egg-shaped curve varies with the egg-shapedness E(θ) of the control section at the volute flow channel expansion angle θ, satisfying: ; Where k(θ) is the coefficient of variation of the egg-shaped curve of the control section at the volute unfolding angle θ, and 0 ≤ k(θ) ≤ 1.5. The coefficient of variation of the initial egg-shaped curve with respect to the starting cross section of the volute is 0 ≤ ≤0.3, The egg-shaped coupling coefficient is 0.5 ≤ ≤1.2, E(θ) is the egg-shapedness of the control section located at the volute unfolding angle θ.

[0048] To ensure that the asymmetric characteristics of the egg shape curve are synchronized with the changes in egg shape degree, k is designed to be a function that changes synchronously with E. Near the rostral tongue, since the egg shape degree E is close to 1, k remains at a relatively small value (close to...). The cross-section is made close to a circle or ellipse to reduce the impact of the impeller outlet jet and local backflow. As the volute channel expansion angle increases, the egg shape E gradually increases, and k increases synchronously, so that the large end gradually extends to the diffuser side, forming a continuously changing asymmetric diffuser channel, which improves the static pressure recovery capability of the middle and rear sections of the volute.

[0049] like Figure 4 As shown, the control section is set along the unfolding direction of the volute flow channel 2, and a corresponding local section coordinate system XOY is established at each unfolding position. The control section forms an asymmetric structure along the Y direction of the local coordinate system, wherein the positive direction of the Y-axis points to the large-end egg-shaped curve, and the negative direction points to the small-end egg-shaped curve. The large-end semi-axis of the large-end egg-shaped curve is characterized by parameter A, the small-end semi-axis of the small-end egg-shaped curve is characterized by parameter a, and the common minor semi-axis of the large-end and small-end egg-shaped curves is characterized by parameter b. The total height of the control section is A+a, and the total lateral width is 2b. Taking the initial section of the volute as the unfolding reference of the volute flow channel unfolding angle θ, the egg-shapedness E(θ) of the control section located at the volute unfolding angle θ is defined as the ratio of the large-end semi-axis A(θ) to the small-end semi-axis a(θ) of the control section, that is: .

[0050] In summary, as the volute flow channel 2 expands from the initial position of the volute tongue towards the outlet, the size and shape of the control section gradually change with the expansion angle. When the egg-shapedness E(θ) is small, the large-end semi-axis A and the small-end semi-axis a are relatively close, the vertical asymmetry of the control section is weak, and the cross-sectional shape tends to be circular or nearly elliptical, which helps to reduce the local flow impact and backflow of the airflow near the volute tongue after entering the volute. As the expansion angle of the volute flow channel gradually increases, the cumulative flow inside the volute continuously increases. By gradually increasing the egg-shapedness E(θ), the large-end semi-axis A gradually increases relative to the small-end semi-axis a, and the asymmetric characteristics of the control section gradually strengthen, thus forming an asymmetric volute flow channel that continuously changes along the expansion direction of the volute.

[0051] The continuous gradual change of the control section along the expansion direction of the volute allows the volute flow channel to gradually transition from a smaller, more regular section in the initial region of the volute tongue to a larger, asymmetric control section in the outlet region. This matches the expansion process of the section with the increase in the cumulative flow within the volute, which helps to reduce local flow separation and backflow within the flow channel, improve the continuity of the flow and the uniformity of the velocity field, and improve the static pressure recovery capability of the volute, thereby improving the overall aerodynamic performance of the centrifugal fan.

[0052] To further verify the performance advantages of this embodiment, simulation comparison tests were conducted using both a traditional rectangular cross-section volute and an egg-shaped cross-section volute as described in this embodiment. The test data are shown in the table below.

[0053]

[0054] The test performance diagram of the egg-shaped cross-section volute in this embodiment is shown below. Figure 5 As shown in (a) above, the test performance diagram of a traditional rectangular cross-section volute is as follows. Figure 5As shown in (b) above, compared with the two, the egg-shaped gradient cross section of this embodiment achieves a smoother diffusion process through continuously changing curvature, which allows the fluid to maintain better adhesion flow along the volute wall, reduces local flow separation and backflow phenomena, improves streamline continuity and velocity field uniformity, and is conducive to improving the overall aerodynamic performance of the centrifugal fan.

[0055] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these equivalent variations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A centrifugal fan asymmetric diffuser volute based on a gradually changing cross section, comprising a volute body (1), wherein a volute flow channel (2) is formed within the volute body (1) for collecting and diffuserizing the outlet airflow of the impeller (3) located therein. Its features are, The outer flow channel streamline of the volute flow channel (2) extends along the Archimedean spiral with the center O' of the volute body (1), and the inner flow channel streamline of the volute flow channel (2) extends along the radius of the impeller (3) with the center O' of the volute body (1), and the starting point of the Archimedean spiral is located on the inner flow channel streamline. The volute flow channel (2) is provided with multiple control sections along the unfolding direction of the Archimedean spiral. The reference point of each control section is located at the corresponding position of the Archimedean spiral. The control sections are all controlled by egg-shaped curves. Adjacent control sections are formed by smooth boundary mixing to form a continuously expanding volute flow channel wall.

2. The centrifugal fan asymmetric diffuser casing based on a gradually varying cross-section according to claim 1, characterized in that, A two-dimensional rectangular coordinate system ZO'V is established for the volute body (1): the center O' of the volute body (1) is taken as the origin O', the V axis is established with the direction of the straight line connecting the starting point of the Archimedes spiral and the center O', and the Z axis is established with the straight line perpendicular to the direction of the straight line connecting the starting point of the Archimedes spiral and the center O'. With the positive direction of the Z-axis as the expansion reference for the volute flow channel expansion angle θ, the volute flow channel (2) is provided with four control sections at the volute flow channel expansion angles θ=0°, 90°, 180° and 270° along the expansion direction of the Archimedes spiral in the two-dimensional rectangular coordinate system ZO'V.

3. The asymmetric diffuser casing of a centrifugal fan based on a gradually varying cross-section according to claim 2, characterized in that, The four control sections defined at the volute flow channel expansion angles θ=0°, 90°, 180° and 270° are the volute starting section, the first control section, the second control section and the volute outlet section, respectively. The volute starting section is the section of the volute flow channel (2) located at the volute tongue of the volute body (1) in the two-dimensional rectangular coordinate system ZO'V. The volute outlet section is the section of the volute flow channel (2) located at the starting point of the Archimedean spiral in the two-dimensional rectangular coordinate system ZO'V. The control section is formed by a closed connection of a large-end egg-shaped curve and a small-end egg-shaped curve, and the large-end egg-shaped curve and the small-end egg-shaped curve transition smoothly at the connection point; Define the major semi-axis of the large-end egg-shaped curve as A, the minor semi-axis of the small-end egg-shaped curve as a, and the common minor semi-axis of the large-end egg-shaped curve and the small-end egg-shaped curve as b, satisfying A≥a>b>0.

4. The asymmetric diffuser casing of a centrifugal fan based on a gradually varying cross-section according to claim 3, characterized in that, The exit section of the volute is taken as the polar angle of the Archimedean spiral. Based on the unfolding reference, obtain the polar angle of the Archimedean spiral at any Archimedean spiral angle. The opening of the volute at the location And it satisfies the series expansion: ； Where R is the radius of the impeller (3), and m is the volute expansion coefficient, with 0.02 ≤ m ≤ 0.

15. This is the polar angle of the Archimedean spiral, expressed in degrees, with the unit being °. when When ≤0.5, the first three terms of the series expansion are used for calculation; when When the value is greater than 0.5, higher-order terms are retained for calculation.

5. The asymmetric diffuser casing of a centrifugal fan based on a gradually varying cross-section according to claim 4, characterized in that, The initial cross-section of the volute is used as the expansion reference for the volute flow channel expansion angle θ. The volute expansion coefficient m is based on the volute width B and the circumferential component of the absolute velocity of the airflow at the impeller (3) outlet. And the transition from the initial section of the volute to the polar angle of the Archimedean spiral. Cumulative flow at the location Sure: Assuming the airflow flows uniformly along the volute channel, the distance from the initial cross-section of the volute to the polar angle of the Archimedean spiral is... Cumulative flow at the location With polar angle Proportional, satisfying: ； Where Q is the total flow rate of the centrifugal fan. From the initial cross section of the volute to the polar angle The cumulative traffic at that location.

6. The asymmetric diffuser casing of a centrifugal fan based on a gradually varying cross-section according to claim 3, characterized in that, A local two-dimensional rectangular coordinate system XOY is established for the control section: with the center of the control section as the origin O, an X-axis is established along the common minor axis of the control section, and a Y-axis is established along the common major axis of the control section. The positive direction of the Y-axis points to the large-end egg-shaped curve, and the negative direction of the Y-axis points to the small-end egg-shaped curve. The large-endian and small-endian egg-shaped curves are parameterized using the coefficient of variation k of the egg-shaped curve, and their curve equations are as follows: Where k is the coefficient of variation of the egg-shaped curve, and satisfies 0≤k≤1.

5.

7. A centrifugal fan asymmetric diffuser casing based on a gradually varying cross-section according to claim 6, characterized in that, Using the initial cross-section of the volute as the development reference for the volute flow channel development angle θ, the egg-shapedness E(θ) of the control section located at the volute development angle θ is defined as the ratio of the large-end semi-axis A(θ) to the small-end semi-axis a(θ) of the control section, that is: ； Where E(θ) is the oval shape of the control section located at the volute unfolding angle θ, A(θ) is the major semi-axis of the control section at the large end at the volute unfolding angle θ, and a(θ) is the minor semi-axis of the control section at the small end at the volute unfolding angle θ. When E=1, the control section degenerates into a near-circular or near-elliptical section. As E increases, the asymmetric characteristics of the control section gradually increase.

8. The asymmetric diffuser casing of a centrifugal fan based on a gradually varying cross-section according to claim 7, characterized in that, Taking the initial cross-section of the volute as the expansion reference for the volute flow channel expansion angle θ, the egg-shapedness E gradually expands along the volute flow channel expansion angle θ, satisfying the following: ； Where E(θ) is the egg-shapedness of the control section located at the volute expansion angle θ, and E(0)=1. ; The final egg shape increment and 0.8 ≤ ≤4, where n is the expanding exponent and 1.5≤n≤3, The maximum volute flow channel expansion angle and 330° ≤ ≤360°.

9. A centrifugal fan asymmetric diffuser casing based on a gradually varying cross-section according to claim 7, characterized in that, The coefficient of variation k of the egg-shaped curve varies with the egg-shapedness E(θ) of the control section at the volute flow channel expansion angle θ, satisfying: ； Where k(θ) is the coefficient of variation of the egg-shaped curve of the control section at the volute unfolding angle θ, and 0 ≤ k(θ) ≤ 1.

5. The coefficient of variation of the initial egg-shaped curve with respect to the starting cross section of the volute is 0 ≤ ≤0.3, The egg-shaped coupling coefficient is 0.5 ≤ ≤1.2, E(θ) is the egg-shapedness of the control section located at the volute unfolding angle θ.

10. The asymmetric diffuser casing of a centrifugal fan based on a gradually varying cross-section according to claim 3, characterized in that, The ratio of the large end semi-axis A to the small end semi-axis a satisfies: 1.0 ≤ A / a ≤ 5.0; The ratio of the common short semi-axis b to the small-end long semi-axis a satisfies: 0.5 ≤ b / a < 1.0; Wherein, A / a=1 corresponds to the egg shape of the initial cross section of the volute; apart from the initial cross section of the volute, as the expansion angle of the volute flow channel increases, A / a>1.0.

Images