Volute, centrifugal fan and volute design method

Abstract

The invention provides a volute, a centrifugal fan and a volute design method.The volute comprises a volute molded line corresponding to an internal air duct of the volute, the volute molded line comprises a starting section, a main diffusion section and an outlet transition section which are sequentially arranged in the airflow direction, and the divergence angle of the volute molded line continuously increases in the airflow direction; the divergence angle gradient of the volute molded line continuously increases to a peak value in the airflow direction and then continuously decreases, and the divergence angle gradient peak point of the volute molded line is located on the main diffusion section. The volute molded line adopts the differentiated divergence angle and the divergence angle gradient change rule so as to meet the functional requirements of all areas of the air flue in the volute.

Description

Technical Field

[0001] This invention belongs to the field of fan technology, specifically relating to a volute, a centrifugal fan, and a volute design method. Background Technology

[0002] The volute of a centrifugal fan can collect the high-speed airflow generated by the high-speed rotation of the impeller and convert the kinetic energy of the airflow into static pressure energy. The diffusion process of the air duct inside the volute directly determines the static pressure recovery efficiency, flow stability, noise level and engineering adaptability of the fan.

[0003] Current volute designs primarily employ mathematical tools such as high-order polynomials, equiangular spirals, and control point-fitted spline curves to construct the profile. The core logic involves pre-setting geometric boundary conditions, solving for high-order functions, and integrating to generate the profile. While this design achieves geometric continuity of the profile, it suffers from the following key limitations: Existing technologies generally treat the diffusion process of the volute duct as a single entity, focusing only on the final overall diffusion ratio and profile continuity. They fail to perform phased functional design for the flow characteristics at different diffusion stages, making it impossible to specifically control the airflow state at different diffusion stages. This leads to problems in practical applications such as boundary layer separation in the volute tongue region, low diffusion efficiency in the main diffusion region, and large pressure pulsations in the outlet region.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a volute, a centrifugal fan, and a volute design method to solve the problem that existing volutes cannot effectively control airflow in different areas within their interior.

[0006] To achieve the above objectives, a specific embodiment of the present invention provides a volute, which includes a volute profile corresponding to its internal air duct. The volute profile includes an initial section, a main diffuser section, and an outlet transition section arranged sequentially along the airflow direction. The expansion angle of the volute profile continuously increases along the airflow direction, and the expansion angle gradient of the volute profile continuously increases to a peak value and then continuously decreases along the airflow direction. The peak point of the expansion angle gradient of the volute profile is located in the main diffuser section.

[0007] In one or more embodiments of the present invention, the expansion angle gradient of the initial segment is between 0 and 0.02° / mm.

[0008] In one or more embodiments of the present invention, the maximum value of the expansion angle gradient of the main diffuser section is between 0.04 and 0.06° / mm.

[0009] In one or more embodiments of the present invention, the expansion angle gradient of the outlet transition section is between 0.01 and 0.03° / mm.

[0010] In one or more embodiments of the present invention, the ratio of the length of the starting segment to the length of the volute profile is between 0.2 and 0.25.

[0011] In one or more embodiments of the present invention, the ratio of the length of the main diffuser section to the length of the volute profile is between 0.5 and 0.6.

[0012] In one or more embodiments of the present invention, the ratio of the length of the outlet transition section to the length of the volute profile is between 0.15 and 0.3.

[0013] In one or more embodiments of the present invention, the volute profile is constructed to satisfy S1 / S2 = 0.4~0.6; wherein S1 is the profile length between the starting point of the main diffuser section and the peak point of the expansion angle gradient, and S2 is the length of the main diffuser section.

[0014] In one or more embodiments of the present invention, the volute further includes a volute tongue and a volute tongue profile corresponding to the volute tongue, the volute tongue profile being tangent to the volute shell profile.

[0015] In one or more embodiments of the present invention, the radius of the volute tongue profile is between 3 and 8 mm.

[0016] On the other hand, a specific embodiment of the present invention provides a centrifugal fan, which includes an impeller and the aforementioned volute.

[0017] In another aspect, a specific embodiment of the present invention provides a volute design method, which includes: Establish constraints on the volute profile, including: the volute profile consists of an initial section, a main diffuser section, and an outlet transition section arranged sequentially along the airflow direction; the expansion angle of the volute profile increases continuously along the airflow direction; the expansion angle gradient of the volute profile increases continuously along the airflow direction to a peak value and then decreases continuously; the peak value of the expansion angle gradient of the volute profile is located in the main diffuser section; generate a volute profile that satisfies the constraints.

[0018] In one or more embodiments of the present invention, generating a volute profile that satisfies the constraints includes: generating a volute profile that satisfies the constraints using any one of polynomial curve fitting, spline curve fitting, or control point curve fitting.

[0019] In one or more embodiments of the present invention, the constraint further includes: the volute profile is constructed to satisfy S1 / S2=0.4~0.6, wherein S1 is the profile length between the starting point of the main diffuser section and the peak point of the expansion angle gradient, and S2 is the length of the main diffuser section.

[0020] In one or more embodiments of the present invention, the constraint further includes: the expansion angle gradient of the initial segment is between 0 and 0.02° / mm.

[0021] In one or more embodiments of the present invention, the constraint further includes: the maximum value of the expansion angle gradient of the main diffuser is between 0.04 and 0.06° / mm.

[0022] In one or more embodiments of the present invention, the constraint further includes: the expansion angle gradient of the exit transition section is between 0.01 and 0.03° / mm.

[0023] In one or more embodiments of the present invention, the constraint further includes: the ratio of the length of the initial segment to the length of the volute profile is between 0.2 and 0.25.

[0024] In one or more embodiments of the present invention, the constraint further includes: the ratio of the length of the main diffuser section to the length of the volute profile is between 0.5 and 0.6.

[0025] In one or more embodiments of the present invention, the constraint further includes: the ratio of the length of the exit transition section to the length of the volute profile is between 0.15 and 0.3.

[0026] Compared with existing technologies, the volute profile of this invention employs differentiated expansion angles and expansion angle gradient variations to match the functional requirements of various regions within the volute's internal airflow duct. In the initial region of the airflow duct, a gentle expansion angle gradient is controlled in the volute profile to achieve stable boundary layer development and effectively prevent airflow separation and noise in the volute tongue region. In the main diffusion region of the airflow duct, the expansion angle gradient of the volute profile first increases to a peak and then decreases, ensuring a precise correspondence between the diffusion intensity and the section with the most abundant airflow kinetic energy and the most stable boundary layer, achieving a concentrated release of diffusion intensity and significantly improving static pressure conversion efficiency. In the outlet transition region of the airflow duct, the expansion angle gradient of the volute profile is controlled to gradually decrease, ensuring smooth airflow deceleration and rectification, and suppressing outlet pressure pulsations and backflow losses. Attached Figure Description

[0027] 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.

[0028] Figure 1 This is a schematic diagram of the volute structure in one embodiment of the present invention; Figure 2 This is a graph of the expansion angle in one embodiment of the present invention; Figure 3 This is a graph of the expansion angle gradient in one embodiment of the present invention; Figure 4 This is a flowchart of a volute design method in one embodiment of the present invention.

[0029] Explanation of key reference numerals: 1. Starting zone, 2. Main diffuser zone, 3. Outlet transition zone, 4. Starting section, 5. Main diffuser section, 6. Outlet transition section, 7. Volute, 8. Air outlet, 9. Impeller. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0031] In the description of this invention, it should be understood that the terms "top", "bottom", "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention 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. Therefore, they should not be construed as limitations on this invention.

[0032] Furthermore, the term "first" is 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, features defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0033] In one embodiment, reference is made to Figure 1As shown, this invention provides a volute, which includes two side plates and a surrounding plate. The two side plates are arranged opposite each other, and the surrounding plate is located between the two side plates. The two side plates and the surrounding plate together enclose an inner cavity. An air outlet 8 communicating with the inner cavity is provided on the volute. The inner cavity is used to install an impeller 9. An air duct for airflow is formed between the inner surface of the surrounding plate and the outer edge of the impeller 9. The air duct includes an initial region 1, a main diffuser region 2, and an outlet transition region 3 arranged sequentially along the airflow direction. The initial region 1 is the upstream region of the air duct and is adjacent to the volute tongue. It is mainly used to guide the airflow smoothly into the main diffuser region 2 and suppress pressure pulsation and aerodynamic noise at the volute tongue 7. The main diffuser region 2 is the middle section of the air duct. It mainly converts the kinetic energy of the airflow into pressure energy efficiently by controlling the expansion law of the profile to achieve a pressurization effect. The outlet transition region 3 is the downstream region of the air duct and is adjacent to the air outlet 8 in the airflow direction. The airflow in the outlet transition region 3 no longer depends on the continuous energy input of the impeller 9. The core function changes from diffusion to smooth guidance and pressure pulsation suppression.

[0034] Furthermore, referring to Figure 1 As shown, the volute includes a volute profile corresponding to the air duct, which is also the extension path of the curved portion of the enclosure. The volute profile includes an initial section 4, a main diffuser section 5, and an outlet transition section 6 arranged sequentially along the airflow direction. The initial section 4 corresponds to the initial region 1, the main diffuser section 5 corresponds to the main diffuser region 2, and the outlet transition section 6 corresponds to the outlet transition region 3. The volute profile is not an equiangular spiral, but rather constructed as a smooth variable-angle spiral. The expansion angle of the volute profile continuously increases along the airflow direction (see reference...). Figure 2 Furthermore, the rate of increase in the expansion angle first gradually accelerates and then gradually slows down; that is, the expansion angle gradient of the volute profile first continuously increases to a peak along the airflow direction, and then continuously decreases (see reference...). Figure 3 Furthermore, the peak point of the expansion angle gradient of the volute profile is located in the main diffuser section 5.

[0035] It is understandable that the expansion angle gradient G is a geometric parameter used to characterize the expansion rate of the expansion angle within a unit length of the profile. The expansion angle gradient G refers to the ratio of the change in expansion angle Δα between two adjacent measuring points on the volute profile to the arc length Δs of the centerline of the duct between the two measuring points. The corresponding calculation formula is G=Δα / Δs, and the unit of expansion angle gradient G is ° / mm.

[0036] In the equiangular spiral design, the constant expansion angle means that the diffusion intensity is uniformly distributed along the duct, and the airflow begins to bear a diffusion load equivalent to that in the main diffusion zone 2 in the initial zone 1. However, in the initial zone 1, the airflow has just exited the impeller 9, resulting in high turbulence and a relatively unstable boundary layer. Excessive diffusion can easily induce boundary layer separation, leading to energy loss and increased noise. Simultaneously, in the main diffusion zone 2, the equiangular spiral design cannot match higher diffusion intensities, limiting the improvement of static pressure conversion efficiency. This application employs a variable-angle spiral with continuously increasing expansion angle, gradually increasing the diffusion intensity from small to large in the initial zone 1. Applying gentle diffusion in the initial zone 1 helps maintain the stability of the airflow boundary layer and suppresses airflow noise. In the main diffusion zone 2, the expansion angle is already relatively large, allowing for stronger diffusion to fully utilize airflow kinetic energy and improve static pressure conversion efficiency, thus achieving a precise match between diffusion intensity and airflow energy state.

[0037] The rate of increase in the diffusion angle exhibits a pattern of initial rapid increase followed by a gradual decrease (i.e., the diffusion angle gradient initially increases and then decreases). Its core purpose is to balance the concentrated release of diffusion intensity with a smooth transition. In the initial stage of the main diffusion zone 2, the airflow boundary layer already possesses good anti-separation capabilities, and the airflow velocity remains high, resulting in the most abundant kinetic energy reserves and a high efficiency in converting kinetic energy into static pressure. Therefore, increasing the rate of increase in the diffusion angle to its peak value first allows for a concentrated release of diffusion intensity in the main diffusion zone 2, maximizing the conversion of kinetic energy into pressure energy and achieving a better static pressure boost. After the peak value of the diffusion angle gradient, the rate of increase in the diffusion angle gradually decreases, causing the diffusion intensity to gradually diminish. This allows the airflow in the exit transition zone 3 to complete airflow rectification and guidance in a gentle adverse pressure environment, avoiding flow separation and eddy current losses caused by excessive diffusion.

[0038] Understandably, in other scenarios, if the rate of increase in the diffusion angle is initially slow and then accelerates, it means that the strongest diffusion can only be applied to the airflow in a region where the kinetic energy has already decayed, significantly reducing the energy conversion efficiency of the airflow. If the rate of increase in the diffusion angle remains high, the diffusion intensity will remain high in the later stages of the main diffusion region 2, while the airflow velocity has already decreased significantly. An excessively strong adverse pressure gradient can easily induce boundary layer separation, causing flow instability and energy loss.

[0039] Therefore, compared with the above schemes, the design of the volute profile in this application can make the peak value of the diffusion intensity precisely correspond to the main diffusion region 2 where the gas kinetic energy is most abundant and the boundary layer is most stable. While maximizing the static pressure conversion efficiency, the volute effectively avoids the risk of flow instability.

[0040] Furthermore, the main function of the initial region 1 is to achieve stable adhesion of the airflow to the wall, prevent boundary layer separation, and provide a stable inflow for the subsequent diffusion process. To ensure stable airflow adhesion and achieve a gradual establishment of diffusion intensity, thus preventing premature boundary layer separation due to excessive diffusion intensity, the expansion angle gradient of the initial segment 4 of the volute profile should match the function of the initial region 1. That is, the expansion angle gradient of the initial segment 4 should be relatively small and change gradually, so that the airflow only undertakes a relatively slow diffusion effect before entering the main diffusion region 2, ensuring that the boundary layer on the wall remains in a stable adhesion state.

[0041] The maximum value of the expansion angle gradient in the initial segment 4 can be calculated using the critical condition formula for wall flow separation derived from the boundary layer momentum integral equation. For a two-dimensional incompressible fluid, the critical condition for boundary layer separation is that the velocity normal gradient at the wall is zero. At this point, the critical reverse pressure gradient within the duct can be expressed as: .

[0042] Where u is the wall tangential velocity, which is the velocity component of the airflow along the tangential direction of the volute wall. Within the boundary layer, the wall tangential velocity u varies with the normal distance y between the airflow and the wall. At the wall (i.e., y=0), the no-slip condition is satisfied (i.e., u=0). At the outer edge of the boundary layer, the wall tangential velocity u approaches the mainstream airflow velocity u0. The mainstream airflow velocity u0 in a conventional centrifugal fan is generally 20~40 m / s.

[0043] dp / ds is the critical adverse pressure gradient, p is the static pressure (i.e., the static pressure of the airflow), and s is the length of the volute profile.

[0044] C is an empirical coefficient, calculated from the semi-empirical formula for the separation critical condition in the two-dimensional incompressible turbulent boundary layer theory. The value of C is generally in the range of 0.02 to 0.03, and its commonly used engineering empirical value is 0.023.

[0045] ρ represents the airflow density. For the airflow inside the volute at normal temperature and pressure, the airflow density is approximately 1.2 kg / m³. 3 ³ .

[0046] δ represents the thickness of the boundary layer at the volute wall, which is between 0.5 and 1 mm under normal operating conditions.

[0047] Under the geometric constraints of the volute duct, the rate of change of the duct cross-sectional area along the airflow direction has a definite mapping relationship with the expansion angle gradient. According to the continuity equation and momentum equation, the growth rate of the adverse pressure gradient within the duct is positively correlated with the rate of change of the expansion angle along the flow direction (i.e., the expansion angle gradient), which can be specifically expressed as follows: That is, the larger the expansion angle gradient G is, the faster the expansion angle of the air duct increases per unit arc length, the more drastic the expansion of the air duct cross-sectional area, and the higher the rate of increase of the adverse pressure gradient, making it easier for the wall boundary layer to separate.

[0048] In a volute duct, neglecting frictional losses, the continuity equation and Bernoulli equation for incompressible steady flow are: α is the expansion angle. The conversion formula between the expansion angle gradient and the critical inverse pressure gradient is: △s is the length of the initial segment 4. It can be seen that the expansion angle gradient G is positively correlated with the critical reverse pressure gradient.

[0049] Substituting the general operating parameters of conventional volutes and centrifugal fans (u0 is 30 m / s, δ is 0.75 m, and C is 0.023) into the above formula, the expansion angle gradient is approximately 0.2° / mm.

[0050] Therefore, when the expansion angle gradient G1 of the initial section 4 is greater than 0.02° / mm, the reverse pressure gradient will approach the critical condition for boundary layer separation, and the risk of unstable separation of the wall airflow will increase significantly. Therefore, the expansion angle gradient G1 of the initial section 4 should be controlled to be less than 0.02° / mm to effectively avoid boundary layer separation and ensure stable airflow adhesion.

[0051] Furthermore, in order to verify the rationality of the range of values ​​for the expansion angle gradient G1 of the initial segment 4, multiple rounds of univariate sensitivity verification experiments were conducted. The control variable method was used, and only the expansion angle gradient of the initial segment 4 was changed. The experimental results are shown in the table below.

[0052]

[0053] Based on the experimental results in the table above, it can be seen that when the expansion angle gradient exceeds 0.02° / mm, the aerodynamic performance is not stable, but rather undergoes a significant abrupt change. The proportion of the airflow separation area and the outlet pressure pulsation increase significantly, the static pressure recovery efficiency decreases significantly, and the flow state of the airflow becomes significantly unstable.

[0054] Furthermore, the main function of the main diffuser 2 is to efficiently convert airflow kinetic energy into pressure energy, achieving a pressurization effect. Specifically, the main diffuser 2 controls the expansion law of the volute profile, causing the cross-sectional area of ​​the duct to gradually increase along the airflow direction, while the airflow velocity gradually decreases. According to Bernoulli's principle, the reduction in kinetic energy is converted into an increase in static pressure energy. Compared to the initial region 1, which focuses on establishing flow stability, the main diffuser 2 focuses more on optimizing diffusion efficiency. The distribution characteristics of the expansion angle gradient of the corresponding main diffuser section 5 directly determine the static pressure recovery capability and the level of flow loss. If the expansion angle gradient is too small, the diffusion intensity is insufficient, and the static pressure increase is limited; if the expansion angle gradient is too large or its distribution is unreasonable, it is easy to cause boundary layer separation, resulting in energy loss and flow instability. Therefore, the profile design of the main diffuser section 5 needs to seek the optimal balance between diffusion efficiency and flow stability.

[0055] It is understandable that, since the expansion angle gradient of the volute profile changes continuously, the expansion angle gradient at the beginning of the main diffuser section 5 is equal to the expansion angle gradient at the end of the initial section 4, and the expansion angle gradient at the end of the main diffuser section 5 is equal to the expansion angle gradient at the beginning of the outlet transition section 6. The maximum value of the expansion angle gradient of the main diffuser section 5 can be based on the static pressure recovery efficiency formula. Let η be the static pressure recovery efficiency, k be the duct shape coefficient of a conventional centrifugal fan casing (industry standard range 120~150), and e be the Euler number, approximately equal to 2.7. Generally, the static pressure recovery efficiency of the main diffuser zone 2 of a conventional casing is between 65% and 80%. However, in this application, the expansion angle of the main diffuser section 5 corresponding to the main diffuser zone 2 is increasing, and the actual static pressure recovery efficiency of the main diffuser zone 2 is significantly greater than that of a conventional casing. Therefore, the static pressure recovery efficiency of the main diffuser zone 2 in this application can reach over 80%.

[0056] However, according to diffuser aerodynamic design theory, in incompressible flow, the static pressure recovery efficiency is limited by factors such as boundary layer development, secondary flow losses, and flow inhomogeneity, and theoretically cannot reach 100%. Even with an ideal profile design, wall friction losses and the effective flow area occupied by the boundary layer always exist, resulting in a theoretical upper limit for static pressure recovery efficiency. Once the static pressure recovery efficiency exceeds 90%, the geometric and flow control costs required for further improvement increase exponentially, with diminishing returns. Therefore, it is more reasonable to maintain the peak static pressure recovery efficiency of the main diffuser region 2 between 80% and 90% in this application. When the peak static pressure recovery efficiency of the main diffuser region 2 is maintained between 80% and 90%, the peak value G2 of the expansion angle gradient of the main diffuser section 5 can be calculated to be 0.04~0.06° / mm according to the calculation formula of static pressure recovery efficiency and expansion angle gradient.

[0057] Furthermore, the outlet transition zone 3 is the terminal section of the duct. Within this section, the airflow has largely completed the conversion of kinetic energy to pressure energy and no longer relies on the continuous energy input from the impeller 9. Its core function shifts from diffusion to smooth flow guidance and pressure pulsation suppression. The main function of the outlet transition zone 3 is to homogenize the airflow velocity by controlling the further expansion or maintenance of the duct cross-sectional area, thus avoiding additional flow losses caused by uneven velocity distribution. On the other hand, the outlet transition zone 3 also needs to suppress any pressure pulsations and eddies that may remain from the upstream diffusion process, ensuring that the airflow exits the volute in a stable and uniform state, thereby reducing overall machine noise.

[0058] To achieve the above functions, the expansion angle gradient of the outlet transition section 6, corresponding to the outlet transition zone 3, should be matched with the function of the outlet transition zone 3. Specifically, the expansion angle gradient of the outlet transition section 6 should gradually slow down the expansion rate of the duct cross-sectional area, ensuring that the airflow in the outlet transition zone 3 no longer experiences significant diffusion, thus avoiding boundary layer separation or flow instability caused by excessive diffusion. At the same time, the gradual decrease in the expansion angle gradient also ensures a smooth transition in the duct shape, avoiding pressure pulsations and vortex shedding induced by geometric abrupt changes, thereby achieving the dual functions of smooth flow guidance and pressure pulsation suppression.

[0059] According to the continuity equation and momentum conservation equation for incompressible fluids, the expansion angle gradient must match the attenuation rate of the airflow velocity; the two satisfy a positive correlation, which can be specifically characterized by the expansion angle gradient. dv / ds is the velocity decay rate of the airflow along the flow direction.

[0060] In the centrifugal fan casing, the airflow velocity v1 at the outlet of the main diffuser zone 2 (i.e., the inlet of the outlet transition zone 3) is typically 10~20 m / s. Ideally, the airflow velocity v2 at the outlet of the outlet transition zone 3 decreases to 0~5 m / s. Depending on the overall dimensions of the casing, the length s of the outlet transition section 6 is typically 50~150 mm. To ensure smooth airflow, the velocity decay rate dv / ds should not be too large to avoid an excessively high reverse pressure gradient, nor should it be too small to prevent insufficient duct expansion leading to backflow.

[0061] Assuming linear velocity decay, the average velocity decay rate in the exit transition zone 3 is... v1-v2=10~20m / s, s=50~150mm, therefore the average velocity decay rate in the exit transition zone 3 is approximately 67s. -1 ~400s -1 between.

[0062] From the continuity equation ,in Let α be the expansion angle. Further derivation yields the relationship between the expansion angle gradient and the velocity decay rate as follows: In the exit transition zone 3, the expansion angle α is typically 0.5~1.5°. Therefore, the expansion angle gradient G3 of the exit transition section 6 can be calculated to range from 0.01~0.03° / mm.

[0063] To verify the range of expansion angle gradient values ​​for the outlet transition section 6, this application employs a univariate control experiment, varying only the expansion angle gradient of the outlet transition zone 3. The experiment measured the outlet pressure fluctuations and flow field uniformity under different values, and the results are shown in the table below.

[0064]

[0065] The results in the table above show that when the expansion angle gradient G3 of the outlet transition section 6 is between 0.01 and 0.03° / mm, the outlet pressure pulsation is stabilized within 1.2 kPa, and the flow field uniformity is stable above 90%. When the expansion angle gradient G3 of the outlet transition section 6 is greater than 0.03° / mm or less than 0.01° / mm, the pressure pulsation shows a significant upward trend, and the flow field uniformity shows a significant downward trend. These results verify that controlling the expansion angle gradient of the outlet transition section 6 within the range of 0.01 to 0.03° / mm can effectively suppress pressure pulsation and ensure flow field uniformity, demonstrating good engineering applicability.

[0066] Furthermore, based on numerous volute design and performance comparison tests, the length of the initial section 4 accounts for 0.2–0.25% of the total volute profile length, the length of the main diffuser section 5 accounts for 0.5–0.6% of the total length, and the length of the outlet transition section 6 accounts for 0.15–0.3% of the total length. These proportions are empirical ranges derived from extensive simulations and engineering practice in this field, and their rationality lies in the matching requirements between each functional section and the corresponding expansion angle gradient design.

[0067] First, the initial section 4 needs to be long enough to ensure stable development of the boundary layer on the wall from the impeller 9 outlet, and to allow the expansion angle gradient to gradually increase from its minimum value to the set value at the inlet of the main diffuser section 5. If the length of this section is less than 0.2, the boundary layer development will be insufficient, and the expansion angle transition will be abrupt, easily inducing pressure pulsations. If it is greater than 0.25, it will encroach on the effective space of the main diffuser section 5, weakening the overall diffusion efficiency. Controlling the length of the initial section 4 within the range of 0.2 to 0.25 is an empirical value for achieving a balance between stable flow initiation and diffusion space allocation.

[0068] Secondly, the expansion angle gradient of the main diffuser section 5 exhibits a trend of first increasing to a peak and then decreasing. This trend requires a sufficient profile length; otherwise, a sudden increase or decrease in the expansion angle gradient is likely to occur. Setting the length ratio of the main diffuser section 5 to 0.5–0.6 allows the gradient peak to fully expand, the diffusion intensity to be released in a concentrated manner, and the static pressure recovery efficiency to change stably.

[0069] Furthermore, the expansion angle gradient of the outlet transition section 6 gradually decreases, and at the end of the outlet transition section 6, it decreases to near zero. This decrease requires an appropriate profile length. If the length of the outlet transition section 6 is too short, the expansion angle gradient decreases too quickly, causing a sudden change in airflow velocity, a sharp increase in the reverse pressure gradient, and a significant increase in outlet pressure pulsation. If the length is too long, the expansion angle gradient decreases too slowly, and the airflow cannot follow the duct contraction in time, easily forming a backflow vortex at the outlet and reducing the uniformity of the flow field. Therefore, controlling the length ratio of the outlet transition section 6 to 0.15–0.3 allows the expansion angle gradient to transition smoothly to a lower level, avoiding both pressure pulsation and backflow.

[0070] Furthermore, this application constrains the location of the peak point of the expansion angle gradient within the main diffuser section 5. Specifically, the starting point of the main diffuser section 5 is defined as the boundary point between the starting section 4 and the main diffuser section 5, and the ending point of the main diffuser section 5 is the boundary point between the main diffuser section 5 and the outlet transition section 6. The profile length from the starting point of the main diffuser section 5 along the airflow direction to the peak point of the expansion angle gradient is S1, and the profile length of the main diffuser section 5 is S2. The volute profile is constructed to satisfy S1 / S2 = 0.4 to 0.6, meaning that the peak point of the expansion angle gradient is approximately located near the midpoint of the main diffuser section 5.

[0071] The peak point of the expansion angle gradient represents the maximum diffusion intensity. Before this peak point, the expansion angle gradient continuously increases along the airflow direction, and the diffusion intensity gradually strengthens. After this peak point, the expansion angle gradient continuously decreases, and the diffusion intensity gradually weakens. Therefore, the location of the peak point directly affects the energy conversion efficiency and flow stability throughout the entire main diffusion section 5.

[0072] When the peak point of the expansion angle gradient is too close to the starting point of the main diffusion section 5, the expansion angle gradient increases abruptly from a small value at the exit of the initial section 4 to its peak within a very short profile length. This rapid increase in the expansion angle gradient leads to a sudden increase in diffusion intensity before the boundary layer has fully adapted, easily triggering boundary layer separation, especially in regions where the mainstream velocity is still high and the boundary layer thickness is thin. Simultaneously, the premature appearance of the peak point results in an excessively long descent of the expansion angle gradient, excessively prolonging the concentrated release of diffusion intensity and weakening the effect of concentrated energy conversion in the most kinetic energy region, making it difficult to achieve optimal static pressure recovery efficiency. When the peak point is too close to the end of the main diffusion section 5, the airflow experiences a long, inefficient diffusion section before reaching peak diffusion, during which some of the kinetic energy has already decayed. When the peak point arrives, the remaining kinetic energy of the airflow is insufficient to support efficient energy conversion, and the airflow enters the exit transition zone 3 before fully utilizing the pressurization effect brought by the peak diffusion, similarly reducing the overall static pressure recovery efficiency. In summary, the ratio S1 / S2 of the peak position of the expansion angle gradient inside the main diffusion section 5 is limited to 0.4 to 0.6 (i.e., the peak point is roughly located near the midpoint of the main diffusion section 5). This achieves an optimal balance between diffusion intensity and flow stability, ensuring that the rising and falling sections of the expansion angle gradient are of similar length. The rising section has sufficient space to allow the gradient to gradually increase from a small value to the peak value, avoiding boundary layer separation caused by abrupt gradient changes. The falling section has sufficient space to allow the gradient to gradually decrease from the peak value, preventing the waste of kinetic energy caused by a sudden drop in the adverse pressure gradient.

[0073] Furthermore, the volute also includes a volute tongue 7, which is mainly used to cut off the backflow of airflow within the volute, avoiding gas circulation losses, and simultaneously guiding the airflow from the impeller 9 outlet smoothly into the diffuser section, optimizing the flow field uniformity. The volute tongue 7 can also rationally distribute the pressure distribution within the volute and suppress aerodynamic noise by controlling the gap and shape, improving the overall efficiency and operational stability of the fan. The volute tongue 7 extends along the volute tongue profile, which is located at the starting point of the volute profile (i.e., the starting point of the initial segment 4). The volute tongue profile is also the wall contour line of the volute tongue 7 region, and the volute tongue profile and the volute profile are connected tangentially. Specifically, at the starting point of the initial segment 4, the end of the volute tongue profile has the same tangential direction as the starting end of the volute profile, avoiding abrupt angle changes at the connection point of the two profiles. This allows the airflow to smoothly transition from the surface of the volute tongue 7 to the wall surface of the volute profile, preventing local eddies or pressure pulsations induced by geometric angles. At the same time, the tangency between the volute profile and the volute tongue profile also reduces the machining difficulty of the volute, helping to ensure profile accuracy.

[0074] Furthermore, the volute tongue profile is an arc, and its radius is set to 3–8 mm. This radius range is determined based on a comprehensive consideration of the flow characteristics and structural strength at the volute tongue 7. If the volute tongue radius is too small (less than 3 mm), the volute tongue 7 will be too sharp, causing drastic velocity gradient changes as the airflow passes through, resulting in high-pressure pulsation and broadband noise. Simultaneously, the sharp edge is prone to stress concentration during processing, affecting structural durability. If the volute tongue radius is too large (greater than 8 mm), it will increase the effective gap between the volute tongue 7 and the outer edge of the impeller 9, weakening the cutting and guiding effect of the volute tongue 7 on the airflow, causing some high-pressure airflow to flow back to the impeller 9 outlet, reducing overall machine efficiency. Controlling the volute tongue radius within 3–8 mm achieves the optimal balance between noise suppression, maintaining aerodynamic efficiency, and ensuring structural reliability. This radius range matches the expansion angle gradient of the aforementioned initial section 4, jointly ensuring stable airflow adhesion in the initial region 1 and providing good incoming flow conditions for subsequent diffusion.

[0075] In one embodiment, reference is made to Figure 1 As shown, this invention provides a centrifugal fan that can be applied to common household appliances such as ventilation equipment, air conditioners, and range hoods. The centrifugal fan includes an impeller 9 and the aforementioned volute casing. The impeller 9 is installed in the inner cavity of the volute casing and can rotate relative to the volute casing. An air duct for airflow is formed between the outer edge of the impeller 9 and the inner surface of the volute casing's surrounding plate. During operation, the impeller 9 is driven by a motor to rotate at high speed, drawing gas in from the air inlet of the volute casing. After being accelerated by the impeller 9, the gas is tangentially thrown out and enters the air duct of the volute casing. By adopting the aforementioned volute casing structure, this centrifugal fan can maintain high static pressure recovery efficiency and low operating noise over a wide range of operating conditions.

[0076] In one embodiment, reference is made to Figure 4 As shown, the present invention provides a volute design method, which includes the following steps.

[0077] S1. Establish the constraints of the volute profile. The constraints include: the volute profile includes the initial section 4, the main diffuser section 5 and the outlet transition section 6 arranged sequentially along the airflow direction; the expansion angle of the volute profile increases continuously along the airflow direction; the expansion angle gradient of the volute profile increases continuously along the airflow direction to the peak value and then decreases continuously; the peak point of the expansion angle gradient of the volute profile is located in the main diffuser section 5. Furthermore, the constraints also include the following: 1. The volute profile is constructed to satisfy S1 / S2 = 0.4~0.6. Wherein, S1 is the profile length between the starting point of the main diffuser section 5 and the peak point of the expansion angle gradient, and S2 is the length of the main diffuser section 5.

[0078] 2. The expansion angle gradient of the initial segment 4 is between 0 and 0.02° / mm.

[0079] 3. The maximum value of the expansion angle gradient of the main diffuser section 5 is between 0.04 and 0.06° / mm.

[0080] 4. The expansion angle gradient of the exit transition section 6 is between 0.01 and 0.03° / mm.

[0081] 5. The ratio of the length of the initial segment 4 to the length of the volute profile is between 0.2 and 0.25.

[0082] 6. The ratio of the length of the main diffuser section 5 to the length of the volute profile is between 0.5 and 0.6.

[0083] 7. The ratio of the length of the outlet transition section 6 to the length of the volute profile is between 0.15 and 0.3.

[0084] S2. Generate a volute profile that satisfies the constraints.

[0085] Specifically, in this step, curve fitting techniques can be used to construct a discrete point sequence or analytical expression for the volute profile. Any method among polynomial curve fitting, spline curve fitting, or control point curve fitting can be used to generate a volute profile that simultaneously satisfies the above constraints.

[0086] When using the polynomial curve fitting method, a polynomial function of appropriate degree (such as fifth or sixth degree) is selected, with the profile length (which can be understood as arc length) as the independent variable and the expansion angle and expansion angle gradient as the dependent variables. The segment node positions are determined according to the length ratio of each segment. At each node, the required expansion angle value and expansion angle gradient value are set (the gradient at the exit of the initial segment 4 is 0.018–0.022° / mm; the gradient at the peak point of the main diffuser segment 5 is 0.04–0.06° / mm, and this point is located near the midpoint of the main diffuser segment 5; the gradient at the end point of the exit transition segment 6 approaches zero), as boundary constraints. After solving the polynomial coefficients, the analytical expression of the expansion angle along the arc length is obtained. Then, the profile coordinates are inversely calculated using geometric relationships (such as the differential equation between the polar radius and the expansion angle).

[0087] When using the spline curve fitting method, cubic splines or B-splines can be used to represent the volute profile segmented by functional sections. The profile length is used as the independent variable, and the expansion angle and expansion angle gradient are used as dependent variables. Conditions of continuous expansion angle and continuous expansion angle gradient are applied at the connection points of each segment, and target values ​​for the expansion angle gradient within each segment are directly specified at the control points (e.g., the gradient in the initial segment 4 remains constant at a small value, the gradient in the main diffuser segment 5 first increases linearly and then decreases linearly, and the gradient in the exit transition segment 6 decreases linearly). A smooth expansion angle distribution curve is generated through spline interpolation, and then integrated to obtain the change of the expansion angle along the arc length, ultimately converting it into profile coordinates. This method has local support characteristics, facilitating independent adjustment of each segment.

[0088] When using the control point curve fitting method, Bézier curves or non-uniform rational B-splines can be used. The profile length, expansion angle, and expansion angle gradient are used as parameters, and the polar radius or polar angle is used as coordinates. A series of control points are arranged to directly define the profile shape. During the design process, the distribution range of each segment on the profile length parameter is first determined based on the length ratio of the three segments of the volute profile. Then, by adjusting the position weights of the control points, the expansion angle (calculated from geometric relationships) and expansion angle gradient (obtained through numerical differentiation) of the profile generated by the control points at each arc length position satisfy the aforementioned constraints (length ratio, gradient continuity, initial increase followed by decrease, peak interval, etc.).

[0089] Of course, in practical applications, the methods for generating volute profiles that satisfy the constraints are not limited to the three methods listed above. Those skilled in the art should understand that any numerical method or geometric construction technique capable of generating a smooth, continuous curve based on constraints such as profile length, expansion angle, and expansion angle gradient can be used to implement the technical solution of this application. For example, intelligent optimization algorithms such as genetic algorithms and particle swarm optimization can be combined with parametric modeling to automatically search for the optimal profile that satisfies the constraints; alternatively, a reverse construction method based on finite element mesh mapping can be used, first pre-setting the target expansion angle gradient distribution, and then inversely deriving the profile coordinates by solving differential equations. Furthermore, for some application scenarios where high accuracy is not required, an engineering approximation method combining manual adjustment of discrete points with fitting of circular arcs or straight lines can be used. As long as the generated volute profile falls within the scope defined by this application in terms of length ratio, expansion angle distribution, and expansion angle gradient variation characteristics, it falls within the protection scope of this application.

[0090] The above is a general scheme of the volute, centrifugal fan and volute design method provided by the present invention. The following is a specific engineering design for engineering verification of its structure.

[0091] Engineering Design 1 This engineering design provides a volute suitable for a rearward centrifugal fan for vehicle air conditioning. The design constraints of the volute are as follows: the application scenario is a rearward centrifugal fan for vehicle air conditioning; the impeller parameters are a rearward impeller with a diameter of 200mm, 6 blades, and a rated speed of 3000rpm; the volute constraints are a maximum radial dimension ≤231mm, a rated air volume of 800m³ / h, and a rated static pressure of 300Pa; the performance targets are a separation area ratio ≤3%, a static pressure recovery efficiency ≥85%, an outlet pressure pulsation ≤1.2kPa, and a flow field uniformity ≥92%.

[0092] Determine the cooperative constraint conditions for the expansion angle gradient: the expansion angle gradient G1 of the initial segment 4 is ≤ 0.02° / mm, the peak value of the expansion angle gradient G2 of the main diffusion segment 5 is 0.05° / mm, the peak value is located at 50% of the arc length of the main diffusion segment 5, and the expansion angle gradient G3 of the outlet transition segment 6 is 0.02~0.03° / mm.

[0093] The profile is constructed using a fifth-order polynomial radius growth rate function, which is integrated to obtain the volute radius function, ensuring the continuity of the profile and the continuity of the second derivative, fully satisfying the above gradient cooperative constraint conditions.

[0094] The simulation results of Engineering Design 1 and the performance indicators of conventional design are shown in the table below.

[0095]

[0096] It can be seen that the volute of Engineering Design 1 has a separation area ratio of 2.8% under test conditions, a static pressure recovery efficiency of 86.2%, an outlet pressure pulsation of 1.15 kPa, and a flow field uniformity of 92.5%. All indicators of its aerodynamic performance test items are better than those of the conventional design.

[0097] Engineering Design 2 This engineering design provides a centrifugal fan volute suitable for household air conditioners. The fan impeller 9 exhibits high outlet airflow velocity and strong flow non-uniformity, placing high demands on volute flow control and noise suppression. Design constraints are as follows: impeller 9 parameters are a forward-curved multi-blade impeller with a diameter of 150mm, 36 blades, and a rated speed of 2000rpm; volute constraints are a maximum radial dimension ≤175mm, a rated airflow of 400m³ / h, and a rated static pressure of 100Pa; performance targets are a separation area ratio ≤3.5%, static pressure recovery efficiency ≥83%, outlet pressure pulsation ≤0.5kPa, and flow field uniformity ≥90%.

[0098] Forward-curved multi-bladed centrifugal fans have higher impeller outlet tangential velocities and stronger inflow disturbances in the volute region, making them more sensitive to gradient constraints. Based on the aforementioned theoretical derivation and considering the flow characteristics of the forward-curved fan, suitable gradient cooperative constraint conditions are determined within the constraint range defined in this application: the expansion angle gradient G1 of the initial segment 4 ≤ 0.019° / mm, the peak expansion angle gradient G2 of the main diffuser segment 5 = 0.045° / mm, with the peak value located at 50% of the arc length of the main diffuser segment 5, and the expansion angle gradient G3 of the outlet transition segment 6 = 0.018~0. 0 28° / mm.

[0099] The profile is constructed using cubic B-spline curves to ensure the continuity of the profile and the continuity of the second derivative.

[0100] The simulation results of Engineering Design 2 and the performance indicators of conventional design are shown in the table below.

[0101]

[0102] It can be seen that the volute of Engineering Design 2 has a flow separation area ratio of 3.2% under test conditions, a static pressure recovery efficiency of 84.1%, an outlet pressure pulsation of 0.4 kPa, and a flow field uniformity of 91.5%. All indicators of its aerodynamic performance test items are better than those of the conventional design.

[0103] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0104] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A volute, characterized in that, The volute includes a volute profile corresponding to its internal air duct. The volute profile includes an initial section, a main diffuser section, and an outlet transition section arranged sequentially along the airflow direction. The expansion angle of the volute profile increases continuously along the airflow direction. The expansion angle gradient of the volute profile increases continuously along the airflow direction to a peak value and then decreases continuously. The peak point of the expansion angle gradient of the volute profile is located in the main diffuser section.

2. The volute according to claim 1, characterized in that, The expansion angle gradient of the initial segment is between 0 and 0.02° / mm; and / or, The maximum value of the expansion angle gradient in the main diffuser section is between 0.04 and 0.06° / mm; and / or, The expansion angle gradient of the exit transition section is between 0.01 and 0.03° / mm.

3. The volute according to claim 1, characterized in that, The ratio of the length of the initial segment to the length of the volute profile is between 0.2 and 0.25; and / or, The ratio of the length of the main diffuser section to the length of the volute profile is between 0.5 and 0.6; and / or, The ratio of the length of the outlet transition section to the length of the volute profile is between 0.15 and 0.

3.

4. The volute according to claim 1, characterized in that, The volute profile is constructed to satisfy S1 / S2 = 0.4~0.6; Wherein, S1 is the profile length between the starting point of the main diffuser section and the peak point of the expansion angle gradient, and S2 is the length of the main diffuser section.

5. The volute according to claim 1, characterized in that, The volute also includes a volute tongue and a volute tongue profile corresponding to the volute tongue, the volute tongue profile being tangent to the volute shell profile.

6. The volute according to claim 5, characterized in that, The radius of the volute tongue profile is between 3 and 8 mm.

7. A centrifugal fan, characterized in that, The centrifugal fan includes an impeller and a volute as described in any one of claims 1 to 6.

8. A volute design method, characterized in that, The volute design method includes: Establish constraints on the volute profile, the constraints including: the volute profile includes an initial section, a main diffuser section and an outlet transition section arranged sequentially along the airflow direction; the expansion angle of the volute profile increases continuously along the airflow direction; the expansion angle gradient of the volute profile increases continuously along the airflow direction to a peak value and then decreases continuously; the peak point of the expansion angle gradient of the volute profile is located in the main diffuser section. Generate the volute profile that satisfies the constraints.

9. The volute design method according to claim 8, characterized in that, The generation of the volute profile that satisfies the constraints includes: The volute profile that satisfies the constraints is generated by using any one of polynomial curve fitting, spline curve fitting, or control point curve fitting.

10. The volute design method according to claim 8, characterized in that, The constraints also include: The volute profile is constructed to satisfy S1 / S2 = 0.4~0.6, where S1 is the profile length between the starting point of the main diffuser section and the peak point of the expansion angle gradient, and S2 is the length of the main diffuser section; and / or, The constraints also include: the expansion angle gradient of the initial segment is between 0 and 0.02° / mm; and / or, The constraints also include: the maximum value of the expansion angle gradient of the main diffuser section is between 0.04 and 0.06° / mm; and / or, The constraints also include: the expansion angle gradient of the exit transition section is between 0.01 and 0.03° / mm; and / or, The constraints also include: the ratio of the length of the initial segment to the length of the volute profile is between 0.2 and 0.25; and / or, The constraints also include: the ratio of the length of the main diffuser section to the length of the volute profile is between 0.5 and 0.6; and / or, The constraints also include that the ratio of the length of the outlet transition section to the length of the volute profile is between 0.15 and 0.3.

Images