Design method of centrifugal fan with pre-guide vane collector

Abstract

The application discloses a design method of a centrifugal fan collector with a front guide vane, and particularly relates to the following: a prototype collector is established, which is composed of a contraction section and a diffusion section connected along an axial direction in sequence, and the overall profile of the prototype collector forms a three-dimensional rotary body structure by revolving around a horizontal central axis of the collector; an optimized design is carried out on the basis of the prototype collector, and the geometric structure of the improved collector is established according to four parameters, i.e., the number of guide vanes, the inlet angle of the guide vanes, the outlet angle of the guide vanes and the length of the guide vanes; and the outlet angle of the guide vanes, the number of guide vanes and the length of the guide vanes are optimized, so as to obtain an optimized collector model. After the design method is adopted, the flow loss near the front disc of the impeller is reduced, the high-intensity vortex structure in the impeller is reduced, the flow loss in the impeller is greatly reduced, and the operation efficiency of the centrifugal fan under the design flow condition is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of ventilation fan collector design technology, specifically relating to a design method for a centrifugal fan collector with front guide vanes. Background Technology

[0002] Centrifugal fans, as widely used general-purpose power equipment, are extensively applied in core sectors of the national economy, including factory ventilation, mine exhaust, power plant boiler ventilation, air conditioning and refrigeration, building ventilation, and various industrial dust removal and material conveying. According to industry statistics, the annual electricity consumption of fan systems in my country accounts for approximately 10% to 15% of the country's total electricity consumption. In typical high-energy-consuming industries such as steel, cement, and thermal power generation, the energy consumption of fans can even reach 20% to 30% of the total electricity consumption of the entire plant. However, in current actual engineering operations, the average operating efficiency of industrial fans is generally less than 65%. The huge installed base, high power consumption, and long-term low operating efficiency create a stark contrast, which means that even a small improvement in fan design could translate into considerable annual energy-saving and carbon-reduction benefits and economic value.

[0003] Centrifugal fans mainly consist of components such as a collector, impeller, volute, and diffuser. The collector, located at the fan inlet, is the air intake device. Its function is to smoothly guide the gas to the impeller, establishing a uniform velocity and pressure field before the impeller inlet to ensure uniform airflow at the impeller inlet, thereby improving the impeller's work efficiency. However, in existing technologies, the design of the collector and impeller is often considered separately, lacking a systematic focus on their coupling and matching relationship. Therefore, from the perspective of collector-impeller coupling control, proposing a new design method for the centrifugal fan collector and conducting optimization design to change the angle of entry into the impeller to reduce flow separation between the collector outlet and the front plate is one of the important ways to improve the efficiency of centrifugal fans. Summary of the Invention

[0004] The purpose of this invention is to provide a design method for a centrifugal fan collector with front guide vanes, which solves the problem of flow separation between the outlet and the front plate of the existing collector.

[0005] The technical solution adopted in this invention is a design method for a centrifugal fan collector with front guide vanes, which is implemented according to the following steps: Step 1, establish the prototype collector: The prototype collector is composed of a contraction section and a diffusion section connected sequentially along the axial direction. Its overall profile rotates around the horizontal central axis of the collector to form a three-dimensional rotating structure. Step 2: Based on the prototype collector, optimize the design and establish the geometry of the improved collector according to four parameters: number of guide vanes, inlet angle of guide vanes, outlet angle of guide vanes, and length of guide vanes. Optimize the outlet angle of guide vanes, number of guide vanes, and length of guide vanes to obtain the optimized collector model.

[0006] The invention is further characterized in that, The contraction section has a conical structure with a straight generatrix. The angle between this straight line and the inlet face of the collector is 58.5°. This generatrix rotates around the central axis to form a conical channel whose inner diameter gradually decreases from the air inlet to the air outlet. The diffuser section has an arc-shaped structure with a radius R = 30.78 mm. The angle between the tangent at the outlet end of this arc and the horizontal line is 52.1°. The rear end of the contraction section and the front end of the diffuser section are smoothly connected by an arc tangent to the straight generatrix, ensuring continuity of the profile at the connection point.

[0007] In step 2, the inlet angle of the guide vane is θ1 = 90°.

[0008] Number of guide vanes The calculation formula is:

[0009] In the formula, c The length of a single guide vane within the flow channel is chord length / axial length, in mm. r The radius of the annular flow channel where the guide vanes are located; σ For the consistency of the guide vanes, σ It ranges from 0.8 to 1.2.

[0010] The range of the guide vane outlet angle θ is 100°~130°; the range of the guide vane length L is 0.00647D3~0.08621D3; D3 is the collector outlet diameter.

[0011] For each of the three parameters, namely the length of the guide vane , guide vane outlet angle and the number of guide vanes Design optimizations were performed to improve overall pressure efficiency. Using the response factor as the objective and maximizing efficiency as the goal, optimization calculations are performed to ultimately obtain the optimal guide vane exit angle θ and the number of guide vanes. By determining the length L of the guide vanes, the optimized collector model can be obtained.

[0012] The parameter optimization process is as follows: First, a solid model of the optimized collector is constructed using 3D modeling software; then, ANSYS CFX software is used to numerically simulate the 3D incompressible flow field inside the centrifugal fan, with the turbulence model selected as... Model; The boundary conditions for the numerical simulation are set as follows: the inlet boundary condition uses mass flow rate, the outlet boundary condition uses average static pressure, the wall condition is set as an adiabatic, smooth, non-slip wall, the reference atmospheric pressure of the calculation environment is set to 101325 Pa, and the working medium is air at 25℃; After the flow field calculation converges, the relevant physical quantities in the simulation post-processing are extracted, and the total pressure efficiency of the centrifugal fan under this working condition is calculated by the following formula;

[0013] In the formula: Q Standard volumetric flow rate at the inlet (unit: m³) 3 / s), It is the difference between the total pressure at the fan outlet and the total pressure at the fan inlet (i.e., total pressure rise, in Pa). The input effective power of the impeller shaft (in W).

[0014] Select the guide vane outlet angle θ and the number of guide vanes sequentially when the total pressure efficiency of the centrifugal fan is maximized. The optimal parameters are formed by combining the guide vane length L with the flow guide vane length L, thereby obtaining the optimal collector model.

[0015] The beneficial effects of this invention are as follows: The centrifugal fan collector design method with front guide vanes of this invention, by changing the incident angle of gas entering the impeller and improving the flow state of gas flowing into the impeller, couples flow control with impeller optimization, which can significantly reduce the flow loss in the centrifugal fan; before adopting this method, there are a large number of vortices in the impeller of the centrifugal fan. After adopting this design method, by effectively controlling the angle of airflow out of the collector, the flow loss near the front plate of the impeller is reduced, the high-intensity vortex structure in the impeller is reduced, and the flow loss in the impeller is greatly reduced, thus achieving a significant improvement in the operating efficiency of the centrifugal fan under the design flow conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the prototype current collector profile in the method of this invention; Figure 2 This is a schematic diagram of the three-dimensional geometric structure of the prototype current collector in the method of this invention; Figure 3 This is a two-dimensional profile diagram of the optimized collector in the method of the present invention; Figure 4 This is a schematic diagram of the three-dimensional geometry of the optimized collector in the method of the present invention; Figure 5 This invention relates to the effect of the number of guide vanes on the efficiency of the fan in the method of this invention. Figure 6 This invention relates to the effect of the guide vane length L on the fan efficiency. Figure 7 This invention relates to the effect of the guide vane outlet angle θ on the fan efficiency in the method of the present invention. Figure 8 This is a comparison diagram of the full pressure rise characteristics of the prototype and optimized model in the method of this invention; Figure 9 This is a comparison chart of the efficiency characteristics of the prototype and optimized model in the method of this invention; Figure 10 This is a diagram showing the impeller inlet airflow angle distribution of the prototype and optimized models in the method of this invention; Figure 11 This is a comparison diagram of the high entropy production distribution of 95% of the impeller blades in the prototype and optimized models of the method of this invention; Figure 12 This is a comparison diagram of the turbulent kinetic energy distribution of the impeller meridional plane between the prototype and optimized models in the method of this invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] Example 1 The present invention relates to a design method for a centrifugal fan collector with front guide vanes, which is implemented according to the following steps: Step 1, establish the prototype collector: The prototype collector is composed of a contraction section and a diffusion section connected sequentially along the axial direction. Its overall profile rotates around the horizontal central axis of the collector to form a three-dimensional rotating structure. The contraction section is a conical structure with a straight generatrix. The angle between this straight line and the inlet end face of the collector (i.e., the plane perpendicular to the central axis) is 58.5°. This straight generatrix rotates around the central axis to form a conical channel with an inner diameter that gradually decreases from the air inlet to the air outlet. The diffuser section has an arc-shaped structure with a radius of R = 30.78 mm. The angle between the tangent direction at the exit end of the arc and the horizontal line (i.e., the direction of the central axis) is 52.1°.

[0019] The rear end of the contraction section and the front end of the diffusion section are smoothly connected by a circular arc tangent to the straight generatrix, ensuring the continuity of the profile at the connection point.

[0020] The complete profile of the prototype collector is as follows Figure 1 As shown; the profile rotates one revolution along its horizontal central axis to form the three-dimensional solid structure of the prototype collector, and its overall shape is as follows. Figure 2 As shown.

[0021] In the prototype centrifugal fan with a collector, there is a significant defect in the matching structure between the collector and the impeller inlet. Specifically, the diffuser section of the prototype collector is small in size, and the throat diameter is designed to be too small, which directly results in an excessively large diffusion angle in the diffuser section. This structural design not only restricts the flow area of ​​the airflow in the diffuser section, but also results in a poor match between the profile design of the collector's diffuser section and the impeller inlet.

[0022] Under the aforementioned unfavorable geometric constraints, when the airflow completes its turning flow within the collector, its actual incident angle is severely mismatched with the optimal inlet angle of the impeller, resulting in a large airflow angle of attack. This angular mismatch does not end at the inlet but continues and is carried into the flow channels inside the impeller. This easily induces significant vortex structures near the impeller front plate. As the rotating components move, the large-area vortices within the flow channels further intensify, leading to distortion of the flow field inside the impeller. Ultimately, this results in a significant increase in fluid flow losses and a substantial decrease in fan operating efficiency. Therefore, it is necessary to improve the inlet matching problem between the collector and the impeller to enhance fan efficiency.

[0023] Step 2: Optimize the design based on the prototype collector. Establish the improved collector's geometry according to four parameters: the number of guide vanes, the guide vane inlet angle θ1, the guide vane outlet angle θ, and the guide vane length L. Specifically: Number of guide vanes The calculation formula is:

[0024] In the formula, c The chord length / axial length of a single guide vane in the flow channel (in mm). Z This refers to the number of guide vanes; r The radius of the annular flow channel where the guide vanes are located; σ For the consistency of the guide vanes, σ The value is 0.8-1.2; Guide vane inlet angle: θ1 = 90°; The guide vane exit angle θ is defined as the angle between the arc of the guide vane and the circumferential velocity, such as... Figure 3 As shown, the magnitude of θ mainly affects the inlet angle of the airflow into the impeller, and the outlet angle θ of the guide vanes ranges from 100° to 130°. Guide vane length L: defined as the distance between the tangent at the throat of the collector and the bottom of the guide vane, such as... Figure 3 As shown, the length L of the guide vane is dimensionless using the collector outlet diameter D3. The value range of the guide vane length L is 0.00647D3~0.08621D3; After obtaining the range values ​​of the three parameters, respectively for the length of the guide vane , guide vane outlet angle and the number of guide vanes Design optimizations were performed to improve overall pressure efficiency. Using the response factor as the objective and maximizing efficiency as the goal, optimization calculations are performed to ultimately obtain the optimal inlet and outlet angles θ of the guide vanes and the number of guide vanes. By determining the length L of the guide vanes, the optimized collector model can be obtained. Specifically, firstly, a solid model of the optimized collector was constructed using 3D modeling software; then, ANSYS CFX software was used to numerically simulate the three-dimensional incompressible flow field inside the centrifugal fan, with the turbulence model selected as... Model. The boundary conditions for the numerical simulation are set as follows: mass flow rate for the inlet boundary condition, average static pressure for the outlet boundary condition, and adiabatic, smooth, non-slip wall condition. The reference atmospheric pressure for the computational environment is set to 101325 Pa, and the working medium is air at 25°C. After the flow field calculation converges, relevant physical quantities are extracted from the simulation post-processing, and the total pressure efficiency of the centrifugal fan under this operating condition is calculated using the following formula.

[0025] In the formula: Q Standard volumetric flow rate at the inlet (unit: m³) 3 / s), It is the difference between the total pressure at the fan outlet and the total pressure at the fan inlet (i.e., total pressure rise, in Pa). The input effective power of the impeller shaft (in W).

[0026] Select the inlet and outlet angles of the guide vanes and the number of guide vanes in sequence when the total pressure efficiency of the centrifugal fan is maximized. The combined parameters of the collector model are the guide vane length L and the optimized parameters of the collector model. The optimized collector design incorporates an airflow guiding and rectifying assembly within the annular airflow channel between the hub and the outer conical fairing. This assembly comprises 23 micro-guide blades evenly distributed circumferentially, each with an airfoil-like thin-blade structure. Each guide blade is set with a specific tilt angle to actively intervene in the airflow direction. Table 1 shows the range of geometric parameters for the optimized collector. Table 1 Collector Geometric Parameters

[0027] Example 2 The present invention relates to a design method for a centrifugal fan collector with front guide vanes, which is implemented according to the following steps: Step 1, establish the prototype collector: The prototype collector profile includes a contraction section and a diffusion section. The cross-section of the collector's contraction section is a straight line. The straight line rotates around the central axis to form a cone shape. The collector's contraction section gradually contracts from the air inlet to the air outlet. The rear end of the collector's contraction section is smoothly connected to the collector's diffusion section by a curve. Step 2: Based on the prototype collector, optimize the design and establish the geometry of the improved collector according to four parameters: the number of guide vanes, the inlet angle θ1 of the guide vanes, the outlet angle θ of the guide vanes, and the length L of the guide vanes.

[0028] Design calculations were performed on three parameters of the collector, with efficiency as the response factor and the target being the maximum efficiency. The optimized collector was modeled using 3D modeling software, and the flow field inside the 3D incompressible centrifugal fan was numerically simulated using ANSYS CFX software, with the k-ω model as the turbulence model. During the numerical simulation, the inlet boundary condition was mass flow rate, the outlet boundary condition was average static pressure, the wall condition was an adiabatic, smooth, non-slip wall, the reference atmospheric pressure was 101325 Pa, and the medium was air at 25°C. The total pressure efficiency characteristics of the centrifugal fan were thus obtained.

[0029] One-factor analysis was performed on each collector variable. Figure 5 The effect of the number of guide vanes on the efficiency of the wind turbine in the method of the present invention is shown in the figure. As can be seen from the figure, the efficiency first increases and then decreases with the increase of the number of vanes, and the wind turbine efficiency is the highest when the number of vanes is 23. Figure 6 The effect of guide vane length L on fan efficiency is shown in the figure. As can be seen from the figure, the efficiency first increases and then decreases with the increase of guide vane length, and the fan efficiency is the highest when the guide vane length L is 0.02155D3. Figure 7 The influence of the guide vane outlet angle θ on the fan efficiency is shown in the figure. As the value of the guide vane outlet angle θ increases, the efficiency first increases and then decreases. The difference between the maximum and minimum efficiency values ​​is within 1%, and the guide vane outlet angle is 110°. The optimal design parameters of the collector can be determined.

[0030] Example 3 The design method of the centrifugal fan collector with front guide vanes of this invention is adopted. The centrifugal fan is optimized, and the final optimized collector geometric parameters are as follows: number of guide vanes: 23; guide vane length L: 0.02155D3; guide vane outlet angle θ: 110°. The three-dimensional geometry is shown below. Figure 4 As shown.

[0031] Example 4 Figure 8 This is a comparison chart of the total pressure rise characteristics of the fan between the prototype collector and the optimized model. In the chart, Q represents the volumetric flow rate (m³ / s).3 / h), Q des The volumetric flow rate under design conditions is Q. des Dimensionless values ​​were applied to the flow rates Q for different volumes. As shown in the figure, the optimized model improved the total pressure rise under the design conditions by 0.99% compared to the prototype. The total pressure rise under the high flow rate and design flow rate conditions was significantly improved, while the total pressure rise under the low flow rate condition was the same as the prototype.

[0032] Example 5 Figure 9 The figure shows a comparison of the efficiency characteristics of the prototype collector and the optimized model. As can be seen from the figure, the optimized model has improved the efficiency by 1.19% under the design conditions compared with the prototype. The efficiency under the high flow rate and design flow rate conditions has been significantly improved, while the efficiency under the low flow rate condition is almost the same as that of the prototype.

[0033] Example 6 Figure 10 The impeller inlet airflow angle distribution diagrams of the prototype and optimized model in the method of this invention are presented. As shown in the diagrams, in the mainstream region below 0.8 blade height, the airflow angle trends of the optimized model and the prototype are basically consistent. However, the initial angle of the optimized model near the hub is lower, indicating an improvement in the airflow situation within the flow channel. The difference lies in the critical region from 0.8 blade height to the impeller front plate. In this region, the prototype exhibits extreme fluctuations, first a sharp drop (below 30°) followed by a dramatic rise to nearly 70°. In this region, the optimized model shows a significantly smoother transition in airflow angle, completely eliminating the lower angle found in the prototype. This fully demonstrates that the added guide structure in this application can effectively mitigate the negative impact of the collector diffuser section profile defects, greatly improve the angle matching degree when the airflow enters the impeller front plate, suppress the generation of vortices in the impeller front plate from the source, and ultimately achieve the goal of reducing internal impeller flow losses and improving fan efficiency.

[0034] Example 7 Figure 11 This is a comparison diagram of the high entropy production distribution of 95% of the impeller blades in the prototype and optimized model of the method of this invention. As can be seen from the figure, the red and yellow high entropy production areas of the prototype are not only widely distributed, but also have obvious large-area high-intensity energy dissipation near the front disk of the impeller. The optimized model improves the flow field structure, and its high entropy production red area is significantly reduced and located at the edge of a narrower specific flow channel. The mainstream flow channel area presents a large-scale low entropy production area. This shows that the flow guiding structure added in this application successfully improves the airflow injection angle matching degree, effectively suppresses the generation of large-area vortices, and greatly reduces the flow loss inside the impeller. Example 8 Figure 12A comparison diagram of the turbulent kinetic energy distribution on the impeller meridional plane in the prototype and optimized models of the method of this invention is provided. As can be seen from the diagram, in the prototype flow channel (left), there is a large area and high intensity of red high turbulent kinetic energy concentration near the top front disk. In the optimized model (right), the high intensity red turbulent kinetic energy near the front disk is significantly reduced, and the mainstream area in the middle of the flow channel exhibits a more uniform and wider medium-low turbulent kinetic energy region.

[0035] The present invention provides a centrifugal fan collector design method with front guide vanes, which can effectively improve the matching problem between the collector and the impeller inlet, improve the airflow incident angle, reduce the high-entropy production area near the front plate of the impeller 95% cross section, and improve the efficiency of the centrifugal fan by reducing the flow loss inside the impeller.

Claims

1. A design method for a collector for a centrifugal fan with front guide vanes, characterized in that, The specific steps are as follows: Step 1, establish the prototype collector: The prototype collector is composed of a contraction section and a diffusion section connected sequentially along the axial direction. Its overall profile rotates around the horizontal central axis of the collector to form a three-dimensional rotating structure. Step 2: Based on the prototype collector, optimize the design and establish the geometry of the improved collector according to four parameters: number of guide vanes, inlet angle of guide vanes, outlet angle of guide vanes, and length of guide vanes. Optimize the outlet angle of guide vanes, number of guide vanes, and length of guide vanes to obtain the optimized collector model.

2. The design method of the collector for a centrifugal fan with front guide vanes as described in claim 1, characterized in that, The contraction section is a conical structure with a straight generatrix. The angle between the straight generatrix and the inlet end face of the collector is 58.5°. The straight generatrix rotates around the central axis to form a conical channel with an inner diameter that gradually decreases from the air inlet to the air outlet.

3. The design method of the collector for a centrifugal fan with front guide vanes as described in claim 2, characterized in that, The diffuser section has an arc-shaped structure with a radius R = 30.78 mm. The angle between the tangent direction at the exit end of the arc and the horizontal line is 52.1°. The rear end of the contraction section and the front end of the diffuser section are smoothly connected by the arc and the straight generatrix, ensuring the continuity of the profile at the connection point.

4. The design method of the collector for a centrifugal fan with front guide vanes as described in claim 1, characterized in that, In step 2, the inlet angle θ1 of the guide vane is 90°.

5. The centrifugal fan collector design method with front guide vanes as described in claim 4, characterized in that, In step 2, the number of guide vanes The calculation formula is: In the formula, c The length of a single guide vane within the flow channel is chord length / axial length, in mm. r The radius of the annular flow channel where the guide vanes are located; σ For the consistency of the guide vanes, σ It ranges from 0.8 to 1.

2.

6. The design method of the collector for a centrifugal fan with front guide vanes as described in claim 5, characterized in that, In step 2, the range of the guide vane outlet angle θ is 100°~130°; the range of the guide vane length L is 0.00647D3~0.08621D3; D3 is the collector outlet diameter.

7. The centrifugal fan collector design method with front guide vanes as described in claim 6, characterized in that, For each of the three parameters, namely the length of the guide vane , guide vane outlet angle and the number of guide vanes Design optimizations were performed to improve overall pressure efficiency. Using the response factor as the objective and maximizing efficiency as the goal, optimization calculations are performed to ultimately obtain the optimal guide vane exit angle θ and the number of guide vanes. By determining the length L of the guide vanes, the optimized collector model can be obtained.

8. The design method of the collector for a centrifugal fan with front guide vanes as described in claim 7, characterized in that, The parameter optimization process is as follows: First, a solid model of the optimized collector is constructed using 3D modeling software; then, ANSYS CFX software is used to numerically simulate the 3D incompressible flow field inside the centrifugal fan, with the turbulence model selected as... Model; The boundary conditions for the numerical simulation are set as follows: the inlet boundary condition uses mass flow rate, the outlet boundary condition uses average static pressure, the wall condition is set as an adiabatic, smooth, non-slip wall, the reference atmospheric pressure of the calculation environment is set to 101325 Pa, and the working medium is air at 25℃; After the flow field calculation converges, the relevant physical quantities in the simulation post-processing are extracted, and the total pressure efficiency of the centrifugal fan under this working condition is calculated by the following formula; In the formula: Q The standard volumetric flow rate is expressed in cubic meters (m³). 3 / s; The difference between the total pressure at the fan outlet and the total pressure at the fan inlet, expressed in Pa. The effective input power of the impeller shaft, in watts (W). Select the guide vane outlet angle θ and the number of guide vanes sequentially when the total pressure efficiency of the centrifugal fan is maximized. The optimal parameters are formed by combining the guide vane length L with the flow guide vane length L, thereby obtaining the optimal collector model.

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