A design method for cross-flow air ducts

Abstract

This invention relates to a design method for cross-flow ducts. A two-dimensional model of the axial cross-flow fan is created, meshed, and imported into a solver. Material properties, boundary conditions, and time steps are set, and the solver is run to monitor the volumetric flow rate Q at the cross-flow duct outlet. v The numerical change of Q v When periodic fluctuations are reached, the solver stops solving; then the time step is reduced, and the solver is run again; the noise model is enabled, and the solver is run again, outputting Q. v And A-weighted sound pressure level dB(A), finally selected Q v The design method identifies the range of variables to be designed when the airflow design requirements are met and the dB(A) noise design requirements are met. Within each range, the minimum value of the variable is selected as the optimal value. The cross-flow duct is then designed according to the optimal value of each variable. This design method is efficient and improves design reliability.

Description

Technical Field

[0001] This invention relates to the field of cross-flow fan technology, and in particular to a design method for cross-flow air ducts. Background Technology

[0002] A cross-flow fan mainly consists of three parts: a rotor, an air duct, and a motor. The structure of existing cross-flow fans can be referenced from the Chinese utility model patent "Cross-flow Air Duct and Fan" (patent number ZL202122411192.3, authorization announcement number CN215672883U). The existing rotor is typically multi-bladed, long cylindrical, with forward-curving multi-bladed blades. The cross-flow air duct includes a volute and a volute tongue. When the rotor rotates, airflow enters the grille from the open part of the rotor.

[0003] Passing through the inside of the impeller, the fluid is discharged into the volute from another grille, forming the working airflow. Currently, most cross-flow duct volutes adopt an Archimedean spiral or logarithmic spiral design, with the fluid being delivered along the tangential direction formed by the spiral.

[0004] However, due to the action of the volute and volute tongue, vortices are formed inside the wind turbine flow field. When the vortex deviates from the center of the wind turbine rotation axis, it causes cross-flow, which affects the pressure and air output efficiency inside the cross-flow duct and generates a large amount of noise.

[0005] To solve the above technical problems, it is necessary to improve the cross-flow duct of the cross-flow fan. However, there is currently no universally accepted design theory for cross-flow ducts. Due to the unique eccentric vortex phenomenon inside, when the size of the cross-flow fan is enlarged, it is found that the performance data after enlargement is completely different from the performance data calculated using similarity criteria. It is precisely because of the failure of similarity criteria that people mainly rely on experience and prototype testing when designing cross-flow ducts. However, relying solely on experience and prototype testing will undoubtedly significantly increase the research and development cycle and cost burden.

[0006] To address this, there is a Chinese invention patent with application number CN201110251388.9 (publication number CN102352865A) entitled "Optimization Design Method for Cross-flow Fans Based on Orthogonal Experiments." This method uses orthogonal experiments to test the structural parameters of the impeller, volute, and casing of a cross-flow fan that require optimization, in order to obtain the optimal combination of structural parameters. However, because this orthogonal experiment method selects a representative set of points based on orthogonality, it can only provide a certain combination of levels used in the experiment and cannot provide clear patterns for further experiments, thus the optimization design is not very precise.

[0007] Therefore, further improvements to existing technologies are needed. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a design method for cross-flow ducts that improves both design efficiency and design reliability, in light of the above-mentioned prior art.

[0009] The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a design method for a cross-flow duct, characterized by comprising the following steps:

[0010] Step 1: Select a variable to be designed;

[0011] Step 2: Create a two-dimensional model of the axial section of the cross-flow fan, and create multiple two-dimensional models by changing the values ​​of the variables to be designed in Step 1.

[0012] Step 3: Divide each 2D model into a mesh to obtain multiple mesh models;

[0013] Step 4: Import each mesh model into the solver and set the material properties and boundary conditions;

[0014] Step 5: Set the time step t1, run the solver, and monitor the volumetric flow rate Q at the outlet of the cross-flow duct. v The numerical change of Q v When a periodic fluctuation is reached, the solver stops solving.

[0015] Step 6: Adjust the time step in Step 5 to t2, where t2 < t1, and rerun the solver until Q... v When a periodic fluctuation is reached, the solver stops solving.

[0016] Step 7: Establish a noise model, set the sound source, sound pressure receiving point, and sound source association length, and enable the noise model;

[0017] Step 8: Calculate the number of steps based on the time step t2 in Step 6, input the number of steps, and run the solver again to output the volumetric flow rate Q at the outlet of the cross-flow duct. v A-weighted sound pressure level dB(A);

[0018] Step 9: Determine whether the two-dimensional model simulation of all variables to be designed has been completed. If yes, proceed to step 10; otherwise, proceed to step 1 and select a new variable to be designed.

[0019] Step 10: Select Q based on the design requirements for air volume and noise. v The range of variables to be designed is determined when the air volume design requirements are met and the dB(A) noise design requirements are met, and then selected within each range. The value of the variable to be designed that corresponds to the minimum value is the optimal value of the variable to be designed.

[0020] Step 11: Design the cross-flow duct according to the optimal value of each variable to be designed in Step 10.

[0021] To optimize the design of the cross-flow duct, preferably, the variables to be designed in step 1 are at least one or more of the following: volute tongue clearance ε1, volute shell clearance ε2, inlet angle θ1, outlet angle θ2, volute tongue position angle δ, and / or volute tongue radius R.

[0022] To achieve the modeling and simulation of the cross-flow duct, the two-dimensional model in step 2 consists of a static domain located within the cross-flow duct and a rotating domain located within the impeller. The static domain and the rotating domain are connected by an interface located on the outer periphery of the impeller. The static domain also includes inlet and outlet lines.

[0023] Preferably, the solver in step 4 is a Fluent solver or a CFX solver.

[0024] To reduce simulation time, t2 in step 6 is selected as... and The minimum value in the range, where n is the rotational speed of the cross-flow fan and f is the noise frequency.

[0025] Preferably, the noise model in step 7 adopts the Ffowcs Williams & Hawkings equation.

[0026] Compared with existing technologies, the advantages of this invention are as follows: By creating a two-dimensional model of the axial cross-flow fan, the cross-flow duct can be simulated. Analyzing the velocity and pressure distribution within the entire cross-flow duct effectively guides designers to create products with superior performance. Furthermore, it allows for the evaluation of parameters down to any point in the flow field, without the influence of external factors, resulting in high accuracy. Additionally, by adjusting the time step to a reasonable range only after a periodic fluctuation in the outlet volumetric flow rate, simulation time is effectively reduced. Therefore, this design method is highly efficient, low-cost, and enables the cross-flow duct to obtain highly accurate performance parameters. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the design variables for the cross-flow fan in an embodiment of the present invention;

[0028] Figure 2 This is a two-dimensional modeling diagram of the cross-flow duct in an embodiment of the present invention;

[0029] Figure 3 for Figure 2 The corresponding structural diagram. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] The design method for the cross-flow duct in this embodiment includes the following steps:

[0032] Step 1: Select a variable to be designed;

[0033] like Figure 1 As shown, the variables to be designed are at least one or more of the following: volute tongue clearance ε1, volute casing clearance ε2, inlet angle θ1, outlet angle θ2, volute tongue position angle δ, and / or volute tongue fillet R. Since these variables are important parameters affecting airflow and noise in existing cross-flow fans, these parameters are prioritized for design. Of course, the variables to be designed are not limited to these parameters; they can also be newly added structures, such as: guide vanes inside the impeller, additional flow channels to improve flow, etc. Figure 1 As shown, the cross-flow duct consists of a volute 1 and a volute tongue 2;

[0034] Step 2: Create a two-dimensional model of the axial section of the cross-flow fan, and create multiple two-dimensional models by changing the values ​​of the variables to be designed in Step 1.

[0035] like Figure 3 As shown, the axial flow field height of the cross-flow fan is approximately equal, therefore, the axial section of the cross-flow fan is used to create a two-dimensional model; as shown... Figure 2 As shown, the two-dimensional model consists of a stationary domain 10 located in the cross-flow duct and a rotating domain 20 located in the impeller 3. The stationary domain 10 and the rotating domain 20 are connected by an interface 30 located on the outer periphery of the impeller 2. The stationary domain 20 also includes lines of an inlet 40 and an outlet 41.

[0036] Step 3: Divide each 2D model into a mesh to obtain multiple mesh models;

[0037] In this embodiment, the two-dimensional model is imported into mesh generation software (such as existing mesh generation software ICEM CFD and Ansys mesh; ICEM CFD provides efficient and reliable analysis models for all popular CAE software worldwide, and Ansys mesh is the core module of the ANSYS Workbench platform, which is responsible for outputting computational meshes for numerous solver modules). To improve convergence, quadrilateral meshes are preferred, but triangular meshes can also be used. Mesh refinement is performed near the impeller, interface, and volute tongue. Boundary layer meshes are created near the wall surface. The mesh quality is checked to ensure that skewness, aspect ratio, etc., are within a good range.

[0038] Step 4: Import each mesh model into the solver and set the material properties and boundary conditions;

[0039] In this embodiment, the solver is either the Fluent solver or the CFX solver; the material properties are set as follows: air is assumed to be incompressible, and its density is set to 1.225 kg / m³. 3 The dynamic viscosity was set to 1.79e-5 Pa·s; the boundary conditions were as follows: the Realizable Ke model was preferred for the turbulence model (the Realizable Ke model is a variation of the standard Ke model, which uses mathematical constraints to improve the model's performance and can be used to predict moderate-intensity swirling flows; this model is a commonly used turbulence model in the Fluent solver); the rotational speed of the rotating domain was set to the speed of the cross-flow fan; a pressure inlet and a pressure outlet were used; an interface connection was created for exchanging velocity, pressure, and other data; the PISO algorithm was preferred for pressure-velocity-pressure coupling.

[0040] The process of setting the material properties and boundary conditions described above is all implemented in the solver;

[0041] Step 5: Set the time step t1, run the solver, and monitor the volumetric flow rate Q at the outlet of the cross-flow duct. v The numerical change of Q v When a periodic fluctuation is reached, the solver stops solving.

[0042] Q v The calculated volumetric flow rate, i.e., air volume.

[0043] Where C is the adjustment coefficient, typically 0.83; l is the length of the cross-flow fan; for example... Figure 3 As shown, y1 and y2 are the first end 50 and the second end 51 of the outlet; v n The normal velocity at the exit; Defined as the line flow rate at the outlet;

[0044] Step 6: Adjust the time step in Step 5 to t2, where t2 < t1, and rerun the solver until Q... v When a periodic fluctuation is reached, the solver stops solving.

[0045] In this embodiment, t2 is selected. and The minimum value in, where n is the rotational speed of the cross-flow fan and f is the noise frequency, which is generally taken as the upper limit of the frequency that the human ear can hear, 20000Hz;

[0046] Step 7: Establish a noise model, set the sound source, sound pressure receiving point, and sound source association length, and enable the noise model;

[0047] In this embodiment, the noise model adopts the Ffowcs Williams & Hawkings equations; the sound pressure receiving point is the location near the outlet; the volute tongue, impeller, volute casing, or all three of these can be used as sound sources.

[0048] Step 8: Calculate the number of steps based on the time step t2 in Step 6, input the number of steps, and run the solver again to output the volumetric flow rate Q at the outlet of the cross-flow duct. v A-weighted sound pressure level dB(A);

[0049] The A-weighted sound pressure level dB(A) mentioned above is obtained by performing a Fourier transform on the sound pressure data at the sound pressure receiving point to obtain the spectrum, and then performing A-weighted calculation on the sound pressure level data of the spectrum.

[0050] In this embodiment, the formula for calculating the number of steps is:

[0051]

[0052] Where [] represents rounding down;

[0053] Step 9: Determine whether the two-dimensional model simulation of all variables to be designed has been completed. If yes, proceed to step 10; otherwise, proceed to step 1 and select a new variable to be designed.

[0054] Step 10: Select Q based on the design requirements for air volume and noise. v The range of variables to be designed is determined when the air volume design requirements are met and the dB(A) noise design requirements are met, and then selected within each range. The value of the variable to be designed that corresponds to the minimum value is the optimal value of the variable to be designed.

[0055] In this embodiment, all Q v The dB(A) data were input into the plotting software Origin Pro (Origin Pro, short for Origin Lab Origin Pro, is a very practical mathematical graphing and analysis tool that provides users with professional mathematical data analysis functions, supports various 2D and 3D graphs, and includes data analysis functions such as statistics, signal processing, curve fitting, and peak analysis). The variable to be designed was used as the x-axis, and Q was used as the metric. v dB(A) and The y-axis is used to facilitate the extraction of the design variable range that meets the conditions;

[0056] Step 11: Design the cross-flow duct according to the optimal value of each variable to be designed in Step 10.

[0057] Traditional testing methods can only evaluate performance at locations where sensors are installed, and are easily affected by external environmental interference, impacting accuracy. The method in this invention, through simulation, can analyze the velocity and pressure distribution of the entire flow field. This flow field analysis effectively guides designers to create products with superior performance. In particular, it can evaluate parameters down to any point in the entire flow field, without being affected by external factors, resulting in high accuracy.

Claims

1. A design method for a cross-flow air duct, characterized in that... Includes the following steps: Step 1: Select a variable to be designed; Step 2: Create a two-dimensional model of the axial section of the cross-flow fan, and create multiple two-dimensional models by changing the values ​​of the variables to be designed in Step 1. Step 3: Divide each 2D model into a mesh to obtain multiple mesh models; Step 4: Import each mesh model into the solver and set the material properties and boundary conditions; Step 5: Set the time step t1, run the solver, and monitor the volumetric flow rate Q at the outlet of the cross-flow duct. v The numerical change of Q v When a periodic fluctuation is reached, the solver stops solving. Step 6: Adjust the time step in Step 5 to t2, where t2 < t1, and rerun the solver until Q... v When a periodic fluctuation is reached, the solver stops solving. Step 7: Establish a noise model, set the sound source, sound pressure receiving point, and sound source association length, and enable the noise model; Step 8: Calculate the number of steps based on the time step t2 in Step 6, input the number of steps, and run the solver again to output the volumetric flow rate Q at the outlet of the cross-flow duct. v A-weighted sound pressure level dB(A); Step 9: Determine whether the two-dimensional model simulation of all variables to be designed has been completed. If yes, proceed to step 10; otherwise, proceed to step 1 and select a new variable to be designed. Step 10: Select Q based on the design requirements for air volume and noise. v The range of variables to be designed is determined when the air volume design requirements are met and the dB(A) noise design requirements are met, and then selected within each range. The value of the variable to be designed that corresponds to the minimum value is the optimal value of the variable to be designed. Step 11: Design the cross-flow duct according to the optimal value of each variable to be designed in Step 10.

2. The design method according to claim 1, characterized in that: In step 1, the variables to be designed are at least one or more of the following: volute tongue clearance ε1, volute shell clearance ε2, inlet angle θ1, outlet angle θ2, volute tongue position angle δ, and / or volute tongue radius R.

3. The design method according to claim 2, characterized in that: The two-dimensional model in step 2 consists of a static domain located in the cross-flow duct and a rotating domain located in the impeller. The static domain and the rotating domain are connected by an interface located on the outer periphery of the impeller. The static domain also includes inlet and outlet lines.

4. The design method according to claim 3, characterized in that: In step 4, the solver used is either the Fluent solver or the CFX solver.

5. The design method according to claim 1, characterized in that: In step 6, t2 is selected. and The minimum value in the range, where n is the rotational speed of the cross-flow fan and f is the noise frequency.

6. The design method according to claim 5, characterized in that: In step 7, the noise model adopts the FfowcsWilliams & Hawkings equation.

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