A CFD-based gearbox heat dissipation simulation method

Abstract

The invention discloses a gearbox heat dissipation simulation method based on CFD, which belongs to the technical field of mechanical transmission. The invention adopts CFD simulation technology to simulate the heat dissipation process of the gearbox under different working conditions, obtains the temperature distribution of the gearbox, the wall forced convection heat transfer coefficient, and gives an evaluation standard for the heat dissipation capacity of the gearbox. The evaluation standard can be used to directly judge the heat dissipation capacity of the gearbox. At the same time, compared with traditional test methods, the method is simple and easy as a whole, significantly improves research efficiency, and reduces research costs.

Description

Technical Field

[0001] The invention belongs to the technical field of mechanical transmission, and in particular relates to a gearbox heat dissipation simulation method based on CFD. Background Art

[0002] In the field of mechanical transmission technology, gearbox transmission is the most widely used transmission form, with the characteristics of accurate transmission ratio, small power loss, high reliability, etc., and can achieve functions such as speed reduction and torque increase, and change the direction of power output. Due to various power losses in the box, the gearbox will generate heat during operation, part of which is convectively exchanged with the surface of the gearbox, causing the temperature of the gearbox to rise, affecting the service life of the gearbox. Another part of the heat is absorbed by the lubricating oil in the box, causing the temperature of the lubricating oil to rise, affecting its lubrication effect, causing gears or bearings to wear, pitting and other failure forms, thereby affecting the transmission characteristics of the gearbox.

[0003] Traditional methods for analyzing and studying gearbox heat dissipation generally use experimental methods to make sample boxes and conduct macroscopic analysis of the gearbox heat dissipation. However, the cost of making sample boxes is high, the test cycle is long, and a corresponding test bench needs to be built.

[0004] Computational Fluid Dynamics (CFD) uses computers and numerical calculations to solve the governing equations of fluids and to simulate fluid problems. Compared with experimental methods, it has the advantages of wide application range, low cost, and short calculation cycle. At present, CFD is rarely used in the field of gearbox heat dissipation. Summary of the invention

[0005] In view of the above problems, the present invention provides a gearbox heat dissipation simulation method based on CFD. Compared with traditional test methods, this method is simpler and easier to implement as a whole, and can significantly improve research efficiency and reduce research costs.

[0006] To achieve the above object, the present invention provides a gearbox heat dissipation simulation method based on CFD, comprising the following steps:

[0007] S1, establishing a gearbox geometry model and a simplified occluding body geometry model, i.e., a solid domain model;

[0008] The gearbox geometry model is a solid model of the gearbox established based on the design drawings of the gearbox using the 3D modeling software CATIA. The tiny geometric structures that have little impact on the calculation results, such as fillets and bolt holes, are cleaned up and saved as *.x_t files for subsequent calculation applications. The 3D modeling software CATIA is a commercial 3D modeling software, and *.x_t is the output file format of the software.

[0009] The simplified shielding body geometry model simulates the shielding effect of the surrounding parts on the gearbox heat dissipation in actual use. According to the design drawings of the surrounding parts of the gearbox, it is simplified and a solid model is established using the 3D modeling software CATIA, and saved as an *.x_t file for subsequent calculation applications.

[0010] S2, pre-processing the solid domain model, mainly including extracting the flow channel to obtain the fluid domain model, selecting the corresponding meshing method and generating a CFD mesh that meets the calculation requirements;

[0011] The fluid domain model is a cubic model including the solid domain model. The flow channel is extracted using the Geometry module in the ANSYS Workbench software, where the ANSYS Workbench software is a commercial multi-physics collaborative simulation software.

[0012] The CFD mesh was divided by importing the fluid domain model generated by the Geometry module into the Meshing module in the ANSYS Workbench software, where the physical preference was set to CFD, the solver preference was set to Fluent, the target skewness was set to 0.9, and the smoothing was set to high;

[0013] Set the surface size adjustment on the gearbox surface to locally encrypt it and set the expansion layer, where the expansion option is set to the first layer thickness, the maximum number of layers is set to 5, the growth rate is set to 1.2, and the first layer height is determined by the Y+WallDistance Estimation online calculator based on the wall y+ value;

[0014] The wall y+ value represents the dimensionless distance to the wall;

[0015] The wall y+ value is calculated as follows:

[0016]

[0017] Where ρ represents the fluid density, u represents the fluid velocity, y represents the distance from the grid point closest to the wall to the wall, and μ represents the fluid viscosity;

[0018] The Y+Wall Distance Estimation online calculator is an online calculation tool produced by CFD-Online. The first layer thickness of the expansion layer can be calculated by inputting the incoming flow velocity, fluid density, viscosity, characteristic length, and y+expected value.

[0019] In the area near the solid domain model, the patch conformal method is used to generate tetrahedral meshes to obtain higher mesh quality, and the sweeping method is used to generate hexahedral meshes in the remaining areas to improve computational efficiency.

[0020] The inspection criteria for the CFD grid are that the minimum grid volume is greater than 0 and the grid quality is greater than 0.3 to ensure the accuracy of the calculation;

[0021] S3, according to the actual working conditions of the gearbox, set the turbulence model, material properties, boundary conditions, solution method, convergence conditions, number of iterations, initialization parameters in the CFD calculation software, perform CFD solution calculation, monitor the wall temperature and wall forced convection heat transfer coefficient h, and save the result file;

[0022] The CFD calculation software is the Fluent module in ANSYS Workbench;

[0023] The turbulence model can be set to RNG k-epsilon turbulence model or SST k-omega turbulence model;

[0024] In the boundary conditions, the flow field inlet is set as the velocity inlet condition, and the incoming flow velocity and temperature are set. The flow field outlet is set as the pressure outlet condition. The inlet and outlet turbulence intensity is set to 5%, the turbulent viscosity ratio is set to 10, the inner wall of the gearbox is set as the volume heat source, and the heat source power is the power loss of the gearbox.

[0025] The solution method is set to steady-state solution, the pressure-velocity coupling is set to SIMPLE scheme, the gradient in spatial discretization is discretized using the Least Squares Cell Based format, and the rest are discretized using the second-order format;

[0026] In the convergence condition, set the energy term convergence condition to 1×10 -6 , the convergence conditions of the remaining items are set to 1×10 -3 , where the convergence condition can be appropriately narrowed to improve the calculation accuracy;

[0027] The number of iterations is set to 500, or adjusted according to the calculation convergence;

[0028] The wall forced convection heat transfer coefficient h represents the convection heat transfer capacity between the gear box and the fluid;

[0029] The wall forced convection heat transfer coefficient h is calculated according to the following formula:

[0030]

[0031] Where A is the wall area, Q is the heat transfer per unit time on area A, t w is the gearbox wall temperature, t ∞ is the fluid temperature at infinity;

[0032] Save the result files *.cas and *.dat for post-processing applications, where *.cas and *.dat are the output file formats of the Fluent module in ANSYS Workbench software;

[0033] S4, post-processing the calculation results to obtain the physical property data under the working condition;

[0034] The calculation results are post-processed using Tecplot software, which imports the *.cas and *.dat files output from S3 and obtains the gearbox wall temperature distribution cloud map, the wall maximum temperature and its position, and the streamline distribution cloud map. Tecplot software is a commercial CFD post-processing software.

[0035] S5, evaluate the heat dissipation capacity of the gearbox under this working condition;

[0036] The evaluation standard of the gearbox heat dissipation capacity is whether the maximum temperature of the gearbox wall is less than or equal to the allowable temperature. If the maximum temperature of the gearbox wall is less than or equal to the allowable temperature, it means that the heat dissipation capacity of the gearbox is sufficient, otherwise it means that the heat dissipation capacity of the gearbox is insufficient, as shown in the following formula:

[0037] t wmax ≤[t]

[0038] Where, t wmax is the maximum temperature of the gearbox wall, [t] is the allowable temperature;

[0039] The allowable temperature is defined as follows:

[0040]

[0041] Where, t omax is the maximum operating temperature of the gear oil, S is the safety factor, generally S=1.3~1.5;

[0042] S6, repeating steps S3-S5 for different working conditions, and judging the heat dissipation capacity of the gearbox according to the obtained physical property data of the gearbox under different working conditions;

[0043] The gearbox has different working gears and working environments under different working conditions. The boundary conditions in step S3 are modified. The modifications include the volume heat source power of the inner wall of the gearbox, the incoming flow velocity and the incoming flow temperature under different working conditions. The CFD solution calculation is repeated many times, and the settlement results are post-processed to obtain the physical property data of the gearbox. The heat dissipation capacity of the gearbox under different working conditions is evaluated through these physical property data.

[0044] Beneficial effects of the present invention:

[0045] The invention provides a CFD-based gearbox heat dissipation simulation method, which uses CFD simulation technology to simulate the heat dissipation process of the gearbox under different working conditions, obtains the temperature distribution of the gearbox, the wall forced convection heat transfer coefficient, and gives an evaluation standard for the heat dissipation capacity of the gearbox. The evaluation standard can be used to directly judge the heat dissipation capacity of the gearbox. At the same time, compared with traditional test methods, this method is simple and easy as a whole, significantly improves research efficiency and reduces research costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the basic flow chart of the present invention.

[0047] Figure 2 It is a schematic diagram of an implementation case of the present invention.

[0048] Figure 3 is a cross-section of the mesh.

[0049] Figure 4 This is a CFD simulation setup flow chart.

[0050] Figure 5 It is a surface temperature distribution cloud diagram of the gear box of the implementation case of the present invention.

[0051] Figure 6 It is a gearbox streamline diagram of an implementation example of the present invention.

[0052] Among them, 1. Fluid domain model, 2. Gearbox geometry model, 3. Simplified occluding body geometry model. DETAILED DESCRIPTION

[0053] The present invention is described in detail below through specific embodiments.

[0054] Implementation Cases

[0055] like Figure 1 A gearbox heat dissipation simulation method based on CFD is shown, comprising the following steps:

[0056] S1, establishing a gearbox geometric model 2 and a simplified occluding body geometric model 3, i.e., a solid domain model;

[0057] The gearbox geometry model 2 is a solid model of the gearbox established based on the design drawings of the gearbox using the 3D modeling software CATIA. The tiny geometric structures that have little impact on the calculation results, such as fillets and bolt holes, are cleaned up and saved as *.x_t files for subsequent calculation applications. The 3D modeling software CATIA is a commercial 3D modeling software, and *.x_t is the output file format of the software.

[0058] The simplified shielding body geometric model 3 simulates the shielding effect of the surrounding parts on the heat dissipation of the gearbox in actual use. According to the design drawings of the surrounding parts of the gearbox, it is simplified and a solid model is established using the 3D modeling software CATIA, and saved as an *.x_t file for subsequent calculation applications;

[0059] S2, pre-processing the solid domain model, mainly including extracting the flow channel to obtain the fluid domain model 1, selecting the corresponding meshing method and generating a CFD mesh that meets the calculation requirements;

[0060] The fluid domain model 1 is a cubic model including a solid domain model, and the flow channel is extracted using the Geometry module in the ANSYS Workbench software, wherein the ANSYS Workbench software is a commercial multi-physics field collaborative simulation software;

[0061] The CFD mesh was divided by importing the fluid domain model generated by the Geometry module into the Meshing module in the ANSYS Workbench software, where the physical preference was set to CFD, the solver preference was set to Fluent, the target skewness was set to 0.9, and the smoothing was set to high;

[0062] Set the surface size adjustment on the gearbox surface to locally encrypt it and set the expansion layer, where the expansion option is set to the first layer thickness, the maximum number of layers is set to 5, the growth rate is set to 1.2, and the first layer height is determined by the Y+WallDistance Estimation online calculator based on the wall y+ value;

[0063] The wall y+ value represents the dimensionless distance to the wall;

[0064] The wall y+ value is calculated as follows:

[0065]

[0066] Where ρ represents the fluid density, u represents the fluid velocity, y represents the distance from the grid point closest to the wall to the wall, and μ represents the fluid viscosity;

[0067] The Y+Wall Distance Estimation online calculator is an online calculation tool produced by CFD-Online. The first layer thickness of the expansion layer can be calculated by inputting the incoming flow velocity, fluid density, viscosity, characteristic length, and y+expected value.

[0068] In the area near the solid domain model, the patch conformal method is used to generate tetrahedral meshes to obtain higher mesh quality, and the sweeping method is used to generate hexahedral meshes in the remaining areas to improve computational efficiency.

[0069] The inspection criteria for the CFD grid are that the minimum grid volume is greater than 0 and the grid quality is greater than 0.3 to ensure the accuracy of the calculation;

[0070] The CFD mesh cross-section diagram is as follows: Figure 3 As shown, the gearbox part is enlarged to show the expansion layer characteristics;

[0071] S3, according to the actual working conditions of the gearbox, set the turbulence model, boundary conditions, material properties, solution method, convergence conditions, number of iterations, initialization parameters in the CFD calculation software, perform CFD solution calculation, monitor the wall temperature and wall forced convection heat transfer coefficient h, and save the result file;

[0072] The CFD calculation software is the Fluent module in ANSYS Workbench. The CFD simulation setting process is as follows: Figure 4 As shown;

[0073] The turbulence model can be set to RNG k-epsilon turbulence model or SST k-omega turbulence model;

[0074] In the boundary conditions, the flow field inlet is set as the velocity inlet condition, and the incoming flow velocity and temperature are set. The flow field outlet is set as the pressure outlet condition. The inlet and outlet turbulence intensity is set to 5%, the turbulent viscosity ratio is set to 10, the inner wall of the gearbox is set as the volume heat source, and the heat source power is the power loss of the gearbox.

[0075] The solution method is set to steady-state solution, the pressure-velocity coupling is set to SIMPLE scheme, the gradient in spatial discretization is discretized using the Least Squares Cell Based format, and the rest are discretized using the second-order format;

[0076] In the convergence condition, set the energy term convergence condition to 1×10 -6 , the convergence conditions of the remaining items are set to 1×10 -3 , where the convergence condition can be appropriately narrowed to improve the calculation accuracy;

[0077] The number of iterations is set to 500, or adjusted according to the calculation convergence;

[0078] The wall forced convection heat transfer coefficient h represents the convection heat transfer capacity between the gear box and the fluid;

[0079] The wall forced convection heat transfer coefficient h is calculated according to the following formula:

[0080]

[0081] Where A is the wall area, Q is the heat transfer per unit time on area A, t w is the gearbox wall temperature, t ∞ is the fluid temperature at infinity;

[0082] Save the result files *.cas and *.dat for post-processing applications. *.cas and *.dat are the output file formats of the Fluent module in ANSYS Workbench software;

[0083] S4, post-processing the calculation results to obtain the physical property data under the working condition;

[0084] The calculation results are post-processed using Tecplot software, which imports the *.cas and *.dat files output from S3 and obtains the gearbox wall temperature distribution cloud map, the wall maximum temperature and its position, and the streamline distribution cloud map. Figure 5 The numbers in the figure represent the temperature (unit: K), and Tecplot software is a commercial CFD post-processing software;

[0085] S5, evaluate the heat dissipation capacity of the gearbox under this working condition;

[0086] The evaluation standard of the gearbox heat dissipation capacity is whether the maximum temperature of the gearbox wall is less than or equal to the allowable temperature. If the maximum temperature of the gearbox wall is less than or equal to the allowable temperature, it means that the heat dissipation capacity of the gearbox is sufficient, otherwise it means that the heat dissipation capacity of the gearbox is insufficient, as shown in the following formula:

[0087] t wmax ≤[t]

[0088] Where, t wmax is the maximum temperature of the gearbox wall, [t] is the allowable temperature;

[0089] The allowable temperature is defined as follows:

[0090]

[0091] Where, t omax is the maximum operating temperature of the gear oil, S is the safety factor, generally S=1.3~1.5;

[0092] S6, repeating steps S3-S5 for different working conditions, and judging the heat dissipation capacity of the gearbox according to the obtained physical property data of the gearbox under different working conditions;

[0093] The gearbox has different working gears and working environments under different working conditions. The boundary conditions in step S3 are modified. The modifications include the volume heat source power of the inner wall of the gearbox, the incoming flow velocity and the incoming flow temperature under different working conditions. The CFD solution calculation is repeated many times, and the settlement results are post-processed to obtain the physical property data of the gearbox. The heat dissipation capacity of the gearbox under different working conditions is evaluated through these physical property data.

[0094] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A gearbox heat dissipation simulation method based on CFD, characterized by: The following steps are involved: S1, establishing a solid domain model, the solid domain model includes a gearbox geometric model (2) and a simplified occluding body geometric model (3); The gearbox geometry model (2) is a solid model of the gearbox established using the 3D modeling software CATIA based on the design drawings of the gearbox. The tiny geometric structures that have little impact on the calculation results are cleaned up and saved as The file is used for subsequent calculations. The 3D modeling software CATIA is a commercial 3D modeling software. is the output file format of the software; The simplified shielding body geometry model (3) simulates the shielding effect of the surrounding components on the gearbox heat dissipation in actual use. According to the design drawings of the surrounding components of the gearbox, it is simplified and a solid model is established using the 3D modeling software CATIA and saved as Files for subsequent calculation applications; S2, pre-processing the solid domain model, mainly including extracting the flow channel to obtain the fluid domain model (1), selecting the corresponding meshing method and generating a CFD mesh that meets the calculation requirements; The fluid domain model (1) is a cubic model including the solid domain model, and the flow channel is extracted using the Geometry module in the ANSYS Workbench software, wherein the ANSYS Workbench software is a commercial multi-physics field collaborative simulation software; The CFD mesh was created by importing the fluid domain model (1) generated by the Geometry module into the Meshing module in ANSYS Workbench software, where the physical preference was set to CFD, the solver preference was set to Fluent, the target skewness was set to 0.9, and the smoothing was set to high; Set the surface size adjustment on the gearbox surface to locally encrypt it and set the expansion layer, where the expansion option is set to the first layer thickness, the maximum number of layers is set to 5, the growth rate is set to 1.2, and the first layer height is based on the wall. y + value, determined by the Y+WallDistance Estimation online calculator; The wall y + value represents the dimensionless distance to the wall; The wall y +The value is calculated as follows: ； In the formula ρ represents the fluid density, u represents the fluid velocity, y represents the distance from the nearest grid point to the wall, μ Indicates fluid viscosity; The Y+Wall Distance Estimation online calculator is an online calculation tool produced by CFD-Online. Input the fluid velocity, fluid density, fluid viscosity, characteristic length, wall y + value can calculate the height of the first expansion layer; In the area near the solid domain model, the patch conformal method is used to generate tetrahedral meshes to obtain higher mesh quality, and the sweeping method is used to generate hexahedral meshes in the remaining areas to improve computational efficiency. The inspection criteria for the CFD grid are that the minimum grid volume is greater than 0 and the grid quality is greater than 0.3 to ensure the accuracy of the calculation; S3, according to the actual working conditions of the gearbox, set the turbulence model, material properties, boundary conditions, solution method, convergence conditions, number of iterations, initialization parameters in the CFD calculation software, perform CFD solution calculation, and monitor the wall temperature and wall forced convection heat transfer coefficient h , and save the result file; The CFD calculation software is the Fluent module in ANSYS Workbench; The turbulence model can be set to RNG k-epsilon turbulence model or SST k-omega turbulence model; In the boundary conditions, the flow field inlet is set as the velocity inlet condition, and the fluid velocity and fluid temperature are set. The flow field outlet is set as the pressure outlet condition. The inlet and outlet turbulence intensity is set to 5%, the turbulent viscosity ratio is set to 10, and the inner wall of the gearbox is set as the volume heat source. The heat source power is the power loss of the gearbox. The solution method is set to steady-state solution, the pressure-velocity coupling is set to SIMPLE scheme, the gradient in spatial discretization is discretized using the Least Squares Cell Based format, and the rest are discretized using the second-order format; In the convergence condition, set the energy term convergence condition to , the remaining terms convergence conditions are set to , where the convergence condition can be appropriately narrowed to improve the calculation accuracy; The number of iterations is set to 500, or adjusted according to the calculation convergence; The wall forced convection heat transfer coefficient h Characterize the convective heat transfer capacity between the gearbox and the fluid; The wall forced convection heat transfer coefficient h Calculate as follows: ； In the formula, A is the wall area, Q is the area per unit time A The heat transfer on t w is the gearbox wall temperature, t ∞ is the fluid temperature at infinity; Save result file and For post-processing applications, and It is the output file format of the Fluent module in ANSYS Workbench software; S4, post-processing the calculation results to obtain the physical property data under the working condition; The calculation results were post-processed using Tecplot software and imported into S3 output. and File, and get the gearbox wall temperature distribution cloud map, the wall maximum temperature and its position, and the streamline distribution cloud map, where Tecplot software is a commercial CFD post-processing software; S5, evaluate the heat dissipation capacity of the gearbox under this working condition; The evaluation standard of the gearbox heat dissipation capacity is whether the maximum temperature of the gearbox wall is less than or equal to the allowable temperature. If the maximum temperature of the gearbox wall is less than or equal to the allowable temperature, it means that the heat dissipation capacity of the gearbox is sufficient, otherwise it means that the heat dissipation capacity of the gearbox is insufficient, as shown in the following formula: ； In the formula, t wmax is the maximum temperature of the gearbox wall, [ t ] is the permissible temperature; The allowable temperature is defined as follows: ； In the formula, t omax is the maximum operating temperature of the gear oil, S is the safety factor, S =1.3~1.5; S6, repeating steps S3-S5 for different working conditions, and judging the heat dissipation capacity of the gearbox according to the obtained physical property data of the gearbox under different working conditions; The gearbox has different working gears and working environments under different working conditions. The boundary conditions in step S3 are modified. The modifications include the volume heat source power of the inner wall of the gearbox, the fluid velocity and the fluid temperature under different working conditions. The CFD solution calculation is repeated many times, and the settlement results are post-processed to obtain the physical properties of the gearbox. The heat dissipation capacity of the gearbox under different working conditions is evaluated through these physical property data.

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