Improved BSL-like turbulence model and calculation method thereof
The improved BSL-like turbulence model, integrating Kok TNT model advantages, enhances simulation accuracy in scramjet engines by addressing mesh and separation zone issues, particularly in adverse pressure gradients and shear flows.
Patent Information
- Application Number
- CN202411687042.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-25
- Publication Date
- 2024-12-27
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
Existing turbulence models, such as the RANS-based models and the Menter BSL two-equation model, struggle with accurately simulating complex flows in scramjet engines due to issues with mesh requirements, simulation of shock waves and shear flows, and prediction of separation zones in adverse pressure gradients.
An improved BSL-like turbulence model that integrates the Kok TNT model's advantages, using a modified control equation and calculation method to enhance simulation capabilities, particularly for strong adverse pressure gradients and shear flows.
The improved model effectively addresses the prediction of separation zones and improves simulation accuracy in adverse pressure gradients while maintaining accuracy in shear flows, offering practical engineering benefits.
Smart Images
Figure CN119203850A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the fields of aerodynamics and computational fluid dynamics, and in particular relates to an improved BSL-like turbulence model and a calculation method thereof. Background Art
[0002] The flow inside a scramjet engine is very complex because it involves shock waves, expansion waves, wave system interference, shock wave / turbulence interaction, shock wave / boundary layer interaction, and the supersonic flow field often contains low-speed areas, so accurate numerical simulation is very difficult. Although RANS simulation has been widely used in engineering practice, the turbulence model established based on the RANS framework has essential defects and is not universal, which brings great difficulties to numerical simulation. Choosing which turbulence model has become a major problem.
[0003] So far, it has developed A series of turbulence models, A series of turbulence models, as well as the MenterBSL two-equation model. Practical experience has proved that: The series of turbulence models have high requirements on the mesh. When the mesh is appropriate, it is very suitable for simulations containing shock waves and wall turbulence, especially kok TNT The model is effective for simulating flows with adverse pressure gradients, but is not as good for simulating shear flows. Model; The series of turbulence models are suitable for shear flow simulation, but they are not effective for shock wave and strong adverse pressure gradient flow simulation. The Menter BSL two-equation model has both Model and The advantage is that the mesh requirements are relatively loose, but for the simulation of strong adverse pressure gradient flow, the predicted separation zone is too small and the effect is not as good as kok TNT Model.
[0004] Currently, there is an urgent need to develop an improved BSL-like turbulence model and its calculation method. Summary of the invention
[0005] One technical problem to be solved by the present invention is to provide an improved BSL-like turbulence model. Another technical problem to be solved by the present invention is to provide an improved calculation method of the BSL-like turbulence model.
[0006] The control equation of the improved BSL-like turbulence model of the present invention is as follows: ; Viscosity coefficient for: ; in, is the density, is the turbulent kinetic energy, is the turbulence frequency, is the turbulent kinetic energy generation term; for Direction speed, for Direction coordinates; For time, is the turbulent viscosity coefficient, is the laminar viscosity coefficient, is the turbulent dynamic viscosity coefficient; and are model constants; is a mixed function, calculated by the following formula: Mixing functions : ; in, and To calculate the mixing function Intermediate variables used in the process, is the distance from the grid cell to the nearest wall; The calculation method of each model constant is: ,in, , ; ; ,in, , ; ,in, , ; ,in, , ; ; is the von Karman constant, .
[0007] The improved calculation method of the BSL-like turbulence model of the present invention comprises the following steps: S10. Calculate the viscosity coefficient of the flow field ; Carry out CFD calculation of the flow field, and calculate the flow field viscosity coefficient based on the Nth step flow field calculation results of CFD combined with the improved BSL-like turbulence model ; Where N is the number of steps to start turbulence calculation; S20. Calculate the mixing function ; S30. Calculation of model constants ; According to the mixed function and model parameters, calculate model constants , include and ; S40. Calculation of turbulent kinetic energy and turbulence frequency ; According to the model constant , combined with the improved BSL-like turbulence model, calculate the turbulent kinetic energy of the CFD step N+1 and turbulence frequency ; S50. Complete iterative calculation; According to the convergence criterion of the flow field CFD calculation, decide whether to continue the iteration or stop the calculation.
[0008] Furthermore, the convergence criterion is that the maximum value of the density gradient of the entire flow field or the maximum value of the total energy gradient decreases by two orders of magnitude, or the inlet and outlet flow error is less than 0.5%.
[0009] The improved BSL-like turbulence model and its calculation method of the present invention are based on the Wilcox 1988 Menter BSL two-equation model. Model replaced with Kok TNT model, and with Combined, played Kok TNT The model's advantages in wall turbulence simulation effectively solve the problem of the small separation zone predicted by the Menter BSL two-equation model. While the prediction accuracy in the shear flow area remains unchanged, it improves the simulation capability of strong adverse pressure gradient flow and has practical engineering value. BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Figure 1 A flowchart of a calculation method of an improved BSL-like turbulence model of the present invention; Figure 2 Schematic diagram of the two-dimensional nitrogen supersonic transverse jet flow field of Example 1; Figure 3 This is a comparison chart of the wall pressure distribution predicted by various turbulence models obtained in Example 1 and the test data results; Figure 4 Schematic diagram of the flow field of the DLR scramjet combustion chamber of Example 2; Figure 5a A comparison diagram of velocity profiles at different flow direction positions predicted by various turbulence models obtained in Example 2 and experimental data (x=67mm); Figure 5b A comparison chart of velocity profiles at different flow direction positions predicted by various turbulence models obtained in Example 2 and experimental data (x=110 mm); Figure 5c A comparison chart of velocity profiles at different flow direction positions predicted by various turbulence models obtained in Example 2 and experimental data (x=142mm); Figure 5d This is a comparison chart of velocity profiles at different flow direction positions predicted by various turbulence models obtained in Example 2 and the experimental data (x=218mm).
[0011] In the figure, the improved BSL-like turbulence model of the present invention is represented as BSL-M; the Menter BSL two-equation model is represented as BSL; the kok TNT turbulence model is represented as TNT; and EXP represents experimental data. DETAILED DESCRIPTION
[0012] The present invention is described in detail below with reference to the accompanying drawings and embodiments.
[0013] The control equation of the improved BSL-like turbulence model of the present invention is as follows: ; Viscosity coefficient for: ; in, is the density, is the turbulent kinetic energy, is the turbulence frequency, is the turbulent kinetic energy generation term; for Direction speed, for Direction coordinates; For time, is the turbulent viscosity coefficient, is the laminar viscosity coefficient, is the turbulent dynamic viscosity coefficient; and are model constants; is a mixed function, calculated by the following formula: Mixing functions : ; in, and To calculate the mixing function Intermediate variables used in the process, is the distance from the grid cell to the nearest wall; The calculation method of each model constant is: ,in, , ; ; ,in, , ; ,in, , ; ,in, , ; ; is the von Karman constant, .
[0014] like Figure 1 As shown, the calculation method of the improved BSL-like turbulence model of the present invention comprises the following steps: S10. Calculate the viscosity coefficient of the flow field ; Carry out CFD calculation of the flow field, and calculate the flow field viscosity coefficient based on the Nth step flow field calculation results of CFD combined with the improved BSL-like turbulence model ; Where N is the number of steps to start turbulence calculation; S20. Calculate the mixing function ; S30. Calculation of model constants ; According to the mixed function and model parameters, calculate model constants , include and ; S40. Calculation of turbulent kinetic energy and turbulence frequency ; According to the model constant , combined with the improved BSL-like turbulence model, calculate the turbulent kinetic energy of the CFD step N+1 and turbulence frequency ; S50. Complete iterative calculation; According to the convergence criterion of the flow field CFD calculation, decide whether to continue the iteration or stop the calculation.
[0015] Furthermore, the convergence criterion is that the maximum value of the density gradient of the entire flow field or the maximum value of the total energy gradient decreases by two orders of magnitude, or the inlet and outlet flow error is less than 0.5%.
[0016] Example 1: This example is used to test the numerical prediction capability of the improved BSL-like turbulence model of the present invention for flow fields with strong adverse pressure gradients. The test flow field is as follows: Figure 2 The two-dimensional nitrogen supersonic transverse jet flow field shown has an incoming flow Mach number of 3.71, a total temperature of 300K, and a total pressure of 1.20MPa.
[0017] It can be seen that Figure 3 As shown, among the three turbulence models, the separation zone predicted by the Menter BSL two-equation model BSL is the smallest, and the difference with the experimental data is the largest; the separation zone predicted by the kok TNT turbulence model TNT is relatively the largest; the improved BSL-like turbulence model BSL-M of the present invention, due to the coupling of the kok TNT turbulence model, will gradually transition to the kokTNT turbulence model near the wall, and the predicted separation zone size is between the Menter BSL two-equation model BSL and the kok TNT turbulence model TNT, which is closest to the experimental data. That is, the improved BSL-like turbulence model BSL-M of the present invention solves the problem of predicting a small separation zone in strong adverse pressure gradient flow, and improves the prediction accuracy of the Menter BSL two-equation model BSL.
[0018] Example 2: This example is used to test the prediction effect of the improved BSL-like turbulence model of the present invention on the development of the central mainstream area and the shear layer. The test flow field is as follows Figure 4 The flow field of the combustion chamber of the DLR scramjet engine shown. The preheated air expands into the combustion chamber through the nozzle. The combustion chamber inlet is 50mm high and 40mm wide. The support plate is 32mm long and 6mm high. Hydrogen is sprayed into the combustion chamber through 15 small holes on the bottom of the support plate. The diameter of the nozzle is 1mm. The jet Mach number of hydrogen is Ma2=1.0. The Mach number of the air flow is Ma1=2.0, the static temperature is 340K, and the static pressure is 1atm.
[0019] It can be seen that Figure 5a~Figure 5d As shown, the prediction results of the improved BSL-like turbulence model BSL-M of the present invention are significantly better than those of the Menter BSL two-equation model BSL and the kok TNT turbulence model TNT, are closer to the experimental results, and have excellent simulation capabilities for shear layers.
[0020] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and the embodiments, and can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional improvements and modifications can be easily realized without departing from the principles of the present invention. Therefore, without departing from the general concept defined by the claims and equivalent scope, the present invention is not limited to the specific details and the illustrations shown and described here.
Claims
1. An improved BSL-like turbulence model, characterized in that: The control equations of the improved BSL-like turbulence model are as follows: ； Viscosity coefficient for: ； in, is the density, is the turbulent kinetic energy, is the turbulence frequency, is the turbulent kinetic energy generation term; for Direction speed, for Direction coordinates; For time, is the turbulent viscosity coefficient, is the laminar viscosity coefficient, is the turbulent dynamic viscosity coefficient; and are model constants; is a mixed function, calculated by the following formula: Mixing functions : ； in, and To calculate the mixing function Intermediate variables used in the process, is the distance from the grid cell to the nearest solid wall; The calculation method of each model constant is: ,in, , ; ； ,in, , ; ,in, , ; ,in, , ; ； is the von Karman constant, .
2. A calculation method for an improved BSL-like turbulence model, which is used for the improved BSL-like turbulence model described in claim 1, characterized in that: The following steps are involved: S10. Calculate the viscosity coefficient of the flow field ; Carry out CFD calculation of the flow field, and calculate the flow field viscosity coefficient based on the Nth step flow field calculation results of CFD combined with the improved BSL-like turbulence model ; Where N is the number of steps to start turbulence calculation; S20. Calculate the mixing function ; S30. Calculation of model constants ; According to the mixed function and model parameters, calculate model constants , include and ; S40. Calculation of turbulent kinetic energy and turbulence frequency ; According to the model constant , combined with the improved BSL-like turbulence model, calculate the turbulent kinetic energy of the CFD step N+1 and turbulence frequency ; S50. Complete iterative calculation; According to the convergence criterion of the flow field CFD calculation, decide whether to continue the iteration or stop the calculation.
3. The calculation method of the improved BSL-like turbulence model according to claim 2, characterized in that: The convergence criterion is that the maximum value of the density gradient of the entire flow field or the maximum value of the total energy gradient decreases by two orders of magnitude, or the inlet and outlet flow error is less than 0.5%.