| At present,the aerodynamic lift of the vehicle driving at high speed has been paid more and more attention at home and abroad.When the speed exceeds 80 km / h,the influence of aerodynamic lift on driving stability can't be ignored.However,the numerical simulation accuracy of aerodynamic lift in the world can't meet the requirements of engineering application.On the one hand,the empirical coefficients related to the classical turbulence model used in vehicle aerodynamics are derived from a single scrambling calculation,which can meet the engineering application require-ments of aerodynamic resistance,however,the aerodynamic lift is very sensitive to the airflow around the body,and it can't be simulated accurately.On the other hand,the usual finite volume method can 't avoid the mesh distortion when the space is discrete,and the empirical equivalent thickness boundary layer mesh does not agree with the actual body boundary layer.The lattice LBM-les method,which can avoid the grid disadvantages,also has restriction in calculation accuracy and efficien-cy from particle topology relation and turbulence model.Due to the inevitable interference factors in wind tunnel test,such as model installation attitude,the double boundary layers on the bottom of the body and the floor of the wind tunnel,it is difficult to measure the aerodynamic lift accurately.In addition,because the center of body wind pressure is difficult to determine,it is difficult to obtain the lift coefficient of the front and rear axis both in the numerical simulation and wind tunnel test,therefore,it is unable to effectively control the aerodynamic lift in engineering application.In view of the above problems,beginning with the data correction of the aerodynamic lift wind tunnel test and the improved lattice LBM-les numerical calculation method,the following specific research work are carried out:1.A study on the data correction of aerodynamic lift wind tunnel test is carried out.The research on the influence of vehicle model installation attitude,body bottom and wind tunnel floor boundary layer on aerodynamic lift measurement are carried out,it is found that wheel clearance and ground boundary layer are the key factors that affect the precision of aerodynamic lift measurement.Aiming at the problem that the boundary layer of the wind tunnel floor can't be measured after the installation of the model,the pressure conversion method using pressure plate mounted array tube is put forward,and the thickness distribution law of the wind tunnel floor boundary layer and the influence law of the suction ratio on the boundary layer thickness are obtained.In order to ensure the quality of the flow field,6% is selected as the best suction rate,and the aerodynamic lift-the clearance between wheel and ground / the thickness of the floor boundary layer are fitted.The aerodynamic lift value of the wheel with no clearance from the ground and the thickness of the boundary layer in accordance with the SAE standard is obtained,and the correction method of the test data of the lift coefficient is established,based on this,more accurate aerodynamic lift wind tunnel test data of many models are obtained.2.The optimization of particle topology relation of lattice LBM-les method is studied.In order to ensure the numerical simulation accuracy during the space scattering,combined with the features of the field flow around car,based on the comparison between the simulation results of finite volume method and experimental results,the main factors affecting the accuracy of numerical sim ulation are analyzed;In order to avoid the problem that the mesh distortion and boundary layer mesh do not conform to the actual flow when the space is dispersed,the lattice LBM-les method is chosen,and the cylinder turbulence with a single flow charact eristic is taken as the research object,by using the experimental design optimization method,the universal criterion of particle topological relationship in lattice LBM-les method is established,and the optimal particle distribution parameters are obtai ned.The comparison between simulation and experimental results show that the optimal particle distribution parameters based on the universal criterion improve accuracy of the lattice LBM-les method for aerodynamic lift calculation by 7.58%.3.The improvement research of lattice LBM-les method is carried out.In order to improve the accuracy and efficiency of aerodynamic lift simulation,on the premise of the same hardware and calculation model,combined with wind tunnel test data,the simulation results of "lattice LBM-les method","Smagorinsky-Lilly","Dynamic Smagorinsky-Lilly" and "Wall-adapting local eddy-viscosity" models,such as comput-ing resource consumption?aerodynamic force?flow field and surface pressure are compared,and then,for the Smagorinsky-Lilly sub-lattice model with the highest computational efficiency and high accuracy,the empirical coefficients are optimized by using the multi-island genetic optimization algorithm.Combined with the optimal particle topology,an improved lattice LBM-les method with both efficiency and accuracy is formed,and the aerodynamic lift error of many models simulated by this method is less than 5%.4.Based on the improved lattice LBM-les method,the aerodynamic lift characteristics of a vehicle under multiple working conditions are studied.To meet the problem that the aerodynamic lift characteristics are obviously different due to the different flow state around the car body,for one car model under different simplified degree and wheel rotates velocity,the characteristics of aerodynamic lift such as flow field,pressure,lift coefficient and power spectrum are studied.In view of the essential difference of the aerodynamic lift characteristics between the vehicle body attitude continuous change and static change,the improved lattice LBM-les method is used to study the continuous lifting of the front of the vehicle during the acceleration process.Thus,the aerodynamic lift variation characteristics of the vehicle under the unstable state of high-speed driving are revealed.5.A method for calculating the aerodynamic lift coefficients of the front and rear axis is researched.In view of the difficulty of determining the center of the wind pressure of the vehicle body,which make the lift coefficients of the front and rear axis are difficult to obtain both in the numerical simulation and wind tunnel test and the aerodynamic lift isn't effectively optimized controlled,based on the SAE standard and HD-2 wind tunnel design code,the relationship between the installation position and force of the shrinkage model in HD-2 wind tunnel are studied,and the equilibrium equations of the six-component force system are derived.A formula for calculating the lift coefficients of the front and rear axis is established under the experimental conditions.Based on this,using the lift coefficient dimensionless,an algorithm for solving the aerodynamic lift coefficient of HD-2 wind tunnel combined with CFD is established.6.The optimization control of the aerodynamic lift of one actual car model is carried out.According to the change characteristics of aerodynamic lift in the unstable state of high-speed driving,closing the bottom of the body,then,the aerodynamic lift reduce by 36.4% and the drag reduce by 4.29%.On the basis of this,the front tooth structure is proposed to avoid the waving of the car body,and using the optimized Latin hypercube method,kriging approximation model and multi-island genetic algorithm,the structural optimization design is carried out,and the aerodynamic lift characteristics and high speed stability of the car are improved.To sum up,by researches based on the LBM-les method modified and the aerodynamic lift data improving of wind tunnel test,the precision of vehicle aerodynamic lift simulation and test data are improved;and a large number of wind tunnel tests and simulation studies are carried out,which provides a theoretical basis and method for solving the aerodynamic lift and enhancing high speed aerodynamic stability of vehicle,and has important theoretical and engineering application value. |
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