Research On The Aerodynamic Characteristics Of Passenger Car Based On Air-inlet Grille

Vehicle population increased year by year,the consumption of energy is also increasing,exacerbating the energy and environmental issues.The air-inlet grille of the car directly affects the internal flow characteristics in the engine compartment,and there is a certain impact on the car air resistance,thus affecting the aerodynamic characteristics and the fuel economy of the vehicle.Therefore,it is indispensable to study the influence of air-inlet grille on the aerodynamic characteristics of automobile in the field of automobile aerodynamics.The air-inlet grille is the only passage for air flow into the engine compartment,which affects the air air-inlet performance of the front of the car in many ways,which in turn determines the flow field characteristics in the engine compartment.Therefore,in view of the research on the aerodynamic characteristics of the automobile,the influence of the air-inlet grille on the characteristics of the engine compartment flow is studied as the focus.Based on the vehicle parametric model,the Computational Fluid Dynamics(CFD)technique is used to simulate the vehicle model of different air-inlet grille,and the variation law of the aerodynamic characteristics of the vehicle is studied.In this thesis,the upper and lower air-inlet grille of the car are parameterized,and the numerical simulation method is used to analyze the velocity field,temperature field,air mass flow of grille and vehicle air resistance coefficient(C_D)of the four schemes under high speed driving condition.These schemes are full open,only upper open,only lower open and full off.The results show that the opening area and position of the grille have a certain influence on the aerodynamic characteristics of the vehicle.Then,the control variable method is used to establish the parametric model of the opening area of the air-inlet grille,the upper and lower grille position and the grille form.Aerodynamic characteristics of the car been depth exploration based on different operating conditions.Through the flow field and thermal field visualization work to qualitative analysis the aerodynamic characteristics of the vehicle.The variation of the aerodynamic characteristics of the vehicle with the relevant parameters of the air-inlet grille is further studied.The study also found an adaptation problem between the engine cooling demand and the internal flow resistance.Active air-inlet grill being possible to timely change the air-inlet air mass flow based on the air-inlet grill cooling requirements,so as to reasonably balance the contradiction between the two conditions.Therefore,in final of the thesis,establish the seven-level opening model from full open to full off.Based on the orthogonal experiment design method,the main factors of the opening degree of the active air-inlet grille,the vehicle speed and the cooling fan speed which influence the internal flow characteristics of the engine compartment had been designed as three factors seven levels a total of 49 groups of programs.The relationship between the opening degree,the vehicle speed,the cooling fan speed,the mass flow rate and the temperature of the radiator is obtained by the simulation analysis of the orthogonal combination schemes.And the predictive regression model equations of air mass flow and temperature calibration are obtained based on response surface fitting method respectively.Based on the vehicle environment,this thesis studies the influence of the air-inlet grille on the aerodynamic characteristics of the vehicle.On the basis,the research on the calibration of the active air-inlet grille is also carried out,which can provide guidance for the design of the air-inlet grille.