Numerical Simulation Of The Internal Flow Field And Optimization Of The Structural Layout In Vehicle Underhood

The internal flow field of vehicle underhood not only affects the aerodynamic drag of the vehicle,but is also closely related to the heat dissipation of underhood.With the continuous development of computer technology,numerical simulation technology has been more and more used to study underhood flow field.Auto intake grille design and the structural arrangement in engine cabin both have a significant impact on underhood internal flow field.In this thesis,the multi-objective optimization design method was adopted,and with the numerical simulation technology,the influence of different intake grille and different underhood layout to the aerodynamic performance and underhood heat dissipation performance were investigated.In the end,several optimized results which the aerodynamic drag is lower and the heat dissipation performance is better than the initial model were obtained.The shape of air-inlet grille of the research model is a common horizontal stripe.First of all,the underhood internal flow field was investigated by numerical simulation,and the rationality of the boundary conditions was ascertained.Then 5 parameters of the model were selected as design variables including the inclination angle of grille represented by ‘A’,the width of grille bar represented by ‘L’,the number of grille bar represented by ‘N’,the displacement distance of radiator and engine represented by ‘D1’ and ‘D2’ respectively.Latin hypercube sampling method was adopted to select 100 samples within the appropriate scope of variables.And then each sample was simulated numerically,got the drag coefficient value Cd,the lift coefficient value Cl,and the air inlet massflow Um of the underhood,constituting 100 groups of sample data.After that,the sample data was analyzed by data mining techniques including total variation and self-organized mapping method,and the influence degree and mechanism of variables on each objective were obtained.Then the approximation model between the variables and objectives was established according to the sample data,and the prediction error of the model was controlled within 10%.After the approximation model was built,NSGA-II evolutionary algorithm was used to search the optimal solution in the whole optimizing range,with the value of aerodynamic drag coefficient and the lift coefficient as low as possible,and the intake mass flow of the underhood to the greatest extent.Finally,two optimized models were built and simulated,and the pressure contour and temperature contour of the two were compared with the counterpart of initial model,showing the value of aerodynamic resistance of the two optimized models was lower and the heat dissipation performance of the underhood of the two models was also improved.The significance of this investigation is that a new application of multi-objective optimization design method was given on automotive aerodynamics,and the results of the research can also provide a reference in the early period of automotive underhood design,including the design of air-inlet grille and layout in underhood.