Numerical Simulation Of The Whole Vehicle Flow Field And Engine Compartment Heat Dissipation Performance Influenced By The Engine Bottom Guard Board

The engine bottom guard board is a protective device at the bottom of the engine designed according to the characteristics of different vehicle types,which is a very important component for the car.First of all,the engine bottom guard board has very important significance to the driving safety of the car.Its protective function can prolong the service life of the engine and reduce the probability of car accident.Secondly,the engine bottom guard board is an important chassis pneumatic component,which can significantly reduce the aerodynamic drag of the car.However,with the increasing function of automobiles and people’s increasing demands on the performance of automobiles,the problem of heat dissipation in engine compartments has become a huge challenge in the development of automobiles.Reasonable structural parameters of engine bottom guard boards have a great impact on the heat dissipation of engine compartments.Therefore,it is necessary to study the optimal parameters when designing the engine bottom guard board.Firstly,based on the relevant basic theory of computational fluid dynamics,a mature mathematical model suitable for the analysis of the flow field inside and outside the vehicle and its calculation method were selected.Then based on the steps of the CFD commercial software analysis,a 3D model including the car body,the chassis and the internal structure of engine compartment was established.The model was divided into grids,and special treatments were performed on the radiator,intercooler and other cooling modules and the fan,and reasonable boundary conditions and solution parameters were set up to realize the establishment of 3D calculation models in CFD commercial software.In addition,a 1D simulation model of the engine cooling system that could be linked with the 3D calculation results was built on the AMEsim platform to realize the 1D/3D co-simulation of the heat dissipation performance of the engine compartment.Based on the established model,the impact of the engine bottom guard board on the aerodynamic characteristics of the car was first analyzed,and it was found that it could significantly improve the flow field in the engine compartment and reduce the air resistance coefficient of the car.Then,the 1D/3D co-simulation method was used to calculate the engine compartment’s internal flow field,temperature field,and working status of the cooling system under three conditions of high-speed,idle,and low-speed climbing,the worst condition of engine compartment heat dissipation was low-speed climbing condition according to the calculation results.According to the design of the existing mainstream engine bottom guard board,the key parameters of its design were extracted: the hemming structure,stiffener,opening form and opening position.These parameters were changed to calculate the low-speed climbing condition,and the engine compartment heat dissipation performance was compared and analyzed.The optimal value of these parameters was got finally.In this thesis,the 1D/3D co-simulation method was used to study the influence of the parameters of the engine bottom guard board on the internal and external flow field of the car as well as the heat dissipation performance of the engine compartment.It has certain guiding significance for the structural design of the engine bottom guard board.