The Numerical Simulation And Analsys Of Couple External Flow Field

As the development of automobile technology and improved transport facilities, the vehicle's practical velocity has greatly been improved, vehicle aerodynamics has already been one of the key research directions in the automotive industry. The traditional and important method for the vehicle aerodynamics is wind tunnel test, which demands strict requirement of the experimental facilities, as well as a long experimental period. With the development of computer technology, computational fluid dynamics (CFD) have shown an increasing important role in the research of automotive aerodynamics. CFD method has characters of short cycle, low cost, without actual vehicle model and so on. It's always used to analysis and guide the design, and provide a scientific basis for the design. What's more, this method also improves product quality, and enhances the role of self-development capabilities both in new products development and existing products improvement. Here, this paper builds a three-dimensional flow field numerical simulation model for a coupe with the existing method of CFD, as well as analyses and optimizes their aerodynamic shape and performance combined with aerodynamic theory.This essay comes from a coupe reverse engineering project. The project builds the three-dimensional model of real car (1:1) with the use of CATIA. During the modeling process, there are some simplifications for some of the details of real car, thinking about the simulation time and computer hardware problems. Then this essay builds the finite element model with the ICEM software.In this paper, tetrahedral+ prism hybrid mesh program was used, and the whole couple surrounded by density body to define the grid surface area. Realizable turbulence model is used, and standard wall function near the wall to enhance the body surface flow simulation accuracy.In the calculation process,Combined with the respective characteristics of first-order upwind and second-order upwind discretization, first-order upwind is applied, iteration after a certain number, second-order upwind discretization is used to improve the calculation accuracy and convergence, to reduce computing time. Finally, after the analysis of the model with the use of FLUENT, we obtains the body surface pressure distribution and the velocity vector. Through the analysis of vehicle's surface speed and pressure characteristics, we can understand the laws and situations for air movement. It is shows that the simulation results obtained meets the flow field characteristics and laws. Then the coupe's aerodynamic resistance coefficient and lift coefficient can be calculated from the results of the aerodynamic simulation. This essay analyzes the structure of the various parts of the external flow field and the law combined with aerodynamics theory, then optimizes its aerodynamic shape according to the actual shape coupe and local optimization results, in order to reduce aerodynamic drag and aerodynamic lift, to improve vehicle economy type and purpose of handling and stability and provide reference for this coupe model improvement.According to the simulation results and the coupe modeling we can seen that, for the coupe, due to its aerodynamic modeling features, the aerodynamic drag coefficient is relatively small, while the aerodynamic lift coefficient instable. For such a high-speed coupe car, out of considerations of security and stability, it has more more practical significance to reduce the aerodynamic lift than aerodynamic drag. The results show that the additional aerodynamic devices for the couple such as empennage have a good regulation for aerodynamic lift, and simpler chassis structure can get better vehicle's aerodynamic performance. For high-speed coupe, the chassis surface can be designed to generate negative lift.