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The shape and configuration of the air ventilation system determines the ventilation performance while influencing the design and structure of a car. It is therefore necessary to decide the configuration of the air ventilation system in the early stages of design. We tried to analyze the pressure level of the ventilation ducts from the aerodynamics simulation results added to the cowl top which had the ventilation intake duct, and so on. Thus we succeeded in designing a new development process that can be used to predict the ventilation performance in a shorter time without the use of prototypes.

The aerodynamic characteristics of the vehicle underbody are one of the critical components to achieve efficient fuel-economical vehicles. On the other hand, computer memory and time make it difficult to make the complex geometry of the underbody of an actual vehicle including the engine room. In this paper, we have investigated a new CFD analysis method using the automatic tetrahedral/prismatic cell generation tools for the analysis of an underbody flow. The CFD analysis results are compared with experimental data. This new method also contributes to reducing the development term of the aerodynamics characteristics with underbody.

Conventional aerodynamic simulations have been carried out by using Supercomputer and over a hundred thousand grid points. It takes a long CPU time to get a result. So this method has been mainly used as a research and demonstration tool. In this paper a practical aerodynamic simulation for early phases of the automobile design is presented. This new method basically uses the conventional (wall function used) k-ε turbulent model which is regarded as the most promising in engineering and industrial fields. Firstly, the third-order upwind scheme is introduced to the convective term to improve flow field and pressure distribution. Secondly, the modified turbulent energy production method (M.P.Method) which was proposed by B.E. Launder[3] in 1993, is introduced to the k-ε turbulent model to reduce the excessive generation of turbulent kinetic energy.

The one-box type automobile's stability on the highway is often influenced by encountering crosswinds or when passing large automobiles such as trucks and buses. This causes the automobile to behave unexpectedly. Many experiments for improving this situation have been carried out. In this respect, the analysis of transient aerodynamic characteristics is important for automobile safety and stability on the highway. Conventional transient aerodynamic simulations require a supercomputer and about million grid points. Also there were few case studies that dealt with situations such as plunging into crosswind and passing an automobile. In this paper, a transient aerodynamic simulation by using a sliding mesh of discontinuous interface and the Arbitrary Lagrangian-Eulerian (ALE) method is presented.

Aerodynamic simulations of automobiles with an airflow type rear spoiler (a spoiler that guides part of the flow on the roof onto the rear window of a one-box or two-box car to reduce the adhesion of snow or dust on the rear window) using a discontinuous interface grid method and around a rear view door mirror using a solution adaptive grid method are presented. These new methods have made it possible to capture the detail phenomena around equipment items such as spoilers and door mirrors, thereby improving the accuracy of the CFD (Computational Fluid Dynamics) simulations and shortening the time required.

Recently, the improvement of the straight line stability has been required in mini-sized vehicles to be equivalent to that of compact cars, particularly the crosswinds stability at high speed. In this study, the new numerical simulation method has been developed, for improving efficiency, by combining the CFD (Computational Fluid Dynamics) analysis with the numerical analysis of vehicle dynamics. The vehicle behavior in the crosswinds is computed using the full-vehicle dynamic simulation model included the 6 components of aerodynamic force of the gravity center.