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Large eddy simulation based on high-performance computing technique was conducted to investigate the unsteady aerodynamic forces acting on a full-scale heavy duty truck subjected to sudden crosswind. The CFD results were applied to evaluate the effect of the unsteady external forces on a vehicle motion, as a first step toward a more reliable vehicle motion analysis. As the first report, the numerical method was validated on the DNW wind-tunnel data by comparing the time-averaged drag and lateral forces at various yawing angles up to 10 degrees. Then the method was applied to the case when the vehicle goes through the crosswind region. The time series of the aerodynamic forces were acquired and discussed through the visualization of instantaneous flow structures around the vehicle. It was observed that drastic undershooting and overshooting of the yawing moment acts on the vehicle during the rushing in and out process.

CFD is becoming an inevitable modern engineering tool in the vehicle aerodynamics. A LES based CFD approach is proposed for analysis for flows with complex geometrical configurations to which detailed experiments, high grid-density LES or DNS cannot be applicable. How CFD results should be evaluated for cases in which the related experiments are not available. The procedure proposed consists of four stages, i.e., inspections of solutions with coarse and fine meshes, reconfirmation of energy spectrum, references to the similar experiments, explanations of results obtained. The procedures are applied to the underbody flows with a semi-complex underbody configuration.

A numerical method specially designed to predict unsteady aerodynamics of road vehicle was developed based on unstructured Large-Eddy Simulation (LES) technique. The code was intensively optimized for the Earth Simulator in Japan to deal with the excessive computational resources required for LES, and could treat numerical meshes of up to around 120 million elements. Moving boundary methods such as the Arbitrary Lagrangian-Eulerian (ALE) or the sliding method were implemented to handle dynamic motion of a vehicle body during aerodynamic assessment. The method can also model a gusty crosswind condition. The method was applied to three cases in which unsteady aerodynamics are expected to be crucial.

The objective of this study is to develop numerical models for the analysis of unsteady vehicle aerodynamics and vehicle motion in gusty crosswind conditions. Several numerical models of transient crosswind gust are proposed and validated on a simplified 2D rectangle, moving at the constant speed, then entering the crosswind region. It is shown that one of the methods called ‘convective crosswind method’ is a promising candidate to accurately describe the dynamics of flow in crosswind. The model is applied to a formula car, and the unsteady aerodynamics acting during the sudden crosswind condition is investigated.

One of the world's largest unsteady turbulence simulations of flow around a formula car was conducted using Large Eddy Simulation (LES) on the Earth Simulator in Japan. The main objective of our study is to investigate the validity of LES for the assessment of vehicle aerodynamics, as an alternative to a conventional wind tunnel measurement or the Reynolds Averaged Navier-Stokes (RANS) simulation. The aerodynamic forces estimated by LES show good agreement with the wind tunnel data (within several percent!) and various unsteady flow features around the car is visualized, which clearly indicate the effectiveness of large-scale LES in the very near future for the computation of flow around vehicles with complex configurations.

To effectively process CFD works in early stage of aerodynamic developments of vehicles, simple but semi-complex configurations of the vehicle underbody should be pursued. Large eddy simulation (LES) was performed on the flow around the vehicle with a semi-complex underbody configuration designed at Volvo Car. Computations with CFD code “FrontFlow-red” were performed for both flat and semi-complex underbody configurations. Unstructured meshes of approximately 22 and 23 millions were used respectively. Differences in the flow fields with flat and semi-complex underbody configurations and rotational effects of the wheels are discussed. LES results are also compared with those with Reynolds averaged Navier-Stokes (RANS) computations.

This paper describes results of the correlation tests between several full-scale automotive wind tunnels in Japan. The tests were carried out during FY 2003 by members of the working group for wind tunnel correlation test, which was organized in JSAE Vehicle Aerodynamics Research Committee. Five wind tunnels were selected, i.e., three open test section type wind tunnels and two closed ones. Four test models were selected, i.e., sedan, station wagon, minivan and hatch back car, all of which are current production models. Tests were done with EADE test conditions. Correlation formulas for drag coefficient, which are based on the previous methods by Mercker and Wiedemann [13] and Mercker [3, 10] respectively for open and closed test section type wind tunnels, were used. Also considered were the differences of the boundary layer thickness between five wind tunnels.

Computational fluid dynamics(CFD) has come out as a modern alternative for reducing the use of wind tunnels in automotive engineering. CFD is now being intensively applied to various stages of aerodynamic design of automobiles. However, the present CFD technology has still many computational problems to be solved in terms of turbulence treatment, numerical method/scheme, etc., i.e., it is still difficult to find an appropriate solution in terms of fluid mechanics, since it strongly depends on the above numerical factors. This review paper describes the following CFD methods now available and their present applications, mainly in the area of vehicle aerodynamics, and shows the present limitations of the various methods: panel method, k-ε turbulence model, Large Eddy Simulation, and quasi-direct simulation with 3rd-order upwind numerical scheme.

In order to successfully launch the info-mobility or IVHS/RTI systems in the society, many advanced technologies could be properly utilized with necessary R&D and related activities. The realizations of the info-mobility related systems also require relatively long time range from concept and R&D stages to final realization of the systems. How to efficiently coordinate these different stages ranging many years could be one of the important and difficult problems we face today to successfully launch the systems in the society. This paper describes the following items with some examples of the past and presently on-going info-mobility related projects in Japan, i.e., roles of public organizations, phases of activities, cooperations between public and private sectors, etc.

This paper proposes a new concept of the info-mobility in which the information plays a key role in the future automobile with advanced functions. The basic “driver-vehicle-road environment” system could be reorganized by using three information systems, i.e. in-vehicle, roadside and wide area ones. Nine info-mobility functions, including those of judging abnormal conditions of driver and vehicle, supporting driver's manipulation, detecting obstacles and external disturbances, recognizing environment, route guidance, etc., are described. Twenty-seven specified functions selected for respective functions and related technological subjects are also discussed.