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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.

Since an automotive headlamp is very complicated structure, CFD (Computational Fluid Dynamics) had the problem of being very difficult. Especially, if radiation is taken into consideration, the memory required for calculation is huge. In the present study, the first aim was to develop the new calculation technology that was called FSI-DM, that is a unique technique, in which the calculation mesh generated in the fluid were made discontinuous on the solid and fluid surface. In this FSI-DM, radiative heat transfer was calculated with using the coarse mesh generated on the solid surface to reduce memory size in order to use practical, and it enable us to predict velocity and temperature on the inner parts of an automotive headlamp comparatively accurately. Next, FSI-DM was further extended so that it would be able to be applied for moisture condensation on the lens surface.

In order to improve thermal endurance, mechanical durability and ventilation performance in a headlamp, it is important to understand heat transfer and flow in an automotive headlamp. Especially in a design stage, understanding natural convection inside the headlamp will make it possible to shorten its development period, which can be fulfilled by Computational Fluid Dynamics (CFD). In the present study, a newly-developed method called Surface Heat Transfer (SHT) method, that is a unique technique for making an accurate estimate of temperature and velocity in the automotive headlamp without involving the couple of the fluid mechanics and the structural mechanics (the coupled fluid solid interaction), was investigated for practical use. An evaluation of SHT method was performed, and CFD results were compared with the experimental results. Consequently, the temperature results by CFD were within ±10 degrees as compared with the experimental results.

The automotive torque converter is one of the most important component parts in the automatic transmission. In recent years, the design demands have been for both high performance and compact size. For the optimized design to satisfy with these demands, it is necessary to analyze the internal flow field of torque converters. The internal flow field around the stator of an automotive torque converter is investigated experimentally in this study by using Particle Image Velocimetry (PIV) technique. The objective of this investigation is to understand the flow field around the stator which has the important role to characterize the torque converter performance. The three-dimensional flow field is reconstructed by using the two-dimensional PIV results at two orthogonal planes.

Large Eddy Simulation (LES) with Smagorinsky model is sued to simulate the induction-compression processes of a motored engine within a cycle. A diesel engine constructed with swirl-generating port and dish-type combustion chamber is used as the model engine. For high Reynolds number flow, the wall-function fitted to generalized curvilinear coordinate is proposed in this paper in order to overcome the over-fine grids arrangement near wall region. In order to restrain the non-physical pressure oscillation, which is the fatal drawback in co-located grids layout used in the present study, the odd-even pressure coupling mode is developed. LES results are compared with PIV experiment. The most important result is that the curves of swirl number and turbulence intensity against crank angle are obtained. Swirl velocity is formed by tangent designed port, but is strengthened by the impingement of discharge onto piston surface.

Heat transfer evaluation and air flow field prediction are important for improving the heatproof capability, durability and ventilation performance of automotive headlamps. In the present study, heat transfer and air flow field in a headlamp model were investigated both experimentally and numerically. The Particle Image Velocimetry (PIV) was employed to measure the velocity field of the heat transfer loop in the headlamp at first. Then, Computational Fluid Dynamics (CFD) simulations were conducted by using the PIV measurement results as boundary conditions for the CFD simulation.

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.

This report shows and estimates some results of the numerical simulation for the flow around a bluff body which is a simplified model of automobile with the slanted rear window. The calculating code adopts a k-ε turbulence model and a finite volume method (FVM) on the body fitted grid system. An effective algorythm based on the SIMPLE method enables the calculations performed within small CPU time. A validation of the simulation results is discussed from the comparison to the experimental data, especially about the prediction of the three-dimensional flow separations behind the rear window and the pressure drag.

For the past several years, construction of Japanese road network has maintained a rapid pace, but those roads, having many automotive tunnels, are affected by mountainous topography. The air pollution in tunnels by exhaust gases from cars, especially those from large-size vehicles, has become problematical in Japan. The purpose of this paper is to clarify the flow behavior, especially wake structure behind trucks, and their aerodynamics characteristics at overtaking in road vehicle tunnels with digital image processing technique and three dimensinoal numerical analysis.