Search Results

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.

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.

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.

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.

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.