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In the present study, a model experiment is performed in order to clarify the ventilation characteristics of car cabin. This study also provides high precision data for benchmark test. As a first step, the ventilation mode is tested, which is one of the representative air-distribution modes. Part 1 describes the properties of the flow field in the cabin obtained by the experiment. Part 2 describes the ventilation efficiencies such as the age of air by using trace gas method. The properties of flow field are measured using particle image velocimetry (PIV). The mean velocity profiles, the standard deviation distribution, and the turbulence intensity distribution are discussed. The brief comparison between experiments and predictions of computational fluid dynamics (CFD) is also presented. In the comparison between experiment and CFD, the results showed similar flow field.

An experimental and numerical study was conducted on the spray and mixture properties of a hole-type injector for direct injection (D. I.) gasoline engines. The Laser Absorption Scattering (LAS) technique was adopted to simultaneously measure the spatial concentration distributions and the mass of the liquid and vapor phases in the fuel spray injected into a high-pressure and high-temperature constant volume vessel. The experimental results were compared to the numerical calculation results using three-dimensional CFD and the multi-objective optimization. In the numerical simulation, the design variable of the spray model was optimized by choosing spray tip penetration, and mass of liquid and vapor phases as objective functions.

Concept of the spray guided direct Injection spark ignition (DISI) was studied to improve the performance of wall-guided DISI. Focusing the effect of multi-hole injector location either centrally-mounted or side-mounted, mixture distribution and ignitability was studied. Computational Fluid Dynamics (CFD) modeling was applied to investigate the history of mixture, ignitable mixture existence around the spark plug in light load condition and homogeneity in full load condition. CFD results showed that side-mounted injection has an advantage over centrally-mounted injection in terms of mixture stability around the spark plug, although the slight disadvantage in homogeneity in full load condition. Side-mounted injection was selected because of robust ignitability potential and further experimental investigation was conducted. Stable combustion window against injection and ignition timing was investigated in experimentally.

Experimental and computational studies were carried out to characterize the spray development and evaporation processes of multi-hole injector for direct injection spark ignition (DISI) engines. The main injector parameter to be investigated in this study is a diverging angle between neighboring two holes. In the experimental study, the influence of the diverging angle on evaporation process of fuel spray from two-hole injector was investigated using Laser Absorption Scattering (LAS) measurement. Smaller diverging angle causes larger spray tip penetration because the momentum of the spray from one hole emphasizes another, when two spray merge to one. Moreover, spray tip penetration decreases at certain diverging angle due to the negative pressure region between two sprays. Mechanisms behind the above spray behaviors were discussed using the detailed information on the spray and ambient gas flow fields obtained by the three dimensional computational fluid dynamics (CFD).

Experiment and CFD have been performed to clarify the distribution of wind noise sources and its generation mechanism for a production vehicle. Three noise source identification techniques were applied to measure the wind noise sources from the outside and inside of vehicle. The relation between these noise sources and the interior noise was investigated by modifying the specification of underbody and front-pillar. In addition, CFD was preformed to predict the noise sources and clarify its generation mechanism. The noise sources obtained by simulation show good agreement with experiment in the region of side window and underbody.

On-road turbulences caused by sources such as atmospheric wind and other vehicles influence the flow field and increases the drag in a vehicle. In this study, we focused on a scenario involving a passing vehicle and investigated its effect on the physical mechanism of the drag increase in order to establish a technique for reducing this drag. Firstly, we conducted on-road measurements of two sedan-type vehicles passed by a truck. Their aerodynamic drag estimated from the base pressure measurements showed different increment when passed by the truck. This result raised the possibility of reducing the drag increase by a modification of the local geometry. Then, we conducted wind tunnel measurements of a simplified one-fifth scale vehicle model in quasi-steady state, in order to understand the flow mechanism of the drag increase systematically.

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.

Conventionally, the effort of gear whine reduction has focused on minimizing the transmission error generated in automobile transmission. In mean time, as demands on gear whine reduction increased, the need of controlling noise transfer path was arisen because transmission error turns into interior noise in those paths [1-2]. In this paper, we provide experimental technologies to clarify the noise transfer path which dominants high frequency gear whine from experimental point of view.

Three-dimensional flows around a vehicle-like bluff body (Ahmed's body) in ground proximity were computed by directly integrating the governing unsteady, incompressible Navier-Stokes equations. A well-established finite-difference procedure was used. The basic equations were formulated in a generalized coordinate system. A third-order upwind scheme was applied to discretize the equations, and the numerical solutions were acquired without any explicit turbulence models. Computations were performed at a high Reynolds number, Re=106 (based on the body length). In order to investigate the influence of the base slant angle, computations were performed for three base slant angles, i.e., 12.5 °, 25 °and 30 °. Extensive flow visualizations, using state-of-the-art computer graphics, were carried out. The present numerical results were found to be in broad agreement with the experiments of Ahmed.

A road vehicle’s cornering motion is known to be a compound motion composed mainly of forward, sideslip and yaw motions. But little is known about the aerodynamics of cornering because little study has been conducted in this field. By clarifying and understanding a vehicle’s aerodynamic characteristics during cornering, a vehicle’s maneuvering stability during high-speed driving can be aerodynamically improved. Therefore, in this study, the aerodynamic characteristics of a vehicle’s cornering motion, i.e. the compound motion of forward, sideslip and yaw motions, were investigated. We also considered proposing an aerodynamics evaluation method for vehicles in dynamic maneuvering. Firstly, we decomposed cornering motion into yaw and sideslip motions. Then, we assumed that the aerodynamic side force and yaw moment of a cornering motion could be expressed by superposing linear expressions of yaw motion parameters and those of sideslip motion parameters, respectively.

In the present study, two kinds of simplified vehicle models, which can reproduce flow structures around the two sedan-type vehicles in the previous study, are constructed for the object and the unsteady flow structures are extracted using Large-Eddy Simulation technique. The numerical results are validated in a stationary condition by comparing the results with a wind-tunnel experiment and details of steady and unsteady flow characteristics around the models, especially above the trunk deck, are investigated. In quasi- and non- stationary manner with regard to vehicle pitch motion, unsteady flow characteristics are also investigated and their relations to an aerodynamic stability are discussed.

This study shows an example in which the conventional aerodynamic evaluation method that focuses on “steady” aerodynamic lift coefficient is not necessarily sufficient to evaluate vehicle's straight-ahead stability at high speed, and proposes a new aerodynamic evaluation method for vehicle stability. In vehicle development, it is generally said that vehicle with lower aerodynamic lift coefficient has better straight-ahead stability at high speed. However, in some cases, straight-ahead stability differs between two vehicles with similar low aerodynamic lift coefficient. It is natural to think that this variation is caused by the difference of suspension characteristics or vehicle body rigidity. But from our experiences, different straight-ahead stability was observed between two vehicles having same suspension characteristics, same vehicle body rigidity and almost similar aerodynamic lift coefficient, but different vehicle configurations.

Recently, computational fluid dynamics (CFD) has made great progress. This paper reviews published papers on aerodynamic noise simulated by CFD and studies to what level CFD can predict aerodynamic noise for basic models and for applied models of automobiles. Based on noise generation mechanisms, aerodynamic noise is basically classified into two types, that is, noise induced by two-dimensional flow and by three-dimensional flow. As typical examples of noise generated by two-dimensional flow, wind throb at opened sliding roof, edge tone at the end of liftgate and aeolian tone generated by a cylindrical antenna are simulated by several computational schemes. As typical examples of three-dimensional flow, noise generated by A-pillar longitudinal vortex and noise from a side view mirror are computed by using a wing model and a actual vehicle, respectively.

Automobiles will have to be applied strict regulations such as Euro7 against PM, HC, CO. The generation of these components are related to fuel deposition to the wall surface of the combustion chamber. Therefore, the fuel injection model of engine combustion CFD requires accurate prediction about the deposition and vaporization of fuel on the combustion chamber. In this study, multiphase flow numerical analysis that simulates fuel behavior on the wall surface was conducted first. Then, two model formulae about the contact area and the heat flux of a liquid film was constructed based on the result of multiphase flow numerical analysis method. Finally, the new film heat transfer model was constructed from these model formulae. In addition, it was confirmed that new heat transfer model can predict the liquid film temperature obtained by multiphase flow numerical analysis method accurately.

As a technology to reduce the heat loss of engines, heat insulation coating to the surface of combustion chamber has been received a lot of attention. In order to maximize the thermal efficiency improvements by the technology, it is important to clarify the location where heat insulation coating can reduce heat loss more effectively, considering the impact on abnormal combustion etc. In this study, transient behavior of wall heat flux distribution on the piston was analyzed using 3D Computational Fluid Dynamics (CFD) for three combustion modes (spark ignition combustion (SI), homogenous charge compression Ignition (HCCI) and spark controlled compression ignition (SPCCI)).