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An automatic transmission torque converter is usually used as a power transmission element, which performs the function of the torque matching and the torque amplification of the engine power output. This is referred to as the fluid performance of the torque converter, which is determined by its blade shape. Therefore, it is necessary to predict the fluid performance of the torque converter at the design stage to determine the blade shape, to which computational fluid dynamics (CFD) analysis can be applied. At present, time-averaged turbulence models such as k-ε (called Reynolds-averaged Navier–Stokes—RANS—model) are often used in such CFD analysis for industrial purposes, and are not limited to torque converters because of its appropriate calculation time. However, major traditional RANS models are less reliable for applications to complex three-dimensional flows in the torque-converter than those to simple pipe, channel and boundary layer flows.

A Lock-Up clutch is installed inside a Torque Converter to improve fuel efficiency. The Lock-Up facing generates heat, and the temperature of the friction surface rises during Slipping Lock-Up. The temperature must be maintained below the acceptable level for ATF (Automatic Transmission Fluid). Therefore, a prediction technics is required at the development stage. Heat flow analysis by CFD (Computational Fluid Dynamics) has been conducted to predict the temperature of the Lock-Up clutch friction surface. In this paper, the target is a Torque Converter with multi plate Lock-Up clutch. An appropriate boundary condition was applied to the flow simulation in order to set the correct total flow rate in the torque converter, and by verifying analysis results, it is confirmed that the prediction of friction surface temperature is close to the data from the experiment. In addition, it is realized that the flow rate has great influence on the temperature of friction surface.

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.

The behavior of spray injections to turbulent duct flows from a slit injector for direct-injection gasoline engines was investigated using a combination of large eddy simulation (LES) and Lagrangian discrete droplet model (DDM). As a result, diffusion of droplets in stronger turbulent flows was observed at a later stage of the injection. Moreover, we compared calculation and experimental results by generating a pseudo-particle image from the calculation result.