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A flow analysis method with quick turnaround time has been studied for application to flows in the engine compartment of vehicles. In this research, a rapid modeling method based on the Cartesian mesh system was developed to obtain flow field information quickly. With this modeling method, the original shape is approximated by many small cubic cells, allowing automatic mesh generation in significantly less time. Moreover, a hierarchical mesh system that reduces the total number of meshes has been introduced. This multi-level mesh system is also highly capable of representing shapes in detail. Another important issue in flow calculations in the engine bay is the treatment of the boundary conditions such as the radiator and cooling fan. With the proposed method, the fluid dynamics characteristics of such components are measured, and characteristics such as the pressure loss/gain and the rotational vector of the fan are reflected in the flow field as empirical models.

A voxel model, which consists of minute cubic cells called voxels to express the shape of an object, can now be generated automatically from CAD data. Moreover, advances in high-speed computational techniques have made it possible to perform a structural analysis using such a voxel model. This paper presents some high-speed computational techniques to realize the analysis in practice and a method to treat a contact condition on the jagged surface that characterizes a voxel model to further expand the scope of application.

The use of higher output engines and more auxiliary units is resulting in greater heat generation in the engine compartment. At the same time, design trends and demands for improved aerodynamic performance are diminishing the cooling air flow rate. These two sets of factors are making the thermal environment in the engine compartment more severe. In this work, heat flow in the engine compartment was investigated by numerical analysis and flow visualization, and flow control devices were devised for optimizing the temperature distribution. This paper discusses the heat flow optimization techniques and presents the results obtained in experiments with an actual vehicle.

Both the external and internal flows of cars are simulated simultaneously. A third-order upwind-difference scheme is used in these simulations. Computational grids are generated by a multi-block transformation and a trans-finite method. Engine compartments are modeled by grid systems but the heat exchanger is simulated as a pressure loss proportional to the dynamic pressure of the flow passing through it. First, the flow for a very simple test model with no wheels and nothing in its engine compartment is simulated and compared with experimental results in order to validate a simulation method for the engine compartment. Pressure distributions on the inner surfaces agree very well with measured values, while pressure distributions on the external surfaces show reasonable agreement except for the roof end and the leading edge of the floor. The predicted drag coefficient is 7% larger than the experimental value. This method is next applied to a prototype car.

Incompressible viscous unsteady airflow around three types of automobiles are simulated. A thirdorder upwind-difference scheme is used in these simulations. In all the analyses, computational grids are generated by a multi-block transformation and a transfinite method in each block. The first two types of automobile have almost the same shape in the front half of the body, and the accuracy of predicting the difference in drag coefficient is investigated. In this case, the bodies are simplified. They have flat under-floors and no wheels. These calculated results are compared with experiments using 1/5 scale models. The difference in drag coefficient between the two types agrees well with the experiments, and also the values themselves agree well. In the last case, a car with wheels and an under-floor resembling a production model is studied. Simulated results are compared with experiments using a real production car with closed front opening and without mirrors.

The acceleration performance of a car equipped with a turbocharged, intercooled engine is affected by the volume of cooling air that flows through the core of the intercooler. Additionally, the volume of cooling air entering the intercooler is influenced by the configuration of the air intake provided in the exterior design. Therefore, in planning a new model it is very important to be able to predict acceleration performance, at an early stage of the vehicle development process, in relation to vehicle styling and engine specifications. The procedures employed so far to predict the volume of air flowing through the intercooler have included two-dimensional finite-difference methods and a panel method. However, because of their simple nature, none of these approaches has provided sufficiently accurate results. This paper presents a new numerical analysis method that has been developed to overcome this problem.

It is very difficult to measure and analyze the internal flows of torque converters because of their complicated construction. In this report, an attempt is made to calculate the characteristics of torque converters by the combination of a one-dimensional flow theory and a finite difference calculation. From the computed results however, it is significant to note, that this experimental result is more useful as a rational design procedure than the pure angular momentum theory.

This paper describes a preliminary study of the role of computational fluid dynamics in analyzing the aerodynamic characteristics of a heavy-duty truck body. Among truck related aerodynamic problems, we selected the soil problem on the vehicle side surfaces as the analysis subject. Because of computer capacity limitations, a half-truck-cab model with a tire and mud guard are used and created by using the multi-block transformation technique. The flow around the cab is simulated by directly integrating the Navier-Stokes equations, approximated by finite-difference equations. Calculated results on the flaw structures around the vehicle body surface where it becomes dirty under wet weather conditions provide some useful information in the search for understanding of soil problems.

Numerical simulation of two-dimensional and three-dimensional air flow in automobile passenger compartments is described. The flow can be expressed by means of an incompressible Navier-Stokes equation for a narrow temperature range. The results were represented visually using animation and a color graphics system. The two-dimensional simulation showed that heat ansfer takes place chiefly by convection in vortices, and that the effects of heat transfer are minimal. In the three-dimensional analysis, shading was used to show the shape inside the compartment, and instantaneous stream lines and temperature distribution were depicted. The three-dimensional stream lines swirl upward at the front seat, and do not reach the back seat. The results gained from this study show that present theoretical flow analysis methods are close to being perfected. Further advances will require additional refinement of supercomputers and graphic engineering workstations.

The computation of the Navier-Stokes equations through the three torque converter components (i.e., the pump, the turbine and the stator) is shown. A third-order-upwind scheme is used in the computation. The flow in each component is first calculated individually. Then, the calculation results for each outlet condition are used as the inlet condition of the next component, and the flow in each component is calculated again. This iterative procedure is terminated when the loss of flow pressure in the three components reaches a steady state. The torque converter performance predicted with this method agrees well with experimental data.