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Three-dimensional flows around a car configuration, a Mazda RX-7, were computed by directly integrating the governing unsteady, incompressible Navier-Stokes equations. A well-established finite-difference procedure was utilized. 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 using any explicit turbulence models. Elaborate numerical results were presented at a high Reynolds number, Re=106 (based on the body length). In order to investigate the influence of the cross wind, computations were carried out for two yaw angles, i.e., 0 degree and 30 degrees. Extensive flow visualizations, using state-of-the-art computer graphics, were performed; details of the three-dimensional flow structure were examined. Well-controlled wind tunnel experiments were also conducted.

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.

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.

Turbulent flows in a model engine having a square piston were analyzed in detail by using a numerical simulation method with higher-order accuracy to perform simulations on an orthogonal homogeneous grid without grid motions. Calculations were performed during several continuous engine cycles. A better understanding of the cycle-by-cycle differences, i.e., cyclic variations, in flow fields may lead to more effective ways of stabilizing combustion.

Large Eddy Simulation of the turbulent premixed-flame in engine is performed in a wide range of the operating conditions such as engine speed, air-fuel ratio, and ignition timing. Firstly, a mathematical formulation suitable for Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) of the compressible turbulence and combusting flows is derived, which is the Multi-Level formulation. And a numerical algorithm based on the formulation is developed in order to calculate precisely the supergrid fluctuations of the physical quantities. As the determinations of the subgrid-turbulence and flame wrinkling, the Yakhot-Orszag turbulence model based on the Renormalization Group theory(RNG theory) and a flame-sheet model are combined with the numerical code. Computations are performed for a real engine with dual intakeport and valves. Obtained computational data agrees well with the experimental data on turbulence-intensity and pressure history.

The spray formation and mixing processes in a direct-injection gasoline engine are examined by using a sophisticated air flow calculation model and an original spray model. The spray model for a spiral injector can evaluate the droplet size and spatial distribution under a wide range of parameters such as the initial cone angle, back pressure and injection pressure. This model also includes the droplet breakup process due to wall impingement. The arbitrary constants used in the spray model are derived theoretically without using any experimental data. Fuel vapor distributions just before ignition and combustion processes are analyzed for both homogeneous and stratified charge conditions.

A theoretical model based on a nonlinear ordinary differential equation was developed, which can estimate the atomization process of fuel droplets after the wall impingement. The phase-space trajectory of the equation for droplet deformation and oscillation varies from oval to parabola with increasing impact velocity. Four different regimes for droplet diameter distribution are derived from this complex feature of the equation. The amount of liquid film remaining on the wall and the number of droplets are estimated from the related mass and energy conservation laws. The model is called the Oval-Parabola Trajectories (OPT) model in the present report. Comparisons made with some fundamental experimetal data confirm that this mathematical model is effective in a velocity range from 2m/s to 40m/s and in a diameter range below 300 micrometers.

Computation of the three-dimensional flow in the intake ports and the cylinders of real engines, including moving valves and piston, has been carried out by solving the Navier-Stokes equations. No explicit turbulence models are used. An extended version of the SIMPLE and ICE method is employed to simulate density variations in engines, which are connected with compression rate, heat transfer, and compressibility. A third-order upwind scheme is combined with this method. Computational results show complex flow fields such as separated flows near the valve seat and small vortices of the order of the mesh size near the end of compression. These computational results are compared with the LDV measurements.

In this paper, a prediction method of the aerodynamic sound emitted from the three-dimensional delta wing of the attack angle at 15 degrees is presented. Computed flow Reynolds numbers range from 2.39x1 05 up to 9.56X 105. The method is based on the assumptions: flow Mach number is much less than unity and the strength of sound source equals Curle's dipole. These assumptions are validated by the experimental works performed in a quiet-flow-noise wind tunnel. Owing to the low Mach number condition, the computation region can be devided into two regions: inner flow region and outer wave region. The incompressible flow computation in the inner region is performed based on the full Navier-Stokes equations. The integration of the N-S equations are executed by using finite-difference method. For high Reynolds flow computation, the nonlinear convection terms are discretized by third-order upwind difference scheme.