Numerical Analysis of the Airflow around Automobiles Using Multi-block Structured Grids

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 agreement in the drag and lift coefficients is excellent. The pressure distribution on the surface also agrees well.

Visualization of computed flow fields is also conducted. In the wake region, the flows have periodic vortical motions. It is found that the motiongraphic system can clearly visualize these periodic changes of flow and is very useful.