抄録
In order to observe the flow around a body, we generally use wind tunnels. However, it does not make a precise repoduction of a body running on the ground plane like automobiles or railway trains, because of existence of a boudary layer on the ground wall of the test section. It is necessary to avoid effects of the boundary layer.
We made a small scale "towing apparatus" and visualized the flow underneath model cars by the smoke wire method. The velocity distribution of underneath flow was made clear. It is influenced by the air flow from radiator-grill to underbody of engine-room. By making the underbody flat a smooth underneath flow is obtained.
