Particle image velocimetry measurements of flow over a wavy wall

The velocity field in a plane that is oriented in the flow direction and perpendicular to the wall was measured for flow over a sinusoidal wavy boundary. The conditions were such that the surface may be considered as fully rough. Visual observations, as well as two-point correlations of the fluctuating velocity field, reveal that the turbulent structure is similar to what is found for flow over a smooth surface even though the mechanisms by which the wall maintains the turbulence are quite different. This provides support for the notion that, far enough away from the wall, the turbulence is universal.