Boundary layer on a moving wall

The use of a moving belt as the upper wall of a water channel with the aim to help researchers who use similar arrangements or planning are discussed. The experiments were conducted in a closed-loop water channel with a free surface having a test section that was 0.54 m wide, 4 m long, and 0.75 m high. The local velocity of the water was measured with a laser Doppler velocimeter operating in single component, backscatter mode and with frequency shifting to allow reverse flow measurement. The streamwise pressure gradient, estimated roughly from measurements of the freestream velocity gradient, would be small enough to have no effect on the boundary layer development. The results demonstrate that the motion of a belt covering partially the free surface of a water channel distorts its boundary layer, both in mean velocity profile and turbulence distribution. Caution must be taken while using moving belts for flow modification or control.