Visualization of Separation Over Sand Waves

Flow pattern and separation over dune-shaped beds have been observed by streaming birefringence. By this visual observation, qualitative measurements were carried out, and the variation of the separation zone length with the Froude and Reynolds Numbers of the flow were established. At low Froude Numbers, the length of separation zone is proportional by the inverse of Froude Number. If the Froude Number of the flow is greater than 0.2, there is no significant change in the separation zone length, and the ratio of the separation zone length to the height of dunes takes 0.32 constant value. This ratio also is a function of flow Reynolds Number in laminar boundary layer, and decreases with increasing Reynolds Numbers. In the case of turbulent boundary layer, this ratio is independent of Reynolds Number.