It is well known that sand waves on the movable bed affect on various phenomena remarkably. Therefore, up to now, mechanism of sand waves have been investigated from many kinds of standpoints. Especially, since formation and development of sand waves are largely depend on the turbulent structure of flow, visualization technique will be powerful for the investigation on their mechanism.
In this paper, we investigated the flow structure over the sand wave model by means of hydrogen bubble method as the basic study of the mechanism of sand waves. Main results obtained through experiments are as follows. 1) Typical flow patterns in the wake region are visualized. By which, formation, development and decay processes of the wake vortex are analyzed. 2) Flow patterns on the reattachment point are also obtained. Where, ejection-or sweep-like motion are obserbed. 3) Very high values are obtained for the streamwise and normal turbulent intensities and also for Reynolds stresses at the reattachment point.
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