Behavior of Sand Surface and Formation of Sand Ripple

Abstract

The desertification is regarded as one of the global subjects in 21th century, because the area up to approximately 6 million ha has been desertified every year. In this paper the behavior of sand surface behind a square block in a wind tunnel is observed using a high-speed video-camera with 10000 frames/s. The velocity profiles are measured using a Pitottube for the boundary layer flow in the wind tunnel. The sand sizes are 0.18∿1.00mm. The initiation of sand flight depends on the sand size, the sand density, the wind velocity and the angle between the sand surface and the flow direction. The sand ripples are formed after the initiation of sand flight in a turbulent boundary layer flow. Relatively larger sands are forcussed on the mountain side of the sand ripples, while relatively smaller sands are on the valley side.