Turbulence burst over four micro-topographies in the wind tunnel

Abstract

Investigating the mechanisms of wind-sand movement is essential to deeply understand sand storm and desertification process, and further to control the wind-sand hazards. It is considered that turbulence burst may have great influence on the motion of sand particles. But current theoretical and experimental studies mostly concentrate on the turbulence burst over flat surface or in the water. Sand dunes and sand ripples are basic forms of desert landscape, and the slope gradient will inevitably affect the frequency of turbulence burst. In this paper, instantaneous velocities over 4 different sand surfaces, including smooth flat bed, flat sand bed, sand bed with ripples and slope bed, are measured using one-dimensional hot wire detector. The results show that for the slope sand surface, wind field in leeward slope region is a buffering zone, which doesn't obey logarithmic function. On the flat sand surface, the distribution of turbulence intensity and Reynolds normal stress are gradually decreasing along the height of boundary layer. On the slope sand surface, the stronger turbulence behavior happens near the top of slope. Based on Mu-level method analysis, it is found that the turbulence bursts on both flat sand surface and sand ripples mainly occur near the surface, and gradually decrease with the height. Compared to flat sand surface, the burst frequency is 30%~50% higher on the sand ripples surface, which indicates that micro-topography have an influence on the turbulence burst. This work may be helpful in understanding the initiation and transportation of sand storm, as well as the desertification process.