A preliminary wind-tunnel study on the effect of wind intermittency on aerodynamic entrainment
1, Jie Zhang1, Yusheng Liu1, Ning Huang1, Yaping Shao2
1Key Laboratory of Mechanics on Disaster and Environment in Western China, Lanzhou University, Lanzhou, Gansu, China, 2The Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany
Aerodynamic entrainment and resuspension of sand (dust) particles are important physical mechanisms of aeolian process, such as sand and dust storm, snowdrift, or air pollution. In his innovative study, Bagnold proposed that saltation is the dominant process whereas aerodynamic entrainment takes up a small proportion which can be ignored. And this viewpoint is accepted by most researchers for a long time. However with the development of computer science and experimental technology, more and more evidences show that aerodynamic entrainment by turbulence may play an important role in Aeolian transport. In this paper, a wind-tunnel experiment on the effect of wind intermittency on aerodynamic entrainment is carried out. The Irwin probes is used to detect the surface stress, and a piece of cloth is hanged in the upstream to generate vertical wind structure and simulate the natural wind gust. Results indicate that wind intermittency has great influences on aerodynamic entrainment. The aerodynamic entrainment rate with cloth can be a magnitude more than that without cloth. Results also show that the traditional way for surface stress estimated by log-law wind profile will underestimate the surface stress at gust wind conditions. Finally an aerodynamic entrainment rate expression with an intermittency index is proposed here.