Take-off threshold velocity of solid particles lying under a turbulent boundary layer

The take-off of free solid particles by wind erosion has been investigated. A preliminary bibliographic study (Foucaut and Stanislas 1995) has enabled an analysis of the Bagnold criterion (1941) to be made and its accordance with the results obtained by White (1982) to be shown, thus leading to a semi-empirical model. This initial study led to a more judicious choice of the primary parameters, allowing a more physical representation of the threshold velocity. In the present study, the criterion validation was carried out in a specific boundary layer wind tunnel, by means of a direct measurement of the threshold velocity. The basic idea was to increase the wind tunnel velocity slowly and linearly and to perform an optical detection of the first take-offs.List of symbols D_p particle diameter - D_Pref reference diameter - _p D_p/D_pref - g gravity - H shape factor = (/) - h⁺ roughness parameter ( =uD_p/2) - R_f =uD_p/ - R_x u_ex/v - û u_e/v - u⁺ flow velocity ( =u/u) - u_e external velocity - u_elim external threshold velocity - û_e u_e/u_elim - u friction velocity - u^* threshold friction velocity - u_tref reference velocity - ^* u^*/u^ref - y⁺ yu/ - _p (_p–)/ - boundary layer thickness - displacement thickness - dynamic viscosity - v kinematic viscosity - momentum thickness - fluid density - _p particle density - standard deviation of particle diameter - shear stressResearch carried out at Ecole des Mines de Douai