Saltating particles in a turbulent boundary layer: experiment and theory

Abstract

International audienceThe work presented here focuses on the analysis of a turbulent boundary layer saturated with saltating particles. Experiments were carried out in a wind tunnel 15m long and 0.6m wide at the University of Aarhus in Denmark with sand grains 242 μm in size for wind speeds ranging from the threshold speed to twice its value. The saltating particles were analysed using particle image velocimetry (PIV) and particletracking velocimetry (PTV), and vertical profiles of particle concentration and velocity were extracted. The particle concentration was found to decrease exponentially with the height above the bed, and the characteristic decay height was independent of the wind speed. In contrast with the logarithmic profile of the wind speed, the grain velocity was found to vary linearly with the height. In addition, the measurements indicated that the grain velocity profile depended only slightly on the wind speed. These results are shown to be closely related to the features of the splash function that characterizes the impact of the saltating particles on a sandbed. A numerical simulation is developed that explicitly incorporates low-velocity moments of the splash function in a calculation of the boundary conditions that apply at the bed. The overall features of the experimental measurements are reproduced by simulation

An improved parameterization of wind‐blown sand flux on Mars that includes the effect of hysteresis

“…Equation (13) indicates that v imp is not dependent on the shear velocity [Kok and Renno, 2009b], which was indeed confirmed by recent wind-tunnel measurements [Rasmussen and Sørensen, 2008;Creyssels et al, 2009]. Moreover, equation (13) yields v imp ≈ 1.2 m/s for 250 mm particles on Earth, which is in good agreement with those measurements [Kok, 2010].…”

Aerodynamic roughness height for gravel-mantled megaripples, with implications for wind profiles near TARs on Mars

“…The rightmost column in Table 1 lists the average of the three shear velocities calculated for the observed wind speeds measured by each anemometer during each recording session. In general, typical u ⁄ values range from 0.2 m/s (for well sorted fine sand both in wind tunnels and in a field setting) to 0.4 m/s (field measurements in diverse desert settings) at the threshold of sand motion (Bagnold, 1941;Greeley and Iversen, 1985;Nickling, 1988;Lancaster and Baas, 1998;Creyssels et al, 2009;Kok et al, 2012). The elevation of the Puna means that the atmospheric pressure and density is considerably lower than at sea level, which translates to the shear velocity at the Puna being about 1.7Â the value at sea level; hence, threshold shear velocity at the Puna study sites should be more like 0.4-0.7 m/s (de Silva et al, 2013;Bridges et al, 2015).…”

Periodic saltation over hydrodynamically rough beds: aeolian to aquatic

“…For saltation over erodible beds, experiments (Creyssels et al 2009, Meyer-Peter & Müller 1948) and numerical simulations (Durán et al 2012) show that there is only one particle flux associated with a given Shields parameter, no matter what the density ratio. In the formulation of the periodic boundaryvalue problem, that means that there is an additional constraint that permits the determination of the upward flux -or equivalently the horizontal particle flux -as part of the solution.…”

“…9 are the experimental values obtained by Creyssels et al (2009) andHo et al (2011) for sand in air. The analytical solution for  = 2500 and St = 3000, as in the experiments, is indistinguishable from that for  = 1000 and St = 1000.…”