Simulation of Eolian Saltation

Abstract

Saltation is important in the transport of sand-sized granular material by wind and in the ejection of dust from the bed both on Earth and on Mars. The evolution of the saltating population and all its characteristic profiles is calculated from inception by pure aerodynamic entrainment through to steady state. Results of numerical simulations of single-grain impacts into granular beds are condensed into analytic expressions for the number and speeds of grains rebounding or rejected (splashed) from the bed. A model is combined with (i) this numerical representation, (ii) an expression for the aerodynamic entrainment rate, and (iii) the modification of the wind velocity profile by saltating grains. Calculated steady state mass fluxes are within the range of mass fluxes measured in wind tunnel experiments; mass flux is nonlinearly dependent on the shear velocity. Aerodynamically entrained grains in the system are primarily seeding agents; at steady state, aerodynamic entrainment is rare. The time for the entire system to reach steady state is roughly 1 second, or several long-trajectory hop times.

Experimental study of aeolian sand ripples in a wind tunnel

“…At high wind velocities, by comparison, aeolian sand flow is large enough to attain the full development stage on a short bed (Andreotti et al, 2010). This phenomenon further confirms that splashing processes and creeping (reptation) sand play important roles in the formation and evolution of aeolian sand ripples (Sharp, 1963;Anderson, 1987;Anderson and Haff, 1988;Rice et al, 1995;Rioual et al, 2000;Durán et al, 2014).…”

“…As early as in the 1940s, Bagnold (1941) found that the wavelength of sand ripples is positively correlated with the mean characteristic path of saltating sand grains, which increases with friction velocity. Later studies, however, showed no direct relationship between these two (Sharp, 1963;Anderson and Haff, 1988;Kok et al, 2012;Lämmel et al, 2012;Yizhaq et al, 2014;Schmerler et al, 2016). Although the initial wavelength of the ripple is about six times the mean reptation length (Seppälä and Lindé, 1978;Anderson 1987), the simulation results failed to explain the dependence of wavelength on wind speed (Anderson 1987;Anderotti et al 2006;Schmerler et al, 2016).…”

“…In contrast, the wind tunnel used here is as long as 24 m, providing a long sand bed for the sand flux to achieve saturation. The increasing tendency of the wavelength with friction velocity has been concluded by many researchers (Bagnold, 1941;Sharp, 1963;Walker, 1981;Anderson and Haff, 1988;Anderson, 1990;Rioual et al, 2000;Andreotti et al, 2006Andreotti et al, , 2013Kok et al, 2012;Lämmel et al, 2012;Durán et al, 2014;Yizhaq et al, 2014;Schmerler et al, 2016), but the reasoning behind this is still in debate (Duran et al, 2014;Schmerler et al, 2016). As early as in the 1940s, Bagnold (1941) found that the wavelength of sand ripples is positively correlated with the mean characteristic path of saltating sand grains, which increases with friction velocity.…”

Periodic saltation over hydrodynamically rough beds: aeolian to aquatic

“…This regime, called saltation, is the primary mode of transport in Aeolian sand transport, and has been investigated theoretically (Bagnold 1941, Bagnold 1966, Owen 1964, Ungar & Haff 1987, Sauermann et al 2001, Andreotti 2004, Jenkins et al 2010, experimentally (Bagnold 1941, Nalpanis et al 1993, Foucaut & Stanislas 1997, Iversen & Rasmussen 1999, Ho et al 2014) and numerically (Anderson & Haff 1988, Kok & Renno 2009). More references can be found in recent reviews on Aeolian transport (Durán et al 2011, Kok et al 2012, Valance et al 2015.…”

Experimental investigation of the concentration profile of a blowing sand cloud

“…Two approaches have been used to study the concentration profile of blowing sand clouds: uses of wind tunnels under controlled conditions (Chepil and Woodruff, 1957;Williams, 1964;Gillette and Walker, 1977;Zhu, 1996) and analytical approaches (Owen, 1964;Anderson and Haff, 1988;Sorensen and McEwan, 1996;Wu et al, 2002). Chepil and Woodruff (1957) related the concentration of eroded soil particles near the surface to height using a power function, whereas Zhu (1996) related sand concentration to height using an exponential function.…”