Aeolian Creep Transport: Theory and Experiment

Abstract

Aeolian sand transport drives geophysical phenomena, such as bedform evolution and desertification. Creep plays a crucial, yet poorly understood, role in this process. We present a model for aeolian creep, making quantitative predictions for creep fluxes, which we verify experimentally. We discover that the creep transport rate scales like the Shields number to the power 5/2, clearly different from the laws known for saltation. We derive this 5/2 power scaling law from our theory and confirm it with meticulous wind tunnel experiments. We calculate the creep flux and layer thickness in steady state exactly and for the first time study the relaxation of the flux toward saturation, obtaining an analytic expression for the relaxation time.

Characterization of Wind‐Blown Sand With Near‐Wall Motions and Turbulence: From Grain‐Scale Distributions to Sediment Transport

“…Although the variation rules of RANS and LES are consistent with those of previous studies, simulation results of RANS significantly deviated from the experimental results at different wind speeds. That is, RANS underestimated aeolian sand flux, while the simulation results of LES were close to those from the wind tunnel experiments Creyssels et al, 2009;Wang et al, 2020), especially by Kawamura (1951). This indicated that turbulence is important to the determination of transport flux.…”

“…When free stream velocity U ∞ changed from 7.58 to 10.82 m s −1 , the mean impact angle in RANS ranged from 11.4° to 13.3°, and the variation range in LES was 12.5°-14.9°, slightly larger than that in RANS (Figure 6d). Different impact angle ranges have been given in previous studies, such as 10°-16° (Bagnold, 1941), 11°-14° (Nalpanis et al, 1993), 10.2°-15° (Rice et al, 1995), and 10°-12° (O'Brien & Neuman, 2016), which showed that the impact angle was <16° (Swann & Sherman, 2013;Wang et al, 2020).…”

“…Namely, either a quadratic or cubic law works reasonably well, as shown by . Moreover, we fitted the experimental results of Creyssels et al (2009) and Wang et al (2020) with two laws. Their correlation coefficients were both >0.98, which further confirmed our conclusion.…”

“…(2009) and Wang et al. (2020) with two laws. Their correlation coefficients were both >0.98, which further confirmed our conclusion.…”

“…Earlier studies of aeolian sand flux and friction velocity show that they satisfy the cubic law (Bagnold, 1941; Hsu, 1971; Kawamura, 1951; Sauermann et al., 2001; Sørensen, 2004; White, 1979; Wu, 2003; Zingg, 1953). Recently, many scientists have suggested that a quadratic law may be more suitable than a cubic one (Creyssels et al., 2009; Durán et al., 2011; Ho et al., 2011; Wang et al., 2020). Therefore, we used both quadratic and cubic law to describe the relationship between transport flux and friction velocity in RANS and LES, and found that the correlation coefficients of the two simulations were all >0.99.…”