Aeolian sand transport: Length and height distributions of saltation trajectories

Ho, Tuan Duc; Valance, Alexandre; Dupont, Pascal; Moctar, Ahmed Ould El

doi:10.1016/j.aeolia.2013.11.004

Cited by 60 publications

(101 citation statements)

References 25 publications

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“…There would appear to be a minimum median velocity, independent of u * , at which particles are ejected from (~0.3 m/s;

{\overset{true~}{u}}_{z} / \sqrt{g d_{50}} ≅

4.0) and then impact (~0.5 m/s;

{\overset{true~}{u}}_{z} / \sqrt{g d_{50}} ≅

6.8) the bed surface. Previous studies of saltation under saturated conditions (e.g., Creyseels et al, , Ho et al, ) also found the particle impact velocity to be independent of u * , but on the order of 1 m/s, while those reported from selected numerical simulations are even slightly higher (Duran et al, ). The relatively low impact velocities measured in the present study likely arise from the capability of EPAS PTV to sample large numbers of splashed particles within just 25 μm of the bed surface.…”

Section: Resultsmentioning

confidence: 81%

Experimental Validation of the Near‐Bed Particle‐Borne Stress Profile in Aeolian Transport Systems

O’Brien

Neuman

2019

JGR Earth Surface

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Self‐regulation of sediment transport by wind is widely assumed to derive from the partitioning of momentum from the fluid flow to the particle cloud. Consequently, the fluid stress on the bed surface is suggested by some to drop below that required to entrain particles, while the cloud is sustained by particle ricochet and splash that derive from the impacts of particles moving ballistically along the bed surface. While these theoretical constructs underpin present‐day numerical models of aeolian saltation, the particle‐borne stress has never been measured directly in either a laboratory or field setting. Such measurements are required for model validation and calibration of numerical simulations and were undertaken in vertical profile in the Trent Environmental Wind Tunnel using particle tracking velocimetry. Test sand was normally distributed with a median diameter of 590 μm. Particle momentum was calculated from the diameter and velocity of each image pair captured using high‐speed photography and then summed within each elevation band. The median diameter of the air‐borne particles was found to increase with friction velocity (u*), suggestive of sorting of the bed surface, and to decrease with elevation. Within a two‐dimensional framework, the vertical and windward components of the particle velocity were found to increase with elevation, with u* having little to no influence. Confirming the results of previous numerical simulations, these experiments show that the normalized particle‐borne stress increases exponentially toward the bed surface; however, within the lowest few millimeters where particle splash dominates, no consistent change is observed with elevation.

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“…There would appear to be a minimum median velocity, independent of u * , at which particles are ejected from (~0.3 m/s;

{\overset{true~}{u}}_{z} / \sqrt{g d_{50}} ≅

4.0) and then impact (~0.5 m/s;

{\overset{true~}{u}}_{z} / \sqrt{g d_{50}} ≅

Section: Resultsmentioning

confidence: 81%

Experimental Validation of the Near‐Bed Particle‐Borne Stress Profile in Aeolian Transport Systems

O’Brien

Neuman

2019

JGR Earth Surface

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“…Wind tunnel experiments ( 30 , 36 – 39 ) and numerical simulations ( 31 , 58 ) support the u * invariance of mean particle speeds near the surface, although recent simulations ( 35 , 70 ) and wind tunnel experiments ( 30 , 37 , 40 ) puzzlingly find that particle speeds far above the sand bed do increase with u * [see Fig. 14 in the review of Kok et al .…”

Section: Discussionmentioning

confidence: 94%

Wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress

2017

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“…The experiments reported here were performed in a 6.6m long wind tunnel with a cross-section of dimensions 0.27m × 0.27m where the nominal air velocity U ∞ (i.e., the air speed outside from the boundary layer) can be varied between 0 to 20m s (see Ho et al [2011Ho et al [ , 2014 for further details). At the upwind edge of the tunnel, a hopper is installed on the roof of the wind-tunnel and delivers a constant and prescribed upwind sand flux Q 0 (see Fig.…”

Section: Experimental Set-up and Protocolmentioning

confidence: 99%

Aeolian Sand Transport in Out‐of‐Equilibrium Regimes

Selmani

Valance

Moctar

et al. 2018

Geophysical Research Letters

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We investigate the relaxation process toward the equilibrium regime of saltation transport in the context of nonuniform conditions. Relaxation phenomena can be described in terms of a characteristic length scale that measures the distance for the particle flux to adapt to a spatial change in flow or boundary conditions. We conducted wind tunnel experiments to document the influence of the upwind mass flux on the relaxation process. For zero upwind mass flux conditions, the relaxation process is monotone and the relaxation length is independent of the wind strength. In contrast, for nonzero upwind flux conditions (obtained by releasing particles in the flow from a finite height), the relaxation process is nonmonotone and is well captured by damped harmonic oscillations. Importantly, the relaxation length increases with increasing air flow velocity but is almost insensitive to the magnitude of the upwind flux. Our experimental outcomes clearly indicate that the relaxation of far from equilibrium transport regimes strongly deviates from a simple exponential behavior.

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Aeolian sand transport: Length and height distributions of saltation trajectories

Cited by 60 publications

References 25 publications

Experimental Validation of the Near‐Bed Particle‐Borne Stress Profile in Aeolian Transport Systems

Experimental Validation of the Near‐Bed Particle‐Borne Stress Profile in Aeolian Transport Systems

Wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress

Aeolian Sand Transport in Out‐of‐Equilibrium Regimes

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