Abstract Protection from windblown-sand is one of the key engineering issues for construction and maintenance of human infrastructures in arid environments. In the last century, several barriers with different shapes have been proposed in order to overcome this problem, but literature lacks of a systematic performance quantitative analysis, and the key geometric parameters that promote sedimentation have not been yet recognized. A deep understanding of the aerodynamics effects of sand barrier on the flow is an unavoidable step to achieve these objectives. The present computational study aims to comparatively analyze different kinds of windblown sand mitigation solid barriers, clarify their working principles, extract from the aerodynamics analysis key geometrical features of the barriers and relate them to the sand trapping performances. Approximated metrics for performance assessment are introduced using aerodynamic parameters. The performances of an innovative solid barrier and the ones of commonly used solid barriers are compared in terms of these metrics. The effects of incoming wind velocity profiles on sand trapping performances are evaluated as well. An empirical dimensionless performance estimator is proposed and used to provide general design guidelines.

Solid barriers for windblown sand mitigation: aerodynamic behavior

Investigations into the design of sand control fence for Gobi buildings

Wind field numerical simulation in forested regions of complex terrain: A mesoscale study using WRF

Using particle-scale simulations of non-suspended sediment transport for a large range of Newtonian fluids driving transport, including air and water, we determine the bulk transport cessation threshold $\Theta^r_t$ by extrapolating the transport load as a function of the dimensionless fluid shear stress (`Shields number') $\Theta$ to the vanishing transport limit. In this limit, the simulated steady states of continuous transport can be described by simple analytical model equations relating the average transport layer properties to the law of the wall flow velocity profile. We use this model to calculate $\Theta^r_t$ for arbitrary environments and derive a general Shields-like threshold diagram in which a Stokes-like number replaces the particle Reynolds number. Despite the simplicity of our hydrodynamic description, the predicted cessation threshold, both from the simulations and analytical model, quantitatively agrees with measurements for transport in air and viscous and turbulent liquids despite not being fitted to these measurements. We interpret the analytical model as a description of a continuous rebound motion of transported particles and thus $\Theta^r_t$ as the minimal fluid shear stress needed to compensate the average energy loss of transported particles during an average rebound at the bed surface. This interpretation, supported by simulations near $\Theta^r_t$, implies that entrainment mechanisms are needed to sustain transport above $\Theta^r_t$. While entrainment by turbulent events sustains intermittent transport, entrainment by particle-bed impacts sustains continuous transport. Combining our interpretations with the critical energy criterion for incipient motion by Valyrakis and coworkers, we put forward a new conceptual picture of sediment transport intermittency.

Izael A. Lima

Papers

CFD simulation of the wind field over a terrain with sand fences: Critical spacing for the wind shear velocity