Gain function analysis of sand transport in a turbulent air flow

Abstract

Abstract Recent work on the modelling of sand transport processes in the wind is concentrating on the effects of turbulence and, in particular, on flow accelerations and particle inertia. An approach is developed here in which the problem is cast in the frequency domain using the particle momentum equation which balances grain inertia against resultant steady and acceleration related fluid forces. A transport gain function is defined which relates the normalized transport spectrum to the normalized, turbulent flow spectrum. Experiments are reported in which the gain function was determined using a hot wire anemometer and a new pin impact probe to make high-frequency measurements of the velocity and sand transport profiles within the saltation layer in a small laboratory wind tunnel. The results were subjected to frequency analysis and the corresponding wind and transport spectra were obtained. Preliminary calculations suggest that the transport gain function is reasonably flat over the range up to 0.4 Hz and, therefore, models based upon gain function analysis may more properly account for sand transport within a turbulent boundary layer.