The present analysis undertakes the problem of surface wind over topography. The main focus is placed upon the effect of oncoming wind oscillations on the velocity field structure around a single sinusoidal shaped 2D hill. Additional effort has been undertaken to recognize the inflow gust influence on the surface shear stress related to the mechanism of wind induced erosion. Numerical simulations have been performed through the use of the phase-averaged form of RNG version of k-ɛ turbulence model. Experimental verification of numerical data has been done in wind tunnels equipped with devices generating unsteady wind boundary layers. The main findings of the simulations reveal: a strong dependence between the characteristics of inflow periodicity and the structure of vortices of the separation region; the mean position of the reattachment point; the phase averaged velocity field; skin friction variability downstream from the hill. The results have significant implications for the prediction of sand transport in unsteady winds.