| Abstract: | One‐dimensional simulations of the unsteady saltation process show that the transport rate's response depends on the amplitude and frequency of the wind fluctuations. At frequencies higher than f ≈ 0·5 Hz the transport rate was found not to respond to the wind changes. The initial overshoot reported by previous investigators was found not to appear for simulation heights smaller than 50 to 60 cm. This is due to the fast propagation of the grains' influence upward in the flow and the immediate deceleration of the wind. Confirmation of these findings comes from reports of experiments conducted in wind tunnels of different sizes. Further test calculations show that the discretization time step size Δt has an influence on the model's temporal behaviour. The reason for this is the better coupling of the wind–sand system when a smaller Δt is used. The implications of bed area choice on the statistical accuracy of predicted transport rate is also demonstrated. In the one‐dimensional case the grain cloud's total forward momentum equals transport rate, which is independent of model geometry. Copyright © 2000 John Wiley & Sons, Ltd. |
