Simulation of wind velocity reduction effect of gravel beds in a mobile wind tunnel atop the Mogao Grottoes of Dunhuang, China

Gravels can protect the intervening erodible surfaces from wind erosion by absorbing the momentum near gravel surfaces. Here we report results of systematic tests using a mobile wind tunnel atop the Mogao Grottoes to examine the wind velocity reduction effect of different gravel beds at different wind speeds. Results reveal that the wind velocity reduction effect of each gravel bed increases with increasing the experimental wind velocity. In sand drift control engineering, the best wind velocity reduction effect can be achieved by partly covering the underlying surfaces with gravels. The best gravel coverages in reducing wind speed for 2, 3 and 5 cm gravels are 25%, 35% and 20%, respectively and the corresponding D/H values are 2.6, 1.1 and 1.8, at which wind velocities can be reduced as much as 3.97 m s− 1 at the height of 4.3 cm and 2.59 m s− 1 at the height of 8.3 cm above gravel beds. In addition, gravel beds at the best coverage in reducing wind speed can also remarkably increase the aerodynamic roughness length and drag coefficient compared with the same bed at 0% coverage. These results can offer some referential significance to the construction of the artificial gravel surfaces against wind erosion.