关键词: 砾石覆盖度, 砾石床面, 风速梯度, 阻风效应, 野外风洞实验

Abstract:

This paper simulated the variation of wind velocity gradient over gravel beds with different gravel coverages in a mobile wind tunnel over Mogao Grottoes, Dunhuang. Results revealed that the wind velocity gradient below the average gravel height changed with gravel coverage in disorder while the wind velocity gradient above the gravel height changed regularly with gravel coverage: wind velocity increased gradually from 5% to 35%, keeping steady from coverage 40% to 80%, and it was the lowest at gravel coverage of 35%. Therefore, the atmospheric boundary layer could be divided into two parts: the layer below the average gravel height was defined as the roughness sub-layer, and the one above the average gravel height the inertia sub-layer. In both sub-layers, the change of the wind velocity gradient with the ratio of gravel-to-gravel distance to the average gravel height (D/H) was similar with that with gravel coverage. In the inertia sub-layer, wind velocity was kept steady at D/H in 0.3-1.5, and increased gradually from 2.0 to 4.0, and it was the lowest at D/H at 1.5. Besides, according to the calculation of the wind-blocking effect, it was the strongest near gravel bed (0.75 H to 1.1 H); in the roughness sub-layer, the wind-blocking effect increased with the increase of height; in the inertia sub-layer the situation was just the opposite. Furthermore, when D/H was 1.5 and D was 3 cm and gravel coverage was 35%, the gravel bed had the best wind-blocking effect, which had referential value for gravel-used sand-control project.

Key words: gravel coverage, gravel bed, wind velocity gradient, wind-blocking effect, mobile wind tunnel experiment