正弦形沙丘背风坡回流区特性研究

Recirculation zone characteristics at the leeward side of a sinusoidal dune

利用开源计算流体力学软件OpenFOAM的标准k-ε湍流模型,对沙丘表面流场进行数值模拟,获得了距沙丘表面不同高度的流场速度分布曲线,考察了沙丘背风坡回流区特性受沙丘高度和宽度的影响,分析了回流区形成的原因。结果表明:沙丘高度较低时,在背风坡贴近沙丘表面的区域气流速度先降低后增加;随着沙丘高度的增加,背风坡气流速度降低更为迅速,气流不稳定,出现回流区。研究还发现:在沙丘宽度或高度一定的情况下,随着宽高比的增加,回流区尺度减小;回流区尺度不仅取决于宽高比,还取决于沙丘宽度与高度的数值。沙丘背风坡回流区萌生时,贴近沙丘表面出现一系列小涡,减小沙丘宽高比,涡的尺度增大、强度增加,演变为回流区。

Using the standard k-ε turbulent model, the flow field over a dune was simulated numerically by use of the open source computational fluid dynamics software OpenFOAM. The velocity distribution curves for the flow field at different heights over the dune were obtained, the influences of the dune height and width on the characteristics of recirculation zone at the leeward side of the dune were explored and the cause of the formation of recirculation zone was analyzed. The results show that when the dune height is small, the velocity of the air close to the dune surface first decreases and then increases at the leeward side. As the dune height increases, the air velocity at the leeward side decreases more rapidly and becomes unstable, as a result, the recirculation zone appears. It is also found that the scale of the recirculation zone decreases with the increase of the aspect ratio of the dune when either the dune width or the dune height keeps constant. The size of the recirculation zone depends not only on the aspect ratio but also on the height and width of the dune. When the recirculation zone at the leeward side initiates, a series of small eddies appear close to the dune surface. With decreasing in the aspect ratio of the dune, both the size and the intensity of the eddies increase, generating the recirculation zone.