基于OpenFOAM的正弦形沙丘表面流场特性研究

Flow Behavior over a Sinusoidal Dune Based on OpenFOAM

基于开源计算流体力学软件OpenFOAM,对沙丘表面流场进行数值模拟,将所得到的沙丘表面风速分布与野外观测结果进行对比,验证数值模拟的准确性.在此基础上,获得了距沙丘表面不同高度的速度分布曲线和沙丘表面上的速度矢量场,探讨了数值模拟结果对计算网格的敏感性,考察了沙丘宽高比对流场特性的影响.结果表明:OpenFOAM的标准k-ε模型能够预测低矮正弦形沙丘表面流场的速度转变特性;在贴近沙丘表面的内层,沙丘表面特定高度处的速度分布曲线相对于沙丘轮廓存在相位提前,随着高度的增加,相位提前量减少,速度变化趋于平缓;网格数目对外层速度分布影响较小,但对内层的速度分布则有重要影响;足够多的网格数目是获得精确的沙丘表面流场信息的必要条件,在沙丘流场数值模拟中应当引起重视;保持沙丘宽度不变,随着沙丘宽高比的减小,沙丘表面速度分布曲线的相位提前量变大,背风坡出现回流区,宽高比越小,回流区的长度与强度越大.

Numerical simulations were performed based on the open source computational fluid dynamics （CFD） software OpenFOAM. The numerically obtained velocity profiles over the dune were compared with the field measured results to validate the accuracy of the numerical simulation. On this basis, the velocity profiles at different heights over the dune as well as the velocity vector field were obtained. The sensitivity of the numerical simulation result to the computational mesh was discussed. Furthermore, the effect of the aspect ratio of the dune on the flow behavior was examined. The results show that the standard k-s turbulence model in OpenFOAM can be used to predict the velocity shift behavior of the flow field over the low sinusoidal dune. In the inner layer close to the dune surface,a phase advance of velocity curve relative to the dune profile is observable within a certain distance over the dune. As the height increases, the phase advance decreases and the velocity begins to flatten. The mesh number has little effect on the velocity profile in the outer layer,while it affects greatly on the velocity profile in the inner layer. It is worth noting that sufficient mesh number is required to attain accuracy information of the flow field over the dune. When the dune width keeps constant, with the decrease in the width-to-height ratio, the phase advance of the velocity profile over the dune increases and the recirculation zone could appear at the leeward. It is found that when the width-to-height ratio becomes smaller, the length and the intensity of the recirculation zone are greater.