边界层网格尺度对泵站流场计算结果影响研究

壁面处的y+值是体现壁面边界层网格尺度的主要参数,对泵站流场数值计算结果有重要影响。为明确不同计算目标对y+的依赖性,以一泵站为研究对象,在网格数量无关性检查的基础上,从网格划分难易程度、数值计算精度和效率方面提出3种网格划分方案:全局非结构网格方案,指定边界层高度的全局非结构网格方案,以及指定边界层高度的分块结构网格方案,对应的y+值分别为10~2 000、10~1 000、10~500。方案二与方案三在模拟得到的流速分布均匀度方面几乎没有差别,涡量场的漩涡数量、涡量值和漩涡核心区分布位置也非常接近,而方案一则与之相差较大。研究发现,当只需了解泵站宏观水力性能时,可采用简单易行的方案一所对应的网格方案,y+范围可适当放宽到0~2 000;当要预测进水部分流场的流动特性,特别是漩涡分布特性时,需确保y+位于1 000以内,可采用方案二的网格方案;若对进水流场进行详细研究,或者进行除涡装置的研究时,则需使得整个计算域的y+满足30~500的要求,即采用方案三的网格方案。

Research for impacts of boundary layer grid scale on flow field simulation results in pumping station

The y⁺ value on a wall is a primary parameter of boundary layer grid scale, and has important influence on the flow field numerical simulation for pumping stations. In order to clarify the requirements of y⁺ for different simulation objectives, a realistic pumping station was adopted and evaluated. Considering of meshing difficulty, numerical computation accuracy and efficiency, three kinds of numerical grid schemes were put forward based on the grid independence analysis. The three schemes were named global unstructured grid, global unstructured grid with specified boundary layer height, and block structure grid with specified boundary layer, respectively, which result in the corresponding value of y + 10~2000, 10~1000, 10~500. The results showed little difference in velocity distribution uniformity between scheme 2 and scheme 3. However, scheme 1 was comparatively large difference with the other two schemes. If the macro hydraulic performance of pump station is the main concern, a simple and easy grid scheme (scheme 1) could meet the satisfaction, y⁺ value could be relaxed appropriately to 0~2000. If the vortex distribution in flow field is the main concern, y⁺ should be less than 1000, the scheme 2 of gridding should be adopted. If the detailed flow structures, or vortex elimination devices become the main concern, y⁺ must be within 30~500,and the scheme 3 is the best choice.