旋翼流动的块结构化网格自适应方法

Block structured adaptive mesh refinement for rotor flows

从旋翼的旋转运动和旋涡环绕流场特点出发,探讨了流场计算中的双网格建模方法,即采用结构化贴体网格随桨叶一起运动,采用背景网格的自适应加密模拟旋涡的空间演化。发展了块结构化的背景笛卡尔网格生成方法,网格以块为单位进行加密或稀疏变化,所有网格块的网格维数相同,采用八叉树数据结构和空间填充Z曲线进行管理,满足自适应加密和并行分区的需求。采用该方法对UH-60A旋翼进行了网格建模,在以桨叶贴体网格为输入的前提下自动生成了初始笛卡尔背景网格,同时针对旋翼的悬停和前飞状态流场,分别采用Landgrebe和Beddoes尾迹模型为网格加密提供线索。在此基础上对空间背景网格进行了自适应加密,最大允许网格加密层次为9层,桨尖涡目标区域的网格尺度为0.01倍弦长。结果表明,当前笛卡尔自适应网格方法足够灵活,能够根据桨尖涡位置变化进行网格加密或稀疏操作,自适应网格加密受最大加密层次、目标加密区域的大小和目标区域的网格间距等因素决定。本文的自适应方法具有网格调整效率高的特点,在提高非定常桨尖涡模拟精度方面有一定的应用前景。

Focusing on the rotating motion and vortex flow of rotors, a dual grid modelling method is discussed, in which body fitted moving structured grids are used to capture the boundary layer flow and background grids with adaptive mesh refinement(AMR) are used for the blade tip vortex flow. A method of generating block structured Cartesian grids is developed, in which the grid refinement or coarsening is performed on blocks with identical grid dimensions. All Cartesian blocks are organized by the octree data structure and spatial filling Z curves, which meets the requirements of adaptive refinement and parallel partition. The dual grid method is applied for the UH-60A rotor simulation. The initial Cartesian background grid is automatically generated with the body fitted blade grid as the input. For rotor flows in hovering and forward flight conditions,the Landgrebe and Beddoes wake models are introduced respectively to adaptively refine the background grids.The maximum allowed number of grid layer is 9 and the grid spacing for the tip vortex filament in the target area is 1% of the chord length. Results show that the present Cartesian grid adaptive method is able to flexibly refine or coarsen grids for the blade tip vortex by controlling the maximum refinement level, the size and grid spacing of the target refinement area for the vortex capturing. The present AMR method is highly efficient in grid adjustment, and shows convincing prospects in improving the simulation accuracy of unsteady blade tip vortices.