DDES方法在复杂旋翼流场计算中的应用

应用延迟脱体涡模拟（DDES）方法，进行了复杂分离流动旋翼流场的数值模拟研究。为控制计算规模，更好地模拟旋翼桨叶近壁面附近区域流动分离及远场尾迹发展，采用了贴体与背景自适应直角网格嵌套的网格系统；同时为提高计算速度，采用了基于分布式存储的数据并行模式，实现了贡献单元搜索、洞切割和流场计算的并行化。计算工作包含一个共轴双旋翼悬停和单旋翼下降状态，目的是分别讨论DDES方法在旋翼表面附近空间区域是否存在大范围分离时计算结果与雷诺平均Navier-Stokes结果之间的差异。计算表明，对于下降状态，DDES方法预测出了更强的尾迹区分离流动；对于桨叶表面基本为附着流动的双旋翼中等桨距角情况，两种方法预测的流场结构相似，仅在下旋翼桨叶气动力和旋翼桨根下方空间区域的诱导速度计算结果上存在微细差异。

Application of DDES method to simulation of complicated rotor flowfield

Characteristics of rotorcraft flow fields which contains complicated airflow detached phenomenon are simulated by Delayed Detached Eddy Simulation (DDES). The embedded grid system constructed by combining adaptive background Cartesian and body-fitted grid is adopted to simulate simultaneously the flow separation in the near wall region and the wake evolution in far fields when the computation resource is limited. The flow fields iteration, hole cutting and donor searching processes are parallelized based on the message passing library (distributed-memory parallelization) to improve computing efficiency. Flow fields of a coaxial rotor in hover and a single rotor in descending state are simulated, aiming to discuss the differences where large range of flow separations near the blade surface region exist or not with DDES and Reynolds-averaged Navier-Stokes method. Results show that in the descending status, more strengthen separations and unsteady phenomenon are predicted in the rotor wake with DDES, the predicted coaxial rotor flow fields are similar with different methods, as the attached flow is dominated with moderate collective blade angle, the slim discrepancy is observed only on the lower rotor blades aerodynamics and induced velocity beneath the rotor root.