基于自适应非结构嵌套网格的旋翼流场模拟

针对直升机旋翼CFD仿真的复杂性,提出了改进的适合于格心格式求解器的非结构嵌套网格算法。采用自适应网格技术在旋翼流场仿真的整个过程中进行网格的自适应加密和疏化操作,以更好地捕捉桨尖涡等流动细节。对于频繁的自适应过程中产生的大量重复点和无用点,采用了高效的交替数字树算法(Alternating digital tree,ADT)和标记-删除-移动算法(Mark,delete,move,MDM)进行删除,节约了不必要的存储。针对格心格式的求解器,采用了基于梯度的网格间插值方式,简化了网格间数值传递的复杂性,同时不降低求解器的精度。对CaradonnaTung旋翼悬停算例和HLISHAPE 7A旋翼悬停算例进行了模拟验证,计算值与实验值吻合,表明本文建立的方法具有良好的鲁棒性和有效性。最后,与未采用自适应时求解器对桨尖涡的捕捉效果进行了对比,结果表明本文所采用的方法可以明显地提高求解器对桨尖涡的捕捉。

Computing Flows Around Rotor by Using Time-Depended Adaptive Grid Based on Unstructured-Cartesian Overset Mesh System

In order to deal with the fluid simulation of the rotor, an algorithm for overset mesh system based on unstructured grids is built. It is suitable for the CFD solver of cell-centred scheme. To capture the blade vortex, the Cartesian grid is adapted all the time during the fluid simulation of the rotor. Alternating digital tree (ADT) algorithm and make, delete, move (MDM) algorithm are used to delete amounts of unused and repeated points generated in every adaptive process. An interpolation method based on gradient is adopted, which greatly simplifies the complexity of the numerical transmission between grids and can satisfy the requirement of accuracy. For Caradonna&Tung and HLISHAPE 7A rotors, calculation in hovering state is conducted and the results are corresponding with the experimental data. It indicates that the algorithm is robust and efficient. After that, the results about capturing blade tip vortex are compared with the simulation without utilizing adaptive gird. It shows that the algorithm can significantly improve the resolution of capturing the blade tip vortex.