飞行器大攻角复杂流动的POD和DMD对比分析

基于非结构/混合网格、耗散自适应2阶混合格式以及脱体涡模拟（detached eddy simulation，DES）方法开展了现代战斗机模型复杂分离流动的数值模拟，并与有限的平均气动力试验数据进行了对比，结果表明计算具有合理性，在此基础上进一步应用本征正交分解（proper orthogonal decomposition，POD）和动力学模态分解（dynamic mode decomposition，DMD）方法对数值模拟流场的非定常特性进行了对比分析.研究表明飞行器背风区流场由一对边条涡的螺旋运动主导，旋涡破裂前在横向空间截面上流场是中性稳定的，同时主涡核的运动是多频耦合的.POD和DMD的对比分析则表明:两者模态配对的方式不同，但主要模态之间具有一定相关性；POD模态中包含多种频率的运动，而且能量较集中于主模态，流场重构效率更高；DMD则将流场的主要特征运动提取为一些单频模态的组合，同时能够给出模态的稳定性. 

POD and DMD Analysis of Complex Separation Flows over a Aircraft Model at High Angle of Attack

The complex separation flow field over a modern fighter model was simulated by using an unstructured/hybrid grid based detached eddy simulation (DES) solver with an adaptive dissipation second-order hybrid scheme in this paper. The comparison with experimental data which is limited to averaged aerodynamic coefficients shows that the simulation results are reasonable, then the unsteady properties of DES flow field were investigated in detail by proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) methods. The study indicates that the flow field in leeward side is dominated by a pair of strake vortexes with spiral motions, before the vortex breakdown taking place the flow is neutrally stable in cross-section plane and the main vortex motions contain multiple frequencies. The comparison of POD and DMD shows that though the modes of the two methods can be made pairs in different ways, there are some relevance between the main modes of the two methods. It also can be found that multiple frequencies are contained in each POD modes and mode energies are more concentrated in the main POD modes, so the flow field reconstruction with POD modes is more efficient. While the DMD method resolves the main properties of flow field into a series of modes which are very close to harmonic motions and the stability analysis of these modes can be given.