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开式凹腔作为超燃冲压发动机中增加掺混和稳焰的装置,其流动稳定性的研究对深入理解凹腔增加掺混和稳焰机理以及凹腔的设计有着重要的学术意义和工程应用价值.基于大涡模拟方法对超燃冲压发动机开式凹腔流动进行数值模拟,分别采用动力学模态分解(dynamic mode decomposition,DMD)和本征正交分解方法(proper orthogonal decomposition,POD)对自激振荡流动进行稳定性分析.DMD方法可准确提取凹腔的振荡频率,与Rossiter模型以及压力脉动FFT分析得到的频率吻合较好,且DMD中对应Rossiter前3阶频率的模态在流动中的主导作用顺序也与FFT分析结果一致,自激振荡中RossiterⅢ模态占据主导作用,同时DMD方法对Rossiter 3阶以上模态频率的预测能力明显强于FFT分析方法.在对低频的提取方面,DMD方法比Rossiter模型更具有优势.与前6阶Rossiter模态对应DMD模态均缓慢收敛,主要表现为剪切层中的分离涡结构和中部及下游区域中的涡结构.前3阶不稳定模态中的分离涡结构主要集中在中部剪切层以及后缘附近区域.POD方法中较少的模态包含流场绝大部分的能量.但是,通过POD方法提取的模态频率在分辨率上效果不佳,提取到最低频率为Rossiter 3阶模态对应的频率,且模态中均存在次频,次频与主频之间的耦合导致模态的形态相差较大.另外,与DMD方法相比POD方法无法判断所提取的模态的稳定性.
Open cavity as scramjet engine to increase mixing and steady flame device, the flow stability of the study to understand the understanding of the cavity to increase mixing and stable flame mechanism and the design of the cavity has important academic significance and engineering application value. A large eddy simulation method was used to simulate the open cavity flow in a scramjet engine. Dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) And the stability of oscillatory flow was analyzed.DMD method can accurately extract the oscillation frequency of the cavity, which is in good agreement with the Rossiter model and the pressure pulsation FFT analysis, and the DMD corresponds to the first three modes of Rossiter frequency dominant in the flow The order of action is also consistent with the result of FFT analysis. The Rossiter Ⅲ mode plays a dominant role in self-oscillation, and the prediction ability of DMD method over the third order mode of Rossiter is significantly stronger than that of FFT analysis. In terms of low frequency extraction, Which is more advantageous than the Rossiter model.The DMD modes corresponding to the first six order Rossiter modes all converge slowly, Vortex structures in the vortex structure and in the middle and downstream regions.The vortex structures in the first three unstable modes are mainly concentrated in the middle shear layer and the vicinity of the trailing edge.The less modalities in the POD method include the flow field Most of the energy.However, the modal frequencies extracted by the POD method are ineffective in resolution, and the lowest frequency is extracted as the frequency corresponding to the third order mode of Rossiter, and the modes have sub-frequency, sub-frequency and main frequency The coupling between the frequencies leads to a large difference in modal morphology. In addition, the POD method can not judge the stability of the extracted modal compared with the DMD method.