高背压进气道中内外流耦合作用的大涡模拟

采用大涡模拟研究了出口堵塞比为50.8%的轴对称进气道流动，重点考察了内外流耦合作用下流动的非定常特性。采用国家数值风洞（NNW）工程仿真软件进行数值模拟，得到的壁面平均压力、瞬时压力分布与试验数据符合良好。分析表明：为匹配出口背压，进气道在喉道区域形成激波串结构，使内流道流场分为上游超声速区、中部激波串区以及下游亚声速区；在激波串区，剧烈的逆压梯度产生了分离激波、激波串、分离区及分离剪切层等复杂结构；伴随着激波串运动和边界层大尺度分离，进气道壁面压力出现宽频脉动特征。脉动压力的时空分布表明：内流道脉动压力以扰动波的形式传播，为此建立的声反馈模型能较好地预测亚声速区的主导频率。相关性分析表明：激波串运动受上下游流动耦合作用，其中，频率为St=0.7的运动主要受上游流动影响，频率为St=0.9的运动主要受下游压力扰动波影响。

Large-eddy simulation of external and internal coupling flow in high back pressure inlet

The airflow in an axisymmetric inlet with an outlet throttling ratio of 50.8% has been investigated using large eddy simulation, primarily focusing on the unsteady characteristics of the external and internal coupling oscillatory flow. The simulation is based on the software of National Numerical Windtunnel (NNW) Project. Contributions of the averaged wall pressure and its fluctuating part have been validated against experimental measurements. Various fundamental phenomena, including the flow structures, unsteady shock waves, and fluctuating pressure have been studied systematically. It is found that the shock train is induced in the throat region to match the backpressure, and accordingly three typical flow regions are classified as the supersonic region, shock train region, and subsonic region. Coupling dynamics between the shock/shear-layer/separated boundary layer are formed in the shock train region as a result of the adverse pressure gradient. With the quasi-periodic unsteady fluid motions in the shock train region, the fluctuating pressure exhibits a broadband spectral feature. The temporal and spatial distributions of the fluctuating pressure are analyzed, which indicates that the fluctuating pressure propagates in the subsonic region in a form of disturbance wave. A feedback model is proposed giving a reasonable prediction of the dominant frequency in the downstream of shock train. Based on the correlation analysis, it is demonstrated that the unsteady motions of the shock train is influenced by the coupling of the upstream and downstream flows. Specifically, it contains an unsteady motion of frequency St=0.7 which is a signature of the upstream flow, and another of frequency St=0.9 that is a signature of the downstream flow.