凹腔对大幅值正激波受迫振荡及其非线性特征作用机理研究

Normal shock-wave/boundary-layer interaction is a typical flow problem in the supersonic intake of a ramjet engine. The large-amplitude forced normal shock-wave oscillation, which is induced by the downstream strong disturbing pressure wave propagation, may trigger the undesirable impact on the intake aerodynamic performance and structural safety. In the previous study, the possibility of mitigating the large-amplitude forced normal shock-wave oscillation with a concave cavity has been revealed. However, the mechanism of the concave cavity on the large-amplitude forced normal shock-wave oscillation, the secondary normal shock-wave and the bifurcation of separation pocket and other nonlinear features has not been interpreted clearly. Based on the theoretical analysis, the numerical simulation and the wind-tunnel experiment, this project will take the description of the interaction between the propagating downstream strong disturbing pressure wave and the normal shock-wave/boundary-layer interaction as a breakthrough, and solve two scientific problems, i.e. the causes of the previous nonlinear features, and the mechanism of the concave cavity on the large-amplitude forced normal shock-wave oscillation and its nonlinear features. Tow topics are included: (1) describing the propagation of downstream strong disturbing pressure wave, and its interaction with the normal shock-wave/boundary-layer interaction, and exploring the factors and formation conditions of the nonlinear features; (2) modeling the correlation between the concave cavity parameters and the forced normal shock-wave oscillation amplitude, and discovering the influence mechanism of the concave cavity. This project will help to enrich the content of the forced normal shock-wave oscillation, and provide theoretical supports for improving the performance of the supersonic intake of a ramjet engine.

正激波-边界层干扰是亚燃冲压发动机超声速进气道内的典型流动现象。下游强扰动压力波传播引起的大幅值正激波受迫振荡对进气道气动性能和结构安全性造成不利影响。前期研究探索了凹腔结构抑制大幅值正激波受迫振荡的可行性。凹腔结构对大幅值正激波受迫振荡，以及二次正激波和分离涡运动分叉等非线性特征的作用机理尚不明晰。本项目采用理论分析、数值模拟和风洞实验，以精细刻画扰动压力波与正激波-边界层干扰之间相互作用为突破口，解决上述非线性特征的形成机理，和凹腔对大幅值正激波受迫振荡及非线性特征的作用机理这两个科学问题。具体内容涵括两个方面：(1)精细刻画下游强扰动压力波传播，及其与正激波-边界层干扰之间的相互作用，探索非线性特征的影响因素和形成条件；(2)建立凹腔结构与正激波受迫振荡幅值之间的关联，探究凹腔结构的影响规律。本项目研究有助于丰富正激波受迫振荡研究内容，支撑提升冲压发动机超声速进气道性能。

超声速进气道是冲压发动机的关键部件之一。其内的大幅值激波受迫振荡一方面导致发动机性能波动，另一方面引起结构振动，甚至疲劳破坏。项目针对大幅值激波受迫振荡问题，提出了凹腔抑制激波受迫振荡的流动控制方法，开展了理论分析和数值仿真研究工作，探究了激波受迫振荡过程中的非线性特征（即二次激波和分离涡运动分叉）的形成机理，阐明了凹腔对激波受迫振荡的抑制机理。二次激波的形成机理主要受激波的波后膨胀影响。大幅值激波运动诱发了较大的流动分离泡，并挤压激波的波后通流流道，形成渐缩形状的等效通流流道，使得气流在其内膨胀并加速，导致了二次激波。分离涡运动分叉的形成机理与出口扰动压缩波的传播有关。出口扰动压缩波由背压增加引起，并向上游传播，使得局部静压增加。但随着背压降低，扰动压缩波形成了局部静压峰值，既不能随激波向上游运动，又不能维持在原有位置，只能以分离涡形式向下游运动。凹腔对激波受迫振荡的作用机理可通过运动激波加功阐明。运动激波向周围气流做功，使得气流总压增加。背压扰动给定时，其做功能力恒定。凹腔结构形成了强激波，在运动激波加功功率恒定的条件下，强激波的运动速度较小，从而抑制了激波受迫振荡幅值。本项目有助于拓宽激波-边界层干扰的研究内容，加深对大幅值激波受迫振荡非线性特征的理解，支撑提升冲压发动机超声速进气道的性能。