Transition mechanisms in cross-flow-dominated hypersonic flows with free-stream acoustic noise
Transition mechanisms in cross-flow-dominated hypersonic flows with free-stream acoustic noise
复制标题
DOI：
10.1017/jfm.2020.346
复制
发表时间：
2020-06
影响因子：
3.7
通讯作者：
Adriano Cerminara;N. Sandham
中科院分区：
文献类型：
--
作者：
Adriano Cerminara;N. Sandham
在高速流动中，向湍流的转变是由多个参数决定的，其中许多参数还没有被完全理解，这导致了开发基于物理的预测方法的问题。在这篇贡献中，我们比较了未扫描和扫描前沿暴露在自由流声干扰下的配置中的过渡机制。直接数值模拟在马赫数为6的情况下进行，具有相同的自由流噪声，包括快或慢的声扰动，具有两种不同的幅度，以探索接受性和转换的线性和非线性方面。对于未扫描的配置，感受性遵循一种既定的机制，该机制涉及快速声学扰动与边界层模式的同步。在高强迫振幅下，相变通过条纹的形成和最终的破裂来进行。在后掠情况下，条纹诱导的转变过程被前缘区域中横流不稳定性的存在所修正。线性稳定性分析证实了横流模式的存在以及较弱的第一和第二模式波的存在。快型和慢型的强迫都独立地激发了一种不寻常的转折机制，与后掠前缘后面的横流不稳定性或未后掠情况下的非线性诱导的横流不稳定性相比，前者涉及的条纹要窄得多。在观察到的转折过程中，横流模式导致了一层薄薄的流向涡度，并在高跨度波数扰动的影响下破裂。这些扰动首先出现在前沿区域。
Transition to turbulence in high-speed flows is determined by multiple parameters, many of which are not fully understood, leading to problems in developing physics-based prediction methods. In this contribution, we compare transition mechanisms in configurations with unswept and swept leading edges that are exposed to free-stream acoustic disturbances. Direct numerical simulations are run at a Mach number of six with the same free-stream noise, consisting of either fast or slow acoustic disturbances, with two different amplitudes to explore the linear and nonlinear aspects of receptivity and transition. For the unswept configuration, receptivity follows an established mechanism involving synchronisation of fast acoustic disturbances with boundary-layer modes. At high forcing amplitudes, transition proceeds via the formation of streaks and their eventual breakdown. In the swept case, the process of streak-induced transition is modified by the presence of a cross-flow instability in the leading-edge region. Linear stability analysis confirms the presence of a cross-flow mode as well as weaker first and second mode waves. Both fast and slow types of forcing independently stimulate an unusual transition mechanism involving significantly narrower streaks than those arising from the cross-flow instability behind the swept leading edge or those induced nonlinearly in the unswept case. In the observed transition process, the cross-flow mode leads to a thin layer of streamwise vorticity that breaks up under the influence of high spanwise wavenumber disturbances. These disturbances first appear in the leading-edge region.