Boundary-layer receptivity of Mach 7.99 flow over a blunt cone to free-stream acoustic waves
Boundary-layer receptivity of Mach 7.99 flow over a blunt cone to free-stream acoustic waves
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DOI：
10.1017/s0022112006009293
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发表时间：
2006-06-10
影响因子：
3.7
通讯作者：
Ma, YB
中科院分区：
文献类型：
--
作者：
Zhong, XL;Ma, YB
感受性现象是环境扰动最初进入边界层并产生扰动波的过程，是涉及高超声速层流-湍流转变的一种重要但尚未被很好理解的机制之一。本文对7.99马赫的轴对称绕7度半角钝锥流动的弱自由流快声波的感受性进行了数值模拟研究。在高超声速绕锥边界层流动中，弯曲激波和熵层的存在显著改变了自由流扰动的感受性过程。在本研究中，定常和非定常流动解均采用五阶激波拟合差分格式求解完整的Navier-Stokes方程，该格式能够准确地考虑弓形激波/自由流扰动的影响。将现有的定常基流数值计算结果与已有的实验和数值计算结果进行了比较。此外，还利用简正波的线性稳定性分析来识别由强迫自由流快声波产生的边界层扰动的主要分量。结果表明，尽管Mack模在锥面上可能是不稳定的，但自由流快声波在锥面的早期区域并不激发第一模和第二模不稳定波。取而代之的是，第二模式激励在第二模式分支I中性点的下游。第二模激励的延迟是因为高超声速边界层感受性是由一个两步共振相互作用过程控制的：(I)强迫波与前缘区附近稳定的边界层波I模之间的共振相互作用；以及(Ii)诱导稳定模I与下游不稳定第二Mack模之间的共振相互作用。相同的感受性机制也解释了当前感受性过程没有产生第一MACK模式分量的结果，因为在快速声波和第一MACK模式之间没有共振相互作用。
The receptivity phenomenon, which is the process of environmental disturbances initially entering the boundary layers and generating disturbance waves, is one of the important but not well understood mechanisms involving laminar-turbulent transition of hypersonic flows. This paper presents a numerical simulation study of the receptivity to weak free-stream fast acoustic waves for a Mach 7.99 axisymmetric flow over a 7 degrees half-angle blunt cone. In hypersonic boundary-layer flow over a blunt cone, the process of receptivity to free-stream disturbances is altered considerably by the presence of a bow shock and an entropy layer. In the present study, both steady and unsteady flow solutions are obtained by computing the full Navier-Stokes equations with a fifth-order shock-fitting finite-difference scheme, which is able to account for the effects of bow-shock/free-stream-disturbance interaction accurately. The current numerical results for the steady base flow are compared with previous experimental and numerical results. In addition, a normal-mode linear stability analysis is used to identify the main components of boundary-layer disturbances generated by forcing free-stream fast acoustic waves. It is found that neither the first mode nor the second-mode instability waves are excited by free-stream fast acoustic waves in the early region along the cone surface, although the Mack modes can be unstable there. Instead, the second mode is excited downstream of the second-mode Branch I neutral stability point. The delay of the second-mode excitation is because the hypersonic boundary-layer receptivity is governed by a two-step resonant interaction process: (i) resonant interactions between the forcing waves and a stable boundary-layer wave mode I near the leading-edge region; and (ii) resonant interactions between the induced stable mode I and the unstable second Mack mode downstream. The same receptivity mechanism also explains the results that no first Mack mode components are generated by the current receptivity process because there is no resonant interaction between fast acoustic waves and the first Mack mode.