A study of compressibility effects in the high-speed turbulent shear layer using direct simulation
A study of compressibility effects in the high-speed turbulent shear layer using direct simulation
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DOI：
10.1017/s0022112001006978
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发表时间：
2002-01
影响因子：
3.7
通讯作者：
C. Pantano;S. Sarkar
中科院分区：
文献类型：
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作者：
C. Pantano;S. Sarkar
湍流剪切层的直接模拟进行了亚音速到超音速马赫数。充分发展的湍流，实现与符合实验室实验的平均速度和湍流强度的配置文件。随着对流马赫数Mc值的增加，剪切层的厚度增长率有很大的减小。与以前的调查一致，它被发现，归一化的压力-应变项随着增加Mc，这导致抑制能量转移从流向横流波动，减少湍流生产中观察到的DNS，最后，减少湍流水平以及剪切层的增长率降低。从压力波动方程出发，在DNS的支持下进行了分析，结果表明，压力-应变项随马赫数的增加而单调减小。的梯度马赫数，这是声学时间尺度的流动畸变的时间尺度的比率，明确的分析表明，是关键的数量，确定减少的压力-应变项在可压缩剪切流。物理解释是，在可压缩流中的有限声速在压力信号从一个点到相邻点的传输中引入了有限的时间延迟，并且由此产生的去相关性的增加导致压力-应变相关性的降低。研究了湍流强度与对流马赫数的关系。结果表明，随着Mc的增加，所有组分均减小，剪切应力也减小。DNS还用于研究在高速情况下由密度比s = ρ2/ρ1参数化的不同自由流密度的影响。结果发现，涡度厚度的时间增长率的变化小于动量厚度增长率的变化。动量厚度增长率随着偏离参考情况s = 1的增加而显著减小。剪切应力的峰值uv作为s的函数仅显示出很小的变化。剪切层的分割流线被观察到移动到低密度流。进行了分析，以解释这种转变和随之而来的动量厚度增长率的减少。
Direct simulations of the turbulent shear layer are performed for subsonic to supersonic Mach numbers. Fully developed turbulence is achieved with profiles of mean velocity and turbulence intensities that agree well with laboratory experiments. The thickness growth rate of the shear layer exhibits a large reduction with increasing values of the convective Mach number, Mc. In agreement with previous investigations, it is found that the normalized pressure–strain term decreases with increasing Mc, which leads to inhibited energy transfer from the streamwise to cross-stream fluctuations, to the reduced turbulence production observed in DNS, and, finally, to reduced turbulence levels as well as reduced growth rate of the shear layer. An analysis, based on the wave equation for pressure, with supporting DNS is performed with the result that the pressure–strain term decreases monotonically with increasing Mach number. The gradient Mach number, which is the ratio of the acoustic time scale to the flow distortion time scale, is shown explicitly by the analysis to be the key quantity that determines the reduction of the pressure–strain term in compressible shear flows. The physical explanation is that the finite speed of sound in compressible flow introduces a finite time delay in the transmission of pressure signals from one point to an adjacent point and the resultant increase in decorrelation leads to a reduction in the pressure–strain correlation. The dependence of turbulence intensities on the convective Mach number is investigated. It is found that all components decrease with increasing Mc and so does the shear stress. DNS is also used to study the effect of different free-stream densities parameterized by the density ratio, s = ρ2/ρ1, in the high-speed case. It is found that changes in the temporal growth rate of the vorticity thickness are smaller than the changes observed in momentum thickness growth rate. The momentum thickness growth rate decreases substantially with increasing departure from the reference case, s = 1. The peak value of the shear stress, uv, shows only small changes as a function of s. The dividing streamline of the shear layer is observed to move into the low-density stream. An analysis is performed to explain this shift and the consequent reduction in momentum thickness growth rate.