Perturbation and initial Reynolds number effects on transition attainment of supercritical, binary, temporal mixing layers
Perturbation and initial Reynolds number effects on transition attainment of supercritical, binary, temporal mixing layers
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扰动和初始雷诺数对超临界、二元、时间混合层的过渡实现的影响
DOI：
10.1016/j.compfluid.2003.10.001
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发表时间：
2004
影响因子：
2.8
通讯作者：
J. Bellan
中科院分区：
文献类型：
--
作者：
N. Okong'o;J. Bellan
二维和三维（2D和3D）的数值模拟进行庚烷/氮（crackically）的超临界混合层初始扰动在不同的波长，包括最不稳定的不可压缩波长。进行模拟与展向（和流向，三维）的扰动，在文献中（直接数值模拟湍流）叠加在平均流，和域的长度是扰动波长的四倍。进行了二维模拟，以确定具有最短的不稳定波长从线性无粘稳定性分析获得的扰动是不稳定的粘性非线性流。对于3D层，扰动的目的是加速层的增长，以达到过渡雷诺数，以及产生类似于在空间混合层中观察到的结构。3D模拟的目的是确定在不同波长扰动混合层是否会影响到湍流的过渡，而不是像以前那样在最不稳定的不可压缩波长扰动混合层。特别是，我们询问是否扰动层在较小的波长，这需要一个较小的域，将减少计算时间。结果表明，只要扰动波长大于二维线性无粘稳定性分析所确定的最短不稳定波长，且初始雷诺数随扰动波长的减小而成比例地增大，就可以在不同的扰动波长下实现转捩。由此获得的过渡态显示不同的动态和混合特性，并显示出强烈的偏离完美气体，理想的混合物。较小的波长扰动被发现有类似的过渡实现的计算要求。
Two- and three-dimensional (2D and 3D) numerical simulations are performed for a heptane/nitrogen (thermodynamically) supercritical mixing layer initially perturbed at different wavelengths, including the most unstable incompressible wavelength. Simulations are performed with spanwise (and streamwise, for 3D) perturbations available in the literature (for direct numerical simulations of turbulent flow) superimposed on the mean flow, and the domain length is four times the perturbation wavelength. The 2D simulations are undertaken to ascertain that perturbations having the shortest unstable wavelength obtained from a linear inviscid stability analysis are unstable for the viscous non-linear flow. For 3D layers, the purpose of the perturbations is to accelerate the growth of the layer in order to attain transitional Reynolds numbers, as well as to generate structures similar to those that have been observed in spatial mixing layers. The goal of the 3D simulations is to ascertain whether perturbing the mixing layer at different wavelengths, in contrast to the most unstable incompressible wavelength as had previously been done, will affect the transition to turbulence. In particular, we inquire whether perturbing the layer at smaller wavelengths, which requires a smaller domain, will reduce the computational time. It is found that transition can be obtained at different perturbation wavelengths, provided that they are longer than the shortest unstable wavelength as determined by the 2D linear inviscid stability analysis, and provided that the initial Reynolds number is proportionally increased as the wavelength is decreased. The transitional states thus obtained display different dynamic and mixture characteristics, and show strong departures from perfect gas, ideal mixtures. The smaller wavelength perturbations were found to have similar computational requirements for transition attainment.