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Study of compressible turbulent flows in supersonic environment by large-eddy simulation.

机译：用大涡模拟研究超音速环境中的可压缩湍流。

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摘要

The numerical resolution of turbulent flows in high-speed environment is of fundamental importance but remains a very challenging problem. First, the capture of strong discontinuities, typical of high-speed flows, requires the use of shock-capturing schemes, which are not adapted to the resolution of turbulent structures due to their intrinsic dissipation. On the other hand, low-dissipation schemes are unable to resolve shock fronts and other sharp gradients without creating high amplitude numerical oscillations. Second, the nature of turbulence in high-speed flows differs from its incompressible behavior, and, in the context of Large-Eddy Simulation, the subgrid closure must be adapted to the modeling of compressibility effects and shock waves on turbulent flows.;The developments described in this thesis are two-fold. First, a state of the art closure approach for LES is extended to model subgrid turbulence in compressible flows. The energy transfers due to compressible turbulence and the diffusion of turbulent kinetic energy by pressure fluctuations are assessed and integrated in the Localized Dynamic ksgs model. Second, a hybrid numerical scheme is developed for the resolution of the LES equations and of the model transport equation, which combines a central scheme for turbulent resolutions to a shock-capturing method. A smoothness parameter is defined and used to switch from the base smooth solver to the upwind scheme in regions of discontinuities.;It is shown that the developed hybrid methodology permits a capture of shock/turbulence interactions in direct simulations that agrees well with other reference simulations, and that the LES methodology effectively reproduces the turbulence evolution and physical phenomena involved in the interaction. This numerical approach is then employed to study a problem of practical importance in high-speed mixing. The interaction of two shock waves with a high-speed turbulent shear layer as a mixing augmentation technique is considered. It is shown that the levels of turbulence are increased through the interaction, and that the mixing is significantly improved in this flow configuration. However, the region of increased mixing is found to be localized to a region close to the impact of the shocks, and that the statistical levels of turbulence relax to their undisturbed levels some short distance downstream of the interaction.;The present developments are finally applied to a practical configuration relevant to scramjet injection. The normal injection of a sonic jet into a supersonic crossflow is considered numerically, and compared to the results of an experimental study. A fair agreement in the statistics of mean and fluctuating velocity fields is obtained. Furthermore, some of the instantaneous flow structures observed in experimental visualizations are identified in the present simulation. The dynamics of the interaction for the reference case, based on the experimental study, as well as for a case of higher freestream Mach number and a case of higher momentum ratio, are examined. The classical instantaneous vortical structures are identified, and their generation mechanisms, specific to supersonic flow, are highlighted. Furthermore, two vortical structures, recently revealed in low-speed jets in crossflow but never documented for high-speed flows, are identified during the flow evolution.
机译：高速环境中湍流的数值分辨率至关重要，但仍然是一个非常具有挑战性的问题。首先，捕获强不连续点（通常是高速流）需要使用震荡捕获方案，该方案由于其固有的耗散性而不适用于湍流结构的分辨率。另一方面，低耗散方案无法解决激波锋面和其他急剧的梯度，而不会产生高振幅的数值振荡。其次，高速流动中湍流的性质与其不可压缩的行为不同，在大涡模拟的背景下，子网格的封闭必须适应湍流中可压缩性效应和冲击波的建模。本文中的描述有两个方面。首先，用于LES的现有封闭方法已扩展到可压缩流中的亚网格湍流模型。评估由于可压缩湍流引起的能量转移以及由于压力波动而引起的湍动能扩散，并将其整合到局部动态ksgs模型中。其次，开发了一种混合数值格式，用于求解LES方程和模型传递方程，该方法将湍流分辨率的中心方案与震荡捕获方法结合在一起。定义了平滑度参数，并将其用于在不连续区域中从基本平滑求解器切换到迎风方案。表明，开发的混合方法可以捕获直接模拟中的冲击/湍流相互作用，从而与其他参考模拟非常吻合，并且LES方法有效地再现了相互作用中涉及的湍流演化和物理现象。然后，采用这种数值方法来研究高速混合中具有实际重要性的问题。作为混合增强技术，考虑了两个冲击波与高速湍流剪切层的相互作用。结果表明，通过相互作用增加了湍流水平，并且在这种流动配置下混合得到了显着改善。然而，发现混合增加的区域位于靠近冲击影响的区域，并且湍流的统计水平在相互作用的下游很短距离内松弛到其不受干扰的水平。与超燃喷射相关的实用配置。从数值上考虑了将超声射流正常喷射到超声速横流中，并将其与实验研究的结果进行了比较。在均值和波动速度场的统计中获得了公平的协议。此外，在本仿真中还确定了在实验可视化中观察到的一些瞬时流动结构。基于实验研究，针对参考案例以及较高的自由流马赫数和较高的动量比的案例，研究了相互作用的动力学。确定了经典的瞬时涡旋结构，并着重介绍了它们的产生机制，这些机制是超声速所特有的。此外，在流动演化过程中，发现了两个涡流结构，这些涡流结构最近在横流的低速射流中发现，但从未记录过高速流。

著录项

  • 作者

    Genin, Franklin.;

  • 作者单位

    Georgia Institute of Technology.;

  • 授予单位 Georgia Institute of Technology.;
  • 学科 Engineering Aerospace.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 234 p.
  • 总页数 234
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 航空、航天技术的研究与探索;
  • 关键词

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