High-speed turbulent boundary layers of a dense gas (PP11) and a perfect gas (air) over flat plates are investigated by means of direct numerical simulations and large eddy simulations. The thermodynamic conditions of the incoming flow are chosen to highlight dense gas effects, and laminar-to-turbulent transition is triggered by suction and blowing. In the paper, the behavior of the fully developed turbulent flow region is investigated. Due to the low characteristic Eckert number of dense gas flows ( $$\hbox {Ec}=U_\infty ^2/c_{p,\infty }T_\infty$$ Ec = U ∞ 2 / c p , ∞ T ∞ ), the mean velocity profiles are largely insensitive to the Mach number and very close to the incompressible case even at high speeds. Second-order velocity statistics are also weakly affected by the flow Mach number and the velocity spectra are characterized by a secondary peak in the outer region of the boundary layer because of the higher local friction Reynolds number. Despite the incompressible-like velocity and Reynolds-stress profiles, the strongly non-ideal thermodynamic and transport-property behavior of the dense gas results in unconventional distributions of the fluctuating thermo-physical quantities. Specifically, density and viscosity fluctuations reach a peak close to the wall, instead of vanishing as in perfect gas flows. Additionally, dense gas boundary layers exhibit higher values of the fluctuating Mach number and velocity divergence and a larger dilatational-to-solenoidal dissipation ratio in the near-wall region, which represents a major deviation from high-Mach-number perfect gas boundary layers. Other significant deviations are represented by the more symmetric probability distributions of fluctuating quantities such as the density and velocity divergence, due to the more balanced occurrence of strong expansion and compression events.

中文翻译：

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稠密气体高速湍流边界层的数值研究

通过直接数值模拟和大涡模拟研究了平板上致密气体 (PP11) 和理想气体 (空气) 的高速湍流边界层。选择进入流的热力学条件以突出稠密气体效应，层流到湍流的转变由吸入和吹气触发。在本文中，研究了完全发展的湍流区域的行为。由于稠密气流的特征埃克特数较低 ( $$\hbox {Ec}=U_\infty ^2/c_{p,\infty }T_\infty$$ Ec = U ∞ 2 / cp , ∞ T ∞ ) ，平均速度分布在很大程度上对马赫数不敏感，即使在高速下也非常接近不可压缩的情况。二阶速度统计也受到流动马赫数的微弱影响，并且速度谱的特征在于边界层外部区域的二次峰，因为局部摩擦雷诺数较高。尽管具有不可压缩的速度和雷诺应力分布，但稠密气体的强烈非理想的热力学和传输特性导致了波动的热物理量的非常规分布。具体而言，密度和粘度波动会在靠近壁面处达到峰值，而不是像完美的气流那样消失。此外，密集的气体边界层在近壁区域表现出更高的马赫数波动值和速度发散以及更大的膨胀与螺线管耗散比，这代表了与高马赫数完美气体边界层的主要偏差。由于强膨胀和压缩事件的发生更加平衡，其他显着偏差由波动量的更对称概率分布表示，例如密度和速度发散。