热化学非平衡效应对湍流边界层的影响
Thermochemical non-equilibrium effects on turbulent boundary layers
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中文总结 AI 辅助
本研究通过DNS模拟高马赫数湍流边界层，揭示热化学非平衡效应改变近壁温度场与化学反应，提出复合广义雷诺类比，为大涡模拟提供亚格子闭合项，深化了高马赫湍流的热化学耦合规律认知。
中文摘要 AI 辅助
本研究采用直接数值模拟（DNS），对高马赫数湍流边界层在三种流动条件下进行研究：低焓量热完全气体、两种高温气体混合物，其中一种处于化学非平衡状态，另一种处于完全热化学非平衡状态。研究考察了双温度模型对湍流统计量的影响，以及湍流、化学和振动能量之间的耦合作用。研究发现，高焓效应几乎不改变速度统计量，但会显著改变近壁温度场；近壁区域出现明显的平动-转动温度与振动温度的差异，使得传统广义雷诺类比（GRA）对振动温度不再适用。为解决该问题，本文提出一种新型复合广义雷诺类比，将基于振动温度的关系与标准公式相结合，其与DNS数据吻合良好。热非平衡效应还会显著改变近壁化学反应：抑制O₂解离，同时促进NO生成，导致O的平均浓度降低，NO的平均浓度升高。对湍流-化学、湍流-振动弛豫相互作用项的谱分析表明，在含能尺度下，温度波动主导这些流动量。通过对所得谱函数积分，本文评估了大涡模拟的亚格子闭合项：在小滤波尺度下，互相关项的量级与温度波动项相当或超过后者；而在大滤波尺度下，温度波动项占主导地位。
英文摘要
This investigation employs direct numerical simulations (DNS) of high-Mach-number turbulent boundary layers under three flow conditions: a low-enthalpy calorically perfect gas, and two high-temperature gas mixtures, one in chemical non-equilibrium state and the other in full thermochemical non-equilibrium state. The influences of the two-temperature model on turbulent statistics and the coupling among turbulence, chemistry, and vibrational energy are examined. It is found that while high-enthalpy effects leave the velocity statistics virtually unchanged, they dramatically modify the near-wall temperature field. A pronounced disparity between the translational-rotational temperature and the vibrational temperature arises in the near-wall region, rendering the conventional generalized Reynolds analogy (GRA) inaccurate for vibrational temperature. To remedy this, a novel composite GRA is proposed that blends a vibrational-temperature-based relation with the standard formulation, and it demonstrates excellent agreement with the DNS data. Thermal non-equilibrium effects also substantially alter near-wall chemical reactions: it suppresses O2 dissociation while promoting NO formation, leading to a corresponding decrease and increase in the mean concentrations of O and NO, respectively. Spectral analyses of the turbulence-chemistry and turbulence-vibrational relaxation interaction terms reveal that temperature fluctuations dominate these flow quantities at energy-containing scales. Integrating the resulting spectral functions, we evaluate subgrid-scale closure terms for large-eddy simulation. At small filtering scales, the magnitude of the cross-correlation term rivals or exceeds that of the temperature fluctuation term, whereas the temperature fluctuation term becomes dominant at larger filter scales.
