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arXiv 2402.10328physics.flu-dyn
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逆压梯度湍流边界层近壁区的湍流活动

Turbulent activity in the near-wall region of adverse pressure gradient turbulent boundary layers

Taygun R. Gungor, Yvan Maciel, Ayse G. Gungor

AI总结:

本文通过对比两个直接数值模拟数据库,研究了逆压梯度湍流边界层中外层湍流对内层结构和能量传递的影响,发现内层湍流能自我维持且能量传递机制不随速度亏损改变。

摘要:

为了理解外层湍流对内层结构和能量传递机制的影响,本文研究了两个直接数值模拟(DNS)数据库。第一个DNS数据库是Gungor等人(2022)的非平衡逆压梯度(APG)湍流边界层(TBL)。其雷诺数和内层压力梯度参数分别达到8000和10以上。形状因子在1.4到3.3之间变化,表明流动具有不同的速度亏损情况。第二个数据库与第一个流动相同,但该流动中的外层湍流被人工消除。湍流在0.15倍局部边界层厚度以上被移除。在分析中,我们选择了四个具有小、中、大和超大速度亏损的流向位置。我们比较了雷诺应力的法向分布,以及能量、产生和压力应变的两点相关性和谱分布。结果表明,无论速度亏损或压力梯度如何,当外层湍流不存在时,内层湍流能够自我维持。两种情况的两点相关性均表明,外层大尺度结构显著影响内层结构。相关等值线的流向范围以压力-粘性单位为尺度。这显示了压力梯度对内层结构影响的重要性。谱分布表明,无论速度亏损如何,内层的能量传递机制可能是相同的,这表明近壁循环可能甚至存在于超大亏损APG TBLs中,尽管其内层的平均剪切远低于小亏损APG TBLs。

英文摘要:

Two direct numerical simulation (DNS) databases are investigated to understand the effect of the outer-layer turbulence on the inner layer's structures and energy transfer mechanisms. The first DNS database is the non-equilibrium adverse-pressure-gradient (APG) turbulence boundary layer (TBL) of Gungor et al. (2022). Its Reynolds number and the inner-layer pressure gradient parameter reach above 8000 and 10, respectively. The shape factor spans between 1.4 and 3.3, which indicates the flow has various velocity defect situations. The second database is the same flow as the first one but the outer layer turbulence is artificially eliminated in this flow. Turbulence is removed above 0.15 local boundary layer thickness. For the analysis, we chose four streamwise positions with small, moderate, large, and very-large velocity defect. We compare the wall-normal distribution of Reynolds stresses, two-point correlations and spectral distributions of energy, production and pressure strain. The results show that the inner layer turbulence can sustain itself when the outer-layer turbulence does not exist regardless of the velocity defect or the pressure gradient. The two-point correlations of both cases show that outer large-scale structures affect the inner layer structures significantly. The streamwise extent of the correlation contours scales with pressure-viscous units. This shows the importance of the pressure gradient's effect on the inner-layer structures. The spectral distributions demonstrate that the energy transfer mechanisms are probably the same in the inner layer regardless of the velocity defect, which suggests the near-wall cycle may exist even in very-large defect APG TBLs where the mean shear in the inner layer is considerably lower than small-defect APG TBLs.

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