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FLUID MECHANICS

机译：流体力学

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Nominally zero-pressure-gradient fully developed flat-plate turbulent boundary layers with heated and unheated isothermal walls at supercritical pressures are studied by solving the full compressible Navier-Stokes equations using direct numerical simulation. With a heated isothermal wall, the wall temperature sets such that the flow temperature varies through the pseudo-critical temperature, and thus pseudo-boiling phenomena occur within the boundary layers. The pseudo-boiling process induces strongly nonlinear real-fluid effects in the flow and interacts with near-wall turbulence. The peculiar abrupt density variations through the pseudo-boiling process induce significant near-wall density fluctuations within the heated transcritical turbulent boundary layers. The large near-wall density fluctuations induce a turbulent mass flux . and the turbulent mass flux amplifies the Favre-averaged velocity fluctuations in the near-wall predominant structures of streamwise low-speed streaks that are associated with the ejection (where ), while reducing the velocity fluctuations in the high-speed streaks associated with the sweep (u' > 0 and v' 0). Although the near-wall low-speed and highspeed streak structures dominate the Reynolds-shear-stress generation, the energized Favre-averaged velocity fluctuations in the low-speed streaks enhance both the mean-density- and density-fluctuation-related Reynolds shear stresses ( and ) in the ejection event and, as a result, alter the Reynolds-shear-stress profile. The large density fluctuations also alter the near-wall viscous-stress profile and induce a near-wall convective flux (due to non-zero ). The changes in the contributions in the stress-balance equation result in a failure of existing velocity transformations to collapse to the universal law of the wall. The large density fluctuations also greatly contribute to the turbulent kinetic energy budget, and especially the mass flux contribution term becomes noticeable as one of the main positive terms. The unheated non-transcritical turbulent boundary layers show a negligible contribution of the real-fluid effects, and the turbulence statistics agree well with the statistics of an incompressible constant-property turbulent boundary layer with a perfect-gas law.
机译：通过使用直接数值模拟求解完全可压缩的Navier-Stokes方程，研究了在超临界压力下具有加热和未加热等温壁的名义零压力梯度完全展开平板湍流边界层。在加热等温壁的情况下，壁温设定为使得流动温度在伪临界温度范围内变化，从而在边界层内发生伪沸腾现象。拟沸过程在流动中引起强烈的非线性实流效应，并与近壁湍流相互作用。通过伪沸腾过程产生的独特的突然密度变化会在加热的跨临界湍流边界层内引起明显的近壁密度波动。较大的近壁密度波动引起湍流质量通量。湍流质量通量放大了与喷射有关的沿流低速条纹的近壁优势结构中Favre平均速度波动（其中），同时减小了与扫掠相关的高速条纹中的速度波动（u'> 0和v'0）。尽管近壁低速和高速条纹结构在雷诺剪切应力产生中占主导地位，但低速条纹中激励的Favre平均速度波动会增加与平均密度和密度波动有关的雷诺剪切应力（和）在弹出事件中，并因此改变了雷诺剪切应力分布。较大的密度波动还会改变近壁粘性应力曲线，并引起近壁对流（由于非零）。应力平衡方程中贡献的变化导致现有速度转换失败，无法塌陷到壁的通用定律。较大的密度波动也极大地影响了湍动能的收支，尤其是质量通量贡献项作为主要的正项之一变得引人注目。未加热的非跨临界湍流边界层对真实流体效应的贡献可忽略不计，并且湍流统计数据与具有完美气体定律的不可压缩恒特性湍流边界层的统计数据非常吻合。

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    《Oceanographic Literature Review》 |2019年第4期|933-945|共13页
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