论文标题
粘性子层中的3D流动运动
3D flow motions in the viscous sublayer
论文作者
论文摘要
我们采用新颖的数字菲涅耳反射全息图来捕获REτ= 400处平滑壁湍流通道流的粘性子层中的3D流。测量结果揭示了子层中不稳定和多样化的流动模式，包括几乎均匀的高速和低速流以及强大的小规模（在粘性壁单元的阶段）旋转运动。壁剪应力的概率密度函数（PDF）在高应力范围内与直接数值模拟（DNS）的概率差异明显差异，这归因于DNS未解决的流向和跨度运动。此外，拉格朗日粒子加速度的PDF在同质各向同性湍流中产生了类似的指数形状，表明撒布利层的间歇性很强。我们发现，高加速度的很大一部分与小规模的蜿蜒运动有关。我们的研究有助于解释子层规模粗糙度对减少文献中报道的阻力分离的影响。
We employ novel digital Fresnel reflection holography to capture the 3D flows within the viscous sublayer of a smooth-wall turbulent channel flow at Reτ=400. The measurements reveal unsteady and diverse flow patterns in the sublayer including nearly uniform high and low speed flows and strong small-scale (on the order of viscous wall units) spanwise meandering motions. The probability density functions (PDFs) of wall shear stresses show a clear discrepancy in high stress range with those from direct numerical simulation (DNS), which is attributed to the unresolved streamwise and spanwise motions by DNS. Moreover, the PDF of Lagrangian particle accelerations yields a stretched exponential shape like that in homogenous isotropic turbulence, indicating strong intermittency in the sublayer. We find a significant fraction of high accelerations is associated with the small-scale meandering motions. Our study helps explain the effect of sublayer-scale roughness on reducing drag and flow separation reported in the literature.
