Ahmadi Somayeh, Roccon Alessio, Zonta Francesco, Soldati Alfredo
1Institute of Fluid Mechanics and Heat Transfer, TU Wien, Vienna, Austria.
2Dipartimento Politecnico di Ingegneria e Architettura, Universitá di Udine, Udine, Italy.
Flow Turbul Combust. 2018;100(4):979-993. doi: 10.1007/s10494-018-9918-2. Epub 2018 Apr 25.
In this work we study the turbulence modulation in a viscosity-stratified two-phase flow using Direct Numerical Simulation (DNS) of turbulence and the Phase Field Method (PFM) to simulate the interfacial phenomena. Specifically we consider the case of two immiscible fluid layers driven in a closed rectangular channel by an imposed mean pressure gradient. The present problem, which may mimic the behaviour of an oil flowing under a thin layer of different oil, thickness ratio / = 9, is described by three main flow parameters: the shear Reynolds number (which quantifies the importance of inertia compared to viscous effects), the Weber number (which quantifies surface tension effects) and the viscosity ratio = / between the two fluids. For this first study, the density ratio of the two fluid layers is the same ( = ), we keep and constant, but we consider three different values for the viscosity ratio: = 1, = 0.875 and = 0.75. Compared to a single phase flow at the same shear Reynolds number ( = 100), in the two phase flow case we observe a decrease of the wall-shear stress and a strong turbulence modulation in particular in the proximity of the interface. Interestingly, we observe that the modulation of turbulence by the liquid-liquid interface extends up to the top wall (i.e. the closest to the interface) and produces local shear stress inversions and flow recirculation regions. The observed results depend primarily on the interface deformability and on the viscosity ratio between the two fluids ().
在这项工作中，我们使用湍流直接数值模拟（DNS）和相场法（PFM）来研究粘性分层两相流中的湍流调制，以模拟界面现象。具体而言，我们考虑由施加的平均压力梯度驱动的封闭矩形通道中两层不混溶流体的情况。当前问题可能模拟了一种油在不同油的薄层下流动的行为，厚度比/ = 9，由三个主要流动参数描述：剪切雷诺数（量化惯性相对于粘性效应的重要性）、韦伯数（量化表面张力效应）以及两种流体之间的粘度比= / 。对于这第一项研究，两层流体的密度比相同（= ），我们保持和恒定，但考虑粘度比的三个不同值：= 1、= 0.875和= 0.75。与相同剪切雷诺数（= 100）下的单相流相比，在两相流情况下，我们观察到壁面剪应力减小，特别是在界面附近有强烈的湍流调制。有趣的是，我们观察到液 - 液界面引起的湍流调制一直延伸到顶壁（即最靠近界面的壁），并产生局部剪应力反转和流动再循环区域。观察到的结果主要取决于界面可变形性和两种流体之间的粘度比（）。
