LES and PTV Measurement of Turbulent Flow in Expanding Concentric Annular Flow-Passage with Rotating Inner-Wall

具有旋转内壁的环形流道广泛应用于工业设备中，例如离心机，滑动轴承和旋转机械。因此，了解这种流道中的流动和换热是很重要的。在这种流道中，多个流动不稳定因素可以同时影响；通过流动和/或内壁旋转引起的剪切流动不稳定性和由于外围和/或通过流动流线曲率引起的离心流动不稳定性。在实际应用中，大部分流动变得湍流，并且横截面积在通流方向上发生变化，使现象进一步复杂化。本文通过大涡模拟（LES）和粒子跟踪测速（PTV）方法，研究了多种流动不稳定因素对湍流流动的影响。研究了两种类型的流道：凹型和凸型，以内壁的形状命名。在PTV测量中，采用二帧法，计算了时间平均速度和湍流强度。在实验中，透流雷诺数Re在1000 ~ 10000之间变化，泰勒数Ta在0 ~ 8000之间变化。Re=1000时，内壁旋转导致下游湍流强度增加。Re=10000时，上游和下游湍流强度均有所增加。内壁旋转引起出口回流。采用二阶有限差分法在曲线坐标系下进行了LES分析。对凹型和凸型通道进行Re=1000（常数）和Ta=0-4000的处理。外围计算尺寸在45度、90度和360度之间变化。在LES结果中，进口附近的流动结构是均匀的，而在下游区域内壁旋转引起湍流。涡的结构取决于泰勒数、流道类型和流道中的位置（上游/下游和靠近内/外壁）。由于回流和紊流的影响，换热系数曲线变得复杂。壁面剪应力和转矩系数的检测进一步阐明了各流道内流动结构的差异。少

An annular flow passage with a rotating inner wall is widely utilized in industrial apparatuses, and the examples are centrifuges, journal bearings, and rotating machinery. Therefore, the understanding of the flow and heat transfer in this type of flow passage is important In this flow passage, multiple flow-instability factors can simultaneously affect; shear flow instability due to through flow and/or inner-wall rotation and centrifugal flow instability due to peripheral and/or through-flow streamline curvatures. In the real applications, most of the flow becomes turbulent, and the cross-sectional area changes in the through-flow direction, which further complicates the phenomena. The objective of this study is to investigate the turbulent flow affected by the multiple flow-instability factors by performing Large Eddy Simulation (LES) and Particle Tracking Velocimetry (PTV) measurement.The two types of flow passages were examined : concave and convex types named after the shape of th … More e inner wall. In the PTV measurement, two-frame method was used, and the time-averaged velocities and the turbulence intensities were calculated. In the experiment, though-flow Reynolds number, Re, was varied from 1000 to 10000, and the Taylor number, Ta, was varied from 0 to 8000. For Re=1000, the inner-wall rotation caused the increased turbulence intensity in the downstream region. For Re=10000, the turbulence intensity increased in both the upstream and downstream regions. The inner wall rotation induced the reversed flow at the outlet.The LES was performed in the curvilinear coordinate system using the second order finite difference method. The concave-and convex-type passages were treated for Re=1000(constant) and Ta=0-4000. The peripheral computational size was varied among 45, 90, and 360 degrees. In the LES result, the flow structure was peripherally uniform near the inlet, and the inner wall rotation induced turbulence in the downstream region. The vortex structure was dependent on the Taylor number, the flow passage type, and the position in the passage (upstream/downstream and near inner/outer wall). The heat transfer coefficient profile became complicated due to the reversed flow and the turbulent transfer. The examination of wall shear stress and torque coefficient further clarified the flow structure difference in each flow passage. Less