论文标题

有限大小球的运动以湍流边界层释放

Motion of finite-size spheres released in a turbulent boundary layer

论文作者

Tee, Yi Hui, Barros, Diogo, Longmire, Ellen K.

论文摘要

特异性重力为1.006、1.054和1.152的单个磁蜡球从摩擦雷诺数的水的光滑壁上释放,re_τ= 680和1320(分别为d^+ = 58和122个粘性单元)。进行了三维跟踪,以了解湍流和壁摩擦对球体运动的影响。最初从墙壁上抬起足够平均剪切的球,然后再向后降。这些举重球在墙壁上方的流体翻译,经历盐酸或重悬于任何轴的旋转时,经历了盐酸或重悬。相比之下,在释放时没有升空的球体主要沿着墙壁滑行。由于较大的壁摩擦,这些较密的球更明显地落在了流体。当他们下游滑行时,他们开始向前滚动,此后发生了小的重复提升事件。这些球体还围绕流向和壁正常轴旋转。在所有情况下,球体轨迹都仅限于缓冲区和对数区域,并且所有墙壁碰撞都是完全无弹性的。即使在球体达到近似末端速度之后,球流速度也从平均值波动高达20%。在平行于壁的平面中,沿跨度方向迁移的球体约有12%的流向距离,这表明跨度力很重要。球体运动学的变化很可能是由边界层中的高和低动量区域诱导的,球体中的涡流脱落和壁摩擦。向前滚动密集球的重复升降归因于马格努斯升降机。

Individual magnetic wax spheres with specific gravities of 1.006, 1.054 and 1.152 were released from rest on a smooth wall in water at friction Reynolds numbers, Re_τ=680 and 1320 (d^+ = 58 and 122 viscous units, respectively). Three-dimensional tracking was conducted to understand the effect of turbulence and wall friction on sphere motions. Spheres subjected to sufficient mean shear initially lifted off of the wall before descending back towards it. These lifting spheres translated with the fluid above the wall, undergoing saltation or resuspension, with minimal rotation about any axis. By contrast, spheres that did not lift off upon release mainly slid along the wall. These denser spheres lagged the fluid more significantly due to greater wall friction. As they slid downstream, they began to roll forward after which small repeated lift-off events occurred. These spheres also rotated about both the streamwise and wall-normal axes. In all cases, the sphere trajectories were limited to the buffer and logarithmic regions, and all wall collisions were completely inelastic. Sphere streamwise velocities fluctuated up to 20% from the mean value even after the sphere had attained an approximate terminal velocity. In the plane parallel to the wall, the spheres migrated in the spanwise direction about 12% of the streamwise distance traveled suggesting that spanwise forces are important. The variations in sphere kinematics were likely induced by high and low momentum zones in the boundary layer, vortex shedding in the sphere wakes, and wall friction. The repeated lift-offs of the forward rolling denser sphere were attributed to a Magnus lift.

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