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首页> 外文期刊>Journal of enhanced heat transfer >EFFECT OF UPSTREAM WALL SHEAR ON FLOW AND MASS (HEAT) TRANSFER ON A FLAT PLATE DOWNSTREAM OF A SHEAR INDUCING MOVINGWALL - A REVIEW
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EFFECT OF UPSTREAM WALL SHEAR ON FLOW AND MASS (HEAT) TRANSFER ON A FLAT PLATE DOWNSTREAM OF A SHEAR INDUCING MOVINGWALL - A REVIEW

机译：上游壁剪对诱导剪力墙的平板流道下游流动和传热的影响-综述

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Flow and mass transfer experiments are conducted to study the effect of wall shear on a two-dimensional turbulent boundary layer. The shear at the boundary is imparted by a moving belt, flush with the wall. In the first case (Case 1), the wall shear is imparted along the direction of the flow. Velocity measurements are taken at 12 streamwise locations with four surface-to-freestream velocity ratios (0, 0.38, 0.52, 0.65) and a momentum-based Reynolds number between 770 and 1776. The velocity data indicate that the location of the "virtual origin" of the turbulent boundary layer "moves" downstream towards the trailing edge of the belt with increasing surface velocity. The highest belt velocity ratio (0.65) results in the removal of the "inner" region of the boundary layer. Measurements of the streamwise turbulent kinetic energy (TKE) show an inner-scaling at locations upstream and downstream of the belt and the formation of a new self-similar structure on the moving surface itself. Good agreement is observed for the variation of the shape factor (H) and the skin friction coefficient (c(f)) with previous studies. Mass transfer measurements using naphthalene sublimation provide the variation of Stanton with Reynolds number on the plate downstream of the moving belt. It shows much reduced mass transfer due to removal of the inner region of the boundary at the highest belt velocity. In the second case (Case 2), the wall shear is in a direction opposite to the incoming flow. Boundary layer measurements are reported for four surface-to-freestream velocity ratios (0, 0.37, -0.50, -0.62) with the Reynolds number (based on the momentum thickness) between 922 and 1951. Velocity profiles downstream of the moving surface show an increased velocity deficit near the wall, which is more pronounced at higher (negative) belt velocity. Streamwise turbulence values downstream of the belt show the growth of a second peak in the logarithmic region of the boundary layer in addition to the normally-observed peak in the buffer region. This suggests the presence of larger length-scale turbulent eddies at locations away from the wall in the boundary layer. Spectral measurements indicate that the turbulent energy content is distributed over a wide portion of the logarithmic region. Mass transfer measurements for this case show little difference from the stationary belt case, which suggests that increased wall turbulence is balanced by an increase in the boundary layer thickness.
机译：进行流动和传质实验以研究壁剪切对二维湍流边界层的影响。边界处的剪切力是由与墙齐平的移动皮带施加的。在第一种情况下（案例1），沿流向施加壁面剪切力。速度测量是在12个流向位置进行的，四个表面与自由流的速度比（0、0.38、0.52、0.65）以及基于动量的雷诺数在770和1776之间。速度数据表明“虚拟原点”的位置湍流边界层的“”以增加的表面速度向下游“运动”到带的后缘。最高的皮带速度比（0.65）导致边界层“内部”区域的去除。流向湍流动能（TKE）的测量结果显示出皮带上游和下游的内部​​结垢，并且在运动表面本身上形成了新的自相似结构。观察到的形状因子（H）和皮肤摩擦系数（c（f））的变化与以前的研究一致。使用萘升华进行的传质测量提供了斯坦顿随移动带下游板上雷诺数的变化。由于以最高传送带速度去除了边界的内部区域，因此显示出传质大大降低。在第二种情况下（案例2），壁剪的方向与流入的方向相反。报告了四种表面与自由流速度比（0、0.37，-0.50，-0.62）的边界层测量结果，雷诺数（基于动量厚度）在922和1951之间。运动表面下游的速度分布显示出壁附近的速度赤字增加，在较高（负）皮带速度下尤为明显。皮带下游的湍流湍流值显示了边界层对数区域中第二个峰值的增长，除了缓冲区中通常观察到的峰值。这表明在边界层中远离壁的位置处存在较大长度的湍流涡流。频谱测量结果表明，湍流能量含量分布在对数区域的很大一部分上。这种情况下的传质测量结果与固定带情况几乎没有区别，这表明壁湍流的增加由边界层厚度的增加所平衡。

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