Velocity Profiles and Wall Shear Stress in Turbulent Transient Pipe Flow
Velocity Profiles and Wall Shear Stress in Turbulent Transient Pipe Flow
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湍流瞬态管流中的速度分布和壁面剪应力
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发表时间：
2009
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通讯作者：
H. Zidouh
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作者：
H. Zidouh
通过电化学技术和超声脉冲多普勒测速技术，结合壁面剪切应力的实验测量的速度分布，被用来分析在瞬态管流下游突然关闭阀门所造成的流动行为。速度数据进行了分析，并相应的壁面剪应力值进行了评估，导致讨论瞬态能量耗散的电化学技术所获得的结果进行比较。基于管道直径的稳定流的雷诺数为Re=140000。结果表明，在初始阶段，对于较大的减速度，用准定常方法来表示非定常摩擦是有效的。对于更高的减速，非定常壁面剪应力始终高于从速度剖面获得的准定常值。瞬时加速度模型的适用范围的检查表明，经验系数的非定常摩擦是密切相关的减速强度。这项研究之所以成为可能，是因为不同阀门关闭的可重复性允许在多次测试中对数据进行平均。
Experimental measurements of the wall shear stress combined to those of the velocity profiles via the electrochemical technique and ultrasonic pulsed Doppler velocimetry, are used to analyse the flow behaviour in transient pipe flow caused by a downstream sudden valve closure. Velocity data are analyzed and the corresponding wall shear stress values are evaluated, leading to a discussion on transient energy dissipation by comparison with results obtained by the electrochemical technique. The Reynolds number of the steady flow based on the pipe diameter is Re=140000 . The results show that the quasi-steady approach of representing unsteady friction is valid during the initial phase for relatively large decelerations. For higher decelerations, the unsteady wall shear stress is consistently higher than the quasi-steady values obtained from the velocity profiles. An examination of the range of applicability of the instantaneous-acceleration model shows that the empirical coefficient of unsteady friction is closely linked to the deceleration intensity. This study is made possible owing to the repeatability of different valve closures allowing data to be averaged over numerous tests.