Obstacle drag in stratified flow

I. Castro, W. Snyder, P. Baines
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引用次数: 41

Abstract

This paper describes an experimental study of the drag of two- and three-dimensional bluff obstacles of various cross-stream shapes when towed through a fluid having a stable, linear density gradient with Brunt-Vaisala frequency, N. Drag measurements were made directly using a force balance, and effects of obstacle blockage (h/D, where h and D are the obstacle height and the fluid depth, respectively) and Reynolds number were effectively eliminated. It is shown that even in cases where the downstream lee waves and propagating columnar waves are of large amplitude, the variation of drag with the parameter K ( = ND/πU) is qualitatively close to that implied by linear theories, with drag minima existing at integral values of K. Under certain conditions large, steady, periodic variations in drag occur. Simultaneous drag measurements and video recordings of the wakes show that this unsteadiness is linked directly with time-variations in the lee and columnar wave amplitudes. It is argued that there are, therefore, situations where the inviscid flow is always unsteady even for large times; the consequent implications for atmospheric motions are discussed.
分层流中的障碍阻力
本文通过实验研究了不同横流形状的二维和三维钝面障碍物在拖曳通过具有稳定的线性密度梯度(Brunt-Vaisala频率为n)的流体时的阻力。阻力测量直接使用力天平进行,有效地消除了障碍物阻塞(h/D,其中h和D分别为障碍物高度和流体深度)和雷诺数的影响。结果表明,即使在下游背风波和传播柱状波振幅较大的情况下,阻力随参数K (= ND/πU)的变化也定性地接近于线性理论所暗示的变化,阻力极小值存在于K的积分值处。在一定条件下,阻力会出现较大的、稳定的周期性变化。同时进行的阻力测量和尾迹的视频记录表明,这种不稳定性与背风波和柱状波振幅的时间变化直接相关。因此,有人认为,在某些情况下,即使在很长时间内,无粘流也总是不稳定的;讨论了由此产生的对大气运动的影响。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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