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近一个世纪以来,流体动力学家们描述湍流时试图将流场因变量分解为确定性的和随机性的分量。本文用一组速度数据检验这一将所测速度分解为可重复分量和随机分量的传统方法。这组数据是在某一90％轴对称缩窄处的远端脉动流中测得的,其雷诺数为人的颈动脉中的典型值。在此大雷诺数下,一个脉动周期中有时会在几个轴向位置上发生转捩。本文主要讨论所选的速度分解方法对于计算表现应力的影响。可以看到,通常从瞬时速度减去平均速度来计算脉动流的雷诺应力的方法,在流动中存在相干的可重复的扰动时,导致对表观应力估计不足。本文采用频域方法进行分解,将随机应力和相干应力结合起来成为一个表观应力。本文作者指出,在我们研究受扰动的脉动血流中红细胞上作用的切应力时,应该考虑的正是这一总的表观应力。
For nearly a century, hydrodynamicists have attempted to decompose flow-dependent variables into deterministic and random components when describing turbulence. In this paper, a set of velocity data is used to test this traditional method of decomposing the measured velocity into repeatable and random components. This set of data is measured in a distal pulsatile flow at a 90% axisymmetric constriction with a Reynolds number typical of the human carotid artery. At this large Reynolds number, there may be times when one pulsation cycle occurs at several axial positions. This article focuses on the impact of the selected velocity decomposition method on the calculation of the apparent stress. It can be seen that the method of calculating the Reynolds stress of a pulsatile flow, usually by subtracting the average velocity from the instantaneous velocity, results in a lack of estimation of the apparent stress when there is a coherent, repeatable disturbance in the flow. In this paper, frequency domain method is used to decompose the stochastic stress and coherent stress into an apparent stress. The authors point out that it is this total apparent stress that should be considered when we investigate the shear stress acting on red blood cells in disturbed pulsatile blood flow.