Lieber B B, Giddens D P
Department of Mechanical and Aerospace Engineering, State University of New York, Buffalo 14260.
J Biomech. 1988;21(4):287-98. doi: 10.1016/0021-9290(88)90259-x.
Traditional attempts at decomposing measured velocities into repeatable and random components are examined for a set of velocity data measured under pulsatile flow conditions distal to a 90% axisymmetric constriction. The Reynolds numbers, which are typical of those found in the human carotid artery, are such that transitional phenomena occur during portions of the pulsatile cycle at several axial stations. The implications of the method selected for velocity decomposition upon the computation of fluctuating or 'apparent' stresses is a point of major focus. It is shown that the usual estimation of Reynolds stresses in a pulsatile flow by subtracting the ensemble-averaged velocity from the instantaneous velocity leads to an underestimation of the apparent stress when coherent or repeatable disturbances exist in the flow. An alternative decomposition using a frequency domain approach is presented which combines both random and coherent stresses into a single apparent stress, and it is proposed that this approach is preferable to the traditional ensemble averaging method when estimating fluctuating stresses in arterial flows.
针对在90%轴对称狭窄远端的脉动流条件下测量的一组速度数据，研究了将测量速度分解为可重复和随机分量的传统方法。雷诺数是人体颈动脉中典型的数值，使得在脉动周期的部分时间内，在几个轴向位置会出现过渡现象。速度分解所选方法对波动或“表观”应力计算的影响是主要关注的一点。结果表明，在脉动流中通过从瞬时速度中减去总体平均速度来通常估计雷诺应力，当流中存在相干或可重复扰动时，会导致表观应力的低估。提出了一种使用频域方法的替代分解方法，该方法将随机应力和相干应力都合并到单个表观应力中，并且建议在估计动脉血流中的波动应力时，这种方法比传统的总体平均方法更可取。
