A COMPUTATIONAL STUDY OF PULSATILE FLOW IN A STENOSIS IN RELATION TO BLOOD DAMA

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 本工作的目标是研究脉动流在一个突然的扩张，这代表了一个建模的狭窄，这是一个异常狭窄的血管。突然膨胀用于获得不利的流动模式，例如分离、再附着和涡流形成，这些可能在狭窄处看到。将使用计算流体动力学（CFD）模拟来获得在平均喉部雷诺数为2000、峰值喉部雷诺数为4600和平均流速为1.25 l/min（代表髂动脉中观察到的流量）时通过突然扩张的流速和湍流特性。髂动脉的横截面为椭圆形，主动脉分叉处的长轴为1.53 cm，短轴为1.3 cm，因此我们模型的入口直径为12 mm，代表了髂动脉的平均直径。喉部雷诺数从低的400到高的4600的变化将产生从层流到湍流的过渡。流动的CFD结果将与使用三分量激光多普勒测速实验技术获得的速度和湍流特性进行比较。虽然以前的研究狭窄的脉动流只进行了使用单组分LDV，本研究使用三组分LDV，使我们能够同时捕获所有三个组成部分的流量，从而使我们能够计算湍流数据，更准确。此外，以前的研究脉动流在狭窄处使用计算技术依赖于直接数值模拟（DNS）技术，以产生准确的流量表示。我们将使用一个计算成本较低的隐式大涡（ILES）技术来预测流动的突然膨胀，并打算表明，ILES模拟结果匹配的实验结果一样准确的DNS。其他研究人员发现，在淹没射流中造成血液损伤的湍流剪切应力的阈值水平为4000。我们将通过比较在突然扩张中测量的湍流应力与该阈值水平来关联脉动狭窄流中可能发生的血液损伤水平。我们假设，在流中的平均湍流剪切应力将是低的稳定流相比，在相似的雷诺数。然而，湍流剪切应力的瞬时值可能大得多，导致更高水平的血液损伤。这项工作可能为研究人员提供有价值的见解，以更好地预测脉动狭窄流中的应力及其对血液损伤和血栓形成的影响。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this work is to study pulsatile flow in a sudden expansion which represents a modeled stenosis which is an abnormal narrowing in a blood vessel . The sudden expansion is used to obtain adverse flow patterns, such as separation, reattachment and eddy formation, that are likely to be seen in stenoses. Computational fluid dynamic (CFD) simulations will be used to obtain velocity and turbulent characteristics of the flow through the sudden expansion at a mean throat Reynolds number of 2000, a peak throat Reynolds number of 4600 and a mean flow rate of 1.25 l/min, which is representative of the flow seen in the iliac artery. The iliac artery is elliptical in cross section with a major axis of 1.53 cm and minor axis of 1.3 cm at the aortic bifurcation, and hence the inlet diameter of our model, which is 12 mm, is representative of the mean diameter of the iliac artery. The variation of the throat Reynolds number from a low of 400 to a high of 4600 will produce flow than transitions from laminar to turbulent. The CFD results of the flow will be compared against the velocity and turbulence characteristics obtained using a three-component laser Doppler velocimetry experimental technique. While previous studies of pulsatile flow in stenoses have only been conducted using one-component LDV, this study uses three-component LDV which enables us to simultaneously capture all three components of flow, and hence allows us to compute turbulence data that is more accurate. Also, previous studies of pulsatile flow in stenoses using computational techniques have relied on direct numerical simulation (DNS) techniques to produce accurate representations of the flow. We will use a less computationally expensive implicit large eddy (ILES) technique to predict the flow in the sudden expansion and intend to show that the ILES simulation results match the experimental results just as accurately as DNS. The threshold level of turbulent shear stress responsible for blood damage in a submerged jet was found to be 4000 by other researchers. We will correlate the levels of blood damage that may occur in pulsatile stenotic flows by comparing the turbulent stress measured in the sudden expansion to this threshold level. We hypothesize that the mean turbulent shear stress in the flow will be low compared to steady flow at similar Reynolds numbers. However, the instantaneous values of turbulent shear stress may be much larger, resulting in higher levels of blood damage. This work may provide valuable insights to researchers to better predict the stresses seen in pulsatile stenotic flows and their implications to blood damage and thrombus formation.