This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. 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.
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