The effect of varying degrees of stenosis on transition to turbulence in oscillatory flows

TL;DR

This study investigates how different degrees and configurations of arterial stenosis influence the transition to turbulence in oscillatory flows, revealing that higher stenosis and frequency promote earlier turbulence onset.

Contribution

It provides a detailed analysis of the effects of stenosis degree, eccentricity, and oscillation frequency on flow transition under oscillatory conditions, a previously underexplored area.

Findings

Higher stenosis degree leads to earlier turbulence transition.

Eccentric configurations promote earlier transition.

Higher oscillation frequency increases flow instability.

Abstract

Many complications in physiology are associated with a deviation in flow in arteries due to a stenosis. The presence of stenosis may transition the flow to weak turbulence. The degree of stenosis as well as its configuration whether symmetric or non-symmetric to the parent artery influences whether the flow would stay laminar or transition to turbulence. Plenty of research efforts focus on investigating the role of varying degrees of stenosis in the onset of turbulence under steady and pulsatile flow conditions. None of the studies, however, have focused on investigating this under oscillatory flow conditions as flow reversal is a major occurrence in a number of physiologic flows, and is of particular relevance in cerebrospinal fluid (CSF) flow research. Following up on the previous work in which a 75% stenosis was studied, this contribution is a detailed investigation of the role of degrees of stenosis on transition in an oscillatory flow. A cylindrical pipe with 25%, 50% and 60% reductions in area in axisymmetric and eccentric configurations is studied for transition with 3 different pulsation frequencies of a purely oscillatory flow. Cycle averaged Reynolds numbers between 1800 and 2100 in steps of 100 are studied for each configuration resulting in 72 simulations each conducted on 76800 CPU cores of a modern supercomputer. It is found that a higher degree of stenosis and eccentricity causes earlier transition to turbulence in oscillatory flow. The results further demonstrate that a higher frequency of oscillation results in larger hydrodynamic instability in the flow, which is more prominent in smaller degrees of stenosis.