Direct numerical simulations of transitional pulsatile flow through a constriction

Abstract

A combined experimental and numerical study of transitional pulsatile flow through a planar constriction is presented. The parametric space that we adopt is similar to the one reported in a variety of past experiments relevant to the flow through stenosed arteries. In general, the flow just downstream of the constriction is dominated by the dynamic of the accelerating/decelerating jet that forms during each pulsatile cycle. We found a switch in the shedding frequency and roll-up dynamics, just after the flow rate approaches its maximum value in the cycle. The flow in the reattached area further downstream is also affected by the jet dynamics. A ‘synthetic’ turbulent-like wall-layer develops, an is constantly supported by streamwise vortices that originate from the spanwise instabilities of the large coherent structures generated by the jet. The relation of these structures to the phase-averaged turbulent statistics and the turbulent kinetic energy budgets is discussed.

A pressure-gradient mechanism for vortex shedding in constricted channels

“…In the inviscid jet problem studied by Gharib, Rambod, and Shariff, 13 the vortex ring "pinches" off after the circulation reaches a comment value based on a variational principle. Beratlis et al 12 did not find the same value of the universal formation number as in the study of Gharib et al 13 and suggests that this could be related to the jet being bounded by walls that play an important role in the flow dynamics. Other vortices are observed to shed after the initial vortex, and this is attributed to a Kelvin-Helmholtz-like instability of the shear layer.…”

“…12 They observe vorticity rollup at the downstream end of the shear layer that eventually sheds. A potential explanation for the initial vortex shedding is given based on common features with inviscid round jets accelerating in a quiescent, unbounded environment.…”

Active and passive in-plane wall fluctuations in turbulent channel flows

“…The pressure Poisson equation is solved directly using fast Fourier transforms in the periodic directions (x 1 and x 3 ) and a tridiagonal matrix algorithm in the wall-normal direction (x 2 ). Beratlis, Balaras & Kiger (2007) and Posa & Balaras (2016) used the same solver with an immersed boundary formulation for treating complex geometries. A description of the numerical scheme along with a detailed validation can be found in Balaras (2004).…”

Large Eddy Simulation of a Stenosed Artery Using a Femoral Artery Pulsatile Flow Profile

“…Turbulent flow in a blood vessel has considerable implications for the integrity of the vessel, particularly the effect on the wall shear stress. Turbulence is generated from the shear layers and moves toward the core of the of the channel, where it decays as it travels downstream.Pulsatile stenotic flows have been the focus of a number of numerical simulations in the past decade, ranging from laminar simulations (4) to standard Reynolds Averaged Navier Stokes (RANS) solutions (5-8) to computationally intensive Direct Numerical Simulation (DNS) models (3,9,10). Not unexpectedly, given the large computational resources required, the DNS models are generally channels, representing a simplified stenosed artery flow, although the work of Sherwin et al (11,12) has utilized axisymmetric constrictions.…”

“…Pulsatile stenotic flows have been the focus of a number of numerical simulations in the past decade, ranging from laminar simulations (4) to standard Reynolds Averaged Navier Stokes (RANS) solutions (5)(6)(7)(8) to computationally intensive Direct Numerical Simulation (DNS) models (3,9,10). Not unexpectedly, given the large computational resources required, the DNS models are generally channels, representing a simplified stenosed artery flow, although the work of Sherwin et al (11,12) has utilized axisymmetric constrictions.…”