Particle Residence Time in pulsatile post-stenotic flow

Abstract

Particle Residence Time (PRT), a measure of a fluid element’s transit time through a region of interest, is a clear indicator of recirculation. The PRT of fluid recirculating downstream of an idealized stenosis geometry is found to vary dramatically under pulsatile flow conditions. Two-dimensional particle tracking velocimetry is used to track particles directly as they exit the stenosis geometry and are entrained into the region of recirculation immediately downstream. A Lagrangian approach permits long pathlines to be drawn, describing each particle’s motion from the instant they enter the domain. PRT along each pathline is compared here for three mean Reynolds numbers; specifically, Rem = 4800, 9600, and 14 400. The pulsatile waveforms are characterized by Strouhal numbers of 0.04, 0.08, and 0.15 and amplitude ratios of 0.50 and 0.95. As the mean Reynolds number is increased, higher fluid velocities are shown to lower PRT. However, the strength of PRT is truly revealed when highlighting the influence pulsatility has on the degree of mixing beyond the stenosis throat. Higher Strouhal numbers correlate with roll-up across the shear layer and increased PRT distribution at all Reynolds numbers in consideration. Similarly, strong temporal velocity gradients generated by a high amplitude ratio carry large volumes of fluid from the jet deep into the recirculation region, contributing to greater PRT.