No abstract

In the present paper, a closely coupled numerical and experimental investigation of pulsatile flow in a prototypical stenotic site is presented. Detailed laser Doppler velocimetry measurements upstream of the stenosis are used to guide the specification of velocity boundary conditions at the inflow plane in a series of direct numerical simulations (DNSs). Comparisons of the velocity statistics between the experiments and DNS in the post-stenotic area demonstrate the great importance of accurate inflow conditions, and the sensitivity of the post-stenotic flow to the disturbance environment upstream. In general, the results highlight a borderline turbulent flow that sequentially undergoes transition to turbulence and relaminarization. Before the peak mass flow rate, the strong confined jet that forms just downstream of the stenosis becomes unstable, forcing a role-up and subsequent breakdown of the shear layer. In addition, the large-scale structures originating from the shear layer are observed to perturb the near wall flow, creating packets of near wall hairpin vortices.

No abstract

No 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.