Rheological effects on pulsatile hemodynamics in a stenosed tube

Transient laminar axisymmetric flow through a tube with a smooth local area reduction of 75% is considered. Using an experimentally validated control volume method, the influence of three rheology models (i.e., Newtonian, power law and Quemada) are investigated. Three Womersley numbers (Wo = r(0)(omega/nu)(1/2): = 4.0, 7.5 and 12.5) are compared for a sinusoidal input pulse which varies between 0 and 400 with a mean Reynolds number of 200. The primary application is pulsatile flow in axisymmetric stenosed artery segments. Results show that for the highest Womersley number considered here, a second co-rotating vortex is formed distal to the primary vortex. Also, the shear-thinning rheological models have a secondary effect on the flow field that primarily appears in terms of subtle changes to the hemodynamic wall parameters (i.e., the time-averaged wall shear stress, spatial wall shear stress gradient, and oscillatory shear index). The non-Newtonian models affect the entrainment of fluid-like particles in the post-stenotic region measurably. The particle residence time (PRT), defined as the ratio of transient to steady residence times, is found to be less than or equal to unity for the majority of fluid elements for all rheologies and Womersley numbers considered. The highest fraction of PRT < 1 is found at moderate Womersley numbers. Pathological fluid elements, where PRT > 10, is found to increase with increasing Wo and is decreased by the non-Newtonian formulations. This is due to a low-shear high-viscosity band that impedes the progress of fluid particles into the near wall region. (C) 2000 Elsevier Science Ltd, All rights reserved.