Separation and reattachment of fluid flow through series vascular constrictions

Abstract

The flow fields in the neighbourhoods of vascular constrictions in series are studied numerically for a Reynolds number range of 5 to 200, spacing ratios of 1,2,3 and ∞ for diameter constriction ratios of 0.2 to 0.8. The effect on streamlines, vorticity, flow separation and reattachment, velocity distribution and wall vorticity as the fluid flow passes through two adjacent vascular stenoses are numerically investigated. With the Reynolds number increased, the separation point of the eddy was noted to move upstream from the constriction surface; and the reattachment point of the recirculating flow moved downstream. If the upstream constriction was more severe than the downstream constriction ( c 1> c 2), a recirculation zone usually filled the valley region between the two constrictions and the pattern of flow tends to amplify the wall vorticity values of the downstream constrictions. For a less severe upstream constriction ( c 1< c 2), when the Reynolds number was increased, the recirculating eddy formed by the first constriction tends to spread beyond the region of the downstream constriction and merged with the eddy formed behind the downstream constriction. This resulted in negative wall vorticity peak occurring in the region of the second constriction at high vascular fluid flow Reynolds number.