Effect of a bend on vortex formation and evolution in a three-dimensional stenosed geometry during pulsatile flow

Abstract

Stenosis at arterial bends alters hemodynamics and instigates abnormal disease progression. This configuration is addressed numerically by exploring pulsatile flow (Reynolds number Re = 300–1200; Womersley number Wo = 7.62–15.24) in arteries encountering bend angles of θ = 20°–60°. Individual influences of stenosis and bend on flow dynamics are investigated. Validations against particle image velocimetry experiments for Re = 800 and Wo = 7.62 are carried out in straight and 60° bend stenosed models. For Re = 300–800, the shear layer along the stenosis rolls up into a primary vortex, that is, constrained by the outer wall forming a secondary vortex. At Re = 1200, shear layers undergo instabilities along the post-stenotic region and develop new vortices that promote disturbances and induce asymmetries over the cross-plane flow structures. These features are not present in a straight stenosed tube, showing that the bend is responsible for flow distortion. During the pulsatile cycle, increasing bend angles intensify the size and strength of vortices, while these are suppressed at higher frequencies. A higher bend of 60° experiences large time-averaged wall shear stress and oscillatory loads. In time, wall loading spatially circumscribes the post-stenotic region followed by wall loading during cycle deceleration. These features are consistent with the skewing of a three-dimensional ring structure formed in a stenosed tube that evolves into disintegrated structures in the post-stenotic region. Overall, simulations reveal that strongly bent stenosed arteries experience aggravated oscillatory loading. In the biomedical context, such arterial geometries will require special attention.