Unsteady Flow Haemodynamics in a Constricted Channel Replicating Atherosclerosis in Carotid Artery

Flow separations and transitions to turbulence are seen in curved vessels, bifurcations, and constrictions, even though blood flows are predominantly laminar. It is also understood that atherosclerosis is closely related to wall shear stress. To understand and get deeper insights of flow physics in a post-stenotic region, numerical simulations were carried out using a simple oscillatory blood flow at Reynolds number range of 200–800 and Womersley number of 5.73 in a 2D straight channel having asymmetrical stenosis models with area occlusion of 35% and 50%. For all models, flow characteristics such as velocity profile, flow separation zones (FSZ), and wall shear stress (WSS) are displayed. The findings show that the establishment and development of FSZs in the post-stenotic area, particularly during flow deceleration, is extremely complicated. A strong shear layer arises at the tip of the stenosis at the commencement of the oscillatory cycle, increasing the flow separation region. Due to acceleration, the flow near the stenosis's throat is always laminar, but it quickly turns chaotic due to shear layer instability at a strong unfavourable pressure gradient. Simultaneously, on the wall opposite to the stenosis, a recirculation region appears and moves downstream synchronous with the reattachment point movement. In certain models, oscillations in WSS (between positive and negative values) were found at different downstream locations. The oscillation amplitude is significantly dependent on the axial location and the degree of stenosis. The wall deformation is closed to each other in the beginning but starts to differ as the Re increases.