Direct numerical simulation of transient turbulence in a stenosed carotid artery

Atherosclerotic plaques inside an arterial wall result in a local occlusion of the artery lumen - a stenosis. The stenosis may trigger transition to turbulence and the onset of turbulence downstream of severe occlusions has been observed in the laboratory experiments. Flow in a stenosed carotid artery has been studied experimentally and numerically by many authors. We have performed model-free three-dimensional direct numerical simulations (DNS) of flow through a carotid artery. A geometric model of the carotid artery was obtained from in-vivo MRA images shown in figure. In this study, we apply the Proper Orthogonal Decomposition (POD) to analyze pulsatile transitional laminar-turbulent flows in a carotid arterial bifurcation. We use high-accuracy DNS results to demonstrate the possibility of analyzing transient turbulence in a stenosed carotid artery by POD. Specifically, we use a mesh with 22,441 tetrahedral elements of 7 variable size, and eights-order polynomial approximation (P = 8) within each element, corresponding to 24,685,100 degrees of freedom per one variable. The total number of quadrature points in the computational domain was above 37 millions. Our simulations confirm that a turbulent state appears during the systolic phase of the cardiac cycle and is localized in the post-stenotic region, with relaminarization occurring further downstream of the stenosis. The possibility to extend the POD analysis to routine clinical tests carried out by ultrasound medical imaging techniques has been analyzed and discussed.