Large eddy simulations for blood dynamics in realistic stenotic carotids

Abstract

In this paper, we consider large eddy simulations (LES) for human stenotic carotids in presence of atheromasic plaque, a pathological condition where transitional effects to turbulence may occur, with relevant clinical implications such as plaque rupture. We provide a reference numerical solution obtained at high resolution without any subgrid scale model, to be used to assess the accuracy of LES simulations. In the context we are considering, ie, hemodynamics, we cannot refer to a statistically homogeneous, isotropic, and stationary turbulent regime; hence, the classical Kolmogorov theory cannot be used. For this reason, a mesh size and a time step are deemed fine enough if they allow to capture all the features of the velocity field in the shear layers developed after the bifurcation. To assess these requirements, we consider a simplified model of the evolution of a 2D shear layer, a relevant process in the formation of transitional effects in our case. Then, we compare the results of LES σ model (both static and dynamic) and mixed LES models (where also a similarity contribution is considered). In particular, we consider a realistic scenario of a human carotid, and we use the reference solution as gold standard. The results highlight the accuracy of the LES σ models, especially for the static model.

High-Frequency Fluctuations in Post-stenotic Patient Specific Carotid Stenosis Fluid Dynamics: A Computational Fluid Dynamics Strategy Study

“…Relative to others, Lancellotti et al . 18 reported using and an “effective” mesh size of as a reference solution, i.e., a time step one order of magnitude larger, and a cell size almost three times smaller. Even with a different working fluid, their Reynolds number was only 25% smaller at the stenosis.…”

Flow Patterns in Carotid Webs: A Patient-Based Computational Fluid Dynamics Study

“…These recirculation zones are observed in healthy carotid bifurcations but increase in size distal to a stenosis. [8][9][10][11][12][13] In addition, frictional force induced by the blood flow (ie, wall shear stress [WSS]) can be investigated by CFD models. WSS affects many pathophysiologic processes related to atherosclerosis and is associated with ischemic stroke.…”

The cardiovascular system: Mathematical modelling, numerical algorithms and clinical applications

“…In these circumstances, suitable mesh refinement is often employed, possibly accompanied by the use of turbulence models. We mention the case of stenotic carotid arteries, for which Stroud, Berger and Saloner (2002) and Grinberg, Yakhot and Karniadakis (2009) use Reynolds-averaged Navier-Stokes (RANS) models, Lee et al (2008), Fischer et al (2007) and Cheung et al (2010) use direct numerical simulation (DNS), and Rayz, Berger and Saloner (2007) and Lancellotti et al (2015) use large eddy simulation (LES). Bazilevs et al (2009) use the VMS formulation to describe transitional effects in the ascending aorta under the influence of the left ventricular assist device (LVAD).…”

“…This is not necessarily the case for some pathological conditions, such as carotid stenosis, yielding a narrowing of the vessel lumen and increased complexity of the geometry together with higher Reynolds numbers: see e.g. Ahmed and Giddens (1984), Lee et al (2008), Kefayati, Holdsworth and Poepping (2014) and Lancellotti et al (2015). The Womersley number W = (2 A f )/µ (where A and f are the characteristic cross-section vessel area and time frequency of the flow rate signal, respectively) is a dimensionless number quantifying the pulsatility of flow.…”