Direct numerical simulation of transitional flow in a stenosed carotid bifurcation

Abstract

The blood flow dynamics of a stenosed, subject-specific, carotid bifurcation were numerically simulated using the spectral element method. Pulsatile inlet conditions were based on in vivo color Doppler ultrasound measurements of blood velocity. The results demonstrated the transitional or weakly turbulent state of the blood flow, which featured rapid velocity and pressure fluctuations in the post-stenotic region of the internal carotid artery during systole and laminar flow during diastole. High-frequency vortex shedding was greatest downstream of the stenosis during the deceleration phase of systole. Velocity fluctuations had a frequency within the audible range of 100–300 Hz. Instantaneous wall shear stress within the stenosis was relatively high during systole (~25-45 Pa) compared to that in a healthy carotid. In addition, high spatial gradients of wall shear stress were present due to flow separation on the inner wall. Oscillatory flow reversal and low pressure were observed distal to the stenosis in the internal carotid artery. This study predicts the complex flow field, the turbulence levels and the distribution of the biomechanical stresses present in vivo within a stenosed carotid artery.

Flow instability and wall shear stress variation in intracranial aneurysms

“…Hydrodynamic instability and transition into turbulence in arterial pulsatile flow has been studied extensively in the past (Nerem et al 1972;Steiger & Reulen 1986;Einav & Sokolov 1993;Blackburn & Sherwin 2007). More recently, high-resolution simulations were performed for stenosed carotids by Fischer et al (2007), Lee et al (2008) and Grinberg et al (2009). In all cases, turbulence or temporal fluctuations were observed in the decelerating systole or near the end of systole.…”

“…CFD simulations in the carotid stenosis (Fischer et al 2007;Lee et al 2008;Grinberg et al 2009) were performed and intermittent turbulence during the decelerating systole was reported. However, the current work seems to be the first numerical study to report flow instability in aneurysms.…”

Simulated hemodynamics in human carotid bifurcation based on Doppler ultrasound data

“…The rheological behavior of blood was simulated considering a constant dynamic viscosity value of 0.0035 kg/(m.s), a reasonable assumption for bulk flow metrics [22,23]. Newtonian rheology is reasonable in the context of fluid precision and uncertainties related to boundary conditions [11,[23][24][25]. The volume-filling finite element meshes consisted of nearly 60000 quadratic hexahedral finite elements.…”

“…Although for large-scale studies of common carotid artery (CCA) bifurcation hemodynamics the use of a typical flow waveform shape is likely sufficient, for a detailed patient study a subject-specific waveform collected in clinical practice, as in our study, yields a more accurate assessment of flow characteristics [9,11,12].…”

Transitional flow in intracranial aneurysms – A space and time refinement study below the Kolmogorov scales using Lattice Boltzmann Method

“…Numerical investigations of fluctuations in physiological flows have been dominated by the use of finite volume method 7 or spectral element methods 32 . Two recent computational studies demonstrate transitional flow in aneurysms 50;51 -these studies employed low-order finite elements but the scheme was tailored to minimize numerical dissipation in order to capture transition.…”