Modelling Poster P-104 S477

CFD STUDY ON FLOW DISTURBANCE IN A STENOSED CAROTID ARTERY BIFURCATION

Felicia Tan (1), Giulia Soloperto (1), Sally Bashford (2), Nigel Wood (1), Simon Thom (2), Alun Hughes (2), Xiao Yun Xu (1)

1. Department of Chemical Engineering, Imperial College London, United Kingdom.

2. National Heart and Lung Institute, International Centre for Circulatory Health, Imperial College London, United Kingdom.

Introduction Newly developed two-equation transitional and turbulence models were employed for prediction of blood flow patterns in diseased carotid arteries where the growth, progression and structure of plaque at rupture are closely linked to low and oscillating wall shear stresses (WSS). Laminar-turbulent transition in the post-stenotic zone can alter the separation zone length, WSS and pressure distribution over the plaque, with potential implications for stresses within the plaque. Methods Following validation using an axisymmetric 75% idealised stenosed tube with well established experimental measurements [Ahmed and Giddens, 1984, Ahmed, 1998] and numerical studies [Sherwin and Blackburn, 2005, Varghese et al., 2007], a magnetic-resonance (MR) image-based model of a 70% stenosed carotid bifurcation was reconstructed and simulated using realistic patient-specific conditions including velocity waveform. Laminar flow, a correlation-based transitional version of Menter's hybrid k- /k- Shear Stress Transport (SST Tran) model and its “scale adaptive simulation” (SAS SST Tran) variant were implemented in pulsatile simulations using ANSYS CFX 11. Velocity profiles, WSS and turbulence intensity were analysed.

Figure 1: Flow separation zones and possible reattachment points in the carotid bifurcation based on laminar flow assumption and a transitional model.

Results The transitional versions of SST gave better overall agreement with experimental data in the validation work. In the patient-specific geometry simulation results, time-averaged WSS (TAWSS) distribution corresponded to velocity gradient, where areas of high WSS such as the throat, were due to high velocity and low WSS regions such as on the inner wall of the internal carotid artery, indicated flow separation and reversal zones. Oscillatory flow was also notable in the reattachment zones. This is shown in the figure. Discussion In the validation work, no model was decisively superior, although the turbulence models fared better than laminar flow assumption in capturing velocity trends. In terms of turbulence intensity, the transitional models also managed to predict correct turbulence magnitudes. The analysis of the patient-specific model showed that the transitional models predicted higher TAWSS values and larger flow separation zones (TAWSS 0) compared to laminar flow. In terms of the engineering correlations incorporated in the latter, the transitional models were considerably more likely to give realistic results. The SAS transitional variant is to be preferred because it gave better agreement in the validation work. The validation results presented for the present application give credence to the comprehensive engineering correlations incorporated in the transition model. This study highlighted the possible suitability of a transitional turbulence flow model in capturing the flow phenomena in moderate to severe stenosed carotid arteries, but more validation data on the physiological case are awaited. References Ahmed, S. A., Exp Therm Fluid Sci, 17(4): 309-318, 1998. Ahmed, S. A., and Giddens, D. P., J Biomech, 17(9):695-705, 1984. Sherwin, S. J., and Blackburn, H. M., J Fluid Mech, 533:297-327, 2005. Varghese et al., J Fluid Mech, 582:281-318, 2007.

16th ESB Congress, Posters Journal of Biomechanics 41(S1)