Banks J, Bressloff N W
Computational Engineering and Design Group, University of Southampton, Highfield, Southampton SO17 1BJ, UK.
J Biomech Eng. 2007 Feb;129(1):40-50. doi: 10.1115/1.2401182.
Under normal healthy conditions, blood flow in the carotid artery bifurcation is laminar. However, in the presence of a stenosis, the flow can become turbulent at the higher Reynolds numbers during systole. There is growing consensus that the transitional k-omega model is the best suited Reynolds averaged turbulence model for such flows. Further confirmation of this opinion is presented here by a comparison with the RNG k-epsilon model for the flow through a straight, nonbifurcating tube. Unlike similar validation studies elsewhere, no assumptions are made about the inlet profile since the full length of the experimental tube is simulated. Additionally, variations in the inflow turbulence quantities are shown to have no noticeable affect on downstream turbulence intensity, turbulent viscosity, or velocity in the k-epsilon model, whereas the velocity profiles in the transitional k-omega model show some differences due to large variations in the downstream turbulence quantities. Following this validation study, the transitional k-omega model is applied in a three-dimensional parametrically defined computer model of the carotid artery bifurcation in which the sinus bulb is manipulated to produce mild, moderate, and severe stenosis. The parametric geometry definition facilitates a powerful means for investigating the effect of local shape variation while keeping the global shape fixed. While turbulence levels are generally low in all cases considered, the mild stenosis model produces higher levels of turbulent viscosity and this is linked to relatively high values of turbulent kinetic energy and low values of the specific dissipation rate. The severe stenosis model displays stronger recirculation in the flow field with higher values of vorticity, helicity, and negative wall shear stress. The mild and moderate stenosis configurations produce similar lower levels of vorticity and helicity.
在正常健康状态下，颈动脉分叉处的血流是层流的。然而，在存在狭窄的情况下，在收缩期较高雷诺数时血流会变得紊乱。越来越多的人认为，过渡k-ω模型是最适合此类流动的雷诺平均湍流模型。本文通过与通过直的、无分叉管道的流动的RNG k-ε模型进行比较，进一步证实了这一观点。与其他地方的类似验证研究不同，由于模拟了实验管道的全长，因此对入口剖面没有做任何假设。此外，结果表明，在k-ε模型中，流入湍流量的变化对下游湍流强度、湍流粘度或速度没有明显影响，而在过渡k-ω模型中，由于下游湍流量的大幅变化，速度剖面显示出一些差异。在这项验证研究之后，过渡k-ω模型被应用于颈动脉分叉的三维参数化计算机模型中，在该模型中，对窦状膨大进行操作以产生轻度、中度和重度狭窄。参数化几何定义为在保持整体形状不变的同时研究局部形状变化的影响提供了一种有力手段。虽然在所考虑的所有情况下湍流水平通常都较低，但轻度狭窄模型产生的湍流粘度较高，这与湍流动能的相对较高值和比耗散率的较低值有关。重度狭窄模型在流场中显示出更强的回流，具有更高的涡度、螺旋度和负壁面剪应力值。轻度和中度狭窄构型产生的涡度和螺旋度水平较低且相似。
