过载负荷下分叉血管的流动数值模拟

Numerical simulation of bifurcating blood vessel flow under overload

背景:人体对于过载负荷的大小具有一定的耐受极限,超过一定强度时会对人体造成损伤,过载对人体血管流动过程的影响是载人航天医学研究的一个重要课题。目的:针对典型的颈部动脉简化分叉三维血管模型进行了非常规重力载荷下的脉动流血管流动形态数值模拟分析。方法:根据人体的正常脉搏周期,计算过程设定0.85 s为一个血液脉动供给周期。对于分叉血管(基于人体颈部动脉分支血管的几何特征进行刚性简化),假设正常状态下主血管与分支血管流量分配为7∶3。基于Fluent计算流体力学软件,通过在控制方程动量源项中添加重力载荷的方法(过载方向X+,过载大小为1 G;过载方向Y+,过载大小为2 G),分析重力过载效应对人体典型血管流动特征的影响。结果与结论:(1)获得了重力过载下的瞬态流场结构、壁面剪切应力的变化情况。由于受到Y+方向过载的影响,分叉血管在不同时刻在流速分布、回流区域大小、剪切应力分布上存在明显差异;(2)超重负荷效应下,分叉位置分支血管内壁面处形成了明显的分离区域且血液流量明显变大,造成主血管段内血液流量减少且发生严重的回流现象;(3)在超重负荷的影响下分支血管段壁面剪切应力明显大于主血管段壁面剪切应力。

BACKGROUND:Human body has a certain tolerance limit to overload,so load beyond certain strength will cause damage to the human body.The effect of overload on the flow of blood vessels is an important medical topic in manned space.OBJECTIVE:To study the flow patterns of pulsating blood vessels under unconventionally gravity load in a typical three-dimensional model of cervical artery.METHODS:Based on normal pulse cycle,we considered 0.85 seconds as pulsating blood supply cycle.The blood flow ratio of main vessels and branch vessels was 7:3.Based on Fluent software,the effects of gravity overload on the flow characteristics of typical blood vessels were analyzed by adding gravity load(1 G of overload at direction of X+;2 G of overload at direction of Y+)to the momentum source of the control equation.RESULTS AND CONCLUSION:The changes of transient flow field structure and shear stress of wall under gravity overload were obtained.Because of the influence of Y+direction of overload,the bifurcating vessels had obvious difference in velocity distribution,size of reflux region and shear stress distribution at different time.Under the effect of overweight load,the blood flow in the main blood vessel decreased and serious reflux occurred.The shear stress on the wall of the branching blood vessel was obviously higher than that on the main blood vessel.