The Influence of Red Blood Cells on the Turbulence Characteristics of Blood.

湍流与速度和压力的随机波动有关，并且可以存在于工程中的许多流动中，包括生物起源的流动。血液几乎总是假设为层流通过大部分动脉系统，然而在主动脉中，在涉及复杂几何形状的情况下，在存在动脉疾病（包括动脉粥样硬化（堵塞）和主动脉瓣狭窄（主动脉瓣变窄））的情况下，流动通常会变成湍流。血液中的粘性剪切对血管的结构组分（例如内皮细胞）具有深远的影响，可能的后果是激活生化途径和机械转导，导致不必要的生物学变化。通常假设血液是单相和牛顿流体，但细胞和血浆蛋白质使流体在低剪切速率下具有非牛顿性质的多相性质。通过数值模拟和实验相结合，将探讨血液中的湍流行为。将考虑血液表现出的多相行为，目的是创建一个完整的数值模型，该模型可用于预测血液及其组分在与心血管医疗器械（瓣膜和泵）相互作用时的行为。将使用计算流体动力学（CFD）完成数值建模，其中将模拟通过血管的稳定血流的初始模型，并了解从层流到过渡流和湍流的发展，这在血液中很明显。然后将使用多普勒超声（DUS）对血液进行体外实验，以了解将血液视为多相流体时血液从层流到湍流的转变，并希望将其与相同粘度的单相流体进行比较。此外，实验将继续与更适用的生物情况，如脉动流，以说明周期性变化的速度，除了看动脉和心血管疾病，如狭窄。在实验之后，收集的数据将用于改进和优化初始数值模型，以期开发一个完整的非牛顿多相模型来预测血液中湍流行为的性质。正在进行的研究在心血管工程和生物力学领域有很高的需求。从长远来看，我们非常需要了解血液及其成分对心血管器械的影响，从而使设计和测试更加清晰，并减少假设。此外，这一水平的研究将允许识别血液损伤，包括预测机械性溶血

Turbulent flows are associated with random fluctuations of velocity and pressure and can exist within many flows in engineering including those of a biological origin. Blood is almost always assumed to be laminar through most of the arterial system, however in the aorta, in cases involving complex geometries, in the presence of arterial diseases including atherosclerosis (blockages) and aortic valve stenosis (narrowing of aortic valve) the flow can often become turbulent. Viscous shearing in blood has profound effects on structural components of vessels, for instance endothelial cells, the possible consequences being the activation of biochemical pathways and mechanotransduction leading to unnecessary biological changes. It is often the assumption that blood is both single phase and a Newtonian fluid, but the cells and plasma proteins makes the fluid multiphasic in nature with non-Newtonian properties at low shear rates. Through a combination of numerical modelling and experimentation, turbulent behaviour in blood will be explored. The multiphase behaviour which blood exhibits will be considered with the purpose of creating a full numerical model which may be used to predict the behaviour of blood and its components when interacting cardiovascular medical devices; valves and pumps. Numerical modelling will be accomplished using Computational Fluid Dynamics (CFD) where an initial model of steady blood flow through a vessel will be simulated with the idea of understanding the development from laminar to transitional flow and into turbulent flow, which is evident in blood. In vitro experimentation on blood using Doppler Ultrasound (DUS) will then be conducted to understand the transition of blood from laminar to turbulent flow when considering blood as a multiphase fluid, with the hope of comparing this with a single phase fluid of the same viscosity. Further from this, experimentation will continue with more applicable biological situations such as pulsatile flow, to account for the periodic variations of velocity, in addition to looking at arterial and cardiovascular diseases such as stenosis. Following up from experimentation, the data gathered will be used to improve and optimise the initial numerical model created in the hope of developing a full non-Newtonian, multiphase model to predict the nature of turbulent behaviour in blood. The research being undertaken has a high demand in the field of cardiovascular engineering and biomechanics. There is a great need to understand how the influence of blood and its components affects cardiovascular devices in the long term, allowing the design and testing to be much clearer with fewer assumptions being made. Further, this level of research will allow the identification of blood damage and including prediction of mechanical haemolysis