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

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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