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Arterial Flows – The Magic of Numerics
Start Date: 5/6/2014Start Time: 3:00 PM
End Date: 5/6/2014End Time: 4:00 PM

725 23rd Street NW, Tompkins Hall 204
Washington, DC 20052

L. Prahl Wittberg
Linné FLOW Center, KTH Mechanics
Stockholm, Sweden

For the localization of vascular diseases, hemodynamics is believed to play an important role. Hemodynami investigations of patient-­specific anatomical models may therefore enhance our understanding of the onset and progress of vascular diseases, provided that the working hypothesis (the pathology of vascular diseases is connected to the predominant flow behavior) is valid.  Concomitant flow phenomena pertaining to aortic anomalies are being numerically investigated. Aortic anomalies can be characterized by changes in the shape of the arch geometry, including widening or narrowing of the aortic diameter, as well as lengthening of parts of the arch. This investigation includes several anatomically different human arteries associated with intrinsic flow phenomena that potentially affect the local blood cell distribution and wall shear stresses. Examples of hemodynamics from patient-­specific geometries of the aortic arch and the renal arteries will be presented.  In the simulations blood is represented by a mixture of Red Blood Cells (RBC) and blood plasma, with the mixture density considered as a function of RBC and plasma densities. The RBC phase is treated as an active scalar, coupled to the blood viscosity represented by the Quemada non-­ Newtonian viscosity model. Bulk flow behavior is assessed by Navier-­Stokes equations for an incompressible fluid, modeling the distribution of RBCs using a transport equation.  An important outcome of the investigation is that the local distribution of the RBCs is clearly affected by the flow structures appearing in these patient-­‐specific geometries. This in turn is directly connected to the local mixture viscosity where a 5% change in local RBC volume fraction will lead to a 40% change in local blood viscosity according to available non-­‐Newtonian models of blood. However, these models have been obtained for simple geometries, correlating blood viscosity to a fixed bulk RBC volume fraction and shear rate.  The effect of fluid inertia is neglected, among the aforementioned factors believed to be important for the macroscopic properties of a fluid in the semi-­‐dilute regime.  Thus, the purpose of this work is two-­‐fold; capture the flow behavior in our circulatory system to increase our understanding of vascular diseases and enhance our knowledge of non-­dilute particle suspensions of RBCs in blood by performing detailed numerical simulations. 

Lisa Prahl Wittberg is an Assistant Professor in the Department of Mechanics at the Royal Institute of Technology (KTH) in Stockholm, Sweden. Dr. Prahl Wittberg completed her graduate work in the Department of Energy Sciences/Div. Fluid mechanics at Lund University, Sweden, in 2007. She was awarded the KTH Postdoctoral Fellowship and the Sweden-America Foundation Postdoctoral Fellowship in 2008 and 2012, respectively. Her research interests lies in the area of multiphase flows, focusing on detailed numerical simulations of complex fluids as well as the flow applications in which these fluids are found. She is involved in several projects including dense particle suspensions of red blood cells and the flow of blood in patient specific geometries, break-up and deformation of droplets connected to fuel injection in spray simulations and fiber suspensions flow related to the papermaking industry.
Cindy Fields Arnold
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