Abstract

CFD methods are widely used for the development of artificial valves. However, choosing the proper flow parameters to characterize the flow to predict the valve function in vivo, is still a big challenge. There is a set of parameters, which are used for flow characterization: pressure drop, maximal velocity magnitude, calculation of the residence time along path line and maximal values or histogramms of wall shear stress, shear stress and turbulence intencity. We propose to use the numerical dye washout method for flow characterization. This allows the assessment of regions with a long or short residence time and therefore predicts the regions of high or low thrombus risk. This successful experimental method is modeled now numerically. This allows a 3D-resolved flow characterization and a possibility to validate the results experimentally. In order to simulate the dye washout, an unsteady flow simulation is performed with the flow solver FLUENT. Furthermore, a species transport model simulating the convective diffusion mixing of species (entering/outflowing blood) is applied. The results are distributions of the fluid fraction for different time steps. These data were used for the dye washout visualization, which was realized using the software AMIRA. Results are images, which represent the projection of the absorbed light intensity. The analysis of the washout process was done by quantifying the time course of the gray value. The method was applied in 5 different mechanical valves. The results show that dye washout flow characterization seems to be a very useful parameter.

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