Modeling Oscillatory Flow in a Cone-and-Plate Device Using Computational Fluid Dynamics
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Calcific aortic heart valve disease has been investigated in literature over the past three decades. Researches have been trying to understand the mechanism by which the calcification occurs on the aortic valve leaflets. Mechanical forces due to the flow of blood have been shown to have a significant contribution to the calcification of the leaflets, however, no one was able to study the native mechanical environment in the heart valve due to the complexity of the geometry. There is a soluble factor that is a known precursor for the disease called Transforming Growth Factor-β1. TGF-β1 is a protein which exists in large amounts in platelets that are flowing in the blood. The mechanism by whichTGF-β1 activates and contributes to the disease is not known, but its known that calcification is seen in areas were disturbed flow exists. This disturbed flow is defined as low and oscillatory shear environment, therefore, researchers studied the activation of TGF-β1 under oscillatory shear versus steady shear using a cone and plate device. There is, however, a lot of ambiguity in the way one produces oscillatory shear in a cone and plate. In this thesis we first study a simple geometry of a parallel plate. We see that abruptly stopping the plate to change directions of translation yields two spikes in the volume averaged shear rate that are 1.6 and 1.2 times higher than the average when stopping and restarting the movement of the plate, respectively. Areas of the fluid which experience elevated shear rates compared to the average constitute 65 percent of the volume of the fluid in the parallel plate. A different shear rate profile was seen when the plate was linearly decelerated to zero then re-accelerated to translate in the opposite direction. We only saw one peak which was 1.3 times higher than the average value with 20 percent by volume of the fluid experiencing shear rate value higher than the average value of 380s−1. Moreover, a sinusoidal oscillation of the plate did not show any spike in the shear rate and 98 percent of the fluid, at the end of the stopping period, experienced shear rate values between 107s−1and 120s−1where the minimum and maximum shear rate values were 106.2s−1and 120.2s−1. We then studied the more complicated geometry of the cone and plate and saw similar behaviors in the volume averaged shear rate profiles compared to those computed in the parallel plate case. Abruptly stopping the cone showed two spikes upon stopping and starting that were both 1.6 times higher than the average. At the end of the sinusoidal rotation we computed a volume averaged value of 175s−1with a minimum shear rate value of 0.001s−1and 963s−1. We further computed that5 percent of the fluid is experiencing shear rate values that are 2x the average value or higher. In the case of the linear deceleration/acceleration, we saw apeak that is 1.7 times higher than the average. We computed that at the end of the stopping period the volume averaged shear rate value is 380s−1with a minimum shear rate value of 0.6s−1and a maximum value of 3973s−1. We further computed that 13 percent of the fluid experiences values of shear rate that are 2x the average value or higher. In the case of the sinusoidal rotation, no spikes in shear rate were seen. At the end of the sinusoidal oscillation, we computed a minimum shear rate value of 0.6s−1, a maximum shear rate value of 1690s−1, and a volume averaged shear rate value of 350s−1. We further computed that 5 percent of the fluid experiences shear rate values that are 2x the average or higher.
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