Effects of the Distribution in Space of the Velocity-Inlet Condition in Hemodynamic Simulations of the Thoracic Aorta

In the present paper the effects of the spatial distribution of the inlet velocity in numerical simulations of the thoracic aorta have been investigated. First, the results obtained by considering in-vivo measured inlet velocity distribution are compared with the ones obtained for a simulation having the same flow rate waveform and plug flow condition at the inlet section. The results of the two simulations are consistent in terms of flow rate waveform, but differences are present in the pressure range and in the wall shear stresses, especially in the foremost part of the ascending aorta. This motivates a stochastic sensitivity analysis on the effect of the distribution in space of the inlet velocity. This distribution is modeled through a truncated-cone shape and the ratio between the upper and the lower base is selected as the uncertain parameter. The uncertainty is propagated through the numerical model and a continuous response surface of the output quantities of interest in the parameter space can be recovered through a "surrogate" model. A stochastic method based on the generalized Polynomial Chaos (gPC) approach is used herein. The selected parameter appears to have a significant influence on the velocity distribution in the ascending aorta, whereas it has a negligible effect in the descending part. This, in turn, produces significant effects on the wall shear stresses in the ascending aorta, confirming the need of using patient-specific inlet conditions if interested in the hemodynamics and stresses of this region.