Numerical Simulation Of Blood Flow In Aorta With Dilation: A Comparison Between Laminar And Les Modeling Methods

Computational modeling methods have been increasingly employed to quantify aortic hemodynamic parameters that are challenging to in vivo measure-ments but important for the diagnosis/treatment of aortic disease. Although the presence of turbulence-like behaviors of blood flow in normal or diseased aorta has long been confirmed, the majority of existing computational model studies adopted the laminar flow assumption (LFA) in the treatment of sub-grid flow vari-ables. So far, it remains unclear whether LFA would significantly compromise the reliability of hemodynamic simulation. In the present study, we addressed the issue in the context of a specific aortopathy, namely aortic dilation, which is usually accompanied by disturbed flow patterns. Three patient -specific aortas with treated/untreated dilation of the ascending segment were investigated, and their geometrical models were reconstructed from computed tomography angiographic images, with the boundary conditions being prescribed based on flow velocity information measured in vivo with the phase contrast magnetic resonance imaging technique. For the modeling of blood flow, apart from the traditional LFA-based method in which sub-grid flow dynamics is ignored, the large eddy simulation (LES) method capable of incorporating the dissipative energy loss induced by tur-bulent eddies at the sub-grid level, was adopted and taken as a reference for exam-ining the performance of the LFA-based method. Obtained results showed that the simulated large-scale flow patterns with the two methods had high similarity, both agreeing well with in vivo measurements, although locally large between-method discrepancies in computed hemodynamic quantities existed in regions with high intensity of flow turbulence. Quantitatively, a switch from the LES to the LFA-based modeling method led to mild (<6%) changes in computed space-averaged wall shear stress metrics (i.e., SA-TAWSS, SA-OSI) in the ascending aortic seg-ment where intensive vortex evolution accompanied by high statistical Reynolds stress was observed. In addition, comparisons among the three aortas revealed that the treatment status of aortic dilation or the concomitant presence of aortic valve disease, despite its remarkable influence on flow patterns in the ascending aortic segment, did not significantly affect the degrees of discrepancies between the two modeling methods in predicting SA-TAWSS and SA-OSI. These findings suggest that aortic dilation per se does not induce strong flow turbulence that substantially negates the validity of LFA-based modeling, especially in simulating macro-scale hemodynamic features.