Investigation of the backflows and outlet boundary conditions for computations of the patient-specific aortic valve flows.

Background: Simulation divergence due to the backflow through the outlet boundary is a common, but not fully addressed challenge in patient-specific simulations of the aortic valve flows.

Objective: The purpose of this study is to develop the outlet boundary conditions aiming to improve convergence of the patient-specific aortic valve computations and to control the backflow in the case of partial reversal of the flow through the outlet.

Methods: Haemodynamic analysis of the aortic valve flows governed by the Navier-Stokes equations is performed by using the finite volume method. The pressure distribution, obtained from the convergent computations driven by the outflow boundary condition, is approximated by the parabolic surface of revolution and prescribed on the outlet as the novel pressure boundary condition.

Results: Various types of outlet boundary conditions are investigated to evaluate their influence on the resulting backflows. The outflow boundary condition produces a smaller backflow than other investigated boundary conditions, but it causes the solution divergence. The proposed outlet boundary condition allows for continuing the solution and preserving the expected backflow.

Conclusions: The proposed outlet boundary condition helps to achieve a convergent solution and to conserve the observed backflow by varying the convexity of the specified pressure surface.