(14e) Novel, Hybrid, Blood Flow Simulations within Large Arterial Vessels

We present novel, hybrid 1D/3D, simulations of time-periodic blood flow through nonaxisymmetric arterial bifurcations. These involve an efficient implementation of the proper (in vivo) outlet boundary conditions, as provided in the form of Fourier frequency impedance coefficients by a 1D model, to a commercial 3D (FLUENT) code. This is achieved through the intermediate use of an approximate ?simulant? model of the outlet pressure/flow relationship corresponding to the full 3D and time-dependent numerical simulation. An adjustable time-periodic function correction term in the simulant model requires input from the full 3D model that has to run iteratively until convergence. Special correction terms allow to taking into account, approximately, of the wall viscoelasticity thereby permitting to interface 3D calculations carried out in a complex but rigid wall geometry to1D model calculations allowing for wall viscoelasticity. The advantage of the proposed hybrid scheme is that it decouples the upstream detailed simulation from the downstream approximate network model offering exceptional versatility. This approach is demonstrated here in a series of detailed 3D simulations of blood flow, performed using the commercial software FLUENT, through an asymmetric arterial bifurcation. Two cases are considered: first a healthy system, patterned after the left main coronary arterial bifurcation, and second a diseased case where an occlusion has developed in one of the daughter vessels, resulting in strengthening the asymmetry of the bifurcation. Rapid convergence of the iterative process was achieved in both cases. Subtle changes occur in the shear patterns of the daughter vessels, while the flow distribution is quite different. In the presence of a stenosis additional regions of low shear develop due to inertial effects.