Influence of Blood Rheology and Outflow Boundary Conditions in Numerical Simulations of Cerebral Aneurysms - Mathematical Methods and Models in Biomedicine - page 159

Fig. 8 WSS magnitude (dyn/cm 2 ) for the clipped geometry with traction-free conditions at the
side-branch, using the Newtonian ( top ) and the Carreau ( middle ) models, and its differences
( bottom ), for the unsteady and steady solutions. The maximum difference is calculated for the
whole geometry, using the maximum value for the percentage
differences in the velocity cross-section between both models are of the order
of 5-8 % and occur inside the aneurysm. The smallest differences occur on the
steady case or at the minimum of diastole, while the higher discrepancies are
observed during the systolic phase of the unsteady flow. The results show that,
even though the average of the difference is low, in some periods of the cardiac
cycle the discrepancies between the Newtonian and non-Newtonian models become
more noticeable. Comparing the two inflow conditions, the variations that appear
inside the aneurysm are higher in all the chosen time instants of the unsteady flow,
highlighting the importance of considering simulations as time dependent. The same
conclusions can be drawn from the WSS distribution, yet here the discrepancies are
more relevant in the main vessel.
In order to analyze the effects of the different outflow conditions, the configu-
ration with the side-branch and a traction-free boundary condition at its outflow is
compared with the clipped geometry using all the considered boundary conditions,
see Fig. 9 and Table 2 . In this particular geometry the side-branch has a substantial
influence on the solution, not only due to its location, inside the aneurysm, but also
due to the large percentage of flow that enters the branch. The traction-free condition