This animation shows the magnitude of vorticity close to the centerplane of a carotid bifurcation that exhibits a severely stenosed internal branch. The inset shows the volume flow rate, Q(t), coming into the common carotid artery (CCA).
Because there is roughly a factor of ten in the dynamic range of the velocity, due to the cardiac cycle, the contours represent the vorticity distribution renormalized by the min and max at each instant in time. In this simulation, the peak velocity is roughly 2.0 m/s at systole, and roughly 0.2 m/s in the diastolic trough.
The flow split between the internal (ICA) and external (ECA) artery is fixed at 0.59Q and 0.41Q, respectively. This is achieved by using superposition for the Stokes subproblem that is solved at each time step of the calculation.
The initial conditions were set by starting with viscosity = 5000 x normal (Re ~= 0), and lowering this while simultaneously ramping the inlet flow velocity to match the time-dependent inlet profile, which is given by the Womersley solution. The image pictured here corresponds to the second cardiac cycle, which shows no visible remnant of the initial condition.
The resolution for this initial calculation is 850,000 velocity points, 550,000 pressure points (2544 spectral elements of 7th-order in velocity). Simulation of a single cardiac cycle (0.75 seconds) required 11 hours of wall-clock time on 256 nodes of the Alpha-based TCS1 at the NSF Pittsburg Supercompting Center.
Last update: July 14, 2002 (pff)