I have two questions regarding the Aorta3d Problem.
1. In the Aorta problem, the boundary condition for outlet is pressure outlet and you set 0 for boundary condition. zero here is gauge pressure, absolute pressure or reference pressure?
when I run the code in some points we have less than zero pressure, is this physical?
2. I read the following paper that is written by Dr Mathias J. Krause. In the paper the authors mentioned that in the code mass fraction for each outlet is evaluated by experimental results.
would you please tell me that in which part of code we can evaluate the mass flux fraction as an input, for example if we have 40% of mass flux for outlet1 and 60% of mass flux for outlet2. something like that.
Aortic Coarctation Simulation Based on the Lattice Boltzmann Method: Benchmark Results
Thanks for your interest.
1/ In Navier-Strokes euations, pressure is defined up to a constant. At the outlet we fix this constant. So it is a reference pressure. Taking the computed pressure distripution you can add any constant pressure you want. So a negative value is fine and still physical.
2/ The paper refers to a different example. There we fixed the mass flow by fixing the velocity. If you want do that in the mentioned example you may set velocity boundary conditions at the two outflows and a pressure condition at the inflow.