[dgnidovec]

Hello fellow Fluent users,

I've been working on a simulation involving laminar and incompressible flow through a simple cylindrical domain (a vein), where I've set up boundary conditions for pressure inlet and mass flow outlet. However, I've run into some puzzling discrepancies between the prescribed values in my User-Defined Function (UDF) and the values that Fluent calculates/consider at the outlet boundary.

More precisely, I know the function of pressure at inlet and the function of the mass flow at outlet. My fluid is incompressible and flow is laminar, hence I prescribe constant value at pressure inlet and only observe pressure gradient from the domain. My driven BC is mass flow at outlet, which is interpolated with linear function from the starting point to the ending point. My ending point values are updated from the 0D model, so I am exchanging them from 0D to 2D model and vice versa. The problem is that my prescribed ending point value is not considered exactly... Fluent takes slightly different values, especially when mass flow rate gets very low... I am aware of numerical precision challanges, but I need additional information about that.

I also encounter that in my axial domain fluid flows in the right direction in the middle of a cylinder, but close to the boundary it flows backwards and it somehow rotate in my domain... I cant figure it out why... I hope my problem is clear enough, otherwise feel free to ask more specific questions.

Any guidance or suggestions would be greatly appreciated. Thank you in advance for your help!

Best regards!