Currently, I am conducting pressure based transient incompressible fluid flow in viscoelastic tube in ANSYS fluent and I would like to create an absorbing boundary condition in the outlet of the tube.

ANSYS Fluent already include non-reflecting outlet boundary conditions (NRBC) but only applies for ideal gas (compressible) flow.

With Pressure Far Field BC, it is available only when density is calculated using ideal gas law.

With Outflow BC, it cannot be used for unsteady flow with variable density.

So, the last option is using UDF in the outlet of the tube and I have difficulty applying it.

I found a thesis that similar to my research approach. (https://folk.ntnu.no/leifh/alumni/2013_Merethe_Sirevaag_Hansen.pdf)

And I would like to create such boundary condition in ANSYS fluent.

In page 27 of the thesis, under Section 3.2 Boundary Conditions, in Subsection 3.2.1, the author applied reflection free boundary condition at the outlet of the vessel. I have short knowledge of how to apply the boundary condition at the outlet of a vessel.

I am learning UDF in ANSYS Fluent, but I am not sure how to apply boundary equation (Eq 104, page 28) at the outlet. I assume it will require to use UDM but the equation require to use the volume flow rate value from previous space step.

I manage to calculate in numerical analysis but Can someone show a tutorial to put Eq 104 in UDF of ANSYS fluent?