[Bisht]

Hello everyone,

I am trying to simulate the rise of water column in a capillary tube but getting some weird results. The parameters are:

Tube diameter- 2 mm, Tube length- 60 mm
Pressure based solver- Piso scheme
Pressure velocity coupling- Presto / Body force weighted pressure discretization
Transient flow, Multiphase- Volume of fluid, Implicit body force activated
Operating pressure- 101325 Pa, Pressure Inlet and Pressure outlet BC, Gauge pressure - 0 Pa (at both inlet and outlet)
Primary phase: Air, Secondary: Water
Volume fraction of water at inlet:1, Volume fraction of water at outlet:0

Gravity activated, Operating density- air, Primary phase- air, Secondary phase- water, Contact angle- 30 degree, Surface tension- 0.072 n/m

Initialization method- Hybrid, Patch condition- volume fraction of air in the tube at t=0 is 1.

With above mentioned parameters, liquid keep rising in the tube till its completely filled even though gravity is activated.
(In case of standard initialization, I am getting floating point error and liquid not rising).

However, if I am using 0 Pa as operating pressure and 101325 as pressure value at both inlet and outlet, results are completely different.

The liquid rises in the tube to the equivalent height obtained by analytical calculation and then recede. The final height is approximately half of the analytical solution and simulation flow time is also not in accordance with the physical time.

I would like to know that am I using the wrong values or it is something else which create these issues with capillary flow simulation.