Multiphase Wall Adhesion - Courant Number Exceeds 250
 

Hi Guys,

I am doing a project in microfluidics where surface tension plays a key role! I am trying to simulate and experiment a 100 um by 100 um straight channel with 3mm length.

When I run the simulation after about 0.4s of the simulation, the courant number exceeds 250 and simulation stops. Given the simplicity of the geometry and using ICEM CFD for meshing, convergence is not an issue in earlier time steps.

Here are some more info of the case:
1- channel is initially filled with water and patched correctly before solving
2- inlet velocity is 0.0045 m/s
3- Contact Angle is 107 degrees (which is very important for us, i.e. Hyrophoic case so capillary pressure is acting against the flow)
4- Time step I tried different ones: 0.01s to 0.0001 and even 0.00001. smallest mesh side is 1e-5 m (I used uniform mesh). So rule of thumb people suggest Delta X/velocity gives 0.0022 seconds.
5- I tried VOF and Eulerian explicit method with default values

I dont understand what is wrong! The simulation goes fine without wall adhesion (e.g. Contact Angle). This is very important for us which then I will be adding particles inside the water to model the whole thing.

Can someone please get back to me? I appreciate your help

Regards,
Payar Radfar