Edmond Lam
Subscriber

Thank you for your reply.

I ran two simple dummy cases for 10 time steps after patching a liquid droplet with a velocity in -x.

The boundary conditions for the 2 cases are exactly the same.

There is no gravity, and the wall that I am measuring forces is at the bottom with wall adhesion enabled, surface tension modelled with CSF.

1) a liquid droplet moving in the -x direction in its vapour:

Here, with only one phase (vapour) in contact with the bottom wall, integral of x-wall shear stress is exactly the same as the force report in (1 0 0). The integral of static pressure is also exactly the same as the pressure component in force report in (0 1 0). However, although the integral of y-wall shear stress is almost zero, the viscous component in force report in (0 1 0) is non-zero, or at least much larger.

2) a liquid droplet moving in the -x direction in its vapour, but also touching the bottom wall:

Here, with both phases in contact with the bottom wall, the integral of x-wall shear stress no longer matches the force report in (1 0 0). The integral of static pressure also no longer matches the pressure component in force report in (0 1 0). And similarly, although the integral of y-wall shear stress is still almost zero, the viscous component in force report in (0 1 0) is still much larger.