multiphase DyM solvers - velocities
 

Hello all,

I'm dealing with interDyMFoam and compressibleInterDyMFoam for quite some time now. At a recent meeting, the question came up which velocity is calculated - relative or absolute.

In this specific case, a closed test tube filled with 50% liquid and 50% air will be "shaken" along the longitudinal axis according to a prescribed oscillation (non-sinusoidal).

Looking at lines 110 and 111 in compressibleInterDyMFoam.C, I find
So, I think the velocity vectors are being "transformed" into the moving reference system, here, the moving domain. Or at least I believe that in the end my output values represent the relative velocity U_rel = U_abs - U_domain, but I'm not entirely sure. In this case, U_domain represents the velocity with which my mesh is moving.

Maybe, someone is able to shed light on that matter. Thank you :)