Erik Kostson
Ansys Employee

First I would propose to use solsh190 instead of shell on the window.

Then the window and the air domain should share topology (as you mentioned) to have a connected mesh between the window and air, and so we do not need contacts between them (so that is the first question answered about contact).

Finally you should always add a FSI flag between these two regions especially if you choose to use shells instead of the solsh190 (need method/swept, and thin swept option with solid shell).

This (FSI) is easy to create just right mouse button click under harmonic acoustics (say were we create loads etc.) and choose Create Automatic -> FSI (if the faces are shared it will create one automatic and it will show up in the tree).

All the best