Federico Alzamora Previtali

The far-field boundary condition is particularly useful when modeling external flows, where the flow behavior at the boundaries is not directly influential on the region of interest. Hence, I would not recommend for this case.

The boundary conditions should be listed in the paper. Perhaps that can give some guidance.

What you are looking to do is similar to this: Supersonic Waves Reflection in a Duct | Ansys Courses.

With that in mind, try and think about how you can reconstruct your domain and assign correct boundary conditions.