Federico Alzamora Previtali

In general, the FW-H model is not applicable to internal flow acoustics such as noise propagation in ducts, but you could have a case where the internal flow is your source and you will be using FW-H to model sound propagation downstream in an external domain.
FW-H solution assumes that the source region radiates sound through a free field environment with no obstacles between the source and receivers. Hence, FW-H will be less sensitive to BCs outside of your source region.