I am trying to model a Doppler shift induced in a microwave signal by a flowing liquid in order to measure the flow speeds. I currently have 2 problems. The first is getting the plane wave to be incident on my flowing liquid at an angle. The plane wave seems to behave when modeled separately but not when combined with the flow block (even when the interaction isn't accounted for in the study). 

The second problem is how model the Doppler interaction within the flowing medium. (I can't see how to adapt the acoustic Comsol Doppler example. Similarly, I can't see how to adapt the radar Comsol example).