refractive effect

czbj

Dear All,

I am now graduate in a university. i have the following questions to ask.

1) what is refractive effects (refraction) in the flow for aeroacoustics (or acoustics)?

2) In the acoustic governing equations (Navier-Stokes equation or Euler equation), which terms mathematically accounts for the refraction?

3) under what circumstances there are significant refractive effects in the flow?

4) whether do Linearized Euler equations consider the refraction in the flow (acoustic field)?

Looking forward to your replies

Thanks in advance