Thanks again for your advice, I really do appreciate it.
The data I want from this steady-state simulation with constant mass flow rate are temperature, pressure, velocity and sound pressure level using broadband noise source model(1st part). Followed by this, I will run a transient simulation with varying mass flow rate to get the spectral analysis of sound pressure level(2nd part).
The only difference between BC for steady and transient simulation is the mass flow rate(and of course the solver control). Part of the reason I chose compressible ideal gas law is because I do not want to have too much difference between my steady and transient simulation. I am not too sure, how big the difference between both of these simulation will be if I choose different properties for density, on top of varying mass flow rate. And also, from the current simulation the air speed inside the muffler can reach up to 0.25 Mach, so it is risky.
For understanding, I had ran a brief transient simulation with constant mass flow rate and to my surprise, the residual converged properly. I never thought about running this simulation because for the 1st part, I just need a rough understanding of the property changes and also, it provide an initial value for my transient simulation in 2nd part. I did also notice the jetting you mentioned.
So now, I am having a dilemma of which setting to choose.
Steady(the norm) or Transient(converged)? Or pseudo transient? Compressible or incompressible?
Otherwise I will just use the result from the current simulation as it is.