I am going to simulate an engine intake manifold by star ccm+ .I have msss flow at inlet and pressure at outlet. Please answer to these questions:

1- These analysis should be compressible or incompressible?

I ran incompressible analysis , and as expected I found little pressure change. But I suspect that, this may be compressible analysis. Kindly guid me for this.

Compressible vs. Incompressible flow depends on the speed of the flow entering the intake. For Mach numbers less than 0.3-0.5(ish), I'd say you are in the incompressible range.

Uh?

Intake manifolds are like musical instruments. Absolutely dominated by pressure waves. I really doubt you are doing a steady flow calc.

Mehndan,

Is this for an engine intake or musical instrument? Can you provide some more background to the problem please?

JT

Hi Thanks for response. Its for engine intake. I got around 150 m/sec velocity when running incompressible analysis, thats why I doubted that, it may be compressible flow. what are your suggestion?

guessing this is for an aircraft - which then raises the question of what pressure altitude are you simulating this model at, because the local speed of sound differs at various altitudes. Something that is compressible at a certain altitude, may or may not be compressible at another.

Drop me an email directly if you need further suggestions

Ahh (sound of penny dropping). I assumed you were studying the intake manifold of a piston engine.