I'm trying to write a program simulating the sound of an petrol car engine, just for fun.
As a part of this, I'm trying to model the sound of air escaping the combustion chamber through an open poppet valve.
I tried modeling the flow of air through a hole as an Aeolian sound (https://en.wikipedia.org/wiki/Aeolian_sound), but I think this is not a good model, since it predicts very high pitched sounds (in the multiple kilohertz range for a regular car engine at full load).
I'm thinking the exhaust sound of a car comes from several phenomena:
1: The direct pressure variation in the exhaust system when the valve opens and hot, high-pressure exhaust gas flows into the exhaust system.
2: Some kind of (pink?) noise from the chaotic, turbulent air flow.
3: Lots of resonances in the engine, car etc.
4: Acoustic resonance in the exhaust system, particularly at certain engine speeds.
(Then we have of course, intake sound, sound of gearbox, accessories, camshafts etc, but that's a later problem)
I think I have some idea to approximate #1, #3 and #4, but I'm stuck regarding #2.
What is the mechanism causing a white/pink-noise sound when air flows through a narrow opening? How could I model this?
