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?



Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Browse other questions tagged or ask your own question.