Intake Obstructions

[nathan s]

In my reading that I have been doing, I haven't been able to find any information on how pressure waves are affected by things like aftercoolers and turbochargers or superchargers.

My question is, how do you treat these obstructions? Do you just treat it like a closed end or like an open end reflection?

Also, if it is a closed end, do you have any kind of pressure waves on the upstream side of the forced induction (throttle body, restrictor, etc)?

That is it for now. Have at it guys!

[nathan s]

In my reading that I have been doing, I haven't been able to find any information on how pressure waves are affected by things like aftercoolers and turbochargers or superchargers.

My question is, how do you treat these obstructions? Do you just treat it like a closed end or like an open end reflection?

Also, if it is a closed end, do you have any kind of pressure waves on the upstream side of the forced induction (throttle body, restrictor, etc)?

That is it for now. Have at it guys!

[MikeWaggoner at UW]

My understanding is that waves don't travel through those things, and that there aren't pressure waves before turbo/superchargers (because they dominate airflow, and don't pulse like piston intakes).

[nathan s]

Yeah, that is kinda what I was thinking. So does that mean an aftercooler can be treated as a closed pipe in terms of wave reflection?

[Ben Inkster]

I can't say i have ever modelled a turbo or supercharger acoustically before, but I do know that these devices will cause pressure pulses.

My first thought is to model them as sinusoidal forcing velocities with a frequency equal to the vane pass frequency.

-Ben Inkster
UWA Motorsport

[nathan s]

Do they cause pulses on the upstream side (through throttle body, restrictor, etc) or just downstream?

I guess waves could come from throttle movement, but am not sure.

[John Bucknell]

Superchargers (blowers or screw compressors) by their very nature are positive displacement, so think about that.

Turbochargers are momentum-adding devices, so think about that.

Aftercoolers can be treated as porous media if they have any turbulators in the air stream.

[Sam Zimmerman]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by nathan s:
In my reading that I have been doing, I haven't been able to find any information on how pressure waves are affected by things like aftercoolers and turbochargers or superchargers.

My question is, how do you treat these obstructions? Do you just treat it like a closed end or like an open end reflection?

Also, if it is a closed end, do you have any kind of pressure waves on the upstream side of the forced induction (throttle body, restrictor, etc)?

That is it for now. Have at it guys! <HR></BLOCKQUOTE>

I haven't checked the forum for a while but let me add my reply. If you have a pipe, it has an impedance that changes with length and geometry. Pressure waves travel before and after a turbo, supercharger, or anything else. If it is possible to set the resonant frequency of the inlet equal to the frequency of the device, you will be better off. How much better off and whether it is worth it is the question.

I believe the other part of your question is whether to model with infinite impedance or zero impedance at the turb/super charger. That is a good question that I don't completely have an answer to. Of course, the wave will not travel through either device but how much will reflect? If I were to just take a guess, treating the supercharger as an infinite impedance item would be pretty close. With the turbo charger I would more likely model it as a very constricted pipe of a very short length.

A cooler is very simply modeled as a butt-load of tiny pipes.

This is all based on the acoustics question you asked and I may be wrong on all of it.