Air Intake tuning?

[par1]

I do understand that intake runner length can be tuned to boost more air & hence, get more performance but,
difficulty to understand meaning of

"air cleaner system which has couple of resonator & side branches. Resonator 1 is tuned at 125 Hz, Resonator 2 is tuned at 140 Hz, Side Branch 1 tuned at 540 Hz & side branch tuned at 840 Hz."

I will appreciate, if anyone can reply

 

[GregLocock]

They are describing the acoustic performance of the air intake. They are using a mixture of expansion chambers (resonators) and side branches - quinkies - quarter wave tuning.

They will only have negligible effects on the volumetric efficiency if they are upstream of the plenum.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[par1]

Now, it clears to me that Resonator/side branch tuning frequency has negilible effect on volumetric efficiency.

But still I have confusion on,

(1) what is the physical significance of, resonator 1 is tuned at 125Hz or Side branch 2 at 840 Hz?

(2) How do we come up specific tuning frequency of different resonator & side branch for the same air intake system?

(like to improve the voulmetric efficiency,we calculate how long the intake valve will be closed & come up with runner length to get more engine performance)

Thank you in advance,

 

[GregLocock]

You look at the external noise problems you have during driveby noise tests, and from interior noise, and tune your intake system to get rid of the problems it causes.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[par1]

I'm sorrry if i'm going for more simple questions,

but does it mean that we had problem with interior & exterior noise. Afer that we came up with the solution do that we did tuning for Resonator 1 at 125 Hz , Resonator 2 at 140 hz or side branch 1 at 540 hz & side branch 2 at 840 hz. (kind of noise wanted to hear)

So what the actual process going on for Resonator 1 at 125 hz or side branch 2 at 840 Hz?

 

[par1]

Did try to understand the associated theory,

Like for a quarter wave tube-
- positive pressure wave goes from beginning to end,
- positive pressure wave goes from end to beginning,
- negative pressure wave goes from beginning to end,
- negative pressure wave goes from end to beginning,
which means that it takes 4 transits of the tube for the situation to return

& for Helmoltz how the air traveling due to pressure difference throgh the neck area similar to single degree of spring damper system

still can't understand the exact meaning of Side branch 1 tuned at 540 Hz & 2 at 840 Hz,, & for the resonator 1,2 at 125 & 140 hz?

Thank you in advance,

 

[GregLocock]

I don't understand what you are asking. Are you trying to reverses engineer someone else's deisgn? In that case just get rid of all the quinkies and resonators and measure the internal and external noise.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[par1]

Not at all doing any kind of reverse engineering & sorry for poor english but asked to understand/investigate previous noise design as kind of begineer.

& the only question i was asking that if side branch 1 is tuned at 540 hz so does it mean that air is vibrating 540 times per second in tube area? or what exactly it means?

& for the resonator 1 at 125 hz so air is vibrating at 125 times per second in neck area? or what exactly it means?

Rectify eroor, if necessary

 

[SomptingGuy]

If side branch 1 is tuned at 540Hz it means that if you were to pull it off and blow over it, that's the frequency you'll hear.

For a quarter wave resonator, pressure is constant at the neck, velocity oscillates at the tuned frequency. And at the closed end it's the other way around. And the length of the whole bit of kit is 1/4 the wavelength of the resonant frequency. You need really long resonators to target the kinds of frequencies that cause problems in cars, hence the other type used ...

A Helmoltz resonator is a bit like a tuned dynamic absorber (remember those from 1st year mechanics?). The cavity is like a spring and the air in the neck is like a mass. And if you do your sums you'll soon realise that they you can dial in some pretty low natural frequencies without requiring 5m of pipework. If you find an odd-shaped plastic can under your hood connected by a pipe to the airway with no apparent function, it'll be Helmholtz.

See also here

http://en.wikipedia.org/wiki/Acoustics

for a brief explanation of Helmholtz resonators.

 

[Rob45]

"A Helmoltz resonator is a bit like a tuned dynamic absorber (remember those from 1st year mechanics?)."

I'm not sure we're dealing with someone who has ever taken a mechanics course, nor for that matter, any other kind of engineering course, based on the numerous posts he's put up here...

 

[par1]

I apologize for any inappropiate question & will try to avoid in future,