FW-H Acoustic Module - Suitable for Internal Flow Aeroacoustics?

Poompil · September 27, 2016, 15:57

My master's work deals with modelling the aeroacoustic noise generation in a "muffler type structure" - that is, with one input into an enclosed space with only one outlet.

I'm trying to determine the noise levels at far-field locations.

First off, is the FW-H analogy suited to a problem like this?
Does it make sense to use the "interior" type source surface (as defined in Fluent's Acoustic Module) when defining the walls of the muffler, and then place receivers in far field locations?

I'm very new to all this, and any insight into acoustic analogy and modelling is appreciated.

Thanks,
Jobin

ab.glb.cfd · October 27, 2016, 10:51

Dear Poompil,

FW-H Analogy can be applied even for internal flows.

There are articles;

1."Aero Acoustic Noise Analysis of a Locomotive Cooling System Ducts and Structure Optimization" published.

2."On the use of the Ffowcs Williams-Hawkings equation to predict far-field jet noise from large-eddy simulations" published.

From my experience, the analogy is more helpful for flows exiting into quiescent atmosphere and to analyze far-field noise spectra > 1 m distance.

I prefer DES/LES simulation for muffler/expansion chamber flow noise analysis, identify the source locations and finally FFT's of PSD and SPL at monitoring points and/microphone locations.

Hope my description helps you clear few things.

Revert to my personal e-mail ID: ab.gulbarga@gmail.com if you need more details.

All the best!

Regards,
Abhijit

Poompil · November 7, 2016, 23:41

The workflow you suggested makes sense to me and it is in fact what I have already adopted.

Thanks for the references - I have taken a quick look at them and it seems promising.

If I were to use FWH to calculate the SPL on the internal surface of my enclosed space, would I be able to extrapolate that to a far field noise value simply using breakout noise?

Regards,
Jobin

ab.glb.cfd · November 8, 2016, 23:04

Breakout noise is more of vibro-acoustics or Aero-vibro-acoustics...

What is that you are planning to evaluate? Flow induced noise due to shell vibrations or pure flow/turbulence induced noise?

FW-H analogy in principle is a Green's function extrapolation to extract noise spectrum considering flow sources at a rigid or imaginary (permeable) surface.

It is suited for pure flow noise and not for vibro/aero-vibro-acoustics.

For breakout noise, coupling is required (transient flow solution + harmonic/acoustic calculation)

Hope my comments helps.

September 27, 2016, 15:57	FW-H Acoustic Module - Suitable for Internal Flow Aeroacoustics?	#1
Poompil New Member Jobin Join Date: Sep 2016 Posts: 5 Rep Power: 10	My master's work deals with modelling the aeroacoustic noise generation in a "muffler type structure" - that is, with one input into an enclosed space with only one outlet. I'm trying to determine the noise levels at far-field locations. First off, is the FW-H analogy suited to a problem like this? Does it make sense to use the "interior" type source surface (as defined in Fluent's Acoustic Module) when defining the walls of the muffler, and then place receivers in far field locations? I'm very new to all this, and any insight into acoustic analogy and modelling is appreciated. Thanks, Jobin

October 27, 2016, 10:51	FW-H Acoustic Module - Suitable for Internal Flow Aeroacoustics?	#2
ab.glb.cfd New Member Abhijit Deshpande Join Date: Jan 2014 Location: Bangalore Posts: 7 Rep Power: 12	Dear Poompil, FW-H Analogy can be applied even for internal flows. There are articles; 1."Aero Acoustic Noise Analysis of a Locomotive Cooling System Ducts and Structure Optimization" published. 2."On the use of the Ffowcs Williams-Hawkings equation to predict far-field jet noise from large-eddy simulations" published. From my experience, the analogy is more helpful for flows exiting into quiescent atmosphere and to analyze far-field noise spectra > 1 m distance. I prefer DES/LES simulation for muffler/expansion chamber flow noise analysis, identify the source locations and finally FFT's of PSD and SPL at monitoring points and/microphone locations. Hope my description helps you clear few things. Revert to my personal e-mail ID: ab.gulbarga@gmail.com if you need more details. All the best! Regards, Abhijit

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November 7, 2016, 23:41		#3
Poompil New Member Jobin Join Date: Sep 2016 Posts: 5 Rep Power: 10	The workflow you suggested makes sense to me and it is in fact what I have already adopted. Thanks for the references - I have taken a quick look at them and it seems promising. If I were to use FWH to calculate the SPL on the internal surface of my enclosed space, would I be able to extrapolate that to a far field noise value simply using breakout noise? Regards, Jobin

November 8, 2016, 23:04		#4
ab.glb.cfd New Member Abhijit Deshpande Join Date: Jan 2014 Location: Bangalore Posts: 7 Rep Power: 12	Breakout noise is more of vibro-acoustics or Aero-vibro-acoustics... What is that you are planning to evaluate? Flow induced noise due to shell vibrations or pure flow/turbulence induced noise? FW-H analogy in principle is a Green's function extrapolation to extract noise spectrum considering flow sources at a rigid or imaginary (permeable) surface. It is suited for pure flow noise and not for vibro/aero-vibro-acoustics. For breakout noise, coupling is required (transient flow solution + harmonic/acoustic calculation) Hope my comments helps.