Aeroacoustic simulation in CFX

Roland R · December 7, 2009, 15:29

Hi,

I have a quite complicated flow domain. The flow is compressible, and there are some locations in the flow field where the Mach Number is large than 1. I have to investigate this flow field in terms of aeroacoustic.

At the moment I have an transient result. In first approach I have defined a new quantity, the sound pressure level, and I have demonstrated the critical locations (e.g. fillets, sudden change of flowdirection) with an iso surface where the SPL is the largest.

Is this approach right?

Regards,

Roland R.

ghorrocks · December 7, 2009, 17:21

But what are you trying to do? You have not explained what you are trying to get out of the analysis.

Roland R · December 8, 2009, 05:21

Oh, sorry, you are right...
The main problem is the too large noise which develops in this part. During the function the inlet pressure expands from 11 bar to 2 bar, besides the flow field includes a lot of chamfers, edges and thin gaps.

The goal of the simulation is to investigate the critical locations which can generate too large noise.

ghorrocks · December 8, 2009, 07:17

You still have not been clear as to what you are trying to do. Are you trying to match a sound pressure level measurement taken from an experiment? Or are you trying to find the sources of the noise so you can reduce the aero noise of the object?

Roland R · December 8, 2009, 12:14

[QUOTE=ghorrocks;239105]You still have not been clear as to what you are trying to do. Are you trying to match a sound pressure level measurement taken from an experiment? Or are you trying to find the sources of the noise so you can reduce the aero noise of the object?[/QUOTE]

Yes yes, the second one

There is not measurement so I have to rely for the CFD simulation.
To tell the truth I don't have experience to the aeroacoustic therefore I tried to approach the problem first with SPL iso surfaces...

ghorrocks · December 8, 2009, 17:58

I have no experience in acoustics modelling so I guess what you say makes sense. Don't forget that the propogation of the sound from the source to the observer is also important as you get reflections, superpositions and all that stuff and that means you cannot just consider the noise source in isolation.

sampath379 · December 8, 2009, 22:48

Quote:

Originally Posted by ghorrocks

But what are you trying to do? You have not explained what you are trying to get out of the analysis.

hi every one i want a project which enable me to learn a software and also for acadamic purpose can any body help me in this i want a project on cfd and better if it can be done on ansys cfx. it should be master level project and no problem if it is all ready done project.

i want tutorials to work upon cfx can any body help me in this matter plz

Roland R · December 9, 2009, 06:25

Quote:

Originally Posted by ghorrocks

I have no experience in acoustics modelling so I guess what you say makes sense. Don't forget that the propogation of the sound from the source to the observer is also important as you get reflections, superpositions and all that stuff and that means you cannot just consider the noise source in isolation.

Yes, It is absolutely clear what you said. I know that the SPL at the iso surface valids just in the flow field. I learned some years ago how can I determine the SPL in certain distance from source of the sound but in my case this problem is much complicated because of the material, the wall thickness, the reflections etc. etc...

Roland R · December 11, 2009, 11:50

Hi,

I would like to look for regions in the flow field where periodic separations can be found. I have defined monitor points in CFX Pre where I can see the pressure while the solver is running. I tried to study these points in the Post too but it is dificult due to the complicated geometry.
What do you think, how can I filter these locations where periodic pressure fluctuation occurs which can be source of the noise.

Regards

Roland

ghorrocks · December 13, 2009, 06:06

If you have set them up as monitor point in Pre then you should have a time history for them. Yo ucan access if through solver manager. Export it as a CSV file then take it into matlab (or excel if you are desperate) and do an FFT on it to find if there are any important frequencies coming through.

Roland R · December 15, 2009, 13:56

OK, I understand, thank you for your answer.

Roland

December 7, 2009, 15:29	Aeroacoustic simulation in CFX	#1
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	Hi, I have a quite complicated flow domain. The flow is compressible, and there are some locations in the flow field where the Mach Number is large than 1. I have to investigate this flow field in terms of aeroacoustic. At the moment I have an transient result. In first approach I have defined a new quantity, the sound pressure level, and I have demonstrated the critical locations (e.g. fillets, sudden change of flowdirection) with an iso surface where the SPL is the largest. Is this approach right? Regards, Roland R.

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December 7, 2009, 17:21		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	But what are you trying to do? You have not explained what you are trying to get out of the analysis.

December 8, 2009, 05:21		#3
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	Oh, sorry, you are right... The main problem is the too large noise which develops in this part. During the function the inlet pressure expands from 11 bar to 2 bar, besides the flow field includes a lot of chamfers, edges and thin gaps. The goal of the simulation is to investigate the critical locations which can generate too large noise.

December 8, 2009, 07:17		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	You still have not been clear as to what you are trying to do. Are you trying to match a sound pressure level measurement taken from an experiment? Or are you trying to find the sources of the noise so you can reduce the aero noise of the object?

December 8, 2009, 12:14		#5
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	[QUOTE=ghorrocks;239105]You still have not been clear as to what you are trying to do. Are you trying to match a sound pressure level measurement taken from an experiment? Or are you trying to find the sources of the noise so you can reduce the aero noise of the object?[/QUOTE] Yes yes, the second one There is not measurement so I have to rely for the CFD simulation. To tell the truth I don't have experience to the aeroacoustic therefore I tried to approach the problem first with SPL iso surfaces...

December 8, 2009, 17:58		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	I have no experience in acoustics modelling so I guess what you say makes sense. Don't forget that the propogation of the sound from the source to the observer is also important as you get reflections, superpositions and all that stuff and that means you cannot just consider the noise source in isolation.

December 11, 2009, 11:50		#9
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	Hi, I would like to look for regions in the flow field where periodic separations can be found. I have defined monitor points in CFX Pre where I can see the pressure while the solver is running. I tried to study these points in the Post too but it is dificult due to the complicated geometry. What do you think, how can I filter these locations where periodic pressure fluctuation occurs which can be source of the noise. Regards Roland

December 13, 2009, 06:06		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	If you have set them up as monitor point in Pre then you should have a time history for them. Yo ucan access if through solver manager. Export it as a CSV file then take it into matlab (or excel if you are desperate) and do an FFT on it to find if there are any important frequencies coming through.

December 15, 2009, 13:56		#11
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	OK, I understand, thank you for your answer. Roland