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April 8, 2009, 03:12 
How to solve acoustics ?

#1 
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Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
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Hi everybody,
I want to simulate a case and get the acoustic emission of it. Since I'm not familiar with it, can someone give me a little crashcourse?  what solver  what commands for acoustics  any added functions before calculating I've not tried yet, maybe the acoustics module is already implemented, so I only have to run a compressible calculation....?? thanks for help. Wolfgang 

April 8, 2009, 06:33 

#2 
Senior Member

Hi Wolfgamg,
you're asking something like a bit of moon ! At the moment there isn't neither any acousticspecific solver in OpenFOAM, nor high order schemes in order to build up your own solver. I tried some month ago to work on a Linearized Euler solver in OF, but the results where very bad, as the existing schemes are not suited for acoustics. So, there are two ways: 1) "Easy" way: you can generate acoustic sources with a turbulent flow model (LES, DES, URANS, RANS + SNGR). Then you have to make them propagate with an external ad hoc code. 2) "Hard" way: start coding high order schemes for OF, then build up an acoustic propagation code (if you success, let me know!!!!) Have a nice day, Ivan 

April 9, 2009, 05:49 

#3 
Senior Member
Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
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hi ivan,
thanks for the reply. could you suggest a "external ad hoc code" or even send it to me? I want to get the acoustics of a 3D Wing tip in order to compare with other wing tips. how exactly would your suggestion no. 1) work? would i have to recall this code for every timestep? does the acousticscalculation affect the numerical solution? So, do I have to give the acoustic result back to the OF calculation? In my case, I only want to compare acoustic results. So i don't need the absolute value of the emmited sound (dB). can I somehow interpret this out of the vorticity results?? any suggests would help. greets, wolfgang 

April 11, 2009, 04:24 

#4  
Senior Member

Quote:
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I the first case, you need the whole procedure, in the second maybe you can just look at an acoustic source field, and you can skip the acoustic propagation step... Hope this could help you, Ivan 

April 14, 2009, 05:54 

#5 
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Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
Posts: 136
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hi ivan,
thx a lot for the moment. yes, i only need to know which configuration is noiser or quieter. could you please describe a little more detailed how to add an "acoustic source field". or is the source for those acoustic programms just the vorticity or pressure values. I have not worked with fields yet. greets 

April 14, 2009, 09:31 

#6 
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Takuya OSHIMA
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Hi Wolfgang,
Perhaps you would anyhow want to start with reading up classic literature about acoustic analogy by Lighthill, Curle and Howe in order to get an idea about how acoustic sources should be calculated. I guess it may be too difficult even for Ivan to present you a definitive guidance because the detailed methodology quite depends on the target Mach numbers and other characteristics of your problem anyway. However as you write, if you are only interested in acoustic sources but don't have to care that much about the propagation, it won't be so difficult to add those acoustic calculations into one of unsteady CFD solvers. Takuya 

May 15, 2009, 12:48 

#7 
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Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
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as a first approximasation for acoustics, i would like to read out the kvalues and the epsilonvalues and calculate them for getting the acoustic power in each cell. after calculation it should be written in a seperate file, so i can visualize in paraFoam.
has some of you c++ guys any idea of how to do this as a c++newbie like i am.???! 

May 18, 2009, 04:20 

#9 
Senior Member
Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
Posts: 136
Rep Power: 10 
Hi 7islands,
thanks a lot, didn't know that function. Is exactly what I needed. Greets 

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