[shahid nadeem]

Hello my dear Friends, Do anybody have idea on how to do acoustics in cfd.

9 persons have viewed it no reply till now.

[FMDenaro]

Acoustic is intrinsic to the fully Navier-Stokes equations formulated for compressible flows. It refers as to the pressure field.
It is, however, also quite common working by splitting the flow field from the study of the acoustic field, one solves the flow then use it to compute tha acoustic field.

[som87]

As far I now CFD is used (for acoustics) either to
1. Directly calculate the noise from solving the N-S equations
2. Use the solution of N-S equations to solve the Ffowcs-Williams and Hawking equation (Ligthill's ).

Thats all to do from CFD

[shahid nadeem]

Thank You very much sir, it would be very nice if you could elaborate it a little and tell us how Broadband noise prediction works.

Hmmm thats what i was wondering CFD is not so good in acoustics, we have different soft like SIDLAB SYSNOISE Etc for noise ok thank you then.

[som87]

if by "CFD", we are talking about "colorful fluid dynamics", then no its not, if we are talking about solving the most badass PDE set, then yea CFD "skill" will be useful in acoustics more than any software

[shahid nadeem]

Well I Dont think so we how can we get the Acoustics Results by changing some values of Far-field etc, In SIDLAB We have an option like sound absorbing material where we can specify the material which we are using to absorb the acoustic energy but in Fluent i dont find any such option.

[liujmljm]

Originally Posted by som87

As far I now CFD is used (for acoustics) either to
1. Directly calculate the noise from solving the N-S equations
2. Use the solution of N-S equations to solve the Ffowcs-Williams and Hawking equation (Ligthill's ).

Thats all to do from CFD

Dear, I have a question. For me, I have a 2d numerical solution NS data. How can get the acoustics solution by using of Lighthill analogy method. Because I found many books on 3d formula. Few books give the exact formula for 2D. How to get it in 2D.

Thank u very much!

[som87]

Originally Posted by liujmljm

Dear, I have a question. For me, I have a 2d numerical solution NS data. How can get the acoustics solution by using of Lighthill analogy method. Because I found many books on 3d formula. Few books give the exact formula for 2D. How to get it in 2D.

Thank u very much!

Sorry for the delayed reply (since i was logged, i didnt receieve any alert in my gmail)
I will try to use my layman's concepts to explain what you can do for 2D acoustics:-
1. take a point(s) in the wake
2. select the fluctuation in terms of velocity/pressure/flow property
3. make the fft
4. plot the fft and select the dominating frequency

--end of story---

Sry, idk if this'll help, but this is all from my part for 2D acoustics

Edit:-
Another approach which I tried (but idk how useful it'll be) is to calculate the local sound speed and normalize it wrt sound speed at free stream.
The contour of this'll give you the estimated propagation of noise.Again, please discuss with some senior in acoustics