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Usman January 22, 2008 14:17

Acoustics using CFD
 
Hi guys

Can we do far field noise prediction using any of the CFD codes. If yes which code is it and how can we set up the boundary conditions to solve light-hill equations. Thanks in advance for you reply.

Usman


Glenn Horrocks January 22, 2008 17:24

Re: Acoustics using CFD
 
Hi,

Strictly speaking yes, you can do far field acoustics with CFX (or any other CFD code) but in practise the fine meshes and timesteps required make it impractical. Acoustics software like SYSNOISE (and their are plenty of others) do far field acoustics far better. I think CFX has an interface with SYSNOISE, if not you can link it using MPCCI. Your CFX support vendor should be able to help you with this.

Glenn Horrocks

CycLone January 22, 2008 17:33

Re: Acoustics using CFD
 
Hi Usman,

CFX can output noise sources to solve the far-field in Sysnoise or other accoustic codes. If it is fan noise you are interested in, there is a Post macro to calculate far-field noise from a steady-state solution.

FLUENT also has some built-in noise capability.

Note that calculating accurate noise sources is key, which may require accurate resolution of turbulent structures, pressure fluctuations, etc. This implies a very small time step and a fine grid, which ultimately equates to a long run time.

-CycLone

Usman January 22, 2008 18:03

Re: Acoustics using CFD
 
Thank you Glenn.

CycLone how small time step are we talking about. I would need to keep my courant number close to unity. So if i use equation C = v*delta t/delta x, i should get time step that i would need to resolve my pressure fluctuations right!

Regards Usman

Usman January 22, 2008 18:04

Re: Acoustics using CFD
 
Woops sorry about the exclamation mark.

Regards Usman


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