[acoustica]

Hallo ,
I working on the field of Computational Aero acoustics. I would like to develop on Acoustic solve for the data from CFX, How long it would be reasonalble to choose openfoam . suggest me I am new to openfoam !!

[Alhasan]

hey have you had any success with Aeroacustics in openFOAM by anychance..???

[skeptik]

Hi!

I'm taking part in project which concerns with developing acoustic library for OF.

Today we have good results using Curle analogue but it's still tested on different cases. Later, Lighthill analogue may be realized as part of this library.

There are a lot of papers concerning with acoustic applications of the OF in the Internet.

If you're newbie in OF, i recommend you to study LES and later, when you'll get a little experience, start to learn OF Programmers Guide.

[Alhasan]

hey, ilya

i have been working with openFOAM for a year now and i have done enough RANS simulations and lil bit of LES, i would just like to know

- if i have to develop a postprocessing tool to convert the velocity fields into sound of some sort or is there any tool available to do this

- or develop a solver ? so solve for the sound

- or can i export the data to fluent to convert the velocity feilds in to sound

thanks,
hasan

[skeptik]

The library's developed in the ISP RAS uses Curle analogue which needs to calculate the force by which body penetrate to the media.

As the output it has acoustic pressure p' obtained from results of the LES simulations, so i think there is no need to develop new solver.

Unfortunately, I don't really know when library will be completed and opened for foamers.

[Alhasan]

im still not getting the idea...!!!! so after the LES simulations has been run.. the acoustic p will be calculated or during the LES simulation it will be calculated

thanks,
hasan.

[skeptik]

It's similar like calculating forces and coefficients via libforces.so in controlDict

[Alhasan]

lets hope the public release of this would be in a month or so ..

[Alhasan]

Hey ilya,

By any chance curle analog that you were working on released ?

and also by any chance do you have any experience with Acoustics in Fluent ? ?

Kind Regards,
Hasan K.J

[skeptik]

Originally Posted by Alhasan

Hey ilya,

By any chance curle analog that you were working on released ?

and also by any chance do you have any experience with Acoustics in Fluent ? ?

Kind Regards,
Hasan K.J

1. Something is released. You can look for it here

Complex online post-processing:
How to implement simple acoustic analogy in OpenFOAM
(Sergei Strizhak, Matvey Kraposhin)

2. I know nothing about acoustics in Fluent or CFX except that using it you can get also wrong results.

[Alhasan]

Hi Ilya,

Thanks for the files i really appreciate it

Will take two or three days to study it well

- But which site or where can i keep up with the updates ? of this simple acoustic analogy ???

- i notice you have a lot of experience with airfoils For some reason I am getting wrong Cp when i manually try to plot it - what equation and how do you extract the data to plot Cp

Kind Regards,
Hasan

[skeptik]

Originally Posted by Alhasan

Hi Ilya,

Thanks for the files i really appreciate it

Will take two or three days to study it well

- But which site or where can i keep up with the updates ? of this simple acoustic analogy ???

- i notice you have a lot of experience with airfoils For some reason I am getting wrong Cp when i manually try to plot it - what equation and how do you extract the data to plot Cp

Kind Regards,
Hasan

I will ask for it as soon as.

I use standart formulas from wikipedia. You should take care about pressure dimension when you use incompressible solver.

[Alhasan]

Hey Ilya,

Small doubt

- By any chance do you know the probe frequency ? what it stands for

- so for P0 in the Cp equation if i use 0 the graph makes sense … but i thought openFOAM used 101325 as default pressure ? is it not ..?

Thanks
Hasan K.j

[Eslam Hashem]

Hello skeptik,
I want ask for noise utility in openfoam, when i use it , i will need to use any other functionobject such as 'curlefunctionObject' or not. in other words, can noise utility be an alternative approach than acoustic analogy.

i will be grateful if you answer my questions

[Alhasan]

Hey Eslam,
I am not getting your question ?
It will be helpful if you explain what you are trying to do ?
Because what Ilya has shared with us here is an acoustic analogy namely Curle's analogy it has been validated and i have double checked it

Regards,
Hasan K.J

[Eslam Hashem]

P { margin-bottom: 0.08in; } Dear Alhasan,

there is a new utility in open foam called noise utility in openfoam 2.2.0 , i asked does this utility may be an alternative tool rather than implementing an acoustic analogy i.e curle's analogy or Ffowcs-Williams and Hawkings [FW-H]

[Alhasan]

Hey Eslam,

I dint know about this noise utility (thanks for the info) just had a look, it appears to be just providing a FFT of the pressure fluctuation data of the surface pressure but nothing else. so you would have to post process this data with some sort of acoustic analogy such as the Curle, FW-H, Ameit, Howes … etc. it looks like they aid you by already providing you a data that has been FFTied so it will be easy to post process

where as with an analogy provided above we can get the sound at a Receiver that is away from the computational domain in the form of SPL and frequency.

Regards,
Hasan K.J

[Alhasan]

here http://www.openfoam.org/version2.2.1/

Noise analysis
A new noise utility generates noise data from the computed pressure, typically extracted using function objects, e.g.probes; the utility uses the noiseFFT library which includes several forms of graphical output including: FFT of the pressure data; narrow-band PFL (pressure-fluctuation level) spectrum; one-third-octave-band PFL spectrum; one-third-octave-band pressure spectrum.

[Eslam Hashem]

Dear Alhasan,

thanks for your help, i appreciate your effort, may i ask you that i do an aero-acoustic study for wind turbines in openfoam and i found that ffowcs-williams and hawkings is the most suitable acoustic analogy, but the above analogy was about curle's analogy , did you found any similar thing about ffowcs-williams and hawkings.

and, does curle's analogy valid for my case or not.

[Alhasan]

Hey Eslam,

ffowcs-williams and haw kings is best for rotating blade noise
it depends what type of simulation you are planning on doing if you are going to use AMI/GGI and simulate a turbine blade spinning I'm quite sure FW-H is the most suitable and Curle won't do you any good.

However if you are planning on doing a steady simulation of just one wind turbine blade being stationary Curle should do you good.

and i haven't come across any implementation of FW-H in openFOAM if you come across please do let me know

Best Regards,
Hasan K.J