[tog]

Dear All

Is OpenFOAM suitable for exterior acoustics problem ? Is there some examples describing this ?

Cheers
Guillaume

[7islands]

Hi Guillaume,
If you mean pure linear acoustics (not aeroacoustics), I'm using it for acoustics, but for interior problems. The reason I use OF only for interior problems is that as of now I don't have a good nonreflective boundary condition code. If we have a good nonreflective b. c. I'm sure OF can also be a powerful tool for exterior acoustics.

What kind of exterior problems are you interested in?

Takuya

[nishant_hull]

Hi Takuya

I need to develop a non-reflective boundary condition for aeroacoustic low mach number problem. I am planning to write a code for non-reflective boundary condition. How difficult it could be? Is there anything similar to this going on in this community? I searched the forum and just find your work somewhat relevant. Could you please guide me how to do it? I know C++ quite well but I need to understand the structure of the relevant section of the code well.

regards,
Nishant

[7islands]

Hi Nishant,

As I'll just be starting next month some works w.r.t. low mach number (very low, Ma < 0.1) exterior sound propagation I'm also now looking for literature about nonreflective boundary conditions that look promising for finite-volume unstructured grids. So in fact your question is my question too Do you have any interesting literature about it?

So far I only have a b.c. that is useful only for predefined incidence vectors (convectiveOutlet).

Looking through this forum Ivan Flaminio Cozza seems to be trying to solve linearized Euler equations with PML so I guess he could share our interest too?

Takuya

[lillberg]

Hi,

Have any of you guys tried the waveTransmissive boundary condition in OpenFOAM? It has worked quite well for me for low mach number vortex induced accoustics(Ma = 0.1-0.2) using compressible solvers.

Regards

/Eric

[ivan_cozza]

Hi guys!
Just yesterday I succeeded in coding a PML boundary condition for the Linearized Euler Equation, so now I think the real big problem for aeroacoustics in OF are the high order non dispersive schemes.
Did someone have allerady do some work in it?
I'm having a look around for some DRP-FV schemes, but all of these are for structured grid, with a large stencil, it's possible to reproduce it in OF?
Have a nice day,
Ivan

[7islands]

Hi,

@Eric: Thanks for the suggestion. However as far as I understand from the code I guess it also has strong dependence in acoustic wave incidence directions, which is not good for my case. If I go that way I would at least have to find a way to properly tweak the sqrt(gamma_/psip) term. But can't be said for sure, anyhow I will test it.

@Ivan: I also had a bit of interest in such schemes around a year ago but just gave up after having had exactly the same problem. Now I'm interested in what you'll find...!

Takuya

[ivan_cozza]

Takuya,
what kind of schemes are you using in your LEE computation now? I've just finished the LEE solver, and I'm doing some classical benchmark case like the gaussian pulse and the monopole, and I'm usin gauss linear scheme, if I try wit gauss cubic (that should be 4th order, if I've understood), there are big ossilations and the solution are not symmetrycal.
So I think that some High Order Scheme implementation is the next step for doing CAA in OpenFOAM...

[nishant_hull]

@takuya..
Its nice to know that somebody is already working on the same area and also have the same motivtion to work on. Hope we can find out a way to go ahead. I have downloaded some article on non-reflective boundary condition. I have some articles on NSCBC (nav stoke charc. bound. condn) and their implementation to some practical problems. If you need them then let me know, I will send it to ur email.

@Ivan: PML also seems to be interesting. I would be interested to see how it could be implemented to OpenFoam. I would be glad if you like me to investigate some part of your problem. i will definitely need some directions from you to start with.
regards,

Nishant

[7islands]

Hi,

@Ivan: At this stage everything is still preliminary (I still do not have a working solver). Though what is somewhat clear is that, as in my case the mach number is very very low I'm planning to use a simplified form of LEE assuming adiabatic and barotropic field [1]. If it is to be implemented in a finite-difference staggered mesh it will most likely be a trivial task that can be done with 2nd order schemes [2]. But I'm still not sure how it should be implemented in finite-volume unstructured and collocated system. There may be a chance I also need such high order schemes.

@Nishant: Ivan showed some interesting hints in another thread. I think the thread can be of help to you as well.

[1] R. Blumrich and D. Heimann, J. of Acoustical Society of America, 446-, 2002
[2] T. Van Renterghem and D. Botteldooren, Applied Acoustics, 201-, 2007

[ivan_cozza]

Hi,

@Takuya: Why are you interested in using staggered grids for LEE? I didn't ever see any staggered implementation of LEE, it seems that collocated grids works fine!
I'm taking a look on some FV high order schemes, but everyone of those requires some access to a big stencil, so, I'm doubting that it should be fine for OF. In alternative, I'm thinking on Discontinuous Galerkin, but it should be necessary to implement a FEM framework, so it can be very hard to do...
Cheers, Ivan

[7islands]

Hi Ivan,
@Staggered grid: it's a story about finite difference solvers so we FOAMers might just have to forget about it.

I'm now attending a conference and had a chance to talk to a person who is doing aeroacousics. The story was roughly the same as discussed here... She said she is sticking on generalized curvilinear structured grid because of larger stencil required for higher order schemes.

Takuya

[ivan_cozza]

Ok, all the same stuff...
I've read about some High Order DRP FVM schemes, but they're based on generalized curvilinear structured grids, and with large stencil, and we're thinking on trying it in OpenFOAM, maybe generating a separate "big stencil" connectivity, but it's quite an hacking. The other possibility is trying with DGM, but it's necessary to introduce internal degree of freedom and shape functions, so it's definitely an hacking!

[wolle1982]

Hi everyboy,

I also want to do some acoustic investigations an airflow around some geometries.

In literature (fluent user guide) I have found the very simple equation that calculates the "acoustic power" due to the vorticity. The equation is

P = alpha * rho * epsilon * ( sqrt(2 * k) / c ) ^ 5

P: acoustic Power [W/m³]
alpha: a rescaled constant
rho: air density
k / epsilon: from turb-modell
c: speed of sound

with this easy equation it should be possible to calculate at least the sound source intensity.

Therefore one needs to calculate the equation using the k and epsilon output of OpenFOAM.

And here I need some help of C++ feasible people:

I do have no experience of using C++. How could the source code look like, that reads out the k and epsilon file of the timestep directoriy and calculates it with the mentioned equation. Then it should output some files that give the acoustic power of each cell.

please help me. I cozuld think, that for a C++ guy it is a very easy stuff to do. However, I myself have no clue.

Thanks.

[nishant_hull]

Which solver do you guys are using for low mach number flow in openfoam?

I am trying to build a sub sonic PISO based algorithm to solve low mach number flow. I want to make a comparision of both the codes. Could you please tell me which code in openfoam are you using?

regards,

Nishant

[alisina]

Originally Posted by lillberg

Hi,

Have any of you guys tried the waveTransmissive boundary condition in OpenFOAM? It has worked quite well for me for low mach number vortex induced accoustics(Ma = 0.1-0.2) using compressible solvers.

Regards

/Eric

hi eric, i have tried waveTransmissive bou. cond. in OF (Ma=0.5), but unfortunately my solutions diverge, OF calculates only a few time steps and than breaks
im new in OF and im working since 2 weeks on this problem, have you any advice for me?

regards

ali

[Linse]

Originally Posted by ivan_cozza

Hi,
In alternative, I'm thinking on Discontinuous Galerkin, but it should be necessary to implement a FEM framework, so it can be very hard to do...
Cheers, Ivan

I just remember having had a thesis by someone named Gassner on discontinuous Galerkin for loan, but unfortunately I do not remember if there had been parts concerning FEM.

For the case you have access to some interloan-thingy, you might try to find it
Actually, the OPAC (library catalogue) of the state library at Munich seems to have some books and theses on that topic. Might be of interest as well for you.
The link to that is http://www.bsb-muenchen.de

Hope it helps a little bit...

[brent_craven]

Hi all,

This thread is a bit old. But, what is the status of anyone's efforts of aeroacoustics in OpenFOAM?

Specifically:
- What solvers are folks using for acoustics?
- Any updates on higher-order schemes or attempts at Discontinuous Galerkin?

[Alhasan]

Hey,
is there any body who has a successfully done acoustics using openFOAM,

and my second doubt will be is there any chance to take the results from openFOAM to fluent to the acoustics for the flow,

thanks

Hasan.

[qi_kk]

Originally Posted by 7islands

Hi Guillaume,
If you mean pure linear acoustics (not aeroacoustics), I'm using it for acoustics, but for interior problems. The reason I use OF only for interior problems is that as of now I don't have a good nonreflective boundary condition code. If we have a good nonreflective b. c. I'm sure OF can also be a powerful tool for exterior acoustics.

What kind of exterior problems are you interested in?

Takuya

hi，i want to achieve additional acoustic field with openfoam, Is there some examples describing this ?Do you have some guidence?

thanks

kk.