[Kinnikuman]

Hello,
I'm new to this CFD forum and the study of flow induced sound. As my research, I need to calculate flow induced sound propagating to a pipe wall and its surroundings.

The figure I'm considering is like the figure below. There is leakage from a pipe flow and it makes strong sound. The sound propagates inside the water, incidents to the pipe and the surrounding and reach the receiver. Also the sound propagates inside the pipe and the surrounding.
Picture2.jpg

I found many papers about structural sound which fluctuation of fluid cause the structural vibration and sound. But it is different from what I want to calculate. I could not find the flow induced sound and it's propagation to the surrounds so far. And I already found that ANSYS cannot simulate this type of calculation.

Would you tell me if OpenFoam or another CFD simulator has ability to calculate my situation? Also if you know any papers that researches similar situations by using any simulation, would you please share it?

[JBeilke]

What you need is "compressible water". cavitatingFoam can do it.

Here is a good explanation:
https://caefn.com/openfoam/solvers-c...ssibilitymodel

and here is a nice example:
https://github.com/Irvise/openfoam_cavitation

Since your receiver is outside of the flow you also need solid-stress and FSI (fluid-structure-interaction).

Arjun is currently implementing the FSI part in "Wildkatze", the rest is already there. This is my way for a similar problem.

[Kinnikuman]

Hi, thank you for your answer.
Would you explain more detail about wildkatze?

The FSI part is important for this calculation, and I’m looking for the similar cases that combines flow induced sound + wave propagation outside the cfd domain.

[arjun]

Originally Posted by Kinnikuman

Hi, thank you for your answer.
Would you explain more detail about wildkatze?

The FSI part is important for this calculation, and I’m looking for the similar cases that combines flow induced sound + wave propagation outside the cfd domain.

Here is about Wildkatze

https://fvus.github.io/wildkatze/


We are working on similar problem at the moment. Targeting something out at the end of the next week.

[Kinnikuman]

Thank you so much for sharing.

Honestly I haven't understood what wildlatze can do well.
The wildkatze calculates the pressure fluctuation inside the water domain and it causes the vibration of the structures. And part of the fluctuation generate sound, is this correct? In case it is different from what I want to calculate.

I want to calculate the wave induced by the turbulence and the wave propagation inside the water and the interaction to the pipe and the surrounding like the figure (Zhang et al. 2023, https://doi.org/10.3390/jmse11102012.) I think it is different from the typical FSI.
Screenshot 2023-11-16 163705.png

Additionally, I want to calculate the flow induced sound using the Lighthill equation or the Ffowcs Williams and Hawkings equation. I think cavitation does not occur in my case and I'm assuming the sound is caused by the turbulence at the leakage wall.

Probably my explanation was bad, if you have any ideas to simulate my case, please let me know. I'm sorry if you understand my problem correctly, in case would you share more information about wildkatze?

[arjun]

Originally Posted by Kinnikuman

Thank you so much for sharing.

Honestly I haven't understood what wildlatze can do well.
The wildkatze calculates the pressure fluctuation inside the water domain and it causes the vibration of the structures. And part of the fluctuation generate sound, is this correct? In case it is different from what I want to calculate.

This part we are working on at the moment. Due to stresses solid shall move. So this was FSI.

Originally Posted by Kinnikuman

I want to calculate the wave induced by the turbulence and the wave propagation inside the water and the interaction to the pipe and the surrounding like the figure (Zhang et al. 2023, https://doi.org/10.3390/jmse11102012.) I think it is different from the typical FSI.
Attachment 97281

Additionally, I want to calculate the flow induced sound using the Lighthill equation or the Ffowcs Williams and Hawkings equation. I think cavitation does not occur in my case and I'm assuming the sound is caused by the turbulence at the leakage wall.

This part you shall be able to do with the current version of Wildkatze. (if you do not need mesh movement then all shall be already there).

We do not have FWH, but we have accoustic perturbation equation. In my opinion the current version of wildkatze seems enough for your case.

[Kinnikuman]

Sounds very nice. Is it possible to share the theory guide or the relative papers? And is it completely free?

[arjun]

Originally Posted by Kinnikuman

Sounds very nice. Is it possible to share the theory guide or the relative papers? And is it completely free?

I quickly ran a 2d set up. See attached gif (sorry can't attach bigger file). It is just a sample test to check set up.

Inlet velocity 100m/sec and water is considered Nobel Abel Stiffened Gas.


About the solver, it is free upto 5 million cells that a demo license that comes with it allows.

[FMDenaro]

arterial beat is an example of what is the sound prodiced in a tube by the fluid-structure interaction modelled as a compressible medium.

[Kinnikuman]

@ arjun
Thank you for sharing the preliminary calculation. But it seems slightly different what I want to calculate. The sound pressure is generated at the leakage and propagates in three media: Water, pipe and surrounding. What I am struggling are mainly two stuffs:
1) How can we calculate sound in acoustically near field? Also, water domain is sound source and propagation. Can we calculate both?

2) How can we calculate impedance boundary condition?

[LuckyTran]

Sound propagation is nearly exact (up to numerical accuracy) with any compressible solver. Sound generation at its source is where the issues are. You either use a sound generation model (i.e. Lighthill's analogy) or you brute force it with LES/DNS.

[Kinnikuman]

@FMdenaro,
Thank you for sharing. It's very interesting and I'm searching the relative papers now.

[Kinnikuman]

@LuckyTran,
Thank you so much for sharing. I think most of acoustic analogy such as Lighthill equation and Ffowcs Williams and Hawkings equations are applicable for far field noise. Are there any way to know the near field sound?

[arjun]

Originally Posted by Kinnikuman

@LuckyTran,
Thank you so much for sharing. I think most of acoustic analogy such as Lighthill equation and Ffowcs Williams and Hawkings equations are applicable for far field noise. Are there any way to know the near field sound?

You are little bit confused about things.

1. As Beilke and LuckyTran pointed out that when you calculate the compressible case you can calculate the noise. Fluent manual calls it direct calculation of noise.

2. You said that you don't need fsi but now you say that you wanted to calculate noise through solid too. This can't be done without fsi.

3. In the case i shown i used compressible formulation for water. I can also use compressible eos for air too (actually i did in some calculations after this). If properly run this calculates your near field noise.

4. You can use turbulence model here to account for turbulence. If the flow field produce noise then it will be calculated.

When you say this is not what you want then can you clarify what noise navier stokes is not covering here.

Unless it is a micro channel where navier stokes are not valid, i suppose this shall produce you good estimate.

[Kinnikuman]

@arjun, @LuckyTran
I'm confusing now. Maybe I misunderstand the physics.

Case 1. What I want to calculate is the sound induced by fluid flow and propagating inside the water itself and the interactions including pipe and surroundings. So I want to combine Lighthill equations and propagation in multiple media (impedance boundary condition?).

Case 2. I think we can also say case 1 as fluid-solid interactions. But based on my literature reviews, FSI in acoustics typically indicates aero vibro acoustics. Sound is induced by the structure vibration which is caused by water fluctuations. This is typically calculated by combining LES and wave equations.

I think these two are slightly different. Sound source for case 1 is water, for case 2 is structure. Case 1 considers the sound propagating in the water and the structure and case 2 considers the sound propagation inside the structure. Or are they same physical phenomena?

[LuckyTran]

Structural vibrations is a form of sound

[Kinnikuman]

@ LuckyTran,
Sorry I can't get it. I thought they are different sound mechanism. Does they actually represent same sound?

[LuckyTran]

Sound induced by structural vibrations is just a cumbersome, convoluted way of saying sound is sound.

[Kinnikuman]

Sorry, still I couldn't get it. So how can we categorize sound induced by flow?

[arjun]

This is what Fluent Theory guide says:




15.1.1. Direct Method

In this method, both generation and propagation of sound waves are directly computed by solving the appropriate fluid dynamics equations. Prediction of sound waves always requires time-accurate solutions to the governing equations. Furthermore, in most practical applications of the direct method, one has to employ governing equations that are capable of modeling viscous and turbulence effects, such as unsteady Navier-Stokes equations (i.e., DNS), RANS equations, and filtered equations used in DES and LES.


The direct method is thus computationally difficult and expensive inasmuch as it requires highly accurate numerics, very fine computational meshes all the way to receivers, and acoustically non-reflecting boundary conditions.

The computational cost becomes prohibitive when sound is to be predicted in the far field (e.g., hundreds of chord-lengths in the case of an airfoil). The direct method becomes feasible when receivers are in the near field (e.g., cabin noise). In many such situations involving near-field sound, sounds (or pseudo-sounds for that matter) are predominantly due to local hydrodynamic pressure which can be predicted with a reasonable cost and accuracy.


Since sound propagation is directly resolved in this method, one normally needs to solve the compressible form of the governing equations (e.g., compressible RANS equations, compressible form of filtered equations for LES). Only in situations where the flow is low and subsonic, and the receivers in the near field consist primarily of local hydrodynamic pressure fluctuations (i.e., pseudo sound), can incompressible flow formulations be used. However, this incompressible treatment will not permit you to simulate resonance and feedback phenomena.