[nic92]

Hi Guys,

I am simulating a droplet flow (gas continuous phase, water dispersed phase) in a duct. I am using the solver TwoPhaseEulerFoam to study the deposition of the heavy phase at the bottom.
At present I am trying to find an appropriate RAS turbulence model. I run some simulation with the mixtureKEpsilon; it works quite well, but it can be used only when the density of the two phases are similar (in this case rho_water/rho_air is around 1000).
Therefore, I would like to use other models, but I see that most of them (continuosGasEpsilon, kOmegaSSTSato, LaheykEpsilon) have been developed for bubbly flow (water continuous phase, gas dispersed phase).

I have two questions:
1. I think that it is a big error to use a model implemented and tuned for bubble flow and use it for droplet flows. Correct?
2. Have you ever found this issue? If so, how did you solve it?

[a.weber]

As I understand, those models are very similar:
Every particle has a drag force in the cont fluid. The "drag energy" is transfered to the cont phase and produces turbulent energy.
I think there is no difference if your particle is solid, liquid or gas.

But I'm not sure if that also counts for the dissipation aswell.

[nic92]

Thanks for your answer.
I definitely decided to use the mixtureKEpsilon. Nevertheless, I encountered another problem. The mixtureKEpsilon is based mainly on the article "Modelling of dispersed bubble and droplet at high phase fractions" (Behzadi, Issa, Rushe). In the article, it is clearly specified that the it can be used both for bubble flow, both for dispersed flow. Nevertheless, if you look carefully at the code of mixtureKEpsilon, the expressions like C_t, beta... have been implemented only for the a flow where the liquid is the continuous phase, the gas is the dispersed one. Moreover, this is in contrast with the idea of many OF solvers to be very general to avoid code duplication.

Does anyone has face a similar problem concerning the use of mixtureKEpsilon for droplet flows?

Thanks in advance,

[nic92]

Hi Foamers,

I really need an article which I can't find up to now. Here I report details:

"Behzadi, A., 2001. Turbulence modelling at high phase fractions.
Technical Report, BRITE/EURAM III (BE 4322), III-30."

I know that it is a technical report of NablaLTD and it is very difficult to have it.
In case you have and want to share, I would be greatly obliged and indebted.

Thanks in advance.

[Elham]

Hi everybody,

I am simulating a water droplet in turbulent air flow inside a channel. I use interFoam. At the very first step of simulation the droplet explodes. I tried to have zero gravity, change the max courant number and max Alpha Courant number, droplet diameter and flow velocity and mapping from a sphere for initial condition to fix the problem but still doesn't work. I will appreciate if anyone can give me a clue to solve it.

Thanks

[nic92]

Originally Posted by Elham

Hi everybody,

I am simulating a water droplet in turbulent air flow inside a channel. I use interFoam. At the very first step of simulation the droplet explodes. I tried to have zero gravity, change the max courant number and max Alpha Courant number, droplet diameter and flow velocity and mapping from a sphere for initial condition to fix the problem but still doesn't work. I will appreciate if anyone can give me a clue to solve it.

Thanks

Try to do:
1. Run the simulation in laminar conditon;
2. Reduce DeltaT in Control dict. Even though you set a maximum Courant number, a first DeltaT is needed.
3. Increase the number of correctors.

[Elham]

Dear Nicolo,

1.Do you mean I should decrease flow velocity or just set laminar in turbulence properties?

I will try number 2 and 3. Thanks for your help.

Cheers,

Elham

[Elham]

Originally Posted by nic92

Try to do:
1. Run the simulation in laminar conditon;
2. Reduce DeltaT in Control dict. Even though you set a maximum Courant number, a first DeltaT is needed.
3. Increase the number of correctors.

Dear Nicolo,

I have increased the number of correctors and so the speed of exploding decreased. Let's say, before changing the number of correctors, alpha.water changed from 1 to 0.0005452 during the first 0.02 sec. Now it changes from 1 to 0.000565251 during 0.05 sec. I also decreased delT. You see that the droplet explodes slower but I still need to fix it.
I don't know how to start with laminar as you mentioned before. I really appreciate if you let me know.

Thanks,

Elham

[Elham]

To update my condition; I changed the correctors and the droplet does not explode anymore but it deforms from a sphere to something unusual. How can I fix it and what is the reason for that?

Thanks for any comment.

[piu58]

> deforms from a sphere to something unusual.

Depending on the size, the droplet may deform remarkably: It may get flattened.

[Mehrez]

Hi,
Could you find this report?
Thanks,
mhrz

Originally Posted by nic92

Hi Foamers,

I really need an article which I can't find up to now. Here I report details:

"Behzadi, A., 2001. Turbulence modelling at high phase fractions.
Technical Report, BRITE/EURAM III (BE 4322), III-30."

I know that it is a technical report of NablaLTD and it is very difficult to have it.
In case you have and want to share, I would be greatly obliged and indebted.

Thanks in advance.