[Pacca]

Hello everyone,


I'm facing a problem I can't solve using FLUENT 18.1 and DPM model. Let me explain everyting.


I'm modeling the combustion between N2O and C2H4. The fuel is injected in gaseous form, while the oxidizer is injected both as liquid droplets. For this reason I activated the DPM model (while the multiphase model is switched off) since I want to track the particles with a lagrangian model.


I defined some cone injection points with droplet particles. The material is n2o liquid while the evaporating species is n2o. The interaction with the continuous phase is activated.


The output of the solver states that all the particles are evaporated (so no trapped or escaped particles) but if I try to plot the DPM n2o species this is null on all the domain and also the outlet mass flow is equal to the fuel inlet mass flow (only C2H4).


I am not sure if I am missing something in the setup or what. Thank you very much in advance for your help.

[Large Epic Simulations]

Can you describe your boundaries?

[Pacca]

Sorry I forgot that!


I have a fuel inlet that is defined as a mass flow inlet, while the oxidizer inlet is defined as an injection cone under the DPM model. The outlet is a pressure outlet.

[Large Epic Simulations]

Have you checked that the evaporating species are the correct one?

[Pacca]

I defined the droplets as n2o liquid (and I create this material because was not already defined in the droplets library) while the evaporating species is set as n2o (a pre-defined fluid in fluent).


I am not sure what is happening, but it's as if the evaporated species is not transferred to the gaseous fluid.

[Large Epic Simulations]

Did you checked the two way coupling box?

[Pacca]

Do you mean the box for the "interaction with the continuous phase"? That's switched on

[Large Epic Simulations]

Try to post some screenshots of yours boundary settings, there could be a lot of things behind your problem.

[Pacca]

Thank you very much for your help! Let me know if other screenshots could be useful.

[Large Epic Simulations]

Dear Pacca, if you wish to observe the DPM related quantities, you should enable the DPM contour plots for the mean values.


Pay also attention to the species specifications on your outlet, that is to say, if you impose the species mass fraction (or flux) of n20 to 0 at the exit you can't see any n2o flowing out of the domain-> the continuity equation will shut your n2o mass fraction to 0 in the whole domain.

[Pacca]

I will enable the mean values box but I would say that this is only for postprocessing, while I can see that in my flowfield also the pressure has a value compatible with the absence of the evaporated n2o.


Regarding the outlet species specification I think that is related to the reversed flow, but I am sure that for the nature of the problem there is none.

[Large Epic Simulations]

Keep me updated

[Large Epic Simulations]

I've just discovered one thing: if yours DPM sources are below values of 10e-9, the vapor will not appear in between the species contours.

[Pacca]

Dear Large Epic Simulations, the liquid injection point injects hundreds of grams of liquid n2o, so I don't see how all the droplets can go below that value.

[Pacca]

So I tried different possibilities but none of them worked. I am still in the same situation of zero DPM mass source.


EDIT: I think I narrowed the problem to my definition of the "droplet particle material" and now I am trying to find the exact properties that cause this behavior.

[Kummi]

Dear Pacca,
Sometimes if diameter is quite higher (10^-4), then the evaporation will not be appropriate. So, go with Rosin-rammler diameter distribution..
and set: Max, mean and min dia as 10^-4,10^-5,10^-6.

Or calculate the diameter ranges using formula as described in user guide

Thank u~~