[sm4096]

i would like to ask about the setup of a combustion chamber in converge that involves the direct injection of two different liquid fuels.

1. spray setup: should we define separate spray setting for each fuel, or is there a way to configure them whiten the dame setup?


2. Turbulence model: since the turbulence characteristics of each spray may be different, how can we assign distinct turbulence model for each spray individually?


thank you,
Mohammad

[zubin.mistry]

Liquid Injection
To setup two different liquid injections:
1. You will have to take setup two different liquids (Materials→ Liquid simulation)
2. Setup different parcels, (Physical Models → Parcels configuration)


Instead if you have a fuel which is multi-component, go to Materials → Composite species and define a composite species based on the mass fraction of different species.


Also, you can define without using composite species. Steps are as follows:
1. Define the relevant species in Materials → Liquid simulation
2. Go Physical Models → Parcel configuration → Edit. Add the relevant species.
3. Parcel Introduction → Injectors → Edit → Parcel/Misc. Add the Mass fraction of the different species involved.


Turbulence and Parcels
To turn on turbulence effects on Lagrangian particles, you can use the turbulent dispersion models that converge has. To setup different spray dissipation coefficients for RANS (Physical Effects → Turbulence Modeling → Physics Effects → Spray dissipation constant) or for LES (Physical Effects → Turbulence Modeling → Physics Effects → Drop turbulent dispersion constant). Please refer to Chapter 14.4.1.2 Turbulent Dispersion, in-order to understand the modeling approach.


Also, having different turbulence models is not recommended within the same region. I would like to understand why you would want that. Changing spray dissipation coefficients will affect all sprays. But different sprays will have different flow dynamics (velocities) and as such turbulent behavior would be different between those sprays with the same global turbulence model.

[sm4096]

Hi Zubin,

Thank you very much for your comments.

I have a question regarding the case setup: why do we need to include the liquid simulation? parcel simulation is not enough for spray?

Secondly, I prefer not to use a different turbulence models. I would like to continue with the standard k-epsilon model, but with different coefficients for each fuel—for example, the turbulent viscosity constants. Is there any way to assign different turbulence model coefficients for each spray?

Lastly, is it appropriate to use turbulent dispersion model instead of RANS?

Thanks again for your help.

[zubin.mistry]

Hi,

1. The liquid properties are specified in the liquid.dat file under the "Liquid simulation" panel. And eulerian liquid is needed (you cannot run lagrangian only simulations) and Gas simulation is active since we inject into an eulerian gas domain. Under Materials Simulation -> Uncheck Liquid Simulation, check Parcel Simulation -> Liquid, Parcel breakup.
2. The modeling constants in turbulence modeling are global. If you want to enable different/custom turbulent dispersion models for different injectors, UDFs are a way to handle them. Advanced Parameters -> UDF selection.
3. Spray turbulent dispersion models are used WITH RANS models, not INSTEAD OF. Please look into the Converge Manual to understand how the turbulent dispersion models work with RANS / LES models in CONVERGE. Page 384 Converge Manual.

Thank you.

[sm4096]

Thank you so much.