Learning Forum

[Zwernjayden]

Which combustion models work when both propellants are 100% dpm. Can I use the non-premixed steady diffusion flamelet, or partially premixed FGM, or do I need to use a species transport model like eddy dissipation?

[Ren]

Could you please provide more details of the problem that you want to simulate?

What you mean by "both propellants"? Are they liquid? Are they going to evaporate?

Are there any other fluids in the domain? Are they liquid or gaseous?

Where and how do the "fuel" and "oxidizer" or any other fluids enter in the computational domain?

 

[fanbo9802]

Hi, Ran. If my case used liquid fuel and liquid oxider(modeled by DPM particle) to simulate spray combustion under atmosphere, when I set the boundary, I should give both fuel and oxider species 1, am i right? But when I finished the initialization, I found that the mass fraction of oxygen is 1, is it normal? Because the combustor should be filled with air rather pure oxygen. 

[Ren]

What is the chemical composition of the liquid oxidiser? Which combustion model are you referring to and what boundaries are you referring to? Screenshots of Fluent dialog boxes would be useful.

[fanbo9802]

The liquid fuel is ethanol and liuquid oxider is liquid oxygen. I wanna use partially permixed combustion, FGM. As Fig shown, the liquid ethanol inject into combustor through axial, while liquid oxygen inject though radial. And I set ethanol and oxygen as 1 in the boundary conditions, and should I set the temperature as the boiling point？With the value of ethanol is 351K, liquid oxygen is 90K, or as the user's guide said, filled with Vaporization Temperature of particle properties, with the value is 271K and 55K.

Fig.1 FGM settings.

And when I running the simulation, I also found that the species distribution shows a wrong result, with the ethanol concertration on the region close to the liquid oxygen injector.  And because of the boundary settings, the mass fraction of species in the whole combustor is oxygen as 1. I think it doesn't meet the realstic conditions. 

Fig.2 Species distribution.

[Ren]

You also mentioned air. Are there any inlet boundaries in the domain and what materials enter the inlets, if there are any.

In the "Boundary" tab as shown in your screenshot, the fuel and oxidizer temperatures should be set to the values corresponding to the vaporization temperature you set for the droplet materials. Please note that these temperatures control the start of droplet vaporization of the DPM model in the CFD simulation.

Check the mass fraction value in the domain. If it's zero then the domain will be O2 only.

[fanbo9802]

Thanks for your reply, Ren. There is no other inlet boundaries in the domain, the species entered into combustor were just ethanol and oxygen, both of them injected as particles. I have got your answer and know how to set the temperatures of boundaries in partially premixed combustion model.  These temperatures control the vaporization, and when the temepratrue reached at boiling point, the particle heat and mass exchange law will switch to the law3 from law2. And because of the mixture only contains oxygen and C2H5OH, so the combustor filled with oxygen when set intilization of mixture fraction as 0. Which means no fuel in domain at the beginning.

But I still wonder weather about why ethanol distribution shows in the Fig.2, it should be oxygen rather ethanol.

[Ren]

Regarding the ethanol plot, is that a converged solution?

[fanbo9802]

It did not converge, diverge instead at the end. I would modified the settings. Thanks for your help, Ren!

[Rob]

Moderator note, https://innovationspace.ansys.com/forum/forums/topic/which-combustion-models-can-i-use-when-fuel-and-oxidizer-are-both-sprays/ may also contain useful information.