The effect of gravity in 1D flame simulation

[Mo Adib]

I know that Cantera's flame solver is based on the equations that used psudo 1D assumption to account for momentum, energy and species, and it ignores the gravity term. The effect of gravity is significant in burner-stabilized premixed flames (cantera.BurnerFlame) causing temperature drop towards the end of domain.

I performed the simulations for ISF-4 premixed flame 1, using two different reaction mechanisms (attached to this post), and compared the Cantera's predictions with temperature profiles suggested by ISF. The temperature different is caused because of ignoring the gravity.

Is there any way to cosider gravity in this simulation?

 

[Chris N]

At this time, the 1D equations aren't in a form that has support for having a user-defined source term like gravity (to the best of my knowledge). A term would have to be added to the governing equations in the src/oneD/StFlow.cpp file I believe if you need to do this.

[Mo Adib]

Yes, you are right. I am have examined Stflow.cpp and done some modifications on the source code, and famaliar to some extent with how discretized equations are implemented. 

The question is considering gravity limited in any way by the 1D assumptions? I noticed that Kee's textbook, which is the basis for the Cantera's solver, does not include gravity term.

[Bryan Weber]

Hi,

I believe the general assumption is that body forces are neglected, such as electric fields or gravity. However, body forces are generally just an additive term in the momentum equation so you can usually just directly include them. See the Wikipedia page on the N-S equations: https://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations If you want to verify, you can go through the 1-D simplifications and just retain the gravity term. See also: https://physics.stackexchange.com/questions/406437/why-dont-the-navier-stokes-equations-simplified-for-hydrodynamics-contain-gravi

[Ray Speth]

Hi,

Before anyone goes down the rabbit hole of adding this term to Cantera's solver, I don't think it's correct that the lack of gravity is the source of the differences. As long as you're constraining the flow to 1D, all it's going to do is add a hydrostatic pressure gradient, which is going to have a negligible effect over a 10 cm domain in a gas. As the flow moves upward and the hydrostatic pressure decreases, it will expand very slightly, leading to a very small temperature drop. However, these results show a drop of several hundred kelvin over this domain. Given these are sooting flames, I would assume that most of that temperature drop is from radiation from the soot particles, which is also an effect not currently modeled in Cantera.

Regards,

Ray

[Mo Adib]

Thanks Ray and Bryan. 

I have already added the gravity source term to Cantera's flame solver, and as Ray predicted it has negligible effect on temperature profile. So, I assume the enthalpy loss from gas due to formation of soot and radiation by particle cause the temperature drop.