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[m.t.vu]

Hi all,

I have been trying to reproduce the results of this paper: "Comparative analysis of hydrogen/air combustion CFD-modeling for 3D and 2D computational domain of micro-cylindrical combustor" but I am nowhere close of getting the same results. (I'm not sure whetehr I am allowed to post the paper in here, so for now I will not do that, unless given permission).

The geometry is shown as follows:

For this, what is given is that this is a hydrogen-air combustion. 

The following assumptions were given: The heat transport and body force caused by concentration gradients can be neglected due to its low value. Moreover, other assumptions are taken for CFD-modeling: steady-state conditions of combustion; no the flux of energy due to a mass concentration gradient (no Duflor effects); work by viscous forces and by pressure is not done; surface oxidation reactions of the metal wall are absent.
I do not think I have to adjust anything in Fluent with these assumptions.

It uses the Eddy Dissipation Concept model. No values were given in here, so I kept the default values.
The RNG k-epsilon was used, the constant values which were given here were C1 and C2, which were kept at the default values as well.
P1 was used for the radiation model.

The specific heat and density were determined by the equations of mixing-law and incompressible-ideal-gas law.
The viscosity is determined by Sutherland viscosity law, however, these values were not given.
The thermal conductivity is computed as average mass fraction of each element, I assume this could be doen with the mass weighted mixing law.
The pressure-based solver was used and the convergence criterion were set to the correct values as well.

This were the given BCs:

I ignored the excess air ratio and the H2 mass flow rate, since I was not sure where to put these.

I entered the mass flow rate H2+air for the mass flow rate in the inlet. I was not able to enter the N2 mass fraction, but while double checking the results, the mass fraction of this seemed correct (it probably automatically entered this after I filled in O2). For the outlet I have tried both the pressure-outlet and outlet-vent (so I was able to put the hydraulic diameters and turbulent intensity in there). It was not specifically mentioned which one was used. For the wall, steel was used and I kept everything else at its default values, since nothing was mentioned furthermore.

 

For the axisymmetric simulations, these were the results:

Figure 1 is the paper, figure 2 is my result.

For some reason, in my simulation the temperature starts around 1100K, while I put 300k for the inlet. Also can be noticed that the wall temperature is much bigger and that the temperature increases very quickly from the start, compared to the paper.

 

Does anyone have an idea what I am doing wrong in here?

 

[Rob]

Assuming your species mixture is H2, O2, H2O and N2 in that order N2 would be whatever isn't the others because of the way Fluent handles species. 

Excess air will be a combustion note, but as the mass flows are then given isn't needed in the set up: you need to do some reading on combustion chemistry. 

P1 isn't really useful for hydrogen flames, so you may want to review the other options. If the paper is older then it may have been used because of the lower computational cost. 

I can't see any chemistry or material values in what you posted: how did you determine these?

[m.t.vu]

The values of the materials were given by Fluent itself already, I did not adjust these. It had options to use a constant value or to use the mixing law, which I chose based on what was given in the paper.

For the mechanism, this was used:

When I'm running this simulation, it gives me a dasac failure which goes away eventually, but the results still seem odd (as shown in the picture before)