CFD Online Discussion Forums - How to run cold flow in reactingFoam?

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How to run cold flow in reactingFoam?

Hello all,

I have just started using OpenFoam for my dissertation on jet flame calculations. I am trying to simulate axisymmetric cold flow in reactingFoam.

I switched off chemistry and reactions in the "constants" folder to simulate cold flow. Is that the correct way to go about doing it ?

Also even if I switch off my chemistry, i still have default product species H2O and CO2 as output files. Why is that?

Would really appreciate any help. Thanks :)

Greetings Harshad

I really didn't get what is exactly your problem. You have switched off the combustion and want to get rid off CO2 and H2O species in results?? (why does it matter):confused:

I think you have used one-step reaction in your case i.e. sth like this:

Code:

species

(

    O2

    H2O

    CH4

    CO2

    N2

);



reactions

{

    methaneReaction

    {

        type         irreversibleArrheniusReaction;

        reaction     "CH4 + 2O2 = CO2 + 2H2O";

        A            5.2e16;

        beta         0;

        Ta           14906;

    }

}

In this case, although you have switched off combustion, you will have zero values for these species in paraview. In case of need to not see these species (I don't know really why):confused::confused::confused: ,I propose to change your combustion model in combustionProperties file to noCombustion. I think (not sure) that this will solve your problem .

Regards
Bobi

Thanks Bobi!, appreciate your help :)

I didnt check the CO2 and H2O species files. I was just confused about why they were output when I was solving a cold flow solution.

Can you also let me know how is the perfect gas equation of state used in a combustion solver in OpenFoam? I am assuming that since reactingFoam is a compressible solver, rho would be obtained from the continuity, velocity from the momentum equations and pressure, temperature from a laplacian and the enthalpy respectively.

How is the equation of state used then?

Greetings Harshad

There is a difference between rhoReactingFoam and reactingFoam solvers. In reactingFoam, rho equation is not solved (although it uses compressible LES sub-grid scale models) and the density is computed from the equation of state. However, in rhoReactingFoam rho equation is solved. (take a look at their src solvers i.e. reactingFoam.C and rhoReactingFoam.C )

Regards
Bobi

Quote:

Originally Posted by babakflame (Post 497170)

There is a difference between rhoReactingFoam and reactingFoam solvers. In reactingFoam, rho equation is not solved (although it uses compressible LES sub-grid scale models) and the density is computed from the equation of state. However, in rhoReactingFoam rho equation is solved. (take a look at their src solvers i.e. reactingFoam.C and rhoReactingFoam.C )

I just started to look into this and was wondering if you could quickly elaborate why the rhoEqn is not solved in the reactingFoam solver?

From what I see, in both solvers the actual equation is included in the source code (in the .C files, as well as in the respective pEqn.H files):

Code:

#include "rhoEqn.H"

Thanks!

-Armin

Why can't I see the velocity residuals in my log file?

Hello,

I am running a simulation using reactingFoam. There is an inlet of fuel and an inlet of air. After running everything ok, I can't see the velocity residuals in my log file. Why?

Code:

Courant Number mean: 0.0774694 max: 0.394132

deltaT = 0.00116279

Time = 1.5



diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0

DILUPBiCG:  Solving for O2, Initial residual = 9.8746e-07, Final residual = 9.8746e-07, No Iterations 0

DILUPBiCG:  Solving for H2O, Initial residual = 9.79843e-07, Final residual = 9.79843e-07, No Iterations 0

DILUPBiCG:  Solving for CH4, Initial residual = 5.35224e-08, Final residual = 5.35224e-08, No Iterations 0

DILUPBiCG:  Solving for CO2, Initial residual = 9.79228e-07, Final residual = 9.79228e-07, No Iterations 0

DILUPBiCG:  Solving for h, Initial residual = 9.8117e-07, Final residual = 9.8117e-07, No Iterations 0

min/max(T) = 300, 1960.5

DICPCG:  Solving for p, Initial residual = 1.47541e-06, Final residual = 8.87219e-07, No Iterations 21

diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0

time step continuity errors : sum local = 7.03266e-08, global = -9.27209e-10, cumulative = -1.08985e-05

DICPCG:  Solving for p, Initial residual = 1.90516e-06, Final residual = 6.1582e-07, No Iterations 1

diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0

time step continuity errors : sum local = 7.03245e-08, global = -9.37162e-10, cumulative = -1.08994e-05

ExecutionTime = 19.53 s  ClockTime = 19 s

Regards,

Lisandro

I have done something similar, I could not understand why rho's residual is always 0.
Ayush