[sanjeev_adhikari]

Hello everyone,

I was facing the problem with time accuracy of the solution using first order Euler ddt. So, i thought of implementing rk4 third order time accuracy. Following represents the



equations:

rho = rhoOld + rkCoef[cycle] *runTime.deltaT()*(-fvc::div(Riemann.rhoFlux()))


momentum equations.
rhoU = rhoUOld + rkCoeff[cycle]*runTime.deltaT()*(-fvc::div(Riemann.rhoUFlux())+fvc::div(tauMC)+fvc:: laplacian(muEff, U));



species transport eqn:
fvScalarMatrix YiEqn
(
rhoYi - rhoYOldi
- rkCoeff[cycle]*runTime.deltaT()*(-fvc::div(Riemann.rhoScalarFlux(i))+
fvm::laplacian(turbulence->muEff(), Yi))
== rkCoeff[cycle]*runTime.deltaT()*reaction->R(Yi)
);


energy eqn


rhoE = rhoEOld + rkCoeff[cycle]*runTime.deltaT()*(
-enFl + fvc::div(sigmaDotU) + fvc::laplacian(turbulence->alphaEff(), h)
+fvc::laplacian(k,T)+reaction->Sh());



well the solver runs fine but temperature of the solution is less by half then it should be.
However other flow structure are also captured. I have doubt over implementation of the species transport equation. As low temperature might be because there was no combustion. As in H2O concentration contour there is not any sign of it.









ps. i am not calculating time step separately. right now just using setDeltaT from openFoam library.



Thank you all.

[sbaffini]

Not an OF expert here but, just two cents:

1) Who's enFl ?

2) Did it work without species?

[sanjeev_adhikari]

Originally Posted by sbaffini

Not an OF expert here but, just two cents:

1) Who's enFl ?

2) Did it work without species?

Thank you for your reply:



enfl is fvc::div(Riemann.rhoEFlux())


i didn't check without species for my case. i started implementing rk4 for all these 4 equations. I think continuity, momentum and energy equations are working fine as the solution obtained captures shock structure as in experimental case. However, i cannot see combustion nor species concentration in those result..



However, i will implement without species and confirm separately too.