alphaEff() myXiFoam

kaizhangqmul · February 15, 2018, 07:35

Dear Friends,

I am trying to implement the new algebraic combustion for XI as that given in ehsanYasariReport.pdf. I remember this worked fine many years ago when i used old version of openfoam.

But now, in 5.x, it gives out a mistake casued by

Code:

tauTurbPrime = (turbulence->alphaEff()-thermo.alpha())/(rho*pow(up,2));

where i found turbulence->alphaEff() = thermo.alpha() = 1e-05......and then tauTurbPrime = 0.
and In,

Code:

S_turbTimeDependent=S_turb*
sqrt(1.+tauTurbPrime/(runTime+tO)*(exp(-1.*(runTime+tO)/tauTurbPrime)-1.));

Division by 0 appeared.

Shouldn't we have turbulence->alphaEff() = turbulent thermal diffusivity + molecular thermal diffusivity and subtract it from thermo.alpha (molecular) gives turbulent thermal diffusivity? but this will always lead to a 0 turbulent thermal diffusivity at time 0 and for this implementation we cant continue.

Can anyone help please?

Best,
Kai.

kaizhangqmul · February 15, 2018, 12:07

feel like i have solved it, but still got some problems that b value could drop below 0 and give error in half way. This error also occur for algebraic Xi model with negative b.

February 15, 2018, 07:35	alphaEff() myXiFoam	#1
kaizhangqmul New Member Join Date: Feb 2018 Posts: 7 Rep Power: 8	Dear Friends, I am trying to implement the new algebraic combustion for XI as that given in ehsanYasariReport.pdf. I remember this worked fine many years ago when i used old version of openfoam. But now, in 5.x, it gives out a mistake casued by Code: tauTurbPrime = (turbulence->alphaEff()-thermo.alpha())/(rhopow(up,2)); where i found turbulence->alphaEff() = thermo.alpha() = 1e-05......and then tauTurbPrime = 0. and In, Code: S_turbTimeDependent=S_turb sqrt(1.+tauTurbPrime/(runTime+tO)(exp(-1.(runTime+tO)/tauTurbPrime)-1.)); Division by 0 appeared. Shouldn't we have turbulence->alphaEff() = turbulent thermal diffusivity + molecular thermal diffusivity and subtract it from thermo.alpha (molecular) gives turbulent thermal diffusivity? but this will always lead to a 0 turbulent thermal diffusivity at time 0 and for this implementation we cant continue. Can anyone help please? Best, Kai. Last edited by kaizhangqmul; February 15, 2018 at 10:41.

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February 15, 2018, 12:07		#2
kaizhangqmul New Member Join Date: Feb 2018 Posts: 7 Rep Power: 8	feel like i have solved it, but still got some problems that b value could drop below 0 and give error in half way. This error also occur for algebraic Xi model with negative b.