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Old   October 29, 2008, 05:03
Default Hi, I noticed that in OF 1.
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Markus Rehm
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I noticed that in OF 1.5 the implementation of chemistryModel::tc() changed:

OF 1.4 says

forAll(rho_, celli)
forAll(RR_, i)
if(RR_[i][celli] < -SMALL)
t[celli] =

and OF 1.5:

for(label celli=0; celli<nCells; celli++)
scalar rhoi = rho_[celli];
scalar Ti = thermo_.T()[celli];
scalar pi = thermo_.p()[celli];
scalarField c(Ns_);
scalar cSum = 0.0;

for(label i=0; i<Ns_; i++)
scalar Yi = Y_[i][celli];
c[i] = rhoi*Yi/specieThermo_[i].W();
cSum += c[i];

forAll(reactions_, i)
const reaction& R = reactions_[i];

R, c, Ti, pi, pf, cf, lRef, pr, cr, rRef

forAll(R.rhs(), s)
scalar sr = R.rhs()[s].stoichCoeff;
t[celli] += sr*pf*cf;
t[celli] = Nr*cSum/t[celli];

Could anyone explain why this change has been made and how the new implementation works?

Thanks in advance. Markus
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Old   October 30, 2008, 07:01
Default This was some time ago so its
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Niklas Nordin
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This was some time ago so its not entirely clear to me...

The first definition is simply an estimation of the shortest time for a species to be driven to zero.

The second is a bit more coupled to the PaSR combustion model in diesel(Engine)Foam.

If you write the reaction rates in terms of a positive, P, and negative, N, term and linearize the negative term around the concentration c.

omega = P - N = P - c/tau_c

you get the definition of tau_c.
This yields a chemical timescale for each species and
If I remember correctly the calculated tau_c is an averaged value over all species and reactions.
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