CFD Online Logo CFD Online URL
Home > Forums > OpenFOAM Running, Solving & CFD


Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Display Modes
Old   October 29, 2008, 05:03
Default Hi, I noticed that in OF 1.
Senior Member
Markus Rehm
Join Date: Mar 2009
Location: Erlangen (Germany)
Posts: 181
Rep Power: 8
markusrehm is on a distinguished road

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
markusrehm is offline   Reply With Quote

Old   October 30, 2008, 07:01
Default This was some time ago so its
Super Moderator
niklas's Avatar
Niklas Nordin
Join Date: Mar 2009
Location: Stockholm, Sweden
Posts: 693
Rep Power: 20
niklas will become famous soon enoughniklas will become famous soon enough
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.
niklas is offline   Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 08:36.