[francisco.angel]

Originally Posted by hans-186

Gents,

I'm running into the same problem. Looking at the reactions in this thread help me a bit, but still not there. If I look at eq. 6.36, 6.37 and the equations below that for the multiplier (d). I still end up with a problem.

If I take the central differencing scheme from Chap. 5 for the central coefficient (pag 136):
ap=aw+ae+Fe-Fw; (Assume A and rho = 1 and D=0)
aw=Fw/2; ae=-Fe/2;
Fw=uw;Fe=ue;

ap=uw/2 -ue/2 + uw/4 -ue/4;

When uw approaches ue (which happens if all works well in a 1D situation) ap goes to 0 and the multiplier (d) approaches infinity. Resulting in all sorts of problems.

I'm not quite sure how the URF solves this issue. Can someone help me figuring out where I'm going wrong?

Those problems (like coefficients going to zero) are due to using the central difference scheme in the convective terms, Patanakar discuses this, this is the reason you move from central difference to schemes like upwind, power, exponential, etc.