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N.P October 24, 2004 23:35

Source Term Linearisation
 
Dear CFX users,

I am encountering problems solving a pretty staight forward Scalar(in steady state). I created an additional variable(F) and i am solving it as a transport equation. Its source term is a second order equation: S=A-B(F*F) where A and B say are constants. In the manual the only requirement for linearisation is to type the source down in the form of S=Sc+Sp*F and ensure Sp is a negative value. So, possible linearisations are: 1. Sc=A-B(F*F), Sp=0, 2. Sc=A , Sp=-B*F, 3. Sc=A+B(F*F), Sp=-2BF, 4. Sc=A+10B(F*F), Sp=-11B*F, I made several attepmps as well as all the above(set them up in CEL)and the solver either gives me a linear solver FINMES error or not better residuals than 5*10^-3 for the additional variable(very unrealistic results with the correct trend being only in the start of the geometry). My other residuals for Mass Fractions , Momentum and mass are in the order of 10^-9 so i believe there is nothing wrong with the mess plus i have already tried several timesteps (even down to 10^-6 and the only thing i managed is to marginally improve the results or delay the FINMES error)and advection schemes. I am getting desperate here. Is there anything else i could try ? Thanks for your time, Nik


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