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Old   January 19, 2006, 05:11
Default convergence building fire
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I'm just a newbee in CFD and I'm trying to model a fire in a building, but I have convergence problems. I use a mechanical outlet for ventilation and passive inlets. Without the fire, flows converge, but when I introduce the fire/smoke, the flows no longer converge: nettsum(R)/pos.sum(R)=1.5%

I use the parameters below. Does anyone have any ideas what could be the problem? And are there any strategies in this? I get the impression the whole field is more or less trial & error, but aren't there some general guidelines/rules of thumb?

kind regards Stefan de Kool

Groups 3, 4, 5 Grid Information

* Overall number of cells, RSET(M,NX,NY,NZ,tolerance) RSET(M,60,104,12,1.000000E-02)

Group 15. Terminate Sweeps LSWEEP = 1000 RESFAC = 1.000000E-03

Group 17. Relaxation RELAX(P1 ,LINRLX, 1.000000E+00) RELAX(U1 ,FALSDT, 1.000000E+01) RELAX(W1 ,FALSDT, 1.000000E-01) RELAX(KE ,LINRLX, 5.000000E-01) RELAX(EP ,LINRLX, 5.000000E-01) RELAX(SMOK,FALSDT, 1.000000E+01) RELAX(TEM1,FALSDT, 1.000000E+01) KELIN = 3

Group 18. Limits VARMAX(P1 ) = 1.000000E+03 ;VARMIN(P1 ) =-1.000000E+03 VARMAX(U1 ) = 1.000000E+03 ;VARMIN(U1 ) =-1.000000E+03 VARMAX(V1 ) = 1.000000E+03 ;VARMIN(V1 ) =-1.000000E+03 VARMAX(W1 ) = 1.000000E+03 ;VARMIN(W1 ) =-1.000000E+03 VARMAX(EP ) = 1.000000E+10 ;VARMIN(EP ) =-1.000000E+10 VARMAX(SMOK) = 2.000000E+00 ;VARMIN(SMOK) = 0.000000E+00 VARMAX(SLEN) = 1.000000E+10 ;VARMIN(SLEN) = 0.000000E+00
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Old   February 10, 2006, 09:16
Default Re: convergence building fire
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If you have a fire source, then the density DEN1 will vary rapidly in the vicinity of the fire source, and so you need to STORE(DEN1) and apply linear relaxation on DEN1, say 0.3. It is advisable to set VARMIN(DEN1)=1.E-5 to protect against negative densities during the course of convergence. Likewise you may also need to limit the temperature TEM1 to prevent non-physical values occuring during the run.
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