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-   -   Discrepancy between steady and transient calculations (http://www.cfd-online.com/Forums/star-cd/76104-discrepancy-between-steady-transient-calculations.html)

Dermer May 14, 2010 06:03

Discrepancy between steady and transient calculations
 
Hello
I have a relatively simple task with Laval nozzle:
v,1,0,0,0
v,2,0,3.319,0
v,3,1,0,0
v,4,0.718,0.991,0
v,5,0.704,1.198,0
v,6,1,3.319,0
vfill 4 5 5 10 1
ctab,4,shell,,,,,,,,off,,light
ctname,4,
ctab,4,shell,5,0,1,1,0,1,0,off,0,light
ctname,4,
csys,1
patch 1 3 6 2 15 100,,,,,,,,,0.85,1
2d3d,axisymmetric
view 0 -1 0
rdef,3,inlet
bzon,3,all (or pick 15 cells)
view 0 1 0
rdef,4,outlet
bzon,4,all (or pick 15 cells)
pmat,1,fluid,AIR
dens,ideal,y,28.96
lvis,suther,1.716e-05,116
spec,constant,1006
cond,constant,0.02637
pmat,1,fluid
turb,ke,1,stan
lowre,off
coke,0.09,1.44,1.92,1.44,-0.33,0.419,1,1.219,0.9,,,
pmat,1,fluid
temp,on,thermal,total,
etc...

Boundary conditions: inlet V=10, dens=1.205,T=293
and I solve this task in two modes: Steady and transient (with timestep 1e-4, 100000 steps)
But: In steady solution i have a correct decision
In transient i have uncorrect decision: fluid accelerates along the length of the nozzle; besides, the flux sum on inlet and outlet do not match

Can you explain the problem?


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