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-   -   Presure results squareBend (http://www.cfd-online.com/Forums/openfoam-solving/96218-presure-results-squarebend.html)

pcaste12 January 16, 2012 13:27

Presure results squareBend
 
Hi,
I've run the squareBend tutorial with several added calculations. I get the following results:
Time = 500

GAMG: Solving for Ux, Initial residual = 0.00114342, Final residual = 0.000104067, No Iterations 4
GAMG: Solving for Uy, Initial residual = 0.000728807, Final residual = 6.92936e-05, No Iterations 3
GAMG: Solving for Uz, Initial residual = 0.0426736, Final residual = 0.00411956, No Iterations 3
GAMG: Solving for p, Initial residual = 0.00292189, Final residual = 0.000205264, No Iterations 3
time step continuity errors : sum local = 1.16781, global = -0.115124, cumulative = -125.995
rho max/min : 0.507862 0.233955
GAMG: Solving for h, Initial residual = 0.00161684, Final residual = 0.000140944, No Iterations 4
ExecutionTime = 179.84 s ClockTime = 181 s

Averages of T : inlet = 1000 outlet = 970.329
Averages of p : inlet = 122930 outlet = 110000
Averages of U : inlet = (468.057 0 0) outlet = (-445.63 0.441477 0.762627)
MassFlows: inlet = -0.439657 outlet = 0.439453

Going back to basics I ve tried to apply some simple formula p=r*rho*T then mass=rho*U*Area (don't be affraid it is just to get an idea ;-) ).
Applying this to outlet gives us rho=0.395 and mout=0.4399 which is very close to the one calculated by openFoam. Doing the same for the inlet is a bit strange rho=0.428 and min=0.501, which is quite far from the calculated one.

I will be very glad to understand my mystake, if you could help me thanks a lot.
Pierre.

pcaste12 January 17, 2012 13:08

Please help
 
So, going a bit further (which are quite cool by the way) I get the following results:
Time = 500

GAMG: Solving for Ux, Initial residual = 7.85017e-09, Final residual = 7.85017e-09, No Iterations 0
GAMG: Solving for Uy, Initial residual = 6.48846e-09, Final residual = 6.48846e-09, No Iterations 0
GAMG: Solving for Uz, Initial residual = 1.30316e-08, Final residual = 5.26334e-09, No Iterations 1
GAMG: Solving for p, Initial residual = 1.64444e-08, Final residual = 2.91877e-09, No Iterations 1
time step continuity errors : sum local = 1.43382e-05, global = 9.50578e-08, cumulative = -375.781
rho max/min : 0.535971 0.305706
GAMG: Solving for h, Initial residual = 8.82731e-09, Final residual = 8.82731e-09, No Iterations 0
GAMG: Solving for epsilon, Initial residual = 1.00608e-08, Final residual = 2.54175e-09, No Iterations 1
GAMG: Solving for k, Initial residual = 1.66265e-08, Final residual = 3.90612e-09, No Iterations 1
ExecutionTime = 188.73 s ClockTime = 189 s

Averages of T : inlet = 1000 outlet = 952.305
Averages of p : inlet = 129606 outlet = 110000
Averages of rho : inlet = 0.450494 outlet = 0.401513
Averages of k : inlet = 739.142 outlet = 1171.94
Averages of epsilon : inlet = 660407 outlet = 4.58901e+06
Averages of U : inlet = (443.962 0 0) outlet = (-432.941 0.798248 -3.89557e-08)
Integrals of U : inlet = (1.10991 0 0) outlet = (-1.08235 0.00199562 -9.73893e-11)
MassFlows: inlet = -0.434892 outlet = 0.434892
End

The rho calculation is equal du mine ==> looks good.
The integral of U which is just Ui*Ai gives the same results than mine==> good.
So finally I don't understand the calculation of MassFlows inlet!! Of course it is wired to have the inlet mass greater than the outlet mass where is the missing mass:confused:? Which calculation is wrong?
The last assumption is that using:
inlet
{
type flowRateInletVelocity;
flowRate 0.5; //0.75;
value uniform (0 0 0);
}
the normal vector is not always on the same direction, but in this case the inlet face is very simple!
Help will be very appreciate.
Thanks,
pierre.


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