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-   -   Problem of simulating of small droplet with radius of 2mm (http://www.cfd-online.com/Forums/openfoam-solving/115807-problem-simulating-small-droplet-radius-2mm.html)

liguifan April 7, 2013 11:57

Problem of simulating of small droplet with radius of 2mm
 
Good morning everyone,

I am trying to simulate a droplet of oil with radius of 2mm fall into a waster base with radius of 10cm and I use setField to initialize the droplet and water base, however, the after 0.4 seconds, the Delta T became some number around 1.5e-16 and the max courant number is around 0.13. ( I use the adjusted timestep), which make no sense to me.

Beside that, by viewing under paraview, I found that the droplet is not even a sphere(actually, I can't even see it). So I doubt the capacity of OpenFoam dealing with such a small droplet.

Can anyone give me some hint about why is this can and how to make it works?

Many thanks!
James

liguifan April 7, 2013 18:18

Here is some log content I got from running the code
Quote:

time step continuity errors : sum local = 0, global = 0, cumulative = 0
GAMGPCG: Solving for pcorr, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 0, global = 0, cumulative = 0
Courant Number mean: 0 max: 0

Starting time loop

Courant Number mean: 0 max: 0
deltaT = 0.00119048
Time = 0.0011904761904761905836

MULES: Solving for alphawater
water volume fraction, min, max = 1 1 1
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 0 0 0
Phase-sum volume fraction, min, max = 1 1 1
MULES: Solving for alphawater
water volume fraction, min, max = 1 1 1
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 0 0 0
Phase-sum volume fraction, min, max = 1 1 1
MULES: Solving for alphawater
water volume fraction, min, max = 1 1 1
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 0 0 0
Phase-sum volume fraction, min, max = 1 1 1
alphawater phase volume in zone internal = 508.292 ml
alphaoil phase volume in zone internal = 0 ml
alphaair phase volume in zone internal = 0 ml
GAMG: Solving for p, Initial residual = 1, Final residual = 0.0236848, No Iterations 6
time step continuity errors : sum local = 1.64387e-05, global = -1.03465e-05, cumulative = -1.03465e-05
GAMG: Solving for p, Initial residual = 0.00074067, Final residual = 2.70641e-05, No Iterations 4
time step continuity errors : sum local = 7.79738e-07, global = -5.07037e-07, cumulative = -1.08535e-05
GAMGPCG: Solving for p, Initial residual = 2.96832e-05, Final residual = 8.98889e-09, No Iterations 3
time step continuity errors : sum local = 2.61834e-10, global = -8.68849e-12, cumulative = -1.08536e-05
ExecutionTime = 3.78 s


Courant Number mean: 6.82615e-06 max: 1.98889e-05
deltaT = 0.00139456
Time = 0.0025850340136054422366

MULES: Solving for alphawater
water volume fraction, min, max = 1 0 1
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 0 0 1
Phase-sum volume fraction, min, max = 1 1 1
MULES: Solving for alphawater
water volume fraction, min, max = 1 0 1
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 4.35967e-09 0 1
Phase-sum volume fraction, min, max = 1 1 1
MULES: Solving for alphawater
water volume fraction, min, max = 1 0 1
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 8.71935e-09 -4.82588e-34 1
Phase-sum volume fraction, min, max = 1 1 1
alphawater phase volume in zone internal = 508.292 ml
alphaoil phase volume in zone internal = 0 ml
alphaair phase volume in zone internal = 4.43198e-06 ml
GAMG: Solving for p, Initial residual = 0.0381303, Final residual = 1.6858e-08, No Iterations 1
time step continuity errors : sum local = 5.30546e-05, global = -1.88254e-05, cumulative = -2.96789e-05
GAMG: Solving for p, Initial residual = 1.93613e-08, Final residual = 1.93613e-08, No Iterations 0
time step continuity errors : sum local = 6.10707e-05, global = -2.57188e-05, cumulative = -5.53978e-05
GAMGPCG: Solving for p, Initial residual = 2.94069e-08, Final residual = 2.94069e-08, No Iterations 0
time step continuity errors : sum local = 9.27571e-05, global = 9.34652e-06, cumulative = -4.60513e-05
ExecutionTime = 7.15 s


Courant Number mean: 0.000483287 max: 0.00911681
deltaT = 0.001635
Time = 0.0042200328407224962576

MULES: Solving for alphawater
water volume fraction, min, max = 1.00001 0 1.00338
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = -1.84692e-05 -0.00432414 1
Phase-sum volume fraction, min, max = 0.999996 0.993861 1.00071
MULES: Solving for alphawater
water volume fraction, min, max = 0.999996 0 1.00406
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = -3.56282e-06 -0.00427731 1
Phase-sum volume fraction, min, max = 0.999993 0.98778 1.00141
MULES: Solving for alphawater
water volume fraction, min, max = 0.999978 0 1.00474
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 1.1343e-05 -0.00423064 1
Phase-sum volume fraction, min, max = 0.999989 0.981739 1.0021
alphawater phase volume in zone internal = 508.281 ml
alphaoil phase volume in zone internal = 0 ml
alphaair phase volume in zone internal = 0.00576554 ml
GAMG: Solving for p, Initial residual = 0.0253438, Final residual = 1.98857e-08, No Iterations 1
time step continuity errors : sum local = 0.000105995, global = -6.39265e-05, cumulative = -0.000109978
GAMG: Solving for p, Initial residual = 0.0473882, Final residual = 0.000306761, No Iterations 1
time step continuity errors : sum local = 1.71959, global = 0.212659, cumulative = 0.212549
GAMGPCG: Solving for p, Initial residual = 1, Final residual = 1.51042e-08, No Iterations 6
time step continuity errors : sum local = 66013.1, global = -9015.75, cumulative = -9015.54
ExecutionTime = 10.62 s


Courant Number mean: 2.72432e+13 max: 1.83728e+17
deltaT = 4.4495e-21
--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1029
Increased the timePrecision from 20 to 21 to distinguish between timeNames at time 0.00422003
Time = 0.00422003284072249625763

--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1029
Increased the timePrecision from 21 to 22 to distinguish between timeNames at time 0.00422003
MULES: Solving for alphawater
water volume fraction, min, max = 0.999978 0 1.00474
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 1.1367e-05 -0.00402082 1
Phase-sum volume fraction, min, max = 0.999989 0.982154 1.0021
--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1029
Increased the timePrecision from 22 to 24 to distinguish between timeNames at time 0.00422003
MULES: Solving for alphawater
water volume fraction, min, max = 0.999978 0 1.00461
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 1.14044e-05 -0.0040187 1
Phase-sum volume fraction, min, max = 0.999989 0.982243 1.0021
--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1029
Increased the timePrecision from 24 to 25 to distinguish between timeNames at time 0.00422003
MULES: Solving for alphawater
water volume fraction, min, max = 0.999978 0 1.00459
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 1.14419e-05 -0.00401781 1
Phase-sum volume fraction, min, max = 0.999989 0.982245 1.0021
--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1029
Increased the timePrecision from 25 to 26 to distinguish between timeNames at time 0.00422003
alphawater phase volume in zone internal = 508.281 ml
alphaoil phase volume in zone internal = 0 ml
alphaair phase volume in zone internal = 0.00581581 ml
GAMG: Solving for p, Initial residual = 1, Final residual = 0.0306118, No Iterations 1
time step continuity errors : sum local = 2.68775e-06, global = 1.07034e-06, cumulative = -9015.54
GAMG: Solving for p, Initial residual = 8.01422e-06, Final residual = 4.91744e-08, No Iterations 1
time step continuity errors : sum local = 1.4253e-06, global = 1.00707e-07, cumulative = -9015.54
GAMGPCG: Solving for p, Initial residual = 5.0605e-06, Final residual = 1.33807e-08, No Iterations 1
time step continuity errors : sum local = 5.50534e-07, global = -8.27593e-08, cumulative = -9015.54
ExecutionTime = 14.02 s


Courant Number mean: 8.80955e-05 max: 0.05748
deltaT = 5.3394e-21
Time = 0.0042200328407224962576349547

--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1029
Increased the timePrecision from 26 to 27 to distinguish between timeNames at time 0.00422003
MULES: Solving for alphawater
water volume fraction, min, max = 0.999978 0 1.00459
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 1.15751e-05 -0.00401756 1
Phase-sum volume fraction, min, max = 0.999989 0.982247 1.00223
--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1029
Increased the timePrecision from 27 to 28 to distinguish between timeNames at time 0.00422003
MULES: Solving for alphawater
water volume fraction, min, max = 0.999978 0 1.00459
MULES: Solving for alphaoil
oil volume fraction, min, max = 0 0 0
MULES: Solving for alphaair
air volume fraction, min, max = 1.17348e-05 -0.0040173 1
Phase-sum volume fraction, min, max = 0.999989 0.982248 1.00254
--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1029
Increased the timePrecision from 28 to 29 to distinguish between timeNames at time 0.00422003
The Delta T become extremely small!

Martin_K_lalelu May 27, 2014 02:15

Hi,

I know its been some time, but do you remember how to solve this problem? My single droplet also develops high Co so that the solver is not longer able to distinguish between different time steps and quits.

Regards
Martin

ahmed_khatibs May 27, 2014 02:31

this may be also due to mesh (deltat).

Tushar@cfd May 27, 2014 03:30

Check CFL criteria

Try reducing deltaT & increase mesh spacing depending upon your requirement

Martin_K_lalelu June 3, 2014 02:53

Thank you!


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