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maka August 4, 2008 14:07

At the start of a turbulent fl
 
At the start of a turbulent flow computations, I noticed that dropping the residual of p eq. to 1e-6 does not change the initial residual of the next corrector much.

-----------------------------
Time = 0.004

Courant Number mean: 0.0548726 max: 0.170667
BICCG: Solving for Ux, Initial residual = 1, Final residual = 5.34374e-07, No Iterations 4
BICCG: Solving for Uy, Initial residual = 0.999839, Final residual = 8.47448e-07, No Iterations 4
BICCG: Solving for Uz, Initial residual = 0, Final residual = 0, No Iterations 0
ICCG: Solving for p, Initial residual = 1, Final residual = 9.97098e-07, No Iterations 249
time step continuity errors : sum local = 1.33137e-17, global = -2.95751e-20, cumulative = -2.95751e-20
ICCG: Solving for p, Initial residual = 0.74558, Final residual = 9.30601e-07, No Iterations 234
time step continuity errors : sum local = 1.58872e-17, global = 3.70654e-20, cumulative = 7.49034e-21
ICCG: Solving for p, Initial residual = 0.538171, Final residual = 8.69653e-07, No Iterations 230
time step continuity errors : sum local = 1.38187e-17, global = -1.02711e-20, cumulative = -2.78078e-21
ICCG: Solving for p, Initial residual = 0.51635, Final residual = 9.26057e-07, No Iterations 231
time step continuity errors : sum local = 1.33423e-17, global = -8.93978e-21, cumulative = -1.17206e-20
Uncorrected Ubar = 5.0267e-29 pressure gradient = 0.1
Writing probes.

ExecutionTime = 151.72 s ClockTime = 152 s

Time = 0.008

Courant Number mean: 0.0548405 max: 0.170667
BICCG: Solving for Ux, Initial residual = 0.0219658, Final residual = 6.56965e-07, No Iterations 2
BICCG: Solving for Uy, Initial residual = 0.307236, Final residual = 4.33099e-07, No Iterations 3
BICCG: Solving for Uz, Initial residual = 1, Final residual = 2.22281e-08, No Iterations 4
ICCG: Solving for p, Initial residual = 0.999661, Final residual = 9.3901e-07, No Iterations 240
time step continuity errors : sum local = 2.18853e-16, global = -2.51684e-20, cumulative = -3.6889e-20
ICCG: Solving for p, Initial residual = 0.786978, Final residual = 9.82379e-07, No Iterations 235
time step continuity errors : sum local = 2.96381e-16, global = 1.05951e-20, cumulative = -2.62939e-20
ICCG: Solving for p, Initial residual = 0.632696, Final residual = 8.12611e-07, No Iterations 233
time step continuity errors : sum local = 6.49584e-17, global = -1.60197e-20, cumulative = -4.23136e-20
ICCG: Solving for p, Initial residual = 0.628708, Final residual = 9.73894e-07, No Iterations 233
time step continuity errors : sum local = 2.36423e-17, global = -9.22162e-21, cumulative = -5.15352e-20
Uncorrected Ubar = 8.93413e-08 pressure gradient = 0.1
Writing probes.

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I have done some testing before but on the fully developed turbulence state. In such cases, at fixed relTol an additional pressure corrector drops both p eq. and local continuity residual by 1 order of magnitude. This makes since according Isaa1985 analysis of error.

I'm not sure why in the above log this was not the case? Thanks.

Best regards,
Maka.


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