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NITA Fractional Step - Residuals & Convergence |
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July 13, 2018, 02:50 |
NITA Fractional Step - Residuals & Convergence
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Member
Leonardo
Join Date: Nov 2017
Posts: 37
Rep Power: 8 |
Hello
This days I found out how NITA Fractional Step speeds up about 10x the CPU-time for simulations around a cylinder. With this feature, I dared to run RANS k-w transition SST with SAS. I understand that NITA performs inner iterations. And this can be "controlled" with Controls->Advanced->Expert. This is well explained in Fluent's manual. But... (there is always a but ) I can not fully understant what is happening inside each time-step. I activated verbosity=1. And I get the following in 1 time-step: iter continuity x-velocity y-velocity k omega time/iter x-momentum equation: tol. 2.6483e-09 0 1.8538e+00 1 9.7318e-03 y-momentum equation: tol. 1.2665e-10 0 3.2576e+00 1 1.5402e-02 x-momentum equation: tol. 2.6483e-09 0 2.3432e-02 1 1.4507e-03 2 2.8526e-04 3 6.6125e-05 y-momentum equation: tol. 1.2664e-10 0 2.6327e-02 1 2.2418e-03 2 4.9086e-04 3 1.2797e-04 pressure correction equation: tol. 9.3473e-16 0 1.8695e-03 1 9.2260e-04 2 4.2316e-04 3 2.1374e-04 4 1.1580e-04 pressure correction equation: tol. 8.9469e-17 0 1.7894e-04 1 1.1491e-04 2 6.7756e-05 3 4.1333e-05 4 2.6478e-05 5 1.6730e-05 6 1.0049e-05 7 6.3437e-06 8 3.9266e-06 9 2.3948e-06 10 1.4192e-06 11 7.1497e-07 12 5.0770e-07 13 3.5760e-07 14 2.3073e-07 15 1.8530e-07 k equation: tol. 6.5366e-12 0 1.5345e-01 1 1.3704e-03 omega equation: tol. 1.8028e-05 0 1.2873e+02 1 9.0926e-01 k equation: tol. 6.5366e-12 0 3.1488e-03 1 1.6761e-04 2 2.6553e-05 3 5.0554e-06 omega equation: tol. 1.8028e-05 0 3.3582e+00 1 8.1995e-02 2 9.8305e-03 9018 1.8695e-03 2.9803e-04 5.2372e-04 8.0712e-03 1.7060e-03 0:00:01 1 9018 1.7894e-04 3.7672e-06 4.2326e-06 1.6562e-04 4.4504e-05 step flow-time vel_out flow-time cl cd 9018 1.5686e+01 5.4330e-01 1.5686e+01 -1.5954e+00 1.7933e+00 Flow time = 15.68559s, time step = 9018 Here the expert configuration is by default. And I want to understand how this values affect the inner iterations, so, what are those numbers for: tol., 0, 1, 2... etc. Where they appear from? What I would like to do is manipulate the configuration to get scaled residuals of 1E-5, which is the number I use with iterative method. Thank you guys! |
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