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rotorDiskSource in parallel

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Old   January 14, 2019, 07:41
Default rotorDiskSource in parallel
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Jernej
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Hi all,

I am interested in incorporating the effect of a propeller using rotorDiskSource class. I am using OpenFOAM-5.x. I have found a work (report and input files) by Capitao Patrao [Capitao Patrao, A.: Description and validation of the rotorDiskSource class for propeller performance estimation. In Proceedings of CFD with OpenSource Software, 2017, Edited by Nilsson. H., http://dx.doi.org/10.17196/OS_CFD#YEAR_2017] from the Chalmers University of Technology. The work gives a fix to the error in how the local forces are calculated and implements more general blade tip correction. I have successfully modified the original OF code. The corrected rotorDiskSource works without any problems when the solver (simpleFoam) is run in serial. However, the difficulties begin in parallel where the output is strange. Below I paste several outputs of rotorDisk.

Serial case:
rotorDisk output:
min/max(AOA) = 1.6620832, 4.5369071
min/max(eps) = 25.235116, 59.281187
Rotor thrust = 671.50036
Rotor torque = 188.8365
Rotor power = 71041.172
Rotor propeller efficiency = 0.80412826
Effective drag = -576.07232
Effective lift = 671.50036

Parallel case (2 partitions):
rotorDisk output:
min/max(AOA) = 1.6619861, 4.5367581
min/max(eps) = 25.235298, 59.278707
Rotor thrust = 664.33664
Rotor torque = 186.83229
Rotor power = 70287.182
Rotor propeller efficiency = 0.80408372
Effective drag = -576.0604
Effective lift = 671.48486

Parallel case (3 partitions):
rotorDisk output:
min/max(AOA) = 1.6621062, 4.5363851
min/max(eps) = 5.729578e+16, -5.729578e+16
Rotor thrust = 0
Rotor torque = 0
Rotor power = 0
Rotor propeller efficiency = nan
Effective drag = -576.04504
Effective lift = 671.45967

Parallel case (6 partitions):
rotorDisk output:
min/max(AOA) = 1.6617572, 4.5364101
min/max(eps) = 25.235737, 45.521711
Rotor thrust = 186.92322
Rotor torque = 52.674087
Rotor power = 19816.238
Rotor propeller efficiency = 0.80247451
Effective drag = -576.03327
Effective lift = 671.44934


Does anybody have some experience in fixing the issue and can give a piece of advice?

Thank you.

Jernej
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Old   January 14, 2019, 08:09
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Jeff
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I had experiments with case running in serial and posing problem in parallel when using ggi coupling interface.

In my case it was traced back to a bug in openmpi implementation

I have no idea if your problem is of the same kind though

Can you post the case?

JF
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Old   January 15, 2019, 13:42
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Hi Jeff,

I am using the original case (prop_incomp_refCase) as described in Proceedings of CFD with OpenSource Software, 2017 (Edited by Nilsson H. http://dx.doi.org/10.17196/OS_CFD#YEAR_2017). Following the link the case files can be downloaded.

Angle of attack, effective lift and drag are invariant to the number of partitions (as expected). What bothers me is that eps, rotor thrust, torque, power, and propeller efficiency are not .

Regards,
Jernej
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Old   January 18, 2019, 19:32
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Luis Eduardo
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How does your flow field look like?

If you generate a slice in one of the rotor planes for all the cases you are running, do they look the same?

It may be just a matter of taking the information from all the processors for the calculation of the variables (usually the sumop() - or something like this - part of the code)

Try the slices, check if the physics make sense.

Best Regards,
Luis
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Old   February 2, 2019, 11:36
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Aleksei
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Hi!
I have a very similar experience using rotorDisk. Like you, I successfully modified the original OF code using Capitao Report. Anyway with corrections or without rotorDisk dont work adequately. Besides problems with parallel run, there are also some oscillation when run simpleFoam in serial. Oscillation in rotor forces generate oscillation in field U which leads to resonance (it`s my explanation ).

You can see how it look like in slice through the rotor (colored by force magnitude).
https://www.youtube.com/watch?v=D7cN2Dcwixw
https://www.youtube.com/watch?v=zQzQw7gU5XE
It was observed in case similar to tutorials simpleFoam/rotorDisk, was slightly changed mesh only.

I managed to get rid of oscillations by decreasing the relaxation factor U to 0.45. Maybe its not good method? Have anyone thoughts about the reason of this strange phenomena?
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