Dual Rotating Cylinder Ansys Fluent Free Stream Velocity Issue

- February 18, 2021 at 1:10 pm
  
  KieranHall
  Subscriber
  
  Hi all,
  I am performing an analysis on two rotating 2D cylinders.
  During my validation stage, I had a single rotating cylinder in my computational domain and I had no issues, the model worked perfectly. Rather strangely, when I included a second rotating cylinder (same angular velocity and diameter as the 1st) the free stream velocity in the domain seemed to almost disappear.
  The angular velocity is 0.68rad/s for both cylinders and their diameter is 3m. The Re is 100,000. The turbulence model used is k-e (Realizable) with Enhanced Wall Functions. The velocity inlet is on the left-hand side of the domain and exits at the left-hand side. No slip has been applied to both cylinders.
  Attached are screenshots of:
  1) The first cylinder rotating and the second is fixed...
  2) Both cylinders rotating (The blue velocity contour plot)...
  
  Would anyone have an idea as to why when the second cylinder is set to rotate, the free stream velocity decreases so much and pretty much dissapears?
  Many thanks,
- February 18, 2021 at 5:14 pm
  
  Rob
  Ansys Employee
  
  It's not disappeared the scale has changed. What did you set the centre of the second cylinder as? n
- February 18, 2021 at 7:11 pm
  
  KieranHall
  Subscriber
  
  Thanks Rob,nThe centre of the second cylinder is on the same axis as the 1st. nMany thanks,nKieran n
- February 18, 2021 at 11:59 pm
  
  YasserSelima
  Subscriber
  
  It is the scale. nTo see it clearer, create vectors of the velocity colored by X-Velocity. n
- February 19, 2021 at 11:31 am
  
  KieranHall
  Subscriber
  
  Thanks Yasser, I tried that but the vectors didn't show much.nn
- February 19, 2021 at 12:06 pm
  
  KieranHall
  Subscriber
  
  Hi guys,nAttached are vector, contour and streamline plots of the domain.nI think I may have been incorrect in my judgement of assuming that the dual rotating cylinder animation would be similar to the single rotating cylinder one.nIn which case, my results must be correct, and you're correct Rob, the scales have just changed. nWould anyone be able to offer a reason as to why the scales change so drastically when both cylinders are rotating? nMany thanks,nKieran nn
- February 19, 2021 at 1:31 pm
  
  YasserSelima
  Subscriber
  
  The scale changes because you get higher value of the velocity.nnPress the button Contpur map color and disable auto range ... now set similar scale n
- February 19, 2021 at 2:09 pm
  
  KieranHall
  Subscriber
  
  I have just figured my problem out... nI had the incorrect rotational axis set for the second cylinder! nThank you Rob and Yasser for you help.nKind regards,nKieran n
- February 22, 2021 at 1:32 pm
  
  Rob
  Ansys Employee
  
  Hence my question! You're welcome. n

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