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-   -   Turbine Analysis - Alternate Rotation Model and Meshing Problems (http://www.cfd-online.com/Forums/cfx/115030-turbine-analysis-alternate-rotation-model-meshing-problems.html)

 sean89dunn March 22, 2013 05:14

Turbine Analysis - Alternate Rotation Model and Meshing Problems

I'm currently performing an analysis on a water turbine in a water channel. I have 2 issues in that my model doesn't converge well at rpm above 191 and depending on if I use the alternate rotation model my torque results vary by approx 20%.

At higher rotation speeds my model takes much longer to converge which I suspect must be due to the bad mesh on the trailing edge of the hydrofoil, it's been the only part of the mesh I can't solve. Are there any methods I could apply to the trailing edge which will mesh well without deforming the "sharpness" of the trailing edge?

The alternate rotation model changes my torque results by approx 20% and I'm not sure if I should be using it. I've read up on it and everything sounds like I should except for the swirling motion of the water after it exits from the turbine. Any advice would be great. I have about 4m of water channel between the rotor (500mm diameter) and the outlet of the channel too

Cheers,
Sean

 ghorrocks March 22, 2013 06:49

Try the geometry and meshign forum for hints on meshing a sharp trailiing edge.

The Alternate rotation model should not make any difference to the final results. It makes me suspicious that your simulation is not fully converged. Also mesh quality and cause issues - your comments about trailing edges makes me suspicious there too.

If the flow has a rotational velocity of approximately zero in the stationary frame of reference then use the alternate rotation model . If the flow has a rotational velocity of approximately zero in the rotating frame of reference then use the default model. If it is in between then use whatever is closest.

 sean89dunn March 23, 2013 23:27

You were right about the alternate rotation model, the solver was stopping after 500 steps when the solution wasn't fully converged which is why I was getting the differences in my results.