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Help With Tidal Turbine Simulation

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Old   January 19, 2014, 12:30
Default Help With Tidal Turbine Simulation
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Nick Osbourne
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Hello everyone,

I am attempting to simulate a horizontal axis tidal turbine in Ansys CFX. The process I have taken so far is below:

I created a simple geometry in Solidworks and imported into Ansys Geometry. I created the fluid domain and used boolean subtract for the turbine. I've attached an image of the fluid domain, which consists of two stationary domains (inlet and outlet) and one rotating domain. For boundary conditions I have:

Inlet: Inlet
Outlet: Outlet
Outside walls: Free slip walls
Turbine walls: No slip walls
Interfaces between stationary and rotating domains: Frozen Rotor

I have run both steady state and transient scenarios. I am using the Shear Stress Transport turbulence model. I have a constant inflow velocity and have set angular velocities for different cases to achieve specific tip speed ratios.

In CFX-Post I utilized the integrated torque function on all of the turbine walls. Then to get power you simply multiply the torque by the angular velocity. I've attached an image of the streamlines from one of the steady state scenarios.

My Questions/Issues are:
1) My Power output that I am reading is far too high (I'm getting Cp values around 6.5)
2) With the transient solution I would expect to be able to create an animation and see the turbine domain rotate. I am however seeing no visual change between timesteps. I am wondering if this is due to the coordinate frame of reference being linked to the rotating reference instead of the stationary's?

I feel like I am either missing an important step, or am misunderstanding a step I have already made. Is there someone with experience that could shed some light for me?

Much appreciated
Attached Images
File Type: jpg Turbine CFD Domain.jpg (20.8 KB, 26 views)
File Type: jpg Turbine Streamlines.jpg (46.3 KB, 28 views)
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Old   January 19, 2014, 17:52
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Glenn Horrocks
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Accuracy is an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

To get the rotor to rotate in a transient simulation you need to use Transient Rotor Stator in the interface parameters. Frozen rotor assumes the rotor is frozen (obviously).
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Old   January 20, 2014, 13:14
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Nick Osbourne
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Hello Ghorrocks, thanks for the reply. I have read through some of the FAQ, in particular the "Why are my results inaccurate" section, and found them quite helpful. Thanks for the tip about the Transient Rotor Stator option, I hadn't noticed this was available for transient solutions.

I will update once I do some trouble shooting.
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