Negative Cp for three straight blades VAWT
 

Hi friends,
This is my first post. I am trying to validate an simulation using ansys CFX with FORTRAN routines, but for this case, the routines don't interfere. The simulation is a case transient, of rotor-stator with sliding mesh. In the article, for the TSR = 2.5, cp is approximately 0.14. The mesh in the work don't have many elements (43 524), but have a good quality (the less is 0.67) and is composite by hexaedra structured elements. The cp obtained in the simulation for the same TSR is about -0.016. I tryed increase the number of elements, but I obtained a similar result. The torque in the blades are calculated by CEL, adding for each blade, the torque in extern and intern side. The wind velocity is 8.5 m/s. Anybody have an idea what problem is it? If need an archive, I could provide. Sorry for my bad english. Thank's for the attention!

I can see a few problems straight away:

* Your mesh is definitely way too coarse. You will need to refine it a lot. I can tell this by the blocky contour lines on your plots.
* You have a lot of user fortran. Why so many? Can't you replace these functions with CEL?
* How are you defining the time step? A very common error is to use too large a time step. I recommend using dynamic time stepping, homing in on 3-5 coefficient loops per iteration. Make sure the initial time step is close, and make sure the max and min time steps are wide enough you never hit them.
* Why are you doing this as a transient rotor stator simulation? This is very slow. Why can't you do it as a frozen rotor simulation?
* Your residual target is very loose. Are you sure this is adequately converged?
* Why do you have your expert parameter defined? Don't use expert parameters unless you need them and you know what they do.

Glenn, thanks for your observations. I am simulating now without Fortran routines, for simplify the problem. The routines are needed only when I am working with evolution of turbine's rotation. The timestep is defined for the expression dt=dtheta*(2pi/360 degree)/rotational velocity. I will try simulate the way you recommended me. The configuration was transient rotor-stator because my advisor request me to do. After solving with a mesh more refined, I post the results with new CCL, and ask for help in more anything :D. Thanks so much!

This simulation will be much faster and easier if you use Frozen Rotor rather than Transient Rotor Stator. So unless you have a good reason to use TRS you should convince your advisor to use Frozen Rotor.

Even better, do a TRS run and compare it to some Frozen Rotor runs. Then you will see the difference for yourself and whether the frozen rotor assumption is appropriate for your case.