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Verification & Validation

Verification

Two important verifications that can be made to check whether the simulation correctly solved the model is to see if mass is balance and if the pressure on the blade has converged. Both have been inspected in the previous section. 

Another essential condition to verify is whether a sufficient number of iterations were performed in obtaining the solution (i.e if the solution converged). The figure below shows how the solution behaves after 5000 iterations. As you can see, the residuals do not change much between 1500 and 5000 iterations and so this is why the solution was deemed to have converged at 1500 iterations. 

Finally, it is crucial to perform a mesh refinement study. A finer mesh can help achieve a more precise solution of the model but is more computationally expensive. A CFD analyst thus has to gauge what mesh size will provide a decently accurate solution at a reasonable computing cost. This is of course very dependent on the desired accuracy of results and the application of the project. 

The following table demonstrates how the results change with a greater number of cells. It is it quite clear that the mesh created in the tutorial is not sufficient in obtaining a sufficiently accurate solution. 

Validation

Blade tip velocity

Torque

Betz's limit

Acknowledgments

This tutorial is made under great help and support from:

• Dr. Rajesh Bhaskaran, Cornell University, 
• Sean Harvey, ANSYS.Inc
• Guang Wu, ANSYS.Inc

Also a big thank you to Robert Zhang (M.Eng) for his help with integrating this tutorial in the wind power class at Cornell University. 

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