Rotor speed decreases to a negative value then oscillates around zero after simulation starts.

[windlover343]

Hello,

I'm working on a simple wind turbine design project for an undergraduate course. For the aeroelastic analysis, I used the 5MW NREL example files and changed some of the data (blade and tower properties in the Elastodyn and Aerodyn files) to match the turbine designed using QBlade. I didn't change any of the Servodyn data since our teacher said the 5MW file data is enough for us.

The problem is after deciding wind speeds and initial rotor speeds, after starting the analysis, for higher wind speeds, the rotor speed decreases to negative speeds then oscillates around 0. It results in a low TSR error and the cp and power values are extremely low and unrealistic.
It’s also a problem at lower speeds that rpm decreases, but it stays positive so the results are more realistic but lower than expected.

Here are some graphs at wind speed 9.2 and initial rpm 12 that show the problem:

I was wondering if anyone knows what is causing this problem and how to solve it.

Thank you!

[jjonkman]

Dear @windlover343,

I assume you are starting from the following r-test model (land-based NREL 5-MW baseline wind turbine without BeamDyn): https://github.com/OpenFAST/r-test/tree/main/glue-codes/openfast/5MW_Land_DLL_WTurb; is that correct? Can you clarify what you changed in this OpenFAST model relative to the model provided in the r-test?

Best regards,