Regarding Tip Loss Model in OpenFAST's FVWM Calculations

[WANGSUYU0809]

Hi，

I am writing to inquire about the FVWM (Free Vortex Wake Model) in OpenFAST. Specifically, I would like to know if the tip loss model is still considered during the calculations using FVWM.

Additionally, from a theoretical perspective, when using FVWM to calculate rotor aerodynamics, should we still consider tip loss correction model?

Thank you for your attention to these questions. I look forward to your response.

Wang Suyu

[jjonkman]

Dear @WANGSUYU0809,

The FVWM of OpenFAST (that is, OLAF, within AeroDyn) intrinsically considers the effect of tip and hub loss. The engineering tip and hub loss models implemented in the BEM theory model of AeroDyn are not used with OLAF.

Best regards,

[WANGSUYU0809]

Dear @jjonkman

Thanks for your answer. I'm recently comparing FVWM result with BEM result, simulating steady operation load case, with fixed rotor speed and fixed pitch angle. I found that there is large difference in the aero power generated by these two methods, so I have compared the Fy (parallel to the rotor plane) distribution along blade span, as shown in the figure below:

It could be seen that FVWM aligns with BEM pretty well from root to mid of blade span, but FVWM result doesn't seem correct from blade mid to blade tip. What reason do you think could cause this problem?

[RBergua]

I'm not sure why there is such a erratic behavior with the aero loads in the second half of the blade span. During the OC6 Phase III project, we looked at the loads along the blade span for the BEM and FVW approaches and observed similar trends between them:

Do you observe that erratic behavior in the force normal to the rotor plane? Does this odd behavior disappear if you make the blade rigid or reduce the time step?

I hope that helps!