Comparing FAST and FLORIS


I’m a student working on wind farm layout and yaw optimization. In short, my work flow consists of generating solutions on FLORIS and then validating them using FAST. So far, I’ve been able to set up both FLORIS and FAST, but one of my problems is bridging the gap between FLORIS and FAST so that the results can be compared.

For example, some questions:

  1. For the FAST for power output do I use ‘GenPower’ or ‘RtAeroPwr’?
  2. How do I go about the inflow? Steady flow ( 0% TI ) in FAST, results in unrealistically long wakes in FLORIS. Can I set for both softwares the same TI?

Would you be able to provide me with some recommendations, please?

Best regards,

Dear @Jorge.Rodrigues,

Regarding (1), AeroDyn output RtAeroPwr is the aerodynamic power and ServoDyn output GenPwr is the electrical power (including mechanical/electrical losses). I would think you’d want to use the latter in FLORIS. That said, my understanding is that power is really only used for reference in FLORIS rather than in any specific calculation.

Regarding (2), I’m not fully sure I understand what you are asking. Are you using OpenFAST to derive the table look-up of aerodynamic performance curves (e.g., thrust as a function of tip-speed ratio and pitch angle) to use within FLORIS? My understanding of FLORIS is that TI is more of a tuning parameter rather than a physical value whereas in OpenFAST, the wind inflow TI is physical characteristic of the inflow. Regardless, often aerodynamic performance curves are calculated in the absence of inflow turbulence.

Best regards,

Dear @Jason.Jonkman

Thank you for answering.

Regarding (2), I should be more precise. For both softwares I’m using the NREL 5MW wind turbine. What I’m looking for is a numerical setup that allows me to compare the power output from FLORIS and FAST. And one of my main concerns is regarding the inflow. Since I have SCADA data, I would like to match the inflow conditions on both softwares.

My question is how can I match the TI between the two softwares, for example: FLORIS is steady state, and in FAST I can set my inflow to steady ie. TI = 0. But now if I want to introduce TI in FLORIS, then by doing the same in FAST the flow is no longer steady. How can I bridge this gap?

From your answer, do I tune FLORIS TI to match FAST? and for FAST use the SCADA inputs?

Dear @Jorge.Rodrigues,

I’m still not really sure I understand what you are doing. OpenFAST models only a single wind turbine (or are you referring to FAST.Farm, which can model a full wind farm including wake and array effects)? For a single wind turbine, the FLORIS output is directly tied to the user-specified aerodynamic performance curve, which you could use OpenFAST to calculate. The TI input to FLORIS would only impact the wake and array effects, not the performance of a single wind turbine.

Best regards,

Yes Im refering to FAST.Fast. Sorry for not being clear. How does that change the picture?

Best regards

Dear @Jorge.Rodrigues,

OK, thanks for clarifying; what you are doing makes more sense now.

FLORIS is steady state, so, you can really only compare the mean output of FAST.Farm to FLORIS. In FAST.Farm, TI is a physical characteristic of the flow, so, you should set TI in FAST.Farm to match known inflow conditions. TI in FLORIS, however, is more like a tuning parameter; you should not set TI to a physical value, rather you can calibrate TI to change the wake behavior.

Best regards,

Thank you for answering, and sorry for any confusion.

Best regards,