Low-complexity static model

Wind & Water Computer-Aided Engineering Software Tools
1

Hi,

I’m trying to create a very simplified model of a Whisper500 tower/turbine assembly. It’s been suggested that I use FAST, but it seems a bit excessive for what I am doing. Eventually, I will work towards a more complicated model, but right now I just want to input the following data for a turbine that is completely shutdown

-hub height & other basic geometries
-airfoil files
-simple wind inflow (maybe even constant)

and get outputs of blade mode shapes & natural frequencies, and possibly root bending moments, tip deflection, and loads. (or some selection from that list)

I don’t even care if its inaccurate because of how little information I provide. I just want to be able to produce results. This is because two other groups are working on determination of mode shapes and natural frequency by 1) modeling in ANSYS and 2) testing the blade experimentally and I would very much like to have something to compare with them. Like I said, I am at the early stages of this model so I am trying to start simple.

Any advice?

Thank you,
Harry Wornick

LANL Wind Turbine Clinic Team - Harvey Mudd College

2

HI, Harry,

For the very beginning model validation/debug, WT_Perf is better. It needs only simple parameters such as hub height. Tower is neglected and blades are assumed to be rigid bodies, it can give you first glance for Cp, Cq, thrust force and force on each blade elements.
[url]National Wind Technology Center's Information Portal | Wind Research | NREL

According to FAST users manual, FAST can calculate the eigen frequencies of blades and tower, but I have never used this feature. NREL offer Modes and BModes software which can calculate the eigen frequencies and eigen mode shapes.
[url]National Wind Technology Center's Information Portal | Wind Research | NREL
[url]National Wind Technology Center's Information Portal | Wind Research | NREL

Normally I use Modes to calculate the eigen frequencies and mode shape, then build FAST model. For predicting tip deflection, aero-elastic-servo coupled loads/blade root bending moments. FAST is pretty good.

3

Do I read correctly that you are only interested in the “shutdown” condition?

If that’s the case, then you only need to calculate forces of drag. Vortex shedding can be guess-timated if you get the Strouhal number from a fluid-dynamics textbook like Hoerner. Natural frequency of the blades can be estimated from tables in Roark’s Formulas for Stress and Strain. How’s that for “back-of-the-envelope”?

There is a lot of public data about the predecessor of the Whisper (H40). The NREL did tests and reports are published on their website - EL-500-34310 and -32748.

4

Thank you all for your comments. This has been really helpful.

I just want to clarify/narrow the focus of my question.

At the present time, I want to be able to compare my results with two other sets of results:

  1. modal analysis performed experimentally on a real blade here in our lab space,
  2. modal analysis performed numerically with ANSYS on a 3D model of the blade.

For now, this is my main motivation. Again, your comments and advice are appreciated.

Thanks,
Harry Wornick

LANL Wind Turbine Clinic Team - Harvey Mudd College

5

If you have blade mass and stiffness properties, use BModes to get mode shapes and frequencies. You don’t even need any wind for that. You do need to set the rpm to get the centrifugal stiffening.