1P variation of loading too high?

Wind & Water Computer-Aided Engineering Software Tools
1

Hi All,

I have an inhouse Matlab BEM code with the usual additions auch as tip loss, stall delay and skewed axial inflow factor. The code is being used to predict dynamic effects on a model turbine (the turbine has very stiff, short blades so blade bending is not a problem). I have also included dynamic inflow (large effect on loads for velocities used) and dynamic stall (neglible effect on loads for velocities used).

When comparing my own experimental and numerical data the code seems to exagerate the once per revolution loading (checked by comparing both data sets with PSD plots). I have attempted to find a pattern to explain why but there doesn’t appear to be one? Has anyone got any suggestions as to where the problem may reside? Could it simply be an effect of BEM or the skewed axial inflow factor and is it fixable?

Thanks,

Pascal

2

Dear Pascal,

Your inability to match test data to simulation data is not at all surprising. First off, BEM is valid only for simple conditions: unstalled, axial flow. Secondly, the values you use for your airfoil coefficients are probably wrong Maybe you used data for the wrong Reynolds Number. And, it’s also likely your test data are not correct.

When I tried to compare our BEM codes to wind-tunnel data, I found I had to make significant changes to the airfoil data to get the simulator to agree with test data. And another annoying thing was that test data varied from test to test because of stall hysteresis.

Whenever I see someone show their simulation agrees with test data, I suspect offsetting mistakes.