Airfoil moment of inertia proportionality

Dear all,

I have modeled a turbine in OpenFAST with two sets of polars to investigate the effect of some aero add-ons on the turbine lifetime.
To perform the life calculation I am using Mlife, one of the necessary input is the “ultimate load” (in the section “Fatigue” of the input file). I wish to analyse the different polars effect on the $B1N?Fy$ and $B1N?Fx$ (edge and flap local forces). Because I do not possess the ultimate loads I had “guess” through trial and error the ultimate loads for $B1N?Fx$ so that they reach exactly 25 years life time.
Rather than doing the same for $B1N?Fy$ and having unrelated mechanical properties, I was wondering if there is a relationship between the edge and flap properties ?

Could the “simple” ratio (I_edge/ I_flap )^4 (power 4 because of the unit of the moment of inertia) have physical sense ?
Or is there a relationship dedicated to airfoils ?

Thanks,

Best regards,

Thomas

Dear Thomas,

You may be able to estimate the value of LUlt, but to truly calculate it for a complex airfoil cross section you’d have to use a sectional analysis tool. See related topics regarding LUlt on this forum for further discussion e.g.:

http://forums.nrel.gov/t/mlife-fatigue-del-calculation/661/29
http://forums.nrel.gov/t/mlife-user-defined-distribution/1970/15

Best regards,

Dear Jason,

Thanks for your quick reply as always. I will look into the links your provided.

I may have to estimate LUlt for both $B1N?Fx$ and $B1N?Fy$ even though it will be “physically true”, at least I will have the correct trend (which is what I am after).

Thanks,

Best regards,

Thomas