Dear Jason,

After understanding the physical significance of the channel Tip-tower clearance (TipClrnc) over the 360º azimuth angle, it is clear that the only interesting region for no interference validation is when the blade points down. My question is, does FAST v8 take into account the thickness of the last airfoil section to calculate this variable? (i.e. if it does not, for an hipothetic 0 pitch, 0 twist, symmetric airfoil the real tip to tower clearance would be approximately: TipClrnc - TowerRadius (at tip height) - (max. thickness last foil)/2, correct me if I am wrong). I know that ElastoDyn does not have any information about the airfoil coordinates at each section but I think that AeroDyn 15 does (but probably is not used with this aim).

Secondly, regarding the critical deflection analysis discussed in IEC 61400-1:3 (2005), it is stated that the deflection in the unfavourable deflection (which will be out of plane) shall be multiplied by three safety factors (material, load and failure consequence) and then the non interference shall be checked. I suppose that FAST does not account for this augmentation of the real out of plane deflection, so, I have written an (in)equation using the FAST output TipClrnc to prove the non-interference condition (considering the above discussed):

min(TipClrnc)-TowerRadius(at tip height)- (distance from tip node to innermost airfoil surface point)-(FS-1)*OoPDefl > 0

where FS is the overall safety factor (material*load*consequence). Do you think that it is right ?

OFFTOPIC: I am using the SWRT turbine setting and geometry (unless blade) to test an own blade design. From CertTest files I have discovered that the tower (h=34 m aprox )diameter is 1.44 m on the base and 0.355 m on the top. Do you think that doing a linear interpolation to find the tower diameter at the height of the tip (blade pointing down) would be reasonable?

Thank you very much for your attention and time

Very best regards,

Alvaro Olcoz Alonso