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Uneven chord distribution with multiple airfoils
Dear QBlade team,
I want to design a blade with three different airfoil shapes (NREL S814 for root-region, S812 for mid-span and S813 for tip-region), with several interpolated airfoils in between the transitions to smooth it out. Now when i hit “optimize” for opt. lift/drag twist and opt. chord according to Albert Betz, the software calculates different chord lengths for the different airfoils, which of course makes sense at first glance.
however, i would like to achieve a nice, even transition. is there any way to improve the chord distribution with the software? So far I have adjusted the chord values manually, but that is not a solution either as i can see the irregularities in the surface at the latest when i export the STL file for 3d printing.
The picture in the appendix should illustrate what I am talking about.
Thank you in advance,
Paul Gaertner
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Hi Paul,
the automatic chord optmization can create these steps if the airfoil characteristics (max Cl, Cl/Cd, etc.) are significantly different.
The only way to eliminate these discontinuities is by smoothing the steps in the twist or chord distribution. While this results in a slightly less optimal blade design, it significantly improves manufacturability.
In the Optimize HAWT Blade Geometry dialog, there is an option to linearize the chord or twist distribution between two custom stations. This feature is useful when you do not want to manually adjust these values at every station.
Alternatively, you can export the blade to the ASCII .bld format and programmatically smooth the distributions using a scripting language or spreadsheet software and reimport the .bld file after the modifications are finished.
BR,
David
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