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  NREL's S-Series airfoils come in thin and thick families.  The thin airfoil families lend themselves to stall regulated wind turbines where performance losses to airfoil soiling are significant. For variable-pitch and variable-speed turbines, airfoil soiling is not a major problem.  Generally, a primary airfoil is grouped with root and tip airfoils.  Most wind turbine blades have a circular section that attaches to the hub.  This is especially important for pitching blades.  There is then a transition from the circular section to the root airfoil section, which usually occurs around the maximum chord.  Between the circular section and the root airfoil section, the transition is faired.  The fairing process should avoid concavities to prevent buckling.  The primary airfoil usually occurs in its pure state around the 75% radius and the tip airfoil is usually pure around the 95% location.  Various interpolation methods are used to define airfoil shapes between the three pure airfoils.  The tip airfoil is also usually retained out to the tip of the blade, but some allowances can be made to accommodate special tip shapes.  The root airfoil usually has the greatest thickness ratio (maximum thickness to chord ratio) and the thickness ratio gets smaller as one approaches the tip.  At the blade root, large airfoil thickness is needed to accommodate blade structural considerations and toward the tip thinner airfoils are needed to minimize drag and blade soiling losses.

The following table lists our S-series airfoil families and their applications:

NREL's S-Series Airfoil Families
Rotor DiameterCategoryRootPrimaryTip
1–3 mThickS835S833S834
3–10 mThickS823-S822
10–20 mThinS804S801S802
20–30 mThickS811S809S810
20–40 m-S814S825S826
30–50 mThickS818S816S817
40–50 mThickS818S830S831

This page was last updated by M. Buhl on 6-July-2012.

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