T HEdesign process of awind-turbine blade requires accurate and reliable prediction methods for the full range of the machine’s operating conditions. But at low values of tip-speed ratio (TSR ≤ 3.0), the stall-controlled turbine blades can operate with stall and can undergo stall-delay phenomenon during operation on the inboard regions of span. The understanding of the stall regime is important to control peak power output for stall-regulated turbines. There are significant differences between two-dimensional (2-D) airfoil flow and three-dimensional (3-D) flow on a rotating blade, particularly for the innermost part of the blade [1,2]. Lift coefficients attained at the inboard sections of a rotating blade are significantly in excess of the maximum value possible in 2-D static test [i.e., the angle of attack (AOA) at which stall occurs is greater for a rotating blade]. This behavior is referred to as the stalldelay phenomenon, which varies along the bladewith the augmented lift decreasing from blade root to tip. To obtain accurate blade sectional aerodynamic characteristics and hence accurate power prediction, the 2-D airfoil data need to be corrected for the inboard 3-D rotational effects. Since the stall-delay phenomenon was first observed by Himmellskamp [3] on propeller blades, many researchers in the helicopter and wind-turbine fields have tried to shed light to this problem.Very recently, Breton et al. [4] analyzed six differentmodels mostly used to correct the airfoil characteristics for 3-D rotational wing aerodynamics. They concluded that none of the models studied correctly represented the 3-D flow physics and that this was ultimately responsible for their lack of generality. The nonuse of stall control for the large-sizewind turbines is probably due to the fact that the stall-delay phenomenon is still not completely understood. The paper aimed at giving the delayed stall events and a simple correction model that reasonably complements the 2-D airfoil characteristics used to a blade element momentum (BEM) method. The model described in the sequel is based on the insight into the separate flow and stall delay documented in a previous paper [5]. II. New Physics-Based Model
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