A solution‐based stall delay model for horizontal‐axis wind turbines

Abstract

This work proposes a new solution‐based stall delay model to predict rotational effects on horizontal‐axis wind turbines. In contrast to conventional stall delay models that correct sectional airfoil data prior to the solution to account for three‐dimensional and rotational effects, a novel approach is proposed that corrects sectional airfoil data during a blade element momentum solution algorithm by investigating solution‐dependent parameters such as the spanwise circulation distribution and the local flow velocity acting at a section of blade. An iterative process is employed that successively modifies sectional lift and drag data until the blade circulation distribution is converged. Results obtained with the solution‐based stall delay model show consistent good agreement with measured data along the National Renewable Energy Laboratory Phase VI and Model Experiments in Controlled Conditions rotor blades at low and high wind speeds. Copyright © 2014 John Wiley & Sons, Ltd.

Detailed analysis of the blade root flow of a horizontal axis wind turbine

“…Chaviaropoulos and Hansen, 2000;Lindenburg, 2003), the change in lift force is linearly proportional to the c/r parameter, whereas for other authors (e.g. Snel et al, 1993;Dowler and Schmitz, 2015) it is proportional to the square of the mentioned parameter. In any case, it can be inferred that the large discrepancy in the local blade solidity between both turbines would lead to a weaker Himmelskamp effect in the NREL 5 MW turbine.…”

“…On the other hand, the local blade solidity c/r, which has also been identified as a fundamental parameter for the Himmelskamp effect (see, e.g., Snel et al, 1993;Chaviaropoulos and Hansen, 2000;Lindenburg, 2003;Dowler and Schmitz, 2015), differs substantially between the TU-Delft and the NREL 5 MW turbines: at r = 0.26R (i.e. the radial position studied in Figs.…”

“…Lindenburg (2003), for instance, estimated that the change of aerodynamic lift and drag due to the Himmelskamp effect is proportional to the square of the local speed ratio ωr/U rel . Dowler and Schmitz (2015) also included a similar parameter, namely 2U rel /ωr (obtained directly from the ratio between the Coriolis and centrifugal forces) in their stall delay model. Interestingly, they also estimated the change of the lift force to be proportional to the square of the mentioned parameter.…”

On the calibration of rotational augmentation models for wind turbine load estimation by means of CFD simulations

“…For Madsen and Rasmussen [8], the combination of centrifugal and Coriolis forces plus radial pressure gradients are the cause of rotational augmentation. Lindenburg [9] assures that Coriolis effects are dominant over centrifugal forces, relieving the adverse pressure gradients on the boundary layer and consequently delaying the separation [10]. For other researches [11,12] the occurrence of the rotational augmentation is based on the blend of Coriolis, centrifugal forces and pressure gradients for the appearance of standing vortices on the blade suction surface.…”

A Numerical Investigation of Dual-Rotor Horizontal Axis Wind Turbines Using an In-House Vortex Filament Code (DR_HAWT)

“…∆C L and ∆C D are the difference between the C L,2D and C D,2D wind tunnel measurements and the 2D C L and C D if hypothetically the flow would remained attached at all angle of attacks[91]. In other words, ∆C L is the difference between C L,2D and the inviscid C L (C L,inv = 2π (α − α 0 ) where α 0 is the zero-lift angle) and ∆C D is the difference between the C D,2D and the drag coefficient at zero angle of attack, C D,0[88][89][90]95]. Sometimes, the extended linear lift (C L,lin ) is used in place of the C L,inv[96].…”