Changes in design driving load cases: Operating an upwind turbine with a downwind rotor configuration

Abstract

This work considers the design driving load cases from a full design load basis analysis on an upwind turbine changed into a downwind configuration. The upwind turbine is a commercial class IIIA 2.1‐MW turbine, manufactured by Suzlon. The downwind turbine shows an increase in the normalized tower clearance by 6%, compared with the upwind concept. Removing the blade prebend increases the normalized minimum tower clearance by 17% in the downwind configuration compared with the upwind configuration. The extreme loads on the longitudinal tower bottom bending moment are seen to generally increase by 17% because of the overhanging gravity moment of the rotor‐nacelle assembly. The extreme blade root bending moments are reduced by 10% flapwise, because of the coning of the rotor in downwind direction. The fatigue loads suffer from the tower shadow, leading to an overall increase of the fatigue loads in the blades with up to 5% in flapwise direction in the downwind configuration. Because of blade deflection and coning direction, the downwind configuration shows a 0.75% lower annual energy production. Removing the prebend increases the annual energy production loss to 1.66%.

Numerical Simulations of Novel Conning Designs for Future Super-Large Wind Turbines

“…Additionally, segmented blades and outboard pitching ideas were discussed as a means of overcoming the increased edgewise loads of load-alignment. Wanke et al [12] compared a 2.1 MW three-bladed upwind turbine with the downwind counterparts. It was concluded that downwind configurations have no clear advantage over the original upwind design.…”

“…The present paper mainly focuses on the aerodynamic aspects related to these designs. In [9][10][11][12][13][14], although different simulation tools were utilized, the aerodynamic computations were all based on Blade Element Momentum (BEM) theory. However, classical BEM theory is not suitable for coned rotors, especially with a large cone angle.…”

“…Crawford corrected the BEM method by applying a vortex method as well as the proper decomposition of the inflow velocity in the rotor plan [17]. The conclusions in the above studies [9][10][11][12][13][14] contain strong uncertainties due to the application of classical BEM to coned rotors. So, it is of vital importance to accurately compare the aerodynamic characteristics of these designs, which is the foundation of all of these concepts.…”

Differences in damping of edgewise whirl modes operating an upwind turbine in a downwind configuration

“…Glasgow et al (1981) measured a significant fatigue load increase in the flapwise bending loads for a downwind configuration compared to an upwind configuration of a 100 kW machine due to the velocity deficit of a truss tower. Zahle et al (2009) predicted a reduction in normal force on the blade of 20 %, due to the rapid fluctuation in the angle of attack as the blade passes through the tower wake. A fatigue load increase of around 20 % for the damage equivalent flapwise blade root bending moment was found by Reiso and Muskulus (2013) when comparing the 5 MW NREL reference turbine in a downwind configuration to the original upwind configuration.…”

Differences in damping of edgewise whirl modes operating an upwind turbine in a downwind configuration

“…A comparison of a full design load basis for a commercial Suzlon class IIIA 2.1MW wind turbine in an upwind configuration and a downwind configuration by Wanke et al (2019) showed, that also the edgewise fatigue load increases significantly, when changing the upwind configuration into a downwind configuration. Only 30% of the fatigue load increase for the edgewise blade root sensor could be associated with the tower shadow effect.…”