Engineering aerodynamics of horizontal axis wind turbines (HAWTs)

This thesis comprises two main original contributions. The first concerns the aeroelastic modelling of a large-scale prototype wind turbine undertaken specifically to explain experimentally observed mechanical instabilities. The second explores the aerodynamic aspect of turbine modelling in greater detail since this is the main identified technical challenge, this process makes use of detailed largescale wind tunnel test data from NREL for model validation purposes. The MS4 prototype wind turbine was modelled using ADAMS/WT software, the aerodynamic model was provided by the NREL AERODYN subroutines. The drivetrain instability of the machine of 0.75Hz was reproduced by the computer simulation. The causes of the instability were found to be negative aerodynamic damping, complex blade bending modes caused by the blade design and rapid yawing and tilting inducing Coriolis forces in the rotor structure. Accurate analysis of the aerodynamic forces acting on the MS4 was not possible because of the lack of detailed data available and the complicated aeroelastic response of its flexible structure. Theoretical comparisons with the results from the NREL wind tunnel tests were made using several different engineering aerodynamic models (including those used with AERODYN). It was found that blade element aerofoil data had a controlling influence on the blade forces predicted through theory. The effect of inflow models was found to be marginal at lower tip speed ratios and to decrease with decreasing tip speed ratio. Experimental blade forces at low tip speed ratios were found to be defined by gross 3 dimensional effects and the use of 2 dimensional aerofoil data led to inaccurate prediction of blade forces. The use of a stall delay model improved results but was not convincing. Yawed flow predictions were again controlled by the blade element aerofoil data used, use of a stall delay model again improved results in a steady state fashion. A dynamic stall model also improved results but the phasing of results towards the blade root was questionable and may be caused by unsuitable time constants or the influence of the delayed stall effect.