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Aerofoil section design and assessment for horizontal axis wind turbines (HAWT)

Objective

To develop blade section design and assessment procedures and associated computer codes to enable designers of horizontal axis wind turbines to identify a precise aerodynamic design requirement and select a corresponding, suitably optimised, set of blade sections for any given application.
This contract aims to develop a method of optimising the aerodynamic design of the rotor of stall regulated constant speed horizontal axis wind turbines. Of the various parameters that have to be considered to achieve an optimal design it was decided to initially concentrate on maximum energy capture. A blade element momentum code has been written which calculates in a novel way the optimum radial lift and drag distributions for a required power level and a specified Weibull wind profile. The technique has been applied to a well known commercial wind turbine rotor and the calculations indicate that a significant improvement in energy capture can be achieved.

The other part of the contract is to design and test aerofoil sections which will give the required optimal lift distribution with minimum drag. 2 alternative approaches to the analysis and design of 2-dimensional aerofoils have been compared. The 2 analysis methods gave similar predictions of experimental data of well established aerofoils and in particular were found to predict the maximum lift coefficient which is necessary for the design of stall regulated machines. Differences in the theoretical assumptions of the methods have been collated. Both methods failed at incidence angles a few degrees beyond that for maximum lift and a different method based on inviscid flow is under development for the deep stall region.

The design methods were used to design sections at 3 radial positions to give the optimal lift characteristics suggested by the blade element code. 2 tip sections of different maximum thickness were selected for testing in a large wind tunnel. Testing will commence shortly and will give data for comparison with the theoretical methods.
The work program involves the development of three areas of interest and their coordination into a design procedure as follows:

1) Desirable blade performance characteristics are to be identified, ranked in order of importance and related to specific section properties. Characteristics such as turbine power curve envelopes, stall characteristics in relation to control problems, limitations on blade noise and roughness sensitivity, etc. will need to be identified as design targets, as also will constraints on the design such as structural modulus requirements. An optimisation model is to be constructed to identify a candidate section which most successfully meets the design requirement at any given spanwise station on the blade.

2) Two of the partners in this project have experience of aerodynamic section design and analysis using 2D flow models which match non-viscid outer flow models to boundary layer calculations. These procedures need further refinement to give better predictions of post-stall behaviour. These two candidate aerodynamic procedures will be developed in parallel to provide the core subroutines of the optimization process.

3) It is proposed to evaluate the success of the aerodynamic performance prediction to a limited extent by wind tunnel experiments on two section designed using the optimising procedures. Further validation will be attempted by carrying out performance calculations for other blade sections in use on HAWT's for which wind tunnel information is already available. Collaboration with institutions possessing such data will be sought.

The anticipated final outcome of this program of work is a set of computer codes available to the HAWT designer to enable him to explore and clarify the section design requirements and to design optimal sections. An essential part of the process would be the evaluation of the benefits of such sections over those in current use.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

UNIVERSITY OF SOUTHAMPTON
Address
University Road, Highfield
Southampton
United Kingdom

Participants (2)

NATIONAL TECHNICAL UNIVERSITY OF ATHENS
Greece
Address
Iroon Polytechnioy 5
15780 Athens
RISOE NATIONAL LABORATORY
Denmark
Address
Frederiksborgvej 399
Roskilde