Analysis and Tests of Pultruded Blades for Wind Turbine Rotors

Abstract

or DOE Information Bridge http://www.doe.gov/bridge/home.html Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste FOREWORDThe National Renewable Energy Laboratory's (NREL's) National Wind Technology Center is supporting the efforts of its industry partners to develop advanced, utilityscale wind turbines. Part of the research being conducted focuses on innovative components and subsystems that eventually may be incorporated into these advanced turbines. PS Enterprises, Inc. (PSE) chose to investigate a flexible, downwind, free-yaw, five-blade rotor system employing pultruded blades.Studies conducted by PSE showed that, for a given rotor solidity, increasing the number of blades reduced the rotor weight. And from previous experience with both helicopter and wind turbine rotors, it was known that the pultrusion process resulted in blades having a very low cost-per-unit-weight. Indeed, pultruded blades were employed on wind turbines by StormMaster, Windtech, Dynergy, and Bergey Windpower. However, in some cases, problems were reported with yaw instability and occasional tower strikes. Furthermore, because pultruded blades are constrained to constant cross sections, without taper or twist, they are known to suffer a degradation in aerodynamic performance. So the challenge of the PSE project was to design and test a dynamically-and structurally-stable rotor that demonstrated the anticipated weight and cost savings while maintaining reasonable aerodynamic performance.PSE assembled a diverse group of consultants from around the United States to work on the project. The expertise of the project participants included aerodynamics, mechanical design, structural dynamics and testing. They worked closely with NREL to accomplish design reviews, modal tests, blade structural tests and field tests. This approach had the effect of adding logistics challenges to the acknowledged technical difficulties.It can be said with virtual certainty that engineering projects of this nature always encounter unexpected difficulties and frequently fall short of the original goals and objectives. In this project, a gearbox failure and subsequent runaway led to an early curtailment of the field-test program. Nevertheless, PSE and its consortium of consultants, completed an exceptional amount of work, the results of which demonstrate great promise for the proposed rotor concept. And to their credit, it was completed within the negotiated budget. PREFACEThis project, supported by NREL under Subcontract No. AAA-4-12272-04, was undertaken to assess the feasibility of using pultruded blades for wind turbine rotors. It represents a more rigorous engineering investigation of pultruded wind turbine blades compared to that performed on the initial rotors using this technology. The early operating experience of these rotors, although it showed pultrusions as a promising new blade technology, was plagued with design and quality control problems. Adequate engineering analysis and component testing had not been performed du...

Feasibility study of pultruded blades for wind turbine rotors

“…The work consisted of the preliminary design of a 400 kW rotor and a field test of a dynamically-scaled version of that design. 1 In addition, several experts in the industry were employed to study specific technical issues related to pultruded blades and to compare cost to that of conventional designs. 2 …”