A blade design methodology for overspeed power regulation of horizontal axis tidal turbines

  • Catherine Gracie-Orr

Student thesis: Doctoral Thesis

Abstract

Employed in tidal turbines, overspeed power regulation (OSPR) can improve the structural robustness and decrease the complexity associated with active pitch methods, while removing the diffculties of operating in stalled flow. This may be a method by which the cost of tidal energy can be brought down. The aim of this research was to investigate the OSPR method, increase understanding of associated benefits and constraints, and develop a methodology for the design of suitable blades. It is identified that: the challenges to OSPR are higher rotational velocities, leading to increased voltage levels, an increased chance of cavitation on the rotor, and potentially detrimental thrust forces; these challenges may be best overcome with blade design alterations limiting the maximum rotational velocity.The blade design methodology uses a design platform to set boundary conditions, an existing blade design as the base case, and a blade element momentum theory (BEMT) tool as the modelling method. Blade root pitch setting, twist and chord length distribution are the variable parameters investigated. A set of ospr performance metrics and a design space sensitivity analysis, with whole-blade cavitation analyses and diagnostic plots of torque and angle of attack, are used to ascertain how function-based and then precise blade design alterations affect rotor performance.Tow tank tests defined base case rotor performance and verified the BEMT tool.Tests on the new blades allowed comparison to the base case test performance and to the BEMT prediction. Simulations showed that the new blade design regulated power without cavitation inception, without an increase in the thrust forces and with only a 3.6% drop in efficiency - as per the set boundary conditions and design requirements. The blade design methodology can be used to overcome challenges associated with overspeed and produce blades which give significant performance improvements for use in OSPR.
Date of Award1 Oct 2015
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council) & Weir Group plc (The)
SupervisorCameron Johnstone (Supervisor) & Joseph Clarke (Supervisor)

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