Simulating variable pitch crossflow water turbines: A coupled unsteady ONERA-EDLIN model and streamtube model

Abstract

This article describes a new method for simulating unsteady hydrodynamics forces and moments on the blades of a crossflow ‘Darrieus’ turbine with active pitch variation. This method is based on the ONERAEDLIN dynamic stall model, coupled with a momentum streamtube model to take into account the turbine interference on the flow. Both models are presented, and compared separately with experimental results for a pitching airfoil for the ONERA-EDLIN model; and for Darrieus turbine for the momentum theory. The model coupling is then detailed and compared with experimental data taken from the open literature [1] The turbine has 2 straight blades with a NACA 0012 section operating in water at a mean chord Reynolds number of 4 104 for tip speed ratio l ¼ 2.5, 5 and 7.5. Good agreement was found for average l ¼ 5, and qualitative agreement could be obtained at low and high l, where dynamic stall effects and interference effects respectively are predominant. This is positive because l ¼ 5 is the closest value from the optimal power production point. Variable pitch is finally introduced in the model and several functions are tested in order to increase efficiency. A maximum increase of 53% on the power coefficient was found to occur with a sinusoidal law. 2012 Elsevier Ltd. All rights reserved. 1. Introduction Tidal turbines are currently the power source that shows the most advantages [2]. No land occupation like a dam, steady predictable power input and output unlike wind turbines, no waste or side effects like fossil or nuclear power plants. These devices can consist of a classic horizontal axis screw-like systems, or crossflow turbines which have many advantages in water [3], such as being independent of the tide direction. Variable pitch crossflow turbines enable a Darrieus system to improve its performance and decrease parasitic forces,mainly responsible for fatigue and systemfailure [4]. They have been studied at IRENAV since 2007 as the SHIVA project. This project of novel tidal turbines deals with three topics,which will be introduced here. Darrieus turbines have been studied extensively during the 70s and 80s, especially by SANDIA organization [5e8]. A reference publication on this topic can be found in [9]. Though almost no Darrieus turbine produced electrical power from wind since early 90s, a renewed interest arose from water turbines because most drawbacks which prevented this system from becoming