1 Structural and Hydrodynamic Model Testing of the Transverse Horizontal Axis Water Turbine R.A. McAdam #1 , G.T. Houlsby #2 , M.L.G. Oldfield #3 # Department of Engineering Science, University of Oxford Parks Road, Oxford OX1 3PJ, UK 1 ross.mcadam@eng.ox.ac.uk 2 guy.houlsby@eng.ox.ac.uk 3 martin.oldfield@eng.ox.ac.uk Abstract— Model tests on two designs of 0.5m diameter transverse flow turbine are described. Measurements were made relevant to both the hydrodynamic and structural performance of the turbines, and a variety of conditions were explored (including flow depth, upstream velocity, flow direction, blade pitch, turbine solidity). This paper concentrates particularly on the measurements of loads on the turbine blades. Keywords— Tidal power, turbine, transverse flow, fluid loading, stresses NOMENCLATURE A Turbine area b Test section width hb A B = Blockage ratio c Blade chord ( ) 2 2 1 u c w C L λ ρ = Equivalent lift coefficient 3 2 1 Au P C P ρ = Power coefficient 2 2 1 Au T C T ρ = Thrust coefficient gh u Fr = Froude number g Gravitational acceleration h Flow depth N Number of blades P Power generated R Turbine radius R Nc S π = 2 Turbine solidity T Thrust on the turbine u Velocity at the test section w Radial load per unit length u R ω = λ Tip Speed Ratio (TSR) ρ Fluid density ω Turbine angular velocity. I. INTRODUCTION While the axial-flow turbine has been widely adopted in the tidal stream industry [1], the scale of such devices is limited by the channel depth at a given tidal location [2]. The Transverse Horizontal Axis Water Turbine (THAWT) is a variant of a Darrieus turbine and has been proposed as an alternative design of tidal energy convertor, which can be more easily scaled by stretching the device across a channel. The turbine is configured with the rotation axis horizontal and perpendicular to the flow. The key feature of the turbine is that the blades are angled and connected to form a structurally stiff truss (Fig. 1). During March-April 2008 a series of tests was carried out on a 0.5 m diameter model THAWT at Newcastle University [3], [4]. These tests were successful in demonstrating that parallel and truss configurations of the THAWT device were capable of exceeding the Lanchester- Betz limit of kinetic power coefficient, used in wind turbine theory, by using blockage effects. Further variations in the device configuration were explored and indicated that the performance of the device was significantly improved by applying a negative 2° fixed offset pitch to the blades. Negative pitch decreases the angle of attack on the upstream side of the turbine with the blade leading edge moved away from the turbine axis, compared to the trailing edge. A second series of tests were carried out in December 2010 – January 2011, with the following purposes: • To provide further verification of the hydrodynamic performance of the turbine, • To provide detailed information on loads on turbine blades, to allow structural design of a full scale turbine, • To provide more detailed characterisation of the flow around and downstream of the turbine, • To provide information that would allow further optimisation of design. As in the previous tests, two main turbine configurations were tested, a “Parallel bladed” device (Fig. 2), which is essentially a standard Darrieus Turbine and a “Truss” THAWT device consisting of three bays (Fig. 1). This latter turbine is more representative of a 5 or 6 bay full-size rotor than the single bay rotor tested in 2008. Over 170 tests were completed, including calibration tests. In this paper we report some of the hydrodynamic results, but concentrate mainly on the measurements of loads in the blades, as this is the area of most novelty.