Towing tank testing of passively adaptive composite tidal turbine blades and comparison to design tool

Abstract

Passively adaptive bend-twist (BT) tidal turbine blades made of non-homogeneous composite materials have the potential to reduce the structural loads on turbines so that smaller more cost effective components can be used. Using BT blades can also moderate the demands on the turbine generator above design conditions. This paper presents experimental towing tank test results for an 828 mm diameter turbine with composite BT blades compared to a turbine with geometrically equivalent rigid aluminum blades. The BT blades were constructed of a graphite-epoxy unidirectional composite material with ply angles of 26.8° to induce BT coupling, and an epoxy foam core. For steady flow conditions the BT blades were found to have up to 11% lower thrust loads compared to rigid blades, with the load reductions varying as a function of flow speed and rotational speed. A coupled finite element model-blade element momentum theory design tool was developed to iterate between the structural (deformation and stresses) and hydrodynamic (power and thrust loads) responses of these adaptive composite blades. When compared to the experimental test results, the design tool predictions were within at least 8% of the experimental results for tip-speed ratios greater than 2.5

MaRINET2 Tidal Energy Round Robin Tests—Performance Comparison of a Horizontal Axis Turbine Subjected to Combined Wave and Current Conditions

“…A similar analysis was undertaken by Murray et al [12] where a horizontal axis turbine of 0.8 m was tested at a tow and a flume tank. As an addition to the work previously developed by Gaurier et al [10], the comparative tests involved investigations related to the performance of two types of blade materials: composite and aluminium.…”

Numerical models to predict the performance of tidal stream turbines working under off-design conditions

“…The experimental data used in the comparison with both numerical models contains some uncertainty associated with the measurements. This uncertainty was reported to be as high as 6 % for some of the torque measurements, see [36]. Therefore, a good level of agreement has been reached between the experimental and the simulation models for the majority of the cases.…”

Tidal Energy Round Robin Tests: A Comparison of Flow Measurements and Turbine Loading

“…In [13,38], errors are reported in the region of 10% (average torque and thrust) and 3% (average power and thrust) for experiments undertaken in the IFREMER flume and the tow tank at the Kelvin-hydrodynamics lab (Strathclyde University), respectively. Both studies use the same equipment, but the investigations are unrelated; i.e., Murrat et al [38] utilises this testing campaign to validate a numerical model and use tow-only conditions, whilst Ref. [13] explores the damping effects of bend-twist composite blades when operating under effects of waves and currents.…”

“…Other attempts to identify turbine model practicalities using RRTs have been reported in [3,4]. Murray et al [3] compared the performance of a HATT in a flume and a tow tank using two types of blade materials: composites and solid aluminium blades. Small variations between power and thrust are obtained which are merely related to the turbulence levels developed in the flume.…”