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

Abstract

This Round Robin Test program aims to establish the influence of the combined wave and current effect on the power capture and performance of a generic tidal turbine prototype. Three facilities offering similar range of experimental conditions have been selected on the basis that their dimensions along with the rotor diameter of the turbine translate into low blockage ratio conditions. The performance of the turbine shows differences between the facilities up to 25% in terms of average power coefficient, depending on the wave and current cases. To prevent the flow velocity increasing these differences, the turbine performance coefficients have been systematically normalized using a time-average disc-integrated velocity, accounting for vertical gradients over the turbine swept area. Differences linked to blockage effects and turbulence characteristics between facilities are both responsible for 5 to 10% of the power coefficient gaps. The intrinsic differences between the tanks play a significant role as well. A first attempt is given to show how the wave-current interaction effects can be responsible for differences in the turbine performance. In these tanks, the simultaneous generation of wave and current is a key part often producing disruptions in both of these flow characteristics.

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

“…Thus, the aim of this work is to evaluate the methodology implemented to assess the performance of a generic tidal stream turbine and the flow characteristics at each facility regarding the quality of the flows and waves generated. This paper complements the work done by [15], where the authors studied in detail the performance of the turbine through non-dimensional analyses using a technique to establish the input flow characteristics and blockage effects.…”

“…The turbine is kept at a constant depth of 1.0 m, to keep it in mid-water conditions according to the depth specifications of most of the tanks used in the RRTs. For a detailed description of the turbine setup, see [15].…”

“…For the bare-basin measurements, the position of the ADV is exactly the same as the rotor hub when operated, i.e., at x = 0 (Figure 3). As presented by [15], depending on the facility, three or five ADV measurement points evenly spread along the vertical and horizontal axis are acquired over the turbine swept area in order to quantify any vertical or lateral velocity gradient (Figure 4). One identified challenge in the field of tidal energy is to adequately characterise the onset flow to calculate the turbine's non-dimensional parameters (see Section 2.5.2).…”

“…A number of wave probes are also placed next to the turbine to verify the wave parameters set for each of the case scenarios. Three resistive wave probes are used at the facilities in IFREMER and FLOWAVE [15]: probes 1-3 as seen in Figure 3. A mix of resistive, ultrasound and dynamic wave probes is used in the CNR-INM tow tank: probes 3-6 as seen in Figure 3, where probes 4 and 6 are ultrasound wave gauges and probe 5 is a dynamic wave gauge.…”

“…The average velocity is then computed as a Disc-Integrated Velocity Average (DIVA) that serve as an input for the calculation of non-dimensional parameters of power and thrust. The DIVA method is described and employed in the associated work done in [15].…”