Abstract
The paper presents an experimental campaign developed to contribute to the current research considering the operation of Horizontal Axis Tidal Turbines within stochastic flow conditions, namely turbulent and wake induced flows. The campaign was conducted at approximately a 1/20th-scale within a recirculating flume. Experiments were conducted over five differing setups, yielding a baseline low Turbulence Intensity case, two high turbulence cases and two upstream device generated wake cases. The experiments were conducted at a range of differing rotor velocities established, in a novel way, by utilising both fixed speed and fixed braking torque control. The paper presents analysis of flow measurements to statistically quantify the stochastic flow conditions impinging on the model-scale tidal turbine. The power, thrust, torque and blade root bending moment of single blade were recorded and analysed against the flow conditions generated under the five cases. The analysis showed that it may well be possible to exploit the accelerated region around an upstream turbine to capture marginally higher power (6% increase) from downstream turbines. Lastly, it was found that the control scheme adopted has a significant impact on power and load fluctuations observed at differing rotor velocities.
Highlights
Energy extraction from the ocean’s tides has gained widespread acceptance as a potential contributor to the UK energy mix [9]
The device control was achieved by the incorporated Permanent Magnet Synchronous Machine (PMSM) housed in the device nacelle and directly coupled to the rotor.control refers to device control where the goal of the system is to maintain a constant set-point rotational velocity
The tests were undertaken at a variety of average rotational speeds, achieved via both speed control and torque control of the PMSM, detailed formulations of the control strategies of the turbine can be found in Ref. [18]
Summary
Energy extraction from the ocean’s tides has gained widespread acceptance as a potential contributor to the UK energy mix [9]. In order to achieve the 20 year lifespan [14] - quoted as being required for cost effective energy extraction - whilst reducing device over-engineering, detailed understanding of HATT operational loads is required. Cross-Correlation of X & Y Rotor Diameter, m Frequency, Hz Power Spectral Density Out-of-plane blade root bending moment blade i, Nm Total Number of Samples Sample number Correlation Coefficient Rotor Radius, m Thrust, N Time, s Time lag, s Turbulence Intensity% Instantaneous fluid velocity, m sÀ1 Fluid Velocity Fluctuating Component, ms-1 section, Section 4, which presents detail analysis of the lab-scale HATT performance and loading under the various test cases with Sections 4.1 and 4.2 present time domain statistics whereas Sections 4.3 and 4.4 detailed frequency domain analysis of the results.
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