Abstract
Vertical axis turbines, which extract kinetic energy from currents, can produce electricity independently from a current’s direction. Hence, this type of turbines raises interest for harvesting energy from tidal currents, where flow changes direction during flood and ebb tides, and where currents present large variation of direction during tide. Methods for representing vertical axis turbines in tidal farms should be implemented in order to predict correctly power production with an acceptable time cost. The Actuator Cylinder (AC) is one of them. Numerical results in terms of wakes, with the study of velocity profiles, and efforts are compared to experiences, as well as showed that the method is sufficiently accurate and for a reasonable computing time, which is of prime importance for tidal turbines farms studies. The Actuator Cylinder method is implemented in ANSYS Fluent in a 2D stationary resolution. The method is then applied to a double levels of two counter-rotating rotors marine turbine designed by Hydroquest. Wake and power production of a single turbine and several farm configurations are studied under different current conditions (magnitude and direction).
Highlights
Over the last few decades, power demand has been increasing drastically, which has raised the importance of designing devices for a sustainable electricity production from renewable sources of energy
Adimensional velocity field in the domain are shown (Figure 11), and adimensional transverse and longitudinal velocity profiles are extracted for cases where γ = 0 ° (Figure 9)
It can be seen that the two wakes join sooner downstream than for a positive velocity, and that the resulting wake is thicker and steeper. This is due to the rotation direction of the rotors: for a positive velocity, rotors tend to lead the flow to the center of the turbine, next to the central duct; for a flow coming backward, rotors slow down the flow on the center of the turbine
Summary
Over the last few decades, power demand has been increasing drastically, which has raised the importance of designing devices for a sustainable electricity production from renewable sources of energy. Hydrokinetic energy of tidal currents seems to be an interesting way of electricity production, with a worldwide available potential of 20 to 25 GW [1]. Tidal turbines, which extract kinetic energy from tidal currents, are some of those devices. Vertical-axis turbines present advantages too, as they work at lower tip-speed ratio (TSR or λ), need less complicated design and are less subjected to vibrations. Vertical-axis turbines can work independently of current orientation, which makes them more appropriate in tidal sites, where flow reverses with the tide and can be deviated from its principal direction
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