Tidal energy is rapidly developing as a source of renewable energy. Horizontal axis tidal turbines are being installed in arrays, where device spacing is an important issue. Array performance will be affected as the flow from upstream devices (i.e. the wake) interacts with down-stream devices. Further experimental data is necessary to understand the characteristics of turbine wakes, in particular the wake far down-stream. This work describes a series of physical tests undertaken to characterise the wakes of scale model tidal turbines. An Acoustic Doppler Velocimeter (ADV) is used to profile the wakes of two turbines operating in six configurations: varying tip speed ratio, blade number, and including a device with contra rotating rotors. The wakes of various turbine configurations are mapped using velocity and turbulence data. Evidence of the wake can still be detected twenty five diameters downstream of the single rotor device, further than some literature suggests. If this is replicated on full scale devices in sea, this may impact the necessary spacing of devices within an array, or the performance of downstream devices. Evidence is found of rotational structure in the wake at eight diameters downstream. This is further than is suggested in most literature. The wake from the contra rotating device recovers faster than the wake from single rotor devices, and the rotational aspect of the near wake is diminished. Thus a contra rotating device could be used advantageously to give a smaller wake footprint for a given amount of power captured. This could allow a more efficiently packed array, increasing the performance of the array over a given area.
|Date of Award||1 Jul 2011|
- University Of Strathclyde
|Supervisor||Cameron Johnstone (Supervisor) & (Supervisor)|