HYDRO 2016 Paper 4A3
This paper discusses methods and instrumentation solutions for the reliable measurement of flow turbulence in tidal channels, which are the preferred locations for tidal energy generation. While the natural geographic constrictions of tidal channels accelerate the flow, thereby increasing the energy density available for extraction, topographical features and curvatures of the channels create intense turbulence in the flow. Numerical models and scale model tests in laboratories attempt to emulate turbulence and predict its impact on the energy converters. However, direct measurements in situ are required to assess and understand the full impact of the turbulence effects and to account for local effects of the sites.
Unfortunately, turbulence is extremely difficult to measure in the harsh conditions that are typical of tidal channels. The most advantageous measurement techniques involve a mix of non-acoustic and acoustic sensors. These can be mounted on the seabed or deployed on anchored floating platforms, which provide measurements in the middle of the water column, at the hub height of tidal turbines. Combining non-acoustic and acoustic sensing technologies makes it possible to characterise the entire turbulent velocity spectrum pertinent to tidal energy generation. The Nemo system is a floating platform that carries a combination of sensing technologies to measure turbulence. Nemo has been developed in Canada out of a collaboration between industry and academia. The system has been tested in tidal channels in Canada and the UK.
Two research and develop projects InSTREAM and TiME are described, which establish methodologies and instrumentation to fully characterise the turbulent flow in and around tidal energy sites.