In situ turbulence replication evaluation and measurement

To develop technology and methods for measuring turbulence at tidal energy sites and laboratory scale simulators. The project is carried out by a consortium consisting of six academic and commercial organisations, three in canada and three in uk, with rsi as the lead

Tidal races are by nature turbulent. This variability of the flow speed affects reliability and efficiency of energy extraction and the operational risks for in-stream turbines used for energy generation. Furthermore, the turbulent wakes downstream of each tidal turbine complicate the efficiency of energy captured at array installations, and the wake may also have environmental implications: e.g. seabed scour. To develop a full understanding of the energy yield and of the structural forces acting on the energy conversion device, i.e., the turbines, it is necessary to quantify mean current speeds and local velocity fluctuations over a range of length scales. The following challenges to predictability of tidal currents have been clearly identified: (i) fluctuations over time scales on the order of hours are observed that cannot be replicated in standard ocean models; (ii) device-scale turbulent fluctuations over time scales of seconds are significant and inherently unpredictable; and (iii) predictions may not be extrapolated more than 100 m from the location of measurement. These issues to the unpredictability for tidal hydrokinetic power. (see Polagye, B. L., J. Epler, and J. Thomson. "Limits to the predictability of tidal current energy." In OCEANS 2010, pp. 1-9. IEEE, 2010). There is an absence of reliable and proven approaches to measuring continuous full-spectrum turbulence in high-speed tidal flows. Instead, estimates of turbulence intensity needed for site characterisation and turbine design are based on remote acoustic measurements, which are impractical, or even impossible, in shallow water-depths of laboratory setups. Furthermore, there is considerable uncertainty due to the noise intrinsic to the Doppler velocity estimate, and the divergent beam geometry of these instruments. The project partners propose the development of a sensor system for measuring turbulence over all length scales that are pertinent for tidal energy generation. The sensor system combines standard flow measurement technology (i.e., acoustic and electro-magnetic) with novel non-acoustic measurement technology (i.e., shear probes) in a way that the system is useful for both laboratory and field applications to detect and resolve the full spectral range of turbulent motion. The sensor system will be deployed at three sites: at the (1) FloWaveTT Energy Research Facility in Edinburgh to test and validate the laboratory configuration; (2) EMEC’s Fall-of-Warness site as a first field location; (3) at the FORCE Minas Passage site as the second field location. The data sets will be compared against each other and analysed for turbulence flow structure using novel theoretical models. The proposed measurement system and methodology are novel and pertinent to the in-stream tidal energy sector. In terms of instrumentation, the project addresses shortcomings of existing measurement technology to reliably and consistently resolve high-wave number turbulent velocity scales, in laboratory and tidal channel settings. The proposed deployment methodology allows “realworld” field measurements to be down-translated to tank-scale measurements and vice-versa, providing developers and manufacturers the ability to evaluate dynamic behaviour of sites and turbine designs at model scale and full scale. The results from this applied research project address technical challenges that ultimately reduce uncertainties in site design, yield assessments, and device design, leading to improved cost structure and access to financing by reducing economic risk.
Project ID: 
9 912
Start date: 
Project Duration: 
Project costs: 
700 000.00€
Technological Area: 
Market Area: 

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