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AbstractSimulating fully resolved Horizontal Axis Tidal Turbine (HATT) geometry for a time period great enough to resolve a fully developed wake, and accurately predict power and thrust characteristics, is computationally very expensive. The BEM-CFD method is an enhanced actuator disk and is able to reduce the computational cost by simulating a time averaged downstream velocity field. Current implementations fall short of accurately determining tip losses, which are a function of the hydrofoil geometry. This work proposes a method of addressing this shortfall by modifying the angle of attack to conform to the constraints outlined in Prandtl's lifting line theory, i.e. the zero lift angle of attack at the hydrofoil tip. The revised model is compared to existing BEM-CFD methods and validated against experimental data. The revised BEM-CFD method presented in this work shows a significant improvement over previous BEM-CFD methods when predicting power and thrust. The coefficient of power is reduced from 0.57 (approx. 30% above experiment) to 0.44 (approx. 3% above experiment). An increase in turbulence intensity in the rotor region, in particular at the wake boundary, improves the recovery of the wake without the addition of empirical turbulence source terms. Good correlation with experimental results for power, thrust and wake prediction, is observed. The model may also be applied to wind turbines.

Abstract Computational fluid dynamics (CFDs) simulation tools are developed to analyse the aerodynamic performance of a novel design vertical axis wind turbine (VAWT) and compared against careful data from a 1.6 m diameter device in a wind tunnel. The study investigates the extent to which a CFD model employing the simplest turbulence representation can provide a useful input to evaluate the impact of several key operational parameters: wind speed, rotor speed, yaw angle and blade pitch angle. The results show that simple turbulence modelling techniques are sufficient to evaluate the performance of the turbine in the designed operating conditions and can predict when the turbine will run outside each parameter’s operational range. However, such a simple turbulence representation may need further refinement to quantify more precisely the extent to which performance is affected when running some way outside this range.

Marine renewable energy (MRE) development will be crucial to achieve worldwide energy decarbonization. In Europe, 1 GW and 40 GW of ocean energy are set to be developed by 2030 and 2050, respectively. Support is essential if wave and tidal stream arrays are to become more economically viable than they currently are. Four recently developed open-access software tools are used in this study to investigate the critical and expensive elements of potential demonstration and commercial scale tidal projects. The tools have been designed and built to assist users with array configurations, foundation and mooring (F&M) design, operation and maintenance (O&M) strategies, and techno-economic analysis. Demonstration of their use is performed in this study to model scenarios for 2 MW, 10 MW, 40 MW, and 100 MW tidal energy projects employing typical 500 kW fixed and 2 MW floating turbines at the West Anglesey Tidal Demonstration Zone in the Irish Sea. The following metrics are examined: the power output and wake losses of staggered and line configurations; the design and costs of simple gravity-based foundations, gravity-based anchors and the four-chain catenary mooring system of a single turbine; the mean O&M costs and farm availability over the project life; and the breakdown of levelized cost of energy (LCoE) for all eight scenarios to ultimately reveal minimum values of 173 EUR/MWh and 147 EUR/MWh for fixed and floating tidal energy technologies, respectively. The thorough analysis facilitated within these four tools to forecast realistic situations in a specific location can help users design a tidal energy project for an area with considerable potential for commercial scale projects, and thus assist the ocean energy community in promoting and nurturing the sector in the years and decades ahead.

AbstractThe presence of Tidal Stream Turbines (TST) for tidal power production, leads to changes in the local physical environment that could affect fish. While other work has considered the implications with respect to conventional hydroelectric devices (i.e. hydroelectric dams), including studies such as physical impact with the rotors and pressure variation effects, this research considers the effects of sudden changes in pressure and turbulence on the hypothetical fish with respect to TSTs. Computational fluid dynamics (CFD) is used to investigate changes to the environment, and thus study the implications for fish. Two CFD methods are employed, an embedded Blade Element representation of the rotor in a RANS CFD model, and a blade resolved geometry using a moving reference frame. A new data interpretation approach is proposed as the primary source of environmental impact data; ‘rate of change of pressure’ with time along a streamtrace. This work also presents results for pressure, pressure gradients, shear rates and turbulence to draw conclusions about changes to the local physical environment. The assessment of the local impact is discussed in terms of the implications to individual fish passing a single or array of TST devices.

Abstract Driven by the need to verify a CFD model of a novel vertical axis wind turbine (VAWT) device, a 1.6 m diameter prototype was designed, built to a high specification and tolerance and then tested in the industry standard MIRA wind tunnel over the full wind range that might be expected in an urban environment. Although the original intention was simply to provide data to verify a CFD model of the specific device – documented separately – it was realised that given (a) the repeatability and quality of the experimental data, and (b) its utility for the authors in verifying their CFD simulations, the data itself might well form the basis for a requirement for a reliable benchmark for the wind engineering community in assessing CFD simulation technology against a specific VAWT device design with the complexity of a housing. The experiments cover a full range of operational conditions for a specific design including the variation of wind speed, wind direction, tip speed ratio and blade pitch angle, recorded in the experiments as well as the torque output and the pressure levels at a range of specific locations. Over 60 tests were carried out in such a way as to assess the repeatability of the measurements; the results showed an overall remarkable degree of consistency.

Abstract The problem of designing the optimal array of tidal stream turbines for the generation of marine renewable energy from the ocean, raises a number of questions about the distribution and layout of turbines in relation to the local bathymetry. The computational overhead of modelling such problems may be significant and costly. This paper aims to clarify the effects of particular phenomena associated with modelling tidal stream turbine arrays. To achieve this we use a RANS computational fluid dynamics model with an embedded blade element actuator disk to investigate various aspects of this problem, while maintaining reduced computational overhead. A study of axially aligned turbines, with each in the wake shadow of the previous turbine shows uniform effects for a 20 diameters downstream spacing, but more complex interaction for 10 diameters spacing. Investigation of the significance of inclusion of the nacelle and tower geometry in a CFD model shows that effects are negligible beyond six diameters downstream. An array of transverse contrarotating turbines are considered, where a device is placed close to and in the wake of a pair of upstream devices. Rotational direction has minimal effect on the power generated, but different turbulence is seen in the wake. Finally, marine currents around a headland are modelled and a single row fence of turbines is placed offshore from the headland at various blockage ratios. Power performance estimates and downstream wakes are created and they show increased power per device and improved total power production as the blockage ratio rises from 0.13 to 0.20. Additionally, the authors use stream surface techniques to visualise the flow which can give new insights to the physical processes observed.

The renewable energy route map for Wales outlines ambitious targets for 50% renewables by 2025. The Welsh coast, subject to tidal ranges of the order of 13 m and tidal flows in excess of 3 m/s, is thus in an ideal position to significantly contribute to these targets. Tidal stream energy is an emerging energy sector and a relatively small number of devices are at various stages of development in Wales. However, before such demonstration devices or arrays can be applied at a larger scale, a number of consents and permissions must be obtained to ensure safe and environmentally responsible deployment. This paper describes the multidisciplinary work that has been undertaken on an area of ocean that could be used for the deployment of a tidal stream turbine. The paper aims to put the scientific work undertaken into the context of device deployment in a complex marine environment and to provide an overview of the surveying and modelling required for the deployment of a single demonstration device off the Welsh coast. The Bristol Channel was chosen as a case study because of its high tidal flows and proximity to national grid connections and support infrastructure. This paper provides an overview of the research carried out during the project; the details of each discipline will be provided in individual papers by the respective subject authors.

Abstract The development of tidal energy converters, and particularly floating tidal energy converters, is an area of increased development in recent years. Testing of a floating tidal energy device over winter 2017/18 led to an opportunity to record and examine strain of a full scale composite turbine blade under operational conditions, with comparison of generating and parked behaviours. Comparison of the recorded data shows that blade strain correlates well with both torque and thrust over the averaging periods specified in IEC62600-200, although examination of frequency spectra generated from the strain data show that higher frequency fluctuations in strain are not necessarily detectable in the larger scale thrust and torque recordings with this particular measurement arrangement. The need for well synchronised clocks on recording systems is also highlighted, along with a cross-correlation method used to recover the alignment of data from different systems to allow comparison between them over periods of a similar order of magnitude to the clock skew between the systems.