scholarly journals On the Variation of Turbulence in a High-Velocity Tidal Channel

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 672 ◽  
Author(s):  
Charles Greenwood ◽  
Arne Vogler ◽  
Vengatesan Venugopal
Keyword(s):  
Maximum Flow ◽  
Tidal Energy ◽  
Test Site ◽  
Streamwise Velocity ◽  
Spatial And Temporal Variation ◽  
Turbulent Structures ◽  
Length Scales ◽  
Marine Energy ◽  
Flow Speeds ◽  
Turbulence Parameters

This study presents the variation in turbulence parameters derived from site measurements at a tidal energy test site. Measurements were made towards the southern end of the European Marine Energy Centre’s tidal energy test site at the Fall of Warness (Orkney, Scotland). Four bottom mounted divergent-beam Acoustic Doppler Current Profilers (ADCPs) were deployed at three locations over an area of 2 km by 1.4 km to assess the spatial and temporal variation in turbulence in the southern entrance to the channel. During the measurement campaign, average flood velocities of 2 ms−1 were recorded with maximum flow speeds of 3 ms−1 in the absence of significant wave activity. The velocity fluctuations and turbulence parameters show the presence of large turbulent structures at each location. The easternmost profiler located in the wake of a nearby headland during ebb tide, recorded flow shielding effects that reduced velocities to almost zero and produced large turbulence intensities. The depth-dependent analysis of turbulence parameters reveals large velocity variations with complex profiles that do not follow the standard smooth shear profile. Furthermore, turbulence parameters based on data collected from ADCPs deployed in a multi-carrier frame at the same location and time period, show significant differences. This shows a large sensitivity to the make and model of ADCPs with regards to turbulence. Turbulence integral length scales were calculated, and show eddies exceeding 30 m in size. Direct comparison of the length scales derived from the streamwise velocity component and along-beam velocities show very similar magnitudes and distributions with tidal phase.

Tidal Energy in Nova Scotia, Canada: The Fundy Ocean Research Center for Energy (FORCE) Perspective

2011 ◽  
Author(s):  
Douglas J. Keefe ◽  
Joseph Kozak
Keyword(s):  
Nova Scotia ◽  
Power Systems ◽  
Tidal Energy ◽  
Test Site ◽  
The United States ◽  
Research Center ◽  
Ocean Energy ◽  
Overhead Transmission Line ◽  
Marine Energy ◽  
Marine Current

Ocean energy developments are appearing around the world including Scotland, Ireland, Wales, England, Australia, New Zealand, Japan, Korea, Norway, France Portugal, Spain, India, the United States, Canada and others. North America’s first tidal energy demonstration facility is in the Minas Passage of the Bay of Fundy, near Parrsboro, Nova Scotia, Canada. The Fundy Ocean Research Center for Energy (FORCE) is a non-profit institute that owns and operates the facility that offers developers, regulators, scientists and academics the opportunity to study the performance and interaction of instream tidal energy converters (usually referred to as TISECs but called “turbines” in this paper.) with one of the world’s most aggressive tidal regimes. FORCE provides a shared observation facility, submarine cables, grid connection, and environmental monitoring at its pre-approved test site. The site is well suited to testing, with water depths up to 45 meters at low tide, a sediment -free bedrock sea floor, straight flowing currents, and water speeds up to 5 meters per second (approximately 10 knots). FORCE will install 10.896km of double armored, 34.5kV submarine cable — one for each of its four berths. Electricity from the berths will be conditioned at FORCE’s own substation and delivered to the Provincial power grid by a 10 km overhead transmission line. There are four berth holders at present: Alstom Hydro Canada using Clean Current Power Systems Technology (Canada); Minas Basin Pulp and Power Co. Ltd. with technology partner Marine Current Turbines (UK); Nova Scotia Power Inc. with technology partner OpenHydro (Ireland) and Atlantis Resources Corporation, in partnership with Lockheed Martin and Irving Shipbuilding. In November 2009, NSPI with technology partner OpenHydro deployed the first commercial scale turbine at the FORCE site. The 1MW rated turbine was secured by a 400-tonne subsea gravity base fabricated in Nova Scotia. The intent of this paper is to provide an overview of FORCE to the international marine energy community during OMAE 2011 taking place in Rotterdam, Netherlands.

Peakedness of Wave Systems Observed on the French Wave Energy Test Site (SEM-REV) Using a Spectral Partitioning Algorithm

2013 ◽  
Author(s):  
Jean-Baptiste Saulnier ◽  
Izan Le Crom
Keyword(s):  
Wave Energy ◽  
Test Site ◽  
Extreme Conditions ◽  
Multiple Wave ◽  
Wave Energy Converters ◽  
Marine Energy ◽  
Partitioning Algorithm ◽  
Spectral Partitioning ◽  
The Individual ◽  
Energy Converters

Located off the Guérande peninsula, SEM-REV is the French maritime facility dedicated to the testing of wave energy converters and related components. Lead by Ecole Centrale de Nantes through the LHEEA laboratory, its aim is to promote research alongside the development of new offshore technologies. To this end, the 1km2, grid-connected zone is equipped with a comprehensive instruments network sensing met-ocean processes and especially waves, with two identical directional Waverider buoys deployed on the site since 2009. For the design of moored floating structures and, a fortiori, floating marine energy converters, the knowledge of the main wave resource — for regular operation — but also extreme conditions — for moorings and device survivability — has to be as precise as possible. Also, the consideration of the multiple wave systems (swell, wind sea) making up the sea state is a key asset for the support of developers before and during the testing phase. To this end, a spectral partitioning algorithm has been implemented which enables the individual characterisation of wave systems, in particular that of their spectral peakedness which is especially addressed in this work. Peakedness has been shown to be strongly related to the groupiness of large waves and is defined here as the standard JONSWAP’s peak enhancement factor γ. Statistics related to this quantity are derived from the measurement network, with a particular focus on the extreme conditions reported on SEM-REV (Joachim storm).

Characterization of Geometrical and Temporal Properties of Large-scale Motions in Turbulent Flows

2021 ◽  
Author(s):  
Christina Tsai ◽  
Kuang-Ting Wu
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Coherent Structures ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Turbulent Structures ◽  
Temporal Properties ◽  
Turbulent Statistics ◽  
Spatial Locations

<p>It is demonstrated that turbulent boundary layers are populated by a hierarchy of recurrent structures, normally referred to as the coherent structures. Thus, it is desirable to gain a better understanding of the spatial-temporal characteristics of coherent structures and their impact on fluid particles. Furthermore, the ejection and sweep events play an important role in turbulent statistics. Therefore, this study focuses on the characterizations of flow particles under the influence of the above-mentioned two structures.</p><div><span>With regard to the geometry of turbulent structures, </span><span>Meinhart & Adrian (1995) </span>first highlighted the existence of large and irregularly shaped regions of uniform streamwise momentum zone (hereafter referred to as a uniform momentum zone, or UMZs), regions of relatively similar streamwise velocity with coherence in the streamwise and wall-normal directions.  <span>Subsequently, </span><span>de Silva et al. (2017) </span><span>provided a detection criterion that had previously been utilized to locate the uniform momentum zones (UMZ) and demonstrated the application of this criterion to estimate the spatial locations of the edges that demarcates UMZs.</span></div><div> </div><div>In this study, detection of the existence of UMZs is a pre-process of identifying the coherent structures. After the edges of UMZs are determined, the identification procedure of ejection and sweep events from turbulent flow DNS data should be defined. As such, an integrated criterion of distinguishing ejection and sweep events is proposed. Based on the integrated criterion, the statistical characterizations of coherent structures from available turbulent flow data such as event durations, event maximum heights, and wall-normal and streamwise lengths can be presented.</div>

scholarly journals The energy yield potential of a large tidal stream turbine array in the Alderney Race

2020 ◽  
Vol 378 (2178) ◽  
pp. 20190502 ◽  
Author(s):  
D. S. Coles ◽  
L. S. Blunden ◽  
A. S. Bahaj
Keyword(s):  
Large Scale ◽  
Tidal Energy ◽  
Yield Potential ◽  
Energy Yield ◽  
Ambient Flow ◽  
Flow Speeds ◽  
Tidal Stream ◽  
Original Array ◽  
Array Performance ◽  
Tidal Stream Turbine

This research provides an updated energy yield assessment for a large tidal stream turbine array in the Alderney Race. The original array energy yield estimate was presented in 2004. Enhancements to this original work are made through the use of a validated two-dimensional hydrodynamic model, enabling the resolution of flow modelling to be improved and the impacts of array blockage to be quantified. Results show that a range of turbine designs (i.e. rotor diameter and power capacity) are needed for large-scale development, given the spatial variation in bathymetry and flow across the Alderney Race. Array blockage causes a reduction in flow speeds in the array of up to 2.5 m s −1 , increased flow speeds around the array of up to 1 m s −1 and a reduction in the mean volume flux through the Alderney Race of 8%. The annual energy yield estimate of the array is 3.18 TWh, equivalent to the electricity demand of around 1 million homes. The capacity factor of the array is 18%, implying sub-optimal array design. This result demonstrates the need for turbine rated speed to be selected based on the altered flow regime, not the ambient flow. Further enhancement to array performance is explored through increases to rotor diameter and changes to device micro-siting, demonstrating the significant potential for array performance improvement. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

scholarly journals Flow–Sediment Turbulent Ejections: Interaction between Surface and Subsurface Flow in Gravel-Bed Contaminated by Fine Sediment

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1589
Author(s):  
Bustamante-Penagos N. ◽  
Niño Y.
Keyword(s):  
Subsurface Flow ◽  
Power Spectra ◽  
Surface Current ◽  
Streamwise Velocity ◽  
Fine Sediment ◽  
Surface Flow ◽  
Subsurface Water ◽  
Turbulent Structures ◽  
Before And After ◽  
Scatter Plots

Several researchers have studied turbulent structures, such as ejections, sweeps, and outwards and inwards interactions in flumes, where the streamwise velocity dominates over vertical and transversal velocities. However, this research presents an experimental study in which there are ejections associated with the interchange between surface and subsurface water, where the vertical velocity dominates over the streamwise component. The experiment is related to a surface alluvial stream that is polluted with fine sediment, which is percolated into the bed. The subsurface flow is modified by a lower permeability associated with the fine sediment and emerges to the surface current. Quasi-steady ejections are produced that drag fine sediment into the surface flow. Particle image velocimetry (PIV) measured the velocity field before and after the ejection. The velocity data were analyzed by scatter plots, power spectra, and wavelet analysis of turbulent fluctuations, finding changes in the distribution of turbulence interactions with and without the presence of fine deposits. The flow sediment ejection changes the patterns of turbulent structures and the distribution of the turbulence interactions that have been reported in open channels without subsurface flows.

scholarly journals Flow and mixing around a glacier tongue

2010 ◽  
Vol 7 (4) ◽  
pp. 1439-1467 ◽  
Author(s):  
C. L. Stevens ◽  
C. L. Stewart ◽  
N. J. Robinson ◽  
M. J. M. Williams ◽  
T. G. Haskell
Keyword(s):  
Tidal Flow ◽  
Side Wall ◽  
Maximum Flow ◽  
Turbulent Energy ◽  
Transport Processes ◽  
Velocity Shear ◽  
Local Flow ◽  
Glacier Tongue ◽  
Flow Speeds ◽  
Local Background

Abstract. A glacier tongue floating in the coastal ocean presents a significant obstacle to the local flow and influences oceanic mixing and transport processes. Here ocean shear microstructure observations at a glacier tongue side-wall show tidally-induced flow pulses and vortices as well as concomitant mixing. Flow speeds within the pulses reached around three times that of the ambient tidal flow amplitude and generated vertical velocity shear as large as 3×10−3 s−1. During the maximum flow period turbulent energy dissipation rates reached a maximum of 10−5 m2 s−3, around three decades greater than local background levels. This is in keeping with estimates of the gradient Richardson Number which dropped to around unity. Associated vertical diffusivities are higher that expected from parameterization, possibly reflecting the proximity of the cryotopography.

scholarly journals Winter and summer differences in probability of fish encounter (spatial overlap) with MHK devices

2018 ◽  
Vol 1 (1 (Aug)) ◽  
pp. 9-18 ◽  
Author(s):  
H. Viehman ◽  
T. Boucher ◽  
A. Redden
Keyword(s):  
Tidal Energy ◽  
Test Site ◽  
Energy Development ◽  
Bay Of Fundy ◽  
Natural Distribution ◽  
Spatial Overlap ◽  
Vertical Distributions ◽  
The Vertical Distribution ◽  
Distribution Of Fish ◽  
Tidal Stage

The likelihood of fish encountering an MHK device, and therefore the risk posed to fish, depends largely on the natural distribution of fish at tidal energy development sites. In temperate locations, such as the Bay of Fundy, seasonal changes in the environment and fish assemblage may alter the likelihood of fish encounters with MHK devices. We examined two one-month hydroacoustic datasets collected in winter 2015 and summer 2016 by an upward-facing echosounder deployed at the Fundy Ocean Research Center for Energy test site in the Minas Passage. Fish density was higher and less variable in winter than in summer, likely due to the presence of migratory vs. overwintering fish. The vertical distribution of fish varied with sample period, diel stage, and tidal stage. The proportion of fish at MHK device depth was greater, but more variable, in summer than in winter. Encounter probability, or potential for spatial overlap of fish with an MHK device, was < 0.002 for winter and summer vertical distributions. More information on the distribution of fish (horizontal and vertical), species present, fish sensory and locomotory abilities, and nearfield behaviours in response to MHK devices is needed to improve our understanding of likely device effects on fish.

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