320 research outputs found
Residual flow, bedforms and sediment transport in a tidal channel modelled with variable bed roughness
Application of TELEMAC-2D and SISYPHE to complex estuarine regions to inform future management decisions
Water Qualit
The Influence of Intra-Array Wake Dynamics on Depth-Averaged Kinetic Tidal Turbine Energy Extraction Simulations
Assessing the tidal stream energy resource, its intermittency and likely environmental feedbacks due to energy extraction, relies on the ability to accurately represent kinetic losses in ocean models. Energy conversion has often been implemented in ocean models with enhanced turbine stress terms formulated using an array-averaging approach, rather than implementing extraction at device-scale. In depth-averaged models, an additional drag term in the momentum equations is usually applied. However, such array-averaging simulations neglect intra-array device wake interactions, providing unrealistic energy extraction dynamics. Any induced simulation error will increase with array size. For this study, an idealized channel is discretized at sub 10 m resolution, resolving individual device wake profiles of tidal turbines in the domain. Sensitivity analysis is conducted on the applied turbulence closure scheme, validating results against published data from empirical scaled turbine studies. We test the fine scale model performance of several mesh densities, which produce a centerline velocity wake deficit accuracy (R2) of 0.58–0.69 (RMSE = 7.16–8.28%) using a k-Ɛ turbulence closure scheme. Various array configurations at device scale are simulated and compared with an equivalent array-averaging approach by analyzing channel flux differential. Parametrization of array-averaging energy extraction techniques can misrepresent simulated energy transfer and removal. The potential peak error in channel flux exceeds 0.5% when the number of turbines nTECs ≈ 25 devices. This error exceeds 2% when simulating commercial-scale turbine array farms (i.e., >100 devices)
Recommended from our members
A wind-tunnel study of flow distortion at a meteorological sensor on top of the BT Tower, London, UK
High quality wind measurements in cities are needed for numerous applications including wind engineering. Such data-sets are rare and measurement platforms may not be optimal for meteorological observations. Two years' wind data were collected on the BT Tower, London, UK, showing an upward deflection on average for all wind directions. Wind tunnel simulations were performed to investigate flow distortion around two scale models of the Tower. Using a 1:160 scale model it was shown that the Tower causes a small deflection (ca. 0.5°) compared to the lattice on top on which the instruments were placed (ca. 0–4°). These deflections may have been underestimated due to wind tunnel blockage. Using a 1:40 model, the observed flow pattern was consistent with streamwise vortex pairs shed from the upstream lattice edge. Correction factors were derived for different wind directions and reduced deflection in the full-scale data-set by <3°. Instrumental tilt caused a sinusoidal variation in deflection of ca. 2°. The residual deflection (ca. 3°) was attributed to the Tower itself. Correction of the wind-speeds was small (average 1%) therefore it was deduced that flow distortion does not significantly affect the measured wind-speeds and the wind climate statistics are reliable
The Rose Tech Explorer - November 16, 1962
https://scholar.rose-hulman.edu/rose_tech_explorer/1042/thumbnail.jp
Modelling extreme concentration from a source in a turbulent flow over rough wall
The concentration fluctuations in passive plumes from an elevated and a groundlevel
source in a turbulent boundary layer over a rough wall were studied using
large eddy simulation and wind tunnel experiment. The predictions of statistics
up to second order moments were thereby validated. In addition, the trend of relative
fluctuations far downstream for a ground level source was estimated using
dimensional analysis. The techniques of extreme value theory were then applied
to predict extreme concentrations by modelling the upper tail of the probability
density function of the concentration time series by the Generalised Pareto Distribution.
Data obtained from both the simulations and experiments were analysed in
this manner. The predicted maximum concentration (?0) normalized by the local
mean concentration (Cm) or by the local r.m.s of concentration fluctuation (crms),
was extensively investigated. Values for ?0/Cm and ?0/crms as large as 50 and 20
respectively were found for the elevated source and 10 and 15 respectively for the
ground-level source
Tidal stream resource assessment uncertainty due to flow asymmetry and turbine yaw misalignment
The majority of tidal energy convertors (TECs) currently under development are of a non-yawing horizontal axis design. However, most energetic regions that have been identified as candidate sites for installation of TEC arrays exhibit some degree of directional and magnitude asymmetry between incident flood and ebb flow angles and velocities, particularly in nearshore environments where topographic, bathymetric and seabed frictional effects and interactions are significant. Understanding the contribution of directional and magnitude asymmetry to resource power density along with off axis rotor alignment to flow could influence site selection and help elucidate optimal turbine orientation. Here, 2D oceanographic model simulations and field data were analysed to investigate these effects at potential deployment locations in the Irish Sea; an energetic semi-enclosed shelf sea region. We find that observed sites exhibiting a high degree of asymmetry may be associated with a reduction of over 2% in annual energy yield when deployment design optimisation is ignored. However, at the majority of sites, even in the presence of significant asymmetry, the difference is \u3c0.3%. Although the effects are shown to have less significance than other uncertainties in resource assessment, these impacts could be further investigated and quantified using CFD and 3D modelling
Characterizing the tidal energy resource of the West Anglesey Demonstration Zone (UK), using TELEMAC-2D and field observations
Water Qualit
- …