Scalable Coupled Ocean and Water Turbine Modeling for
Scalable Coupled Ocean and Water Turbine Modeling for Assessing Ocean Energy Extraction Authors Stefano Deluca, Stefania Zanforlin, Benedetto Rocchio, Patrick J. Haley Jr. , Corbin Foucart, Chris Mirabito, Pierre F. J. Lermusiaux Charleston - October 22 -25, 2018
Tidal Energy & Turbines • In the near future, exploiting tidal current energy could become an economically and technically feasible way of producing renewable energy and meeting our sustainability targets. • Horizontal axis or cross-flow turbines, also known as Vertical Axis Water Turbines (VAWTs), can be used. • Despite some disadvantages, VAWTs appear as a very promising technology.
Tidal Energy & Turbines: Review • Research efforts are directed towards a better understanding of the fluid-dynamic behavior of these rotors. o S. ed-Dı n Fertahi et al. , “CFD performance enhancement of a low cut-in speed current Vertical Tidal Turbine through the nested hybridization of Savonius and Darrieus, ” Energy Convers. Manag. , vol. 169, no. February, pp. 266– 278, 2018. o S. Derakhshan, M. Ashoori, and A. Salemi, “Experimental and numerical study of a vertical axis tidal turbine performance, ” Ocean Eng. , vol. 137, no. January, pp. 59– 67, 2017. o P. Ouro and T. Stoesser, “An immersed boundary-based large-eddy simulation approach to predict the performance of vertical axis tidal turbines, ” Comput. Fluids, vol. 152, pp. 74– 87, 2017. o L. Priegue and T. Stoesser, “The influence of blade roughness on the performance of a vertical axis tidal turbine, ” Int. J. Mar. Energy, vol. 17, pp. 136– 146, 2017. o P. Marsh, D. Ranmuthugala, I. Penesis, and G. Thomas, “The influence of turbulence model and two and three-dimensional domain selection on the simulated performance characteristics of vertical axis tidal turbines, ” Renew. Energy, vol. 105, pp. 106– 116, 2017. • Moreover, the mutual interaction of different turbines and wake characteristics are under investigation in order to achieve a better tidal farm planning and operation. o S. Zanforlin, “Advantages of vertical axis tidal turbines set in close proximity: A comparative CFD investigation in the English Channel, ” Ocean Eng. , vol. 156, pp. 358– 372, May 2018. o M. Nuernberg and L. Tao, “Experimental study of wake characteristics in tidal turbine arrays, ” Renew. Energy, vol. 127, pp. 168– 181, 2018. o V. Patel, T. I. Eldho, and S. V. Prabhu, “Experimental investigations on Darrieus straight blade turbine for tidal current application and parametric optimization for hydro farm arrangement, ” Int. J. Mar. Energy, vol. 17, pp. 110– 135, 2017. o S. Zanforlin, F. Burchi, and N. Bitossi, “Hydrodynamic Interactions Between Three Closely-spaced Vertical Axis Tidal Turbines, ” Energy Procedia, vol. 101, pp. 520– 527, Nov. 2016.
Tidal Energy & Turbines: Site assessment • To assess the hydrokinetic potential of an area of interest a 4 D regional ocean circulation codes must be used. • Currently, literature lacks best practices or methodologies as to how ocean velocity data should be used to efficiently identify the highest potential sites in relation to the turbine geometrical features. • 3 D CFD simulations, albeit very accurate, may require long computational times. • Unfeasible for a site assessment study of a wide area! • A lower-order but more efficient method able to accomplish a preliminary power assessment analysis is presented. • Validated against high-resolution 2 D CFD data. • Used with dynamic ocean flow data obtained from ocean circulation modeling software to predict the harvestable tidal power in the southern Cape Cod region, prior to environmental impact study.
VAWT Model Description • We employ a turbine performance description routine developed at University of Pisa to evaluate the turbine load and power output based upon the Actuator Disk/Cylinder (AD/C) model and the Blade Element Momentum (BEM) theory. • Momentum sources that simulate the effect of the turbine blades on the flow are analytically evaluated, obviating the need to model the blades in the computational domain. • Our model can be applied to different VAWT rotors such as Darrieus (straight-bladed) and others of arbitrary geometry and hydrofoil shape.
VAWT Unsteady Effects • Unlike to HAWTs, VAWTs cannot be considered to work under steady conditions since, during operation, the blades encounter ample and generally fast variation in angle of attack. • Unsteady phenomena arise that heavily influence the rotor performance and, therefore, cannot be neglected. • Our code is equipped with sub-models that allow to evaluate the effects of the most important of these phenomena such as dynamic stall, flow curvature and tip losses.
Software Working Modes • The software we developed can be used in two different configurations: DMST and Hybrid mode. • The former uses a one-dimensional approach proposed by Paraschivoiu. • The latter consists of coupling our code with a CFD solver able to accept external forcing terms in the time-dependent Navier-Stokes momentum equations. • Currently, the Hybrid mode has been implemented in CFD solver ANSYS Fluent via the integrated User-Defined Function (UDF) feature. • DMST mode, which this work focuses on, has been implemented in a MATLAB code. • The turbine domain is divided into a series of streamtubes parallel to the flow direction, each split into two linked upstream and downstream halves. • An inviscid, steady, one dimensional flow is assumed. • For each half streamtube, mass, momentum and energy balances are solved in their integral form.
DMST Theory
DMST Validation • Due to the absence of a computational grid in DMST models, the setup of our DMST routine consists only in choosing the total number of upstream and down-streamtubes. • Sensitivity analysis on the DMST routine showed that no meaningful variation of results is obtained for more than 40 streamtubes, therefore, such a value has been chosen for all the simulations in this work. Turbine Geometry Radius 3. 16228 m N. of blades 4 Airfoil type NACA 0015 Chord 0. 42162 m
DMST Validation Results DMST Hybrid 2 D CFD
DMST Validation Results DMST Hybrid 2 D CFD
Cape Cod Power Assessment
Cape Cod Power Assessment: Data • The ocean flow data has been obtained from simulations run with the PE CFD code based on the work by Haley et al. and developed by the MSEAS group of Massachusetts Institute of Technology. • The PE software is able to model multiscale ocean dynamics governed by primitive equations (PEs) over the tidal scales of our interest, also accounting for complex bathymetry. • Tidal-period-averaged velocity data in the above-mentioned region simulated between August 13 2017 and August 18 2017 have been used as inputs for the DMST routine.
Cape Cod Power Assessment: Results
Cape Cod Power Assessment: Results
Conclusions and future work
Thanks for your attention
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