Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S16: Tidal Energy |
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Chair: Arindam Banerjee, Lehigh University Room: 4c3 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S16.00001: A hybrid approach for power prediction of tidal stream turbine using transient blade element momentum theory Cong Han, Ashwin Vinod, Arindam Banerjee, Thomas Lake, Michael Togneri, Ian Masters Blade Element Momentum (BEM) method is traditionally used to evaluate hydrodynamic performance of wind/tidal turbine blades. Steady-state BEM predictions are based on the assumption that the inflow is uniform at the rotor plane. Majority of tidal energy sites have high levels of Free-Stream Turbulence (FST) and power prediction in those scenarios needs to account for fluctuations in the free-stream. In addition, any variation in hydrofoil (lift-drag) dynamics due to FST needs to be also accounted for. A hybrid approach was implemented to predict the performance of a tidal turbine model in a water tunnel test section. Lift/drag characteristics of a SG6043 hydrofoil was measured in a water tunnel facility fitted with an active grid turbulence generator at Lehigh University. The inflow properties measured using an ADV along with lift/drag measurements are used an input to a transient BEM code. Validation and verification of this hybrid method is done by comparing the transient BEM predictions to the experimental torque-thrust measurements with a scaled turbine model under elevated FST conditions. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S16.00002: Wake dynamics behind two closely spaced vertical axis turbines Catherine Wilson, Valentine Muhawenimana, Stephanie Mueller, Pablo Ouro, Aldo Benavides, Carlos Duque The technology for harnessing kinetic energy from rivers via turbines has evolved at a slower pace than in wind or tidal environments. Widely adopted in these fields due to their high energy conversion rates, horizontal axis turbines operate at high rotational speeds in high velocity environments, which can drastically impact ecosystems. Alternatively, vertical axis turbines are designed to operate at lower rotational speeds, and with the advantage of their rectangular cross-section, efficiently extract kinetic energy from river streams while reducing environmental impact. This research tested two small-scale vertical axis turbines in a hydraulic flume, measuring their wakes up to 10 diameters downstream and across the flume width. The three-bladed devices rotated at a constant speed equivalent to their optimum energy conversion rate. From ADV velocity measurements, results in terms of mean velocities and turbulence fluctuations show that the individual wakes merge into a single low-velocity wake and this directly affects the flow processes involved. Flow measurements also captured the tip vortices developed during the upstroke and downstroke rotation of the turbines. Comparisons of these wake dynamics were analysed for two lateral spacings of 1.5 and 2.0 turbine diameters. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S16.00003: An investigation of the effect of upstream turbulence on Ocean Current Turbines: Large Eddy Simulations and Wake Interaction Models Peyman Razi, Praveen Ramaprabhu, Christopher Vermillion, Mike Muglia Arrays of Ocean Current Turbines (OCTs) deployed in the gulf-stream could provide a reliable source of renewable energy. In planning OCT array layouts, it is critical to consider the effects of upstream and wake turbulence on downstream devices. We extend a low-order analytical wake interaction model to include near-wake and turbulence effects in the upstream. The wake interaction model has been validated using Large Eddy Simulations (LES), which were driven by a synthetic turbulence inlet field generated to simulate properties of ocean turbulence from field measurements in the Gulf Stream. Individual turbines in the simulations are modeled using the widely used boundary element method. We find that both the turbulence intensity and the spectral content (narrowband vs. broadband) of the inlet flow conditions are relevant to the turbine wake properties, and the performance of the array. The results from the LES are compared with the modified wake interaction model. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S16.00004: Numerical Simulation of a Drag-driven Vertical Axis Hydrokinetic Turbine in Open Channel Flow JinJin Gao, Yuan Zheng, Michele guala, Lian Shen A drag-driven vertical axis hydrokinetic turbine, partially embedded in a relatively shallow channel streambank, is expected to partially absorb the kinetic energy of the river. To study its performance and wake characteristics, numerical simulation of the turbine in an open channel flow is conducted. Large-eddy simulation of the flow in an arbitrarily complex domain involving moving or stationary boundaries is carried out to investigate the structure of turbulence in the wake of the turbine and optimize its performance. The complex turbine geometry, including the rotor and the cavity along the bank, is captured by the immersed boundary method. Coupled level-set and volume-of-fluid method is used to capture the deformable free surface. The power coefficients of the turbine at different angular velocities, and tip speed ratios, are calculated and compared against the experimental data. The simulation results reveal the wake flow structures generated by the turbine and will be used to improve the blade design. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S16.00005: Cross-Flow Turbine Array Interactions Isabel Scherl, Benjamin Strom, Steven L. Brunton, Brian L. Polagye Cross-flow turbines, also known as vertical-axis turbines, use blades that rotate about an axis perpendicular to the incoming flow to convert the kinetic energy in moving fluid to mechanical energy. Arrays of cross-flow turbines with optimized geometries and control strategies have been shown to out-perform geometrically-identical turbines in isolation. In this work, the performance of a two-turbine array in a recirculating water channel was experimentally optimized across sixty-four unique array configurations. For each configuration, turbine performance was optimized using “tip-speed ratio control” where rotation rate for each turbine is optimized individually and using “coordinated control” where we operated the turbines at equal rotation rates and optimized the rotation rate and phase difference between the two rotors. By contrasting configuration and control cases, we explore the hydrodynamic interactions and hypothesize how operating conditions affect array performance. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S16.00006: Reliability of effective performance coefficients in the context of turbine-wake interaction Olivier Gauvin-Tremblay, Guy Dumas In the planning of turbine array deployment and for the performance prediction of its constituent turbines, the use of effective performance coefficients within simplified turbine models is found to be very useful. Instead of being based on the far field upstream velocity as conventional drag and power coefficients, the effective coefficients are based on a local velocity, representative of the local conditions experienced by each turbine in the array. It has already been shown that effective performance coefficients take inherently into account blockage effects and allow good performance predictions for confined turbines. However, because of turbine-wake interaction, the characteristics of the local flow also include different types of perturbation such as shear, large temporal fluctuations and turbulence. Through URANS tandem cross-flow turbine simulations, this study provides some physical insight into turbine-wake interactions and on the effect of flow perturbations on effective performance coefficients. Although the different types of perturbation affect significantly and differently the dimensional power of turbines, they are found to yield similar effective performance coefficients, which is quite encouraging for the future developments of simplified turbine models. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S16.00007: Coherent Structure Dynamics of the wake developed downstream horizontal hydrokinetic tidal turbines using three coupled DES-Actuator Model approaches Jorge Sandoval, Karina Soto, Clemente Gotelli, Cristian Escauriaza Numerical simulations are necessary tools to assess the interactions between the surrounding flow and Marine Hydrokinetic (MHK) turbines. They provide detailed information and support a wide range of application cases. The representation of these interactions implies three key modelling decisions: (1) A flow solver approach to compute the velocity and pressure field; (2) a computational turbine representation in the model; (3) a methodology to compute the local interaction between the flow and the turbine blades. In this study we present a comprehensive analysis of the hydrodynamic behaviour of the wake generated downstream a tidal turbine using three different actuator approaches to represent turbines in the flow: Actuator Disks Model (ADM), a model based on Blade-Element Momentum (BEM) theory and an Actuator Lines Model (ALM). Each computational turbine models was coupled with a Detached-Eddy Simulation (DES) flow solver and compared with experimental results. We demonstrated that the dynamical formulation of the model has a strong influence in both instantaneous and mean flow field, especially in the topology and dynamics of turbulent coherent structures. These mechanisms control the evolution of the wake downstream the devices and lead wake recovery dynamics. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S16.00008: Performance Assessment of a Wells Turbine with Morphing Blades Kellis Kincaid, David MacPhee Wells turbines are often used to harvest energy from ocean waves when paired with an oscillating water column. Due to the necessity of self-rectifying characteristics in this design, blades are typically mounted normal to the flow direction, resulting in a narrow effective operating region and unfavorable attack angles as flow rate through the turbine increases. Various methods have been proposed to solve this issue, including guide vanes, active and passively actuated blades, and a static blade setting angle which takes advantage of the asymmetric nature of the reversing flow through the turbine in realistic operating conditions. This work uses a solver based in the OpenFOAM framework to investigate any performance gains realized by incorporating a flexible or "morphing" trailing edge to the turbine blades. With this modification, blades can deflect passively due to aerodynamic forces, resulting in lower effective angles of attack, higher torque output, and delayed onset of stall. In this work, simulation results for both flexible and rigid turbines are analyzed and compared, with discussions on flow structures and material deformations as they relate to turbine performance. [Preview Abstract] |
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