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 L14: Energy: Hydropower and General |
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Chair: Oscar Curet, Florida Atlantic University Room: 307/308 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L14.00001: Influence of sea bed slope on the performance of a shore-fixed oscillating water column wave energy converter Piyush Mohapatra, Trilochan Sahoo, Anirban Bhattacharyya The oscillating water column (OWC) devices have been quite effective in harnessing energy from the ocean waves at prototype scales. A numerical study was carried out to analyze the influence of sea bed slope on the hydrodynamic efficiency of such a device. A computational fluid dynamics (CFD) based numerical wave tank (NWT) was developed using ANSYS-Fluent which uses a multiphase volume of fluid (VOF) method to simulate the ocean waves. The power take-off (PTO) unit of the device is modeled as a porous jump in the flow field to impose the pressure jump versus flow characteristics of the turbine. The sea bed beneath the OWC chamber is varied in accordance with slope height and slope length. The fluid flow parameters inside the chamber and the hydrodynamic efficiency of the chamber are calculated for various sloping bed conditions. The efficiency is plotted against the incident wave frequency and it was observed that the efficiency curve reaches a maximum for a certain incoming wave frequency. It was observed that depending on the sea bed slope not only the value of the peak efficiency varies but also there is a phase shift in the efficiency plot. It was verified that for a few of the slopes there is an improvement in hydrodynamic capture efficiency. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L14.00002: Characterization of a Mangrove-Like System for Tidal Energy Harvesting: Effect of root and path diameter. Daniel O. Gomez Vazquez, Eduardo E. Castillo Charris, Amirkhosro Kazemi, Oscar Curet Tidal energy is a potential source of renewable energy for many coastal locations in the US. However, many of the conventional devices to convert hydrokinetic energy to electrical energy are not necessarily apt in these locations. Inspired by mangrove roots - a tree that is abundant along the tidal stream in tropical and sub-tropical areas, we designed a novel device to harvest hydrokinetic energy from tidal currents. This device consists of one or multiple oscillating cylinders, partially submerged in the water and an electric generator composed of fixed magnets and a winding. A steel plate provides a restoring spring force for the system. The device was tested in a recirculating water tunnel for different cylinder diameters, array sizes and flow speeds. The kinematics and the voltage output were measured for the different conditions. The flow downstream the model was measured using Particle Image Velocimetry. In general, the device starts to oscillate at a critical flow speed and reach a maximum velocity until the motion decreases. The maximum amplitude oscillation and voltage output tend to increase with larger cylindrical diameters and when the cylinders were closer to each other. The power performance and wake structure are also compared. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L14.00003: Energy Harvesting from Mangrove-like Structure in Tandem and Staggered Arrangements. Eduardo E. Castillo, Daniel O. Gomez Vazquez, Amirkhosro Kazemi, Oscar Curet This work investigates the performance of a mangrove-inspired structure that uses vortex induced-vibration to harvest hydrokinetic energy. The device consists of a coil and magnets attached to a vertical wood cylinder submerged in water and connected to a thin steel plate. This cantilever configuration allows only oscillations perpendicular to the flow. Three independent devices were placed in tandem and staggered arrangement in a water tunnel to measure the power generation and the kinematics of the three devices. Reynolds numbers ranged from 200 to 1500, based on cylinder diameter. It was found that the energy generated was proportional to the oscillation's amplitude. The results show that in both arrangements as the velocity of the flow increases, the amplitude of oscillation increases from cero to a region with high values to then decrease to cero for high velocities. The up-stream device shows a delay in that behavior, compare to the other devices, but reach higher frequency of the oscillations. Additionally, we measured the flow structure to explore the hydrodynamic interaction within the devices. These renewable energy devices could have applications to power small actuators or sensors to monitor coastal infrastructure. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L14.00004: Numerical simulation of a horizontal axis tidal turbine with a passive load-control system Weidong Dai, Ignazio Maria Viola, Riccardo Broglia Load fluctuations on Horizontal Axis Tidal Turbines (HATT) may result in fatigue failures, and this is one of the main factors that affect the reliability and durability of tidal turbines. While passive load-control systems for horizontal axis wind turbine have been well studied, there are few studies about such systems for tidal turbines. We propose a passive pitching mechanism to mitigate the change of angle of attack and, in this way, to lower the fatigue loading. We studied the fluid mechanics of a HATT with and without the passive pitching mechanism in open channel flow conditions. The flow field around the blades and forces on the blades were computed numerically both with a commercial and an in-house finite-volume CFD code, and validated with experimental data. We found that the use of passive pitching mechanism can reduce the amplitudes of thrust fluctuations by around 80{\%} without affecting the mean power generated. We also observed that this mechanism can mitigate the fluctuation of power output by around 20{\%}. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L14.00005: A total-flow design of geothermal power generator using Turgo turbines Tzu-Yuan Lin, HSIEH-CHEN TSAI We combine Turgo turbines and two-phase supersonic nozzles to design a total-flow geothermal power generator. The high-pressure subcooled liquid from the well forms supersonic flashing jets through the nozzles and the high-speed two-phase jets imping turbine blades obliquely to drive the Turgo turbine. This new generator converts geothermal power directly from the geothermal fluid without implementing any phase separator or heat exchanger, which results in a simple and easy-to-maintain system. Compared with traditional Organic Rankine Cycle (ORC) generators, results from theoretical analysis and field tests in Yilan, Taiwan show that the new design of geothermal power generator has a competitive geothermal efficiency operating at moderate reservoir enthalpy. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L14.00006: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 3:03PM - 3:16PM |
L14.00007: CFD Simulations of Floating Offshore Wind Turbine Platform Mostafa Elaskalany, Maysam Mousaviraad Computational modeling of offshore wind turbines imposes significant challenges due to the multiphysics nature of the system that involves both the turbine and the support structure. To provide reliable experimental data for validation of simulation tools, the OC5 DeepCwind floating semi-submersible wind system was designed and tested through DOE support. The purpose of this work is to develop and validate a high-fidelity computational solver for floating offshore platforms that is capable of modeling incident waves, sea current, hydrodynamics, mooring dynamics, and foundation dynamics. The high-performance fluid solver is based on URANS CFD methods, is capable of modeling incoming waves, including stochastic/random ocean waves based on specified spectrum, and resolves the nonlinear wave dynamics. Validation studies are presented for free decay as well as wave-only excitation in regular waves free to surge, heave, and pitch motions. Further computational studies are carried out in unidirectional irregular stochastic waves, including uncertainty quantification (UQ) for random input wave parameters. Future studies will include coupling with fully resolved turbine blades modeling, as well as stochastic optimization studies for improved hydrodynamics and aerodynamics. [Preview Abstract] |
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