Towing Tank Measurements Of Hydrodynamic Performance Of A Horizontal Axis Tidal Turbine Under Unsteady Flow Conditions

Tidal turbines harness hydrokinetic energy resulting from ocean tidal flows to generate power. This type of power generation is a potential source of clean, reliable renewable energy. However, the technology is still under development. The effects of unsteady flow conditions, specifically surface gravity waves, on tidal turbines have not been completely analyzed. The effects of waves on performance characteristics were assessed for a model horizontal axis tidal turbine selected by the Department of Energy and designed by the National Renewable Energy Laboratory (NREL). The performance characteristics of the 1/25th scale model turbine were tested under unsteady flow conditions. Parameters including wave height, wave length and tow speed for the experiment were scaled to properly model flow conditions that a horizontal axis tidal turbine was expected to experience at a full scale. First, turbine rotational speed, torque and thrust were measured for steady flow conditions and unsteady flow conditions characterized by a range of incoming waves. Turbine performance characteristics, including thrust and power coefficients, were obtained as functions of rotor tip speed ratio for the unsteady flow conditions tested. The second experiment involved a detailed fluid flow survey in the near wake of the turbine with and without one of the waves utilized in the first experiment, as measured by Acoustic Doppler Velocimeters. The results provided a characterization of velocity fields in the near wake of the turbine, necessary information for the placement of multiple turbines in a larger array.

The book encompasses novel CFD techniques to compute offshore wind and tidal applications. Computational fluid dynamics (CFD) techniques are regarded as the main design tool to explore the new engineering challenges presented by offshore wind and tidal turbines for energy generation. The difficulty and costs of undertaking experimental tests in offshore environments have increased the interest in the field of CFD which is used to design appropriate turbines and blades, understand fluid flow physical phenomena associated with offshore environments, predict power production or characterise offshore environments, amongst other topics.

This book is a printed edition of the Special Issue "Marine Propulsors" that was published in JMSE

Renewable Energies Offshore includes the papers presented in the 1st International Conference on Renewable Energies Offshore (RENEW2014), held in Lisbon, 24-26 November 2014. The conference is a consequence of the importance of the offshore renewable energies worldwide and an opportunity to contribute to the exchange of information on the dev

This book provides a comprehensive overview of boundary layer flows, including laminar and turbulent flows. Chapters discuss such topics as the nature of transition, the effect of two-dimensional and isolated roughness on laminar flow, and progress in the design of low-drag airfoils. They also present theoretical and experimental results in boundary layer flows and discuss directions for future research.

Hydrokinetic turbines convert the energy of flowing water into usable electricity. Axial flow and cross flow turbines are the most common forms of hydroNinetic turbine, however cross flow turbine performance and the impact of surface waves are not well understood. Tests were conducted to observe the effects of waves on the performance characteristics of a cross flow turbine promulgated by the Department of Energy’s Reference Model Project, specifically Reference Model 2. Testing of a 1:6 scale model was conducted in the large towing tank in the USNA Hydromechanics Laboratory. Baseline (no wave) turbine performance was compared to published data on the same model turbine. Additionally, tests were conducted with incident waves and at various turbine depths and various tow speeds. The average turbine performance characteristics improved slightly as depth decreased due to acceleration of the constricted flow near the surface. Waves did not significantly change the performance of the turbine when averaged over of an entire cycle and several wave periods. This was the case even though the test waves created a velocity shear across the entire span of the blade. The waves were found to impart cyclic signatures in the torque measurement which may have consequences for instantaneous blade loading and power output from the device. A computational model was developed to predict turbine performance and compares favorably to the experiment.

The Twenty-Second Symposium on Naval Hydrodynamics was held in Washington, D.C., from August 9-14, 1998. It coincided with the 100th anniversary of the David Taylor Model Basin. This international symposium was organized jointly by the Office of Naval Research (Mechanics and Energy Conversion S&T Division), the National Research Council (Naval Studies Board), and the Naval Surface Warfare Center, Carderock Division (David Taylor Model Basin). This biennial symposium promotes the technical exchange of naval research developments of common interest to all the countries of the world. The forum encourages both formal and informal discussion of the presented papers, and the occasion provides an opportunity for direct communication between international peers.