L.M.C. Gato

The energy conversion performance of several types of Wells turbine designs

Abstract Several types of single-plane and multiplane Wells turbines are investigated and compared. The turbines’ aerodynamic losses and overall performances are presented and two successful methods of swirl energy recovery are studied in detail. Guide vanes were fitted to a monoplane turbine whereas the rotors of a biplane turbine were contra-rotated. A double-shaft biplane turbine was also tested. The contra-rotating turbine had an operational range which was similar to that of the monoplane turbine with guide vanes, achieved a similar peak efficiency, but performed better in the post-stall region and also was found to be able to accommodate a much higher pressure-flow ratio.

Analysis of Wells turbine design parameters by numerical simulation of the OWC performance

This paper investigates by numerical simulation the influence of the Wells turbine aerodynamic design on the overall plant performance, as affected by the turbine peak efficiency and the range of flow rates within which the turbine can operate efficiently. The problem of matching the turbine to an oscillating water column (OWC) is illustrated by taking the wave climate and the OWC of the Azores power converter. The study was performed using a time-domain mathematical model based on linear water wave theory and on model experiments in a wave tank. Results are presented of numerical simulations considering several aerodynamic designs of the Wells turbine, with and without guide vanes, and with the use of a bypass pressure-relief valve.

Aerodynamics of the wells turbine

Abstract The paper describes a theoretical and experimental investigation concerning the aerodynamic performance of the Wells turbine, a self-rectifying axial-flow turbine suitable for energy extraction from reciprocating air flow. The turbine consists essentially of a rotor with untwisted aerofoil blades of symmetrical cross section, set radially at 90° angle of stagger. Numerical results were computed from a streamline curvature throughflow method and compared with analytically obtained results from a linear actuator disk model. Unidirectional steady-flow measurements were performed with a turbine of about 0.6 m rotor diameter and several numbers of blades, and included flow rate, pressure drop and torque, as well as velocity and pressure distributions. Experimental results are compared with theoretical values.

Performance of a High-Solidity Wells Turbine for an OWC Wave Power Plant

The paper describes an experimental investigation, and presents the results of the aerodynamic performance of a high-solidity Wells turbine for a wave power plant. A monoplane turbine of 0.6 m rotor diameter with guide vanes was built and tested. The tests were conducted in unidirectional steady airflow. Measurements taken include flow rate, pressure drop, torque, and rotational speed, as well as velocity and pressure distributions. Experimental results show that the presence of guide vanes can provide a remarkable increase in turbine efficiency.

Turbine-controlled wave energy absorption by oscillating water column devices☆

Abstract The paper deals with phase control as a method of increasing the energy absorption by oscillating water column (OWC) devices, from regular as well as from irregular waves. The power take-off machine considered is a modified version of the self-rectifying axial-flow Wells air turbine, whose rotor blades are of variable setting angle; this allows the air pressure and flow rate to be controlled independently from each other. Results of numerical simulations are presented for three different control strategies applied to energy absorption from irregular waves by an OWC device of simple, two-dimensional geometry. Experimental data from a turbine model are used in the simulation.

Aerodynamics of the wells turbine: Control by swinging rotor-blades

Abstract The paper describes a theoretical and experimental investigation of the aerodynamic performance of a version of the Wells turbine modified such that its rotor blades can be set at a varying angle. Unidirectional steady-flow measurements were performed with a turbine of about 0.6 m rotor diameter. The results show that the modified turbine can provide a way of increasing the amount of energy produced from ocean waves by efficiently phase-controlling an oscillating water column type of device.

Performance of the Wells Turbine With Variable Pitch Rotor Blades

The Wells turbine is an axial-flow air-turbine designed to extract energy from the ocean waves. The turbine is self-rectifying, ie.e., produces and unidirectional time-averaged torque from a reciprocating flow. The paper describes an experimental investigation on the aerodynamic performance of a modified version of the Wells turbine, whose rotor blades can be set at varying angle (as in a Kaplan turbine) while the turbine is in motion. The purpose of the work is to investigate whether, and to what extent, the modification to the turbine can enable it to achieve phase control-a method of tuning the energy-absorbing device to the incident waves-and avoid aerodynamic stall on the turbine rotor blades at peaks of air flow rate under conditions of real irregular ocean waves. Experimental results obtained with a model turbine are compared with predicted values from a quasi-three-dimensional computational method of flow analysis.

Air Turbine and Primary Converter Matching in Spar-Buoy Oscillating Water Column Wave Energy Device

The oscillating water column (OWC) equipped with an air turbine is possibly the most reliable type of wave energy converter. The OWC spar-buoy is a simple concept for a floating OWC. It is an axisymmetric device (and so insensitive to wave direction) consisting basically of a (relatively long) submerged vertical tail tube open at both ends and fixed to a floater that moves essentially in heave. The air flow displaced by the motion of the OWC inner free-surface, relative to the buoy, drives an air turbine. The choice of air turbine type and size, the regulation of the turbine rotational speed and the rated power of the electrical equipment strongly affect the power performance of the device and also the equipment’s capital cost. Here, numerical procedures and results are presented for the power output from turbines of different sizes equipping a given OWC spar-buoy in a given offshore wave climate, the rotational speed being optimized for each of the sea states that, together with their frequency of occurrence, characterize the wave climate. The new biradial self-rectifying air turbine was chosen as appropriate to the relatively large amplitude of the pressure oscillations in the OWC air chamber. Since the turbine is strongly non-linear and a fully-nonlinear model of air compressibility was adopted, a time domain analysis was required. The boundary-element numerical code WAMIT was used to obtain the hydrodynamic coefficients of the buoy and OWC, whereas the non-dimensional performance curves of the turbine were obtained from model testing.© 2013 ASME

An experimental investigation into the effect of rotor blade sweep on the performance of the variable-pitch Wells turbine

Abstract The paper describes an experimental investigation into the effect of rotor blade sweep on the performance of the variable-pitch Wells turbine. The blades tested included two sets of eight symmetrical constant chord NACA 0015 blades (one set had 30° backward sweep, while the other was unswept), two rotor solidities and blade pitch angles of 0° and 20°. The aim of the present experiments was to investigate and compare the aerodynamic performance of the backward swept and unswept blades for different rotor solidities and pitch angles. The measurements covered flowrate, pressure drop, torque and rotor speed. Traversing work with the aid of a directional total static pressure probe yielded more detailed information on the performance of each set of rotor blades. Experimental results have shown that the swept back design of the blades produces a positive value of efficiency and torque over a much wider operating range than the standard unswept NACA 0015 blades, but at the expense of peak efficiency.

Performance of the Biplane Wells Turbine

The paper describes experimental investigation of the biplane Wells turbine for a wave power plant. Performance of the biplane turbine was investigated in unidirectional steady air flow by varying the model configurations using solidity, gap to chord ratio and stagger angle. It was concluded that the performance of the biplane turbine is considerably influenced by inviscid and viscous flow effects. Adjacent upstream and downstream pressure distributions will either suppress or enhance one-another depending on stagger given sufficiently small G/c ratio. The viscous effect from the upstream wake seems to defer stall by advancing boundary layer transition.