Oscillating Water Column

About: Oscillating Water Column is a research topic. Over the lifetime, 1379 publications have been published within this topic receiving 18958 citations.

A comparison between experimental and numerical analysis of a wells turbine

Abstract: Wave energy is one of the renewable energy sources with the highest potential. Several pilot plants have been built based on the principle of the Oscillating Water Column (OWC). Among the different solutions that have been suggested, the Wells turbine has gained particular attention due to its simplicity and reliability. The majority of available studies concentrate on the steady operation of theWells turbine, while only few analyze its performance under an unsteady and bi-directional air flow, as determined by the presence of the OWC system. In this work, experimental and numerical performance of a high-solidity Wells turbine with NACA0015 profiles under the bi-directional flow generated by a hydraulic piston is compared. The numerical simulations have been conducted using commercial CFD software and focus on unsteady predictions, with particular attention to the behavior of the flow upstream and downstream of the rotor, flow hysteresis between acceleration and deceleration phases and differences between intake and exhaust strokes due to the non-symmetrical configuration of the machine. NOMENCLATURE Ft tangential force per unit length Ft tangential force per unit length P static pressure P ∗ non-dimensional static pressure drop P ∗∗ non-dimensional static pressure drop (with local flow variables) f piston frequency f non-dimensional piston frequency c blade chord r radius r∗ non-dimensional radius (r − rh)/(rt − rh) rt tip radius rh hub radius T torque T ∗ non-dimensional torque T ∗∗ non-dimensional torque (with local flow variables) U blade speed Va axial velocity (absolute) Vt tangential velocity (absolute) Wa axial velocity (relative) Wt tangential velocity (relative) φ flow coefficient φl local flow coefficient ω rotational speed ρ density

Pneumatic performance improvement of an onshore dual chamber OWC using a CFD model

Abstract: A CFD model developed on the OpenFOAM environment is used to study the key physical processes inside a Dual Chamber Oscillating Water Column device installed onshore. The air pressures and free surface elevations inside the chambers, as well as the vertical velocities inside the holes are evaluated. The pneumatic performance of the device is evaluated for three damping conditions. Results show that the present CFD model is a powerful tool to help on the design of oscillating water columns. It can generate, propagate water waves, and reproduce with high accuracy the key physical processes inside the water chambers. Results show that the pneumatic efficiency improves 300%, from 20% up to 60%, by imposing a higher damping condition in both chambers.

Energy harvesting capability of single-chamber oscillating water column wave energy device model on controlled wave height and period

Abstract: The urgency of electricity demand and environmentally friendly power generator made ocean wave energy as one of many renewable energies that could be implemented in Indonesia because many of its coastlines have the power enough to generate electricity locally and regionally. This research is mainly discussing the model’s capability to generate electricity based on various wave height and period. This energy harvester model made in the laboratory with 1:16 scale, so the other variable component also following this scale. The turbine used in this experiment using Wells turbine with seven blades following the profile guidelines of NACA 0024. The result of this research shows that the power generated by the turbine correlates to wave height and wave period. The output generated by this energy harvester model could achieve 21.2 kilowatts in one hour on average or 339.4 kilowatts in one hour if upscaled to its real size.

Experimental analysis of the unsteady flow inside a Wells turbine

Abstract: One of the most promising technologies for sea-wave energy conversion is the one based on the Oscillating Water Column (OWC) principle. The system is composed of two units, an open chamber that converts the sea water motion into an alternating air-flow, and a turbine driven by the latter. The alternating flow of air requires a turbine capable of maintaining the same direction of rotation. The Wells turbine represents the simplest and most reliable device for this purpose. It is a self-rectifying axial turbine characterized by a rotor with symmetric blades staggered at 90 degrees relative to the axis of rotation. The vast majority of experimental works on Wells turbines and OWC devices analyzed their performance from a global point of view, often under steady conditions, in order to evaluate the pressure drop through the rotor, the torque produced and thus the turbine efficiency. This paper presents an experimental analysis of the three-dimensional flow inside a Wells turbine which operates in a facility capable of reproducing the alternating air-flow typical of an OWC system. The investigation is based on local flow measurements using several probes in order to describe the non-stationary air-flow, both up- and down-stream of the rotor at different heights, along the span of the blade. The investigation, conducted on a high-solidity turbine, details the behavior of the flow field inside the machine, aiming to provide a detailed description that can guide the aerodynamic optimization of the entire system (chamber and turbine) for a better energy conversion.

Simulation and Characteristics Analysis of On-Shore OWC System Proposal as Distributed Generation Resource Considering the Irregular Wave Interaction

Abstract: This article presents the simulation and characterization of an on-shore oscillating water column (OWC) system as part of a distributed generation network considering the irregular interaction of sea waves. The main issue is the adequate calculation of the power generated considering the real variations of the sea waves, employing the stochastic analysis of the wave height and period. The characterization of the wave height was carried out using the Fisher-Tippett Type 1 function, and for the wave period, an empirical probability density function to obtain the instantaneous and accumulated power in an annual period. A basic on-shore OWC system was proposed with different physical dimensions. The theoretical and numerical results present a very similar performance for both turbines (600 W and 25 kW) analyzed. Regarding the 600 W turbine, the resulting accuracy is ≈94.5%, which implies that the annual generated power is 3.13 ± 1.02 MWh/year and the overall efficiency is 23.51% ± 1.9%. However, due to the reduced power generated, the chamber dimensions were modified, achieving 160.61 ± 9.99 MWh/year with an accuracy of ≈93.2%, based on an installed power capacity proposal using a 25 kW turbine. Also, the average overall efficiency for both turbines considering the irregular wave interaction is ≈23.5% and ≈21.1% for 600 W and 25 kW turbines, respectively.