Experimental analysis of the unsteady flow inside a Wells turbine

Fabio Licheri,Tiziano Ghisu,Pierpaolo Puddu,Francesco Cambuli

doi:10.1051/e3sconf/202131211009

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.

Highlights

Ocean energy represents one the most attractive renewable sources in virtue of its high availability and predictability [1]
The plants based on the Oscillating Water Column (OWC) principle can be considered made of two main units: a chamber, partially submerged under the sea level, where the wave motion induces an alternative movement of the air trapped in the chamber, and a turbine, placed at the top of the chamber and driven by the air-flow
This paper presents a local flow analysis for a Wells turbine coupled with an OWC simulator, housed in the Department of Mechanical, Chemical and Materials Engineering (DIMCM) at the University of Cagliari [9, 10]

Summary

Introduction

Ocean energy represents one the most attractive renewable sources in virtue of its high availability and predictability [1]. For this reason, several researches have been carried out during the last four decades, presenting different solutions to harvest wave energy and convert it into electrical energy. The plants based on the OWC principle can be considered made of two main units: a chamber, partially submerged under the sea level, where the wave motion induces an alternative movement of the air trapped in the chamber, and a turbine, placed at the top of the chamber and driven by the air-flow. A number of authors have studied Wells turbines both with numerical [5,6,7,8] and experimental [9,10,11,12] approaches

Methods

Results

Conclusion