A study on the performance of a cross-flow air turbine utilizing an orifice for OWC wave energy converters

Abstract

Ocean energy which includes tidal energy, ocean thermal energy conversion, wave energy

and other marine energy currents, hold an enormous amount of untapped energy that, if

exploited extensively, have a potential for contributing significantly to the electricity supply

of countries facing the sea. One of the most successful and most extensively investigated

devices for extracting wave energy is the Oscillating Water Column (OWC). OWCs have

been widely developed due to its potential deployment if various water conditions and its

simplicity in design. The common OWC wave energy converter consists of fixed or floating

structure, which opens to the sea below the water surface and absorbs wave energy, and a

turbine coupled to a generator. Wave motion inside the chamber induces an exhalation and

inhalation of the trapped air which drive the bi-directional turbine at the opening of the

device. The turbine is connected to a generator so that mechanical motion from the rotating

blade is converted to an electrical energy.

A cross-flow air turbine is a candidate for use of a self-starting turbine due to its

characteristic, high coefficient at a low tip speed ratio. In addition, it has excellent stabilityand low noise. With its characteristics this turbine may be more suitable at places where

require low noise compared to typical commercialized air turbines such as Wells and impulse

turbine. In this research, the investigation of cross-flow air turbine for OWC wave energy

converter have been undertaken. First, a numerical analysis of the turbine by CFD have been

conducted in order to acquire its performance characteristics in various range of the flow

rate with different rotational speed of the rotor. Model scale analysis was proposed to design

and compare with experimental model, and 1/16 model scale was determined. In addition,

the orifice plate as substitute was adopted not only to simulate the behavior of the turbine by

numerical analysis and experiment but also to verify the CFD result with the experiment

result. The size of the orifice plate was determined by matching the pressure drop between

upstream and downstream of turbine and orifice. Thus, the comparative study between

orifice plates and turbine simulation have been proposed.