Experimental investigation in a Wells turbine under bi-directional flow

In this work an experimental study of flow through a Wells turbine with NACA0015 profiles submitted to an unsteady and bi-directional flow is presented. The experimental set-up of the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari (DIMCM), can simulate the real operation of a wave energy conversion device based on the principle of an oscillating water column (OWC) equipped with a Wells turbine. The set-up consists of a piston, controlled by a hydraulic system, that moves inside a cylindrical chamber open at the top where the Wells turbine is placed. The piston movement generates the airflow driving the turbine. Experimental investigations were carried out in proximity of the rotor blade using three-dimensional aerodynamic probes to perform a careful characterization of the flow field upstream and downstream of the turbine. The dynamic characteristic of the turbine in terms of dimensionless flow parameters was also determined. The real entity of the hysteresis phenomenon was highlighted for the phases of acceleration and deceleration of the unsteady flow through the turbine. Moreover, the existence of an appropriate correlation between the conventional dimensionless coefficients and a measurable and reliable physical variable was investigated. (C) 2013 Elsevier Ltd. All rights reserved.