Aerodynamic Characterization of a Wells Turbine Under Bi-Directional Airflow

This work deals with the experimental study of the flow in a Wells turbine submitted to an unsteady and bi-directional airflow. The investigations were carried out on an experimental set-up that can simulate the real operating conditions of a wave energy conversion device using a two-dimensional hot-wire anemometer probe to analyse the flow field upstream and downstream of the turbine during its non-stationary operation. In addition to local measurements, the position of the piston that simulates the wave motion, the driving torque and the turbine rotational speed were also measured. These surveys allowed determination of the turbine instantaneous performances by analysing the aerodynamic flow characteristic at mid-span in the blade-to-blade plane downstream of the rotor. The flow distribution was obtained for the phase of inflow and outflow at different values of rotational speed which was kept constant during data acquisition. The results showed asymmetric behaviour for the two phases of intake and exhaust stroke of the piston and during acceleration and deceleration of the flow. The real entity of the hysteresis phenomenon that arose during the phases of acceleration and deceleration of the unsteady flow was evaluated considering velocity distribution in close proximity of the rotor. (C) 2013 The Authors. Published by Elsevier Ltd