Oscillating flow rig for air turbine testing

Abstract

Oscillating water column (OWC) devices equipped with an air turbine are the most extensively studied and possibly the most reliable wave energy converters (WEC). Self-rectifying air turbines are usually employed, being the key element of the power-take-off system. Experimental testing the air turbine in realistic operating conditions is a fundamental step in turbine and WEC development. These turbines are, by definition, operating under oscillating airflows. The present paper describes the development of a novel test-rig designed to test self-rectifying air turbines under both steady and variable unidirectional airflows, and subsequent demonstration tests performed on an axial-flow impulse turbine. A real-time hardware-in-the-loop flow controller was implemented, providing the means to not only experimentally characterise the turbine's performance under realistic wave conditions, but, as importantly, to develop new advanced turbine-generator control strategies that further increase overall efficiency and survivability. Results show that a unidirectional oscillating-flow test-rig with a calibrated fan and fast-actuating valve system can adequately reproduce airflows that are characteristic of an OWC air turbine's operational regime. The hardware-in-the-loop simulator implemented in an oscillating-flow test-rig appears as an innovative, integrated solution for turbine testing in realistic operating flow conditions, but in a laboratory-controlled environment at a small fraction of the costs.