Experimental study of the turbulent flow in the wake of a horizontal axis tidal current turbine

A scaled-model of a horizontal axis tidal current turbine (HATCT) is tested in the CNR-INM Circulating WaterChannel. The experiments are designed to establish in the first place the performances of the turbine atdifferent working settings. The second goal is to investigate the hydrodynamics generated by the turbine in thenear wake using the Particle Image Velocimetry (PIV) technique. For this purpose, velocity measurements areperformed in a longitudinal plane and phase-locked to the rotor angle in order to resolve the wake structure atdifferent working regimes. The analysis of the axial and radial velocity fields reveals the flow features of theslipstream, as well as its expansion and dependence on the turbine operating parameters. Analysis of the non-diagonal terms of the Reynolds stress tensor provides insight into the onset of tip vortex pairing and of vortexinstabilities. Furthermore the separate contributions of transport, production and dissipation to the turbulentkinetic energy in the wake field are discussed in detail. The vortex unsteadiness is captured and correlated withthe evolution of the kinetic energy transport and production terms. Understanding these phenomenologies isan important step to develop computational tools able to estimate the radiated noise or the potential impactof turbulence on performances of further rotors placed in the wake, as in an array of tidal turbines.