Wind & Renewable Energy

Biography

Biography: David Greenblatt

Abstract

Recent demand has driven renewed interest in vertical axis wind turbines (VAWTs) due to their insensitivity to wind direction, proximity of the generator to the ground and low noise levels. A drawback of VAWTs is the dynamic stall their blades experience as they pitch beyond their static stall angle, resulting in power losses and large unsteady loads imposed on the drive train. During the last four years, our research group has made significant progress in controlling VAWT dynamic stall by means of pulsed dielectric barrier discharge (DBD) plasma actuators. We produce plasma pulses at frequencies that correspond to flow instability frequencies, thereby generating blade-spanwise vortices that transfer high momentum fluid to the blade surface. This ameliorates or eliminates dynamic stall. We constructed and tested small double-bladed VAWT with dielectric barrier discharge plasma actuators installed on the upwind blade’s leading-edges. Introducing the pulses produced a 35% increase in gross turbine power. We complemented this study by performing particle image velocimetry measurements on the blades while subjected to pulsed plasma actuations and observed that the dynamic stall vortex was significantly ameliorated. Recently we have focused on feed-forward and closed-loop flow control and we achieved a remarkable net turbine power increases of more than 10%. Following this, we developed a scheme for switching between inboard and outboard control on the blades, thus facilitating both upwind and downwind dynamic stall control. Our present efforts are aimed at maximizing net turbine power output by means of closed-loop control and field-testing a 2 kilowatt proof-of-concept demonstrator.