Visualization by PIV of dynamic stall on a vertical axis wind turbine

Abstract

The aerodynamic behavior of a vertical axis wind turbine (VAWT) is analyzed by means of 2D particle image velocimetry (PIV), focusing on the development of dynamic stall at different tip speed ratios. The VAWT has an unsteady aerodynamic behavior due to the variation with the azimuth angle h of the blade's sections' angle of attack, perceived velocity and Reynolds number. The phenomenon of dynamic stall is then an inherent effect of the operation of a VAWT at low tip speed ratios, impacting both loads and power. The present work is driven by the need to understand this phenomenon, by visualizing and quantifying it, and to create a database for model validation. The experimental method uses PIV to visualize the development of the flow over the suction side of the airfoil for two different reference Reynolds numbers and three tip speed ratios in the operational regime of a small urban wind turbine. The field-of-view of the experiment covers the entire rotation of the blade and almost the entire rotor area. The analysis describes the evolution of the flow around the airfoil and in the rotor area, with special focus on the leading edge separation vortex and trailing edge shed vorticity development. The method also allows the quantification of the flow, both the velocity field and the vorticity/circulation (only the results of the vorticity/ circulation distribution are presented), in terms of the phase locked average and the random component. List of symbols

Numerical investigation of vortex dynamics in an H-rotor vertical axis wind turbine

“…Ferreira et al have done extensive research to understand the dynamic stall phenomenon on an H-rotor. They used PIV to visualize the shedding and convection of vortices (Simão Ferreira, 2009). They also numerically investigated dynamic stall using different turbulence models and further compared the influence of turbulence models on the accuracy of dynamic stall prediction.…”

Vertical axis wind turbine in a falling soap film

“…A reasonable approach is to first decouple the problem and develop an understanding of the flow around an individual VAWT. Much of the recent experimental work related to VAWTs has focused on blade-level aerodynamics, such as dynamic stall and tip vortex shedding, [5][6][7] as well as near wake analysis of the mean flow and Reynolds stresses. 6,8 Motivated by a desire to develop intuition about the spatio-temporal evolution of the VAWT wake, we constructed a qualitative flow visualization experiment using a miniature, 3-bladed VAWT in a gravity-driven soap film tunnel (Fig.…”

Aerodynamic Models and Wind Tunnel for Straight-bladed Vertical Axis Wind Turbines

“…According to literature survey, the most widely studied and best validated models can be broadly classified into two categories-Rotor blade model and Streamtube model. These models are basically based on calculation of flow velocity and power through turbine by equating the streamwise aerodynamic force on blades with the rate of change of momentum of air, which is equal to the overall change in velocity times the mass flow rate [4]. The force is also equal to the average pressure difference across the rotor.…”