Vortex Generators for Flow Separation Control

Abstract

Vortex generators have become a ubiquitous sight on the modern wind turbine blade. These small, passive devices can increase the energy extraction potential of a rotor, but their subtle footprint disguises the technical difficulties associated with designing and integrating them onto wind turbine blades. The complexity of rotor inflow and the blade-bound flow present specific challenges for the design of vortex generators. Flow three dimensionality effects along the blades have conventionally been factored into design tools using correction factors for two-dimensional airfoil performance characteristics. However, the introduction of local perturbations in the form of streamwise vortices adds an additional layer of complexity. Indeed, the interaction of the vortex generator and flow three-dimensionality is ill-understood, and thus, so are its design implications. Furthermore, the passive nature of vortex generators means that a lot of variables influence their performance, making design optimisation a costly process. This thesis aims to improve the physical understanding of vortex generator physics in the context of wind energy applications, paving the way for more effective engineering tools. The objective is tackled by reviewing the state of the art, benchmarking existing tools and experiments, defining, measuring and simulating relevant test cases, and developing a new design tool. A measurement campaign is conducted in a boundary layer wind tunnel using non-intrusive PIV measurements for assessing the details and dynamics of streamwise vortices. A second measurement campaign maps the performance of the DU-97-W300 airfoil section with vortex generators in a conventional closed-loop wind tunnel. Inviscid vortex theory is employed for modelling vortex dynamics. Xfoil features throughout as a design tool and itself as the subject of an improved airfoil design tool incorporating vortex generators.