A review of methods for vortex identification in hydroturbines

Vortex is one of typical structures of the unsteady flow inside the hydroturbines, leading to significant pressure fluctuation, prominent vibration of the units, and fatigue of turbine components. In order to reveal the complex vortex structures in the hydroturbines, a large amount of advanced methods for vortex identification and visualization have been developed and also are currently being intensively investigated by researchers. In this review, the vortex identification methods are reviewed in great detail with many illustrating examples and quantitative comparisons between different methods. The vortex identification methods are classified based on five different taxonomies. The identification of several typical vortices (e.g. vortex rope in draft tube, Kármán vortex, and inter-blade vortex) in hydroturbines (including reversible pump turbines, Francis turbine, Kaplan turbine etc.) have been shown and discussed. Furthermore, experimental techniques for vortex observation have been also summarized and discussed. This review provides a practical guidance to the researchers for performing vortex identification.