Author(s): Rui Aleixo; Silvia Amaral; Teresa Viseu; Solange Mendes; Teresa Alvarez; Carlos Alberto; Rui M. L. Ferreira
Keywords: Surface Image Velocimetry; PIV; PTV; Dam-breach
Surface image velocimetry is an optical based technique used to determine the flow field of the free surface of an open surface flow. It often relies on known algorithms, such as the ones for Particle Image Velocimetry (PIV), Particle Tracking Velocimetry (PTV) and Optical Flow. A well-known example of surface image velocimetry is the Large-Scale PIV approach, used frequently in field applications. The characteristics of the free surface such as: oscillations, light reflections and surface waves bring an additional layer of complexity to the velocity field determination that are normally not taken into account by many existing PIV or PTV algorithms. This fact can lead to erroneous estimations of the surface velocity field, and it needs to be addressed. In this paper, a discussion on the advantages and disadvantages of Surface Image Velocimetry are presented, and methods to address the aforementioned issues are presented and applied to a transient open surface flow associated with the dam-breach flow. In this flow, besides its severe transient character, waves, light reflection and lack of seeding affect the free surface, which constitutes a rather complete case study. Finally, a discussion between the requirements of the image acquisition setup in terms of hardware with focus on frame rate, sensor resolution and optics is made to determine the criteria for which consumer grade cameras can be used as scientific instruments for surface image velocimetry.