Particle tracking velocimetry (PTV) and its application to analyse free surface flows in laboratory scale models

Abstract

The methodology and application of particle tracking velocimetry (PTV) for surface flow velocity measurements are presented in a conventional laboratory scale model characterised both by large vortices and turbulence, making use of the fact that PTV allows to take reliable measurements in flows exposed to strong deformations typical in turbulent shear layers. The experimental setup included a river reach with main channel and wide floodplain of different roughness. Surface PTV measurements were carried out by a CCD camera with 30 frames per second frame rate and vertical camera axis. In the evaluation of the recordings an algorithm suitable to be applied in flows with strong strains was needed, capable to find corresponding particles even by highly deformed neighbourhoods. For this aim a modification of the so-called velocity gradient tensor method was used. The reconstructed velocity fields were used first to visualize the mean flow field, then to identify and investigate the various flow structures by means of the swirling strength analysis.