X-ray PTV Measurements of Solitary Waves

Abstract

The aim of this study is to measure velocity fields and accurate surface elevation in solitary waves utilizing a fast Xray PTV system. It is difficult to measure the free surface of water waves with the optical measurement techniques available today. This is partly due to refraction and reflection of light rays by the surface of the waves, or by reflections of light rays by the wall of the wave tank. The interface between water and air will then get an inaccurate location in images captured by visual light. The use of microelectronics in image sensors, have made it possible to capture images with both high spatial and temporal resolution. In this study, X-ray measurements with high resolution in space and time have been performed on solitary waves. Two perpendicular X-ray systems are utilized. Surface elevation measurements with accuracy of 0.12 mm are presented, and cross-waves due to wall effects are observed when the average wave height is subtracted from the images. Particles that absorb X-ray are seeded into the water and PTV is used to find velocities in the flow field. The two X-ray systems provided enough information to produce a 3D reconstruction of the flow field. The velocities measured are compared to velocities computed by a Boundary Integral Model (BIM). There seems to be discrepancy between the computed and the measured velocities, which may be linked to inaccuracy in the particle’s location or linked to the large size of the particles.