Stationary and unstationary turbulent flow measurements using particle image velocimetry (PIV).

摘要

Both stationary and unstationary turbulent flows were studied by measuring the full-field velocity vector fields using Particle Image Velocimetry (PIV). Two digital PIV systems were developed, (1) a high resolution PIV system with a high-speed full-frame interline transfer digital camera and two-resonant Nd:YAG laser, and (2) a cinematographic PIV system with a high frame rate digital camera and a copper vapor laser. Airflow in a two-pass square channel was investigated for stationary turbulent flow measurement with the high resolution PIV system based on an intermittent sampling of images. The measured data, including detailed main and secondary flows, are compared with earlier heat transfer data from Ekkad and Han, 1997. The PIV measurement result explains the heat transfer phenomenon in detail and suggests a method of heat transfer enhancement for two-pass flows. The innovative cinematographic PIV system was applied for the non-periodical unstationary turbulent flows of an obliquely descending vortex under the surf-zone breaking wave. The results show that the successfully developed cinematographic PIV system has great potential to use for the study of time-resolved transient two-dimensional turbulent flows. In addition, a uniquely temporal post-processing enhances the accuracy of the PIV data for the case of continuous sampling using cinematographic PIV.