Optical measurements of bubbles and spray in wind/water facilities at high wind speeds

An optical technique to measure the size distribution and velocity of bubbles and spray is presented and evaluated. A bright field setup with a matched telecentric lens and illumination is used. The hardware was optimized to get high quality data and to allow for velocity measurements of particles. Several image processing algorithms for determining radius, position and velocity of particles were developed and evaluated. The presented technique has an error in size below 1% for particles bigger than 10 px and an error below 10% for smaller particles with a smallest detectable radius of 3 px. First experimental results from the new Kyoto High Wind-Speed wind-wave facility (bubble measurements) and the Heidelberg linear wind-wave facility (spray measurements) show the high potential of the new technique.