Abstract
In this study, the laser tomography method was applied to measure the void fraction distribution of the water jet in radial direction and axial direction. The continuous laser beam emitted by Nd:YAG green laser (wavelength=532nm, beam diameter=0.25mm) is introduced into the water jet in normal to the flow direction. The laser beam is emitted toward the photo detector, which is located at the opposite side. The photo detector can detect the transmissivity of the laser beam passing across the cross section of the jet. By detecting the laser at the photo detector, we can get the transmissivity distribution of the jet in radial direction. By using this measured transmissivity distribution data, we can reconstruct the void fraction distribution inside of the jet by using the tomography method. For the image reconstruction, we applied ML-EM method (Maximum Likelihood — Expectation Maximization) and assumed that the water jet droplet follows some specific distribution. By using these techniques, the void fraction distribution of the extreme high speed water jet can be successfully measured.
