Simultaneous measurement method of size and 3D velocity components of droplets in a spray field illuminated with a thin laser-light sheet

Abstract

A measurement technique to simultaneously obtain the size and 3D velocity components of droplets in a spray field illuminated by a thin laser-light sheet has been proposed. This technique is based on the optical processes of in-focus and out-of-focus imaging of spray droplets using a stereoscopic camera arrangement. The patterns obtained by this technique represent the distributions of glare-point pairs and defocused images with interference fringes generated by the imaging of reflection and first-order refraction rays scattered from each droplet illuminated by the laser light. The size of a droplet is evaluated by the glare-point separation and the fringe order of the interferogram. The velocity of each droplet is obtained by 3D particle tracking velocimetry (3D-PTV) based on the tracking of the glare-point pair and the defocused image generated by a droplet. For this technique, the three-dimensional optical arrangement corresponding to the scattering angle and the stereo-viewing angle, and the algorithm for stereoscopic matching of both images have been developed. The accuracy of this technique for the size and 3D velocity measurements was evaluated by applying a calibration technique, and the feasibility of this technique has been confirmed by applying it to the measurements of a spray field issuing from a swirl nozzle. From the results obtained, it has been verified that the error in the size measurement is within 1.5% and that for the velocity measurement is less than 3%.