Yoshio Zama

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

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%.

Simultaneous measurement of size and velocity of droplets in spray by using optical images of different two kinds

In general, spray field is a complicated and three-dimensional two-phase flow. The structure of it indicates strong correlation between size and velocity of droplets. Thus simultaneous measurement of size and velocity of the individual droplet in the spray is needed. In the recent years, the techniques based on Interferometric laser imaging for droplet sizing (ILIDS) for the simultaneous measurement of droplet size and velocity were proposed as a field measurement technique, and the most of them are basically 2D measurement. However, multi-dimensional field measurement is indispensable for understanding of spray flow.In this report, a technique of simultaneous measurement of size and 3D velocity field of droplets is based on the characteristic of light scattered from droplets. In this technique, droplet size was estimated by number of interference fringes, and 3D velocity field was reconstructed with 3D-PTV. Moreover, holography technique has been applied in order to separate the overlapping interferometric image, and its feasibility was verified.

Three-Dimensional Velocity and Droplet Size Measurements of Spray Flow (Keynote Paper)

The present investigation describes an application of a novel technique of simultaneous measurement of droplet size and three-dimensional components of velocity in a high density spray with swirl. The spray has a complicated and three-dimensional structure caused by mixing with surrounding airflow entrained by high speed fuel jet issuing from a nozzle. The breakup process of fuel film to fine-droplet-cloud, the droplet size dispersion and the velocity distribution of droplets are important factors in practical application of fuel spray for combustors. The conventional technique can be applied to local measurement of droplet speed and size. Recent methods, based on optical and image processing techniques, provide measurement of the velocity and droplet size distribution in observation area or volume. Maeda et al. proposed an excellent measurement technique of the size and the velocity distribution of droplet in spray based on interferometric laser imaging in which the fringe pattern is generated at the out of focus plane by interference between 0th order and 1st order refractions of droplet illuminated by high power laser light sheet. And also, in this technique, the separation of overlapping droplets image has been successfully done by optical method. As a practical application, the size and velocity distributions of droplets in a high density spray without swirl have been measured by this technique. In general, the droplet motion in a spray field is highly three-dimensional. Especially, a spray generated by a swirl nozzle shows complicated droplet motion in the three-dimensional field. In order to analyze the configuration of a complicated spray field, three-dimensional velocity measurement of droplets must be required. In the present paper, a combined measurement technique of the size and three velocity components of droplets in three-dimensional spray field based on doublet imaging technique of droplets and stereoscopic PIV method has been developed. And its feasibility and applicability was confirmed by practical application to measurements of spray fields induced by a swirl jet nozzle using in gas turbine.© 2003 ASME