Feasibility and Uncertainties Associated with Two-Angle Imaging of Sprays: A Focus on 3D Velocity Measurements

Backlight imaging is a standard experimental technique used for the measurement of liquid fragment size and velocity in multiphase flows. When used with appropriate microscope lenses, quantitative information on the spray structure can be attained, including measurement of non-spherical objects. A critical issue resides in the nature of the measurement which is line integrated from a single viewing angle. This fundamental limitation makes it impossible to resolve three dimensional information from the images. This paper presents the use of a pair of high speed cameras and long working distance microscopes oriented at 90 degrees to each-other, and synchronized to two high speed diode lasers. By assuming a particular fragment consists of multiple threedimensional ellipsoids, an approximate fragment volume and velocity can be derived. Mono-dispersed drops generated by different syringe sizes along with micro-polyspheres are used as calibration tools to examine the feasibility of combined volume and velocity measurement from two viewing angles. The results reported in this work focus on velocity measurements which yield an uncertainty of up to 15% when compared to theory.