ANALYSIS OF TWO-DIMENSIONAL LIQUID SPRAY IMAGES: THE SURFACE-BASED SCALE DISTRIBUTION

摘要

The drop-size distribution is a very important characteristic of liquid sprays. From a mathematical point of view these distributions are defined for spherical drops. Furthermore, the experimental diagnostics widely used to measure spray drop-size distribution characterize the droplets by a single length-scale equivalent to a diameter. However, more recent techniques based on spray image processing clearly show that a high proportion of liquid droplets are barely spherical, especially those issued from primary atomization processes. In the present paper, a new description of 2D liquid spray images is presented: the surface-based scale distribution. This distribution and its series of mean scales are functions of the shape of the particles. In the first part of the paper, this description is applied for theoretical sets of objects with controlled shape and size. Characteristic features of the surface-based scale distribution and of the corresponding mean scale series are emphasized from these applications. These features are of practical interest for the determination of the scale distribution characteristics of real 2D liquid spray images presented in the second part of the paper. Among other results, it is found that the ratios of the mean-scales to the traditional mean-diameters, which quantify the deformation of the objects, appear to be mainly a characteristic of the atomization mechanism. Finally, although it has not been explored here, an interesting aspect of this scale distribution is that it can be applied on atomizing liquid flows, opening new fields of investigation.