ID 40

Advanced Processing for Spray Flux Measurements Using Phase-Doppler Interferometry

 

Abstract:

Accurate liquid flux measurements are a valuable aspect of spray characterization and yet optical methods to generate these data are few. Phase-Doppler interferometry can provide high quality liquid flux measurements if the effective sampling area as a function of droplet diameter can be characterized. However, in previous work comparing mechanical patternation and phase-Doppler data, the authors demonstrated that the flux values reported by such instruments can overestimate the flux by more than a factor of nine unless the droplet trajectories were essentially parallel to the interference fringe velocity vector (Bade & Schick, Atomization and Sprays, 2011). In practice, this is a difficult condition to satisfy as either the nozzle or instrument must rotate as the measurement location is traversed through the spray.

In this work, the authors demonstrate a two-part method for calculating accurate liquid flux from phase-Doppler data without a parallel trajectory requirement. The first part is an improved geometric model of the measurement volume that can determine the theoretical sampling area for each droplet based on its diameter and three-dimensional velocity vector. The second aspect of the method is consideration of the changing nature of the scattered light signal associated with arbitrary trajectories. E.g., a droplet’s far-field scattering may switch from refraction- to reflection-dominant. Such changes may result in the rejection of a droplet measurement – reducing the apparent flux. Mechanical patternation is compared to this new method of data processing using both new spray data and archived data from the 2011 work, demonstrating significant flux accuracy improvements.