SIMULTANEOUS DROPLET SIZE AND GAS-PHASE TURBULENCE MEASUREMENTS IN A SPRAY FLOW USING PHASE-DOPPLER INTERFEROMETRY

A recently developed method to increase the sensitivity of a phase-Dop pler interferometer (PDI) has been applied to an annular air flow inte racting with a spray under isothermal conditions in order to demonstra te the applicability of the method to obtaining velocity and turbulenc e characteristics of the gasphase in a two-phase flow. A conventional PDI system operated in the first order refraction mode cannot be confi gured to efficiently detect small seed particles in the presence of la rge droplets due to the limited dynamic range of the photodetectors. I t is therefore difficult or impossible to obtain seed particle detecti on rates sufficient for turbulence measurements. Doping the spray with a very small quantity of dye preferentially attenuates the light inte nsity scattered by large droplets, thus allowing the PDI system to det ect small seed particles without damaging the photodetectors when larg e particles are present in the flow. Application of this method to a t wo-phase flow produced by a pressure-swirl atomizer coaxially located within an annular air jet has resulted in profiles of axial mean and f luctuating velocities and shear stresses as well as integral time scal es and turbulent energy spectra.