UNCERTAINTIES IN PHASE DOPPLER MEASUREMENTS OF SPRAYS

Spray measurements represent the highest number of applications for Phase-Doppler Anemometry (PDA). For such applications PDA has proved itself an excellent technique for measuring spherical particles. The technique utilizes a linear relationship between the particle diameter and the phase of the Doppler burst when a single (geometrical optics) scattering mode dominates the scattered light. Uncertainties of the measurements arise, however, when more scattering modes may contribute to the light, and when the received phase becomes noisy due to distortion of the wave fronts in dense sprays. This paper reports on investigations to characterize such uncertainties and to devise ways of avoiding them utilizing the three-detector configuration of a Dantec PDA in combination with phase discrimination, a method for sorting particles in flows where a single type of particle may scatter in more than one mode or different types of particles scattering in independent modes. Tests were conducted on a water droplet spray to characterize the phase measurements for varying gain and scattering angle.