A 3-Dimensional Model of the Probe Volume in Duel-Beam Interferometry Measurements
J F. Widmann, Cary Presser
A three-dimensional model of the probe volume in duel-beam interferometry measurements was developed to evaluate the effect of laser beam alignment errors. Simulations of droplets passing randomly through the probe volume of a two-component duel-beam interferometry system were conducted for various levels of beam misalignment. Of particular interest is the probe area for different droplet trajectories, path length distributions through the probe volume, and the correlation between the gate time on the two channels. It is shown that even for the case of perfectly aligned laser beams, the probe area is a function of the droplet trajectory. An analytical solution consisting of two terms was developed for the probe area with respect to droplet trajectory. The first term corresponds to the probe area calculation commonly used in the interpretation of duel-beam interferometry data, and the second term represents the trajectory dependence of the probe area. The analysis is applicable to both laser Doppler velocimetry (LDV) and phase Doppler interferometry (PDI).