Measurements of droplet size in a two-phase mixing layer using an optical probe with new shape design

Overview & Synopsis

Most current turboreactors or rocket engines use gas assisted atomization to produce a fuel spray. Atomization is carried out by the destabilization of a slow liquid film, sheet or jet of fuel by a fast gas stream. To optimize such engines, themechanisms leading to droplets formation need to be precisely understood. Among these, the stripping mechanism has been thoroughly investigated and phenomenological models provideing some drop characteristics are already available. Yet, these proposals were tested over a limited range of flow conditions and our objective is to check their validity over a wider range of liquid and gas flow velocities. In that perspective, new optical probes with short (10 μm) sensing lengths have been manufactured. We discuss their performances in terms of drop size, velocity and flux measurements in comparison with former versions of such sensors those sensing lengths is at least twice longer. The new sensor is then used in a two-phase mixing layer. Chords distributions as well as the Sauter mean diameter are presented for gas velocities between 20 m/s and 90 m/s and for dynamic pressure ratio M from to 2 and 16. The analysis of these results indicates that the mean drop size primarily depends on gas velocity. Also, the distributions of the chords normalized by the mean value are weakly modified when changing M. These features indicate that the destabilizing mechanisms are quite similar over the considered range of flow conditions.