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Experiments and Numerical Studies of Spray in Crossflow

The present study focuses on the investigation of spray structure from an airblast injector in the presence of a crossflow; and attempts to gain some insight that can further lead to the development of fuel injection system for gas turbine combustors.

The first part of this study focusses on liquid jet injection in a crossflow of air. Jet trajectory and effect of nozzle geometry on jet breakup are investigated. Proper Orthogonal Decomposition (POD) analysis is used to gain further insights into the breakup process.

In the second part of this investigation, spray structure, trajectory, droplet sizing and droplet velocities are studied. Using the spray structure images, trajectory equations have been derived by multi-variable regression for predicating trajectory and penetration. An interesting phenomenon of spray bifurcation is observed at low Gas to Liquid Ratio (GLR) in the atomizer. The reasons for bifurcation are found by probing high speed images and droplet size measurements. Droplet sizes and velocity are measured by Particle Direct Image Analysis (PDIA) and Particle Tracking Velocimetry (PTV). Velocity vectors are obtained for different droplet sizes, and the effect of drag is shown on droplet trajectory.

After using water and ambient air in the initial experiments; the next set of experiments are done using ethanol, decane, Aachen surrogate and Jet-A1 fuel in a high temperature air cross flow. The cross flow air is pre-heated up to 1450C and the effect of evaporation is studied on spray trajectory. Droplet size measurement is used to examine the effect of evaporation. This configuration actually provides an ideal method to study the rate of evaporation on micron size droplets in a convective air flow. The last part of the study focuses on numerical simulation of the above mentioned experimental studies. A novel approach to simulate two phase boundary condition for airblast atomizer is developed. Input boundary conditions for temperature and velocity are given as measured in experiments. Droplet size distributions obtained from the experiments are used for defining atomizer boundary condition. The simulation results are found to be in reasonable agreement with the experimental results.