| Scope and method of study. Different methods of digital holography were investigated to determine their ability to measure the properties of a spray produced by an aerated-liquid jet. The chosen method was then used to observe the properties of the spray at different downstream locations. Different test conditions of: 1 mm and 0.5 mm injector exit diameters, 4% and 8% GLR, 25 and 50 jet diameters downstream, and jet-to-freestream momentum ratios of 0.74 and 4, were observed to determine their effects. The observations were made by producing maps of the Sauter mean diameter distribution throughout the spray, as well as volume fraction plots showing the concentration of the droplets within the spray.; Findings and conclusions. An aerated jet in crossflow was studied and it was found that digital holographic microscopy was the best method for resolving the smallest droplets within the spray. Using this technique Sauter mean diameter maps were produced and the different effects could be investigated. It was found that the gas-to-liquid mass flow rate ratio had the most effect on droplet sizes, and the SMD could be normalized by this film thickness to produce comparable SMD sizes across different test conditions. This was in contrast to the effect of jet diameter which had little effect on the spray. It was also found that the jet-to-freestream momentum ratio strongly affected the penetration height of the spray into the crossflow while having a small effect on the droplet sizes. Evidence of secondary breakup was also found between the two downstream locations. This evidence was the reduction in droplet sizes, and a study of the aerodynamic forces on the droplets in this area. It was found that at the 4% GLR conditions secondary breakup is likely occurring due to the larger droplets produced at this condition. |
