Spray angle and droplet size analysis for gas turbine fogging

Abstract

The performance of fogging impaction pin nozzles is highly dependent on the spray droplet sizes and spray angles. The risk of compressor blade erosion and corrosion increase if large water particles are present. In the compressor path, effective water droplet evaporation is determined by droplet sizes, water droplets distribution, and concentration within the fogging system. Big droplets are hard to evaporate in time and will invade on Gas Turbine Air Inlet Guide Vane and compressor blades and eventually cause erosion and corrosion due to water hammering. The sizes of droplet and spray angles depend a lot on the impaction pin angles and nozzle orifice geometry but their relationships causing water hammering is still unknown. This study aimed to establish relationships of impaction pin angles and nozzle orifice diameters geometrical effect towards spray angles and droplets sizes for Alstom GT13E2 Gas Turbine inlet fogging. Both experimental data and numerical techniques were used in this research. Image Feature Consolidation Technique and shadowgraph methods were used in the experimental works to capture and analyse the flow output from the impaction pins. Two-dimensional and three-dimensional numerical techniques were employed by varying pressure and pin angles to determine their effects on the spray angles. A multiphase model was used in numerical modelling. The results showed that the small nozzle orifices and small impaction pin angles operated at high pressure produced smaller droplet sizes. A high-pressure flow seemed to produce a smaller spray angle. The spray angle was increased by almost 50% if the orifice size was reduced by 0.5mm. The spray angle was increased about 6% when the pin angle was reduced from 60° to 45° and 2% for pin angle reduction from 45° to 30 °. This research reveals that the optimized impaction pin angles for Alstom GT13E2 Gas Turbine are 30° to 57°. With that, the number of nozzles can be optimized by 7%. Three reference charts, namely Number of Nozzle Chart (NONC), Spray Angle Chart (SAC), and Number of Nozzle According Orifice Size Chart (NONAOSC), are established from this research. The charts can be used to estimate the number of nozzles that are needed for Alstom GT13E2 Gas Turbine model operation, which is according to pin angle and orifice size.