Overspray and Interstage Fog Cooling in Compressor Using Stage-Stacking Scheme – Part 1: Development of Theory and Algorithm

Compressor intercooling has traditionally been employed to reduce compressor work and augment gas turbine output power. Conventional intercooling schemes are usually applied through nonmixed heat exchangers between two compressor stages or by cooling the outside of the compressor casing. Any cooling schemes that may affect the flow field inside the compressors have not been favorably considered due to concerns of any disturbance that might adversely affect the compressor's performance stability. As the inlet fog cooling scheme has become popular as an economic and effective means to augment gas turbine output power on hot or dry days, consideration has been given to applying fog cooling inside the compressors by injecting fine water droplets between stages (i.e. interstage fogging). This paper focuses on developing a stage-bystage wet-compression theory for overspray and interstage fogging that includes the analysis and effect of pre-heating and pre-cooling at each small stage of the overall compressor performance. An algorithm has been developed to calculate the local velocity diagram and allow a stage-by-stage analysis of the fogging effect on airfoil aerodynamics and loading with known 2-D meanline rotor and stator geometries. Thermal equilibrium model for water droplet evaporation is adopted. The developed theory and algorithm are integrated into the system-wise FogGT program to calculate the overall gas turbine system performance.