Controlling the flow distribution characteristics in the secondary air system of a gas turbine

Abstract

Increased gas turbine system efficiency is accompanied by increases in turbine inlet temperature, mass flow rate, and pressure. Because the turbine blade is exposed to high temperatures and high pressure, the secondary air system (SAS) should be designed to optimize operating conditions and blade life. The cooling air discharged from the compressor flows into the rotating disk through the pre-swirl system, then into the receiver holes during the respective stage of the turbine. In this study, the flow distribution characteristics of the secondary cooling air, which flows into the first-stage turbine blade and the second-stage cavity, were analyzed using validated computational fluid dynamics (CFD) methodology. CFD techniques were validated by comparative analysis of various CFD techniques on the experimental data of Bath University and Hanyang University in the previous studies. To apply the k-ω SST turbulence model, which was the most effective technique, the grids near the wall was constructed with y+ one or less. The frozen rotor method was applied to the stationary-rotating interface to satisfy the change in pitch ratio for each components. As a result, methodologies had been devised to control each flow properties while maintaining SAS efficiency through a change in system outlet area. When the swirl ratio was maintained at one, it was possible to change the mass flow rate for the outlet area without reducing the system efficiency. On the other hand, the outlet static pressure could be changed for the outlet area regardless of the swirl ratio, but the choked flow occurred below a specific pressure ratio. Finally, mass flow rate and static pressure at the receiver hole outlet could be controlled respectively, and the performance curves of the SAS within the designable range were also presented.