3D CFD Ingestion Evaluation of a High Pressure Turbine Rim Seal Disk Cavity

Abstract

The amount of cooling air assigned to seal high pressure turbine rim cavities is critical for performance as well as component life. Less air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk life. Excessive purge air adversely affects performance. The minimum purge (i.e. sealing) air requirement to control ingestion is also influenced by annulus circumferential pressure fluctuation present over the rim seal cavity. Its interaction with the platform gap resistance and the amount of purge air needs to be understood in order to reliably predict performance and component life. Work has commenced to investigate opportunities in reducing disk cavity purge flow requirements by studying ways to control ingestion. The study has been initiated with 3D CFD model setup/run mode options to benchmark main/cavity flow field interactions. The selection of the appropriate CFD model fidelity, however, is one of the main goals of this work. The CFD model phase has 3 options to be evaluated; 1) steady solution with mixing plane aft of the cavity, 2) steady solution with mixing plane forward of the cavity, 3) unsteady solution. Option 1 has been completed and is the subject of this paper. A reference HP turbine stage and disk cavity from an engine design was selected for the CFD study. The steady flow solution model captured the oscillatory movement and penetration depth of ingestion by varying purge flow rate and observing the impact on the mixing plane forward and aft of the disk cavity. Moreover, the influence of upstream stator vane airfoil fillet shape was also investigated. The entrained flow was established by starving the cavity and integrating the outflow along the disk. This value along with the nominal and intermediate cavity purge flows were validated against relevant sealing flow design correlations. At a radial location near the rim, an ingestion mixing efficiency value versus purge flow rate was obtained which correlates well with recent unsteady flow results from the literature.