The Influence of HPT Forward Disc Cavity Platform Axial Overlap Geometry on Mainstream Ingestion

Abstract

In this paper, 3D unsteady and mixing plane CFD simulations including the mainstream full stage on two tested configurations plus a third cavity geometry variance are reported. The sector models were run at test conditions and compared with the corresponding matched Network 1-D flow model to derive the sensitivity of HPT stage forward disc cavity platform axial overlap geometry and supplied purge flow to cavity ingestion dynamics. The first configuration includes no axial overlap (i.e. ΔX/ΔR = 0); the second configuration increases axial overlap by 70% (ΔX/ΔR = 1.82); the third configuration has a larger rim cavity axial spacing and a smaller platform axial overlap (i.e. ΔX/ΔR = 1.67). The unsteady and mixing plane 3D CFD models of the three configurations are run across supplied purge flows ranging from nominal to 35% of the nominal. This was done to obtain a good comparison and to justify the need for unsteady solutions in disc cavity ingestion studies. For each configuration, the CFD predicted mainstream pressure pulse decay profile inside the cavity along with absolute, relative, and static temperatures related to the amount of ingestion that mixes with the supplied flow at several radial heights in the cavity are extracted on a time-averaged and pitch-wise averaged basis. The applied CFD-Network process yields cavity sealing effectiveness versus supplied purge flow and validates platform conductance factors used in 1-D Network flow model. In particular, the unsteady CFD results for the tested configurations were able to reproduce the Network-matched rim cavity effectiveness data at the critical location more closely. The sensitivity results indicate that although, the zero overlap geometry (configuration-1) has insufficient purge flow as evident by the low upper cavity effectiveness, the amount becomes sufficient as the platform axial overlap increases for configuration-2. The influence of increasing rim cavity axial spacing (configuration-3) allows for the same effectiveness to be achieved under a smaller platform axial overlap and lower purge flow supply.

A Comparison of Single and Double Lip Rim Seal Geometries

“…Seal Eccentricity The impact of seal axial movement and various overlap shapes has been studied (e.g. Popovic and Hodson [33] [34], Mirzamoghadam et al [35]). However, industrial gas turbine shafts are long relative to rim seal clearances, so static radial deflections, or eccentricity, are also a source of uncertainty during engine operation.…”

Unsteady 360 Computational Fluid Dynamics Validation of a Turbine Stage Mainstream/Disk Cavity Interaction

“…Their full ring unsteady CFD study set the stage for future work with different cavity/rim geometry variations in order to improve the understanding of the rim seal ingestion process. Still, sector steady/unsteady CFD studies performed the same year by Mirzamoghadam et al [14] on the influence of HPT forward disk cavity platform axial overlap geometry revealed interesting results on upper rim cavity effectiveness (g c ) versus supplied purge flow.…”

Pressure Distortion Effects on Rim Seal Performance in a Linear Cascade

“…Higher pressures beneath the platform cause purge flow to exit the seal rather than hot gas to enter under the platform. Increasing the overlap at the seal exit decreases hot gas ingress into the seal and increases the cooling effect of the purge flow on the downstream blade endwall [1,17].…”