In order to seal the roto r-stator disc -rim cavities in the turbine section of gas turbine engines against hot gas ingestion, at least one labyrinth seal with several teeth is required in the rim cavity . In accordance with t he seal clearance and tooth pitch , an interesting interact ion between the supplied cooling flow and hot gas ingestion occur s that affect s the net coolant flow and cavity temperature . Understanding this interaction and the relationship between seal design and the composition of the net flow leaving the rim cavity is critical in balancing turbine efficiency gain versus part life reduction. The high pressure turbine rim cavity of an industrial gas turbine was modeled for each of seven labyrinth seal design s using a 3-D CFD model under steady state condition s. It was found that a very high degree of turbulent mixing of mainstream and purge -coolant gases occurs in the large middle cavity to give much more uniform temperatures in the three -tooth labyrinth designs considered. In addition, an enhanced understanding of the effects of seal clearance and tooth pitch of the three -tooth labyrinth on ingress heating in the rim cavity area was obtained.