Ingestion of hot gas from the flowpath into the gaps between the rotor and stator can cause turbine components to overheat and lead to deterioration in component life. To prevent this, modern gas turbines, both industrial and aerospace, use compressor bleed air to provide positive outflow through the rim seal (known as “purge” flow). This purge flow can be a substantial fraction of the total flow bled off of the compressor and as such it represents a substantial performance penalty. Past efforts have focused primarily on generating correlative orifice models using experimental data. These results are limited in their applicability by the geometry and conditions tested. In this research MIT, in collaboration with GE Energy and GE Aviation, seeks to investigate the fundamental flow physics in the turbine rim cavity region. Of particular interest is the response of the wheelspace and rim cavity to external stimuli set up by the main annulus flow such as flow unsteadiness due to rotor stator interactions. Rig data being collected by GE will be used to assess the analysis and to guide the investigation. Understanding these mechanisms is fundamental to optimizing seal design and minimizing the purge flow requirements, thus minimizing the associated performance penalty.