A new rig has been designed and commissioned at the University of Genova to study the flow field within a turbine interstage cavity and its interaction with the main flow path. The rig is a large scale one-and-half stages, rotating test facility, opportunely designed to reproduce the main features characterizing the cavity flows developing in real low pressure modules of turbogas engines. The effects due to swirl factor and the coolant injected into the cavity to prevent the thermomechanical failure of the disks have been investigated. The rig allows the evaluation of the leakage mass flow rate and the measurement of the seal discharge coefficient in the different operating conditions, as well as the characterization of viscous, rotational and coolant related effects on the main flow path, especially in terms of secondary flow structures and vane row efficiency. Pressure signals acquired into the cavity provide a direct measure of the pressurization level of the fore and rear cavities, as well as the analysis of the effects induced by rotation and coolant flow on the pressure drop provoked by the teeth. Results clearly show that once the cooling flow rate reaches a datum threshold level an iso-pressure condition (with respect to the main flow at the vane leading edge) is established into the fore part of the cavity, and the gas ingestion from the main annulus is avoided. This “purged” condition significantly modifies the near wall flow developing across the vane. The boundary layer entering the vane row is not sucked into the cavity, and simultaneously at the vane exit plane there is poor interaction between the cavity flow and the near wall flow leaving the vane. Total pressure measurements upstream and downstream of the vane clearly highlight the modification of the secondary flow structures for the different conditions tested. Overall, results reported into the paper demonstrate the capability of the new rig to provide a direct estimation of the discharge coefficient of a realistic turbine cavity system for different coolant flow rates and swirl factors, as well as to understand the effects on the flow path near wall behavior due to cavity-main flows interaction, that should be properly accounted for during the design phases, and should be properly reproduced during cascade testing.

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