ANALYSIS OF THE SEALING FLOW RATE ON LOSS PRODUCTION MECHANISMS IN LPT STAGE

In the present work, numerical simulations have been carried out to model the flow behavior within an aeroengine rotor/stator cavity system of low pressure turbine, and to investigate the interaction process between the main flow and the flow entering/exiting from the cavity system. Different sealing flow rates injected into the cavity to prevent thermomechanical failure of the disks have been simulated. Experimental results acquired in a cold-flow facility reproducing one-and-half Low Pressure Turbine axial flow stage have been used to validate the simulations. Cavity characteristic mass flow rates and the total pressure loss distribution coefficient have been computed for different sealing flow rates to understand the effect that this parameter has on the stage performance and leakage flow ingested into the cavity. The time mean effect related to the rotor/stator interaction, provoking ingestion in the cavity of the wake generated by the upstream rotor bars and blockage effects related to the presence of the downstream bars have also been considered. The results confirm that unsteady calculation procedures are necessary if the aim is to correctly capture the effect induced by the leakage flow on the cavity sealing capability. Moreover, the increase of the mass flow rate injected into the cavity leads to the enhancement of the strength of the loss core in the lower 50% span observed downstream of the vane, also inducing local variation of flow angle close to the hub, associated with the flow exiting from the cavity. The results provide a clearer picture on the mechanisms responsible for producing additional losses and how this mechanism is affected by the sealing flow rate.