Analysis of the sealing flow rate on loss production mechanisms in LPT stage

Authors

Dario Barsi  - University of Genova, Italy
Davide Lengani - University of Genova, Italy
Daniele Simoni - University of Genova, Italy
Francesco Bertini - AvioAero
Matteo Giovannini - Morfo Design
Filippo Rubechini - Morfo Design

Abstract

The reduction of the leakage flow rate and the optimization of sealing systems is today a key point for improving the performance of modern gas turbines, since the losses due to the interaction process between the main flow and those entering /leaving the cavities is among the most relevant for the case of stator/rotor cavity systems. In the present work, numerical simulations are employed to model and describe the flow behaviour within a typical aeroengine turbine cavity system and to investigate the interaction process between the main flow and the flow entering/exiting from a cavity system representative of LPT for aeroengine applications. Experimental results acquired in a cold-flow facility reproducing one-and-half Low Pressure Turbine axial flow stage equipped with an engine-like cavity system and upstream and downstream rotor rows have been used to validate the simulations. Several turbulence models have been tested to investigate their effect on the flow field into the cavity and on overall performance parameters. Comparison with experimental results will also identify the best model also for future investigations. Moreover, the effect related to the rotor/stator interaction, provoking ingestion into the cavity of the wake generated by the upstream rotor bars and blockage effect related to the presence of the downstream bars will be inspected. To this aim, both steady and unsteady calculations were carried out through the commercial solver Numeca. Several calculations, varying the flow rate of cooling air injected inside the cavity, were carried out to identify the value of the flow rate capable of sealing the cavity, avoiding the ingestion of flow from the main channel. Cavity discharge coefficient and the total pressure loss distribution have been computed for the different sealing flow rate to understand the effect that this parameter has on the stage efficiency and leakage flow through the cavity. Finally, results presented into the work provide a clearer picture on the mechanisms responsible for producing additional losses and how this mechanisms are affected by the sealing flow rate, thus helping the designer in further improvement the LPT stage efficiency.