59932 - Analysis of the Loss Production Mechanism Due to Cavity-Main Flow Interaction in a Lpt Stage 

In the present work URANS simulations are presented to describe the unsteady interaction process between the flow ingested/ejected from a cavity system and the main flow evolving into a Low Pressure Turbine (LPT) stage. Particular care is posed on the analysis of the loss generation mechanisms acting into the LPT passage, outside the stator row prior to reach the cavity exit plane, and finally in the rear part of the axial gap separating the cavity flow ejection section and the leading edge plane of the downstream rotor row. The simulated geometry reproduces a typical engine cavity configuration, with a static wall, in the following identified as “T -bar”, installed on the bottom of a stator row, jointly with upstream and downstream rotor rows reproduced by means f moving bars. Experimental results of the total pressure loss coefficient distribution, measured at the axial position where the cavity flow is re-entering into the main annulus, have been used to validate the simulations. This experimental data cannot explain and quantify alone the overall interaction process between the cavity flows and the main flow, that exhibit the maximum loss penalty prior to enter into the downstream rotor row. Contour plots of phase-averaged quantities and streamline distribution will be shown to adequately capture the unsteady interaction process between the flow exiting from the cavity and the dominant secondary flow structures generated into the vane row. A deep inspection of the loss amount along the axial direction makes evident that losses generated into the vane row are substantially increased prior to enter into the downstream rotor rows, due to cavity main flow interaction. Results shown into the paper open new perspectives for future optimization of a real LPT turbine stage, that cannot avoid to include at every design phase at least a simplified model of the cavity system and its related phenomena in loss generation.