A NUMERICAL STUDY ON THE AERODYNAMIC PERFORMANCE OF A SHROUDED LOW-PRESSURE TURBINE WITH SOLID AND HONEYCOMB LANDS

This paper examines how leakage flow from the blade tip of shrouded blades influences the aerodynamic performance of a two-stage shrouded LPT, considering various labyrinth seal configurations. The investigation was conducted through a steady-state 3D RANS analysis. The blade tip architecture includes two types of labyrinth seals (stepped and straight seals) and two types of casing (solid and honeycomb land). The evaluation of aerodynamic performance for both the turbine stages and the labyrinth seal was based on fundamental parameters including stage efficiency, leakage fraction, and discharge coefficient. Our investigations were classified into two topics. Firstly, the aerodynamic performance of unshrouded and shrouded blades was compared in a wide range of clearance sizes. For both blade types, as the clearance size increases, the leakage flow increases, and the isentropic efficiency of all stages decreases. However, the shrouded turbine showed a lower decrease in stage efficiency as the clearance increased in comparison to the unshrouded turbine. Secondly, the effects of casing type (solid and honeycomb lands) were compared and complex flow phenomena occurring in the tip leakage were analyzed. For this particular study's findings, it was observed that in the case of a stepped seal, the use of honeycomb land resulted in increases in both leakage flow and discharge coefficient compared to solid land, consequently leading to a decrease in stage efficiency. However, when it came to the straight seal, the utilization of honeycomb land decreased both leakage flow and discharge coefficient, thus contributing to an increase in efficiency.