Introduction of Axisymmetric Grooves as a Tip Seal Treatment for Small-Core Turbines

Abstract

Abstract The aerodynamic penalties associated with the tip gap flow in axial turbines remains a challenging problem for turbine manufacturers. As modern gas turbines with small-core architectures are brought online, the influence of the tip gap continues to grow. While technologies to reduce tip losses have been implemented into the blades, little attention has been paid to the casing around the rotor. In this study, an introduction of axisymmetric groove enhancements for the casing are examined computationally. These studies use the National Experimental Turbine (NExT) geometry, an engine-representative high-pressure turbine blade. Steady, RANS simulations are used to assess the basic characteristics of grooves, such as depth, location, and arrangement. The objective of this introductory study was to determine the feasibility of impacting the tip leakage vortex formation and the associated losses in rotor efficiency. Furthermore, analyses were done with different tip gap heights along with both flat- and squealer-tipped blades. Tip seals with a single groove are demonstrated to improve rotor aerodynamic efficiency relative to ungrooved seals by 0.4 points when applied to flat-tipped rotor blades and 0.15 points with squealer tips. Arrays of grooves show improvements for flat-tipped blade performance by 0.76 points, while having little additional aerodynamic effect on squealer tip over single-groove designs. Finally, grooved tip seals appear to exert greater influence on turbine aerodynamic performance at larger tip gaps, indicating that grooved tip seals alter the sensitivity of rotor performance to the tip clearance gap.