Effect of Various Tip Clearance Squealer Design on Turbine Stage Efficiency

This paper presents investigation of nine tip squealer design variants based on full 3D Navier-Stokes CFD calculations. In particular two main design features have been studied: the impact of relative squealer cavity rim extension and the impact of pressure side squealer cavity rim inclination on stage efficiency. All these cases have been compared for two values of relative radial gaps 0.6% and 1.36%. Obtained numerical results were validated against the experimental data measured on the E³ blade cascade test rig given in the open literature. As the overall outcome for these numerical investigations two zones with different vortex structures and different sealing features have been found. Moreover the size of these zones determines the level of the tip clearance leakage and losses for various tip squealer designs. The obtained loss values and corresponding change of the stage efficiency level as well as flow structure details were compared for all studied cases, providing insight into turbine stage aerodynamics with respect to minimal and maximal radial clearance.