Effects of Inlet Swirl on Hot Streak Migration Across Tip Clearance and Heat Transfer on Rotor Blade Tip

This paper presents an investigation on the hot streak migration across tip clearance and heat transfer on blade tip in a high pressure (HP) gas turbine with different inlet swirl directions and clocking positions. The geometry is taken from the first stage of GE-E³ turbine engine. Two swirl directions (positive and negative) and two circumferential clocking positions (aligning with S1 nozzle leading edge and mid passage) for inlet hot streak and swirl have been employed and investigated, respectively. Two cases with only hot streak at different inlet circumferential positions are adopted as the baseline in this study. By solving the unsteady compressible Reynolds-averaged Navier-Stokes equations, the time dependent solutions were obtained. The results indicate that the influence of inlet swirl on pressure distribution focuses on the suction side. Positive swirl attracts more hot fluid to the upper endwall, when it aligns with nozzle stator leading edge. Because of the squeezing mechanism between positive swirl and leakage flow, the heat transfer on rotor blade tip is more uniform. While negative swirl increases tip leakage flow and the heat load at the first half on tip surface. In all cases with swirl, the heat load at the second half on blade tip is effectively reduced, which is good for cooling rotor blade tip. If the stator is cooled effectively, inlet positive swirl aligning with nozzle vane leading edge will be the best choice for protecting rotor blade tip. By comparing with the results of previous literature, it is concluded that whatever arrangement the blade rows locate, the swirl direction which is opposite to the leakage flow should be chosen for protecting not only blade surface but also blade tip when the inlet swirl exists.