INVESTIGATION OF STAGGERED LABYRINTH TIP SHROUD ON FLOW MECHANISM OF LOW-PRESSURE TURBINE

In this paper, the unsteady simulations of shrouded low-pressure turbine with staggered and conventional labyrinth cavities is conducted for investigations of the improvement mechanism of labyrinth structures for aerodynamic performance. Current tip shroud cavity design principle is based on the total pressure loss propogational related to leakage fraction. Staggered labyrinth seal, however, reduces the total pressure loss more than the linearly evaluation. Static pressure ratio between each fin gap is reduced in staggered labyrinth seal configuration, thus reducing the input momentum in each sub-cavity devided by fins. Secondary eddies of cavity flow is controlled and oscillations of pressure wave propogation is strengthened by circumferential migration and reduced room in each sub-cavity, resulting in stable toroidal vortices and reduction of viscous loss. Strengthened interaction in shroud outlet gap and reduced leakage fraction lead to the blockage of leakage mass flow, thus controlling the secondary loss structure of mixing of leakage jet in main flow. Research in this paper provides a reference for reducing the difficulties in the overdesign for leakage related efficiency loss in turbine design, and offers the idea for evaluating the efficiency loss more properly.