EFFECTS OF LABYRINTH FIN WEAR ON AERODYNAMIC PERFORMANCE OF TURBINE STAGES: PART I - BENDING DAMAGES

Labyrinth seals are widely applied in turbo machines because of their geometrical simplicity, convenient installation, reliable operation and excellent sealing performance. However, in realistic operation process, they usually encounter transient conditions (starting-up, shutting down, etc.) and unavoidable vibrations, which may cause wear in the labyrinth fins. After rubbing, the sealing performance of labyrinth seal will be varied in contrast to the original design. Correspondingly, the aerodynamic efficiency of the turbine stage will be affected by the variation of leakage flow in rubbing process. However, in published literature with respect to the labyrinth seal wear, most of the attention has been paid on revealing sealing performance degradation of labyrinth seal itself. Few studies have been concentrated on the influence of labyrinth seal wear on aerodynamic performance of turbine stages. In such background, the present paper utilizes the numerical methods to investigate the effects of labyrinth seal bending damages on aerodynamic performance of turbine stages. Firstly, under several assumptions, the bending geometrical model was established to describe different degrees of bending damages. Secondly, using three-dimensional RANS simulations, the effects of effective clearance variation due to bending on leakage flow and flow fields in turbine stages were investigated. The overall performance of the turbine stages with teeth-bending damages was also compared with the original design case. The influence of the forward bending and backward bending of labyrinth seals were analyzed and compared with each other. The total-total isentropic efficiency of turbine stages, leakage rates, outlet flow angles, reaction degrees and profile static pressure distributions, entropic distributions and flow fields in seals were obtained and compared to the original design case. The results indicate that the leakage rates in the worn labyrinth seal are quite relevant to the effective clearance, especially for the backward bending damages. As the effective clearances in backward bending cases are increased by 0.2-0.6mm, the isentropic efficiency of turbine stages is decreased by about 1-2%. However, for the forward bending damages, the aerodynamic performance and leakage rates in turbine stages are not sensitive to the effective clearance.