Session: 14-02: Brush/Labyrinth Seal

Paper Number: 152291

Numerical Investigation on the Leakage Characteristics of a Straight-Through Labyrinth Seal With Novel Hole-Pattern Structures 

Labyrinth seals are used to minimize leakage flows and enhance the thermal efficiency of turbomachinery applications. Several configurations have been developed to enhance the sealing effectiveness of labyrinth seals by using honeycomb structures, however, novel hole-pattern applications remain to be accomplished. Previous experimental studies have shown that the leakage flow rate is strongly influenced by honeycomb and hole-pattern structures. Analytical models are typically used to estimate the leakage flow rate by relying on empirically derived coefficients. In literature, these coefficients are not properly correlated for both conventional and novel hole-pattern structures.

This paper aims to develop an analytical model to estimate accurate leakage flow rates by identifying the parameters influencing leakage characteristics of hole-pattern structures in labyrinth seal applications. There are limited efforts taken to investigate hole-pattern structures with labyrinth seals, therefore, conventional and novel hole-pattern structures are developed to examine the effects on the leakage characteristics in a broad range of operating conditions. In this study, the leakage characteristics of such hole-pattern structures are numerically investigated using a computational fluid dynamics (CFD) model featuring the design of experiments (DOE) and benchmark simulation cases. The Reynolds-Averaged Navier Stokes (RANS) equations were solved using ANSYS Fluent. Validation and benchmark studies were performed using Stocker and Childs test results to enhance the fidelity of the computational models. The numerical studies revealed that the vortex formation is heavily influenced by hole geometry and highlighted the effective clearance change with swirling flow in the labyrinth seal. By modulating the geometrical features of hole pattern, it is numerically shown that, sealing effectiveness is heavily dependent on clearance-to-hole diameter ratio, hole shape, and hole angle. The flow coefficients were correlated for the extensive application range of conventional and novel hole-pattern structures. Exponential behavior is observed in flow coefficients for hole-pattern structures and compared with the honeycomb results for trade-off studies. Derived flow coefficients cover an extensive geometric variation by accounting for the changes observed in turbulence kinetic energy and effective clearance that give further details about relevant flow characteristics and their influence on leakage predictions.

The numerical results show that the leakage flow rate is the function of clearance-to-hole diameter ratio in addition to the hole shape, hole angle, and hole depth. In a certain range, the novel hole-pattern structures are more effective sealing solutions than the honeycomb structures. An analytical model is proposed for the straight-through labyrinth seals which captures the sensitivity of sealing effectiveness to hole-pattern shapes. The proposed analytical model offers systematic leakage predictions for conventional and novel hole-pattern structures in preliminary design studies.

Presenting Author: Gürkan Ertuğral TRMOTOR Power Systems Inc.

Presenting Author Biography: Gurkan Ertugral is an aerothermal design engineer at TRMOTOR Power Systems Inc. Before joining his professional career, he was a research fellow at Massachusetts Institute of Technology (MIT) where he focused on problems related to experimental and computational fluid dynamics. Overall, his research interests include thermal-fluid sciences and computational methods. He has authored conference papers in ASME Turbo Expo Turbomachinery Technical Conference.

Authors:

Gürkan Ertuğral TRMOTOR Power Systems Inc.
Özhan Öksüz TRMOTOR Power Systems Inc.