Session: 03-10: Fluid Power

Paper Number: 131377

131377 - Determination of the Equivalent Rotordynamic Coefficients and Leakage of a T-Type Labyrinth Seal 

Rotating machinery requires the adequate sealing to improve the efficiency and stability by reducing the secondary leakage between high-pressure and low-pressure regions. Different types of annular gas seals are used for multiple turbomachinery applications. This includes finger, leaf, brush (for more specialized applications), hole and honeycomb patterned seals. In comparison to other configurations, labyrinth seals are mostly used due to their high robustness and low manufacturing costs in rotating machinery applications. The labyrinth seals are designed to minimize the overall leakage from the system and reduce the vibration effects due to fluid structure interactions. The recently introduced T-type labyrinth seal contributes to reducing the fluid-induced excitations in the aero-engines in comparison to conventional labyrinth seals. The stability of the seals is an important factor but keeping the minimum leakage from the system is also a main parameter for labyrinth seals. This study is focused on identifying the key parameters affecting the seal leakage and propose an optimized design parameters to lessen the overall leakage effects through the labyrinth seal. Seal clearance from the rotor surface plays an important role in the performance and efficiency of the seal in terms of rotor dynamics and leakage rate. Therefore, a parametric analysis is required to determine the optimal clearance which not only reduces the leakage but also minimizes the overall contribution to the vibration of the system. It is known that the T-type seals have a T shape teeth which provides a greater increase in the inward radial aerodynamic force. This inward force is due to the enhanced Lomakin effect of the seal flow field. The earlier research has shown that the leakage of T-type labyrinth seal is approximately 23.6% to 25.3% less than the straight through (i.e., conventional) labyrinth seals by keeping the same tip clearance and axial length for the seal. This paper focuses on performing the sensitivity analysis using the design of experiments (DOEs) along with the steady-state computational fluid dynamics (CFD) to determine the optimum tip clearance for the reduced leakage rate of a T-type labyrinth seal. Since the fluid-induced excitations play a significant role in the rotordynamic system, equivalent rotordynamic coefficients are extracted using steady-state CFD simulation based on the circular whirl orbit and perturbation analysis, where the small perturbation is applied to the rotor, which is generally 10% of the seal clearance. In this study, conventional labyrinth seal is numerically modelled at first, and the model is verified through test results in the existing literature. In addition, the numerical results are also compared with existing simulation results in literature. Furthermore, a comparatively analysis is carried out with the conventional seal designs to validate the stability, consistency and accuracy of the results. The effective damping of conventional and T-type labyrinth seals is also calculated using the equivalent rotordynamic coefficients. The previous research on the T-type seals is used for benchmarking and validation of the analysis. In conclusion this study highlights the key factors contributing in the overall seal leakage and propose the design parameters to reduce the overall seal leakage. The fluid induced vibration are also incorporated in the analysis to ensure that the seal clearance is not contributing to the overall vibration of the system.

Presenting Author: Muhammad Mubashar Ashraf Virginia Polytechnic Institute and State University