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research-article

Conceptual Flutter Analysis of Labyrinth Seals Using Analytical Models. Part II: Physical Interpretation

[+] Author and Article Information
Almudena Vega

Dept. of Fluid Mechanics and Aerospace Propulsion, Universidad Polit├ęcnica de Madrid, 28040 Madrid, Spain
almudena.vega@upm.es

Roque Corral

Advanced Engineering Direction, Industria de Turbopropulsores S.A.U., 28108 Madrid, Spain
roque.corral@itpaero.es

1Corresponding author.

ASME doi:10.1115/1.4041377 History: Received July 25, 2018; Revised August 21, 2018

Abstract

A simple non-dimensional model to describe the flutter onset of labyrinth seals is presented. The linearized equations for a control volume which represents the inter-fin seal cavity, retaining the circumferential unsteady flow perturbations created by the seal vibration, are used. An analytical expression for the non-dimensional work-per-cycle is derived. It is concluded that the stability of a two-fin seal, depends on three non-dimensional parameters, which allow explaining seal flutter behavior in a comprehensive fashion. These parameters account for the effect of the pressure ratio, the cavity geometry, the fin clearance, the nodal diameter, the fluid swirl velocity, the vibration frequency and the torsion center location in a compact and interrelated form. It was found that the physics of the problem strongly depends on the non-dimensional acoustic frequency. When the discharge time of the seal cavity is much greater than the acoustic propagation time, the damping of the system is very small and the amplitude of the response at the resonance conditions is very high. The model not only provides a unified framework for the stability criteria derived by Ehrich and Abbot, but delivers an explicit expression for the work-per-cycle of a two-fin rotating seal. All the existing and well established engineering trends are contained in the model, despite its simplicity. The second part of this paper analyzes in depth the implications of the model and outlines the extension to multiple cavity seals.

Copyright (c) 2018 by ASME
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