Impact of Frequency Dependence of Gas Labyrinth Seal Rotordynamic Coefficients on Centrifugal Compressor Stability

Vannini, Giuseppe; Thorat, Manish; Childs, Dara W.; Libraschi, Mirko

doi:10.1115/gt2010-22039

Cited by 5 publications

(2 citation statements)

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“…The latest research results show that many annular seals possess frequency-dependent rotordynamic coefficients, including the labyrinth seal [16,17], pocket damper seal [17], hole-pattern seal [18,19], etc. Interaction between the acoustic waves in a circumferential annulus and the rotor excitation frequency is the cause of the frequency dependency [20].…”

Section: Introductionmentioning

confidence: 99%

Orbit Decomposition Method for Rotordynamic Coefficients Identification of Annular Seals

et al. 2021

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The elliptical orbit whirl model is widely used to identify the frequency-dependent rotordynamic coefficients of annular seals. The existing solution technique of an elliptical orbit whirl model is the transient computational fluid dynamics (CFD) method. Its computational time is very long. For rapid computation, this paper proposes the orbit decomposition method. The elliptical whirl orbit is decomposed into the forward and backward circular whirl orbits. Under small perturbation circumstances, the fluid-induced forces of the elliptical orbit model can be obtained by the linear superposition of the fluid-induced forces arising from the two decomposed circular orbit models. Due to that the fluid-induced forces of circular orbit, the model can be calculated with the steady CFD method, and the transient computations can be replaced with steady ones when calculating the elliptical orbit whirl model. The computational time is significantly reduced. To validate the present method, its rotordynamic results are compared with those of the transient CFD method and experimental data. Comparisons show that the present method can accurately calculate the rotordynamic coefficients. Elliptical orbit parameter analysis reveals that the present method is valid when the whirl amplitude is less than 20% of seal clearance. The effect of ellipticity on rotordynamic coefficients can be ignored.

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Section: Introductionmentioning

confidence: 99%

Orbit Decomposition Method for Rotordynamic Coefficients Identification of Annular Seals

et al. 2021

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“…The numerical results presented by Thorat and Childs 24 show frequency dependence of stiffness and damping coefficients of labyrinth seals when rotor speed approaching to Mach 1. Vannini et al 25 numerically investigated the effect of frequency dependence of labyrinth seal rotordynamic coefficients on centrifugal compressor stability, and pointed out that stability analysis performed with the original model without taking into account frequency-dependent coefficients are conservative. Thus, it is important to determine the frequencydependent rotordynamic coefficients of the labyrinth seal for correctly predicting the rotor stability.…”

Section: Introductionmentioning

confidence: 99%

Numerical comparisons of rotordynamic characteristics for three types of labyrinth gas seals with inlet preswirl

Feng

2016

Proceedings of the Institution of Mechanical Engineers, Part A:

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Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates are presented and compared with three types of labyrinth gas seals, which include a tooth-on-stator (TOS) labyrinth seal, a tooth-on-rotor (TOR) labyrinth seal, and an interlocking-tooth (INT) labyrinth seal. These three labyrinth seals represent the typical labyrinth seal designs used in rotating machinery as shaft seals to limit leakage and ensure a robust rotordynamic design. The three labyrinth seals have the identical rotor diameter, sealing clearance, tooth number, and profile. Using a proposed transient computational fluid dynamics (CFD) method based on the multi-frequency elliptical orbit whirling model, transient CFD solutions were conducted at rotational speed of 7000 r/min, inlet pressure of 6.9 bar, ambient out pressure, and three inlet preswirl ratios up to 1.0. The accuracy and availability of the present transient CFD method were demonstrated with the experiment data of frequency-dependent rotordynamic coefficients of the TOS labyrinth seal with different rotational speeds and inlet preswirl ratios. The rotordynamic coefficients were generally well-predicted by the present numerical method, with direct stiffness and direct damping modestly under predicted ($67% and $34%, respectively). Numerical results compared leakage flow rates and rotordynamic coefficients for three labyrinth seals, while paying special attention to the cross-coupling stiffness, effective damping, crossover frequency, and swirl velocity development along the flow direction in seal. The INT and TOS labyrinth seals consistently leaks less than the TOR labyrinth seal across all preswirl ratios, respectively, by factors of 27% and 5%. The TOS labyrinth seal is relatively most stable, followed by the INT labyrinth seal and then the TOR labyrinth seal. The stability of labyrinth seals can be improved by reducing the swirl velocity at the seal entrance (installing anti-swirl devices) and in the seal cavity (applying ''textured'' or ''pocket'' stator surfaces).

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Prediction of Rotordynamic Coefficients for Short Labyrinth Gas Seals Using Computational Fluid Dynamics

Pugachev

Kleinhans

Gaszner

2012

Journal of Engineering for Gas Turbines and Power

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The analysis is presented for the computational fluid dynamics (CFD)-based modeling of short labyrinth gas seals. Seal leakage performance can be reliably predicted with CFD for a wide operating range and various sealing configurations. Prediction of seal influence on the rotordynamic stability, however, is a challenging task requiring relatively high comptiter processing power. A full 3D eccentric CFD model of a short staggered three-tootJi-on-stator labyrinth seal is built in ANSYS CFX. An extensive grid independence sttidy is carried out showing influence of the grid refinement on the stiffness coefficients. Three methods for the prediction of stiffness and damping coefficients as well as the effect of turbulence modeling, boundary conditions, and solver parameters are presented. The rest of the paper shows the results of a parameter variation (inlet pressure, preswirl, and shaft rotational speed] for two labyrinth seals with a tooth radial clearance of 0.5 mm and 0.27 mm, respectively. The latter was compared with experimental data in Pugachev

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Impact of Frequency Dependence of Gas Labyrinth Seal Rotordynamic Coefficients on Centrifugal Compressor Stability

Cited by 5 publications

References 0 publications

Orbit Decomposition Method for Rotordynamic Coefficients Identification of Annular Seals

Orbit Decomposition Method for Rotordynamic Coefficients Identification of Annular Seals

Numerical comparisons of rotordynamic characteristics for three types of labyrinth gas seals with inlet preswirl

Prediction of Rotordynamic Coefficients for Short Labyrinth Gas Seals Using Computational Fluid Dynamics

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