Radial growth predictions of rotating labyrinth seals are conventionally obtained from one-dimensional analytical models. However, these predictions quantitatively differ within themselves by about 5-500%. Simulations using three-dimensional finite element method (FEM) are carried out in this paper for a typical labyrinth seal, subjected to high rotational speed and temperature, for a range of radius-to-length ratio of the rotor. Taking the predicted values by FEM as reference, four analytical models are assessed and their errors are quantified. These errors are found to be independent of rotational speed and temperature but significantly vary with the radius-to-length ratio of the rotor. Based on this finding, simple analytical models, together with correction factor charts, are suggested. © 2018 Walter de Gruyter GmbH, Berlin/Boston.

A. Seshadri Sekhar

Department of Mechanical Engineering

B. V.S.S.S. Prasad

Sivakumar Subramanian

Deformation

finite element method

Forecasting

Gas turbines

Seals

Analytical predictions

Correction factors

HIGH ROTATIONAL SPEED

LABYRINTH SEAL

ONE DIMENSIONAL ANALYTICAL MODEL

RADIUS-TO-LENGTH RATIO

THERMAL GROWTH

THREE-DIMENSIONAL FINITE ELEMENT METHOD

Analytical models

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

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IIT Madras

International Journal of Turbo and Jet Engines

In this article, a generic framework, which takes into account of both the centrifugal and thermal effects, is introduced towards rotordynamic characterization of rotating labyrinth gas turbine seals. A well-established labyrinth seal clearance-leakage model, based on a combined three-dimensional computational fluid dynamics and finite element methodology, along with a second-order rotordynamics model is engaged. The influence of combined centrifugal and thermal radial growth on the rotordynamic characteristics of a generic rotating labyrinth gas turbine seal is explored. For a given rotational speed, the computed rotordynamic seal forces and coefficients, including the stability parameters are compared with the one without considering thermal growth (ambient condition), as a function of pressure ratio and temperature. The results show a significant variation of the crucial seal coefficients with the inclusion of thermal growth and the influence largely varies with both temperature and pressure ratio. Of particular interest is the onset of instability detected at an elevated temperature, regardless of pressure ratio, which necessitates the inclusion of thermal growth so as to avoid early rotor/seal failures. The inherent flow field investigation corroborates well with the rotordynamic characteristics of the seal and its combined centrifugal and thermal effects. © 2017 Elsevier Ltd

International Journal of Mechanical Sciences

Rotordynamic characterization of rotating labyrinth gas turbine seals with radial growth: Combined centrifugal and thermal effects

The present work proposes a design procedure along with guidelines for the choice of initial clearance of a typical rotating gas turbine seal in a secondary air system. The basis for the design is to prevent seal rubbing against stator, by ensuring that the centrifugal and thermal growths of the seal are within the safe operating limits. As a case study, a six-tooth straight-through rotating labyrinth seal configuration is considered with wide ranging seal parameters, namely the seal inner radius (25-700 mm), speed (1000-5000 rad/s), temperature (200-650 °C) and pressure ratio (1.1-2.5). By means of an iterative process, which involves computational fluid dynamics and finite element analysis techniques, and with a choice of initial clearance, an extensive database is generated. The results are presented in terms of non-dimensional variables, namely seal clearance ratio, centrifugal growth ratio, thermal growth ratio, operating clearance ratio due to centrifugal growth and operating clearance ratio due to thermal growth. It is found that the value of clearance ratio depends significantly on the dimensionless radial position. For a seal clearance ratio of 0.01, at 3000 rad/s, the leakage flow rate gets reduced by 18 and 4%, respectively for pressure ratios of 1.1 and 2.5, when the centrifugal growth alone is considered. When both centrifugal and thermal growths are considered, the percentage reduction becomes about 70% for the same seal operating at 3000 rad/s and 204 °C, and it is as high as 95% at 426 °C. © 2016 Institution of Mechanical Engineers.

Fulltext

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

On the choice of initial clearance and prediction of leakage flow rate for a rotating gas turbine seal

The rotordynamic characteristics of gas turbine seals have been investigated in numerous previous studies. However, the effects of centrifugal growth were often ignored; and no extensive studies have been reported. To this end, the present work examines numerically the influence of centrifugal growth on the rotordynamic characteristics of a typical rotating labyrinth gas turbine seal. A computational framework developed based on combined 3D FE/CFD methodology along with an appropriate rotordynamic model has been employed. For a given seal clearance and eccentricity, various flow and operating conditions are investigated covering a range of pressure ratios and rotational speeds. A substantial variation in both the cross-coupled stiffness and direct damping is noticed and the influence increases with rotational speed. The stability characteristics reveal that centrifugal growth of the seal has a detrimental effect at relatively low pressure ratio and high rotational speed combinations. The computational approach is validated against a typical labyrinth seal results reported in the literature. © 2016 Elsevier Ltd. All rights reserved.

Tribology International

Rotordynamic characteristics of rotating labyrinth gas turbine seal with centrifugal growth

A computational methodology is proposed to predict the running clearance of a six-tooth straight-through rotating labyrinth seal numerically by taking into account both the centrifugal and thermal growths. Four different angular velocities ranging from 0 to 3000 rad/s are chosen to study the influence of rotation on the leakage flow rate. The detailed leakage flow fields and the structural deformations are presented. Further, different pressure ratios in the range of 1.1 to 2.5 have been investigated for a wide range of initial clearances. The methodology is validated against the available data in the literature. It is found out that there is a significant reduction in leakage flow rate by incorporating the radial growth for a particular operating condition. However, for a given initial clearance, the rotation has negligible effect on the reduction in the leakage flow rate, except at pressure ratios lower than 1.7. Further; the rotation has more prominent effect for smaller clearance values. Copyright © 2013 by ASME.

Proceedings of the ASME Turbo Expo

Performance analysis of a rotating labyrinth seal with radial growth

Computational and experimental investigations are carried out to estimate leakage flow rate in a static straight-through labyrinth seal. Tests were conducted over a range of pressure ratios, varying from 1.003 to 1.897, for three clearance values of 0.2, 0.36 and 0.6 mm respectively. The measured values of leakage flow parameter are corroborated with the results obtained from the simulations using FLUENT computer package. The agreement was within 8.6%. The flow details, e.g., the stream line pattern, velocity vectors, static pressure and turbulent kinetic energy in a typical seal passage, are presented. © 1997 by ASME.

Computational and experimental investigations of straight -through labyrinth seals

ANSYS Mechanical APDL for Finite Element Analysis

Chapter and Section Numbering for Selected ANSYS Mechanical APDL 17.2 Documentation

Assessment of Analytical Predictions for Radial Growth of Rotating Labyrinth Seals

Journal	Data powered by TypesetInternational Journal of Turbo and Jet Engines
Publisher	Data powered by TypesetWalter de Gruyter GmbH
ISSN	03340082
Open Access	No