Dynamic Forces From Single Gland Labyrinth Seals: Part II—Upstream Coupling

1994 ◽  
Vol 116 (4) ◽  
pp. 694-700 ◽  
Author(s):  
K. T. Millsaps ◽  
M. Martinez-Sanchez
Keyword(s):  
Azimuthal Velocity ◽  
Labyrinth Seal ◽  
Quantitative Agreement ◽  
Lumped Parameter Model ◽  
Strong Impact ◽  
Labyrinth Seals ◽  
New Model ◽  
Large Pressure ◽  
Calculated Effect ◽  
The Face

The standard lumped parameter model for flow in an eccentrically offset labyrinth seal, which assumes constant upstream and downstream boundary conditions, has been extended to include the effects of a nonuniform upstream cavity flow due to coupling. This new model predicts that the upstream perturbations in pressure and azimuthal velocity caused by this coupling can have a very strong impact on the pressure distribution in the seal gland itself. Augmentation by a factor of four, over the uniform inlet model, is predicted under some circumstances. Although no precise comparison to the experimental data with this new model was possible, due to the lack of control over the face seal venting the upstream cavity to the center hub plenum, the calculated effect of this coupling was shown to be approximately what was required to restore quantitative agreement between the data and theory. The new theory can explain the anomalously large pressure nonuniformity previously found by other authors in short seals as well as the first few glands of multicavity seals.

scholarly journals Dynamic Forces From Single Gland Labyrinth Seals: Part II — Upstream Coupling

1993 ◽  
Author(s):  
Knox T. Millsaps ◽  
Manuel Martinez-Sanchez
Keyword(s):  
Azimuthal Velocity ◽  
Labyrinth Seal ◽  
Quantitative Agreement ◽  
Lumped Parameter Model ◽  
Strong Impact ◽  
Labyrinth Seals ◽  
New Model ◽  
Large Pressure ◽  
Calculated Effect ◽  
The Face

The standard lumped parameter model for flow in an eccentrically offset labyrinth seal, which assumes constant upstream and downstream boundary conditions, has been extended to include the effects of a non-uniform upstream cavity flow due to coupling. This new model predicts that the upstream perturbations in pressure and azimuthal velocity caused by this coupling, can have a very strong impact on the pressure distribution in the seal gland itself. Augmentation by a factor of four, over the uniform inlet model, is predicted under some circumstances. Although no precise comparison to the experimental data with this new model was possible, due to the lack of control over the face seal venting the upstream cavity to the center hub plenum, the calculated effect of this coupling was shown to be approximately what was required to restore quantitative agreement between the data and theory. The new theory can explain the anomalously large pressure non-uniformity previously found by other authors in short seals as well as the first few glands of multi-cavity seals.

Synchronous Rotor Vibration Driven by Fluid Forces From a Geometrically Imperfect Labyrinth Seal

1995 ◽  
Author(s):  
Knox T. Millsaps ◽  
William C. Williston
Keyword(s):  
Labyrinth Seal ◽  
Radial Force ◽  
Lumped Parameter Model ◽  
Solution Technique ◽  
Labyrinth Seals ◽  
Fluid Forces ◽  
Lumped Parameter ◽  
Manufacturing Tolerances ◽  
Vibration Problems ◽  
Wear Damage

The radial force acting on a rotor, due to an asymmetric pressure distribution inside the seal gland, generated from a slightly non-circular single gland labyrinth seal rotating inside a circular outer casing is investigated theoretically. A fluid mechanical lumped parameter model for the flow in and out of the seal as well as the flow around the gland in the seal is developed. The model includes first and second knife imperfections as well as rotating gland depth variations. Knife non-circularity on the rotor may be due to manufacturing tolerances or defects from in service wear damage. An appropriate solution technique for the coupled one-dimensional equations is presented. Results from this model are presented that indicate these fluid induced forces are comparable in magnitude to those generated by a rotating unbalance under some conditions. Considerations for design are given for avoiding synchronous vibration problems due to non-circular labyrinth seals.

Dynamic Forces From Single Gland Labyrinth Seals: Part I—Ideal and Viscous Decomposition

1994 ◽  
Vol 116 (4) ◽  
pp. 686-693 ◽  
Author(s):  
K. T. Millsaps ◽  
M. Martinez-Sanchez
Keyword(s):  
Inviscid Flow ◽  
Labyrinth Seal ◽  
Lumped Parameter Model ◽  
Solution Technique ◽  
Linear Perturbation ◽  
Labyrinth Seals ◽  
Frequency Dependent ◽  
Lumped Parameter ◽  
Reduced Parameters ◽  
Force Decomposition

A theoretical and experimental investigation on the aerodynamic forces generated by a single gland labyrinth seal executing a spinning/whirling motion has been conducted. A lumped parameter model, which includes the kinetic energy carryover effect, is presented along with a linear perturbation solution technique. The resulting system is nondimensionalized and the physical significance of the reduced parameters is discussed. Closed-form algebraic formulas are given for some simple limiting cases. It is shown that the total cross force predicted by this model can be represented as the sum of an ideal component due to an inviscid flow with entry swirl and a viscous part due to the change in swirl created by friction inside the gland. The frequency-dependent ideal part is solely responsible for the rotordynamic direct damping. The facility designed and built to measure these frequency dependent forces is described. Experimental data confirm the validity and usefulness of this ideal/viscous decomposition. A method for calculating the damping coefficients based on the force decomposition using the static measurements only is presented.

scholarly journals Refined Turbulence Modeling for Swirl Velocity in Turbomachinery Seals

2003 ◽  
Vol 9 (6) ◽  
pp. 451-459 ◽  
Author(s):  
Namhyo Kim ◽  
David L. Rhode
Keyword(s):  
Functional Form ◽  
Source Term ◽  
Turbulence Modeling ◽  
Laser Doppler Anemometry ◽  
Labyrinth Seal ◽  
Labyrinth Seals ◽  
New Model ◽  
Swirl Velocity ◽  
Model Predictions ◽  
Turbulence Generation

A generalized new form of the rotation-sensitive source term coefficient previously proposed by Bardina and colleagues as an extension of the standardk-εturbulence model was developed. The proposal made by Bardina and colleagues focused on rotating flows without significant turbulence generation, and the result was a negative-valued constant coefficient. The new functional form developed here for the coefficient has global as well as local dependence. The new model predictions of laser Doppler anemometry measurements of swirling flows in labyrinth seals were compared with the swirl distribution measurements and with the standardk-εmodel (i.e., no rotation source term) predictions. It was found that for the labyrinth seal cases for which detailed measurements are available, the standardk-εmodel gives unsatisfactory predictions, whereas the new model gives significantly improved predictions.

scholarly journals Dynamic Forces From Single Gland Labyrinth Seals: Part I — Ideal and Viscous Decomposition

1993 ◽  
Author(s):  
Knox T. Millsaps ◽  
Manuel Martinez-Sanchez
Keyword(s):  
Inviscid Flow ◽  
Labyrinth Seal ◽  
Lumped Parameter Model ◽  
Solution Technique ◽  
Linear Perturbation ◽  
Labyrinth Seals ◽  
Frequency Dependent ◽  
Lumped Parameter ◽  
Reduced Parameters ◽  
Carry Over

A theoretical and experimental investigation on the aerodynamic forces generated by a single gland labyrinth seal executing a spinning/whirling motion has been conducted. A lumped parameter model which includes the kinetic energy carry-over effect is presented along with a linear perturbation solution technique. The resulting system is nondimensionalized and the physical significance of the reduced parameters is discussed. Closed form algebraic formulas are given for some simple limiting cases. It is shown that the total cross-force predicted by this model can be represented as the sum of an ideal component due to an inviscid flow with entry swirl and a viscous part due to the change in swirl created by friction inside the gland. The frequency dependent ideal part is solely responsible for the rotordynamic direct damping. The facility designed and built to measure these frequency dependent forces is described. Experimental data confirm the validity and usefulness of this ideal/viscous decomposition. A method for calculating the damping coefficients based on the force decomposition using the static measurements only is presented.

‘Bonbibi’ Could Wait Till Our Boss Decides: Looking at the Changing Face of the Indian Sundarbans

2021 ◽  
pp. 239386172110146
Author(s):  
Prama Mukhopadhyay
Keyword(s):  
Strong Impact ◽  
Interstate Migration ◽  
World Economic Forum ◽  
Fishing Community ◽  
Indian Sundarbans ◽  
Local Perception ◽  
Cultural Life ◽  
Previous Decade ◽  
The Face ◽  
World Economic

Internal migration constitutes a major source of steady flow of population in India, and reports published by the World Economic Forum (WEF),1 2017 state that interstate migration in the country has doubled during 2001–2011, compared to the previous decade.2 In developing countries, such migration is often considered to be an effective way for income diversification for the economically marginalised sections of the society, even though its effect on ‘human development’ is oft debated. This article would engage with this debate and bring out how migration from the Indian part of the Sundarbans to other parts of the country is not only changing the demography of the region but is also having a strong impact on the local perception and attachment towards the deltaic landscape. By bringing in ethnographic details from a village in the Indian Sundarbans, which was predominately inhabited by the fishing community earlier, this article would bring out how traditional occupations like fishing are slowly losing their popularity in the face of the lure of out-migration, as the very identity of the ‘indigenous’ Sundarban fisher folks—who were once rightfully considered to be the true conservator of the forests—is changing. From there, this article would engage with the broader debate of rethinking whether migration can be considered as a positive indicator of development in such ecologically fragile areas like the Sundarban deltas, which used to indeed have a distinct economic, social and cultural life of its own.

Influence of a Honeycomb Facing on the Flow Through a Stepped Labyrinth Seal

2000 ◽  
Vol 124 (1) ◽  
pp. 140-146 ◽  
Author(s):  
V. Schramm ◽  
K. Willenborg ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Theoretical Work ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Experimental Investigations ◽  
Labyrinth Seals ◽  
Numerical Predictions ◽  
Flow Through ◽  
Aero Engines

This paper reports numerical predictions and measurements of the flow field in a stepped labyrinth seal. The theoretical work and the experimental investigations were successfully combined to gain a comprehensive understanding of the flow patterns existing in such elements. In order to identify the influence of the honeycomb structure, a smooth stator as well as a seal configuration with a honeycomb facing mounted on the stator wall were investigated. The seal geometry is representative of typical three-step labyrinth seals of modern aero engines. The flow field was predicted using a commercial finite volume code with the standard k-ε turbulence model. The computational grid includes the basic seal geometry as well as the three-dimensional honeycomb structures.

Lateral Forces From Single Gland Rotor Labyrinth Seals in Turbines

2004 ◽  
Vol 126 (3) ◽  
pp. 626-634 ◽  
Author(s):  
Bum Ho Song ◽  
Seung Jin Song
Keyword(s):  
Axial Direction ◽  
Labyrinth Seal ◽  
Turbine Stage ◽  
Labyrinth Seals ◽  
Flow Response ◽  
Lateral Forces ◽  
Downstream Flow ◽  
Shrouded Rotor ◽  
Upstream Flow ◽  
Sealing Gap

Even though interest in labyrinth seal flows has increased recently, an analytical model capable of predicting turbine flow response to labyrinth seals is still lacking. Therefore, this paper presents a new model to predict flow response in an axial turbine stage with a shrouded rotor. A concentric model is first developed, and this model is used to develop an eccentric model. Basic conservation laws are used in each model, and a nonaxisymmetric sealing gap is prescribed for the eccentric model. Thus, the two models can predict the evolution of a uniform upstream flow into a nonuniform downstream flow. In turbines with concentric shrouded rotors, the seal flow is retarded in the axial direction and tangentially underturned. In turbines with eccentric shrouded rotors, flow azimuthally migrates away from and pressure reaches its peak near the maximum sealing gap region. Finally, the rotordynamic implications of such flow nonuniformities are discussed and compared against eccentric unshrouded turbine predictions.

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

2010 ◽  
Author(s):  
Giuseppe Vannini ◽  
Manish R. Thorat ◽  
Dara W. Childs ◽  
Mirko Libraschi
Keyword(s):  
Molecular Weight ◽  
Numerical Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Labyrinth Seals ◽  
Frequency Dependent ◽  
Rotordynamic Coefficients ◽  
Frequency Independent ◽  
Rotor Surface ◽  
Independent Model

A numerical model developed by Thorat & Childs [1] has indicated that the conventional frequency independent model for labyrinth seals is invalid for rotor surface velocities reaching a significant fraction of Mach 1. A theoretical one-control-volume (1CV) model based on a leakage equation that yields a reasonably good comparison with experimental results is considered in the present analysis. The numerical model yields frequency-dependent rotordynamic coefficients for the seal. Three real centrifugal compressors are analyzed to compare stability predictions with and without frequency-dependent labyrinth seal model. Three different compressor services are selected to have a comprehensive scenario in terms of pressure and molecular weight (MW). The molecular weight is very important for Mach number calculation and consequently for the frequency dependent nature of the coefficients. A hydrogen recycle application with MW around 8, a natural gas application with MW around 18, and finally a propane application with molecular weight around 44 are selected for this comparison. Useful indications on the applicability range of frequency dependent coefficients are given.

Progressive Clearance Labyrinth Seal for Turbo-Machinery Applications

2011 ◽  
Author(s):  
Binayak Roy ◽  
Hrishikesh V. Deo ◽  
Xiaoqing Zheng
Keyword(s):  
Theoretical Models ◽  
Labyrinth Seal ◽  
Tip Clearance ◽  
Labyrinth Seals ◽  
Lower Efficiency ◽  
Thermal Transients ◽  
Low Leakage ◽  
Packing Ring ◽  
Lift Off ◽  
Large Rotor

Turbomachinery sealing is a challenging problem due to the varying clearances caused by thermal transients, vibrations, bearing lift-off etc. Leakage reduction has significant benefits in improving engine efficiency and reducing emissions. Conventional labyrinth seals have to be assembled with large clearances to avoid rubbing during large rotor transients. This results in large leakage and lower efficiency. In this paper, we propose a novel Progressive Clearance Labyrinth Seal that is capable of providing passive fluidic feedback forces that balance at a small tip-clearance. A modified packing ring is supported on flexures and employs progressively tighter teeth from the upstream to the downstream direction. When the tip-clearance reduces below the equilibrium clearance, fluidic feedback forces cause the packing ring to open. Conversely, when the tip-clearance increases above the equilibrium clearance, the fluidic feedback forces cause the packing ring to close. Due to this self-correcting behavior, the seal provides high differential pressure capability, low leakage and non-contact operation even in the presence of large rotor transients. Theoretical models for the feedback phenomenon have been developed and validated by experimental results.

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