Prediction of Incompressible Flow in Labyrinth Seals

1986 ◽  
Vol 108 (1) ◽  
pp. 19-25 ◽  
Author(s):  
D. L. Rhode ◽  
J. A. Demko ◽  
U. K. Traegner ◽  
G. L. Morrison ◽  
S. R. Sobolik
Keyword(s):  
Numerical Model ◽  
Incompressible Flow ◽  
Computer Code ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Labyrinth Seals ◽  
New Approach ◽  
Cpu Time ◽  
Carry Over ◽  
Good Agreement

A new approach was developed and tested for alleviating the substantial convergence difficulty which results from implementation of the QUICK differencing scheme into a TEACH-type computer code. It is relatively simple, and the resulting CPU time and number of numerical iterations required to obtain a solution compare favorably with a previously recommended method. This approach has been employed in developing a computer code for calculating the pressure drop for a specified incompressible flow leakage rate in a labyrinth seal. The numerical model is widely applicable and does not require an estimate of the kinetic energy carry-over coefficient for example, whose value is often uncertain. Good agreement with measurements is demonstrated for both straight-through and stepped labyrinths. These new detailed results are examined, and several suggestions are offered for the advancement of simple analytical leakage as well as rotordynamic stability models.

Simulation of Subsonic Flow Through a Generic Labyrinth Seal

1986 ◽  
Vol 108 (4) ◽  
pp. 674-680 ◽  
Author(s):  
D. L. Rhode ◽  
S. R. Sobolik
Keyword(s):  
Subsonic Flow ◽  
Computer Code ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Labyrinth Seals ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Flow Through ◽  
Carry Over ◽  
Single Cavity

A new method for predicting the leakage through labyrinth seals has been developed and is shown to provide realistic results which agree with measurements. It utilizes a finite-difference computer code which was developed in order to compute the pressure drop across a single cavity of the seal. This quantity is obtained at several leakage flow Mach numbers to be used subsequently in predicting the leakage rate. The model is widely applicable and does not require an estimate of the kinetic energy carry-over coefficient, whose value is often uncertain for many untested configurations. Detailed cavity distributions of basic flowfield quantities are also presented and examined. Specifically, the predicted results of four seal leakage mass flow rates at given cavity inlet pressure and temperature are compared, and important variations are examined. Also, realistic approximations of flow variable distributions within a single cavity are made from the included figures to assist in the development of analytical methods.

Tooth Thickness Effect on the Performance of Gas Labyrinth Seals

1992 ◽  
Vol 114 (4) ◽  
pp. 790-795 ◽  
Author(s):  
D. L. Rhode ◽  
R. I. Hibbs
Keyword(s):  
Finite Difference ◽  
Computer Code ◽  
Thickness Effect ◽  
Turbulence Energy ◽  
Length Scale ◽  
Labyrinth Seals ◽  
Cpu Time ◽  
Reservoir Conditions ◽  
Turbulence Length ◽  
Turbulence Length Scale

A previously validated finite difference computer code was revised to allow the specification of upstream and downstream reservoir conditions as boundary conditions, whereas the domain extends only from the seal inlet to outlet plane. As a result of this special revision, the required execution CPU time is approximately only one hour on a VAX 8650 computer for three-cavity, straight-through seals. A parametric study focusing on tooth thickness showed that streamwise swirl development was only slightly higher for the thickest tooth. Further, for straight-through seals it was found that leakage is almost independent of tooth thickness and that the second cavity yields a definite increase in turbulence energy and turbulence length scale over the first cavity.

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.

Hybrid Brush Pocket Damper Seals for Turbomachinery

2000 ◽  
Vol 122 (2) ◽  
pp. 330-336 ◽  
Author(s):  
Hector E. Laos ◽  
John M. Vance ◽  
Steven E. Buchanan
Keyword(s):  
Active Vibration Control ◽  
Design Feature ◽  
Aircraft Engine ◽  
Computer Code ◽  
Labyrinth Seal ◽  
Dual Function ◽  
Rotating Shaft ◽  
Labyrinth Seals ◽  
Low Leakage ◽  
Brush Seal

Pocket damper seals perform a dual function: both sealing the pressurized gas around a rotating shaft and providing large amounts of vibration damping. The annular cavity between the labyrinth seal teeth is subdivided into separate annular cavities around the circumference of the rotor by partitioning walls. Also, the upstream and downstream teeth have different radial clearances to the rotor. These seals have been shown to provide a remarkable amount of direct damping to attenuate vibration in turbomachinery, but they generally leak more than conventional labyrinth seals if both seals have the same minimum clearance. Conversely, brush seals allow less than half the leakage of labyrinth seals, but published test results show no significant amount of damping. They are considered to be a primary choice for the seals in new aircraft engine designs because of their low leakage. This paper will describe a recently invented hybrid brush/pocket damper seal that combines high damping with low leakage. Previous brush seal results were studied and calculations were made to select a brush seal to combine with the pocket damper design. The result is a hybrid seal with high damping and low leakage. A special design feature can also allow active vibration control as a bonus benefit. A computer code written for the original pocket damper seal was modified to include the brush element at the exit blade. Results from the computer code indicate that the hybrid seal can have less leakage than a six bladed (or 6 knives) labyrinth seal along with orders of magnitude more damping. Experimental evaluations of the damping and leakage performance of the hybrid seal are being conducted by the authors. The experimental work reported here tested the damping capability of the new hybrid brush seal by exciting the seal journal through an impedance head. A conventional six-bladed labyrinth seal of the same working dimensions was also tested. The brush hybrid pocket damper seal is found to leak less than the labyrinth seal while producing two to three times more damping than the original pocket damper seal (orders of magnitude more than the conventional labyrinth). [S0742-4795(00)01102-9]

Numerical Investigations of Leakage Performance Degradations in Labyrinth and Flexible Seals Due to Wear

2020 ◽  
Author(s):  
Xinbo Dai ◽  
Xin Yan ◽  
Kun He ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Labyrinth Seal ◽  
Leakage Rate ◽  
Labyrinth Seals ◽  
Element Analysis ◽  
Numerical Investigations ◽  
Forward Bending ◽  
The Finite Element Analysis ◽  
Before And After ◽  
Computational Fluid Dynamics Cfd ◽  
Wear Damage

Abstract The Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) methods are utilized to investigate the leakage performance degradations in two kinds of flexible seals (i.e. forward bending and backward bending) and two kinds of shroud labyrinth seals (i.e. with straight fins and chamfered fins) in rubbing events. With the existing experimental data, FEA methods for contacting simulations and CFD methods for leakage rate and flow pattern predictions are carefully examined. The wear characteristic and leakage performance between labyrinth seals and flexible seals are compared before and after rub. The results show that, in rubbing process, the labyrinth seal with straight (symmetrical) fins is likely to undergo the mushrooming damage, whereas the labyrinth seal with chamfered (asymmetrical) fins is likely to undergo the tooth-bending damage. In rubbing process, compared with the labyrinth seal, the flexible seal has a superior characteristic in resisting the wear damage due to increased flexibility of fin. For a labyrinth seal with 0.3mm design clearance and a flexible seal with 0.15mm design clearance, the 0.5mm radial displacement of rotor will result in 110% increase of leakage rate for labyrinth seal, and 7% increase of leakage rate for flexible seal after wear. Under the same conditions, the forward bending flexible seal has a lower leakage rate than the backward bending flexible seal before and after rub.

Experimental and Computational Analysis of a Gas Compressor Windback Seal

2007 ◽  
Author(s):  
G. L. Morrison ◽  
Adnan Al-Ghasem
Keyword(s):  
Standard Deviation ◽  
Gas Flow ◽  
Computational Analysis ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Screw Thread ◽  
Shaft Speed ◽  
Flow Paths ◽  
Carry Over

A gas windback seals is similar to a labyrinth seal except the cavity is one continuous channel which winds around the shaft like a screw thread. One application is in gas compressors to isolate lubrication oil from the gas flow paths. A CFD based study of clearance, pressure ratio, and shaft speed has been performed. One seal geometry was experimentally studied to provide verification of the CFD accuracy. An empirical model for the leakage rate has been developed which fits the data with a standard deviation of 0.8%. The effects of pressure ratio and shaft speed upon the leakage rate are independent of each other. Analysis of the CFD results indicate that the kinetic energy carry over coefficient is substantially less for the windback seal operating at low differential pressures and gas densities than for a labyrinth seal operating under typical conditions.

Hybrid Brush Pocket Damper Seals for Turbomachinery

1999 ◽  
Author(s):  
Hector E. Laos ◽  
John M. Vance ◽  
Steven E. Buchanan
Keyword(s):  
Active Vibration Control ◽  
Design Feature ◽  
Aircraft Engine ◽  
Computer Code ◽  
Labyrinth Seal ◽  
Dual Function ◽  
Rotating Shaft ◽  
Labyrinth Seals ◽  
Low Leakage ◽  
Brush Seal

Pocket damper seals perform a dual function: both sealing the pressurized gas around a rotating shaft and providing large amounts of vibration damping. The annular cavity between the labyrinth seal teeth is subdivided into separate annular cavities around the circumference of the rotor by partitioning walls. Also, the upstream and downstream teeth have different radial clearances to the rotor. These seals have been shown to provide a remarkable amount of direct damping to attenuate vibration in turbomachinery, but they generally leak more than conventional labyrinth seals if both seals have the same minimum clearance. Conversely, brush seals allow less than half the leakage of labyrinth seals, but published test results show no significant amount of damping. They are considered to be a primary choice for the seals in new aircraft engine designs because of their low leakage. This paper will describe a recently invented hybrid brush/pocket damper seal that combines high damping with low leakage. Previous brush seal results were studied and calculations were made to select a brush seal to combine with the pocket damper design. The result is a hybrid seal with high damping and low leakage. A special design feature can also allow active vibration control as a bonus benefit. A computer code written for the original pocket damper seal was modified to include the brush element at the exit blade. Results from the computer code indicate that the hybrid seal can have less leakage than a six bladed (or 6 knives) labyrinth seal along with orders of magnitude more damping. Experimental evaluations of the damping and leakage performance of the hybrid seal are being conducted by the authors. The experimental work reported here tested the damping capability of the new hybrid brush seal by exciting the seal journal through an impedance head. A conventional six-bladed labyrinth seal of the same working dimensions was also tested. The brush hybrid pocket damper seal is found to leak less than the labyrinth seal while producing two to three times more damping than the original pocket damper seal, (orders of magnitude more than the conventional labyrinth).

Dynamic Response Analysis of Balance Drum Labyrinth Seal Groove Geometries Optimized for Minimum Leakage

2015 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Neal Morgan ◽  
Vahe Hayrapetian ◽  
Bruno Schiavello
Keyword(s):  
Dynamic Response ◽  
Dynamic Properties ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Response Analysis ◽  
Test Cases ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Overall Stability ◽  
Optimization Loop

Annular labyrinth seals often have a destabilizing effect on pump rotordynamics due to the large cross-coupled forces generated when the fluid is squeezed by an oscillating rotor. In this study several novel groove geometries are investigated for their effect on the rotordynamic coefficients of the labyrinth seal. The groove cavity geometry of a baseline 267 mm balance drum labyrinth seal with a clearance of 0.305 mm and 20 equally spaced groove cavities were optimized for minimum leakage. From the pool of possible groove designs analyzed, nine test cases were selected for maximum or minimum leakage and for a variety of groove cavity shapes. The rotordynamic coefficients were calculated for these cases using a hybrid CFD-bulk flow method. The rotordynamic coefficients obtained by this method were then used with a rotordynamic model of the entire pump to determine the overall stability. Results show that labyrinth seal’s groove shape can be optimized to generate lower leakage rates, while the effects on dynamic properties are only minimally changed. If the seal dynamic response needs to be modified in addition to targeting a lower leakage rate, for instance to exhibit increased damping values, then the leakage rate and the damping coefficient need to be set as objective functions in the optimization loop.

Incompressible flow in a labyrinth seal

1980 ◽  
Vol 100 (4) ◽  
pp. 817-829 ◽  
Author(s):  
H. Stoff
Keyword(s):  
Turbulence Model ◽  
Incompressible Flow ◽  
Computer Code ◽  
Labyrinth Seal ◽  
Main Stream ◽  
Mean Flow ◽  
Rotating Shaft ◽  
Vortex Pattern ◽  
Mean Pressure ◽  
Flow Vortex

The incompressible flow in a labyrinth seal is computed using the ‘κ−ε’ turbulence model with a pressure-velocity computer code in order to explain leakage phenomena against the mean pressure gradient. The flow is axisymmetric between a rotating shaft and an enclosing cylinder at rest. The main stream in circumferential direction induces a secondary mean flow vortex pattern inside annular cavities on the surface of the shaft. The domain of interest is one such cavity of an enlarged model of a labyrinth seal, where the finite difference result of a computer program is compared with measurements obtained by a back-scattering laser-Doppler anemometer at a cavity Reynolds number of ∼ 3 × 104and a Taylor number of ∼ 1·2 × 104. The turbulent kinetic energy and the turbulence dissipation rate are verified experimentally for a comparison with the result of the turbulence model.

Design of Experiments to Investigate Geometric Effects on Fluid Leakage Rate in a Balance Drum Seal

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Neal R. Morgan ◽  
Alexandrina Untaroiu ◽  
Patrick J. Migliorini ◽  
Houston G. Wood
Keyword(s):  
Design Of Experiments ◽  
Low Pressure ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Upstream Region ◽  
Working Fluid ◽  
Cfd Model ◽  
Labyrinth Seals ◽  
Starting Point ◽  
Designed Experiment

Annular labyrinth seals are designed as tortuous paths that force a working fluid to expand and contract repeatedly through small clearances between high and low pressure stages of turbomachinery. The resulting expansion and recirculation reduces kinetic energy of the flow and minimizes leakage rate between regions of high and low pressure through the seal. Most current seal geometries are selected based on what has worked in the past, or by incremental improvements on existing designs. In the present research, a balance drum used in a multistage centrifugal pump was chosen as a starting point. A design of experiments (DOEs) study was performed to investigate the influence of groove scale on leakage rate across the seal for a fixed pressure differential. The computational fluid dynamics (CFD) model of the selected labyrinth seal has an upstream region leading to 20 evenly spaced semicircular grooves along a 267 mm seal length, with a clearance region of 0.305 mm. The seal geometry was specified by a set of five variables. The variables allow for variation in scale of the semicircular grooves within a pattern of five independently scaled grooves repeated four times along the seal length. The seal was constructed with a parameterized CFD model in ansys-CFX as a 5 deg sector of the full 3D seal. A noncentral composite designed experiment was performed to investigate the effects of five parameters on leakage rate in the system. This study demonstrates a practical approach for investigating the effects of various geometric factors on leakage rate for balance drum seals. The empirical ten-parameter linear regression model fitted to the results of the experimental design yields suggested groove radii that could be applied to improve performance of future seals.

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