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

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Alexander O. Pugachev ◽  
Ulrich Kleinhans ◽  
Manuel Gaszner
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Turbulence Modeling ◽  
Labyrinth Seal ◽  
Radial Clearance ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Processing Power ◽  
Gas Seals ◽  
Stiffness And Damping

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 computer processing power. A full 3D eccentric CFD model of a short staggered three-tooth-on-stator labyrinth seal is built in ANSYS CFX. An extensive grid independence study 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 and Deckner, 2010, “Analysis of the Experimental and CFD-Based Theoretical Methods for Studying Rotordynamic Characteristics of Labyrinth Gas Seals,” Proceedings of ASME Turbo Expo 2010, Paper No. GT2010-22058.

Leakage and Rotordynamic Coefficients of Brush Seals With Zero Cold Clearance Used in an Arrangement With Labyrinth Fins

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Manuel Gaszner ◽  
Alexander O. Pugachev ◽  
Christos Georgakis ◽  
Paul Cooper
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Dynamic Test ◽  
Radial Clearance ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Stiffness Coefficients ◽  
Brush Seal ◽  
Stiffness And Damping

A brush-labyrinth sealing configuration consisting of two labyrinth fins upstream and one brush seal downstream is studied experimentally and theoretically. Two slightly different brush seal designs with zero cold radial clearance are considered. The sealing configurations are tested on the no-whirl and dynamic test rigs to obtain leakage performance and rotordynamic stiffness and damping coefficients. The no-whirl tests allow identification of the local rotordynamic direct and cross-coupled stiffness coefficients for a wide range of operating conditions, while the dynamic test rig is used to obtain both global stiffness and damping coefficients but for a narrower operating range limited by the capabilities of a magnetic actuator. Modeling of the brush-labyrinth seals is performed using computational fluid dynamics. The experimental global rotordynamic coefficients consist of an aerodynamic component due to the gas flow and a mechanical component due to the contact between the bristle tips and rotor surface. The computational fluid dynamics (CFD)–based calculations of rotordynamic coefficients provide, however, only the aerodynamic component. A simple mechanical model is used to estimate the theoretical value of the mechanical stiffness of the bristle pack during the contact. The results obtained for the sealing configurations with zero cold radial clearance brush seals are compared with available data on three-tooth-on-stator labyrinth seals and a brush seal with positive cold radial clearance. Results show that the sealing arrangement with a line-on-line welded brush seal has the best performance overall with the lowest leakage and cross-coupled stiffness. The predictions are generally in agreement with the measurements for leakage and stiffness coefficients. The seal-damping capability is noticeably underpredicted.

Segmentation Effects on Brush Seal Leakage and Rotordynamic Coefficients

2015 ◽  
Author(s):  
Alexander O. Pugachev ◽  
Manuel Gaszner ◽  
Christos Georgakis ◽  
Paul Cooper
Keyword(s):  
Electrical Discharge ◽  
Electrical Discharge Machining ◽  
Labyrinth Seal ◽  
Performance Characteristics ◽  
Radial Clearance ◽  
Single Plane ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Brush Seal ◽  
Stiffness And Damping

This paper studies the effect of brush seal segmentation on the seal performance characteristics. A brush-labyrinth sealing configuration arranged of one brush seal downstream and two labyrinth fins upstream is studied experimentally and theoretically. The studied brush seal is of welded design installed with zero cold radial clearance. The brush seal front and back rings as well as the bristle pack are segmented radially in a single plane using the electrical discharge machining technique. The segmentation procedure results in loss of bristles at the site of the cuts altering the leakage flow structure in the seal and its performance characteristics. Two test rigs are used to obtain leakage, as well as rotordynamic stiffness and damping coefficients of the seal at different pressure ratios. The CFD-based model is used to predict the seal performance and to study in detail local changes in the flow field due to the segmentation. A back-to-back comparison of the performance of non-segmented and segmented brush seals, as well as baseline labyrinth seal is provided. The obtained results demonstrate that the segmentation in general negatively affects the performance of the studied brush-labyrinth sealing configuration. However, the segmented brush seal shows increased direct damping coefficients.

scholarly journals Rotordynamic Coefficient and Leakage Test Results for Interlock and Tooth-on-Stator Labyrinth Seals

1988 ◽  
Author(s):  
Dara W. Childs ◽  
David A. Elrod ◽  
Keith Hale
Keyword(s):  
Labyrinth Seal ◽  
Damping Coefficient ◽  
Test Results ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Leakage Test ◽  
Stiffness And Damping ◽  
Rotordynamic Coefficient

Test results (leakage and rotordynamic coefficients) are presented for an interlock and tooth-on-stator labyrinth seals. Tests were carried out with air at speeds out to 16,000 cpm and supply pressures up to 7.5 bars. The rotordynamic coefficients consist of direct and cross-coupled stiffness and damping coefficients. Damping-coefficient data have not previously been presented for interlock seals. The test results support the following conclusions: (a) The interlock seal leaks substantially less than labyrinth seals. (b) Destabilizing forces are lower for the interlock seal. (c) The labyrinth seal has substantially greater direct damping values than the interlock seal. A complete rotordynamics analysis is needed to determine which type of seal would yield the best stability predictions for a given turbomachinery unit.

Measured Rotordynamic and Leakage Characteristics of a Tooth-on-Rotor Labyrinth Seal With Comparisons to a Tooth-on-Stator Labyrinth Seal and Predictions

2015 ◽  
Author(s):  
Stephen P. Arthur ◽  
Dara W. Childs
Keyword(s):  
Cavity Length ◽  
Labyrinth Seal ◽  
Diameter Ratio ◽  
Radial Clearance ◽  
Rotor Speed ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Leakage Characteristics ◽  
Identical Diameter ◽  
Length To Diameter Ratio

Rotordynamic and leakage data are presented for a see-through tooth-on-rotor (TOR) labyrinth seal with comparisons to a see-through tooth-on-stator (TOS) labyrinth seal. Measurements for both seals are also compared to predictions from XLLaby. Both seals have identical diameter and can be considered as relatively long labyrinth seals. The TOR seal has a length-to-diameter ratio of 0.62, whereas the TOS seal is longer and has a length-to-diameter ratio of 0.75. Both seals also differ by number of teeth, tooth height, and tooth cavity length. TOR labyrinth tests were carried out at an inlet pressure of 70 bar-a (1,015 psia), pressure ratios of 0.4, 0.5, and 0.6, rotor speeds up to 20,200 rpm, a radial clearance of 0.1 mm (4 mils), and three preswirl ratios. For comparison, TOS labyrinth tests were run at identical conditions as the TOR tests but for only one positive preswirl ratio. TOR labyrinth measurements show a pronounced dependence of rotordynamic coefficients on rotor speed, especially when compared to prior documented TOS labyrinth seal tests run at a radial clearance of 0.2 mm (8mils). The TOR labyrinth cross-coupled stiffness is higher in magnitude and increases at a higher rate than that of the TOS labyrinth across all test speeds. However, the TOR labyrinth effective damping was determined to be greater due to higher measurements of direct damping. Measured leakage rates for the TOR labyrinth were approximately 5–10% less than the TOS labyrinth. XLLaby underpredicted the rotordynamic coefficients for both seals. However, as with measurements, it predicted the TOR labyrinth to have higher effective damping than the TOS labyrinth.

Performance Evaluation of Gas Turbine Labyrinth Seals Using Computational Fluid Dynamics

2007 ◽  
Author(s):  
Bambang I. Soemarwoto ◽  
Johan C. Kok ◽  
Koen M. J. de Cock ◽  
Arjen B. Kloosterman ◽  
Gerrit A. Kool ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Stokes Equations ◽  
Real Life ◽  
Labyrinth Seal ◽  
Test Case ◽  
Analysis Tool ◽  
Labyrinth Seals ◽  
Seal Design ◽  
Flow Through

The paper presents an investigation on the characteristics of flow through labyrinth seals. The focus of the paper lies in the application of the Computational Fluid Dynamics (CFD) methodology. The Reynolds-Averaged Navier-Stokes equations are employed as the flow governing equations. Turbulence is incorporated through a variant of the two-equation k-ω turbulence model. Three test cases are considered. The first test case concerns a labyrinth seal configuration with a honeycomb land. The computational results are compared to those obtained from seal test rig measurements. The second test case addresses the same labyrinth seal where the honeycomb land is replaced by a solid smooth land. The third test case addresses the flow through a labyrinth seal with canted knives. The CFD method is considered as an analysis tool complementary to rig-testing and enables investigating the effect of new seal design features. Additionally CFD is seen as a tool to support the correct representation of test-data in semiempirical engineering models for seal design. An industrial perspective is presented towards the exploitation of these modeling capabilities for real-life design of seals.

Measurements of the Leakage and Rotordynamic Performance of Interlocking Labyrinth Seals

2018 ◽  
Author(s):  
Keith Gary ◽  
Dara W. Childs ◽  
Mauricio A. Ramirez
Keyword(s):  
Dynamic Pressure ◽  
Labyrinth Seal ◽  
Magnetic Bearings ◽  
Radial Clearance ◽  
Labyrinth Seals ◽  
Pressure Transducers ◽  
Rotordynamic Coefficients ◽  
Frequency Independent ◽  
Improved Stability ◽  
Reaction Forces

Leakage and rotordynamic measurements are presented for an interlocking-labyrinth gas seal. Magnetic bearings and differential-pressure transducers are used to measure dynamic forces in the labyrinth seal following the approach of Wagner et al. in 2009. Magnetic bearings precess the rotor creating a dynamic pressure wave that is measured and integrated to find the reaction forces. The interlocking seal has 3 teeth on the stator and 2 teeth on the rotor creating 4 cavities. Each cavity has an axial length of 6 mm, and all teeth have a 5 mm height. Teeth on the rotor and stator, respectively, create a 0.2 mm radial clearance with respect to the stator and rotor. All tests are conducted at ∼ 167 Hz (10 krpm) rotor speed with, and without, swirl brakes for a range of precession frequencies from 10–50 Hz forward and backward. Inlet pressure is varied between 2.75 ∼ 4.83 bar, and pressure ratios vary between 0.5 ∼ 0.8. Static results are presented for leakage, inlet preswirl, and cavity pressure. Dynamic results are presented for rotordynamic coefficients. Dynamic results show behavior that is unique to each cavity and are presented for the entire seal as well as for each cavity individually. Cross-coupled stiffness of the entire seal increases with increasing precession frequency, yet all other rotordynamic coefficients are frequency independent. The seal shows improved stability via increased effective damping with the use of swirl brakes when considering the entire seal. Negative direct damping values are seen in all but the third cavity.

Experimental Results for Labyrinth Gas Seals With Honeycomb Stators: Comparisons to Smooth-Stator Seals and Theoretical Predictions

1989 ◽  
Vol 111 (1) ◽  
pp. 161-168 ◽  
Author(s):  
Larry Hawkins ◽  
Dara Childs ◽  
Keith Hale
Keyword(s):  
Flow Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Experimental Results ◽  
Test Results ◽  
Labyrinth Seals ◽  
Model Predictions ◽  
Theoretical Predictions ◽  
Gas Seals ◽  
Stiffness And Damping

Experimental measurements are presented for the rotordynamic stiffness and damping coefficients of a teeth-on-rotor labyrinth seal with a honeycomb stator. Inlet circumferential velocity, inlet pressure, rotor speed, and seal clearance are primary variables. Results are compared to (a) data for teeth-on-rotor labyrinth seals with smooth stators, and (b) analytical predictions from a two-control-volume compressible flow model. The experimental results show that the honeycomb-stator configuration is more stable than the smooth-stator configuration at low rotor speeds. At high rotor speeds, the stator surface does not affect stability. The theoretical model predicts the cross-coupled stiffness of the honeycomb-stator seal correctly within 25 percent of measured values. The model provides accurate predictions of direct damping for large clearance seals; however, the model predictions and test results diverge with increasing running speed. Overall, the model does not perform as well for low clearance seals as for high clearance seals.

CFD-Predicted Rotordynamic Coefficients for a 20-Teeth-on-Stator Labyrinth Seal at High Supply Pressure Conditions

2012 ◽  
Author(s):  
Alexander O. Pugachev ◽  
Heiko Degen
Keyword(s):  
Experimental Data ◽  
Gas Turbines ◽  
Goodness Of Fit ◽  
Labyrinth Seal ◽  
Coefficient Of Determination ◽  
Radial Clearance ◽  
Rotordynamic Coefficients ◽  
Supply Pressure ◽  
Cfd Method ◽  
Stiffness And Damping

A twenty-teeth-on-stator labyrinth seal with a tooth radial clearance of 0.1 mm is modeled using a CFD method to predict leakage performance, as well as stiffness and damping coefficients. The calculations are performed at a supply pressure of 70 bar for three shaft rotational speeds (10200 rpm, 15200 rpm, and 20200 rpm), three preswirl ratios (low, medium, and high), and three pressure ratios (0.1, 0.35, and 0.5). The predicted performance of the seal is compared to experimental data obtained by Picardo and Childs (Picardo, A. and Childs, D.W., 2005, “Rotor-dynamic Coefficients for a Tooth-on-Stator Labyrinth Seal at 70 Bar Supply Pressures: Measurements Versus Theory and Comparison to a Hole-Pattern Stator Seal,” ASME J. Eng. Gas Turbines Power, 127, pp. 843–855). The results from CFD simulations follow the experimental data. Leakage performance is underpredicted by up to 19.8%. Direct and cross-coupled stiffness coefficients are in reasonable agreement with the measurements. However, predicted cross-coupled stiffness increases slower with increasing preswirl ratio than the experimental cross-coupled stiffness. Direct damping is also in agreement with the measured values with the exception of the high preswirl ratio at 20200 rpm. Cross-coupled damping reveals the largest deviations between predictions and experiments. Additionally, the coefficient of determination is calculated for all experimental rotordynamic coefficients to estimate the goodness of fit for the raw test data.

Performance Analysis of Hybrid Brush Pocket Damper Seals Using Computational Fluid Dynamics

2016 ◽  
Author(s):  
Alexander O. Pugachev ◽  
Clemens Griebel ◽  
Stacie Tibos ◽  
Bernard Charnley
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Excitation Frequency ◽  
Operating Conditions ◽  
Single Frequency ◽  
Cfd Model ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Brush Seal ◽  
Stiffness And Damping

In this paper, a hybrid brush pocket damper seal is studied theoretically using computational fluid dynamics. In the hybrid sealing arrangement, the brush seal element with cold clearance is placed downstream of a 4-bladed, 8-pocket, fully partitioned pocket damper seal. The new seal geometry is derived based on designs of short brush-labyrinth seals studied in previous works. Transient CFD simulations coupled with the multi-frequency rotor excitation method are performed to determine frequency-dependent stiffness and damping coefficients of pocket damper seals. A moving mesh technique is applied to model the shaft motion on a predefined whirling orbit. The rotordynamic coefficients are calculated from impedances obtained in frequency domain. The pocket damper seal CFD model is validated against available experimental and numerical results found in the literature. Bristle pack in the brush seal CFD model is described as porous medium. The applied brush seal model is validated using the measurements obtained in previous works from two test rigs. Predicted leakage characteristics as well as stiffness and damping coefficients of the hybrid brush pocket damper seal are presented for different operating conditions. In this case, the rotordynamic coefficients are calculated using a single-frequency transient simulation. By adding the brush seal, direct stiffness is predicted to be significantly decreased while effective damping shows a more moderate or no reduction depending on excitation frequency. Effective clearance results indicate more than halved leakage compared to the case without brush seal.

CFD Prediction and Test Results of Stiffness and Damping Coefficients for Brush-Labyrinth Gas Seals

2010 ◽  
Author(s):  
Alexander O. Pugachev ◽  
Martin Deckner
Keyword(s):  
Porous Medium ◽  
Three Dimensional ◽  
Great Influence ◽  
Dynamic Test ◽  
Labyrinth Seal ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Brush Seal ◽  
Gas Seals ◽  
Stiffness And Damping

This paper presents ongoing investigations on calculation and measurement of rotordynamic coefficients for brush-labyrinth gas seals. The seals are tested on static and dynamic test rigs to measure leakage, pressure distribution, and seal specific forces. To predict seal performance a full three-dimensional eccentric CFD model is considered. Rotordynamic coefficients are calculated using the whirling rotor method. The bristle pack of the brush seal is modeled using the porous medium approach. The prediction results show some deviations in absolute values of stiffness and damping coefficients in comparison with the experimental values, but the trends are similar. Comparing with a staggered labyrinth seal, the brush seal improves rotordynamic characteristics in most cases. Position of the brush seal in sealing configuration has a great influence on the stiffness and damping coefficients, while leakage performance remains relatively unaffected. The capability of the brush seal model based on the porous medium approach to predict rotordynamic coefficients is discussed.

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