Rotordynamic Force Coefficients of a Hybrid Brush Seal: Measurements and Predictions

2009 ◽  
Author(s):  
Luis San Andre´s ◽  
Adolfo Delgado ◽  
Jose´ Baker
Keyword(s):  
Test System ◽  
Operating Conditions ◽  
Single Frequency ◽  
Viscous Damping ◽  
Domain Identification ◽  
Damping Coefficients ◽  
Brush Seal ◽  
Brush Seals ◽  
Lift Off ◽  
Stiffness And Damping

Brush seals effectively control leakage in air breathing engines, albeit only applied for relatively low-pressure differentials. Hybrid brush seals (HBS) are an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse shaft rotation operation. A HBS incorporates pads contacting the shaft on assembly; and which under rotor spinning, lift off due to the generation of a hydrodynamic pressure. The ensuing gas film prevents intermittent contact, reducing wear and thermal distortions. The paper presents rotordynamic measurements conducted on a test rig for evaluation of HBS technology. Single frequency shaker loads are exerted on a test rotor holding a hybrid brush seal and measurements of rotor displacements follow for operating conditions with increasing gas supply pressures and two rotor speeds. A frequency domain identification method delivers the test system stiffness and damping coefficients. The HBS stiffness coefficients are not affected by rotor speed though the seal viscous damping shows a strong frequency dependency. The identified HBS direct stiffness decreases ∼15% as the supply/discharge pressure increases Pr = 1.7 to 2.4. The HBS cross-coupled stiffnesses are insignificant, at least one order of magnitude smaller than the direct stiffnesses. A structural loss factor (γ) and dry friction coefficient (μ) represent the energy dissipated in a HBS by the bristle-to-bristle and bristle-to-pads interactions. Predictions of HBS stiffness and damping coefficients correlate well with the test derived parameters. Both model predictions and test results show the dramatic reduction of the seal equivalent viscous damping coefficients as the excitation whirl frequency increases.

Rotordynamic Force Coefficients of a Hybrid Brush Seal: Measurements and Predictions

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Luis San Andrés ◽  
José Baker ◽  
Adolfo Delgado
Keyword(s):  
Test System ◽  
Operating Conditions ◽  
Single Frequency ◽  
Viscous Damping ◽  
Domain Identification ◽  
Damping Coefficients ◽  
Brush Seal ◽  
Brush Seals ◽  
Lift Off ◽  
Stiffness And Damping

Brush seals effectively control leakage in air breathing engines, albeit only applied for relatively low-pressure differentials. Hybrid brush seals (HBS) are an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse shaft rotation operations. A HBS incorporates pads contacting the shaft on assembly; and which under rotor spinning, lift off due to the generation of a hydrodynamic pressure. The ensuing gas film prevents intermittent contact, reducing wear, and thermal distortions. This paper presents rotordynamic measurements conducted on a test rig for evaluation of HBS technology. Single frequency shaker loads are exerted on a test rotor holding a hybrid brush seal, and measurements of rotor displacements follow for operating conditions with increasing gas supply pressures and two rotor speeds. A frequency domain identification method delivers the test system stiffness and damping coefficients. The HBS stiffness coefficients are not affected by rotor speed though the seal viscous damping shows a strong frequency dependency. The identified HBS direct stiffness decreases ∼15% as the supply/discharge pressure increases Pr=1.7–2.4. The HBS cross-coupled stiffnesses are insignificant, at least one order of magnitude smaller than the direct stiffnesses. A structural loss factor (γ) and dry-friction coefficient (μ) represent the energy dissipated in a HBS by the bristle-to-bristle and bristle-to-pad interactions. Predictions of HBS stiffness and damping coefficients correlate well with the test derived parameters. Both model predictions and test results show the dramatic reduction in the seal equivalent viscous damping coefficients as the excitation whirl frequency increases.

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.

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

2013 ◽  
Author(s):  
Manuel Gaszner ◽  
Alexander O. Pugachev ◽  
Christos Georgakis ◽  
Paul Cooper
Keyword(s):  
Dynamic Test ◽  
Operating Conditions ◽  
Radial Clearance ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Stiffness Coefficients ◽  
Brush Seal ◽  
Brush Seals ◽  
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 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.

Analysis of Performance and Rotordynamic Force Coefficients of Brush Seals With Reverse Rotation Ability

2004 ◽  
Author(s):  
Adolfo Delgado ◽  
Luis San Andre´s ◽  
John F. Justak
Keyword(s):  
Pressure Ratio ◽  
Nonlinear Partial Differential Equation ◽  
Forced Response ◽  
Operating Conditions ◽  
Partial Differential ◽  
Force Coefficients ◽  
Brush Seal ◽  
Brush Seals ◽  
Discharge Pressure ◽  
Stiffness And Damping

Multiple-shoed brush seals represent an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse rotation operation. The novel configuration incorporates pads contacting the shaft, and which under rotor spinning; lift off due to the generation of hydrodynamic pressures. The ensuing gas film prevents intermittent contact; thus lowering the operating temperature and thermal distortions, and even eliminating bristles’ wear. A computational analysis for the equilibrium and dynamic forced response of a brush seal with reverse rotation capability is presented. Small amplitude rotor motions about an equilibrium position lead to a nonlinear partial differential equation for the static pressure field, and a set of first order linear partial differential equations to determine the rotordynamic force coefficients, stiffness and damping, as function of the excitation frequency and other operating conditions. Predictions for the stiffness and damping coefficients of a 20 shoe-brush seal configuration operating over a range of rotor speeds are detailed. The parametric study varies the nominal gas film thickness, the supply to discharge pressure ratio, and the bristle bed structural loss (damping) coefficient. The results show that the film clearance and supply to discharge pressure ratio do not affect the shoed-brush seal force coefficients. On the other hand, the direct stiffness drops rapidly as the operating speed increases. The shoed-brush seal offers whirl frequency ratios much lower than 0.50 due to the (structural) damping arising from friction among the brush seal bristles.

Breaking the Swirl With Brush Seals: Numerical Modeling and Experimental Evidence

2008 ◽  
Author(s):  
Peter Helm ◽  
Alexander Pugachev ◽  
Matthias Neef
Keyword(s):  
Experimental Evidence ◽  
Swirl Flow ◽  
Operating Conditions ◽  
Brush Seal ◽  
Stable Operating ◽  
Beneficial Impact ◽  
Rotor Surface ◽  
Brush Seals ◽  
Experimental Values ◽  
The Impact

Striving for smaller losses in turbomachinery has led to many advancements in the design of seals. Modern sealing concepts such as brush seals hold a great potential to increase the efficiency of both flight engines and stationary turbines. At the same time, in order to maintain stable operating conditions of the rotor, swirl-induced forces must be kept at a minimum in the sealing channels. Therefore, the influence of the permeable and flexible bristle pack of brush seals on the flow around the rotor surface must be known. In this paper the swirl flow in the cavities of two different seal geometries is studied experimentally and numerically. A conventional three-tooth labyrinth serves as a reference. A second seal arrangement with a bristle pack upstream of two teeth is compared with the reference labyrinth. The swirl is evaluated experimentally from total and static pressure measurements in various axial and circumferential positions. Additionally, the axial swirl distribution is calculated using computational fluid dynamics (CFD). Here, the numerical model of the brush seal is based on the porous medium approach and is calibrated using the experimental values of the leakage and the bristle clearance by adjusting the thickness of the bristle pack. The calibrated CFD model is then used to study the impact of the brush seal on the swirl component of the sealing flow. The observed significant decrease of the swirl by the brush seal shows good agreement with the experimental data. The impact of changes in bristle pack clearance on the swirl is also investigated and compared with experimental evidence. The aim is to show that the brush seals have a natural tendency to interrupt seal swirl. They can therefore be used for swirl control in order to create a beneficial impact on the dynamic stability of turbomachines.

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.

Influence of Lubrication Oil on the Performance of Carbon Fibre Brush Seals for Aero-Engines Bearing Chambers

2019 ◽  
Author(s):  
Bilal Outirba ◽  
Patrick Hendrick
Keyword(s):  
Carbon Fibre ◽  
Rotational Speed ◽  
Fibre Length ◽  
Operating Conditions ◽  
Geometrical Parameters ◽  
Labyrinth Seals ◽  
Brush Seal ◽  
Lubrication Oil ◽  
Brush Seals ◽  
Aero Engines

Abstract Carbon fibre brush seals are an alternative to labyrinth seals in aero-engines lubrication systems due to better sealing ability with low power loss. However, the use of brush seals still raises concerns about coking issues. In addition, the influence of oil on the brush seal behaviour needs to be fully assessed. This paper provides an experimental investigation of the effect of lubrication oil on the performance of carbon fibre brush seals under static and dynamic conditions. Eight brush seal samples of various geometrical designs were submitted to an environment recreating the working conditions of a modern aero-engine bearing chamber in terms of rotational speed, air pressure, and oil type of injection and temperature. The test results indicated that the performance of carbon fibre brush seals was deeply influenced by the presence of oil within fibres. Oil deeply influences leakage performance, depending on geometrical parameters (density, fibre length and interference) and operating conditions (oil temperature, rotational speed). Brush seal fibre pack is mainly prone to hydrodynamic lift and oil soaking, which is defined by the ability of lubrication oil to fill in properly the interstices between fibres. Viscosity and surface tension may be the key properties influencing oil soaking. Seal torque data corroborates the presence of a hydrodynamic lift. In addition, in absence of differential pressure, seal torque decrease with when oil temperature increases indicates the existence of a critical viscosity. Finally, oil lubrication within the bristles allows reduction of the inter-bristle friction, thus limiting hysteresis.

Evaluation of Flow Behavior for Clearance Brush Seals

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Yahya Dogu ◽  
Mahmut F. Aksit ◽  
Mehmet Demiroglu ◽  
Osman Saim Dinc
Keyword(s):  
Flow Field ◽  
Flow Behavior ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Brush Seal ◽  
Sealing Performance ◽  
Computational Fluid Dynamics Analysis ◽  
Flow Features ◽  
Brush Seals ◽  
Initial Clearance

The industrial applications of brush seals have been increasing due to their superior sealing performance. Advances in the understanding of seal behavior have been pushing the design limits to higher-pressure load, temperature, surface speed, and rotor excursion levels. The highest sealing performance can be achieved when the bristle pack maintains contact with the rotor surface. However, due to many design and operational constraints, most seals operate with some clearance. This operating clearance cannot be avoided due to rotor runouts, transient operating conditions, or excessive bristle wear. In some applications, a minimum initial clearance is required to ensure a certain amount of flow rate for component cooling or purge flow. Typically, brush seal failure occurs in the form of degraded sealing performance due to increasing seal clearance. The seal performance is mainly characterized by the flow field in close vicinity of the bristle pack, through the seal-rotor clearance, and within the bristle pack. This work investigates the flow field for a brush seal operating with some bristle-rotor clearance. A nonlinear form of the momentum transport equation for a porous medium of the bristle pack has been solved by employing the computational fluid dynamics analysis. The results are compared with prior experimental data. The flow field for the clearance seal is observed to have different characteristics compared to that for the contact seal. Outlined as well are the flow features influencing the bristle dynamics.

Fundamental Design Issues of Brush Seals for Industrial Applications

2002 ◽  
Vol 124 (2) ◽  
pp. 293-300 ◽  
Author(s):  
Saim Dinc ◽  
Mehmet Demiroglu ◽  
Norman Turnquist ◽  
Jason Mortzheim ◽  
Gayle Goetze ◽  
...  
Keyword(s):  
High Speed ◽  
Failure Modes ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Design Parameters ◽  
Design Criteria ◽  
Seal Design ◽  
Brush Seal ◽  
Brush Seals ◽  
As Stress

Advanced seals have been applied to numerous turbine machines over the last decade to improve the performance and output. Industrial experiences have shown that significant benefits can be attained if the seals are designed and applied properly. On the other hand, penalties can be expected if brush seals are not designed correctly. In recent years, attempts have been made to apply brush seals to more challenging locations with high speed (>400 m/s), high temperature (>650 °C), and discontinuous contact surfaces, such as blade tips in a turbine. Various failure modes of a brush seal can be activated under these conditions. It becomes crucial to understand the physical behavior of a brush seal under the operating conditions, and to be capable of quantifying seal life and performance as functions of both operating parameters and seal design parameters. Design criteria are required for different failure modes such as stress, fatigue, creep, wear, oxidation etc. This paper illustrates some of the most important brush seal design criteria and the trade-off of different design approaches.

Transient Temperature Measurements in the Contact Zone Between Brush Seals of Kevlar and Metallic Type for Bearing Chamber Sealing Using a Pyrometric Technique

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Michael Flouros ◽  
Martin Stadlbauer ◽  
Francois Cottier ◽  
Stephan Proestler ◽  
Stefan Beichl
Keyword(s):  
Contact Zone ◽  
Operating Conditions ◽  
Temperature Measurements ◽  
Transient Temperature ◽  
Labyrinth Seals ◽  
Brush Seal ◽  
Aero Engine ◽  
Rotating Surface ◽  
Brush Seals ◽  
Engine Bearing

For the past 25 years brush seal technologies have evolved into the aero engine designs and, more generally, into the gas turbine world, not only for sealing gas areas at different pressure levels but also for sealing gas/liquid environments. This is the case in an aero engine where the bearing chambers are sealed. Aero engine bearing chambers enclose oil lubricated components such bearings and gears. In order to avoid contamination of the turbo machinery through oil loss, air blown seals are used to retain the oil into the bearing chamber. Oil loss may cause coking or ignition with the probability of an uncontained destruction of rotating parts such as disks or blades. It may also cause contamination of the air conditioning system with oil fumes thus causing health problems to the passengers and crew from such exposure. The most widely known seals for bearing chamber sealing are the labyrinth seals, however, in recent years brush seals and carbon seals have also been used. The latter are contact seals; that is, they may be installed having zero clearance to the rotating part and lift during operation when their air side is pressurized. During this survey an actual aero engine bearing chamber was modified to run with brush seals in a simulating rig. Two types of brush seals were used: (a) with bristles made of Kevlar, and (b) bristles made of a metallic material. Both types were installed with an overlap to the rotor. The targets set were twofold: (a) to measure the transient temperatures in the rotor and particularly in the contact zone between the bristles and the rotor, and (b) to measure the air leakage through the seals at different operating conditions. In order to obtain the transient temperature measurements with high fidelity, a new pyrometric technique was developed and was applied for the first time in brush seals. This technique has enabled placement of the pyrometer into the bristle's pack of the seal adjacent to the rotating surface and it could record the frictional temperature evolution in the bristles/rotor contact zone during acceleration or deceleration of the rotor. Additionally, the air consumption of the seals was measured and was compared to the air consumption through the labyrinth seals. For the metallic brush seal, up to 80% of the required sealing air can be saved, which can result, in turn, into a reduction in fuel burned by up to 1%. Furthermore, a design simplification of the bearing chamber architecture can be achieved by taking into account the reduced air flow. Even though the rotor was accelerated to high speeds up to 19,500 rpm, the produced temperature overshoots in the seal/rotor contact zone have caused no deterioration in either the materials or the oil.

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