Experimental Investigation on the Influence of Geometrical Parameters on the Frictional Heat Input and Leakage Performance of Brush Seals

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Manuel Hildebrandt ◽  
Corina Schwitzke ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Input ◽  
Geometric Parameters ◽  
Contact Forces ◽  
Frictional Heat ◽  
Transient Temperature ◽  
Geometrical Parameters ◽  
Labyrinth Seals ◽  
Decisive Influence ◽  
Brush Seal ◽  
Brush Seals

Because of the superior sealing characteristics compared to labyrinth seals, brush seals found an increased spread in turbomachinery in recent years. Their outstanding sealing performance results mainly from their flexibility. Thus, a very small gap between the rotor and bristle package can be obtained without running the risk of severe detrimental deterioration in case of rubbing. Rubbing between rotor and seal during operation might occur as a result of e.g., an unequal thermal expansion of the rotor and stator or a rotor elongation due to centrifugal forces or maneuver forces. Thanks to the flexible structure of the brush seal the contact forces during a rubbing event are reduced; however, the frictional heat input can still be considerable. Particularly, in aircraft engines with their thin and lightweight rotor structures, the permissible material stresses can easily be exceeded by an increased heat input and thus harm the engine's integrity. The geometry of the seal has a decisive influence on the resulting contact forces and consequently the heat input. The complex interactions between the geometric parameters of the seal and the heat input and leakage characteristics are not yet fully understood. This paper presents the investigation of the influence of the geometric parameters of a brush seal on the heat input into the rotor and the leakage behavior. Two seals with different packing densities were tested under relevant engine conditions with pressure differences ranging from 1 to 7 bar, relative surface speeds ranging from 30 to 180 m/s, and radial overlaps ranging from 0.1 to 0.4 mm. The transient temperature rise during the rub event was recorded with 24 thermocouples in close proximity to the rub contact embedded in the rotor structure. By comparing the temperature curves with the results of a thermal finite element (FE) analysis of the rotor the heat input into the rotor was calculated iteratively. It could be shown that the packing density has a decisive influence on the overall operating behavior of a brush seal. Furthermore, results for the heat flux distribution between seal and rotor are shown.

Experimental Investigation on the Influence of Geometrical Parameters on the Frictional Heat Input and Leakage Performance of Brush Seals

2017 ◽  
Author(s):  
Manuel Hildebrandt ◽  
Corina Schwitzke ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Input ◽  
Geometric Parameters ◽  
Contact Forces ◽  
Frictional Heat ◽  
Transient Temperature ◽  
Geometrical Parameters ◽  
Element Analysis ◽  
Decisive Influence ◽  
Brush Seal ◽  
Brush Seals

Because of the superior sealing characteristics compared to labyrinth seals, brush seals found an increased spread in turbomachinery in recent years. Their outstanding sealing performance results mainly from their flexibility. Thus, a very small gap between the rotor and bristle package can be obtained without running the risk of severe detrimental deterioration in case of rubbing. Rubbing between rotor and seal during operation might occur as a result of e.g. an unequal thermal expansion of the rotor and stator or a rotor elongation due to centrifugal forces or manoeuvre forces. Thanks to the flexible structure of the brush seal the contact forces during a rubbing event are reduced, however the frictional heat input can still be considerable. Particularly in aircraft engines with their thin and lightweight rotor structures the permissible material stresses can easily be exceeded by an increased heat input and thus harm the engine’s integrity. The geometry of the seal has a decisive influence on the resulting contact forces and consequently the heat input. The complex interactions between the geometric parameters of the seal and the heat input and leakage characteristics are not yet fully understood. This paper presents the investigation of the influence of the geometric parameters of a brush seal on the heat input into the rotor and the leakage behaviour. Two seals with different packing densities were tested under relevant engine conditions with pressure differences ranging from 1 to 7 bar, relative surface speeds ranging from 30 to 180 m/s and radial overlaps ranging from 0.1 to 0.4 mm. The transient temperature rise during the rub event was recorded with 24 thermocouples in close proximity to the rub contact embedded in the rotor structure. By comparing the temperature curves with the results of a thermal finite element analysis of the rotor the heat input into the rotor was calculated iteratively. It could be shown that the packing density has a decisive influence on the overall operating behaviour of a brush seal. Furthermore, results are obtained for the heat flux distribution between seal and rotor are shown.

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.

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.

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

2012 ◽  
Author(s):  
Michael Flouros ◽  
Martin Stadlbauer ◽  
Francois Cottier ◽  
Stephan Proestler ◽  
Stefan Beichl
Keyword(s):  
Contact Zone ◽  
Operating Conditions ◽  
Temperature Measurements ◽  
Transient Temperature ◽  
The European Union ◽  
Labyrinth Seals ◽  
Brush Seal ◽  
Aero Engine ◽  
Brush Seals ◽  
Engine Bearing

For the past 25 years brush seal technologies evolved into the aero engine designs and more general 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 like disks or blades. It may also cause contamination of the air conditioning system with oil fumes thus cause health problems to the passengers and crew from such exposure. The most widely known seals for bearing chamber sealing are the labyrinth seals but in the recent years also brush seals and carbon seals are 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 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 placing the pyrometer into the bristle’s pack of the seal adjacent to the rotating surface and 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 return into a reduction in fuel burned by up to 1%. Further, 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 19500rpm, the produced temperature overshoots in the seal/rotor contact zone have caused no deterioration in either the materials or the oil. This work is part of the European Union funded research programme ELUBSYS (Engine LUBrication System TechnologieS) within the 7th EU Frame Programme for Aeronautics and Transport (AAT.2008.4.2.3).

Influence of Geometrical Parameters on the Performance of Brush Seals for Aero-Engines Bearing Chambers

2015 ◽  
Author(s):  
Bilal Outirba ◽  
Patrick Hendrick
Keyword(s):  
Aircraft Engine ◽  
Labyrinth Seal ◽  
Friction Torque ◽  
Secondary Flows ◽  
Geometric Parameters ◽  
Geometrical Parameters ◽  
Backing Plate ◽  
Brush Seal ◽  
Seal Oil ◽  
Brush Seals

Recent developments in the aeronautic domain focus on the optimization of the lubrication oil system for civil aircraft gas turbine engines, in order to reduce air and oil consumptions. Specifically, over the last few decades, as brush seals have shown tremendous leakage performance in sealing secondary flows compared to classic labyrinth seal, an increasingly popular idea is to extend their utilization to bearing chambers applications. In the frame of the European FP7 E-Break project, the Aero-Thermo-Mechanics department of ULB collaborates with French aircraft engine manufacturer SNECMA in order to investigate experimentally the brush seal behaviour in an environment simulating the bearing chamber working conditions. The aim is first to deepen the brush seal behaviour knowledge by identifying the most influential geometric parameters acting on the leakage performance on both sides of the seal (oil and air), and on its wear, and by evaluating the friction torque and the dissipated heat. The paper will first highlight the effect of the brush seals geometric parameters on the air consumption and the torque friction. Results highlight a trade-off to be made between these two performance levels. Also, relations have been developed to predict the performance of a carbon brush seal with non-canted bristles. The bristle free length and the axial density must carefully be chosen first to dictate the brush seal porosity. The distance between the backing plate and the front plate acts as a secondary parameter to adjust the bristle pack stiffness, and it is proposed to mount such a carbon brush seal with a reduced interference to limit the effect of the brush seal wear on the air consumption. Finally, the carbon brush seals performance was compared with the latest ones, with promising results being shown to expect carbon brush seals to be employed at a higher scale in bearing chambers in the future.

Rotating Brush Seal Design and Performance Testing

2021 ◽  
Author(s):  
Neelesh Sarawate ◽  
Deepak Trivedi
Keyword(s):  
Centrifugal Force ◽  
Compact Space ◽  
Performance Testing ◽  
Labyrinth Seals ◽  
Test Setup ◽  
Seal Design ◽  
Brush Seal ◽  
Brush Seals ◽  
Dynamic Seal ◽  
And Performance

Abstract Brush seals are widely used in various turbomachinery applications because they provide reduced leakage than labyrinth seals in a compact space. Brush seals are generally mounted on static components and their flexible bristle tips engage the rotor to form a dynamic seal. In this paper, development of a brush seal mounted on a rotor is discussed. Benefits of this enhancement to brush seal include avoiding localized rubs on the rotor, which reduces heating of a local spot and resulting rotor bow and instabilities. The bristles are angled circumferentially instead of axially and are supported by a conical backplate. Under rotation, the bristles are pushed towards the backplate by the centrifugal force. Seal configurations are designed to fit into interstage and inter-shaft locations. A modeling approach for predicting stiffness and operating stresses in these seals also is outlined. A test setup is developed to characterize the performance of rotating brush seals under engine-representative centrifugal force and pressure differentials. Presented results demonstrate that brush seal can achieve tight effective gaps and desired performance after undergoing initial wear.

Measured Influence of Clearance and Eccentricity on Brush Seal Leakage Characteristics

2020 ◽  
Author(s):  
Manish R. Thorat ◽  
Brian Bauer
Keyword(s):  
Experimental Results ◽  
Labyrinth Seals ◽  
Blow Down ◽  
Interference Fit ◽  
Leakage Model ◽  
Rotation Direction ◽  
Brush Seal ◽  
Leakage Characteristics ◽  
Brush Seals ◽  
Initial Clearance

Abstract Brush seals are used in turbomachinery for reduced leakage as compared to conventional seals such as labyrinth seals. Early applications tended to favor having a line-to-line to a slight interference fit of the bristles to the shaft, but more recent applications have favored the use of a slight initial clearance fit for the purpose of reducing bristle wear. In these brush seals with clearance, the phenomenon of bristle blow-down largely negates the leakage degradation due to clearance, with bristles bending to reduce the clearance gap. This paper presents experimental results for a 10.5 inch bore brush seal with 0.0028 inch bristle diameter. Bristle blow-down is characterized with measurements at three different clearances then compared to a calibrated brush seal leakage model. Tolerances in brush installation may lead to a brush seal bore that is eccentric to the rotor. The influence of this seal eccentricity on measured leakage performance is also characterized in the paper. Seal eccentricities up to 55% of brush fence height are tested. Effective clearances for eccentric operation are estimated from the measurements. Brush seals are described as unidirectional seals because the bristles have a lay angle in the direction of rotation. This paper also investigates the influence of rotation direction on measured leakage performance of brush seal. This influence is characterized by non-pressurized reverse rotation operation and measurement of leakage performance prior to and after reverse rotation operation.

Brush Seal Frictional Heat Generation: Test Rig Design and Validation Under Steam Environment

2016 ◽  
Author(s):  
M. Raben ◽  
J. Friedrichs ◽  
J. Flegler
Keyword(s):  
Steam Turbine ◽  
Heat Generation ◽  
Gas Turbines ◽  
Frictional Heat ◽  
Narrow Gap ◽  
Test Rig ◽  
Frictional Heat Generation ◽  
Brush Seal ◽  
Rotor Surface ◽  
Brush Seals

Sealing technology is a key feature to improve efficiency of steam turbines for both new power stations and modernization projects. One of the most powerful sealing alternatives for reducing parasitic leakages in the blade path of a turbine as well as in shaft sealing areas is the use of brush seals, which are also widely used in gas turbines and turbo compressors. The advantage of brush seals over other sealing concepts is based on the narrow gap that is formed between the brush seal bristle tips and the mating rotor surface together with its radial adaptivity. While the narrow gap between the bristle tips and the rotor leads to a strongly decreased flow through the seal compared with conventional turbomachinery seals, it is important to be aware of the tight gap that can be bridged by relative motion between the rotor and the brush seal, leading to a contact of the bristles and the rotor surface. Besides abrasive wear occurrence, the friction between the bristles and the rotor leads to heat generation which can be detrimental to turbine operation due to thermal effects, leading to rotor bending connected to increasing shaft vibrations. In order to investigate the frictional heat generation of brush seals, different investigation concepts have been introduced through the past years. To broaden the knowledge about frictional heat generation and to make it applicable for steam turbine applications, a new testing setup was designed for the steam test rig of the Institute of Jet Propulsion and Turbomachinery - TU Braunschweig, Germany, enabling temperature measurements in the rotor body under stationary and transient operation in steam by using rotor-integrated thermocouples. Within this paper, the development of the instrumented new rotor design and all relevant parts of the new testing setup is shown along with the testing ability by means of the validation of the test rig concept and the achieved measurement accuracy. First results prove that the new system can be used to investigate frictional heat generation of brush seals under conditions relevant for steam turbine shaft seals.

Brush Seal Bristle Wear Analysis

2007 ◽  
Author(s):  
Mahmut F. Aksit ◽  
John A. Tichy ◽  
O. Saim Dinc
Keyword(s):  
High Surface ◽  
Labyrinth Seals ◽  
Backing Plate ◽  
Wear Analysis ◽  
Contact Loads ◽  
Brush Seal ◽  
Operation Rate ◽  
Brush Seals ◽  
And Performance ◽  
Analysis Models

Turbomachinery sealing applications require accommodating large rotor excursions at high surface speeds. Achieving seal compliance under such demanding conditions combined with typical high operating temperatures poses a major engineering challenge. Formed by a dense pack of bristles, brush seals have emerged as viable alternatives to conventional labyrinth seals. Being contact seals, brush seals undergo unavoidable bristle wear in operation. Rate and extent of bristle wear determines seal life and performance. Detailed understanding of brush seal contact loads is necessary to estimate seal wear performance. The complicated nature of bristle behavior under various combinations of pressure load and rotor interference requires computer analysis to study details that may not be available through analytical formulations. This work presents a summary of a 3-D computational brush seal tip force and wear analysis. The analysis models a representative brush segment with bristles formed by 3-D beam elements. Bristle interlocking and frictional interactions (interbristle, bristle-backing plate and bristle-rotor) are included to better calculate resulting seal stiffness and tip forces. Results are compared to stiffness measurements and full scale seal wear tests.

Improvement of Conventional Seals for Stator-Rotor Cavities of Heavy-Duty Gas Turbines by Application of Interstage Brush-Seals

2013 ◽  
Author(s):  
Marco Mantero ◽  
Alessandro Vinci ◽  
Luca Bozzi ◽  
Enrico D’Angelo
Keyword(s):  
Gas Turbines ◽  
Operating Conditions ◽  
Design Flow ◽  
Heavy Duty ◽  
Labyrinth Seals ◽  
Flow Process ◽  
Brush Seal ◽  
Temperature And Pressure ◽  
Brush Seals ◽  
Secondary Air

In order to achieve significant secondary air savings in heavy duty gas turbines, a remarkable item of improvement is the reduction of seal flows for turbine stator-rotor cavities. The optimization of such flows allows to avoid waste of air, obligatory with standard labyrinth seals, to ensure the minimum sealing flow rate in all operating conditions. Based on the experience gained in the design of sealing system of stator-rotor cavities with standard seals, the project of installation of inter-stage brush-seals was undertaken incorporating such devices into the vane seal rings of 2nd and 3rd turbine stages of a AE94.3A Gas Turbine (GT). The paper offers a detailed description of the installation project. The following describes in detail the design flow process and the calculation methodologies used, step by step, to define the geometry of brush-seals in order to ensure mechanical integrity and durability, needed in the commercial operation, without thereby affecting the performance. The first prototype of brush-seal devices has been installed on a AE94.3A4 unit of the Ansaldo fleet. In order to verify the behavior of stator-rotor sealing system, in particular in terms of temperature and pressure variations, vane seal rings have been equipped with special instrumentation. A series of tests to optimize the set points of bleed control valves was carried out.

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