Thermal and Flow Phenomena Associated With the Behavior of Brush Seals in Aero Engine Bearing Chambers

2014 ◽  
Author(s):  
Michael Flouros ◽  
Patrick Hendrick ◽  
Bilal Outirba ◽  
Francois Cottier ◽  
Stephan Proestler
Keyword(s):  
Contact Zone ◽  
Heat Generation ◽  
Gas Turbines ◽  
Engine Oil ◽  
Transient Temperature ◽  
Aero Engine ◽  
Brush Seals ◽  
Secondary Air ◽  
Aero Engines ◽  
Engine Bearing

Due to the increasing fuel cost and environmental targets, the demand for more efficient gas turbines has risen considerably in the last decade. One of the most important systems in a gas turbine is the secondary air system which provides cooling air to the disks and to the blades. It also provides air for sealing of the bearing chambers. The amount of secondary air that is extracted from the compressor is a performance penalty for the engine. In aero engines, bearing chambers are in most cases sealed by the most traditional type of seal, the labyrinth seal. Bearing chambers contain the oil lubricated components like bearings and gears. In order to avoid oil migration from the bearing chamber into the turbo machinery the seals are pressurized by air thus a pressure difference is set up across the seal which retains the lubricant into the bearing chamber. Oil loss can lead to a number of problems like oil fire or coking with the probability of an uncontained destruction of the aero engine. Oil fumes can also cause contamination of the air conditioning system of the aircraft thus cause discomfort to the passengers. Beside labyrinth seals other types of seals such as brush seals and carbon seals are used. Both the latter are contact type seals, that is, they may be installed with zero gap and lift during operation when they get pressurized. Brush seals particularly may even have an overlap with the rotating part. An original aero engine bearing chamber was modified by MTU Aero Engines to run with brush seals in a simulating rig in Munich. Two types of brush seals were used for testing: a) brush seal with bristles made of Kevlar fibers and b) with bristles made of steel. Both types were installed having 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 calculate the heat generation by the seals which could enable predictions of the heat generation in future applications (i.e. scaling to bigger rotor diameters). To that effect numerical models using ANSYS CFX were created. Additionally, a coupled CFD and Finite Element Analysis (FEA) approach was applied to simulate flow and bristle’s behavior. 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 as reported in [5]. This technique has enabled positioning of the pyrometer [15] into the bristles pack of the seal adjacent to the rotating surface. The pyrometer can record the frictional temperature evolution in the bristles/rotor contact zone during accelerations or decelerations of the rotor. The sealing air demand can be reduced up to 97% with brush seals compared to traditional three fin labyrinth. It has been estimated that this can result in a reduction in fuel burned by up to 1%. Further, the reduction in air flow has additional potential benefits such as a possible simplification of the bearing chamber architecture (vent less chamber). Even though the rotor was accelerated up to 19500rpm, the temperature induced 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).

Thermal and Flow Phenomena Associated With the Behavior of Brush Seals in Aero Engine Bearing Chambers

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Michael Flouros ◽  
Patrick Hendrick ◽  
Bilal Outirba ◽  
Francois Cottier ◽  
Stephan Proestler
Keyword(s):  
Contact Zone ◽  
Gas Turbines ◽  
Temperature Measurements ◽  
Transient Temperature ◽  
Brush Seal ◽  
Aero Engine ◽  
Brush Seals ◽  
Secondary Air ◽  
Aero Engines ◽  
Engine Bearing

Due to the increasing fuel cost and environmental targets, the demand for more efficient gas turbines has risen considerably in the last decade. One of the most important systems in a gas turbine is the secondary air system, which provides cooling air to the disks and to the blades. It also provides air for sealing of the bearing chambers. The amount of secondary air that is extracted from the compressor is a performance penalty for the engine. In aero engines, bearing chambers are in most cases sealed by the most traditional type of seal, the labyrinth seal. Bearing chambers contain the oil lubricated components like bearings and gears. In order to avoid oil migration from the bearing chamber into the turbomachinery, the seals are pressurized by secondary air; thus, a pressure difference is setup across the seal, which retains the lubricant into the bearing chamber. Oil loss can lead to a number of problems like oil fire or coking with the probability of an uncontained destruction of the aero engine. Oil fumes can also cause contamination of the air conditioning system of the aircraft thus cause discomfort to the passengers. Beside labyrinth seals, other types of seals such as brush seals and carbon seals are used. Both the latter are contact type seals, that is, they may be installed with zero gap and lift during operation when they get pressurized. Brush seals particularly may be installed having an overlap with the rotating part. An original aero engine bearing chamber was modified by MTU Aero Engines to run with brush seals in a simulating rig in Munich. Two types of brush seals were used for testing: (a) a brush seal with bristles made of Kevlar fibers and (b) a brush seal with bristles made of steel. 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 calculate the heat generation by the seals which could enable predictions of the heat generation in future applications (i.e., scaling to bigger rotor diameters). For the heat transfer calculations, numerical models using ansys cfx were created. Additionally, a coupled computational fluid dynamics (CFD) and finite element analysis (FEA) approach was applied to simulate flow and bristle's behavior. 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 as reported by Flouros et al. (2013, “Transient Temperature Measurements in the Contact Zone Between Brush Seals of Kevlar and Metallic Type for Bearing Chamber Sealing Using a Pyrometric Technique,” ASME J. Gas Turbines Power, 135(8), p. 081603) and Flouros et al. (2012, “Transient Temperature Measurements in the Contact Zone Between Brush Seals of Kevlar and Metallic Type for Bearing Chamber Sealing Using a Pyrometric Technique,” ASME Turbo Expo 2012, Copenhagen, Paper No. GT2012-68354). This technique has enabled positioning of the pyrometer (SensorthermGmbH, www.sensortherm.com) into the bristles pack of the seal adjacent to the rotating surface. The pyrometer could record the frictional temperature evolution in the bristles/rotor contact zone during accelerations or decelerations of the rotor. The sealing air demand can be reduced up to 97% with brush seals compared to traditional three fin labyrinth. It has been estimated that this can result in a reduction in fuel burned up to 1%. Further, the reduction in air flow has additional potential benefits such as a possible simplification of the bearing chamber architecture (vent less chamber). Even though the rotor was accelerated up to 19,500 rpm, the temperature induced 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

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).

Experimental Testing of Carbon Brush Seals for Aero Engines Bearing Chambers

2014 ◽  
Author(s):  
Bilal Outirba ◽  
Patrick Hendrick
Keyword(s):  
Experimental Testing ◽  
Secondary Flows ◽  
Engine Oil ◽  
Oil Consumption ◽  
Test Rig ◽  
Turbine Engine ◽  
Aero Engine ◽  
Recent Developments ◽  
Brush Seals ◽  
Aero Engines

This paper provides the first step in sizing carbon brush seals for aero-engine oil bearing chambers applications. Recent developments in the aeronautic domain focus strongly on the reduction of aero-engine specific oil consumption. For instance, optimizing the civil aircraft gas turbine engine lubrication oil system is considered as one of the main targets in this research. Specifically, brush seals have shown tremendous leakage performance in sealing secondary flows compared to classic labyrinth seals over the last few decades. Therefore, an attractive idea is to extent their utilization to oil bearing chamber applications. To perform the experimental part of the study, a test rig has recently been built at ULB. This test rig will be described in this paper. A parametrical study has been performed in stationary conditions, and at very low rotation speed. A particular attention was given to the air consumption and the torque friction losses. Finally, a test simulating the effects of a rotor excursion on the brush seal performance has been made.

scholarly journals Feasibility Study on Oil Droplet Flow Investigations Inside Aero Engine Bearing Chambers: PDPA Techniques in Combination With Numerical Approaches

1995 ◽  
Author(s):  
A. Glahn ◽  
M. Kurreck ◽  
M. Willmann ◽  
S. Wittig
Keyword(s):  
Numerical Methods ◽  
Flow Field ◽  
Flow Analysis ◽  
Field Analysis ◽  
Oil Droplet ◽  
Droplet Flow ◽  
Aero Engine ◽  
Secondary Air ◽  
Numerical Approaches ◽  
Engine Bearing

The present paper deals with oil droplet now phenomena in aero engine bearing chambers. An experimental investigation of droplet sizes and velocities utilizing a Phase Doppler Particle Analyzer (PDPA) has been performed for the first time in bearing chamber atmospheres under real engine conditions. Influences of high rotational speeds are discussed for individual droplet size classes. Although this is an important contribution to a better understanding of the droplet flow impact on secondary air/oil system performance, an analysis of the droplet flow behaviour requires an incorporation of numerical methods because detailed measurements as performed here suffer from both strong spatial limitations with respect to the optical accessibility in real engine applications and constraints due to the extremely time consuming nature of an experimental flow field analysis. Therefore, further analysis is based on numerical methods. Droplets characterized within the experiments are exposed to the flow field of the gaseous phase predicted by use of our well-known CFD code EPOS. The droplet trajectories and velocities are calculated within a Lagrangian frame of reference by forward numerical integration of the particle momentum equation. This paper has been initiated rather to show a successful method of bearing chamber droplet flow analysis by a combination of droplet sizing techniques and numerical approaches than to present field values as a function of all operating parameters. However, a first insight into the complex droplet flow phenomena is given and specific problems in bearing chamber heat transfer are related to the droplet flow.

Film Flow Characteristics of Droplet Cooling in a Simplified Bearing Chamber

2013 ◽  
Author(s):  
E. D. Kay ◽  
H. Power ◽  
S. Hibberd
Keyword(s):  
Gas Turbines ◽  
Flow Characteristics ◽  
Temperature History ◽  
Design Parameters ◽  
Flow Conditions ◽  
Internal Surfaces ◽  
Aero Engine ◽  
Oil Flow ◽  
Oil Films ◽  
Engine Bearing

Droplet-cooled oil films develop on the internal surfaces of an aero-engine bearing chamber and are a primary mechanism in removing heat from the chamber as oil is continuously collected and externally cooled and recycled. Predicting the internal oil temperature and oil temperature history is an important thermal problem which becomes more apparent with potential increases in operating temperatures of gas turbines. Studying interacting oil flow and thermal processes within a simplified bearing chamber geometry provides useful information on the trends and characteristics which can arise under different applied flow conditions (e.g. mass flow rate of oil through the system) and insight to the effect chamber design parameters may have on oil degradation and cooling of chamber walls. Thin oil films develop on the walls of a bearing chamber as oil is injected or shed from bearings and impinges on the walls under a strong airflow set in motion by rotating components. Typically the film is also subject to a heat flux from the hot chamber walls and the droplets provide an important cooling effect through “heat-to-oil” mechanisms. We present a mathematical model for the depth-averaged flow and associated heat transfer by thin oil films on the walls of a simplified aero-engine bearing chamber. Cases corresponding to generic flow conditions relevant to an aero-engine bearing chamber are presented. Characteristics of the film and the efficacy of the flow regime to transfer heat from the chamber is explored through calculating residence times and time histories of oil particles as they make a transit of the internal system.

scholarly journals A Coupled 1D Film Hydrodynamics and Core Gas Flow Model for Air-Oil Flows in Aero-Engine Bearing Chambers

2017 ◽  
Author(s):  
B. Kakimpa ◽  
H. P. Morvan ◽  
S. Hibberd
Keyword(s):  
Shear Stress ◽  
Operating Conditions ◽  
Engine Oil ◽  
Interface Shear ◽  
Interface Shear Stress ◽  
Oil Film ◽  
Film Model ◽  
Aero Engine ◽  
Film Interface ◽  
Engine Bearing

A robust 1D film hydrodynamic model has been sequentially coupled with a 1D core gas model and used to predict the instantaneous mean core gas speed, film interface shear stress and liquid film distribution within an idealised bearing chamber. This novel approach to aero-engine bearing chamber simulation provides a predictive tool that can be used for the fast and reliable exploration of a set of bearing chamber design and operating conditions characterised by the: chamber dimensions, air/oil fluid properties, shaft speed, sealing air flows, oil feed rates and sump scavenge ratios. A preliminary validation of the model against available bearing chamber flow measurements from literature shows good agreement. The model represents a significant step change in predictive capabilities for aero-engine oil system flows compared to previous semi-empirical models. The bearing chamber is idealised as a one-dimensional (2D) domain with a predominantly azimuthal flow in both the rotational oil film and core gas such that axial components may be ignored. A 1D system of depth-averaged film hydrodynamics equations is used to predict oil film thickness and mean speed distributions in the azimuthal direction under the influence of interface shear, gravity, pressure gradient and surface tension forces. The driving shear stress in the film model is obtained from the 1D core-gas model based on an azimuthal gas momentum conservation equation which is coupled to the film model through the interface shear stress and film interface velocity.

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.

Two-Phase Flow Pressure Drop in Corrugated Tubes Used in an Aero-engine Oil System

2015 ◽  
Vol 138 (6) ◽  
Author(s):  
Michael Flouros ◽  
Andreas Kanarachos ◽  
Kyros Yakinthos ◽  
Christina Salpingidou ◽  
Francois Cottier
Keyword(s):  
Pressure Drop ◽  
Two Phase Flow ◽  
Operating Conditions ◽  
Engine Oil ◽  
Phase Flow ◽  
Test Results ◽  
Two Phase ◽  
Aero Engine ◽  
Flow Pressure ◽  
Engine Bearing

In modern aero-engines, the lubrication system holds a key role due to the demand for high reliability standards. An aero-engine bearing chamber contains components like bearings and gears. Oil is used for lubrication and for heat removal. In order to retain the oil in a bearing chamber, pressurized seals are used. These are pressurized using air from the compressor. In order to avoid overpressurization of the bearing chamber, air/oil passages are provided in the bearing chamber. At the top, a vent pipe discharges most of the sealing air and at the bottom, a scavenge pipe is used for discharging the oil by means of a pump (scavenge pump). The scavenge pipe is setup in most cases by tubes of circular or noncircular cross sections. When the scavenge pipe has to be routed in a way that sharp bends or elbows are unavoidable, flexible (corrugated) pipes can be used. Because of the corrugation, considerable flow resistance with high-pressure drop can result. This may cause overpressurization of the bearing compartment with oil loss into the turbomachinery with possibility of ignition, coking (carbon formation), or contamination of the aircraft’s air conditioning system. It is therefore important for the designer to be capable to predict the system’s pressure balance behavior. A real engine bearing chamber sealed by brush seals was used for generating different air/oil mixtures thus corresponding to different engine operating conditions. The mixtures were discharged through a scavenge pipe which was partly setup by corrugated tubes. Instead of a mechanical pump, an ejector was used for evacuating the bearing chamber. An extensive survey covering the existing technical literature on corrugated tube pressure drop was performed and is presented in this paper. The survey has covered both single-phase and multiphase flows. Existing methods were checked against the test results. The method which was most accurately predicting lean air test results from the rig was benchmarked and was used as the basis for extending into a two-phase flow pressure drop correlation by applying two-phase flow multiplier techniques similar to Lockhart and Martinelli. Comparisons of the new two-phase flow pressure drop correlation with an existing correlation by Shannak are presented for mixtures like air/oil, air/water, air/diesel, and air/kerosene. Finally, numerical analysis results using ansys cfx version 15 are presented.

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