An Investigation of Flow, Mechanical, and Thermal Performance of Conventional and Pressure-Balanced Brush Seals

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Michael J. Pekris ◽  
Gervas Franceschini ◽  
David R. H. Gillespie
Keyword(s):  
Test Rig ◽  
Blow Down ◽  
Active Pressure ◽  
University Of Oxford ◽  
Seal Design ◽  
Passive Pressure ◽  
Brush Seal ◽  
Fuel Consumption Benefit ◽  
Brush Seals ◽  
Secondary Air

Compliant contacting filament seals such as brush seals are well known to give improved leakage performance and hence specific fuel consumption benefit compared to labyrinth seals. The design of the brush seal must be robust across a range of operating pressures, rotor speeds, and radial build-offset tolerances. Importantly the wear characteristics of the seal must be well understood to allow a secondary air system suitable for operation over the entire engine life to be designed. A test rig at the University of Oxford is described which was developed for the testing of brush seals at engine-representative speeds, pressures, and seal housing eccentricities. The test rig allows the leakage, torque, and temperature rise in the rotor to be characterized as functions of the differential pressure(s) across the seal and the speed of rotation. Tests were run on two different geometries of bristle pack with conventional, passive, and active pressure-balanced backing ring configurations. Comparison of the experimental results indicates that the hysteresis inherent in conventional brush seal design could compromise performance (due to increased leakage) or life (due to exacerbated wear) as a result of reduced compliance. The inclusion of active pressure-balanced backing rings in the seal designs are shown to alleviate the problem of bristle–backing ring friction, but this is associated with increased blow-down forces which could result in a significant seal-life penalty. The best performing seal was concluded to be the passive pressure-balanced configuration, which achieves the best compromise between leakage and seal torque. Seals incorporating passive pressure-balanced backing rings are also shown to have improved heat transfer performance in comparison to other designs.

An Investigation of Flow, Mechanical and Thermal Performance of Conventional and Pressure-Balanced Brush Seals

2012 ◽  
Author(s):  
Michael J. Pekris ◽  
Gervas Franceschini ◽  
David R. H. Gillespie
Keyword(s):  
Test Rig ◽  
Blow Down ◽  
Active Pressure ◽  
University Of Oxford ◽  
Seal Design ◽  
Passive Pressure ◽  
Brush Seal ◽  
Fuel Consumption Benefit ◽  
Brush Seals ◽  
Secondary Air

Compliant contacting filament seals such as brush seals are well known to give improved leakage performance and hence specific fuel consumption benefit compared to labyrinth seals. The design of the brush seal must be robust across a range of operating pressures, rotor speeds and radial build-offset tolerances. Importantly the wear characteristics of the seal must be well understood to allow a secondary air system suitable for operation over the entire engine life to be designed. A test rig at the University of Oxford is described which was developed for the testing of brush seals at engine-representative speeds, pressures and seal housing eccentricities. The test rig allows the leakage, torque and temperature rise in the rotor to be characterized as functions of the differential pressure(s) across the seal and the speed of rotation. Tests were run on two different geometries of bristle-pack with conventional, passive and active pressure-balanced backing ring configurations. Comparison of the experimental results indicates that the hysteresis inherent in conventional brush seal design could compromise performance (due to increased leakage) or life (due to exacerbated wear) as a result of reduced compliance. The inclusion of active pressure-balanced backing rings in the seal designs are shown to alleviate the problem of bristle-backing ring friction, but this is associated with increased blow-down forces which could result in a significant seal-life penalty. The best performing seal was concluded to be the passive pressure-balanced configuration, which achieves the best compromise between leakage and seal torque. Seals incorporating passive pressure-balanced backing rings are also shown to have improved heat transfer performance in comparison to other designs.

Design Parameters of Brush Seals and Their Impact on Seal Performance

2012 ◽  
Author(s):  
H. Schwarz ◽  
J. Friedrichs ◽  
J. Flegler
Keyword(s):  
Steam Turbine ◽  
Gas Turbine ◽  
Large Scale ◽  
Design Parameters ◽  
Test Rig ◽  
Pressure Drops ◽  
Seal Design ◽  
Brush Seal ◽  
Extreme Load ◽  
Brush Seals

Brush seals, which were originally designed for gas turbine applications, have been successfully applied to large-scale steam turbines within the past decade. From gas turbine applications, the fundamental behavior and designing levers are known. However, the application of brush seals to a steam turbine is still a challenge. This challenge is mainly due to the extreme load on the brush seal while operating under steam. Furthermore, it is difficult to test brush seals under realistic conditions, i.e. under live steam conditions with high pressure drops. Due to these insufficiencies, 2 test rigs were developed at the University of Technology Braunschweig, Germany. The first test rig is operated under pressurized air and allows testing specific brush seal characteristics concerning their general behavior. The knowledge gained from these tests can be validated in the second test rig, which is operated under steam at pressure drops of 45 bar and temperatures up to 450 °C. Using both the air test rig and the steam test rig helps keep the testing effort comparably small. Design variants can be pre-tested with air, and promising brush seal designs can consequently be tested in the steam seal test rig. The paper focuses on a clamped brush seal design which, amongst others, is used in steam turbine blade paths and shaft seals of current Siemens turbines. The consequences of the brush assembly on the brush appearance and brush performance are shown. The clamped brush seal design reveals several particularities compared to welded brushes. It could be shown that the clamped bristle pack tends to gape when clamping forces rise. Gapping results in an axially expanding bristle pack, where the bristle density per unit area and the leakage flow vary. Furthermore, the brush elements are usually assembled with an axial lay angle, i.e. the bristles are reclined against the backing plate. Hence, the axial lay angle is also part of the investigation.

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.

Effects of Geometry on Brush Seal Pressure and Flow Fields—Part II: Backing Plate Configurations

2005 ◽  
Vol 128 (2) ◽  
pp. 379-389 ◽  
Author(s):  
Yahya Dogu ◽  
Mahmut F. Aksit
Keyword(s):  
Constant Pressure ◽  
Decisive Role ◽  
Flow Fields ◽  
Control Flow ◽  
Blow Down ◽  
Backing Plate ◽  
Seal Design ◽  
Pressure Fields ◽  
Brush Seal ◽  
Flow Features

Brush seal dynamic behavior is strongly related to pressure and flow fields. Developments in brush seal design have led to geometric modifications to control flow field and consequent brush seal issues including blow-down, hang-up, and pressure stiffening. Some of the geometric enhancements have been found to have common use as backing plate modifications. Over the two decades of brush seal evolution, many backing plate configurations have been suggested in numerous patent disclosures. Even so, literature on the effects of geometric modifications on pressure and flow fields remains limited. This study numerically investigates brush seal pressure and flow fields for such common conceptual backing plate configurations as single and multiple grooves, with and without by-pass passages. The CFD analysis presented employs a bulk porous medium approach for the bristle pack. The effectiveness of various backing plate configurations outlining important flow features is discussed. Results indicate that backing plate configurations have a decisive role in shaping seal pressure fields. In general, it has been found that all cases having bypass configuration leak more. Moreover, the major portion of the seal leakage through fence height is fed from the backing plate cavity. The single backing plate groove forms a constant pressure behind the bristle pack. In contrast, multiple grooves form multiple constant pressure regions.

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.

Design and Validation of a New Test Rig for Brush Seal Testing Under Engine Relevant Conditions

2011 ◽  
Author(s):  
D. Pfefferle ◽  
K. Dullenkopf ◽  
H.-J. Bauer
Keyword(s):  
High Surface ◽  
Test Rig ◽  
Friction Forces ◽  
Brush Seal ◽  
Main Emphasis ◽  
Rotor Surface ◽  
Brush Seals ◽  
Gap Height ◽  
Radial Gap ◽  
Gap Width

Brush seals play an increasing role in turbomachinery due to their improved behavior towards leakage and their capability to compensate for gap variations caused by thermal expansion and rotor excursions. The flexible bristles of brush seals are able to endure short-term reductions in gap width without severe damage. Consequently the necessary gap between the rotor and brush seal can virtually be reduced to zero, leading to a considerable reduction in air leakage of up to 80 percent. However the reduced gap height increases the probability of rubbing between the bristle package and the rotor surface. The friction forces generated can cause an unwanted heat load on the rotor, bristles and leakage air. In addition, the surfaces involved are exposed to abrasion effects. Especially in the thin and lightweight rotor structures of aircraft engines, the additional heat impact can lead to a problematic level of material stress. To study these effects and to give reliable quantitative design rules, a versatile test rig for brush seals was designed and built. The simulation of seal behavior under relevant engine conditions is the main emphasis of this rig, including high pressure drop, leakage flow and high surface speed. The key feature is the possibility to vary the axis symmetric radial gap width during the test rig operation by up to a 0.5 mm overlap. The so caused rubbing induces a transient rotor temperature rise which is measured via a set of 12 thermocouples embedded in the rotor. These temperature readings can be used to calculate the brush seal heat impact on the rotor structure. Preliminary results with moderate differential pressure and rotor speed proved the functionality of the test rig and confirmed the global approach of the project.

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.

Axial Inclination of the Bristle Pack, a New Design Parameter of Brush Seals for Improved Operational Behavior in Steam Turbines

2014 ◽  
Author(s):  
H. Schwarz ◽  
J. Friedrichs ◽  
J. Flegler
Keyword(s):  
Design Parameter ◽  
Rotational Velocity ◽  
Operating Conditions ◽  
Design Parameters ◽  
Leakage Flow ◽  
Rotating Shaft ◽  
Blow Down ◽  
Seal Design ◽  
Back Plate ◽  
Brush Seals

Within this paper, the axial inclination of the bristle pack as a new design parameter for brush seals for use in a steam turbine and other rotating equipment is discussed. It is widely known that the behavior of brush seals can be influenced by important main design parameters of the bristle pack such as, but not limited to, the bristle thickness, the lay angle or the bristle length. Furthermore, the variation of the front and back plate results in different seal characteristics [1]. Each one of these parameters also has an influence on bristle damping, the blow down capability and thus the leakage flow. In addition, under changing and transient operating conditions, the radial adaptivity, which is essential for accommodating shaft deflection, is also a very important property. For a comprehensive seal design, the wear characteristic and deterioration effects have to be considered beside the above mentioned properties. At the Technical University of Braunschweig, brush seals are experimentally investigated with above focus on different test rigs. These rigs allow a detailed sealing performance investigation including live bristle pack observations and blow down measurement using cold air as well as brush seal investigations using live steam conditions up to 50bars and 450°C and a rotating shaft with representative rotational velocity. The paper shows and discusses experimental results of different axial inclinations of the bristle pack, while testing with constant front and back plate designs. The influences on the blow down, the axial behavior of the bristle pack, the leakage flow and the bristle pack stiffness are shown. The new effect of a rotating blow down type of bristle oscillation is also shown and discussed and finally a classification of the seal behavior depending of the different axial inclination is given.

Experimental and Numerical Investigations on Leakage Flow Characteristics of Two Kinds of Brush Seals

2018 ◽  
Author(s):  
Yuanqiao Zhang ◽  
Jun Li ◽  
Xin Yan ◽  
Zhigang Li
Keyword(s):  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Blow Down ◽  
Brush Seal ◽  
Leakage Coefficient ◽  
Computational Fluid Dynamics Cfd ◽  
Brush Seals ◽  
Deflector Plate ◽  
Hysteresis Characteristics

The leakage characteristics of interference and clearance brush seals were experimentally measured and numerically simulated in this paper. The leakage coefficients of the brush seals without a deflector plate at different pressure differentials were firstly measured. The effect of deflector plate and clearance on seal performance and the detailed flow field of the brush seal were numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions coupled with a Non-Darcian Porous Medium model. In addition, this study experimentally investigated the hysteresis characteristic of interference and clearance brush seals without deflector plates, and presented detailed investigations on the blow down effect of clearance brush seal using Computational Fluid Dynamics (CFD) as mentioned above and Finite Element Method (FEM) approaches. The obtained results show that the leakage coefficient and blow-down effect of the brush seal with a deflector plate is lower than that of the brush seal without a deflector plate at the same pressure difference and the clearance between the bristle pack and shaft will increase the leakage coefficient significantly. The different hysteresis characteristics of interference and clearance brush seals are illustrated and discussed.

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.

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