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.

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.

An Investigation of Heat Generation Characteristics of Brush Seals

2007 ◽  
Author(s):  
Mehmet Demiroglu ◽  
John A. Tichy
Keyword(s):  
Contact Force ◽  
Heat Generation ◽  
Operating Conditions ◽  
Frictional Heat ◽  
Design Parameters ◽  
Frictional Heat Generation ◽  
Operation Conditions ◽  
Seal Design ◽  
Wide Range ◽  
Brush Seals

Brush seals are considered as a category of compliant seals, which tolerate a great high level of interference between the seal and the rotor or shaft. Their superior leakage characteristics have opened many application fields in the turbo-machinery world, ranging from industrial steam turbines to jet engines. However, brush seal designers have to find a trade-off between the lower parasitic leakage but higher heat generation properties of brush seals for given operation conditions. As brush seals can maintain contact with the rotor for a wide range of operating conditions, the contact force/pressure generated at the seal-rotor interface becomes an important design parameter for sustained seal performance and longevity of its service life. Furthermore, due to this contact force at the interface, frictional heat generation is inevitable and must be evaluated for various design and operating conditions. In this paper, frictional heat generation at the sealrotor interface is studied. To capture temperature rise at the interface, a thermal image of the seal and rotor is taken with an infrared camera under various operating conditions. The temperature map of the rotor is compared to results from thermal finite element analysis of the rotor to back calculate the heat flux to the rotor. A closed form equation for frictional heat generation is suggested as a function of seal design parameters, material properties, friction coefficient and empirical factors from testing.

CAE Based Brush Seal Characterization for Stiffness and Stress Levels

2015 ◽  
Author(s):  
E. Tolga Duran ◽  
Mahmut F. Aksit ◽  
Murat Ozmusul
Keyword(s):  
Operating Conditions ◽  
Design Parameters ◽  
Backing Plate ◽  
Seal Design ◽  
Brush Seal ◽  
Stress Levels ◽  
Brush Seals ◽  
Main Effects ◽  
State Pressure

Brush seals are complex structures having variety of design parameters, all of which affect the seal behavior under turbine operating conditions. The complicated nature of the seal pack and frictional interactions of rotor, backing plate and bristles result in nonlinear response of the brush seal to variances of design parameters. This study presents CAE based characterization of brush seals, which aims to investigate the main effects of several brush seal design parameters on brush seal stiffness and stress levels. Characterization work of this study includes free-state rotor rub (unpressurized seal), steady state (pressure load without rotor interference) and pressurized-rotor interference conditions.

Fundamental Design Issues of Brush Seals for Industrial Applications

2001 ◽  
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.

Preliminary Investigations for a Pressure Balanced Back Plate at Low Inclined Brush Seals

2015 ◽  
Author(s):  
H. Schwarz ◽  
J. Friedrichs
Keyword(s):  
Steam Turbine ◽  
Renewable Energy Sources ◽  
Test Facility ◽  
Design Parameters ◽  
Blow Down ◽  
Pressure Drops ◽  
Brush Seal ◽  
Plate Design ◽  
Back Plate ◽  
Brush Seals

Within this paper a continuation in brush seal testing for flexible load regimes in a steam turbine is given. Besides the well-known main design parameters of brush seals, e.g. the bristle pack thickness, the bristle diameter or the lay angle of the bristle pack, this paper focuses on the axial inclination of the bristle pack and particularly the affinity of bristle pack oscillations at low inclined bristle packs and small pressure differences. As it was presented in GT2014-26330, the axial inclination of the bristle pack is an important design parameter for brush seals. Along with a clearly increased blow-down capability and a reduced stiffness the seals tend to exhibit an enhanced axial bristle pack width during pressurization. It was previously shown that a low axial inclination of the bristle pack results in a loose package and in bristle pack oscillations until pressure differences of 10 bar. Above pressure drops of 10 bar the resulting higher abrasive behavior stops and a well sealing brush seal with a loose bristle pack is given. Regarding the renewable energy sources for necessary changes in steam turbine operations, a flexible sealing system with an enhanced wide operating range is requested. To capture all positive behaviors of low inclined brush seals for pressure differences until 10 bar, a design to safely avoid bristle pack oscillations is required. With this background low inclined brush seals with a new back plate design were tested at the Institute’s cold air test facility in Braunschweig up to a pressure difference of 4 bar. The facility allows detailed sealing performance investigations including real time bristle pack observations. The present paper shows and discusses overall experimental results of brush seals with different axial inclinations mounted with an adjustable back plate to determine the influence of the back plate design on the bristle pack oscillations. Furthermore, these new results together with older measurements from 2012 were used to develop a theory regarding the changes that result from contact between the bristle pack and the adjusted back plate. Finally, the design for a pressure balanced back plate will be shown.

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.

Operational Performance and Locally Resolved Outflow of Brush Seals

2019 ◽  
Author(s):  
Fabian Schur ◽  
Jens Friedrichs
Keyword(s):  
Operational Performance ◽  
Design Parameters ◽  
Steam Turbines ◽  
Test Rig ◽  
Rotating Shaft ◽  
Experimental Conditions ◽  
Widespread Application ◽  
Backing Plate ◽  
Brush Seals ◽  
The Impact

Abstract As a result of the superior leakage efficiency of brush seals compared to conventional labyrinth seals, compliant contacting filament seals are used to increase the efficiency of jet engines as well as stationary gas and steam turbines. The widespread application of brush seals at different and varying pressure differences combined with variable contacting velocities at the rotor surface requires a profound understanding of the influences of different design parameters on the operational leakage performance. In order to systematically investigate the impact of different design parameters on sealing performance, a new cold air test rig was developed. The new test rig with rotating shaft enables hot-wire anemometry measurements downstream of the seals. These measurements provide insight into the locally resolved flow structure in addition to the integral leakage measurements. For the investigations, one welded and five different clamped brush seals at rotational speeds up to 3000rpm and pressure differences across the seals up to 500kPa are considered. Therefore, the influence of two different designs on the flow through the bristles is presented. For the clamped brush seals, variations of the front and backing plate are investigated. Additionally, the effects of bristle diameter and three different axial inclinations of the bristle pack on the sealing efficiency are shown. Furthermore, initial wear development during the first 30 to 60 hours of brush seal operation at varying experimental conditions is presented and linked to the design parameters. Consequently, the effects of major design aspects on the operational performance of brush seals are examined and presented.

Brush Seals Used in Steam Environments: Chronological Wear Development and the Impact of Different Seal Designs

2015 ◽  
Author(s):  
M. Raben ◽  
J. Friedrichs ◽  
J. Flegler ◽  
T. Helmis
Keyword(s):  
Abrasive Wear ◽  
Contact Force ◽  
Operating Conditions ◽  
Test Facility ◽  
Working Fluid ◽  
Two Stage ◽  
Blow Down ◽  
Frictional Contacts ◽  
Brush Seals ◽  
The Impact

During the last decades a large effort has been made to continuously improve turbomachine efficiency. Besides the optimization of the primary flow path, also the secondary flow losses have been reduced considerably, due to the use of more efficient seals. Brush seals, as a compliant contacting filament seal, have become an attractive alternative to conventional labyrinth seals in the field of aircraft engines as well as in stationary gas and steam turbines. The aim of today’s research related to brush seals is to understand the characteristics and their connections, in order to be able to make performance predictions, and to ensure the reliability over a defined operating period. It is known that inevitable frictional contacts lead to an abrasive wear on the rotor side as well as on the bristle side. The wear situation is essentially influenced by the resulting contact force at the seal-to-rotor interface during the operating time. This contact force depends on the seal’s blow down capability, which is mainly determined by the geometrical design of the bristle pack, e.g. the axial inclination of the investigated seal design, in combination with the design and material of the surrounding parts, as well as the thermal boundary conditions. For realistic investigations with representative circumferential velocities the TU Braunschweig operates a specially developed steam test rig which enables live steam investigations under varying operating conditions up to 50 bar and 450 °C. Wear measurements and the determination of seal performance characteristics, such as blow down and bristle stiffness, were enabled by an additional test facility using pressurized cold air up to 8 bar as working fluid. This paper presents the chronological wear development on both rotor and seal side, in a steam test lasting 25 days respectively 11 days. Interruptions after stationary and transient intervals were made in order to investigate the wear situation. Two different seal arrangements, a single tandem seal and a two-stage single seal arrangement, using different seal elements were considered. The results clearly show a continuous wear development and that the abrasive wear of the brush seal and rotor is mainly due to the transient test operation, particularly by enforced contacts during shaft excursions. Despite the increasing wear to the brushes, all seals have shown a functioning radial-adaptive behavior over the whole test duration with a sustained seal performance. Thereby, it could be shown that the two-stage arrangement displays a load shift during transients, leading to a balanced loading and unloading status for the two single brush seals. From load sharing and in comparison with the wear data of the tandem seal arrangement, it can be derived that the two-stage seal is less prone to wear. However, the tandem seal arrangement, bearing the higher pressure difference within one configuration, shows a superior sealing performance under constant load, i.e. under stationary conditions.

Analysis of Contact Mechanics for Rotor-Bristle Interference of Brush Seal

2003 ◽  
Vol 125 (2) ◽  
pp. 414-421 ◽  
Author(s):  
R. J. Stango ◽  
H. Zhao ◽  
C. Y. Shia
Keyword(s):  
Contact Force ◽  
Flexural Rigidity ◽  
Operating Conditions ◽  
Contact Forces ◽  
Design Parameters ◽  
Attractive Alternative ◽  
Seal Design ◽  
Brush Seal ◽  
Wide Range ◽  
Deformation Mechanics

Brush seals have proven to be an attractive alternative to labyrinth seals for turbomachinery applications. This innovation in seal technology utilizes both the high temperature capability of special-alloy wire and the flexural adaptability of fibers to accommodate a wide range of operating conditions that are encountered during service. The effectiveness of the seal is principally derived from the bristles ability to endure forces imparted by both the fluid and shaft, and yet maintain contact between the filament tips and the surface of the rotor. Consequently, contact forces generated along the interface of the fiber tip and rotor are an important consideration for both the design and performance of the rotor-seal assembly. This paper focuses on evaluating brush seal forces that arise along the surface of the rotor due to the dimensional disparity or interference between the rotor-fiber. Filament tip contact forces are computed on the basis of an in-plane, large deformation mechanics analysis of a cantilever beam, and validation of the model is assessed by using an electronic balance for measuring the shear and normal force exerted by a bristle tip onto a flat, hardened surface. Formulation of the mechanics problem is briefly reviewed, and includes the effect of Coulombic friction at the interface of the fiber tip and rotor. Filament contact force is used as a basis for computing bearing stress along the fiber-rotor interface. Results are reported for a range of brush seal design parameters in order to provide a better understanding of the role that seal geometry, friction, and bristle flexural rigidity play in generating rotor contact force.

Computational Fluid Dynamics Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Yahya Dogu ◽  
Ahmet S. Bahar ◽  
Mustafa C. Sertçakan ◽  
Altuğ Pişkin ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Ratio ◽  
Plate Thickness ◽  
Operating Conditions ◽  
Design Parameters ◽  
Backing Plate ◽  
Brush Seal ◽  
Front Plate ◽  
Brush Seals

Brush seals require custom design and tailoring due to their behavior driven by flow dynamic, which has many interacting design parameters, as well as their location in challenging regions of turbomachinery. Therefore, brush seal technology has not reached a conventional level across the board standard. However, brush seal geometry generally has a somewhat consistent form. Since this consistent form does exist, knowledge of the leakage performance of brush seals depending on specific geometric dimensions and operating conditions is critical and predictable information in the design phase. However, even though there are common facts for some geometric dimensions available to designers, open literature has inadequate quantified information about the effect of brush seal geometric dimensions on leakage. This paper presents a detailed computational fluid dynamics (CFD) investigation quantifying the leakage values for some geometric variables of common brush seal forms functioning in some operating conditions. Analyzed parameters are grouped as follows: axial dimensions, radial dimensions, and operating conditions. The axial dimensions and their ranges are front plate thickness (z1 = 0.040–0.150 in.), distance between front plate and bristle pack (z2 = 0.010–0.050 in.), bristle pack thickness (z3 = 0.020–0.100 in.), and backing plate thickness (z4 = 0.040–0.150 in.). The radial dimensions are backing plate fence height (r1 = 0.020–0.100 in.), front plate fence height (r2 = 0.060–0.400 in.), and bristle free height (r3 = 0.300–0.500 in.). The operating conditions are chosen as clearance (r0 = 0.000–0.020 in.), pressure ratio (Rp = 1.5–3.5), and rotor speed (n = 0–40 krpm). CFD analysis was carried out by employing compressible turbulent flow in 2D axisymmetric coordinate system. The bristle pack was treated as a porous medium for which flow resistance coefficients were calibrated by using literature based test data. Selected dimensional and operational parameters for a common brush seal form were investigated, and their effects on leakage performance were quantified. CFD results show that, in terms of leakage, the dominant geometric dimensions were found to be the bristle pack thickness and the backing plate fence height. It is also clear that physical clearance dominates leakage performance, when compared to the effects of other geometric dimensions. The effects of other parameters on brush seal leakage were also analyzed in a comparative manner.

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