Experimental Characterization of Variable Bristle Diameter Brush Seal Leakage, Stiffness and Wear

2013 ◽  
Author(s):  
Deepak Trivedi ◽  
Binayak Roy ◽  
Mehmet Demiroglu ◽  
Xiaoqing Zheng
Keyword(s):  
Wear Behavior ◽  
Pressure Loading ◽  
Blow Down ◽  
Friction Forces ◽  
Brush Seal ◽  
Wide Range ◽  
Successful Design ◽  
Brush Seals ◽  
And Performance

Brush seals are used in a wide variety of turbomachinery for sealing rotor-stator and stator-stator clearances. Application of traditional brush seals is limited by their life and performance at high differential pressures. GE’s patent-pending Variable Bristle Diameter (VBD) brush seal overcomes the limitations of the traditional brush seal by sandwiching a layer of fine bristles, with better sealing capability, between adjacent rows of stiffer bristles capable of withstanding larger differential pressure and flow disturbance. The General Electric VBD design uses thick bristles both in front and back rows. In addition to leakage performance, for successful design it is important to understand the force interactions between a brush seal bristle pack and the rotor. The important failure mechanisms to avoid include overheating and rotor dynamic instabilities caused by excessive brush seal forces. Brush seal stiffness, defined as brush seal force per unit circumferential length per unit incursion of the rotor, depends on the complex interaction of the pressure-dependent inter-bristle forces, the blow-down forces and the friction forces between the backplate and the bristle pack. Furthermore, brush seals exhibit different hysteresis and wear behavior under different pressure loading conditions. In this article, we present experimentally measured leakage, stiffness and wear characteristics of three different VBD brush seal designs subjected to a wide range of pressure loading.

Stiffness Measurement for Pressure-Loaded Brush Seals

2011 ◽  
Author(s):  
Rahul A. Bidkar ◽  
Xiaoqing Zheng ◽  
Mehmet Demiroglu ◽  
Norman Turnquist
Keyword(s):  
Gas Turbines ◽  
Design Parameters ◽  
Test Results ◽  
Pressure Loading ◽  
Friction Forces ◽  
Test Fixture ◽  
Hysteresis Behavior ◽  
Brush Seal ◽  
Wide Range ◽  
Brush Seals

Brush seals are widely used as flexible seals for rotor-stator and stator-stator gaps in power generation turbo-machinery like steam turbines, gas turbines, generators and aircraft engines. Understanding the force interactions between a brush seal bristle pack and the rotor is important for avoiding overheating and rotor dynamic instabilities caused by excessive brush seal forces. Brush seal stiffness (i.e. brush seal force per unit circumferential length per unit incursion of the rotor) is usually measured and characterized at atmospheric pressure conditions. However, the inter-bristle forces, the blow-down forces and the friction forces between the backplate and the bristle pack change in the presence of a pressure loading, thereby changing the stiffness of the brush seal in the presence of this pressure loading. Furthermore, brush seals exhibit different hysteresis behavior under different pressure loading conditions. Understanding the increased brush seal stiffness and the increased hysteresis behavior of brush seals in the presence of a pressure loading is important for designing brush seals for higher pressure applications. In this article, we present the development of a test fixture for measuring the stiffness of brush seals subjected to a pressure loading. The fixture allows for measurement of the bristle pack forces in the presence of a pressure loading on the seal while the rotor is incrementally pushed (radially) into the bristle pack. Following the development of this test fixture, we present representative test results on three sample seals to show the trends in brush seal stiffness as the pressure loading is increased. Specifically, we study the effect of different brush seal design parameters on the stiffness of brush seals over a wide range of pressure loadings. These test data can be used for developing predictive models for brush seal stiffness under pressure loading. Furthermore, we demonstrate the utility of this fixture in studying the hysteresis exhibited by brush seals along with the importance of the backplate pressure balance feature present in several brush seal designs. The test results validate the bilinear force-displacement curves previously reported in the literature.

A Test Facility for the Measurement of Torques at the Shaft to Seal Interface in Brush Seals

1999 ◽  
Vol 121 (1) ◽  
pp. 160-166 ◽  
Author(s):  
P. E. Wood ◽  
T. V. Jones
Keyword(s):  
Contact Pressure ◽  
Indirect Measurement ◽  
Test Facility ◽  
Axial Loads ◽  
Rotating Shaft ◽  
Brush Seal ◽  
Wide Range ◽  
Bearing Assembly ◽  
Brush Seals ◽  
Wide Speed Range

An important factor in the performance of brush seals for a wide range of gas turbine applications is the rate of wear at the seal to shaft interface, which is dependent on the contact pressure that exists between the bristles and rubbing surface. This is dependent on a variety of effects. Principally, these are the aerodynamic forces bending the bristles onto the rubbing surface, frictional effects within the bristle pack and at the backing ring that arise with the application of pressure differential, geometrical changes due to centrifugal and thermal growths, and transient differential movements of the rotor that develop in flight manoeuvres. In order to investigate the effect of these phenomena on contact pressure, a test facility has been devised in which the torque exerted by a brush seal on a rotating shaft is used as an indirect measurement of contact pressure. This has necessitated the design of a test facility in which all system torques can be fully calibrated. Consequently, a pressure balanced design has been adopted in which applied seal differential and pressure levels have a minimal effect on axial loads at the rotor bearing assembly. The primary method of torque measurement is the instantaneous deceleration of the rotor. Thus, measurements over a wide speed range are acquired with high frequency instrumentation. The means whereby small parasitic torques are evaluated and corrected is given. Results demonstrating the dependence of contact pressure on seal differential and pressure levels are presented.

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.

Synthesis, growth, structure analysis and performance characterization of DOST crystal: a nonlinear functional material with a wide range of applications

CrystEngComm ◽  
2020 ◽  
Vol 22 (48) ◽  
pp. 8362-8373
Author(s):  
Zhe Yu ◽  
Tianhua Wang ◽  
Guanjun Wang ◽  
Kai Xu ◽  
Qingtang Cui ◽  
...  
Keyword(s):  
Structure Analysis ◽  
Nonlinear Optical ◽  
Functional Material ◽  
Nonlinear Optical Crystal ◽  
Nonlinear Functional ◽  
Growth Structure ◽  
Wide Range ◽  
Optical Crystal ◽  
And Performance

A new non-centrosymmetric organic ion nonlinear optical crystal, DOST.

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.

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.

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.

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 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.

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.

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