Role of Distributed Interbristle Friction Force on Brush Seal Hysteresis

2006 ◽  
Vol 129 (1) ◽  
pp. 199-204 ◽  
Author(s):  
H. Zhao ◽  
R. J. Stango
Keyword(s):  
Friction Force ◽  
Numerical Solutions ◽  
Contact Forces ◽  
Design Parameters ◽  
Eccentric Rotation ◽  
Seal Design ◽  
Numerical Studies ◽  
Fibrous Network ◽  
Brush Seal ◽  
Uniformly Distributed Loads

Brush seals comprised of closely packed fine-diameter wires are an important innovation in seal technology for turbo-machinery. During service, brush seal bristles are subjected to a complex system of forces that are associated with various working loads including—but not limited to—aerodynamic forces, bristle tip∕rotor contact force, and interbristle interactions. The latter interactions are associated with contact forces that are exerted onto a bristle by adjacent fibers, as both forces and displacements are transmitted throughout the fibrous network. Such interbristle contact forces can be represented as uniformly distributed loads along the lateral surface of the fiber, or as applied discrete loads at various locations along the bristle length. In this paper, the role that uniformly distributed interbristle friction force plays in brush seal hysteresis is examined and reported. The origin of this frictional load is attributed to conjugate interbristle shear forces that arise due to compaction and aggregate displacement of the bristle pack during service. This, in turn, gives rise to a uniformly distributed internal micromoment that resists bending deformation. Numerical studies are reported for a brush seal whose bristle tips are subjected to rotor induced loading that is associated with bristle∕rotor interference or eccentric rotation of the shaft. In order to extend the range of applicability of numerical solutions, results are reported in terms of nondimensional brush seal design parameters. Results indicated that interbristle friction force can give rise to a delayed filament displacement as well as an incomplete bending recovery of bristles. The latter phenomenon can inevitably result in hysteretic “gapping,” i.e., the formation of an annular or crescent space between the rotor and bristle tips, thereby increasing vulnerability of the seal to leakage.

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.

Effect of Flow-Induced Radial Load on Brush Seal/Rotor Contact Mechanics

2004 ◽  
Vol 126 (1) ◽  
pp. 208-215 ◽  
Author(s):  
Haifang Zhao ◽  
Robert J. Stango
Keyword(s):  
Flexural Rigidity ◽  
Reaction Force ◽  
Contact Forces ◽  
Design Parameters ◽  
Radial Load ◽  
Bending Stress ◽  
Seal Design ◽  
Brush Seal ◽  
Rotor Surface ◽  
Brush Seals

Brush seals comprised of special-alloy wire bristles are currently being used in lieu of traditional labyrinth seals for turbomachinery applications. This advancement in seal technology utilizes close-packed bristles that readily undergo lateral deformation arising from aerodynamic loads as well as loads imparted by the rotor surface. Thus, during operation, filament tips remain in contact with the rotor surface, which, in turn, inhibits leakage between successive stages of the turbine, and increases engine efficiency. However, contact forces generated at the interface of the rotor and fiber tips can lead to eventual bristle fatigue and wear of the seal/rotor system. Therefore, it is important that reliable modeling techniques be developed that can help identify complex relationships among brush seal design parameters, in-service loads, and contact forces that arise during the operation of turbomachinery. This paper is concerned with modeling and evaluating bristle deformation, bending stress, and bristle/rotor contact forces that are generated at the interface of the fiber and rotor surface due to radial fluid flow, and augments previous work reported by the author’s, which assessed filament tip forces that arise solely due to interference between the bristle/rotor. The current problem derives its importance from aerodynamic forces that are termed “blow-down,” that is, the inward radial flow of gas in close proximity to the face of the seal. Thus, bristle deformation, bristle tip reaction force, and bristle bending stress is computed on the basis of an in-plane, large-displacement mechanics analysis of a cantilever beam that is subjected to a uniform radial load. Solutions to the problem are obtained for which the filament tip is constrained to lie on the rotor surface, and includes the effect of Coulombic friction at the interface of the fiber tip and rotor. Contact forces are obtained for a range of brush seal design parameters including fiber lay angle, flexural rigidity, and length. In addition, the governing equation is cast in non-dimensional form, which extends the range of applicability of solutions to brush seals having a more general geometry and material composition.

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.

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.

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.

Development of an End-Effector for Mitigation of Collisions

2021 ◽  
Author(s):  
Domenico Tommasino ◽  
Matteo Bottin ◽  
Giulio Cipriani ◽  
Alberto Doria ◽  
Giulio Rosati
Keyword(s):  
Numerical Simulations ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Contact Forces ◽  
Design Parameters ◽  
End Effector ◽  
Linear Behavior ◽  
Stable Mechanism ◽  
Robot Tasks ◽  
The Impact

Abstract In robotics the risk of collisions is present both in industrial applications and in remote handling. If a collision occurs, the impact may damage both the robot and external equipment, which may result in successive imprecise robot tasks or line stops, reducing robot efficiency. As a result, appropriate collision avoidance algorithms should be used or, if it is not possible, the robot must be able to react to impacts reducing the contact forces. For this purpose, this paper focuses on the development of a special end-effector that can withstand impacts and is able to protect the robot from impulsive forces. The novel end-effector is based on a bi-stable mechanism that decouples the dynamics of the end-effector from the dynamics of the robot. The intrinsically non-linear behavior of the end-effector is investigated with the aid of numerical simulations. The effect of design parameters and the operating conditions are analyzed and the interaction between the functioning of the bi-stable mechanism and the control system is studied. In particular, the effect of the mechanism in different scenarios characterized by different robot velocities is shown. Results of numerical simulations assess the validity of the proposed end-effector, which can lead to large reductions in impact forces.

Direct Sensitivity Analysis of Multibody Systems: A Vehicle Dynamics Benchmark

2019 ◽  
Vol 14 (2) ◽  
Author(s):  
Alfonso Callejo ◽  
Daniel Dopico
Keyword(s):  
Sensitivity Analysis ◽  
Multibody Systems ◽  
Automatic Differentiation ◽  
Time Integration ◽  
General Purpose ◽  
Contact Forces ◽  
Design Parameters ◽  
Computational Techniques ◽  
Computationally Efficient ◽  
Integration Algorithm

Algorithms for the sensitivity analysis of multibody systems are quickly maturing as computational and software resources grow. Indeed, the area has made substantial progress since the first academic methods and examples were developed. Today, sensitivity analysis tools aimed at gradient-based design optimization are required to be as computationally efficient and scalable as possible. This paper presents extensive verification of one of the most popular sensitivity analysis techniques, namely the direct differentiation method (DDM). Usage of such method is recommended when the number of design parameters relative to the number of outputs is small and when the time integration algorithm is sensitive to accumulation errors. Verification is hereby accomplished through two radically different computational techniques, namely manual differentiation and automatic differentiation, which are used to compute the necessary partial derivatives. Experiments are conducted on an 18-degree-of-freedom, 366-dependent-coordinate bus model with realistic geometry and tire contact forces, which constitutes an unusually large system within general-purpose sensitivity analysis of multibody systems. The results are in good agreement; the manual technique provides shorter runtimes, whereas the automatic differentiation technique is easier to implement. The presented results highlight the potential of manual and automatic differentiation approaches within general-purpose simulation packages, and the importance of formulation benchmarking.

Analysis of Tribological Performance of Piston Ring Lubrication

2011 ◽  
Author(s):  
Yibin Guo ◽  
Wanyou Li ◽  
Dequan Zou ◽  
Xiqun Lu ◽  
Tao He
Keyword(s):  
Film Thickness ◽  
Friction Force ◽  
Power Loss ◽  
Piston Ring ◽  
Design Parameters ◽  
Oil Film ◽  
Starved Lubrication ◽  
Piston Ring Lubrication ◽  
Cylinder Bore ◽  
Lubrication Conditions

In this paper a mixed lubrication model considering lubricant supply conditions on cylinder bore has been developed for the piston ring lubrication. The numerical procedures of both fully flooded and starved lubrication were included in the model. The lubrication equations and boundary conditions at the end of strokes were discussed in detail. The effects of piston ring design parameters, such as ring face profile and ring tension, on oil film thickness, friction force and power loss under fully flooded and starved lubrication conditions due to available lubricant supply on cylinder bore were studied. The simulation results show that the oil available in the inlet region of the oil film is important to the piston ring friction power loss. With different ring face crown heights and tensions, the changes of oil film thickness and friction force were apparent under fully flooded lubrication, but almost no changes were found under starved lubrication except at the end of a stroke. In addition, the oil film thickness and friction force were affected evidently by the ring face profile offsets under both fully flooded and starved lubrication conditions, and the offset towards the combustion chamber made a large contribution to forming thicker oil film during the expansion stroke. So under different lubricant supply conditions on the cylinder bore, the ring profile and tension need to be adjusted to reduce the friction and power loss. Moreover, the effects of lubricant viscosity, surface composite roughness, and engine operating speed on friction force and power loss were also discussed.

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.

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