Brush Seal Frictional Heat Generation—Test Rig Design and Validation Under Steam Environment

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Markus Raben ◽  
Jens Friedrichs ◽  
Johan 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.

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.

Investigation of Conjugate Heat Transfer in Brush Seals Using Porous Media Approach Under Local Thermal Non-Equilibrium Conditions

2015 ◽  
Author(s):  
Bo Qiu ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Heat Generation ◽  
Frictional Force ◽  
Conjugate Heat Transfer ◽  
Frictional Heat ◽  
Equilibrium Conditions ◽  
Frictional Heat Generation ◽  
Brush Seal ◽  
Brush Seals

As a type of contacting seal technology, brush seals provide superior sealing performance and flexible behavior. Brush seals have found increasing application in more challenging high-temperature locations in recent years. Thus, the frictional heat generation between the seal bristles and mating surfaces is becoming another major concern for stable operation of brush seals. This study presents detailed investigations on the conjugate heat transfer behavior of brush seals using Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) approaches. A dual-energy equation was proposed to describe the conjugate heat transfer in the porous bristle pack region under local thermal non-equilibrium conditions. The heat transfer CFD model was established with consideration of anisotropic thermal conductivity and a radius-dependent porosity of the bristle pack. The frictional heat generation was calculated from the product of the bristle-rotor frictional force and sliding velocity. The bristle-rotor frictional force was obtained from the brush seal FEM model with consideration of internal friction and aerodynamic load on the bristles. The temperature distribution of the brush seal was predicted at various operational conditions using the iterative CFD and FEM brush seal model. The effects of pressure ratios and rotational speeds on the temperature distribution and bristle maximum temperature of the brush seal were investigated based on the developed numerical approach. The effect of frictional heat generation on brush seal leakage was also analyzed.

Numerical Investigations on the Heat Transfer Behavior of Brush Seals Using Combined Computational Fluid Dynamics and Finite Element Method

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Bo Qiu ◽  
Jun Li
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Finite Element Method ◽  
Computational Fluid Dynamics ◽  
Finite Element ◽  
Heat Generation ◽  
Frictional Heat ◽  
Frictional Heat Generation ◽  
Brush Seal ◽  
Brush Seals

Brush seals have been applied in more and more challenging high-temperature locations. The high speed bristle-rotor friction causes a considerable heat generation which accelerates the bristles wear. The frictional heat generation at bristle-rotor interface becomes another major concern in brush seal applications. This study presented detailed investigations on the heat transfer characteristics and contact mechanics of brush seals using a combined computational fluid dynamics (CFD) and finite element method (FEM) brush seal model. The CFD model of brush seal for mass and heat transfer employed Reynolds-averaged Navier–Stokes (RANS) solutions coupled with non-Darcian porous medium approach. The nonlinear contact model of brush seal was established using FEM with considerations of internal frictions (bristle to rotor, bristle to backing plate, and bristle to bristle) and aerodynamic loads on bristles. The numerical method involved iterations between CFD and FEM models to better evaluate the heat transfer behaviors of the brush seal with consideration of bristle deflections. The frictional heat generation was calculated from the product of bristle-rotor frictional force and sliding velocity. The bristle deflections and temperature distributions of the brush seal were predicted at various operational conditions using the iterative CFD and FEM brush seal model. The effects of pressure differential and rotational speed on the contact behavior, temperature distribution and bristle maximum temperature of brush seals were numerically investigated using the developed approach. The detailed pressure contours and streamline distributions of the brush seal were also illustrated.

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.

Oil Brush Seals in Turbomachinery: Flow Analyses and Closed-Form Solutions

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Ertuğrul Tolga Duran
Keyword(s):  
Closed Form ◽  
High Speed ◽  
Closed Form Solution ◽  
Frictional Heat ◽  
Rotor Speed ◽  
Test Rig ◽  
Lifting Force ◽  
Operation Conditions ◽  
Rotor Surface ◽  
Brush Seals

Abstract Brush seals are one of the most important dynamic seals used in oil and oil mist applications in industrial turbines and aviation. Flexible bristle structure is the main structural superiority of brush seals, which enables precise clearance control and high performance in compensating rotor transients. The viscous medium between the high-speed rotor surface and brush seal bristles generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. Shear heating at moderate and high rotor surface speeds results in an increase in temperature and stabilization of lifting force, which is known as high-speed lift stabilization. Strong temperature–viscosity dependency of lube oils possesses the need for a detailed analysis and understanding of the effect of shear heat on hydrodynamic lift of brush seals in oil applications. To provide a better understanding about the critical balance of hydrodynamic lift force with rotor speed, temperature, and pressure, this work presents an analytical study to investigate pressure profile and shear heat temperature rise in liquid sealing medium within the hydrodynamic lift clearance. A closed-form solution to pressure and temperature distribution in axial and radial directions has been obtained by solving continuity, Navier–Stokes, and thermal energy equations for brush seals. The thermal and pressure functions are evaluated for linear and nonlinear pressure drop approaches, and the results are compared with each other. Deviation in nonlinear and linear pressure, resulting temperature level differences, and effect of rotor speed are detailed within the content of this study. The provided closed-form functions for pressure and temperature profiles are useful for designers since these can be utilized for turbine operation conditions. Dynamic test rig design for high-speed leakage performance measurement of turbomachinery seals is detailed, where the test rig can also be adopted for stiffness, frictional heat, power loss, torque loss, and bucket tip stability testing in oil and air environment. The test setup can also be used for testing dynamic seals other than brush seals.

Brush Seal Temperature Distribution Analysis

2005 ◽  
Vol 128 (3) ◽  
pp. 599-609 ◽  
Author(s):  
Yahya Dogu ◽  
Mahmut F. Aksit
Keyword(s):  
Heat Flux ◽  
Temperature Distribution ◽  
Heat Generation ◽  
Operating Conditions ◽  
Frictional Heat ◽  
Distribution Analysis ◽  
Cfd Analysis ◽  
Oxidation Rates ◽  
Frictional Heat Generation ◽  
Brush Seal

Brush seals are designed to survive transient rotor rubs. Inherent brush seal flexibility reduces frictional heat generation. However, high surface speeds combined with thin rotor sections may result in local hot spots. Considering large surface area and accelerated oxidation rates, frictional heat at bristle tips is another major concern especially in challenging high-temperature applications. This study investigates temperature distribution in a brush seal as a function of frictional heat generation at bristle tips. The two-dimensional axisymmetric computational fluid dynamics (CFD) analysis includes the permeable bristle pack as a porous medium allowing fluid flow throughout the bristle matrix. In addition to effective flow resistance coefficients, isotropic effective thermal conductivity as a function of temperature is defined for the bristle pack. Employing a fin approach for a single bristle, a theoretical analysis has been developed after outlining the brush seal heat transfer mechanism. Theoretical and CFD analysis results are compared. To ensure coverage for various seal designs and operating conditions, several frictional heat input cases corresponding to different seal stiffness values have been studied. Frictional heat generation is outlined to introduce a practical heat flux input into the analysis model. Effect of seal stiffness on nominal bristle tip temperature has been evaluated. Analyses show a steep temperature rise close to bristle tips that diminishes further away. Heat flux conducted through the bristles dissipates into the flow by a strong convection at the fence-height region.

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 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.

Brush Seal Temperature Distribution Analysis

2005 ◽  
Author(s):  
Yahya Dogu ◽  
Mahmut F. Aksit
Keyword(s):  
Heat Flux ◽  
Temperature Distribution ◽  
Heat Generation ◽  
Operating Conditions ◽  
Frictional Heat ◽  
Distribution Analysis ◽  
Cfd Analysis ◽  
Oxidation Rates ◽  
Frictional Heat Generation ◽  
Brush Seal

Brush seals are designed to survive transient rotor rubs. Inherent brush seal flexibility reduces frictional heat generation. However, high surface speeds combined with thin rotor sections may result in local hot spots. Considering large surface area and accelerated oxidation rates, frictional heat at bristles tips is another major concern especially in challenging high temperature applications. This study investigates temperature distribution in a brush seal as a function of frictional heat generation at bristle tips. The two-dimensional axisymmetric CFD analysis includes the permeable bristle pack as a porous medium allowing fluid flow throughout the bristle matrix. In addition to effective flow resistance coefficients, isotropic effective thermal conductivity as a function of temperature is defined for the bristle pack. Employing a fin approach for a single bristle, a theoretical analysis has been developed after outlining the brush seal heat transfer mechanism. Theoretical and CFD analysis results are compared. To ensure coverage for various seal designs and operating conditions, several frictional heat input cases corresponding to different seal stiffness have been studied. Frictional heat generation is outlined to introduce a practical heat flux input into the analysis model. Effect of seal stiffness on nominal bristle tip temperature has been evaluated. Analyses show a steep temperature rise close to bristle tips that diminishes further away. Heat flux conducted through the bristles dissipates into the flow by a strong convection at fence height region.

Improved Understanding of Blow-Down in Filament Seals

2008 ◽  
Author(s):  
Gervas Franceschini ◽  
Terry V. Jones ◽  
David R. H. Gillespie
Keyword(s):  
Gas Turbines ◽  
Flow Resistance ◽  
Large Scale ◽  
Scale Model ◽  
Blow Down ◽  
Pressure Distributions ◽  
Brush Seal ◽  
Large Scale Model ◽  
Rotor Surface ◽  
Brush Seals

Brush seals are used to provide flow resistance between rotating and stationary components in gas turbines. Compliant filament seals such as brush seals exhibit a phenomenon called blow-down where the filaments deflect towards the rotor surface when a differential pressure is applied across the seal. This phenomenon is desirable as it enables seal contact to be maintained during rotor contractions and eccentric excursions. This paper describes an aerodynamic mechanism which can cause the blow-down of bristles. Importantly it shows that distortion of the bristle pack is not necessary to achieve blow-down. Experimental and computational investigations of a large scale model representative of a section of a brush seal are also reported. The measured and predicted detailed pressure distributions thus obtained are used to validate the model of blow-down presented.

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