Improved Understanding of Blow-Down in Filament Seals

2010 ◽  
Vol 132 (4) ◽  
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 toward 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.

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.

scholarly journals Detailed Experimental Studies of Flow in Large Scale Brush Seal Model and a Comparison With CFD Predictions

1999 ◽  
Author(s):  
L. H. Chen ◽  
P. E. Wood ◽  
T. V. Jones ◽  
J. W. Chew
Keyword(s):  
Large Scale ◽  
Experimental Studies ◽  
Flow Characteristics ◽  
Resistance Coefficient ◽  
Scale Model ◽  
Anisotropic Flow ◽  
Pressure Distributions ◽  
Brush Seal ◽  
Dimensional Parameters ◽  
Measured Pressure

A five times scale model of an engine brush seal has been manufactured. The bristle stiffness and pressure were chosen to satisfy close similarity of the relevant non-dimensional parameters, and the choice of parameters is described. The comparison of flow characteristics for the model seal and an engine seal confirmed the non-dimensional similarity. Detailed pressure measurements were performed within the bristle pack by employing hollow bristles. This novel measurement allowed insight to be obtained into the operation of both clearance and interference seals. In particular, the measured pressure variation in the region of the bristle tips was significant. The deflection of the bristles was determined by comparing the bristle tip pressures with the static pressures along the shaft. Hence the compaction of the pack in this region was found directly. A numerical modelling of brush seals employing anisotropic flow resistance has been developed. Predictions were compared with the measured pressure distributions within the pack. This enabled sensible selection of the pack resistance distribution to be made. Although uniform anisotropic resistance throughout the pack gave reasonable flow rate characteristics, the pressure distribution was not reproduced. A variation of resistance coefficient consistent with the observed compaction was required to give a solution comparable with the experiments.

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.

Experimental and Numerical Investigations on the Leakage Flow Characteristics of the Labyrinth Brush Seal

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Jun Li ◽  
Bo Qiu ◽  
Zhenping Feng
Keyword(s):  
Experimental Data ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Leakage Rate ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Blow Down ◽  
Pressure Distributions ◽  
Brush Seal ◽  
Brush Seals

The leakage rate of the labyrinth brush seal was experimentally measured and numerically investigated in this paper. Four different rotational speeds of 0, 1500, 2400 and 3000 rpm were utilized to investigate the effects on the leakage rate of the labyrinth brush seal. In addition, five different pressure ratios and two initial clearances were also adopted to study the influences of pressure ratio and clearance size on the leakage rate of the labyrinth brush seal. The leakage rates of the experimental labyrinth brush seal at different rotational speeds, pressure ratios, and initial clearances were also predicted using Reynolds-averaged Navier-Stokes (RANS) solutions coupling with a non-Darcian porous medium model. The rotor centrifugal growth and bristle blow-down effects were considered in the present numerical research. The rotor centrifugal growth at different rotational speeds was calculated using the finite element method (FEM). The variation of the sealing clearance size with rotor centrifugal growth and bristle blow-down was analyzed. The numerical leakage rate was in good agreement with the experimental data. The effects of rotational speeds, pressure ratios, and clearance sizes on the leakage flow characteristics of brush seals were also investigated based on the experimental data and numerical results. The detailed leakage flow fields and pressure distributions of the brush seals were also presented.

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.

Detailed Experimental Studies of Flow in Large Scale Brush Seal Model and a Comparison With CFD Predictions

2000 ◽  
Vol 122 (4) ◽  
pp. 672-679 ◽  
Author(s):  
L. H. Chen ◽  
P. E. Wood ◽  
T. V. Jones ◽  
J. W. Chew
Keyword(s):  
Large Scale ◽  
Experimental Studies ◽  
Flow Characteristics ◽  
Resistance Coefficient ◽  
Scale Model ◽  
Anisotropic Flow ◽  
Pressure Distributions ◽  
Brush Seal ◽  
Dimensional Parameters ◽  
Measured Pressure

A five times scale model of an engine brush seal has been manufactured. The bristle stiffness and pressure were chosen to satisfy close similarity of the relevant non-dimensional parameters, and the choice of parameters is described. The comparison of flow characteristics for the model seal and an engine seal confirmed the non-dimensional similarity. Detailed pressure measurements were performed within the bristle pack by employing hollow bristles. This novel measurement allowed insight to be obtained into the operation of both clearance and interference seals. In particular, the measured pressure variation in the region of the bristle tips was significant. The deflection of the bristles was determined by comparing the bristle tip pressures with the static pressures along the shaft. Hence the compaction of the pack in this region was found directly. A numerical modeling of brush seals employing anisotropic flow resistance has been developed. Predictions were compared with the measured pressure distributions within the pack. This enabled sensible selection of the pack resistance distribution to be made. Although uniform anisotropic resistance throughout the pack gave reasonable flow rate characteristics, the pressure distribution was not reproduced. A variation of resistance coefficient consistent with the observed compaction was required to give a solution comparable with the experiments. [S0742-4795(00)01703-8]

Flow Resistance Coefficients of Porous Brush Seal As a Function of Pressure Load

2017 ◽  
Author(s):  
Yahya Doğu ◽  
Mustafa C. Sertçakan ◽  
Koray Gezer ◽  
Mustafa Kocagül
Keyword(s):  
Pressure Distribution ◽  
Flow Resistance ◽  
Radial Pressure ◽  
Blow Down ◽  
Static Test ◽  
Backing Plate ◽  
Pressure Load ◽  
Brush Seal ◽  
Brush Seals ◽  
Resistance Coefficients

Developments in brush seal analyses tools have been covering advanced flow and structural analyses since brush seals are applied at elevated pressure loads, temperatures, surface speeds, and transients. Brush seals have dynamic flow and structural behaviors that need to be investigated in detail in order to estimate final leakage output and service life. Bristles move, bend and form a grift matrix depending on pressure load. The level of pressure load determines the tightness of the bristle pack, and thus, the leakage. In the CFD analyses of this work, the bristle pack is treated as a porous medium. Based on brush seal test data, the flow resistance coefficients (FRC) for the porous bristle pack are calibrated as a function of pressure load. A circular seal is tested in a static test rig under various pressure loads at room temperature. The FRC calibration is based on test leakage and literature based axial pressure distribution on the rotor surface and radial pressure distribution over the backing plate. The anisotropic FRC are treated as spatial dependent in axi-symmetrical coordinates. The fence height region and the upper region of bristle pack have different FRC since the upper region is supported by backing plate while bristles are free to move and bend at the fence height region. The FRC are found to be almost linearly dependent on the pressure load for investigated conditions. The blow-down is also calculated by incorporating test leakage and calibrated FRC.

Flow Resistance Coefficients of Porous Brush Seal as a Function of Pressure Load

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Yahya Doğu ◽  
Mustafa C. Sertçakan ◽  
Koray Gezer ◽  
Mustafa Kocagül
Keyword(s):  
Pressure Distribution ◽  
Flow Resistance ◽  
Radial Pressure ◽  
Blow Down ◽  
Static Test ◽  
Backing Plate ◽  
Pressure Load ◽  
Brush Seal ◽  
Brush Seals ◽  
Resistance Coefficients

Developments in brush seal analyses tools have been covering advanced flow and structural analyses since brush seals are applied at elevated pressure loads, temperatures, surface speeds, and transients. Brush seals have dynamic flow and structural behaviors that need to be investigated in detail in order to estimate final leakage output and service life. Bristles move, bend, and form a grift matrix depending on pressure load. The level of pressure load determines the tightness of the bristle pack, and thus, the leakage. In the computational fluid dynamics (CFD) analyses of this work, the bristle pack is treated as a porous medium. Based on brush seal test data, the flow resistance coefficients (FRC) for the porous bristle pack are calibrated as a function of pressure load. A circular seal is tested in a static test rig under various pressure loads at room temperature. The FRC calibration is based on test leakage and literature-based axial pressure distribution on the rotor surface and radial pressure distribution over the backing plate. The anisotropic FRC are treated as spatial dependent in axisymmetrical coordinates. The fence height region and the upper region of bristle pack have different FRC since the upper region is supported by backing plate, while bristles are free to move and bend at the fence height region. The FRC are found to be almost linearly dependent on the pressure load for investigated conditions. The blow-down is also calculated by incorporating test leakage and calibrated FRC.

Experimental and Numerical Investigations on the Leakage Flow Characteristics of the Labyrinth Brush Seal

2012 ◽  
Author(s):  
Jun Li ◽  
Bo Qiu ◽  
Shengke Jiang ◽  
Xianglin Kong ◽  
Zhenping Feng
Keyword(s):  
Experimental Data ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Leakage Rate ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Blow Down ◽  
Pressure Distributions ◽  
Brush Seal ◽  
Brush Seals

The leakage rate of the labyrinth brush seal was experimentally measured and numerically investigated in this paper. Four different rotational speeds with 0, 1500, 2400 and 3000 rpm were utilized to investigate the effects on the leakage rate of the labyrinth brush seal. In addition, five different pressure ratios and two initial clearances were also adopted to study the influences of pressure ratio and clearance size on the leakage rate of the labyrinth brush seal. The leakage rate of experimental labyrinth brush seal at different rotational speeds, pressure ratios and initial clearances were also predicted using Reynolds-Averaged Navier-Stokes (RANS) solution coupling with non-Darcian porous medium model. The rotor centrifugal growth and bristle blow-down effects were considered in the present numerical research. The rotor centrifugal growth at different rotational speeds was calculated using Finite Element Method (FEM). The variation of sealing clearance size with rotor centrifugal growth and bristle blow-down was analyzed. The numerical leakage rate was in good agreement with the experimental data. The effects of rotational speeds, pressure ratios and clearance sizes on the leakage flow characteristics of brush seals were also investigated based on the experimental data and numerical results. The detailed leakage flow fields and pressure distributions of brush seals were also presented.

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