CFD Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions

2015 ◽  
Author(s):  
Yahya Doğu ◽  
Mustafa C. Sertçakan ◽  
Ahmet S. Bahar ◽  
Altuğ Pişkin ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Pressure Ratio ◽  
Plate Thickness ◽  
Operating Conditions ◽  
Design Parameters ◽  
Operational Parameters ◽  
Backing Plate ◽  
Brush Seal ◽  
Front Plate ◽  
Brush Seals ◽  
Geometric Variables

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 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=0.040–0.150in.), distance between front plate and bristle pack (z2=0.010–0.050in.), bristle pack thickness (z3=0.020–0.100in.), and backing plate thickness (z4=0.040–0.150in.). The radial dimensions are backing plate fence height (r1=0.020–0.100in.), front plate fence height (r2=0.060–0.400in.), and bristle free height (r3=0.300–0.500in.). The operating conditions are chosen as clearance (r0=0.000–0.020in.), pressure ratio (Rp=1.5–3.5), and rotor speed (n=0–40krpm). CFD analysis was carried out by employing compressible turbulent flow in 2-D axi-symmetric 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.

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.

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

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.

Analysis of Performance and Rotordynamic Force Coefficients of Brush Seals With Reverse Rotation Ability

2004 ◽  
Author(s):  
Adolfo Delgado ◽  
Luis San Andre´s ◽  
John F. Justak
Keyword(s):  
Pressure Ratio ◽  
Nonlinear Partial Differential Equation ◽  
Forced Response ◽  
Operating Conditions ◽  
Partial Differential ◽  
Force Coefficients ◽  
Brush Seal ◽  
Brush Seals ◽  
Discharge Pressure ◽  
Stiffness And Damping

Multiple-shoed brush seals represent an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse rotation operation. The novel configuration incorporates pads contacting the shaft, and which under rotor spinning; lift off due to the generation of hydrodynamic pressures. The ensuing gas film prevents intermittent contact; thus lowering the operating temperature and thermal distortions, and even eliminating bristles’ wear. A computational analysis for the equilibrium and dynamic forced response of a brush seal with reverse rotation capability is presented. Small amplitude rotor motions about an equilibrium position lead to a nonlinear partial differential equation for the static pressure field, and a set of first order linear partial differential equations to determine the rotordynamic force coefficients, stiffness and damping, as function of the excitation frequency and other operating conditions. Predictions for the stiffness and damping coefficients of a 20 shoe-brush seal configuration operating over a range of rotor speeds are detailed. The parametric study varies the nominal gas film thickness, the supply to discharge pressure ratio, and the bristle bed structural loss (damping) coefficient. The results show that the film clearance and supply to discharge pressure ratio do not affect the shoed-brush seal force coefficients. On the other hand, the direct stiffness drops rapidly as the operating speed increases. The shoed-brush seal offers whirl frequency ratios much lower than 0.50 due to the (structural) damping arising from friction among the brush seal bristles.

Brush Seal Free State Stiffness Analyses, Tests and Inspection on Dynamic Effects

2015 ◽  
Author(s):  
E. Tolga Duran ◽  
Mahmut F. Aksit ◽  
Murat Ozmusul
Keyword(s):  
Load Capacity ◽  
Dynamic Stiffness ◽  
Operating Conditions ◽  
Test Results ◽  
Wear Rates ◽  
Backing Plate ◽  
Brush Seal ◽  
Study Test ◽  
Brush Seals ◽  
Interference Measurements

While the efficiency of a brush seal is measured by its leakage rate, the overall performance of the seal is mostly affected by wear rate and durability. Seal stiffness and hysteresis behavior play important roles in determining the leakage performance and rotor stability due to the fact that they directly affect wear rates and pressure load capacity of the seal. The complicated nature of the bristle, rotor and backing plate interactions at typical operating conditions makes it difficult to determine the stiffness and durability of brush seals. In this study, test and computer aided engineering (CAE) methodologies have been developed to simulate brush seal stiffness and stress levels at unpressurized conditions. Unpressurized stiffness tests have been conducted by using two different test rigs, one of which uses a simple metallic pad and the other one uses a full-sized rotor for seal interference measurements. Test results for the two different rigs have been compared and the drawbacks of the simple stiffness test rig have been detailed in this study. CAE analyses at unpressurized conditions have been conducted by using 3D finite element (FE) models, and analyses have been correlated with the stiffness tests. The influence of rotor rotation has also been analyzed at unpressurized seal conditions. Transient simulation results also demonstrated good agreement with the dynamic stiffness tests of the brush seals.

Brush Seal Structural Analysis and Correlation With Tests for Turbine Conditions

2015 ◽  
Author(s):  
E. Tolga Duran ◽  
Mahmut F. Aksit ◽  
Murat Ozmusul
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Dynamic Test ◽  
Operating Conditions ◽  
Contact Forces ◽  
Backing Plate ◽  
Contact Loads ◽  
Brush Seal ◽  
Stress Levels ◽  
Brush Seals

Bristle tip contact forces and resulting stress levels under engine conditions are critical to optimizing brush seal performance as well as to achieving operational safety. Literature survey reveals the lack of test data and analysis methods for evaluating seal stiffness and stress levels under operating conditions. In an attempt to meet this need, a custom test rig design and methodology has been developed to perform stiffness tests under pressure and rotor speed of 3000 rpm. Finite element simulations have been performed for brush seals and results have been correlated with the test data of this study. Considering the critical importance of contact loads on brush seal overall performance and system health, and due to the complicated structure of brush seals, where bristles are contacting with each other as well as with the backing plate and the rotor, CAE analyses with high fidelity is required to simulate the test and turbine operating conditions. For this purpose, FE methodology has been developed for structural analyses of brush seals. 3D finite element models of brush seals have been constructed and simulations have been performed for pressurized rotor-rub conditions. CAE model of brush seals includes rotor-bristle, bristle pack-backing plate and inter-bristle contacts with friction. Simulations with non-rotating rotor and transient analyses with rotating rotor have been conducted, and the extracted bristle tip force levels are correlated with the test results. Inertial effects during dynamic tests have also been simulated through transient analyses and results show good agreement with the dynamic test data. Displacement and stress profiles obtained from correlated FE models give better understanding of brush seal behavior under turbine operating conditions.

Characterization of Brush Seal Permeability

2016 ◽  
Author(s):  
Thomas G. Gresham ◽  
Brian K. Weaver ◽  
Houston G. Wood ◽  
Alexandrina Untaroiu
Keyword(s):  
Porous Media ◽  
Cfd Simulation ◽  
Flow Direction ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Backing Plate ◽  
Physical Mechanisms ◽  
Brush Seal ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through

A basis for the study of flow through a brush seal is established by applying the fundamentals of porous media fluid mechanics. Permeability, the measure of a medium’s ability to transmit flow, is one of the most important factors needed to characterize a brush seal’s ability to reduce leakage. Previous studies have indicated that the performance of a brush seal is highly dependent on operating conditions. By investigating how the permeability is affected by the operating conditions (pressure ratio specifically), further understanding of the performance of this type of seal is developed. Experimental data in the literature was used in tandem with computational fluid dynamics (CFD) simulation results in order to characterize how the permeability of a single-stage brush seal changes as the pressure ratio changes. For each value of pressure ratio, the permeability of the CFD model was adjusted until the leakage calculated from the model matched experimentally measured values. The physical mechanisms behind the observed variations in permeability are discussed. Explanations are proposed based on flutter and deformation of the bristles and how these phenomena can affect the internal tortuosity of the bristle pack. As pressure across the bristles increases, it is expected that they will bend under the backing plate to align with the flow direction in the clearance region, but the increase in pressure will also act to compress the bristle pack in the flow direction, decreasing the spacing between bristles and reducing their ability to move relative to each other, thereby reducing the effective permeability of the bristle pack. By demonstrating the dependence of permeability on operating conditions, it is shown that the common assumption of constant permeability coefficients can often result in an insufficient model. Assumptions regarding the model of a bristle pack as an isotropic porous media are discussed, and the validity and utility of this model are assessed. This paper provides important insight into what a reasonable value of permeability of a typical brush seal is, and how that value may change as a function of operating conditions.

Pressure Distributions Below Brush Seals at Varying Operating Conditions

2018 ◽  
Author(s):  
Fabian Schur ◽  
Jens Friedrichs ◽  
Johan Flegler ◽  
Christos Georgakis ◽  
Thomas Polklas
Keyword(s):  
Radial Pressure ◽  
Operating Conditions ◽  
Optical Measurements ◽  
Design Parameters ◽  
Test Rig ◽  
Axial Pressure ◽  
Backing Plate ◽  
Pressure Distributions ◽  
Flow Through ◽  
Brush Seals

The influences of different manufacturing methods and design parameters of brush seals and their complex interactions with the flow through the bristle pack complicate the modeling of the flow through brush seals. While radial pressure distributions along the backing plate and the leakage behaviour of various brush seal designs are published, experimental data on axial pressure distributions on the surface of the shaft is insufficient. In order to gain a better understanding of the phenomena associated with the flow through brush seals, the axial pressure distributions in the sealing gap below six different brush seals are measured on a cold air test rig at rotational speeds up to 3000rpm and pressure differences across the seals up to 500kPa with an axial resolution of 0.2mm. By investigating a welded and five different clamped brush seals, the influence of two different designs on the flow through the bristles is shown. For the clamped brush seals the design of the front and backing plate is varied. Moreover, the effects of bristle diameter and three different axial inclinations of the bristle pack on the axial pressure distribution are presented. Therefore, the effects of the major design aspects on axial pressure distributions at the interface between brush seals and rotor are examined and the results are supported by optical measurements taken on the rotating and a stationary test rig.

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.

Brush Seal Structural Analysis and Correlation With Tests for Turbine Conditions

2015 ◽  
Vol 138 (5) ◽  
Author(s):  
E. Tolga Duran ◽  
Mahmut F. Aksit ◽  
Murat Ozmusul
Keyword(s):  
Test Data ◽  
Three Dimensional ◽  
Dynamic Test ◽  
Operating Conditions ◽  
Contact Forces ◽  
Backing Plate ◽  
Contact Loads ◽  
Brush Seal ◽  
Stress Levels ◽  
Brush Seals

Bristle tip contact forces and resulting stress levels under engine conditions are critical for optimizing brush seal performance as well as for achieving operational safety. Literature survey reveals the lack of test data and analysis methods for evaluating seal stiffness and stress levels under operating conditions. In an attempt to meet this need, a custom test rig design and methodology have been developed to perform stiffness tests under pressure and rotor speed of 3000 rpm. Finite element (FE) simulations have been performed for brush seals and results have been correlated with the test data of this study. Considering the critical importance of contact loads on brush seal overall performance and system health, and due to the complicated structure of brush seals, where bristles are contacting with each other as well as with the backing plate and the rotor, computer-aided engineering (CAE) analyses with high fidelity is required to simulate the test and turbine operating conditions. For this purpose, FE methodology has been developed for structural analyses of brush seals. Three-dimensional FE models of brush seals have been constructed and simulations have been performed for pressurized rotor-rub conditions. CAE model of brush seals includes rotor–bristle, bristle pack–backing plate, and interbristle contacts with friction. Simulations with nonrotating rotor and transient analyses with rotating rotor have been conducted, and the extracted bristle tip force (BTF) levels are correlated with the test results. Inertial effects during dynamic tests have also been simulated through transient analyses and results show good agreement with the dynamic test data. Displacement and stress profiles obtained from correlated FE models give better understanding of brush seal behavior under turbine operating conditions.

Sign in / Sign up

Export Citation Format

Share Document