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Akşit, Mahmut Faruk - One of the best experts on this subject based on the ideXlab platform.

  • Brush Seal performance measurement system
    ASME (American Society of Mechanical Engineers), 2009
    Co-Authors: Aksoy Serdar, Akşit, Mahmut Faruk, Duran, Ertuğrul Tolga
    Abstract:

    Brush Seals are rapidly replacing conventional labyrinth Seals in turbomachinery applications. Upon pressure application, Seal stiffness increases drastically due to frictional bristle interlocking. Operating stiffness is critical to determine Seal wear life. Typically, Seal stiffness is measured by pressing a curved shoe to Brush bore. The static-unpressurized measurement is extrapolated to pressurized and high speed operating conditions. This work presents a Seal stiffness measurement system that is capable of measuring Brush Seal stiffness under engine operating pressure and speed condition which is not available in open literature. Stiffness measurement system design, testing methodology and calibration procedure are discussed

  • A study of Brush Seal oil pressure profile including temperature-viscosity effects
    AIAA (American Institute of Aeronautics and Astronautics), 2008
    Co-Authors: Akşit, Mahmut Faruk, Duran, Ertuğrul Tolga
    Abstract:

    After proven performance in air applications, Brush Seals are being considered for oil and oil mist Sealing in aero-engines, turbines and generators. The viscous medium between the high speed rotor surface and bearing surfaces formed by Brush Seal bristle tips generates a hydrodynamic lifting force that determines Seal clearance and leakage rate in oil Sealing applications. Hydrodynamic lift force and Seal clearance have strong dependence on oil temperature and viscosity. In a previous study, short bearing theory has been applied to a single bristle to obtain a solution for hydrodynamic lift force developing at a bristle tip. Rather than individual bristles, this work evaluates pressure for the bristle rows. Applying the Reynolds bearing theory to the control volume between bristle tips and the rotor surface fluid pressure distribution is obtained under each bristle row. Effective temperature and effective viscosity approach has been adopted. Pressure distribution for each bristle row in the rotor axial direction is evaluated. Then, pressure profiles for each bristle row are combined to yield the axial pressure profile under the entire Brush pack

  • 3-D analysis of high density Brush stiffness with friction-pressure coupling
    A-Z İleri Mühendislik Ltd., 2008
    Co-Authors: Akşit, Mahmut Faruk
    Abstract:

    Achieving efficient Sealing around high speed rotating bodies poses real engineering challenges. In recent years, dense Brush structures found common use in turbomachinery Sealing applications. As they maintain their flexibility at elevated temperatures, which are typical in gas turbines, high density Brush Seals made of super-alloy bristles found popularity among engine designers. Inherent flexibility of Brush Seals allows fibers to compact under pressure load. Due to the frictional interaction between the fibers and the backing plate as well as within the fibers themselves, Brush Seals are known to exhibit pressure stiffening and hysteresis behavior. While hysteresis affects Seal performance after a rotor excursion, pressure stiffening is critical in determining heat generation and Seal wear during hard rubs. Typically Brush-rotor contact occurs at very high surface speeds. If not managed properly, high contact loads may result in extreme wear and damage to rotor. In order to ensure engine operational safety Brush Seal stiffness should be controlled through Seal design and detail analysis. In addition to the physical complexity of these dense Brush structures, frictional contacts among the bristles themselves, between the bristles and the support plates, and between the bristles tips and the high speed rotor further increase the analysis complexity, and make it a major undertaking if not impossible. 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 3-D computational Brush Seal structural FE model that can be used to calculate bristle forces. The analysis includes 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 simulate pressure-stiffness coupling. The results indicate that rotor interference has some effect on Seal tip forces in the absence of any pressure loading. However, upon application of small pressure loads, Seal stiffness is generally dominated by pressure-stiffness coupling

  • 3-D ANALYSIS OF A HIGH DENSITY Brush WITH FRICTIONAL CONTACT INTERACTIONS
    A-Ztech Ltd., 2007
    Co-Authors: Akşit, Mahmut Faruk
    Abstract:

    The physical complexity of dense Brush structures presents major challenges to analyzers. As they maintain their flexibility at elevated temperatures, which are typical in gas turbines, high density Brush Seals made of super-alloy bristles found popularity among engine designers. Typically Brush-rotor contact occurs at very high surface speeds. If not managed properly, this may result in extreme wear conditions and damage to rotor. In order to ensure engine operational safety Brush contact loads should be controlled through Seal design and detail analysis. In addition to the physical complexity of these dense Brush structures, frictional contacts among the bristles themselves, between the bristles and the support plates, and between the bristles tips and the high speed rotor further increase the analysis complexity, and make it a major undertaking if not impossible. Detailed understanding of Brush Seal contact loads is necessary to estimate Seal and rotor 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 3-D computational Brush Seal structural FE model that can be used to calculate bristle stress, tip force, and do wear analysis. The analysis includes 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 simulate pressure-stiffness coupling. Various analysis results are presented and compared to full scale Seal wear tests

  • Brush Seal temperature distribution analysis
    2006
    Co-Authors: Dogu Yahya, Akşit, Mahmut Faruk
    Abstract:

    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

Yuchi Kang - One of the best experts on this subject based on the ideXlab platform.

Jinbin Liu - One of the best experts on this subject based on the ideXlab platform.

Meihong Liu - One of the best experts on this subject based on the ideXlab platform.

  • numerical analysis of flow across Brush elements based on a 2 d staggered tube banks model
    Aerospace, 2021
    Co-Authors: Xiaolei Song, Meihong Liu, Xueliang Wang, Taohong Liao, Junfeng Sun
    Abstract:

    In order to improve efficiency in turbomachinery, Brush Seal replaces labyrinth Seals widely in the secondary air system. A 2-d staggered tube bank model is adopted to simulate the gas states and the pressure character in Brush Seal, and computational fluid dynamics (CFD) is used to solve the model in this paper. According to the simulation results, the corrected formula of the Euler number and dimensionless pressure are given. The results show that gas expands when flow through the bristle pack, and the gas expansion closes to an isotherm process. The dynamic pressure increases with decreasing static pressure. The Euler number can reflect the Seal performance of Brush Seals in leakage characteristics. Compared with increasing the number of rows, the reduction of the gap is a higher-efficiency method to increase the Euler number. The Euler number continually increases as the gap decreases. However, with the differential pressure increasing, Euler number first increases and then decreases as the number of rows increases. Finally, the pressure distribution on the surface of end rows is asymmetric, and it may increase the friction between the bristles and the back plate.

  • Analysis of Drag of Bristle Based on 2-D Staggered Tube Bank
    Lecture Notes in Electrical Engineering, 2020
    Co-Authors: Xiaolei Song, Meihong Liu, Yuchi Kang, Baodi Zhang
    Abstract:

    In this paper, a 2-D staggered tube bank of bristle pack is established to examine the effect of flow on bristle pack, and Gambit is used to generate the mesh. The Resistance of the bristle in the transient condition is analyzed using simulation with Fluent. The resistance of the Brush Seal includes friction drag, pressure drag, and interference drag. Results show that the pressure drag plays the leading role owing to the shape of the bristle, and pressure drag increases slowly in the axial direction but increases significantly in the end row. The drag grows gradually with increasing pressure. The results also show that when the value of bristles gap decreases, the drags in the front rows increases more slowly but decrease significantly in the end row.

  • predicting aerodynamic resistance of Brush Seals using computational fluid dynamics and a 2 d tube banks model
    Tribology International, 2018
    Co-Authors: Meihong Liu, Yuchi Kang, Sharon Kaowalter, Wureguli Reheman, Jinbin Liu
    Abstract:

    Aerodynamic resistance of a Brush Seal was mainly studied. The velocity distribution along three specified lines was presented. By considering the pressure differential, Reynolds number and Euler n ...

  • predicting aerodynamic resistance of Brush Seals using computational fluid dynamics and a 2 d tube banks model
    Tribology International, 2018
    Co-Authors: Meihong Liu, Yuchi Kang, Sharon Kaowalter, Wureguli Reheman, Jinbin Liu
    Abstract:

    Aerodynamic resistance of a Brush Seal was mainly studied. The velocity distribution along three specified lines was presented. By considering the pressure differential, Reynolds number and Euler n ...

  • numerical simulation of the flow field characteristic in a two dimensional Brush Seal model
    8th International Workshop of Advanced Manufacturing and Automation IWAMA 2018; Changzhou; China; 25 September 2018 through 26 September 2018, 2018
    Co-Authors: Jinbin Liu, Meihong Liu, Yuchi Kang, Yongfa Tan
    Abstract:

    The numerical model was established using the two-dimensional cross section of staggered tube bundle of bristles, and the flow field was numerically solved by Fluent. This work presents velocity of flow and the variation range of flow velocity under transient state at the-last bristles gap are much higher than those of the front row, which leads to severe wear of the last row of bristles; as the bristle row number increases, the leakage decreases rapidly, then decreases slowly; the leakage increases linearly with the increase of the pressure difference; the Brush drag force slowly increases along the axial direction but increases significantly at the last row; the drag force increases linearly with differential pressure increasing.

Dogu Yahya - One of the best experts on this subject based on the ideXlab platform.

  • Flow Resistance Coefficients of Porous Brush Seal as a Function of Pressure Load
    'ASME International', 2018
    Co-Authors: Dogu Yahya, Sertcakan, Mustafa C., Gezer Koray, Kocagul Mustafa
    Abstract:

    Dogu, Yahya/0000-0003-0474-2899WOS: 000444148300014Developments 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 he almost linearly dependent on the pressure load for investigated conditions. The blow-down is also calculated by incorporating test leakage and calibrated FRC.Turkish Ministry of Science, Industry and Technology, Ankara, Turkey; TUSAS Engine Industries, Inc. (TEI), Eskisehir, TurkeyThis work was funded by "Turkish Ministry of Science, Industry and Technology, Ankara, Turkey" and "TUSAS Engine Industries, Inc. (TEI), Eskisehir, Turkey.

  • Computational Fluid Dynamics Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions
    'ASME International', 2016
    Co-Authors: Dogu Yahya, Sertcakan, Mustafa C., Bahar, Ahmet S., Piskin Altug, Arican Ercan, Kocagul Mustafa
    Abstract:

    Dogu, Yahya/0000-0003-0474-2899WOS: 000371125300019Brush 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 (z(1) = 0.040-0.150 in.), distance between front plate and bristle pack (z(2) = 0.010-0.050 in.), bristle pack thickness (z(3) = 0.020-0.100 in.), and backing plate thickness (z(4) = 0.040-0.150 in.). The radial dimensions are backing plate fence height (r(1) = 0.020-0.100 in.), front plate fence height (r(2) = 0.060-0.400 in.), and bristle free height (r(3) = 0.300-0.500 in.). The operating conditions are chosen as clearance (r(0) = 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.Turkish Ministry of Science, Industry and Technology"Ministry of Science, Industry & Technology - Turkey; "TUSAS Engine Industries, Inc. (TEI), Eskisehir, Turkey"This work was funded by "Turkish Ministry of Science, Industry and Technology," and "TUSAS Engine Industries, Inc. (TEI), Eskisehir, Turkey.

  • CFD INVESTIGATION OF Brush Seal LEAKAGE PERFORMANCE DEPENDING ON GEOMETRIC DIMENSIONS AND OPERATING CONDITIONS
    Amer Soc Mechanical Engineers, 2015
    Co-Authors: Dogu Yahya, Sertcakan, Mustafa C., Bahar, Ahmet S., Piskin Altug, Arican Ercan, Kocagul Mustafa
    Abstract:

    ASME Turbo Expo: Turbine Technical Conference and Exposition -- JUN 15-19, 2015 -- Montreal, CANADADogu, Yahya/0000-0003-0474-2899WOS: 000377639300035Brush 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 (z(1)=0.040-0.150in.), distance between front plate and bristle pack (z(2)=0.010-0.050in.), bristle pack thickness (z(3)=0.0200.100in.), and backing plate thickness (z(4)=0.040-0.150in.). The radial dimensions are backing plate fence height (r(1)=0.020-0.100in.), front plate fence height (r(2)=0.060-0.400in.), and bristle free height (r(3)=0.300-0.500in.). The operating conditions are chosen as clearance (r(0)=0.0000.020in.), pressure ratio (R-p=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.Int Gas Turbine Ins

  • Brush Seal temperature distribution analysis
    2006
    Co-Authors: Dogu Yahya, Akşit, Mahmut Faruk
    Abstract:

    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

  • Effects of geometry on Brush Seal pressure and flow fields - Part II: Backing plate configurations
    ASME (American Society of Mechanical Engineers), 2006
    Co-Authors: Dogu Yahya, Akşit, Mahmut Faruk
    Abstract:

    Brush Seal dynamic behavior is strongly related to pressure and flow fields. Developments in Brush Seal design have led to geometric modifications to control flow field and consequent Brush Seal issues including blow-down, hang-up, and pressure stiffening. Some of the geometric enhancements have been found to have common use as backing plate modifications. Over the two decades of Brush Seal evolution, many backing plate configurations have been suggested in numerous patent disclosures. Even so, literature on the effects of geometric modifications on pressure and flow fields remains limited. This study numerically investigates Brush Seal pressure and flow fields for such common conceptual backing plate configurations as single and multiple grooves, with and without by-pass passages. The CFD analysis presented employs a bulk porous medium approach for the bristle pack. The effectiveness of various backing plate configurations outlining important flow features is discussed. Results indicate that backing plate configurations have a decisive role in shaping Seal pressure fields. In general, it has been found that all cases having bypass configuration leak more. Moreover, the major portion of the Seal leakage through fence height is fed from the backing plate cavity. The single backing plate groove forms a constant pressure behind the bristle pack. In contrast, multiple grooves form multiple constant pressure regions

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