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Öğe 1-D Modelling Comparative Study to Evaluate Performance and Emissions of a Spark Ignition Engine Fuelled with Gasoline and LNG(E D P Sciences, 2016) Yontar, Ahmet Alper; Dogu, YahyaIn this study, a spark-ignition engine fuelled with gasoline and LNG was modelled in 1-D at wide open throttle by using Ricardo-Wave software. Different engine speeds ranging from 1500rpm to 4500rpm with an increment of 500rpm were studied to evaluate the effects of gasoline and LNG on engine performance and exhaust emissions. It is determined that LNG decreases engine performance and emissions as well, at especially high speeds.Öğe Brush seal temperature distribution analysis (conferenceObject)(Amer Soc Mechanical Engineers, 2005) Dogu, Yahya; Aksit, Mahmut F.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.Öğe CFD Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions(Amer Soc Mechanical Engineers, 2015) Dogu, Yahya; Sertçakan, Mustafa C.; Bahar, Ahmet S.; Pişkin, Altuğ; Arıcan, Ercan; Kocagül, MustafaBrush 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.Öğe CFD Investigation of Labyrinth Seal Leakage Performance Depending on Mushroom Shaped Tooth Wear(Amer Soc Mechanical Engineers, 2015) Dogu, Yahya; Sertçakan, Mustafa C.; Bahar, Ahmet S.; Piskin, Altuğ; Arıcan, Ercan; Kocagül, MustafaConventional labyrinth seal applications in turbomachinery encounter a permanent teeth tip damage and wear during transitional operations. This is the dominant issue that causes unpredictable seal leakage performance degradation. Since the gap between the rotor and the stator changes depending on engine transitional operations, labyrinth teeth located on the rotor/stator wear against the stator/rotor. This wear is observed mostly in the form of the labyrinth teeth becoming a mushroom shape. It is known that as a result of this tooth tip wear, leakage performance permanently decreases, which negatively affects the engine's overall efficiency. However, very limited information about leakage performance degradation caused by mushroom wear is available in open literature. This paper presents a study that numerically quantifies leakage values for various radii of mushroom shaped labyrinth teeth by changing tooth-surface clearance, pressure ratio, number of teeth, and rotor speed. Analyzed parameters and their ranges are mushroom radius (R2=0-0.508mm), clearance (c(r)=0.254-2.032mm), pressure ratio (R-p=1.5-3.5), number of teeth (n(t)=1-12), and rotor speed (n=0-80krpm). CFD analyses were carried out by employing compressible turbulent flow in 2-D axi-symmetrical coordinate system. CFD leakage results were also compared with well-known labyrinth seal semi-empirical correlations. Given a constant clearance, leakage increases with the size of the mushroom radius that forms on the tooth. This behavior is caused by less flow separation and flow disturbance and the vena contracta effect for flow over the smoothly shaped mushroom tooth tip compared to the sharp-edged tooth tip. This leakage increase is higher when the tooth tip wear is considered as an addition to the unworn physical clearance, since the clearance dominates the leakage. The leakage affected by the number of teeth was also quantified with respect to the mushroom radius. The rotational effect was also studied as a secondary parameter.Öğe Computational Fluid Dynamics Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions(Asme, 2016) Dogu, Yahya; Bahar, Ahmet S.; Sertcakan, Mustafa C.; Piskin, Altug; Arican, Ercan; Kocagul, MustafaBrush 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.Öğe Computational Fluid Dynamics Investigation of Labyrinth Seal Leakage Performance Depending on Mushroom-Shaped Tooth Wear(Asme, 2016) Dogu, Yahya; Sertcakan, Mustafa C.; Bahar, Ahmet S.; Piskin, Altug; Arican, Ercan; Kocagul, MustafaConventional labyrinth seal applications in turbomachinery encounter a permanent teeth tip damage and wear during transitional operations. This is the dominant issue that causes unpredictable seal leakage performance degradation. Since the gap between the rotor and the stator changes depending on engine transitional operations, labyrinth teeth located on the rotor/stator wear against the stator/rotor. This wear is observed mostly in the form of the labyrinth teeth becoming a mushroom shape. It is known that, as a result of this tooth tip wear, leakage performance permanently decreases, which negatively affects the engine's overall efficiency. However, very limited information about leakage performance degradation caused by mushroom wear is available in open literature. This paper presents a study that numerically quantifies leakage values for various radii of mushroom-shaped labyrinth teeth by changing tooth-surface clearance, pressure ratio, number of teeth, and rotor speed. Analyzed parameters and their ranges are mushroom radius (R = 0-0.508 mm), clearance (c(1) = 0.254-2.032 mm), pressure ratio (R-p = 1.5-3.5), number of teeth (n(t) = 1-12), and rotor speed (n = 0-80 krpm). Computational fluid dynamics (CFD) analyses were carried out by employing compressible turbulent flow in 2D axisymmetrical coordinate system. CFD leakage results were also compared with well-known labyrinth seal semi-empirical correlations. Given a constant clearance, leakage increases with the size of the mushroom radius that forms on the tooth. This behavior is caused by less flow separation and flow disturbance, and the vena contracta effect for flow over the smoothly shaped mushroom tooth tip compared to the sharp-edged tooth tip. This leakage increase is higher when the tooth tip wear is considered as an addition to the unworn physical clearance, since the clearance dominates the leakage. The leakage affected by the number of teeth was also quantified with respect to the mushroom radius. The rotational effect was also studied as a secondary parameter.Öğe Design And Cfd Analysis Of A 150 Kw 8-Stage Orc-Rot (Organic Rankine Cycle - Radial Outflow Turbine) And Performance Degradation Due To Blade Tip Clearance Of Labyrinth Seal(Amer Soc Mechanical Engineers, 2018) Dogu, Yahya; Gunaydin, Ibrahim; Kilicaslan, Zeynal; Ileri, Tacettin; Soganci, SinanIn this study, blade tip leakages were calculated for a Radial Outflow Turbine (ROT) designed for an Organic Rankine Cycle (ORC) at a 150kW power output. Since the turbine blade sizes are relatively very small for low-capacity systems, the leakages through the blade tip clearances considerably affect the turbine isentropic efficiency. Therefore, labyrinth seals were applied at the blade tips and the ROT's performance degradation due to blade tip leakages was investigated. In order to determine the preliminary ROT sizes, an in-house developed 1-D code was utilized. The blade profiles were optimized with CFD analyses to reach high power output and isentropic efficiency. The designed ROT has 8 stages. Toluene is used as the cycle fluid at inlet conditions of 24bar of total pressure, 310 degrees C and outlet conditions of 0.25bar of static pressure. These conditions are chosen for exhaust conditions of a common biogas engine. Thus, the ORC is supposed to operate at a heat source temperature of 460 degrees C and a heat sink temperature of 35 degrees C. The turbine speed of 14000 rpm is determined. The CFD model for the entire 3-D turbine geometry is built in the FlowVision software. The real gas equation is employed for the compressible flow. The SST turbulent flow model is employed. The CFD model uses transient state and rotating frame approaches. Four blade tip configurations were analyzed. The CFD results reveal the followings. The turbine isentropic efficiency is calculated to be 87.62% for the unshrouded geometry with no clearance, which is an ideal case. For a manufacturable and manageable blade tip clearance of 0.2 mm, the turbine isentropic efficiency is calculated to be 71.03% for the unshrouded geometry. The shrouded geometry with the same clearance increases the efficiency to 74.03%. When a labyrinth seal is applied to the shrouded geometry, the efficiency reaches to 77.03%. The best practice in terms of turbine power output and efficiency is the shrouded geometry with labyrinth seal applications.Öğe Evaluation of flow behavior for clearance brush seals(Asme-Amer Soc Mechanical Eng, 2008) Dogu, Yahya; Aksit, Mahmut F.; Demiroglu, Mehmet; Dinc, Osman SaimThe industrial applications of brush seals have been increasing due to their superior sealing performance. Advances in the understanding of seal behavior have been pushing the design limits to higher-pressure load, temperature, surface speed, and rotor excursion levels. The highest sealing performance can be achieved when the bristle pack maintains contact with the rotor surface. However due to many design and operational constraints, most seals operate with some clearance. This operating clearance cannot be avoided due to rotor runouts, transient operating conditions, or excessive bristle wear. In some applications, a minimum initial clearance is required to ensure a certain amount of flow rate for component cooling or purge flow. Typically, brush seal failure occurs in the form of degraded sealing performance due to increasing seal clearance. The seal performance is mainly characterized by the flow field in close vicinity of the bristle pack, through the seal-rotor clearance, and within the bristle pack. This work investigates the flow field for a brush seal operating with some bristle-rotor clearance. A nonlinear form of the momentum transport equation for a porous medium of the bristle pack has been solved by employing the computational fluid dynamics analysis. The results are compared with prior experimental data. The flow field for the clearance seal is observed to have different characteristics compared to that for the contact seal. Outlined as well are the flow features influencing the bristle dynamics.Öğe Experimental investigation of effects of single and mixed alternative fuels (gasoline, CNG, LPG, acetone, naphthalene, and boron derivatives) on a commercial i-DSI engine(TAYLOR & FRANCIS INC, 2020) Dogu, Yahya; Yontar, Ahmet Alper; Kantaroglu, EmrahA commercial i-DSI (Intelligent-Dual Sequential Ignition) engine is tested to investigate performance and emissions for single fuels and alternative fuels mixed into gasoline. The novelty of the study is the first time testing of the unconventional mixture of boron derivatives and quantification and comparison of real engine characteristics for 11 different fuels for the same commercial engine. Tested single fuels are gasoline (G100), CNG (CNG100), and LPG (LPG100). While the engine runs with gasoline, gaseous fuels are injected into the intake line at a mass rate of 10% CNG (CNG10) and 5% LPG (LPG5). The engine is also tested by adding 25-50% acetone (A25-A50) and 50% naphthalene (N50) into gasoline. Tests are also performed by mixing boron derivatives of borax-pentahydrate (BP), anhydrous-borax (AB), and boric-acid (BA) into gasoline. Tested fuels worsen engine performance compared to gasoline, except for brake specific fuel consumption (BSFC). There is a positive change in emissions for tested fuels compared to gasoline, except that NOx increases 4-5 times for CNG and LPG. One of the important findings is that, for boron-gasoline mixtures, the torque reduces by 4.0% for BP, 4.4% for AB, and 4.4% for BA. The volumetric efficiency decreases by 6.3% for BP, 7.3% for AB, and 8.5% for BA. The BSFC decreases 5.8% for BP, increases 0.4% for AB and decreases 15.2% for BA. Boron derivatives dissolved in gasoline diversely affect combustion and give some advantage in particular for BA and BP in terms of BSFC. In addition, boron-gasoline reduces the formation of HC and NOx.Öğe Influence of acetone addition into gasoline for i-DSI engine(Springer India, 2022) Kantaroglu, Emrah; Yontar, Ahmet Alper; Dogu, YahyaDespite the notable properties of acetone due to its volatility and oxygen content as a fuel additive, very few studies have been limited to small size special purpose engines. A comparative testing and 3D in-cylinder combustion CFD studies are presented for acetone-gasoline blend in an i-DSI commercial car engine as the first time. The blends contain mass ratio of acetone by 0-2-5-10-20% (G100-A2-A5-A10-A20). In testing, torque reduced 0.33% (A2), 0.66% (A5), 0.84% (A10), and 1.45% (A20) compared to gasoline. The BSFC decreased by 0.27% (A2), 0.55% (A5), 0.79% (A10), and increased 0.26% (A20). Volumetric efficiency decreased by 3.2-6.4-5.1-11.5% for A2-A5-A10-A20. The CO emission for blends is less than gasoline by 1.5% (A2), 4.0% (A5), 15.2% (A10), and 33.6% (A20). The CO2 decreased 0.8% (A2), and increased 1.3% (A5), 4.6% (A10), and 11.4% (A20). The HC reduced by 7.0% (A2), 10.1% (A5), 23.8% (A10), and 34.4% (A20). The NOx formation increased by 3.6% (A2), 4.4% (A5), 27.6% (A10), and 87.8% (A20). Acetone addition decreased torque and slightly increased BSFC. CO and HC decreased while CO2 and NOx increased with increasing acetone ratio. Acetone indeed improves the combustion while its final effect on engine performance is not found to be favorable.Öğe INVESTIGATION OF RADIAL PRESWIRL NOZZLE - COVERPLATE SYSTEM USING CFD(Amer Soc Mechanical Engineers, 2023) Erdem, Erinc; Yalcinkaya, Abdulkadir; Sertcakan, Mustafa Cem; Sal, Sinan; Dogu, YahyaThis article focuses on a radial preswirler system using CFD, and the effect of different parameters such as the number and the angle of the holes at the preswirl nozzle exit, and the diameter of the preswirl nozzles have been investigated. Three-dimensional steady CFD simulations on a 22.5deg sector model showed a non-monotonic trend of swirl velocity at the inlet of the receiver holes and associated flow angles when different preswirl nozzle configurations are tested. Sudden rise in swirl ratio can be attributed to interactions of adjacent nozzle jets. Due to this flow feature swirl velocities are enhanced up to a certain angle where the interaction starts to diminish. Free vortex assumption in between nozzle exit and receiver inlet holds, as angular momentum of the nozzle jet is much more dominant compared to torques exerted by stator surfaces.Öğe INVESTIGATION OF RADIAL PRESWIRL NOZZLE – COVERPLATE SYSTEM USING CFD(American Society of Mechanical Engineers (ASME), 2023) Erdem, Erinc; Yalcinkaya, Abdulkadir; Sertcakan, Mustafa Cem; Sal, Sinan; Dogu, YahyaThis article focuses on a radial preswirler system using CFD, and the effect of different parameters such as the number and the angle of the holes at the preswirl nozzle exit, and the diameter of the preswirl nozzles have been investigated. Three-dimensional steady CFD simulations on a 22.5deg sector model showed a non-monotonic trend of swirl velocity at the inlet of the receiver holes and associated flow angles when different preswirl nozzle configurations are tested. Sudden rise in swirl ratio can be attributed to interactions of adjacent nozzle jets. Due to this flow feature swirl velocities are enhanced up to a certain angle where the interaction starts to diminish. Free vortex assumption in between nozzle exit and receiver inlet holds, as angular momentum of the nozzle jet is much more dominant compared to torques exerted by stator surfaces. © 2023 by ASME.Öğe Investigation of the effects of gasoline and CNG fuels on a dual sequential ignition engine at low and high load conditions(Elsevier Sci Ltd, 2018) Yontar, Ahmet Alper; Dogu, YahyaIn this study, a dual sequential spark ignition engine is separately tested either with gasoline or CNG at low and high loads. In addition, numerical engine analyses are performed by constructing a 1-D engine model in Ricardo-Wave software. Engine performance parameters in catalogue are generally given at full load conditions. However, during engine lifetime, vehicle engines rarely run at full load (wide open throttle) while engines work especially at the partial throttle openings. Engine characteristics (engine performance and exhaust emissions) are strong functions of throttle opening level. For this reason, determining engine characteristics at partial throttle openings at which engine mostly runs provides valuable information. In this study, partial throttle openings of 25% and 75% defined as low and high load conditions are examined for gasoline and CNG, as well. For this aim, the Honda L13A4 i-DSI (intelligent dual sequential ignition) engine was tested and engine characteristics were measured. This engine has unique features of dual sequential ignition with variable timing, asymmetrical combustion chamber, and diagonally positioned spark-plugs. Tests and numerical analyses were performed at specified low and high load conditions for gasoline and CNG by varying the engine speed from 1500 rpm to 4000 rpm with an increment of 500 rpm without excepting 2800 rpm. Engine characteristics were determined for the investigated parameters. Tests and 1-D model results are fairly matching each other. The average deviation between them is about 5.4%. Results show that the maximum torque for gasoline at 2800 rpm and 100% throttle opening reduced 12.6% and 26.3% for throttle openings of 75% and 25%, respectively. Compared to gasoline, CNG reduced the torque 15.6% and 19.6% for throttle openings of 75% and 25%, respectively. In general, CNG usage decreases all engine performance parameters (torque, power, volumetric efficiency, specific fuel consumption) and emissions (CO2, HC), except NOx formation.Öğe Labyrinth Seal Leakage Degradation Due to Various Types of Wear(Asme, 2017) Dogu, Yahya; Sertcakan, Mustafa C.; Gezer, Koray; Kocagul, Mustafa; Arican, Ercan; Ozmusul, Murat S.This paper systematically presents a complete leakage comparison for various types of wear experienced by labyrinth seals. Labyrinth seals used in turbine engines are designed to work at a clearance during steady-state engine operations. The tooth tip rubs the stator and wears either itself or the stator surface during transient operations, depending on the material properties of the tooth and stator. Any type of wear that increases clearance or deforms the tooth tip will cause permanent and unpredictable leakage degradation. This negatively affects the engine's overall efficiency, durability, and life. The teeth have been reported to wear into a mushroom profile or into a rounded profile. A rub-groove on the opposing surface may form in several shapes. Based on a literature survey, five rubgroove shapes are considered in this work. They are rectangle, trapezoid (isosceles and acute), triangle, and ellipse. In this work, leakage degradation due to wear is numerically quantified for both mushroomed and rounded tooth wear profiles. It also includes analyses on rounded teeth with the formation of five rub-groove shapes. All parameters are analyzed at various operating conditions (clearance, pressure ratio, number of teeth, and rotor speed). Computational fluid dynamics (CFD) analyses are carried out by employing compressible turbulent flow in a 2D axisymmetrical coordinate system. CFD analyses show that the following tooth-wear conditions affect leakage from least to greatest: unworn, rounded, and mushroomed. These are for an unworn flat stator. It is also observed that rub-groove shapes considerably affect the leakage depending on the clearance. Leakage increases with the following groove profiles: triangular, rectangular, acute trapezoidal, isosceles trapezoidal, and elliptical. The results show that any type of labyrinth seal wear has significant effects on leakage. Therefore, leakage degradation due to wear should be considered during the engine design phase.Öğe Labyrinth Seal Leakage Degradation Due to Various Types of Wear(Asme, 2017) Dogu, Yahya; Sertcakan, Mustafa C.; Gezer, Koray; Kocagul, Mustafa; Arican, Ercan; Ozmusul, Murat S.This paper systematically presents a complete leakage comparison for various types of wear experienced by labyrinth seals. Labyrinth seals used in turbine engines are designed to work at a clearance during steady-state engine operations. The tooth tip rubs the stator and wears either itself or the stator surface during transient operations, depending on the material properties of the tooth and stator. Any type of wear that increases clearance or deforms the tooth tip will cause permanent and unpredictable leakage degradation. This negatively affects the engine's overall efficiency, durability, and life. The teeth have been reported to wear into a mushroom profile or into a rounded profile. A rub-groove on the opposing surface may form in several shapes. Based on a literature survey, five rubgroove shapes are considered in this work. They are rectangle, trapezoid (isosceles and acute), triangle, and ellipse. In this work, leakage degradation due to wear is numerically quantified for both mushroomed and rounded tooth wear profiles. It also includes analyses on rounded teeth with the formation of five rub-groove shapes. All parameters are analyzed at various operating conditions (clearance, pressure ratio, number of teeth, and rotor speed). Computational fluid dynamics (CFD) analyses are carried out by employing compressible turbulent flow in a 2D axisymmetrical coordinate system. CFD analyses show that the following tooth-wear conditions affect leakage from least to greatest: unworn, rounded, and mushroomed. These are for an unworn flat stator. It is also observed that rub-groove shapes considerably affect the leakage depending on the clearance. Leakage increases with the following groove profiles: triangular, rectangular, acute trapezoidal, isosceles trapezoidal, and elliptical. The results show that any type of labyrinth seal wear has significant effects on leakage. Therefore, leakage degradation due to wear should be considered during the engine design phase.Öğe Leakage Degradation of Straight Labyrinth Seal Due to Wear of Round Tooth Tip and Acute Trapezoidal Rub-Groove(Asme, 2017) Dogu, Yahya; Sertcakan, Mustafa C.; Gezer, Koray; Kocagul, Mustafa; Arican, Ercan; Ozmusul, Murat S.In this paper, labyrinth seal leakage is numerically quantified for an acute trapezoidal rubgroove accompanied with a rounded tooth, as a function of rub-groove sizes and toothgroove axial positions. Analyses parameters include clearance, pressure ratio, number of teeth, and rotor speed. Labyrinth seals wear during engine transients. Radial incursion and axial movement of the rotor-stator pair cause the labyrinth teeth to rub against the unworn stator surface. The labyrinth teeth and/or stator wear depending on their material hardness. Wear damage in the form of material loss or deformation permanently increases seal clearance, and thus, leakage. This leakage is known to be dependent on the shape and geometry of the worn tooth and the stator rub groove. There are two types of reported tooth tip wear. These can be approximated as a mushroom shape and a round shape. The stator rub-groove shapes can be approximately simulated in five forms: rectangle, trapezoid (isosceles and acute), triangle, and ellipse. In this paper, the acute trapezoidal rub-groove shape is specifically chosen, since it is the most similar to the most commonly observed rub-groove form. The tooth tip is considered to be rounded, because the tooth tip wears smoothly and a round shape forms during rub-groove formation. To compare the unworn tooth, the flat stator is also analyzed as a reference case. All analyzed parameters for geometric dimensions (groove width, depth, wall angle, and tooth-groove axial position) and operating conditions (flow direction, clearance, pressure ratio, number of teeth, and rotor speed) are analyzed in their practical ranges. Computational fluid dynamics (CFD) analyses are carried out by employing a compressible turbulent flow solver in a 2D axisymmetrical coordinate system. CFD analyses show that the rounded tooth leaks more than an unworn sharp-edged tooth, due to the formation of a smooth and streamlined flow around the rounded geometry. This smooth flow yields less flow separation, flow disturbance, and less of vena contracta effect. The geometric dimensions of the acute trapezoidal rub-groove (width, depth, wall angle) significantly affect leakage. The effects of clearance, pressure ratio, number of teeth, and rotor speed on the leakage are also quantified. Analyses results are separately evaluated for each parameter.Öğe Leakage Degradation of Straight Labyrinth Seal Due to Wear of Round Tooth Tip and Acute Trapezoidal Rub-Groove (conferenceObject)(Amer Soc Mechanical Engineers, 2016) Dogu, Yahya; Sertcakan, Mustafa C.; Gezer, Koray; Kocagul, Mustafa; Arican, Ercan; Ozmusul, Murat S.In this paper, labyrinth seal leakage is numerically quantified for an acute trapezoidal rub-groove accompanied with a rounded tooth, as a function of rub-groove sizes and tooth-groove axial positions. Analyses parameters include clearance, pressure ratio, number of teeth, and rotor speed. Labyrinth seals wear during engine transients. Radial incursion and axial movement of the rotor-stator pair cause the labyrinth teeth to rub against the unworn stator surface. The labyrinth teeth and/or stator wear depending on their material hardness. Wear damage in the form of material loss or deformation permanently increases seal clearance, and thus, leakage. This leakage is known to be dependent on the shape and geometry of the worn tooth and the stator rub groove. There are two types of reported tooth tip wear. These can be approximated as a mushroom shape and a round shape. The stator rub-groove shapes can be approximately simulated in five forms: rectangle, trapezoid (isosceles and acute), triangle, and ellipse. In this paper, the acute trapezoidal rub-groove shape is specifically chosen, since it is the most similar to the most commonly observed rub-groove form. The tooth tip is considered to be rounded, because the tooth tip wears smoothly and a round shape forms during rub-groove formation. To compare the unworn tooth, the flat stator is also analyzed as a reference case. All analyzed parameters for geometric dimensions (groove width, depth, wall angle, tooth-groove axial position,) and operating conditions (flow direction, clearance, pressure ratio, number of teeth, rotor speed) are analyzed in their practical ranges. CFD analyses are carried out by employing a compressible turbulent flow solver in a 2-D axi-symmetrical coordinate system. CFD analyses show that the rounded tooth leaks more than an unworn sharp-edged tooth, due to the formation of a smooth and streamlined flow around the rounded geometry. This smooth flow yields less flow separation, flow disturbance, and less of vena contracta effect. The geometric dimensions of the acute trapezoidal rub-groove (width, depth, wall angle) significantly affect leakage. The effects of clearance, pressure ratio, number of teeth, and rotor speed on the leakage are also quantified. Analyses results are separately evaluated for each parameter.Öğe A Study of Cloth Seal Leakage Performance Based on Geometry and Pressure Load(MDPI, 2020) Gorgun, Erdem; Aksit, Mahmut Faruk; Dogu, YahyaMetal cloth seals have been used increasingly in gas turbines due to their flexibility and superior leakage performance. Leakage performance of a metal cloth seal depends on operating conditions, slot and geometric dimensions. These parameters need to be investigated for the best leakage performance. In this study, pressure drop and critical geometric parameters of typical cloth seal form are investigated with an experimental setup. Slot depth, cloth width, sealing gap, shim thickness, surface roughness, pressure drop, offset and mismatch are selected parameters for the screening experiments. Sixteen experiments were conducted following a two-level Resolution IV fractional factorial experiment design for eight parameters. The results indicated that strong parameters for the leakage performance are pressure drop, cloth width, slot depth and offset. Leakage rate is increased with an increase in slot depth, gap, shim thickness, pressure drop and mismatch. During screening experiments, the experiment with minimum flow rate has 86% lower leakage rate than the experiment with maximum flow rate. For main experiments, a Box-Behnken experiment design is applied to analyze nonlinear effects of four strong parameters on the leakage rate. A closed-form equation is derived based on the data and presented in this study.
