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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 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 Robotics and Servo Press Control Applications: Experimental Implementations(Ieee, 2016) Dulger, L. C.; Das, M. T.; Halicioglu, R.; Kapucu, S.; Topalbekiroglu, M.Three case studies are performed in robotics and industrial servo press mechanism by using system's nonlinear dynamics. Robotic systems and servo crank press are currently available in Mechanical Engineering Department's laboratory (Gaziantep University/Turkey). Identification and simulation studies are carried out to get dynamic behavior of the systems of interest. Different motion trajectories are applied according to the requirements for all. Soft computing techniques are studied on these systems. Traditional PID is also applied. Control techniques are implemented as PSO-NN (Particle Swarm Optimization-Neural Network), BP (Back Propagation), PSO-PID; PID and also CasFF (Cascade Feed-Forward) control in laboratory testing in this study. All of the studies are given as experimental base herein.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 Applications on Haptic Rehabilitation(Ieee, 2015) Kütük, M. Erkan; Dülger, L. Canan; Daş, M. TaylanPopulation of patients who need upper extremity physical rehabilitation is increasing. It is foreseen in near future that contraction in the number of therapist will create a huge problem. In this study, upper extremity rehabilitation robots are focused and some examples are given on haptic rehabilitation. Haptic devices can provide three-dimensional information exchange between human and computer. Force feedback is implemented by modeling sense of touch perceived in real environment. Information about contents and infrastructure facilities of the work in progress in cooperation with Mechanical Engineering and Medicine Faculty are given.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 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 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 Oil temperature analysis of brush seals(2008) Duran, Ertuğrul Tolga; Aksit, Mahmut Faruk; Doğu, YahyaDue to their superior performance and stable leakage characteristics, brush seals are one of the dynamic seals used in oil and oil mist applications in aero-engines and turbines. The viscous medium between the high speed rotor surface and brush seal bristles generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. The analytical solution to bristle lifting force can be obtained by using Reynolds formulation. However, there is a strong dependence on oil temperature and viscosity. This work presents a solution to oil temperature using nonlinear pressure distribution. Starting with continuity and Navier Stokes equations, temperature and nonlinear pressure distribution is derived by solving the thermal energy and reduced continuity equations simultaneously. Results of oil temperature estimates using nonlinear pressure analysis are compared with the results of a previous work using linear pressure assumption. Findings indicate that for low rotor surface speeds oil temperature distribution is almost the same for both linear and nonlinear pressure cases. Difference in oil temperature estimates increases with increasing rotor surface speeds. Copyright © 2007 by ASME.Öğe Brush seal temperature distribution analysis (Conference Paper)(2005) Doğu, 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. Copyright © 2005 by ASME.Öğe Evaluation of brush seal performance for oil sealing applications(2003) Akşit, Mahmut Faruk; Bhate, Nitin; Bouchard, Charles; Demiroğlu, Mehmet; Doğu, YahyaOil sealing at high speeds is one of the major problems engineers should address in turbomachinery design. High temperatures faced in oil sumps in aircraft engines, and large seal sizes typical in land based turbine applications further complicate the problem. Labyrinth seals can overcome problems faced with carbon seals in high temperature and large size applications. On the other hand, use of labyrinth seals may result in high leakage rates leading to increased oil consumption, unintended oil contamination in some flow cavities, early oil degradation or even fires in some cases. Successful engine secondary flow path applications of brush seals lead to questions of their applicability for oil sealing. Because brush seals are contact seals, oil temperature rise and coking become major issues in addition to leakage performance. This paper presents an investigative study of brush seal leakage and coking performance using common lube oil. Both metallic and non-metallic prototypes have been tested under static and dynamic conditions. It has been concluded that properly designed brush seals can achieve lower leakage rates than labyrinth seals without causing coking problems. © 2003 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Öğe Investigation of brush seal flow characteristics using bulk porous medium approach (Conference Paper)(2003) Doğu YahyaThe flow behavior through a brush seal has been investigated by developing a flow analysis procedure with a porous medium approach. In order to increase the brush seal performance and use at more severe operating conditions, the complex flow in the bristle pack has become the major concern affecting seal features such as blow-down, hang-up, hysteresis and bristle flutter. In this study, an axi-symmetric CFD model is employed to calibrate anisotropic permeability coefficients for the bristle pack based on available experimental data; leakage, axial pressure on the rotor surface and radial pressure on the backing plate. A simplified form of the force balance equation is introduced for the flow in the porous bristle pack. Different sets of permeability coefficients are defined for fence height region below the seal backing plate and the upper region of the seal to correlate the different physical structures and behavior of these regions during operation. The upper region is subject to more stiffening due to backing plate support while fence height region is free to spread and bend in the axial direction. It is found that flow resistance for upper region should be 20% higher than fence height region in order to match the experimental pressure within the bristle pack. Analysis results prove that the brush seal is well represented as a porous medium with this approach. Based on the model developed, characteristic flow and pressure fields in the entire bristle pack have been explored.
