Labyrinth Seal Leakage Degradation Due to Various Types of Wear

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Yahya Dogu ◽  
Mustafa C. Sertçakan ◽  
Koray Gezer ◽  
Mustafa Kocagül ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Pressure Ratio ◽  
Tooth Wear ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Labyrinth Seals ◽  
Engine Design ◽  
Acute Triangle ◽  
Computational Fluid Dynamics Cfd ◽  
Compressible Turbulent Flow ◽  
Cfd Analyses

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 rub-groove 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.

Labyrinth Seal Leakage Degradation due to Various Types of Wear

2016 ◽  
Author(s):  
Yahya Dogu ◽  
Mustafa C. Sertçakan ◽  
Koray Gezer ◽  
Mustafa Kocagül ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Pressure Ratio ◽  
Tooth Wear ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Labyrinth Seals ◽  
Engine Design ◽  
Acute Triangle ◽  
Compressible Turbulent Flow ◽  
Cfd Analyses ◽  
Transient Operations

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 rub-groove 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, rotor speed). CFD analyses are carried out by employing compressible turbulent flow in a 2-D axi-symmetrical 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.

Numerical and Experimental Investigation on the Effect of Swirl Brakes on the Labyrinth Seals

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Dan Sun ◽  
Shuang Wang ◽  
Cheng-Wei Fei ◽  
Yan-Ting Ai ◽  
Ke-Ming Wang
Keyword(s):  
Pressure Ratio ◽  
Flow Characteristics ◽  
Labyrinth Seal ◽  
Impedance Method ◽  
Swirl Ratio ◽  
Labyrinth Seals ◽  
Rotating Speed ◽  
Simulation And Experiment ◽  
Computational Fluid Dynamics Cfd ◽  
Static Flow

Swirl brake influences the static and rotordynamic characteristics of labyrinth seal which are important in the prediction of turbomachine stability. To study the influence of the swirl brakes on improving seal stability, the effects of swirl brakes on the static and rotordynamic characteristics of labyrinth seals were investigated by the combination of numerical simulation and experiment. First, it was performed to the effects of swirl brake on the static flow characteristics of labyrinth seal with swirl ratio and pressure distribution based on computational fluid dynamics (CFD). And then a comparison between leakage predicted by the CFD model and measurement was presented to verify the accuracy of the simulation. Moreover, an experiment was implemented to analyze the rotordynamic characteristics of labyrinth seal using an improved impedance method based on an unbalanced synchronous excitation method on a rotor test rig. The influences of swirl brake density, length, inlet/outlet pressure ratio, and rotating speed were measured and discussed, respectively. The CFD numerical results show that the swirl brake effectively reduces the seal swirl ratio (∼60–75% less), circumferential pressure difference (∼25–85% less) so that the seal destabilizing forces decrease. With the increasing of the swirl vanes density and length, the seal leakage drops (∼8–20% less). The experimental rotordynamic characteristics results show that it is more obvious to reduce the cross-couple stiffness (∼50–300% less) and increase the direct damping (∼50–60% larger) with the increasing in the number and length of the swirl vanes, and thus the swirl brake improves the seal rotordynamic stability. The efforts of this paper provide a useful insight to clearly understand the effects of swirl brakes on the labyrinth seal static and rotordynamic characteristics, which is beneficial to improve the design of annular seals.

Leakage and Windage Heating in Stepped Labyrinth Seals

2019 ◽  
Author(s):  
Kali Charan Nayak ◽  
Nomesh P. Kandaswamy ◽  
Syed Faheemulla
Keyword(s):  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Vital Role ◽  
Step Height ◽  
Axial Position ◽  
Radial Clearance ◽  
Labyrinth Seals ◽  
Geometric Factors ◽  
Pitch Ratio ◽  
Computational Fluid Dynamics Cfd

Abstract Stepped labyrinth seals are used in multiple locations in the gas turbine with the intent to reduced leakage compared to straight labyrinth seals. However the selection of geometric factors in stepped labyrinth seals is critical to allow lower leakage in its operating envelope. Particularly the step height and axial position during the running condition play a vital role. The influence of these factors on the leakage, swirl development and windage heating in stepped labyrinth seal has not been thoroughly investigated in the previously published work. This paper focuses to study above effects with numerical simulations in a smooth four-fin stepped labyrinth seal. Specifically, a 2D axi-symmetric computational fluid dynamics (CFD) model is developed utilizing commercial finite volume-based software incorporating the standard k-ε turbulence model. Using this model, a broad parametric study is conducted by varying step height, axial position of the knife from the step, radial clearance and pressure ratio for a four-teeth stepped labyrinth seal. It has been observed that the seal leakage reduces with increase in step height to pitch ratio up to 0.35 and with further increase it tails off. The axial position of the tooth has strong influence on the flow structure and swirl development in the seal pocket.

Leakage Degradation of Straight Labyrinth Seal Due to Wear of Round Tooth Tip and Acute Trapezoidal Rub-Groove

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Yahya Dogu ◽  
Mustafa C. Sertçakan ◽  
Koray Gezer ◽  
Mustafa Kocagül ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Groove Width ◽  
Axial Position ◽  
Rotor Speed ◽  
Wall Angle ◽  
Round Shape ◽  
Number Of Teeth ◽  
Cfd Analyses

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, 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.

Leakage Degradation of Straight Labyrinth Seal due to Wear of Round Tooth Tip and Acute Trapezoidal Rub-Groove

2016 ◽  
Author(s):  
Yahya Dogu ◽  
Mustafa C. Sertçakan ◽  
Koray Gezer ◽  
Mustafa Kocagül ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Groove Width ◽  
Axial Position ◽  
Rotor Speed ◽  
Wall Angle ◽  
Round Shape ◽  
Number Of Teeth ◽  
Cfd Analyses

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 contract a 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.

Benefit and Critical Factors for the Performance of the Boundary Layer Ingesting Propulsion

2020 ◽  
Author(s):  
B. J. Lee ◽  
May-Fun Liou ◽  
Mark Celestina ◽  
Waiming To
Keyword(s):  
Boundary Layer ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Power Saving ◽  
Propulsive Efficiency ◽  
Engine Design ◽  
Feasible Range ◽  
Shaft Power ◽  
Cfd Analyses ◽  
The Given

Abstract The benefit of the boundary layer ingestion (BLI) is described in the perspective of the propulsion and engine development. A power saving map of the BLI engines is derived based on the correlation of the wake velocity ratio of the ingested boundary layer profile and the propulsive efficiency. The ratio of the mass flow rate between BLI and non-BLI propulsors is introduced to quantify the power saving of the BLI engine relative to a clean inlet flow engine which generates same amount of thrust. The wake recovery factor from the jet flow out of the BLI engine is employed to find an adequate sizing of the BLI engine for the given design requirement. The effects of the fan pressure ratio on the power saving are also investigated to explore the feasible range of the BLI engine design. The derived correlation is validated with CFD analyses. A numerical experiment is carried out by varying the wake velocity ratio through different BLI engines sized with respect to an influencing body. Consequently, the propulsor efficiency is quantified and presented by the saving in the actual shaft power. The efficiency penalty, pressure ratio of the BLI fan stage are correlated with the power saving and the correlation is validated through BLI2DTF and R4 fan stage CFD analyses based on rig test data.

Numerical Investigations of Leakage Performance Degradations in Labyrinth and Flexible Seals Due to Wear

2020 ◽  
Author(s):  
Xinbo Dai ◽  
Xin Yan ◽  
Kun He ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Labyrinth Seal ◽  
Leakage Rate ◽  
Labyrinth Seals ◽  
Element Analysis ◽  
Numerical Investigations ◽  
Forward Bending ◽  
The Finite Element Analysis ◽  
Before And After ◽  
Computational Fluid Dynamics Cfd ◽  
Wear Damage

Abstract The Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) methods are utilized to investigate the leakage performance degradations in two kinds of flexible seals (i.e. forward bending and backward bending) and two kinds of shroud labyrinth seals (i.e. with straight fins and chamfered fins) in rubbing events. With the existing experimental data, FEA methods for contacting simulations and CFD methods for leakage rate and flow pattern predictions are carefully examined. The wear characteristic and leakage performance between labyrinth seals and flexible seals are compared before and after rub. The results show that, in rubbing process, the labyrinth seal with straight (symmetrical) fins is likely to undergo the mushrooming damage, whereas the labyrinth seal with chamfered (asymmetrical) fins is likely to undergo the tooth-bending damage. In rubbing process, compared with the labyrinth seal, the flexible seal has a superior characteristic in resisting the wear damage due to increased flexibility of fin. For a labyrinth seal with 0.3mm design clearance and a flexible seal with 0.15mm design clearance, the 0.5mm radial displacement of rotor will result in 110% increase of leakage rate for labyrinth seal, and 7% increase of leakage rate for flexible seal after wear. Under the same conditions, the forward bending flexible seal has a lower leakage rate than the backward bending flexible seal before and after rub.

Leakage and Cavity Pressures in an Interlocking Labyrinth Gas Seal: Measurements vs. Predictions

2019 ◽  
Author(s):  
Luis San Andrés ◽  
Tingcheng Wu ◽  
Jose Barajas-Rivera ◽  
Jiaxin Zhang ◽  
Rimpei Kawashita
Keyword(s):  
Mass Flow ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Inlet Pressure ◽  
Steam Turbines ◽  
Rotor Speed ◽  
Labyrinth Seals ◽  
Gas Seals

Abstract Gas labyrinth seals (LS) restrict secondary flows (leakage) in turbomachinery and their impact on the efficiency and rotordynamic stability of high-pressure compressors and steam turbines can hardly be overstated. Amongst seal types, the interlocking labyrinth seal (ILS), having teeth on both the rotor and on the stator, is able to reduce leakage up to 30% compared to other LSs with either all teeth on the rotor or all teeth on the stator. This paper introduces a revamped facility to test gas seals for their rotordynamic performance and presents measurements of the leakage and cavity pressures in a five teeth ILS. The seal with overall length/diameter L/D = 0.3 and small tip clearance Cr/D = 0.00133 is supplied with air at T = 298 K and increasing inlet pressure Pin = 0.3 MPa ∼ 1.3 MPa, while the exit pressure/inlet pressure ratio PR = Pout/Pin is set to range from 0.3 to 0.8. The rotor speed varies from null to 10 krpm (79 m/s max. surface speed). During the tests, instrumentation records the seal mass flow (ṁ) and static pressure in each cavity. In parallel, a bulk-flow model (BFM) and a computational fluid dynamics (CFD) analysis predict the flow field and deliver the same performance characteristics, namely leakage and cavity pressures. Both measurements and predictions agree closely (within 5%) and demonstrate the seal mass flow rate is independent of rotor speed. A modified flow factor Φ¯=m.T/PinD1-PR2 characterizes best the seal mass flow with a unique magnitude for all pressure conditions, Pin and PR.

Numerical Analysis of Honeycomb Labyrinth Seals: Cell Geometry and Fin Tip Thickness Impact on the Discharge Coefficient

2015 ◽  
Author(s):  
Alessio Desando ◽  
Andrea Rapisarda ◽  
Elena Campagnoli ◽  
Roberto Taurino
Keyword(s):  
Discharge Coefficient ◽  
New Technologies ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Pollutant Emissions ◽  
Cell Diameter ◽  
Labyrinth Seals ◽  
Cell Pattern ◽  
Divergent Flow ◽  
Impact Reduction

The design of the newest aircraft propulsion systems is focused on environmental impact reduction. Extensive research is being carried out with the purpose of improving engine efficiency, enhancing crucial features, in order to decrease both fuel consumption and pollutant emissions. A lot of improvements to fulfill these objectives must be made, focusing on the optimization of the main engine parts through the utilization of new technologies. The leakage flow reduction in the turbo machinery rotor-stator interaction is one of the main topics to which numerous efforts are being devoted. Labyrinth seals, widely employed in the aerospace field thanks to their simple assembly process and maintenance, can be the means to achieve these objectives. This paper mainly focuses on the optimization of the labyrinth seal stator part, characterized, in modern Low Pressure Turbines (LPT), by a honeycomb cell pattern. The first phase of this study deals with the implementation and validation of a Computational Fluid Dynamics (CFD) numerical model, by using the experimental data available in the literature. Discharge coefficients obtained by numerical simulations, performed at different clearances and pressure ratios on both smooth and honeycomb non-rotating labyrinth seals, are presented and compared to the literature data. Then, for both convergent and divergent flow conditions, the effects on the discharge coefficient due to variations in several cell pattern parameters (i.e. cell diameter, depth and wall thickness) and fin tip thickness are shown. For these analyses the values of clearance and pressure ratio are set at a constant value.

Experimental Rotordynamic Coefficient Results for: (a) A Labyrinth Seal With and Without Shunt Injection and (b) A Honeycomb Seal

1998 ◽  
Author(s):  
Elias A. Soto A. ◽  
Dara W. Childs
Keyword(s):  
Pressure Ratio ◽  
Injection Pressure ◽  
Labyrinth Seal ◽  
Surface Velocity ◽  
Labyrinth Seals ◽  
Honeycomb Seal ◽  
Radial Injection ◽  
Rotor Surface ◽  
Rotordynamic Coefficient ◽  
Better Than

Centrifugal compressors are increasingly required to operate at higher pressures, speeds, and fluid density. In these conditions, compressors are susceptible to rotordynamic instabilities. To remedy this situation, labyrinth seals have sometimes been modified by using shunt injection. In shunt injection, the gas is taken from the diffuser or discharge volute and injected into an upstream chamber of the balance-piston labyrinth seal. The injection direction can be radial or against rotation. This study contains the first measured rotordynamic data for labyrinth seals with shunt injection. A comparison has been made between conventional labyrinth seals, labyrinth seal with shunt injection (radial and against rotation), and a honeycomb seal. Labyrinth seals with injection against rotation are better able to control rotordynamic instabilities than labyrinth seals with radial injection; however, the leakage is slightly higher. The leakage comparison for all seals demonstrates that the honeycomb seal has the best flow control. Test data are presented for a top rotor surface velocity of 110 m/sec, a supply pressure of 13.7 bars, and IPr = 0.95 (injection pressure is 1.05 = 1/0.95 times the seal inlet pressure). For these conditions, and considering effective damping, the labyrinth seal with injection against rotation is better than the honeycomb seal when the pressure ratio across the seal PR<0.45. On the other hand, the honeycomb seal is better when PR>0.45. The effectiveness of the shunt-injection against rotation in developing effective damping is reduced with increasing rotor surface velocity.

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