Computational Fluid Dynamics Investigation of Labyrinth Seal Leakage Performance Depending on Mushroom-Shaped Tooth Wear

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Yahya Dogu ◽  
Mustafa C. Sertçakan ◽  
Ahmet S. Bahar ◽  
Altuğ Pişkin ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Performance Degradation ◽  
Permanent Teeth ◽  
Tooth Surface ◽  
Limited Information ◽  
Rotor Speed ◽  
Number Of Teeth

Conventional 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 (cr = 0.254–2.032 mm), pressure ratio (Rp = 1.5–3.5), number of teeth (nt = 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.

CFD Investigation of Labyrinth Seal Leakage Performance Depending on Mushroom Shaped Tooth Wear

2015 ◽  
Author(s):  
Yahya Doğu ◽  
Mustafa C. Sertçakan ◽  
Ahmet S. Bahar ◽  
Altuğ Pişkin ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Pressure Ratio ◽  
Tooth Wear ◽  
Labyrinth Seal ◽  
Performance Degradation ◽  
Permanent Teeth ◽  
Tooth Surface ◽  
Limited Information ◽  
Rotor Speed ◽  
Vena Contracta ◽  
Number Of Teeth

Conventional 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=0–0.508mm), clearance (cr=0.254–2.032mm), pressure ratio (Rp=1.5–3.5), number of teeth (nt=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.

scholarly journals Theoretical and experimental investigation on maximum pressure loads of labyrinth seal’s teeth

2018 ◽  
Vol 10 (10) ◽  
pp. 168781401879434 ◽  
Author(s):  
Jie Jiang ◽  
Yiyong Yang ◽  
Yongjian Li ◽  
Weifeng Huang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Maximum Pressure ◽  
Test Results ◽  
Dynamics Model ◽  
Computational Fluid Dynamics Model ◽  
Pressure Load ◽  
Sound Structure

The pressure loads acting on the teeth of a labyrinth seal are usually not uniform. Sometimes, one tooth would take almost half of the total pressure difference, which is detrimental to the teeth’s working life and sealing effect. Therefore, the estimation of maximum pressure load on the teeth is helpful to design a sound structure of labyrinth seal. This article analyzes the influence of teeth number, boundary condition, clearances, and structure parameters on maximum pressure loads of labyrinth seal teeth in low pressure ratio conditions ( PR≤ 0.5, PR = Pout/ Pin). Both the computational fluid dynamics model and test results show that teeth number and pressure load are main factors influencing the maximum pressure load on teeth. Finally, a fitting equation is given to estimate the maximum pressure load on labyrinth seal teeth and its results are in good agreement with the computational fluid dynamics model.

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.

Effect of Cavities in Suddenly Expanded Flow at Supersonic Mach Number

CFD letters ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 57-71
Author(s):  
Atifatul Ismah Ismail
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Mach Number ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Base Pressure ◽  
Sudden Expansion ◽  
Expansion Level ◽  
Computational Fluid Dynamics Cfd ◽  
Base Drag

The contribution from the base drag due to the sub-atmospheric pressure is significant. It can be more than two-thirds of the net drag. There is a need to increase the base pressure and hence decrease the base drag. This research examines the effect of Mach Number on base pressure. To accomplish this objective, it controls the efficacy in an enlarged duct computed by the numerical approach using Computational Fluid Dynamics (CFD) Analysis. This experiment was carried out by considering the expansion level and the aspect cavity ratio. The computational fluid dynamics method is used to model supersonic motion with the sudden expansion, and a convergent-divergent nozzle is used. The Mach number is 1.74 for the present study, and the area ratio is 2.56. The L/D ratio varied from 2, 4, 6, 8, and 10, and the simulated nozzle pressure ratio ranged from 3 to 11. The two-dimensional planar design used commercial software from ANSYS. The airflow from a Mach 1.74 convergent-divergent axi-symmetric nozzle expanded suddenly into circular ducts of diameters 17 and 24.5 mm with and without annular rectangular cavities. The diameter of the duct is taken D=17mm and D=24.5mm. The C-D nozzle was developed and modeled in the present study: K-ε standard wall function turbulence model was used with the commercial computational fluid dynamics (CFD) and validated. The result indicates that the base pressure is impacted by the expansion level, the enlarged duct size, and the passage’s area ratio.

Abstract WP121: An Evaluation of Hemodynamics Across Intracranial Steno-occlusive Lesions by Computational Fluid Dynamics

Stroke ◽  
2016 ◽  
Vol 47 (suppl_1) ◽  
Author(s):  
Florence SY Fan ◽  
Vincent HL Ip ◽  
Alexander YL Lau ◽  
Anne YY Chan ◽  
Lisa WC Au ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Pressure Difference ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Strongly Correlated ◽  
Hemodynamic Parameters ◽  
Moderate Correlation ◽  
Anterior Circulation

Introduction: Intracranial atherosclerotic steno-occlusive disease (ICAS) is a major cause of stroke worldwide and portends a high risk of recurrence. Computational fluid dynamics (CFD) is a novel technique developed to solve and analyze the dynamic effects of fluid flow. We aimed to analyse hemodynamics across ICAS using CFD on processed CTA images and explore the correlation between the degree of arterial stenosis and hemodynamic flow status. Methods: We recruited patients with symptomatic ICAS from Acute Stroke Unit, Prince of Wales Hospital. All patients received CTA and DSA as vascular workup. Using CFD analysis of processed CTA images, we first defined the hemodynamic parameters, including pressure difference, pressure ratio, pressure gradient, shear strain rate ratio (SSR), wall shear stress (WSS) ratio and velocity ratio, across the stenosed vessels, and then we correlated the severity of stenosis as defined by DSA, with these parameters. Results: Among the 53 recruited patients (mean age 62.9 years, 69.8% males), 45 (85%) had lesions in the anterior circulation. The severity of stenosis showed a weak-to-moderate correlation with pressure difference (rs=0.392, p=0.004), pressure ratio (rs=-0.429, p=0.001) and pressure gradient (rs=0.419, p=0.002). There was no significant correlation between the severity of stenosis with SSR ratio, WSS ratio and velocity ratio. Among patients with anterior circulation stroke or TIA, the severity of stenosis showed a weak to moderate correlation with pressure difference (rs=0.381, p=0.01), pressure ratio (rs=-0.426, p=0.004) and pressure gradient (rs=0.407, p=0.005). For patients with posterior circulation stroke or TIA, the severity of stenosis was strongly correlated with pressure difference (rs=0.714, p=0.047) and pressure ratio (rs=-0.714, p=0.047); and very strongly correlated with velocity ratio (rs=0.833, p=0.01). Conclusions: The severity of ICAS showed only weak-to-moderate correlation with hemodynamic parameters across the culprit lesion. Thus, risk stratification and treatment based solely on stenotic severity may be inadequate. Our findings may guide further research in estimating stroke risks and selection of high-risk patients who may benefit from adjunctive treatments.

scholarly journals A zonal approach for estimating pressure ratio at compressor extreme off-design conditions

2018 ◽  
Vol 20 (4) ◽  
pp. 393-404 ◽  
Author(s):  
José Galindo ◽  
Roberto Navarro ◽  
Luis Miguel García-Cuevas ◽  
Daniel Tarí ◽  
Hadi Tartoussi ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Internal Combustion Engines ◽  
Pressure Ratio ◽  
Internal Combustion ◽  
Operating Conditions ◽  
Combustion Engines ◽  
One Dimensional ◽  
Performance Map

Zero-dimensional/one-dimensional computational fluid dynamics codes are used to simulate the performance of complete internal combustion engines. In such codes, the operation of a turbocharger compressor is usually addressed employing its performance map. However, simulation of engine transients may drive the compressor to work at operating conditions outside the region provided by the manufacturer map. Therefore, a method is required to extrapolate the performance map to extended off-design conditions. This work examines several extrapolating methods at the different off-design regions, namely, low-pressure ratio zone, low-speed zone and high-speed zone. The accuracy of the methods is assessed with the aid of compressor extreme off-design measurements. In this way, the best method is selected for each region and the manufacturer map is used in design conditions, resulting in a zonal extrapolating approach aiming to preserve accuracy. The transitions between extrapolated zones are corrected, avoiding discontinuities and instabilities.

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.

Computational Fluid Dynamics Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Yahya Dogu ◽  
Ahmet S. Bahar ◽  
Mustafa C. Sertçakan ◽  
Altuğ Pişkin ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Ratio ◽  
Plate Thickness ◽  
Operating Conditions ◽  
Design Parameters ◽  
Backing Plate ◽  
Brush Seal ◽  
Front Plate ◽  
Brush Seals

Brush seals require custom design and tailoring due to their behavior driven by flow dynamic, which has many interacting design parameters, as well as their location in challenging regions of turbomachinery. Therefore, brush seal technology has not reached a conventional level across the board standard. However, brush seal geometry generally has a somewhat consistent form. Since this consistent form does exist, knowledge of the leakage performance of brush seals depending on specific geometric dimensions and operating conditions is critical and predictable information in the design phase. However, even though there are common facts for some geometric dimensions available to designers, open literature has inadequate quantified information about the effect of brush seal geometric dimensions on leakage. This paper presents a detailed computational fluid dynamics (CFD) investigation quantifying the leakage values for some geometric variables of common brush seal forms functioning in some operating conditions. Analyzed parameters are grouped as follows: axial dimensions, radial dimensions, and operating conditions. The axial dimensions and their ranges are front plate thickness (z1 = 0.040–0.150 in.), distance between front plate and bristle pack (z2 = 0.010–0.050 in.), bristle pack thickness (z3 = 0.020–0.100 in.), and backing plate thickness (z4 = 0.040–0.150 in.). The radial dimensions are backing plate fence height (r1 = 0.020–0.100 in.), front plate fence height (r2 = 0.060–0.400 in.), and bristle free height (r3 = 0.300–0.500 in.). The operating conditions are chosen as clearance (r0 = 0.000–0.020 in.), pressure ratio (Rp = 1.5–3.5), and rotor speed (n = 0–40 krpm). CFD analysis was carried out by employing compressible turbulent flow in 2D axisymmetric coordinate system. The bristle pack was treated as a porous medium for which flow resistance coefficients were calibrated by using literature based test data. Selected dimensional and operational parameters for a common brush seal form were investigated, and their effects on leakage performance were quantified. CFD results show that, in terms of leakage, the dominant geometric dimensions were found to be the bristle pack thickness and the backing plate fence height. It is also clear that physical clearance dominates leakage performance, when compared to the effects of other geometric dimensions. The effects of other parameters on brush seal leakage were also analyzed in a comparative manner.

scholarly journals Parametric Output of Penetration Length in De-Laval Nozzle using Computational Fluid Dynamics

2020 ◽  
Vol 8 (6) ◽  
pp. 585-592
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Laval Nozzle ◽  
Pressure Ratio ◽  
Research Work ◽  
Variable Pressure ◽  
Penetration Length ◽  
Rocket Nozzle ◽  
Half Angle ◽  
De Laval Nozzle

A Contour shaped rocket nozzle, commonly known as Bell nozzle, is a more efficient form of a De-Laval nozzle useful for operation at different altitudes resulting in variable pressure ratio across the nozzle. Here the penetration length during the flow is calculated in a De-Laval nozzle using Computational fluid dynamics (CFD). The TOP nozzle] by G.V.R. Rao is modeled and simulated using CFD analysis by varying the divergent half angle of the bell nozzle. The geometry of different divergent angle of the bell nozzle is modeled using MATLAB code. The modeled geometry and mesh of the nozzle is simulated in ANSYS-FLUENT software. The simulation shows the variation in different flow parameter at different divergent half angles. The analysis so far for the same is done in a conical shaped rocket nozzle at the cost of varying the divergent length for changing the divergent half angle of the nozzle. This project simulates bell nozzle with constant divergent length. The simulation model is verified and validated using experimental and computational data at an NPR (Nozzle pressure ratio) of 1000. As the Rao Nozzle is used currently in rocket, missile, and satellite control systems worldwide. This research work to show how the penetration length effect the Mass-Weighted average Mach number in a particular designed bell nozzle with different divergent half angle. Based on the results obtained, the discussion is done about the parameters and the conclusion is given

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