scholarly journals One-Dimensional Computation Method of Supercritical CO2 Labyrinth Seal

2020 ◽  
Vol 10 (17) ◽  
pp. 5771
Author(s):  
Yuming Zhu ◽  
Yuyan Jiang ◽  
Shiqiang Liang ◽  
Chaohong Guo ◽  
Yongxian Guo ◽  
...  
Keyword(s):  
Supercritical Co2 ◽  
Discharge Coefficient ◽  
Internal Flow ◽  
Labyrinth Seal ◽  
Experimental Results ◽  
Computation Method ◽  
Labyrinth Seals ◽  
Two Phase ◽  
One Dimensional ◽  
Experimental Correlation

An actual one-dimensional(1-D) computation method for a labyrinth seal is proposed. Relevant computation hypotheses for the 1-D method are analyzed and the specificity of internal flow in an SCO2 (supercritical CO2) labyrinth seal is explored in advance. Then, the experimental correlation discharge coefficient and the residual kinetic energy coefficient used in SCO2 labyrinth seals are proposed. In addition, the speed of sound in two-phase flow is corrected in the 1-D method. All recent experimental results of the SCO2 labyrinth seal are sorted out and the latest experimental results of a stepped-staggered labyrinth seal are proposed to verify the accuracy and applicability of the 1-D method. Finally, the sealing efficiency of the SCO2 labyrinth seals are analyzed using the 1-D method.

Advanced Labyrinth Seals for Steam Turbine Generators

2006 ◽  
Author(s):  
Ahmad D. Vakili ◽  
Abraham J. Meganathan ◽  
Sricharan Ayyalasomayajula ◽  
Stephen Hesler ◽  
Lewis Shuster
Keyword(s):  
High Performance ◽  
Internal Flow ◽  
Life Time ◽  
Labyrinth Seal ◽  
Two Dimensional ◽  
Steam Turbines ◽  
Labyrinth Seals ◽  
Turbine Generators ◽  
High Performance Composite ◽  
Steam Leakage

A new class of knives (C-Shaped) for reduced labyrinth seal discharge has been designed and assessed through two dimensional numerical modeling of the seal’s internal flow passages. Modeling procedures used for the analysis have been previously validated by comparison with static labyrinth seal experiments. The objectives of the new seal are to: 1) reduce flow leakage through the seal and 2) introduce structural flexibility in the knives so that design clearances could be maintained even after rub events during startup. The baseline chosen for comparative evaluation is an N2 packing used in GE steam turbines. The new seals have compliant C-shaped knives instead of the straight knives, found in an N2 packing. The best performing configuration has one tall ‘C’ shaped long knife and three ‘C’ shaped short knives in each stage. It was found that the best configuration at clearances similar to the baseline seal reduces flow leakage by 42%. Two dimensional numerical structural analyses showed that the new seal knife is more flexible than a straight knife. This is also intuitive by virtue of its geometric profile. A non-dimensional geometric parameter correlates with the degree of flexibility in the knife. These results indicate a potential for design of labyrinth seals that maintain lower design clearances throughout their life time by carefully selecting the knives’ geometric parameters and incorporating high performance composite materials. Then, the new design would result in significantly lower steam leakage.

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.

scholarly journals Analysis of flow and phase interaction characteristics in a gas-liquid two-phase pump

2018 ◽  
Vol 73 ◽  
pp. 69 ◽  
Author(s):  
Wenwu Zhang ◽  
Zhiyi Yu ◽  
Yongjiang Li
Keyword(s):  
Discharge Coefficient ◽  
Flow Direction ◽  
Pure Water ◽  
Internal Flow ◽  
Turbulent Dispersion ◽  
Dispersion Force ◽  
Phase Interaction ◽  
Two Phase ◽  
Structured Grid ◽  
Interphase Force

To analyze the characteristics of internal flow and phase interaction in a gas-liquid two-phase pump, the influence of Inlet Gas Void Fraction (IGVF), discharge coefficient, and medium viscosity were investigated using medium combinations of air-water and air-crude. Simulations were performed using ANSYS_CFX at different IGVFs and various values of discharge coefficient. Structured grid for the full flow passage was generated using ICEM_CFD and TurboGrid. Under conditions of IGVF = 0% (pure water) and IGVF = 15%, the reliability of numerical method was proved by means of the comparison with the experimental data of external characteristic. The results for air-water combination showed a uniform gas distribution in the inlet pipe, and formation of a stratified structure in the outlet pipe. The gas in impeller gathered at the hub because of the rotation of the impeller, also, the interphase forces increased with the increased IGVF. For the two medium combinations, the drag force was the largest interphase force, followed by added mass and lift forces, and then the turbulent dispersion force was the least, which can be neglected. Because of the larger viscosity of crude than that of water, the variation trend of interphase forces in the impeller is relatively smooth along the flow direction when the medium combination was air-crude.

Effects of rotational speed on the leakage behavior, temperature increase, and swirl development of labyrinth seal in a compressor stator well

2016 ◽  
Vol 231 (13) ◽  
pp. 2362-2374 ◽  
Author(s):  
Gaowen Liu ◽  
Xiaozhi Kong ◽  
Yuxin Liu ◽  
Qing Feng
Keyword(s):  
Flow Characteristics ◽  
Internal Flow ◽  
Labyrinth Seal ◽  
Swirl Flow ◽  
Tip Clearance ◽  
Experimental Results ◽  
Test Rig ◽  
Experimental Conditions ◽  
Rotating Speed ◽  
Set Up

The stator well in a compressor is the space between the rotor and stator inside the mainstream annulus flow. Labyrinth seals are normally used to control the internal flow in the stator well. The upstream and downstream rotating cavities of the labyrinth seal can lead to substantial temperature rise and swirl development in this region. Additionally, due to the centrifugal expansion and thermal expansion, the tip clearance of labyrinth seal changes dramatically at different rotational speeds and temperatures in the stator well. A test rig capable to establish different rotational speeds and pressure ratios was designed according to the simplified model of the labyrinth seal in a compressor stator well (one stage). The leakage flow rate and change in total temperature across the stator well were measured. This paper also contains the experimental results of swirl ratios in the outlet rotating cavity to reveal the swirl development. Special emphasis in this work lies on acquiring the working tip clearance precisely. The set up tip clearance was measured with plug gauges, while the radial displacements of labyrinth ring and stator casing were measured separately with two high precision laser distance sensors. Two-dimensional, axisymmetric swirl flow numerical simulations were performed to get a further understanding about the basic flow characteristics and to evaluate their ability to predict the experimental results. The computational results of discharge coefficient, windage heating, and swirl ratio were compared to those obtained from test rig measurements. Particularly, when calculating, the tip clearance, the inlet parameters, and the outlet parameters of numerical model at a specific rotating speed were set to be the same with the experimental conditions.

scholarly journals Experimental Study of the Static and Dynamic Characteristics of a Long (L/D = 0.75) Labyrinth Annular Seal Operating Under Two-Phase (Liquid/Gas) Conditions

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Hari Shrestha ◽  
Dara W. Childs ◽  
Dung L. Tran ◽  
Min Zhang
Keyword(s):  
Volume Fraction ◽  
Silicone Oil ◽  
Dynamic Stiffness ◽  
Labyrinth Seal ◽  
Radial Clearance ◽  
Labyrinth Seals ◽  
Two Phase ◽  
Annular Seal ◽  
The Stability ◽  
Gas Volume

AbstractA two-phase annular-seal stand at the Turbomachinery Laboratory of Texas A&M University is utilized to experimentally investigate a labyrinth seal operating under two-phase flow conditions (a mixture of silicone oil and air). A long labyrinth seal (length-to-diameter ratio L/D = 0.75, diameter D = 114.729 mm, and radial clearance Cr = 0.213 mm) is tested at a supply pressure of 62 bars-g with inlet gas volume fraction GVFi ranging from 90 to 100%. Tests were conducted at three pressure ratios PR (0.3, 0.4, 0.5), three rotating speeds (5, 10, 15 krpm), six GVFi (90%, 92%, 94%, 96%, 98%, and 100%), and three inlet-preswirl inserts, namely, zero, medium, and high. Specifically, the ratio between the fluid's circumferential velocity and the shaft surface's velocity are in ranges of 0.0–0.2, 0.5–1.6, and 0.5–2.7 for the zero, medium, and high preswirls respectively. The direct dynamic stiffness KΩ is negative. As GVFi decreases (more liquid), KΩ becomes more negative for the zero preswirl. The effect of changing GVFi on KΩ for the medium and high preswirls is not as clear as for the zero preswirl. For the zero preswirl, as GVFi decreases, the cross-coupled dynamic stiffness kΩ and direct damping C damping increase. However, the effective damping Ceff values converge to almost the same positive value for higher frequencies. Hence, there is no significant effect of change in GVFi for the zero preswirl. For the high preswirl, as GVFi decreases, kΩ decreases and C increases. As GVFi decreases, Ceff becomes less negative and eventually becomes positive for frequencies higher than Ωc. This result indicates that at certain frequencies, the presence of liquid can make the labyrinth seals with high preswirl more stable. For the seal tested, a compressor running at 15 krpm and PR (ratio of seal exit pressure and seal inlet pressure) = 0.5 with the first critical speed of 7500 rpm (125 Hz) would experience an increase in stability with presence of liquid in the flow stream for the medium and high preswirls. However, for the range of GVFi considered here, if swirl brakes are used in a compressor application to reduce the preswirl, there would be no impact of liquid presence on the stability of the compressor. Concerning static measurements, leakage rate m˙ increases with decreases in GVFi but remains unchanged with increasing preswirl.

Experimental Results for Labyrinth Gas Seals With Honeycomb Stators: Comparisons to Smooth-Stator Seals and Theoretical Predictions

1989 ◽  
Vol 111 (1) ◽  
pp. 161-168 ◽  
Author(s):  
Larry Hawkins ◽  
Dara Childs ◽  
Keith Hale
Keyword(s):  
Flow Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Experimental Results ◽  
Test Results ◽  
Labyrinth Seals ◽  
Model Predictions ◽  
Theoretical Predictions ◽  
Gas Seals ◽  
Stiffness And Damping

Experimental measurements are presented for the rotordynamic stiffness and damping coefficients of a teeth-on-rotor labyrinth seal with a honeycomb stator. Inlet circumferential velocity, inlet pressure, rotor speed, and seal clearance are primary variables. Results are compared to (a) data for teeth-on-rotor labyrinth seals with smooth stators, and (b) analytical predictions from a two-control-volume compressible flow model. The experimental results show that the honeycomb-stator configuration is more stable than the smooth-stator configuration at low rotor speeds. At high rotor speeds, the stator surface does not affect stability. The theoretical model predicts the cross-coupled stiffness of the honeycomb-stator seal correctly within 25 percent of measured values. The model provides accurate predictions of direct damping for large clearance seals; however, the model predictions and test results diverge with increasing running speed. Overall, the model does not perform as well for low clearance seals as for high clearance seals.

Flexible Seal Strip Design for Advanced Labyrinth Seals in Turbines

2013 ◽  
Author(s):  
N. Herrmann ◽  
K. Dullenkopf ◽  
H.-J. Bauer
Keyword(s):  
High Speed ◽  
Discharge Coefficient ◽  
Life Time ◽  
Labyrinth Seal ◽  
Labyrinth Seals ◽  
Seal Design ◽  
Discharge Rates ◽  
Balanced Designs ◽  
Cooling Effects ◽  
The Impact

The paper discusses the potential benefit of flexible seal strips in labyrinth seals for turbines. By reducing the radial stiffness compared to a standard straight and stiff knife, seal clearance could be reduced without significantly reducing the seal durability and long-term performance. As contact between the seal strips and the rotor can occur especially during transient operating phases, a more flexible design of the seal strips can prevent damage and wear, keeping the discharge rates constantly low. However, the pressure difference across the fin will cause a deflection of the seal strip due to the increased flexibility and thus creating an additional possible risk for an unwanted contact. Pressure balanced designs and supports on the low pressure side are used on the investigated seal designs to eliminate that risk. To give evidence of possible performance gain a standard labyrinth seal configuration is compared to two configurations with segmented and curved seal strips. In a first step, the discharge coefficient and the leakage rates for the nominal seal design are calculated using two-dimensional CFD. In order to investigate the impact of a worn seal tip on the leakage flow, the geometry change due to a rubbing event is simulated with FEA tools. Therefore, a specific high-speed wear model is implemented and calibrated by experimental data, enabling the correct cooling effects and plastic deformation. The discharge coefficient and the leakage mass flow rates of the worn geometry are then again modeled with CFD for the various seal configurations and compared to the unworn state. The study shows that a wise combination of the advantages of flexible curved seal strips can be used to reduce the leakage rates significantly, improving the life time of seal elements at the same time.

scholarly journals Experimental Study of the Static and Dynamic Characteristics of a Long (L/D=0.75) Labyrinth Annular Seal Operating Under Two-Phase (Liquid/Gas) Conditions

2019 ◽  
Author(s):  
Hari Shrestha ◽  
Dara W. Childs ◽  
Dung L. Tran ◽  
Min Zhang
Keyword(s):  
Volume Fraction ◽  
Silicone Oil ◽  
Dynamic Stiffness ◽  
Labyrinth Seal ◽  
Radial Clearance ◽  
Labyrinth Seals ◽  
Two Phase ◽  
Annular Seal ◽  
The Stability ◽  
Gas Volume

Abstract A 2-phase annular-seal stand (2PASS) at the Turbomachinery Laboratory of Texas A&M University is utilized to experimentally investigate a labyrinth seal operating under 2-phase flow conditions (a mixture of silicone oil and air). A long labyrinth seal (length-to-diameter ratio L/D = 0.75, diameter D = 114.729 mm, and radial clearance Cr = 0.213 mm) is tested at a supply pressure of 62 bars-g with inlet gas volume fraction GVFi ranging from 90–100%. Tests were conducted at three pressure ratios PR (0.3, 0.4, 0.5), three rotating speeds (5, 10, 15 krpm), six GVFi (90%, 92%, 94%, 96%, 98%, 100%), and three inlet-preswirl inserts, namely, zero, medium, and high. Specifically, the ratio between the fluid’s circumferential velocity and the shaft surface’s velocity, are in ranges of 0.0–0.2, 0.5–1.6, and 0.5–2.7 for the zero, medium, and high preswirls, respectively. The direct dynamic stiffness KΩ is negative. As GVFi decreases (more liquid), KΩ becomes more negative for the zero preswirl. The effect of changing GVFi on KΩ for the medium and high preswirls is not as clear as for the zero preswirl. For the zero preswirl, as GVFi decreases, the cross-coupled dynamic stiffness kΩ and direct damping C damping increases. However, the effective damping Ceff values converge to almost the same positive value for higher frequencies. Hence, there is no significant effect of change in GVFi for the zero preswirl. For the high preswirl, as GVFi decreases, kΩ decreases and C increases. As GVFi decreases, Ceff becomes less negative and eventually becomes positive for frequencies higher than Ωc. This result indicates that at certain frequencies, the presence of liquid can make the labyrinth seals with high preswirl more stable. For the seal tested, a compressor running at 15 krpm and PR (ratio of seal exit pressure and seal inlet pressure) = 0.5 with the first critical speed of 7500 rpm (125 Hz) would experience an increase in stability with presence of liquid in the flow stream for the medium and high preswirls. However, for the range of GVFi considered here, if swirl brakes are used in a compressor application to reduce the preswirl, there would be no impact of liquid presence on the stability of the compressor. Concerning static measurements, leakage rate ṁ increases with decreases in GVFi but remains unchanged with increasing preswirl.

Effect of Rotation on Leakage and Windage Heating in Labyrinth Seals With Honeycomb Lands

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Kali Charan Nayak
Keyword(s):  
Experimental Data ◽  
Rotational Speed ◽  
High Performance ◽  
Discharge Coefficient ◽  
Labyrinth Seal ◽  
Labyrinth Seals ◽  
High Speeds ◽  
Numerical Predictions ◽  
Critical Rotational Speed ◽  
Honeycomb Cell

Abstract One of the basic assumptions of the traditional labyrinth seal leakage calculation is that rotation has minimal or no effect on seal leakage. With the advancement of gas turbine technology, to achieve high performance, seals are run at tight clearances and very high rotational speeds. Due to tight clearances and high speeds, the temperature rise across the seal can be very significant in reducing the seal flow due to the Raleigh line effect. The influence of rotation on the flow dynamics inside the seal region has not previously been studied in detail. In this study the effect of rotation is studied for smooth and honeycomb cells at various seal clearances and rotational speeds. The main objective of this study is to understand the influence of rotation on seal leakage. However, the effect of rotation on swirl and windage heating is also investigated. For this study, the author leveraged the validated 3D computational fluid dynamics methodology for a stationary and rotating labyrinth from previous studies. However, before performing studies on rotation, the numerical modeling approach is benchmarked against experimental data on rotation with smooth stator lands by Waschka et al. The numerical predictions show good agreement with the experimental data. As the rotational speed increases, seal discharge coefficient remains constant until a critical rotational speed is reached. This critical speed is shown to depend non-dimensionally on the ratio of Taylor number to Reynolds number (Ta/Re). As Ta/Re increases above 0.1, seal discharge coefficient can reduce by up to 25% depending on the seal clearance, fin tip speed, and honeycomb cell size.

Three-Dimensional CFD Rotordynamic Analysis of Gas Labyrinth Seals

2001 ◽  
Author(s):  
J. Jeffrey Moore
Keyword(s):  
Shear Stress ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Internal Flow ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Navier Stokes ◽  
Labyrinth Seals ◽  
Navier Stokes Equations ◽  
Rotordynamic Forces

Abstract Labyrinth seals are utilized inside turbomachinery to provide non-contacting control of internal leakage. These seals can also play an important role in determining the rotordynamic stability of the machine. Traditional labyrinth seal models are based on bulk-flow assumptions where the fluid is assumed to behave as a rigid body affected by shear stress at the interfaces. To model the labyrinth seal cavity, a single, driven vortex is assumed and relationships for the shear stress and divergence angle of the through flow jet are developed. These models, while efficient to compute, typically show poor prediction for seals with small clearances, high running speed, and high pressure (Childs, 1993). In an effort to improve the prediction of these components, this work utilizes three-dimensional computational fluid dynamics (CFD) to model the labyrinth seal flow path by solving the Reynolds Averaged Navier Stokes equations. Unlike bulk-flow techniques, CFD makes no fundamental assumptions on geometry, shear stress at the walls, as well as internal flow structure. The method allows modeling of any arbitrarily shaped domain including stepped and interlocking labyrinths with straight or angled teeth. When only leakage prediction is required, an axisymmetric model is created. To calculate rotordynamic forces, a full 3D, eccentric model is solved. The results demonstrate improved leakage and rotordynamic prediction over bulk-flow approaches compared to experimental measurements.

Sign in / Sign up

Export Citation Format

Share Document