Optimization of Labyrinth Seal for Screw Compressor

2007 ◽  
Author(s):  
M. Selvaraji ◽  
Sam P. Joseph ◽  
N. Nirmal
Keyword(s):  
Heat Transfer ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Heat Transfer Analysis ◽  
Lubricating Oil ◽  
Screw Compressor ◽  
Labyrinth Seals ◽  
Gas Leakage ◽  
Working Medium

There is a growing demand for compressed air in the industry for various applications. Majority of industrial requirements is in line with screw compressor operating range. Design and construction of screw compressors are demanding tasks that require advanced calculations and theoretical knowledge. Clearances play a major role in the performance and reliability aspects of a screw compressor. Seals are provided in compressors to fit around rotor shafts in order to prevent the leakage of lubricating oil and working medium. However there is a small clearance between the seal and rotor shaft, which can cause potential leakage of the working medium. The performance of the compressor is directly related to the leakage rate through the seals. The labyrinth seal is a special type of seal, used in screw compressors and turbo-machinery for sealing purpose. Labyrinth seal is a non-contacting type seal that uses a tortuous path to minimize the gas leakage. The pressure drop occurs at each labyrinth tooth as the medium is squeezed between the labyrinth tooth and the rotor. The leakage through the seal is directly related to the labyrinth profile and also the clearance between the rotor and the labyrinth tooth. The present work is carried out to reduce the leakage through the labyrinth seal by optimising the tooth profile and operating clearances. Heat transfer analysis is carried out on the housing of the labyrinth seal to find out the boundary temperature of the seal. Also the heat transfer analysis on the labyrinth seal followed by Thermo-structural analysis is carried out to find out the accurate operating clearance of the seal. By using CFD as a tool, the optimisation is carried out on different design configurations of labyrinth seal by comparing the deviation in leakage rates. Effect of rotor speed, width of seal and pressure ratio on air leakage rate is also investigated. A set of labyrinth seals has been designed based on the above optimisation and tested in the compressor. The results have been compared with the CFD prediction.

Experimental Investigation on Leakage Loss and Heat Transfer in a Straight Through Labyrinth Seal

2011 ◽  
Author(s):  
Mirko Micio ◽  
Bruno Facchini ◽  
Luca Innocenti ◽  
Francesco Simonetti
Keyword(s):  
Heat Transfer ◽  
Pressure Ratio ◽  
Reynolds Numbers ◽  
Labyrinth Seal ◽  
Experimental Results ◽  
Leakage Loss ◽  
Labyrinth Seals ◽  
Flow And Heat Transfer ◽  
Sealing Performance ◽  
Stationary Test

Labyrinth seals are extensively used in turbomachinery to prevent high pressure gas from flowing into a region of low pressure. Because of thermal expansions and centrifugal forces, the actual seal clearance can vary based on engine conditions. Pressure ratio, Reynolds number, tip geometry, and seal clearance all affected the sealing performance. This paper deals with its influence on the leakage flow and heat transfer coefficient through a thirteen teeth straight through labyrinth seal. Three gaps were experimentally investigated using a stationary test rig. The experiments covered a range of Reynolds numbers between 5000 and 50000 and pressure ratios between 1.0 and 2.7. Cavity pressure measurements along the seal were also performed in order to characterize each constriction. In addition, 2D PIV measurements were made on the plane containing the seal teeth to obtain a high local resolution of the velocity distribution and the flow field within the seal. Experimental results show a strong influence of clearance on both leakage loss and heat transfer as well as on the development of the flow fields. A simplified model to calculate the leakage mass flow rate is presented and validated comparing its prediction capability with experimental data. In order to improve the agreement between numerical and experimental results a correction of published correlations is proposed.

scholarly journals Numerical Simulation of Secondary Flow in Gas Turbine Disc Cavities, Including Conjugate Heat Transfer

1996 ◽  
Author(s):  
Y.-H. Ho ◽  
M. M. Athavale ◽  
J. M. Forry ◽  
R. C. Hendricks ◽  
B. M. Steinetz
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Conjugate Heat Transfer ◽  
Gas Flow ◽  
Numerical Study ◽  
Labyrinth Seal ◽  
Temperature Fields ◽  
Heat Transfer Analysis ◽  
Flow Rates ◽  
Turbine Disc

A numerical study of the flow and heat transfer in secondary flow elements of the entire inner portion of the turbine section of the Allison T-56/501D engine is presented. The flow simulation included the interstage cavities, rim seals and associated main path flows, while the energy equation also included the solid parts of the turbine disc, rotor supports, and stator supports. Solutions of the energy equations in these problems usually face the difficulty in specifications of wall thermal boundary conditions. By solving the entire turbine section this difficulty is thus removed, and realistic thermal conditions are realized on all internal walls. The simulation was performed using SCISEAL, an advanced 2D/3D CFD code for predictions of fluid flows and forces in turbomachinery seals and secondary flow elements. The mass flow rates and gas temperatures at various seal locations were compared with the design data from Allison. Computed gas flow rates and temperatures in the rim and labyrinth seal show a fair 10 good comparison with the design calculations. The conjugate heat transfer analysis indicates temperature gradients in the stationary intercavity walls, as well as the rotating turbine discs. The thermal strains in the stationary wall may lead to altered interstage labyrinth seal clearances and affect the disc cavity flows. The temperature, fields in the turbine discs also may lead to distortions that can alter the rim seal clearances. Such details of the flow and temperature fields are important in designs of the turbine sections to account for possible thermal distortions and their effects on the performance. The simulation shows that the present day CFD codes can provide the means to understand the complex flow field and thereby aid the design process.

Effects of Inlet Preswirl and Cell Diameter and Depth on Honeycomb Seal Characteristics

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Xin Yan ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Temperature Increase ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Navier Stokes ◽  
Cell Diameter ◽  
Total Temperature ◽  
Honeycomb Seals ◽  
Honeycomb Cell

Three-dimensional Reynolds-averaged Navier–Stokes solutions are employed to investigate the discharge and total temperature increase characteristics of the stepped labyrinth seal with honeycomb land. First, the relations between the windage heating number and the circumferential Mach number at different Reynolds numbers for different honeycomb seals are calculated and compared with the experimental data. The obtained numerical results show that the present three-dimensional periodic model can properly predict the total temperature increase in honeycomb seals. Then, a range of pressure ratios, three inlet preswirl ratios, four sizes of honeycomb cell diameter, and nine sizes of cell depth are selected to investigate the influence of inlet preswirl ratios and honeycomb geometry sizes on the discharge and total temperature increase characteristics of the stepped labyrinth seal. It shows that the leakage rate increases with the increase in cell diameter, and the cell depth has a strong influence on the discharge behavior. However, the influence of the inlet preswirl on the leakage rate is found to be little in the present study. For the total temperature increase characteristic, the inlet preswirl ratio and pressure ratio have more pronounced influence than those of cell depth and diameter. Furthermore, the relations between the leakage rate and cell depth and diameter, as well as the relations between the windage heating power and cell depth and diameter, are not monotonic functions if the pressure ratio is kept constant.

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.

Experimental and Computational Analysis of a Gas Compressor Windback Seal

2007 ◽  
Author(s):  
G. L. Morrison ◽  
Adnan Al-Ghasem
Keyword(s):  
Standard Deviation ◽  
Gas Flow ◽  
Computational Analysis ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Screw Thread ◽  
Shaft Speed ◽  
Flow Paths ◽  
Carry Over

A gas windback seals is similar to a labyrinth seal except the cavity is one continuous channel which winds around the shaft like a screw thread. One application is in gas compressors to isolate lubrication oil from the gas flow paths. A CFD based study of clearance, pressure ratio, and shaft speed has been performed. One seal geometry was experimentally studied to provide verification of the CFD accuracy. An empirical model for the leakage rate has been developed which fits the data with a standard deviation of 0.8%. The effects of pressure ratio and shaft speed upon the leakage rate are independent of each other. Analysis of the CFD results indicate that the kinetic energy carry over coefficient is substantially less for the windback seal operating at low differential pressures and gas densities than for a labyrinth seal operating under typical conditions.

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.

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.

Dynamic Response Analysis of Balance Drum Labyrinth Seal Groove Geometries Optimized for Minimum Leakage

2015 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Neal Morgan ◽  
Vahe Hayrapetian ◽  
Bruno Schiavello
Keyword(s):  
Dynamic Response ◽  
Dynamic Properties ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Response Analysis ◽  
Test Cases ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Overall Stability ◽  
Optimization Loop

Annular labyrinth seals often have a destabilizing effect on pump rotordynamics due to the large cross-coupled forces generated when the fluid is squeezed by an oscillating rotor. In this study several novel groove geometries are investigated for their effect on the rotordynamic coefficients of the labyrinth seal. The groove cavity geometry of a baseline 267 mm balance drum labyrinth seal with a clearance of 0.305 mm and 20 equally spaced groove cavities were optimized for minimum leakage. From the pool of possible groove designs analyzed, nine test cases were selected for maximum or minimum leakage and for a variety of groove cavity shapes. The rotordynamic coefficients were calculated for these cases using a hybrid CFD-bulk flow method. The rotordynamic coefficients obtained by this method were then used with a rotordynamic model of the entire pump to determine the overall stability. Results show that labyrinth seal’s groove shape can be optimized to generate lower leakage rates, while the effects on dynamic properties are only minimally changed. If the seal dynamic response needs to be modified in addition to targeting a lower leakage rate, for instance to exhibit increased damping values, then the leakage rate and the damping coefficient need to be set as objective functions in the optimization loop.

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