Labyrinth Seal Discharge Coefficient for Rectangular Cavities

2009 ◽  
Author(s):  
Saikishan Suryanarayanan ◽  
Gerald L. Morrison
Keyword(s):  
Discharge Coefficient ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Prediction Equation ◽  
Prediction Algorithm ◽  
Expansion Factor ◽  
Clearance Ratio ◽  
Compressibility Effect ◽  
Tooth Width ◽  
Carry Over

A labyrinth seal leakage prediction equation can be developed by considering the seal as a series of orifices and cavities. CFD simulations are used to investigate the discharge coefficient’s dependence of each tooth upon the seal geometry and flow conditions for multi-toothed, teeth on stator, straight through labyrinth seals with rectangular cavities. The discharge coefficient for the first tooth of the labyrinth seal was found to be a function of tooth width to clearance ratio and Reynolds number. It was found that the ratio of the discharge coefficients of a downstream tooth of the labyrinth seal to that of the inlet tooth is a function of the carry over coefficient. The carry over coefficient is a measure of the amount of kinetic energy entering a cavity that is dissipated by turbulence in the cavity. It was observed that the expansion factor (compressibility effect) is a function of tooth pressure ratio. The models developed in this paper for discharge coefficient and expansion factor coupled with the carry over coefficient model presented in our earlier work provide a leakage prediction algorithm that is validated against prior experiments.

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.

scholarly journals Optimizing the Geometric Parameters of a Straight-Through Labyrinth Seal to Minimize the Leakage Flow Rate and the Discharge Coefficient

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 705
Author(s):  
Seung Il Baek ◽  
Joon Ahn
Keyword(s):  
Flow Rate ◽  
Axial Length ◽  
Discharge Coefficient ◽  
Labyrinth Seal ◽  
Geometric Parameters ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Leakage Flow Rate ◽  
Tooth Width ◽  
Cavity Width

A straight-through labyrinth seal is one of the most popular non-contacting annular seals through which energy dissipation by turbulence viscosity interaction is achieved with a series of teeth and cavities. The geometric parameters of the straight-through labyrinth seal, such as clearance, tooth width, tooth height, cavity width, and tooth inclination angle, affect its performance. The space for installing a labyrinth seal in turbomachinery is limited, and so it is important to optimize its geometry for a fixed axial length in order to minimize the leakage flow rate and the discharge coefficient. The objective of the current study is to understand the effects of changing the geometric parameters of the seal on the leakage flow rate and the discharge coefficient, and to determine the optimized geometry for a fixed axial length. When the whole axial length is fixed, the most effective way to decrease the discharge coefficient is to reduce the cavity width by increasing the number of cavities. However, if the number of cavities is too high, the beneficial effect of more cavities can be reversed. The results of this study will help turbomachinery manufacturers to design a more efficient labyrinth seal. Numerical simulations of leakage flow for the straight-through labyrinth seal were carried out using Reynolds-Averaged Navier–Stokes (RANS) models, and the results for their discharge coefficients and pressure distributions were compared to previously published experimental data.

Influence of Labyrinth Clearance on the Flow of Rotating Orifices in a Parallel Labyrinth-Orifice System

2020 ◽  
Author(s):  
Jie Wang ◽  
Shuiting Ding ◽  
Tian Qiu ◽  
Ziqiang Gao
Keyword(s):  
Discharge Coefficient ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Labyrinth Seal ◽  
Chamber Wall ◽  
Flow State ◽  
Aero Engine ◽  
Air System ◽  
Secondary Air ◽  
Cooling Air

Abstract Orifices, especially rotating orifices, are an important flow element of the secondary air system in a modern aero-engine, and their discharge coefficient depends on the geometry, the operating point and the surrounding environment. The influence of Reynolds number, pressure ratio, rotational speed, inlet chamfer, inclination angle, length-to-diameter ratio, etc. on the discharge coefficient of rotating orifices under the assumption of room temperature and adiabatic has been reported in many literatures. However, the rotating speed, the temperature of the gas in the front and rear chambers of rotating orifices and the temperature of the chamber wall change continuously during the actual operation of the engine, especially during the acceleration and deceleration of the engine, which will cause deformation of the chamber wall and the rotating components, resulting in a large change in the labyrinth seal clearance on the periphery of the rotating orifice disk. Although the change of the seal clearance can be evaluated by some methods, it still has a crucial influence on the fluid flow in the front cavity of rotating orifices, which may affect the discharge coefficient of rotating orifices, thereby affecting the amount of cooling air flowing through rotating holes. Therefore, the knowledge of the influence of labyrinth seal clearance should be considered into the discharge coefficient of rotating orifices, which is essential for a reasonable distribution of the cooling air in the second air system under various working conditions and ensures the safety and reliability of the aero-engine in all-inclusive line. This paper presents the relationship between the discharge coefficient of rotating orifices and theoretical velocity ratio in the relative frame of reference (U/Wax) under different labyrinth seal clearance conditions, which is based on the study of the flow state in the front chamber of rotating orifices under different seal clearances, rotating speeds and pressure ratios. The results indicate that with the increase of the labyrinth seal clearance on the periphery of the rotating orifices disk, the discharge coefficient of rotating orifices decrease under the condition of small velocity ratio, while the discharge coefficient is almost unchanged under the large velocity ratio. Comparing the flow field structure and velocity field under the condition of different labyrinth seal clearances, the same pressure ratio and the same velocity ratio, the reasons for the influence of labyrinth seal clearance on the discharge coefficient of rotating orifices are analyzed.

Effect of Tooth Height, Tooth Width and Shaft Diameter on Carry-Over Coefficient of Labyrinth Seals

2009 ◽  
Author(s):  
Saikishan Suryanarayanan ◽  
Gerald L. Morrison
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Labyrinth Seal ◽  
Major Effect ◽  
Labyrinth Seals ◽  
Shaft Diameter ◽  
Tooth Width ◽  
Pitch Ratio ◽  
Carry Over ◽  
Coefficient Of Discharge

The accuracy of rotodynamic analysis of any turbomachinery is dependent upon the accuracy of seal leakage prediction. An expression for the leakage through a labyrinth seal can be developed by combining the coefficient of discharge under each tooth and a carryover coefficient to account for the dissipation of kinetic energy of the jet emerging from under each tooth in the subsequent cavity through turbulence viscosity interaction. While most popularly used leakage models consider the carry-over coefficient only as a function of clearance and pitch, it was established in our earlier work that Reynolds number and clearance/pitch ratio have a major effect on the carry-over coefficient. This work extends the carry-over coefficient model presented by Saikishan Suryanarayanan and G.L. Morrison [1] for incompressible, straight through, rectangular cavity, tooth on stator labyrinth seals by studying and incorporating the effect of tooth width, pitch, tooth height and shaft diameter in addition to Reynolds number and clearance on the carry-over coefficient. It is shown that the tooth width/pitch ratio has a significant effect upon the carry-over coefficient.

Super-Fine Structure in the Critical Flow-Rate of Critical Flow Venturi Nozzles

2002 ◽  
Author(s):  
Masahiro Ishibashi
Keyword(s):  
Fine Structure ◽  
Steady State ◽  
Discharge Coefficient ◽  
Constant Pressure ◽  
Pressure Ratio ◽  
Critical Flow ◽  
Time Intervals ◽  
Critical Flow Rate ◽  
A Value ◽  
Long Time

It is shown that critical flow Venturi nozzles need time intervals, i.e., more than five hours, to achieve steady state conditions. During these intervals, the discharge coefficient varies gradually to reach a value inherent to the pressure ratio applied. When a nozzle is suddenly put in the critical condition, its discharge coefficient is trapped at a certain value then afterwards approaches gradually to the inherent value. Primary calibrations are considered to have measured the trapped discharge coefficient, whereas nozzles in applications, where a constant pressure ratio is applied for a long time, have a discharge coefficient inherent to the pressure ratio; inherent and trapped coefficients can differ by 0.03–0.04%.

scholarly journals Leakage Characteristic Identification of Labyrinth Seals on Reciprocating Piston through Transient Simulations

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Lingzi Wang ◽  
Jianmei Feng ◽  
Mingfeng Wang ◽  
Zenghui Ma ◽  
Xueyuan Peng
Keyword(s):  
Flow Rate ◽  
Pressure Ratio ◽  
Piston Compressor ◽  
Pressure Change ◽  
Labyrinth Seal ◽  
Relative Molecular Mass ◽  
Geometrical Parameters ◽  
Leakage Flow ◽  
Reciprocating Motion ◽  
Leakage Flow Rate

In the reciprocating labyrinth piston compressor, the characteristic of the internal leakage is crucial for the leakage management and performance improvement of the compressor. However, most of the published studies investigated the rotor-stator system, and those who study the reciprocating piston-cylinder system basically focus on the effects of the geometrical parameters. These conclusions could not directly be applied to predict the real-time leakage flow rate through the labyrinth seal because of the fast reciprocating motion of the piston, which will cause continually pressure change in two compression chambers, and then the pressure fluctuation will affect the flow through the labyrinth seal. A transient simulation model employing the multiscale dynamic mesh, which considers the effect of the reciprocating motion of the piston in the cylinder, is established to identify the characteristics of the internal leakage. This model was verified by a specially designed compressor, and the influence of various parameters was analyzed in detail. The sealing performance decreased linearly with the increase in the pressure ratio, and higher pressure inlet leads to higher leakage flow under the same pressure ratio. The labyrinth seal performance positively correlated to the increase of the rotational speed. Leakage characteristics of five working mediums were carried out, and the results indicated that the relative leakage decreased with an increase in the relative molecular mass. From this study, the realistic internal leakage flow rate under different operating parameters in the reciprocating labyrinth piston compressor could be predicated.

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.

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.

Effects of Tooth Width on Gas Labyrinth and Windback Seals Operating at Low Pressure Ratios

2007 ◽  
Author(s):  
Gerald L. Morrison ◽  
Chae Hwan Lim
Keyword(s):  
Low Pressure ◽  
Labyrinth Seal ◽  
Screw Thread ◽  
Tooth Width ◽  
Accepted Standard ◽  
Additional Amount ◽  
The Difference ◽  
Low Pressures

The difference in leakage rates for labyrinth and windback seals is studied. It is determined that the leakage under the teeth of a windback seal is within ± 3% of a labyrinth seal with the same cavity/tooth design. The windback leaks an additional amount due to fluid passing through the long conduit composed of the continuous screw thread like channel. At low pressures and low differential pressures across the seal, the effect of tooth width upon the leakage in labyrinth and windback seals is opposite to the normal accepted standard of thinner teeth leak less.

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