Labyrinth seal

About: Labyrinth seal is a research topic. Over the lifetime, 2652 publications have been published within this topic receiving 16876 citations.

Machinery Vibration and Rotordynamics

Abstract: PREFACE. 1 Fundamentals of Machine Vibration and Classical Solutions. The Main Sources of Vibration in Machinery. The Single Degree of Freedom (SDOF) Model. Using Simple Models for Analysis and Diagnostics. Six Techniques for Solving Vibration Problems with Forced Excitation. Some Examples with Forced Excitation. Illustrative Example 1. Illustrative Example 2. Illustrative Example 3. Illustrative Example 4. Some Observations about Modeling. Unstable Vibration. References. Exercises. 2 Torsional Vibration. Torsional Vibration Indicators. Objectives of Torsional Vibration Analysis. Simplified Models. Computer Models. Kinetic Energy Expression. Potential Energy. Torsional Vibration Measurement. French s Comparison Experiments. Strain Gages. Carrier Signal Transducers. Frequency-modulated Systems. Amplitude-modulated Systems. Frequency Analysis and the Sideband System. French s Test Procedure and Results. A Special Tape for Optical Transducers. Time-interval Measurement Systems. Results from Toram s Method. Results from the Barrios/Darlow Method. References. Exercises. 3 Introduction to Rotordynamics Analysis. Objectives of Rotordynamics Analysis. The Spring Mass Model. Synchronous and Nonsynchronous Whirl. Analysis of the Jeffcott Rotor. Polar Coordinates. Cartesian Coordinates. Physical Significance of the Solutions. Three Ways to Reduce Synchronous Whirl Amplitudes. Some Damping Definitions. The "Gravity Critical". Critical Speed Definitions. Effect of Flexible (Soft) Supports. Rotordynamic Effects of the Force Coefficients A Summary. The Direct Coefficients. The Cross-coupled Coefficients. Rotordynamic Instability. Effect of Cross-Coupled Stiffness on Unbalance Response. Added Complexities. Gyroscopic Effects. Effect of Support Asymmetry on Synchronous Whirl. False Instabilities. References. Exercises. 4 Computer Simulations of Rotordynamics. Different Types of Models. Bearing and Seal Matrices. Torsional and Axial Models. Different Types of Analyses. Eigenanalysis. Linear Forced Response (LFR). Transient Response. Shaft Modeling Recommendations. How Many Elements. 45-Degree Rule. Interference Fits. Laminations. Trunnions. Impeller Inertias via CAD Software. Stations for Added Weights. Rap Test Verification of Models. Stations for Bearings and Seals. Flexible Couplings. Example Simulations. Damped Natural Frequency Map (NDF). Modal Damping Map. Root Locus Map. Undamped Critical Speed Map. Mode Shapes. Bode/Polar Response Plot. Orbit Response Plot. Bearing Load Response Plot. Operating Deflected Shape (ODS). Housing Vibration (ips and g s). References. 5 Bearings and Their Effect on Rotordynamics. Fluid Film Bearings. Fixed-geometry Sleeve Bearings. Variable-geometry Tilting Pad Bearings. Fluid Film Bearing Dynamic Coefficients and Methods of Obtaining Them. Load Between Pivots Versus Load on Pivot. Influence of Preload on the Dynamic Coefficients in Tilt Pad Bearings. Influence of the Bearing Length or Pad Length. Influence of the Pivot Offset. Influence of the Number of Pads. Ball and Rolling Element Bearings. Case Study: Bearing Support Design for a Rocket Engine Turbopump. Ball Bearing Stiffness Measurements. Wire Mesh Damper Experiments and Computer Simulations. Squeeze Film Dampers. Squeeze Film Damper without a Centering Spring. O-ring Supported Dampers. Squirrel Cage Supported Dampers. Integral Squeeze Film Dampers. Squeeze Film Damper Rotordynamic Force Coefficients. Applications of Squeeze Film Dampers. Optimization for Improving Stability in a Centrifugal Process Compressor. Using Dampers to Improve the Synchronous Response. Using the Damper to Shift a Critical Speed or a Resonance. Insights into the Rotor Bearing Dynamic Interaction with Soft/Stiff Bearing Supports. Influence on Natural Frequencies with Soft/Stiff Bearing Supports. Effects of Mass Distribution on the Critical Speeds with Soft/Stiff Bearing Supports. Influence of Overhung Mass on Natural Frequencies with Soft/Stiff Supports. Influence of Gyroscopic Moments on Natural Frequencies with Soft/Stiff Bearing Supports. References. Exercises. Appendix: Shaft With No Added Weight. 6 Fluid Seals and Their Effect on Rotordynamics. Function and Classification of Seals. Plain Smooth Seals. Floating Ring Seals. Conventional Gas Labyrinth Seals. Pocket Damper Seals. Honeycomb Seals. Hole-pattern Seals. Brush Seals. Understanding and Modeling Damper Seal Force Coefficients. Alford s Hypothesis of Labyrinth Seal Damping. Cross-coupled Stiffness Measurements. Invention of the Pocket Damper Seal. Pocket Damper Seal Theory. Rotordynamic Testing of Pocket Damper Seals. Impedance Measurements of Pocket Damper Seal Force Coefficients (Stiffness and Damping) and Leakage at Low Pressures. The Fully Partitioned PDS Design. Effects of Negative Stiffness. Frequency Dependence of Damper Seals. Laboratory Measurements of Stiffness and Damping from Pocket Damper Seals at High Pressures. The Conventional Design. The Fully Partitioned Design. Field Experience with Pocket Damper Seals. Two Back-to-Back Compressor Applications. Case 1. Case 2. A Fully Partitioned Application. Designing for Desired Force Coefficient Characteristics. The Conventional PDS Design. The Fully Partitioned Pocket Damper Seal. Leakage Considerations. Some Comparisons of Different Types of Annular Gas Seals. References. 7 History of Machinery Rotordynamics. The Foundation Years, 1869 1941. Shaft Dynamics. Bearings. Refining and Expanding the Rotordynamic Model, 1942 1963. Multistage Compressors and Turbines, Rocket Engine Turbopumps, and Damper Seals, 1964 Present. Stability Problems with Multistage Centrifugal Compressors. Kaybob, 1971 72. Ekofisk, 1974 75. Subsequent Developments. New Frontiers of Speed and Power Density with Rocket Engine Turbopumps. The Space Shuttle Main Engine (SSME). High-pressure Fuel Turbopump (HPFTP). Rotordynamic Instability Problem. Noncontacting Damper Seals. Shaft Differential Heating (The Morton Effect). References. INDEX.

An Iwatsubo-Based Solution for Labyrinth Seals: Comparison to Experimental Results

Abstract: The basic equations are derived for compressible flow in a labyrinth seal. The flow is assumed to be completely turbulent in the circumferential direction where the friction factor is determined by the Blasius relation. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order pressure distribution is found by satisfying the leakage equation while the circumferential velocity distribution is determined by satisfying the momentum equation. The first-order equations are solved by a separation of variables solution. Integration of the resultant pressure distribution along and around the seal defines the reaction force developed by the seal and the corresponding dynamic coefficients. The results of this analysis are compared to published test results.

Combined brush seal and labyrinth seal segment for rotary machines

Abstract: A brush seal is comprised of arcuate seal segments having ends cut in a radial direction with bristles “canted” at an approximate 45° angle relative to radii of the segments, leaving triangular regions adjacent one end of each segment devoid of bristles at the segment interfaces. The brush seals are retrofit into conventional labyrinth seals with the backing plate for the bristles comprising a labyrinth tooth profile extending fully 360° about the seal, including those areas where bristles are not present. The sealing capacity is not substantially degraded, while affording significant sealing improvements over conventional labyrinth seals. Additionally, when retrofit into labyrinth seals with radial movement, the individual labyrinth seal segments are free to move radially independently of one another during transients.

Brush seals and combined labyrinth and brush seals for rotary machines

Abstract: Brush seals are retrofitted into existing turbine labyrinth seal rings to create a fail-safe seal design at locations wherever labyrinth seals are currently used, including interstage shaft seals, rotor end seals, bucket (or blade) tip seals and spill strips. Brush seals, per se, when used in place of labyrinth seals, can result in considerable span reductions of steam turbines, or machines with more turbine stages for a given span. Application to end packings results in the potential elimination of gland sealing/exhauster systems. Brush seal life can be improved by retrofitting brush segments to labyrinth seal segments that are either spring-backed, or use pressure loads to obtain design clearances only after steady state operating conditions are achieved. The brush seals are provided with backing plates shaped like labyrinth teeth, resulting in a fail-safe design. Also, the use of existing labyrinth teeth as bristle backing plates results in a brush seal with diminished susceptibility to hysteresis when compared to conventional brush seal designs. Low friction coatings can also be used to reduce brush seal hysteresis. Incorporation of brush seals in labyrinth seal rings that are either spring-backed or held in place by pressure forces results in extremely low brush seal wear.

Three-Dimensional CFD Rotordynamic Analysis of Gas Labyrinth Seals

Abstract: Labyrinth seals are utilized inside turbomachinery to provide noncontacting 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.* 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 anti rotordynamic prediction over bulk-flow approaches compared to experimental measurements.