The Measurement and Prediction of Rotordynamic Forces for Labyrinth Seals

1988 ◽  
Author(s):  
D. W. Childs ◽  
D. L. Rhode
Keyword(s):  
Labyrinth Seals ◽  
Rotordynamic Forces

Rotordynamic Forces Due to Rotor Sealing Gap in Axial Turbines

2003 ◽  
Author(s):  
Woo June Kim ◽  
Seung Jin Song
Keyword(s):  
Tangential Force ◽  
Axisymmetric Flow ◽  
Perturbation Approach ◽  
Aerodynamic Forces ◽  
Flow Induced Vibration ◽  
Labyrinth Seals ◽  
Aerodynamic Damping ◽  
Axial Turbines ◽  
Rotordynamic Forces ◽  
Unsteady Effects

Turbines have been susceptible to flow-induced vibration. In such vibrations, direct damping and cross stiffness effects of aerodynamic forces determine rotordynamic stability. Previous research efforts have been focused mostly on either isolated labyrinth seals or unshrouded turbines. Recently, steady flow in a turbine with a statically offset shrouded rotor has been modeled, and some stiffness predictions have been obtained. The model couples the seal flow to the main passage flow and uses a small perturbation approach to determine non-axisymmetric flow conditions. Seal gland pressure asymmetry and tangential force asymmetry were found to be responsible for the destabilizing stiffness force generation. However, aerodynamic damping (i.e. unsteady) effects in shrouded turbines with whirling rotors have not yet been examined. Therefore, this paper presents a new model to predict unsteady flow field response in such turbines. The model uses basic conservation laws. Input parameters include aerodynamic parameters, geometric parameters, and a prescribed rotor whirl. From the calculated unsteady perturbations in velocity and pressure, the damping effects of aerodynamic forces have been analyzed for the first time. The results show that aerodynamic damping is primarily due to the variation in the magnitude of seal gland pressure asymmetry. Also, damping in shrouded axial turbines is found to be much smaller than that in unshrouded turbines.

Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor: Part 1 — Measurement

2019 ◽  
Author(s):  
Jieun Song ◽  
Suyong Kim ◽  
Tae Choon Park ◽  
Bong-Jun Cha ◽  
Dong Hun Lim ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
System Level ◽  
Labyrinth Seals ◽  
Stiffness Coefficients ◽  
Pressure Distributions ◽  
Order Of Magnitude ◽  
Direct Stiffness ◽  
The Cross ◽  
Rotordynamic Forces ◽  
Pressure Perturbations

Abstract Centrifugal compressors can suffer from rotordynamic instability. While individual components (e.g., seals, shrouds) have been previously investigated, an integrated experimental or analytical study at the compressor system level is scarce. For the first time, non-axisymmetric pressure distributions in a statically eccentric shrouded centrifugal compressor with eye-labyrinth seals have been measured for various eccentricities. From the pressure measurements, direct and cross-coupled stiffness coefficients in the shrouded centrifugal compressor have been determined. Thus, the contributions of the pressure perturbations in the shroud cavity and labyrinth seals have been simultaneously investigated. The cross-coupled stiffness coefficients in the shroud and labyrinth seals are both positive and one order of magnitude larger than the direct stiffness coefficients. Furthermore, in the tested compressor, contrary to the common assumption, the cross-coupled stiffness in the shroud is 2.5 times larger than that in the labyrinth seals. Thus, the shroud contributes more to rotordynamic instability than the eye-labyrinth seals.

Influence of Rotor Axial Thermal Growth on Rotordynamic Forces of High-Low Labyrinth Seals in Steam Turbines

2005 ◽  
Author(s):  
Jinxiang Xi ◽  
David L. Rhode
Keyword(s):  
Flow Direction ◽  
Leakage Flow ◽  
Steam Turbines ◽  
Labyrinth Seals ◽  
Operational Conditions ◽  
Rotordynamic Coefficients ◽  
Thermal Growth ◽  
Start Up ◽  
Tentative Explanation ◽  
Rotordynamic Forces

Rotors in steam turbines experience significant axial shifting during start-up and shut-down process due to thermal expansion. This axial-shifting could significantly alter the flow pattern and the flow-induced rotordynamic forces in labyrinth seals, which in turn, can considerably affect the rotor-seal system’s performance. This paper investigates the influence of the rotor-axial-shifting on leakage rate and rotordynamic forces for high-low labyrinth seals under different geometrical and operational conditions. A well-established CFD-perturbation model was employed to predict the rotordynamic coefficients. A surprisingly large effect was found for rotordynamic characteristics due to changes in seal configurations caused by rotor axial shifting. It was also found that less destabilizing effect arose from rotor-axial-shifting in the leakage flow direction whereas a more destabilizing effect arose from shifting against the leakage flow direction. A tentative explanation was proposed for the large sensitivities of dynamic forces to the off-design operations with rotor-axial-shifting.

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.

Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor—Part 1: Measurement

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Jieun Song ◽  
Suyong Kim ◽  
Tae Choon Park ◽  
Bong-Jun Cha ◽  
Dong Hun Lim ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
System Level ◽  
Labyrinth Seals ◽  
Stiffness Coefficients ◽  
Pressure Distributions ◽  
Order Of Magnitude ◽  
Direct Stiffness ◽  
The Cross ◽  
Rotordynamic Forces ◽  
Pressure Perturbations

Abstract Centrifugal compressors can suffer from rotordynamic instability. While individual components (e.g., seals, shrouds) have been previously investigated, an integrated experimental or analytical study at the compressor system level is scarce. For the first time, non-axisymmetric pressure distributions in a statically eccentric shrouded centrifugal compressor with eye-labyrinth seals have been measured for various eccentricities. From the pressure measurements, direct and cross-coupled stiffness coefficients have been determined. Thus, the contributions of the pressure perturbations in the shroud cavity and labyrinth seals have been simultaneously investigated. The cross-coupled stiffness coefficients in the shroud and labyrinth seals are both positive and one order of magnitude larger than the direct stiffness coefficients. Furthermore, in the tested compressor, contrary to the common assumption, the cross-coupled stiffness in the shroud is 2.5 times larger than that in the labyrinth seals. Thus, not only eye-labyrinth seals but also shrouds need to be considered in rotordynamic analysis.

scholarly journals Rotordynamics of Turbine Labyrinth Seals with Rotor Axial Shifting

2006 ◽  
Vol 2006 ◽  
pp. 1-11 ◽  
Author(s):  
Jinxiang Xi ◽  
David L. Rhode
Keyword(s):  
High Performance ◽  
Flow Direction ◽  
Leakage Flow ◽  
Steam Turbines ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Dynamic Forces ◽  
Inlet Swirl ◽  
Tentative Explanation ◽  
Rotordynamic Forces

Rotors in high-performance steam turbines experience a significant axial shifting during starting and stopping processes due to thermal expansion, for example. This axial shifting could significantly alter the flow pattern and the flow-induced rotordynamic forces in labyrinth seals, which in turn, can considerably affect the rotor-seal system performance. This paper investigates the influence of the rotor axial shifting on leakage rate as well as rotordynamic forces in high-low labyrinth seals over a range of seal clearances and inlet swirl velocities. A well-established CFD-perturbation model was employed to predict the rotordynamic coefficients. A surprisingly large effect was detected for rotordynamic characteristics due to rotor shifting. It was also found that a less destabilizing effect arose from rotor axial shifting in the leakage flow direction, whereas a more destabilizing effect arose from shifting against the leakage flow direction. Further, a tentative explanation was proposed for the large sensitivities of dynamic forces to rotor axial shifting.

Three-Dimensional CFD Rotordynamic Analysis of Gas Labyrinth Seals

2003 ◽  
Vol 125 (4) ◽  
pp. 427-433 ◽  
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

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 and rotordynamic prediction over bulk-flow approaches compared to experimental measurements.

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