Development of Scallop Cut Type Damper Seal for Centrifugal Compressors

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Naohiko Takahashi ◽  
Haruo Miura ◽  
Mitsuhiro Narita ◽  
Noriyo Nishijima ◽  
Yohei Magara
Keyword(s):  
High Pressure ◽  
Perturbation Analysis ◽  
Flow Model ◽  
Frame Of Reference ◽  
Bulk Flow ◽  
Rotating Frame ◽  
Rotordynamic Coefficients ◽  
Neighboring Region ◽  
Rotor Surface ◽  
Honeycomb Seals

This paper deals with a new type of damper seal developed for a high-pressure centrifugal compressor. Honeycomb seals and hole pattern seals are popularly used as damper seals and provide superior rotordynamic damping characteristics. Honeycomb seals are expensive because the manufacturing process is complex. Hole pattern seals are easier to manufacture, but they are still expensive. Use of a scallop pattern is one way to reduce manufacturing cost and time. A new seal that has a scallop pattern and small teeth on the stator surface is proposed. This pattern is cut on the stator surface using a disk type tool. To estimate the rotordynamic coefficients of this new seal, a bulk flow model code that is based on a two-control-volume model developed by Matsuda for labyrinth seals was newly developed. This model uses the Hirs model for the viscous shear stresses. The friction factor coefficients for the rotor surface, the stator surface, and the surface between the two-control-volumes were determined by computational fluid dynamics (CFD) steady analysis. The rotordynamic coefficients can also be obtained by using CFD perturbation analysis. The high accuracy of the bulk flow model was demonstrated by comparing its results with CFD perturbation analysis results. In the perturbation analysis, the whirling motion was treated as a steady-state problem by using a rotating frame of reference. For the damper seal, the rotor surface and its neighboring region were treated with a rotating frame of reference and the neighboring region of the stator was treated with a stationary frame of reference. The damping property of the new seal was evaluated by conducting rotor stability tests using a high-pressure compressor with an electromagnetic exciter. The new seal equipped with swirl brakes was used for the balance piston of the compressor. Stability was evaluated by exciting the rotor during operation and identifying the eigenvalues of the rotor. The experimental results showed that the new seal increases damping. Comparison of the damping effect with calculations based on the bulk flow analysis showed good agreement.

Development of Scallop Cut Type Damper Seal for Centrifugal Compressors

2014 ◽  
Author(s):  
Naohiko Takahashi ◽  
Haruo Miura ◽  
Mitsuhiro Narita ◽  
Noriyo Nishijima ◽  
Yohei Magara
Keyword(s):  
High Pressure ◽  
Perturbation Analysis ◽  
Flow Model ◽  
Frame Of Reference ◽  
Bulk Flow ◽  
Rotating Frame ◽  
Rotordynamic Coefficients ◽  
Neighboring Region ◽  
Rotor Surface ◽  
Honeycomb Seals

This paper deals with a new type of damper seal developed for a high-pressure centrifugal compressor. Honeycomb seals and hole-pattern seals are popularly used as damper seals and provide superior rotordynamic damping characteristics. Honeycomb seals are expensive because the manufacturing process is complex. Hole-pattern seals are easier to manufacture, but they are still expensive. Use of a scallop pattern is one way to reduce manufacturing cost and time. A new seal that has a scallop pattern and small teeth on the stator surface is proposed. This pattern is cut on the stator surface using a disc type tool. To estimate the rotordynamic coefficients of this new seal, a bulk flow model code that is based on a two-control-volume model developed by Matsuda for labyrinth seals was newly developed. This model uses the Hirs model for the viscous shear stresses. The friction factor coefficients for the rotor surface, the stator surface and the surface between the two control volumes were determined by CFD steady analysis. The rotordynamic coefficients can also be obtained by using CFD perturbation analysis. The high accuracy of the bulk flow model was demonstrated by comparing its results with CFD perturbation analysis results. In the perturbation analysis, the whirling motion was treated as a steady state problem by using a rotating frame of reference. For the damper seal, the rotor surface and its neighboring region were treated with a rotating frame of reference and the neighboring region of the stator was treated with a stationary frame of reference. The damping property of the new seal was evaluated by conducting rotor stability tests using a high-pressure compressor with an electromagnetic exciter. The new seal equipped with swirl brakes was used for the balance piston of the compressor. Stability was evaluated by exciting the rotor during operation and identifying the eigenvalues of the rotor. The experimental results showed that the new seal increases damping. Comparison of the damping effect with calculations based on the bulk flow analysis showed good agreement.

A Comparison of Rotordynamic-Coefficient Predictions for Annular Honeycomb Gas Seals Using Three Different Friction-Factor Models

2002 ◽  
Vol 124 (3) ◽  
pp. 524-529 ◽  
Author(s):  
Rohan J. D’Souza ◽  
Dara W. Childs
Keyword(s):  
Friction Factor ◽  
Flow Model ◽  
Factor Model ◽  
Control Volume ◽  
Bulk Flow ◽  
Shear Stresses ◽  
Steam Turbines ◽  
Frequency Range ◽  
Rotordynamic Coefficients ◽  
Rotordynamic Coefficient

A two-control-volume bulk-flow model is used to predict rotordynamic coefficients for an annular, honeycomb-stator/smooth-rotor gas seal. The bulk-flow model uses Hirs’ turbulent-lubrication model, which requires a friction factor model to define the shear stresses at the rotor and stator wall. Rotordynamic coefficients predictions are compared for the following three variations of the Blasius pipe-friction model: (i) a basic model where the Reynolds number is a linear function of the local clearance, fs=ns Rems (ii) a model where the coefficient is a function of the local clearance, and (iii) a model where both the coefficient and exponent are functions of the local clearance. The latter models are based on data that shows the friction factor increasing with increasing clearances. Rotordynamic-coefficient predictions shows that the friction-factor-model choice is important in predicting the effective-damping coefficients at a lower frequency range (60∼70 Hz) where industrial centrifugal compressors and steam turbines tend to become unstable. At a higher frequency range, irrespective of the friction-factor model, the rotordynamic-coefficient predictions tend to coincide. Blasius-based Models which directly account for the observed increase in stator friction factors with increasing clearance predict significantly lower values for the destabilizing cross-coupled stiffness coefficients.

Interrelated Rotordynamic Effects of Cylindrical and Conical Whirl of Annular Seal Rotors

1991 ◽  
Vol 113 (3) ◽  
pp. 470-480 ◽  
Author(s):  
E. A. Baskharone ◽  
S. J. Hensel
Keyword(s):  
Finite Element ◽  
Flow Model ◽  
Computational Procedure ◽  
Rotordynamic Coefficients ◽  
Conical Whirl ◽  
Conical Rotor ◽  
Annular Seal ◽  
Rotor Surface ◽  
Flow Variables ◽  
Sample Case

A comprehensive approach for computing the dynamic coefficients of an annular seal is presented. The coefficients are partly those associated with a uniform lateral eccentricity mode of the rotor (known as the cylindrical whirl mode) and with an angular eccentricity (which gives rise to a conical whirl type). The rotor excitation effects in both cases are treated as interrelated by recognizing the fluid-exerted moments resulting from the lateral eccentricity and the net fluid force resulting from the angular eccentricity. In all cases, the rotor is assumed to undergo a whirling motion around the housing centerline. The computational procedure is a finite-element perturbation model in which the zeroth-order undisplaced-rotor flow solution in the clearance gap is obtained through a Petrov-Galerkin approach. Next, the rotor translational and angular eccentricities, considered to be infinitesimally small, are perceived to cause virtual distortions of varied magnitudes in the finite element assembly which occupies the clearance gap. Perturbations in the flow variables including, in particular, the rotor surface pressure, are then obtained by expanding the finite-element equations in terms of the rotor eccentricity components. The fluid-exerted forces and moments are in this case computed by integration over the rotor surface, and the full matrix of rotordynamic coefficients, in the end, obtained. The computational model is verified against a bulk-flow model for a sample case involving a straight annular seal. Choice of this sample model for validation was made on the basis that no other existing model has yet been expanded to account for the mutual interaction between the cylindrical and conical rotor whirl, which is under focus in this study.

A Novel Bulk-Flow Model for Pocket Damper Seals

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Filippo Cangioli ◽  
Giuseppe Vannini ◽  
Thomas Chirathadam
Keyword(s):  
Flow Model ◽  
Control Volume ◽  
Dynamic Pressure ◽  
Bulk Flow ◽  
Order System ◽  
Shear Stresses ◽  
Flow Area ◽  
Rotordynamic Coefficients ◽  
Recirculating Flow ◽  
Numerical Predictions

Abstract In this paper, a novel bulk-flow model for pocket damper seals (PDS) is introduced. The model is based on two control volumes (CVs) for each circumferential pocket of the seal. The continuity, circumferential momentum, and energy equations are considered for each control volume. The circumferential recirculating flow within the pocket is modeled for the first time. The boundary layer theory is used to estimate the recirculating flow area, and the Swamee–Jain friction factor correlation allows for defining the dissipation of the circumferential velocity. The perturbation method is used to solve the partial derivative governing equations in the zeroth- and first-order system of equations. The rotordynamic coefficients are evaluated by integrating the dynamic pressure and rotor shear stresses along the circumferential direction. The predictions are compared to the experimental data, which refer to test conditions representative of high-pressure centrifugal compressors. Numerical predictions are accurate for both high positive–negative inlet preswirl ratios. Leakage predictions are also aligned with measurements. Finally, sealing selection approach is introduced in the paper for comparing the dynamic behavior of two different sealing technologies and identifying stable regions as a function of the rotor natural frequency and preswirl ratio.

Hole-Pattern and Honeycomb Seal Rotordynamic Forces: Validation of CFD-Based Prediction Techniques

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Kenny Krogh Nielsen ◽  
Kasper Jønck ◽  
Harald Underbakke
Keyword(s):  
Frequency Dependence ◽  
Bulk Flow ◽  
Rotordynamic Coefficients ◽  
Damping Characteristics ◽  
Honeycomb Seal ◽  
Modeling Techniques ◽  
Honeycomb Seals ◽  
Prediction Techniques ◽  
Rotordynamic Forces ◽  
Stiffness And Damping

This paper deals with modeling of hole-pattern and honeycomb seals. These are frequently used as balance piston seals in high pressure centrifugal compressor applications as they have the potential to facilitate superior rotordynamic damping characteristics while providing good leakage control. On the other hand it is also well-established that the rotordynamic performance of hole-pattern and honeycomb seals is very sensitive to convergence and divergence in the streamwise direction. The Isotseal bulk-flow code has shown difficulties in predicting the rotordynamic coefficients for convergent seal geometries or in cases with negative preswirl. This has led to increased interest in CFD-based analysis of seal dynamics. CFD-based models generally have less assumptions and are applicable for complex geometries or operating ranges not covered by bulk-flow codes. The CFD-based Instationary Perturbation Model (IPM) is utilized for the analysis of the hole-pattern and honeycomb seals. The rotordynamic forces are obtained by means of a time-dependent perturbation of the rotor position with respect to the stator. A sequence of perturbation frequencies is utilized to obtain the frequency dependence of the rotordynamic seal force coefficients. A strong effort has been put into validating the CFD-based perturbation modeling techniques against published experimental seal test data and the paper describes selected validation cases. A constant-clearance hole-pattern seal and a convergent honeycomb seal are analyzed and the results are compared to experimental results. The frequency dependence of the rotordynamic stiffness and damping characteristics of the seals is very well-captured for both types of seals.Finally, the IPM method was applied to a convergent hole-pattern seal to investigate the effects of eccentricity on the rotordynamic coefficients. The results are consistent with available experimental data.

Lock-up characteristics of floating ring seals considering rotor whirling motion

2017 ◽  
Vol 232 (4) ◽  
pp. 437-452
Author(s):  
Peng Xia ◽  
Zhan-sheng Liu ◽  
Jia-jia Yan ◽  
Guang-hui Zhang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Friction Force ◽  
Nonlinear Model ◽  
Flow Model ◽  
Bulk Flow ◽  
Circular Trajectory ◽  
Rotordynamic Coefficients ◽  
Whirling Motion ◽  
Ring Seal

This paper presents a lock-up condition with rotor whirling motion to predict the lock-up area for floating ring seals in liquid turbopumps. To calculate the hydrodynamic forces with arbitrary rotor motion, bulk flow model is modified with explicitly considering the squeeze velocity and temporal inertia. Finite element method is implemented to solve the transient nonlinear model. The effect of lock-up position on leakage and rotordynamic coefficients of floating ring seals is studied and shows insensitivity to eccentricity within moderate eccentric area (<0.5), which indicates that predicting lock-up area with the lock-up condition is feasible for application. With circular trajectory of rotors, the effects of rotor whirling radius and friction force on lock-up area are investigated. The results show that the lock-up area shrinks toward rotor whirling center, with the increase in the rotor whirling radius and decrease in the friction force. Further, a coupled method of rotor trajectory and floating ring seal lock-up area is presented to consider the interaction between rotors and floating ring seals. The results show that the effect of the interaction on the lock-up area is almost negligible, as lock-up position of floating ring seals has little effect on rotor trajectory. In addition, the effect of the seal configuration on the lock-up area is studied.

Measured Comparison of Leakage and Rotordynamic Characteristics for a Slanted-Tooth and a Straight-Tooth Labyrinth Seal

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Naitik J. Mehta ◽  
Dara W. Childs
Keyword(s):  
Inclination Angle ◽  
Flow Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Inlet Pressure ◽  
Radial Clearance ◽  
Rotordynamic Coefficients ◽  
Seal Design ◽  
Number Of Teeth

Measured results are presented to compare rotordynamic coefficients and leakage of a slanted-tooth labyrinth seal and a straight-tooth labyrinth seal. Both seals had identical pitch, depth, and number of teeth. The teeth inclination angle of the teeth on the slanted-tooth labyrinth was 65 deg from the normal axis. Experiments were carried out at an inlet pressure of 70 bar-a (1015 psi-a), pressure ratios of 0.4, 0.5, and 0.6, rotor speeds of 10.2, 15.35, and 20.2 krpm, and a radial clearance of 0.2 mm (8 mils). One zero and two positive inlet preswirl ratios were used. The results show only minute difference in the rotordynamic coefficients between the two seals. The slanted-tooth labyrinth seal consistently leaked approximately 10% less at all conditions. Predictions were made using a one control volume bulk-flow model (1CVM) which was developed for a straight-tooth labyrinth seal design. 1CVM under-predicted the rotordynamic coefficients and the leakage.

Rotordynamic Characteristics Prediction for Hole-Pattern Seals Using Computational Fluid Dynamics

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Manish R. Thorat ◽  
James R. Hardin
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Test Data ◽  
Flow Model ◽  
Bulk Flow ◽  
Pitot Tube ◽  
Single Frequency ◽  
Test Case ◽  
Swirl Ratio ◽  
Rotordynamic Coefficients

Abstract The experimental setup for a hole-pattern seal is modeled using computational fluid dynamics (CFD) and results compared with measured test data and bulk flow model (ISOTSEAL) predictions. The inlet swirl boundary condition for prior CFD analyses of this test case have either been assumed or based on pitot-tube measurements. In this paper, the validity of each is investigated by including radial inlet nozzles with the inlet plenum in the model geometry. A transient mesh deformation technique with multiple frequency journal excitations is used to determine frequency-dependent rotordynamic coefficients. This multifrequency excitation method is validated against single frequency sinusoidal journal excitation. An empirical limit on the number of frequencies that can be packed in a multifrequency excitation signal to provide a reasonable estimate of rotordynamic coefficients is provided. Rotordynamic coefficients estimated using CFD compare well with measured rotordynamic coefficients. For the given test data, the ISOTSEAL bulk flow model does not provide good correlation for cross-coupled stiffness if the measured swirl ratio at the inlet of the seal is used in the prediction. However, improvement in correlation for cross-coupled stiffness is obtained if the swirl ratio found from CFD analysis is used in the bulk flow model, indicating that pitot-tube measurements of swirl may not be accurate.

A Novel Bulk-Flow Model for Pocket Damper Seals

2019 ◽  
Author(s):  
Filippo Cangioli ◽  
Giuseppe Vannini ◽  
Thomas Chirathadam
Keyword(s):  
Flow Model ◽  
Control Volume ◽  
Dynamic Pressure ◽  
Bulk Flow ◽  
Order System ◽  
Shear Stresses ◽  
Flow Area ◽  
Rotordynamic Coefficients ◽  
Recirculating Flow ◽  
Numerical Predictions

Abstract In this paper a novel bulk-flow model for pocket damper seals (PDS) is introduced. The model is based on two control volumes for each circumferential pocket of the seal. The continuity, circumferential momentum and energy equations are considered for each control volume. The circumferential recirculating flow within the pocket is modelled for the first time. The boundary layer theory is used to estimate the recirculating flow area, and the Swamee-Jain friction factor correlation allows for defining the dissipation of the circumferential velocity. The perturbation method is used to solve the partial derivative governing equations in the zeroth and first-order system of equations. The rotordynamic coefficients are evaluated by integrating the dynamic pressure and rotor shear stresses along the circumferential direction. The predictions are compared to the experimental data, which refer to test conditions representative of high-pressure centrifugal compressors. Numerical predictions are accurate for both high positive-negative inlet pre-swirl ratios. Leakage predictions are also aligned with measurements. Finally, sealing selection approach is introduced in the paper for comparing the dynamic behaviour of two different sealing technologies and identifying stable regions as a function of the rotor natural frequency and pre-swirl ratio.

Hole-Pattern and Honeycomb Seal Rotordynamic Forces: Validation of CFD-Based Prediction Techniques

2012 ◽  
Author(s):  
Kenny Krogh Nielsen ◽  
Kasper Jønck ◽  
Harald Underbakke
Keyword(s):  
Frequency Dependence ◽  
Bulk Flow ◽  
Rotordynamic Coefficients ◽  
Damping Characteristics ◽  
Honeycomb Seal ◽  
Modeling Techniques ◽  
Honeycomb Seals ◽  
Prediction Techniques ◽  
Rotordynamic Forces ◽  
Stiffness And Damping

This paper deals with modeling of hole-pattern and honeycomb seals. These are frequently used as balance piston seals in high pressure centrifugal compressor applications as they have the potential to facilitate superior rotordynamic damping characteristics while providing good leakage control. On the other hand it is also well-established that the rotordynamic performance of hole-pattern and honeycomb seals is very sensitive to convergence and divergence in the streamwise direction. The ISOTSEAL bulk-flow code has shown difficulties in predicting the rotordynamic coefficients for convergent seal geometries or in cases with negative preswirl. This has lead to increased interest in CFD-based analysis of seal dynamics. CFD-based models generally have less assumptions and are applicable for complex geometries or operating ranges not covered by bulk-flow codes. The CFD-based Instationary Perturbation Model (IPM) is utilized for the analysis of the hole-pattern and honeycomb seals. The rotordynamic forces are obtained by means of a time-dependent perturbation of the rotor position with respect to the stator. A sequence of perturbation frequencies is utilized to obtain the frequency dependence of the rotordynamic seal force coefficients. A strong effort has been put into validating the CFD-based perturbation modeling techniques against published experimental seal test data and the paper describes selected validation cases. A constant-clearance hole-pattern seal and a convergent honeycomb seal are analyzed and the results are compared to experimental results. The frequency dependence of the rotordynamic stiffness and damping characteristics of the seals is very well-captured for both types of seals. Finally the IPM method was applied to a convergent hole-pattern seal to investigate the effects of eccentricity on the rotordynamic coefficients. The results are consistent with available experimental data.

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