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.

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.

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.

Sensitivity Analysis of the One-Control Volume Bulk-Flow Model for a 14 Teeth-on-Stator Straight-Through Labyrinth Seal

2017 ◽  
Author(s):  
Filippo Cangioli ◽  
Paolo Pennacchi ◽  
Giacomo Riboni ◽  
Giuseppe Vannini ◽  
Lorenzo Ciuchicchi ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Friction Factor ◽  
Flow Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Bulk Flow ◽  
Mathematical Treatment ◽  
Dynamic Coefficients ◽  
The One

Since the 80s, academic research in the rotordynamics field has developed mathematical treatment for the prediction of the dynamic coefficients of sealing components. Dealing with the straight-through labyrinth seal, Iwatsubo [1], at a first stage, and Childs [2], later on, have developed the one-control volume bulk flow model. The model allows evaluating the surrounding fluid forces acting on the rotor, analyzing the fluid dynamics within the seal: the continuity, circumferential momentum and energy equations are solved for each cavity. To consider axial fluid dynamics, correlations, aiming to estimate the leakage and the pressure distribution, are required. Several correlations have been proposed in the literature for the estimation of the leakage, of the kinetic energy carry-over coefficient (KE), of the discharge coefficient and of the friction factor. After decades of research in the field of seal dynamics, the bulk-flow model has been confirmed as the most popular code in the industries, however, it is not clear which is the best set of correlations for the prediction of seal dynamic coefficients. This paper allows identifying the most accurate combination of correlations to be implemented in the bulk-flow model. The correlations are related to: the leakage formula, the flow coefficient, the KE and the friction factor. Investigating the results of several models (32 models), which consider different sets of correlations, in comparison to the experimental data (performed by General Electric Oil & Gas), it is possible to observe the dependence, of the model correlations, on the operating conditions. The experimental results, performed using a 14 teeth-on-stator labyrinth seal, investigate several operating conditions of pressure drop.

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.

scholarly journals Comparison of Hirs’ Equation With Moody’s Equation for Determining Rotordynamic Coefficients of Annular Pressure Seals

1987 ◽  
Vol 109 (1) ◽  
pp. 144-148 ◽  
Author(s):  
C. C. Nelson ◽  
D. T. Nguyen
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Incompressible Flow ◽  
Flow Model ◽  
Bulk Flow ◽  
Rotordynamic Coefficients ◽  
Relative Roughness ◽  
Direct Stiffness ◽  
Pressure Seal

The rotordynamic coefficients of an incompressible-flow annular pressure seal were determined using a bulk-flow model in conjunction with two different friction factor relationships. The first, Hirs’ equation, assumes the friction factor is a function of Reynolds number only. The second, Moody’s equation, approximates Moody’s diagram and assumes the friction factor is a function of both Reynolds number and relative roughness. For each value of relative roughness, Hirs’ constants were determined so that both equations gave the same magnitude and slope of the friction factor. For smooth seals, both relationships give the same results. For rough seals (e/2H0 = 0.05) Moody’s equation predicts 44 percent greater direct stiffness, 35 percent greater cross-coupled stiffness, 19 percent smaller cross-coupled damping, 59 percent smaller cross-coupled inertia, and nominally the same direct damping and direct inertia.

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

2013 ◽  
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° 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.

Fluid Force Moment on a Centrifugal Impeller Shroud in Precessing Motion

1997 ◽  
Vol 119 (2) ◽  
pp. 366-371 ◽  
Author(s):  
Yoshinobu Tsujimoto ◽  
Yoshiki Yoshida ◽  
Hideo Ohashi ◽  
Norihiro Teramoto ◽  
Shin Ishizaki
Keyword(s):  
Flow Model ◽  
Tangential Velocity ◽  
Inviscid Flow ◽  
Bulk Flow ◽  
Centrifugal Impeller ◽  
Shear Stresses ◽  
Leakage Flow ◽  
Fluid Force ◽  
Clearance Flow ◽  
Force Moment

Experimental results of fluid moment on a centrifugal impeller shroud in precessing motion are discussed based on the bulk flow model to elucidate the fundamental flow mechanism. It is shown that the backshroud/casing clearance flow and the destabilizing fluid force moment can be simulated by the bulk flow model fairly well if the measured behavior of the resistance is correctly incorporated in the model. From the calculations with and without steady and unsteady wall shear stresses, the unsteady component of the clearance flow is shown to be basically a two-dimensional inviscid flow induced by the change in the flow thickness. The effects of the leakage flow rate and the resistance at the leakage flow entry are discussed, paying attention to the steady tangential velocity of the leakage flow.

A Bulk-Flow Model of Angled Injection Lomakin Bearings

2002 ◽  
Author(s):  
Luis San Andre´s ◽  
Thomas Soulas ◽  
Florence Challier ◽  
Patrice Fayolle
Keyword(s):  
Flow Model ◽  
Control Volume ◽  
Dynamic Performance ◽  
Bulk Flow ◽  
Computational Method ◽  
Design Parameters ◽  
Dynamic Force ◽  
Injection Angle ◽  
Flow Equations ◽  
Force Coefficients

The paper introduces a bulk-flow model for prediction of the static and dynamic force coefficients of angled injection Lomakin bearings. The analysis accounts for the flow interaction between the injection orifices, the supply circumferential groove, and the thin film lands. A one control-volume model in the groove is coupled to a bulk-flow model within the film lands of the bearing. Bernoulli-type relationships provide closure at the flow interfaces. Flow turbulence is accounted for with shear stress parameters and Moody’s friction factors. The flow equations are solved numerically using a robust computational method. Comparisons between predictions and experimental results for a tangential-against-rotation injection water Lomakin bearing show the novel model predicts well the leakage and direct stiffness and damping coefficients. Computed cross-coupled stiffness coefficients follow the experimental trends for increasing rotor speeds and supply pressures, but quantitative agreement remains poor. A parameter investigation evidences the effects of the groove and land geometries on the Lomakin bearing flowrate and force coefficients. The orifice injection angle does not influence the bearing static performance, although it largely affects its stability characteristics through the evolution of the cross-coupled stiffnesses. The predictions confirm the promising stabilizing effect of the tangential-against-rotation injection configuration. Two design parameters, comprising the feed orifices area and groove geometry, define the static and dynamic performance of Lomakin bearing. The analysis also shows that the film land clearance and length have a larger impact on the Lomakin bearing rotordynamic behavior than its groove depth and length.

Thermo-elasto bulk-flow model for labyrinth seals in steam turbines

2018 ◽  
Vol 119 ◽  
pp. 359-371 ◽  
Author(s):  
Filippo Cangioli ◽  
Steven Chatterton ◽  
Paolo Pennacchi ◽  
Leonardo Nettis ◽  
Lorenzo Ciuchicchi
Keyword(s):  
Flow Model ◽  
Bulk Flow ◽  
Steam Turbines ◽  
Labyrinth Seals

A Comparison of Experimental Results and Theoretical Predictions for the Rotordynamic Coefficients of Short (L/D = 1/6) Labyrinth Seals

1991 ◽  
Author(s):  
Joseph M. Pelletti ◽  
Dara W. Childs
Keyword(s):  
Flow Model ◽  
Control Volume ◽  
Pressure Ratio ◽  
Experimental Results ◽  
Rotor Speed ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Supply Pressure ◽  
Test Conditions ◽  
Theoretical Predictions

Abstract Experimental results for the rotordynamic coefficients of short (L/D = 1/6) teeth-on-stator and teeth-on-rotor labyrinth seals are presented. The effects that pressure ratio (fluid density), rotor speed, fluid pre-swirl and seal clearance have on these coefficients are studied. Tests were run out to speeds of 16000 rpm with a supply pressure of 17.3 bar and seal clearances ranging from 0.229–0.419 mm. The experimental results are compared with theoretical predictions of a two control volume compressible flow model. The experimental results show that decreases in pressure ratio and increases in rotor speed are stabilizing while increases in fluid pre-swirl and seal clearance are destabilizing for both seal configurations. The theoretical model correctly predicts the effects of pressure ratio, rotor speed and fluid pre-swirl on the cross-coupled stiffness. It also predicts reasonable values for direct damping for all test conditions. However, the theory incorrectly predicts the effect of seal clearance on these coefficients. Consequently the theoretical predictions are much better for the large clearance seals.

Sign in / Sign up

Export Citation Format

Share Document