Rotordynamic analysis for stepped-labyrinth gas seals using Moody’s friction-factor model

2001 ◽  
Vol 15 (9) ◽  
pp. 1217-1225 ◽  
Author(s):  
Tae Woong Ha
Keyword(s):  
Friction Factor ◽  
Factor Model ◽  
Gas Seals

A New Friction Factor Model and Entrance Loss Coefficient for Honeycomb Annular Gas Seals

1999 ◽  
Vol 122 (3) ◽  
pp. 622-627 ◽  
Author(s):  
Amro M. Al-Qutub ◽  
D. Elrod ◽  
Hugh W. Coleman
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Uncertainty Analysis ◽  
Friction Factor ◽  
Factor Model ◽  
Loss Coefficient ◽  
Curve Fit ◽  
Honeycomb Seals ◽  
Gas Seals ◽  
Number Curve

A new experimental friction factor model for a honeycomb surface was developed using a static seal tester. Three clearances and three lengths were tested for the seals, and Reynolds number ranged from 3000 to 49,000. It was found that the friction factor was a function of Reynolds number and seal clearance only. The clearance effect was dominant and the friction factor was found to increase with increased clearance. A new uncertainty analysis was developed for the experimental friction factor when calculating friction factor using Mach number curve fit. The entrance loss coefficient was found to be constant for both smooth and honeycomb seals. The entrance loss coefficient of Honeycomb seals was found to be 50 percent higher than that of smooth seals. [S0742-4787(00)02102-0]

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 Design to Improve the Effective Damping Characteristics of Hole-Pattern-Stator Annular Gas Seals

2006 ◽  
Author(s):  
Dara W. Childs ◽  
Yoon-Shik Shin ◽  
Brent Seifert
Keyword(s):  
Friction Factor ◽  
Flow Path ◽  
Test Results ◽  
Static Stiffness ◽  
Hole Depth ◽  
Negative Test ◽  
Damping Characteristics ◽  
Jump Phenomena ◽  
The Cross ◽  
Gas Seals

Predictions are presented for hole pattern seals for which the hole depth is varied axially, showing that various depth patterns can significantly improve damping performance in terms of both increasing the seal’s effective damping and reducing its cross-over frequency — the frequency at which effective damping changes from positive to negative. Test results are presented for the seal with the best variable hole depth (VHD) pattern showing an increase in peak damping by a factor of 1.6 over a constant hole depth (CHD) design, versus predictions of 2.7. The cross over frequency is reduced by approximately 40%. The VHD seal has a significant negative static stiffness that probably arises from a friction-factor jump phenomena, not flow path divergence. The VHD seal leaks less than a comparable CHD design.

An Entrance Region Friction Factor Model Applied to Annular Seal Analysis: Theory Versus Experiment for Smooth and Honeycomb Seals

1989 ◽  
Vol 111 (2) ◽  
pp. 337-343 ◽  
Author(s):  
D. Elrod ◽  
C. Nelson ◽  
D. Childs
Keyword(s):  
Friction Factor ◽  
Factor Model ◽  
Experimental Results ◽  
Entrance Region ◽  
Analysis Theory ◽  
Annular Seal ◽  
Theory Versus ◽  
Direct Stiffness ◽  
Honeycomb Seals

A friction factor model is developed for the entrance-region of a duct. The model is used in an annular gas seal analysis similar to Nelson’s (1984). Predictions of the analysis are compared to experimental results for a smooth-stator/smooth-rotor seal and three honeycomb-stator/smooth-rotor seals. The model predicts leakage and direct damping well. The model overpredicts the dependence of cross-coupled stiffness on fluid prerotation. The model predicts direct stiffness poorly.

An Annular Gas Seal Analysis Using Empirical Entrance and Exit Region Friction Factors

1990 ◽  
Vol 112 (2) ◽  
pp. 196-204 ◽  
Author(s):  
D. A. Elrod ◽  
D. W. Childs ◽  
C. C. Nelson
Keyword(s):  
Shear Stress ◽  
Friction Factor ◽  
Factor Models ◽  
Exit Region ◽  
Dynamic Coefficients ◽  
Friction Factors ◽  
Direct Stiffness ◽  
Gas Seals ◽  
Rotor Dynamic ◽  
Better Than

Wall shear stress results from stationary-rotor flow tests of five annular gas seals are used to develop entrance and exit region friction factor models. The friction factor models are used in a bulk-flow seal analysis which predicts leakage and rotor-dynamic coefficients. The predictions of the analysis are compared to experimental results and to the predictions of Nelson’s analysis (1985). The comparisons are for smooth-rotor seals with smooth and honeycomb-stators. The present analysis predicts the destabilizing cross-coupled stiffness of a seal better than Nelson’s analysis. Both analyses predict direct damping well and direct stiffness poorly.

scholarly journals Friction-Factor Data for Flat-Plate Tests of Smooth and Honeycomb Surfaces

1992 ◽  
Vol 114 (4) ◽  
pp. 722-729 ◽  
Author(s):  
T. W. Ha ◽  
Dara W. Childs
Keyword(s):  
Flat Plate ◽  
Friction Factor ◽  
Smooth Surface ◽  
Factor Model ◽  
Test Apparatus ◽  
Cell Width ◽  
Plate Test ◽  
Friction Factors ◽  
Line Flow ◽  
Factor Data

Friction-factors for honeycomb surfaces are measured with a flat plate tester. The flat plate test apparatus is described and a method is discussed for determining the friction-factor experimentally. The friction-factor model is developed for the flat plate test based on the Fanno Line Flow. The comparisons of the friction-factor are plotted for smooth surface and twelve-honeycomb surfaces with three-clearances, 6.9 bar to 17.9 bar range of inlet pressure, and 5,000 to 130,000 range of the Reynolds number. The optimum geometries for the maximum friction-factor are found as a function of cell width to cell depth and clearance to cell width ratios.

scholarly journals An Accurate and Computationally Efficient Explicit Friction Factor Model

2016 ◽  
Vol 06 (03) ◽  
pp. 237-245 ◽  
Author(s):  
Uchechukwu Herbert Offor ◽  
Sunday Boladale Alabi
Keyword(s):  
Friction Factor ◽  
Factor Model ◽  
Computationally Efficient

scholarly journals A study of friction factor model for directional wells

2017 ◽  
Vol 26 (2) ◽  
pp. 489-504 ◽  
Author(s):  
Ahmed A. Elgibaly ◽  
Mohammed Shehata Farhat ◽  
Eric W. Trant ◽  
Mohammed Kelany
Keyword(s):  
Friction Factor ◽  
Factor Model
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