scholarly journals Discussion: “Theory Versus Experiment for the Rotordynamic Coefficients of Annular Gas Seals: Part 1—Test Facility and Apparatus” (Childs, D. W., Nelson, C. E., Nicks, C., Scharrer, J., Elrod, D., and Hale, K., 1986, 108, pp. 426–431)

1986 ◽  
Vol 108 (3) ◽  
pp. 432-432 ◽  
Author(s):  
R. C. Hendricks
Keyword(s):  
Test Facility ◽  
Rotordynamic Coefficients ◽  
Theory Versus ◽  
Gas Seals

scholarly journals Theory Versus Experiment for the Rotordynamic Coefficients of Annular Gas Seals: Part 1—Test Facility and Apparatus

1986 ◽  
Vol 108 (3) ◽  
pp. 426-431 ◽  
Author(s):  
D. W. Childs ◽  
C. E. Nelson ◽  
C. Nicks ◽  
J. Scharrer ◽  
D. Elrod ◽  
...  
Keyword(s):  
Pressure Ratio ◽  
Excitation Frequency ◽  
Tangential Velocity ◽  
Test Facility ◽  
Rotordynamic Coefficients ◽  
Air Supply ◽  
Theory Versus ◽  
Leakage Characteristics ◽  
Gas Seals ◽  
A Current

A facility and apparatus are described for determining the rotordynamic coefficients and leakage characteristics of annular gas seals. The apparatus has a current top speed of 8000 cpm with a nominal seal diameter of 15.24 cm (6 in.). The air-supply unit yields a seal pressure ratio of approximately 7. The inlet tangential velocity can also be controlled. An external shaker is used to excite the test rotor. The apparatus has the capability to independently calculate all rotordynamic coefficients at a given operating condition with one excitation frequency.

scholarly journals Theory Versus Experiment for the Rotordynamic Coefficients of Annular Gas Seals: Part 2—Constant-Clearance and Convergent-Tapered Geometry

1986 ◽  
Vol 108 (3) ◽  
pp. 433-437 ◽  
Author(s):  
C. C. Nelson ◽  
D. W. Childs ◽  
C. Nicks ◽  
D. Elrod
Keyword(s):  
Experimental Test ◽  
Experimental Results ◽  
Test Facility ◽  
Rotordynamic Coefficients ◽  
Theory Versus ◽  
Direct Stiffness ◽  
Gas Seals ◽  
Predicted Values

An experimental test facility is used to measure the leakage and rotordynamic coefficients of constant-clearance and convergent-tapered annular gas seals. The results are presented along with the theoretically predicted values. Of particular interest is the prediction that optimally tapered seals will have significantly larger direct stiffness than straight seals. The experimental results verify this prediction. Generally the theory does quite well, but fails to predict the large increase in direct stiffness when the fluid is prerotated.

Theory Versus Experiment for the Rotordynamic Coefficient of Labyrinth Gas Seals: Part II—A Comparison to Experiment

1988 ◽  
Vol 110 (3) ◽  
pp. 281-287 ◽  
Author(s):  
D. W. Childs ◽  
J. K. Scharrer
Keyword(s):  
Experimental Test ◽  
Damping Coefficient ◽  
Test Facility ◽  
Radial Clearance ◽  
Test Results ◽  
Rotordynamic Coefficients ◽  
Theory Versus ◽  
Gas Seals ◽  
Predicted Values ◽  
Rotordynamic Coefficient

An experimental test facility is used to measure the leakage and rotordynamic coefficients of teeth-on-rotor and teeth-on-stator labyrinth gas seals. The test results are presented along with the theoretically predicted values for the two seal configurations at three different radial clearances and shaft speeds to 16,000 cpm. The test results show that the theory accurately predicts the cross-coupled stiffness for both seal configurations and shows improvement in the prediction of the direct damping for the teeth-on-rotor seal. The theory fails to predict a decrease in the direct damping coefficient for an increase in the radial clearance for the teeth-on-stator seal.

scholarly journals Experimental Rotordynamic Coefficient Results for Teeth-on-Rotor and Teeth-on-Stator Labyrinth Gas Seals

1986 ◽  
Vol 108 (4) ◽  
pp. 599-604 ◽  
Author(s):  
D. W. Childs ◽  
J. K. Scharrer
Keyword(s):  
Experimental Test ◽  
Tangential Velocity ◽  
Operating Conditions ◽  
Test Facility ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Gas Seals ◽  
First Time ◽  
Rotordynamic Coefficient

An experimental test facility is used to measure the rotordynamic coefficients of teeth-on-rotor and teeth-on-stator labyrinth gas seals. Direct damping coefficients are presented for these seals for the first time. The results are presented for the two seal configurations at identical operating conditions, and show that, in a rotordynamic sense, the teeth-on-stator seal is more stable than the teeth-on-rotor seal, for inlet tangential velocity in the direction of rotation.

Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals—Part II: Smooth and Honeycomb Geometries

2002 ◽  
Vol 124 (4) ◽  
pp. 963-970 ◽  
Author(s):  
M. P. Dawson ◽  
D. W. Childs
Keyword(s):  
Control Volume ◽  
Test Facility ◽  
Radial Clearance ◽  
Cell Width ◽  
Volume Model ◽  
Numerical Predictions ◽  
Dynamic Impedance ◽  
Honeycomb Seals ◽  
Gas Seals ◽  
Honeycomb Cell

Results are presented from tests conducted using an experimental test facility to measure the leakage and dynamic impedance of smooth and honeycomb straight-bore annular gas seals. The test seals had a 114.3 mm (4.500 in.) bore with a length-to-diameter ratio of 0.75 and a nominal radial clearance of 0.19 mm (0.0075 in.). The honeycomb cell depth for both seals was 3.10 mm (0.122 in.), and the cell width was 0.79 mm (0.031 in.). Dynamic impedance and leakage measurements are reported using air at three supply pressures out to 1.72 Mpa (250 psi), three speeds out to 20,200 rpm, and exit-to-inlet pressure ratios of 40% and 50%. Comparisons to the predictions from the two-control-volume model of Kleynhans and Childs [1] are of particular interest. This model predicts that honeycomb seals do not fit the conventional frequency independent model for smooth annular gas seals. The experimental results verify this new theory. Numerical predictions from a computer program incorporating the new two-control-volume model of Kleynhans and Childs [1] correlate well with both measured seal leakage and dynamic impedances for the honeycomb seals.

Theory Versus Experiment for Short (L/D = 1/6) Honeycomb and Smooth Annular Pressure Seals

1993 ◽  
Author(s):  
Dara W. Childs ◽  
George F. Kleynhans
Keyword(s):  
Pressure Ratio ◽  
Surface Friction ◽  
Computer Code ◽  
Cell Width ◽  
Rotordynamic Coefficients ◽  
Test Parameters ◽  
Theoretical Predictions ◽  
Theory Versus ◽  
Honeycomb Cell ◽  
Parameter Ranges

Abstract A study which compares theoretical predictions of experimental rotordynamic and leakage results is presented for short (L/D = 1/6) honeycomb and smooth annular pressure seals. A computer code used in this comparison has been developed from a theory that employs a perturbation analysis of the governing equations flow and uses Moody’s pipe friction relationship for the surface friction of the rotor and stator. This study was undertaken to investigate how well an existing code could predict these characteristics with input provided from recorded test data and independent flat-plate tests. The results examine the effect that the following independent test parameters have on the experimental measurements and theoretical predictions: inlet preswirl, rotor speed, inlet pressure, pressure ratio across seal, seal clearance, and honeycomb cell width. Experimental results show that leakage is reduced by decreasing the honeycomb cell width. Rotordynamically, the short seals are stabilizing over all test parameter ranges. However, the short seals did not perform as favorably as longer (L/D = 1/3) seals. In general, the theory overpredicts rotordynamic coefficients and leakage.

scholarly journals Theoretical Rotordynamic Coefficients of Labyrinth Gas Seals: a Parametric Study on a Bulk Model

1999 ◽  
Vol 5 (1) ◽  
pp. 67-76 ◽  
Author(s):  
Paola Forte ◽  
Fabio Latini
Keyword(s):  
Flow Characteristics ◽  
Perturbation Approach ◽  
Rotordynamic Coefficients ◽  
Volume Model ◽  
Complex Models ◽  
Gas Seals ◽  
Bulk Model ◽  
Stiffness And Damping ◽  
Good Agreement

To date, available mathematical bulk models for the determination of linearized rotordynamic coefficients of labyrinth gas seals yield results which are not always in good agreement with the experimental ones. The object of this work is to discuss the limits of these models and to point out possible improvements and aspects that need further investigation.After a study of the steady flow characteristics with an FEM code, a parametric computer program, based on a known two-volume model, has been developed. A perturbation approach has been applied to the governing equations of the bulk model to calculate the stiffness and damping coefficients. Predicted coefficients are compared to the results of an earlier one-volume model.The model has also been tested with different expressions of the axial velocities in the two volumes and different laws for leakage and shear stress. The theoretical results are compared to the published experimental ones, pointing out the small effect of the various parameters in improving the correlation and the need of more complex models.

Eccentricity Effects on the Rotordynamic Coefficients of Plain Annular Seals: Theory Versus Experiment

1997 ◽  
Vol 119 (3) ◽  
pp. 443-447 ◽  
Author(s):  
O. R. Marquette ◽  
D. W. Childs ◽  
L. San Andres
Keyword(s):  
High Speed ◽  
Small Motion ◽  
Rotordynamic Coefficients ◽  
Annular Seal ◽  
Theory Versus ◽  
High Speed Data ◽  
Static Eccentricity ◽  
Good Signal ◽  
Good Agreement ◽  
Annular Seals

Reliable high-speed data are presented for leakage and rotordynamic coefficients of a plain annular seal at centered and eccentric positions. A seal with L/D = 0.45 was tested, and measured results have good signal-to-noise ratios. The influence on rotordynamic coefficients of pressure drop, running speed, and static eccentricity was investigated. There is an excellent agreement between experimental and theoretical results in the centered position, even for direct inertia terms, which have not shown good agreement with predictions in past studies. However, the rotordynamic coefficients are more sensitive to changes in eccentricity than predicted. These results suggest that, in some cases, annular seals for pumps may need to be treated more like hydrodynamic bearings, with rotordynamic coefficients which are valid for small motion about a static equilibrium position versus the present eccentricity-independent coefficients.

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