Discussion: “Annular Honeycomb Seals: Test Results for Leakage and Rotordynamic Coefficients; Comparisons to Labyrinth and Smooth Configurations” (Childs, D., Elrod, D., and Hale, K., 1989, ASME J. Tribol., 111, pp. 293–300)

1989 ◽  
Vol 111 (2) ◽  
pp. 300-301 ◽  
Author(s):  
J. K. Scharrer
Keyword(s):  
Test Results ◽  
Rotordynamic Coefficients ◽  
Honeycomb Seals

scholarly journals Annular Honeycomb Seals: Test Results for Leakage and Rotordynamic Coefficients; Comparisons to Labyrinth and Smooth Configurations

1989 ◽  
Vol 111 (2) ◽  
pp. 293-300 ◽  
Author(s):  
D. Childs ◽  
D. Elrod ◽  
K. Hale
Keyword(s):  
Labyrinth Seal ◽  
Test Results ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Stiffness Coefficients ◽  
Shaft Rotation ◽  
Honeycomb Seal ◽  
Cell Dimensions ◽  
Honeycomb Seals ◽  
Rotordynamic Coefficient

Test results are presented for leakage and rotordynamic coefficients for seven honeycomb seals. All seals have the same radius, length, and clearance; however, the cell depths and diameters are varied. Rotordynamic data, which are presented, consist of the direct and cross-coupled stiffness coefficients and the direct damping coefficients. The rotordynamic-coefficient data show a considerable sensitivity to changes in cell dimensions; however, no clear trends are identifiable. Comparisons of test data for the honeycomb seals with labyrinth and smooth annular seals shows the honeycomb seal had the best sealing (minimum leakage) performance, followed in order by the labyrinth and smooth seals. For prerotated fluids entering the seal, in the direction of shaft rotation, the honeycomb seal has the best rotordynamic stability followed in order by the labyrinth and smooth. For no prerotation, or fluid prerotation against shaft rotation, the labyrinth seal has the best rotordynamic stability followed in order by the smooth and honeycomb seals.

Measurements of Rotordynamic Coefficients of Hybrid Bearings With (a) a Plugged Orifice, and (b) a Worn Land Surface

2002 ◽  
Vol 124 (2) ◽  
pp. 363-368 ◽  
Author(s):  
F. Laurant ◽  
D. W. Childs
Keyword(s):  
Test Data ◽  
Land Surface ◽  
Rocket Engine ◽  
Liquid Rocket Engine ◽  
Test Results ◽  
Rotordynamic Coefficients ◽  
Hybrid Bearing ◽  
Liquid Rocket

Test results are presented for the rotordynamic coefficients of a hybrid bearing that is representative of bearings for liquid-rocket-engine turbopump applications. The bearing is tested in the following two degraded conditions: (a) one of five orifices plugged, and (b) a locally enlarged clearance to simulate a worn condition. Test data are presented at 24,600 rpm, with supply pressures of 4.0, 5.5, and 7.0 MPa, and eccentricity ratios from 0.1 to 0.5 in 0.1 increments. Overall, the results suggest that neither a single plugged orifice nor significant wear on the bearing land will “disable” a well-designed hybrid bearing. These results do not speak to multiple plugged orifices and are not an endorsement for operations without filters to prevent plugging orifices.

Experimental Test Results for Four High-Speed, High-Pressure, Orifice-Compensated Hybrid Bearings

1994 ◽  
Vol 116 (1) ◽  
pp. 147-153 ◽  
Author(s):  
N. M. Franchek ◽  
D. W. Childs
Keyword(s):  
High Speed ◽  
Load Capacity ◽  
Pressure Ratio ◽  
Reynolds Numbers ◽  
Orifice Diameter ◽  
Test Results ◽  
Rotordynamic Coefficients ◽  
Geometric Configurations ◽  
Overall Performance ◽  
Mass Terms

In this study, four hybrid bearings having different geometric configurations were experimentally tested for their static and dynamic characteristics, including flowrate, load capacity, rotordynamic coefficients, and whirl frequency ratio. The four bearings included a square-recess, smooth-land, radial-orifice bearing (baseline), a circular-recess bearing, a triangular-recess bearing, and an angled-orifice bearing. Each bearing had the same orifice diameter rather than the same pressure ratio. Unique to these test results is the measurement of the added mass terms, which became significant in the present tests because of high operating Reynolds numbers. Comparisons of the results were made between bearings to determine which bearing had the best performance. Based on the parameters of interest, the angled-orifice bearing has the most favorable overall performance.

CFD Assessment of Rotordynamic Coefficients in Labyrinth Seals

2014 ◽  
Author(s):  
Sai S. Sreedharan ◽  
Giuseppe Vannini ◽  
Hiteshkumar Mistry
Keyword(s):  
High Speed ◽  
Test Results ◽  
Active Magnetic Bearings ◽  
Test Rig ◽  
Labyrinth Seals ◽  
Cfd Simulations ◽  
Flow Solver ◽  
Rotordynamic Coefficients ◽  
Pressure Test ◽  
Dynamic Seal

Seals used in high speed centrifugal compressors are prone to generate rotordynamic (RD) instabilities. To further understand their influence, a CFD based approach is developed. The objective of the current study is to numerically investigate and characterize the RD coefficients, representative of the dynamic seal forces. Experiments were carried out at high pressure test rig (up to 200 bar seal inlet pressure) which runs at 10000 RPM and has a high pre-swirl (about 0.9) along the same direction of rotor rotation. The rotor shaft in the experiment was instrumented with active magnetic bearings (AMBs) to linearly excite the rotor at three different frequencies: 28 Hz, 70 Hz and 126 Hz. Each frequency is characterized by amplitude of vibration and a phase. CFD simulations were carried out using commercial flow solver, using similar boundary conditions as that of experiments. The paper describes details of CFD model and its comparison against experiments. Numerical results show reasonable agreement of RD coefficients with test results. This job has to be considered as a first approach to CFD methodology applied to annular seals for the authors.

Preswirl and Mixed-Flow (Mainly Liquid) Effects on Rotordynamic Performance of a Long (L/D = 0.75) Smooth Seal

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Dung L. Tran ◽  
Dara W. Childs ◽  
Hari Shrestha ◽  
Min Zhang
Keyword(s):  
Dynamic Instability ◽  
Silicone Oil ◽  
Dynamic Stiffness ◽  
Radial Clearance ◽  
Inlet Temperature ◽  
Test Results ◽  
Transition Flow ◽  
Two Phase ◽  
Rotordynamic Coefficients ◽  
Transition Flow Regime

Abstract Measured results are presented for rotordynamic coefficients and mass leakage rates of a long smooth annular seal (length-to-diameter ratio L/D = 0.75, diameter D = 114.686 mm, and radial clearance Cr = 0.200 mm) tested with a mixture of silicone oil (PSF-5cSt) and air. The test seal is centered, the seal exit pressure is maintained at 6.9 bars-g while the fluid inlet temperature is controlled within 37.8–40.6 °C. It is tested with three inlet-preswirl inserts, namely, zero, medium, and high (the preswirl ratios (PSRs), i.e., the ratio between the fluid's circumferential velocity and the shaft surface's velocity, are in ranges of 0.10–0.18, 0.30–0.65, and 0.65–1.40 for zero, medium, and high preswirls, respectively), six inlet gas-volume fractions GVFi (0%, 2%, 4%, 6%, 8%, and 10%), four pressure drops PDs (20.7, 27.6, 34.5, and 41.4 bars), and three speeds ω (3, 4, and 5 krpm). The targeted test matrix could not be achieved for the medium- and high-preswirl inserts at PD ≥ 27.6 bars due to the test-rig stator's dynamic instability issues. Spargers were used to inject air into the oil, and GVFi values higher than 0.10 could not be consistently achieved because of unsteady surging flow downstream from the sparger mixing section. Leakage mass flow rate m˙ and rotordynamic coefficients are measured, and the effect of changing inlet preswirl and GVFi is studied. The test results are then compared with predictions from a two-phase, homogeneous-mixture, bulk-flow model developed in 2011. Generally, both measurements and predictions show little change in m˙ as inlet preswirl changes. Measured m˙ remains unchanged or slightly increases with increasing GVFi, but predicted m˙ decreases. Measured m˙ is comparable to predicted values but consistently lower. Dynamic-stiffness coefficients are measured using an ensemble of excitation frequencies and curve-fitted well by frequency-independent stiffness Kij, damping Cij, and virtual mass Mij coefficients. Planned tests with the medium- and high-preswirl inserts could not be accomplished at PD = 34.5 and 41.4 bars because the seal stator became unstable with any finite injection of air. The test results show that the instability arose because the seal's direct stiffness K became negative and increased in magnitude with increasing GVFi. The model predicts a drop in K as GVFi increases, but the test results dropped substantially more rapidly than predicted. Also, the model does not predict the observed strong tendency for K to drop with an increase in preswirl in moving from the zero-to-medium and medium-to-high preswirl inserts. The authors believe that the observed drop in K due to increasing GVFi is not explained by either (a) a reverse Lomakin effect from operating in the transition flow regime or (b) the predicted drop in K at higher GVFi values from the model. A separate and as yet unidentified two-phase flow phenomenon probably causes the observed results. The negative K results due to increasing GVFi and moving from the zero to medium, and medium to high preswirl observed here could explain the instability issue (sudden subsynchronous vibration) on a high-differential-pressure helico-axial multiphase pump (MPP), reported in 2013. Effective damping Ceff combines the stabilizing effect of direct damping C, the destabilizing effect of cross-coupled stiffness k, and the influence of cross-coupled mass mq. As predicted and measured, increasing inlet preswirl significantly increases k and decreases Ceff, which decreases the seal's stabilizing properties. Ceff increases with increasing GVFi—becomes more stable.

scholarly journals Rotordynamic Coefficient and Leakage Test Results for Interlock and Tooth-on-Stator Labyrinth Seals

1988 ◽  
Author(s):  
Dara W. Childs ◽  
David A. Elrod ◽  
Keith Hale
Keyword(s):  
Labyrinth Seal ◽  
Damping Coefficient ◽  
Test Results ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Leakage Test ◽  
Stiffness And Damping ◽  
Rotordynamic Coefficient

Test results (leakage and rotordynamic coefficients) are presented for an interlock and tooth-on-stator labyrinth seals. Tests were carried out with air at speeds out to 16,000 cpm and supply pressures up to 7.5 bars. The rotordynamic coefficients consist of direct and cross-coupled stiffness and damping coefficients. Damping-coefficient data have not previously been presented for interlock seals. The test results support the following conclusions: (a) The interlock seal leaks substantially less than labyrinth seals. (b) Destabilizing forces are lower for the interlock seal. (c) The labyrinth seal has substantially greater direct damping values than the interlock seal. A complete rotordynamics analysis is needed to determine which type of seal would yield the best stability predictions for a given turbomachinery unit.

Measured Static and Rotordynamic Characteristics of a Smooth-Stator/Grooved-Rotor Liquid Annular Seal

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
J. Alex Moreland ◽  
Dara W. Childs ◽  
Joshua T. Bullock
Keyword(s):  
Radial Clearance ◽  
Test Results ◽  
Dynamic Features ◽  
Axial Pressure ◽  
Pressure Drops ◽  
Rotordynamic Coefficients ◽  
Annular Seal ◽  
Direct Stiffness ◽  
Static Eccentricity ◽  
Dynamic Variables

Electric submersible pumps (ESPs) utilize grooved-rotor/smooth-stator (SS/GR) seals to reduce leakage and break up contaminants within the pumped fluid. Additionally, due to their decreased surface area (when compared to a smooth seal), grooved seals decrease the chance of seizure in the case of rotor-stator rubs. Despite their use in industry, the literature does not contain rotordynamic measurements for smooth-stator/circumferentially grooved-rotor liquid annular seals. This paper presents test results consisting of leakage measurements and rotordynamic coefficients for a SS/GR liquid annular sdeal. Both static and dynamic variables are investigated for various imposed preswirl ratios (PSRs), static eccentricity ratios (0–0.8), axial pressure drops (2–8 bars), and running speeds (2–8 krpm). The seals' static and dynamic features are compared to those of a smooth seal with the same length, diameter, and minimum radial clearance. Results show that the grooves reduce leakage at lower speeds (less than 5 krpm) and higher axial pressure drops, but does little at higher speeds. The grooved seal's direct stiffness is generally negative, which would be detrimental to pump rotordynamics. As expected, increasing preswirl increases the magnitude of cross-coupled stiffness and increases the whirl frequency ratio (WFR). When compared to the smooth seal, the grooved seal has smaller effective damping coefficients, indicative of poorer stability characteristics.

Influence of Groove Size on the Static and Rotordynamic Characteristics of Short, Laminar-Flow Annular Seals

2007 ◽  
Vol 129 (2) ◽  
pp. 398-406 ◽  
Author(s):  
Dara W. Childs ◽  
Matthew Graviss ◽  
Luis E. Rodriguez
Keyword(s):  
Energy Equation ◽  
Groove Depth ◽  
Added Mass ◽  
Equation Model ◽  
Radial Clearance ◽  
Pressure Perturbation ◽  
Test Results ◽  
Rotordynamic Coefficients ◽  
Test Conditions ◽  
Groove Test

Test results are presented for a smooth seal and three centrally grooved seals that are representative of buffered-flow oil seals in centrifugal compressors. The seals are short (L∕D≅0.21), with a diameter of 117mm and a nominal radial clearance of 0.085mm, netting the clearance-to-radius ratio 0.0015. The grooves have groove depth to clearance ratios (Dg∕Cr) of 5, 10, and 15. Test conditions include three shaft speeds from 4000rpm to 10,000rpm, three inlet oil pressures from 24bar to 70bar, and seal eccentricity ratios from 0 (centered) to 0.7. Dynamic results include stiffness, damping, and added-mass coefficients; static results include stator position, attitude angles, and seal leakage. Stiffness, damping, and mass coefficients plus leakage are compared for the seal geometries. Results show that all rotordynamic coefficients consistently decrease with increasing seal groove depths, and seal leakage is largely unchanged. Comparisons are also made between experimental results and predictions from a computer program based on a Reynolds + energy equation model. The model includes the assumption that a groove is large enough to create separate lands within the seal, creating a zero or negligible pressure perturbation within the groove. Test results show that even the deepest groove depth tested is not deep enough to satisfy this assumption.

Test Results for Leakage and Rotordynamic Coefficients of Floating Ring Seals in a High-Pressure, High-Speed Turbopump

2005 ◽  
Vol 48 (3) ◽  
pp. 273-282 ◽  
Author(s):  
Y. B. LEE ◽  
S. K. SHIN ◽  
K. RYU ◽  
C. H. KIM ◽  
GUNHEE JANG
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Test Results ◽  
Rotordynamic Coefficients
Sign in / Sign up

Export Citation Format

Share Document