Experimental Rotordynamic Force Coefficients for a Diffusion Bonded Compliant Hybrid Journal Gas Bearing Utilizing Fluid-Filled Hermetic Dampers

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Keith Gary ◽  
Bugra Ertas
Keyword(s):  
Dynamic Testing ◽  
Companion Paper ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Squeeze Film Dampers ◽  
Lower Excitation ◽  
Excitation Frequencies ◽  
Gas Bearing ◽  
Asme Paper

Abstract Dynamic force coefficients are presented from experimental results of a radial gas bearing with hermetically sealed squeeze film dampers (HSFDs) in the bearing support. HSFDs are a relatively new technology aimed to increase damping levels in gas bearings while sustaining an oil-free bearing sump. Past HSFD designs proved bulky and contained many components making it difficult to employ in size-limited environments such as jet engines, while the diffusion bonded bearing discussed in this paper provides a compact integral design. Details of the design are found in a companion paper by Ertas (Ertas, B. H., 2019, “Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers,” ASME Paper No. GT2018-76312). Test results for a 3 in. (76.2 mm) diameter bearing using a test rig providing static loads up to 80 lbs (356 N), controlled-dynamic orbital motion, and speeds up to 27 krpm are shown. Results include frequency- and speed-dependent direct and cross-coupled rotordynamic force coefficients. Dynamic testing showed little dependence on rotor speed or static load and exhibited frequency dependency at lower excitation frequencies. Cross-coupled terms are generally an order of magnitude lower than direct terms. Results show the direct stiffness coefficients increasing with frequency, while direct damping decays radically with frequency. Comparison of the overall gas bearing coefficients with the companion paper (Ertas, B. H., 2019, “Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers,” ASME Paper No. GT2018-76312), showing bearing support coefficients, reveals a drastic reduction in damping when engaging the gas film. The results also indicate that the bearing can withstand vibration levels representative of a large rotor system critical speed at lower excitation frequencies.

Experimental Rotordynamic Force Coefficients for a Diffusion Bonded Compliant Hybrid Journal Gas Bearing Utilizing Fluid-Filled Hermetic Dampers

2019 ◽  
Author(s):  
Keith Gary ◽  
Bugra Ertas
Keyword(s):  
Dynamic Testing ◽  
New Technology ◽  
Companion Paper ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Lower Excitation ◽  
Order Of Magnitude ◽  
Excitation Frequencies ◽  
Gas Bearing

Abstract Dynamic force coefficients are presented from experimental results of a radial gas bearing with hermetically sealed squeeze film dampers (HSFD) in the bearing support. HSFDs are a relatively new technology aimed to increase damping levels in gas bearings while sustaining an oil-free bearing sump. Past HSFD designs proved bulky and contained many components making it difficult to employ in size limited environments such as jet engines, while the diffusion bonded bearing discussed in the present paper provides a compact integral design. Test results for a three-inch diameter bearing using a test rig providing static loads up to 80 lbs, controlled-dynamic orbital motion, and speeds up to 27 krpm are shown. Results include frequency and speed dependent direct and cross-coupled rotordynamic force coefficients. Dynamic testing showed little dependence on rotor speed or static load and exhibited frequency dependency at lower excitation frequencies. Cross-coupled terms are generally an order of magnitude lower than direct terms. Results show the direct stiffness coefficients increasing with frequency while direct damping decays radically with frequency. Comparison of the overall gas bearing coefficients with a companion paper [1], showing bearing support coefficients, reveals a drastic reduction in damping when engaging the gas film. The results also indicate the bearing can withstand vibration levels representative of a large rotor system critical speed at lower excitation frequencies.

Compliant Hybrid Gas Bearing Using Integral Hermetically Sealed Squeeze Film Dampers

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Bugra Ertas
Keyword(s):  
Squeeze Film ◽  
Force Coefficients ◽  
Overall Design ◽  
Single Piece ◽  
Squeeze Film Dampers ◽  
Tilting Pad ◽  
Support Force ◽  
Bearing Design ◽  
Gas Bearing ◽  
Gaining Insight

AbstractThis paper focuses on an integral gas-film lubricated bearing concept developed to enable the oil-free operation of super-critical carbon dioxide (sCO2) turbomachinery. The externally pressurized tilting pad bearing concept possesses a flexible bearing support with an integral hermetically sealed squeeze film damper. Unlike the past concepts using modular hermetic squeeze film dampers presented, the bearing design in this work utilizes advanced manufacturing methods to yield an integral single piece design in efforts to reduce space envelope, cost, and improve overall design reliability. The paper advances a detailed description of the bearing design and identification of bearing support force coefficients. Nonrotating benchtop tests show the influence of vibration amplitude, frequency, and damper cavity pressurization on force coefficients for two different viscosity fluids. Results indicate an increase in stiffness and a decrease in damping when increasing the frequency of excitation. Damper cavity pressurization was shown to eliminate squeeze film cavitation for the vibration amplitudes and frequency range in the study. Additionally, the paper advances a transient fluid–structure interaction (FSI) analysis aimed at gaining insight on the interaction of flexible elements bounding a hermetic fluid volume experiencing sinusoidal vibratory motion. The analysis considers an idealized damper model with and without a vibration transmission post while varying diaphragm modulus of elasticity for three excitation frequencies. Computational results were able to capture the increase in stiffness and the decrease in damping and show that the flexibility of the bounding elements influence the damper cavity volume change and phase ultimately affecting dynamic cavity pressures and force coefficients.

Analysis of Short Squeeze Film Dampers With a Central Groove

1992 ◽  
Vol 114 (4) ◽  
pp. 659-664 ◽  
Author(s):  
Luis A. San Andres
Keyword(s):  
Squeeze Film ◽  
Inertia Force ◽  
Dynamic Force ◽  
Fluid Inertia ◽  
Dynamic Flow ◽  
Low Frequencies ◽  
Squeeze Film Damper ◽  
Force Coefficients ◽  
Squeeze Film Dampers ◽  
Combined Action

A novel analysis for the dynamic force response of a squeeze film damper with a central feeding groove considers the dynamic flow interaction between the squeeze film lands and the feeding groove. For small amplitude centered motions and based on the short bearing model, corrected values for the damping and inertia force coefficients are determined. Correlations with existing experimental evidence is excellent. Analytical results show that the grooved-damper behaves at low frequencies as a single land damper. Dynamic force coefficients are determined to be frequency dependent. Analytical predictions show that the combined action of fluid inertia and groove volume—liquid compressibility affects the force coefficients for dynamic excitation at large frequencies.

Frequency Dependancy of Dynamic Force Coefficients for Hermetic Squeeze Film Dampers Utilizing Fluid-Bounding Flexible Structures

2021 ◽  
Author(s):  
Bugra Ertas ◽  
Keith Gary
Keyword(s):  
Fluid Dynamics ◽  
Flexible Structures ◽  
Analytical Models ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Design Modification ◽  
Frequency Dependency ◽  
Force Coefficients ◽  
Squeeze Film Dampers ◽  
Frequency Independent

Abstract The following paper focuses on the dynamic behavior of hermetic squeeze film dampers (HSFD) that utilize fluid-bounding flexible members as a part of the support structure. More specifically, the current paper advances an engineering design modification to the existing HSFD concept, which is aimed at rendering the dynamic force coefficients frequency independent. The paper builds on past HSFD testing and modeling approaches to develop higher fidelity analytical models, which are used to investigate different damper configurations while taking keen interest in the frequency dependency of force coefficients. The analytical study leverages commercially available finite element analysis (FEA) and computational fluid dynamics (CFD) software to conduct several fluid-structure-interaction (FSI) simulations of various damper architectures. In addition to the FSI analysis a more computationally efficient reduced order model (ROM) was developed, coupling structural flexibility with the fluid dynamics in the damper. Ultimately, these design tools were used to identify critical design features and configurations needed for constant linear frequency independent force coefficients. The results show a damper configuration with minimal frequency dependency of the stiffness and damping coefficients when incorporating pass through channels in combination with accumulator volumes. The paper also uses the improved design approach of the HSFD to put forth a notional integrated bearing design incorporating the new HSFD concept.

Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers

2019 ◽  
Author(s):  
Bugra Ertas
Keyword(s):  
Past Research ◽  
Squeeze Film ◽  
Force Coefficients ◽  
Overall Design ◽  
Single Piece ◽  
Squeeze Film Dampers ◽  
Tilting Pad ◽  
Support Force ◽  
Bearing Design ◽  
Gas Bearing

Abstract The following paper focuses on an integral gas-film lubricated bearing concept developed to enable the oil-free operation of super-critical carbon dioxide (sCO2) turbomachinery. The externally pressurized tilting pad bearing concept possesses a flexible bearing support with an integral hermetically sealed squeeze film damper. Unlike the initial concepts using modular hermetic squeeze film dampers presented in past research, the bearing design in this work utilizes advanced manufacturing methods to yield an integral single piece design developed to reduce space envelope, cost, and improved overall design reliability. The paper advances a detailed description of the bearing design and identification of bearing support force coefficients. Non-rotating bearing support test results show the influence of vibration amplitude, frequency, and damper cavity pressurization on force coefficients for two different viscosity fluids. Results indicate an increase in stiffness and a decrease in damping when increasing the frequency of excitation. Damper cavity pressurization was shown to eliminate squeeze film cavitation for the vibration amplitudes and frequency range in the study. Additionally, the paper advances a transient fluid-structure interaction (FSI) analysis aimed at gaining insight on the interaction of flexible elements bounding a hermetic fluid volume experiencing sinusoidal vibratory motion. The analysis considers an idealized damper model with and without a vibration transmission post while varying diaphragm modulus of elasticity for three excitation frequencies. Computational results were able to capture the increase in stiffness and decrease in damping and show that the flexibility of the bounding elements influence the damper cavity volume change and phase; ultimately effecting dynamic cavity pressures and force coefficients.

Experimental Identification of Dynamic Force Coefficients for a 110 mm Compliantly Damped Hybrid Gas Bearing

2014 ◽  
Author(s):  
Adolfo Delgado
Keyword(s):  
Load Capacity ◽  
Excitation Frequency ◽  
Dynamic Test ◽  
Inlet Pressure ◽  
Dynamic Force ◽  
Metal Mesh ◽  
Gas Bearings ◽  
Force Coefficients ◽  
Test Parameters ◽  
Gas Bearing

Compliant hybrid gas bearings combine key enabling features from both fixed geometry externally pressurized gas bearings and compliant foil bearings. The compliant hybrid bearing relies on both hydrostatic and hydrodynamic film pressures to generate load capacity and stiffness to the rotor system, while providing damping through integrally mounted metal mesh bearing support dampers. This paper presents experimentally identified force coefficients for a 110 mm compliantly damped gas bearing using a controlled-motion test rig. Test parameters include hydrostatic inlet pressure, excitation frequency, and rotor speed. The experiments were structured to evaluate the feasibility of implementing these bearings in large size turbomachinery. Dynamic test results indicate weak dependency of equivalent direct stiffness coefficients to most test parameters except for frequency and speed, where higher speeds and excitation frequency decreased equivalent bearing stiffness values. The bearing system equivalent direct damping was negatively impacted by increased inlet pressure and excitation frequency, while the cross-coupled force coefficients showed values an order of magnitude lower than the direct coefficients. The experiments also include orbital excitations to simulate unbalance response representative of a target machine while synchronously traversing a critical speed. The results indicate that the gas bearing can accommodate vibration levels larger than the set bore clearance while maintaining satisfactory damping levels.

On the Experimental Dynamic Force Performance of a Squeeze Film Damper Supplied Through a Check Valve and Sealed With O-Rings

2021 ◽  
Author(s):  
Luis San Andrés ◽  
Bryan Rodríguez
Keyword(s):  
Dynamic Pressure ◽  
Excitation Frequency ◽  
Check Valve ◽  
Forced Response ◽  
Single Frequency ◽  
Squeeze Film ◽  
Dynamic Force ◽  
Viscous Damping ◽  
Test Rig ◽  
Force Coefficients

Abstract In rotor-bearing systems, squeeze film dampers (SFDs) assist to reduce vibration amplitudes while traversing a critical speed and also offer a means to suppress rotor instabilities. Along with an elastic support element, SFDs are effective means to isolate a rotor from its casing. O-rings (ORs), piston rings (PRs) and side plates as end seals reduce leakage and air ingestion while amplifying the viscous damping in configurations with limited physical space. ORs also add a centering stiffness and damping to a SFD. The paper presents experiments to quantify the dynamic forced response of an O-rings sealed ends SFD (OR-SFD) lubricated with ISO VG2 oil supplied at a low pressure (0.7 bar(g)). The damper is 127 mm in diameter (D), short in axial length L = 0.2D, and the film clearance c = 0.279 mm. The lubricant flows into the film land through a mechanical check valve and exits through a single port. Upstream of the check valve, a large plenum filled with oil serves to attenuate dynamic pressure disturbances. Multiple sets of single-frequency dynamic loads, 10 Hz to 120 Hz, produce circular centered orbits with amplitudes r = 0.1c, 0.15c and 0.2c. The experimental results identify the test rig structure, ORs and SFD force coefficients; namely stiffness (K), mass (M) and viscous damping (C). The ORs coefficients are frequency independent and show a sizeable direct stiffness, KOR ∼ 50% of the test rig structure stiffness, along with a quadrature stiffness, K0∼0.26 KOR, demonstrative of material damping. The lubricated system damping coefficient equals CL = (CSFD + COR); the ORs contributing 10% to the total. The experimental SFD damping and inertia coefficients are large in physical magnitude; CSFD slightly grows with orbit size whereas MSFD is relatively constant. The added mass (MSFD) is approximately four-fold the bearing cartridge mass; hence, the test rig natural frequency drops by ∼50% once lubricated. A computational physics model predicts force coefficients that are just 10% lower than those estimated from experiments. The amplitude of measured dynamic pressures upstream of the plenum increases with excitation frequency. Unsuspectedly, during dynamic load operation, the check valve did allow for lubricant backflow into the plenum. Post-tests verification demonstrates that, under static pressure conditions, the check valve does work since it allows fluid flow in just one direction.

Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical End Seal: Centered Circular Orbit Tests

2006 ◽  
Author(s):  
Luis San Andre´s ◽  
Adolfo Delgado
Keyword(s):  
Dry Friction ◽  
Companion Paper ◽  
Single Frequency ◽  
Squeeze Film ◽  
Mechanical Seal ◽  
Damping Force ◽  
Force Coefficients ◽  
Damping Coefficients ◽  
The Individual ◽  
Aircraft Application

The damping capability of squeeze film dampers (SFDs) relies on adequate end sealing to prevent air ingestion and entrapment. The paper presents the parameter identification, procedure and damping coefficients, of a test SFD featuring a mechanical seal that effectively eliminates lubricant side leakage. The test damper reproduces an aircraft application intended to contain the lubricant in the film lands for extended periods of time. The test damper journal is 2.54 cm in length and 12.7 cm in diameter, with a nominal clearance of 0.127 mm. The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice ports. In a companion paper (ASME GT2006-90782), single frequency - unidirectional load excitation tests were conducted, without and with lubricant in the squeeze film lands, to determine the seal dry-friction force and viscous damping force coefficients. Presently, tests with single frequency excitation loads rendering circular centered orbits excitations are conducted to identify the SFD force coefficients. The identified parameters include the overall system damping and the individual contributions from the squeeze film, dry friction and structural damping. The identified system damping coefficients are frequency and motion amplitude dependent due to the dry friction interaction at the mechanical seal interface. Identified squeeze film force coefficients, damping and added mass, are in good agreement with predictions based on the full film, short length damper model.

Damping and Inertia Coefficients for Two Open Ends Squeeze Film Dampers With a Central Groove: Measurements and Predictions

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Luis San Andrés
Keyword(s):  
Short Length ◽  
Operating Conditions ◽  
The Other ◽  
System Stability ◽  
Squeeze Film ◽  
Inertia Force ◽  
Frequency Domain Method ◽  
Force Coefficients ◽  
Squeeze Film Dampers ◽  
Static Eccentricity

Aircraft engine rotors are particularly sensitive to rotor imbalance and sudden maneuver loads, since they are always supported on rolling element bearings with little damping. Most engines incorporate squeeze film dampers (SFDs) as means to dissipate mechanical energy from rotor vibrations and to ensure system stability. The paper quantifies experimentally the forced performance of a SFD comprising two parallel film lands separated by a deep central groove. Tests are conducted on two open ends SFDs, both with diameter D = 127 mm and nominal radial clearance c = 0.127 mm. One damper has film lands with length L = 12.7 mm (short length), while the other has 25.4 mm land lengths. The central groove has width L and depth 3/4 L. A light viscosity lubricant flows into the central groove via three orifices, 120 deg apart and then through the film lands to finally exit to ambient. In operation, a static loader pulls the bearing to various eccentric positions and electromagnetic shakers excite the test system with periodic loads to generate whirl orbits of specific amplitudes. A frequency domain method identifies the SFD damping and inertia force coefficients. The long damper generates six times more damping and about three times more added mass than the short length damper. The damping coefficients are sensitive to the static eccentricity (up to ∼ 0.5 c), while showing lesser dependency on the amplitude of whirl motion (up to 0.2 c). On the other hand, inertia coefficients increase mildly with static eccentricity and decrease as the amplitude of whirl motion increases. Cross-coupled force coefficients are insignificant for all imposed operating conditions on either damper. Large dynamic pressures recorded in the central groove demonstrate the groove does not isolate the adjacent squeeze film lands, but contributes to the amplification of the film lands’ reaction forces. Predictions from a novel SFD model that includes flow interactions in the central groove and feed orifices agree well with the test force coefficients for both dampers. The test data and predictions advance current knowledge and demonstrate that SFD-forced performance is tied to the lubricant feed arrangement.

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