Forced Coefficients for a Short Length, Open Ends Squeeze Film Damper With End Grooves: Experiments and Predictions

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Sung-Hwa Jeung ◽  
Luis San Andrés ◽  
Gary Bradley
Keyword(s):  
Aircraft Engine ◽  
Groove Depth ◽  
Forced Response ◽  
Short Length ◽  
Effective Length ◽  
Single Frequency ◽  
Squeeze Film ◽  
Thin Film Flow ◽  
Static Eccentricity ◽  
Total Oil

Squeeze film dampers (SFDs) are effective to ameliorate shaft vibration amplitudes and to suppress instabilities in rotor–bearing systems. Compact aero jet engines implement ultra-short length SFDs (L/D ≤ 0.2) to satisfy stringent weight and space demands with low parts count. This paper describes a test campaign to identify the dynamic forced response of an open ends SFD (L = 25.4 mm and D = 125.7 mm), single film land, and oil fed through three holes (120 deg apart), operating with similar conditions as in an aircraft engine. Two journals make for two SFD films with clearances cA = 0.129 mm and cB = 0.254 mm (small and large). The total oil-wetted length equals Ltot = 36.8 mm that includes deep end grooves, width and depth = 2.5 × 3.8 mm, for installation of end seals. In the current experiments, the end seals are not in place. A hydraulic static loader pulls the bearing cartridge (BC) to a preset static eccentricity (eS), and two electromagnetic shakers excite the BC with single frequency loads to create circular orbits, centered and off-centered, over a prescribed frequency range ω = 10–100 Hz. The whirl amplitudes range from r = 0.05cA–0.6cA and r = 0.15cB–0.75cB while the static eccentricity increases to eS = 0.5cA and eS = 0.75cB, respectively. Comparisons of force coefficients between the two identical dampers with differing clearances show that the small clearance damper (cA) provides ∼4 times more damping and ∼1.8 times the inertia coefficients than the damper with large clearance (cB). The test results demonstrate damping scales with ∼1/c3 and inertia with ∼1/c, as theory also showed. Analysis of the measured film land pressures evidence that the deep end grooves contribute to the generation of dynamic pressures enhancing the dynamic forced response of the test SFDs. A thin film flow model with an effective groove depth delivers predictions that closely match the test damping and inertia coefficients. Other predictions, based on the short length bearing model, use an effective length Leff ∼ 1.17L to deliver damping coefficients 15% larger than the experimental results; however, inertia coefficients are ½ of the identified magnitudes. The experiments and analysis complement earlier experimental work conducted with centrally grooved SFDs.

Forced Coefficients for a Short Length, Open-Ends Squeeze Film Damper With End Grooves: Experiments and Predictions

2015 ◽  
Author(s):  
Luis San Andrés ◽  
Sung-Hwa Jeung ◽  
Gary Bradley
Keyword(s):  
Aircraft Engine ◽  
Groove Depth ◽  
Forced Response ◽  
Short Length ◽  
Effective Length ◽  
Single Frequency ◽  
Squeeze Film ◽  
Thin Film Flow ◽  
Static Eccentricity ◽  
Total Oil

Squeeze Film Dampers (SFDs) are effective to ameliorate shaft vibration amplitudes and to suppress instabilities in rotor-bearing systems. Compact aero jet engines implement ultra-short length SFDs (L/D ≤ 0.2) to satisfy stringent weight and space demands with low parts count. This paper describes a test campaign to identify the dynamic forced response of an open ends SFD (L=25.4 mm, D=125.7 mm), single film land and oil fed through three holes (120° apart), operating with similar conditions as in an aircraft engine. Two journals make for two SFD films with clearances cA=0.129 mm and cB=0.254 mm (small and large). The total oil wetted length equals Ltot=36.8 mm that includes deep end grooves, width and depth = 2.5 × 3.8 mm, for installation of end seals. In the current experiments, the end seals are not in place. A hydraulic static loader pulls the bearing cartridge (BC) to a preset static eccentricity (eS) and two electromagnetic shakers excite the BC with single frequency loads to create circular orbits, centered and off-centered, over a prescribed frequency range ω=10–100Hz. The whirl amplitudes range from r=0.05cA–0.6cA and r=0.15cB–0.75cB while the static eccentricity increases to eS=0.5cA and eS=0.75cB, respectively. Comparisons of force coefficients between the two identical dampers with differing clearances show that the small clearance damper (cA) provides ∼4 times more damping and ∼1.8 times the inertia coefficients than the damper with large clearance (cB). The test results demonstrate damping scales with ∼1/c3 and inertia with ∼1/c, as theory also shows. Analysis of the measured film land pressures evidence that the deep end grooves contribute to the generation of dynamic pressures enhancing the dynamic forced response of the test SFDs. A thin film flow model with an effective groove depth delivers predictions that closely match the test damping and inertia coefficients. Other predictions, based on the short length bearing model, use an effective length Leff ∼1.17L to deliver damping coefficients 15% larger than the experimental results; however, inertia coefficients are ½ of the identified magnitudes. The experiments and analysis complement earlier experimental work conducted with centrally grooved SFDs.

Forced Response of a Squeeze Film Damper and Identification of Force Coefficients From Large Orbital Motions

2004 ◽  
Vol 126 (2) ◽  
pp. 292-300 ◽  
Author(s):  
Luis San Andre´s ◽  
Oscar De Santiago
Keyword(s):  
Excitation Frequency ◽  
Air Entrainment ◽  
Forced Response ◽  
Effective Length ◽  
Single Frequency ◽  
Squeeze Film ◽  
Inertia Force ◽  
Damping Force ◽  
Squeeze Film Damper ◽  
Force Coefficients

Experimentally derived damping and inertia force coefficients from a test squeeze film damper for various dynamic load conditions are reported. Shakers exert single frequency loads and induce circular and elliptical orbits of increasing amplitudes. Measurements of the applied loads, bearing displacements and accelerations permit the identification of force coefficients for operation at three whirl frequencies (40, 50, and 60 Hz) and increasing lubricant temperatures. Measurements of film pressures reveal an early onset of air ingestion. Identified damping force coefficients agree well with predictions based on the short length bearing model only if an effective damper length is used. A published two-phase flow model for air entrainment allows the prediction of the effective damper length, and which ranges from 82% to 78% of the damper physical length as the whirl excitation frequency increases. Justifications for the effective length or reduced (flow) viscosity follow from the small through flow rate, not large enough to offset the dynamic volume changes. The measurements and analysis thus show the pervasiveness of air entrainment, whose effect increases with the amplitude and frequency of the dynamic journal motions. Identified inertia coefficients are approximately twice as large as those derived from classical theory.

Transient Response of a Short-Length (L/D = 0.2) Open-Ends Elastically Supported Squeeze Film Damper: Centered and Largely Off-Centered Whirl Motions

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Luis San Andrés ◽  
Sean Den ◽  
Sung-Hwa Jeung
Keyword(s):  
Dynamic Load ◽  
Short Length ◽  
Single Frequency ◽  
Squeeze Film ◽  
Test Rig ◽  
Sweep Frequency ◽  
Transient Events ◽  
Frequency Excitation ◽  
Static Eccentricity ◽  
Sine Sweep

Commonly employed in air breathing (gas turbine) engines, squeeze film dampers (SFDs) reduce the amplitude of rotor vibration while traversing system critical speeds or in transient events such as during a maneuver load, a hard landing, a blade loss, or an engine startup/shutdown sequence that could instantaneously shift a damper journal eccentricity (es) to near its clearance (c). Experiments investigate the dynamic force performance of an open ends, short-length (L/D = 0.2) SFD test rig with radial clearance c = 267 μm and undergoing centered (es/c = 0) to largely off-centered (es/c → 1) whirl orbit motions induced by both a large static load plus a dynamic load. Four rods, symmetrically arranged to resemble a squirrel cage, elastically support the SFD test rig. A hydraulic load system displaces the test damper structure into static eccentricity (es/c). One of two types of dynamic load with amplitude FX = FY excite the SFD: a single-frequency, stepping from low frequency to high frequency discretely; or a sine-sweep frequency growing linearly with time at 6 Hz/s, 33 Hz/s, 40 Hz/s, or 55 Hz/s. For motions departing from es/c = 0.0, 0.95, and 0.99, the dynamic load uses a sine-sweep frequency varying from 5 Hz to 245 Hz and evolving rapidly at ∼33 Hz/s. Measurements of SFD displacements characterize the behavior of the SFD rig during its transient response which crosses two system natural frequencies. For motions departing from a largely off-centered condition (es → c), the dynamic load forces the damper to whirl with highly elliptical orbits, in particular while crossing a resonance (damped natural frequency). Moreover, the dynamic motions departing from es ∼ c are smaller in amplitude than those arising from a centered condition (es/c = 0). The larger damping produced by a very small squeeze film thickness explains the difference in response amplitude. At a largely off-centered condition (es/c = 0.99) and a low excitation frequency (f < 40 Hz), intermittent contact between the damper journal and its housing occurs as evidenced by a large magnitude recorded dynamic pressure (on the order of MPa). For whirl motions around various static eccentricity positions, es/c = 0.0–0.75, the dynamic load covers a frequency range from 10 Hz to 100 Hz using either a single-frequency excitation or a sine-sweep frequency excitation with a slow growth rate ∼6.5 Hz/s to induce a quasi-steady-state response. The experimental procedure builds complex stiffness in the frequency domain for identification of SFD stiffness, damping, and added mass force coefficients, (K, C, M)SFD. For motions centered around small to large static eccentricities, es/c = 0–0.75, the identified (K, C, M)SFD coefficients from sine-sweep frequency dynamic loads coincide with those extracted from single-frequency dynamic load tests over the same frequency range. Short-length SFD theory predictions for damping coefficients agree with the experimental results. Predicted added mass or inertia coefficients, like the model, fall short of the target experimental magnitudes. The test results give practitioners the credence to certify the ability of a SFD to control rotor response amplitude during typical transient events.

Transient Response of a Short-Length (L/D=0.2) Open-Ends Elastically Supported Squeeze Film Damper: Centered and Largely Off-Centered Whirl Motions

2016 ◽  
Author(s):  
Luis San Andrés ◽  
Sean Den ◽  
Sung-Hwa Jeung
Keyword(s):  
Dynamic Load ◽  
Short Length ◽  
Single Frequency ◽  
Squeeze Film ◽  
Test Rig ◽  
Sweep Frequency ◽  
Transient Events ◽  
Frequency Excitation ◽  
Static Eccentricity ◽  
Sine Sweep

Commonly employed in air breathing (gas turbine) engines, squeeze film dampers (SFDs) reduce the amplitude of rotor vibration while traversing system critical speeds or in transient events such as during a maneuver load, a hard landing, a blade loss, or an engine startup/shutdown sequence that could instantaneously shift a damper journal eccentricity (es) to near its clearance (c). Experiments investigate the dynamic force performance of an open ends, short-length (L/D=0.2) SFD test rig with radial clearance c=267 μm and undergoing centered (es/c=0) to largely off-centered (es/c → 1) whirl orbit motions induced by both a large static load plus a dynamic load. Four rods, symmetrically arranged to resemble a squirrel cage, elastically support the SFD test rig. A hydraulic load system displaces the test damper structure into static eccentricity (es/c). One of two types of dynamic load with amplitude FX=FY excite the SFD: a single-frequency, stepping from low frequency to high frequency discretely; or a sine-sweep frequency growing linearly with time at 6 Hz/s, 33 Hz/s, 40 Hz/s, or 55 Hz/s. For motions departing from es/c=0.0, 0.95, and 0.99 the dynamic load uses a sine-sweep frequency varying from 5 Hz to 245 Hz and evolving rapidly at ∼33 Hz/s. Measurements of SFD displacements characterize the behavior of the SFD rig during its transient response which crosses two system natural frequencies. For motions departing from a largely off-centered condition (es → c), the dynamic load forces the damper to whirl with highly elliptical orbits, in particular while crossing a resonance (damped natural frequency). Moreover, the dynamic motions departing from es∼c are smaller in amplitude than those arising from a centered condition (es/c=0). The larger damping produced by a very small squeeze film thickness explains the difference in response amplitude. At a largely off-centered condition (es/c=0.99) and a low excitation frequency (f < 40 Hz), intermittent contact between the damper journal and its housing occurs as evidenced by a large magnitude recorded dynamic pressure (on the order of MPa). For whirl motions around various static eccentricity positions, es/c=0.0–0.75, the dynamic load covers a frequency range from 10 Hz to 100 Hz using either a single-frequency excitation or a sine-sweep frequency excitation with a slow growth rate ∼6.5 Hz/s to induce a quasi-steady-state response. The experimental procedure builds complex stiffnesses in the frequency domain for identification of SFD stiffness, damping, and added mass force coefficients, (K, C, M)SFD. For motions centered around small to large static eccentricities, es/c=0–0.75, the identified (K, C, M)SFD coefficients from sine-sweep frequency dynamic loads coincide with those extracted from single-frequency dynamic load tests over the same frequency range. Short-length SFD theory predictions for damping coefficients agree with the experimental results. Predicted added mass or inertia coefficients, like the model, fall short of the target experimental magnitudes. The test results give practitioners the credence to certify the ability of a SFD to control rotor response amplitude during typical transient events.

Experimental Performance of an Open Ends, Centrally Grooved, Squeeze Film Damper Operating With Large Amplitude Orbital Motions

2014 ◽  
Author(s):  
Luis San Andrés ◽  
Sung-Hwa Jeung ◽  
Gary Bradley
Keyword(s):  
Large Amplitude ◽  
Mechanical Energy ◽  
Groove Depth ◽  
Forced Response ◽  
Dynamic Loads ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Force Coefficients ◽  
Static Eccentricity ◽  
Physics Model

Aircraft engines customarily implement Squeeze Film Dampers (SFDs) to dissipate mechanical energy caused by rotor vibration and to isolate the rotor from its structural frame. The paper presents experimental results for the dynamic forced performance of an open ends SFD operating with large amplitude whirl motions, centered and off-centered. The test rig comprises of an elastically supported bearing with a damper section, 127 mm in diameter, having two parallel film lands separated by a central groove. Each film land is 25.4 mm long with radial clearance c = 0.251 mm. The central groove, 12.7 mm long, has a depth of 9.5 mm (38c). An ISO VG 2 lubricant flows into the groove via three 2.5 mm orifices, 120 degrees apart, and then passes through the film lands to exit at ambient condition. Two orthogonally placed shakers apply dynamic loads on the bearing to induce circular orbit motions with whirl frequency ranging from 10 Hz to 100 Hz. A static loader, 45° away from each shaker, pulls the bearing to a static eccentricity (es). Measurements of dynamic loads and the ensuing bearing displacements and accelerations, as well as the film and groove dynamic pressures, were obtained for eight orbit amplitudes (r = 0.08c to ∼0.71c) and under four static eccentricities (es = 0.0c to ∼0.76c). The experimental damping coefficients increase quickly as the bearing offset increases (es/c→0.76) while remaining impervious to the amplitude of whirl orbit (r/c→0.51). The inertia coefficients decrease rapidly as the orbit amplitude grows large, r>0.51c, but increase with the static eccentricity. A comparison with test results obtained with an identical damper but having a smaller clearance (cs = 0.141 mm) [1], show the prior damping and inertia coefficients are larger, ∼5.0 and ∼2.2 times larger than the current ones. These magnitudes agree modestly with theoretical ratios for damping and inertia coefficients scaling as (c/cs)3 = 5.7 and (c/cs) = 1.8, respectively. In spite of the large difference in depths between a groove and a film land, the magnitudes of dynamic pressures recorded at the groove are similar to those in the lands. That is, the groove profoundly affects the dynamic forced response of the test damper. A computational physics model replicates the experimental whirl motions and predicts force coefficients spanning the same range of whirl frequencies, orbit radii and static eccentricities. The model predictions reproduce with great fidelity the experimental force coefficients. The good agreement relies on the specification of an effective groove depth derived from one experiment.

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.

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.

Experimental Performance of an Open Ends, Centrally Grooved, Squeeze Film Damper Operating With Large Amplitude Orbital Motions

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Luis San Andrés ◽  
Sung-Hwa Jeung
Keyword(s):  
Large Amplitude ◽  
Gas Turbines ◽  
Mechanical Energy ◽  
Forced Response ◽  
Dynamic Loads ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Force Coefficients ◽  
Squeeze Film Dampers ◽  
Static Eccentricity

Aircraft engines customarily implement squeeze film dampers (SFDs) to dissipate mechanical energy caused by rotor vibration and to isolate the rotor from its structural frame. The paper presents experimental results for the dynamic forced performance of an open ends SFD operating with large amplitude whirl motions, centered and off-centered. The test rig comprises of an elastically supported bearing with a damper section, 127 mm in diameter, having two parallel film lands separated by a central groove. Each film land is 25.4 mm long with radial clearance c = 0.251 mm. The central groove, 12.7 mm long, has a depth of 9.5 mm (38c). An ISO VG 2 lubricant flows into the groove via three 2.5 mm orifices, 120 deg apart, and then passes through the film lands to exit at ambient condition. Two orthogonally placed shakers apply dynamic loads on the bearing to induce circular orbit motions with whirl frequency ranging from 10 Hz to 100 Hz. A static loader, 45 deg away from each shaker, pulls the bearing to a static eccentricity (es). Measurements of dynamic loads and the ensuing bearing displacements and accelerations, as well as the film and groove dynamic pressures, were obtained for eight orbit amplitudes (r = 0.08c to ∼0.71c) and under four static eccentricities (es = 0.0c to ∼0.76c). The experimental damping coefficients increase quickly as the bearing offset increases (es/c → 0.76) while remaining impervious to the amplitude of whirl orbit (r/c → 0.51). The inertia coefficients decrease rapidly as the orbit amplitude grows large, r > 0.51c, but increase with the static eccentricity. A comparison with test results obtained with an identical damper but having a smaller clearance (cs = 0.141 mm) (San Andrés, L., 2012, “Damping and Inertia Coefficients for Two Open Ends Squeeze Film Dampers With a Central Groove: Measurements and Predictions,” ASME J. Eng. Gas Turbines Power, 134(10), p. 102506), show the prior damping and inertia coefficients are larger, ∼5.0 and ∼2.2 times larger than the current ones. These magnitudes agree modestly with theoretical ratios for damping and inertia coefficients scaling as (c/cs)3 = 5.7 and (c/cs) = 1.8, respectively. In spite of the large difference in depths between a groove and a film land, the magnitudes of dynamic pressures recorded at the groove are similar to those in the lands. That is, the groove profoundly affects the dynamic forced response of the test damper. A computational physics model replicates the experimental whirl motions and predicts force coefficients spanning the same range of whirl frequencies, orbit radii, and static eccentricities. The model predictions reproduce with great fidelity the experimental force coefficients. The good agreement relies on the specification of an effective groove depth derived from one experiment.

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

2012 ◽  
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° 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 ∼three times more added mass than the short length damper. The damping coefficients are sensitive to the static eccentricity (up to ∼0.5c) while showing lesser dependency on the amplitude of whirl motion (up to 0.2c). 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 SFD forced performance is tied to the lubricant feed arrangement.

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

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Luis San Andrés ◽  
Sanjeev Seshagiri
Keyword(s):  
Gas Turbines ◽  
Short Length ◽  
System Stability ◽  
Single Frequency ◽  
Squeeze Film ◽  
Test Results ◽  
Piston Rings ◽  
Damping Coefficients ◽  
Squeeze Film Dampers ◽  
San Andres

Aircraft engine rotors, invariably supported on rolling element bearings with little damping, are particularly sensitive to rotor imbalance and sudden maneuver loads. Most engines incorporate squeeze film dampers (SFDs) as a means to dissipate mechanical energy from rotor motions and to ensure system stability. The paper experimentally quantifies the dynamic forced performance of two end sealed SFDs with dimensions and an operating envelope akin to those in actual jet engine applications. The current experimental results complement and extend prior research conducted with open ends SFDs (San Andrés, 2012, “Damping and Inertia Coefficients for Two Open Ends Squeeze Film Dampers With a Central Groove: Measurements and Predictions,” ASME J. Eng. Gas Turbines Power, 134, p. 102506). In the tests, two journals make for two SFD configurations, both with a diameter D = 127 mm and nominal radial film clearance c = 0.127 mm. One short length damper has film lands with extent L = 12.7 mm, while the other has 25.4 mm ( = 2L) land lengths. A central groove of length LG = L and depth at ¾ L separates the film lands. A light viscosity lubricant is supplied into the central groove via three orifices, 120 deg apart, and then flows through the film lands whose ends are sealed with tight piston rings. The oil pushes through the piston rings to discharge at ambient pressure. In the tests, a static load device pulls the damper structure to increasing eccentricities (maximum 0.38c) and external shakers exert single-frequency loads 50–250 Hz, inducing circular orbits with amplitudes equaling ∼5% of the film clearance. The lubricant feed and groove pressures and flow rates through the top and bottom film lands are recorded to determine the flow resistances through the film lands and the end seals. Measured dynamic pressures in the central groove are as large as those in the film lands, thus demonstrating a strong flow interaction, further intensified by the piston ring end seals which are effective in preventing side leakage. Dynamic pressures and reaction loads are substantially higher than those recorded with the open ends dampers. Comparisons to test results for two identical damper configurations but open ended (San Andrés, 2012, “Damping and Inertia Coefficients for Two Open Ends Squeeze Film Dampers With a Central Groove: Measurements and Predictions,” ASME J. Eng. Gas Turbines Power, 134, p. 102506) demonstrate at least a threefold increase in direct damping coefficients and no less than a double increment in added mass coefficients. Predictions from a physics-based model that includes the central groove, the lubricant feed holes, and the end seals' flow conductances are in agreement with the test results for the short length damper. For the long damper, the predicted damping coefficients are in good agreement with the measurements, while the added masses are under-predicted by ∼25%.

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