Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Luis San Andrés
Keyword(s):  
Power Loss ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Experimental Program ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Large Expansion ◽  
Gas Seals ◽  
Gas Volume

As oil fields deplete, in particular in deep sea reservoirs, pump and compression systems work under more strenuous conditions with gas in liquid and liquid in gas mixtures, mostly inhomogeneous. Off-design operation affects system overall efficiency and reliability, including penalties in leakage and rotordynamic performance of secondary flow components, namely seals. The paper details a bulk-flow model for annular damper seals operating with gas in liquid mixtures. The analysis encompasses all-liquid and all-gas seals, as well as seals lubricated with homogenous (bubbly) mixtures, and predicts the static and dynamic force response of mixture lubricated seals; namely: leakage, power loss, reaction forces, and rotordynamic force coefficients, etc., as a function of the mixture volume fraction (βS), supply and discharge pressures, rotor speed, whirl frequency, etc. A seal example with a nitrogen gas mixed with light oil is analyzed. The large pressure drop (70 bar) causes a large expansion of the gas within the seal even for (very) small gas volume fractions (βS). Predictions show leakage and power loss decrease as β→1; albeit at low βS (< 0.3) (re)laminarization of the flow and an apparent increase in mixture viscosity, produce a hump in power loss. Cross-coupled stiffnesses and direct damping coefficients decrease steadily with increases in the gas volume fraction; however, some anomalies are apparent when the flow turns laminar. Mixture lubricated seals show frequency-dependent force coefficients. The equivalent damping decreases above and below βS ∼ 0.10. The direct stiffness coefficients show atypical behavior: a low βS = 0.1 produces stiffness hardening as the excitation frequency increases. Recall that an all liquid seal has a dynamic stiffness softening as frequency increases due to the apparent fluid mass. The predictions call for an experimental program to quantify the static and dynamic forced performance of annular seals operating with (bubbly) mixtures and to validate the current predictive model results.

Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals

2011 ◽  
Author(s):  
Luis San Andre´s
Keyword(s):  
Power Loss ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Experimental Program ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Large Expansion ◽  
Gas Seals ◽  
Gas Volume

As oil fields deplete, in particular in deep sea reservoirs, pump and compression systems work under more strenuous conditions with gas in liquid and liquid in gas mixtures, mostly inhomogeneous. Off-design operation affects system overall efficiency and reliability, including penalties in leakage and rotordynamic performance of secondary flow components, namely seals. The paper details a bulk-flow model for annular damper seals operating with gas in liquid mixtures. The analysis encompasses all-liquid and all-gas seals, as well as seals lubricated with homogenous (bubbly) mixtures, and predicts the static and dynamic force response of mixture lubricated seals; namely: leakage, power loss, reaction forces and rotordynamic force coefficients, etc., as a function of the mixture volume fraction (βS), supply and discharge pressures, rotor speed, whirl frequency, etc. A seal example with a Nitrogen gas mixed with light oil is analyzed. The large pressure drop (70 bar) causes a large expansion of the gas within the seal even for (very) small gas volume fractions (βS). Predictions show leakage and power loss decrease as β → 1; albeit at low βS (<0.3) (re)laminarization of the flow and an apparent increase in mixture viscosity, produce a hump in power loss. Cross-coupled stiffnesses and direct damping coefficients decrease steadily with increases in the gas volume fraction; however some anomalies are apparent when the flow turns laminar. Mixture lubricated seals show frequency dependent force coefficients. The equivalent damping decreases above and below βS∼0.10. The direct stiffness coefficients show atypical behavior: a low βS = 0.1 produces stiffness hardening as the excitation frequency increases. Recall that an all liquid seal has a dynamic stiffness softening as frequency increases due to the apparent fluid mass. The predictions call for an experimental program to quantify the static and dynamic forced performance of annular seals operating with (bubbly) mixtures and to validate the current predictive model results.

Leakage and Force Coefficients of a Grooved Wet (Bubbly Liquid) Seal for Multiphase Pumps and Comparisons With Prior Test Results for a Three Wave Seal

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Xueliang Lu ◽  
Luis San Andrés ◽  
Tingcheng Wu
Keyword(s):  
Pressure Drop ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pressure Ratio ◽  
Excitation Frequency ◽  
Gas Content ◽  
Bubbly Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Ring Seal

Abstract In the subsea oil and gas industry, multiphase pumps and wet gas compressors are engineered choices saving transportation and separation facility costs. In these machines, seals handling multiple phase components must be able to operate without affecting the system efficiency and its dynamic stability. This paper, extending prior work conducted with uniform clearance and wavy surface annular seals, presents measurements of leakage and dynamic force coefficients in a grooved seal whose dimensions are scaled from an impeller wear ring seal in a boiler feed pump. The 14-grooves seal has diameter D = 127 mm, length L = 0.34 D, and clearance c = 0.211 mm; each groove has shallow depth dg ∼2.6 c and length Lg ∼ 3.4% L. At a shaft speed of 3.5 krpm (surface speed = 23.3 m/s), a mixture of air in ISO VG 10 oil with inlet gas volume fraction (GVF) ranging from 0 (just oil) to 0.7 (mostly air) lubricates the seal. The pressure ratio (inlet/exit) is 2.9. The flow is laminar since the liquid is viscous and the pressure drop is low. The measured mixture mass flow decreases continuously with an increase in inlet GVF. The seal stiffnesses (direct K and cross coupled k), added mass (M), and direct damping (C) coefficients are constant when the supplied mixture is low in gas content, GVF ≤ 0.1. As the gas content increases, 0.2 ≤  GVF ≤ 0.5, the seal direct dynamic stiffness becomes nil with an increase in excitation frequency, whereas k and C reduce steadily with GVF. In general, for GVF ≤ 0.5, the direct damping is invariant with frequency; variations appearing for GVF = 0.7. Compared against a three wave annular seal, the grooved seal offers much lower force coefficients, in particular the viscous damping. Thus, for laminar flow operation (heavy oil) with a low pressure drop as in a wear ring seal, a three wave seal is recommended as it also offers a significant centering stiffness.

On the Influence of Gas Content on the Rotordynamic Force Coefficients of a Three-Wave (Air in Oil) Annular Seal for Multiple Phase Pumps

2019 ◽  
Author(s):  
Luis San Andrés ◽  
Xueliang Lu ◽  
Tingcheng Wu
Keyword(s):  
Oil And Gas ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Gas Content ◽  
Radial Clearance ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Wet Gas

Abstract The subsea oil & gas industry efficiently uses multiphase pumps and wet gas compressors to eliminate upstream oil and gas separation stations, hence saving up to 30% in capital expenditures. Subsea multiphase process facilities must operate reliably for extended lengths of time while the wells, as they deplete, produce a process fluid varying from a pure liquid, to a mixture of gas and liquid, and to eventually just gas. The variation of gas volume fraction (GVF), by affecting the leakage and dynamic forced performance of sealing elements, alters turbomachinery performance to produce both an increase in synchronous speed rotor vibrations and a reduction in rotor dynamic stability. Prior laboratory work shows that plain cylindrical surface annular seals operating with a fluid flow in the laminar flow regime produce no direct (centering) stiffness and a large added mass, in particular for the liquid only condition. The early work also advanced a simple three-wave shape seal (akin to lobes) that generates a significant direct stiffness, impervious to GVF as large as 90%, and hence aids to increase the natural frequency of a vertical pump. Dynamic load tests for this wavy-seal configuration operating with a gas in liquid mixture [air in light ISO VG 10 oil] are the subject of this paper that presents dynamic force coefficients vs. excitation frequency (ω) while the shaft turns at a speed (Ω) equal to 3.5 krpm (23.3 m/s surface speed), a typical operating speed for multiphase pumps. The test seal has length L = 43 mm, diameter D = 127 mm, and a mean radial clearance cm = 0.191 mm. For operation with a pure liquid (GVF = 0), the seal force coefficients are frequency independent, thus a stiffness (K) - damping (C) − Mass (M) model fully characterizes the test article. On the other hand, for operation with an air in oil mixture, the test seal dynamic stiffness coefficients vary greatly with excitation frequency; the direct dynamic stiffness hardens while the cross coupled stiffness decreases as the frequency approaches running speed (ω &lt; Ω) and then increases for super synchronous frequency excitations (ω &gt; Ω). For operation with GVF from 0.1 to 0.8, the wavy seal produces a positive centering dynamic stiffness with large magnitude; a most desirable feature for a vertically installed pump. Notably, the seal direct damping coefficient (C) does not depend on the excitation frequency though reduces continuously as the inlet GVF increases from 0 to 1. For operation with either a pure liquid or a pure air conditions, a computational fluid dynamics (CFD) analysis accurately captures the seal leakage and force coefficients. The current research product adds relevant test data to better the design selection of seals in multiphase pumps.

Leakage and Force Coefficients of a Grooved Wet (Bubbly Liquid) Seal for Multiphase Pumps and Comparisons With Prior Test Results for a Three Wave Seal

2019 ◽  
Author(s):  
Xueliang Lu ◽  
Luis San Andrés ◽  
Tingcheng Wu
Keyword(s):  
Pressure Drop ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pressure Ratio ◽  
Excitation Frequency ◽  
Gas Content ◽  
Bubbly Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Ring Seal

Abstract In the subsea oil and gas industry, multiphase pumps and wet gas compressors are engineered choices saving transportation and separation facility costs. In these machines, seals handling multiple phase components must be able to operate without affecting the system efficiency and its dynamic stability. This paper, extending prior work conducted with uniform clearance and wavy surface annular seals, presents measurements of leakage and dynamic force coefficients in a grooved seal whose dimensions are scaled from an impeller wear ring seal in a boiler feed pump. The 14-grooves seal has diameter D = 127 mm, length L = 0.34 D, and clearance c = 0.211 mm; each groove has shallow depth dg ∼2.6 c and length Lg ∼ 3.4% L. At a shaft speed of 3.5 krpm (surface speed = 23.3 m/s), a mixture of air in ISO VG 10 oil with inlet gas volume fraction (GVF) ranging from 0 (just oil) to 0.7 (mostly air) lubricates the seal. The pressure ratio (inlet/exit) is 2.9. The flow is laminar since the liquid is viscous and the pressure drop is low. The measured mixture mass flow decreases continuously with an increase in inlet GVF. The seal stiffnesses (direct K and cross coupled k), added mass (M), and direct damping (C) coefficients are constant when the supplied mixture is low in gas content, GVF ≤ 0.1. As the gas content increases, 0.2 ≤ GVF ≤ 0.5, the seal direct dynamic stiffness becomes nil with an increase in excitation frequency, whereas k and C reduce steadily with GVF. In general, for GVF ≤ 0.5 the direct damping is invariant with frequency; variations appearing for GVF = 0.7. Compared against a three wave annular seal, the grooved seal offers much lower force coefficients, in particular the viscous damping. Thus, for laminar flow operation (heavy oil) with a low pressure drop as in a wear ring seal, a three wave seal is recommended as it also offers a significant centering stiffness.

On the Leakage, Torque, and Dynamic Force Coefficients of Air in Oil (Wet) Annular Seal: A Computational Fluid Dynamics Analysis Anchored to Test Data

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Luis San Andrés ◽  
Jing Yang ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Liquid Content ◽  
Liquid Stream ◽  
Force Coefficients ◽  
Annular Seal ◽  
Gas Volume

Subsea pumps and compressors must withstand multiphase flows whose gas volume fraction (GVF) or liquid volume fraction (LVF) varies over a wide range. Gas or liquid content as a dispersed phase in the primary stream affects the leakage, drag torque, and dynamic forced performance of secondary flow components, namely seals, thus affecting the process efficiency and mechanical reliability of pumping/compressing systems, in particular during transient events with sudden changes in gas (or liquid) content. This paper, complementing a parallel experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power, and dynamic force coefficients of a smooth surface, uniform clearance annular seal supplied with air in oil mixture whose inlet GVF varies discretely from 0.0 to 0.9, i.e., from a pure liquid stream to a nearly all-gas content mixture. The test seal has uniform radial clearance Cr = 0.203 mm, diameter D = 127 mm, and length L = 0.36 D. The tests were conducted with an inlet pressure/exit pressure ratio equal to 2.5 and a rotor surface speed of 23.3 m/s (3.5 krpm), similar to conditions in a pump neck wear ring seal. The CFD two-phase flow model, first to be anchored to test data, uses an Euler–Euler formulation and delivers information on the precise evolution of the GVF and the gas and liquid streams' velocity fields. Recreating the test data, the CFD seal mass leakage and drag power decrease steadily as the GVF increases. A multiple-frequency shaft whirl orbit method aids in the calculation of seal reaction force components, and from which dynamic force coefficients, frequency-dependent, follow. For operation with a pure liquid, the CFD results and test data produce a constant cross-coupled stiffness, damping, and added mass coefficients, while also verifying predictive formulas typical of a laminar flow. The injection of air in the oil stream, small or large in gas volume, immediately produces force coefficients that are frequency-dependent; in particular the direct dynamic stiffness which hardens with excitation frequency. The effect is most remarkable for small GVFs, as low as 0.2. The seal test direct damping and cross-coupled dynamic stiffness continuously drop with an increase in GVF. CFD predictions, along with results from a bulk-flow model (BFM), reproduce the test force coefficients with great fidelity. Incidentally, early engineering practice points out to air injection as a remedy to cure persistent (self-excited) vibration problems in vertical pumps, submersible and large size hydraulic. Presently, the model predictions, supported by the test data, demonstrate that even a small content of gas in the liquid stream significantly raises the seal direct stiffness, thus displacing the system critical speed away to safety. The sound speed of a gas in liquid mixture is a small fraction of those speeds for either the pure oil or the gas, hence amplifying the fluid compressibility that produces the stiffness hardening. The CFD model and a dedicated test rig, predictions and test data complementing each other, enable engineered seals for extreme applications.

On the Influence of Gas Content on the Rotordynamic Force Coefficients of a Three-Wave (Air in Oil) Annular Seal for Multiple Phase Pumps

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Luis San Andrés ◽  
Xueliang Lu ◽  
Tingcheng Wu
Keyword(s):  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Gas Content ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Pump Efficiency ◽  
Force Coefficients ◽  
Annular Seal ◽  
Design Selection

Abstract Subsea multiphase pumps must operate reliably with a process fluid transitioning from a pure liquid, to a mixture of gas and liquid, and to eventually just gas; and pressure seals controlling secondary leakage paths are important for both pump efficiency and dynamic stability considerations, in particular, for flows with a sizable gas volume fraction (GVF). Early work advances a three-wave shape seal that generates significant direct stiffness and hence aids to increase the natural frequency of a vertical pump. This paper details dynamic load tests and produces rotordynamic force coefficients for the wavy-seal operating with a gas in liquid mixture made of air in light ISO VG 10 oil. For operation with pure liquid, GVF = 0, a stiffness (K), damping (C), and added mass (M) model fully characterizes the test article. For operation with a mixture, the seal dynamic stiffness coefficients vary greatly with excitation frequency; the direct dynamic stiffness hardens while the cross coupled stiffness decreases as the whirl frequency approaches shaft speed and then increases for super synchronous frequency. For operation with GVF from 0.1 to 0.8, the seal produces a large positive centering dynamic stiffness. Notably, the seal direct damping coefficient does not depend on frequency though reduces continuously as the inlet GVF increases from 0 to 1 (all gas). The current research adds relevant test data and unique dynamic force coefficients to the design selection of seals in multiphase pumps.

On the Leakage, Torque and Dynamic Force Coefficients of an Air in Oil (Wet) Annular Seal: A CFD Analysis Anchored to Test Data

2018 ◽  
Author(s):  
Luis San Andrés ◽  
Jing Yang ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Liquid Content ◽  
Liquid Stream ◽  
Force Coefficients ◽  
Annular Seal ◽  
Gas Volume

Subsea pumps and compressors must withstand multi-phase flows whose gas volume fraction (GVF) or liquid volume fraction (LVF) varies over a wide range. Gas or liquid content as a dispersed phase in the primary stream affects the leakage, drag torque, and dynamic forced performance of secondary flow components, namely seals, thus affecting the process efficiency and mechanical reliability of pumping/compressing systems, in particular during transient events with sudden changes in gas (or liquid) content. This paper, complementing a parallel experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power and dynamic force coefficients of a smooth surface, uniform clearance annular seal supplied with an air in oil mixture whose inlet GVF varies discretely from 0.0 to 0.9, i.e., from a pure liquid stream to a nearly all gas content mixture. The test seal has uniform radial clearance Cr = 0.203 mm, diameter D = 127 mm, and length L = 0.36 D. The tests were conducted with an inlet pressure/exit pressure ratio equal to 2.5 and a rotor surface speed of 23.3 m/s (3.5 krpm), similar to conditions in a pump neck wear ring seal. The CFD two-phase flow model, first to be anchored to test data, uses an Euler-Euler formulation and delivers information on the precise evolution of the GVF and the gas and liquid streams’ velocity fields. Recreating the test data, the CFD seal mass leakage and drag power decrease steadily as the GVF increases. A multiple-frequency shaft whirl orbit method aids in the calculation of seal reaction force components, and from which dynamic force coefficients, frequency dependent, follow. For operation with a pure liquid, the CFD results and test data produce a constant cross-coupled stiffness, damping, and added mass coefficients, while also verifying predictive formulas typical of a laminar flow. The injection of air in the oil stream, small or large in gas volume, immediately produces force coefficients that are frequency dependent; in particular the direct dynamic stiffness which hardens with excitation frequency. The effect is most remarkable for small GVFs, as low as 0.2. The seal test direct damping and cross-coupled dynamic stiffness continuously drop with an increase in GVF. CFD predictions, along with results from a bulk-flow model (BFM), reproduce the test force coefficients with great fidelity. Incidentally, early engineering practice points out to air injection as a remedy to cure persistent (self-excited) vibration problems in vertical pumps, submersible and large size hydraulic. Presently, the model predictions, supported by the test data, demonstrate that even a small content of gas in the liquid stream significantly raises the seal direct stiffness, thus displacing the system critical speed away to safety. The sound speed of a gas in liquid mixture is a small fraction of those speeds for either the pure oil or the gas, hence amplifying the fluid compressibility that produces the stiffness hardening. The CFD model and a dedicated test rig, predictions and test data complementing each other, enable engineered seals for extreme applications.

CFD Analysis of the Influence of Gas Content on the Rotordynamic Force Coefficients for a Circumferentially Grooved Annular Seal for Multiple Phase Pumps

2021 ◽  
Author(s):  
Tingcheng Wu ◽  
Luis San Andrés ◽  
Xueliang Lu
Keyword(s):  
Volume Fraction ◽  
Excitation Frequency ◽  
Experimental Results ◽  
Pure Liquid ◽  
Phase Flow ◽  
Cfd Analysis ◽  
Two Phase ◽  
Force Coefficients ◽  
Gas Volume Fraction ◽  
Gas Volume

Abstract Pumping efficiency and rotordynamic stability are paramount to subsea multiphase pump operation since, during the life of a well, the process fluid transitions from a pure liquid to a mixture of gas in liquid to just gas. Circumferentially grooved seals commonly serve as balance pistons in pumps while also restricting secondary flow. Prior experimental results obtained with a grooved seal operating with a mixture of air and mineral oil show the seal rotordynamic force coefficients vary significantly with the gas volume fraction (GVF). This paper, complementing an exhaustive experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power, and dynamic force coefficients of a circumferentially grooved seal supplied with air in oil mixture with a GVF varying from 0 to 0.7. The test seal has fourteen grooves, an overall axial length of 43.6 mm and a radial clearance of 0.211 mm. The 127 mm diameter rotor spins at constant angular speed (Ω = 3,500 rpm). The mixture enters the seal at a supply pressure (Pin) of 2.9 bar(a), and the seal exit pressure (Pout) is 1 bar(a). The CFD two-phase flow simulations utilize the Euler-Euler multiphase model to predict the mass flow rate and the pressure field as a function of the operating conditions. Using a multi-frequency shaft orbit motion method, the CFD simulations deliver the variations of reaction force on the rotor with respect to the excitation frequency. For a pure liquid condition (GVF = 0), both the CFD and experimental results produce constant stiffness, damping and added mass coefficients. The experimental and CFD results demonstrate the seal rotordynamic force coefficients are quite sensitive to the gas volume fraction (GVF). When introducing a small amount of air into the oil (GVF = 0.1), the direct damping coefficient increases by approximately 10%. For operation with a mixture with inlet GVF &gt; 0.1, the cross-coupled stiffness coefficients develop strong frequency dependent characteristics. In contrast, the direct damping coefficient has a negligible variation with excitation frequency. The CFD predictions, as well as the experimental results, evidence that air injection in a liquid stream can significantly change the seal rotordynamic characteristics, and thus can affect the rotordynamic stability of a pump. An accurate CFD analysis thus enables engineers to design reliable grooved seals operating under two-phase flow conditions.

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.

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