Squeeze Film Damper Research Articles

Theoretical and Experimental Investigation of Porous Tilting Pad Gas Bearings with Hermetic Squeeze Film Dampers Based on Multilayer Diaphragm Structure

A novel porous tilting pad gas bearing (PTPGB) with hermetic squeeze film dampers based on multilayer diaphragm structure (MLD-HSFD) is proposed for oil-free turbomachinery. A dynamic model of MLD-HSFDs including the frequency dependence effect is presented by considering the compressibility of the damper fluid. An experimental test rig was assembled to measure the performance of MLD-HSFDs. The model predicts well the test data, including the frequency dependence of force coefficients. A comprehensive theoretical model of PTPGBs with MLD-HSFDs is proposed based on the implementation of the isothermal compressible Reynolds equation coupled to a flexible support and porous models. The effects of thickness of diaphragms thickness, bearing clearance, and supply pressure on bearing performance are discussed.

Experimental Verification of and Physical Interpretation for Adsorption-Dependent Squeeze-Film Damping

The squeeze-film-damping effect is one of the main limits in many precision experiments, especially in the study of short-range interactions, and its physical mechanism is still not very clear. We develop a torsion pendulum to measure the damping effects caused by the thermal motion of residual gas between a cubic test mass and a pair of symmetric movable plates. The measured results are consistent with the model that synthesized the elastic and inelastic collisions by introducing a thermal accommodation coefficient (TAC). In our research, the pressure dependence of the TAC, which can be expressed as an exponential decay function, is also observed. This dependence may imply that the elastic collisions correspond to the simple bouncing of residual gas molecules, while the inelastic collisions correspond to the adsorption and desorption cycle of gas molecules on the surface. The method in this work and the discovered TAC pressure dependence are instructive for the analysis of residual-gas effects in weak-force measurements, as well as the deviation correction of rarefied gas pressure measurements based on the squeeze-film-damping effect.

A Study on the Thermal Properties of Oil-Film Viscosity in Squeeze Film Dampers

Considering the variation in temperature of the oil film in squeeze film dampers (SFDs) caused by squeezing, a more comprehensive analysis of SFD can be obtained. Aiming to investigate the viscosity thermal effect of the oil film in SFDs, this study established a 3D CFD solution model. Based on the total energy model, the viscosity thermal effect was performed. With the mixture multi–phase flow model, the Zwart–Gerber–Belamri (Z–G–B) cavitation model, and the use of the additional mass coefficient, the two–phase flow phenomenon in SFDs was discussed. The oil film at various temperatures and the temperature distribution of different oil types under different working conditions were analyzed. Furthermore, the influence of the SFD thermal effect on the two–phase flow phenomenon were particularly carried out. Meanwhile, the simulation results of the SFD thermal effect were experimentally verified. The results revealed that the maximum temperature of the SFD oil film was enhanced with the increase in the eccentricity ratio and precession frequency. The temperature of the oil film was closely related to the oil dynamic viscosity. The dynamic viscosity of the oil was reduced, which was caused by the SFD thermal effect, thus leading to decreased oil–film damping, enlarging the vaporization level and the range of vapor cavitation, as well as the ingested air amount. CFD simulation results of the thermal effect were in good agreement with the experimental data, which verified the accuracy of the proposed model.

A data driven method applied on nonlinear vibration of flexible rotor supported on centralized squeeze film damper

This paper discusses the application of Dynamic Mode Decomposition (DMD) on vibration response of flexible rotor supported by a Centralized Squeeze Film Damper (CSFD). The mathematics behind DMD and its applications to rotor vibration data such as linearization, reconstruction has been established. Vibration data from the flexible rotor system supported on CSFD exhibits both linear and nonlinear behavior. Further, DMD has been applied on periodic and quasi-periodic vibration data of CSFD for prediction and forecasting. DMD is observed to have successfully linearized a nonlinear system with the linear Henkel Matrix. The reconstruction and forecasting of time series data from rotor has been achieved with a maximum error of 0.2% even for nonlinear vibration data. Further, White Gaussian Noise has been intermixed with CSFD data to demonstrate the noise reduction capability of DMD method for nonlinear systems. Lastly, the application of DMD algorithm on experimental data from Jeffcott rotor based test setup has been shown.

Noise multiplication and bandwidth of photodetectors employed with Taylor dispersion in micro optical fiber channel system

Abstract This work has clarified the noise multiplication and bandwidth of photodetectors employed with Taylor dispersion in micro optical fiber channel system. The simulation performance evaluation of slide and squeeze film damping and fluidics mechanics. The damping ratio versus gap distance for a cantilever beam and a mass suspended from beams are determined. The damping ratio with gap size for a suspended mass with and without holes is reported. The damping ratio variations with the gap distance variations for a mass suspended from beams is clarified. The velocity field for fluid flow in a circular channel, a square channel, a rectangular channel, a parabolic channel and a triangular channel is estimated. Besides the velocity field for the fluid flow in a channel with and without slip is outlined. The spreading of a diffusion front in one dimension in a resting fluid and the dispersion coefficient in a square channel [Taylor dispersion in micro fluidic channels] are clarified. The 2D diffusion profile of a solute in a T mixer and normalized concentration versus the channel width for the solute at the outlet of H filter are determined.

Dynamic Characteristics of Elastic Ring Squeeze Film Damper Oscillated by Bearing Contact Force

Dynamic Characteristics of Elastic Ring Squeeze Film Damper Oscillated by Bearing Contact Force

Dynamical modeling and experimental validation for squeeze film damper in bevel gears

Squeeze film damper (SFD) effectively reduces rotor motion amplitude while crossing critical speeds for vibration and noise reduction in a wide application of aero-engine rotor system. The squirrel cage elastic support (SCES) as an essential component of SFD, accurate modelling of SCES using component modal synthesis (CMS) to account for its flexibility, and calculation of nonlinear oil film forces for SFD using the finite difference method. The CMS method is also used to model the bevel gear wheel body and to establish a finite element nodal dynamics model of the gear-rotor-bearing-SFD system considering time-varying mesh stiffness, tooth clearance, gyroscopic effects, transmission error excitation and SFD oil film forces. The modal frequency of the gear shaft in aero-engine power transmission is exercised to verify the established bevel gear model. Moreover, a bevel gear test platform with SFD is established to study the vibration reduction effect of SFD. It is found that SFD can effectively improve the transmission of the bevel gear system, and the flexibility of the SCES makes the critical speed shift. Actually, the smaller the stiffness of SCES, the more the critical speed is moved to the left. By using CMS to determine the flexibility of bevel gear and SCES, it can show the complete phenomenon of the dynamic behaviors of the bevel gear system with SFD.

Impact of Whirl and Axial Motion on Ball Bearing Turbocharger Dynamics

Ball bearing turbochargers (TCs) incorporate an angular contact ball bearing cartridge to reduce friction and oil consumption, improving the efficiency of internal combustion engines. In this investigation, axial and radial TC rotor motion was experimentally measured and used to develop a model of the TC rotor-bearing system, allowing for a detailed analysis of the TC bearing under varying operating conditions. In order to achieve the experimental objectives of this investigation, eddy-current proximity probes were used to measure the radial motion at the turbine and compressor sides of the TC. The measured radial motion shows whirl with subharmonics at low speed. The measured axial motion of the rotor was found to increase with TC speed. In order to analytically investigate the bearing dynamics, a complete TC model was developed that includes the mass distribution and flexibility of the TC compressor, shaft and turbine, and squeeze-film dampers (SFDs) that support the bearing cartridge. The model was used to replicate the whirl and axial motion of the test rig and then to determine which model parameters could be adjusted to minimize whirl without negatively affecting the bearing dynamics. Simulation results revealed that centrifugal effects cause a change in the bearing internal geometry, with a small clearance becoming a preload at higher speeds. When this effect is coupled with less compliant SFDs, the subharmonics are reduced and the overall sliding and number of large load cycles at the ball–race contacts are minimized, contributing to lower bearing friction and improved overall life.

Influence of a transient bubble dynamics cavitation model for squeeze film dampers on the run‐up behaviour of a turbocharger rotor

AbstractThe force response of squeeze film dampers and hydrodynamic bearings is significantly influenced by the occurence of cavitation inside the lubricant films. The viscosity of the occuring mixture of oil and air bubbles is vastly different than that of pure lubricant and therefore changes the pressure build‐up and thereby the stiffness and damping properties of the lubrication films. To accurately predict the force response of a squeeze film damper, the cavitation and its effect on the pressure build‐up therefore has to be taken into account. Well known cavitation algorithms for lubrication problems, like the Elrod algorithm or the two‐phase‐model, neglect the transient nature of outgassing and assume instantaneous bubble formation and collapse. In the presented paper, a transient bubble dynamics model based on the Rayleigh‐Plesset‐Scriven equation is utilised instead and its effect on the rotordynamic behaviour of a turbocharger rotor is examined based on fully transient multi body dynamics simulations.

The Numerical Identification of Basins of Attraction for the Vibration Response of the Rigid Rotor with Squeeze Film Dampers

The article deals with the computational study of the rigid rotor coupled with squeeze film dampers. Various techniques such as the method of computation of the synchronous response with a circular centred orbit, the harmonic balance method, and the direct time integration method are used to analyse the nonlinear behaviour of the rotor system. The results indicate that the rotor system can exhibit both a synchronous circular response with a large orbit radius and a nonsynchronous response with a quasiperiodic character. However, both responses are undesirable in rotating machinery and should be avoided. The new results are presented to provide insight into the impact of initial conditions on the vibration response via basins of attraction. The simulations show that: (i) the basins of attraction are more sensitive to the choice of the initial velocities than displacements, (ii) the basins of attraction are noticeably dependent on the rotor speed in the region of a nonsynchronous response, and (iii) the border between the basins of attraction can be smooth or without a clear structure. The research brings clear conditions defined by parameters such as the dimensionless SFD constant, unbalance, and rotational speed for the suppression of undesirable nonlinear phenomena. The results suggest that the damper can effectively improve the vibration response of high-speed rotating machinery, but its design must be chosen appropriately.

Frequency dependency of dynamic force coefficients for hermetic squeeze film dampers utilizing fluid-bounding flexible structures

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 introduces analytical models, which are used to explain the frequency dependency of force coefficients observed in past experimental testing of HSFD. Furthermore, the insights gained from the analytical models are used to conceive a new frequency independent damper architecture. 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.

Design process and simulations for the rotor system of a high-efficiency 22 kW micro-gas-turbine range extender for electric vehicles

This paper proposes a design process for a high-efficiency micro-gas-turbine (MGT)-based range extender(RE). The study includes a conceptual system design and a detailed design of an MGT RE. This design adopts a two-spool intercooled and recuperated high-speed MGT. The study focuses on the design of a low-pressure (LP) rotor system integrated with an electric generator, where a permanent magnet synchronous generator (PMSG) with a round transversally polarized bar permanent magnet (PM) is selected as a generator type. The turbine and compressor sides of the rotor are supported by dual back-to-back angular contact ball bearings modeled using a detailed five degrees of freedom contact model. The bearing cartridge is supported by squeeze film dampers (SFDs). The SFD that supports the bearings is modeled with a linear spring and an oil-film damper. Simulation results dictate that stresses in the magnet and sleeve vary due to several design parameters, thus time-efficient simulation is strongly required for effective design optimization. Also, the results indicate that the SFD design optimization range leading to acceptable rotordynamics requirements is narrow.

Nonlinear Dynamic Responses of a Rotor-Bearing System with Eccentric Squeeze Film Dampers

A squeeze film damper (SFD) is a commonly used component in aeroengine support structures. However, eccentric SFDs are often employed in practical applications. Existing research in this field has mainly focused on simple rotor models and frequency-domain solution techniques. In this study, a rotor system tester with and without an eccentric SFD was built, and a simulation model based on the finite element method and fixed interface modal synthesis method was proposed. Then, the nonlinear dynamic response of the rotor system during run-up and run-down was studied based on the tester and simulation model. The results show that an eccentric SFD affords zero frequency and a series of double frequencies in the rotor system response. An eccentric SFD may cause the increase of the critical speed, amplitude jump, and displacement amplitude oscillation of the rotor system during run-up/run-down. Additionally, it may cause the acceleration response at the mounting bracket to significantly increase when the rotor system is suddenly accelerated.

High-Speed Digital Photography of Vapor Cavitation in a Narrow Gap Flow

Digital photography of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, demands a high time-resolution and a solution to approaching the particular spatial restrictions. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for vapor bubble generation and collapse is about one millisecond, respectively. The authors have developed a Journal Bearing Model Experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. Compared with other methods, e.g., pulsed laser, electrical discharge, tube arrest, applied to produce vapor bubbles, the work on hand applies a dynamic variation of the minimum film thickness to produce suction cavitation, which proves the applicability of this novel approach to study vapor cavitation in fluid films similar to lubricant flows. The results are obtained by means of digital high-speed photography of vapor bubbles from inception to implosion triggered by the dynamic variation of the minimum film thickness of a narrow gap flow. Moreover, the results are set in relation to a general overview of cavitation processes.

An efficient method for transient response of rotor systems based on squeeze film damper

The rotor system operation includes a series of nonlinear factors, and the optimization of computational methods is vital to increasing industrial productivity. Here we show a method(LCM, local coefficient method) actualized by coefficients interpolation to rapidly calculate the unbalance response of the oil film-supported rotor system. A database with various coefficients is developed to approximate the time-varying oil film force of dampers. The performance difference between the LCM and the conventional method was given in various unbalanced masses and operating conditions. We perform experimental tests and numerical analysis to quantify the effectiveness and efficiency of the LCM. In addition, we elaborate on parameters that affect the accuracy and suggest the application range of the LCM for general rotor system.

Dynamic Characteristics of Rotor-Squeeze Film Damper-Support System Excited by Base Harmonic Excitations Using MHB-AFT Method

Abstract When operating at high speed, aeroengines mounted on the aircrafts also perform complicated maneuvering flights along with the aircrafts. The engine rotor systems will undergo forced motions excited by base movements and mass unbalance, which may lead to severe vibrations. Squeeze film damper (SFD) is generally used for vibration damping in aeroengine, but it also introduces structural nonlinearity like bistable jump. Moreover, the reliability of SFD is also affected by base excitations. Therefore, it is necessary to investigate the nonlinear dynamic behavior of rotor-SFD-support system excited by base motions. Taking a muti-disk rotor shaft supported by two SFDs with squirrel cages as the research object to simulate a gas generator in a turboshaft engine, the steady-state responses of the rotor system were calculated by multidimensional harmonic balance combined with alternating frequency/time domain method (MHB-AFT). The effects of base harmonic rotations and mass unbalance on steady-state responses of rotor system were investigated. The results indicate that the time-varying parametric excitations of base motions have strong effects on amplitude–frequency response of transverse displacement of rotor system. The critical speeds and resonant amplitudes of responses change with the magnitude and frequency of several base harmonic rotations. The variation of the frequency of base harmonic motion has the most significant impact on the amplitude–frequency response of transverse displacement of rotor system. The increase of base harmonic frequency will lead to multiple local peaks in the response curves, especially in the case of base harmonic rolling motion. In addition, the combination of base harmonic rotation around pitching and yawing axes results in significantly different response characteristics. Therefore, the influence of base harmonic motions should be considered during the structural design and damping optimization of SFDs.

Assembly Characteristics and Experimental Study of Rotor System with Elastic Ring Squeeze Film Damper

Assembly Characteristics and Experimental Study of Rotor System with Elastic Ring Squeeze Film Damper

Performance Analysis and Test Verification of Porous Tilting Pad Bearings with Hermetically Sealed Squeeze Film Damper in Parallel

Performance Analysis and Test Verification of Porous Tilting Pad Bearings with Hermetically Sealed Squeeze Film Damper in Parallel

Bandwidth Optimization of MEMS Accelerometers in Fluid Medium Environment.

There is a constraint between the dynamic range and the bandwidth of MEMS accelerometers. When the input acceleration is comparatively large, the squeeze film damping will increase dramatically with the increase in the oscillation amplitude, resulting in a decrease in bandwidth. Conventional models still lack a complete vibration response analysis in large amplitude ratios and cannot offer a suitable guide in the optimization of such devices. In this paper, the vibration response analysis of the sensing unit of an accelerometer in large amplitude ratios is first completed. Then, the optimal design of the sensing unit is proposed to solve the contradiction between the dynamic range and the bandwidth of the accelerometer. Finally, the results of the vibration experiment prove that the maximum bandwidth can be achieved with 0~10g external acceleration, which shows the effectiveness of the design guide. The new vibration analysis with the complete model of squeeze film damping is applicable to all sensitive structures based on vibration, not limited to the MEMS accelerometer studied in this thesis. The bandwidth optimal scheme also provides a strong reference for similar structures with large oscillation amplitude ratios.

A Model and Experimental Validation for a Piston Rings—Squeeze Film Damper: A Step Toward Quantifying Air Ingestion

Abstract Rotor-bearing systems often rely on squeeze film dampers (SFDs) to increase the dynamic stability and reduce rotor motion amplitudes while traversing critical speeds. In aircraft engines, to increase the damping capacity within a limited physical space, piston rings (PRs) seal the axial ends of a squeeze film land. However, lubricant still leaks through the slit in the PR abutted ends, and air enters into the film to make a bubbly oil mixture with a much reduced damping capability. This paper presents a volume of fluid (VOF) model for a PR sealed ends SFD facing ambient air (not submerged in lubricant and prone to air entrainment) and delivers predictions benchmarked against experimental results obtained in a dedicated test rig. A lubricant feeds pressure and flows large enough to prevent air ingestion vary with the damper geometry, the lubricant inlet and outlet conditions, and the kinematics of the journal. A parametric study for a typical SFD shows the period-averaged gas volume fraction (GVF) increases as the journal squeeze film velocity (vs) increases and as the film clearance decreases. Most importantly, the location of the PR slit relative to the feedhole affects the amount of air drawn into the film. When the PR slit faces a feedhole, the film land is mostly filled with a pure lubricant. The GVF increases as the arc distance from the PR slit to the feedhole increases. The physical model, anchored by the test data, effectively addresses a fundamental challenge in SFD design and operation; namely, quantifying the amount of air ingested and its effect on the damper forced performance.