Short Squeeze Film Dampers Research Articles

Simulation Analysis of Non-concentric Squeeze Film Damper

Squeeze film dampers are components that provide additional damping for rotating motors. In general, in order to achieve the best results of the squeeze film damper, it is necessary to appropriately increase the damping value, reduce the stiffness and set a reasonable eccentricity. In the process of designing the squeeze film damper, we can apply the rotor dynamics module of COMSOL software to model and simulate it, so as to achieve better simulation results and lay a foundation for the subsequent development and design of the product. In COMSOL software, in order to simplify the modeling of rotor components, we usually model squeeze film dampers based on the damping coefficient. The model calculates the damping coefficient for a short squeeze film damper and compares the results with the analytically calculated values. In addition, the damping coefficient depends on the position of the journal in the damper, i.e., the magnitude of the eccentricity. In this paper, by analyzing the dimensionless damping coefficient, bearing stiffness, journal displacement, and fluid load at different eccentricity, and plotting the fluid pressure distribution and the average oil film flow rate of the squeeze film damper, we can find the most suitable range of eccentricity and the damage-prone part of the damper, which can provide an important reference for the actual design of the squeeze film damper.

Dynamic Characteristics of MR Fluid Short Squeeze Film Damper in Terms of Reynolds Number

Magnetorheological (MR) fluids are suspensions of fine micron-sized particles suspended in an appropriate carrier medium. Their rheological properties can be controlled by the application of an appropriate magnetic field and can be used in a variety of applications where damping and stiffness characteristics need to be controlled at a particular excitation frequency, based on the requirements. This cannot be accomplished with conventional fluids and thus MR fluids find application in squeeze film dampers of aircraft jet engines to provide variable damping in accordance with the magnetic field, at a particular excitation frequency. Limited information is available on the stiffness and damping characteristics of magnetorheological fluid squeeze film dampers in the literature. This paper provides information on the stiffness and damping characteristics of MR fluids used as external damping medium in Squeeze film Dampers in terms of the Reynolds number of the squeeze film. The paper calibrates the stiffness and damping characteristics of particular magnetorheological fluid squeeze film damper theoretically in terms of Reynolds number of the squeeze film for two clearance and L/D ratios operating at low eccentricity ratios, using a constant field viscosity model. The stiffness and damping characteristics are found to decrease with the increase in Reynolds number. The Reynolds number of the squeeze film is very low, highlighting the fact that the flow in the film has ceased and has solidified in accordance with the literature. The dynamic coefficients are presented in the form of empirical equations based on the theoretical investigations for different clearance, L/D ratio and eccentricity ratio, in terms of Reynolds number of the damper and enables its easy evaluation for a particular damper configuration by a mere knowledge of the Reynolds number of the squeeze film. The results assist the designer in obtaining the stiffness and damping characteristics of the squeeze film damper, based on the Reynolds number. Alternatively, the stiffness and damping characteristics of the squeeze film damper are calibrated in terms of Reynolds number for particular damper configurations. However, the research focuses on the stiffness and damping coefficients for a limited number of damper configurations under a constant excitation frequency whilst a large number of clearances, L/D ratios and excitation frequencies have not been taken into account .This research is thus intended only to showcase the method of approach by selecting finite number of damper configurations. Future work should be focused towards investigations that present the empirical equations for the entire range of clearance, L/D ratio and eccentricity ratio.

Analysis of the influence of lubricant supply conditions on the pressure distribution in squeeze-film dampers

One of the most common ways to reduce vibration in aircraft engines is the use of damping devices. Squeeze-film dampers are the dampers most widely used in aircraft engine designs. The efficiency of squeeze-film dampers is determined by their damping capacity which depends, among other parameters, on the static pressure of oil supply to the damper. This article proposes a method for calculating the static pressure in the feed groove of a hydrodynamic damper depending on the geometric size of the end gap and the value of the lubricant supply pressure. The parameters influencing the static pressure in the damper end gap are determined. Calculations are performed for different values of a hydrodynamic damper end gap, the number and diameter of the supply ports. All calculations presented in the article were performed for a short squeeze-film damper with end gaps and throttles. For comparison of parameters, the dynamic pressure was also calculated for a long squeeze-film damper. It was shown that the size of the end gap has the strongest impact on the pressure in the groove of a squeeze-film damper. It was also shown that the dynamic pressure in the gap may be significantly higher than the static pressure of supply, and failure of the lubricating film may result. In addition, it was also shown that the size of the damper end clearance affects the lubricant flow through the damper.

Experimental and Analytical Investigation of Short Squeeze-Film Damper (SFD) Under Circular-Centered Orbit (CCO) Motion

Modern rotating machines operate at higher shaft speeds, crossing a few bending critical speeds, which often induce large dynamic loads on the bearing supports that may increase the rotor orbital whirl motion. Accurate prediction of squeeze-film damper (SFD) forces is the key issue for designers to arrive at a suitable design. An experimental setup was developed with eccentric shaft to find the damper forces. Submerged type damper with relatively large clearance was considered for the present work. It results in higher gap Reynolds number (Re) which varies from 1.5 to 15 in the present case. Four force sensors are used to measure the damper forces and two eddy current probes were used to measure the damper orbit. Circular-centered orbit (CCO) of eccentricity ratio (e) 0.176 was used in the present work. Theoretical modeling of SFD forces is considered with viscous, inertial, temporal contributions under laminar and turbulent conditions. Modified Reynolds equation with short damper approximation is used to derive the SFD forces for 2π- film. Fourier coefficients of measured forces and displacements are estimated and used to extract the 1× components and phase information. Radial and tangential forces were calculated from the measured total forces to find the contributions of viscous and inertial forces. Experimental forces are compared with theoretically predicted forces and they are in good agreement with the experimental results.

Coupled Lateral and Torsional Nonlinear Transient Rotor–Bearing System Analysis With Applications

This paper provides a time transient method for solving coupled lateral and torsional analysis of a flexible rotor–bearing system including gyroscopic effects, nonlinear short journal bearings, nonlinear short squeeze film dampers (SFDs), and external nonlinear forces/torques. The rotor is modeled as linear, and the supporting components, including bearings and dampers, are modeled as nonlinear. An implicit Runge–Kutta method is developed to solve the nonlinear equations of motion with nonconstant operating speed since the unbalance force and the gyroscopic effect are related to both the rotational speed and the acceleration. The developed method is compared with a previous torsional analysis first to verify the nonlinear transient solver. Then the coupled lateral and torsional analysis of an example flexible three-disk rotor, perhaps representing a compressor, with nonlinear bearings and nonlinear dampers driven by a synchronous motor is approached. The acceleration effects on lateral and torsional amplitudes of vibration are presented in the analysis. The developed method can be used to study the rotor motion with nonconstant rotational speed such as during startup, shutdown, going through critical speeds, blade loss force, or other sudden loading.

Effect of Temperature and Electric Field on the Damping and Stiffness Characteristics of ER Fluid Short Squeeze Film Dampers

Squeeze film dampers are novel rotor dynamic devices used to alleviate small amplitude, large force vibrations and are used in conjunction with antifriction bearings in aircraft jet engine bearings to provide external damping as these possess very little inherent damping. Electrorheological (ER) fluids are controllable fluids in which the rheological properties of the fluid, particularly viscosity, can be controlled in accordance with the requirements of the rotor dynamic system by controlling the intensity of the applied electric field and this property can be utilized in squeeze film dampers, to provide variable stiffness and damping at a particular excitation frequency. The paper investigates the effect of temperature and electric field on the apparent viscosity and dynamic (stiffness and damping characteristics) of ER fluid (suspension of diatomite in transformer oil) using the available literature. These characteristics increase with the field as the viscosity increases with the field. However, these characteristics decrease with increase in temperature and shear strain rate as the viscosity of the fluid decreases with temperature and shear strain rate. The temperature is an important parameter as the aircraft jet engine rotors are located in a zone of high temperature gradients and the damper fluid is susceptible to large variations in temperature.

자기 베어링 시스템을 가진기로 이용한 스퀴즈 필름 댐퍼의 동특성 계수 규명

The dynamic characteristics of an ell-lubricated, short squeeze film damper (SFD) with a central feeding groove are derived based on a theoretical analysis considering the effect of a groove, and identified experimentally using an Active Magnetic Bearing (AMB) system as an exciter. In order to get the theoretical solution, the fluid film forces of the grooved SFD are analytically derived so that the dynamic coefficients of the SFD can be expressed in terms of its design parameters. For the experimental validation of the analysis, a test rig using an AMB as an exciter is proposed. As an exciter. the AMB represents a mechatronic device to levitate and position the test Journal without any mechanical contact, to generate relative motions of the Journal inside the tested SFD and to measure the generated displacements during experiments with fairly high accuracy. Using this test rig, experiments are extensively conducted with various values of clearance, which Is one of the most important design parameters. in order to investigate its effect on the dynamic characteristics and the performance of the SFD. Damping and Inertia coefficients of the SFD that are experimentally Identified are compared with the analytical results to demonstrate the effectiveness of the applied analysis. It Is also shown that the AMB is an ideal device for tests of SFDs.

Effect of a circumferential feeding groove in a short squeeze-film damper

The present work investigates the effects of a circumferential feeding groove in a short squeeze-film damper (SFD) on fluid force and dynamic responses of a rotor in SFDs. The groove is taken as a special damper to analyse the effects. The dynamic performance of the SFD with the groove is attributed to two film lands, the special damper and their interactions. From this viewpoint, the fluid force in the groove is analysed on the basis of the linearized Navier-Stokes equations. Analysis of the fluid force in film lands is carried out using a simplified Navier-Stokes equation to include fluid inertia. Then, from the continuity condition and the Navier-Stokes equation, fluid interactions between the groove and the film lands are investigated. The two analyses are combined together by investigation of the interactions, resulting in new models for fluid force predictions. The new models are compared with published work. The comparisons show that the new models give better predictions and correction with experimental data than traditional theory. The new models provide a significant improvement on the results obtained by traditional theory, especially for tangential force. Based on the new models, the present work also analyses effects of the groove on the unbalance response and stability of a rigid rotor in SFDs. Comparisons with published work show that the groove affects the unbalance response of a rotor system. The effects of the groove on dynamic coefficients of SFD cause the response of the rotor system to be stable for some range of system parameters, being different from the results of traditional theory. This is important for designing a rotor system.

Fluid forces in short squeeze-film damper bearings

This paper has studied influences of fluid inertia on fluid velocity profiles and provided an axial inertia velocity profile for short squeeze film damper bearings (SFDs) using as a starting point a simplified Navier–Stokes equation. The velocity profile reasonably represents influences of fluid inertia on fluid flow. From the inertia velocity profile, present work develops new theoretical models for fluid forces in cylindrical short SFDs. Published experimental work confirms that the new models for fluid forces are better than traditional short-SFD theory, especially for tangential force. The new models show that the damping coefficient for 2 π film is related to fluid inertia.

Effect of a circumferential feeding groove on fluid force in short squeeze film dampers

The present work studies fluid forces in a squeeze film damper with a circumferential feeding groove. The groove is taken as a special damper to analyse fluid forces. The dynamic performance of the squeeze film damper is attributed to the special damper, two film lands, and their interactions. From this viewpoint, dynamic effects in the groove are studied based on linearized Navier-Stokes equations to consider effects of variations of fluid velocity and pressure in the groove on forces in the damper. Investigations on film lands are conducted by using a simplified Navier-Stokes equation to include fluid inertia. Then, the two part analyses are combined together by studying the interactions of the flow and the pressure between the groove and film lands from the continuity condition and a Navier-Strokes equation, resulting in new models for force predictions. The new models are compared with experimental results and published work. Comparisons show the new models give better predictions and correlation with experimental data than traditional theory. The new models give a significant improvement on results obtained by traditional theory, especially for tangential force. Based on the new models, the effects of the groove on fluid forces are studied.

Force Coefficients for a Centrally Grooved Short Squeeze Film Damper

Abstract A centrally grooved short squeeze film damper (SFD), together with its lubricant supply mechanism (LSM), is analyzed, using an integrated theoretical model. It is shown that the traditional analysis for such a damper, where the effects of the central groove and the LSM are ignored, can lead to a seven-fold underestimation of the magnitude of the hydrodynamic force coefficients. The new theory gives predictions for the damping coefficients which are in good agreement with corresponding experimental results. Moreover, a five-fold improvement is obtained for both the temporal and convective inertia coefficients, at low values of eccentricity. The new model leads to the prediction of a nonzero fluid static force which, in conformity with experimental results, is linearly related to the supply pressure. The existence of this static force has not been explained by previous theoretical work on SFDs.

Analysis of a Short Squeeze-Film Damper Operating with Electrorheological Fluids

This paper addresses the lubrication analysis of a short squeeze-film damper operating with electrorheological (ER) fluids which have large and reversible changes in yield shear stresses with respect to an applied electric field. The ER fluids are assumed to be modeled as Bingham fluids. The governing lubrication equation for the ER short squeeze-film damper is developed on the basis of a Bingham fluid model, and the equation is subsequently solved in order to investigate the effects of the ER fluids on the damping capability of the damper. It is shown that a substantial increase in both direct and cross-coupled damping is accomplished by increasing the yield shear stress of the ER fluids. This significant improvement of the damping capability suggests that the ER short squeeze-film damper could be very effective for reducing the vibration and controlling the critical speeds of a rotor system.

Effect of a Circumferential Feeding Groove on the Dynamic Force Response of a Short Squeeze Film Damper

The effect of a circumferential feeding groove on the dynamic force response of a short length, open end squeeze film damper is studied experimentally. Damper configurations with increasing groove depths and journal orbit radii were tested for several conditions of whirl frequency and lubricant viscosity. Significant levels of dynamic pressure were measured at the circumferential groove, and relatively large tangential (damping) forces are produced at the groove which contribute considerably to the damping characteristics of the SFD test articles. Radial forces of substantial magnitude are determined at the groove and at the thin film land where the squeeze film Reynolds number is typically less than 1. The circumferential groove is thought to induce an inertia like effect into the film land. The experimental results correlate well with the predictions from a groove volume-circumferential flow model developed.

Unbalance Response of a Jeffcott Rotor Incorporating Short Squeeze Film Dampers

The steady-state unbalance response of a Jeffcott rotor incorporating short squeeze film dampers executing circular centered whirl is obtained by a fast algorithm. Savings in execution time of the order of fifty times are gained over numerical integration. Fluid inertia forces are included in the model of the squeeze film dampers. The fast algorithm allows parametric studies to be performed. It is shown that fluid inertia results in the excitation of a second mode for the Jeffcott rotor, decreases the possibility of jump resonance, and decreases the useful range of vibration isolation of the dampers. It is also shown that a squeeze film damper with no centering spring (or a very soft spring) may be advantageous with regards to the unbalance response and the vibration isolation capability of the dampers.

Closed-Form, Steady-State Solution for the Unbalance Response of a Rigid Rotor in Squeeze Film Damper

This paper considers the steady-state response due to unbalance of a planar rigid rotor carried in a short squeeze film damper with linear centering spring. The damper fluid forces are determined from the short bearing, cavitated (π film) solution of Reynold’s equation. Assuming a circular centered orbit, a change of coordinates yields equations whose steady-state response are constant eccentricity and phase angle. Focusing on this steady-state solution results in reducing the problem to solutions of two simultaneous algebraic equations. A method for finding the closed-form solution is presented. The system is nondimensionalized, yielding response in terms of an unbalance parameter, a damper parameter, and a speed parameter. Several families of eccentricity-speed curves are presented. Additionally, transmissibility and power consumption solutions are present.