Characteristics Of Squeeze Film Damper Research Articles

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.

Vibration attenuation characteristics of squeeze film dampers in spiral bevel gear systems

A central drive bevel gear system of aero-engines extracts power from a high-pressure rotor. The high speed of the high-pressure rotor aggravates the gear system's vibration. This work adopts squeeze film dampers (SFD) as damping devices to suppress excessive vibration of the spiral bevel gear rotor system. This paper establishes the general Reynolds equation of SFD and calculates the nonlinear oil-film force of SFD in real-time based on the finite element method. Besides, the finite element method and Timoshenko beam element are employed to model the flexible gear shaft. Then, the dynamic model of the spiral bevel gear system supported by SFDs is established, including the nonlinear oil-film force of SFD and time-varying meshing stiffness of the gear system. The dynamic response of the spiral bevel gear system is analyzed theoretically and experimentally to study the vibration attenuation characteristics of SFD. The findings indicate that SFD can effectively suppress the vibration amplitude of the system at high speeds. The theoretical analysis and experimental amplitude are within an order of magnitude, and the changing trend is consistent.

Numerical simulation and influence factors analysis for dynamic characteristics of squeeze film damper

To accurately and efficiently calculate the dynamic characteristics of squeeze film damper (SFD), the influences of different parameters on computational fluid dynamics simulation were analyzed. The simulation was verified by theoretical formula of SFD based on the short bearing and semi-oil film hypothesis considering the oil film inertia force. Numerical simulation results have shown that mesh stiffness value can guarantee the convergence without influence on results. The mesh sizes have obvious influence on simulation results, while the influence of circumferential mesh size is comparatively weak. When there are more than 200-time steps in a cycle or more than 2 cycles are selected, it will take more computation time but with less influence on results. When the length-diameter ratio of SFD is smaller, the numerical calculation results have a better agreement with the theoretical results. The research will provide a reference for the options of simulation parameters of SFD while taking into account both analysis precision and computer time.

Supply groove effects on characteristics of squeeze film damper

Variation of film pressure was studied by short bearing hypothesis and differential method for grooving on film inner-face. The results were compared with those of FLUENT analysis. Then, effects of the position of groove were studied on film pressure and damping through differential method. The results shown that short bearing hypothesis cannot conform to the actual situation considering grooving. The effect of grooving on the pressure distribution of film was researched by differential method, and the results are consistent with the FLUENT simulation analysis. Side grooving has less effect on film pressure and damping, so it is recommended when the design and assembly conditions are allowed.

Mathematical models of squeeze film dampers in rotor dynamics of gas turbine engines

The paper focuses on the choice of mathematical models of squeeze film dampers and methods of their numerical implementations for gas turbine engine rotor dynamics problems. The present contribution is aimed at establishing criteria for the application of mathematical models of a squeeze film damper depending on the damper characteristics and operating conditions. The models are grouped by the dimension of the considered physical space, i.e. three-dimensional, two-dimensional and one-dimensional modeling patterns. The work presents principles of setting boundary conditions for mechanical seals to be adequately simulated. Criteria of assessing the necessity of taking into account such physical phenomena as turbulence, fluid inertia, and cavitation are presented. The proposed mathematical models are primarily developed for the computation of integral characteristics of squeeze film dampers, such as reaction forces and dynamic stiffness and damping coefficients required for solving rotor dynamics problems.

Vibration Characteristics of Squeeze Film Damper during Maneuver Flight

AbstractThe rotor systems of an aero engine will endure additional centrifugal force and gyroscopic moment during maneuver flight. A maneuver fly mechanical simulator is designed and experimental investigations on dynamics of squeeze film damper (SFD) under the different additional centrifugal force and gyroscopic moment are carried out. The results show that the maneuver flight weaken effectiveness of the SFD, the additional centrifugal force and gyroscopic moment caused by maneuver flight will change film damping, film stiffness. And the influence of maneuver flight can be effective relieved by increasing the film clearance.

Calibration of the Stiffness and Damping Characteristics of a Magnetorheological Fluid Long Squeeze Film Damper in Terms of Reynolds Number

Magnetorheological (MR) fluids are suspensions of fine micron-sized magnetizable particles in a suitable carrier liquid. The rheological properties of the fluid can be controlled by application of a suitable magnetic field and can be used in a variety of applications where variable damping and stiffness characteristics are required, based on the requirements of the rotor dynamic system. In this work, the stiffness and damping characteristics of MR fluid long squeeze film damper operating at low eccentricity ratios are calibrated in terms of Reynolds number of the squeeze film for different clearance and L/D ratios. A theoretical constant magnetic field viscosity model is developed, based on the literature, and is subsequently used to evaluate the theoretical stiffness and damping coefficients, at a particular excitation frequency. The results indicate that the stiffness and damping coefficients decrease with increasing Reynolds number of the squeeze film and is found to be abysmally low, indicating that the flow has ceased and the film has solidified. This is in accordance with the literature that predicts the formation of chain-like semi-solid structures, restricting the flow, and consequently increasing the viscosity, under the influence of the magnetic field. This change in viscosity, in turn, influences the stiffness and damping coefficients and the Reynolds number of the squeeze film. The stiffness and damping coefficients are found to increase with decreasing clearance, increasing L/D ratio, and eccentricity ratio. The results of the investigation assist the designer in obtaining the stiffness and damping characteristics of the squeeze film damper based on the Reynolds number of the squeeze film. Conversely, the stiffness and damping characteristics of the squeeze film damper are calibrated in terms of the Reynolds number of the squeeze film for different damper configurations.

Experimental Study of the Radial and Tangential Forces in a Whirling Squeeze Film Damper

The present work introduces the main results of a detailed experimental program aimed at investigating the influence of the design parameters and of the working conditions on the global characteristics of squeeze film dampers (SFD) for serial aircraft engines. The SFD is sealed at both ends and is executing circular centered orbits. The results are presented for the tangential and the radial global force in the SFD and the leakage flow rate. The pressure field inside the SFD could also be measured and shows the influence of the inertia force, of the cavitation, and probably of the turbulence regime, as well as the interaction of these effects with the feeding groove. The limits of the existing theoretical models are also demonstrated. Review led by Bill Marscher

Floating ring squeeze film damper: theoretical analysis

The non-linear characteristics of squeeze film dampers can frequently promote multi-stable operation, e.g. jump, or aperiodic response in rotating machinery. Such undesirable operation can sometimes be avoided in rigid rotor systems by replacing the rigidly supported damper housing with a flexibly mounted rigid ring or ‘floating’ ring, but its applicability to flexible rotor systems is uncertain. This paper investigates theoretically the potential of such a modified damper in avoiding aperiodic response in a flexible rotor rig, built to validate theoretical predictions. Parameters investigated include the stiffness of the damper ring mount, its mass and its damping for various unbalance loads. For the parameter range investigated, the frequency response was highly dependent on the stiffness and the unbalance, somewhat dependent on the mass, and virtually insensitive to the damping. While aperiodic solutions could be avoided, a careful choice of parameters is needed to avoid excessive vibrations.

Blade Excitation by Elliptical Whirling in Viscous-Damped Jet Engines

An extension of the author’s earlier method of analyzing multi-shaft jet engine dynamics accounting for flexibility of bladed disks is outlined to calculate the first whirl harmonic for given nonlinear characteristics of squeeze-film dampers. A second whirl harmonic, of which experimental verification is found in Campbell’s paper of 1924, is shown induced by orbit ellipticity. The possibility that this harmonic, especially due to backward whirling, may be a source of blade excitation at higher frequencies than currently recognized from linear analysis is discussed by relating some engine experience.