scholarly journals A Simplified Method for Predicting the Stability of Aerodynamically Excited Turbomachinery

2006 ◽  
Vol 129 (4) ◽  
pp. 724-729 ◽  
Author(s):  
Albert F. Storace
Keyword(s):  
Natural Frequencies ◽  
Design Tool ◽  
System Stability ◽  
Squeeze Film ◽  
Real Eigenvalue ◽  
Turbine Engine ◽  
Squeeze Film Dampers ◽  
Simplified Method ◽  
Stability Method ◽  
The Stability

A modal stability (MS) method is presented for the quick and accurate prediction of the stability of aerodynamically excited turbomachinery using real eigenvalue/eigenvector data obtained from a rotordynamics model. The modal stability method provides a means to compare the work of stabilizing damping forces to the work of destabilizing aerodynamic cross-coupled stiffness forces to predict the onset of whirl instability. The MS method thus indicates that unstable or self-excited whirling (sometimes called whipping) at one of the system’s natural frequencies is initiated when the destabilizing work equals or exceeds the stabilizing work. This approach provides a powerful design tool to quickly ascertain the effects of squeeze-film dampers, and turbine engine architecture, including bearing locations and bearing support structure stiffness, on system stability.

Analysis and Experimental Investigation of the Stability of Intershaft Squeeze Film Dampers—Part 2: Control of Instability

1978 ◽  
Vol 100 (3) ◽  
pp. 558-562 ◽  
Author(s):  
D. H. Hibner ◽  
P. N. Bansal ◽  
D. F. Buono
Keyword(s):  
Experimental Investigation ◽  
Stability Analysis ◽  
Shear Deformation ◽  
System Stability ◽  
Squeeze Film ◽  
Viscous Damper ◽  
Test Rig ◽  
Squeeze Film Dampers ◽  
Stability Maps ◽  
The Stability

The results of an analytical and experimental investigation showing the existence of an intershaft viscous damper instability were presented in reference [1]. In the present investigation, a more comprehensive stability analysis is used to study the stability of the test rig which incorporates a modified intershaft bearing support. The analysis is applicable to large multi-mass, rotor-bearing systems and includes the effects of gyroscopic moments, shear deformation, bearing support flexibility, and damping. The results of the stability analysis are presented in the form of system stability maps which clearly indicate the effectiveness of the modification in improving the instability onset speed of the system. Also presented are the results of an experimental investigation which substantiate the analytical predictions.

scholarly journals Analytical and Experimental Investigation of the Stability of the Rotor-Bearing System of a New Small Turbocharger

1987 ◽  
Author(s):  
H. R. Born
Keyword(s):  
Experimental Investigation ◽  
Dynamic Stability ◽  
Squeeze Film ◽  
Test Results ◽  
Flow Capacity ◽  
Squeeze Film Dampers ◽  
Rotor Bearing ◽  
The Stability ◽  
Turbine Design ◽  
Bearing System

This paper presents an overview of the development of a reliable bearing system for a new line of small turbochargers where the bearing system has to be compatible with a new compressor and turbine design. The first part demonstrates how the increased weight of the turbine, due to a 40 % increase in flow capacity, influences the dynamic stability of the rotor-bearing system. The second part shows how stability can be improved by optimizing important floating ring parameters and by applying different bearing designs, such as profiled bore bearings supported on squeeze film dampers. Test results and stability analyses are included as well as the criteria which led to the decision to choose a squeeze film backed symmetrical 3-lobe bearing for this new turbocharger design.

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.

Analytical and Experimental Investigation of the Stability of Intershaft Squeeze Film Dampers—Part 1: Demonstration of Instability

1977 ◽  
Vol 99 (1) ◽  
pp. 47-52 ◽  
Author(s):  
D. H. Hibner ◽  
R. G. Kirk ◽  
D. F. Buono
Keyword(s):  
Analytical Model ◽  
High Speed ◽  
Rotor System ◽  
Dynamics Simulation ◽  
Squeeze Film ◽  
Response Analysis ◽  
Turbine Engine ◽  
Engine Vibration ◽  
Bearing Loads ◽  
The Stability

Modern high-speed multishaft gas tubine engines incorporate viscous damped bearings to decrease overall system vibration and bearing loads. As viscous damper technology is applied to advanced engine design, more sophisticated analytical and experimental techniques are required to prove new concepts. This analysis will present the results of an investigation of the feasibility of damping engine vibration with a viscous damped intershaft bearing on a two-shaft gas turbine engine. Experimental results from a rotor dynamics simulation rig indicate an instability of the rotor system at speeds above a fundamental critical speed. An analytical model of the two-rotor system is presented and the results of both a classical stability analysis and a time transient response analysis verify the experimental data. The analytical model may be used to predict the stability of two-shaft engines which incorporate an intershaft damped bearing.

scholarly journals Stability Analysis of a Gear Pair System Supported by Squeeze-Film Dampers

2001 ◽  
Vol 7 (2) ◽  
pp. 143-151 ◽  
Author(s):  
T. N. Shiau ◽  
J. R. Chang ◽  
S. T. Choi
Keyword(s):  
Steady State ◽  
Stability Analysis ◽  
Harmonic Balance Method ◽  
Squeeze Film ◽  
Hybrid Technique ◽  
Gear Pair ◽  
Mesh Stiffness ◽  
Gear Mesh ◽  
Squeeze Film Dampers ◽  
The Stability

This paper examines the stability of the steady-state periodic response of a gear pair system supported by squeeze-film dampers. The steady-state response of the system is obtained by using the hybrid technique of Harmonic Balance Method and Time Collocation. The Fioquet-Liapunov theory is used to perform the stability analysis of the first variation equations with periodic coefficients, which is generated by the perturbation technique. The stability charts on gear mesh stiffness, spin ratio, disk unbalance, gravity, and squeeze-film damper are used to perform parameter studies. The numerical results show that the unstable region always occurs when the spin ratio is near the second coupled mode of the gear pair system. Furthermore, the mesh stiffness has a significant influence on the coupled critical speeds. Therefore, it plays an important role in determining the spin ratio stability range.

Experiments on the Dynamic Behavior of a Supercritical Rotor

1982 ◽  
Vol 104 (2) ◽  
pp. 364-369
Author(s):  
M. Botman ◽  
M. A. Samaha
Keyword(s):  
Strain Energy ◽  
Squeeze Film ◽  
Maximum Speed ◽  
Stability Behavior ◽  
Squeeze Film Dampers ◽  
Rolling Element ◽  
Speed Range ◽  
In Series ◽  
The Stability ◽  
Desirable Effect

Tests have been performed on supercritical rotors to determine the sensitivity to unbalance and the suitability of balancing techniques. Results are presented for a rotor with an overhanging disk and supported on two rolling element bearings in series with squeeze-film dampers. The rotor has two flexural modes with high relative strain energy in the speed range up to 55,000 rpm. After completion of the balancing exercise the rotor could be run to maximum speed and was found to be stable and free from half-frequency whirl instability, depending on the oil inlet pressure of the dampers. Pressurization of the dampers and increasing the clearance of the dampers had a very desirable effect on the stability behavior and the unbalance response.

Feasibility of Applying Active Lubrication to Reduce Vibration in Industrial Compressors

2004 ◽  
Vol 126 (4) ◽  
pp. 848-854 ◽  
Author(s):  
Ilmar F. Santos ◽  
Rodrigo Nicoletti ◽  
Alexandre Scalabrin
Keyword(s):  
Load Condition ◽  
Squeeze Film ◽  
Design Solution ◽  
Maximum Speed ◽  
Stability Margins ◽  
Damping Coefficients ◽  
Squeeze Film Dampers ◽  
Tilting Pad ◽  
Tilting Pad Bearings ◽  
The Stability

In this paper the complete set of modified Reynolds’ equations for the active lubrication is presented. The solution of such a set of equations allows the determination of stiffness and damping coefficients of actively lubricated bearings. These coefficients are not just dependent on Sommerfeld number, as it would be the case of conventional hydrodynamic bearings, but they are also dependent on the excitation frequencies and gains of the control loop. Stiffness as well as damping coefficients can be strongly influenced by the choice of the control strategy, servo valve dynamics and geometry of the orifices distributed over the sliding surface. The dynamic coefficients of tilting-pad bearings with and without active lubrication and their influence on an industrial compressor of 391 Kg, which operates with a maximum speed of 10,200 rpm, are analyzed. In the original compressor design, the bearing housings are mounted on squeeze-film dampers in order to ensure reasonable stability margins during full load condition (high maximum continuous speed). Instead of having a combination of tilting-pad bearings and squeeze-film dampers, another design solution is proposed and theoretically investigated in the present paper, i.e., using actively lubricated bearings. By choosing a suitable set of control gains, it is possible not only to increase the stability of the rotor-bearing system, but also enlarge its operational frequency range.

scholarly journals A Chambered Porous Damper for Rotor Vibration Control: Part II — Imbalance Response and Bladeloss Simulation

1991 ◽  
Author(s):  
J. Walton ◽  
M. Martin
Keyword(s):  
Steady State ◽  
Gas Turbine ◽  
Squeeze Film ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Turbine Engine ◽  
Wide Range ◽  
Squeeze Film Dampers ◽  
Damper Design ◽  
Control Part

In this paper, results of experimental rotordynamic evaluations of a novel, high load chambered porous damper design, are presented. The chambered porous damper concept was evaluated for gas turbine engine application since this concept avoids the non-linearities associated with high eccentricity operation of conventional squeeze film dampers. The rotordynamic testing was conducted under large steady state imbalance and simulated transient bladeloss conditions for up to 0.254 mm (0.01 in) mass c.g offset or 180 gm-cm (2.5 oz-in) imbalance. The chambered porous damper demonstrated that the steady state imbalance and simulated bladeloss transient response of a flexible rotor operating above its first bending critical speed could be readily controlled. Rotor system imbalance sensitivity and logarithmic decrement are presented showing the characteristics of the system with the damper installed. The ability to accommodate high steady state and transient imbalance conditions make this damper well suited to a wide range of rotating machinery, including aircraft gas turbine engines.

Some Bond Graph Structural Properties: Eigen Spectra and Stability

1989 ◽  
Vol 111 (3) ◽  
pp. 382-388 ◽  
Author(s):  
A. Zeid
Keyword(s):  
Canonical Form ◽  
Bond Graph ◽  
Design Tool ◽  
System Stability ◽  
Stability Estimates ◽  
Graphical Modeling ◽  
Linear And Nonlinear ◽  
The Stability ◽  
Time Invariant

What does the structure of the bond graph reveal about the eigenvalues of linear systems and about the stability of the linear and nonlinear systems they represent? In an earlier work, estimates of the eigen spectra of systems were given based on the structural classification of a canonical form of the bond graph. This work provides stability criteria based on the structure of the bond graph canonical form for linear and nonlinear time invariant dynamic systems. Tighter bounds on the eigen spectrum are also provided for the class of systems with uniform tree simple full graphs. It is shown that if a system is modeled by a standard bond graph whose canonical form is of the simple full or simple partial class, then estimates of the system stability, asymptotic stability, or instability can be obtained directly from the properties of the resistance field. The stability estimates can be automated and are obtained prior to the derivation of the dynamic equations. The stability properties can be used also as a design tool to suggest stabilizing feedback at the graphical modeling stage of the design process.

Subharmonic and Quasi-Periodic Motions of an Eccentric Squeeze Film Damper-Mounted Rigid Rotor

1994 ◽  
Vol 116 (3) ◽  
pp. 357-363 ◽  
Author(s):  
J. Y. Zhao ◽  
I. W. Linnett ◽  
L. J. McLean
Keyword(s):  
Numerical Integration ◽  
Least Square ◽  
Harmonic Series ◽  
Squeeze Film ◽  
Maximum Speed ◽  
Rigid Rotor ◽  
Squeeze Film Damper ◽  
Squeeze Film Dampers ◽  
The Stability ◽  
Nonsynchronous Vibrations

When a squeeze-film damper is operated eccentrically, the nonlinear damper forces are no longer radially symmetric and subharmonic and quasi-periodic vibrations may be excited by the rotor unbalance. In this study, the unbalance response of a rigid rotor, supported on an eccentric squeeze film damper, is first approximated by a harmonic series whose coefficients are determined by the collocation method, together with a nonlinear least-square regression. The stability of the resulting periodic solution is then examined using the Floquet transition matrix method. For sufficiently large values of the unbalance and the damper static radial misalignment, it is shown that the approximate harmonic motion loses its stability and bifurcates into a stable subharmonic motion and a quasi-periodic motion at speeds above twice the system critical speed. This analytical finding is verified by a numerical integration in forms of the Poincare´ map, the rotor trajectory, the bifurcation diagram, and the power spectrum. It is suggested that stability analysis and numerical integration should always be incorporated into an approximate analytical method to achieve an adequate approximation. The results of this study show that the introduction of squeeze-film dampers may give rise to the undesirable nonsynchronous vibrations, which limits the maximum speed at which dampers should be used.

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