Inertia and Turbulence Effects on Dynamic Characteristics and Stability of Rotor-Bearings Systems

1991 ◽  
Vol 113 (1) ◽  
pp. 58-64 ◽  
Author(s):  
Giuseppe Capone ◽  
Michele Russo ◽  
Riccardo Russo
Keyword(s):  
Reynolds Number ◽  
Dynamic Characteristics ◽  
Stability Limit ◽  
Reynolds Numbers ◽  
Journal Bearings ◽  
Clearance Ratio ◽  
Oil Film ◽  
Turbulence Effects ◽  
The Stability ◽  
Rotor Bearings

The influence of turbulence and inertia of oil film on the dynamic characteristics and stability of rotor-bearings systems is theoretically analyzed for various Reynolds number values. The rotor is assumed to be rigid, symmetrical, balanced, and supported in two identical aligned journal bearings. The fluid film forces are evaluated under the short bearing assumption. Stiffness, damping, and acceleration coefficients, and the stability limit curves are reported versus modified Sommerfeld number for various Reynolds numbers and for radius-clearance ratio R/C = 500.

Stability of Jeffcott Rotor Operating in Tilting 3-Pad Journal Bearings with Turbulent Oil Film

2009 ◽  
Vol 147-149 ◽  
pp. 450-455
Author(s):  
Stanislaw Strzelecki ◽  
Sobhy M. Ghoneam
Keyword(s):  
Theoretical Investigation ◽  
Dynamic Characteristics ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Oil Film ◽  
Temperature Distributions ◽  
Jeffcott Rotor ◽  
Oil Flow ◽  
The Stability ◽  
Oil Film Pressure

This paper introduces the results of theoretical investigation on the dynamic characteristics of tilting 3-pad journal bearing that operates with turbulent oil film. The Reynolds, energy, viscosity and geometry equations determine the oil film pressure, temperature distributions, and oil film resultant force that are the grounds for the dynamic characteristics of bearing. These equations were solved simultaneously on the assumption of adiabatic laminar or adiabatic turbulent oil flow in the bearing gap. The stability and system damping of Jeffcott rotor operating in tilting 3-pad journal bearing was determined.

Parametric Excitation Instability of a Rigid Unbalanced Rotor in Short Turbulent Journal Bearings

1993 ◽  
Vol 207 (3) ◽  
pp. 149-160 ◽  
Author(s):  
M Russo ◽  
R Russo
Keyword(s):  
Reynolds Number ◽  
Parametric Excitation ◽  
Reynolds Numbers ◽  
Journal Bearings ◽  
Oil Film ◽  
Unbalanced Rotor ◽  
Stability Maps ◽  
Synchronous Orbit

The influence of oil-film turbulence on the parametric excitation instability of a symmetrical unbalanced rotor in short bearings is analysed for different values of Reynolds number. The method of calculating the journal orbit is described together with the method for predicting the synchronous orbit whose stability is to be evaluated. In addition to examples of calculated and predicted orbits, stability maps are given for dimensionless unbalance values equal to 0.2, 0.3 and 0.4 and for the Reynolds numbers of 2500, 5000 and 10000.

Tertiary solutions and their stability in rotating plane Couette flow

1998 ◽  
Vol 358 ◽  
pp. 357-378 ◽  
Author(s):  
M. NAGATA
Keyword(s):  
Reynolds Number ◽  
Couette Flow ◽  
Stability Boundary ◽  
Streamwise Vortex ◽  
Reynolds Numbers ◽  
Time Dependent ◽  
Plane Couette Flow ◽  
Streamwise Direction ◽  
The Stability ◽  
Oscillatory Instabilities

The stability of nonlinear tertiary solutions in rotating plane Couette flow is examined numerically. It is found that the tertiary flows, which bifurcate from two-dimensional streamwise vortex flows, are stable within a certain range of the rotation rate when the Reynolds number is relatively small. The stability boundary is determined by perturbations which are subharmonic in the streamwise direction. As the Reynolds number is increased, the rotation range for the stable tertiary motions is destroyed gradually by oscillatory instabilities. We expect that the tertiary flow is overtaken by time-dependent motions for large Reynolds numbers. The results are compared with the recent experimental observation by Tillmark & Alfredsson (1996).

scholarly journals Dynamic Characteristics of the Oil Film in Journal Bearings

1982 ◽  
Vol 1982 (151) ◽  
pp. 292-298 ◽  
Author(s):  
Yoshiyuki Yamamoto ◽  
Hideomi Ohtsubo ◽  
Shin Morishita
Keyword(s):  
Dynamic Characteristics ◽  
Journal Bearings ◽  
Oil Film

Comparison Between Linear and Nonlinear Transient Analysis Techniques to Find the Stability of a Rigid Rotor

1999 ◽  
Vol 121 (1) ◽  
pp. 198-201 ◽  
Author(s):  
Ram Turaga ◽  
A. S. Sekhar ◽  
B. C. Majumdar
Keyword(s):  
Transient Analysis ◽  
Stability Limit ◽  
Journal Bearings ◽  
Quantitative Comparison ◽  
Rigid Rotor ◽  
Analysis Techniques ◽  
Analysis Technique ◽  
Nonlinear Transient ◽  
Nonlinear Transient Analysis ◽  
The Stability

The subsynchronous whirl stability limit of a rigid rotor supported on two symmetrical finite journal bearings has been studied using the linearised perturbation method and the nonlinear transient analysis technique. A quantitative comparison for journal bearings with different l/d ratios has been provided.

Stability of non-parabolic flow in a flexible tube

1999 ◽  
Vol 395 ◽  
pp. 211-236 ◽  
Author(s):  
V. SHANKAR ◽  
V. KUMARAN
Keyword(s):  
Reynolds Number ◽  
Velocity Profile ◽  
Asymptotic Analysis ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Flexible Tube ◽  
Developing Flow ◽  
Parabolic Flow ◽  
High Reynolds ◽  
The Stability

Flows with velocity profiles very different from the parabolic velocity profile can occur in the entrance region of a tube as well as in tubes with converging/diverging cross-sections. In this paper, asymptotic and numerical studies are undertaken to analyse the temporal stability of such ‘non-parabolic’ flows in a flexible tube in the limit of high Reynolds numbers. Two specific cases are considered: (i) developing flow in a flexible tube; (ii) flow in a slightly converging flexible tube. Though the mean velocity profile contains both axial and radial components, the flow is assumed to be locally parallel in the stability analysis. The fluid is Newtonian and incompressible, while the flexible wall is modelled as a viscoelastic solid. A high Reynolds number asymptotic analysis shows that the non-parabolic velocity profiles can become unstable in the inviscid limit. This inviscid instability is qualitatively different from that observed in previous studies on the stability of parabolic flow in a flexible tube, and from the instability of developing flow in a rigid tube. The results of the asymptotic analysis are extended numerically to the moderate Reynolds number regime. The numerical results reveal that the developing flow could be unstable at much lower Reynolds numbers than the parabolic flow, and hence this instability can be important in destabilizing the fluid flow through flexible tubes at moderate and high Reynolds number. For flow in a slightly converging tube, even small deviations from the parabolic profile are found to be sufficient for the present instability mechanism to be operative. The dominant non-parallel effects are incorporated using an asymptotic analysis, and this indicates that non-parallel effects do not significantly affect the neutral stability curves. The viscosity of the wall medium is found to have a stabilizing effect on this instability.

scholarly journals Experiments on the Stability of Various Water-Lubricated Fixed Geometry Hydrodynamic Journal Bearings at Zero Load

1973 ◽  
Vol 95 (4) ◽  
pp. 434-445 ◽  
Author(s):  
F. T. Schuller
Keyword(s):  
Journal Bearings ◽  
Shaft Speed ◽  
Clearance Ratio ◽  
Fractional Frequency ◽  
Trailing Edges ◽  
Minimum Film Thickness ◽  
Maximum Stability ◽  
The Stability ◽  
The One ◽  
Offset Factor

Stability tests were conducted with 3.8 centimeter-(1.5 in.-) diameter, 3.8 centimeter-(1.5 in.-) long, fixed geometry hydrodynamic journal bearings in water at 300 K (80 deg F) with zero load. Five fixed geometry bearings were rated in order of diminishing stability as follows: (1) three-tilted-lobe bearing (offset factor of 1.0), (2) herring-bone-groove bearing, (3) one-segment, three-pad, shrouded Rayleigh-step bearing, (4) three-tilted-lobe journal with axial grooves (offset factor of 1.0) mated with a plain bearing, and (5) three-centrally-lobed bearing with axial grooves (offset factor of 0.5). Maximum stability in lobed bearings and journals is achieved when the lobes are tilted so that the points of minimum film thickness occur near the trailing edges. The herringbone-groove journals had a maximum stability (maximum fractional frequency whirl onset speed) when the groove to ridge clearance ratio was closest to 2.1, as predicted by incompressible flow theory. The one-segment, three-pad shrouded Rayleigh-step bearing configuration was the most stable of the four step-bearing configurations tested. The tilted-lobe journals mated with plain bearings were unique in that, in some tests, the bearings could be run to a shaft speed twice the shaft speed at which initial fractional frequency whirl occurred before any sign of bearing distress was observed.

Journal Orbits and Their Stability for Rigid Unbalanced Rotors

1995 ◽  
Vol 117 (4) ◽  
pp. 709-716 ◽  
Author(s):  
Renato Brancati ◽  
Ernesto Rocca ◽  
Michele Russo ◽  
Riccardo Russo
Keyword(s):  
Orbital Motion ◽  
Journal Bearings ◽  
Stability Parameter ◽  
Parameter Plane ◽  
Linear Motion ◽  
Motion Equations ◽  
Unbalanced Rotor ◽  
Stable Operating ◽  
The Stability ◽  
Rotor Bearings

With reference to a rigid symmetrical unbalanced rotor on lubricated journal bearings and adopting the short bearing theory, synchronous orbits and orbits with a 1/2 component described by the journal are determined as approximated solutions of the system of non-linear motion equations. The method also makes it possible to evaluate the stability of the above solutions and thus of the journal orbital motion. For different values of dimensionless unbalance of the rotor, examples of orbits thus obtained are given and, in the modified Sommerfeld number-stability parameter plane, the stability areas of the solutions are identified, in particular, the area of stability of the small synchronous orbits corresponding to the stable operating condition of the rotor-bearings system.

The Stability of Water Flow Over Heated and Cooled Flat Plates

1968 ◽  
Vol 90 (1) ◽  
pp. 109-114 ◽  
Author(s):  
Ahmed R. Wazzan ◽  
T. Okamura ◽  
A. M. O. Smith
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Stream Temperature ◽  
Heated Wall ◽  
Flat Plates ◽  
Critical Reynolds Numbers ◽  
The Stability ◽  
Sommerfeld Equation

The theory of two-dimensional instability of laminar flow of water over solid surfaces is extended to include the effects of heat transfer. The equation that governs the stability of these flows to Tollmien-Schlichting disturbances is the Orr-Sommerfeld equation “modified” to include the effect of viscosity variation with temperature. Numerical solutions to this equation at high Reynolds numbers are obtained using a new method of integration. The method makes use of the Gram-Schmidt orthogonalization technique to obtain linearly independent solutions upon numerically integrating the “modified Orr-Sommerfeld” equation using single precision arithmetic. The method leads to satisfactory answers for Reynolds numbers as high as Rδ* = 100,000. The analysis is applied to the case of flow over both heated and cooled flat plates. The results indicate that heating and cooling of the wall have a large influence on the stability of boundary-layer flow in water. At a free-stream temperature of 60 deg F and wall temperatures of 60, 90, 120, 135, 150, 200, and 300deg F, the critical Reynolds numbers Rδ* are 520, 7200, 15200, 15600, 14800, 10250, and 4600, respectively. At a free-stream temperature of 200F and wall temperature of 60 deg F (cooled case), the critical Reynolds number is 151. Therefore, it is evident that a heated wall has a stabilizing effect, whereas a cooled wall has a destabilizing effect. These stability calculations show that heating increases the critical Reynolds number to a maximum value (Rδ* max = 15,700 at a temperature of TW = 130 deg F) but that further heating decreases the critical Reynolds number. In order to determine the influence of the viscosity derivatives upon the results, the critical Reynolds number for the heated case of T∞ = 40 and TW = 130 deg F was determined using (a) the Orr-Sommerfeld equation and (b) the present governing equation. The resulting critical Reynolds numbers are Rδ* = 140,000 and 16,200, respectively. Therefore, it is concluded that the terms pertaining to the first and second derivatives of the viscosity have a considerable destabilizing influence.

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