Whirling with Spring Bearings and Rough Snubbers

1963 ◽  
Vol 67 (625) ◽  
pp. 66-67
Author(s):  
B. Irons
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Critical Speed ◽  
Peak Amplitude ◽  
Amplitude Response ◽  
Critical Speeds ◽  
Bearing Load

To an increasing extent, aero gas turbine manufacturers are supporting high speed rotors on spring bearings, in order to escape the consequences of lightly damped and inconveniently placed critical speeds. While experience has been generally good, engineering doubts periodically arise.(a) By introducing the flexible bearings, the critical speed is reduced, say, from 9,000 r.p.m. to 3,000 r.p.m. At 3,000 r.p.m. a peak amplitude response is experienced, although the bearing load is comparatively low. (Some spring bearing designs incorporate damping as an accidental feature, many do not, and very few have damping designed into them.) The peak amplitude at 3,000 r.p.m. can rub the seals or overstress the spring, and to prevent this the bearing amplitude is restricted by a circular stop known here as the “snubber.”

Formation of Standing Waves in Radial Tires

1984 ◽  
Vol 12 (1) ◽  
pp. 44-63 ◽  
Author(s):  
Y. D. Kwon ◽  
D. C. Prevorsek
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Unit Length ◽  
Standing Waves ◽  
Rolling Resistance ◽  
Damping Coefficient ◽  
Circular Membrane ◽  
Critical Speeds ◽  
Steel Cord ◽  
The Individual

Abstract Radial tires for automobiles were subjected to high speed rolling under load on a testing wheel to determine the critical speeds at which standing waves started to form. Tires of different makes had significantly different critical speeds. The damping coefficient and mass per unit length of the tire wall were measured and a correlation between these properties and the observed critical speed of standing wave formation was sought through use of a circular membrane model. As expected from the model, desirably high critical speed calls for a high damping coefficient and a low mass per unit length of the tire wall. The damping coefficient is particularly important. Surprisingly, those tire walls that were reinforced with steel cord had higher damping coefficients than did those reinforced with polymeric cord. Although the individual steel filaments are elastic, the interfilament friction is higher in the steel cords than in the polymeric cords. A steel-reinforced tire wall also has a higher density per unit length. The damping coefficient is directly related to the mechanical loss in cyclic deformation and, hence, to the rolling resistance of a tire. The study shows that, in principle, it is more difficult to design a tire that is both fuel-efficient and free from standing waves when steel cord is used than when polymeric cords are used.

Estimating Critical Speeds of Stepped Shafts with Flexible Bearings

1971 ◽  
Vol 8 (03) ◽  
pp. 327-333
Author(s):  
R. H. Salzman
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Design Stage ◽  
Normal Range ◽  
Critical Speeds ◽  
Stepped Shaft ◽  
Bearing Stiffness ◽  
Variable Support ◽  
Method Show ◽  
Good Agreement

This paper presents a semi-graphical approach for finding the first critical speed of a stepped shaft with finite bearing stiffness. The method is particularly applicable to high-speed turbine rotors with journal bearings. Using Rayleigh's Method and the exact solution for whirling of a uniform shaft with variable support stiffness, estimates of the lowest critical speed are easily obtained which are useful in the design stage. First critical speeds determined by this method show good agreement with values computed by the Prohl Method for the normal range of bearing stiffness. A criterion is also established for determining if the criticals are "bearing critical speeds" or "bending critical speeds," which is of importance in design. Discusser E. G. Baker

Critical Speeds, Divergence, and Flutter Instability in High-Speed Planetary Gears

2012 ◽  
Author(s):  
Christopher G. Cooley ◽  
Robert G. Parker
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Numerical Results ◽  
Planetary Gears ◽  
Critical Speeds ◽  
Flutter Instability ◽  
Divergence Instability ◽  
Translational Mode

The structured properties of the critical speeds and associated critical speed eigenvectors of high-speed planetary gears are given. Planetary gears have only planet, rotational, and translational mode critical speeds. Divergence instability is possible at speeds adjacent to critical speeds. Numerical results verify the critical speed locations. Divergence and flutter instabilities are investigated numerically for each mode type.

High-Speed Rotor Suspension Formed by Fully Floating Hydrodynamic Radial and Thrust Bearings

1964 ◽  
Vol 86 (2) ◽  
pp. 149-160 ◽  
Author(s):  
Juraj Dworski
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Critical Speed ◽  
Vibrational Excitation ◽  
Turbine Rotor ◽  
Continuous Operation ◽  
Flexible Rotor ◽  
Actual System ◽  
Apparent Absence ◽  
Thrust Bearings

The hydrodynamic suspension of a 44,000-rpm gas turbine rotor is described with emphasis on interaction between the flexible rotor and its supports. Bearings with relatively large clearances are shown to allow continuous operation at the rotor first critical-speed of 22,000 rpm. The apparent absence of hydrodynamic system instabilities is attributed to the use of simple floating-sleeve bearings. A parametric study of the influence of bearing clearances upon vibrational excitation relief is presented together with test data collected on actual system hardware.

Rotor Dynamics in Design of a High Speed Cryogenic Pump for Geo Stationary Launch Vehicles

2014 ◽  
Author(s):  
Srinivasa R. Jammi
Keyword(s):  
High Speed ◽  
Rotor Dynamics ◽  
Rotor System ◽  
Peak Amplitude ◽  
Beam Model ◽  
Rolling Element Bearings ◽  
Launch Vehicles ◽  
Critical Speeds ◽  
Highly Nonlinear ◽  
Rolling Element

On January 5th 2014 the Indian Space Research Organization successfully launched its Geo Stationary Launch Vehicle with an indigenous Cryogenic engine. One of the main design aspects is in its rotor dynamics to predict the peak amplitude unbalance whirl and the speed at which it occurs. This engine has several key technologies, one of them specifically is coupled rotors, viz., Turbine, Hydrogen Pump and Oxidizer supported on seven nonlinear rolling element bearings and several seals all mounted in a flexible casing. The conventional beam model initially adopted failed to predict the speed at which peak unbalance response occurs. The rotor system was first developed in a solid model to determine the critical speeds of the rotor alone considering its 40000 rpm centrifugal loads with bearings treated as linear. Then, unbalance whirl of this rotor system was developed by codes specially developed for this purpose. The rolling element bearings are found to be highly nonlinear with large bearing radial forces at critical speeds. An iterative procedure was developed to match the bearing force and unbalance whirl to determine peak amplitude response speeds. Subsequently, seals and the influence of casing and internal pressures were accounted in the analysis. This paper describes the advanced rotor dynamic design of this pump.

The Dynamic Analysis of SFD-Sliding Bearing Flexible Rotor System Based on Optimization Design

2012 ◽  
Vol 159 ◽  
pp. 355-360
Author(s):  
Ji Yan Wang ◽  
Rong Chun Guo ◽  
Xu Fei Si
Keyword(s):  
High Speed ◽  
Optimization Design ◽  
Critical Speed ◽  
Structural Parameters ◽  
Rotor System ◽  
Flexible Rotor ◽  
Optimization Analysis ◽  
Sliding Bearing ◽  
Critical Speeds ◽  
Design Variables

The paper establishes the mechanical model of SFD-sliding bearing flexible rotor system, adopting Runge-Kutta method to solve nonlinear differential equation, thus acquiring the unbalanced response curve and then gaining the first two critical speeds of the system. Meanwhile, the paper analyzes the sensitivity of the system on the first two critical speeds towards structural parameters, offering design variables to optimization analysis. Based on sensitivity analysis, genetic algorithm is employed to give an optimization analysis on critical speed, which aims to remove critical speed from working speed as much as possible. The critical speed ameliorates after the optimization which supplies theoretical basis as well as theoretical analysis towards the dynamic stability of high-speed rotor system and provides reference for the design of such rotor system.

scholarly journals High-Speed Rotor Suspension Formed by Fully Floating Hydrodynamic Radial and Thrust Bearings

1963 ◽  
Author(s):  
Juraj Dworski
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Critical Speed ◽  
Vibrational Excitation ◽  
Turbine Rotor ◽  
Continuous Operation ◽  
Flexible Rotor ◽  
Actual System ◽  
Apparent Absence ◽  
Thrust Bearings

The hydrodynamic suspension of a 44,000-rpm gas-turbine rotor is described with emphasis on interaction between the flexible rotor and its supports. Bearings with relatively large clearances are shown to allow continuous operation at the rotor first critical speed of 22,000 rpm. The apparent absence of hydrodynamic system instabilities is attributed to the use of simple floating-sleeve bearings. A parametric study of the influence of bearing clearances upon vibrational excitation relief is presented together with test data collected on actual system hardware.

scholarly journals Improvement of Tilting-Pad Journal Bearing Operating Characteristics by Application of Eddy Grooves

Lubricants ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 18
Author(s):  
Eckhard Schüler ◽  
Olaf Berner
Keyword(s):  
High Speed ◽  
Journal Bearing ◽  
Load Capacity ◽  
Fluid Film ◽  
Operating Characteristics ◽  
Fluid Film Bearings ◽  
Tilting Pad ◽  
Bearing Load ◽  
Bearing Loads ◽  
Tilting Pad Journal Bearing

In high speed, high load fluid-film bearings, the laminar-turbulent flow transition can lead to a considerable reduction of the maximum bearing temperatures, due to a homogenization of the fluid-film temperature in radial direction. Since this phenomenon only occurs significantly in large bearings or at very high sliding speeds, means to achieve the effect at lower speeds have been investigated in the past. This paper shows an experimental investigation of this effect and how it can be used for smaller bearings by optimized eddy grooves, machined into the bearing surface. The investigations were carried out on a Miba journal bearing test rig with Ø120 mm shaft diameter at speeds between 50 m/s–110 m/s and at specific bearing loads up to 4.0 MPa. To investigate the potential of this technology, additional temperature probes were installed at the crucial position directly in the sliding surface of an up-to-date tilting pad journal bearing. The results show that the achieved surface temperature reduction with the optimized eddy grooves is significant and represents a considerable enhancement of bearing load capacity. This increase in performance opens new options for the design of bearings and related turbomachinery applications.

Taylor-vortex instability and annulus-length effects

1976 ◽  
Vol 75 (1) ◽  
pp. 1-15 ◽  
Author(s):  
J. A. Cole
Keyword(s):  
Critical Speed ◽  
Taylor Vortex ◽  
Vortex Instability ◽  
Critical Speeds ◽  
Taylor Vortices ◽  
Torque Measurements ◽  
Concentric Cylinders ◽  
Theoretical Predictions ◽  
Range Of Values ◽  
Visual Observations

Critical speeds for the onset of Taylor vortices and for the later development of wavy vortices have been determined from torque measurements and visual observations on concentric cylinders of radius ratios R1/R2 = 0·894–0·954 for a range of values of the clearance c and length L: c/R1 = 0·0478–0·119 and L/c = 1–107. Effectively zero variation of the Taylor critical speed with annulus length was observed. The speed at the onset of wavy vortices was found to increase considerably as the annulus length was reduced and theoretical predictions are realistic only for L/c values exceeding say 40. The results were similar for all four clearance ratios examined. Preliminary measurements on eccentrically positioned cylinders with c/R1 = 0·119 showed corresponding effects.

scholarly journals Wall Temperature Measurements in Gas Turbine Combustors With Thermographic Phosphors

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Patrick Nau ◽  
Zhiyao Yin ◽  
Oliver Lammel ◽  
Wolfgang Meier
Keyword(s):  
Gas Turbine ◽  
Wall Temperature ◽  
Gas Turbines ◽  
High Speed ◽  
Bluff Body ◽  
Temperature Measurements ◽  
Transient Temperature ◽  
High Time Resolution ◽  
Ceramic Surface ◽  
Precessing Vortex Core

Phosphor thermometry has been developed for wall temperature measurements in gas turbines and gas turbine model combustors. An array of phosphors has been examined in detail for spatially and temporally resolved surface temperature measurements. Two examples are provided, one at high pressure (8 bar) and high temperature and one at atmospheric pressure with high time resolution. To study the feasibility of this technique for full-scale gas turbine applications, a high momentum confined jet combustor at 8 bar was used. Successful measurements up to 1700 K on a ceramic surface are shown with good accuracy. In the same combustor, temperatures on the combustor quartz walls were measured, which can be used as boundary conditions for numerical simulations. An atmospheric swirl-stabilized flame was used to study transient temperature changes on the bluff body. For this purpose, a high-speed setup (1 kHz) was used to measure the wall temperatures at an operating condition where the flame switches between being attached (M-flame) and being lifted (V-flame) (bistable). The influence of a precessing vortex core (PVC) present during M-flame periods is identified on the bluff body tip, but not at positions further inside the nozzle.

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