Supression of Rotor Instability
The following principles are effective for increasing the stable operating speed range of a rotor: a. raise the lowest, critical speed of the system b. increase the external system damping The first requirement can be achieved by increasing the bearing
- PDF / 2,208,864 Bytes
- 30 Pages / 481.89 x 691.654 pts Page_size
- 9 Downloads / 214 Views
SUPRESSION OF ROTOR INSTABILITY N.F. Rieger
Procedure for Suppressinf-j Unstable ·:Ihirling of Rotors The following principles are effective for increasing the stable operating speed range of a rotor: a.
raise the lowestcritical speed of the system
b.
increase the external system damping
The first requirement can be achieved by increasing the
bearin~
radial
stiffness or the bending stiffness of the rotor, or both.
The second require-
ment can be met by using a bearinrr or support type which inherently contains more non-rotating velocity damping.
It should be noted that the
increase of any damping which rotates with the shaft itself has a stabilizing effect below the bending critical speed, and a
destabilizin~
effect above the
bending critical speed. Stabilization of Rotors in Fluid-Film Bearings r.~ore-Stable
Bearing Types
Several investigations have been carried out to assess the relative stability of different bearing types. shown in figure 1.
Pinkus [1] compared the bearing types
Hydraulically loaded bearinr.s and tilting pad bearmgs
were found to be the most stable, i.e., to give rise to the highest instability threshold speed for the rotor system.
O. Mahrenholtz (ed.), Dynamics of Rotors © Springer-Verlag Wien 1984
Plain cylindrical bearings were the
142
N.F. Rieger
least stable.
The self-energizing bearing shown in figure 2 was designed
to increase bearing loading by transferring pressure from the lower half of the bearing to the upper half.
During testing, the top of the self-energizing
be a r i n g was uti Ii zed to apply an additional external load to the journal. By closing either valve 1 or valve 2, the bearing could be either selfenergi zed or externally loaded.
o o
CYlIHORICAL
PRESSURi:
Fi~ure
1
ELLIPTICAL
SYMM
AS."" THREE'LOaE
THREE' lDB£
TILTING AIIO
Bearings Tested by Pinkus to Compare Stabi lity [1]
~ PRESSURE OIL SUPPLY
PRESSUP.E OIL SUPPLY
Figure 2
Self-Energizing Bearing Pinkus [1]
Suppression of Rotor Instability
143
Tondl t 2] also undertook an experimental investigation to compare several basic types of bearinfl geometry for their ability to resist initiation of unstable self-excited whirling.
Tests were made on cylindrical and
elliptical bearings, and also on specific multi-lobe bearing designs, flexibleelement bearings, and on two loose-bushing bearing designs.
Of these, one
design had a cylindrical bushing and the other had a flexible-element loose bushing element. Tondl's tests showed that self-excited whirling was always very intensive for plain cylindrical bearings.
Elliptical bearings exhibited better
resistance to initiation of self excited whirling, i.e., the instability threshold speed was higher than for plain bearings.
Tondl found that the multi-lobe
bearings shown in figure 3 were also relatively stable.
Figure 3
In such bearings
Multi-Lobe Bearings Tested by Tondl [2]
direct contact between the journal and the bushing surface appears to be possible only in small areas.
Followinf.j the
machinin~
of the original bush-
Data Loading...