Bearing designs, which shape the surface to create artificial fluid-film wedges in the absence of any applied radial load, generate radial restoring forces to keep journals from whirling. Helical- or herringbone-grooved journals or rotors show most promise of stable operation, with no sacrifice in load capacity

Anderson, W. J.

Cunningham, R. E.

Fleming, D. P.

English

NASA Technical Reports Server

April 1968	 Brief 68-10134 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Shallow Grooves in Journal Improve Air Bearing Performance 
Groove	 Groove 
Rotation	 Rotation 
Stationary Bronze
Sleeve 
Steel Rotor 
PARTIALLY GROOVED ROTOR 
Lightly loaded rotors (journals) running in gas-
lubricated, plain journal bearings are inherently 
unstable. Tangential film forces, which predominate 
under light load conditions, cause the rotor to precess 
or "whirl" about the bearing center. The frequency of 
this motion is approximately one-half that of the 
rotational speed and is generally referred to as half-
frequency whirl. This is a self-excited instability which 
produces an outward spiraling of the rotor when 
speed is increased. If contact of rotor and bearing 
occurs, a destructive seizure usually results. 
A number of self-acting bearing designs which have 
been studied exhibit somewhat stable operating 
characteristics. These designs shape the bearing sur- 
face to create artificial fluid-film wedges in the 
absence of any applied radial load, and radial restor-
ing forces are generated which tend to keep the journal 
from whirling. These designs achieve a certain degree 
of stability, but at the expense of load capacity. The 
helical- or herringbone-grooved journal or rotor
,-	 ,— \ 
Stationary Bronze 
Sleeve 
Steel Rotor 
FULLY GROOVED ROTOR 
shows the most promise of stable operation, with no 
sacrifice in load capacity. Shallow grooves formed in 
a herringbone pattern act like a pump when the rotor 
turns, and air is pumped from the bearing ends 
toward the middle. The pressure distribution that 
results is similar to that obtained in a hydrostatic gas 
bearing. Attitude angles in herringbone grooves and 
hydrostatic bearings are small and radial restoring 
forces high. The difference, however, is that the 
pressure in a herringbone bearing increases sig-
nificantly with increasing speed. 
Rotors, 1 1/2 inches in diameter by 12 1/4 inches 
long, with herringbone grooves having varying 
geometries were tested to speeds up to 60,830 rpm. 
The rotors were mounted in cylindrical bronze sleeves 
and operated in a vertical position to negate gravity 
forces. The dynamic attitude of the rotors in the bear-
ings was continuously monitored and whirl onset 
speeds recorded. Different sets of bronze sleeves were 
used to determine the effects of clearance on whirl 
contnucd overlcafl 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000134 2020-03-12T05:29:22+00:00Z
onset speeds. No external load was applied to the 
bearings. Test results in low- and high-clearance 
sleeves indicated that half-frequency whirl is most 
affected by the radial clearance. Five partially grooved 
rotors ran stably to maximum speeds of 55,000 to 
59,000 rpm when clearances ranged from 370 to 500 
microinches. When clearances were increased from 
550 to 710 microinches, the five rotors experienced 
half-frequency whirl. Limited test results with two 
rotors having identical groove geometry , except for 
groove length and comparable clearances, indicate 
that a fully grooved bearing is more stable than a 
partially grooved one.
Note: 
Technical details may be obtained from: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B68-10134 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. E. Cunningham, 
D. P. Fleming, and W. J. Anderson 
(LEW-10396) 
Brief 68-10134	
.	 Category 05


Shallow grooves in journal improve air bearing performance

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