A damping seal between a high speed rotor member and stator member that separates pressurized fluid compartments is described. It is characterized by the rotor member having a smooth outer surface and the stator member having its bore surface roughened by a plurality of pockets or depressions

Vonpragenau, G. L.

English

NASA Technical Reports Server

United States Patent [191 
von Pragenau 
[54] DAMPING SEAL FOR TURBOMACHINERY 
[75] Inventor: George L. von Pragenau, Huntsville, 
Ala. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 692,875 
[22] Filed: Jan. 18,1985 
Related U.S. Application Data 
[63] Continuation of Ser. No. 489,902, Apr. 28, 1983. 
[51] Int. Cl.4 ........................ F16S 15/44; FOlD 11/08 
[52] U.S. C1. ....................................... 277/53; 415/174 
[58] Field of Search ............................. 277/87, 53, 54; 
4 15/4 1 5 
[11] Patent Number: 4,545,586 
[45] Date of Patent: Oct. 8, 1985 
[561 References Cited 
U.S. PATENT DOCUMENTS 
2,327,867 6/1943 Meyer ...................... 277/87 
2,998,991 9/1961 Spencer ............................... 415/174 
3,137,602 6/1964 Lincoln .... 
3,867,001 2/1975 Moskowitz ............... 
4,060,250 11/1977 Davis et a]. ....... 
4,162,077 4/1979 Crow et al. .. 
4,384,725 5/1983 Nenov ........ 
4,429,883 2/1984 Nakanishi . 
Primary Examiner-Robert I. Smith 
Attorney, Agent, or Firm-Joseph H. Beumer; John R. 
Manning; Leon D. Wofford, Jr. 
[571 ABSTRACT 
A damping seal between a high speed rotor member 
(30) and stator member (33) that separates pressurized 
fluid compartments which is characterized by the rotor 
member having a smooth outer surface and the stator 
member having its bore surface roughened by a plural- 
ity of pockets or depressions. 
6 Claims, 3 Drawing Figures 
17 
https://ntrs.nasa.gov/search.jsp?R=19860011317 2020-03-23T06:36:03+00:00Z
U.S. Patent Oct. 8,1985 4,545,586 
17 
FIG. 1 
4.545.586 
DAMPING SEAL FOR TURBOMACHINERY 
This application is a continuation, of application Ser. 
No. 489,902, filed 4-28-83. 
ORIGIN O F  THE INVENTION 
The invention described herein was made by an em- 
ployee of the United States and may be manufactured 
and used by or for the Government of the United States 
for governmental purposes without the payment of any 
royalties thereon or therefor. 
TECHNICAL FIELD 
This invention relates to a seal for the gap that exists 
between fixed and rotating portions that separate pres- 
surized fluid compartments which, because of its unique 
characteristics is identified as a damping seal. The seal 
because it both damps rotor motion and significantly 
reduces fluid leakage across the gap is a suitable re- 
placement for labyrinth seals and squeeze film dampers. 
BACKGROUNDART 
Squeeze film dampers are commonly used to avoid 
high vibrations and instability encountered in high per- 
formance rocket engines and aviation turbomachinery. 
Squeeze film dampers are annular supports of major 
bearings and respond to the lateral bearing loads such 
that rotor motion is damped, especially at rotor reso- 
nances (i.e. critical speeds). In a typical squeeze film 
damper a viscous fluid, e.g. oil, is trapped in an annular 
groove which houses a bearing support ring. The fluid 
is sealed with O-rings between the groove walls and the 
bearing support ring. The support ring assumes differ- 
ent eccentric positions relative to the groove by follow- 
ing the lateral motions of the rotor bearing. The damp- 
ing fluid is thus rushed and squeezed circumferentially 
inside the annular groove which causes a damping ef- 
fect. A supply source replenishes the damping fluid to 
keep the groove filled when leaks occur through the 
O-rings on the groove walls. The groove contains occa- 
sionally a circumferential wave spring to better center 
the bearing and to provide more stiffness in supporting 
the bearings. Too much stiffness, however, diminishes 
the damping effect and too little stiffness permits exces- 
sive rotor motion and rubbing. 
Accordingly, what is proposed is a damping seal that 
restricts leakage like a labyrinth seal and, also, extends 
the stable rotor speed range to more than twice the first 
critical speed. 
DISCLOSURE OF THE INVENTION 
In accordance with this invention, a damping seal is 
provided with a stator part having a roughness for stabi- 
lization and sealing and a rotor part which is smooth. 
The stator part forms a narrow seal gap with the smooth 
rotor surface. The stator part has its inner bore surface 
roughened with pockets of regular or random patterns. 
The roughness produces a high flow resistance that 
keeps the leakage lower than in labyrinth seals but also 
hinders circumferential flow (Couette flow). 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a partial cross-section of a high pressure 
pump utilizing the damping seals according to the pres- 
ent invention. 
. FIG. 2 is an idealized view of the invention showing 
the stator part and rotor part. 
2 
FIG. 3 is a partial cross-section of FIG. 2 showing the 
fluid Couette flow in the seal gap. 
5 INVENTION 
BEST MODE FOR CARRYING OUT THE 
Referring to FIG. 1 wherein is shown a partial cross- 
sectional view of a high pressure pump for the space 
shuttle main engine wherein damping seals 11,12, 13,14 
according to the present invention are utilized between 
lo the inlet of the impeller 16 and surrounding housing 17, 
and the discharge portion 18 of the impeller 16 and the 
surrounding housing 17. As shown, the cyrogenic fluid 
being pumped flows in the direction of the arrows 20,21 
15 from the high pressure side of the impeller 16 to the 
lesser pressure side through the damping seals 11, 12, 
13, 14. The impeller 16 seal surface is smooth and the 
housing 17 seal surface is roughened. The impeller 16 
has a speed of rotation from 30,000 to 34,000 rpm. 
Referring to FIG. 2 wherein is shown in detail an 
idealized view of the damping seal which has a rotor 
part 30 which a smooth outer surface 32 which would 
correspond to the impeller 16 seal surface of FIG. 1 and 
a stator part 33 with an outer bore surface roughened 
25 with triangular pockets 34 which would correspond 
with the housing 17 seal surface of FIG. 1. 
In this embodiment, triangular pockets 34 produce 
turbulence to reduce leakage 28 and circumferential 
flows 35. Two pocket walls 29 are angled 60 degrees to 
30 the rotor’s longitudinal and rotational axis to enhance 
the fluid exchange in and out of the pockets 34. The 
base wall of the triangular pockets 34 extends longitudi- 
nally to the rotor’s axis. The pocket’s flow collides with 
35 the leakage crossing the mouth opening of the pocket 34 
causing the fluid leakage 28 and circumferential flows 
35 to slow down. The isogrid pattern shown for triangu- 
lar pocket 34 generates the most flow resistance for 
least pocket volumn. The triangular pockets 34 have the 
40 highest ratio of perimeter ver.sus area of all regular 
polygones and thus offers the highest flow resistance in 
all directions. Other regular and irregular patterns of 
cylindrical, honeycomb, diamonds, and other shaped 
pockets could be used but with less effect. 
Damping seals require a pocket depth (ks) versus 
rotor surface roughness (kr) ratio that range from 10 to 
10,000. It is the roughness ratio (k&) that determines 
the friction ratio which in turn determines the ratio of 
rotor surface velocity (w) (angle velocity of rotor times 
50 the radius of the rotor) versus the fluid circumferential 
velocity (v). The objective is to reach a high ratio (w/v) 
because this ratio sets the rotational speed limit of the 
rotor. The first critical speed of the rotor times the ratio 
(w/v) is approximately the speed limit for a rotor stabi- 
55 lized by damping seals. The approximate relationship is 
20 
45 
w / v  = 1 +&/! (1) 
60 
Where: 
w = Rotor surface velocity 
v = Fluid circumferential velocity 
fs= Stator surface friction for fluid 
fr=Rotor surface friction for fluid. 65 
Moody’s well published pipe friction equation with the 
seal gap as the hydraulic radius gives for turbulent flow 
the approximate relationship 
4,545,586 
3 
3 (2) 
L/fr = KZ 
Where: 
ks=Pocket depth of stator, inch 
k,= Rotor surface roughness, inch. 
A substitution of equation (2) into (1 )  gives the follow- 
ing: 
3 (3) 
w/v  = 1 + uk,/k, 
which yields the seal’s velocity ratio w/v which speci- 
fies the rotor rotational speed limit. 
A more accurate rotor speed limit is obtained through 
the analysis given in NASA Technical Paper 1987, 
March 1982 (Published on June 8, 1982) in conjunction 
with complex rotor dynamic simulations taking into 
account other whirl drivers such as turbine tip clear- 
ance effects (Alford forces). The accurate speed limit is 
slightly less than the approximate speed limit mainly 
because other whirl drivers are included. For example, 
if the first critical speed is at 10,000 RPM then the ap- 
proximate speed limit for stable operation is 50,000 
RPM assuming a velocity ratio (w/v) of five. 
What is desired is to apply damping seals generously 
to suppress whirl drivers and to maintain the high speed 
limit set by the damping seal’s velocity ratio (w/v). 
A typical design with a 2.9 inch seal diameter, 0.6 
inch seal length, 0.006 inch seal gap, 0.000032 inch rotor 
roughness, and 2,000 psi pressure drop has 0.02 inch 
deep pockets with a 0.075 inch width to a side, and a 
wall thickness of 0.0025 inch. The velocity ratio (w/v) 
is 5.  Sufficient wall thickness is required to avoid fatigue 
when rubbing occurs. The full pocket depth is the 
roughness value. The roughness value for the stator 
pockets reaches a limit less than the depth, however, for 
very deep pockets because the fluid near the bottom 
does not participate in the fluid exchange. 
The stator part roughness 33 produces a high flow 
resistance that keeps the leakage lower than labyrinth 
seals and also hinders the circumferential flow. The 
circumferential flow is the Couette flow 35, as shown in 
FIG. 3, due to the shear forces generated by a rotor 
turning in a viscous and often turbulent fluid film. The 
Couette flow 35 will assume half the rotor speed for 
equally smooth stator and rotor surfaces. The high 
speed Couette flow of the smooth stator and rotor sur- 
faces generates a driver for half speed whirls at the first 
significant rotor resonance. Contrarily, damping seals 
of the present invention exhibit Couette flows as low as 
one-sixth the rotor speed and whirls are avoided. 
The small leakage flow of damping seals induces 
stiffness and damping effects when the gap between the 
rotor and stator changes at each circumferential posi- 
tion as the rotor moves laterally. The leakage resistance 
increases where the gap narrows and decreases where 
the gap opens. The fluid injected axially by the pressur- 
ized upstream compartment causes a high pressure in 
the narrow gap area that is diametrically opposite to the 
open gap area where lower pressure is induced. The 
integral result is a stiffness effect. The area where the 
gap becomes smaller rushes more fluid downstream 
than the diametrically opposite area where the gap 
becomes larger storing momentarily the fluid. The rush- 
ing and storing of fluid causes another pressure distribu- 
tion proportional to lateral rotor velocity. Diametri- 
4 
cally opposite high and low pressure forces are gener- 
ated that add damping to the stiffness effect. The whirl 
driving force is caused by the circumferential Couette 
flow that twists the axial flow into a helix. Flow zones 
5 approaching a narrow gap area divert more flow down- 
stream while the opposite is true for flow zones ap- 
proaching an open gap area.Diametrically opposed 
high and low pressure areas are generated perpendicu- 
lar to the zones of the stiffness effect adding a forward 
10 whirl driver. See NASA Technical Paper 1987, March 
1982, written by the inventor, and which was published 
June 8, 1982. It is considered practical for the damping 
seal to achieve velocity ratios of ten to one. 
Thus, has been disclosed a unique damping seal that 
may serve as a replacement for labyrinth seals or other 
rotating shaft seals that separate pressurized compart- 
ments. The damping seal takes over the dynamic func- 
tion of a squeeze film damper and is mounted at several 
shaft seal locations. The seal consists of two parts; the 
2o stator with a rough bore surface and the rotor which 
has a smooth shaft running inside the stator. 
As the damping seal of the present invention will fit in 
places of conventional shaft seals it is possible to reclaim 
turbomachines that are troubled by expensive shut- 
25 downs. No extra space is required for the damping seals 
because of their dual function a seals and dampers. Ro- 
tors can be stiffly supported by mounting the bearings 
directly to hard points and by adding multiple supports 
3o with each damping seal. High critical speeds are the 
result which together with high seal damping increases 
speed limit and bearing life. Rotor motion is also re- 
duced which permits tighter clearances to achieve high 
efficiency in energy conversion. Turbomachinery thus 
35 designed will be light and compact. Rotational speed 
limits of approximately 3 to 6 times the first critical 
speed are feasible. 
The embodiments described are considered illustra- 
tive of the invention and changes and variations may be 
40 made without departing from the scope of the claims. 
I claim: 
1. In a high speed turbomachinery, a journal bearing 
for increasing rotor speed significantly and damping 
rotor motion, comprising: 
an elongated stator portion having a bore along its 
longitudinal axis; 
an elongated rotor portion situated within said bore 
of said stator portion with a small gap therebe- 
tween; 
a high pressure fluid volume on one side of said stator 
and rotor portions and a low pressure fluid volume 
on the other side of said stator and rotor portions so 
said small gap is filled with fluid leaking from said 
high pressure fluid side to low pressure fluid side 
and thereby acting as a journal support; 
said rotor portion having a smooth rigid outer surface 
on the surface of said rotor portion facing the stator 
portion said smooth rigid outer surface of said 
rotor portion having a typical roughness of 
said stator portion having an outer surface provided 
with shallow patterned pockets facing said rotor 
portion for providing high roughness for all fluid 
flow directions so as to reduce leakage rate of fluid 
across said gap, and rotor whirl forces are reduced, 
said pockets having a pocket depth corresponding 
to 10 to 10,000 times the roughness depths of said 
smooth rigid outer surface of said rotor portion and 
45 
50 
55 
60 0.000032 inch; 
65 
4,545,586 
5 6 
having rigid side walls with a substantial thickness 
that prevent fatigue and break-up of the walls when 
rubbing contact with said rotor portion occurs. 
2. In a high speed turbomachinery, the journal bear- 
said pattern surface on said stator portion is com- 
posed of a plurality of triangular shaped pockets 
being spaced to form a perimeter wall between 
adjacent pockets with substantial thickness. 
an elongated rotor portion situated within said bore 
of said stator portion with a small gap therebe- 
tween; 
a high pressure fluid on one side of said stator and 
rotor portions and a low pressure fluid on the other 
side of said stator and rotor portions so said small 
gap is filled with fluid leaking from said high pres- 
sure fluid side to said low pressure fluid sides and 
thereby acts as a journal support; 
said rotor portion having a smooth rigid outer surface 
on the surface of said rotor portion facing the stator 
portion; 
said stator portion having a roughened surface pro- 
vided with depressions on said stator portion facing 
said rotor portion so as to result in a reduced leak- 
age rate of fluid across said gap and rotor whirl 
forces are reduced, said depressions having side 
walls with a substantial thickness to prevent fatigue 
and break-up of the walls when rubbing contact 
wherein said fluid within said gap has a fluid velocity 
ratio of approximately ten to one as determined by 
the following parameters relationship: 
ing according to claim 1, wherein: 5 
3. 
said triangular shaped pockets have one side extend- 
ing longitudinally to the rotational axis of said 
rotor portion and the other side angles 60 degrees 
to the rotational axis of said rotor portion. 
4. In high speed turbomachinery, a journal bearing 
for damping rotor motion and providing stable high 
speed operation, comprising 
an elongated stator portion having a bore along its 
longitudinal axis; 20 with said rotor portion occurs; and 
an elongated rotor portion situated within said bore 
of said stator portion with a small gap therebe- 
tween; 
a high pressure fluid on one side of said stator and 
rotor portions and a low pressure fluid on the other 
gap is filled with fluid leaking from said high pres- 
sure fluid side to said low pressure fluid side and 
thereby acting as a journal support; 
said rotor portion having a smooth rigid outer surface 30 
on the surface of said rotor portion facing the stator 
portion; 
said stator portion having an outer surface provided 
cause a reduced leakage rate of fluid across said 
pressions having side walls with a substantial thick- 
when rubbing contact with said rotor portion oc- 40 
curs; and 
wherein said fluid within said gap has a fluid velocity 
in the range of ten to one as determined by the 
following parameter relationship: 
a high speed turbomachinery, the journal bear- 10 
ing according to claim 2, wherein; 
15 
25 3 
side of said stator and rotor portions so said small w / v  = 1 + E 
Where: 
w/v=Fluid velocity ratio 
w =Rotor surface velocity v = Fluid circumferential 
velocity k,= Depth of surface depression on stator 
surface within the range of 10 to 10,000 times the 
value of k, 
0.000032 inch. 
comprising: 
rotating within the bore of an elongated stator 
portion with a small open gap therebetween divid- 
ing a high pressure fluid volume one side of said 
portions from a low pressure fluid volume on the 
other side of said portions; 
sealing and damping means for sealing said gap be- 
tween said rotor portion and damping radial rotor 
motion and avoiding rotor whirl thereby increas- 
ing rotor speeds and bearing life; 
said sealing and damping means being composed of a 
smooth rigid outer surface with a typical roughness 
w/v = Fluid velocity ratio of 0.000032 roughness on said rotor portion, and 
w=Rotor surface velocity rigid patterned surface pockets on said stator por- 
v = Fluid circumferential velocity tion providing high roughness for all fluid flow 
k,=Depth of surface depression on stator surface directions to reduce fluid leakage along said gap 
within the range of 10 to 10,000 times the value of and to hinder circumferential flow; 
kr 55  said patterned surface having a depression depth in 
kr= Rotor surface roughness value of approximately the range of 10 to 10,000 times the depression depth 
0.000032 inch. of said smooth rigid outer surface of the rotor por- 
5. A sealing and damping means replacement for tion, said pockets also having pocket walls with 
journal bearings in high speed turbomachinery, com- substantial thickness to prevent fatigue and break- 
prising: up of the walls should rubbing contact with said 
an elongated stator portion having a bore along its rotor occurs. 
with depressions facing said rotor portion so as to 35 
gap, and rotor whirl forces are reduced, said de- 
ness that prevent fatigue and break-up of the walls an having an rotor portion 
kr=Rotor surface roughness 
'. A high pressure turbomachinery rotor 
Of approximately 
and 
45 
3 
w/v  = 1 + Uk,/k, 
Where: 
50 
6o 
longitudinal axis; * * * * *  
65 


Damping seal for turbomachinery

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