In separate series of T-700 engine tests, direct comparisons were made between the forward-facing labyrinth and dual-brush compressor discharge seals. Compressor speeds to 43,000 rpm, surface speeds to 160 m/s (530 ft/s), pressures to 1 MPa (145 psi), and temperatures to 680 K (765 F) characterized these tests. The wear estimate for 40 hr of engine operations was less than 0.025 mm (0.001 in.) of the Haynes 25 alloy bristles running against a chromium-oxide-coated rub runner. The pressure drops were higher for the dual-brush than for the forward-facing labyrinth seal, implying better seal characteristics and engine performance for the brush seal. Modification of the secondary flow path requires that changes in cooling air and engine dynamics be accounted for

Csavina, Kristine R.

Griffin, Thomas A.

Hendricks, Robert C.

Pancholi, Arvind

Sood, Dvandra

English

NASA Technical Reports Server

N95- 13607-
t,_ a-o
RELATIVE PERFORMANCE COMPARISON BETWEEN BASELINE LABYRINTH AND DUAL-BRUSH
COMPRESSOR DISCHARGE SEALS IN A T-700 ENGINE TEST __SZ" _ ZI 5 _
Robert C. Hendricks
NASA Lewis Research Center
Cleveland, Ohio
Thomas A. Griffin
Vehicle Propulsion Directorate
U.S. Army Research Laboratory
NASA Lewis Research Center
Cleveland, Ohio
Kristine R. Csavina
Sverdrup Technology, Inc.
NASA Lewis Research Center Group
Brook Park, Ohio
and
Arvind Pancholi and Dvandra Sood
General Electric Corporation
Lynn, Massachusetts
ABSTRACT
In separate series of T-700 engine tests, direct comlxu'isons were made between the forward-facing labyrinth and dual-brush compressor
discharge seals. Compressor speeds to 43 000 rpm, surface speeds to 160 m/s (530 ft/s), pressures to 1 MPa (145 psi), and temperatures
to 680 K (765 OF)characterizedthese tests. The wear estimate for 40 hrof engine operationswas less than 0.025 mm (0.001 in.) of the
Haynes 25 alloy bristlesmrmingagainst a chromium-oxide-coatedmb runner. The pressuredrops were higherforthe dual-brushthan for
the forward-facinglabyrinth seal, implying bette_ seal characteristics and engine performancefor the brush seal. Modification of the
secondaryflow pathrequiresthat changes in cooling air and engine dynamicsbeaccountedfor.
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INTRODUCTION
Labyrinth seals are efficient, readily integrated into designs, and generally easy to _I into engines but are inherently unstable
0tendricks ct aL, 1992). However, installing a simple swift break significantly enhances the stability margin and midgates this drawback
(Childs et al., 1989). Details of theoxy, experiments, and design methods for labyrinth seals and configurations are provided by Tmtnovsky
(1977). Forward-facing labyrinth tooth configurations with a variety of rub interfaces (e.g., honeycomb) were _'udied in detail by Stocker
et al. (1977) under a U.S. Air Force contract with codes developed by Morrison and Chi (1985), Dernko et al. (1988), and Rhode et al.
(1988) and by Rocketdyne (internal Rocketdyne report). Optimization procedures are available from MTI fnc. (private communication from
W. Shapiro) and are being implemented into the NASA seals codes progran.
Brush seal systems are efficient, stable, contact seals that are usually interchangeable with labyrinth shaft seals but require a smooth rub
runner interface and an interference fit upon installation. The major unknowns and needed research are tribological (e.g., life or interface
friction and wear) because of the following performance demands: pressure drops over 2.1 MPa (300 psi), temperatures to over 1090 K
(1500 °F), and surface speeds to 460 m/s (1500 ft/s). Current research supported by the Navy (private communication from W. Voorhees),
the U.S. Army (private communication from R. Bill and G. Bobula), and the U.S. Air Force's Wright Patterson Air Force Base is addressing
these issues and shows promise in meeting these demands.
In this paper we compare the relative pressure drop differences between the baseline labyrinth and dual-brush compressor discharge seals
at compressor discharge pressures to 1 MPa (145 psi) and temperatures to 680 K (765 °F) with operating speeds to 43 000 rpm.
ENGINE FLOW PATH
The power stream airflow through the compressor and the secondary airflow leakage past the compressor discharge seal are illustrated
in Fig. 1. The compressor discharge seal package and associated drain tube are located immediately downstream of the impeller and labeled
CDS. The drain tube was opened after a series of runs and swabbed for debris.
COMPRESSOR DISCHARGE SEAL
Labyrinth Seal System
The nominal 71-ram (2.8-in.) diameter forward-facing labyrinth seal system is illustrated in Fig. 2. The labyrinth teeth rub into a felt-
metal type of interface, forming the seal system. Note that the teeth are not all forward facing and are used in different ways to satisfy
different engine operating requirements_ A simulated exploded view of the seal system is given in Fig. 3 and clearly illustrates the forward-
facing teeth of the rotor. However, the housing shown in the figure is for the brush seal.
306
Brush Seal System
The brush seal system replacement package is illustrated in Fig. 4. The dual brush, nominally 71 mm (2.8 in.) in diameter, runs against
a chromium-oxide-coated mb runner interface as shown schematically. The basic seal system was envisioned by General Electric and
manufactured by Cross Mfg. Ltd. (Flower, 1990). It has 0.071-ram (0.0028-in.) diameter, Haynes 25 bristles angled 43 ° to 50 ° to the
interface with approximately 98 to 99 per millimeter of circumference (2500 per inch of circumference) and a nominal interference fit of
0.127 mm (0.005 in.) at installation. Figure 5 gives a post-test exploded view of the brush seal system with associated instrumentation lines
(cut after testing). Figure 6 provides a side-by-side comparison of the forward-facing labyrinth seal (righ0 and the chromium-oxide-coated
rub runner replacement (left); these represent the rotating interface.
APPARATUS AND INSTRUMENTATION
Pretest and post-test photographs of the dual brush and its installation in the seal system are shown as a series in Fig. 7. Figu_ 8 depicts
the dual brush prior to testing. Figure 7(a) shows the upstream view of the instrumented housing; four thermocouples are attached to the
side plates with upstream and downstream pressure taps. Figure 7Cu) shows a direct view from the downstream side, and Fig. 7(c) is an
isometric view showing the "shiny" nature of the bristle interface. Actual brush seal dimensions, rub runner coating, and installation of
instrumentation are proprietary.
ENGINE SEAL INSTALLATION AND OPERATIONS
The T-700 compressor section was lust assembled with the labyrinth seai and run as a baseline for comparison. After a test series was
completed, the engine was shipped to the Corpus Christi overhaul facility. The compressor discharge seal labyrinth system was removed
and the brush seal system was installed. The brush seal system was installed without special waxes, which can lead to bristle distortions
and irregular bristle voidage. These waxes hold the bristles off the rotor during installation and readily "burn out" at a low temperature.
Operations consisted of the standard break-in procedures with data taken primarily under steady conditions. The engine was operated
a total of 20 hr, including break-in, from ground to flight idle. Compressor speeds were to 43 000 rpm with seal housing temperatures to
680 K (765 °F). Local conditions at various compressor discharge pressures are given in Table I. The compressor discharge seal leakage
was vented through the drain tube (Fig. 1) and metered by using a calibrated orifice. Because leakage data results were noisy, pressure drop
was judged a more reliable indicator of leakage. The debris coUeeted in the drain tube was a "lubricant powder," but the spectra indicated
several contaminant metals from elsewhere in the engine. Rotor roughness, brush construction, and upstream debris generation play a major
role in determining the spectrum. Although neither radial nor axial rotor positions were monitored, such position sensors should be an
integral part of the engine dynamics.
307
RESULTS
Post-test measurements of the brush and inspection of the bristles revealed a smooth bristle interface with some characteristic shear wear
(Fig. 9) but little other visible damage. The brush wear pa_erns (Figs. 10 and 11) were att_uted to the engine dynamics although no
dynamic tracking instrumentation was available. The patterns are interesting in that they are 15 ° from the ar_irotation pin. (GE is to provide
clocking and determine ff that point is associated with a compressor bearing position or loading point.) The patterns for the upstream seal
differed from those for the downstream seal (see also Fig. 4), indicating a differential in pressure drop across each of the seals. It is
anticipated that about 40 percent of the total pressure drop across the dual brush occurred across the first brush and 60 percent across the
second brush (Flower, 1990, and private communication from R. Flower of Cross Mfg. Ltd.). Such loading resulted in stiffer bristles in
the second brush and implies a greater bristle wear. Preload and operational loads are important design life parameters (private
communication from Wright Patterson Air Force Base), but data to quantize these parameters are not available.
Another variation in the wear pattern is attributed to the rotor machining or coating variations (Fig. 11). The rotor showed a small
eccentricity and was investigated for metallic transfer, but no significant transfer was found. The chromium oxide interface was worn
smoother by the rubbing brush bristle interface, implying some form of wear or material smearing without significant transfer of the
chromium oxide (CxO).
During the test series the drain pipe (Fig. 1) was swabbed for debris. When these samples were in turn investigated with a scanning
electron microscope (SEM), nickel, chromium, and tungsten lines were observed along with other unexplainable peaks of salts (e.g.,
Fig. 12). The nickel, chromium, and tungsten lines characterize bristle materials and some possible coating wear. The debris was fine and
difficult to locate and isolate within the tube. Other metal sources and rubbing surfaces could have also produced such debris, but we
attributed it to bristle wear.
The CrO-coated rub runner exhibited slight wear scars but no spallation or coating degradation otherwise. These wear bands are readily
visible in Fig. 6, where the upper band is associated with the upstream (high-pressure side) brush; see also Fig. 5. The upstream wear
surface is characterized by Fig. 13(a) and the downstream wear surface by Fig. 13(b). The CrO coating is characterized by light and gray
areas, and the energy spectrum shows the light areas to be an NiCr composition and the gray areas to be predominantly Cr. The light and
gray areas of the matrix or unrubbed material between the bands is illustrated in Figs. 13(c) and (or). Simglarly, for the upstream wear band
in Figs. 13(e) and (0 and for the downstream wear band in Figs. 13(g) and (11). There appears to be no material transfer from the bristles
to the rotor and only minor scarring and polishing.
The result of interest here is that the initial design interference was 0.127 mm (0.005 in.) and the post-test estimate of interference was
0.101 mm (0.004 in.), or perhaps a maximum wear of 0.025 mm (0.001 in.).
Although direct flow measurements were not available, the pressure drops for each comparable compressor discharge pressure setting
were higher for the brush seal system than for the labyrinth seal system (Tables I and II). The implication is that for the same engine
308
operating conditions the dual-brash system leaked less than the baseline forward-facing labyrinth seal system. Also implied is enhanced
engine efficiency.
It is impottam to recognize that more efficient seals cannot simply be installed without computing and accounting for the secondmy
airflows necessary for the cooling and engine dynamics associated with the seal leakage modifications.
SUMMARY
In a series of T-700 engine tests, direct comparisons were made between a forward-facing labyrinth seal configuration and a dual-brash
compressor discharge seal. The nominal seal diameter was 71 nun (2.8 in.). The test conditions included compressor discharge pressures
to 1 MPa (145 psi), temperatures to 680 K (765 °F), operating speeds to 43 000 rpm, and surface speeds to 160 rrds (530 ft/s) with the
working fluid being nominally dry ambient air. The bristle wear was estimated to be less than 0.025 mm (0.001 in.) in 40 hr of engine
operations.
Direct flow measurements were not available. The pressure drops at each comparable compressor discharge lxessure setting were higher
for the brush seal system than for the labyrinth seal system, implying that for the same engine operating conditiora the dual-brush system
leaked less than the baseline forward-facing labyrinth seal system. Also implied is enhanced engine efficiency.
More efficient seals cannot simply be installed into an engine without computing and accounting for the seconda_ airflows necessary
for the cooling and engine dynamics associated with the seal leakage modifications_
ACKNOWLEDGMENTS
The authors wish to thank Chris Conrad, Edward Chisolm, Dan Erbacher, Dave Evanoff, Joe Flowers, Stephen Grozner, Tim Hawk,
Teresa Kline, Paul Lemerrneier, Karl Owen, Edith Parrott, Jeffry Paulin, Barry Piendl, Joe Shivak, Don Striebing, Queito Thomas, and the
Corpus Christi T-700 Engine Assembly Area.
REFERENCES
Childs, D.W., Ramsey, CJ., and Pelletti, J.M., 1989, "Rotordynamic-Coefficient Test Results for the SSME HPOTP Turbine Interstage
Seal for the Current and Improved Swirl Brake," NASA Lewis Grant NAG3-181, Turbomachine Laboratories Report 338-TL-3-89,
Texas A&M University, College Station, TX 77843.
Demko, J.A., Morrison, G.L., and Rhode, D.L., 1988, "The Prediction and Measurement of Incompressible Flow in a Labyrinth Seal,"
AIAA Paper No. 88--0190.
Flower R., 1990, "Brush Seal Development Systems," AIAA Paper 90-2143.
309
Hcndricks, R.C., Carlile, J.A., and Liang, A.D., 1992, "Some Sealing Concepts--A Review. Part A-Industrial, Proposed, and Dynamic;
Part B--Brush Seal Systems," Presented at the ISROMAC--4, The Fourth International Symposium of Transport 13henomenaand Dynamics
of Rotating Machinery, Honolulu, Hawaii, U.S.A., Apr. 5-8.
Morrison, G.L., and Chi, D., 1985, "Incompressible Flow in Stepped Labyrinth Seals," ASME Paper No. 85-FE-4.
Rhode, D.L., Ko, S.H., and Morrison, G.L., 1988, "Numerical and Experimental Evaluation of a New Low Leakage Labyrinth Seal,"
AIAA/ASME/SAE/ASEE 24th Joint Propulsion Conference, July 11-13, 1988, Boston, MA, Paper No. 88-2884.
Stocker, H.L., Cox, D.M., and Holle, G.F., 1977, "Aerodynamic Performance of Conventional and Advanced Design labyrinth Seals With
Solid-Smooth, Abradable, and Honeycomb Lands," NASA CR-135307.
Trutnovsky, K., 1977, "Contactless Seals. Foundations and Applications of Flows Through Slots and Labyrinths," NASA "IT F 17352.
310
TABLE I.---T-700 COMPRESSOR DISCHARGE SEAL
AND ENGINE TEST PARAMETERS
co.fijpn6o. Compressor
speed,
rpm
BasO;,_- 29 600
Brush
Diff_,_=cc
Baseline 35 500
Brush"
Difference
B_li_ 38 300
Brush
Differ, race
Baseline 41 300
Brush 40 400
Diffe_nce
Baseline 43 190
Brush 42 340
Diffe_-e
Baseline and 43 090
(a) On way up
Tulb;,,,-
qxn i_esstwe,
10 500 50
14 0(30 70
79
17400 90
20000 120
20000
19 000 145
20 000
19 700 155
discharge
Iowwcasme-
cavity
exhaust
tempenttme,
°F
348
321
49e
458
578
5O2
688
599
765
673
710
Im_lIer
cavity
I_ressm'e,
i_ia
37.5
39.5
46.7
53.1
57.5
59.2
74.2
76.0
87.6
89.9
95.6
CDLPCE
pre_sta_
pm
16.2
15.4
17.0
16.3
18.4
16.8
21.2
18.7
23.9
20.8
21.8
Pl'--_bsurc
diffmmce,
21.3
24.1
2.8
29.7
36.8
7.1
39.1
42.4
3.3
53.0
57.3
4.3
63.7
69.1
5A
73.8
Baseline and 42 500
h'mh
Baseline 41 400
Bmsh
Diffenmce
Baseline 38 400
Bntsh 37 800
Difference
Baseline 35 600
Brush 34 8O(3
Diffenmee
Baseline 29 700
Brush 31 700
Difference
(b) On way down
20 000 I 145
20 000 I 120
683
69O
6O5
17 400 [ 90 581
18 100 [ 516
14 000 I 70
14 600 I 473
10 500 I 50 378
10 5O0 I 59 379
89.9
74.1
76.4
57.7
59.1
46.8
48.2
37.6
42.9
20.9
21.2
18.9
18.5
16.9
16.9
16.0
16.1
15.8
69.0
52.9
57.5
4.6
39.2
42.2
3.0
29.9
32.2
2.3
21.5
27.1
5.6
arpm overshot and then backed down to "run through"the compressor critical speed. (Note: this is not the case m the way
_w..)
311
i
TABLE II.mRELATIVE PRESSURE DROPS FOR
BASEUNE COMPRESSOR DISCHARGE
LABYRINTH AND BRUSH
SEAL SYSTEMS
Com_r_sor
lXX_surc,
50
#70, b79
9O
120
145
(.) Onway_
PrcSStb'_
LO'b_,,h- '_'1_,¢6.e,
psi
2.8
7.1
3.3
4.3
5.4
(b) On way down
120 4.6
90 3.0
70 2.3
aSO,b59 5.6
312
Compressor discharge (CDP)
seal low-pressure tube
Flowmeter
Airflow
(a) Airflow schematic.
Co) Location of CDP flowmeter.
Figure 1 ._Schematic of engine airflow and location of flowmeter.
313
= 2,553--
2.247
1.847
- 1.837
- 1.452
_- 0.798 -_
0.788
i teeth ,"-0-020"
(angled) i 0.060 R
equal_ [ o.36o
spaced7 equ_/
2.4267, Ld_ t
2.4263 1.941 5, t
(diam A) 1.9411 l(diamB)
_ 0.125
0.115
0.040
2.3305,
2.3205
d_n
2.4305,
2.4295
d_arn
_-- 16 ° all teeth
/ except 14 °
.._'_ front five
0.040
0.020R _ .,,,-- No
typ.-., /;, step
• alk_ed
0.015 36°
34o 
Radius 44o
4places---, __\X_
No step allowed -_
Angled teeth Straight teeth
Figure 2._Schematic of labyrinth compressor discharge seal
system. (Seal teeth and axis established by diameters A and
B to be concentric within 0.003 full indicator reading. No steps
allowed on tooth face or at fillet radius. All dimensions are in
inches.)
c-g3-04723
Figure 3.--Simulated exploded view of labyrinth compressor
discharge seal systerrL
314
CDP cavity static
./
pressure baskets
(location 12:00 and 3:00 / i
aft looking forward (ALF))
CDP cavity air I- t
thermocoupl s ./t-
(location 12:00
and 3:00 ALF) _" i
/-'- CDLP cavity static
pressure baskets
!1 / (location 12:00
CDP seal / and 3:00 ALF) /--- Brush seal cartridge
/ / metal therrnocouples/ / (location 12:00 and
] / 3:00 ALF)
.... /__._ \
/ \
Brush seal cartridge _/ _ Rotating COP seal
(a) Brush seal package and airflow.
t
88.2-mm
(3.47-in.) diam
92.3 mm
(3.75 in.) diam
Flow
Chromium-carbide
rub runner
80 mm 0.178-0.25 mm
12.795 in.) (0.007-0.010 in.)
10 mm l
(0.4 in.) _-
\\\
\\N
J
1.4 mm _
(0.055 in.)
4.83 mm
-4--- (0.19 in.)
t
73-ram
(2.875-in.)
diam
(b) Illustration of dual-brush compressor discharge seal system.
Figure 4.--Dual-brush compressor discharge seal system and schematic of aJrfiow.
J
C-92-05587
315
C-93-04721
Figure 5.--Exploded view of dual-brush compressor discharge
seal system (after test).
;-93-04722
Figure 6,_Compressor discharge seal rotors for labyrinth seal
(right) and brush seal (left).
316
(a) Upstream view.
C-93-02710
(b) Downstream view.
C-93-02712
C-93-02711
(c) Isometric view.
Figure 7.--Dual-brush compressor discharge seal system after testing.
317
(a) Dual-brush seal.
(b) Seal package cavity and housing.
Figure 8.--Dual-brush seal package installation.
318
Rgure 9._Closeup views of bristles.
319
teP
=j
Figure 10.--Wear pattem for compressor discharge seal upstream
brush.
11r
,g
z,
Figure 11 .---Coating wear pattern for compressor discharge seal
rub runner.
320
2000 T M 5000 - W
t Cr 4000 -1500
1000
I_1 /_SI T'l hi
0 8 10 4 6 8 10
Energy, keY Energy, keV
(a) Particle A. (b) Particle B.
1ot w1200
10001_ Cr Co
" Cr M
" Fe COw W
0 2 4 6 8 10
Energy, keV
(c) Particle C.
Figure 12.--SEM peaks associated with drain pipe debris.
321
_ Upper wear band
Flow Lower wear band
(a) Upstream (lower) wear band.
3000 - - Ni
8
2000-
1000-
Cr
Cr Ni
0' 2 4 6 8 10
Energy, keV
(b) Downstream (upper) wear band. (c) Light area in coating matdx between bands.
Figure 13.---SEM peaks associated with chromium-carbide-coated rub runner.
322
8000-- 4000-
Cr
3O00
Ni
4000- _ 2000. Cr0
2000- 1ot iCrco' 
0 10 0_0
Energy, keV Energy, keV
(d) Gray area in coating matrix between bands. (e) Light area in upstream (lower) wear band.
8OOO
6OOO
4000
0
2000--
(f) Gray area in upstream (lower) wear band.
Figure 13.--Continued.
Cr
CF
.... , ilL
I I4 e
Energy, keY
!
I
8
t
10
323
3000--
2000 - -
o
1000--
Ni
CF
I cr • Ni
Si Co
0 2 4 6 8 10
Energy, keV
(g) Light area in downstream (upper) wear band.
{ot_
-I
o
8000-
6OOO
40OO
CF
Cr
0 2 4 6 8 10
Energy, keY
(h) Gray area in downstream (upper) wear band.
F_gure 13.---Concluded.
324


Relative performance comparison between baseline labyrinth and dual-brush compressor discharge seals in a T-700 engine test

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