NASA Technical Reports Server (NTRS) 19970015335: Effects of Slag Ejection on Solid Rocket Motor Performance

14 Pages·0.96 MB·English

by  NASA Technical Reports Server (NTRS)

NA SA-CR-204Z ',]
I
I II I II_ •I # : -
AIAA 95-2724
Effects of Slag Ejection on Solid
Rocket Motor Performance
R. Harold Whitesides and David C. Purinton
ERC, Incorporated
Huntsville, AL
John E. Hengel and Stephen E. Skelley
NASA/Marshall Space Flight Center
Huntsville, AL
31st AIAA/ASME/SAE/ASEE
Joint Propulsion Conference and Exhibit
July 10-12, 1995/San Diego, CA
I I II
For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics
370 L'Enfant Promenade, S.W., Washington, D.C. 20024
EFFECTS OF SLAG EJECTION ON SOLID ROCKET MOTOR PERFORMANCE
R.Harold Whitesldes* andDavid C. Pudnton**
ERC, Incorporated
Huntsville, Alabama
JohnE. Hengel*** andStephen E. Skelley****
NASA Marshall Space FlightCenter
Huntsville, Alabama
Ab_ract ln(roduction
In past fidngs of the Reusable Solid Rocket Space Shuttle Mission STS-54, launched
Motor (RSRM) both static test and flight motors 13 January 1993, experienced a short duration
have shown small pressure perturbations pressure deviation in the right-hand Reusable
occurring pdmadly between 65 and 80 seconds. Solid Rocket Motor (RSRM-29B) of 13.9 psi at
A joint NASA/Thiokol team Investigation 67.5 seconds into the bum. Pressure
concluded that the cause of the pressure perturbationsandsome roughnessofthe pressure
trace have been general characterisUcs of
perturbations was the pedodic Ingestion and
ejection of molten aluminum oxide slag from the RSRM's with previous occurrences approaching
cavity around the submerged nozzle nose which the magnitude of RSRM-29B; however, this
tends to trap and collect Individual aluminum incident resulted in the largest vehicle thrust
oxide droplets from the approach flow. The Imbalance calculated to date. A joint
conclusions of the team were supported by NASA/Marshall Space Flight Center and Thiokol
numerous data and observations from special team was assembled to conduct an in-depth
testsincludinghigh speed photographicfilms, real Investigation of the exact cause of the pressure
time radiography, plume calodmeters, perturbationsand to determine the limiting case.
accelerometers, strain gauges, nozzle TVC After extensive analyses and testing, including
system force gauges, and motor pressure and speciallyinstrumentedfull scale motor static tests,
thrustdata. A simplisticslag ballisticsmodel was the joint MSFC/Thiokol team concluded that the
formulated to relate a given pressureperturbation source of the pressure perturbations was the
to a required slag quantity. Also, a cold flow periodic ingestion and discharge of molten
model using air and water was developed to aluminum oxide slag from the reservoir around
provide data on the relationshipbetween the slag the submerged nozzle nose which serves to trap
flow rate and the chamber pressure increase. and collect individual aluminum droplets from the
Boththe motor andthe cold flow model exhibited approach flow. A similar phenomena has been
low frequency oscillations in conjunction with observed inother large solidrocket boosterswith
pedods of slag ejection. Motor and model aluminized composite propellants andsubmerged
nose nozzles. The conclusions of the
frequencies were related to scaling parameters.
The data indicatethat there is a periodicityto the Investigation group were supported by numerous
slag entrainment and ejection phenomena which observations and data Including flight and static
is possibly related to organized oscillations from motorhigh speed photographic films, static motor
instabilities inthe dividing streamllne shear layer Real Time Radiography, chamber pressure and
which impinges on the underneath surface of the thrust data, plume calorimeter data, nozzle
nozzle. acoelerometer data, case and nozzle strain data,
andnozzle TVC systemforce data andmore.
* Manager, Propulsion;AIAA Associate Fellow
Obiectives
** Engineer, PropulsionAnalysisGroup
*** Senior Aerospace Engineer, ED34
****Aerospace Engineer, ED34 A combined analytical and experimental
approach was adopted to develop an
Copyright © 1995 by the Amedcan Institute of
understanding of the effects of slag ejection on
Aeronautics and Astronautics, Inc. All dghts
motor performance. A simplistic quasi-steady
reserved.
analytical model was formulated for the purpose
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of determiningthe instantaneousslagflowrate integrated to determine the total slag quantity
andthetotalquantityofslagrequiredto producea discharged.
given pressureperturbation. The analyticalmodel The analysis steps and equations utilized
of the ejection of a stream of slagwas also used are as follows for a given motor pressure
to evaluate the relationship between thrust and perturbation. The differential form of the
pressure during the slag ejection event. The continuity equation is solved for the effective
analytical model was supported by comparison throat area asafunction oftime.
with static motor test results and cold flow model
data. The objectives of the coldflow model tests fp,rdV÷vrdP
were to demonstrate that simulated slag ejection 1,°tY) tYJJ
through a rocket motor nozzle will produce an (1)
dt dt RT
increase in chamber pressure and to obtain
quantitative measurements ofthe amplitude ofthe
where
pressure increase relative to the simulated slag
flow rate. This data could be related to the full
scale motor throughthe application of appropriate (2)
dd--_t=pp.rb.A= (Mass Generation)
scaling parameters and used to calibrate the
analytical slag ballistics model. A secondary
and
objective of the cold flowtestswas to investigate
potential internal motortriggeringmechanisms for
slag ejection. The triggering mechanism is I'Yl_t'l At
-.-u = (Mass Discharge) (3)
defined to be the causal factor inthe process of dt C*
sudden and periodicentrainment of slag from the
reservoir undemeath the nozzle intothe gas flow The motor surface area, bum rate and other
andsubsequent expulsionthroughthe nozzle. ballistic parameters are used to calculate an
effective throat area versus time during the
SlagI_allisti_ Mode! pressureperturbation. Thethroat area blockageis
then calculated by subtractingthe effective throat
Model area from the nominal throat area without
blockageatthe appropriatetimes.
An analytical slag ballistics model was
conceived to determine the quantity of expelled Aldock= Atnomlnl - Ateff_.t_ (4)
slag associated with a given pressure
perturbation. Since the time duration of the rise The next step is atrajectorycalculation of
time of a pressure perturbation was long (-0.8
asingle sphere inan assumed parade of spheres
sec.) compared tothe acousticwave travel time in as they fly through the nozzle. The sphere
the motor(0.03 sec.) aquasi-steadyapproachwas diameter isdetermined by setting the frontal area
utilizedtodevelop the model. The model isbased ofthe spheretothe throat blockage. The flowfield
on the concept of calculating a time-dependent through the nozzle is calculated from the one-
quasi-steady slag flow rate through the nozzle
dimensional, compressible, isentropic flow
throat from the continuityequation. The velocity equations. The velocity of the slag sphere at a
of the slag is computed from a trajectory analysis specifictime step is given by
of a hypotheticalsphere of slagas itfliesthrough 1
the nozzle. The slag stream is treated as a
continuous parade of spheres. The cross
sectional flow area of the stream or the sphere
diameter iscalculated from atransient calculation
ofthe amount ofthroat area blockage requiredto where GF= Vehicle acceleration
produce a given pressure increase. The slag is Fo = Drag forceon slagsphere
assumed to be a slurry mixture of molten M== Mass ofslagsphere
aluminum oxide and combustiongases and has a AL= Distance traveled, Incremental
densityof "K"timesthe density ofaluminum oxide
at combustion temperature where K is The drag force is based on the differential
approximately 0.2. The instantaneous slag flow betweentheslagvelocity andthe gas velocity and
rate is calculated for time steps spanning the a drag coefficient of 0.5. The mass of the slag
entire period of apparent nozzle blockage and sphere is based on a diameter from the throat
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areablockageanda density for the slag slurry in Figure 1. The slag flow rate calculated by the
calculated from t_hedensity of molten aluminum model during the 0.8 seconds of nozzle blockage
oxide (110 Ibm/ft_) multiplied by a factor, K. The is shown inFigure 2. The Integrated slag weight
value of "K"isset to 0.20 based on a correlation is 1446 Ibm. Parametric calculations were
ofthe coldflowmodel data. performed with the model to determine the
variation of slag weight and the thrust
Once the slag slurry velocity profile enhancement factor with pressure perturbation
through the nozzle iscalculated, the slagflowrate amplitude. Results are plotted in Figure 3. The
at the throat plane is calculated by applying the pressure perturbationswere assumed to occur in
continuityequation at each time step. the same 0.8 second time pedod. The thrust
enhancement isthe thrust Increase withslag flow
(s) divided bythe thrustincrease without slag flowfor
r_ = Ps" Ablock "Vldaglhroat
a given pressure perturbation. It may also be
stated asthe percent change in thrust divided by
The total slagweight dischargedduringa pressure
the percent change in pressure dudng a slag
perturbationis then determined by integratingthe
induced pressureperturbation. The values above
above equation over the time interval of nozzle
unity are due to the momentum effects of slag
blockage. Also, the total thrust is calculated by
ejectionwhichappear to be moresignificant atthe
adding the slag momentum at the nozzle exit
lower pressure amplitudes. Without the slag
plane tothe gasthrust.
momentum effect, the throat area reduction
reduces the thrust to pressure ratio which would
= +F,,g (7)
result in a thrust enhancement value less than
where
unity. The thrust enhancement value dudng a 9
Fga= = Pc" Atenectlve "CFM (8) psipressureperturbationfor static motortestQM1
and was calculated directly from measured thrust and
F$1ag=r_ •V$1age_ (9) pressure data to be 1.3 which required a slag
densityfactorof 0.3 toagree withmodel resultsas
Thethrustto pressureratio isthen calculated by shown in Figure 4. The cold flow model
simulationusingwater yielded a"K" value of0.2
.,,
F FtotaI (10)
,(io
P Pc I =
Increases inthrust to pressure ratio are predicted :f
for certain quasi-steadyslag ejectionevents which
are primarily attributed to the thrust increase
associated with the slag momentum term. This I_= T -- "SRM _B. 'T1_64
resultisconsistentwithMurdock's studyI ofthrust |= _r
perturbations from single and multiple bodies 625 -- I,,I==I=IIo==_ ,__J•
passingthrough a solid rocket nozzle. He found 636465666768897071 727374757677
that the total impulse from a mass ejection event Tim (S=cond=)
isalways positive,
Figure 1. Nozzle Blockage Analysis
Results
25O0
This simplistic, analytical model was used
to model the pressure perturbation in RSRM-29B
for the STS-54 flight. This motor exhibited a 21050000 J f'-'_ "_
pressureperturbationof 13.9 psiat approximately
67 seconds. The motor pressure and model
_1000 1"o1111r_$1;ndlll8,110
results are shown in Figure 1. The calculated
pressure during blowdown after the nozzle is SO0 Olm:m_rgt4-144S
unblocked goes below the motor data due to the
use ofa constant bum surface. The major output 67 67.1 67.2 67.3 67.4 67.5 67.6 67.7 87.8 67.9 68
of the analysis is the calculated nozzle throat Time(==¢oMs)
blockageasafunction oftime which isalsoshown
Figure2. RSRM 29-B, STS-54 Slag Flowrate
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whichwasusedto generatea set of model naturally entrained by the air flow and expelled
predictionaslsoshowninFigure4. Althoughhigh through the nozzle in a manner to simulate a
accuracyin predictingthe thrustenhancement horizontalstatic motor firing. The model was also
ratio is not claimed for the model, the apparent provided with a centedine axial fluid injector to
agreement between motordata and model results enable data comparison with an earlier precursor
supports the realism of thrust enhancement model with a converging diverging 10 percent
values greaterthan unity. scale nozzle and centedine water injection. A
sketch of the model is provided in Figure 5. The
dashed line near the wall represents the scaled
35OO AnalyticalModel positionof the bum surface at 67 seconds. The
3OOO K=0.20 jm model wallsare nonporousand allflowissupplied
I
AnalyticalModel -t down the bore of the model. The first joint
2ooo K=,0.30 f .r J upstream of the nozzle represents the aft field
f,- joint includingthe inhibitor. A photograph of the
J
1500
._looo /" .4-.I" installed model and water injection system is
U) shown in Figure 6. The model is disconnected
5C0 from the exhaust diffuser andthe view is looking
upstream. A portion of the nozzle exit is visible
0 2 4 6 8 1012141618202224262830 along with the model chamber and the forward
Pr,.u_ s_e Amplitu(dpeOd)
plenum into which four facility air supply pipes
Figure 3. Predicted Slag Weights deliver the total model flow. Each of the four
facility supply pipes includes a choked metering
nozzle to prevent model chamber pressure
1.8 = Analyt_,a!Model excursions related to slag ejection from affecting
the mass flowrate of airthrough the model. The
1.4 '_ "-'= AnalyticalModel stainlesswater supplytubing is routed to each of
K=0.30
12 remote operated valves positioned
1.2 _ "_- QM1StaticTe=t
circumferentially around the model adjacent to
each injection port located in the aft end of the
chamber cavity underneaththe nozzle nose. The
large linesand portsare designed to minimize the
0.6 F
0.4 water injectionvelocity. Water is delivered to the
0 2 4 6 8 1012141618202224262830 model from apressurizedtank through a metering
Pressure SpikeAmplitude(l_d)
odfica andcontrolledby remote operatingvalves.
Figure 4. Thrust Enhancement Factor
The RSRM 6.5 percent Scaled Slag
Cold FlowSlaa Model Ejection Model was tested inthe Marshall Space
Flight Center Solid Rocket Motor Air Flow Facility
Model Descdotion (SAF).,: This facility hasthe capability to testa 10
percent scale RSRM at full scale Reynolds
A simulationofthe effectsof slagejection number. The facility is a pressure blowdown
on motor performance were achieved using a systemwitha tank storage capacity of 9100 cubic
scaled air flowmodel withwater to simulate slag, feet at1960 psla. A flowrate ofupto 320 Ibn'Vsec
An existing horizontal bed solid rocket motor air can be delivered to the model at pressures to
flow test facility and model chamber hardware 1200 psla. Thedelivered airisfilteredand passed
were adapted to the desiredtest configuration. A through a calibrated ventud for metering. The
6.5 percent scaled RSRM nozzle withsubmerged model Inlet pressure is controlled by a quiet trim
nose and the full length contoured expansion control valve withan automated feedback control
sectionwas designed withfixed gimbal angles of system. The mass flow through the system is
0, 2, and 4 degrees. The chamber to throat exhausted tothe atmospherethrough the diffuser,
contraction ratiosimulates amotorbum time of67 an exhaust pipe, and then a vertical 85dB
seconds when slag ejection is active. Water silencer. The diffuser enables the test model to
injection ports were provided underneath the operate at the fullscale boosternozzle expansion
nozzle noseinthe aft end ofthe cavity to enable ratiowithout flow separation. For air, this results
flooding the cavity with water at low velocities. inexit plane pressuresdownto3psi.
This would provide a pool of simulatedslag to be
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THROAT PLANE
S'rAIS45.S_)7 RSRM
22.937
R_ r........L
_PROPELLANT SURFACE AT O_VITY FLUID
INJECTION PORT
Ir/'.__.ONDS BURN TIME
AFT END OF PROPELLANT
RSRM SCALED NOZZLE
AXIAL FLUID INJECTOR
Figure 5. RSRM 6.5% Scaled SlagEjection Model
Figure6. Cold FlowSlag EjectionModelandFacility
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The cold flow slag model was portion shows the data after a 100 point moving
instrumented with total pressure and temperature average was performed. The sudden start
probes, static pressure taps and dynamic pressure transient and the overshoot in both chamber
gauges. Pressure data was measured using pressure and water flow rate, as calculated from
differential pressure transducer modules as part of the orifice pressure differential, is readily
a 256 channel electronic scanning data recording apparent. However, as the mean water flow rate
system. The data is recorded, stored, and settles out, the chamber pressure maintains a
converted to engineering units on a Hewlett- mean offset from the value before water flow.
Packard computer. In addition, a miniature video The DC values for the chamber pressure increase
system and camera in the model chamber was and water flow rate are determined from the 100
used to observe the fluid activity around the point moving average plotted in the lower portion
nozzle nose during the ejection event. of Figure 7.
In order for the subscale cold flow slag 645 18
ejection model results to be applicable to the full 640 16_
.__
scale RSRM, it is important to employ certain 635 14g
scaling parameters in the design of the model and 630
the selection of operating conditions. The most 625
straight forward scaling parameter to satisfy is the 620 8_
air flow Reynold's Number. This will assure _I 615 6 o-
E
similarity in the structure of the highly turbulent 61o
flowfield. The model Reynold's Number is 605 2 _
matched to the full scale motor value of 40.8E06 6OO 0
25 30 35 40 45 50
at the throat by proper selection of the model
operating chamber pressure. The Weber Number
(ratio of surface tension forces to dynamic forces) 645 I 18
was matched within 42 percent to attempt to ___640 I i i______ 16_
replicate behavior of the entrained droplets in the ,_ 635 14
flowfield. Properties of air and water were used in (P 630
the model and properties of molten aluminum 625 lO :_
E 620 8_
oxide and combustion gases in the motor. The
._ 615 ....
match between the fluid droplet to gas flow E 610 :\ 4 _
momentum ratio was also calculated. Lastly, the ] _ .... Water FlowRateJ___ {
605 i I I
nominal water injection flow rate to the model was 600 0
calculated to provide the same percent blockage 25 30 35 40 45 5O
of the nozzle throat area as experienced in the full Time (seconds)
scale RSRM 29-B. This nozzle throat blockage is Figure 7. Cold Flow Model Test Data
approximately 2 percent and the slag ballistics
model was used to calculate the required water The DC values for the chamber pressure increase
flow rate.
are plotted against the water flow rate in Figure 8.
The slag ballistics model was applied to the cold
Test Results and Correlation
flow nozzle flowfield using air and water properties
to calculate chamber pressure increases over a
The model test conditions were varied
similar range of water flow rates where the "K"
about nominals to investigate the effect of the value was adjusted to minimize the square root of
controlled parameters on the test results. the sum of the squares for the deviations between
Operating test conditions and summary results are data and model predictions. The resulting value
tabulated in Table I for representative runs. The of "K" is 0.20 and the calibrated slag ballistics
pressure increase listed is the time-averaged shift model prediction is represented by the solid line.
in model chamber pressure experienced during The "K"value of 0.20 represents the mass fraction
the period of water injection. The frequency and of water in the entrained "slurry" mixture of air and
dynamic amplitude results will be discussed in a water. The data could obviously be somewhat
later section. Test results for a representative run, better represented by a _inear regression fit;
number 99-0, are shown in Figure 7 at a data rate however, the slag ballistics model correlation is
of 100 samples per second. The upper portion based on a physical, mechanical model which
shows the raw test data for the run while the lower
provides the means to apply the cold flow data to
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TableI. ExperimentaDlatafromRSRMScaledSlagEjectionModel
Chamber Water Gimbal Pressure Lowest
Run No. Pressure, Flow Rate, Angle, Increase, Frequency, Amplitude,
psia Ibm/sec De_]rees psid Hertz RMS psi
98-0 619 0.83 0 2.30 1.56 0.110
97-0 621 4.89 0 12.73 1.95 0.258
99-0 611 10.72 0 25.36 2.73 0.279
102-0 301 2.47 0 6.50 1.56 0.172
101-0 303 7.62 0 15.33 2.34 0.222
53-0 625 0.95 4 7.15 1.56 0.111
51-0 626 3.60 4 11.92 2.34 0.123
52-0 628 5.30 4 15.45 2.73 0.131
44-0 470 1.40 4 5.15 1.95 0.176
45-0 468 8.46 4 20.73 2.73 0.147
49-0 313 7.50 4 16.38 1.56 0.272
48-0 313 10.93 4 21.90 3.12 0.152
TEM-10 was the first static test motor
PredictfonK=O20
30 .623 psia J instrumented for detection of slag accumulation
25 • Data-623 psia J j_ and ejection as it relates to pressure perturbations.
The special additional instrumentation included
Data-465psia
2o _f real time radiography (RTR), plume calorimeters,
Data -310psia °J and nozzle accelerometers. The nozzle was not
vectored for this test which makes the results
60
_ lO r • .J
more relevant to the cold flow tests and for
_ 5
studying the relationships between slag ejection
n
0 and low frequency oscillations. Nozzle vectoring
1 2 3 4 5 6 7 8 9 lO 11 is known from other tests to be capable of causing
Water Flowrate (Ibm/sec) large slag ejection events depending on the
timing, magnitude, and direction of the nozzle
Figure 8. Cold Flow Model Data Correlation
movement. An overall pressure trace is shown in
Figure 9. The roughness in the pressure trace
the full scale by switching to the motor nozzle
beginning just before 60 seconds is evident along
fiowfield and using combustion gas and molten
with a small pressure blip at approximately 69
aluminum oxide properties.
seconds. A PSD isoplot of the spectral analysis is
Motor and Model Low Frequency Oscillations
Motor Observations
70o
The pressure perturbation investigation for
flight STS-54 revealed that pressure perturbations 40O \
for a number of both static and flight motors tend
to occur at a frequency of approximately 0.6
JZ
Hertz. The shapes and magnitude of the pressure o 100
perturbations are similar between static and flight 0
0 10 20 30 40 50 50 70 80 90 100 110 120
motors and the time of highest activity (68-72
Time(seconds)
seconds) is similar although the time of initial
activity is several seconds earlier for static Figure 9. TEM-10 Chamber Pressure Data
motors. Nozzle vectoring can induce strong
pressure perturbations traceable to slag ejection shown in Figure 10. The first longitudinal mode at
but pressure perturbations also occur without any 15 Hertz is visible on the right of the figure. Also,
nozzle vectoring on static test motors. a very low frequency oscillation in the 0.5 to 3.0
Hertz range commences at about 54 seconds and
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American Institute of Aeronautics and Astronautics
continues until about 80 seconds. It diminishes data andthe resultsare shown inFigure 13. The
then rebuilds until motor web time. These low two lines correspond to a time period of 19.8
frequency oscillationshave been observed at the seconds to 40.6 seconds, when no slag is being
same time spans in numerous static and flight ejected, andatime periodof 50.2 to 78.2 seconds
motors. The build in amplitude of these low which includes slag ejection. A significant
frequency oscillations appears to be associated increase in energy between 0.5 and 3 Hertz is
with slag ejection although there are "ballistic" evident during the period of slag ejection. The
frequencies present inthedata atvery lowvalues. largest gain is at the lowest plotted frequency of
"Ballistic"frequencies result from undulations in 0.5 Hertz. Lower frequencies are not plotted to
the pressure trace caused by sudden changes in eliminate the contribution of "ballistic"frequencies
propellant bum surface area from geometric inthe results.
effects such as burning across a thickened case
insulation zone over a factory joint. These
frequencies are at very low values of 0.1 to 0.2
Hertz. They do not appear,to be the explanation
for the frequencies observed between 0.5 and 3
Hertz.
Figure 11. TEM-10 RealTime Radiography Data
Frequency (Herb:)
Figure 10. TEM-10 Dynamic Chamber Pressure
RTR film showsthat at about 40 seconds
slag begins collecting under the nozzle nose
cavity although the propellant is not completely
consumed underthe nose untilabout 65 seconds. ,,o_.,='_.,.,.¢.='. .....
A spectral analysis of the motion of the slag
Fig. 12. TEM-10 Dynamic Plume Heat Flux Data
underneath the nozzle nose, as measured from
film density gradients, also Indicates a low
frequency activity beginning at approximately 55
0.03 iI I 1 I
seconds and increasing in magnitude with bum
0.025 \ S1e9c.8o-nd4s0.6 --
time. Figure 11 showsthe frequency range ofthe
0.02 '_ 50.2 -78.2
slag motion to be primarily in the 0.5 to 3 Hertz
range. Calorimeter data for plume radiation 0.015 ... _ 8eoonds
shown in Figure 12 also exhibits low frequency 0.01 _"/
oscillations up to 3 Hertz beginning about 55
t 0.005 _ ..
seconds and building in amplitude during the
0
periodassociatedwithslagejection.
0.5 1 1.5 2 2.5 3 3.5 4 4.5 S 5.5
Frequency (Hertz)
A power spectral density calculation was
performed for the dynamic head end pressure Figure 13. TEM-10 Chamber Pressure PSD
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Figure 14 shows the correspondingturbulent eddies associated with the separated
significanptercentagiencreaseinamplitudeofthe flow undemeath the nozzle nose and the
dynamic pressure oscillations (between
asymmetries ofthe aft case region causedby both
frequencies of 0.5 to 5.5 Hertz) that occurs nozzle gimballing and the presence of the slag
beginning at approximately 55 seconds. (Six reservoir itself. The dynamic pressure of the gas
seconds must be added to plot scale values due flowapproachingthe nozzle isvery highat 3.5 psi
to length of sample period in analysis.) The and capable of exerting high forces and
bottom portion of Figure 14 shows that the low accelerations on the order of one-hundred g's on
frequency oscillations am present in the motor the slag globules. These turbulent gas dynamic
before the pedod ofslag ejectionimplyingthat the forcesresult in slagbeing entrained and expelled
basicperiodic gas dynamic phenomena is always throughthe nozzle before the slag reservoirfillsto
present and significant amplitude Increasesresult the level of the nose tlp. Thus the submerged
whenthe phenomena interactswithslagejection. nozzle nose cavity becomes "aerodynamically
full" before it becomes "geometrically full'. The
0.3 entrainment and expulsion of the slag Is naturally
pedodic because of the large scale turbulence
O.25 existing Inthe aft dome region of the submerged
nozzle motor.
!
__0.15 The shear layer formed by the dividing
streamline between the flow entedng the nozzle
0.1 J_ and the stationary, recimulating vortex of the
0,05
separated flow underneath the nozzle nose is the
0 prime suspected source of the pedodic turbulent
0 10 20 30 40 50 60 70 80 90 I00110120
disturbances. Instability Induced excitation
sourcesare frequently associated withflowswhich
'.°°I j include the presence of shear layers. Shear
5.00 layers which impinge on surfaces or edges are
particularly prone to generating instabilities. The
/ {11 ....... impingement of a disturbancein a shear layer on
a downstream surface provides an upstream
feedback mechanism which can leadto organized
$=o IUl" ,L,
oscillationsof the shear layer.3 The shear layer
associated with the dividing streamline
1.oo I { i -r_V LPU _¢- /u,.-,u-
0.00 l undemeath the RSRM nozzle nose does, in fact,
0 10 20 30 40 50 80 70 80 90 100 110 120 Impinge on the underneath surface of the nozzle
noseas showninFigure 15. This result tsfrom a
Time(seconds)
steady state CFD solution of the RSRM aft end
Figure 14. TEM-10 Dynamic Chamber Pressure flowfleldatabum time of67 seconds.
Thus the periodicity of slag entrainment
NOSE
and ejection though the nozzle is supported by
DIVIDING
numerous observationsassociated with static and
flight motors. The Real Time Radiography film
shows the formation of a slag reservoir
underneaththe nozzle nosedudng the laterhalfof
the motor bum time whlch undoubtedlyis formed
from a collection of Individual "droplets" which
have Impacted the underneath side of the nozzle
and/or the aft case dome. This observation Is
3AVITY
consistent with other large motors withcomposite
aluminized propellants. Furthermore, the slag
reservoir appears to be severely and periodically Figure 15. Dividing Streamline Plot
disturbed and chumed up by the gas flow into a
"slumj"or mixture ofslag andgas. The motion of The structure of the mean flowfield inthe
this slurry mixture is ddven by the large scale aft nozzle cavity of a 7.5 percent scale air flow
9
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