Baughman, L Eugene

Burgess, Warren C , Jr

English

NASA Technical Reports Server

RM E54K30 
RESEARCH MEMORANDUM 
NOTE ON THE SCAVENGE OF 6-INCH-DIAMETER RAM-JET 
EXHAUST IN MACH 3.1, 1- BY I-FOOT 
SUPERSONIC TUNNEL 
By Warren C. Burgess, Jr., and L. Eugene Baughman 
Lewis Flight Propulsion Laboratory 
Cleveland, Ohio 
NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 
WASHINGTON 
February 18, 1955 
Declassified December 3, 1958 
https://ntrs.nasa.gov/search.jsp?R=19930088572 2020-06-17T23:27:05+00:00Z
IS 
• 
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NACA RM E54K30 
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 
RESEARCH MEMORANDUM 
NOTE ON THE SCAVENGE OF 6-INCH-DIAMETER RAM-JET EXHAUST 
IN MACH 3 . 1, 1- BY I -FOOT SUPERSONIC TUNNEL 
By Warren C. Burgess, Jr ., and L. Eugene Baughman 
SUMMARY 
The exhaust of a 6- inch- diameter ram- jet engine mounted in the Lewis 
1- by I - foot, Mach 3 . 1 supersonic tunnel was scavenged successfully with 
a 6.6-inch-diameter scoop. Limiting values of exhaust- to- stream static-
pressure ratios and scavenge- system total- pressure ratios were determined 
for complete scavenging of the products of combustion. The scavenge-
system operation influenced the engine exhaust -nozzle pressures under 
conditions of unstable scavenge flow . 
INTRODUCTION 
Aircraft power- plant combustion research in return-type supersonic 
tunnels requires consideration of exhaust scavenging to avoid contamina-
tion of the tunnel air by the by- products of combustion. Presented 
herein are the results of a scavenge study made at the Lewis laboratory 
in 1952 . Although the data pertain to a unique system, their publication 
is stimulated by the continued interest in the scavenging problem and 
the absence of published data related thereto . 
The influence of the ram-jet fuel -air ratio and the exhaust-nozzle 
configuration upon the ability of the system to scavenge effectively 
were determined, and the effect of the proximity of the scavenge system 
on the engine operation was evaluated . Total pressures indicating 
the power required for tunnel and scavenge- system operation were also 
measured . 
No attempt was made to improve the system performance by varying 
the scavenge configuration . 
2 NACA RM E54K30 
SYMBOLS 
The following symbols are used in this report: 
D body diameter at nozzle exit (station 2), in. 
fla fuel-air ratio 
M Mach number 
P total pressure 
Pe static pressure at nozzle exit (station 2) 
Ps stream static pressure at nozzle exit (station 2) 
q dynamic pressure, ~ PV2 
r body radius at nozzle exit (station 2), in. 
T t otal temperature, oR 
x distance downstream of nozzle exit 
y radial distance measured from the nozzle axis 
engine temperature- rise ratio, T2/TO 
Subscripts : 
o stagnation 
1 free-stream station ahead of model 
2 nozzle exit 
3 scavenge scoop inlet 
4 scavenge system discharge 
5 tunnel diffuser discharge 
APPARATUS AND PROCEDURE 
The Lewis 1- by I - foot, Mach 3 . 1 nonreturn tunnel was used for the 
scavenge investigation . I nlet air was supplied to the tunnel bellmouth 
at approxi mately 50 pounds per squar e inch absolute pressure, 50° F 
temperature, and 2 . 2xIO-5 specific humidity. 
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NACA RM E54K30 3 
The engine and scavenge-system installations are presented in 
figure 1. A partially exploded view of the engine is presented in fig-
ure 2. The ram-jet engine was 6 inches in diameter, 60 inches in length, . 
and was equipped with a 300 half-angle single co~e inlet. The internal 
geometry consisted of a subsonic diffuser, a combination spray bar and 
impinging-jet fuel system, a can-type baffle, a length of combustion 
chamber, and a convergent-divergent exhaust nozzle. Two convergent-
divergent exhaust nozzles with design Mach numbers of 2.35 and 1.96 
having different throat areas were used, thereby permitting two ranges 
of engine total-temperature rise (~ ~ 2 and ~ ~ 4, respectively) without 
resulting in subcritical inlet operation. Both nozzles expanded the 
flow to the full engine diameter at the exit. Propylene oxide was 
utilized as a fuel. 
The scavenge system included a 6.6-inch-diameter scoop mounted, as 
shown in figure 1, 3 inches downstream of the engine exit. A submerged 
spray coolant system (fig. 1) was located inside the scoop lip to lower 
the gas temperature in the vicinity of the scoop shell and thus prevent 
its possible structural failure and increase the total pressure of the 
exhaust jet. The scavenged gases were ducted through the tunnel side 
plate to the exhaust line as indicated in figure 1. 
Pitot and static instrumentation were located throughout the engine 
and were used in determining engine operating conditions such as pres-
sure recovery and nozzle static pressures. In addition, pi tot and 
static rakes located in the tunnel exit and in the scavenge system were 
used to determine the operating pressure ratios. The jet-wake boundaries 
were surveyed with the temperature and humidity probes shown in figure 3. 
The humidity probe merely sampled the air, which was passed through a 
dew-point meter. A spike inlet was used on this probe to increase the 
pressure in the air-sampling circuit. 
RESULTS AND DISCUSSION 
Engine 
o The 30 half-angle single cone inlet of the ram-jet engine was 
designed for a mass-flow ratio of 0.76, which corresponded to a 9.7 
percent capture of the tunnel flow. Stable subcritical operation was 
impossible with this inlet because of choking of the main streamj and, 
consequently, the investigation presented herein is for supercritical 
inlet operation with inlet-flow patterns of the type illustrated by 
the schlieren photograph in figure 4. 
The combustion process was steady for both nozzle configurations 
(~ = 2 and ~ = 4) up to the maximum values of fuel-air ratio used. The 
maximum fuel-air ratio for the ~ = 2 nozzle configuration was 0.04, 
_J 
1-
4 NACA RM E54K30 
corresponding to a near- critical inlet condition and a combustion 
efficiency of 40 per cent . The fuel - air- ratio limit for the ~ ~ 4 
nozzle configuration was between 0 . 04 and 0 . 05 J at which point thermal 
choking of the tunnel occurr ed at the nozzle exit . The combustion 
efficiency corr esponding to this limiting condition was even less than 
the ~ ~ 2 nozzle efficiency . These low efficiencies indicate the 
probability of continued combustion downstream of the nozzle . 
Exhaust Jet 
A typical schlieren photograph of the ~ = 2 nozzle exhaust is 
presented in figure 5 for a fuel - air ratio of 0 . 017 with the scavenge 
system removed from the tunnel . As the fuel- air r atio increased J the 
exhaust - to- stream static-pressure ratio Pe!ps ( to be called hereinafter 
jet static - pressure ratio ) increased} and the jet- wake widened . The 
Mach number of the external flow just upstream of the nozzle exit was 
determined to be approximately 2 . 2 . 
Quantitative measurements of the jet boundar ies were obtained for 
a range of operating conditions from measurements of moisture and 
temperature . Typical humidity and temperature profiles are presented 
in figur e 6 . The humidity traverse plots indicate the limits of the 
moistur e - contaminated jet . The temperature profiles indicate the extent 
of conduction and turbulent transport of heat . The jet boundary is 
defined by the radius at which the values of temperature and/or humidity 
reach a minimum . The jet boundaries as determined from a limited number 
of such surveys are summarized in the following table . Stations at 0 . 1-
and 1 . 5-body diameter s downstream of the nozzle exit are considered for 
several values of jet static- pressur e ratio Pe! ps which exert a direct 
influence on the jet spreading . 
Jet stati c- ~et boundary) Nozzle Remar ks 
pressure y!r 
ratio) 
Pe! ps 
0 . 1 Diameter downstream of no zzle 
0 . 86 1.03 ~ = 2 Temper ature survey 
. 95 1.02 ~ = 2 Humidi ty survey 
1.00 1.11 ~ = 4 Temper ature and 
humidity survey 
1.5 Diamet ers downs t r eam of noz zle 
0 .84 1.25 ~ 
"" 
2 Temper ature survey 
. 95 1.15 ~ = 2 Humidity survey 
1 . 00 1.25 ~ ~ 2 Temper ature su rvey 
1. 03 1. 33 ~ = 4 Temperature survey 
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NACA RM E54K30 5 
Of interest to the scavenge problem is the fact that the boundaries 
extended beyond the body diameter at only 0 . 1 diameter downstream even 
though the flow was overexpanded within the nozzle . This spreading 
may have resulted from the 2 .50 divergence angle of the nozzle or from 
the turbulent transport of fluid into the boundary layer from the 
external engine surface. 
Exhaust Scavenging 
In figure 7 a sketch of the scavenge scoop selected for the present 
installation is shown superimposed on assumed linear variations of jet 
boundary between the two stations surveyed . The data show consider able 
scatter and it was necessary in some cases to estimate boundaries by 
joining points at different jet static-pressure ratios but) in general) 
they indicate the possibility of stream contamination in some cases 
with jet static-pressure ratios greater than 0 . 85 . 
The variation in jet static-pressure ratio with engine fuel-air 
ratio is shown in figure 8 for both the ~ = 2 and ~ = 4 nozzles . 
These data were obtained with the scavenge scoop in position and opera -
ting supercritically. All operating conditions yielding values of jet 
static-pressure ratio greater than approximately 0.8 to 0 . 84 resulted 
in contamination of the stream flow as measured with a humidity sampler, 
5.6 scoop diameters downstream of the scavenge scoop . In a general way, 
then, these data confirm the predictions from the profile surveys . The 
~ = 2 nozzle data points were obtained with supercritical operation of 
the scoop (fig . 9(a)), whereas the ~ = 4 points correspond to steady 
subcritical scoop operation (fig . 9(b) ). Subcritical flow was usually 
present with the ~ = 4 configuration as an apparent r esult of the 
relatively low nozzle-exit Mach.number , and continued combustion of the 
exhaust jet into the scavenge duct . 
Reduction of the scavenge- system total- pressure ratio PO/P4 
below the minimum operating values both contaminated the stream flow 
and influenced the pressures within the nozzle . High-speed motion-
picture schlieren photography indicated that, in these cases, unsteady 
scoop operation was present with shock waves oscillating from within the 
scoop to within the nozzle . The effect increased as the scavenge system 
was fUrther throttled . 
Operating Pressure Ratios 
Stagnation pressure ratios for the tunnel and scavenge- system 
operation are presented in table I . The subscripts refer to the stations 
indicated in figure 1 . 
6 NACA RM E54K30 
Prediction of scavenge-system total-pressure ratios requires, in 
addition to a knowledge of engine characteristics, an evaluation of the 
piping losses and the effects of combustion of unburned fuel ahead of 
and within the scavenge system. An approximation of the piping losses 
has been made for the subcritical scoop (f/a = 0, see footnote d, 
table r). The piping losses from stations 3 to 4 are estimated to be 
1 . 6q based on experimental pressures. 
SUMMARY OF RESULTS 
From an investigation of the scavenging of the exhaust of a 6-inch-
diameter ram-jet engine in a Mach 3.1, 1- by l-foot supersonic tunnel, 
the following results were obtained: 
1. Scavenge scoop size can apparently be satisfactorily estimated 
from temperature and humidity surveys of the jet boundaries. 
2. With a 6.6-inch-diameter scavenge system located 3 inches down-
stream of the engine exit, the exhaust gas was successfully scavenged 
for jet static-pressure ratiOS up to 0.85. 
3 . Reduction of scavenge-system total-pressure ratio by throttling 
beyond some critical value resulted in unsteady operation with the 
scavenge-scoop shock wave oscillating from within the scoop to within 
the engine exhaust nozzle. 
LewiS Flight Propulsion Laboratory 
National Advisory Committee for Aeronautics 
Cleveland, Ohio, November 29, 1954 
3158 
TABLE I. - OPERATING PRESSURE RATIOS 
Item Experimental 
pressure 
ratios 
Normal shock 
calculation 
Empty tunnel performance 
Startinga 
Operatingb 
Tunnel performance with engine and scavenge 
system installed 
Tunnel starting: 
f /a = 0 ; scoop supercritical 
Tunnel operating: 
f la = 0 ; scoop supercritical 
f / a = 0 . 04; -. = 2 engine and scoop supercri tical 
Scavenge- system performance 
contamination 
Supercritical scoop: 
f /a = 0; no coolant 
for no tunnel 
f / a = 0; coolant 
f /a = 0 . 039; -. = 2 
f /a=0.04;-'=2 
f!a=0.04 ;-'= 2 
engine; small coolant 
engine ; increased coolant 
engine; no coolant 
Subcritical scoop: 
f/a ~ 0; no coolant 
PO/P5 
4.1 
4 .0 
4.46 
4.18 
4 .35 
PO/P4 
8.19 
10.49 
5.43 
5.70 
7.83 
9.27d 
aInitially establishing supersonic flow throughout test s ection. 
3.38 
3.38 
4.43 c 
6 .52 
bMinimum pressure ratio which may be r ealized with supersonic flow maintained 
throughout test-section areas. 
cExperimental values of scoop inlet Mach number and PO/P3 were used in this 
calculation. 
dPiping losses were calculated from this point for system. 
r 
~ 
~ 
l:z:J 
U1 
II>-
?<1 
VI 
o 
-.l 
station 
I 
~ Nozzl e surface 
 I T = 4 Nozzle surface 
Deta il I I 
(Nozzle surfaces Station 2 
superimposed) 
------ -:.;-
/ 
o 1 
Mach 3 .1 nozzle 
(Vie" rotated 900 ) 
rEt W Station 4 
injection 
Section A- A 
- 3" 
\ Diffuser 
L Humidity probe 
Scavenge intake system 
!CD-3974 ! 
Figure 1. - Ram- jet engine and scavenge- system installat ion . 
't = 2 
DistaDce Radial 
upstr eam distance 
of nozzle from 
exit, nozzle 
x , axiS , 
in. y, 
in. 
0 2 . 900 
2 .25 2 . 800 
2 . 75 2 . 760 
3 .25 2 . 705 
3.75 2 .640 
4. 25 2 .520 
4 . 75 2 .500 
5 .25 2 .420 
5. 75 2 .340 
6 .25 2 . 252 
6 . 75 2.160 
7.25 2 .065 
7 . 75 1.960 
8 .00 1.915 
8 .25 1.920 
8 . 75 2 _000 
9 .25 2 .160 
9 . 75 2 .410 
10 .16 2 .690 
't = 4 
Distance Radial 
upstr eam distance 
of nozzle from 
exit, nozzle 
x, axis, 
in . y, 
in . 
0 2 .900 
2 .25 2 .800 
2 .75 2 . 768 
3.25 2 . 730 
3 . 75 2 .688 
4 .25 2 .638 
4.75 2 .530 
5 .25 2 .520 
5 . 75 2 .455 
6.25 2.382 
I 
6 . 75 2 . 310 
7 .00 2 .270 
7 . 25 2 .273 
7 . 75 2 .275 
8 . 25 2 .290 
8 . 75 2 _320 
9.25 2 .367 
9 . 75 2 .472 
10 .16 2 .690 
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~ 
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600 Cone 
~ Inlet section ~ 
f 
section 
Mod.el support strut 
Fuel - nozzle assexbly 
-- . L ':ml- ty:pe 
baffl e 
I 'tmbustion I - I 
i -::hamber I~ 
nozzle 
C-30748 
Figure 2 . - Components of 6- inch- diameter r am- jet engine. 
~ 
~ 
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CJ1 
~ 
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o 
to 
10 
f 
0.09" 
+ 
NACA RM E54K30 
(a) Humidity probe; X5. 
Radiation bar 
(b) Aspirating thermocouple; X5. 
Figure 3. - Instruments used in exhaust-jet survey. 
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NACA RM E54K30 
Figure 4. - Schlieren photograph showing inlet-flow pattern. 
Figure 5. - Schlieren photograph of exhaust jet. Fuel-air ratio, 0.0171 
jet static-pressure ratio, 0.56. 
11 
12 
r:r.. 
0 
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Q) 
8 
+> til 
H 
Q) 
Pi 
8 Q) 
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r-I 
til 
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0 
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NACA RM E54K30 
60X10- 4,-----,----,-----,----,-----r----.--------------~ 
'\ ~ 1 40r-~--+_~--~~~\~\~+-~--~--~~ 
~ 
I~ 9 20 ~--~----_r----+_----~~;+--r-_r----+_--~----_+----~ \~ 
(a) Specific humidity profile. 
1600 
1200 
SOO 
q \ Survey Nozzle Jet static-plane , design, pressure 
\ )\ x/D 't ratio, Pe/ps 
\\ 0 0.1 2 0.78 <) . 1 2 .S6 0 . 1 4 1.01 
\ ~ ~ 1.5 2 .S4 b.. 1.5 2 .95 
Y \\ 
400 
\' it\ 
"\ ~\ 
~ ~ ~ 
o . 4 . S 1 . 2 1.6 
Total distance ratio , y/r 
(b) Total-temperature profile . 
Figure 6 . - Typical exhaust- jet profiles. 
t 
l-
t 
C 
- -- ---------------- -- - "-
NAeA RM E54K30 13 
0 Temperature 
0 Humidity 
--- 't"= 2 
't"= 4 
Jet static-
1.6 pressure -
ratio) 
Pe/ps 
~ 1.2 
~ 
"' » 
i--i 
al 
.3:003 
1-----Pe/ ps 
-
--- _ ---~84 to . 99 
1 . 01 l.----~ 
--
-- ._-0 I ~ -- .95 ~~.::::; t:.-I-1- Scavenge- scoop inlet ____ 
. 85 
<d 
~ 
;::j 
0 
.8 p 
~ 
Q) 
'r:> 
I 
~ 
Ul 
~ 
..c: 
>< 
.4 ~ 
o . 4 . 8 1.2 1.6 
Radial distance from nozzle exit) x/D 
Figure 7 . - Exhaust-jet spreading. 
14 NACA RM E54K30 
1.0 
CIl Nozzle design, 
~ 't" 
<lJ p.. 0 2 
"' 
0 4 
0 Tailed points ·ri 
.p 
.8 cd denote 
1-1 
contamination 
<lJ 
~ 
CIl 
CIl 
<lJ 
1-1 p.. 
I 
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·ri 
.p 
cd 
.p 
CIl 
.p 
<lJ 
t-:l 
.4 
0 .01 .02 .03 .04 .05 
Fuel-air ratio, fla 
Figure 8. 
- Scavenge effectiveness. 
NACA RM E54K30 15 
(a) Supercritical scoop operation of r: 2 nozzle configuration. 
(b) Subcri tical scoop operation of r = 4 nozzle configuration.. 
F~ 9. - ~chlieren pho~ograph8 of ethaust jet into· 8cavenge inlet showing svpercrit106l 
aDd subcritical scoop operation. 
NACA-Langley 


Note on the Scavenge of 6-inch-diameter Ram-jet Exhaust in Mach 3.1, 1- by 1-foot Supersonic Tunnel

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