Pulse pressure distortion effects imposed on inlet of turbofan engin

Wenzel, L. M.

English

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N A S A  T E C H N I C A L  N A S A  TM X-1928 
M E M O R A N D U M  
I 
EXPERIMENTAL INVESTIGAnON OF 
THE EFFECTS OF PULSE P I .. DISTORTIONS IMPOSED ON THE INLET 
12: OF A TURBOFAN ENGINE 
https://ntrs.nasa.gov/search.jsp?R=19700001716 2020-03-23T21:03:45+00:00Z
THE EFFECTS OF PULSE PRESSURE DISTORTIONS IM- 
POSED OW THE INLET OF A TURBOFAN ENGINE 
1. Report N o .  
NASA TM X-1928 
7. Author(s) 8 .  Performing Organizat ion Report  N o .  
Leon M. Wenzel E-5247 
2. Government Access ion  No .  3. Rec ip ient 's  Catalog N o .  
9. Performing Organizat ion Nome and Address 
Lewis Research Center 
National Aeronautics and Space Administration 
Cleveland, Ohio 44135 
2. Sponsoring Agency N a m e  and Address 
National Aeronautics and Space Administration 
Washington, D. C. 20546 
4.  T i t l e  and Subti t le  EXPERIMENTAL INVESTIGATION OF 5. Report D a t e  
5 .  Supplementory N o t e s  
10.  Work U n i t  No .  
720-03 
11 .  Contract  or Gront N o .  
113. Type  o f  Report ond P e r i o d  Covered 
Technical Memorandum 
14 .  Sponsoring Agency Code  
16. Abstract  
A YTF-30 -P-1 turbofan was operated in  an altitude chamber.  A distortion device cap- 
able of effecting pulse depressions in  inlet p ressure  was installed ahead of the engine. 
The pulses could be varied in duration and amplitude. The portion of the inlet duct sub- 
jected to distortion could be varied circumferentially from 60' to 360' in  60' sectors .  
The engine s ta l l  sensitivity a s  a function of pulse duration and distortion sector  angle was 
mapped. The amplitude of pulse necessary to s ta l l  the engine was found to be an  inverse 
function of pulse duration. The engine was most sensitive to distorted sec to r s  of 180' 
and 240'. Transient recordings of engine p ressures  and p ressure  ra t ios  during s t a l l  a r e  
presented. Also, data a r e  presented which indicate the circumferentialpropagationrate c 
a p ressure  pulse traveling through the engine to be 20' per  stage.  
17. K e y  Words ( S u g g e s t e d  b y  Author ( s ) )  
Turbofan 
pulse p ressure  distortion 
Compressor  s ta l l  
18. Distr ibut ion Statement 
Unclassified - unlimited 
* F o r  sa le  by the Clearinghouse for  Federal  Scientific and Technical Information 
Springfield, Virginia 2215 1 
Inlet 
19. Security C lass i f .  ( o f  th is  report) 
Unclassified 
20. Security C loss i f .  (of  th is  page) 21- No .  of  P a g e s  22. p r i c e *  
Unclassified 17 $3.00 
EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF PULSE PRESSURE 
DISTORTIONS IMPOSED ON THE INLET OF A TURBOFAN E N G I N E  
by Leon M. Wenzel 
Lewis Research Center 
SUMMARY 
A YTF-30-P-1 turbofan was operated in an altitude chamber. A distortion device 
capable of effecting pulse depressions in inlet pressure was installed ahead of the engine. 
The pulses could be varied in duration and amplitude. The portion of the inlet duct sub- 
jected to distortion could be varied circumferentially from 60' to 360' in 60' sectors.  
Engine stal l  sensitivity a s  a function of pulse duration and distortion sector angle was 
mapped. The amplitude of pulse necessary to stall  the engine was found to be an  in- 
verse function of pulse duration. The engine was most sensitive to distorted sectors  of 
180' and 240'. 
Transient recordings of engine pressures and pressure ratios during stall a r e  pre-  
sented. Also, data a r e  presented which indicate the circumferential propagation ra te  
of a pressure pulse traveling through the engine to be 20' per stage. 
INTRODUCTION 
The tolerance of turbojet engines to dynamic distortions in inlet pressure is cur- 
rently of great interest (e. g . ,  ref. l ) .  This report  presents the results of an investiga- 
tion in which portions of the inlet of a YTF-30-P-1 turbofan engine were subjected to 
single pulse depressions in pressure. Distortion sector angle, pulse duration, and 
pulse amplitude were varied; the engine stall  limits were defined with respect to these 
parameters.  
Transient recordings of engine pressures and compressor stage group pressure 
ratios during stal l  a r e  presented for  several inlet conditions. Also, data a r e  presented 
which give the ra te  of circumferential propagation of an inlet pressure pulse a s  it 
progresses through the compressor. 
SYMBOLS 
2 P pressure,  psi ( ~ / c m  )
Subscripts : 
f fan duct 
t total 
2 inlet duct 
2. 1 after first fan stage 
2. 3 fan discharge 
2.6 mid low compressor 
3 low -compressor discharge 
3.12 mid high compressor 
4 high-compressor discharge 
APPARATUS 
Tests  were conducted on a UTF-30-P-1 turbofan engine installed in an altitude 
chamber. The axial locations of the pressure instrumentation stations of interest in 
this report a r e  shown in figure 1. At each of the stations indicated, two pressure trans- 
ducers a r e  provided; one each on the right and left sides of the engine. Miniature pres- 
sure  transducers a r e  used, mounted s o  a s  to have essentially flat frequency response to 
400 hertz. 
A secondary jet system is located in the engine inlet duct. The system consists of 
54 jet nozzles evenly spaced over the inlet annulus. The 54 nozzles a r e  composed of 
s ix groups of nine nozzles each. The individual groups each cover a sextant of the inlet. 
The jet system operates by flowing counter to the primary inlet airflow. The resulting 
momentum exchange causes a total-pressure loss across the jet system. 
Airflow to each of the six nozzle groups is controlled by a servodriven valve having 
high response (about 150 Hz). The valves can be operated independently to give dis- 
tortion patterns covering 60' multiples of the inlet. 
The inlet and jet system a r e  also shown schematically in figure 1. The jets a r e  
36 inches (91 cm) upstream of the engine face, and the open end of the bellmouth is  
129 inches (328 em) upstream of the jets. This installation is described more fully in 
reference 2. 
The electrical signals supplied to the servovalves were formed on a desk-top analog 
computer. A gating circuit was provided to se t  pulse duration. Pulse .amplitude was 
independently controlled. , The pulses generated could be switched to drive any desired 
combination of the six valves. 
TEST PROCEDURE 
The engine and tes t  chamber were se t  up to 8600-rpm low rotor speed, rated ex- 
2 haust nozzle area ,  and 7.5-psia (5.17-N/cm ) inlet pressure.  All valves were s e t  to 
near closed and secondary flow rates equalized. The valves to be driven and the pulse 
duration were chosen and appropriate computer settings made. The initial pulse am- 
plitude was set.  The recording system was started and the pulse initiated, opening the 
prescribed number of valves. If engine stall did not occur, an increment was added to 
the pulse amplitude, the computer reset,  and a larger  pulse initiated. This process 
was repeated until engine stall  was encountered. The time required to adjust the pulse 
amplitude and rese t  the computer was ample for  transients induced by the previous pulse 
to die out. Stall points were obtained in this manner f o r  distortion sector angles from 
60' to 360°, and for pulse durations from 6 to 100 milliseconds. 
RESULTS AND DISCUSSION 
Figure 2 presents the conditions of pulse amplitude and duration which induced engine 
stal l  for distortion sector angles of 60' to 360'. The ordinate of this plot is the voltage 
level supplied to the servodriven distortion valve (or valves) from the computer. It is 
proportional to the amount which the servovalve (or valves) opened. 
The shape of the curves indicates that the amplitude of pulse which the engine can 
tolerate varied inversely with duration. Also, the engine is most sensitive to distortion 
angles around 180' and 240'. 
Figure 3 is similar to figure 2; the ordinate in  this figure is the magnitude of the 
pressure pulse in the secondary a i r  supply just upstream of the jet nozzles. More 
scat ter  is noted in this figure, but the similarity in the shape of the curves indicates that 
the servovalves did follow their input signal. 
It  is recognized that figures 2 and 3 a r e  plotted in te rms of artificial variables. The 
primary variable, engine inlet pressure, could not be measured precisely because of 
low signal level and poor wave shape. However, a s  an indication of the inlet pressure 
perturbations involved, for pulses in the 3- to 5-volt range in figure 2, inlet pressure 
2 
reductions of about 0.4 psi  (0.276 ~ / c m  ) were imposed on the steady-state pressure 
2 level of 7 .5  psia (5.17 N/cm ). These numbers a r e  not intended a s  calibrations, but 
only to give an indication of the pressure perturbation amplitudes experienced. 
Figures 4 to 6 a r e  transient recordings of engine stall for  distortion angles of 60°, 
180°, and 360°, respectively. These transients a r e  typical of the stal l  boundary points 
in figure 2. The right (90') - and left (270') -side engine pressures and the right- and 
left-side pressure ratios a r e  shown for  each distortion angle. Total pressure a t  a par- 
ticular engine station and circumferential location is indicated on each trace (e. g . ,  
't2.3-273 o signifies total pressure a t  engine station 2 .3  (see fig. 1) and a circumfer- 
ential location of 273'). For  this entire investigation, the distorted a r e a  was centered 
a s  nearly a s  possible about the right side. 
The test  procedure for this investigation was to initiate increasingly larger pulses 
in inlet pressure until stall  occurred. The pulses which did not induce stal l  can be used 
to measure the rate a t  which an inlet pressure pulse propagates circumferentially a s  it 
travels back through the engine. 
The measurement of this circumferential propagation necessitates an understanding 
of the response of the inlet duct. The configuration of the duct is shown in figure 7, with 
transport times upstream and downstream indicated. Figure 8 shows an analytical 
response of engine inlet pressure to jet flow. The one-dimensional model used to gen- 
era te  these responses is based on the method of Willoh (ref. 3). 
The trapezoidal waveform in jet flow is typical of those achieved in the testing. 
The complex waveform of engine inlet pressure is made up of a primary pulse traveling 
downstream from the jet nozzles, plus a secondary pulse which travels upstream, r e -  
flects off the open inlet, and then travels back downstream to the pressure station. The 
time required for the reflected pulse to reach the pressure station is approximately 
22 milliseconds. 
If only a portion of the inlet is perturbed, the inlet duct pressure transducer c i r -  
cumferentially located directly behind the distortion (Pt2 will measure both the 
primary and reflected pulses. However, the transducer located on the opposite side of 
the inlet duct (Pt2 270 o) will measure only the reflected pulse. This behavior is illus- 
trated in figure 9. Transient recordings of inlet and compressor pressures during a 
nonstalling (i. e .  , below the stal l  boundary of fig. 2) 120' pulse a r e  shown in this figure. 
A long-duration depression is noted in Pt2 - indicating that both primary and r e -  
fleeted pulses passed by. In Pt2-2700, only the reflected pulse is seen. 
Similar differences can be noted in the traces for stations 2 .3  and 2.6. However, 
a t  station 3, the primary pulse can be seen. Thus, the axial distance required for c i r -  
cumferential propagation can be determined. 
Figure 10 summarizes this distance required for  circumferential propagation for 
the various distortion angles tested. Indicated on this figure a r e  the distorted angle, 
the distortion pattern, and the minimum angle through which the primary pulse must 
propagate. The results show that the axial distance required for the pulse to propagate 
circumferentially varies directly with the propagation angle. Propagation rate is seen 
to be 20' per stage. 
SUMMARY OF RESULTS 
A YTF-30-P-1 turbofan engine was operated in an altitude chamber. Air jets, 
driven by high-response servovalves, were installed in the engine inlet duct. The jets 
were operated to effect single pulse depressions in engine inlet pressure.  The distorted 
portion of the inlet was varied circumferentially by sextants from 60' to 360'. Pulse 
duration was varied from 6 to 100 milliseconds. 
The engine stal l  sensitivity a s  a function of pulse duration and distortion sector 
angle was mapped. The pulse amplitude required to stall  the engine was found to be an 
inverse function of pulse duration. The engine was most sensitive to distortion sectors  
of 180' and 240'. 
Transient recordings of engine pressures and pressure ratios during stal l  a r e  pre-  
sented. Data a r e  also presented which indicate the circumferential propagation of an 
inlet pressure pulse a s  it travels axially through the engine. The propagation rate was 
measured to be 20' per stage. 
Lewis Research Center, 
National Aeronautics and Space Administration, 
Cleveland, Ohio, August 27, 1969, 
720-03. 
REFERENCES 
1. Reid, C. : The Response of Axial Flow Compressors to Intake Flow Distortion. 
Paper 69-GT-29, ASME, Mar. 1969. 
2. Povolny, John H. : Stall and Distortion Investigation of a YTFSO-P-1 Turbofan 
Engine. Paper presented a t  the AFAPL Airframe - Propulsion Compatibility Sym- 
posium, Miami Beach, Fla. , June 24-26, 1969. 
3. Willoh, Ross G. : A Mathematical Analysis of Supersonic Inlet Dynamics. NASA TN 
D-4969, 1968. 

10 Distor t ion 
2 8 
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a, wl  
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4 6 8 1 0  20 40 60 80 100 
Pulse durat ion,  msec 
Figure 2. - Stal l  boundary as func t ion  of pulse 
amplitude, pulse durat ion,  and distor t ion 
angle. 
. 801- Distor t ion 
sector angle, 
de9 
" 4  6 8 10 20 40 60 80 100 
Pulse durat ion,  msec 
Figure 3. - Stall boundary as func t ion  of jet absolute 
pressure pulse amplitude, pulse durat ion,  and 
distor t ion angle. 
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Pressure 
Secondary station 2 
Pr imary  
flow 
Transport  
t imes, msec 
Figure 7. - In let  duct  conf igurat ion indicat ing pressure pulse t ransport  t imes. 
Time, msec 
Figure 8. - Analytical i n le t  duct response calculated for jet flow 
pulse shown. 
(a) Stations 2 to  2.6. (b) Stations 3 to  4. 
Figure 9. - Engine pressures for 15-millisecond, 120° pulse which did not effect stall. 
Ci rcumferen t ia l  Distor t ion C i rcumferen t ia l  P r imary  pulse 
angle, propagation f i r s t  observed 
deg angle, at left -side 
deg engine station- 
o r t ion  
le 60 150 3. 12 
\ 
Distorted sector -' 
Figure 10. - Summary of axial distance requ i red  for  c i r cumferen t ia l  propagation, 
for var ious d istor t ion angles. 
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Experimental investigation of the effects of pulse pressure distortions imposed on the inlet of a turbofan engine

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