The 15-stage experimental axial-flow compressor was investigated at 78.5 percent of design speed, which falls in the region of the surge-limit line discontinuity. In this region indications of multiple characteristic curves of compressor operation had been found. On the basis of previous stage-matching analyses, these multiple performance characteristics appear to be the result of multiple-valued stage performance characteristics. At this speed of 78.5 percent, at least six separate characteristic performance curves were found, associated with five different numbers of rotating stall configurations, from zero to four stall zones. It was difficult in many cases to repeat a given performance curve by approaching the test speed in a similar manner, and many of the curves were not stable, the no-stall curve being the only definitely repeatable one. In some cases a jump from one curve to another took place at the surge point, while in others the change occurred within the usual limits of a conventional performance curve and without any sudden obvious changes in observed data. In general, as the number of zones in the rotating-stall pattern decreased, the maximum weight flow, maximum efficiency, and maximum pressure ratio of the resultant curves were increased. It appears, therefore, that multiple performance characteristics at the given speed are encountered in the region of the discontinuity of the surge line

Filippi, Richard E

Lucas, James G

English

NASA Technical Reports Server

RESEARCH MEMORANDUM 
MULTIPLE  OVER-ALL P E R F O R U N C E  AND  ROTATING-STALL 
CHARACTERISTICS O F  A  15-STAGE  EXPERIMENTAL 
AXIAL-FLOW  COMPRESSOR AT AN 
INTERMEDIATE SPEED 
By James G. Lucas and Richard E. Filippi 
Lewis Flight Propulsion Laboratory 
NATIONAL AD*VISORY COMMITTEE 
FOR AERONAUTICS 
WASHINGTON 
July 2, 1954 
https://ntrs.nasa.gov/search.jsp?R=19930088374 2020-06-17T08:04:56+00:00Z
NACA RM E54229 
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NATIONAL ADVISORY  COWITITEE FOR AERONAUTICS 
MULTIPLE OTTER-AIL PEBFORMANCE BMD ROTATING-STALL CEARACTWISTICS 
OF A 15-S’I!AGE ExpERlMENTAL AXIAL-FLOW COMPRESSOR 
By James G. Lucas and Richard E. Fi l ipp i  
The 15-stage experimental axial-flow congressor was investigated at 
78.5 percent of design speed, which falls i n  the region of the surge- 
l i m i t  l ine discontinuity.  In this region indications of  multiple char- 
ac t e r i s t i c  curves of campressor operation had been found. On the basis 
of previous stage-matching analyses, these multigle performance char- 
ac te r i s t i c s  appear t o  be the result of multiple-valued stage performance 
character is t ics .  A t  t h i s  speed of 78.5 percent, at least six separate 
character is t ic  performance curves were found, associated wtth f i v e  dif- 
ferent  numbers of rotating-stall configurations, from zero to four stall 
zones. It was d i f f i c u l t  i n  many cases to repeat a given performance 
curve by approaching the t e a t  speed i n  a similar manner, and many of the 
curvee were not stable, the no-stal l  curve being the o d y   d e f i n i t e l y  re- 
peatable one. In  some cases a jwrg from one curve t o  another took place 
at the surge point, wkile i n  others the change occurred within the usual. 
limits of a conventional performance curve and wlthout any sudden obvious 
changes i n  observed data. In  general, as the number of zones in  the  
rotating-stall  pattern decreased, the maximum weight flow, maximum ef’fi- 
ciency, and maximum pressure  ra t io  of the resultant curves were increased. 
It appears, therefore, that multiple performance character is t ics  a t  
a given speed are encountered in   the  region of the  discontinuity of the 
surge  line. 
IXEIODUCTION 
The 15-stage expertmental axial-flow cornpressor w a s  t es ted  at the 
NACA Lewis 1ab.oratory t o  determine i ta   over -a l l  performance character- 
i s t i c s .  The r e su l t s  of these tests indicate that multiple-valued per- 
formance characteristic curves existed over the range of 70 t o  81 per- 
cent of design speed, which i s  approximately the speed range of the 
surge-limit  l ine discontinuity.  Such r e su l t s  had been anticipated by the 
stage-stacking analysis of reference 1, which assumed that the inlet 
2 HACA RM E54C29 
L 
stages had characteristic  curves of the discontinuoue  or  double-branched , 
type. This analysis, whichglso assumed an interaction effect  causing 
several  inlet  s tages  to  stall  when any one of them s ta l led ,  c lear ly  showed 
that at  least two over-all  characterist ic curve6 could be obtained at a 
given compressor speed i n  the range where the inlet stages operate near 
the peak of their characteristic curves. I n  addition, in this same speed 
range the axial depth or  penetration of the stall  effects  ( the number of 
stages affected by interactions) could vary, depending upon the stall con- 
di t ions.  This variation of interaction effects could result i n  a m u l t i -  
p l i c i t y  of compressor performance characteristic curves at any given 
speed In t h i s  intermediate-speed range. The potent ia l  of multiple-valued n 
performance curves a t  a given speed i s  proved emer-imentally in rererence 
2, which shows three separate performance character is t ics  iGr a three- 
stage compressor operated at a single speed. 
d a 
N 
In order to study this problem, the 15-stage experimental axial-flow 
compressor was invest igated-at  a speed of 78.5 percent of design by us ing  
several  modes of approach to this speed. The over-all  performance and 
rotat ing-stal l   character is t ics  that could be obtained at t h i s  iapeed were 
evaluated. The results are presented herein. 
The apparatus  and  instrumentation  are  the same 8s o u t l i n e d   i n r e f -  < 
erence 3. 
The normal tes2  procedure of approaching a test speed from a lower Y 
speed with wide-open discharge thrott le and then closing the th ro t t l e  at 
C O n S t a U t  speed was not folldwed i n  the present  tes ts .  The,data reported 
herein were obtained by approaching the t e s t  speed f'rom both the high- 
and low-speed ranges, and along various 1ine.s of const.ant discharge- 
t h ro t t l e  opening. These l i nes  wil be re fer red  to  as " thro t t le  l ines ."  
A l l  points marked "approximate observed data" were obtained A t h  
only a single total-pressure t u b e  at the cotqressor discharge. Other 
points marked "actual data" yere obtained  and  calculated by the method 
presented i n  reference 4. 
Compressor Over-All Performance 
The over-all  performance character is t ics  of the present compressor 
are  presented  in  f igure 1 as over-all  total-pressure  ratio  and  adiabatic 
temperature-rise efficiency plotted as functions of equivalent w e i g h t  
flow at- equivalent speeds from 30 t o  100 percent af design. w 
EIACA RM E54C29 3 
Over-All Performance at 78.5-Percent Design Speed 
4 
In order to verify the results of reference 1, tests were run showing 
conclusively that any speed i n  the range from about 70 t o  about 81 per- 
cent of design would exhibit a t  least two characteristlc curves of stable 
operation. A speed of 78.5 percent of &sign was chosen for the present 
investigation after preliminary tests had shown evidences of several  char- 
acteristic cmves obtainable a t  this epeed. The investigation was con- 
ducted at this speed by approaching it from both the high- and low-speed 
sides and along eeveral different  throt t le  lines, since it was anticipated 
that the mode of approach t o  the operating speed, and the compressor oper- 
a t ing and stall conditions present at the time the approach was started, 
would determine the operating and stall  condztions a t  the  t e s t  speed. Al- 
though the rate of  approach would probably have some effect  on which char- 
ac t e r i s t i c  curve was reached during a cer ta in  approach, the very high in- 
ertia of the test r i g  prevented any investigation of such t ransient   effects  
as m i g h t  be encountered in engine operation. 
... .. . 
The o v e r - a l l  performance of the coqressor indicated at 78.5-percent 
speed is presented  in  figures 2 and 3 as plo ts  of  over-all total-pressure 
r a t i o  and adiabatic effLciency against equivalent weight flow. 
Approach from low-speed side. - The first approach t o  the test speed 
was made by increasing speed along the approximate t h r o t t l e   l i n e  marked 
T1 on figure 2. CQeration at 78.5-percent speed after this approach was 
on curve A at the data point indicated as A , and at this condition 
there were four  rotat ing-stal l  zones present. 'The discharge throttle was 
and higher flows with four   rotat ing-stal l  zones present a t  a l l  points.  
c 
- opened with resulting  operation down curve A t o  lower pressure ratios 
When the t h r o t t l e  was closed from the maximum flow point indicated 
on curve A, compressor operation moved to point Al, possibly discontin- 
uously, and there were s t i l l  four stall  zones present, although as viewed 
on the oscilloscope, there was a very low-frequency rotat ing exgansion 
and contraction cycle that periodically varied, the circumferential width 
of the rotating-stall  zones.  Further closing of the discharge throttle 
resulted in  operation  at   an  essentially  constant pressure r a t i o  with a 
reduction i n  weight flow. A data point on this constant-pressure-ratio 
character is t ic  was arbi t rar i ly  taken at point A,, wlth three stall  
regions present. When the t h r o t t l e  m 8  closed very slightly more, the 
compressor surged, indicating that goint A2 was  very close t o  a surge 
point. Operation after the compressor was brought out of surge by open- 
ing the throt t le  somewhat appeared t o  be along curve A. Although the 
number of zones i n  t h e  stall pat tern a t  point A2 was different  from 
that of curve A, it was thought that the surge point of  curve A, as 
obtained by closing the th ro t t l e  a t  78.5-percetlt speed from the  point 
.) 
V obtained after approaching along the or iginal  t h r o t t l e  l i n e  T1, would 
4 NACA RM E5G29 
be at about  point A. wlth f.our stall zones present. However, this 
assumption was not ckecked. 
I n  an attempt to reach pbint Al again, for the purpose of deter- 
mining its operat ing curve,  the or iginal  throt t le  l ine T1 was foUowed 
c lose ly   in  approachtug 78.5-sercent speed and the th ro t t l e  ms then 
opened. Instead of remaining. on curve A as had previously been the 
case, the courpressor operation moved t o  curve B, probably discontinu- 
ously, although the path of operation was not def inl te ly  established. 
A6 the th ro t t l e  m s  closed, the compressor operation moved  up curve B 
with two rota t ing-s ta l l  zones present, although most of the points ob- 
served along this curve had associated WLth them s t a l l  zones spaced 
asymmetrically around the circumference. For example, the two s t s l l  
zones m i g h t  have been displaced by 900 or 120° rather than 180°. A t  a 
point just  above the maximum pressure rat io  l i m i t  of curve B, surge oc- 
curred, and after a s l igh t  opening of the th ro t t l e  the compressor was 
found t o  be operating on curve A. Whether surge caused the shift i n  
operation or the shift occurred immediately before surge could not be 
ascertained. 
R 
& 
A t  another da8e the test speed was again approached approximately 
along t he  th ro t t l e  l i ne  TZ with resultant operation at about the center 
of curve C with three  rotating-stall. zones present. As th-throttle was 
opened, the three circmferent ia l ly  asymmetric stall  zone8 changed t o  t w o  
circumferentially asymmetric s t a l l  zones and the weight flow increased 
about 4 pounds per second, possibly discontinuously, with resultant oper- 
ation on curve D. The two stall zones pers is ted as the   th ro t t le  was Y 
opened and then closed along durve D un tU  j u s t  before surge occurred, 
a t  which point there was only one stall zone present. This single-stall- 
zone pat tern remained after surge, and curve D was then found t o  be re -  
peatable over its flii.l  range. 
I n  addition to the curves j u s t  discussed, several others were found. 
' Curve C y  which wa6 previously mentioned, has three ro ta t ing-s ta l lzones  
with all points displaying either circumferential asymmetry or the 
expansion-contraction  effect  already  described. Curve E is a locus Of 
some points which, in addition to those of  curve A, exhibi t - rour  rotat ing-  
stall zones. The two sections of the curve were determined separately and  
are shown joined by a dashed line, aince they may i n   r e a l i t y  not be p a t s  
of a single continuous curve. . An indication had been found of another 
curve at the same speed b u t  with a considerably lower weight-flow range 
than that of  curve A. However, this curve has not been presented because 
of  lack of accurate point determinations and because no ro ta t ing-s ta l l  
data w e r e  taken at the t i m e .  
a 
The majority of the s ta l l  zone6 measured extended about l / Z  t o  3/4 
of the radial depth of the anndus from the  t ip .  
V 
W A  RM E54C29 5 
Lh’ co 
OI 
P 
It probably would be possible  to  obtain  other  characteristic  curves, 
perhaps many of them, at the t e s t  speed by using a t i l l   d i f f e r e n t  modes of  
approach from. the low-speed side. However, their value would probably be 
smal l  in   evaluat ing any further general effects of multiple character- 
i s t i c  curves than those already given here. Similarly, there are many 
more speeds in the intermediate range which could have been investigated 
but which would probably show effect ively the same results. 
A general  trend  can be observed of maximum w e i g h t  f l o w  as re l a t ed  
t o  number of ro ta t ing-s ta l l  zones f o r  each of the curves of figure 2. 
With the exception of the slight discrepancy found i n  camparing the two- 
and one-stall-zone curves (B and D),  it is  quite evident that, as the 
number of ro ta t ing-s ta l l  zones is decreased, the maximum w e i g h t  f l o w  of 
the result ing characterist ic curve is increased. With the increase in  
maximum weight flow of the speed curve, the peak pressure ratio is also 
increased, as would be expected, since the inlet stages operate at lower 
angles of a t tack and therefore  c loser  to  the peaks of their individual 
pressure-ratio curves. This increase in  w e i g h t  f l o w  and peak pressure 
ratio indicates an improvement i n  stage matching that may result from 
a decrease i n  the nmiber of steges affected by interact ion due t o  ro- 
t a t ing  stall  or a decrease in the deterioration of stage performance as 
a result of rotat ing stall  instigated by an inlet stage. 
An incidental point that was observed during this investigation 
bears reporting at this t i m e .  mter the compressor was brought out of the  
surge that occurred on curve E by opening the discharge t h r o t t l e  some- 
what, there w e r e  three st& zones i n  the first stage and two stall zones 
in  the  four th  stage. This lasted only a f e w  seconds, after which the 06- 
cflloscope showed three stall zones i n  both stages, and operation appeared 
t o  be on curve C.  Perhaps for these f e w  seconds there was a three-s ta l l -  
zone pat tern at the inlet that w a s  nearly expended and was replaced before 
the f o u r t h  stage by an unstable  two-stall-zone  pattern that eventually 
s p l i t   i n t o  a three-stall-zone pattern. 
Approach from high-speed side. - Curve F was determined by increas- 
ing the compressor speed u n t i l  the unstalled condition wa8 reached, then 
closing the discharge throttle and decreasing the speed along a constant 
t h r o t t l e   l i n e   u n t i l  the speed of 78.5 percent was reached at point F . 
This curve is stable and repeatable after surge and exhibits no rotatyng- 
stall pat tern at any t i m e .  
This no-stall curve is related t o  the curves previously discussed i n  
the same manner that these curves are re l a t ed  to  one another; that is, as 
the rider of &&ll zones i 6  decreased, the rnaximum w e i g h t  flow and 
surge pressure ratio are increased. 
6 
Erficiency at 78.5-Percent Design Speed 
IiACA RM E54C29 
From the-three curves of figure 3, which are the efficiency pl&a 
corresponding to curves A, B, and F of figure 2, and which represent 
operation with four, tm, and no ro ta t ing-s ta l l  zones, respectively, i t  
can be seen that the peak efficiency of each curve becomes higher as the 
number of ro t a t ing - s t a l l  zones I s  decreased, or similarly,  as the max- 
imum weight flow is increased. j The explanat-ion fo r  t h i s  is the eane a8 
for  the increased peak pre6sure:ratio;  that is, the inlet stages 8re 
operating at lower angles o f -a t t ack  and therefore  closer  to their indi-  (0 4 
vidu&L peak eff ic iencies .  Although no efficiency data were taken for the cu a 
observed points shown on f igure:  2, it was emected that the peak efficien- 
c ies  for the three- and one-stall-zone curves woulLprobably follow the 
6ame trend. Further evidence t o  support the observation that the higher 
maxbum-weight-flow curves have:higher p a  eff ic iencies  i s  shown i n  
figure 3. Point %, which is on a higher weight-flow curve than curve 
A, although it has the same number of rotat ing stalls, has an ef'riciency 
higher than the peak efficiency measured on curve A. 
SUMMARY OF RESULTS 
The following results were obtained from an investigation at 78.b- 
percent design speed of the experimental 15-stage axial-flow compressor: 
1. Six different characterist ic curves of operation a t  a given in- 
termediate speed of 78.5 percent were indicated. Each of these curves 
deems to  be accompanied by a def in i te  number of ro ta t ing-s ta l l  zones, 
although a given number of rotating-stall zones does not necessarily 
determine EL single operation cmve. 
2. In general, as the number of ro ta t ing-s ta l l  zones is decreased, 
the result ing operation curve h g ~  a higher maximum weight flow, higher 
peak efficiency, and higher surge  pressure  ratio.  
3. When the speed is decreased to the test speed *om the unstalled 
conditions, a single operation curve is determined. However,  when the 
speed is increased t o  the test speed from the etalled condition, the 
resulting operation could be on any one of several curvee. 
Lewis Flight Propulsion Laboratqry 
Rational Advisory Committee for Aeronautics 
Cleveland, Ohio, April 7, 1954 
ch’ 
cn co c 
7 
1. Benser, W i l l i a m  A.: Analysis of Part-Speed Operation  for High-  
Pressure-Ratio  Multistage Axlal-Flow Compressors. W A R M  E53Il5, 
1953. 
2. Foster, D. V.: The Performance of the 108 Compressor F i t t e d  with Low 
Stagger Free Vortex Blad ing .  Rep. No. R . I l 6 ,  British H.G.T.E., 
June 1952. 
3. Lucas, James G., Finger, Harold B., and Fil ippt ,  Richard E. : meet 
of Inlet-Annulus Area Blockage on Over-All Performance and Stall 
CharacteristicB of an Experimental =-Stage Axial-Flow Compressor. 
NACA RM E55LZ8, 1954. 
4.  W A  Subcommittee on Compressors: Standard Procedures for Rating and 
Testing  Multistage Axial-Flow Compressors. NACA TN 1138, 1946. 
I NACA RM 254C29 
MACA RM E54C29 
c 
b 
E q u i v a l e n t  w e i g h t  flow, lb/sec 
Figure 2. - O v e r - a l l  total-pressure ratio at 78.5-percent 
design speed. 
9 
10 
" 
80 90 100 110 
Eqlzivalent weight flow, lb/sec 
120 
Figure 3. - Over-a l l  compressor e f f ic iency  a t  78.5- 
percent d-esign speed. 
NACA-Langley - 7 - 2 - 5 1  - SI0 
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Multiple over-all performance and rotating-stall characteristics of a 15-stage experimental axial-flow compressor at an intermediate speed

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