Tests were made at a mean inlet Mach number of 0.2 with area suction applied to conical diffusers with expansion angles of 30 degrees and 50 degrees and exit to inlet area ratios of 2. Air-flow separation was eliminated with suction mass flows of 3 and 4 percent of the inlet mass flows for the 30 degrees and 50 degrees diffusers, respectively

Hall, Leo P

Holzhauser, Curt A

English

NASA Technical Reports Server

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https://ntrs.nasa.gov/search.jsp?R=19930084516 2020-06-17T18:42:39+00:00Z
. ..c- TECH LIBRAIiY KAFB, NM
.,
NATIONAL ADVISORY COMMITTEE FOR
TECHNICAL NOTE 3793
EXPLORATORY INVESTIGATION OF THE USE
TO ELIMINATE AIR-FLOW SEPARATION
AERONAUTICS Iuluullllilllllll
D0bbL3L ‘
OF AREA SUCTION
IN DEFUSE2?S
HAVING
By Curt A.
IARGE EXPANSION ANGLES
Holzhauser and Leo P. Hall
SHY
An exploratory investigation has been made with area suction used for
boundary-layer control in conical diffusers with expansion angles of 30°
and 50° and with an area ratio of 2. These tests> made at a mean inlet
Mach number of about 0.22 indicated that the air-flow separation was elim-
inated by the use of area suction; and the resulting total-pressure and
static-pressure losses were less than those for a 10° diffuser without
boundary-layer control. The air-flow separation was eliminated in the 30°
and 50° diffusers with suction mass flows of 3 and 4 percent of the inlet
mass flows2 respectively.
INTRODUCTION
The results of experimental investigations have shown that separation
of the boundary layer occurs in diffusers that have total expansion angles
greater than about 15°. !J?hisair-flow separation results in total-pressure
and static-pressure lossesj and in nonuniform velocity profiles at the exit
of the diffuser (refs. 1 to 4). In order to improve these characteristics
investigations have been conducted where the boundary layer in the diffuser
has been re-energized with vortex generators or blowing through slots> or
the boundary layer in the diffuser has been removed by suction through
slots (refs. 5.to n). The results of some of these tests showed that
large improvements were made; however, air-flow separation did not appear
to be eliminated in the conical diffusers with total expansion angles
greater than about 30°.
Since area suction (suction applied over a distributed area) was
effective in eliminating air-flow separation on a wing at high angles of
attack (ref. 12)j exploratory tests were initiated to determine whether
area suction would eliminate air-flow separation in diffusers with large
expansion angles. These exploratory tests were conducted using a 30°
.. . .— .. . . ._._ ___ -
—-—— —- --— -—— .. .—
. ,...
..-
2 NACA TN 3793
and a ~“ conical diffuser with various extents of porous area. For com-
parative purposes, a 10° conical diffuser with no porous surface was also .
tested. Due to the exploratory nature of these tests, the tests were per-
formed with only one inlet boundary-layer condition and for a mean inlet 4
Mach number of about 0.2.
NOTATION
—_.—
speed of sound,
cross-sectional
acceleration of
ft/sec
area, sq ft
gravity, ft/sec2
local total pressure, lb/sq ft
arithmetic average total pressure, lb/sq ft 4
ratio of average total-pressure loss to theoretical incompressible
(% -E2)/z=
value for an abrupt expsnsion,
[1-(AJA=)]2
length of diffuser, measured along center line,
w lb/see
mass flow of air, -, —
g ft/sec2
-—
u
average Mach numbers ~
local static pressure, lb/sq ft
arithmetic average static pressure, lb/sq ft
P- 5=
static-pressure coefficient, —
q
dynamic pressure, H - p, lb/sqft
radial distance> in.
radius, in.
local veloci~, ft/sec
velocity outside of the boundary layer, ft/sec
.— -.—. ______ ._ — -.
in.
———. -—
3‘*
IWCA TN 3793 .
u average velocity at a given cross section, ft/sec
w weight rate of flow, lb/see
x longitudinal distance along center line of diffuser, measured from
b~ginning of diffuser, =.
Y distance
g
R=
ratio of
~
R=
ratio of
v. ratio of
value,
!.
J.
2e
1
2
P
s
diffuser
inlet, 2
exit
from wall of diffuser, in.
boundary-layer displacement thickness to inlet radius
boundary-layer momentum
average static-pressure
(F2 - Fl)hz
1- (A~&)2
expamsion angle, deg
thickness to inlet radius
rise
Subscripts
inches upstream of beginning
plenum chamber
suction
to theoretical incompressible
of diffuser
MODELANDAPP-TTJS
.
The test apparatus and different diffuser sections are shown in fig-
ure 1. The three conical diffusers tested had expansion angles of 10°,
30°, and 50°, and they had exit area to inlet area ratios of 2 to 1.
The 10° diffuser was constructed from wood and finished with Fiberglas.
The 30° and 50° diffusers were constructed from commercially produced
porous sintered stainless steel with a thiclmess of about 1/16 inch. The
flow characteristics of this porous material were such that 6 cubic feet
per second per square foot would pass through the material when a pressure
difference of 60 pounds per square foot was applied across the material.
The extent of porous area was controlled by covering a portion of the
.- ..— ..—. ..-. -.. —————— .— --- - ——.— . . .-.— — —.
4 NACA TN 3793
porous area with a nonporous tape about 0.003 inch thick. For some of
the tests, the porous stainless steel was completely covered with this
~.
nonporous tape to simulate a diffuser without boundary-layer control.
The main air flow was sucked through the test apparatus by a constant-
speed-motor and centrifugal-pumpcombination. The air-flow rate was con-
trolled by throttling the exit of the pump. A static-pressureorifice at
station 1 and a total-pressure tube in the 32-tich-diameterbellmouth
(fig. l)wereused asareference dynamic pressure. The average dynamic
pressure at station 1 was determined from a survey made with a probe
inserted at station 1. For the suction tests, the air was sucked through
the porous steel by a centrifugal pump driven by a variable-speedmotor.
The quantity of air removed by this suction pump was measured bya stand-
ard AWE orifice meter.
The pressures at the exit of the diffusers (station 2) were measured
with a fixed rake spanuing the cross section of the diffuser. This rake
consisted of 26 total-pressure and 8 static-pressuretubes. Twenty of
the total-pressure tubes were arranged so as to be centered in regions of
equal area, and they were connected to an integrating board so that an
area-weighted average of the total pressures could be obtained. static-
pressure orifices were located in the wall of the diffuser so that the
longitudinal distribution of the static yressure could be measured. The
boundary-layer profiles at station 1, two inches forward of the inlet of
the diffuser, were measured with a probe consisting of a total-pressure
and a static-pressure
urements of the inlet
tube. This probe was in the duct only when meas-
boundary-layer profile were desired.
TESTS
Tests were made of the 30° and 50° diffusers with various extents
and locations of porous area. These tests were made at an inlet Mach
number of about 0.2, and they were performed with various suction mass
fl.owe. Tests were also made with the porous area of the 30° and 50°
diffusers sealed and with the 10° diffuser in order to obtain data which
could be compared
diffusers.
with previously reported data
RESUUl?SAND DISCUSSION
for similar conical
m.
..tal-Pressureand Static-Pressure Losses
The total-pressure and static-pressure loss factors, Kand 1 - q,
for the 30° and 50° difflmers with area suction and for conical diffusers
without boundary-layer control are compared.in figure 2. These factors
are used to express the performance of a diffuser in terms which tend to
.
—-——— ——- - -——-—— —--- ...— . .. . . . . —_____ . ___
NACA TN 3793 5
be independent of the area ratio. The parameters K and q have also been
referred to as the diffuser loss factor and the diffuser effectiveness,
respectively. It can be seen that erea suction greatly reduced the loss
factors; in fact, the values were less than those measured for the 10°
diffuser of the present test. The data for the diffusers without boundary-
layer control were obtained from references 1, 2, 3, 4, and 10, and they
are presented as bands of data because of the differences in values
reported. Values for the 30° and 50° diffusers with the porous areas
sealed could not be accurately measured with the apparatus used because
of the-unsteady flow resulting from the separation of the boundary layer.
However, the approximate values of loss factors measured for these dif-
fusers were within the bands of data shown in figure 2. With suction
applied, the flow in the diffuser was very steady.
The effect of area suction on the total-pressure, static-pressure,
and velocity distributions at the exit of the 30° and 50° diffusers (sta-
tion 2) is shown in figure 3. These data for the 30° and 50° diffusers
with suction are compared with those for the 10° diffuser without suction
in figure 4. This figure shows that area suction reduced the total-
pressure losses to values less than those of the 10° diffuser, indicating
that the air-flow separation normally attendant with wide-angle diffusers
was eliminated by the use of area suction. Jn figure 4, it is also seen
that the static-pressure distribution at the exit of the diffuser with
suction became less uniform as the diffuser angle was increased from 10°
to 300 to 500. This type of pressure gradient would be expected in poten-
tial flow ti a wide-angle diffuser (see ref. 13).
It should be pointed out that a comparison of the velocity profiles
at the exit of the diffusers (fig. 4) does not provide a comparison of
the boundary-layer profiles because of the previously noted nonuniform
static-pressure distribution. However, the boundary-layer thickness at
the exit of the diffuser can be determined from the total-pressure dis- l
tributions presented in figure 4. A comparison of these distributions
shows that the boundary-layer thicknesses at the exit of the 30° and 50°
diffusers with suction were less than that of the 10° diffuser. Further,
the shape of the total-pressure distributions (fig. 4) tidicates that the
boundary layer in the diffusers with suction is at least as stable as that
in the 10° diffuser. Since there is little or no separation at the exit
of the 10° diffuser, it can be concluded that area suction has eliminated
the air-flow separation that existed in the 30° and 50° diffusers without
boundary-layer control. A typical inlet boundary-layer profile measured
in these tests is shown h figure 5. These measurements show that a thin,
stable, turbulent boundary layer existed at the inlet of the diffusers.
The longitudinal distributions of static-pressure coefficient along
the walL of the 30° and 50° diffusers presented h figure 6 show that area
suction increased the static-pressure recovery along the entire length of
the diffusers. The longitudinal distributions of static-pressure coeffi-
cient for the 30° and 50° diffusers with suction are compared with that
-. . . . ..— - . —.._______ _
—
—— --- —-— .— .- .___
6 IWK!ATN 3793
for the 10° difftmer fi figure 7. The data of this figure indicate that
area suction permits equivalent static-pressure recovery to be obtained
with a diffuser onlya fraction of the length of the 10° diffuser.
..
Suction Requirements
The effect of suction mass flow on the total-pressure recovery of
the ~0° and 50° diffusers is shown h figure 8 for several lengths of
porous area. It csa be seen that a large increase in total-pressure
recovery is obtained with small.suction flow ratios. It can be ascer-
tained from the data presented in previous figures that air-flow separa-
tion has been eliminated in the diffuser when the suction flow ratio is
sufficient to insure essentially complete total-pressure recovery. It
can also be seen in this figure that it iB not necessary, or even desira-
ble from a suction flow standpoint, to apply area suction down the enttie
length of the diffuser. The suction mass-flow ratios and the pumping
pressure coefficients regyired for the 30° and 50° diffusers at the lowest
suction maas-flow ratio where separation was indicated to be eliminated w
are summarized in the following table:
The relatively large pumping pressure coefficients required for the 50°
diffuser resulted because sufficient inflow velocities could be obtained
through the dense porous stainless steel only by providing a large pres-
sure differential. It would be expected that these pumping pressure
coefficients could be reduced by the use of a porous material that had a
greater porosity near the beginning of the diffuser. Based on other
applications of area suction (e.g., ref. 12) it would be expected that
the use of a material with a tapered porosity could also reduce the
suction mass-flow ratios required to elidnate separation.
CONCIJJSIONS
Exploratory tests were made with area suction a~lied to conical
diffusers with expansion angles of 30° and 50°. These tests, made at a
mean inlet Mch number of approximately 0.2, indicated that the air-flow
separation was eliminated by use of area suction, and that the resulting
total-pressure and static-pressure losses were less than those for a 10°
,,
—
— —————
NACA TN 3793
diffuser without boundary-layer control. The air-flow separation was
eliminated in the 30° and 50° diffusers with suction mass flows of 3
and 4 percent of the Met mass flows, respectively.
7
Ames Aeronautical Laboratory
National Advisory Committee for Aeronautics
JfoffettField, Calif., Jhne 27, 1956
1. Gibson, A. H.: On the
REFERENCES
Resistance to Flow of Water Throu~ Pipes or
Passages Having Divergent Boundaries. Royal Society o; Edaburgh
h~S., VO1. 48, pt. 1, 19~-19~, pp. 97-116.
.
2. Gibson, A. H.: Hydraulics and Its Application. Fourth cd., D. Van
Nostrand Co., 1930, pp. 92-93.
3. Peters, H.: Conversion of Energy in Cross Sectional Divergences Under
Different Conditions of Inflow. NACATM 737, 1934.
4. Little, B. H., Jr., and Wilbur, Stafford W.: Perfo~ce and Boundary-
Layer Data llrom12° and 23° Conical Diffusers of Area Ratio 2.o at
Mach Numbers U@ to Choking and Reynolds Numbers Up to 7.5x106.
NACA Rep. 1201, 1954.
5. Valentine, E. Floyd, and Carroll, Raymond B.: Effects of sever-
Arrangements of Rectangdar Vortex Generators on the Static-fiessure
Rise Through a Short 2:1 Diffuser. NACA RM L50104, 1951.
6. Wood, Chsxles C.: Preliminary Iirrestigationof the Effects of Rectan-
gular Vortex Generators on the Performance of a Short 1.9:1 Straight-
WallAnnular Diffuser. NACARML51G09, 1951.
7. Henry, JohnR., and Wilbur, Stafford W.: FYeliminary Investigation of
the Flow in an Annular-Diffuser-Tailpipe Combtition With an Abrupt
Area Expansion and Suction, hqjection, and Vortex-Generator Flow
Controls. NACARML53K30, 1954.
8. Ackeret, J.: Removing Boundary Iayer by Suction. NACA TM 395, 1926.
9. Biebel, William J.: Iow-l?ressureBoundary-Layer Control in Diffusers
and Bends. llACAIJRL-84, 1945. (Formerly NACAARR L5C24)
10. Gratzer, L. B., and Smith, R. H.: Boundary Layer Control for Wide
Angle Diffusers. Aero. Lab. Rep. 300, Univ.of Washington, Nov. 22,
1948.
—.. . ____ __ _ -.
— — .
8 N/WA”TN 3793
I-1. Manoni, L. R.: Wide Angle Diffusers Employing Boundary Iayer Control.
Rep. R-95460-12, Research Dept., United Aircraft Corp., Mar. 19,
1952.
d
1.2.Holzhauserj Curt A ., and Martin, Robert K.: The Use of Leadfig-Edge
Area Suction to hcrease the Maximum Lift Coefficient of a 35°
u
Swept-BackWing . NACARMA52G17, 1952.
13. Rouse, Hunter: Elementary Mechanics of Fluids, Chapter II. John Wiley
and Sons, hC., 1946.
,
u
.1
..-— .—
— —..— . . .
I
t
.
m
I
I
““-t’4Tr 70”
2011 dj&
\
Flou
—.
1011 &l
I
Diffuser
(30° shown) ‘
411~~ / 7
Plenum chamber
Q)
—.—
kY Mdnd.rflolvplmtp
Suotion pump for
boundarplayer control
(a) Over-all setup.
Figure 1.- Dimensional characteristics of teat apparatm.
10 NACA TN 3793
Sta
1
Sta
2
.
.
<
.Msxmum porous
area
&a
1 2
T
RI -
I d--
----
.-”--.
!
1
I
! < L;
. .Msxmumporous
1 area
—
!50°~
I
I
..
.....
Note: ~ “isthe inlet
k: -
radius and is equal
“%- ,89: to five inches
&a
1 2
(b) Diffuser details.
Figure 1.- Concluded.
—. ... —- -.———- -----—- --
.—— ---- --- ---
.1.
1.
10
!4
f 1’
m
m.
2
it .
~
j“
.
0 10 20 30 40 ~ (h
2e
—.
NO boundqy-m control
(rai?erenoea 1,2,3,4, end
NO bcmxkuy-laywr O(KltiOl
(preaeart investigation)
mJ5 = 0,04, xjz = 0.16
mJy = 0.06, %/t = O.~
10)
1.4
El”
0
F
I 1.2
l-l q
o 10 20 30 @ go &l
20
Figure 2.- Variation of diffueer total-pressure end static-pressme 10ES factors with expaneion
eagle for conical diffusers with sad without =ea suction; ml = O.2, A2/AL = 2.
.i’
. .
1.0
.8
.6
.4
.2 {1
0
.2
1)
.4
.6
.8
1.0
0 .2 .4 .6 .8 1.0
~ %-H
-—
q
0 .2 .4 .6 .8 1.0
p-%
;1
.
\
\
I
I
I
I
SeKied { I
Wbh suction -- ~
I
1
r ‘“
I
I
I
/
I
1
0 .2 .4 .6 .8 1.0
u
—
(a) 2e = 30°, sealed and with euction (~/ml = 0.04, x/2 = 0.16).
Figure 3.- Effect of area
at
suction on the total-pressure,
the exit of the diffuser; xl =
static-pressure, and velocity profiles
0.2, A41=2.
3
w
w
,
1.0
.8
.6
.4
.2’
0
-i .2
.4
.6
.8
1.0
I )
[1
[
(
Sealed
o .2 .4 .6 .8 1.0 o .2 .4 .6 .8 1.0
2Qi
Cll
>%
. \
\
;
1
I I
,
/
J
I
sealed I
With suction I
/‘
I
I
1
I
/“
//
o .2 .4 ,6 .8 1.0
u
—
ill
(b) ZW =50°, sealed sndwith suction (~/m,= 0.(%, x/2 =0.15).
Figure 3.- Concluded.
,I
I
.
I
1.0
.8
.6
.4
.2
0
; .2
A
.6
.8
1.0
o .2 .4 .4 .8 1.0
~=E@I
%
o .2 .4 .6 .8 1.0
P:;x
o .2 .4 .6 .8 1.0
u
=
u~
g
Figure k.- Caqarison of total-preaeure, Btatlc-pressure, and velocity distributions at exit of
10° diffuser ti_th those of 30° and 50° diffusers with area suction, mB/ml = 0.04 and 0.06, Es
respectlv~ly; Ml = 0.2, &JA~ - 2.
$
*
.I
I
,
.16
,~w=
.14 oherautmd.etios
#
- O.cdlo
z
.12
~ - ooa131
%
.lo .
-i
.00-
.06
“o .1 .2 .3 .4 .5 .6 .7 .8 . .9 1.0
u
=
u
Fi~e 5.- Inlet boundery-layer proffle for 10° Mffueer; El = 0.2, &/Al = 2.
I
I
16 NACA TN 3793
P
(a)
-0 4
-m2
0
.2
.4
.6
.8
1.0
‘With suction
P
-1.2 -.8 -.4 0 .4 .8 1.2 1.6 2.o 2.4 2.8
Ratio of longitudinal distance to inh% radius, x/~
26 = 30°,sealed and with suction (mS/m= = 0.04, x/Z = 0.16).
-m 4
Diffuser 1~length
-*2
0
.2
.4 \ Sealed
With suotion
.6
.8 4
1.0
-1.2-.8 -.4 0 .4 .8 1.2 1.6 2.o 2.4 2.8
Ratio of longitudinal distance to inlet radius, x/~
(b) 2e = 50°,sealed and with suction (mS/m= = 0.06, x/Z = 0.15).
Figure 6.- Effect of area suction on the longitudinal static-pressure
coefficients along the wall of the diffuser; El = 0.2, A2/A1 = 2.
. . . .. —- .—— — --. .— .—. ______ ________
=!
-* 4 w
-a
w
,*
LA!
-. 2 \
/1 \ I!kLt $Or
o 29 -100
.2
–-–2 Q = SOO,m#q = 0.06, X/?UO.~
.4 1 \
P
\
\
\
.6-
\
\
.8
.
1.0
-* 8 0 .8 1.6 2.4 3.2 4.o 4.8 5.6
Ratio of longitudinal Wd.snce to Met radiua, x/+
—
—
Figure 7.- C_ison of the longitudinal distributions of static-pressure coefficfsnlm along the
10° diffuser, 300 diffuser tith suction, end the 50° diffuser with suction; ~1 = !3.2, A=/Al = 2.
1.0
.8
1# .7
I
.6
1+
l5
.4
,
I
Siation 1
//&/ O 0.06
/ q .16
#
A .26—_
II I7 I I I
::02 0 .02 .04 .06 .08 .IO .U .~ .16 .18 .20
Ratio of sutionto inlet mass flows, m@l
(a) 2e =30°
1.0
.9
1 .6
d
.5
I II I I I q .33
A .!3.
o .69
.4 “ ~. v .87
‘~ Is’ 1.00
do2 o
.02 .04 .06 .08 .10 .12 J& .16 .18 .20
Ratio of suotionto inlet mass flows, ms/ml
(b) 2e =50°
Figure 8.- Variation of total-pressure rec~ery with suction mass flow
for several efients of-porous area; Ml = 0.2, &/AX = 2.
NACA .Ia@ey Field,%.
—...—
.
.
,
.


Exploratory investigation of the use of area suction to eliminate air-flow separation in diffusers having large expansion angles

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