A two dimensional momentum integral analysis was used to examine the effect of changing inlet area ratio, diffuser area ratio, and the ratio of ejector length to width. A relatively wide range of these parameters was considered. It was found that for constant inlet area ratio the augmentation increases with the ejector length, and for constant length: width ratio the augmentation increases with inlet area ratio. Scale model tests were used to verify these trends and to examine th effect of aspect ratio. On the basis of these results, an ejector configuration was selected for fabrication and testing at a scale representative of an ejector wing aircraft. The test ejector was powered by a Pratt-Whitney F401 engine developing approximately 12,000 pounds of thrust. The results of preliminary tests indicate that the ejector develops a thrust augmentation ratio better than 1.65

Alden, R. E.

Bevilacqua, P. M.

Mefferd, L. A.

English

NASA Technical Reports Server

DESIGN A/_) TEST OF A PROTOTYPE SCALE EJECTOR WING
L. A. Mefferd, R. E. Alden and P. M. Bevilaqua
Rockwell International
Columbus Aircraft Division
Abstract
The use of analysis and scale model testing to design a full scale (proto-
type) ejector wing is described. A two-dimenslonal momentum-integral
analysls was used to examine the effect of changing inlet area ratio,
diffuser area ratio, and the ratio of ejector length to width. A rela-
tively wide range of these parameters was considered. It was found that
for constant inlet area ratio the augmentation increases with the
ejector length, and for constant length: width ratio the augmentation
increases with inlet area ratio. Scale model tests were used to verify
these trends and to examine the effect of aspect ratio.
On the basis of these results, an ejector configuration was selected for
fabrication and testing at a scale representative of an ejector wing air-
craft designed to perform the U. S. Navy Type '_" mission. The test
ejector was powered by a Pratt-Whltney F401 engine developing approxi-
mately 12,000 pounds of thrust. The results of preliminary tests indicate
that the ejector is developing a thrust augmentation ratio better than
= 1.65. This is essentially the same level of augmentation obtained
in the model scale tests. It is concluded that the combination of
analysis and scale model testing can be used to design full size ejectors,
although questions of scale and temperature effects remain.
437
https://ntrs.nasa.gov/search.jsp?R=19800001892 2020-03-21T02:14:04+00:00Z
INTRODUCTION
Since the cost of developing an aircraft at prototype scale is prohibi-
tive, it has been usual to employ analytic methods and scale model test-
ing in the initial stages of development. However, ejector development
has been carried out largely by empirical and cut-and-try methods because
suitable methods of ejector analysis and modelling had not been devised.
Until recently only one-dlmensional analyses of ejector performance were
available.l,2, 3 These analyses were useful in identifying someof the
factors that affect ejector performance and in establishing ideal levels
of performance9 but such parametric methods cannot be used for actual
design purposes. For this it is necessary to predict the rate of
entrainment due to the turbulent mixing within the ejector. Recently,
Bevilaqua and McCullough4 developed a two-dimensional, finite different
analysis using integral methods for the jet entrainment, while Gilbert
and Hill 5 used a mixing length model to calculate entrainment, and
DeJoodeand Patankar6 used a two-equation turbulence model.
Various studies of ejector scale effects have given inconclusive results.
The earliest study of aircraft ejector scale effect performed at the
Pennsylvania State University 7 indicated that thrust augmentation
increases with the ejector scale; however, aircraft scale ejectors built
by Boeing8 and DeHavilland 9 produced less augmentation than the labora-
tory models from which they were developed. Full scale Rockwell ejectors
have generally performed as well as smaller models, but a limited study
of the effects of size again suggested that augmentation increases with
the scale. I0
The purpose of this paper is to show that recently developed two-
dimensional methods of analysis can be used with scale model testing to
design prototype ejector wing aircraft. In the next section the use of
the integral method to predict performance trends for a wide range of
configurations is described. The results of scale model tests of three
ejector configurations are compared to the analytic trends in the fol-
lowing section. In the last section test results from a prototype-scale
eiector wing are compared to the analytic and scale models predictions.
METHODOFANALYSIS
Weundertook to design a full scale ejector wing for a transport type
aircraft such as that shownin Figure i. The integral method of
analysis 4 was used to make the initial trade-offs between ejector inlet
area ratio and length to width ratio. Although the more sophisticated
turbulence models5,6 could be expected to give greater accuracy, such
methods are too expensive and time consuming to use for parametric
studies, which require manyconfigurations to be analyzed. The integral
method is a two-dimensional analysis in which the jet velocity profiles
are assumedto have a self-preserving shape. Since there is a primary
direction of flow (through the ejector) it is assumedthat the thin
shear layer approximation is applicable. This reduces the governing
438
1Figure i. V/STOL aircraft utilizing ejector thrust
augmentation in the wing.
elliptic equations to a parabolic set which can be solved by marching in
the streamwise direction. A control volume approach was utilized to put
the differential equations in finite difference form. The mass and
momentum conservation equations are integrated over a control volume
coinciding with the walls of the shroud and having length_ dx 9 in the
streamwise direction. Pressure and shearing stresses act on the fluid
in the control volume at the walls and on the upstream and downstream
faces.
The velocity distribution is represented by the superposition of a self-
preserving jet velocity profile on a uniform stream. An explicit closure
assumption relating the turbulent stresses to the mean flow was not made;
however 9 the use of self-preserving mean velocity profiles is equivalent
to an assumption that the stresses are proportional to the rate of strain.
In this case the rate of entrainment can be specified by one empirical
constant. These equations are solved simultaneously at each dx step
through the ejector by straightforward algebraic procedures.
Although solution of the ejector equations has thus been transformed to
an initial value problem that can be solved by a streamwise marching
procedure_ the basic elliptic character of the flow remains unchanged.
This means that the velocities at the ejector inlet cannot be arbitrarily
specified_ but must be compatible with an outer flow that satisfies
boundary conditions on the shroud and at infinity. Compatibility of the
inner and outer flows is obtained by iterating on the inlet velocity until
the exhaust pressure matches the static pressure outside the ejector exit.
439
This entrainment method provides a relatively simple procedure for cal-
culating the turbulent mixing and entrainment within the ejector. It
requires very short computing time, considerably less than one second
on an IBM 370. Limitations of the program include the inability to com-
pute compressibility effects and the influence of curvature on the tur-
bulence in the Coanda jets.
Parametric trades between ejector throat width, W, and shroud length, L,
were made by varying W at constant L/W, and by varying L/W at constant
W. Results indicate that the larger inlet area ratios, A2/A0, at con-
stant L/W consistently demonstrated higher levels of performance for the
entire range of diffuser area ratios. A2/A0 was varied by changing the
throat width, keeping A 0 constant. This was done for each of several
different L/W's. A2/A 0 is plotted against the maximum @ (thrust augmenta-
tion ratio) attainable at that L/W, Figure 2. Thrust augmentation ratio
1.8_
17
Maximum
Thrust
Augmentation
1.6
1.5
0
- LENGTH/WIDTH RATIO 2.0
12 14 16 18 20
Inlet Area Ratio
Figure 2. Predicted thrust augmentation ratio as a
function of ejector geometry.
440
is defined as: total thrust/isentropic thrust. Since the computer pro-
gram cannot predict separation, the diffuser area ratio which produced
the peak performance was projected from previous emperical correlations
between L/W and maximumdiffuser area ratio, A3/A2, for rectangular aug-
menters. The analysis indicated:
- A change in A2/AO, in the A2/A 0 = I0 to 16 range, has a sizable
effect on augmentation.
- Augmentation is less sensitive to A2/A 0 in the A2/A 0 = 16 to 20
region; the percent increase with increasing A2/A 0 begins to
decline.
- An increase in L/W produces an increase in augmentation at each
A2/A 0. L/W testing performed shows that this rate of increase
declines with increasing L/W.
MODEL TESTS
Te_ting to verify the analysis was carried out on the following three
basic augmenter configurations. A typical configuration is shown in
Figure 3.
Average
Configuration A2/A 0 L/W
Average
L W
(in) (in) AR
I 13.1 1.53 6.15 4.02 8.488
2 17.3 1.55 8.2 5.32 6.415
3 17.3 1.73 9.22 5.32 6.415
As was done in the analysis, A2/A 0 was varied by changing the throat
width, keeping A0 constant. In Figure 4 the measured change in aug-
mentation with diffuser area ratio is shown for two inlet area ratios
at L/W = 1.53 and for two shroud lengths at A2/A 0 = 17.6.
The maximum performance from each of the test configurations was slightly
below the predicted value; the trends produced compared favorably (Figure
5). The discrepancy in absolute values between the analysis and the test
values is at least partly related to the fact that the analysis is for
2-D flow disregarding endwall effects. Local _ values near the endwalls
are considerably lower than midspan values, thus lowering the average
va lue.
441
\
\
18
16
1.4
1.2
1.0
Figure 3. Scale model ejector utilized for
all three test configurations.
I
.I
/fI/ /
/
I I I
A2/A 0 = 17.6
l..- ---
13.4f 0 1.4
1.2
J
/
1.0
I
IJ
L/W = 1.53
I 1.0
1.5 2.0 1.O 1.5
Diffuser Area Ratio Diffuser Area Ratio
Figure 4. lhrust augmentation ratio measured for
the scale model ejectors.
I I T
L/W = 1.73
A2/A 0 = 17.6
2.0
442
Maximum
Thrust
Augmentation
1.8
1.5
10
LENGTH/WIDTH RATIO 2.0
1.7
1.5
./" /i _ _-
I I I 1
12 14 16 18 20
Inlet Area Ratio
Figure 5. Comparison of predicted (--) and
measured (- - -) thrust augmentation ratio.
FULL SCALE PROTOTYPE TESTS
Utilizing results from the analysis and from the small scale model test-
ing, a full scale prototype ejector wing configuration was selected for
fabrication and testing. A size was chosen that was representative of
an ejector wing aircraft configured to perform the U. S. Navy Type A
mission. A section through the full scale prototype augmenter wing is
shown superimposed on the airplane ejector wing in Figure 6.
443
iV
L
_SECTION
/
PLANFORM
Figure 6. Comparison of aircraft wlng design (- - -) and
prototype ejector wlng tested (--).
Particular attention was given to the design parameters which had been
identified by both the analytical and empirical studies as producing
significant effects on augmenter performance. This effort resulted in
the augmenter wing which is shown in Figure 7.
444
IFigure 7. Prototype scale ejector wing shown rotated
90° to minimize ground effects.
The major parameters of the configuration are"
Span
Throat (W)
Flap Length (L)
AO
Flow Split
245.8 inches
38 inches
60 inches
561 sq inches
(Coanda 9 20%; Center Nozzle, 55%; Endwalls, 5%)
The large scale augmenter test facility was intentionally designed to
feature a high degree of testing flexibility. This flexibility allows
variations in a number of major augmenter geometric parameters such as
throat width (W), flap length (L), Coanda nozzle gap (t), and diffuser
flap angle (SF)- The test facility as a whole also allows a great deal
of testing flexibility and includes the capability to rotate the entire
augmenter panel, vary the static height of the augmenter panel above the
ground plane, and provisions for "taxi" and "flight" testing modes.
Specific instrumentation and recording capability can be added as
required.
445
The complete test article consists of a ninety (90) foot steel boom, a
thirty (30) foot model support frame, engine mount facility for cradling
the XF401U. S. Navy engine (this engine being available on site for
use), two twenty (20) foot flaps with both flaperon units and extender
surfaces, the twenty (20) foot centerbody, the air distribution systems
consisting of the plenum, and various pieces of ducting hardware, and
the boom tie-down structure.
Initial testing of the full scale prototype augmenter wing has shown
that the configuration is developing a thrust augmentation ratio in the
= 1.65 range.
Large scale performance measurements (throat velocity, flow quality)
indicate that its overall performance level can be increased. Utilizing
the flexibility built in the large scale augmenter evaluation will per-
mlt: (a) increasing L/W, (b) limited variations in A2/Ao, and (c) increas-
ing A3/A 2 delaying flow separation to higher values of diffuser area
ratio. Comparison of test results from this configuration with those
obtained from its scale model counterpart indicate that the large scale
ejector is currently obtaining augmentation ratios similar to the model
at comparable A3/A 2 ratios, all other design parameters being consistent
(Figure 8).
Thrust
Augmentation
Ratio
1.8
1.6 Mod
1.4_
1.2--
! I t I I I _ | I 1 J1.0
.0 1.2 1.4 1.6 1.8 2.0
Diffuser Area Ratio
Figure 8. Comparison of measured thrust augmentation
ratio at prototype and model scales.
446
This result suggests that apparent scale effects in previous tests were
probably related to differences in internal ducting, primary jet tempera-
ture, method of construction, and other features that were not scaled.
However, the present results should not be taken as proof that there are
no scale effects. For example, in modeling the characteristics of jets,
it [s necessary that the Reynolds number be held constant. This is
because small scale eddy motions are affected by Reynolds number; how-
ever, it is the large scale eddies that control the rate of entrainment
and these are independent of Reynolds number. Thus, if the Reynolds
numbers for both the original and model jets are large enough to insure
that the flow is turbulent, equality of Reynolds number is not necessary
to scale jet entrainment. On a more elementary level, the "square-cube
law" for scaling implies that frictional effects are greater in small
ejector models, because the model has greater wall surface (L2) in rela-
tion to volume (L3) than a full scale ejector. As long as the model is
not made too small, frictional forces are almost negligible and maynot
reduce the augmentation significantly. Since the effect of increasing
the temperature of the primary jet is to reduce the augmentation, these
effects may have been equal and opposite in the present tests.
CONCLUSION
With the use of physical reasoning and mathematical analysis, scale model
testing can be used for initial development of prototype scale ejectors.
Nowever, further study of ejector scale and temperature effects is needed
to separate extraneous influences from true scale effects.
I,
.
.
.
o
•
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Salter, G. R., "Method for Analysis of V/STOL Aircraft Ejector,"
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Gilbert C. E. and Hill, P. G., "Analysis and Testing of Two-
Dimensional Slot Nozzle Ejectors with Variable Area Mixing Sections,
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DeJoode, A. D. and Patankar, S. V., "Prediction of Three-Dimensional
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448


Design and test of a prototype scale ejector wing

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