Note: Descriptions are shown in the official language in which they were submitted.
~135;~
This invention relates to irnprovements in
jet nozzles.
Jet nozzles are comrnonly used for powered
lift aircraft, for the blown wings or flaps of such aircraft.
Such nozzles usually take the form of a slot, and may
discharge into a diffuser which has an entrance opening near the
nozzle into which additional air may be drawn. In such a case the
additional air mixes in the diffuser with the jet stream from
the nozzle and increases the thrust produced. The combination
of the nozzle and diffuser is commonly called an ejector.
A disadvantage of previous slotted jet
nozzles used in ejectors has been that the jet stream emerging
from the slot does not spread uniformly across the height of
the diffuser, and therefoxe the entrainment and mixing of
additional air have not been optimized. In an attempt to
solve this disadvantage, slotted nozzles have been built in
which the normal linearly extending slot at the end of the
nozzle has been changed to a series of vertically segmented
nozzles hav~ing flared ends spaced closely together. This spreads
the jet stream more uniformly across the diffuser in a direction
normal to the plane of the jet stream and improves the
entrainment and mixing of additional air. However, although
this provides a substantial increase in overall thrust as
compared with a plain slotted nozzle, the structure con-
stituted by the large number of vertically segmented nozzles
adds to the manufacturing cos-t and weight of the aircraft.
More significantly,the flared ends of the nozzles cause
considerable loss of efficiency due to air resistance.
Accordingly, the invention in one of its
aspects provides a nozzle arrangement for spreading the jet
-- 2 --
~3~iZ36
stream more uniformly across the throat of the diffuser.
According to this aspect of the invention, the rear edge of
the nozzle has a series of notches soaced therealong. Each
notch has a narrow front apex, a rear opening substantially
wider than its apex, and each notch widens substantially
smoothly and progressively from its apex to its rear opening.
The sides oft~le notch diverge from each other at an angle
which, at least over a major portion of the length of the
sides, exceeds 60 degrees and preferably exceeds 90 degrees.
It is lound that these notches, particularly those in which
the angle of divergence of the sides exceeds 90 degrees, can
produce thrust augmentation greater than that which has been
achieved with vertically segmented nozzles, and at greatly
reduced weight and cost.
The notch system according to the invention
may also be used in ejectors having circular jet nozzles, and
with nozzles which are used simply for blowing over flaps
without diffusers.
It is also common practice to form the
circular nozzles of jet engines in a complex shape, for
example with indented fingers,to deploy the jet in a manner
which reduces noise. In some cases slots in the circular
nozzles have been used for this purpose, for example as shown
in U.S. patent 3,743,185. Unfortunately, both the indented
fingers and the slots employed have resulted in considerable
; loss of thrust of the nozzle. U.S. patent 3,743,185
indicates that a five percent loss in thrust is suffered
for a ten PNdB noise reduction. This thrust loss can be
reduced by use of the notches of the invention, placed
around the periphery of the jet nozzle~ Not only is
Z3~;
the thrust loss is reduced in this way, but at the
same time noise reduction is achieved.
It is found that the controlled spreading
of the jet which is achieved by using notches having a diverg--
ence angle of 60 degrees or more can also be achieved by using
notches having a much narrower angle of divergence (as low as zero
degrees) provided that internal fairing structure is placed between
the notches, -to guide and confine the flow of gas to the notches.
Therefore in another aspect the invention provides a nozzle
system for a jet stream comprising: nozzle structure having a
rear edge, a plurality of nozzles spaced along said rear edge,
each nozzle having a tapered rear end and a notch in said rear
end, each notch having a front apex and a rear opening wider
than said apex, each notch widening smoothly and progressively
from said apex to said rear opening, gas supply means within
said structure for conducting pressurized gas to said nozzles,
and fairing means within said structure separating said
notches from each other, for guiding gas from said gas supply
means to said notches, and for confining the flow of gas
to said notches, for said nozzles to spread said jet stream
while presenting a low resistance to gas flowing over said
nozzle structure.
Further objects and advantages of the
invention will appear from the following description, taken
together with the accompanying drawings, in which:
Fig. 1 is a cross-sectional view showing a
prior art ejector;
Fig. 2 is a perspective view showing the
nozzle portion of the ejector oE Fig. l;
~L~35~3~
Fig. 3 is a cross-sectional view showing
a further prior art ejector;
- Fig. 4 is a perspective view showing the
nozzle portion of the ejector of Fig. 3;
` Fig. 5 is a cross-sectional view showing
an ejector according to the invention;
Fig. 6 is a perspective view showing the
nozzle portion of the ejector of Fig. 5;
Fig. 7 is a top view of the ejector portion
; 10 f Fig. 6;
Fig. 8 is a cross-sectional view showing
diagrammatically the operation of a rectangular notch;
Fig. 9 is a perspective view showing the
rectangular notch the operation of which is illustrated in
~` Fig. 8;
Fig. 10 is a cross-sectional view showing
diagrammatically the operation of a divergent notch of
the invention;
Fig. ll is an ~nd view illustrating in
idealized fashion the gaseous elements emerging from the
Fig. 10 notch;
Fig. 12 is a top view showing a modified
notch of the invention;
Fig. 13 is a perspective view showing
notches formed in one side only of a nozzlei
Fig. 14 is a perspective view showing
notches arranged in staggered fashion in a nozzle;
Fig. ]5 is a perspective view showing
notches arranged in one side of a nozzle and flap system;
, 3~ Fig. 16 is a perspective view showing a
.,
notched nozzle system for use in a VTOL aircraft;
-- 5
~35Z3~
Fig. 17 is a plan view of the bottom of
a modified nozzle for the Fig. 16 system;
Fig. 18 is a side view of a circular jet
nozzle having notches according to the invention, in
combina-tion with an annular shroud;
Fig. 19 is an end view of the nozzle
of Fig. 18;
Fig. 20 is a side view similar to Fig. 18
but showing a turbo fan engine;
Fig. 21 is a diagrammatic view showing a
modified notch of the invention; -
Fig. 22 is a cross-sectional diagrammatic
view showing vectors representing gas flows;
Fig. 23 is a cross-sectional view along
lines 23-23 of Fig. 7 showing a fairing used to guide gas
flows;
Fig. 24 is a top view similar to that of
Fig. 7 but showing a modified form of internal fairings;
Fig. 25 is a perspective view similar to
2n that of Fig~ 6 but showing a modified nozzle structure;
Fig. 26 is a top view, partly cut away, of
a portion of the nozzle structure of Fig. 25;
Fig. 27 is a top view of a nozzle duct of
the Fig. 2~ nozzle structure;
Fig. 28 is a side view of the duct of Fig. 27;
Fig. 29 is a sectional view taken along lines
29-29 of Fig. 27;
Fig. 30 is an end sectional view similar to
Fig. 13 but showing internal fairings~ and
Fig. 31 is a perspective view of a portion
of the structure of Fig. 30.
~3S;~3~i
Reference is first made to Figs. l and 2,
which show a standard ejector 2 currently used in many
aircraft. Such an ejector is for example shown in U.S.
patents 3,259,340 and 3,442,470, both issued to The DeHavilland
Aircraft of Canada; U.S. patent 3,841,568 issued to The
Boeing Company, and U.S. patent 3,860,200 issued to Rockwell
International Corporation.
The ejector 2 shown in Fig. 1 may be
incorporated into the wing 4 of an aircraft. The wing 4
has a duct 6 extending spanwise therealong, the duct 6
being pressurized with air or other fluid from the aircraft
engine or engines, by means not shown. The air from the
duct 6 is blown outwardly through a rectangular slot 7 at
the end of a nozzle 8, the path of the air being indicated
by arrows 10. The air travels rearwardly between upper and
lower flaps 12, 14, which together form a diffuser, and exits
from the rear opening between the flaps. The flaps 12, 14 are
pivotally fixed to the wing 4 by hinge structure which is
not shown but which may be the same for example as that shown
in U.S. patent 3,442,470.
As the blown air indicated by arrows 10
travels between the upper and lower flaps, i~c entrains
secondary or additional air, indicated by arrows 16. The
secondary air mixes with the primary air blown out the
., ~
'~- nozzle 8, increasing the mass of the air which is blown
out the rear of the ejector 2. This increases or augments
the thrust of the nozzle 8.
Unfortunately, the total pressure distribution
at the rear of the flaps 12, 14 (which pressure distribution
is indicated by graph 18 in F g 1) has a pressure peak 19a
~l~S;~3~
midway between the flaps, and the pressure falls off to very
]ow values l9b at '.he top and bottom of the diffuser, i.e.
near the flaps. This reduced pressure at the edges of the
diffuser is extremely undesirable, because it results in-
inefficient entrainment of secondary air and inefficient
- interchange of momentum.
To deal with th:is problem, the prior art
has adopted the solution shown in Figs. 3 and 4. In Figs. 3
and 9, in which primed reference numerals indicate parts
corresponding to those of Figs. 1 and 2, the slot 7 at the
rear end of the nozzle 8' has been closed and replaced by
a series of vertically segmented nozzles 20 spaced fairly
closely together along the rear edge of the nozzle 8'. The
nozzles 20 are flared to direct the jet flow from the duct 6
more closely to the opposed inner surfaces of the flaps
12', 14'. This results in a pressure distribution which
is much more uniform across the distance separating flaps
12', 14', the improved pressure distribution being indicated
by graph 18' in Fig. 3. The nozzles 20 are placed suffic-
iently closely together that the jet streams issuingtherefrom merge laterally and produce a relatively uniform
pressure distribution lengthwise between the flaps 12', 14'.
Tests have indicated that the use of flared
segmented nozzles can produce fairly substantial improvements
in thrust augmentation. For example, in one test which was
conducted, the augmentation ratio of apparatus such as that
shown in Fig. 1 was 1.38, i.e. the thrust produced was 1.38
times that which would have been produced had the mass flow
directed through nozzle 8 been directed instead through a
simple ideal nozzle. When the apparatus shown in Figs. 3
-- 8 --
and 4 was used instead, the augmentation ratio increased
considerably; in one test, it increased to 1.57.
Unfortunately, as previously indicated,
the projection of the flared segmented nozzles 20 into the
airstream creates considerable losses due to friction.
The nozæles 20 also of course add weight to the aircraft. The
inventors have discovered that a similar effect as that
produced by the nozzles 20 can be achieved (and in fact in some
respects even a better performance can be achieved) by
replacing the nozzles 20 with simple notches formed in the
trailing edge of nozzle 8. An example of this system is
shown in Figs. S to 7, in which double prime reference
numerals indicate parts corresponding to those of Figs. 1 and 2.
In the Figs. 5 to 7 structure, the slot 7
at the rear edge of the nozzle has been closed, as in the
Figs. 3 and 4 structure, and the segmented nozzles 20 have
been replaced by triangular notches 30~ The notches 30
are spaced along the trailing edge of the nozzle 8'' in the
same positions as the segmented nozzles 20 so that the jet
streams emerging therefrom will merge laterally and produce
fairly uniform pressure distribution lengthwise of the
ejector structure. At the same time the notches ensure a
high degree of uniformity of pressure distribution across
the depth of the ejector (i.e. in the direction of arrow A-A).
It is found that the notches 30 can perform
as well as, or better than, the seymented nozzles 20 in
producing a uniform pressure distribution across the depth
of the ejector. A typical pressure distxibution which may
be achieved is indicated by graph 32 in Fig. 5. However, to
achieve good results in the Figs 5 to 7 structure described,
;236
the angle x (Fig. 7) between the sides of each notch 30
should be relatively wide. It is found that angle x
should be at least 60 ~egrees and is preferably substantially
more, for example 90 degrees or more. In fact, preferably
angle x is about 100 degrees and can be even greater if
desired. Angle x will normally not exceed about 145 degrees,
however, except in special circumstances. The preferred
range for Angle x is 90 to 120 degrees.
The physical mechanism by which the notches
30 operate is illustrated aiagrammatically and in simplified
manner in Figs. 8, 9, and 10. Fig. 8 illustrates, with
arrows marked A, B, C, D, E, the manner in which a jet stream
wi]l issue from a rectangular notch 34 (Fig. 9) in the end
of a nozzle 36. Each arrow A to E represents an element
j of the jet stream. As shown, when each element is of
equal size, then each element will continue to discharge
substantially in the direction from which it issues from
the notch 34 in Fig. ~, and too much spreading of the jet
stream will be produced. The very wlde spreading results
in a substanial reduction of efficiency of the nozzle
and also degrades the performance of the ejector in
entraining secondary air.
However, if the diverging notch 30 of Figs.
4 to 6 is used in place of the rectangular notch 34, then a
different result occurs, as shown in Fig. 10. Since jet
element "A" is now adjacent to a jet element "B" which is
discharging at a lesser angle to the centre plane 38 of the
nozzle and which is substantially larger, element "A" will
now tend to bend downstream and follow the direction oE
element "B':. This occurs by virtue of the Coanda effect.
-- 10 --
'''
"
~3~
Since the largest element is element E which discharges
parallel to the plane 38 of the nozzle, the result is that
the elements A to D all bend downstream and tend to follow
a direction parallel to the centre plane 38, as indicated
by the dotted lines in Fig. 10. However, as shown in Figs. 9
and 10, the jet is substantially spread at a location near
the exit of the nozzle 8" and thus produces a more uniform
pressure distribution across the depth of the ejector 2".
This extent of the spreading can be controlled by adjusting
the length (in a front to rear direction) of the notches, - -
as well as by controlling their angle of divergence. A
60 degree angle of divergence will produce a "taller"
spread than will a 145 degree angle of divergence. It is
undesirable for the jet from the nozzle to be spread so
much that it hits the diffusers 12", 1~", since this increases
losses, and therefore the actual angle of the aivergence
will vary with the application.
In the same set of tests as that discussed
previously, in which an augmentation ratio of 1.38 was
achieved with the Fig. 1 apparatus and an augmentation of
1.57 was achieved with the Fig. 3 apparatus, the apparatus
of Figs. 5 to 7 achieved an augmentation ratio of 1.68,
while at the same time eliminating the need for the flared
segmented nozzles 20. One of the factors in the improved
performance of the Figs. 5 to 7 apparatus as compared with
that of Figs. 3 and 4 is thought to be that the drag of
the flared nozzles 20 in the very high velocity gas streams
in the throat of the ejector 2' has been eliminated.
It will be appreciated that various forms
may be selected for the notches 30. For example, the
~35Z36
notches need not be exactly triangular; the apex of each
notch may be curved and the sides may be non-linear, as
shown for notch 40 in Fig. 12. In all cases, however, the
sides of the notch at least over most of the length of the
notch should diverge smoothly and progressively and the
angle of divergence should be at least 60 degrees, and
preferahly at least 90 degrees. As indicated, a divergence
angle of approximately 100 degrees has been found to produce
excellent results.
Although the notches 30 have been shown as
cut through both surfaces bounding the nozzle 8", the
notches 30 may instead be cut through one such surface 42
(Fig. 13) only, and not through the other surface 44
(depending upon the ejector configuration used). Alter-
natively, or ln addition, the notches 30 may be staggered
by placing them alternately in surfaces 42, 44, as shown
in Fig. 14.
It will also be appreciated that the
notches 30 may be used in con~unction with only one flap,
such as either flap 12 or flap 14. Such an arrangement
is shown in Fig. 15, in which the aircraft wing is indicated
at 50, the nozzle at 52, a diverging notch (like notch 30)
at 54, and the single flap (which may be a landing flap)
at 56. This arrangement, except for the notches 54, is
similar to that shown in U.S. patent 3,161,377. The Fig. 15
arrangement also illustrates that the trailing end of the
nozzle 52 need not be fully closed when the diverging notches
of the invention are used, but can if desired be provided
with a narrow slot 58. The slot 58 will usually be somewhat
narrower than that of the slot which would have been used if
- - 12 -
, .
~3L35Z3~
the notches 54 were not present, so that the total area of
the slot 58 plus the notches 54 is of the same order as
that of the slot which would have been used if notches 54
were not present. In the Fig. 15 version, the no~ches
54 are located only in the upper rear edge of the nozzle
52, since no spreading of the jet stream in a downward
direction would usually be required in this arrangement.
Another application of the slots is
shown n Fig. 16. Fig. 16 shows a typical high performance
ejector configuration for a VTOL aircraft. In this config-
uration, a jet stream from the engines (not shown) is blown
through nozzles 60, 62, 64, and downwardly between flaps
66, 67, as indicated by arrows 68. Secondary air is inducted
from above the nozzles, as indicated by arrows E, and is
entrained in jet streams. The nozzles 60, 62, 64 and provided
with diverging notches 70 of the design described which may be
staggered with respect to each other so that the "fingers"
of the jets which issue from the slots in~erlace with one
another. If desired, the trailing ends of the nozzles 60,
62, 64 may be closed except for the notches, as previously
described. ~lternatively, as shown in Fig. 17, the nozzles
60, 62, 64 may have a narrow rectangular slot 72 in their
trailing ends, with the diverging notches 70 located in the
edges of the surfaces bounding the slot 72. This may provide
less spreadingof the jet stream than would occur if the slot
22 were closed, but the combination may be desirable
under some circu-mstances. The extent of the spreadingmay
be adjusted by controlling the width of the slot 72 and
the number, spacing, front to rear leng-th, and divergence
of the notches 70. It will be appreciated that in the
- 13 -
~3~36
Figs. 5 to 7 and Figs. 13 and 14 embodiments of the
invention, a narrow rear slot in the end of the nozzle
may also be provided, in addition to the divergent notches
of the invention.
The notched nozzle of the invention may also
be used with a cylindrical jet nozzle, as indicated in Figs.
18 and l9. Figs. 18 and l9 show a cylindrical jet nozzle 80
having a series of diverging notches 82 of the design
described, spaced around its circular trailing edge. A
cylindrical diffuser 84 is fixed to the jet nozzle, by struts
indicated at 86, to produce thrust augmentation. The iet
nozzle 80 may in some cases contain a bullet-shaped centre
body indicated in dotted lines at 88, in which case the
nozzle will be annular. The body 88 may be the fairing
end of the shaft of a turbine (not shown), or it may
simply be a movable body used to adjust -the size of the
exit area of the jet nozzle 80.
In the Fig. 18 structure the flow indicated
by arrows 89 may be ordinary secondary air or may alter-
natively be another propulsive stream, such as bypass airin the case of a turbofan engine. Fig. 20, where primed
reference numerals indicate parts corresponding to those
of Figs. 18 and l9, shows this latter arrangement.Fig; 20
shows the jet nozzle 80' of a turbofan engine 90
- with a cylindrical shroud 84' encircling the nozzle 80'. In
; the turbofan engine 90 there is a central core 92 of high
~ velocity hot gas and an outer annular sheath 94 of lower
velocity cooler gas. It is found that maximum thrust is
obtained by mixing the two streams 92, 94 to achieve
more uniformity with regard to velocity and temperature.
- 14 -
~3~23~
This function is carried out by the notches 82', without
the need for costly heavy mixing hardware which has been
used in the past.
It will also be appreciated that nozzles
such as those shown in Figs 5 to 7, 13 to 15, 18 and 19
may be used without any diffusers. In that event there will
be no thrust augmentation, but the notches will reduce the
noise produced by the jetstream issuing from the nozzle, while
degrading the nozzle efficiency less than would notches
having a narrower angle of divergence. It is found that
use of notches having a divergence angle of about 100
degrees results in a nozzle efficiency loss of only between
1.5 and 2 percent, as contrasted with the 5 percent or
greater loss experienced with prior slots placed in nozzles.
Reference is next made to Fig. 21, which
shows diagrammatically one side of a notch 96 which
corresponds for example to notch 30 of Fig. 6. In the
Fig. 21 embodiment, the edges 98 of the notch 96 are
slightly outwardly curved or bulged, to help guide the
gaseous elements in an inward direction. The curved
edges 98 reduce the amount by which for example element
(Fig. 10) must be bent and therefore help to improve the
efficiency of the nozzle. The extent of the curvature
~; of edges 98 will be limited so that fabrication of separate
; elements will not be needed and so that there are no large
obstructions projecting into the gas stream to increase
frictional losses. The notch angle will then be at least
60 degrees, as viewed in plan. The edges of any of the
- notches shown in the previous embodiment of the inventor
3C may also be slightly bulged, if desired.
- 15 -
~3523~
The only factor which has been discussed
so far as limiting the spreading of the jet by the notches is
the Coanda effect. However, the extent of the spreading is
controlled not only by the Coanda effect but also by other
factors. Reference is made to Fig. 22, which is similar
to Fig. 10 and shows notch 30 in nozzle 36. The stream of
gas flowing toward notch 30 is indicated by arrow 102.
Vector 104 indicates the direction in which an element of
gas wouid tend to issue f~om notch 30 in the absence of the
Coanda effect and in the absence of gas movement in the
direction of arrow 102. Vector 106 represents the com-
ponent of movement of the gas due to its velocity in the
direction of arrow 102, and vector 108 is the re-
~; sultant of vectors 104 and 106.
~ It will be seen that vector 108 more
closely approaches the direction of arrow 102 as the wedge
angle 110 increases and as the velocity vector 106 increases.
The extent to which the wedge angle 110 can be increased
is obviously limited, but the velocity vector 106 can beincreased by the use of internal fairings, which are shown
in dotted lines at 112 in Figs. 6 and 7 and are also shown
in Fig. 23. The fairings 112 are simply curved light small
strips set into the nozzle 8" between the notches 30. The
fairings 112 guide the gas flow smoothly to the notches
,
-~ 30 and increase the nozzle efficiency by reducing internal
losses. In addition with reference to Fig. 7, it will be
appreciated that the gas velocity is normally the highest
where the gas stream is "squeezed" the most. In the absence
of the fairings 112, the velocity of the gas in the direction
of arro~7 102 is normally higher at point 114 than upstream at point
116. The fairings 112 serve not only to direct the flow but
also to confine it as it approaches the notches 30.
-16-
Therefore the fairings 112 increase the velocity of the
flow at point 116/ thus increasing the size of velocity
vector 106. This causes the initial direction of the
vector 108 representing an emerging gas element near
the apex of notch 30 to be more closely aligned with
the direction 102 of the gas flow into the notch 30. Less
bending over by the Coanda effect of the gas element
represented by vector 108 is therefore required. Since
a sma]ler Coanda effect is needed, the divergence angle
of the notch 3D can be less than that indicated previously.
If the gas flow is squeezed sufficiently, for example by
means of lobed internal fairings 112' as shown in Fig. 24,
then the increase in velocity at point 116 (Fig. 7) can be
very substantial as compared with the velocity in the absence
of any internal fairings. The notch angle x can then be -
substantially reduced and yet the totai height of the
jet plume emerging from the notch 30 will still be limited
to the desired dimension. With appropriate internal fairings
-~ 112 or 112', it is found that a given limited plume height
which previously required a 90 notch angle to achieve
(i.e. a lesser angle would have resulted in an unduly tall
plume) can now be achieved with a notch angle of only
approximately 30.
Reference is next made to Figs. 25 to 29,
which show another embodiment of the invention. In the Figs.
25 to 29 embodim~nt a duct 6"' located in a wing 4"'carries
pressurized gas to notches 120 located at the rear edge of
the wing. The gas is carried to the notches 120 by cylindrical
ducts 122, each of which has a tapered tip 124. The tapered
tip 124 contains the notch 120. As seen from abovQ, the
- 17 -
~3~23~
notch 120 has a straiyht front edge 126 oriented at right
angles to the direction of flow, and sides 128 which di~erge
at a narrow angle x' from each other. In the example shown,
angle x' is approximately 27~. As viewed ~rom the end,-the
sides 128 of the notch 120 are curved or bulged outwardly,
so that the notch 120 has a generally elliptical shape as
viewed from the end, being wider at its centre than at its
top and bottom. The widened centre permits an increased
flow of gas to travel outwardly from along the mid plane of
the notch (as represented diagrammatically by gas element
130) compared with the volume of gas exiting at the top and
bottom of the notch (as represented diagrammatically by gas
element 132). This enhances the Coanda effect, thereby
limiting the height of the gas plume as desired. It is
found that the notch angle of about 27 degrees used in Figs.
; 25 to 29 embodiment is approximately equivalent to a notch
` angle of 90 degrees used in Figs. 5 to 7 embodiment without
fairings, i.e. the 27 degree notch with the ducts shown will
produce approximately the same plume height as a 90 degree
notch without fairings. However, the efficiency of the
Figs. 25 to 29 embodiment is greater than that of the Figs. 5
,
to 7 embodiment since the internal losses are lower, because
the gases are more smoothly guided to the notches in the
Figs. 25 to 29 embodiment. In general, it is found that when
fairing structure is used, such as that constituted by ducts
122 or by fairings 112, 112', then the notch angle can be
about 60 degrees less than the notch angle needed to produce
the same degree of spreading without such fairing structure.
For example, when the fairing structure is used, notches
having a zero notch angle (i.e. U-shaped notches) will provide
- 18 -
~35~3~
approximately the same degree of spreading as notches ha~ins
a 60 notch angle, without fairings. In general a notch
angle of at least 25 is preferred when fairings are used,
but this will depend on the application and as indicated, a
U-shaped notch (zero notch angle) can be used with fairings,
in some applications.
The internal fairings 112, 112' are relatively
simple to fabricate and add little weight, since they can be
small, light strips. If desired, the trailing edges of
the fairings 112 can be removed at point 140 (Fig. 23), and
this will have only a very small effect on efficiency. The
ducts 122 shown in Figs. 25 to 29 effectively constitute
internal fairings but add more weight and are more expensive
to fabricate than the internal-fairings 112. However, use of
the ducts 122 has the advantage that it eliminates the
need to pressurize a flat plate structure, so that the
remainder of the nozzle structure can be made considerably
lighter. In addition the internal efficiency of the~ Figs.
25 to 29 structure is higher since the gas flows are better
guided. At the same time, the flared nozzle structure 20
shown in Fig. 4 has been eliminated, thus eliminating
not only considerable weight and manufacturing expense,
but also the substantial friction losses which occur due
to the drag of the flared nozzle 20 in the high velocity
- gas streams which are present.
The same internal fairing concept may be
applied to the Figs. 18 to 20 embodiments, as shown in Figs.
30 and 31, in which triple primed referenced numerals
indicate parts corresponding to those of Fig. 18. In the
,3 Figs 30, 31 embodiment internal fairings 140 are placed
-- 19 --
1~5Z~3~
between the notches 82"~, extending between the bullet
shaped body 88"' and the nozzle 80"'. The fairings 140
are not required to guide the flow, but by confining the
flow as it passes the notches 82"', the speed of the flow
past the notches is increased and therefore the extent of
spreading of the plumes created by the notches is decreased.
However, since the internal fairings in the Figs. 29, 30
embodiment tend to obstruct the gas flow, they will normally
be use~ only in special applications.
The Figs. 18 and 19 embodiment, without the
; bullet shaped body, may be used as an ejector or an injector
pump, in which case the shroud 84 serves as a mixing duct.
;~ Normally an outwardly flared defuser would be located at
,
the end of the duct 84 for this application. It is found
that with the wide angle notches 82 shown in Figs. 18 and
19, the pumping capacity can be approximately doubled
with the same length mixing duct or alternatively the
length of the mixing duct 84 can be halved.
- 20 -
