Leaky-type exhaust nozzle for jet propulsion devices

May 30, 1961 _{A FERRI} 2,986,002

LEAKY-TYPE EXHAUST NOZZLE FOR JET PROPULSION DEVICES

Sheets-Sheet 1

Filed June 5, 1957

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ABENT

May 30, 1961 _{A FERRI} 2,986,002

LEAKY-TYPE EXHAUST NOZZLE FOR JET PROPULSION DEVICES

Sheets-Sheet 2

Filed June 5, 1957

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INVENTOR

ANTONIO FERRI

BY

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AGENT

United States Patent Office _p , _M²-^{986 002}

Patented May 30, 1961

2,986,002

LEAKY-TYPE EXHAUST NOZZLE FOR JET PROPULSION DEVICES

Antonio. Ferri, Rockville Centre, N.Y., assignor to CurtissWright Corporation, a corporation of Delaware

Filed June 5,1957, Ser. No. 663,672

Claims. (Cl. 60—35.6)

My invention relates to an exhaust nozzle for jet propulsion devices. More particularly, the invention is directed to a leaky-type nozzle having particular application to aircraft jet engines.

Variable geometry exhaust nozzles for jet engines are well known. The construction of a convergent nozzle may be such as to provide for variations in the exit area of the nozzle, and a convergent-divergent nozzle may be constructed so that both its throat and exit areas may be varied. The type of structure provided for this purpose is generally complex and in a convergent-divergent nozzle the complexity and weight of the structure may be intolerable. A practical convergent-divergent type of nozzle construction for a jet engine consists of a convergent nozzle disposed within an engine casing, which extends for some distance beyond the end of the nozzle. The converging walls of the nozzle are movable so that the throat area may be varied, and expansion of gases beyond the nozzle throat is controlled by a secondary jet flowing over the nozzle thereby eliminating the necessity of providing an adjustable divergent section. This nozzle construction does have some disadvantages, however, in that a very long shroud is required for properly controlling expansion with the secondary jet. In addition, the performance of this type of nozzle construction is not entirely satisfactory since losses resulting with such a construction are quite large. Furthermore, the converging wall of the nozzle is generally formed of overlapping sections so that the sections may be moved relative to one another to vary the throat. It is very difficult to cool such overlapping portions and any leakage of hot air between the sections may damage the nozzle.

It is an object of the invention to provide a nozzle construction of the described type having features resulting in a decrease in the length of the shroud required to obtain a given expansion of nozzle exhaust gases.

It is another object of the invention to provide such a nozzle construction by means of which the angularity of flow at the exit of the converging nozzle may be reduced to result in improved nozzle performance.

It is still another object of the invention to provide such a nozzle construction which may be assembled from a small number of parts and which is light in weight.

Other objects and advantages of the invention will become apparent during a reading of the specification.

To obtain the objects and advantages of the invention, I provide a converging nozzle within a jet engine casing extending some distance beyond the exhaust end of the nozzle. In accordance with the invention, such nozzle is comprised of a number of segments which converge to the nozzle throat, and each such segment is separated by a gap through which gases in the nozzle may escape. Gases expand beyond the throat of the nozzle and the expansion of these gases along with gases escaping through the gaps between the segments are controlled by a secondary jet flowing over the segments. By permitting a portion of the gases flowing in the nozzle to escape through the gaps, it is possible to decrease the angularity of flow of the exhaust gases at the throat of the nozzle, and.to decrease the length of the shroud required for obtaining a given expansion. Preferably, the segments of the nozzle are movable radially for controlling the size of the throat and areas of the gaps between the segments.

Referring to the drawings:

Fig. 1 is a longitudinal sectional view showing the nozzle construction of the invention.

Fig. 2 is an end view of the showing in Fig. 1.

Fig. 3 is a perspective view of the nozzle clearly show19 ing the nozzle segments.

Fig. 4 is a longitudinal sectional view of the nozzle construction showing apparatus for controlling the position of nozzle segments.

As shown in the drawings, the nozzle construction in15 eludes a converging nozzle 1 for receiving the exhaust gases of a jet engine, and a shroud 2 which encases the nozzle 1 and extends some distance beyond the exit end 3 of the nozzle. The shroud 2 is a continuation of a wall 4 which may be part of the engine housing and which 20 forms a passage 5 with a cylindrical section 6 connecting with the nozzle 1.

The nozzle 1 consists of a plurality of segments 7 which converge to define a throat 8 at the exhaust end of the nozzle. Such segments are separated one from the other 25 by gaps 9. These gaps preferably extend throughout the converging length of the nozzle and gradually taper from the nozzle end 3 where they are of maximum width to the cylindrical section 6 where the gaps close. As shown, the gaps extend between adjacent longitudinal edge porS0 tions Sa and Sb of the segments which edge portions extend outwardly with respect to the nozzle axis and bend away from each other.

In the operation of the nozzle, engine exhaust gases expand in the nozzle 1. A portion of such gases escape 35 through the gaps 9 and the remainder of the gases flow out of the exit end 3 of the nozzle. The gases escaping through the gaps 9 and flowing out of the exit end 3 of the nozzle further expand in a region encased by the shroud 2. The expansion of such gases is controlled by a sec40 ondary jet 10 flowing through the passage 5 and between the nozzle 1 and shroud 2 which jet may (for example) be drawn through openings 11 in the engine casing controlled by flaps 11' disposed circumferentially about said casing. By suitably controlling the flaps 11' through ⁴⁵ linkages 12 and 13, and other suitable actuating mechanism, the jet 10 may be controlled to regulate the expansion of exhaust gases from the nozzle 1 so as to provide a jet of exhaust gases at the end 14 of the shroud 2 haying a velocity everywhere in the direction of the thrust ⁵⁰ axis, and a static pressure at 14 equal to atmospheric pressure, such regulation providing for a maximum thrust. Instead of drawing air from the atmosphere to provide the jet 10, combustion gases may be used for the purpose of providing such a jet. In a gas turbine engine com55 pressed air from the compressor may be used for this purpose.

With the conventional type of nozzle construction of the type described wherein the converging nozzle has a continuous wall, expansion within the nozzle and beyond 60 the exit end of the nozzle is of the axially symmetric type. All expansion waves are produced in a plan and reflected at the axis. As a consequence, it is necessary with this type of construction to provide a rather long shroud to obtain maximum thrust. As has been indicated 65 hereinbefore, in the nozzle construction of the invention a portion of the exhaust gases escape through gaps in the converging nozzle to expand in the region within the shroud 2. Jets of gas escaping through the various gaps interfere with the jet stream 10 which tends to cause the 70 escaping gas streams to become parallel. The expansion of the gas flowing out of the gaps 9 is more nearly of the two-dimensional type than of the axially-symmetric

2,986,002 type and is more rapid than axially-symmetric expansion. Accordingly, with the nozzle construction of the invention, a given expansion may be obtained in a shorter length than, with the aforesaid conventional construction, and the required length of the shroud for maximum effectiveness may be considerably reduced. Even with a shroud of reduced length, the nozzle construction of the invention will provide a jet at the exit end of the shroud which flows more nearly parallel to the axis of the nozzle than the jet obtained with the convention type nozzle, and losses are reduced as a result.

In the nozzle construction of the invention, the throat 8 may be readily varied in size by providing suitable apparatus for moving the nozzle segments 7 radially, inwardly and outwardly. Such apparatus as may be used for moving the segments 7 in a radial direction is shown in Fig. 4 wherein reference character 15 denotes a hydraulically operated piston movable in a cylinder 16 in response to control signals from a remote location. Each of the segments 7 connects with the shroud 2 by linkages 17 and 18, connects with a ring 19 through the said linkages and rod 2® such that when the piston 16 moves in one direction or the other the segments 7 will be moved radially, inwardly or outwardly.

If desired, the segments 7 may be connected to cylindrical section 6 by hinges to facilitate their radial movement; however, such movement may be accomplished without such provision being made since by reason of the described construction of the converging nozzle the segments will nevertheless move substantially about the end of the cylindrical section.

In effect, the combination of the converging portion of the nozzle with the rearwardly extending portion of the shroud forms a convergent-divergent nozzle, but with the divergence taking place in the shroud, without such a defining diverging wall as would be found in the prior art. As is well known, some portions of a fluid escaping under pressure from a simple convergent nozzle may have components of motion in a backward direction; a familiar illustration of this is the fact that it is possible to get wet by spray from an ordinary hose nozzle, while standing behind the nozzle. At the very least, with the conventional converging nozzle there will be turbulence of the fluid immediately adjacent the nozzle, rather than smooth expansion, and expansion waves produced in a plane and reflected at the axis.

As a consequence, use in the prior art of a converging nozzle having a continuous wall, within a shroud, requires a very long shroud for the flow to smooth out and reach a static pressure equal to atmospheric pressure with a velocity everywhere in the direction of the thrust axis. If a converging-diverging nozzle with continuous walls is used, it is necessary to provide adjustment of the divergent portion consonant with variability in the throat, in order to have an efficient nozzle.

The present invention, on the other hand, obviates the necessity for either a long shroud or an adjustable divergent section. This is achieved by allowing gas expansion from a convergent nozzle within a short shroud and suppressing turbulence and damping expansion waves by controlling the expansion by the two means cited, namely, leakage of exhaust gas in an axial direction through apertures in the convergent nozzle upstream from the throat, and by shaping the expanding flow with a secondary, generally annular jet.

It will now be clear that I have provide a nozzle construction having obvious advantages over prior art construction, including the advantages of reducing the length of the shroud required for a nozzle construction of the described type and improving the performance of such nozzle construction by reducing the losses therein. Also, the weight of the nozzle construction is reduced by reason of the shortening of the shroud, and complexity in the structure is avoided. With the gap structure of the invention, there are no overlapping segments which are difficult to keep cool and no complex system of linkages is required for varying the throat and exit areas.

While I have described my invention in detail, it will 5 be appreciated that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit of the invention.