FR2800129A1 - GAS TURBINE ENGINE EXHAUST NOZZLE - Google Patents

Abstract

A gas turbine engine exhaust nozzle (16) comprising a substantially frustoconical nozzle wall (15, 17), and a plurality of circumferentially arranged nozzle flaps (18, 20) which extend in a direction generally downstream to from a downstream periphery of the nozzle wall (15, 17); characterized in that the nozzle flaps (18, 20) are inclined radially inwards at an angle up to 20degree with respect to the wall nozzle (15, 17).

Description

The present invention relates generally to the nozzles

  gas turbine engine exhaust, and in particular improvements in noise reduction to the nozzle arrangements used on

  gas turbine engines used to propel airplanes.

  Gas turbine engines are widely used to propel aircraft. As is well known, the engine basically provides propulsive power by generating a high speed flow of gas which is ejected backwards through an exhaust nozzle. A single high speed gas flow is produced by a turbojet gas turbine engine. However today, more commonly two streams, a central exhaust and a secondary exhaust, are generated by a gas turbine engine with a ducted fan or a secondary gas turbine engine. The high speed gas flow produced by gas turbine engines generates a significant amount of noise, which is known as exhaust noise. This noise is generated due to the high speed of the exhaust stream, or exhaust streams, and the mixing of the streams with the surrounding atmosphere, and in the case of two streams, when the central and secondary streams mix . The degree of noise generated is determined by the speed of the flow and the manner in which the flows

  mix when ejected through the exhaust nozzle.

  Growing environmental concerns require that the noise produced by gas turbine engines, and in particular by aircraft gas turbine engines, be reduced and considerable work has been done to reduce the noise produced by mixing the gas stream (s) at high speed. Many various designs of exhaust nozzles have been used and proposed to control and modify the manner in which high speed exhaust gas flows mix. With ducted fan gas turbine engines, special attention has been paid to the central flow and to the mixture of central and secondary exhaust flows. This is the reason why the speed of the central flow is considerably higher than that of the secondary flow as well as of the surrounding atmosphere and therefore the central exhaust flow generates a significant amount of exhaust noise. The mixing of the central flow with the secondary flow has also been found to generate a significant proportion of exhaust noise due to the difference in speed of the central and secondary flows. A current common design of exhaust nozzles which is widely used is a hump type nozzle which includes a coiled embossed central nozzle (sometimes referred to as a mixer) with circumferentially arranged alternate bumps which direct the central exhaust flow radially outward in the secondary exhaust stream, and the secondary exhaust stream radially inward in the central exhaust stream while generating mixing flows between the two streams. This pushes the flows to

  mixing which improves the mixing of flows and thus reduces the noise generated.

  While providing a degree of noise suppression, this type of nozzle is relatively complex in both manufacturing and design. In addition, when such nozzles are applied to a high-dilution double-flow turbojet, the performance and aerodynamic losses generated by the hump mixer are significant. In addition, such nozzles generally require, for optimum performance, an extended secondary nozzle with the downstream end of the secondary nozzle disposed downstream of the downstream end of the mixer / central hump nozzle. This adds considerable weight, drag, and cost to installation, and today short secondary nozzles are preferred with which the central hump type nozzles are less efficient and are also less damaging to engine performance than when used in a

long hood arrangement.

  An alternative nozzle design that is designed to reduce noise

  exhaust system is proposed and described in document GB 2 289 921.

  In this document, several circumferentially spaced notches, of various configuration, size, spacing and specific shape, are provided in the downstream periphery of a generally circular central exhaust nozzle. Such a nozzle design is considerably simpler to manufacture than conventional humpback designs. This prior art document describes that the notches generate vortices in the exhaust streams. These vortices improve and control the mixture of central and secondary flows which, as claimed, reduces exhaust noise. A model test of nozzles similar to those described in document GB 2 289 921 has shown that a significant reduction in noise and a significant suppression of noise can be obtained. However, the parameters and details of the design proposed in GB 2 289 921 are not optimal and there is a continual desire to improve

  even more the design of the nozzle.

  It is therefore desirable to provide an improved gas turbine engine exhaust nozzle which is quieter than conventional exhaust nozzles and / or which offers

improvements in general.

  According to a first aspect of the present invention, there is provided a gas turbine engine exhaust nozzle comprising a substantially frustoconical nozzle wall, and a plurality of circumferentially arranged nozzle flaps which extend in a direction generally downstream to from a downstream periphery of the nozzle wall, characterized in that the nozzle flaps are inclined radially towards

  the interior at an angle up to 20 relative to the nozzle wall.

  An exhaust nozzle as described above produces improved exhaust noise characteristics. It is believed that the inclination of the flaps, with angles up to 20, generates stronger vortices in the exhaust flow through the nozzle. These stronger vortexes provide improved control and improved mixing of exhaust flow thereby reducing perceived exhaust noise

  generated by the exhaust flow.

  Preferably, the flaps are cut at a point or taper circumferentially in a downstream direction. The flaps may in particular be of a substantially trapezoidal shape. Alternatively, the

  shutters may have a substantially rectangular shape at the square.

  Preferably, the flaps are arranged circumferentially around the periphery of the nozzle to define notches of substantially trapezoidal shape between adjacent flaps. Alternatively, the flaps can be arranged circumferentially around the periphery of the nozzle for

  define substantially V-shaped notches between adjacent flaps.

  o0 The edges of the shutters can be curved.

  Preferably, the nozzle flaps are inclined radially towards

  the interior at an angle of up to 10 from the nozzle wall.

  Preferably, the exhaust nozzle is a hot stream nozzle. The exhaust nozzle can also or alternatively be

  a secondary exhaust nozzle.

  According to a second aspect of the present invention, there is provided a set of exhaust nozzles of a gas turbine engine with a ducted fan comprising a central exhaust nozzle and a nozzle

  secondary exhaust, as described above.

  An exhaust nozzle assembly of a ducted fan gas turbine engine may include an external secondary exhaust nozzle as described above and a central exhaust nozzle

  internal hump mixer type.

  Preferably, the downstream end of the secondary nozzle is located

  further downstream than the downstream periphery of the central exhaust nozzle.

  Alternatively, the downstream end of the secondary nozzle is located upstream of

  the downstream periphery of the central exhaust nozzle.

  The present invention will now be described by way of example only with reference to the accompanying drawings in which: - Figure 1 is a schematic section of a gas turbine engine with ducted fan incorporating an exhaust nozzle according to the present invention - Figure 2 is a more detailed schematic perspective view of the exhaust nozzle of the ducted fan gas turbine engine shown in Figure 1; - Figure 3 is a schematic partially cut away view of a central exhaust nozzle of the gas turbine engine with a ducted fan and of the exhaust nozzle shown in Figures 1 and 2; FIG. 4 represents the effect of the nozzle flaps on a noise associated with a broadband shock with respect to the frequency for model data on a real scale, in a

lossless atmosphere.

  With reference to FIG. 1, a gas turbine engine with a ducted fan 10 comprises, in series of axial flow, an air inlet 5, a propellant fan 2, a hot vein 4 and a set of nozzles exhaust 16 all arranged around a central engine axis 1. The hot stream 4 comprises, in series of axial flow, a series of

  compressors 6, a combustion chamber 8, and a series of turbines 9.

  The direction of air flow through the engine 10 in operation is represented by arrow A and the terms upstream and downstream used throughout

  of this description are used with reference to this direction of flow

  general. The air is sucked through the air inlet 5 and is compressed and accelerated by the blower 2. The air from the blower 2 is divided between a flow of hot vein 4 and a secondary flow. The flow from the hot vein 4 enters the hot vein 4, flows through the hot vein compressors 6 where it is further compressed, and in the combustion chamber 8 where it is mixed with fuel therein brought, and burned inside the combustion chamber 8. The combustion of the fuel with the compressed air by the compressors 6 generates a flow of high energy gas at high speed which leaves the combustion chamber 8 and s flows downstream through the turbines 9. When the high energy gas flow flows through the turbines 9, it rotates the turbine rotors extracting energy from the gas flow which is used to drive the blower 2 and the compressors 6 via motor shafts 11 which are connected in a driving manner to the turbine rotors 9 with the compressors 6 and the blower 2. Having flowed through the turbines 9, the flow of high energy gas from the fuel chamber ion 8 still has a significant amount of energy and speed and it is ejected in the form of a central exhaust stream, through the exhaust nozzle assembly of engine 16 to provide propellant thrust. The rest of the air from, and accelerated by, the blower 2 flows through a secondary duct 7 arranged around the hot vein 4. This flow of secondary air, which was accelerated by the blower 2, flows to the exhaust nozzle assembly 16 where it is ejected, in the form of a secondary exhaust stream to provide further propellant thrust

  useful, and in fact the majority of it.

  The speed of the secondary exhaust flow is significantly lower than that of the central exhaust flow. A turbulent mixture of the two exhaust streams in the region and downstream of the exhaust nozzle assembly 16, as well as the mixture of the two streams with the surrounding ambient air and downstream of the exhaust 16 generates a large component of the noise generated by the engine 10. This noise is known as exhaust noise. Efficient mixing and effective control of the mixing of the two exhaust streams together and with ambient air is necessary to reduce the noise generated. The mixture and its control is

  performed by the exhaust nozzle assembly 16.

  In the embodiment shown, the exhaust nozzle assembly 16 comprises two concentric sections, namely a radially external secondary exhaust nozzle 12 and an internal central exhaust nozzle 14. The central exhaust nozzle 14 is

  defined by a generally frustoconical central nozzle wall 15. This

  ci defines the external extent of an annular central exhaust duct 30 through which the flow of the hot vein is ejected from the hot vein 4. The internal extent of the central exhaust duct 30 is defined by a structure engine plug 22. A plurality of circumferentially spaced flaps 20 extend from the downstream end of the central exhaust nozzle 14 and the central nozzle walls 15. The flaps 20 and the exhaust nozzles 12, 14 are shown more clearly in FIG. 2. As shown, the flaps 20 have a trapezoidal shape with the sides of the flaps 20 which are cut in a point circumferentially towards one another in the downstream direction. The flaps are regularly arranged circumferentially so that a notch 21 or space is defined by and between adjacent flaps 20. The notches 21 are complementary to the shape of the flap 20 and therefore have a trapezoidal shape on the central nozzle 14, with the notches 21 opening

  circumferentially in a downstream direction.

  The nozzle 14 is generally similar to those described and shown in document GB 2 289 921 which is incorporated here for reference. The number of flaps 20, and therefore of the notches 21, defined in the central exhaust nozzle 14 and also in the secondary exhaust nozzle 12 (described below), the width of the notches 21, the inclination of the notches 21 , the width of notches 21, the angular offset between the notches 21, and the angular spacing between the notches 21 are all substantially the same and in the same fields as described in the document GB 2 289 921. It should however be noted that in document GB 2 289 921, only the central nozzle 14 is provided with flaps 20 and notches 21 while, as described below, according to the present invention, the secondary exhaust nozzle 12 can also

  have flaps 20 and notches 21.

  Referring to Figure 3, the flaps 20 of the central exhaust nozzle 14 are inclined radially inward so that the flaps protrude into the central duct 30 (relative to an extended line 24, shown in the Figure 3, the profile of the central nozzle wall 15 immediately upstream of the flaps 20) and are, in operation, incident on the central exhaust flow which is ejected through the central exhaust nozzle 14. The angle incidence P of the flaps 20 is defined with respect to an extended line 24 of the profile of the central exhaust nozzle wall 15 immediately upstream of the flaps 20. The profile of the central nozzle wall 15 immediately upstream of the flaps 20 itself makes an angle oa (typically between 10 and 20) relative to axis 1 of the motor. It has been found that by tilting the flaps 20, and by making an angle of incidence 1, there is an effect on the suppression of noise. When the angle of incidence 1 is increased to 20, the noise reductions are improved. However with angles of incidence 3 beyond 20, there is a further small improvement in noise reduction. In addition, with these higher angles of incidence p, the aerodynamic losses due to the effect that the flaps 20 have on the central exhaust flow increases. Therefore, preferably, the flaps 20 are inclined with

  angles of incidence P3 up to 10.

  The flaps 20 and the inclination of the flaps 20 reduces the low and medium frequency noise generated by the exhaust and the engine 10, typically in the frequency range of 50-500 kHz. However, in some cases they increase the noise generated at higher frequencies. The noise at medium and low frequencies is however the most critical in terms of perceived noise level and the noise at higher frequencies is masked by the noise generated elsewhere in the motor 10. Consequently, overall the flaps produce a reduction in the perceived exhaust noise generated. Another reason why the shutters 20 are preferably inclined with the increased frequency of the high frequency noise sometimes associated with the inclined flaps 20 at greater angles of incidence.

angles of incidence 1 to 10.

  The flaps 20 are believed to induce flow vortices in the exhaust flow through and around the nozzle 14. These vortexes are generated from the sides of the flaps 20 and increase the levels of local turbulence in the shear layer. which develops between the central and secondary exhaust flows downstream of the exhaust nozzle assembly 16. This swirl and this turbulence increase and control the mixing speed between the central exhaust flow, the exhaust flow secondary, and ambient air. This reduces the speeds downstream of the exhaust assembly 16, compared to a conventional nozzle, and also reduces the low and medium frequency noise generated by the exhaust streams. The increased turbulence generated by the flaps 20 in the initial part of the shear layers immediately downstream of the exhaust nozzle assembly 16 causes an increase in the high frequency noise generated. The inclination of the flaps 20 radially inward increases the strength of the vortices produced and thus improves the reduction of the perceived noise. However, the angle of incidence f3 of the flaps 20 should not be too large as this can induce a flow separation which will generate, rather than reduce, noise and adversely affect the

  aerodynamic performance of the nozzle 14.

  The secondary exhaust flow 12 is also defined by a generally frustoconical secondary nozzle wall 17 which is concentric and disposed radially towards the outside of the central exhaust nozzle 14. The secondary nozzle wall 17 defines the external extent of an annular secondary exhaust duct 28 through which

  the secondary flow from the motor is ejected from the motor 10.

  The internal extent of the secondary exhaust duct 28 is defined by an external wall of the hot stream 4. The secondary nozzle is similar to the central exhaust nozzle 14 and a plurality of circumferentially flap spaces 18 extend from the downstream end of the nozzle

  secondary exhaust 12 and secondary nozzle walls 17.

  As with the central nozzle 14, the flaps 18 have a trapezoidal shape with the sides of the flaps 18 which taper circumferentially in the downstream direction. The flaps 18 are regularly circumferentially arranged so that a V-shaped notch 19 or a V-shaped space is defined by and between adjacent flaps 18. The secondary nozzle flaps 18 affect the secondary exhaust flow and noise generated in a similar way to the flaps of the nozzle

central exhaust 20.

  An increase in the number of vortices generated by such exhaust nozzle designs, by providing more flaps 18, 20 around the circumference of the nozzle 12, 14, further reduces the exhaust noise generated. However, experiments have shown that a minimum spacing of the vortices, and therefore a circumferential spacing and width of the flaps 18, 20, must be maintained in order to reduce the interaction and the coalescence of the vortices. The coalescence and interaction of the vortices reduces the noise suppression provided by such designs of exhaust nozzles 12, 14. In particular, it has been found that the separation between the vortices produced by the same flap 18, 20 (and this fact the circumferential width of the flap 18, 20) must be greater than the separation (and therefore the circumferential width of notch 19, 21) between vortices produced by adjacent flaps 18, 20. This is due to the direction of rotation of the vortices produced, with the vortices generated by the same flap 18, 20 rotating in such a way that they are more able to interact and to

melt together.

  This is due to the fact that the trapezoidal flaps 18, 20 are preferred. It will be appreciated however that square or rectangular shutters could

  also be used. The edges of the flaps 18, 20 and the flaps 18, 20 themselves

  same could also be curved. Triangular flaps are not desirable, however, since the vortices produced by each side of such a flap will tend to be coincident, thereby producing less vortex of reduced force around the circumference and thus less noise reduction. The length of such a flap is also longer than necessary, thus unnecessarily adding weight to the exhaust nozzle 12, 14, and adding additional aerodynamic drag and loss of performance without significant improvement in noise. In addition, the stress produced by a shutter thus formed will tend to increase the

  probability of mechanical failure of such a triangular flap in operation.

  With the arrangement of the flaps 18 shown on the secondary exhaust nozzle 12, with V-shaped notches 19 between the flaps 18, a large number of flaps 18 and therefore a larger number! Significant vortexing can be generated while still maintaining the necessary separation of the vortexes. A similar arrangement could be used on the central exhaust nozzle 14, however, due to the smaller diameter of the central exhaust nozzle 14, a trapezoidal notch 21 is preferred to provide the necessary separation between the adjacent flaps 20 Furthermore, on smaller diameter nozzles, such as the central exhaust nozzle 14, it has been found that the use of V-shaped notches can restrict the flow between the flaps which reduces the resistance and the generation of individual vortices produced and thereby noise suppression. This may outweigh the benefits of generating more vortexes by producing more flaps. In addition, V-shaped notches result in a concentration of stresses at their apices which under severe stress conditions can lead to problems of

  constraints and failure of the nozzle.

  The effect of V-shaped notches on aerodynamic performance is, however, better than trapezoidal notches, V-shaped notches being aerodynamically more efficient. Since the secondary exhaust provides the majority of the engine thrust, a loss of aerodynamic performance of the secondary exhaust nozzle 12 has a greater effect on the overall performance of the engine.

  than the aerodynamic performance of the central exhaust nozzle 14.

  Therefore, it is preferable to use V-shaped notches on the secondary exhaust nozzle 12 and to accept some of the above-described problems that they can produce. On the central exhaust nozzle 14 however, since the aerodynamic performance losses are less significant, notches of trapezoidal shape are preferred

  to eliminate the problems mentioned above.

  It is believed that the inclination of the flaps 18, 20 is more beneficial on the central exhaust nozzle 14. This is due to the fact that the relative pressure difference between the central and the secondary is greater than that between the secondary and the ambient ambient air with the result that the secondary exhaust flow restricts and constrains the central exhaust flow more than the ambient atmosphere constricts and constrains the secondary exhaust flow. Therefore, in order to improve and control the mixing of the central exhaust stream and provide noise suppression, stronger vortexes, generated by inclined flaps 18, 20, must be generated at the central exhaust to overcome the effect of the secondary exhaust flow radially outside

of the central exhaust flow.

  The flaps 20 should have a length L sufficient to generate the required flow vortices as described below, and the document GB 2 289 921 specifies that the flaps 18, 20 must have a length L between% and 50% at l end of the nozzle diameter Dc, Db. However, it has been found that the use of long flaps, situated at around 50% at the end of the given range, induces excessive aerodynamic losses which adversely affect performance, particularly when they are inclined. Consequently, it has been determined that the central flaps 20 should have a length L of approximately 10% of the diameter of the central exhaust nozzle Dc, while the secondary flaps 18 should have a length L of approximately 5% of the diameter secondary exhaust nozzle Db. The secondary flaps 18 have a shorter percentage length since the secondary produces more of the propulsive thrust of the engine and therefore any loss of performance of the secondary will have a greater effect on the overall performance of the engine. In addition, although the percentage size is lower, since the secondary has a larger diameter than the central, the actual physical size of the central flaps 20 and secondary flaps 18

is not that different.

  During tests on exhaust nozzle assembly models 16 shown in Figure 2 and described above, a reduction of 5dB in the peak sound pressure level compared to

  an arrangement of conventional smooth frustoconical nozzles has been obtained.

  It has also been found that the noise reductions provided by using flaps 18 on the secondary exhaust nozzle 12 and by using flaps 20 on the central exhaust nozzle 14 are cumulative. It will therefore be appreciated that in other embodiments, flaps 18, 20 can be used on the secondary exhaust nozzle 12 or on the central exhaust nozzle 14 alone to give some improved degree of noise suppression . The flaps 20 of the central exhaust nozzle and the flaps 18 of the secondary exhaust nozzle can also be inclined with different angles of incidence 13.

  FIG. 4 shows the effect of the nozzle flaps 18, 20 on the noise associated with a broadband shock for model data on a real scale, in a lossless atmosphere. FIG. 4 is associated with test results deduced from an arrangement of flaps 18, 20 such

as shown in Figure 2.

  When the compression ratio of a set of converging nozzles 16 becomes supercritical, the exhaust flow downstream of the nozzle 12, 14 becomes more extensive and shocks are formed in the exhaust flow. The presence of shocks results in an additional noise source known as noise associated with broadband shocks. This source of noise associated with shocks originates in jet aircraft both single and coaxial and can be heard in the passenger cabin of the aircraft (not shown) under cruising conditions. Such high noise levels can also occur at the top of the ascent phase of an aircraft route, but are more annoying for passengers in cruising conditions due to the weather.

passed in cruising condition.

  As the noise propagates from the engine 10 to the cabin, there will be little attenuation by the atmosphere. However, in order to reduce cabin noise to comfortable or acceptable levels, aircraft airframe manufacturers must take steps to reduce noise as it travels through the aircraft fuselage. Since noise can reach the cabin via several transmission paths, such treatment inevitably results in significant increases in the

cost and weight of the aircraft.

  An application of the nozzle flaps 18, 20 as described here, and in particular those applied to the secondary nozzle 12, results in an increase in the frequency of peak impact noise. These higher frequencies are more easily attenuated by acoustic treatment, and increasing the frequency therefore helps to reduce noise levels in the cabin. In addition, it can reduce the cost and weight of the acoustic treatment of the fuselage for the same cabin noise level because

it doesn't have to be extreme.

  FIG. 4 shows experimental results obtained during a large-scale test of an exhaust 16 of an engine with a high dilution rate at compression rates of typical cruising nozzles. Figure 4 shows the effect of the nozzle flaps 18,20 on the noise associated with a broadband shock with respect to frequency for full-scale model data, in a lossless atmosphere. Line 32 refers to an exhaust without flaps and line 34 refers to an exhaust 16 having flaps 18, 20 as shown in Figure 2. It can be seen that there is a frequency shift and a reduction general noise up to a certain frequency. Shifting peak noise from one frequency to a higher frequency is beneficial since higher frequency noise is more easily attenuated and less annoying for passengers

in the cabin.

  Furthermore, in other embodiments of the invention, a secondary exhaust nozzle using flaps as described above can be used in conjunction with a conventional forced hump type central exhaust mixer / nozzle . Such an arrangement has also been tested and has shown improved noise suppression compared to an exhaust assembly which uses a central bump type mixer / nozzle with a conventional secondary exhaust nozzle. Although the invention has been described and shown with reference to an arrangement of engines of the short hood type in which the secondary duct 28 and the secondary exhaust nozzle 12 terminate upstream of the central exhaust duct 30 and the nozzle 14, the invention can also be applied, in other embodiments, to engine arrangements of the long hood type in which the secondary duct 28 and the secondary exhaust nozzle 12 terminate downstream of the duct d central exhaust 30 and the nozzle 14. The invention is however particularly beneficial for arrangements with a short hood since with such arrangements conventional noise suppression treatments of the exhaust are not practical, in particular where

  high dilution rates are also used.

  The invention is also not limited to ducted fan gas turbine engines 10 with which in this embodiment it has been described and to which the invention is particularly suitable. In other embodiments, it can be applied to other arrangements of gas turbine engines in which two exhaust streams, one exhaust stream or any number of exhaust streams, are

  ejected from the engine through one or more exhaust nozzles.

Claims (14)

Claims   1.- exhaust nozzle (16) of a gas turbine engine comprising a substantially frustoconical nozzle wall (15, 17), and a plurality of circumferentially arranged nozzle flaps (18, 20) which extend in one direction generally downstream from a downstream periphery of the nozzle wall (15, 17); characterized in that the nozzle flaps (18, 20) are inclined radially inwards at an angle of up to 20 relative to the nozzle wall (15, 17).   2.- exhaust nozzle (16) of a gas turbine engine according to claim 1, characterized in that the flaps (18, 20) taper   circumferentially in a downstream direction.   3.- exhaust nozzle (16) of a gas turbine engine according to claim 1 or 2, characterized in that the flaps (18, 20) have a substantially trapezoidal shape.   4.- exhaust nozzle (16) of a gas turbine engine according to claim 1, characterized in that the flaps (18, 20) have a shape   substantially rectangular or square.   5.- Exhaust nozzle (16) of gas turbine engine according to   any one of claims 1 to 3, characterized in that the   flaps (18, 20) are arranged circumferentially around the periphery of the nozzle (16) to define notches of shape   substantially trapezoidal (19, 21) between adjacent flaps (18, 20).   6.- Exhaust nozzle (16) of gas turbine engine according to   any one of claims 1 to 3, characterized in that the   flaps (18, 20) are arranged circumferentially around the periphery of the nozzle (16) to define notches substantially in   V shape (19, 21) between adjacent flaps (18, 20).   7.- Exhaust nozzle (16) of gas turbine engine according to   any one of the preceding claims, characterized in   that the edges of the flaps (18, 20) are curved.   8.- Exhaust nozzle (16) of gas turbine engine according to   any one of the preceding claims, characterized in   that the nozzle flaps (18, 20) are inclined radially inwards at an angle of up to 100 relative to the wall of nozzle (15, 17).   9. Exhaust nozzle (16) of gas turbine engine according to   any one of the preceding claims, characterized in   that the exhaust nozzle (16) is a hot stream nozzle (14).   10.- Exhaust nozzle (16) of gas turbine engine according to   any one of the preceding claims, characterized in   that the exhaust nozzle (16) is an exhaust nozzle secondary (12).   11.- Exhaust nozzle assembly (16) of turbine engine   gas blower according to any one of claims   1 to 10, characterized in that the exhaust nozzle (16) comprises a central exhaust nozzle (14) and an exhaust nozzle secondary (12).   12.- Exhaust nozzle assembly (16) of a gas turbine engine with a ducted fan characterized in that the exhaust nozzle assembly (16) comprises a secondary exhaust nozzle   external (12) according to any one of claims I to 8 and a   internal central exhaust nozzle (14) of the hump mixer type.   13.- exhaust nozzle assembly (16) of a gas turbine engine with a ducted fan according to claim 12, characterized in that the downstream end of the secondary nozzle (12) is located further downstream than the downstream periphery of the exhaust nozzle central (14).   14.- exhaust nozzle assembly (16) of a gas turbine engine with a ducted fan according to claim 10, characterized in that the downstream end of the secondary nozzle (12) is located upstream   from the downstream periphery of the central exhaust nozzle (14).