GB2231092A

GB2231092A - Jet engine

Info

Publication number: GB2231092A
Application number: GB9002858A
Authority: GB
Inventors: Klaus Heinig; Fritz Kennepohl; Michel Ulf
Original assignee: Deutsche Forschungs und Versuchsanstalt fuer Luft und Raumfahrt eV DFVLR; MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: Deutsches Zentrum fuer Luft und Raumfahrt eV; MTU Aero Engines AG
Priority date: 1989-02-08
Filing date: 1990-02-08
Publication date: 1990-11-07
Also published as: DE3903713A1; DE8915860U1; FR2642793A1; GB9002858D0

Description

l,' 0113:2 1 M&C FOLIO: 230P60266 WANGDOC: 1016k "Jet Engine" The present

invention relates to a jet engine comprising a gas turbine and an afterburner arranged downstream thereof.

Jet engines of this type are used for military aeroplanes, which are intended to achieve the maximum possible performance with low weight and low fuel consumption. The known jet engines have the disadvantage, however, of an extremely loud flight noise, which is not substantially reduced even when the afterburner is switched off. During take-off and landing and also during low-level flying, a high level of noise disturbance is inflicted upon the environment, which is particularly annoying in peacetime.

An object of the present invention is to provide a jet engine of the type described in such a way that the engine noise is significantly reduced when the afterburner is switched off.

The invention provides a jet engine as claimed in Claim 1.

An essential advantage of the present invention is that the structural length, and therefore the weight, of the engine remains substantially unchanged as compared with conventional engines. On account of the relatively substantial length of conventional afterburners it is possible to achieve a good degree of mixing and efficiency and thus a considerable reduction in noise. In this connection, the reduction in noise is achieved by mixing secondary air with the gas-turbine exhaust gases at a relatively high Mach number, the mixing of the two air flows resulting in a reduction of the jet speed at the same time as an increase in the mass flow.

A substantial intensive mixing of the primary air jet (gas turbine) and the secondary air jet is achieved since the primary air jet is split in a primary nozzle into small partial flows, and also since the secondary air is fed to the openings arranged directly behind the primary nozzle; thus the secondary air can mix well with the individual primary air flows.- Depending upon structural circumstances, such as the main the length of the afterburner tube, various embodiments of the primary nozzle are possible. In a further embodiment, the primary nozzle may be inserted into the flow channel and may be withdrawn again, so that during the operation of the afterburner it does not 1 1 i i 3 F represent an impediment to the flow and is not adversely affected by the high temperatures which occur. Alternatively, it is possible for the primary nozzle to be installed securely in the engine, for example as a mixer nozzle on an afterburner injection device. In this connection it is possible for the primary nozzle to be attached to the injection nozzles or on the flame holders arranged downstream thereof or to be integrated therein.

In a further alternative embodiment of the primary nozzle it is made flower-shaped or star-shaped in cross-section, the secondary flow being fed inwards conically directly outside the flower-shaped nozzle wall. In particular, a nozzle of this type can be constructed as a folding nozzle, so that the star-shaped cross-section is adjustable.

With an adequate length of the afterburner tube it is also possible to make the primary nozzle circularly convergent or convergent-divergent, which results in insignificant flow losses. This embodiment, however, requires a longer mixing zone.

In a further alternative embodiment of the invention the primary nozzle is constructed as a multiple nozzle. In this connection, the secondary air openings are 1 4 constructed in such a way that the secondary air can flow around the nozzles, thus ensuring a good mixing.

The secondary air, which is fed in by way of the secondary air openings, can be sucked radially from the outside through appropriate closable openings in the outer wall of the engine or aeroplane and can be fed approximately radially to the inside. Alternatively, it is also possible to provide secondary air ducts from the engine inlet in an axial direction to the secondary air openings.

For adaptation to different operating conditions of the engine, it is advantageous to make the (swung-in) primary nozzle variable in its crosssection.

The quantity of air of the secondary flow preferably amounts to approximately 0.6 to 1.1 times the quantity of the primary flow.

According to a further advantageous embodiment of the invention the injection devices - required for the injection of fuel during the operation of the afterburner - and the flame holders are removable. In this way it is possible to provide an engine suitable for low-level practice flights and having a securely installed primary nozzle which, where necessary, can be 1 converted relatively quickly by dismantling the primary 1 nozzle and fitting the injection devices into an engine suitable for the operation of the afterburner.

In a further advantageous embodiment of the invention the inside of the afterburner housing is lined with sound-absorbing material (perforated screen) which may be used at the same time as a heat shield.

Embodiments of the invention will now be described in greater detail below with reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic longitudinal section through a jet engine, Fig. 2 is a diagrammatic longitudinal section through a further jet engine, Fig. 3 is a diagrammatic cross-section through a primary nozzle of a jet engine according to the invention, Fig. 4 is a diagrammatic cross-section through a further primary nozzle of a jet engine according to the invention, and Fig. 5 is a diagrammat1Lc lateral elevation of the 6 primary nozzle of Fig. 4.

A jet engine la, which essentially comprises a gas turbine 2 and an afterburner 3 arranged downstream thereof, is shown diagrammatically in longitudinal section in Fig. 1. The gas turbine 2 comprises a lowpressure rotor 4 with the blade system of a low-pressure and a mediumpressure compressor 5. A high-pressure rotor 6 with a high-pressure compressor blade system 7 is arranged downstream of the compressor 5. A plurality of turbine stages 9 are provided downstream of an annular combustion chamber 8. An annular afterburner injection device 10 and annular flame holders 11 are arranged downstream of the turbine stages 9. This central part of the engine is surrounded by a bypass duct 12 in such a way that part of the gas flow is diverted downstream of the lowpressure compressor 5 and, while avoiding the central part of the engine,. is remixed with the gas flow downstream of the central part of the engine.

The afterburner injection device 10 and the flame holder 11 belong functionally to the afterburner 3, which further comprises an afterburner tube 13 and an adjustable thrust nozzle 14.

A pivotable primary nozzle 17, which is shown in the NI Z 7 1 51 swung-in position in Fig. 1, is arranged downstream of the gas turbine 2 in the flow duct 16. The primary nozzle (17) essentially comprises individual tapered segment portions which are provided with small nozzles and which can be swung in and out in the afterburner housing 15 by way of links 18. In the swung-in state. this primary nozzle 17 substantially "closes" the entire flow duct 16, so that the primary flow, which flows through the central part of the engine and the bypass duct 12, must flow through the apertures 19 of the primary nozzle 17.

The secondary air flow passes through closable openings 20 in the outer skin 21 of the aeroplane into secondary air ducts 22, and arrives in the flow duct 16, by way of the secondary air openings 23 distributed as far as possible over the entire periphery of the afterburner housing 15. The secondary air there mixes with the primary air flow which has passed through the apertures 19. The mixing occurs along the length of the afterburner tube 13, so that a homogeneous gas flow with a roughly uniform gas velocity is present in the region of the thrust nozzle 14. On account of the admixture of the secondary air it is possible to reduce substantially the gas flow velocity at the outlet of the thrust nozzle 14 and thus the noise emission during the mixing of the jet with the outside air.

8 A further embodiment of a jet engine 1b illustrated in Fig. 2 is constructed essentially as the jet engine la. An essential difference is that the secondary air, which is mixed with the primary flow by way of the secondary air openings 23b, is no longer supplied substantially radially, but is brought up from the region of the engine inlet 24 by way of axially extending secondary air ducts 22b. In this case it is possible to construct a single annular secondary air duct 22b.

In the embodiment illustrated in Fig. 2 the primary nozzle 17b is flowershaped in cross-section, as a result of which a good mixing of the two air flows can be achieved with little flow loss. This flower-shaped design of the primary nozzle 17b is illustrated in cross-section in Fig. 3.

The design of the primary nozzle 17c as a multiple nozzle is.illustrated in Fig. 4. In this case the diameter of the nozzles 25 is selected to be so great that the flow loss is minimized with optimum mixing of the two air flows. This embodiment of the primary nozzle 17c can also, as indicated by broken lines, be divided into individual portions which are secured so as to be pivotable by means of links 18, as illustrated in Fig. 1.

Z -kl 9 1 1 Fig. 5 shows this embodiment of the primary nozzle in longitudinal section.

Figs. 6 and 7 show, as a further embodiment of the primary nozzle, a folding nozzle 17e, which comprises plates 26 connected together by means of hinges 27. In the folded-in state, as illustrated, the nozzle opens out into a star-shaped flow cross-section, and in the folded-out state the plates rest against the inner wall of the afterburner and close the secondary air openings 23.

Claims

Claims:

1. A jet engine comprising a gas turbine and an afterburner housing, wherein a primary nozzle for main flow of the gas turbine is provided downstream of the gas turbine, and secondary air openings are provided in the afterburner housing for feeding ambient air into the afterburner housing, the primary nozzle and the secondary air openings being adjustable relative to one another in order to attain an intensive mixing of air.

2. A jet engine as claimed in Claim 1, wherein an afterburner injection device and a flame holder are removably arranged in the afterburner housing.

3. A jet engine as claimed in Claim 1, wherein the primary nozzle is secured on an afterburner injection device or a flame holder, or is integrated therein.

4. A jet engine as claimed in any one of the preceding claims, wherein the primary nozzle is flower-shaped or star-shaped in cross-section.

5. A jet engine as claimed in any one of the preceding claims, wherein the primary nozzle is variable in its cross-section.

_I -a n 1 i 11 7,

6. A jet engine as claimed in Claim 4 or 5, wherein the primary nozzle comprises foldable elements.

7. A jet engine as claimed in any one of the preceding claims, wherein the secondary air openings are closable.

8. A jet engine according to Claim 1, wherein the primary nozzle has a circular cross section and converges in the direction of air flow.

9. A jet engine as claimed in any one of the preceding claims, wherein the primary nozzle is constructed as a multiple nozzle.

10. A jet engine as claimed in any one of the preceding claims, wherein the primary nozzle comprises tapered segment portions secured to the periphery of the afterburner housing so as to be inwardly pivotable.

11. A jet engine as claimed in any one of the preceding claims, wherein secondary air ducts extend substantially radially from the secondary air openings as far as the outer skin of the engine or aeroplane.

12. A jet engine as claimed in any one of claims 1 to 10, wherein secondary air ducts are guided axially from the secondary air openings as far as the engine inlet.

12

13. A jet engine as claimed in any one of the preceding claims, wherein the afterburner housing is lined on the inside with sound-absorbing material. - A, 1 I i E

14. A jet engine substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.

v Plablithed 1990 as The patent office, State House. 6671 High Holborn. LondonWC1R4TP.Furtlier copies maybe obtainedfrom The Patent Office. Sales Brimch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Kent. Con. 1187