GB2099082A - Contrarotating turbojet - Google Patents

Abstract

The turbojet comprises a single stage turbine 12 driving a single stage axial compressor 11, wherein the compressor and turbine stages are each constituted by a pair of contrarotating wheels or moving grids 13 & 22, 37 & 35, neither of said stages being provided with a fixed grid. <IMAGE>

Description

SPECIFICATION Simplified contra rotating turbojet The invention relates to a simplified contra rotating turbojet.

It relates more particularly to a single or dual flow contrarotating turbojet which comprises a single stage turbine driving a single stage axial flow compressor.

BACKGROUND OF THE INVENTION Turbojets have been used for some forty years, mainly to propel aircraft. They constitute engines that are relatively complex in structure and high in cost, which has limited their use to aircraft or the like for which extremely high overall construction costs are acceptable.

Both the compressors and the turbines of such turbojets have multiple stages, each of which is constituted by a moving wheel of blades and a fixed grid of nozzles. A pluraliy of stages is used, not only in order to obtain the desired final power, but also because increasing the number of stages inproves efficiency.

To limit the number of stages necessary in multiple stage turbojets, proposals have been made to replace the fixed grids of nozzles by additional moving wheels of blades which rotate in the opposite direction to the original moving wheels of the respective stages. This technique produces a notable increase in the compression ratio per stage (to about three times) thus enabling the number of wheels to be reduced, for given power and efficiency in a turbojet. This leads to improvements in mass and in cost.

In the turbines and the compressors of turbojets of this type, -the successive wheels rotating in opposite directions are alternately mounted on a conventional inner rotor and on an outer rotor which is concentric with the internal rotor, said rotors and their wheels being interleaved.

In such embodiments, the blades of the outer rotor have to perform not only their aerodynamic function, but also a structural function which ieads, in practice, to a compromise being adopted which takes into account the mechanical characteristics of the alloys being used while diminishing the aerodynamic performance of the blades.

In particular, one prior proposal (U.S. Patent number 2 608 821) describes a turbojet which, in order to reduce the peripheral velocity of the ends of the blades, comprises two contrarotating compressor wheels, the first of which cooperates with fixed inlet blades to constitute a first stage and the second of which cooperates with fixed outlet blades to constitute a second compressor stage, and with a similar arrangement being provided for the turbine, with the compressor wheels being connected to respective turbine wheels by concentric shafts.

A turbojet has also been proposed (U.S. Patent number 2 575 682) where both the compressor and the turbine are single stage machines. The term "stage" must be understood, as is now common practice, to mean a set of successive members each of which deflects or re-establishes the axial speed of the gas flow, with the last element returns the direction of the flow to the upstream conditions.

However, both the turbine and the compressor of said turbojet include a fixed grid in addition to two contrarotating wheels.

SUMMARY OF THE INVENTION In a first aspect, the present invention provides a simplified contrarotating turbojet comprising a single stage turbine driving a single stage axial compressor, wherein the single turbine stage and the single compressor stage are each constituted by a pair of contrarotating wheels or moving grids, neither of said stages being provided with a fixed grid.

An extremely simple turbojet is thus obtained, which nonetheless multiplies the inlet pressure by a factor of about three, which is exceptionally light, and with high enough efficiency to find immediate and advantageous applications.

Up to the present, known missiles have generally been rocket propelled, sometimes with a ramjet taking over from the rocket once the missile has reached a high enough speed.

Proposals have been made for turbojet propelled missiles. but with turbojets known up to the present, their use has been limited to subsonic missiles, since until recently, small motors could not operate at temperatures higher than 1 0000C, and thus thrust at supersonic speeds has been limited.

In a second aspect, the invention provides an air-to-ground missile, ie. a missile for launching from an aircraft or the like against a target on the ground, wherein the missile includes a simplified turbojet in accordance with the invention as a propulsion unit.

Because of the high compression ratio (about three) which can be obtained from each stage of the contrarotating type, it is possible to produce a turbojet of sufficiently high efficiency to propel a missile which, once launched from an aircraft, is capable of executing its mission perfectly satisfactorily at supersonic speeds, without using rockets, and under conditions of cheapness and lightness unobtainable when using other kinds of turbojet.

A simplified turbojet in accordance with the invention may be single flow or dual flow. The dual flow arrangement is particularly well adapted to equipping aircraft of considerably smaller size than those which are currently turbojet powered, thus providing an additional range of machines for light aviation.

BRIEF DESCRIPTION OF THE DRAWINGS In the following description, given by way of example, reference is made to the accompanying drawings, in which: Figure 1 is a diagrammatic half axial section through a first embodiment of a turbojet in accordance with the invention; and Figure 2 is a diagrammatic half axial section through a second embodiment of a turbojet in accordance with the invention.

MORE DETAILED DESCRIPTION Reference is made initially to Figure 1.

A turbojet comprises a single stage axial compressor 11 and a single stage turbine 12. The unstream wheel 13 of the compressor stage comprises blades 1 4 with bases 1 5 mounted on a central disk 16 depending from an inner shaft 17 whose upstream end 18 is mounted on a fixed portion 21 of the turbojet by means of a bearing 1 9.

The second wheel 22 of the compressor stage comprises blades 23 with bases 24 mounted on a central disk 25 depending from an outer shaft 26 which is disposed co-axially around the inner shaft 1 7 and which is connected thereto at its upstream end by a bearing 27. The outer shaft 26 is outside the inner shaft 17, but is centrally located in the turbojet, in particular it is inside the annulus of blades 23.

The downstream end 28 of the inner shaft 1 7 is supported on a fixed portion 31 of the turbojet by means of a bearing 29. A disk 32 depends from the shaft 1 7 adjacent to its downstream end 28, and mounted thereon are the bases 33 of blades 34 of the downstream wheel 35 of the single turbine stage. The other wheel 37 of the said single turbine stage has blades 36 with bases 38 mounted on a disk 39 depending from the outer shaft 26 whose downstream end 41 rests on the downstream end 28 of the inner shaft 17 by means of a bearing 42.

Air entering the compressor 11 is compressed by the combined action of the wheels 13 and 22 rotating in opposite directions in the single stage of the compressor 11, giving a compression ratio of about 2.8 to 3. The compressed air then enters a combustion chamber 43 which is delimited by annular walls 44 and 45, where the air is heated by combustion and in expanding drives the wheels 37 and 35 of the single stage of the turbine 12 in opposite directions to each other before reaching the exhaust nozzle via an annular channel 46.

In one particular embodiment, the wheels 1 3, 22, 37, and 35 have the following characteristics: Wheel 13: outside velocity 450 m/s inside velocity 300 m/s Wheel 22: outside velocity 350 m/s inside velocity 250 m/s Wheel 37: ouside velocity 350 m/s inside velocity 280 m/s Wheel 35: ouside velocity 450 m/s inside velocity 300 m/s The temperatures and pressures of the gas flow are as follows:

Wheel reference 13 22 37 ~~ 35 Temperature (OK) 488 400 1500 1400 Pressure (bars) 1.013 3 2.8 1.7 Such a turbojet is lightweight, and cheap, both in cost price and in fuel consumption.

It is particularly well adapted to propelling an air-to-ground missile for launching from an aircraft flying at a speed near to Mach 0.8. Propelled by the turbojet, the missile rapidly accelerates to supersonic speed.

Reference is now made to Figure 2. This figure shows a dual embodiment of the turbojet which is similar in many ways to the single flow embodiment described with reference to Figure 1. Components of the dual flow embodiment which correspond to equivalent components the single flow embodiment are given the same reference numerals plus 100.

In the dual flow embodiment a first portion of the airflow from the outlet from the compressor wheel 122 is directed by a first annular channel 151 to the combustion chamber 1 52 whence it escapes to drive the single stage of the turbine 112, passing first through the wheel 1 37 and then through the wheel 135, said wheels rotating in opposite directions, and the flow of gas then being directed to the exhaust nozzle by an annular channel 146.

At the same time, a second portion of the air flow that has passed through the compressor 111 is directed directly to a secondary exhaust nozzle by a second annular channel or jacket 1 53 which surrounds the combustion chamber 1 52 but in which no combustion takes place.

The dual flow turbojet thus constituted is particularly well adapted to propelling light aircraft.

Claims (7)

1 . A simplified contrarotating turbojet comprising a single stage turbine driving a single stage axial compressor, wherein the single turbine stage and the single compressor stage are each constituted by a pair of contrarotating wheels or moving grids, neither of said stages being provided with a fixed grid.

2. A turbojet according to claim 1, wherein the single compressor stage provides a compression ratio that is near to three.

3. A turbojet according to claim 1 or 2, wherein it is of the single flow type.

4. A turbojet according to claim 1 or 2, wherein it is of the dual flow type.

5. An air-to-ground missile, propelled by a turbojet according to claim 3.

6. An aircraft, propelled by a turbojet according to claim 4.

7. A simplified contrarotating turbojet substantially as described with reference to or as claimed by Fig. 1 or Fig. 2 of the drawings.