GAS TURBINE ENGINE

Abstract

An aircraft gas turbine engine includes a fan arranged to be driven by a gas turbine engine core. The core includes a first core module including a first compressor and a fan drive turbine interconnected by a first shaft, and a second core module including a second compressor and a second turbine interconnected by a second shaft, the first and second core modules being axially spaced. The gas turbine engine further includes an intercooler arrangement configured to cool core airflow between the first and second compressors, the intercooler arrangement including a cooling air duct provided in heat exchange relationship with a compressor duct provided between the first and second compressors, the cooling air duct including a fan air inlet configured to ingest fan air downstream of the fan, wherein the cooling air duct includes a flow modulation valve configured to modulate air mass flow through the fan air inlet.

Claims

1. An aircraft gas turbine engine comprising: a fan arranged to be driven by a gas turbine engine core, the core comprising a first core module comprising a first compressor and a first turbine interconnected by a first shaft, and a second core module comprising a second compressor and a fan drive turbine interconnected by a second shaft, the first and second core modules being axially spaced; an intercooler arrangement configured to cool core airflow between the first and second compressors, the intercooler arrangement comprising a cooling air duct provided in heat exchange relationship with a compressor duct provided between the first and second compressors, the cooling air duct comprising a fan air inlet configured to ingest fan air, downstream of the fan, wherein the cooling air duct comprises a flow modulation valve configured to modulate air mass flow through the fan air inlet.

2. A gas turbine engine according to claim 1, wherein the core comprises a compressor provided axially rearwardly of the fan drive turbine.

3. A gas turbine engine according to claim 1, wherein the fan drive coupling comprises a gearbox arranged such that the fan drive turbine rotates at a higher rotational speed than the fan in use.

4. A gas turbine engine according to claim 3, wherein the gearbox has an input:output ratio of between 1 and 5.

5. A gas turbine engine according to claim 1 wherein the second core compressor comprises a low pressure compressor coupled to the fan drive turbine by a low pressure shaft.

6. A gas turbine engine according to claim 1, wherein the gas turbine engine comprises an exhaust duct configured to redirect forward flowing exhaust air from the fan drive turbine to a rearward direction.

7. An aircraft comprising a gas turbine engine in accordance with claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 shows a prior gas turbine engine;

[0019] FIG. 2 shows a schematic cross sectional side view of a first gas turbine engine in accordance with the present disclosure; and

[0020] FIG. 3a and FIG. 3b show a close-up of the part of the component of FIG. 2 shown in box D;

DETAILED DESCRIPTION

[0021] FIGS. 2 and 3 show a first gas turbine engine 110 in accordance with the present invention. The engine 110 comprises a ducted fan 113 provided within a fan nacelle 121 which defines a bypass passage 148. The fan 113 provides a propulsive air flow B which flows parallel to an axial direction X. A forward direction is defined by an axial direction anti-parallel to this direction.

[0022] The engine 110 further comprises an engine core 175. The core 175 comprises a first core module 190 comprising a first compressor in the form of a low pressure compressor 114 configured to draw core flow air A into the core 175 from an inlet 149 positioned downstream of the fan 113. The first core module 190 further comprises a first turbine in the form of a low pressure fan drive turbine 119 interconnected by a first shaft in the form of a low pressure shaft 177. The core 175 further comprises a second core module 191 comprising a second compressor in the form of a high pressure compressor 115 and a high pressure turbine 117 interconnected by a second shaft in the form of a high pressure shaft 127. The first and second modules 190, 191 are separated in an axial direction X, i.e. they do not overlap in the axial direction. In this embodiment, each component of the first module 190 is provided forwardly (i.e. in a direction opposite to the axial direction X) of each component of the second module 191. Consequently, though the shafts 127, 177 rotate about a common engine axis 111, the shafts do not overlap in an axial direction.

[0023] The core 175 defines a core airflow path A. The fan 113 is driven by the fan drive turbine 119 via a fan drive coupling. The fan drive coupling comprises an output shaft 125 which is coupled to the fan 113 via a reduction gearbox 126. The gearbox 126 is driven by the fan drive shaft 177, and is configured to drive the output shaft, and so the fan, at a lower rotational speed than the input shaft 177. The gearbox 126 provides a reduction ratio, such that the ratio between the input shaft 177 rotational speed and the fan 113 rotational speed is approximately 4:1. The gearbox 126 may comprise further toothed gear wheels, and may comprise a planetary or star gearbox configuration. Alternatively, the gearbox may comprise a differential drive, or a continuously variable transmission or belt drive.

[0024] Both the compressors 114, 115 generally comprise multi-stage axial flow compressors. At a rearward end of the low pressure compressor 114 is a low pressure compressor outlet 134. Air from the low pressure compressor 114 is directed in operation to the low pressure compressor outlet 134, into an inter-compressor core air duct 135. The inter-compressor core air duct 135 extends rearwardly toward a rear end of the gas turbine engine core 175. Surrounding at least part of the inter-compressor core air duct 135 is an intercooler fan air duct 136. The intercooler fan air duct 136 comprises a hollow passage having an inlet 137 at a forward end configured to ingest fan air from within the fan nacelle 121, downstream of the fan 113, to define an intercooler airflow C.

[0025] A heat exchanger matrix 150 is provided at an aft end of the intercooler fan air duct 136 and inter-compressor core air duct 135. Air from the ducts 135, 136 is in thermal contact within the heat exchanger matrix. In view of the temperature difference between the high temperature compressed airflow A within the inter-compressor duct 135 and low temperature intercooler airflow C within the intercooler duct 137, heat is exchanged from the compressed airflow A to the intercooler airflow C. Consequently, the intercooler duct 136 and inter-compressor core air duct 135 together form a compressor intercooler 150, thereby reducing the work required by further compressor stages, and increasing thermal efficiency.

[0026] The intercooler duct 136 further comprises an intercooler cooling flow modulation valve 138 configured to modulate intercooler airflow C mass flow rate. FIGS. 3a and 3b show a cross section of the region D(i) and D(ii) of FIG. 2 respectively. It will be understood that the positions shown in the top and bottom half of FIG. 2 are for illustrative purposes, and in practice, the flow modulate valve is likely to be in the same position at all engine circumferential positions.

[0027] In FIGS. 3a and 3b, the valve 138 is shown in a closed and an open position respectively. As can be seen, the flow modulation valve 138 comprises an axially movable exhaust plug 162, which is moveable between a closed position (shown in FIG. 3a) and an open position (shown in FIG. 3b) by a valve actuator 163 in the form of a hydraulic ram. As will be understood, the plug 162 may be moveable to intermediate positions between the open and closed positions. When in the open position, the airflow C mass flow rate is relatively high, resulting in a large amount of compressor air intercooling. On the other hand, when in the closed position, the airflow C mass flow rate is relatively low, or is shut off completely, such that little or no compressor air intercooling is provided. Consequently, the degree of intercooling can be controlled.

[0028] The exhaust plug 162 is shaped such that, when in the closed position, the intercooler duct 136 and plug 162 form a continuous surface, which tapers in a rearward direction in a “boat tail” configuration. Consequently, the intercooler duct 136 and plug 162 provide minimal drag when in the closed position. Similarly, a front surface 164 is angled downwardly, such that the plug provides minimal drag when in the open position. The shape of the plug 162 may be such that it uses the Coanda effect to redirect airflow C back towards a rearward direction.

[0029] The inter-compressor duct 135 comprises an elbow 180 at a rearward, downstream in core flow A end, which redirects core flow A at the downstream end by substantially 180° to a forward direction. The core flow A is thereby directed in operation into an inlet of the high pressure compressor 115. In operation, the high pressure compressor 115 further raises the pressure of the core air flow A in operation, and urge the core air flow A forwardly.

[0030] Axially forwardly (i.e. downstream in core flow A) of the high pressure compressor 115 is the combustor 130, which is of conventional construction. In the combustor 130, fuel is provided and burnt with the compressed air from the high pressure compressor 115 in operation to increase the temperature of the core air flow A.

[0031] The high pressure turbine 117 is provided axially forwardly (i.e. downstream in core flow A) of the combustor 130. In use, the high pressure turbine 117 directs flow forwardly, while extracting energy from the flow to drive the high pressure shaft 127, which is coupled to the high pressure compressor 115, to thereby drive the high pressure compressor 115 in operation.

[0032] Axially forwardly (i.e. downstream in core flow A) of the high pressure turbine 117 is the low pressure fan drive turbine 119, which is of similar construction to the high pressure turbine 117, comprising a plurality of rotors and stators. The low pressure fan drive turbine 119 is coupled to both the low pressure compressor 114 and the gearbox 126. Consequently, the low pressure turbine 119 drives the fans 113 and the low pressure compressor 114 via the shaft 177 in operation.

[0033] Between the low pressure turbine 119 and the low pressure compressor 114 is a core exhaust passage 145, which is configured to receive hot combustion products from a downstream end of the low pressure fan drive turbine 119 in the core air flow A. The core exhaust passage 145 turns core air flow A approximately 180°, and so redirects air rearwardly in use. Core air A from the core exhaust passage 145 mixes with fan air B downstream within the nacelle 121.

[0034] Consequently, the above arrangement defines a “reverse flow” architecture, in which core flow A flows in a forward direction during at least part of the compression and expansion processes, i.e. in an opposite direction to the fan efflux, since at least one core turbine 117, 119 is provided forwardly of at least one core compressor.

[0035] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0036] For example, the fans could comprise variable pitch blades. In such a case, a cold flow thrust reverse mechanism may be provided.

[0037] The first and second shafts need not be co-axial, and could be offset relative to one another.

[0038] A plurality of fans could be provided, each being driven by the fan drive turbine. A recuperator could be provided, configured to exchange heat from relatively high temperature exhaust air downstream of the fan drive turbine, and relatively low pressure compressed core air downstream of the high pressure compressor.