Gas turbine provided with an unducted propeller comprising a cooling air duct and a variable bleed valve exhaust duct

Abstract

The invention relates to a gas turbine (110) comprising - two unducted propellers; - a main duct (171); - at least one compression stage (145) located in the main duct (171); - a cooling duct (173) extending from a cooling inlet and opening into the main duct (171), the cooling inlet being located upstream of the or each compression stage (145); - a heat exchanger (174) located in the cooling duct (173); - an exhaust duct (175) opening into the main duct (170) and into the cooling duct (173) so that the air flowing through the exhaust duct (175) ventilates the heat exchanger (174); and - a variable bleed valve (176) configured to regulate the flow rate in the exhaust duct (175).

Description

[0001] Description

[0002] Title of the invention: Unducted propeller gas turbine comprising a cooling air channel and a variable wastegate ejection channel.

[0003] FIELD OF THE INVENTION

[0004] The invention relates to a propulsion gas turbine with an unducted propeller and in particular to air cooling in these systems. The invention is of particular interest when applied to gas turbomachines for aircraft propulsion.

[0005] STATE OF THE ART

[0006] A gas turbine 10 is known comprising a fan composed of an unducted upstream propeller and, downstream, an unducted downstream propeller or fixed rectifier.

[0007] The terms upstream and downstream are defined in relation to the general flow direction of gases through the gas turbine.

[0008] The propulsion system extends along an axis and comprises successively, in the direction of flow of the gases in the turbomachine, the fan, an air inlet configured to supply air:

[0009] - a compression section which may include a low pressure compressor and a high pressure compressor,

[0010] - a combustion chamber,

[0011] - a turbine section which may include a high pressure turbine, and

[0012] - a low pressure turbine.

[0013] Air entering through the air inlet is finally expelled from the gas turbine through a main outlet, located downstream of the low-pressure turbine.

[0014] The upstream propeller and the low-pressure compressor are rotated by the low-pressure turbine via a first drive shaft, while the high-pressure compressor is rotated by the high-pressure turbine via a second drive shaft.

[0015] In operation, a flow of air is compressed by the low- and high-pressure compressors and fuels combustion in the combustion chamber, the expansion of which drives the high- and low-pressure turbines. The air propelled by the upstream propeller and the combustion gases exiting through the gas outlet downstream of the turbines exert a reaction thrust on the propulsion system and, through it, on a vehicle or machine such as an aircraft.

[0016] A speed reduction gearbox is driven by the first drive shaft. This in turn drives the upstream propeller, which rotates at a reduced rotational speed compared to the rotational speed of the drive shaft.

[0017] Air entering through the air inlet flows through a channel to the low-pressure compressor. Upstream of the low-pressure compressor, a blade wheel placed in the channel is driven by the drive shaft. The blade wheel comprises a plurality of compression blades and increases the pressure of the air flowing in the channel downstream. Upstream and / or downstream of the blade wheel is a fixed blade wheel or stator. A complementary channel extends from the channel, downstream of the inlet stator, to a complementary outlet opening onto the exterior of the body of the propulsion system. The complementary channel has an annular shape and extends around the axis of the propulsion system. The air outlet is located downstream of the fixed downstream propeller and upstream of the main outlet.

[0018] The additional channel allows for cooling a heat exchanger, particularly for the purpose of cooling the speed reduction box. Such an additional channel also contributes to part of the engine's thrust.

[0019] However, such an additional channel complicates the structure of the propulsion system.

[0020] There is therefore a need for a simpler complementary channel structure that provides a cooling function.

[0021] STATEMENT OF THE INVENTION

[0022] An object of the invention is to propose a simpler structure allowing greater cooling power than in the prior art. The object is achieved within the framework of the present invention thanks to a gas turbine comprising

[0023] - two unducted propellers,

[0024] - a main channel,

[0025] - at least one compression stage located in the main channel, the main channel being configured to supply the compression stage with air,

[0026] - a cooling channel extending from a cooling inlet opening into the main channel, the cooling inlet being located upstream of the or each compression stage with reference to a direction of air flow,

[0027] - a heat exchanger located in the cooling channel,

[0028] - an ejection channel opening into the main channel and into the cooling channel so that the air passing through the ejection channel ventilates the heat exchanger, and

[0029] - a variable discharge valve configured to adjust an air flow rate in the discharge channel.

[0030] The terms upstream and downstream are defined in relation to the direction of air flow through the gas turbine.

[0031] Since the cooling inlet is located upstream of any compression stage in the main channel, all the compression stages located in the main channel are thus grouped downstream of the cooling inlet, which makes it possible to simplify the structure compared to the prior art. In addition, the air entering the cooling channel is not, unlike the prior art, heated by a compression stage located in the main channel upstream of the cooling inlet, so that the air entering the cooling channel is colder and offers greater cooling power compared to the prior art.

[0032] The following features can also be provided in the gas turbine:

[0033] - a combustion chamber located downstream of the compression stage relative to the direction of air flow,

[0034] - the main channel extending from a main inlet which is located between the two propellers, - the direction of air flow directed from the main inlet to the compression stage,

[0035] - the cooling channel extending from the cooling inlet to a cooling outlet opening outside the gas turbine located downstream of the unducted propellers

[0036] - the ejection channel opening into the main channel downstream of the compression stage.

[0037] Such a gas turbine is advantageously and optionally completed by the following different characteristics taken alone or in combination:

[0038] - the variable discharge valve comprises a rotary valve configured to be rotated;

[0039] - the variable discharge valve includes a sliding gate;

[0040] - a flow modulator configured to adjust a flow rate of a flow passing through the cooling inlet from the main channel to the cooling channel;

[0041] - the flow modulator is placed at the cooling inlet;

[0042] - the flow modulator is placed at the cooling outlet, the modulator comprising a rotary valve configured to be rotated;

[0043] - the flow modulator includes a variable section of the cooling channel;

[0044] - the flow modulator comprises a rotary valve configured to be rotated about an axis;

[0045] - the axis is placed upstream of the cooling inlet, the rotary valve being configured to be rotated between a closed position where the rotary valve covers the cooling inlet and an open position where the rotary valve is inside the cooling channel;

[0046] -the shaft is positioned downstream of the cooling inlet, the rotary valve being configured to be rotated between a closed position where the rotary valve covers the cooling inlet and an open position where the rotary valve is outside the cooling channel; and - the flow modulator comprises a sliding gate.

[0047] The invention further relates to an aircraft comprising a gas turbine as just presented.

[0048] The invention also relates to a method for controlling the gas turbine presented above, the method comprising, when the rotational speed of one of the two propellers exceeds a first predetermined speed, a step of canceling the air flow flowing from the main channel into the ejection channel, and optionally a step of opening the cooling channel so that air flows from the main channel into the cooling channel.

[0049] Such a method is advantageously and optionally supplemented by the following different characteristics taken alone or in combination:

[0050] - the first predetermined speed is equal to 80% of a maximum propeller rotation speed;

[0051] - a step of adapting an air flow rate passing through the cooling inlet of the main channel to the cooling channel with respect to a cooling requirement of the heat exchanger, the gas turbine comprising a flow modulator configured to adjust a flow rate of a flow passing through the cooling inlet of the main channel to the cooling channel;

[0052] - when the rotational speed of the propeller is lower than the first predetermined speed and higher than a second predetermined speed, a step of partially opening the variable discharge valve so that air flows from the main channel to the ejection channel;

[0053] - when the rotational speed of the unducted propeller is lower than the first predetermined speed and higher than a second predetermined speed, a step of reducing an air flow rate passing through the cooling inlet of the main channel to the cooling channel, the ejection channel of the gas turbine opening into the cooling channel downstream of the flow modulator; - when the rotational speed of the unducted propeller is lower than a second predetermined speed lower than the first predetermined speed or when the dynamic pressure upstream of the main channel falls below a minimum value, a step of fully opening the ejection channel and a step of canceling an air flow rate passing through the cooling inlet of the main channel to the cooling channel, the ejection channel opening into the cooling channel downstream of the flow modulator; and

[0054] - the second predetermined speed is between 40% and 80% of a maximum propeller rotation speed.

[0055] DESCRIPTION OF FIGURES

[0056] Other characteristics and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and must be read in conjunction with the appended drawings in which: Figure 1 is a schematic representation of a gas turbine according to one embodiment of the invention; Figures 2 to 9 are schematic representations of a detail of the gas turbine according to different embodiments of the invention.

[0057] DETAILED DESCRIPTION OF THE INVENTION

[0058] Az turbine

[0059] Figure 1 shows a gas turbine 110 according to one embodiment of the invention.

[0060] The gas turbine 110 extends along an axis A. The gas turbine 110 comprises two unducted propellers 121 and 131 which form a fan. In particular, the fan is composed of the unducted upstream propeller 121 rotatable about the axis A which is located upstream of the unducted downstream propeller 131 or fixed rectifier. The gas turbine also comprises a main channel 170 which extends through the turbine essentially parallel to the axis of the turbine from a main inlet 170 to a main outlet 180 opening outside the turbine casing.

[0061] The main channel 171 is configured to circulate an air flow in a general gas flow direction, represented by the arrow G in FIG. 1, from the main inlet 170 to the main outlet 180 which is therefore located downstream of the main inlet 170.

[0062] The terms upstream and downstream are defined in relation to the general flow direction of gases through the gas turbine.

[0063] Between the two propellers, that is to say downstream of an upstream propeller 121 and upstream of a downstream propeller 131, the gas turbine has in its casing the main inlet 170 of the main channel 171.

[0064] In this same embodiment of the invention, and throughout the main channel 171, the gas turbine 110 successively comprises in the direction G of gas flow:

[0065] - at least one compression stage forming for example a compression section, the compression section being able to comprise upstream a low pressure compressor 145 and downstream a high pressure compressor 127,

[0066] - a combustion chamber 128.

[0067] A compression stage is understood to be a set of a moving blade wheel (or rotor with moving blades) and a fixed blade wheel (or stator with fixed blades), the moving blade wheel being able to be located upstream or downstream of the fixed blade wheel. This compression stage, by rotating the moving blade wheel, can create an increase in air pressure downstream of the stage compared to upstream of the stage.

[0068] In the main channel 171, the gas turbine 110 further comprises, downstream of the combustion chamber 128, a turbine section which may comprise upstream a high-pressure turbine 129, and downstream a low-pressure turbine 150. The gas turbine is also supplied with air by the main channel 171. The main channel 171 is configured to supply air entering through the air inlet 170 to at least one compression stage and the combustion chamber. More precisely, it is the air compressed by the at least one compression stage which is moved in the main channel 171 to the combustion chamber and which ensures its supply. This supply is carried out according to the flow direction G from the main inlet 170 to the compression stages.

[0069] The gas turbine 110 also includes a cooling channel 173 that extends from a cooling inlet opening into the main channel 171 to a cooling outlet 178 opening outside the gas turbine 110. The cooling inlet is located upstream of the or each compression stage of the main channel 171. In other words, no compression stage is located between the main inlet 170 and the cooling inlet. In other words, any compression stage in the main channel 171 is located downstream of the cooling inlet.

[0070] Locating the cooling inlet upstream of all the compression stages in the main channel corresponds to an arrangement of the part of the turbine around the cooling inlet whereby any compression stage that would be located upstream of this inlet is replaced by a compression stage in the low-pressure compressor, the cooling inlet being upstream of this low-pressure compressor. Such a configuration is advantageous because, on the one hand, it occupies less space in the main channel upstream of the combustion chamber and, on the other hand, it simplifies the structure of the complementary channel, here called the cooling channel. Indeed, the elimination of a compression stage upstream of the cooling inlet means the elimination of the moving blade wheel and the fixed blade wheel (or stator). Such a configuration also makes it possible to obtain a higher overall compression efficiency.

[0071] The cooling channel 173 is located radially further outward than the main channel 171, that is to say that the main channel is located between the axis A of the gas turbine 110 and the cooling channel 173. The cooling channel 173 may have an annular shape and extend around the axis A of the gas turbine 110. The air outlet 178 is located downstream of the fixed downstream propeller 131 and upstream of the main outlet 180. Still in the same embodiment of the invention illustrated in FIG. 1, the gas turbine 110 comprises a heat exchanger 174 located in the cooling channel. The heat exchanger 174 is configured to be cooled by the air flowing through the main duct. The heat exchanger can be used in particular to ensure the cooling of a speed reduction gearbox configured to drive the upstream propeller 121 in rotation.Different heat exchanger technologies can be considered such as volumetric, surface, finned exchangers, etc.

[0072] According to this same embodiment, the gas turbine 110 comprises an ejection channel 175 opening into the main channel 170 as well as a variable discharge valve 176 configured to adjust a flow rate of a stream flowing through the ejection channel 175.

[0073] The ejection inlet of the ejection channel which opens onto the main channel 170 is located downstream of at least one compression stage located in the main channel, such that the ejection inlet is located downstream of the cooling inlet and these inlets are separated by at least one compression stage. The ejection inlet may for example be located downstream of the low-pressure compressor 145.

[0074] The ejection channel 175 extends from the main channel radially outward.

[0075] The ejection channel 175 opens into the cooling channel 173 downstream of the ejection inlet and upstream of the cooling outlet 178.

[0076] The ejection channel 175 opens into the cooling channel 173 so that the air passing through the ejection channel ventilates the heat exchanger. In other words, a flow flowing in the flow direction and passing through the ejection channel ventilates the heat exchanger downstream. This corresponds to the ejection channel 175 opening into the cooling channel 173 on or upstream of the heat exchanger 174, that is to say that the position in the cooling channel 173 where the ejection channel 175 opens is the position of the heat exchanger 174 in the cooling channel or a position further upstream than the position of the heat exchanger 174 in the cooling channel. The variable discharge valve 176 may be located at the intersection between the ejection channel 175 and the main channel 170. This intersection defines an ejection inlet of the ejection channel 175.

[0077] According to a particular aspect of the invention, the variable discharge valve 176 comprises a rotary valve configured to be rotated about a fixed axis, as illustrated in Figures 2 to 5 and 7 to 9.

[0078] The fixed axis can be located downstream of the ejection channel 175 and positioned to rotate the valve between a closed position where the valve covers the ejection inlet thus separating the ejection channel and the main channel, and an open position where the valve is inside the main channel, in this case referred to as a bailing valve. Alternatively, in the open position the valve can be inside the ejection channel, in this case referred to as a non-bailing valve. In this variant, the valve in the open position can be pressed against a wall of the ejection channel, or even be integrated into and continuous with a wall of the ejection channel.

[0079] According to another particular aspect of the invention, the variable discharge valve 176 comprises a sliding gate, as illustrated in FIG. 6. The sliding gate is configured to be translated in a direction parallel to the ejection inlet and having a non-zero projection in the general direction of gas flow. The sliding gate can slide downstream to a closed position where the valve covers the ejection inlet, thus separating the ejection channel and the main channel, and upstream to an open position where the sliding gate is located upstream of the ejection inlet. Alternatively, the sliding gate can slide downstream to an open position where the sliding gate is located downstream of the ejection inlet, and upstream to a closed position where the valve covers the ejection inlet, thus separating the ejection channel and the main channel.

[0080] Optionally to the previously presented implementations of the invention, the turbine 110 includes a flow modulator 172 configured to adjust a flow rate of a flow passing through the cooling inlet of the main channel 171 to the cooling channel 173. The flow modulator 172 may be located at the intersection between the cooling channel 173 and the main channel 170, defining the cooling inlet.

[0081] In this case, the ejection channel opens into the cooling channel downstream of the flow modulator 172.

[0082] When the flow modulator 172 is located at this location, the flow modulator may be in a first option a rotary valve configured to be rotated about a fixed axis denoted B in Figures 2 and 3.

[0083] This fixed axis can be placed upstream of the cooling inlet. The rotary valve is then configured to be rotated between a closed position 172b where the valve covers the cooling inlet and an open position 172a where the valve is inside the cooling channel, as illustrated in Figure 2.

[0084] This fixed axis may alternatively be placed downstream of the cooling inlet. The rotary valve is then configured to be rotated between a closed position 172d where the valve covers the cooling inlet and an open position 172c where the valve is inside the cooling channel, as illustrated in Figure 3.

[0085] When the flow modulator 172 is located at the cooling inlet, the flow modulator may be in a second option a sliding door, as illustrated in Figures 5 and 6. The sliding door is configured to be translated in a direction parallel to the cooling inlet and having a non-zero projection in the general direction of gas flow. The sliding door can slide downstream to a closed position where the flow modulator covers the cooling inlet thus separating the cooling channel and the main channel, and upstream to an open position where the sliding door is located upstream of the cooling inlet.Alternatively, the sliding gate may slide downstream to an open position where the sliding gate is located downstream of the ejection inlet, and upstream to a closed position where the valve covers the ejection inlet thereby separating the ejection channel and the main channel. In summary, when the flow modulator 172 is placed at the cooling inlet:.

[0086] - the flow modulator 172 may comprise a rotary valve configured to be rotated about an axis, and advantageously the axis is placed upstream of the cooling inlet, the rotary valve being configured to be rotated between a closed position where the rotary valve covers the cooling inlet and an open position where the rotary valve is inside the cooling channel 173, or the axis is placed downstream of the cooling inlet, the rotary valve being configured to be rotated between a closed position where the rotary valve covers the cooling inlet and an open position where the rotary valve is outside the cooling channel 173;

[0087] -the flow modulator 172 may include a sliding door.

[0088] The flow modulator 172 may also be located at the cooling outlet 178, as illustrated in FIG. 4. In this case, the ejection channel opens into the cooling channel upstream of the flow modulator 172.

[0089] In this case, the flow modulator 172 is a rotary valve configured to be rotated about a fixed axis. This fixed axis is placed upstream of the cooling outlet 178. The rotary valve is then configured to be rotated between a closed position 172f where the valve covers the cooling outlet and an open position 172e where the valve is outside the cooling channel, as illustrated in FIG. 4.

[0090] The flow modulator 172 may finally be a variable section of the cooling channel. This variable section may be located at different locations in the cooling channel. The ejection channel may open into the cooling channel either upstream or downstream of the variable section formed by the flow modulator 172.

[0091] Ordering process

[0092] A gas turbine as just described makes it possible to implement a control method according to the invention to optimize the cooling of the heat exchanger 174. In a first implementation, the control method comprises, when the rotational speed of an unducted propeller exceeds a first predetermined speed, a step of canceling the air flow flowing from the main channel 171 into the ejection channel 175, and optionally a step of opening the cooling channel so that a flow flows through the cooling channel.

[0093] The unducted propeller mentioned above is the upstream propeller 121 which is movable. This propeller compresses the downstream air including the air entering the main channel, and in particular the incoming air passing from the main channel to the cooling channel.

[0094] In the absence of flow modulator 172, the air passes freely from the main channel 171 to the cooling channel 173, no step of opening the cooling channel is therefore necessary.

[0095] In the option where a flow modulator 172 is present, a step of opening the cooling channel makes it possible to configure the modulator 172 to allow the passage of air so that a flow flows from the main channel 171 into the cooling channel 173. Figure 7 illustrates the situation where the gas turbine includes the flow modulator 172 at the cooling inlet, the flow modulator 172 being configured to allow the passage of air between the main channel 171 and the cooling channel 173.

[0096] The step of canceling the flow rate of the stream flowing through the ejection channel is accomplished by controlling the variable discharge valve 176 to close the passage between the main channel and the ejection channel.

[0097] As illustrated in Figure 7, the discharge valve 176 blocks the passage of air between the main channel 171 and the ejection channel 175.

[0098] In this situation, an air flow F1 passes from the main channel to the cooling channel 173, while no air flow passes from the main channel to the ejection channel 175. The air flow F2 which passes through the exchanger 174, flow F2 which is the extension of the air flow F1, makes it possible to ventilate and cool the exchanger 174.

[0099] The first predetermined speed corresponds to a speed beyond which the open cooling channel is traversed by a sufficient air flow to cool the heat exchanger 174 satisfactorily. This air flow through the cooling channel is ensured by the compression of the blade root of the upstream propeller 121 and by the dynamic flight pressure. These two pressure factors allow ventilation of the exchanger.

[0100] The first predetermined speed may correspond to a cruising speed of an aircraft driven by the gas turbine. The cruising speed corresponds to the speed reached in normal flight of the aircraft between takeoff and landing. The first predetermined speed may be equal to 80% of the maximum rotational speed of the propeller.

[0101] Compared to the prior art in which a mobile compression blade wheel is located upstream of the cooling inlet, the flow rate in the cooling channel necessary to ensure sufficient ventilation of the exchanger is reduced. Indeed, the absence of the mobile compression blade wheel makes the air flow passing from the main channel to the cooling channel cooler and at the same flow rate, the cooling power is greater. The air flow F1, F2 through the cooling channel also depends on the section of the cooling outlet 178 opening outside the gas turbine 110. This section of the cooling outlet 178 is sized to meet the cooling requirement.

[0102] Optionally in the first implementation, the method can be applied to a gas turbine comprising a flow modulator 172 as presented above. In this case, the method can comprise a step of adapting an air flow rate passing through the cooling inlet of the main channel 171 to the cooling channel 173 with respect to a cooling requirement of the heat exchanger 174. The supply of the third flow is actively regulated by the flow modulator, which makes it possible to optimize the performance according to the cooling requirements of the engine.

[0103] In a second implementation, the method further comprises, compared to the first implementation, when the rotational speed of the unducted propeller is lower than the first predetermined speed and exceeds a second predetermined speed, a step of partially opening the discharge valve so that a flow flows through the ejection channel. Figure 8 illustrates this situation.

[0104] When the propeller speed decreases and takes a value below the first predetermined value, the air flow F3 passing from the main channel 171 to the cooling channel 173 via the cooling inlet is not sufficient to cool the heat exchanger 174. In this case, the discharge valve 176 is activated to open the air passage between the main channel and the ejection inlet of the ejection channel. A second air flow F4 compressed by at least one compression stage 145 located upstream of the ejection inlet flows through the ejection channel 175. This second flow F4 opens into the cooling channel on or upstream of the heat exchanger 174. The overall flow F5 flowing through the heat exchanger 174 is the sum of the flows F3 and F4. In this way, the exchanger can be cooled satisfactorily despite the decrease in the rotation speed of the propeller.

[0105] The geometry of the cooling channel and the ejection channel can be designed to promote the flow in the cooling channel by exploiting the Venturi effect produced in the cooling channel by the flow of the second stream in the ejection channel.

[0106] The second predetermined speed may correspond to a speed of an aircraft set in motion by the gas turbine during takeoff or descent idle. The second predetermined speed is then between 40% and 80% of the maximum rotational speed of the propeller.

[0107] As an option of the second implementation, the method can be applied to a gas turbine comprising a flow modulator 172 which is placed in the cooling channel 173 further upstream than the position where the ejection channel 175 opens into the cooling channel 173. In this case, the method can additionally comprise, compared to the second implementation, when the rotational speed of the unducted propeller is lower than the first predetermined speed and exceeds a second predetermined speed, or when the dynamic pressure at the inlet of the main channel 170 falls below a minimum value, a step of reducing the air flow passing through the cooling inlet of the main channel 171 to the cooling channel 173. The reduction in the flow is produced by the flow modulator 172 which is partially closed to reduce the flow passing from the main channel to the cooling channel.As previously stated, the second flow produced by the ejection channel allows additional cooling of the exchanger, but it may also be sufficient on its own to cool the exchanger 174 as desired. Indeed, when the rotational speed of the propeller is reduced, the heating of the engine is also reduced. The cooling requirement may therefore be sufficiently low so that the air flow passing through the ejection channel is sufficient. In this case, it is possible to close the flow modulator 172. As it is placed upstream of the ejection channel, its closure does not reduce the air flow from the ejection channel 175 into the cooling channel 173. The closure of the modulator may be total so that there is no air flow passing from the main channel 171 into the cooling channel 173.This also makes it possible to avoid a backflow of the flow passing through the ejection channel 175 and which would then pass through the cooling channel 173 upstream, that is to say towards the cooling inlet.

[0108] In a third implementation, the method is applied to a gas turbine comprising a flow modulator 172 which is placed in the cooling channel further upstream than the position where the ejection channel opens into the cooling channel. This third implementation comprises, in addition to the steps of the method according to the first implementation and / or according to the second implementation, when the rotational speed of the unducted propeller is lower than the second predetermined speed or when the dynamic pressure at the inlet of the main channel 170 falls below a minimum value, a step of fully opening the ejection channel 175 and a step of canceling an air flow passing through the cooling inlet of the main channel to the cooling channel 173.

[0109] Figure 9 illustrates this situation.

[0110] When the propeller speed decreases and takes a value below the second predetermined value, or when the dynamic pressure at the inlet of the main channel 170 falls below a minimum value, the air flow passing through the cooling channel produces even lower ventilation and cooling of the heat exchanger 174. The second flow passing through the ejection channel is then the only one to allow sufficient cooling of the exchanger.

[0111] The variable discharge valve 176 is then configured to maximize the airflow F6 passing from the main channel 171 to the ejection channel 175.

[0112] The flow modulator 172 is then configured to cancel the air flow passing from the main channel into the cooling channel through the cooling inlet. Since the flow modulator is placed upstream of the ejection channel, its closure does not decrease the air flow from the ejection channel into the cooling channel. The overall flow F7 flowing through the heat exchanger 174 is the extension of the flow F6.

[0113] In summary, the second implementation may comprise, when the rotational speed of the propeller is lower than the first predetermined speed and higher than a second predetermined speed, a step of partially opening the variable discharge valve 176 so that air flows from the main channel 171 to the ejection channel 175, and optionally, if the ejection channel 175 opens into the cooling channel 173 downstream of the flow modulator 176, a step of reducing an air flow rate passing through the cooling inlet from the main channel 171 to the cooling channel 173.

[0114] In addition, the control method may further comprise, when the rotational speed of the unducted propeller is lower than a second predetermined speed lower than the first predetermined speed or when the dynamic pressure at the inlet of the main channel 170 falls below a minimum value, a step of completely opening the ejection channel 175 and a step of canceling an air flow passing through the cooling inlet of the main channel 171 to the cooling channel 173, the second predetermined speed being able to be between 40% and 80% of a maximum rotational speed of the propeller.

Claims

DEMANDS 1. Gas turbine (110) comprising - two unfaired propellers (121, 131), - a main canal (171), - at least one compression stage (145) located in the main channel (171), the main channel (171) being configured to supply the compression stage (15) with air, - a cooling channel (173) extending from a cooling inlet opening into the main channel (171), the cooling inlet being located upstream of the compression stage(s) (145) with reference to a direction of air flow (G), - a heat exchanger (174) located in the cooling channel (173), - an ejection channel (175) opening into the main channel (170) and into the cooling channel (173) so that the air passing through the ejection channel (175) ventilates the heat exchanger (174), and - a variable discharge valve (176) configured to regulate an air flow in the ejection channel (175).

2. Gas turbine according to claim 1 wherein the variable discharge valve (176) comprises a rotary valve configured to be rotated.

3. Gas turbine according to claim 1 wherein the variable discharge valve (176) comprises a sliding gate.

4. Gas turbine according to any one of the preceding claims comprising a flow modulator (172) configured to regulate a flow rate from the main channel cooling inlet (171) to the cooling channel (173).

5. Gas turbine according to claim 4 in which the flow modulator (172) is placed at the cooling inlet.

6. Gas turbine according to claim 4, wherein the flow modulator (172) is placed at the cooling outlet (178), the modulator comprising a rotary valve configured to be rotated.

7. Gas turbine according to any one of claims 1 to 3 wherein the flow modulator (172) comprises a variable section of the cooling channel (173).

8. Aircraft comprising a gas turbine (110) according to any one of the preceding claims.

9. Method of controlling a gas turbine (110) according to any one of claims 1 to 7, comprising, when the rotational speed of one of the two propellers exceeds a first predetermined speed, a step of canceling the air flow from the main channel (171) into the ejection channel (175), and optionally a step of opening the cooling channel (173) so that air flows from the main channel (171) into the cooling channel (173).

10. Method according to claim 9 wherein the first predetermined speed is equal to 80% of a maximum propeller rotation speed.

11. Method according to any one of claims 9 or 10 of controlling a gas turbine (110) according to any one of claims 4 to 7 comprising a step of adapting an air flow passing through the cooling inlet of the main channel (171) to the cooling channel (173) with respect to a cooling requirement of the heat exchanger (174).

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