Patent Description:
It is known to pressurise and ventilate a cabin of an aircraft using engine bleed air which is bled from a compressor section of the core of a gas turbine engine. Bleeding high pressure air from the gas turbine engine reduces its efficiency and thereby increases its fuel consumption.

Blower systems which make use of engine bleed air which is bled from a lower pressure source of a gas turbine engine (such as a bypass duct) and which subsequently compress the engine bleed air prior to delivering it to the cabin are also known, as described in <CIT>, <CIT> and <CIT>.

United States Patent Application Publication <CIT> relates to a bleed air and engine start system. A compressor includes a housing, an impeller disposed within a cavity of the housing, a first port in the housing to direct air onto the impeller to rotate the impeller in a first mode, and a second port in the housing oriented to provide air to the impeller in a second mode. The impeller is operatively coupled to a drive shaft. In the first mode, the impeller drives the drive shaft. In the second mode, the drive shaft rotates the impeller to draw air from the first port and increase the pressure of the air.

European Patent Application Publication <CIT> relates to an intercooled cooling air system that uses a cooling compressor as an engine starter.

European Patent Application Publication <CIT> relates to an aircraft cabin blower system comprising a hydraulic circuit.

United States Patent Application Publication <CIT> relates to a cabin blower system comprising a toroidal continuously variable transmission.

According to a first aspect, there is provided a blower system for providing air to an airframe system, comprising: a rotor configured to be mechanically coupled to a spool of a gas turbine engine, the rotor comprising a plurality of compressor blades on a first side of the rotor, and a plurality of turbine blades or a plurality of impulse scoops on a second side of the rotor; wherein the rotor is configured to: in a blower mode, be driven to rotate in a first direction by the spool and to function as a centrifugal compressor, the plurality of compressor blades on the first side of the rotor configured to direct air to an airframe discharge port for supply to the airframe system; and in an engine drive mode, receive air from an external air source via one or more impingement ports configured to direct the received air onto the plurality of turbine blades or the plurality of impulse scoops on the second side of the rotor and thereby drive the rotor to rotate in the same first direction to drive the spool to rotate.

In the engine drive mode the rotor may drive the spool to rotate for starting the gas turbine engine. Additionally or alternatively, the engine drive mode may be used to drive the spool to rotate at a speed below a starting speed of the engine, for example to reduce or prevent the formation of thermal bow of engine components.

The blower mode may be a cabin blower mode, such that at least a portion of the air discharged to the airframe discharge port is supplied to an aircraft cabin.

The impingement port is configured (e.g. located relative to the rotor and/or arranged to direct air onto the rotor in a predefined direction) so that rotor rotates in the same direction in both the cabin blow mode and the engine drive mode.

It may be that the blower system further comprises a variable transmission for mechanically coupling the rotor to the spool.

The impingement port may be one of a plurality of impingement ports, each configured to direct air onto the rotor and thereby cause the rotor to rotate.

It may be that blower system is configured to provide a recirculation pathway for recirculating compressed air in the blower mode, and wherein the recirculation pathway includes the or each impingement port.

The blower system may further comprise: a primary valve configured to isolate the airframe discharge port from the airframe system in the engine drive mode; and a secondary valve configured to isolate the or each impingement port from the external air source in the blower mode.

According to a second aspect there is provided a gas turbine engine for an aircraft, the gas turbine engine comprising a blower system in accordance with the first aspect.

According to a third aspect there is provided an aircraft comprising a blower system in accordance with the first aspect or a gas turbine engine in accordance with the second aspect.

For example, the gas turbine engine may have any desired number of shafts (or spools) that connect turbines and compressors, for example one, two or three shafts.

The gearbox may be a reduction gearbox (in that the output to the fan is a lower rotational rate than the input from the core shaft). Any type of gearbox may be used. For example, the gearbox may be a "planetary" or "star" gearbox, as described in more detail elsewhere herein.

According to an aspect, there is provided an aircraft comprising a blower system or a gas turbine engine as described and/or claimed herein.

Examples will now be described with reference to the accompanying drawings, which are purely schematic and not to scale, and in which:.

The bypass duct <NUM> may comprise an engine bleed port <NUM> for supplying air from the bypass duct to a blower system or the like. In other examples, the engine core <NUM> may comprise an engine bleed port <NUM>.

The low pressure turbine <NUM> (see <FIG>) drives the shaft <NUM> (or spool), which is coupled to a sun wheel, or sun gear, <NUM> of the epicyclic gear arrangement <NUM>.

Note that the terms "low pressure turbine" and "low pressure compressor" as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan <NUM>) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft <NUM> (or spool) with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan <NUM>).

Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in <FIG> has a split flow nozzle <NUM>, <NUM> meaning that the flow through the bypass duct <NUM> has its own nozzle <NUM> that is separate to and radially outside the core engine nozzle <NUM>. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct <NUM> and the flow through the core <NUM> are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine <NUM> may not comprise a gearbox <NUM>.

A diagram of an example blower system <NUM> for providing air to an airframe system is shown schematically in <FIG>. The blower system <NUM> comprises a rotor <NUM> which is configured to be mechanically coupled to a spool <NUM> of a gas turbine engine. The spool may, for example, be the high-pressure (HP) spool of a two- or three- shaft gas turbine or an intermediate pressure (IP) spool of a three-spool engine, though any one or more spools of a gas turbine engine may be coupled to the rotor. The rotor <NUM> is disposed within a rotor housing <NUM>. In the example of <FIG>, the blower system <NUM> comprises a variable transmission <NUM> for mechanically coupling the rotor <NUM> to the spool <NUM>.

The rotor <NUM> is configured to be driven to rotate by the spool <NUM> in a blower mode to draw air from an engine bleed port <NUM>, such that the blower system <NUM> compresses air it receives from the gas turbine engine. The compressed air is discharged to an airframe discharge port <NUM> for supply to an airframe system <NUM> for an airframe pressurisation purpose. The airframe pressurisation purpose may be, for example, wing anti-icing, fuel tank inerting, cargo bay smoke eradication and/or aircraft cabin pressurisation. The engine bleed port <NUM> is in fluid communication with an air pathway (shown schematically at <NUM>) of the gas turbine engine. Accordingly, in the blower mode, the rotor <NUM> draws air from the air pathway <NUM> of the gas turbine engine and supplies air to the airframe system <NUM>, for example to pressurise and/or ventilate an aircraft cabin.

The rotor <NUM> is configured to function as a compressor in the blower mode, such that air supplied to the airframe system <NUM> is at a higher pressure than air drawn from the air pathway <NUM> of the gas turbine engine. As a result, the rotor <NUM> is not required to draw air from a relatively high pressure region of the gas turbine engine in order to supply pressurised air to the airframe system <NUM>. Instead, the rotor <NUM> may draw air via the engine bleed port <NUM> from a relatively low pressure region of the gas turbine engine, such as from a bypass duct <NUM> of the gas turbine engine as shown in <FIG>. If the rotor <NUM> were alternatively required to draw air from a relatively high pressure region of the gas turbine engine (e.g. the high pressure compressor), an efficiency of the gas turbine engine may be reduced. Therefore, the blower system <NUM> provides a more efficient airframe system pressurisation and ventilation system when incorporated into an aircraft. In addition, this approach reduces a scope for contamination of the air supply to the airframe system <NUM>.

The rotor <NUM> is driven to rotate in the blower mode by the variable transmission <NUM>, which itself receives drive input from the spool <NUM>, for example through an accessory gearbox of the gas turbine engine. The speed of rotation of the spool <NUM> depends on the operating point of the gas turbine engine, which dictates a speed of the spool <NUM>. The variable transmission <NUM> allows a rotational speed of the rotor <NUM> in the blower mode to be decoupled from a rotational speed of the spool <NUM>, so that a compression performance of the rotor <NUM> in the blower mode is not solely governed by the operating point of the gas turbine engine (e.g. it can be controlled to operate at a target speed independent of the rotational speed of the spool, and/or at a variable speed ratio relative to the rotational speed of the spool). Inclusion of a variable transmission <NUM> within the blower system <NUM> therefore provides more versatile and adaptable means for supplying pressurised air to an airframe system. Various suitable variable transmission types will be apparent to those of ordinary skill in the art. For example, the variable transmission <NUM> may comprise an electric variator, as described in <CIT>.

The rotor <NUM> is also configured to be able to receive compressed air from an external air source <NUM> via an impingement port <NUM> to drive the spool <NUM> to rotate in an engine drive mode. The impingement port <NUM> is configured to direct air onto the rotor <NUM> and thereby cause the rotor <NUM> to rotate, which in turn drives the spool <NUM>. The impingement port <NUM> may be one of a plurality of impingement ports, each configured to direct air onto the rotor <NUM> and thereby cause the rotor <NUM> to rotate.

The external air source <NUM> may be provided by, for example, an auxiliary power unit (APU) of the aircraft or ground starting equipment (GSE). In the example of <FIG>, the rotor <NUM> is configured to discharge air to the engine bleed port <NUM> in the engine drive mode. However, it will be appreciated that the rotor <NUM> may discharge air elsewhere in the engine drive mode, such as to a dedicated auxiliary port, for example. Air discharged from the rotor <NUM> via a dedicated auxiliary port may be used for other purposes, for example for cooling other systems and/or components of the gas turbine engine and/or the aircraft in the engine drive mode.

The rotor <NUM> is configured to function as a turbine in the engine drive mode, such that the spool <NUM> can be driven to rotate by the rotor <NUM>. Generally, the blower system <NUM> can drive rotation of the spool <NUM> to a rotational speed which is sufficient to enable the gas turbine engine to successfully execute an ignition process. Consequently, the blower system <NUM> dispenses with a need to provide a dedicated air turbine starting system or an electric starting system to the gas turbine engine, each of which are associated with additional weight and system complexity. Additionally or alternatively, the blower system <NUM> may be able to drive the spool <NUM> to rotate at a lower speed, for example to prevent the formation of a bowed engine rotor condition following engine shutdown or to reduce a bowed engine rotor condition prior to engine start.

In the example of <FIG>, the blower system <NUM> further comprises a primary valve <NUM> which is configured to isolate the airframe discharge port <NUM> from the airframe system <NUM> in the engine drive mode, and to permit flow to the airframe system <NUM> in the blower mode. Similarly, in this example the blower system <NUM> further comprises a secondary valve <NUM> configured to isolate the impingement port <NUM> from the external air source <NUM> in the blower mode, and to permit flow from the external air source <NUM> in the engine drive mode. The secondary valve <NUM> may be further configured to control a mass flow and a pressure of an air flow from the external air source <NUM> to the airframe discharge port <NUM> in the engine drive mode.

The use of the blower system <NUM> allows for a system in which the rotor <NUM> rotates in the same rotation direction (i.e. clockwise or anti-clockwise) in both the engine drive mode and the blower mode. In this way, in the engine drive mode of the blower system <NUM> the rotor <NUM> will drive the spool <NUM> to rotate in the same direction that the spool <NUM> rotates when it drives the rotor <NUM> in the blower mode. This allows for the omission of a separate reversing mechanism to permit the spool <NUM> to be driven to rotate in its starting direction, which will be the same as the direction it rotates during when driving the rotor <NUM> in the blower mode of the blower system <NUM>. A separate reversing mechanism would result in additional mechanical efficiency losses in, and increased weight of and/or a reduced reliability of, the blower system <NUM>.

<FIG> also schematically shows a gas turbine engine <NUM> comprising the first example blower system <NUM>. The gas turbine engine <NUM> may be in accordance with the gas turbine engine <NUM> described above with respect to <FIG> and/or <FIG>.

Various examples of a rotor for use in the rotor <NUM> of the blower system <NUM> will now be described with reference to Figures 5A-10B.

<FIG> show a front view, a cross-sectional view and a radial view, respectively, of a first example rotor <NUM> disposed within a first example rotor housing <NUM>. The rotor <NUM> comprises a plurality of rotor blades <NUM> and is configured to function as a centrifugal compressor in the blower mode. Each of the plurality of rotor blades <NUM> is disposed on a first side <NUM> (i.e. a first axial side of the rotor with reference to the rotation axis of the rotor) of the rotor <NUM> and has a leading side 512A and a trailing side 512B with respect to a direction of rotation in the blower mode (i.e. a direction to compress air flowing through the rotor <NUM>). The expressions leading side and trailing side are not to be confused with the expressions "leading edge" and "trailing edge", which respectively relate to the loci of maximum curvature at upstream and downstream ends of an aerofoil over which a flow passes along a chordwise extent. In contrast, the rotor blades of the present example function as a centrifugal compressor with the flow being generally radial along the blades. For such blades, the leading side is the side which generally faces the direction of rotation, whereas the trailing side is that which generally opposes the direction of rotation.

The example rotor housing <NUM> defines a circumferentially-extending plenum chamber <NUM> (best shown in <FIG>) on a first side (i.e. a first axial side of the housing with reference to the rotation axis of the rotor) which comprises a plurality of impingement ports <NUM>. In a variant example, the rotor housing <NUM> may only comprise a single impingement port. The plenum chamber <NUM> is configured to receive compressed air from an external air source. Each of the plurality of impingement ports <NUM> are configured to direct air from the plenum chamber <NUM> onto the rotor <NUM> (in this example, onto the first side) to impinge onto the blades <NUM> and thereby cause the rotor <NUM> to rotate in the engine drive mode. In this example, the plenum chamber <NUM> and each of the plurality of impingement ports <NUM> is located in a radially outer region of the rotor housing so that the impingement ports direct flow onto a radially outer region of the blades <NUM>.

The plurality of impingement ports <NUM> are configured to direct air onto the trailing side 512B of each rotor blade <NUM> and thereby cause the rotor <NUM> to rotate. The plurality of impingement ports <NUM> are configured so that the rotor <NUM> rotates in the same direction in both the blower mode and the engine drive mode.

An airframe discharge port <NUM> is configured to receive air from the first axial side <NUM> of the rotor <NUM> in the blower mode. Accordingly, in the example of <FIG>, the airframe discharge port <NUM> and the or each impingement port <NUM> is configured to receive air from and to direct air onto the same axial side <NUM> of the rotor <NUM>. Therefore, the first side <NUM> of the rotor <NUM> is configured to function as a compressor in the blower mode and also to function as a turbine in the engine drive mode of the blower system <NUM>. The rotor <NUM> is therefore able to operate as both a compressor and a turbine in respective modes of the blower system <NUM> while remaining geometrically compact and lightweight.

The rotor housing <NUM> may further define a diffuser <NUM> disposed around and outside of a periphery of the rotor <NUM> (i.e. outside of the region circumscribed by the rotor tips). The diffuser <NUM> may be, for example, a variable height diffuser which may be adjusted so as to modify a compression performance of the rotor <NUM> in the blower mode. In the example of <FIG>, the airframe discharge port <NUM> is shown as being disposed around the diffuser <NUM> of the rotor <NUM>. However, it will be appreciated that in other examples, the airframe discharge port <NUM> may be otherwise disposed with respect to the rotor <NUM> so as to receive air from the first axial side <NUM> of the rotor <NUM> in the blower mode.

<FIG> show an axial view and a detailed perspective view, respectively, of a second example rotor <NUM> disposed within a second example rotor housing <NUM>. The rotor <NUM> comprises a plurality of rotor blades <NUM> and is configured to function as a centrifugal compressor in the blower mode. Each of the plurality of rotor blades <NUM> is disposed on a first axial side <NUM> of the rotor <NUM> and has a leading side 612A and a trailing side 612B with respect to a direction of rotation in the blower mode. The direction of rotation in the blower mode is the rotational direction in which the rotors would cause compression of the respective flow. The direction of rotation may be specified by the mechanical connection of the rotor <NUM> to the engine spool as described above.

The rotor housing <NUM> defines a plurality of impingement ports <NUM> for use in the engine drive mode. Each of the plurality of impingement ports <NUM> extends through the rotor housing <NUM> and is configured to receive compressed air from an external air source and to direct air onto the rotor <NUM> to thereby cause the rotor <NUM> to rotate. In this example, each of the plurality of impingement ports <NUM> is located outside of a periphery <NUM> of the rotor <NUM> (i.e. outside of a region circumscribed by rotation of the rotor tips). In addition, each of the plurality of impingement ports <NUM> has a substantially circular cross-section in this example. However, it will be appreciated that in other examples, each of the plurality of impingement ports <NUM> may have a cross-section of any suitable geometry.

Specifically, the plurality of impingement ports <NUM> are configured to direct air onto the trailing side 612B of each rotor blade <NUM> to cause the rotor <NUM> to rotate in the same direction of rotation as in the blower mode.

Each of the plurality of impingement ports <NUM> extends through the rotor housing <NUM> at an extension angle which enables air to be directed onto the trailing side 612B of each rotor blade <NUM> at a predetermined impingement angle with respect to a radial direction from the rotation axis of the rotor through the respective impingement port. The predetermined impingement angle may be selected to as to optimise a turbine efficiency of the rotor <NUM> when functioning as a turbine in the engine drive mode of the blower system <NUM>. The predetermined impingement angle may be, for example, between <NUM> degrees and <NUM> degrees. Preferably, the predetermined impingement angle may be between <NUM> degrees and <NUM> degrees. More preferably, the predetermined impingement angle may be approximately <NUM> degrees.

As in the example of <FIG>, an airframe discharge port and the or each impingement port <NUM> is configured to receive air from and to direct air onto the same side <NUM> of the rotor <NUM>.

<FIG> shows a radial view (i.e. along a radial axis with respect to the rotation axis of the rotor) of a third example rotor <NUM> disposed within a third example rotor housing <NUM>. The rotor <NUM> is generally configured to function as a centrifugal compressor in the blower mode and as a turbine in the engine drive mode, as in the first and second example rotors and rotor housing as described above. The rotor <NUM> comprises a plurality of compressor blades <NUM> disposed on a first side <NUM> of the rotor <NUM>. Each of the plurality of compressor blades <NUM> is configured to direct air toward the airframe discharge port in the blower mode in the same manner as the rotor blades <NUM>, <NUM> of the first and second examples. In addition, the rotor <NUM> comprises a plurality of turbine blades <NUM> disposed on a second axial side <NUM> of the rotor <NUM>, wherein the second side <NUM> opposes the first side <NUM>. The first and second sides may be separated by a wall of the rotor <NUM> that prevents flow migrating from one side of the other. For example, the wall may take the form of a disc forming a base of impeller channels defined between the compressor blades <NUM> on the first side.

The rotor housing <NUM> defines a plurality of impingement ports <NUM> axially adjacent the rotor <NUM> on the second side. Each of the plurality of impingement ports <NUM> extends through the rotor housing <NUM> and is configured to receive compressed air from an external air source and to direct the air onto the second side <NUM> of the rotor <NUM> to cause the rotor <NUM> to rotate, and to rotate in the same direction as the direction of rotation of the compressor blades <NUM> to cause compression in the blower mode.

The plurality of turbine blades <NUM> disposed on the second side <NUM> are configured for expanding air when driven to rotate by the air, whereas the plurality of compressor blades <NUM> disposed on the first side <NUM> are configured for compressing air when mechanically driven to rotate. In other words, the first side <NUM> of the rotor <NUM> is adapted to function as a compressor, while the second side <NUM> of the rotor <NUM> is adapted to function as a turbine. In this particular example, the second side <NUM> is adapted to function as a reaction turbine.

By providing separate compressor and turbine blades, a geometry of each of the plurality of rotor blades <NUM> may be selected so as to optimise a compressor efficiency of the rotor <NUM> when functioning as a compressor in the blower mode without any need to compromise a turbine efficiency of the rotor <NUM> when functioning as a turbine in the engine drive mode. Likewise, a geometry of each of the plurality of turbine blades <NUM> may be selected so as to optimise the turbine efficiency of the rotor <NUM> when functioning as a turbine in the engine drive mode without any impact on the compressor efficiency of the rotor <NUM> when functioning as a compressor in the blower mode. As a result, both the compressor efficiency and the turbine efficiency of the rotor <NUM> may be somewhat optimised without a need for variable geometry features within the rotor <NUM> or the rotor housing <NUM>, such as rotatable vanes.

<FIG> shows a rear view of a sector of a fourth example rotor <NUM> disposed within a fourth example rotor housing <NUM>. The fourth example rotor <NUM> is similar to the third example rotor <NUM> described above with reference to <FIG> in that it comprises a plurality of turbine blades <NUM> disposed on a second side <NUM> of the rotor <NUM> which opposes a first side thereof. The first side of the rotor <NUM> comprises a plurality of compressor blades as described above with reference to <FIG>, with the rotor <NUM> being configured to have its respective functions when rotating in the same direction in each of the respective modes. However, in contrast to the third example rotor housing <NUM>, the fourth example rotor housing <NUM> defines a plurality of impingement ports <NUM> which are disposed radially outward of a periphery <NUM> of the rotor <NUM>.

Each of the plurality of impingement ports <NUM> is configured to receive compressed air from an external air source and to direct air onto the second side <NUM> of the rotor <NUM> to cause the rotor <NUM> to rotate.

<FIG> shows a perspective view of a second side <NUM> of a fifth example rotor <NUM> which opposes a first side thereof. The first side of the rotor <NUM> comprises a plurality of compressor blades as described above with reference to <FIG>. The second side <NUM> comprises a plurality of impulse scoops <NUM>. The plurality of impulse scoops <NUM> are configured to receive air from respective impingement ports such as those described with reference to the third and fourth examples above, so as to be driven to rotate in the engine drive mode (once again, in the same direction of rotation as that in the blower mode when the rotor is mechanically driven by the engine spool to compress air).

However, while the plurality of turbine blades of the third example rotor <NUM> and of the fourth example rotor <NUM> are configured such that the second side of the rotor functions as a reaction turbine in the engine drive mode, the plurality of impulse scoops <NUM> are configured such that the second side <NUM> functions as an impulse turbine in the engine drive mode. The plurality of impulse scoops <NUM> may provide a more geometrically compact and lightweight rotor <NUM> than the example rotors <NUM>, <NUM> which comprise a plurality of turbine blades <NUM>, <NUM> as shown in <FIG> and <FIG>.

For illustrative purposes, the plurality of scoops <NUM> shown in Figure 9A comprises a first scoop 919A, a second scoop 919B and a third scoop 919C. In the example of <FIG>, each scoop has a different geometry and construction to illustrate various forms which such scoops may take. However, it will be appreciated that in other examples, each of the plurality of scoops <NUM> may have a substantially identical geometry and construction to one another. In addition, the plurality of scoops <NUM> may comprise any number of scoops.

In a similar way to the third example rotor <NUM> and the fourth example rotor <NUM>, the fifth example rotor <NUM> is configured to function as a centrifugal compressor in the blower mode. Likewise, the airframe discharge port is configured to receive air from a first side of the rotor <NUM> in the blower mode, whereas the or each impingement port is configured to direct air onto the second side <NUM> of the rotor <NUM> in the engine drive mode.

The first scoop 919A has a complex geometry comprising a protruding guide which protrudes beyond a substantially continuous surface of the second side to direct air into a blind hole of the first scoop. It may therefore be particularly complex to manufacture and may be associated with inefficiencies when the rotor <NUM> is operating as a compressor in the blower mode. The alternative second scoop 919B has a simpler construction without a protruding guide over a blind hole. However, it may be that a thickness of the second side <NUM> of the rotor <NUM> may be insufficient (or a thickness is required to increase) to allow the second scoop 919B to have sufficient depth for its purpose without compromising the integrity of the rotor <NUM> or breaking through to the first side of the rotor. The further alternative third scoop 919C is similar in geometry and construction to the second scoop 919B but is disposed on a step 919C' which provides additional local thickness to the rotor <NUM> in the region proximal to the third scoop 919C. The third scoop 919C is considered to provide a particularly good balance of manufacturing complexity, performance and weight.

<FIG> shows a side view of a sector of an example rotor housing <NUM>, the features of which may be combined with any of the example rotor housing described above. As shown in <FIG>, a blower system <NUM> according to the present disclosure may be configured to provide a recirculation pathway for recirculating compressed air from the rotor in the blower mode. The recirculation pathway may include a plurality of impingement ports (illustrated with reference numeral <NUM> in <FIG>), such that the or each impingement port functions as a recirculation bleed port in the blower mode in addition to providing the respective function of an impingement port to cause the rotor to rotate in the engine drive mode. The example rotor housing <NUM> defines a plurality of impingement ports <NUM>, wherein each impingement port <NUM> also functions, in the blower mode, as a recirculation bleed port.

<FIG> shows an aircraft <NUM> comprising a blower system <NUM> as described above with reference to <FIG> (optionally modified according to any of the further examples). <FIG> shows an aircraft comprising a gas turbine engine <NUM> in accordance with the gas turbine engine <NUM> described above with respect to <FIG>.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. In particular, while various embodiments which comprise a rotor configured to function as a centrifugal compressor in the blower mode have been described and illustrated, it will be understood that other embodiments may comprise a rotor configured to function as an axial compressor in the blower mode. In addition, while the present disclosure primarily concerns blower systems for providing air to a cabin of an aircraft, the disclosed blower systems may also be used for providing air to other structures.

Claim 1:
A blower system (<NUM>) for providing air to an airframe system (<NUM>), comprising:
a rotor (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to be mechanically coupled to a spool (<NUM>) of a gas turbine engine (<NUM>), the rotor comprising a plurality of compressor blades on a first side of the rotor and a plurality of turbine blades (<NUM>, <NUM>) or a plurality of impulse scoops (<NUM>) on a second side of the rotor;
wherein the rotor is configured to:
in a blower mode, be driven to rotate in a first direction by the spool and to function as a centrifugal compressor, the plurality of compressor blades on the first side of the rotor configured to direct air to an airframe discharge port (<NUM>, <NUM>) for supply to the airframe system; and
in an engine drive mode, receive air from an external air source (<NUM>) via one or more impingement ports (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to direct the received air onto the plurality of turbine blades or the plurality impulse scoops on the second side of the rotor and thereby drive the rotor to rotate the same first direction to drive the spool to rotate.