Patent Description:
Gas turbine engines are known and typically include a fan delivering air into a bypass duct as propulsion air. Further, the fan delivers air into a compressor section where it is compressed. The compressed air passes into a combustion section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate.

It is known to provide cooling air from the compressor to the turbine section to lower the operating temperatures in the turbine section and improve overall engine operation. Typically, air from the high compressor discharge has been tapped, passed through a heat exchanger, which may sit in the bypass duct and then delivered into the turbine section. The air from the downstream most end of the compressor section is at elevated temperatures.

A prior art gas turbine engine, having the features of the preamble of claim <NUM> is provided in <CIT>.

In an aspect of the present invention, a gas turbine engine is provided, as set forth in claim <NUM>.

In another embodiment according to any of the previous embodiments, the second leg is positioned to be upstream of the first leg relative to a flow of bypass air between the core housing and the fan housing.

In another embodiment according to any of the previous embodiments, the first and second legs are provided with structure to increase a cross-sectional surface area of an outer peripheral surface of the first and second legs.

In another embodiment according to any of the previous embodiments, the turbine section drives a gear. The gear further drives the cooling compressor.

In another embodiment according to any of the previous embodiments, the gear also drives an accessory gearbox.

In another embodiment according to any of the previous embodiments, there is an upper bifurcation and a lower bifurcation, and the heat exchanger is in the upper bifurcation.

In another embodiment according to any of the previous embodiments, there is an upper bifurcation and a lower bifurcation, and the heat exchanger is in the lower bifurcation.

In another embodiment according to any of the previous embodiments, the bifurcations extend generally to sides of the core housing and the fan housing and the heat exchanger is in one of the bifurcations.

In another embodiment according to any of the previous embodiments, the valve is in the air inlet.

In another embodiment according to any of the previous embodiments, the valve has a pair of flaps which can pivot outwardly to a closed position and pivot.

toward each other to an open position, and the control controls the position of said flaps.

In another embodiment according to any of the previous embodiments, the valve is mounted in the air outlet.

In another embodiment according to any of the previous embodiments, the valve includes a flap valve pivoting between a position at which it extends outwardly into a bypass duct and to a closed position at which it blocks flow through the outlet.

<FIG> schematically illustrates an example gas turbine engine <NUM> that includes a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section <NUM> drives air along a bypass flow path B while the compressor section <NUM> draws air in along a core flow path C where air is compressed and communicated to a combustor section <NUM>. In the combustor section <NUM>, air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through the turbine section <NUM> where energy is extracted and utilized to drive the fan section <NUM> and the compressor section <NUM>. Although the disclosed non-limiting embodiment depicts a turbofan gas turbine engine, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines; for example a turbine engine including a three-spool architecture in which three spools concentrically rotate about a common axis and where a low spool enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that enables an intermediate pressure turbine to drive a first compressor of the compressor section, and a high spool that enables a high pressure turbine to drive a high pressure compressor of the compressor section.

The example engine <NUM> generally includes a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A relative to an engine static structure <NUM> via several bearing systems <NUM>. It should be understood that various bearing systems <NUM> at various locations may alternatively or additionally be provided.

The low speed spool <NUM> generally includes an inner shaft <NUM> that connects a fan <NUM> and a low pressure (or first) compressor section <NUM> to a low pressure (or first) turbine section <NUM>. The inner shaft <NUM> drives the fan <NUM> through a speed change device, such as a geared architecture <NUM>, to drive the fan <NUM> at a lower speed than the low speed spool <NUM>. The high-speed spool <NUM> includes an outer shaft <NUM> that interconnects a high pressure (or second) compressor section <NUM> and a high pressure (or second) turbine section <NUM>. The inner shaft <NUM> and the outer shaft <NUM> are concentric and rotate via the bearing systems <NUM> about the engine central longitudinal axis A.

A combustor <NUM> is arranged between the high pressure compressor <NUM> and the high pressure turbine <NUM>. In one example, the high pressure turbine <NUM> includes at least two stages to provide a double stage high pressure turbine <NUM>. In another example, the high pressure turbine <NUM> includes only a single stage. As used herein, a "high pressure" compressor or turbine experiences a higher pressure than a corresponding "low pressure" compressor or turbine.

The example low pressure turbine <NUM> has a pressure ratio that is greater than about <NUM>. The pressure ratio of the example low pressure turbine <NUM> is measured prior to an inlet of the low pressure turbine <NUM> as related to the pressure measured at the outlet of the low pressure turbine <NUM> prior to an exhaust nozzle.

The mid-turbine frame <NUM> further supports bearing systems <NUM> in the turbine section <NUM> as well as setting airflow entering the low pressure turbine <NUM>.

Airflow through the core airflow path C is compressed by the low pressure compressor <NUM> then by the high pressure compressor <NUM> mixed with fuel and ignited in the combustor <NUM> to produce high speed exhaust gases that are then expanded through the high pressure turbine <NUM> and low pressure turbine <NUM>. The mid-turbine frame <NUM> includes vanes <NUM>, which are in the core airflow path and function as an inlet guide vane for the low pressure turbine <NUM>. Utilizing the vane <NUM> of the mid-turbine frame <NUM> as the inlet guide vane for low pressure turbine <NUM> decreases the length of the low pressure turbine <NUM> without increasing the axial length of the mid-turbine frame <NUM>. Reducing or eliminating the number of vanes in the low pressure turbine <NUM> shortens the axial length of the turbine section <NUM>. Thus, the compactness of the gas turbine engine <NUM> is increased and a higher power density may be achieved.

The disclosed gas turbine engine <NUM> in one example is a high-bypass geared aircraft engine. In a further example, the gas turbine engine <NUM> includes a bypass ratio greater than about six (<NUM>), with an example embodiment being greater than about ten (<NUM>). The example geared architecture <NUM> is an epicyclical gear train, such as a planetary gear system, star gear system or other known gear system, with a gear reduction ratio of greater than about <NUM>.

In one disclosed embodiment, the gas turbine engine <NUM> includes a bypass ratio greater than about ten (<NUM>:<NUM>) and the fan diameter is significantly larger than an outer diameter of the low pressure compressor <NUM>. It should be understood, however, that the above parameters are only exemplary of one embodiment of a gas turbine engine including a geared architecture and that the present disclosure is applicable to other gas turbine engines.

The fan section <NUM> of the engine <NUM> is designed for a particular flight condition -- typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>). The flight condition of <NUM> Mach and <NUM>,<NUM> ft. (<NUM>), with the engine at its best fuel consumption - also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')" - is the industry standard parameter of pound-mass (lbm) of fuel per hour being burned divided by pound-force (lbf) of thrust the engine produces at that minimum point.

In another non-limiting embodiment the low fan pressure ratio is less than about <NUM>.

"Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R)/(<NUM>°R)]<NUM> (where °R = K x <NUM>/<NUM>). The "Low corrected fan tip speed", as disclosed herein according to one non-limiting embodiment, is less than about <NUM> ft/second (<NUM>/s).

The example gas turbine engine includes the fan <NUM> that comprises in one non-limiting embodiment less than about <NUM> fan blades. In another non-limiting embodiment, the fan section <NUM> includes less than about <NUM> fan blades. Moreover, in one disclosed embodiment the low pressure turbine <NUM> includes no more than about <NUM> turbine rotors schematically indicated at <NUM>. In another non-limiting example embodiment the low pressure turbine <NUM> includes about <NUM> turbine rotors. A ratio between the number of fan blades <NUM> and the number of low pressure turbine rotors is between about <NUM> and about <NUM>. The example low pressure turbine <NUM> provides the driving power to rotate the fan section <NUM> and therefore the relationship between the number of turbine rotors <NUM> in the low pressure turbine <NUM> and the number of blades <NUM> in the fan section <NUM> disclose an example gas turbine engine <NUM> with increased power transfer efficiency.

Gas turbine engines designs are seeking to increase overall efficiency by generating higher overall pressure ratios. By achieving higher overall pressure ratios, increased levels of performance and efficiency may be achieved. However, challenges are raised in that the parts and components associated with a high pressure turbine require additional cooling air as the overall pressure ratio increases.

The example engine <NUM> utilizes air bleed <NUM> from an upstream portion of the compressor section <NUM> for use in cooling portions of the turbine section <NUM>. The air bleed is from a location upstream of the discharge <NUM> of the compressor section <NUM>. The bleed air passes through a heat exchanger <NUM> to further cool the cooling air provided to the turbine section <NUM>. The air passing through heat exchanger <NUM> is cooled by the bypass air B. That is, heat exchanger <NUM> is positioned in the path of bypass air B.

A prior art approach to providing cooling air is illustrated in <FIG>. An engine <NUM> incorporates a high pressure compressor <NUM> downstream of the low pressure compressor <NUM>. As known, a fan <NUM> delivers air into a bypass duct <NUM> and into the low pressure compressor <NUM>. A downstream most point, or discharge <NUM> of the high pressure compressor <NUM> provides bleed air into a heat exchanger <NUM>. The heat exchanger is in the path of the bypass air in bypass duct <NUM>, and is cooled. This high pressure high temperature air from location <NUM> is delivered into a high pressure turbine <NUM>.

The downstream most point <NUM> of the high pressure compressor <NUM> is known as station <NUM>. The temperature T3 and pressure P3 are both very high.

In future engines, T3 levels are expected to approach greater than or equal to <NUM>°F (<NUM>). Current heat exchanger technology is becoming a limiting factor as they are made of materials, manufacturing, and design capability which have difficulty receiving such high temperature and pressure levels.

<FIG> shows an engine <NUM> coming within the scope of this disclosure. A fan <NUM> may deliver air B into a bypass duct <NUM> and into a low pressure compressor <NUM>. High pressure compressor <NUM> is positioned downstream of the low pressure compressor <NUM>. A bleed <NUM> taps air from a location upstream of the downstream most end <NUM> of the high pressure compressor <NUM>. This air is at temperatures and pressures which are much lower than T3/P3. The air tapped at <NUM> passes through a heat exchanger <NUM> which sits in the bypass duct <NUM> receiving air B. Further, the air from the heat exchanger <NUM> passes through a compressor <NUM>, and then into a conduit <NUM> leading to a high pressure turbine <NUM>. This structure is all shown schematically.

Since the air tapped at point <NUM> is at much lower pressures and temperatures than the <FIG> prior art, currently available heat exchanger materials and technology may be utilized. This air is then compressed by compressor <NUM> to a higher pressure level such that it will be able to flow into the high pressure turbine <NUM>.

An auxiliary fan <NUM> may be positioned upstream of the heat exchanger <NUM> as illustrated. The main fan <NUM> may not provide sufficient pressure to drive sufficient air across the heat exchanger <NUM>. The auxiliary fan will ensure there is adequate airflow in the circumferential location of the heat exchanger <NUM>. The auxiliary fan <NUM> may allow the heat exchanger to be made smaller.

In one embodiment, the auxiliary fan may be variable speed, with the speed of the fan varied to control the temperature of the air downstream of the heat exchanger <NUM>. As an example, the speed of the auxiliary fan may be varied based upon the operating power of the overall engine.

<FIG> shows an alternative system. In <FIG>, air, at <NUM>, downstream of the cooling compressor <NUM>, may be delivered through a vane <NUM> which is part of a diffuser downstream of a high pressure compressor <NUM>. The air is shown moving at <NUM> to cool the high pressure compressor <NUM>. Optionally, the air at <NUM> is delivered to cool the high pressure turbine <NUM>. An intermediate combustor <NUM> is shown. In embodiments, the air may flow to both <NUM> and <NUM>, or either. Generically, the airflow downstream of the cooling compressor cools a rotating component, which may be the high pressure compressor, or the high pressure turbine.

If the compressor is cooled, this cooling air will reduce metal temperature arising from the compression process. It is known that the pressures and temperatures seen by the high pressure compressor raises challenges at elevated temperatures and because of thermal gradients as the pressures and temperatures increase. Providing the cooling air at <NUM> to the rear section of the high pressure compressor cools disks and hubs in the high pressure compressor, beneficially.

Referring to <FIG>, a temperature/entropy diagram illustrates that a lower level of energy is spent to compress air of a lower temperature to the desired P3 pressure level. Cooler air requires less work to compress when compared to warmer air. Accordingly, the work required to raise the pressure of the air drawn from an early stage of the compressor section is less than if the air were compressed to the desired pressure within the compressor section. Therefore, high pressure air at P3 levels or higher can be obtained at significantly lower temperatures than T3. As shown in <FIG>, to reach a particular pressure ratio, <NUM> for example, the prior system would move from point <NUM> to point <NUM>, with a dramatic increase in temperature. However, the disclosed or new system moves from point <NUM> to point <NUM> through the heat exchanger, and the cooling compressor then compresses the air up to point <NUM>. As can be appreciated, point <NUM> is at a much lower temperature.

<FIG> shows a detail of compressor <NUM> having an outlet into conduit <NUM>. A primary tower shaft <NUM> drives an accessory gearbox <NUM>. The shaft <NUM> drives a compressor rotor within the compressor <NUM>. The shafts <NUM> and <NUM> may be driven by a bull gear <NUM> driven by a turbine rotor, and in one example, with a high pressure compressor rotor.

<FIG> shows an example wherein a gear <NUM> is driven by the shaft <NUM> to, in turn, drive a gear <NUM> which drives a compressor impeller <NUM>. An input <NUM> to the compressor impeller <NUM> supplies the air from the tap <NUM>. The air is compressed and delivered into the outlet conduit <NUM>.

By providing a gear ratio increase between the compressor impeller <NUM> and the high spool bull gear <NUM>, the compressor impeller may be driven to operate an optimum speed. As an example, the gear increase may be in a range of <NUM>:<NUM> - <NUM>:<NUM>, and in one embodiment, <NUM>:<NUM>.

Details of the engine, as set forth above, may be found in <CIT>.

<FIG> shows a feature of gas turbine engine <NUM>. A core housing <NUM> is shown having a radially outer surface <NUM>. A nacelle or fan housing <NUM> has a radially inner surface <NUM>. A bypass duct receiving bypass air B is defined between the surfaces <NUM> and <NUM>. As known, elements, such as electronic or hydraulic connections (<NUM>, shown schematically), must extend between the housings <NUM> and <NUM>. Thus, so-called bifurcation ducts <NUM> and <NUM> are formed between the two housings. Bifurcation duct <NUM> would be at a vertically lower location while bifurcation duct <NUM> would be at a vertically upper location when the engine is mounted on an aircraft.

<FIG> shows an alternative bifurcation duct arrangement <NUM>. Fan housing <NUM> surrounds the core engine <NUM>. Bifurcations <NUM> and <NUM> extend generally at <NUM>:<NUM> o'clock and <NUM>:<NUM> o'clock directions as opposed to the <NUM>:<NUM>/<NUM>:<NUM> o'clock directions of <FIG> embodiment may be utilized if an engine is mounted on a wing, whereas, the <FIG> embodiment may be utilized for fuselage mounted engines.

The teachings of this disclosure could extend to packaging a heat exchanger in any of these four locations.

A challenge with the engine defined in <FIG> and <FIG> is that placing the heat exchanger in the path of the bypass air blocks the airflow somewhat. There is already blockage from the bifurcation ducts. Thus, the additional blockage may be undesirable for some applications.

As shown in <FIG>, the heat exchanger <NUM> has a first leg portion <NUM> received within the core housing <NUM>, and extending to a leg portion <NUM> within the bifurcation duct <NUM>. A turning portion <NUM> is actually outward of the surface <NUM> and within the fan housing <NUM>. The turning portion <NUM> returns the flow into a second leg <NUM>, which extends back radially toward a center of the engine to an outlet <NUM>. Outlet <NUM> communicates downstream to the cooling compressor <NUM>, which is also within the core housing.

Stated in one way, air is delivered into a heat exchanger first leg <NUM> within the core housing. The leg extends outwardly of the core housing and into the at least one bifurcation duct <NUM>, and to a second leg <NUM> extending back toward a center axis of the engine, and back into the core housing to deliver the air to a cooling compressor <NUM>.

The heat exchanger <NUM> can be said to communicate air from within core housing <NUM>, into bifurcation duct <NUM>, then into fan housing <NUM>. The air then flows back inwardly into bifurcation duct <NUM>, the core housing <NUM> and to a high pressure turbine.

<FIG> also shows an upstream end <NUM> and downstream end <NUM> of the bifurcation duct which receives the heat exchanger.

<FIG> discloses an embodiment according to the invention wherein there are a plurality of legs <NUM> extending through the bifurcation duct to the turning portion <NUM>. In this embodiment, the legs <NUM> may be discrete heat exchanger bodies leading into a common header <NUM>. It should be understood that if the legs <NUM> are the inlets, there also are a plurality of similar outlets. In addition, fins <NUM> are shown schematically to increase the effective area of the outer surface of the legs <NUM>. Any number of other ways of increasing the surface area may be utilized.

<FIG> shows an embodiment wherein the inlet <NUM> leads to the turning portion <NUM>, and then to the outlet <NUM>. As illustrated by the bypass flow B, the outlet leg <NUM> is upstream of the inlet leg <NUM>. In this manner, the air passing across leg <NUM> has not been heated by the hotter air in leg <NUM>.

<FIG> shows the bifurcation duct <NUM> having side walls <NUM>. In the prior art, the bifurcation duct need not allow airflow. However, once the heat exchanger <NUM> is mounted within the bifurcation duct, air desirably passes over the heat exchanger. Thus, an enlarged opening <NUM> is formed on an upstream end and one or more outlets <NUM> are formed on a downstream end.

By placing the heat exchanger within the bifurcation duct, the restriction to flow caused by the inclusion of the heat exchanger is dramatically reduced.

<FIG> shows a bifurcation embodiment <NUM> having a heat exchanger <NUM>. A body <NUM> includes a forward inlet <NUM>, similar to inlet <NUM>, and rear outlets <NUM>, similar to outlet <NUM>. As shown, a valve <NUM> is open in this position to the inlet <NUM> and through the outlets <NUM>. A control <NUM> can control the valve.

As shown in <FIG>, control <NUM> has now moved flaps <NUM> on the valve <NUM> to a closed position at which it blocks flow into the inlet. This will occur when further cooling of the heat exchanger <NUM> is not needed. This will provide more efficient use of the bypass air as the bypass air will not be directed into the bifurcation duct when cooling is not necessary.

<FIG> shows an embodiment <NUM> wherein a heat exchanger <NUM> is positioned within the bifurcation duct. The inlet <NUM> does not receive a valve, but rather the outlets <NUM> receives the valve <NUM>. In this embodiment, the control <NUM> pivots the valves <NUM> as flaps between the illustrated open position, at which airflow is allowed, into a closed position, shown in phantom, at which airflow is prevented. This would operate in a similar manner to the <FIG> embodiment.

Claim 1:
A gas turbine engine (<NUM>; <NUM>) comprising;
a plurality of rotating components housed within a compressor section (<NUM>) and a turbine section (<NUM>);
a tap (<NUM>) connected to said compressor section (<NUM>), a heat exchanger (<NUM>; <NUM>; <NUM>; <NUM>) connected downstream of said tap (<NUM>), and a cooling compressor (<NUM>; <NUM>) connected downstream of said heat exchanger (<NUM>; <NUM>; <NUM>; <NUM>), and said cooling compressor (<NUM>; <NUM>) connected to deliver air to at least one of said rotating components; and
a core housing (<NUM>) having an outer peripheral surface (<NUM>) and a fan housing (<NUM>) defining an inner peripheral surface (<NUM>), at least one bifurcation duct (<NUM>, <NUM>; <NUM>, <NUM>) extending between said outer peripheral surface (<NUM>) to said inner peripheral surface (<NUM>), and said heat exchanger (<NUM>; <NUM>; <NUM>; <NUM>) disposed within said at least one bifurcation duct (<NUM>, <NUM>; <NUM>, <NUM>),
wherein air is delivered into a heat exchanger first leg (<NUM>) within said core housing (<NUM>), the first leg (<NUM>) extending outwardly of said core housing (<NUM>) and into said at least one bifurcation duct (<NUM>, <NUM>; <NUM>, <NUM>), and to a second leg (<NUM>) extending back toward a center axis (A) of the engine (<NUM>; <NUM>), and back into said core housing (<NUM>) to deliver the air to said cooling compressor (<NUM>; <NUM>), and
wherein there is an air inlet (<NUM>; <NUM>; <NUM>) for air to pass over said heat exchanger (<NUM>; <NUM>; <NUM>; <NUM>) in said at least one bifurcation duct (<NUM>, <NUM>; <NUM>, <NUM>) and an air outlet (<NUM>; <NUM>; <NUM>),
characterized in that:
there is a valve (<NUM>; <NUM>) in at least one of said air inlet (<NUM>; <NUM>; <NUM>) and air outlet (<NUM>; <NUM>; <NUM>), and
there are a plurality of first legs (<NUM>) and a plurality of second legs (<NUM>), wherein said plurality of first legs (<NUM>) and said plurality of second legs (<NUM>) communicate with a common header (<NUM>) to turn air from the first legs to the second legs.