Patent Description:
Vanes are commonly arranged in a circumferential array spanning an annulus through which a working fluid is directed. A vane typically comprises an aerofoil with a pressure side wall and a suction side wall which meet one another at a leading edge and a trailing edge. The pressure and suction side walls border a central chamber into which cooling air may be delivered through a radially directed inlet. An array of outlets is commonly provided adjacent the trailing edge of the vane. The outlets are directed to deliver spent cooling air into the main working fluid flow which is directed over the pressure side wall and suction side wall.

The provision of air systems, in particular cooling-air systems for gas turbine engines, is known. Often, such systems when provided for cooling purposes in the hot section of the engine are dimensioned or designed such that they give adequate cooling under the most adverse conditions, for example at maximum power and the associated highest temperature ranges. Commonly, the source of cooling air is air taken off from the compressor.

During different operating conditions, the temperature of the hot section varies and can often be below the highest experienced. Consequently, non-adaptive cooling systems can result in excessive air mass flow and overcooling under operating conditions requiring lesser cooling. A larger air mass than is needed is supplied to the turbine and subsequently exhausted. Where the cooling air is sourced from the compressor, the efficiency of the turbine is compromised leading to increased specific fuel consumption and in the case of aircraft powered by such engines, the range of the aircraft may be reduced.

Prior published US patent <CIT> seeks to address the described limitations by introducing adaptive valve control. An embodiment described in <CIT> is reproduced in <FIG>.

<CIT>, <CIT>, <CIT> and <CIT> disclose examples of cooled vanes.

<FIG> shows, in highly simplified representation, a side view of a partial area of an aircraft gas turbine. A combustion chamber is here indicated by the reference numeral <NUM>. A downstream turbine features a turbine casing <NUM> within which stator vanes <NUM> of a first stage and rotor blades <NUM> of the first stage are shown. The rotor blades <NUM> are attached to a rotor disk <NUM> of the first stage in a conventional manner.

Further in the downstream direction, a stator vane <NUM> of a second stage is shown which is associated with a rotor blade <NUM> of the second stage, this rotor blade <NUM> again being attached to a rotor disk <NUM> of the second stage. Reference numeral <NUM> indicates a turbine exit guide vane.

<FIG> further shows, in highly simplified form, a piston-cylinder unit <NUM> which is a part of an embodiment of the device for air mass flow control according to the present invention. The piston-cylinder unit <NUM> is located in the area of an inlet duct <NUM>, exposed to a cooling air flow, with flow in the inlet duct issuing into an air duct <NUM> branching off from the inlet duct <NUM>. The inlet duct <NUM> and air duct <NUM> may, for example, be used for ducting air from the cooling air flow to cool the stator vanes <NUM> or <NUM>, respectively.

In the downstream direction, a counter-pressure duct <NUM> is provided by which pressure, for instance, from the turbine section of the engine, is applied to the rearward area of the piston <NUM> of the piston-cylinder unit <NUM>. Furthermore, the piston-cylinder unit <NUM> comprises a spring <NUM> by which a suitable pre-load is applied to the piston <NUM> to bias the piston in the desired direction.

During operations with a high pressure difference, the pressure force in the inlet duct <NUM> exceeds the sum of the pressure force in the counter-pressure duct and of the pre-load force of the spring <NUM>. The piston <NUM> is accordingly displaced such that the flow area of the air duct <NUM> is cleared. During operations with a low pressure difference, the pressure force in the counter-pressure duct <NUM>, together with the pre-load force applied by the spring <NUM>, exceeds the pressure force in the inlet duct <NUM>, with the effect that the piston <NUM> is displaced to partly cover the free cross-section of the air duct <NUM>, thus reducing the supply of air.

The present invention seeks further to make efficient use of air flows for the purposes of cooling vanes.

In a first aspect the invention provides a vane cooling system for a gas turbine engine as set out in claim <NUM>. Optional features are included in the dependent claims.

At lower power operation, the vane is cooled by cooling fluid from the first cooling fluid feed. The pressure and temperature of this feed may be optimized for a known low power operating condition of the engine. For example, this may be a cruising condition. When the engine is operating at this known condition, the flow adjustment device may be partially or wholly closed to maintain a low constant flow or cease flow entirely. During operations which require higher power (and so increased cooling effort), the flow adjustment device may be adjusted to increase the flow introducing a top-up of cooling fluid from the second cooling fluid feed.

The first and second cooling fluids may tap from the same location on the compressor or different locations on the compressor. For example, the first and/or second cooling fluid feeds may tap off upstream of the outlet guide vane (OGV) of the compressor.

The flow adjustment device may have a simple open-closed configuration. Alternatively, the flow adjustment device may be variable to provide a variable range of settings when open as well as a closed setting.

The radially outer inlet crosses an axially extending annular cavity between a radially outer casing and the radially outer end of the vane. Optionally, the radially outer inlet is arranged in fluid communication with the axially extending annular cavity.

Between vanes, the axially extending annular cavity is defined by the radially outer casing and a segmented annular blade ring. Within an engine, the segmented annular blade ring sits radially adjacent tips of rotating blades of a rotor arranged axially adjacent the stator. Segments of the annular blade ring are suspended from a radially inner surface of the radially outer casing, for example by means of segment hooks. The segments may define one or more radially inwardly directed gaps through which cooling fluid may pass from the axially extending annular cavity into an annulus in which the vane is located.

In some embodiments, the segments and adjacent radially outer casing may be configured to maintain a constant pressure in the axially extending annular cavity when cooling air enters the radially outer inlet. In an option, this may be achieved by dividing the annular space bounded by the casing and the segment into multiple compartments each in fluid communication. Entry and exit holes connecting the compartments may be proportioned to balance pressures within the axially extending annular cavity. Such an arrangement can discourage seal leakage to beneficially direct more cooling fluid to surfaces in need of cooling.

In a second aspect the invention provides a gas turbine engine as set out in claim <NUM>. Optional features are included in the dependent claims.

Embodiments of the invention will now be described with reference to the accompanying Figures in which:.

<FIG> has been described in more detail above.

<FIG> shows a stator vane <NUM> spanning an annulus <NUM> of a gas turbine engine the vane has a hollow cavity <NUM> which has a radially inner inlet <NUM> and a radially outer inlet <NUM>. Along a trailing edge of the stator vane is an array of outlets <NUM> opening through the wall of the vane <NUM> and directed in line with a flow of working fluid <NUM> flowing through the annulus <NUM>. Axially upstream of the vane <NUM> (with respect to the direction of flow <NUM> of the working fluid), is a compressor (not shown). A first feed <NUM> is tapped from the compressor. The feed is arranged in fluid communication with the radially outer inlet <NUM>. The feed <NUM> entering the radially outer inlet <NUM> may be controlled by means of a flow restrictor <NUM> obstructing a path of the feed <NUM> to the inlet <NUM>. The feed <NUM> may be opened or closed by means of valve <NUM>. The inlet <NUM> passes through an annular casing <NUM> into the cavity <NUM> crossing an axially extending annular cavity <NUM>. Downstream of the vane <NUM>, the axially extending annular cavity <NUM> is bounded on a radially inward side and an axially downstream side by a segmented ring <NUM>. Segments of the segmented ring <NUM> are suspended from the casing <NUM> by means of suspension hooks <NUM>.

Rear inner <NUM> and rear outer <NUM> discharge flows are drawn into the annulus <NUM> to join the working fluid flow <NUM>. A flow may pass through a sloped bulk head <NUM> via one or more orifices <NUM>.

A second feed <NUM> supplies a radially inner inlet <NUM>. Proportions of orifice <NUM> and inlet <NUM> are selected so as optimize cooling flow in the cavity <NUM> for a cruising operation of the engine. During a cruising operation the valve <NUM> to first feed <NUM> may be closed. During a higher power operation such as maximum take-off, the valve <NUM> is opened allowing the flow in the cavity <NUM> to be topped up with air from feed <NUM>. The valve <NUM> may be adjustable to provide an optimum flow for the operating condition.

A flow <NUM> passes into the axially extending annular cavity <NUM> and a pressure differential downstream of the vane throat <NUM> draws a portion back into the working fluid flow <NUM> in the annulus <NUM> via a gap <NUM> between a chordal seal and the segmented ring, and a gap <NUM> between or through the seal segments. A further portion of the flow <NUM> may be exhausted.

<FIG> shows a second embodiment of a vane cooling system in accordance with the invention. The arrangement has many features in common with the arrangement of <FIG>.

A stator vane <NUM> spanning an annulus <NUM> of a gas turbine engine the vane has a hollow cavity <NUM> which has a radially inner inlet <NUM> and a radially outer inlet <NUM>. Along a trailing edge of the stator vane is an array of outlets <NUM> opening through vane <NUM> and directed in line with a flow of working fluid <NUM> flowing through the annulus <NUM>. Axially upstream of the vane <NUM> (with respect to the direction of flow <NUM> of the working fluid), is a compressor (not shown). A first feed <NUM> is tapped from the compressor upstream. The feed is arranged in fluid communication with the radially outer inlet <NUM>. The feed <NUM> entering the radially outer inlet <NUM> may be controlled by means of a flow restrictor <NUM> obstructing a path of the feed <NUM> to the inlet <NUM>. The feed <NUM> may be opened or closed by means of valve <NUM>. The inlet <NUM> passes through an annular casing <NUM> into the cavity <NUM> crossing an axially extending annular cavity <NUM>. Downstream of the vane <NUM>, the axially extending annular cavity <NUM> is bounded on a radially inward side and axially rearward by a segmented ring <NUM>. Segments of the segmented ring <NUM> are suspended from the casing <NUM> by means of suspension hooks <NUM>.

A second feed <NUM> supplies a radially inner inlet <NUM>. Proportions of orifice <NUM> and inlet <NUM> are selected so as optimize cooling flow in the cavity <NUM> for a cruising operation of the engine. During a cruising operation the valve <NUM> to first feed <NUM> is closed or turned to a constant low flow. During a higher power operation such as maximum take-off, the valve <NUM> is opened allowing the flow in the cavity <NUM> to be topped up with air from feed <NUM>. The valve <NUM> may be adjustable to provide an optimum flow for the operating condition.

In contrast to the embodiment of <FIG>, the space between the casing <NUM> and radially adjacent segment <NUM> is divided so as to define three compartments 64a, 64b, 64c. As can be seen, the compartments are in serial fluid communication provided by holes between compartments 64a and 64b and a hole between compartment 64b and 64c. Pressure differentials across the dividing walls between the compartments encourage impingement of leakage air 71a along a radially inner surface of the casing <NUM> to assist cooling. Spent air 71b is directed back through the segment and exits 71c to re-join the main work fluid flow <NUM> at a position just downstream of a throat plane <NUM> of a blade which sits adjacently downstream of the vane.

<FIG> shows a third embodiment of the invention, the arrangement has many features in common with the embodiment of <FIG>. The Figure shows a stator vane <NUM> spanning an annulus <NUM> of a gas turbine engine the vane <NUM> has a hollow cavity <NUM> which has a radially inner inlet <NUM> and a radially outer inlet <NUM>. The cavity is divided by a wall 423a. The wall 423a extends substantially in parallel with a pressure surface side wall of the vane <NUM>. The radially inner inlet <NUM> enters the cavity to a first side of the wall 423a and the radially outer inlet <NUM> enters the cavity to an opposite side of the wall 423a.

Along a trailing edge of the stator vane <NUM> is an array of outlets <NUM> opening into a throat plane <NUM> of the vane <NUM> and directed in line with a flow of working fluid <NUM> flowing through the annulus <NUM>. Axially upstream of the vane <NUM> (with respect to the direction of flow <NUM> of the working fluid), is a compressor (not shown). A first feed <NUM> is tapped from the compressor upstream. The feed is arranged in fluid communication with the radially outer inlet <NUM>. The feed <NUM> entering the radially outer inlet <NUM> may be controlled by means of a flow restrictor <NUM> obstructing a path of the feed <NUM> to the inlet <NUM>. The feed <NUM> may be opened or closed by means of valve <NUM>. The inlet <NUM> passes through an annular casing <NUM> into the cavity <NUM> crossing an axially extending annular cavity <NUM>. Downstream of the vane <NUM>, the axially extending annular cavity <NUM> is bounded on a radially inward side and an axially downstream side by a segmented ring <NUM>. Segments of the segmented ring <NUM> are suspended from the casing <NUM> by means of suspension hooks <NUM>.

A plurality of outlets <NUM> is arranged along the pressure side wall surface of the vane <NUM>. A second feed <NUM> supplies a radially inner inlet <NUM>. Proportions of orifice <NUM> and inlet <NUM> are selected so as optimize cooling flow in the pressure side wall side of the cavity <NUM> for a cruising operation of the engine. During a cruising operation the valve <NUM> to first feed <NUM> may be closed. Coolant supplied to the radially inner inlet <NUM> travels into the pressure side wall side cavity and exits through the outlets <NUM> to join the oncoming work fluid flow <NUM> as it passes through a passage between circumferentially adjacent vanes.

During a higher power operation such as maximum take-off, the valve <NUM> is opened allowing flow into cavity <NUM> from feed <NUM>. The valve <NUM> may be adjustable to provide an optimum flow for the operating condition. Spent coolant flow joins the main work fluid flow as it exits via the outlets <NUM>.

<FIG> shows a fourth embodiment of the invention, the arrangement has many features in common with the embodiment of <FIG>.

The figure shows a stator vane <NUM> spanning an annulus <NUM> of a gas turbine engine the vane has a hollow cavity <NUM> which has a radially inner inlet <NUM> and a radially outer inlet <NUM>. The cavity is divided by a wall 553a. The wall 553a extends substantially in parallel with a pressure surface side wall of the vane <NUM>. The radially inner inlet <NUM> enters the cavity to a first side of the wall 553a and the radially outer inlet <NUM> enters the cavity to an opposite side of the wall 553a.

Along a trailing edge of the stator vane <NUM> is an array of outlets <NUM> opening through vane <NUM> and directed in line with a flow of working fluid <NUM> flowing through the annulus <NUM>. Axially upstream of the vane <NUM> (with respect to the direction of flow <NUM> of the working fluid), is a compressor (not shown). A first feed <NUM> is tapped from the compressor upstream. The feed <NUM> is arranged in fluid communication with the radially outer inlet <NUM>. The feed <NUM> entering the radially outer inlet <NUM> may be controlled by means of a flow restrictor <NUM> obstructing a path of the feed <NUM> to the inlet <NUM>. The feed <NUM> may be opened, closed or have its flow adjusted by means of valve <NUM>. The inlet <NUM> passes through an annular casing <NUM> into the cavity <NUM> crossing an axially extending annular cavity <NUM>. Downstream of the vane <NUM>, the axially extending annular cavity <NUM> is bounded on a radially inward side and axially rearward by a segmented ring <NUM>. Segments of the segmented ring <NUM> are suspended from the casing <NUM> by means of suspension hooks <NUM>.

A plurality of outlets <NUM> is arranged along the pressure side wall surface of the vane <NUM>. A second feed <NUM> supplies a radially inner inlet <NUM>. Proportions of orifice <NUM> and inlet <NUM> are selected so as optimize cooling flow in cavity <NUM> for a cruising operation of the engine. During a cruising operation the valve <NUM> to first feed <NUM> is closed. Coolant supplied to the radially inner inlet <NUM> travels into the pressure side wall side cavity and exits through the outlets <NUM> to join the oncoming work fluid flow <NUM> as it passes through a passage between circumferentially adjacent vanes.

During a higher power operation such as maximum take-off, the valve <NUM> is opened allowing flow into the suction side wall side of the cavity <NUM> from feed <NUM>. The valve <NUM> may be adjustable to provide an optimum flow for the operating condition. Spent coolant flow joins the main work fluid flow <NUM> as it exits the outlets.

Claim 1:
A vane cooling system for a gas turbine engine, the vane cooling system comprising:
a vane (<NUM>,<NUM>,<NUM>,<NUM>) arranged on a stator and having a cavity (<NUM>,<NUM>,<NUM>,<NUM>) extending continuously from a radially inner end to a radially outer end of the vane (<NUM>,<NUM>, <NUM>,<NUM>),
wherein the vane (<NUM>,<NUM>, <NUM>,<NUM>) has a radially inner inlet <NUM>,<NUM>,<NUM>,<NUM> and a radially outer inlet (<NUM>,<NUM>,<NUM>,<NUM>);
a second cooling fluid feed (<NUM>,<NUM>,<NUM>,<NUM>) in communication with the radially inner inlet (<NUM>,<NUM>,<NUM>,<NUM>) and a first cooling fluid feed (<NUM>,<NUM>,<NUM>,<NUM>) in communication with the radially outer inlet (<NUM>,<NUM>,<NUM>,<NUM>); wherein the second cooling fluid feed (<NUM>,<NUM>,<NUM>,<NUM>) has a higher pressure than the first cooling fluid feed (<NUM>,<NUM>,<NUM>,<NUM>);
characterised in that:
the radially outer inlet (<NUM>,<NUM>,<NUM>,<NUM>) crosses an axially extending annular cavity (<NUM>,<NUM>,<NUM>,<NUM>) between a radially outer casing (<NUM>,<NUM>,<NUM>,<NUM>) and the radially outer end of the vane (<NUM>,<NUM>,<NUM>,<NUM>) and the radially outer inlet (<NUM>,<NUM>,<NUM>,<NUM>) is arranged in fluid communication with the axially extending annular cavity (<NUM>,<NUM>,<NUM>,<NUM>), wherein downstream of the vane (<NUM>,<NUM>, <NUM>,<NUM>), the axially extending annular cavity (<NUM>,<NUM>,<NUM>,<NUM>) is defined by a radially outer casing (<NUM>,<NUM>,<NUM>,<NUM>) and a segmented annular blade ring (<NUM>), segments of the annular blade ring (<NUM>) being suspended from a radially inner surface of the radially outer casing (<NUM>,<NUM>,<NUM>,<NUM>); and the vane cooling system has a flow adjustment device (<NUM>,<NUM>,<NUM>,<NUM>) arranged for adjusting a flow of the first cooling fluid feed into the radially outer inlet (<NUM>,<NUM>,<NUM>,<NUM>).