Patent Description:
In an aerospace gas turbine engine, pressurized air may be used to control the operation of a pneumatically-operated compressor bleed valve that may be selectively opened and closed to maintain the operability of the gas turbine engine. Depending on the operating conditions of the gas turbine engine and on the source of the pressurized air, some debris could potentially be carried by the pressurized air and the presence of such debris in the pressurized air delivered to the compressor bleed valve may not be desirable.

<CIT> discloses prior art systems for filtering particles from an airflow.

<CIT> discloses a prior art air filtration system for a gas turbine engine pneumatic system.

<CIT> discloses a prior art inertial particle separator for an engine inlet.

According to a first aspect of the present invention, there is provided an orifice pack for delivering pressurized air to a compressor bleed valve as set forth in claim <NUM>.

According to a further aspect of the present invention, there is provided a compressor bleed valve arrangement for selectively bleeding air from a compressor as set forth in claim <NUM>.

According to a further aspect of the present invention, there is provided a gas turbine engine as set forth in claim <NUM>.

The following description discloses systems and methods for feeding pressurized air to a pneumatically-operated compressor bleed valve of a gas turbine engine. In some situations, venting a portion of the pressurized air upstream of the compressor bleed valve may prevent some of the debris carried by the pressurized air from being delivered to the compressor bleed valve. In some situations, ejecting contaminants from the stream of pressurized air upstream of the compressor bleed valve may promote reliability and consistency in the operation of the compressor bleed valve.

The term "connected" may include both direct connection (in which two elements contact each other) and indirect connection (in which at least one additional element is located between the two elements).

The term "substantially" as used herein may be applied to modify any quantitative representation which could permissibly vary without resulting in a change in the basic function to which it is related.

<FIG> illustrates an exemplary gas turbine engine <NUM> (referred hereinafter as "engine <NUM>"), which may be of a type preferably provided for use in subsonic flight of an aircraft. Engine <NUM> may comprise, in serial flow communication, propeller <NUM> through which ambient air is propelled, compressor <NUM> for pressurizing the air, combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and turbine section <NUM> including one or more turbines for extracting energy from the combustion gases. Compressor <NUM> of engine <NUM> may be a multi-stage compressor, and thus may comprise a plurality of axial and/or centrifugal compressor stages. Compressor <NUM>, combustor <NUM> and turbine section <NUM> may be operatively disposed along gas path <NUM> of engine <NUM>. In some embodiments, engine <NUM> may be a reverse-flow turboprop gas turbine engine. Even though <FIG> illustrates a turboprop engine, it is understood that the systems and methods described herein may be incorporated into other types of engines including engines of the turbofan and turboshaft type. It is also understood that the systems and methods described herein may be incorporated into aircraft and ground-based gas turbine engine applications.

Engine <NUM> may include a system <NUM> for feeding pressurized air that is used as "muscle air" to control a function of a compressor bleed valve <NUM> (referred hereinafter as "bleed valve <NUM>") of engine <NUM>. Bleed valve <NUM> may be pneumatically-operated and may be opened to release air from compressor <NUM> to ambient environment <NUM>. Bleed valve <NUM> may be opened to relieve pressure in a portion of gas path <NUM> at a stage of compressor <NUM>. Bleed valve <NUM> may be a poppet valve having a hole, usually round or oval and a tapered plug, usually a disk shape on the end of a shaft. The shaft may guide the plug portion by sliding through a valve guide. A pressure differential may be used to seal the valve and, under certain operating conditions, open the valve. In some embodiments, bleed valve <NUM> may be similar to the type of air bleed valve disclosed in <CIT>. System <NUM> may receive pressurized air from gas generator casing <NUM> of engine <NUM> and may distribute the pressurized air between bleed valve <NUM> and ambient environment <NUM> (e.g. atmosphere) as explained below.

The function of bleed valve <NUM> may be controlled by forces acting on opposite sides of bleed valve <NUM> which may relate to the respective air pressures P1, P2 at different locations along gas path <NUM>. In some embodiments of bleed valve <NUM>, a spring may be provided to bias bleed valve <NUM> toward the open or closed position. In reference to <FIG>, pressure P1 may be taken in gas path <NUM> at an intermediate stage of compressor <NUM>, and P2 may be taken in gas path <NUM> downstream of the location of P1. For example, pressure P2 may be taken downstream of compressor <NUM> and upstream of combustor <NUM> so that pressure P2 may be higher than pressure P1. Pressure P2, or another pressure indicative thereof, may be acquired via bleed air taken from gas path <NUM> at the desired location along gas path <NUM>. The system <NUM> comprises an orifice pack <NUM>, <NUM>' configured for delivering "cleaned/decontaminated" bleed air to the bleed valve <NUM>. In some embodiments, pressure P2 may be taken at a location along gas path <NUM> providing the highest pressure within engine <NUM>. Changes in the P1/P2 pressure relationship may cause bleed valve <NUM> to move between the open and closed positions. During operation of engine <NUM>, bleed valve <NUM> may be controlled by P1/P2 to maintain the operability of engine <NUM>. In some situations, bleed valve <NUM> may, for example, prevent compressor stall at relatively low operating speeds of engine <NUM>.

<FIG> illustrates an exemplary embodiment of the orifice pack <NUM>. The orifice pack <NUM> may be provided in the form of a fitting including a vent for discharging contaminants/particles carried by the pressurized air into the ambient environment <NUM>. Conceptually, it can be said that the orifice pack <NUM> is a conduit including an inlet <NUM> for receiving the pressurized (e.g., bleed) air F, a first outlet (e.g. a contaminated air outlet) <NUM> for releasing a first portion F1 of pressurized air F from conduit, and a second outlet (e.g. a clean air outlet) <NUM> for releasing a second portion F2 of pressurized air from the conduit. First portion F1 and second portion F2 of pressurized air F may be different from each other so that F = F1 + F2. Typically, the conduit is configured so that a main portion of the pressurized air F is discharged through the first outlet <NUM> (F1 > F2). The first portion F1 is vented into the atmosphere <NUM> and the second portion F2 is directed to the pneumatically-actuated bleed valve <NUM>. In some embodiments, the inlet <NUM> and the first outlet <NUM> are axially aligned along a central axis of the conduit and the second outlet <NUM> is disposed axially therebetween and oriented along a direction intersecting the central axis. In some embodiments, the inlet <NUM> and the first and second outlets <NUM>, <NUM> may be sized to provide a desired flow rate and pressure drop across each of the inlet orifice and the outlet orifices. Such sizing may be based on specific operating parameters of engine <NUM> and the desired operating behaviour of bleed valve <NUM>. As will be seen hereinafter, the inlet <NUM> and/or the outlets <NUM>, <NUM> may include replaceable inserts to facilitate the use of orifice packs of similar configurations on different engines.

In some embodiments, the orifice pack <NUM> is provided in the form of a "tee" having a body <NUM> including a primary branch defining a diffusion chamber <NUM> between inlet <NUM> and the first outlet <NUM> and a secondary branch branching off at right angles from the primary branch at an axial location of the body <NUM> generally corresponding to a downstream end of the diffusion chamber <NUM>. The secondary branch defines an outlet passage <NUM>' extending through the wall of the diffusion chamber <NUM> in the primary branch. The secondary branch fluidly connects the diffusion chamber <NUM> to the second outlet <NUM>, which is, in turn, connected in fluid communication to a control port of the bleed valve <NUM>.

The diffusion chamber <NUM> is configured for reducing the velocity and increasing the static pressure of the air passing through the system <NUM>. According to some embodiments, the diffusion chamber <NUM> may have a cylindrical configuration, including a constant circular cross-sectional area.

In some embodiments, inlet <NUM> may include an inlet orifice defining a constriction (i.e., narrowing or reduced cross-sectional area of the available flow passage) relative to the diffusion chamber <NUM>. In some embodiments, the inlet <NUM> may include an orifice insert 26a adapted to be removably installed in a central inlet bore 26b of body <NUM>. For instance, the orifice insert 26a may be threadably engaged with an internally threaded portion of the inlet bore 26b. In this way, a set of differently calibrated orifice inserts offering different flow cross-sectional areas may be selectively installed at the inlet end of the body <NUM> according to the flow parameters of the intended application.

As illustrated in <FIG>, according to the invention, the first outlet <NUM> is provided in the form of a vent detachably mounted to an end of the body <NUM> axially opposite to inlet <NUM>. According to the exemplary embodiment shown in <FIG>, the vent is a two-piece body including a tapered extension piece 28a and an outlet orifice piece 28b. As will be seen hereinafter, the tapered extension piece 28a improves the orifice pack's ability to eject contamination to provide cleaner air to the bleed valve <NUM> when fed high pressure air from the gas generator section <NUM>.

Still referring to <FIG>, it can be appreciated that the tapered extension piece 28a defines a tapering passage 28c. The outlet orifice piece 28b defines a first outlet passage 28d. The tapering passage 28c and the first outlet passage 28d are axially aligned in serial flow communication when the two pieces of the vent are assembled to one another. Likewise, the diffusion chamber <NUM> and the tapering passage 28c are aligned longitudinally and sequentially along the central axis of the primary branch of the orifice pack <NUM> when the extension piece 28a is mounted to the body <NUM>. The tapering passage 28c converges towards the central axis in an axial direction away from the diffusion chamber <NUM> (i.e. passage 28c tapers in a downstream direction relative to a flow of air through the orifice pack <NUM>) for venting the first portion F1 of the pressurized air F from the diffusion chamber <NUM>. The tapering passage 28c helps the contaminants travel to the first outlet passage 28d without bouncing back, thereby improving the orifice pack's ability to eject contaminants carried in the air through the outlet passage 28d of the vent. This reduces the chances of contaminants travelling through the second outlet <NUM> and into the bleed valve <NUM>. The extension piece 28a also moves the outlet orifice of the vent further downstream from the secondary outlet <NUM> (i.e. the clean air outlet), which may also improve particle separation.

As shown in <FIG>, the diffusion chamber <NUM> has a diameter (B) and the tapering passage 28c has a length (A) along the central axis. According to at least some embodiments of system <NUM>, a useful range of taper sizes has been determined to be: <NUM> ≤ A/B ≤ <NUM>. However, it is understood that other ranges may be suitable depending on the intended application.

Still referring to <FIG>, according to the invention, the tapering passage 28c has a cross-sectional area at an inlet end that is at least equal to that of the diffusion chamber so as to avoid the presence of a flow constriction at the interface D between the diffusion chamber <NUM> and the downstream tapering passage 28c. The relative sizing of the cross-sectional area of the diffusion chamber <NUM> and the tapering passage <NUM> is selected to eliminate a protrusion into the gas path that could interfere with the contamination particles travelling towards the outlet passage 28d.

According to one or more embodiments, the taper extension piece 28a is threadably mounted to the body <NUM>. According to the embodiment shown in <FIG>, the body <NUM> has a connecting end axially opposite to the inlet <NUM>, the connecting end defining and internally threaded bore <NUM> around the central axis of the primary branch of the body <NUM> at the outlet end of the diffusion chamber <NUM>. The internally threaded bore <NUM> has a diameter greater than that of the diffusion chamber <NUM> to accommodate the extension piece 28a. The taper extension piece 28a has a male end 28a' with external threads for threaded engagement with the internally threaded bore <NUM> of the body <NUM>, thereby allowing the extension piece 28a to be detachably mounted in series with the diffusion chamber <NUM>. The internally threaded bore <NUM> and the male end 28a' of the extension piece 28a are sized so that the male end 28a' of the extension piece 28a does not protrude radially inwardly relative to the diffusion chamber <NUM>.

Like extension piece 28a, the outlet orifice piece 28b has an externally threaded end 28b' threadably engageable with complementary internal threads of a threaded bore 28a" defined at an end of the extension piece 28a opposite to its male end 28a'. The interface C between the downstream end of the extension piece 28a and the outlet orifice piece 28b is sized to minimize steps and gaps that could interfere with the flow of contamination particles. A minimal step can, however, be intentionally provided between the tapered extension piece 28a and outlet orifice piece 28b to help the entire orifice pack assembly continue to produce the necessary pressure for the bleed valve <NUM>.

According to the embodiment shown in <FIG>, it can be appreciated that the first outlet passage 28d has a cross-sectional area which is slightly smaller than the cross-sectional area at an outlet end of the tapering passage 28c, thereby providing for a flow constriction at interface C between the tapering passage 28c and the first outlet passage 28d.

<FIG> illustrates another embodiment which essentially differs from the embodiment shown in <FIG> in that the vent has a monolithic body. Indeed, according to this embodiment, the taper extension piece incorporate the secondary orifice feature, thereby reducing the number of parts in the assembly compared to the arrangement described above with reference to <FIG>. According to this embodiment, the cross-sectional area of the first outlet passage 28d is equal to the cross-sectional area at the outlet end of the tapering passage 28c.

In operation, the orifice pack <NUM>, <NUM>' channels the high-pressure air through the inlet <NUM> into the diffusion chamber <NUM> from which a first portion F1 of the air vents to atmosphere <NUM> through the tapering passage 28c and the first outlet passage 28d. A second portion F2 of the air is tapped from the downstream end of the diffusion chamber <NUM> just upstream of the tapering passage 28c and fed to the bleed valve <NUM> via the second outlet <NUM>. Any contamination taken from the gas generator case <NUM> will pass through the orifice pack inlet <NUM> and the major part will vent to atmosphere <NUM> through the first outlet <NUM>. The tapering passage 28c extending axially in continuity from the diffusion chamber <NUM> will help the contamination particles carried by the air to flow toward the first outlet passage 28b, thereby reducing the chances of contaminants travelling to the bleed valve <NUM> via the second outlet <NUM>.

Claim 1:
An orifice pack (<NUM>; <NUM>') for delivering pressurized air to a compressor bleed valve (<NUM>), the orifice pack (<NUM>; <NUM>') comprising:
a body (<NUM>) defining a diffusion chamber (<NUM>) extending along a central axis, the diffusion chamber (<NUM>) having an inlet (<NUM>) fluidly connectable to a source of pressurized air;
a vent (<NUM>) removably mounted to the body (<NUM>), the vent (<NUM>) having a tapering passage (28c), the diffusion chamber (<NUM>) and the tapering passage (28c) aligned longitudinally and sequentially along the central axis when the vent (<NUM>) is mounted to the body (<NUM>), the tapering passage (28c) converging towards a first outlet passage (28d) in an axial direction away from the diffusion chamber (<NUM>) for venting a first portion (F1) of the pressurized air from the diffusion chamber (<NUM>); and
a second outlet passage (<NUM>') branching off from the diffusion chamber (<NUM>) at an axial location between the inlet (<NUM>) and the tapering passage (28c), the second outlet passage (<NUM>') fluidly connectable to the compressor bleed valve (<NUM>) for directing a second portion (F2) of the pressurized air from the diffusion chamber (<NUM>) to the compressor bleed valve (<NUM>);
characterized in that the tapering passage (28c) has a cross-sectional area at an inlet end thereof that is at least equal to that of the diffusion chamber (<NUM>) so as to avoid the presence of a flow constriction at an interface (D) between the diffusion chamber (<NUM>) and the tapering passage (28c).