Patent Description:
Gas turbines are rotationally coupled to a load, such as a generator, by a load coupling. The load coupling includes, for example, a shaft that couples at a forward end to the rotor shaft of the gas turbine and at a rearward end to a rotating shaft of the load. A number of bearings may be used to rotationally support the rotor shaft, the load coupling, and the rotating shaft of the load. The load coupling extends through a tunnel, e.g., a cylindrical housing, within an exhaust housing of the gas turbine. Exhaust from the gas turbine passes through the exhaust housing radially externally of the tunnel. Cooler gas than the exhaust may enter the tunnel from a forward end thereof to provide some cooling of the load coupling. The load coupling may also be cooled by circulating air toward a rearward end of the load coupling and the exhaust housing using external blowers.

<CIT> discloses a gas turbine engine system, comprising a gas turbine including a rotor shaft and an exhaust housing, a load coupling coupled to a rear end of the rotor shaft of the gas turbine and extending through the exhaust housing of the gas turbine, and a system for cooling the load coupling. The system for cooling the load coupling comprises a shroud in the form a cylindrical heat insulating material which is mounted about the load coupling to define an inlet passage between the shroud and the load coupling. The system further comprises an outlet passage in the form of a vent pipe which is passed through the heat insulating material. The system further comprises a fan including a set of blades which are coupled to the load coupling and arranged to draw air into the inlet passage as the set of blades rotates with the load coupling, wherein the air is then discharged to the outside through the vent pipe.

<CIT> discloses gas turbine engine system, comprising a gas turbine including a rotor shaft and an exhaust housing which defines an exhaust gas passage, a load coupling coupled to a rear end of the rotor shaft of the gas turbine and extending through the exhaust housing of the gas turbine, and a system for cooling the load coupling, the system comprising a shroud in the form a cylindrical sleeve which is mounted about the load coupling to define an inlet passage between the shroud and the load coupling. Cooling air is supplied via a ventilation duct from an air intake plenum of the gas turbine to the inlet passage inside the sleeve to cool the load coupling and is then discharged through an open end of the sleeve into the exhaust gas passage defined by the exhaust housing.

The invention is as defined in claim <NUM> and dependent claims <NUM>-<NUM>.

The drawings are intended to depict only typical aspects of the disclosure and therefore should not be considered as limiting the scope of the disclosure.

As an initial matter, in order to clearly describe the subject matter of the current disclosure, it will become necessary to select certain terminology when referring to and describing relevant machine components within a gas turbine. To the extent possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. Unless otherwise stated, such terminology should be given a broad interpretation consistent with the context of the present application and the scope of the appended claims. Those of ordinary skill in the art will appreciate that often a particular component may be referred to using several different or overlapping terms. What may be described herein as being a single part may include and be referenced in another context as consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single part.

In addition, several descriptive terms may be used regularly herein, and it should prove helpful to define these terms at the onset of this section. These terms and their definitions, unless stated otherwise, are as follows. As used herein, "downstream" and "upstream" are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through the turbine engine or, for example, the flow of air through the combustor or coolant through one of the turbine's component systems. The term "downstream" corresponds to the direction of flow of the fluid, and the term "upstream" refers to the direction opposite to the flow (i.e., the direction from which the flow originates). The terms "forward" and "rearward" or "aft," without any further specificity, refer to directions, with "forward" referring to the front or compressor end of the gas turbine system, and "rearward" and "aft" referring to the rearward section of the gas turbine system, i.e., closer to the load in a rear-end drive gas turbine system.

It is often required to describe parts that are disposed at differing radial positions with regard to a center axis. The term "radial" refers to movement or position perpendicular to an axis. For example, if a first component resides closer to the axis than a second component, it will be stated herein that the first component is "radially inward" or "inboard" of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is "radially outward" or "outboard" of the second component. The term "axial" refers to movement or position parallel to an axis. Finally, the term "circumferential" refers to movement or position around an axis. It will be appreciated that such terms may be applied in relation to the center axis of the turbine, i.e., the rotor shaft and/or load coupling thereof.

It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur or that the subsequently describe component or element may or may not be present, and that the description includes instances where the event occurs or the component is present and instances where it does not or is not present.

Where an element or layer is referred to as being "on," "engaged to," "connected to" or "coupled to" another element or layer, it may be directly on, engaged to, connected to, or coupled to the other element or layer, or intervening elements or layers may be present.

As indicated above, the disclosure provides a turbine load coupling cooling system. The system adds a set of blades to the load coupling and a shroud along the load coupling in order to introduce air from the ambient or from ventilation ductwork about the load coupling, and to redirect the hot air away from the load coupling to reduce the temperature of the load coupling during operation. The intention of the cooling system is to cool the load coupling by adding a set of blades, i.e., a propeller, and a physical division in a space between the exhaust housing and load coupling using a shroud. The cooling system separates the flow of the air from the hot exhaust, creating a trap for both gases and keeping the colder air in contact with the load coupling. The system provides a reliable cooling system for various load couplings, new and old, and reduces the high temperature of the load coupling during operation. The system also cools other structure such as instrumentation, sensors, bearing housings and fluid piping that may be inside parts of the system. In addition, the system avoids the need to use more specialized materials in the load coupling to address higher temperatures, thus saving costs for the end user.

<FIG> is a schematic diagram for an illustrative gas turbine (GT) system <NUM>. GT system <NUM> may be considered as including a multi-stage axial flow compressor <NUM> having a rotating shaft <NUM>. Air enters the inlet of compressor <NUM> at point <NUM> and is compressed by axial flow compressor <NUM> and then is discharged to a combustor <NUM> where fuel such as natural gas is burned to provide high energy combustion gases which drive a gas turbine <NUM>. In gas turbine <NUM>, the energy of the hot gases is converted into work, some of which is used to drive compressor <NUM> through rotating shaft <NUM>, with the remainder available for useful work to drive a load, such as a generator <NUM>, via a rotor shaft <NUM> (i.e., an extension of rotating shaft <NUM>) for producing electricity. Exhaust from GT system <NUM> is collected in an exhaust housing <NUM>.

<FIG> shows an enlarged schematic view of GT system <NUM> and, in particular, exhaust housing <NUM> and a load coupling <NUM>. <FIG> shows a partial cross-sectional, perspective view of exhaust housing <NUM> and load coupling <NUM>. As shown, exhaust housing <NUM> includes an outer enclosure <NUM> including a tunnel <NUM> extending axially therethrough. Tunnel <NUM> can have any cross-sectional shape, but oftentimes has a cylindrical cross-section. Tunnel <NUM> has an inner surface <NUM>. Exhaust housing <NUM> is positioned at a rearward end of gas turbine <NUM> and receives gas turbine exhaust <NUM>. Exhaust housing <NUM> collects the various exhaust flows and redirects exhaust <NUM> for subsequent heating use or for release to atmosphere after any necessary environmental treatment. Exhaust housing <NUM>, including tunnel <NUM>, can be made of any material, such as metal or metal alloys, capable of withstanding the high temperatures of exhaust <NUM>, e.g., at or above <NUM> (~<NUM>°F).

A load coupling <NUM> extends through tunnel <NUM> of exhaust housing <NUM>. As shown in <FIG>, load coupling <NUM> couples rotor shaft <NUM> of gas turbine <NUM> to a rotating shaft <NUM> of load <NUM>, such as a generator, allowing rotational power to be transmitted to load <NUM> from gas turbine <NUM>. More particularly, load coupling <NUM> couples to a rear end <NUM> (<FIG>) of rotor shaft <NUM> of gas turbine <NUM> and extends through tunnel <NUM> of exhaust housing <NUM> of gas turbine <NUM>. Load coupling <NUM> can include any structure capable of coupling two rotating shafts <NUM>, <NUM>, and of withstanding the mechanical forces applied thereto. Load coupling <NUM> can include, for example, a metal or metal alloy shaft <NUM>. Load coupling <NUM> may also include a forward shaft coupler <NUM> coupling shaft <NUM> to rotor shaft <NUM>, and a rearward shaft coupler <NUM> coupling shaft <NUM> to rotating shaft <NUM> of load <NUM>. Each shaft coupler <NUM>, <NUM> may include any now known or later developed system of coupling rotating elements, such as but not limited to paired, radially extending flanges that can be bolted together. Any number and variety of bearings (not all shown) may be provided to rotationally support the various shafts. For example, a gas turbine (GT) bearing <NUM> may rotationally support rotor shaft <NUM> and/or load coupling <NUM> upstream of exhaust housing <NUM>.

As shown in <FIG> and <FIG>, exhaust <NUM> enters exhaust housing <NUM> and is collected and directed vertically (e.g., radially outward from load coupling <NUM>). Exhaust housing <NUM> may also include an optional frusto-conical rear section <NUM> contiguous with tunnel <NUM> to direct exhaust <NUM> radially within exhaust housing <NUM>. Exhaust <NUM> may be used, for example, as a heating source in any now known or later developed manner. The hot exhaust <NUM> has a temperature, e.g., at or above <NUM> (~<NUM>°F), which is too hot to provide cooling for load coupling <NUM>. Here, tunnel <NUM> prevents the hot exhaust <NUM> from directly contacting load coupling <NUM>. However, current GT systems <NUM> are using higher firing temperatures, resulting in hotter exhaust <NUM> that negatively affects cooling of load coupling <NUM>, despite the presence of tunnel <NUM>.

<FIG> and <FIG> also show a system <NUM> for cooling load coupling <NUM>, according to embodiments of the disclosure. As noted, load coupling <NUM> is coupled to gas turbine <NUM> and disposed within exhaust housing <NUM>. System <NUM> includes a shroud <NUM> configured to be mounted about load coupling <NUM> and a set of blades <NUM> configured to draw air <NUM> (<FIG>) over load coupling <NUM>. Tunnel <NUM> is radially spaced from shroud <NUM>. Thus, shroud <NUM> acts to separate a space <NUM> between load coupling <NUM> and tunnel <NUM> into separate passages <NUM>, <NUM>. More particularly, shroud <NUM> defines an inlet passage <NUM> between shroud <NUM> and load coupling <NUM>, and an outlet passage <NUM> between shroud <NUM> and exhaust housing <NUM>, e.g., tunnel <NUM> and/or frusto-conical rear section <NUM>. Exhaust housing <NUM> includes inner surface <NUM> (of tunnel <NUM>) that defines outlet passage <NUM> with shroud <NUM>. Inlet passage <NUM> is shown as radially inward of outlet passage <NUM>.

Shroud <NUM> may have a forward end <NUM> that is axially spaced from an end of load coupling <NUM>, e.g., near forward shaft coupler <NUM>, such that gas can pass from inlet passage <NUM> to outlet passage <NUM> about forward end <NUM> of shroud <NUM>. Hence, inlet passage <NUM> and outlet passage <NUM> are fluidly coupled together around forward end <NUM> of shroud <NUM> within tunnel <NUM>. As shown best in <FIG>, tunnel <NUM> and load coupling <NUM> (and more particularly, forward shaft coupler <NUM> of load coupling <NUM>) define a radial opening <NUM> at a forward end of load coupling <NUM>. As will be described, a gas <NUM> from an upstream source may enter through radial opening <NUM> and mix with air in inlet and outlet passages <NUM>, <NUM>. The upstream source of gas <NUM> may include any upstream structure. In one non-limiting example, the upstream source may be, in part, exhaust <NUM> and leakage from a housing for GT bearing <NUM> used to rotatably support rotor shaft <NUM>. It is noted that, because gas <NUM> is not as hot as exhaust <NUM>, gas <NUM> may provide some level of cooling for load coupling <NUM>, instrumentation, sensors, bearing housings and/or fluid piping within of shroud <NUM>. In one non-limiting example, gas <NUM> may have a temperature in a range of <NUM> (~<NUM>°F) to <NUM> (~<NUM>°F).

<FIG> shows a perspective view of an illustrative shroud <NUM> apart from GT system <NUM> (<FIG>). Shroud <NUM> may include any structure and have any shape capable of segregating space <NUM> (<FIG>), as described. In one embodiment, shroud <NUM> may have a cylindrical or slightly frusto-conical shape. As shown in <FIG>, shroud <NUM> can be more cylindrical and, as shown in <FIG>, shroud <NUM> can be more frusto-conical. In any event, shroud <NUM> may have at least one of a forward end <NUM> and a rear end <NUM> thereof with an outwardly flared surface <NUM>, e.g., to direct gas in a desired direction. In alternative embodiments, outwardly flared surface(s) <NUM> may be omitted. Shroud <NUM> may be made of any material, such as a metal or metal alloy, capable of withstanding the environment within space <NUM>. Shroud <NUM> may also include a shroud mount <NUM> configured to mount shroud <NUM> in exhaust housing <NUM> in a spaced manner about load coupling <NUM>. Shroud mount <NUM> may include any now known or later developed mounting system capable of positioning shroud <NUM> as described in space <NUM>. In one non-limiting example, shown in <FIG> and <FIG>, shroud mount <NUM> may include one or more arms <NUM> for coupling, e.g., with bolts, welds, or other fasteners, to exhaust housing <NUM>, such as to tunnel <NUM>. In other cases, shroud <NUM> may be mounted to any form of structure <NUM> positioned between exhaust housing <NUM> and load coupler <NUM> near rearward shaft coupler <NUM>. In one non-limiting example, structure <NUM> may include a protective grille. Other mounting solutions may also be possible. In any event, as shown in <FIG>, shroud <NUM> may optionally include a number of segments <NUM> that are configured to collectively form shroud <NUM> in a mounted state. Each segment <NUM> may provide any angular extent and any axial extent of shroud <NUM> deemed appropriate for easing installation of shroud <NUM>. In the non-limiting example shown, each segment <NUM> provides <NUM>° of shroud <NUM> and the full axial extent thereof. As will be recognized, any form of segmentation can be implemented to ease installation of shroud <NUM>, e.g., on new or older GT systems <NUM>.

As noted, system <NUM> for cooling load coupling <NUM> also includes a set of blades <NUM> configured to couple to load coupling <NUM>. <FIG> shows a rearward perspective view, and <FIG> shows an enlarged forward perspective view of load coupling <NUM> and set of blades <NUM>. Set of blades <NUM> may include any number of blades <NUM> required to create the desired air <NUM> flow rate, volume, etc., over load coupling <NUM>. As shown best in <FIG>, set of blades <NUM> (i.e., each blade <NUM>) are angled or curved so that they operate to draw air <NUM> along load coupling <NUM>, i.e., in inlet passage <NUM>. More particularly, as shown best in <FIG>, set of blades <NUM> are angled or curved to draw air <NUM> into inlet passage <NUM> as set of blades <NUM> rotate with load coupling <NUM>. Each blade <NUM> may have the same angle or curve, or they may vary. In certain embodiments, shown for example in <FIG>, each blade <NUM> in set of blades <NUM> may extend to a larger radial distance at an axially forward end <NUM> thereof than at an axially rearward end <NUM> thereof. That is, they extend increasingly farther radially outward towards shroud <NUM> as air <NUM> passes into inlet passage <NUM>. However, other variations in radial extent of blades <NUM> may also be employed. Axially forward ends <NUM> of blades may approach or contact load coupling <NUM> (see e.g., <FIG>), and axially rearward ends <NUM> are coupled to rearward shaft coupler <NUM> via a blade mount <NUM>. Air <NUM> may be sourced from any location, such as from ambient around generator <NUM>, a ventilation system, a flow-creating propeller, or other source.

<FIG> shows an enlarged perspective view of set of blades <NUM>. Set of blades <NUM> includes blade mount <NUM> configured to couple to shaft coupler <NUM> at a rearward end of the load coupling <NUM>. As shown, blade mount <NUM> may include a plurality of segments <NUM> to ease installation of set of blades <NUM>. Any number of segments <NUM> can be provided, e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc. Each segment <NUM> includes at least one blade <NUM> of set of blades <NUM>. In this manner, set of blades <NUM> can be easily coupled to load coupling <NUM> in parts. In one embodiment, each segment <NUM> includes a radially extending arcuate flange <NUM> having a number of mounting holes <NUM> therein configured to match openings in, for example, rearward shaft coupler <NUM>. Axially rearward ends <NUM> of blades <NUM> are fixedly coupled to a respective flange <NUM>. In this manner, set of blades <NUM> can be mounted to load coupling <NUM> as it is being coupled to rotating shaft <NUM> of load <NUM>. Flange(s) <NUM> can replace washers or act as extensions of washers used with fasteners <NUM> that are part of rearward shaft coupler <NUM>.

<FIG> shows a rearward perspective view of load coupling <NUM> and set of blades <NUM>, according to an alternative embodiment. <FIG> shows an enlarged perspective view and <FIG> shows a side view of one of the blades <NUM>, according to the alternative embodiments. Here, each blade <NUM> is individually coupled to load coupling <NUM>. In one example, each blade <NUM> may be coupled to load coupling <NUM> by a respective fastener <NUM>, e.g., bolts or bolt/nut combinations, through openings <NUM> therein. Fasteners <NUM> may be part of, for example, rearward shaft coupler <NUM>. In <FIG>, blades <NUM> may be held in position by fasteners <NUM>. Where necessary, additional structure may be employed to limit or prevent rotation, e.g., lock washers, male-female mating surfaces on blades <NUM> and load coupling <NUM>, etc. As shown in <FIG>, each blade <NUM> in set of blades <NUM> is angled or curved so that they operate to draw air <NUM> along load coupling <NUM>, i.e., in inlet passage <NUM>. More particularly, as shown best in <FIG>, each blade <NUM> is angled or curved to draw air <NUM> into inlet passage <NUM> as set of blades <NUM> rotate with load coupling <NUM>. Each blade <NUM> may have the same angle or curve, or they may vary.

<FIG> shows a rearward perspective view of load coupling <NUM> and set of blades <NUM>, and <FIG> shows an enlarged perspective view one of blades <NUM>, according to other alternative embodiments. Here, each blade <NUM> may include a positioning element <NUM> configured to hold a position of a respective blade <NUM> relative to at least load coupling <NUM>, other blades <NUM>, and shaft coupler <NUM>. Positioning element <NUM> is configured to maintain a position of a blade <NUM> and, in particular, to limit rotation of blade <NUM> relative to at least load coupling <NUM>. Positioning element <NUM> may replace the structures listed previously herein to limit rotation, e.g., lock washers, or it may be used in conjunction with those structures. In one example, positioning element <NUM> may include an extension <NUM>, <NUM> extending from sides <NUM> of blades <NUM> that engage with similar extensions <NUM>, <NUM> on an adjacent blade <NUM>. In the example shown, an extension <NUM> engages with an extension <NUM> of adjacent blade <NUM> to hold the blade position and limit rotation of one or both blades <NUM>. In this manner, positioning elements <NUM> act to hold the blades' positions, interlock the blades and at least limit, and ideally prevent, rotation of blades <NUM> relative to at least load coupling <NUM>. While a particular shape and size of positioning elements <NUM> have been disclosed, a large variety of alternative shapes and size of elements may be used. As shown in <FIG>, as in the previous embodiment, each blade <NUM> in set of blades <NUM> may be angled or curved so that they operate to draw air <NUM> along load coupling <NUM>, i.e., in inlet passage <NUM>. That is, each blade <NUM> may be angled or curved to draw air <NUM> into inlet passage <NUM> as set of blades <NUM> rotate with load coupling <NUM>. Each blade <NUM> may have the same angle or curve, or they may vary.

With regard to the embodiments of <FIG>, while each fastener <NUM> is shown with a respective blade <NUM>, that is not necessary in all cases. For example, in some cases, different numbers of blades <NUM> may be used, including but not limited to with: every other fastener <NUM> or every third fastener <NUM>. In any of the embodiments described herein, the number of blades <NUM> (among other factors such as blade size, curvature, etc.) can be controlled to control the volume of air drawn in to cool load coupling <NUM>.

As will be recognized, regardless of form, cooling system <NUM> can be mounted in a new GT system <NUM>, or it can be retrofitted to an older GT system <NUM>. The installation can occur in a manufacturing setting or on-site of a power plant.

In operation, a method of cooling load coupling <NUM> of gas turbine <NUM> includes drawing air <NUM> into space <NUM> through which load coupling <NUM> passes within exhaust housing <NUM> of the gas turbine. Air <NUM> is drawn by set of blades <NUM> rotating with load coupling <NUM> into space <NUM> and, more particularly, into inlet passage <NUM> defined between shroud <NUM> and load coupling <NUM>. Using shroud <NUM> to divide space <NUM>, air <NUM> can be drawn forward between shroud <NUM> and load coupling <NUM>, i.e., in inlet passage <NUM>. Inlet passage <NUM> and outlet passage <NUM> fluidly couple together around forward end <NUM> of shroud <NUM>, e.g., within tunnel <NUM>. Hence, air <NUM> passes about forward end <NUM> of shroud <NUM>, and then passes rearward between shroud <NUM> and exhaust housing <NUM>, e.g., tunnel <NUM> and/or frusto-conical rear section <NUM>, and eventually out of exhaust housing <NUM>. Hence, air <NUM> flows in a forward direction in inlet passage <NUM> (upstream when compared to working fluids in gas turbine <NUM> and exhaust <NUM>), and a rearward direction in outlet passage <NUM> toward shaft coupler <NUM> at a rearward end of load coupling <NUM>. As shown in <FIG> and <FIG>, in contrast to systems that blow air at exhaust housing <NUM>, cooling system <NUM>, i.e., shroud <NUM> and set of blades <NUM>, are axially within exhaust housing <NUM>, allowing improved, direct application of air <NUM> to load coupling <NUM>. Some limited amount of gas <NUM> (<FIG>) may also enter space <NUM> through radial opening <NUM> (<FIG>) to cool. However, the hotter exhaust <NUM> does not enter space <NUM>, and is prevented from entering space <NUM> by air <NUM> in the space.

Embodiments of cooling system <NUM> cool load coupling <NUM> by adding a set of blades, i.e., a propeller, and a physical division in space <NUM> between exhaust housing <NUM> and load coupling <NUM>. Hence, cooling system <NUM> separates the flow of air <NUM> from the hot exhaust <NUM>, creating a trap for both temperature gases and keeping the colder air <NUM> in contact with load coupling <NUM>. Cooling system <NUM> thus provides reliable cooling for various load couplings <NUM>, new and old, and reduces the high temperature of the load coupling during operation. The system also cools other structure such as instrumentation, sensors, bearing housings and fluid piping that may be inside parts of the system, to avoid failure or coking of these parts. In addition, cooling system <NUM> avoids the need to use more specialized materials in the load coupling to address high temperatures, thus saving costs for the end user.

Accordingly, a value modified by a term or terms, such as "about," "approximately" and "substantially," are not to be limited to the precise value specified. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. "Approximately," as applied to a particular value of a range, applies to both end values and, unless otherwise dependent on the precision of the instrument measuring the value, may indicate +/- <NUM>% of the stated value(s).

Claim 1:
A system (<NUM>) for cooling a load coupling (<NUM>) coupled to a gas turbine (<NUM>) and disposed within an exhaust housing (<NUM>), the system (<NUM>) comprising:
a shroud (<NUM>) configured to be mounted about the load coupling (<NUM>), the shroud (<NUM>) defining an inlet passage (<NUM>) between the shroud (<NUM>) and the load coupling (<NUM>) and an outlet passage (<NUM>) between the exhaust housing (<NUM>) and the shroud (<NUM>); and
a set of blades (<NUM>, <NUM>) configured to couple to the load coupling (<NUM>), the set of blades (<NUM>, <NUM>) angled to draw air (<NUM>) into the inlet passage (<NUM>) as the set of blades (<NUM>, <NUM>) rotate with the load coupling (<NUM>);
characterised in that
the shroud (<NUM>) defines an outlet passage (<NUM>) between the exhaust housing (<NUM>) and the shroud (<NUM>);
wherein the exhaust housing (<NUM>) defines a tunnel (<NUM>) radially spaced from the shroud (<NUM>), and the inlet passage (<NUM>) and the outlet passage (<NUM>) fluidly couple together around a forward end (<NUM>) of the shroud (<NUM>) within the tunnel (<NUM>), wherein the air (<NUM>) flows in a forward direction in the inlet passage (<NUM>) and a rearward direction in the outlet passage (<NUM>); and
wherein the tunnel (<NUM>) and the load coupling (<NUM>) define a radial opening (<NUM>) at the forward end (<NUM>) of the load coupling (<NUM>) through which a gas (<NUM>) from an upstream source enters and mixes with the air (<NUM>) in the inlet and outlet passages (<NUM>, <NUM>).