Gas turbine engine ejector

An ejector comprises a primary nozzle having an annular wall forming part of an outer boundary of an exhaust portion of a primary flow path of a gas turbine engine. The annular wall has a downstream end defining a plurality of circumferentially distributed lobes. The ejector further comprises a secondary nozzle having an annular wall disposed about the primary nozzle, the primary nozzle and the secondary nozzle defining a secondary flow passage therebetween for channeling a secondary flow. The secondary nozzle defines a mixing zone downstream of an exit of the primary nozzle. A flow guide ring is mounted to the primary nozzle lobes. The ring has an aerodynamic surface extending from a leading edge to a trailing edge respectively disposed upstream and downstream of the exit of the primary nozzle. The aerodynamic surface of the ring is oriented to guide the high velocity primary flow into the mixing zone.

TECHNICAL FIELD

The application relates generally to aircraft gas turbine engines and, more particularly, to aft section of the engine including an ejector.

BACKGROUND OF THE ART

In gas turbine engines, hot high velocity air exits from the turbine through the core gas path. The exhaust gases may be constrained by an exhaust case section in the form of a corrugated annular case extension having lobes. Turbofan engines generally use exhaust mixers in order to increase the mixing of the high and low velocity exhaust gas flows. Turbo-shaft and turbo-prop engines may be provided with similar devices sometimes referred to as ejectors. Exhaust mixers/ejectors may experience thermal variation and/or radial deflection due to exposure to the high and low velocity flows. In addition, exhaust ejector/mixers may be prone to vibrations, which have negative consequences for the surrounding hardware. As such, it is generally desirable to increase the stiffness or rigidity of the exhaust case. Various configurations of exhaust ejector/mixers have been proposed to date in order to try to increase the stiffness or reduce deflection thereof.

Also, the aerodynamic performance of ejectors is often limited by the ability of the primary flow to entrain the secondary cooling flow. Increasing the ejector capacity of pumping secondary mass flow would also be desirable from an aerodynamic point of view.

SUMMARY

In one aspect, there is provided an ejector for a gas turbine engine of the type having a main axis and a primary flow passage channeling a high velocity primary flow, the ejector comprising: a primary nozzle having an annular wall forming part of an outer boundary of an exhaust portion of the primary flow passage, the annular wall having a downstream end defining a plurality of circumferentially distributed radially inner lobes; a secondary nozzle having an annular wall disposed about the primary nozzle, the primary nozzle and the secondary nozzle defining a secondary flow passage therebetween for channeling a secondary flow, the secondary nozzle defining a mixing zone downstream of an exit of the primary nozzle where the high velocity primary flow and the secondary flow mix together; and a flow guide ring mounted to the circumferentially distributed lobes in the exhaust portion of the primary flow passage centrally about the main axis of the engine, the flow guide ring having an aerodynamic surface extending from a leading edge to a trailing edge respectively disposed upstream and downstream of the exit of the primary nozzle, the aerodynamic surface being oriented to guide the high velocity primary flow into the mixing zone.

In accordance with another general aspect, there is provided a gas turbine engine having an engine casing enclosing a compressor section, a combustor and a turbine section defining a main gas path serially extending therethrough along a main axis of the engine, and comprising: an ejector projecting from an aft end of the engine casing axially downstream from an engine center body forming an aft end portion of an inner boundary of the main gas path, the ejector comprising a primary nozzle having an annular wall forming an outer boundary of the main gas path for guiding a primary flow, the annular wall having a downstream end defining a plurality of circumferentially distributed lobes, and a flow guide ring mounted to the circumferentially distributed lobes in the main gas path centrally about the main axis and downstream of the engine center body; the flow guide ring having an aerodynamic surface configured to minimize diffusion of the primary flow towards the main axis of the engine.

DETAILED DESCRIPTION

FIG. 1illustrates a turbo-shaft gas turbine engine10of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a compressor section14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases. The gas turbine engine10includes a core engine casing20which encloses the turbo machinery of the engine. The main air flow passes through the core of the engine via a main gas path26, which is circumscribed by the core engine casing20and allows the flow to circulate through the multistage compressor14, combustor16and turbine section18as described above.

At the aft end of the engine10, an engine center body22is centered about a longitudinal axis X of the engine10, the engine center body22being connected to an aft end of the turbine section18. The engine center body can take the form of an exhaust cone depending on the application. The engine center body22has an outer surface, which defines an inner wall of the main gas path26so that the combustion gases flow therearound. An ejector/mixer30forms the outer wall of the aft end of the main gas path26. As best seen inFIG. 2, the ejector/mixer30includes a primary nozzle having an annular wall34with a radial fastening ring or flange32upstream thereof. The fastening ring32is adapted to be mechanically fastened to the aft portion20a(FIG. 1) of the casing20.

Referring toFIGS. 2 and 3, in further detail, the annular wall34of the primary nozzle, includes and defines a plurality of circumferentially distributed radially inner lobes36extending axially rearwardly from a front frusto-conical portion of the annular wall34to a downstream edge37, i.e. a trailing edge thereof. The lobes36include side, radially-extending, walls38with a bight forming an arcuate trough40. The trough40presents a convex surface41on the radially inner or central side of the annular wall34.

An annular support member includes an annular blade42extending concentrically about the longitudinal axis X of the engine10. In the embodiment shown, the blade42comprises an annular longitudinal, flat bar. The blade42is interrupted only at form-fitting joint areas44. The joint areas44are located on the blade42to correspond with the convex surfaces41of the lobes36. The joint areas44are curved so that it complements the convex surface41, as shown inFIG. 3. The curved joint area44is concave relative to the convex surface41of the lobe36. The blade42is spaced radially outwardly and independent from the engine center body22and floats with respect thereto. The blade42in one embodiment is a thin sheet metal strip capable of being welded to the sheet metal forming the annular wall34. In the embodiment shown inFIGS. 2 and 3, the thin sheet metal strip is formed into a continuous ring.

As mentioned, the ejector/mixer30is solely connected to the engine10at the aft end20aof the core engine casing20, and so, the ejector/mixer30is effectively cantilevered from the core engine casing20. This cantilevered configuration allows the lobes36of the exhaust ejector/mixer30to vibrate at one or more modes in the engine operating frequency range, while remaining relatively stiff. In addition, the thermal variations in the exhaust mixer30due to the high and low velocity flows through the main gas path26may cause axial and radial displacements in the ejector/mixer30, which can accordingly be absorbed by the exhaust ejector/mixer30. Moreover, the downstream end37of the ejector/mixer30, which would otherwise be prone to deflection, is reinforced by the blade42which serves to increase the rigidity of the exhaust ejector/mixer30and thus inhibit movement at the downstream end37thereof. By joining all the lobes36together with the blade42, any movement of the ejector/mixer30is reduced, as are the vibrations thereof. In addition, by providing a blade42which is independent of the exhaust engine center body22, i.e. it is free to move relative thereto such as to absorb any vibrations or thermal growth mismatches therebetween. The blade42is able to accommodate any axial or radial displacements due to such thermal variations. As such, the ejector/mixer30provides enhanced rigidity and may accommodate thermal variations, vibrations and other displacements, as required.

Another embodiment is shown inFIGS. 4 and 5. In this case, the blade is made up of blade segments142a,142b. . .142n. Each segment has a length corresponding to the distance between the center lines of two adjacent lobes36. Each end of the segment terminates in a partially formed concave curve to complement part of the convex surface41of the lobe36. For instance, as shown inFIG. 5, corresponding ends of segments142aand142bmake-up the form fitting joint area144.

The blade42,142may be located at different axial positions along the convex surfaces41of the lobe36.FIG. 3illustrates a blade42being spaced upstream from the trailing edge37, of the lobe36. As shown inFIG. 5, the blade142is located at or slightly downstream from the trailing edge37, of the lobe36. The blade42,142may be fixed to the convex surfaces41of the lobes36at joint areas44,144using a combination of resistance, fusion or ball tack welding with a brazing application, or other types of suitable bonding that are well known in the art.

The injector/mixer30, in the present embodiment, acts to induce cool air, exterior of the engine casing20, to be drawn radially inwardly through the lobes36to cool the mechanical parts of the injector/mixer30. As previously mentioned, the support member is often, according to the prior art, subject to thermal stresses caused by the entrained cool air and of the hot air exiting the turbine18.FIGS. 6 and 7show the gases flow in the ejector/mixer30. The blade42,142is disposed directly in the main gas path26and is shaped to be laminar with the flow of the hot gases, as can be seen in bothFIGS. 6 and 7. The blade42is essentially exposed only to the hot gases flowing in the main gas path26. This reduces the thermal gradient in the blade42,142.

The embodiments described show a turbo-shaft engine. However, in the case of a turbofan engine, cool air from the fan is directed to the ejector/mixer30which in such a case would have inner and outer alternating lobes to best mix the hot gases with the cool air. U.S. Pat. No. 5,265,807 Steckbeck et al 1993; U.S. Pat. No. 7,677,026 Conete et al 2010; and U.S. Pat. No. 8,739,513 Lefebvre et al 2014 describe exhaust mixers which are herewith incorporated by reference.

The above described embodiments provide an improved exhaust ejector/mixer for a gas turbine engine where the thermal stresses on the support member are reduced for improved longevity.

It is noted that the ejector/mixer and the support member could be made by additive manufacturing processes, such as direct metal laser sintering. Therefore, the ejector/mixer and the support member could be made monolithically.

For some gas turbine engine applications, such as turbo shaft and turbo prop applications, where the engine center body22ends axially upstream of the turbine exhaust nozzle exit (seeFIG. 9), the exhaust section is referred to as an ejector. As will be seen hereinafter, for such applications, the support member may also act as a flow guide ring to guide the primary flow when leaving the primary nozzle and, thus, enhance the ejector aerodynamic performance.

FIG. 8illustrates an ejector200comprising a primary nozzle201, a secondary nozzle203concentrically mounted about the primary nozzle201and a flow guide ring205concentrically mounted inside the primary nozzle201.

As mentioned hereinbefore with respect to the embodiments shown inFIGS. 1 to 7, the primary nozzle201has an annular wall234forming part of the outer boundary of an exhaust portion of the main or primary flow passage of the engine. The annular wall234has a downstream end formed with circumferentially distributed radially inner lobes236. The flow guide ring205is attached to the radially inner surface of the lobe valleys as described herein above.

The secondary nozzle203has an annular bell-shaped wall extending from the engine compartment wall case (not shown) about the primary nozzle201. As best shown inFIG. 9, the primary nozzle201and the secondary nozzle203define a secondary flow path207therebetween for guiding a secondary flow of cooling air. The secondary nozzle203extends axially downstream of the primary nozzle201and defines a mixing zone209at the exit of the primary nozzle201where the high velocity primary flow mixes with the secondary flow.

Referring conjointly toFIGS. 8 and 9, it can be appreciated that primary nozzle201of the ejector200extends axially downstream of the engine center body22(i.e. the inner boundary of the primary flow passage ends upstream of its outer boundary).

As a result, the primary flow tends to diffuse towards the engine centerline downstream of the end of the center body22.

The addition of a properly designed flow guide ring205can prevent the annular high momentum primary flow from diffusing and guide the flow through the annular zone between the flow guide ring205and the primary nozzle201where the primary and secondary flows mix. Due to this fact, the capacity of pumping secondary mass flow may be improved.

According to the embodiment illustrated inFIGS. 8 and 9, the flow guide ring205has a cone shape with a proper angle (P1) with respect to engine axis (seeFIG. 9). This is to ensure that the primary flow is well guided without separation when leaving the primary nozzle and entering the mixing zone. The ring cone draft angle (P1) may be in the range of about 0° to about 10° and is preferably about 5°. Depending on the application, the flow guide ring205could be cylindrical or airfoil as well.

As shown inFIG. 9, the flow guide ring205has an aerodynamic surface extending axially from a leading edge205ato a trailing edge205b. According to the illustrated embodiment, the leading edge205aand the trailing edge205bare respectively disposed upstream and downstream of the primary nozzle exit to properly guide the primary flow leaving the primary nozzle201into the mixing zone209. According to the illustrated embodiment, the flow guide ring205projects out of the primary nozzle201or extends downstream from the exit of the primary nozzle201by a distance (P5) for extended flow guidance in the mixing zone and avoidance of flow separation across the ring205. For a particular application, the distance (P5) is in the range of about 0 to about 1 inch.

The length (P2) of the guide ring205and its axial installation position (P3) relative to the end of the center body22may also influence the aerodynamic performance of the ejector200. It is understood that (P2) and (P3) can be optimized depending on different applications. According to a particular application, the ring length (P2) is in the range of about 0.5 to about 2 inches and the ring205is installed axially at the primary nozzle exit.

The radial installation position of the guide ring (P4) may vary depending on various conditions. According to the illustrated embodiment, the ring205is installed at the lobe valley. It is also understood that the lobe design and the number of lobes236may vary depending on the applications. According to the illustrated embodiment, the lobes236have a draft angle (P6) of about 0° to about 5° (FIG. 10). Such a small draft angle can help prevent reverse back secondary flow. The number of lobes may vary depending on the size of the engine. For the exemplified application given above, the number of lobes may range between 8 and 10.

Various permutations of the above parameters of the flow guide ring can be used to improve the ejector pumping capacity.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the invention may be used with various types of gas turbine engines where cool and hot gases may simultaneously be in contact with the machinery involved. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.