US20130087632A1

US20130087632A1 - Gas turbine engine exhaust ejector nozzle with de-swirl cascade

Info

Publication number: US20130087632A1
Application number: US13/270,284
Authority: US
Inventors: Patrick Germain
Original assignee: Pratt and Whitney Canada Corp
Current assignee: Pratt and Whitney Canada Corp
Priority date: 2011-10-11
Filing date: 2011-10-11
Publication date: 2013-04-11

Abstract

The exhaust ejector nozzle has a tubular wall defining an exhaust flow passage leading to an outlet plane, and a de-swirl cascade including a plurality of circumferentially interspaced fins each having a first end connected to the wall adjacent the outlet plane and a second end extending into the exhaust flow passage. The de-swirl cascade can maintain the pumping action of the ejector in high swirl exhaust conditions.

Description

TECHNICAL FIELD

The application relates generally to exhaust ejectors of gas turbine engines and, more particularly, to handling residual swirl in the turbine exhaust.

BACKGROUND OF THE ART

Gas turbine exhaust ejectors typically consist of a high-velocity primary flow that leaves a primary component, referred to as a nozzle and transmits momentum to the surrounding medium by shear forces, thereby entraining the surrounding medium into a secondary flow. The primary and secondary flows then proceed into a secondary component having a larger diameter and referred to as a shroud. Typically, the nozzle is made integral to the engine, whereas the shroud is made integral to the aircraft.
The entrainment of secondary flow with such ejectors is sensitive to residual swirl from the turbine exhaust. The residual swirl can be particularly high at operating conditions such as ground idle and rotor-locked (hotel mode) conditions, for instance. Beyond a certain threshold of swirl angle, the pumping process of the ejector can become unsatisfactory. Known methods to address this concern remained not completely satisfactory from the efficiency, cost and/or weight perspective. Accordingly, there remains room for improvement in addressing the ejector swirl.

SUMMARY

In one aspect, there is provided an exhaust ejector nozzle for a gas turbine engine, the exhaust ejector nozzle comprising a tubular wall having a radially inner surface delimiting an exhaust flow passage leading, along an exhaust flow direction, to an outlet plane of the exhaust ejector nozzle, the outlet plane being circumscribed by a downstream edge of the radially inner surface relative the exhaust flow direction, the radially inner surface of the tubular wall defining a central axis, the central axis and the radially inner surface being associated with an exhaust flow orientation; and a de-swirl cascade including a plurality of circumferentially interspaced fins each having a first end connected to the radially-inner surface of the tubular wall adjacent the downstream edge and associated outlet plane, a second end extending into the exhaust flow passage along a given span, and a chord oriented normal to the span.
In a second aspect, there is provided a gas turbine engine comprising an ejector having a nozzle and a cowl at an exhaust region, the nozzle extending from a turbine exhaust case of the gas turbine engine, the ejector nozzle having a tubular wall defining an exhaust flow passage leading to an outlet plane, and a de-swirl cascade including a plurality of circumferentially interspaced fins each having a first end connected to the wall adjacent the outlet plane and a second end extending into the exhaust flow passage.
In a third aspect, there is provided a method of de-swirling an external portion of an exhaust gas flow in an ejector nozzle of a gas turbine engine prior to mixing with a secondary flow in an ejector action, the method including exposing at least the external portion of the exhaust flow inside the ejector nozzle to a de-swirl cascade including a plurality of circumferentially interspaced fins; the exhaust flow reaching an outlet plane of the ejector nozzle subsequently to said exposing.
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures, in which:

FIG. 1 is a schematic cross-sectional view of an example of a gas turbine engine;

FIG. 2 is an oblique schematic view showing an ejector nozzle connected to a turbine exhaust case;

FIG. 3 is an end view of the components of FIG. 2.

FIG. 4 is a side view of an alternate embodiment of an ejector nozzle.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a turbine engine. In this example, the turbine engine 10 is a turboshaft engine generally comprising in serial flow communication, a multistage compressor 12 for pressurizing the air, a combustor 14 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section 16 for extracting energy from the combustion gases. The turbine engine terminates in an exhaust section.
In this example, the exhaust section includes an exhaust ejector 18 which is used to draw an external flow of air for ventilation, cooling, or the like. The exhaust ejector 18 in this embodiment generally includes a nozzle 22 and a shroud 27. The nozzle 22 has a tubular wall 26 which guides a flow of exhaust gasses exiting the turbine section 16. The exhaust gasses travelling through the nozzle 22 and subsequently exiting will be referred to in this specification as the primary flow 23 which travels in a direction generally indicated by the arrow. Henceforth, an inlet plane 44 of the nozzle 22 can be defined as being circumscribed by a first edge 46 of the tubular wall 26, positioned upstream relative to the average flow direction of the primary flow 23. An outlet plane 48 can be defined as being generally circumscribed by a second edge 50 of the tubular wall 26, positioned downstream relative to an average flow direction of the primary flow 23. The first edge 46 and second edge 50 can be circular, and can alternately be elliptical if the corresponding plane is slanted, for instance.
The primary flow 23 can be annular around a center body 32 or circular, such as in alternate embodiments where the center body 32 is recessed for instance. The exact average orientation of respective portions of the primary flow 23 will be affected by the configuration of the tubular wall 26, center body 32 as well as by other aerodynamic considerations known to those skilled in the art. The configuration of the exhaust flow path of the primary flow 23 through the nozzle 22 is affected by the shape of the radially-inner surface 31 of the tubular wall 26. A central axis 29 can thus be defined relative the tubular wall 26. Areas located nearer to the axis 29 can thus be referred to as being radially-inner, whereas areas located relatively farther to the axis are relatively radially-outer. Accordingly, the tubular wall 26 can be said to have a radially-inner surface 31 (FIG. 2) exposed to the primary flow 23 and an opposite radially-outer surface, a portion of which may be exposed to a radially-outer surrounding medium.
During normal operation of the ejector 18, the energy from the velocity of the primary flow 23 of exhaust gasses entrains a surrounding, radially-outer, secondary flow 25 of the surrounding medium by shear fluid friction forces into a secondary component of the exhaust ejector 18 referred to as the shroud 27, which has a larger inlet plane 52 cross-sectional area than the cross-sectional area of the outlet plane 48 of the nozzle 22 to allow for entry of both the primary flow 23 and the secondary flow 25. The inlet plane 52 of the shroud 27 can thus be said to radially exceed the inlet plane 48 of the nozzle 22.
FIGS. 2 and 3 show an example of an exhaust ejector nozzle 22. In this embodiment, the nozzle 22 is provided as an individual component shown connected to a turbine exhaust case 24, but it will be understood that in an alternate embodiment, the nozzle 22 can be a portion or extension of the turbine case itself, for instance. Further, referring to the illustrated embodiment, the exhaust nozzle 22 can be seen to have a tubular wall 26, being here generally cylindrical, and a radially-inner surface 31 of the tubular wall 26 defines an exhaust flow passage. The tubular wall 26 can be cambered, curved or bent to some extent depending on the intended use, in which case the central axis 29 follows the curve or camber; further, one end or both ends of the tubular wall 26 can be bent or slanted off the radial orientation, for instance.
The nozzle inlet 28, which bears the upstream edge 46 of the tubular wall 26, is connected to the turbine exhaust case 24 in this case. The tubular wall 26 also has an opposite outlet end 30 bearing the downstream edge 50 of the tubular wall 26. In this embodiment, the outlet end 30 is slanted, so the edge 50 of the tubular wall 26 is elliptical to some extent instead of being circular. An inlet plane 44 can be defined as the entry into the nozzle 22 whereas an outlet plane 48 can be defined as the exit, circumscribed by the downstream edge 50. In this embodiment, a centerbody 32 is shown connected to the turbine casing 24 by struts at the inlet plane 44 of the nozzle. Although the presence of the centerbody 32 and struts are typical, the shape, position, and configuration thereof can vary in alternate embodiments. Typically, the struts and fins are independent of each other. However, in some cases, the designer may want to clock the fins such that no wake from the struts is aligned with any of the fins.
Ejector pumping breakdown can result from high swirl angles in the shear layer between the primary and secondary flows. The breakdown is exacerbated by possible hub separation and migration of the flow towards the shroud 27. The pumping breakdown is naturally to maintain conservation of angular momentum, with the separated flow near the hub substantially in a solid body rotation. A solution is to implement a partial cascade 34 before the nozzle exit plane 48 to reduce the swirl angle in the area where the pumping shear forces occur between the primary and secondary flows.
To this end, in this embodiment, the exhaust nozzle 22 further comprises a de-swirl cascade 34 including a plurality of circumferentially interspaced fins 36 each having a first end 38 connected to the wall 26, and more particularly connected to the radially-inner surface 31 of the tubular wall 26, and a second end 40 extending into the exhaust flow passage, in a direction which will be characterized here as being radially-inward from the radially inner surface 31. It will be noted here that the ducting is generally annular in shape and is positioned adjacent the outlet end 30 of the tubular wall 26.
To provide the ejector function, the primary flow 23 exiting the nozzle 22 interacts with a surrounding medium to entrain a secondary flow into the shroud 27. Referring to FIG. 3, the inner peripheral portion 60 of the primary flow 23 (schematically shown here delimited on the one hand by an arbitrarily positioned dashed line and on the other hand by the inner surface 31 of the tubular wall 26) travelling inside the nozzle, i.e. the portion of the primary flow 23 which is adjacent the radially-inner surface 31 and in the inner periphery of the tubular wall 26, will have a significantly greater effect in the ejector pumping action onto the surrounding medium, once it has passed through the outlet plane 48 of the nozzle, than a more central, or radially-inner portion 42 of the primary flow 23. This is because although a certain amount of mixing can occur, at least a high percentage of the inner peripheral portion 60 of the primary flow 23 which travels close to the radially inner surface 31 of the tubular wall 26 near the outlet plane 48 will remain in a radial position allowing it to interact with the surrounding medium, which is located radially-outwardly. The radially-inner portion 42 of the primary flow 23 which is located more radially inwardly is separated from the surrounding medium by the inner peripheral portion 60 layer of the primary flow 23 and interacts indirectly with the surrounding medium if at all. Addressing the swirl in a radially inner region is thus less likely to produce an effect on the ejector pumping action, just as partially addressing the swirl at an upstream position along the exhaust gas passage is less likely to be effective because subsequent mixing of the exhaust gasses may allow an unsatisfactory amount of swirl to return into the portions of the exhaust gas flow which contribute to the ejector action.
Referring more particularly to FIG. 4, an annular critical region 62 of the exhaust flow passage in the nozzle is defined, being both adjacent the outlet plane 48 and adjacent the radially-inner surface 31 (as illustrated by numeral 60 in FIG. 3). Strategically controlling the swirl in this specific region inside the nozzle may be more susceptible to having a significant effect on the ejector pumping action than in regions located more radially inwardly or more upstream from the outlet plane, and thus may be achieved at satisfactory added weight, pressure, and costs.
Even if high swirl is present across the entire cross-section of the exhaust gasses of the primary flow inside the nozzle, it can be satisfactory to control the swirl only partially, and strategically in the inner peripheral portion 60 of the primary flow 23 and in the annular region 62 near the outlet plane 48. Rreferring back to FIG. 3, the fins 36 can extend only partially into the primary flow 23 in the direction extending across the flow, radially-inward from the tubular wall 26, and can be positioned adjacent the outlet end 30 of the tubular wall 26, i.e. adjacent the outlet plane 48. This strategic positioning of the fins 36 connected to the tubular wall 26 of the nozzle 22 can strategically control the swirl in high swirl conditions to preserve the ejector pumping action with a limited amount of extra weight, pressure loss, and/or cost.
In the illustrated embodiment, the configuration of the de-swirl cascade 34 is designed to reduce the swirl in the exhaust gases strategically in order to maintain the ejector secondary flow pumping action even in conditions where there is a high degree of swirl in the exhaust gasses (such as a swirl angle of 40° or 50° for instance). The de-swirl cascade 34, and more specifically the fins thereof, is positioned near the critical region 62 of the ejector flow which eventually meets and shears with the secondary flow into the pumping action.
In the illustrated embodiment, and referring to FIG. 4, in the direction of exhaust gas flow, the fins 36 have an upstream end 72 at a first longitudinal or axial position, and extend along their chord c (FIG. 4) to a downstream end 74. For practical purposes, the downstream end of the fins 36 can be separated from the outlet plane 48 by a spacing distance d in this embodiment, but it will be understood that in alternate embodiments, the downstream end 74 of the fins can coincide with the downstream edge of the radially-inner surface 31, i.e. the outlet plane 48. If the distance d is too long, the deswirl action through the fins will be partially lost as the high swirl near the center will migrate radially outwards, thereby favouring the breakdown of ejector pumping. In an alternate embodiment, the fins can be connected to the nozzle inner wall surface 31 and protrude past the outlet plane.
Because the region of the primary flow 23 which is responsible for the pumping action of the secondary flow 25 is more importantly the region 60 thereof which is located adjacent to the wall, the fins 36 can be designed to extend only partially into the primary flow 23 area, in the inner-peripheral region 60, such as better seen in FIG. 3, to favour the low-weight, low-pressure losses aspects. The span s of the fins 36 can represent only a fraction of the dimension of the primary flow area 42. In this specific case, they can be seen to extend through around less than half of the primary flow area 42 which can be delimited between the center body 32 and the radially-inner surface 31 for instance. In alternate embodiments, the fins 36 can extend across the entire primary flow area 42 and/or optionally be interconnected by a structural ring or centerbody, for instance.
In the illustrated embodiment, an aim was to sufficiently control the swirl to maintain the ejector pumping action in high-swirl conditions, while optimizing weight and pressure losses added by the fins 36. To this end, the span I and chord c can be adjusted to minimum or optimum dimensions, and the fin count can also be adjusted to a minimum or optimum value yielding results considered as satisfactory. The stagger angle can be close to zero, but can alternately be adjusted to maintain low pressure losses. The fins 36 can be seen to extend more or less normal from the wall 26, radially inward, and have their chord parallel to the central axis 29, or alternately inclined therefrom by a stagger angle. The final adjustment of these design parameters will be typically be selected to achieve a trade-off between the ejector ability to function at both high swirl and aero design conditions (SFC), in which the swirl is typically low. Other design aspects are to be considered such as structural integrity and manufacturability.
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 fins can be provided closer to nozzle inlet instead of being adjacent the nozzle outlet, and the span, chord, fin count and stagger angle can vary. The de-swirl cascade can be applied to exhaust ejector nozzles of any suitable turbine, such as turboshafts, turboprops and APUs for instance. 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 scope of the appended claims.

Claims

What is claimed is:

1. An exhaust ejector nozzle for a gas turbine engine, the exhaust ejector nozzle comprising a tubular wall having a radially inner surface delimiting an exhaust flow passage leading, along an exhaust flow direction, to an outlet plane of the exhaust ejector nozzle, the outlet plane being circumscribed by a downstream edge of the radially inner surface relative the exhaust flow direction, the radially inner surface of the tubular wall defining a central axis, the central axis and the radially inner surface being associated with an exhaust flow orientation; and a de-swirl cascade including a plurality of circumferentially interspaced fins each having a first end connected to the radially-inner surface of the tubular wall adjacent the downstream edge and associated outlet plane, a second end extending into the exhaust flow passage along a given span, and a chord oriented normal to the span.

2. The ejector nozzle of claim 1 wherein the span of the fins extends only partially into the exhaust flow passage.

3. The ejector nozzle of claim 2 wherein the span extends less than halfway into the primary flow area.

4. The ejector nozzle of claim 2 wherein the span extends along an inner peripheral region of the exhaust flow passage.

5. The ejector nozzle of claim 1 wherein the chord is inclined by a stagger angle relative to the central axis.

6. The ejector nozzle of claim 1 wherein the span, the chord, the stagger angle, and an interspacing between the fins are selected to sustain a pumping action of the ejector in high swirl conditions.

7. The ejector nozzle of claim 1 wherein the fins extend normal to the radially-inner surface.

8. The ejector nozzle of claim 1 wherein the second end of the fins is a free end.

9. The ejector nozzle of claim 1 wherein the fins are immediately adjacent the outlet plane.

10. The ejector nozzle of claim 1 wherein the fins are spaced from the downstream edge by a spacing distance which is small relative to the span and the chord.

11. The ejector nozzle of claim 1 wherein the span and the chord are of the same order of magnitude.

12. The ejector nozzle of claim 1 wherein the tubular wall is cambered and the central axis is correspondingly curved.

13. A gas turbine engine comprising an ejector having a nozzle and a cowl at an exhaust region, the nozzle extending from a turbine exhaust case of the gas turbine engine, the ejector nozzle having a tubular wall defining an exhaust flow passage leading to an outlet plane, and a de-swirl cascade including a plurality of circumferentially interspaced fins each having a first end connected to the wall adjacent the outlet plane and a second end extending into the exhaust flow passage.

14. The ejector nozzle of claim 13 wherein the fins extend partially into a primary flow area of the exhaust flow passage.

15. The ejector nozzle of claim 14 wherein the fins extend less than halfway into the primary flow area.

16. The ejector nozzle of claim 13 wherein the fins are oriented in an axial orientation relative the tubular wall.

17. The ejector nozzle of claim 13 wherein the free end of the fins extends normal to the wall.

18. The ejector nozzle of claim 13 wherein the fins are immediately adjacent the outlet plane.

19. The ejector nozzle of claim 13 wherein the fins have a span, chord, stagger angle, and interspacing selected to sustain a pumping action of the ejector in high swirl conditions.

20. A method of de-swirling an external portion of an exhaust gas flow in an ejector nozzle of a gas turbine engine prior to mixing with a secondary flow in an ejector action, the method including

exposing at least the external portion of the exhaust flow inside the ejector nozzle to a de-swirl cascade including a plurality of circumferentially interspaced fins;

the exhaust flow reaching an outlet plane of the ejector nozzle subsequently to said exposing.