The application relates generally to turbofan aero-engines and, more particularly to an improved turbine exhaust case including a mixer for such engines.
In order to increase the effective thrust of turbojet engines, bladed fans have been added to a turbine driven shaft thereof to affect the flow of a quantity of atmospheric air through an annular bypass duct surrounding the turbojet. Hot gases exhausted from the engine core and the bypass airstream are mixed together before expulsion through a single nozzle. In order to perform the mixing function, mixers have been attached to the downstream end of a shroud of the turbine exhaust case (TEC). A swirling flow of exhaust gases from the turbine exit is conventionally deswirled by a plurality of deswirling struts located within the TEC, upstream of the mixer as shown in
Accordingly there is a need to provide an improved mixer.
In one aspect, there is provided a turbine exhaust case (TEC) of a turbofan aeroengine including a mixer for mixing exhaust gases with a bypass air stream, the TEC comprising an annular hub and an annular shroud with said mixer located at a downstream end of the shroud, the mixer surrounding the hub to form an annular exhaust gas duct positioned radially therebetween, a plurality of deswirling struts circumferentially spaced apart with respect to a central axis of the TEC and located within an axial length of the mixer between an upstream end where exhaust gases enter the mixer and a downstream end of the mixer where exhaust gases are discharged from the mixer and mixes with the bypass air stream, the deswirling struts each having a cambered profile and extending radially across the annular exhaust gas duct and interconnecting the mixer and the hub.
In another aspect, there is provided a turbofan aeroengine comprising a turbine exhaust case (TEC) positioned downstream of a turbine section for directing a flow of gases exhausted from the turbine section, the TEC including an inner annular hub surrounded by an annular outer wall, a downstream end section of the outer wall being in a circumferential wavy configuration to form a plurality of axially extending lobes defining alternative crests and valleys extending divergently to a downstream end of the TEC, the crests defining internal axial and radially-outward passages for directing gases exiting from the turbine section to pass through the TEC, and the valleys defining external axial and radially-inward passages for directing a bypass air stream to pass along an external surface of the TEC, resulting in mixing of the gases with the bypass air stream, a plurality of circumferentially spaced deswirling struts each having a cambered profile and located within an axial length of the wavy configuration for deswirling a rotational component of the gases passing through the TEC.
Further details of these and other aspects of the described subject matter will be apparent from the detailed description and drawings included below.
Reference is now made to the accompanying figures in which:
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
Referring to
It should be noted that the terms “upstream” and “downstream” used herein and hereinafter refer to the direction of a fluid flow passing through the main fluid path of the engine. It should also be noted that the terms “axial”, “radial” and “circumferential” are used with respect to the central axis 34.
The mixer 30 according to one embodiment such as shown in
The inner surface 46 may define inner passageways (not numbered) axially and radially-outwardly along the respective crests 52 for directing the exhaust gases flowing through the annular exhaust gas duct 40. The outer flow surface 48 may define external passageways (not numbered) axially and radially-inwardly along the respective valleys 54 for directing the bypass airstream coming through the annular bypass air duct 32 to flow through the mixer 30. Therefore, the internal and external passageways of the mixer 30 may in combination establish a vortex system downstream of the mixer 30 to encourage mixing between the bypass airstream and the turbine exhaust gases during operation of the aeroengine.
Referring to FIGS. 1 and 3-5, the mixer 30 according to one embodiment may include a plurality of deswirling struts 58 circumferentially spaced apart with respect to the central axis 34. The deswirling struts 58 may be disposed within an axial length of the mixer 30, between the upstream end 42 and the downstream end 44 of the mixer 30. The deswirling struts 58 may extend radially across the annular exhaust gas duct 40 and may interconnect the mixer 30 and the hub 36 of the TEC 28.
The deswirling struts 58 each include a leading edge 60 and a trailing edge 62. The trailing edge 62 of each deswirling strut 58 according to one embodiment may circumferentially align with a bottom of the valley 54 such as a bottom line 64 (see
Optionally, the deswirling struts 58 may each have a cambered profile, for example including a convex side 66 and a concave side 68 extending between the leading and trailing edges 60 and 62 as shown in the cross-sectional view of the deswirling strut 58 in
According to one embodiment the deswirling of the swirling flow 70 of the exhaust gases discharged from the low pressure turbine assembly 38 and passing through the annular exhaust gas duct 40, may be accomplished within the mixer 30 by both the deswirling struts 58 and the mixer lobes 50. The swirling flow 70 of exhaust gases passing through the annular exhaust gas duct 40 near the hub 36 may be deswirled by the deswirling struts 58. The swirling flow 70 of the exhaust gases passing through the annular exhaust gas duct 40 near the shroud 38 may be deswirled by the lobes 50 of the mixer 30. With the configuration as described in the above embodiments, the deswirling and mixing functions may be accomplished within a much shorter axial length of the TEC and mixer in contrast to conventional TEC and mixer configurations, thereby advantageously saving engine and nacelle weight. The configuration of the above-described embodiments, can deswirl the swirling flow of exhaust gases and mix the exhaust gases with the bypass air stream with a performance equivalent to or better than that of conventional separate mixer and TEC struts.
The size, shape and position of the deswirling struts may be optimized based on the application and are dependent on the flow conditions including the residual swirl condition from the low pressure turbine assembly 18. The deswirling struts according to the described embodiments may be incorporated into any conventional TEC mixer when the swirl in the exhausted gases is required to be removed. For example, some of the described embodiments may be applicable to TEC mixers in which the axial length of the valleys of the mixers are longer than the axial length of the crests of the mixers.
Alternatively, the deswirling struts 58 may be axially located within the mixer 30 such that the leading edge 60 of each of the deswirling struts 58 axially aligns with the start point 56 of the divergently extending crests 52 and valleys 54, as shown by broken line 60a in
Optionally, each of the valleys 54 of the mixer 30 may be connected with one of the deswirling struts. Also optionally, every second one of the valleys 54 of the mixer 30 may be connected with one of the deswirling struts. Furthermore, the deswirling struts may be circumferentially located at other intervals of the valleys 54 of the mixer 30.
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 described subject matter. Modifications which fall within the scope of the described subject matter 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.
Number | Date | Country | |
---|---|---|---|
61879723 | Sep 2013 | US |