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EP-4299891-B1 - ROTATABLY DRIVEN EXHAUST MIXER

EP4299891B1EP 4299891 B1EP4299891 B1EP 4299891B1EP-4299891-B1

Inventors

  • LABRECQUE, MICHEL
  • NGUYEN, KEVIN

Dates

Publication Date
20260513
Application Date
20230627

Claims (14)

  1. An exhaust mixer arrangement (32; 32') for a turbofan engine (10) having an annular bypass passage (24) for channelling a bypass flow, and a core passage (26) for channelling a core flow around a central axis (30), the exhaust mixer arrangement (32; 32') comprising: a mixer body (33) having an annular wall (34) extending around the central axis (30), the annular wall (34) defining a plurality of circumferentially distributed alternating inner and outer lobes (42, 44), with each inner lobe (42) protruding into the core passage (26), and each outer lobe (44) protruding into the annular bypass passage (24); a driving unit (50) operatively connected to the mixer body (33) for selectively driving the mixer body (33) in rotation about the central axis (30); and a controller (62) operatively connected to the driving unit (50), the controller (62) operational to control a rotational speed of the mixer body (33) as a function of a flight operating condition, characterised in that : the mixer body is mounted for 360-degree rotation about the central axis (30); and the inner and outer lobes (42, 44) are angled in a direction of rotation of the mixer body (33).
  2. The exhaust mixer arrangement (32; 32') according to claim 1, wherein the driving unit (50) comprises an actuator (52) drivingly connected to a transmission (54), the transmission (54) drivingly connected to the mixer body (33).
  3. The exhaust mixer arrangement (32; 32') according to claim 2, wherein the transmission (54) includes a gear (56; 58) drivingly connected to the mixer body (33).
  4. The exhaust mixer arrangement (32; 32') according to claim 3, wherein the gear (56) includes a series of teeth projecting from an outer flange at an upstream end (36) of the mixer body (33).
  5. The exhaust mixer arrangement (32; 32') according to claim 3 or 4, wherein the gear (56) is a worm wheel in meshing engagement with a worm drivingly connected to the actuator (52).
  6. The exhaust mixer arrangement (32; 32') according to any preceding claim, wherein the controller (62) is configured to initiate the rotation of the mixer body (33) during a descent/approach phase of a flight.
  7. The exhaust mixer arrangement (32; 32') according to claim 6, wherein the controller (62) is configured to vary the rotational speed of the mixer body (33) during the descent/approach phase of the flight.
  8. The exhaust mixer arrangement (32; 32') according to any preceding claim, wherein a lock (60) is engageable with the mixer body (33) to selectively lock the mixer body (33) against rotation.
  9. A turbofan engine (10) comprising: a fan (12); a compressor (14) downstream of the fan (12); a turbine (18) fluidly connected to the compressor via the core passage (26); and the exhaust mixer arrangement (32; 32') according to any preceding claim, the exhaust mixer arrangement (32; 32') fluidly connected to the annular bypass passage (24) and the core flow passage downstream of the turbine (18).
  10. The turbofan engine (10) according to claim 9, further comprising a turbine exhaust case having a circumferential array of struts (20b) extending radially between a radially outer annular wall (20c) and a radially inner annular wall (20d), the mixer body (33) engaged on an annular railing (46) provided on an outer surface of the radially outer annular wall (20c) of the turbine exhaust case.
  11. The turbofan engine (10) according to claim 10, wherein bearings are provided between the radially outer annular wall (20c) of the turbine exhaust case and the mixer body (33).
  12. The turbofan engine (10) according to any of claims 9 to 11, wherein the controller (62) is configured to maintain the mixer body (33) stationary during a cruise flight segment.
  13. A method of mixing a core flow and a bypass flow surrounding the core flow with an exhaust mixer (32; 32') having circumferentially alternating inner and outer lobes (42, 44) respectively extending into the core flow and the bypass flow, the method comprising circulating the core flow through the exhaust mixer (32; 32') and the bypass flow around the exhaust mixer (32; 32'), characterised in that : the method further comprises, during a descent/approach segment of a flight, driving the exhaust mixer (32; 32') in rotation at a selected rotational speed in a swirl direction of the core flow; and the inner and outer lobes (42, 44) are angled in a direction of rotation of the exhaust mixer (32; 32').
  14. The method according to claim 13, wherein the selected rotational speed is smaller than a swirl velocity of the core flow.

Description

TECHNICAL FIELD The application relates generally to turbofan engines and, more particularly, to a turbine exhaust mixer for such engines. BACKGROUND OF THE ART In turbofan engines, high velocity gases from the turbofan core is mixed with low velocity air from the bypass duct, and this fluid mixture is then exhausted from the engine. Turbofan engines generally use exhaust mixers in order to increase the mixing of the high and low velocity fluid flows. The exhaust mixers have lobes that enhance the mixing of the flows and augment thrust. Typically, aggressive lobe designs are used to promote better mixing. However, aggressive lobes designs come with trade-offs. Alternatives are thus desirable. US 2014/090359 A1 relates to a mixer that performs reciprocating rotary motion for a confluent-flow nozzle. US 2017/130672 A1 relates to a chevron nozzle for an engine of an aircraft having at least one nozzle ring and chevrons arranged on the nozzle ring, the nozzle ring together with the chevrons designed so as to be freely rotating. SUMMARY In one aspect of the invention, there is provided an exhaust mixer arrangement for a turbofan engine as claimed in claim 1. In a further aspect of the invention, there is provided a method of mixing a core flow and a bypass flow surrounding the core flow as claimed in claim 13. Various embodiments of the above aspects of the invention are as claimed in the dependent claims. DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanying figures in which: Fig. 1 is a schematic cross section view of a long cowl turbofan engine having a rotatably driven exhaust mixer;Fig. 2 is an isometric view of an exemplary mixer body of the rotatably driven exhaust mixer;Fig. 3 is an isometric view of a rotatably driven mixer arrangement comprising a controller operatively connected to a driving unit drivingly connected to a rotatable exhaust mixer body rotatably mounted to a turbine exhaust case (TEC);Fig. 4 is a schematic cross-section view illustrating an annular railing and bearing arrangement at a mounting interface between the mixer body and the TEC; andFig. 5 is schematic view of a short cowl turbofan engine having a rotatably driven exhaust mixer. DETAILED DESCRIPTION Fig. 1 illustrates a turbofan engine 10 of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan 12 through which ambient air is propelled, a compressor section 14 for pressurizing the air, a combustor 16 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section 18 for extracting energy from the combustion gases. The turbofan engine 10 includes a first casing 20 which encloses the turbo machinery of the engine, and a second, outer casing 22 extending outwardly of the first casing 20 such as to define an annular bypass passage 24 therebetween. The air propelled by the fan 12 is split into a first portion which flows around the first casing 20 within the bypass passage 24, and a second portion which flows through a main gas path or annular core passage 26, which is defined within the first casing 20 and allows the flow to circulate through the multistage compressor 14, combustor 16 and turbine section 18 as described above. The first casing 20 may be composed of a number of axially serially interconnected cases, including a turbine exhaust case (TEC) 20a (Fig. 3) extending downstream from the last stage of turbine blades of the turbine section 18. As shown in Fig. 3, the TEC 20a may comprise an array of circumferentially spaced-apart struts 20b extending between a radially outer annular wall 20c and a radially inner annular wall 20d, the radially outer and an inner annular walls 20c, 20d concentrically disposed around a central axis 30 (e.g. the engine centerline). The radially outer and inner annular walls 20c, 20d respectively form part of the outer and inner flow boundary walls of the core passage 26. As exemplified in Fig. 1, an axisymmetrical bullet or tail cone 28 may be centrally mounted to the rear end of the TEC 20a so as to project axially rearwardly therefrom. The tail cone 28 defines a rearmost extension of the inner flow boundary wall of the core passage 26. Referring to Figs. 1 to 3, it can be seen that the engine 10 further comprises an exhaust mixer arrangement. The exhaust mixer arrangement generally comprises an exhaust mixer 32 for mixing the core flow and the bypass flow at the discharge end of the engine 10. According to some embodiments, the exhaust mixer 32 is mounted to the TEC 20a inside the outer casing 22 so as to surround at least a portion of the tail cone 28. The mixer 32 acts as a rearmost portion of the outer wall defining the core passage 26 and a rearmost portion of the inner wall defining the bypass passage 24. The hot gases from the main gas path 26 and the cooler air from the bypass passage 24 are, thus, mixed together by the exhaust mixer 32 at th