Air cooling design for tail-cone generator installation

The application relates generally to a system and method for cooling a tail-cone mounted generator.

One or more generators may be positioned in the tail-cone of an engine to provide additional electrical power during normal engine operating conditions as well as emergency situations. However, an engine tail-cone may be quite hot and, thus, in order to ensure proper operation of the generator(s), it is desirable to provide a cooling system to ensure that the temperature of the generator remains acceptable despite being subjected to high temperature flows. Still, known cooling systems usually require installation of additional components in the engine system and may therefore add to the weight and complexity of the engine, in addition to increasing aerodynamic drag.

There is therefore a need for an improved system and method for cooling a tail-cone mounted generator.

In one aspect, there is provided a system for cooling a generator mounted in a cavity of an engine tail-cone, the engine comprising a casing having the tail-cone coupled thereto, a core compartment within the casing, and an intake for drawing air into the casing, the system comprising a bypass passage defined between the casing and the core compartment, the bypass passage adapted to divert a bypass portion of the air therethrough; at least one fairing coupled to the tail-cone in fluid communication with the bypass passage and the tail-cone cavity, the at least one fairing configured to direct the bypass portion of the air towards the tail-cone cavity; and a support strut coupled to the casing in fluid communication with the bypass passage and the tail-cone cavity and adapted to expel the bypass portion of the air from the tail-cone cavity towards the bypass passage.

In another aspect, there is provided a method for cooling a generator mounted in a cavity of an engine tail-cone, the engine comprising a casing having the tail-cone coupled thereto, a core compartment within the casing, and an intake for drawing air into the casing, the method comprising diverting a bypass portion of the air through a bypass passage defined between the casing and the core compartment; directing the bypass portion of the air through at least one fairing in fluid communication with the bypass passage and the tail-cone cavity and towards the tail-cone cavity; and expelling the bypass portion of the air from the tail-cone cavity and towards the bypass passage through a support strut in fluid communication with the bypass passage and the tail-cone cavity.

In a further aspect, there is provided a system for cooling a generator mounted in a cavity of an engine tail-cone, the engine comprising a casing having the tail-cone coupled thereto, a core compartment within the casing, and an intake for drawing air into the casing, the method comprising means for diverting a bypass portion of the air through a bypass passage defined between the casing and the core compartment; means for directing the bypass portion of the air through at least one fairing in fluid communication with the bypass passage and the tail-cone cavity and towards the tail-cone cavity; and means for expelling the bypass portion of the air from the tail-cone cavity and towards the bypass passage through a support strut in fluid communication with the bypass passage and the tail-cone cavity.

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine, in accordance with an illustrative embodiment;

FIG. 2 is a schematic cross-sectional view of a tail-cone of the gas turbine engine of FIG. 1 ;

FIG. 3 is a top perspective view of a fairing routed through a lobe mixer, in accordance with an illustrative embodiment;

FIG. 4 is a partial schematic cross-sectional view of the fairing of FIG. 3 ;

FIG. 5 a is a perspective view of the lobe mixer of FIG. 3 ; and

FIG. 5 b is a cross-sectional view of the fairing of FIG. 3 routed through a cold lobe of the lobe mixer of FIG. 5 a.

Referring to FIG. 1 , a turbofan gas turbine engine 10 of a type typically provided for use in subsonic flight and presented for illustrative purposes, includes a housing or nacelle 12 , a core casing or Turbine Exhaust Case (TEC) 14 , a low pressure spool assembly seen generally at 16 , and a high pressure spool assembly seen generally at 18 . The low pressure spool assembly 16 includes a fan assembly 20 , a low pressure compressor assembly 22 , and a low pressure turbine assembly 24 . The high pressure spool assembly 18 includes a high pressure compressor assembly 26 and a high pressure turbine assembly 28 . the core casing 14 surrounds the low and high pressure spool assemblies 16 and 18 in order to define a main fluid path (not shown) therethrough. In the main fluid path, there is provided a combustor 30 to constitute a gas generator section 32 .

The core casing 14 defines with the low pressure compressor assembly 22 a low pressure compressor inlet 34 for receiving a portion of ambient air 36 . A portion 37 of the air 36 is then compressed by the fan assembly 20 and further by the low pressure compressor assembly 22 and the high pressure compressor assembly 26 . The compressed air 37 is then forced into the combustor 30 . A mixture of the compressed air 37 and fuel injected by a fuel injecting means (not shown) generates combustion gases for rotating the low and high pressure turbine assemblies 24 and 28 and powering the low and high pressure compressor assemblies 22 and 26 and the fan assembly 20 . A radial spacing between the nacelle 12 and the core casing 14 further defines an annular bypass duct or passage 38 , which permits a portion 40 of the air 36 to bypass the engine 10 . As such, the bypass air 40 is illustratively at a lower temperature than the hot exhaust flowing through the core casing 14 and discharging from the combustor 30 . Due to the radial symmetry of the engine 10 relative to the engine axis A, a second bypass duct 41 is illustratively provided above the engine axis A.

Referring to FIG. 2 in addition to FIG. 1 , the gas turbine engine 10 further includes an annular turbine exhaust duct 42 attached to the core casing 14 . The core casing 14 illustratively comprises an annular inner case 44 and an annular outer case 46 . A plurality of circumferentially spaced apart airfoils 48 extend radially between the inner and outer cases 44 , 46 to thereby structurally connect same. A bearing housing 50 is co-axially connected to the inner case 44 for supporting an aft end of a main shaft (not shown) of the low pressure spool assembly 16 . A lobe mixer 52 is illustratively installed in the exhaust duct 42 and attached to the rear end of the outer case 46 to mix the core exhaust flow with the bypass flow from the bypass duct 38 . A mounting flange 54 may further be integrated with the outer case 46 at a front end thereof for securing the annular turbine exhaust duct 42 to the engine core casing 14 . The engine core casing 14 is in turn structurally connected to the nacelle 12 through a plurality of radially extending support struts (reference 56 in FIG. 3 ) positioned within the annular bypass duct 38 .

A tail-cone 58 may further be attached to a rear end of the inner case 44 of the annular turbine exhaust duct 42 to cover an opening defined by the rear end of the inner case 44 and thus provide an aerodynamic fairing. A generator 60 may be arranged within a cavity 62 of the tail-cone 58 and driven by the low pressure spool assembly 16 . It may therefore be desirable to insulate the generator 60 from the core exhaust flow from the exhaust duct 42 .

Referring to FIG. 3 , generator services 64 , such as electrical cables or other lines used for servicing the engine 10 and/or aircraft (not shown), are illustratively routed through at least one fairing 66 spanning across the bypass duct 38 . The fairing 66 may comprise a fairing inlet 68 and illustratively provides an aerodynamic shape around the services 64 . The fairing 66 may indeed be provided with an increased sweep angle to form an S-shape. With such a shape, the fairing's relative thickness, which is the ratio between the maximum thickness of the fairing 66 in the direction extending transversely to the flow divided by the dimension that the fairing 66 occupies in the longitudinal direction of the flow, may be reduced. Thus, overall parts count and weight of the engine 10 may be lowered in addition to decreasing aerodynamic drag. It should be understood that, due to the radial symmetry of the engine 10 relative to the engine axis A of FIG. 1 , a pair of fairings 66 may be used, with each fairing 66 being provided on either side of, i.e. above or below, the engine axis A. The fairings 66 may then be in fluid communication with respective ones of the bypass ducts 38 and 41 . It should also be understood that more than two fairings as in 66 may be used on either side of the engine axis A, the number of fairings 66 varying according to the desired cooling effect to be achieved.

Referring to FIG. 3 and FIG. 4 , a portion 70 1 of the bypass duct air 40 flowing through the annular bypass duct 38 illustratively enters through the fairing inlet 68 and flows into the fairing 66 towards the tail-cone cavity 62 . Once the stream of air 70 1 reaches the tail-cone cavity 62 , the stream 70 1 illustratively separates into at least two air streams 72 and 74 and flows around the tail-cone mounted generator 60 for cooling thereof. The air streams 72 and 74 may then recombine into the air stream 70 2 , which passes through the hollow strut 56 and exits at an outlet 76 to meet the bypass duct air 40 . A cooling circuit is thus illustratively created for cooling the tail-cone mounted cavity 62 and the generator 60 . The cooling circuit may also supplement a conventional oil cooling system, which may be used to cool the generator 60 .

In order to enable the cooling air 70 1 to flow through the fairing 66 and the generator 60 , a pressure differential may be achieved between the fairing inlet 68 and the outlet 76 . For this purpose, the outlet 76 is illustratively positioned in the same plane B, which is shown in cross-section on FIG. 4 , as the fairing inlet 68 . The plane B is illustratively perpendicular to the longitudinal plane (not shown) of the engine 10 , the longitudinal plane being shown in cross-section as axis A on FIG. 1 . With the fairing inlet 68 and outlet 76 both positioned in the plane B, the air 70 1 entering the fairing 66 at the inlet 68 may be at the same static pressure as the air 70 2 exiting the strut 56 at the outlet 76 . The static pressure illustratively represents the pressure of still air and is measured perpendicular to the surface of the aircraft (not shown), and accordingly of the engine 10 . By ensuring that both the fairing inlet 68 and the outlet 76 are at the same static pressure, reverse air flow may be prevented. In particular, a reverse flow of the cooling air 70 2 into the strut 56 , through the tail-cone cavity 62 , and into the fairing 66 may be prevented.

The flow of cooling air 70 1 , 70 2 may further be driven by the difference between the total air pressure and the static air pressure, namely the ram or dynamic pressure created by the motion of the aircraft (not shown). The ram pressure may indeed result from the movement of the air through the fairing 66 and the tail-cone cavity 62 . With the fairing inlet 68 and the outlet 76 at the same static pressure, circulation of the cooling air 70 1 , 70 2 may simply be achieved by the aircraft's movement during flight and complexity of the cooling system may therefore be reduced.

Referring to FIG. 5 a in addition to FIG. 4 , the lobe mixer 52 illustratively comprises a body 80 defining inner or hot lobes 82 and outer or cold lobes 84 . The lobes 82 and 84 may be used for directing and mixing flows of hot air from the exhaust duct 42 and flows of cold air from the bypass duct 38 . Indeed, the hot lobes 82 illustratively define outer open-ended channels or chutes 86 for transferring the high-speed hot core exhaust into the low-speed bypass duct air 40 . The cold lobes 84 illustratively define inner open-ended channels or chutes 88 for transferring the bypass duct air 40 into the hot core exhaust. Merging and mixing of the hot and cold air streams can therefore be achieved. As flow velocity is proportional to temperature, this may in turn reduce the speed of the core exhaust and increase the speed of the bypass flow, thereby making the distribution of the ejected air streams uniform. The overall perceived noise level may accordingly be lowered since noise produced by the engine 10 increases with increased relative difference in velocity between the core and bypass flows.

The fairing 66 may be routed through a cold lobe 84 1 , which illustratively directs the bypass duct air 40 towards the core exhaust. In order to shield the fairing 66 from direct impingement of the hot core exhaust, the distal portion (not shown) of the lobe 84 1 may be extended. For this purpose, the lobe 84 1 may comprise a pair of opposite shields 90 a and 90 b , which extend axially away from opposite side edges 92 a and 92 b of the chute 88 1 . A shield 94 may also be provided, which extends radially away from a middle edge 96 of the chute 88 1 . Provision of both shields 90 a , 90 b , and 94 illustratively increases the coverage and heat insulation provided by the cold lobe 84 1 . The fairing 66 run through the lobe 84 1 may therefore be better shielded from the hot core exhaust, and heat transfer to the cooling air 70 1 routed through the fairing 66 may be reduced. A cooler environment may thus be provided inside the fairing 66 as the latter crosses the hot core airflow.

Since a plurality of fairings as in 66 may be provided for cooling the generator 60 , it should be understood that more than one cold lobe as in 84 1 may be adapted to route a fairing 66 therethrough. As such, although only the cold lobe 84 1 has been illustrated as comprising shields 90 a , 90 b , and 94 , it should be understood that a plurality of the cold lobes 84 may comprise shields 90 a , 90 b , and 94 .

Referring to FIG. 5 b , a cooler environment may further be maintained inside the fairing 66 by provision of a spacing 98 between an outer surface 100 of the fairing 66 and the inner surface 94 of the lobe 84 1 when the fairing 66 is positioned within the cold lobe 84 1 . Indeed, despite the hot core exhaust impinging on the lobe 84 1 , air within the spacing 98 between the lobe 84 1 and the outer surface 100 of the fairing 66 illustratively remains at a temperature which is intermediate between the temperature of the core exhaust and the temperature of the cooling air flowing through the fairing 66 . As a result, heat transfer from the core exhaust to the cooling air may be lowered.

The fairing 66 thus illustratively acts as a physical barrier by shielding the generator services 64 from the surrounding core exhaust. In addition, the cooling air 70 1 flowing through the fairing 66 may reduce direct hot air impingement on the generator services 64 and maintain a cool environment around the generator services 64 . As electrical resistance and losses increase with increased temperature, cooling the environment surrounding the generator services 64 may enable smaller gauge wires to be used for the generator services 64 . The current carrying capability of generator power feeder cables (not shown) and other cables constituting the generator services 64 may also be increased by routing such cables through the cooled fairing 66 . The loading on the generator 60 may in turn be increased. As such, the overall weight and envelope of the fairing arrangement 66 and of the generator services 64 may be reduced.

Heat transfer within the tail-cone cavity 62 between the cooling air 70 1 and the hot exhaust air may further be prevented by the double-walled structure of the tail-cone 58 . Thermal induced stress may indeed be reduced by attaching the faring 66 to an inner wall ( 59 ) of the tail-cone 58 . Since core exhaust illustratively impinges on the outer wall (not shown) of the tail-cone 58 , the inner wall may remain cooler than the outer wall (not shown). Thus, coupling the fairing 66 to the inner wall may improve heat insulation of the air 70 1 routed through the fairing 66 , and thus ultimately enhance the cooling effect achieved by the fairing 66 .

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. 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.