HEAT EXCHANGER INTEGRATION

Abstract

A front centre body (FCB) structure for a geared turbofan engine comprises a plurality of vanes extending across the inlet duct to a low pressure compressor and integrates a heat exchanging arrangement to control the temperature of the gearbox of the turbofan engine.

Claims

1.-22. (canceled)

23. A front center body (FCB) structure for a geared turbofan engine, comprising: a central hub and a coaxial shroud spaced from said hub and defining an annular passage between the hub and shroud for communicating air to a compressor; and a body including a plurality of vanes extending across the passage from the hub to the shroud, wherein one or more of the vanes are provided with a fluid passage within the respective vane extending from, and returning to, a portion of the respective vane intersecting with the hub.

24. The structure of claim 23, wherein each of the one or more vanes intersects with an outer surface of the hub and an inner surface of the shroud.

25. The structure of claim 23, wherein each vane has a fluid inlet from the hub to the vane and a fluid outlet from the vane to the hub; and wherein the fluid passage within each respective vane is arranged to communicate a coolant from a gearbox of the geared turbofan engine through the respective vane via a respective inlet and outlet.

26. The structure of claim 25, wherein the fluid passage within each respective vane defines a cooling path extending from the gearbox, or a heat exchanger associated with the gearbox, into the respective vane and back to the gearbox or heat exchanger.

27. The structure of claim 23, wherein each vane has a peripheral wall having an outer surface against which air is configured to flow and an opposing inner surface facing into the vane, wherein the respective fluid passage is arranged to be proximate to the inner surface of the respective vane.

28. The structure of claim 27, wherein the respective fluid passages alternate in direction from the hub towards the shroud and from the shroud towards the hub.

29. The structure of claim 27, wherein the respective fluid passages are in contact with the inner surface of the respective vane.

30. The structure of claim 27, wherein the respective fluid passages are arranged proximate a leading edge of the respective vane.

31. The structure of claim 23, wherein at least one cavity is provided between inner and outer surfaces of at least one of the vanes to define at least one of the fluid passages.

32. The structure of claim 31, wherein the cavity extends from a leading edge of the at least one of the vanes towards a trailing edge thereof.

33. The structure of claim 23, wherein the shroud is provided with a circumferential cavity extending between a radially inward wall and a radially outward wall, said cavity extending along all or part of the axial length of the annular passage.

34. The structure of claim 23, wherein the hub is provided with a circumferential cavity extending between a radially inward wall and a radially outward wall, said cavity extending along all or part of the axial length of the annular passage.

35. The structure of claim 33, wherein the circumferential shroud cavity and/or the circumferential hub cavity extend circumferentially between adjacent vanes.

36. The structure of claim 31, wherein the at least one cavity defines a fluid passage.

37. The structure of claim 23, wherein an inlet to a fluid passage is at an upstream end of a respective vane and an outlet is at a downstream end of the respective vane.

38. The structure of claim 27, wherein at least one vane fluid passage is in fluid communication with at least one shroud and/or hub cavity to allow fluid to flow there between.

39. The structure of claim 36, wherein each vane fluid passage is in fluid communication with an adjacent shroud cavity and/or hub cavity.

40. A geared turbofan engine comprising at least one inlet duct arranged to communicate air to a low pressure compressor, wherein the inlet duct(s) comprise a plurality of vanes and wherein one or more vanes are provided with an internal heat exchanger in thermal communication with a gearbox of said engine.

41. The geared turbofan engine of claim 42, wherein a coolant path is provided between the gearbox and the one or more vanes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] One or more embodiments will now be described, by way of example only, and with reference to the following figures in which:

[0039] FIG. 1 shows a cross-section of a geared turbo fan engine;

[0040] FIG. 2 shows a cross-section through a geared turbofan engine;

[0041] FIG. 3 shows a cross-section through a heat exchanger arrangement described herein;

[0042] FIG. 4 shows a pair of guide vanes incorporating a heat exchanging conduit;

[0043] FIG. 5 illustrates the cooling zones of the front centre body;

[0044] FIG. 6 shows a fluid passage through a single vane which intersects with the shroud and hub;

[0045] FIG. 7 shows a cross section through the wall of the shroud;

[0046] FIG. 8 shows a cross-section through the vane;

[0047] FIG. 9 shows an alternative serpentine arrangement of fluid path;

[0048] FIGS. 10A, 10B and 10C illustrate arrangements of fluid paths adjacent to the inner surface of the vane; and

[0049] FIGS. 11 and 12 relate to the heat transfer calculations described herein.

[0050] Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The disclosure is further described with reference to the examples described herein. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the disclosure covers not only individual embodiments but also combination of the embodiments described herein.

DETAILED DESCRIPTION

[0051] FIG. 1 shows a cross-section of a geared turbo fan engine 1 incorporating a duct as described in detail below.

[0052] The skilled person will understand the principal components of a gas turbine engine and their operation. In summary the engine 1 comprises an air intake 2 which permits air to flow into the engine to the fan 3 located at the upstream end of the engine. All of the components are housed within the engine nacelle 4.

[0053] The engine comprises a bypass channel downstream of the fan and a central engine core which contains the compressors, combustors and turbines. The core of the engine is formed of a first low pressure compressor 5 and a second high pressure compressor 6. This multi-stage compressor arrangement takes air from ambient pressure and temperature to high temperature and pressure. Compressed air is then communicated to the combustion chamber 7 where fuel is injected and combustion occurs.

[0054] The combustion gases are expelled from the rear of the combustions chamber 7 and impinge first on a high pressure turbine 9 and then on a second low pressure turbine before leaving the rear of the engine through the core nozzle 11. Thrust from the engine is created by two gas flows: a first from the fan nozzle 8 (receiving thrust from the fan) and secondly from the exhaust gases from the core nozzle 11.

[0055] Turning to the operation of the engine, a geared turbofan (GTF) is distinguished from a normal gas turbine engine because the centrally located shaft 13, which runs along the length of the engine, is coupled at an upstream end to a gearbox 14. The gearbox allows the fan to rotate at a different speed to the compressor and allows the relative speeds of the fan and compressor to be optimised. Specifically the gearing ratio allows the fan to rotate at a lower speed than the compressor.

[0056] In order to save weight a convenient gearbox to use is an epicyclic gearbox, that is a gearbox with a centrally located sun gear and a plurality (normally 3) of circumferentially positioned planetary gears that are meshed with the central sun gear and rotate relative to the sun gear when the sun gear is itself rotated (in this case by the compressor shaft 13).

[0057] Depending on how the gearbox is configured (which will be well understood by someone skilled in the art) the output of the gearbox may be connected to the planetary gears (by means of a gear carrier) or alternatively to an annular gear surrounding the planetary gears (and also meshed thereto).

[0058] In the present case the output of the gearbox is coupled to the fan blade hub 15 which comprises a plurality of fan blades 3. In operation the low pressure shaft drives the gearbox which in turn drives the fan. Air is then driven through the engine through the bypass channel 8 and through the core (containing the compressors and combustors).

[0059] Although GTF engines are highly efficient, a drawback with their design is that the gearbox can become extremely hot and requires cooling. Cooling is conventionally achieved by means of a large oil reservoir, pump and cooling circuit. The cooling circuit fluidly connects the sump of the gearbox (that is the gearbox body containing the coolant and lubricant) to a heat exchanger which can dissipate heat from the coolant (typically an oil) and return the coolant back to the gearbox. Thus, the gearbox can be conveniently cooled using such a cooling circuit in combination with a pump. The heat exchanger may be conveniently located on an outer surface of the engine for example so as to benefit from the cold airflow the engine will experience at altitude when the gearbox is operating at maximum speed. This additionally removes heat from the engine which would otherwise increase the overall operating temperature of the engine. In a GTF engine the heat that is needed to be dissipated from the gearbox is substantially higher than normal requiring additional heat exchanging capacity within or around the bypass channel.

[0060] According to the present disclosure an unconventional approach is used wherein cooling is performed inside the engine and specifically inside the ducting used to supply air to the compressors.

[0061] As described below, according to the present disclosure heat is exchanged into the duct which introduces air into the engine core (or low pressure compressor). Convention in the industry says that it is hugely disadvantageous to engine performance to heat air entering the compressor. Consequently conventional arrangements use the conveniently abundant cold air that is available in and around the bypass channel.

[0062] Turning to FIG. 2 a cross-section through a geared turbofan engine is shown.

[0063] The GTF engine comprises an inlet duct 16 which receives air passing through the blades 3. The inlet duct 16 comprises a plurality of guide vane 17 illustrated by the hatched cross-section 17 in FIG. 2. It will be appreciated that the inlet duct is a circumferentially extending annular passage surrounding the hub and arranged to communication air to the low pressure compressor 5, which also extends around the periphery of the axis 13. Air is ingested into the compressor 5 through the duct 16 and past a plurality of radially extending guide vanes 17. The guide vanes are hollow and act to direct the airflow towards the compressor 5.

[0064] Conventional gearbox cooling is achieved by using the cold air in the bypass channel 8 where air can be diverted into heat exchangers. In contrast the present disclosure provides cooling for the gearbox within the core section of the engine, and specifically in the air inlet guide vanes 17.

[0065] As illustrated schematically in FIG. 3 a coolant path 18 is arranged within the guide vane 17. The coolant 18 originates from the gearbox 17 where heat is generated by the rotation and meshing of the gears. A lubricant or coolant, such as an oil, is used to collect heat within the gearbox 14. The oil is then directed to the coolant path or passage 18 either directly or via a primary heat exchanger 19. The coolant may be arranged to flow directly to the flow path or passage 18 (illustrated by the dotted lines) or may be arranged to flow through the heat exchanger (the operation of which will be understood by someone skilled in the art).

[0066] The flow of coolant from the gearbox, either directly or indirectly, to a heat exchanging arrangement within the guide vane 17 is, as described above, entirely counterintuitive.

[0067] FIG. 3 also illustrates the shroud 20 and the hub 21. The surface of the hub 21 rotates with the engine and the shroud remains static. The annular space between the hub and shroud defines the inlet duct 16 to the compressor 5. The annular space extends circumferentially around the engine core.

[0068] FIG. 4 illustrates a pair of adjacent vanes 22a, 22b. The vanes extend between the outer surface of the hub 21 where they both intersect and the inner surface of the shroud 20, again where they intersect. As illustrated in FIG. 4 each vane 22a, 22b is provided with a fluid/coolant inlet 23a, 23b and an associated fluid/coolant outlet 24b (23b not being visible in FIG. 4). Each vane has a leading edge 24a, 24b and a trailing edge 25a, 25b. Leading edge means leading in an airflow perspective.

[0069] As illustrated in FIG. 4 fluid or coolant may advantageously be introduced towards the leading edge of the vane. Thus, the fluid/coolant at the highest temperature is introduced into the vane at its coldest zone i.e. the leading edge. Fluid or coolant may be introduced, for example, from a circumferential manifold 26 allowing each vane to be in fluid communication with the gearbox or gearbox heat exchanger.

[0070] As airflow passes between the adjacent vanes and between the hub 21 and shroud 20 the air is caused to impinge on a number of surfaces maximising heat exchange. This is shown in FIG. 5.

[0071] FIG. 5 illustrates a simplified inlet duct with only 4 vanes 17. The surfaces against and along which heat transfer can take place are illustrated by:

[0072] A—the hub outer surface;

[0073] B—the shroud inner surface;

[0074] C—the vane pressure side; and

[0075] D—the vane suction side.

[0076] Thus, heat exchange can occur on any of the faces of the duct facing the airflow.

[0077] FIGS. 6, 7 and 8 illustrate one arrangement of the fluid passages within the vane and shroud/hub.

[0078] FIG. 6 shows a cross-section through a single vane 17 which intersects with the shroud 20 and hub 21. FIG. 6 also illustrates a shroud cavity 26 and a hub cavity 27 which are formed within the walls of the shroud and hub and which are arranged immediately adjacent to the airflow channel (the duct). The two cavities extend, as shown, along the length of the channel.

[0079] FIG. 6 also illustrates coolant inlets 28 and coolant outlets 29. The inlets and outlets allow coolant to be introduced into the cavities 26, 27 and to flow along each cavity (adjacent to the wall of the shroud and hub) towards their respective outlets. This thereby allows heat exchange to take place via conduction of heat from the coolant in the cavities to the airflow within the airflow channel.

[0080] Turning to FIG. 7 a cross-section A-A′ through the shroud 21 is shown. As shown the cavity is formed between an inner wall and outer wall of the shroud (or a portion of the shroud close to the duct). This cavity receives and communicates coolant, such as oil, along the cavity from the inlet to the outlet.

[0081] FIG. 7 also illustrates a plurality of fins 29 which may extend from the shroud wall and into the airflow. This may substantially increase the thermal conductivity of the shroud thereby increasing the heat dissipation from the coolant. It will be recognised that a similar feature may be added to the hub surface (not shown).

[0082] FIG. 8 shows a cross-section B-B′ through the vane 17. As shown the vane 17 comprises a fluid passage 30 adjacent to the outer surface or wall of the vane. As illustrated by the arrows the fluid passage is arranged to communicate the coolant along the length of the vane from the leading edge 24a to the trailing edge 25a. As shown coolant may be introduced through inlet 31 from the gearbox and returned to the gearbox from the outlet 32.

[0083] FIG. 9 shows an alternative serpentine arrangement of fluid path within the vane 17. In such an arrangement the coolant is configured to flow through the vane in an alternating direction from hub to shroud and from the leading edge towards the trailing edge where the coolant outlets from the vane to return to the gearbox. As discussed above the fluid path may advantageously be adjacent to the inner surface of the vane so as to maximise the heat dissipation.

[0084] FIGS. 10A, 10B and 10C illustrate arrangements of fluid paths adjacent to the inner surface of the vane (in contrast to the cavity shown in FIG. 8). FIG. 10A corresponds to the arrangement shown in FIG. 9. FIGS. 10B and 10C show examples of fluid paths being arranged along the inner surface of the vane.

[0085] FIGS. 11 and 12 relate to the heat transfer calculations discussed at page 15 below.

[0086] Referring to FIG. 11, to remove the generated heat from the gearbox, an oil system is used. The oil which is heated up through the gearbox is then re-directed through the FCB heat-exchanger where the cold air in the core is used as the cooling medium.

[0087] To check the feasibility of this concept, the required cooling energy, i.e., the lost energy from the gearbox transmission is compared with the amount of available energy that can be facilitated in the FCB heat exchanger. The amount of available energy for cooling (Preq) is a function of the surface area (AFCB), the heat transfer coefficient (HTCeq) and the temperature difference between the hot and cold side (Toil−Tgas).

[00001]$P_{\mathrm{req}}=P_{\mathrm{FAN}}\left(1-{\eta }_{\mathrm{Gearbox}}\right)$$P_{\mathrm{available}}=A_{\mathrm{req}}{\mathrm{HTC}}_{\mathrm{eq}}\left(T_{\mathrm{oil}}-T_{\mathrm{gas}}\right)$$A_{\mathrm{req}}=\frac{P_{\mathrm{req}}}{{\mathrm{HTC}}_{\mathrm{eq}}\left(T_{\mathrm{oil}}-T_{\mathrm{gas}}\right)}$$A_{\mathrm{FCB}}=A_{\mathrm{endwalls}}+A_{\mathrm{struts}}$

[0088] The question now becomes: How much surface area is required to keep the temperature of the oil below a certain threshold value. A reasonable maximum temperature of a typical oil is estimated to be 435 K. The heat transfer coefficient (HTC) is a function of the hot and cool medium and is estimated to be HTCgas=200 and HTCoil=3000 and the equivalent HTC thus become:

[00002]${\mathrm{HTC}}_{\mathrm{eq}}=\frac{1}{1/{\mathrm{HTC}}_{\mathrm{gas}}+1/{\mathrm{HTC}}_{\mathrm{oil}}}=188$

[0089] The power of the fan and the core temperature is taken from a representative geared turbofan (VINK, see FIG. 1) with a bypass ratio of 15, overall pressure ratio of 70 and a thrust range of 84 klbf.

[00003]$P_{\mathrm{req}}=P_{\mathrm{FAN}}\left(1-{\eta }_{\mathrm{Gearbox}}\right)=15000\left(1-0.995\right)=74.85\mathrm{kW}$$T_{\mathrm{gas}}=284K$$A_{\mathrm{req}}=\frac{P_{\mathrm{req}}}{{\mathrm{HTC}}_{\mathrm{eq}}\left(T_{\mathrm{oil}}-T_{\mathrm{gas}}\right)}=2.65m^2$

[0090] To assess if the required surface area of the heat exchanger is feasible it is compared to the preliminary layout of the VINK engine. FIG. 12 illustrates the available cooling surface areas. Assuming the FCB in the VINK engine to have 19 struts, the total surface area is sufficient for the heat exchanger to cool the gearbox:

[0091] A.sub.hub=0.793 m.sup.2

[0092] A.sub.shroud=0.852 m.sup.2

[0093] A.sub.blade=1.04 m.sup.2

[0094] .Math.A.sub.avail=2.69 m.sup.2

[0095] Aspects of the disclosure extend to a method of cooling a geared turbofan engine gearbox using the airflow within the inlet duct of such an engine.