WO2021151693A1

WO2021151693A1 - Flow control device actuation

Info

Publication number: WO2021151693A1
Application number: PCT/EP2021/050892
Authority: WO
Inventors: Daren Healy; Denys Custance
Original assignee: Airbus Operations Limited
Priority date: 2020-01-28
Filing date: 2021-01-18
Publication date: 2021-08-05
Also published as: GB2591471A; GB202001186D0

Abstract

An apparatus includes an outlet configured to output hot air, a flow control device movable between a first position and a second position, and a phase change actuator. The phase change actuator is connected to the flow control device and configured to move the flow control device between the first position and the second position at a predetermined temperature where a change of phase of a working substance of the phase change actuator occurs. In the second position, the flow control device may be configured to interact with an airflow and/or the hot air so as to protect a structure downstream of the outlet from overheating. The flow control device may be a vortex generator. In the second position, the vortex generator may be configured to interact with an airflow and/or the hot air from the outlet so as to redirect and/or reduce the temperature of the hot air.

Description

FLOW CONTROL DEVICE ACTUATION

FIELD OF THE INVENTION

[0001] The present invention relates to an apparatus with a moveable flow control device for interacting with an airflow.

BACKGROUND OF THE INVENTION

[0002] The various systems on aircraft often require outlets that output air into the atmosphere. This air is often outputted at elevated temperatures, for example the engines typically include an exhaust outlet from the engine pre-cooler (also known as a heat-exchanger) that outputs air at high temperatures (e.g. -190 degrees).

[0003] This often necessitates the use of protective barriers around the outlet, such as titanium shielding, so as to protect the aircraft structure downstream of the outlet. This provides a number of undesirable knock-on effects, for instance by adding the protective barrier, the weight and cost of the aircraft and the complexity of the manufacturing are increased.

SUMMARY OF THE INVENTION

[0004] A first aspect of the invention provides an apparatus comprising: an outlet configured to output hot air, a flow control device movable between a first position and a second position; and a phase change actuator connected to the flow control device and configured to move the flow control device between the first position and the second position at a predetermined temperature where a change of phase of a working substance of the phase change actuator occurs; wherein, in the second position, the flow control device is configured to interact with an airflow and/or the hot air so as to protect a structure downstream of the outlet from overheating.

[0005] A further aspect of the invention provides an apparatus comprising: an outlet configured to output hot air, a flow control device movable between a first position and a second position, wherein the flow control device is a vortex generator; and a phase change actuator connected to the vortex generator and configured to move the vortex generator between the first position and the second position at a predetermined temperature where a change of phase of a working substance of the phase change actuator occurs; wherein, in the second position, the vortex generator is configured to interact with an airflow and/or the hot air from the outlet so as to redirect and/or reduce the temperature of the hot air.

[0006] With this arrangement, the hot air from the outlet can be cooler and/or controlled so as to protect a structure downstream of the outlet. The hot air can even be redirected towards a specific target location, such as away from the structure, towards an inlet, or towards another desirable location.

[0007] The temperature at which the working substance of the phase change actuator changes phase is said to be a 'predetermined temperature'. It will be understood by the skilled person that the change in phase occurs over a narrow temperature range, rather than a specific singular temperature value.

[0008] Phase change actuators are based on well-known and well established technology, and as a result the phase change actuators can be manufactured to actuate the flow control device at a precise and well defined temperature (or temperature range). A particular advantage of this is that the flow control device is only deployed when required, as it would be aerodynamically inefficient to have the flow control device interacting with the airflow at all times. As such, the flow control device can be moved between the first position, in which the flow control device substantially does not interact with the airflow and/or hot air, and the second position, in which the flow control device is configured to interact with the airflow and/or hot air. Therefore, the flow control device can be configured to only be in the second position (deployed position) at elevated temperatures.

[0009] Furthermore, phase change actuators are passively controlled devices and so the mechanism can be designed so that the actuation between the first and second positions is entirely passively operated. The phase change actuator is able to harness the energy from the heat source, and use that energy to reduce or change the effect of that heat source downstream.

[0010] In addition, the mechanism can be designed so that the location of the phase change actuator and the flow control device are different, so that the phase change actuator and flow control device can each be positioned in their individual optimum positions. The optimum position of the flow control device and the phase change actuator are often different, which means that if the two devices could not be located at different locations the performance of the apparatus would potentially be limited.

[0011] A further aspect of the invention provides an aircraft comprising the assembly.

[0012] A further aspect of the invention provides a method of controlling an airflow over the surface of a structure using the assembly, the method comprising: heating the working substance of the phase change actuator to the predetermined temperature to move the flow control device from the first configuration to the second configuration.

[0013] The flow control device may be a vortex generator.

[0014] The apparatus may further comprise a structure, wherein the vortex generator is configured to interact with the airflow and/or the hot air so as to protect the structure from overheating.

[0015] The phase change actuator may be arranged adjacent the structure. As a result, the temperature of the phase change actuator may be configured to substantially correspond to the temperature of the structure.

[0016] The flow control device may be arranged upstream of the structure.

[0017] The movement of the flow control device by the phase change actuator may be passively controlled.

[0018] The phase change actuator may be mechanically connected to the flow control device so as to move the flow control device from the first position to the second position.

[0019] In the second configuration, the flow control device may be configured to be positioned in an airflow with a temperature lower than a temperature around the phase change actuator.

[0020] In the second configuration, the flow control device may be configured to be positioned in an airflow with a temperature lower than a temperature of the airflow around the structure. [0021] The temperature difference may be at least 50 degrees C. The temperature difference may be at least 100 degrees C.

[0022] The phase change actuator may be configured to be heated by the hot air from the outlet, or by heat from around the outlet. The phase change actuator may be configured to be heated by a heat source, e.g. that heats the hot air.

[0023] The flow control device may be arranged in the hot air outputted by the outlet.

[0024] The flow control device may be configured to attach to a surface, and wherein in the second position, the flow control device extends at an oblique angle to the surface.

[0025] The flow control device may be configured to attach to a surface, and wherein in the first position, the flow control device extends at least substantially perpendicular to the surface. In the first position, the flow control device may lie substantially flush with the surface.

[0026] The working substance of the phase change actuator may be configured to change phase at temperatures above 50 degrees C, or above 150 degrees C, or above 190 degrees C, or below 300 degrees C.

[0027] The working substance of the phase change actuator may be configured to change phase between a solid in the first configuration and a liquid in the second configuration. The working substance of the phase change actuator may be configured to change phase between a liquid in the first configuration and a gas in the second configuration.

[0028] A phase change from a liquid to a gas phase may provide a larger change in volume, and thereby increase the degree of actuation. This needs to be balanced against an increase in compressibility in the gas phase, which can decrease the accuracy of the actuation.

[0029] The assembly may be an aircraft assembly for an aircraft.

[0030] The outlet may be one of a hot air exhaust outlet, an engine outlet, auxiliary power unit outlet, and an air conditioning unit outlet. [0031] The outputted hot air may be heated by a heat source. The heat source may be one of an engine, an auxiliary power unit, and an air conditioning unit.

[0032] The outlet may be on an engine pylon.

[0033] The structure may be an outer aerodynamic surface. The structure may be a wing leading edge or a wing upper cover.

[0034] The method may further comprise the step of cooling the working substance of the phase change actuator below the predetermined temperature to move the flow control device from the second configuration back to the first configuration.

[0035] The assembly may be on an aircraft, and the step of heating the working substance of the phase change actuator to the predetermined temperature may be performed during a take-off or a landing manoeuvre of the aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[0037] Figure 1 shows an aircraft;

[0038] Figure 2 shows a perspective view of the aircraft of Figure 1;

[0039] Figure 3 shows a port wing of the aircraft;

[0040] Figure 4 shows the upper surface of the pylon of the engine according to a first example;

[0041] Figure 5 A shows a schematic of the apparatus in a first position according to the first example;

[0042] Figure 5B shows a schematic of the apparatus in a second position according to the first example;

[0043] Figure 6 shows the upper surface of the pylon of the engine according to a second example;

[0044] Figure 7 shows a side view of the engine pylon of Figure 6; [0045] Figure 8A shows a schematic of the apparatus in a first position according to the first example;

[0046] Figure 8B shows a schematic of the apparatus in a second position according to the first example;

[0047] Figure 9A shows the apparatus in a first position according to the first example;

[0048] Figure 9B shows the apparatus in a second position according to the first example;

[0049] Figure 10 shows the upper surface of the pylon of the engine according to a third example;

[0050] Figure 11 A shows an example of a flow control device in a first position;

[0051] Figure 11B shows the flow control device of Figure 11A in a second position;

[0052] Figure 12A shows a further example of the flow control device in a first position;

[0053] Figure 12B shows the flow control device of Figure 12A in a second position;

[0054] Figures 13 A & 13B show the arrangement for moving the flow control device of Figures 12A & 12B between the first and second positions;

[0055] Figure 14 shows an air conditioning outlet positioned on the bottom of an aircraft fuselage;

[0056] Figure 15 shows a first example of an auxiliary power unit outlet near the tail of an aircraft;

[0057] Figure 16 shows a second example of an auxiliary power unit outlet near the tail of an aircraft.

DETAILED DESCRIPTION OF EMBODIMENT(S)

[0058] Figure 1 shows an existing aircraft 1 with port and starboard fixed wings 2, 3, engines 9, a fuselage 4 with a nose end 5 and a tail end 6, the tail end 6 including horizontal and vertical stabilising surfaces 7, 8. The aircraft 1 is a typical jet passenger transonic transport aircraft but the invention is applicable to a wide variety of fixed wing aircraft types, including commercial, military, passenger, cargo, jet, propeller, general aviation, etc. with any number of engines attached to the wings or fuselage.

[0059] Each wing 2, 3 of the aircraft 1 has a cantilevered structure with a length extending in a span-wise direction from a root to a tip, the root being joined to the aircraft fuselage 4. The wings 2, 3 are aft swept and have a number of flight control surfaces. In alternative examples, the wings 2, 3 are forward swept or straight.

[0060] Each wing 2, 3 has a leading edge 11 and a trailing edge 12. The leading edge 11 is at the forward end of each wing 2, 3 and the trailing edge 12 is at the rearward end of each wing 2, 3.

[0061] The wings 2, 3 are similar in construction so only the port wing 2 will be described in detail.

[0062] The engine 9 is an underwing engine 9, as shown in Figure 2. The engine 9 is mounted below the wing 2. The engine 9 is mounted to the wing 2 by a pylon 10. The pylon 10 extends forward of the leading edge 11 of the wing 2, as shown in Figure 3.

[0063] The pylon 10 has an upper surface 13. The pylon upper surface 13 extends forward of the leading edge 11 of the wing 2.

[0064] Figure 4 shows a more detailed perspective view of the upper surface 13 of the pylon 10 and the leading edge 11 of the wing 2, showing a pre-cooler exhaust outlet 15 that exhausts from the engine 9 in the region indicated by the dotted circle 14 indicated on Figure 3.

[0065] The engine 9 has a pre-cooler exhaust outlet 15. The pre-cooler exhaust outlet 15 acts as a hot-air exhaust outlet. The pre-cooler exhaust outlet 15 exhausts hot air from the pre-cooler of the engine 9. The engine 9 may have other hot air exhaust outlets.

[0066] In this particular example, the pre-cooler exhaust outlet 15 comprises vents 16, although in alternative examples the outlet 15 may not include vents 16. The vents 16 are arranged on the upper surface 13 of the pylon 10. The number, location and configuration of the vents 16 may vary. The vents 16 are exposed to the airflow over the wing 2 during normal operation of the aircraft 1. The vents 16 are disposed forward of the leading edge 11 of the wing 2. [0067] Hot air (shown by line 17) from the pre-cooler exhaust outlet 15 is vented through the engine 9, through the pylon 10, and vented into the airflow forward of the leading edge 11 of the wing 2 through the vents 16 of the exhaust outlet 15. Hot air from the pre-cooler exhaust outlet 15 is therefore vented aft towards the leading edge 11 of the wing 2 and over the wing 2 in a generally chordwise direction. The majority of the hot air is vented over the upper surface of the wing 2, although at least a portion may vent over the lower surface of the wing 2.

[0068] This hot air 17 can heat up regions of the aircraft structure aft of the outlet 15, potentially damaging, or otherwise causing detrimental performance of, the structure. To mitigate this problem, the aircraft 1 includes an apparatus for interacting with the airflow 17.

[0069] The apparatus includes a flow control device 20 attached to the upper surface of the pylon 10. As such the flow control device 20 is forward of the leading edge 11 of the wing 2. The flow control device is forward of the outlet 15. In this particular example, the flow control device 20 is a vortex generator arrangement 20. The vortex generator arrangement 20 comprises a pair of vortex generators 21a, 21b. Each vortex generator 21a, 21b includes a base 22a, 22b attached to the pylon 10, and a vane 23a, 23b that is movable about a pivot axis relative to the base 22a, 22b so as to lie flush to the surface of the pylon 10 in a first position of the vortex generator 21 or extend into the airflow in a second position.

[0070] The vortex generators 21a, 21b are configured to interact with an airflow upstream of the outlet 15, so that the airflow 27 from the vortex generators 21a, 21b interacts with the hot air 17 from the outlet 15 and cools the hot air 17, as shown in Figure 4. For instance, this interaction causes the hot air 17 to mix better with the atmospheric air, thereby protecting the structure downstream of the outlet 15. This protects the structure of the aircraft 1, for example the pylon 10 and wing 2 structures, aft of the outlet 15 from overheating due to the hot air 17. In this particular example, the airflow 27 from the vortex generators 21a, 21b interacts with the hot air 17 as soon as it leaves the outlet 15. [0071] The vortex generators 21a, 21b are movable between a first position, in which the vortex generators 21a, 21b substantially do not interact with the airflow over the vortex generators 21a, 21b, and a second position, in which the vortex generators 21a, 21b interact with the airflow over the vortex generators 21a, 21b, as shown in Figures 5A and 5B respectively.

[0072] To move the vortex generators 21a, 21b between the first and second positions, the apparatus includes corresponding phase change actuators 24a, 24b, such that each vortex generator 21a, 21b is mechanically connected to a respective phase change actuator 24a, 24b. In an alternative example, each vortex generator 21a, 21b is mechanically connected to a common phase change actuator 24.

[0073] Phase change actuators contain a working substance that changes phase, for example from a solid to a liquid at a predetermined temperature. As this phase change occurs, the volume of the working substance increases significantly, with the liquid volume greater than the original solid volume. The resultant liquid, being largely incompressible and encased in a rigid housing, will move a piston that forms part of the phase change actuator and extend the actuator as the volume of the working substance increases.

[0074] The phase change actuators 24a, 24b are configured to move the vortex generators 21a, 21b from the first position to the second position at the predetermined temperature of the phase change actuators 24a, 24b. An advantage of phase change actuators over other known actuators is that they are passively operated. Any movement can be configured to occur at a predetermined temperature that is determined by the composition of the phase change working substance they are made from. This temperature can be reliably predetermined.

[0075] The phase change actuators 24a, 24b are positioned adjacent the structure of the aircraft that requires protection, and downstream of the vortex generators 21a, 21b and the outlet 15. In this particular example, the phase change actuators 24a, 24b are positioned adjacent a leading edge of the wing 2 above the pylon 10. [0076] Figure 5A shows the vortex generators 21a, 21b in the first position, wherein the vane 23a, 23b is flush with the surface of the pylon 10 so that the interaction of the vortex generator 21a, 21b with the airflow is minimal.

[0077] As the engine 9 operates, a flow of hot air 17 flows from the outlet 15 through the vents 16. The hot air 17 contacts a heatsink 25a, 25b positioned adjacent each of the phase change actuators 24a, 24b so that the heat of the hot air 17 heats up the phase change actuator 24a, 24b via each heatsink 25a, 25b.

[0078] At a predetermined temperature, for example 190 degrees, the working fluid of the phase change actuators 24a, 24b is heated such that the liquid in the actuators 24a, 24b changes phase to a gas. This phase change causes the vortex generators 21a, 21b, which are connected to respective actuators 24a, 24b, to move to the second position.

[0079] The second position is shown in Figure 5B, in which the vane 23a, 23b extends from the surface of the pylon 10 into the airflow. By extending into the airflow, the vortex generator is able to interact with the airflow and redirect the airflow so as to mitigate any increase in temperature caused by the hot air 17.

[0080] When the phase change actuators 24a, 24b are cooled below the predetermined temperature, in this case by cooling the heatsinks 25a, 25b adjacent to the actuators 24a, 24b, each vortex generator 21a, 21b returns to the first position. This is caused by the gas in the phase change actuators 24a, 24b changing phase back to a liquid phase.

[0081] It will be understood that in alternative examples, each vortex generator 21a, 21b may be actuated by a common phase change actuator 24.

[0082] The apparatus is particularly useful when the atmospheric conditions are warm, or when the aircraft 1 is going relatively slowly, which is often the case during take-off and landing manoeuvre of the aircraft 1. In these phases of flight, the air over the aircraft 1, in particular the wings 2,3, is turbulent due to the deployment of slats and flaps. This means that the aerodynamic effects of the flow control device 20 are small with respect to the turbulence already present over the aircraft 1.

[0083] The hot air 17 exhausted from the outlet 15 may be particularly hot during the landing manoeuvre, as the aircraft 1 may have been running for an extended period. [0084] In the first example, described above, the flow control device 20 is positioned upstream of the outlet 15. In alternative examples, the flow control device 20 may be positioned anywhere from which the flow control device 20 is able to interact with an airflow so as to mitigate the effects of the hot air 17 from the outlet 15.

[0085] In a second example, shown in Figures 6 to 9, the vortex generators 21a, 21b are positioned on a side of the pylon 10 substantially in-line, in the chordwise direction, with the outlet 15. Note that only one of the vortex generators 21b is visible in Figures 6 and 7.

[0086] The second example functions substantially the same as the first example. The vortex generators 21a, 21b interact with an airflow, in this case an airflow along the side of the pylon 10 coincident with the vents 16 in a chordwise direction, so that the airflow 27 generated by the vortex generators 21a, 21b interacts with the hot air 17 from the outlet 15 and cools the hot air 17.

[0087] In this particular example, the airflow 27 from the vortex generators 21a, 21b interacts with the hot air 17 at a position downstream of the outlet 15, such that the hot air 17 emerging from the outlet 15 is not immediately cooled by the interaction of the vortex generators 21a, 21b with an airflow.

[0088] In this example, in order to redirect the airflow 27 towards the heatsink 25a, 25b of each phase change actuator 24a, 24b, the vane 22a, 22b of each vortex generator 21a, 21b is angled with respect to a longitudinal axis 31 of the engine 9, as shown in Figure 7.

[0089] Figure 8A and 9A shows the vortex generators 21a, 21b in the first position, wherein the vane 23 a, 23b is flush with the side of the pylon 10 so that there is substantially no interaction of the vortex generator 21a, 21b with the airflow.

[0090] As the hot air 17 heats the heatsink 25a, 25b, the hot air 17 also heats the phase change actuators 24a, 24b. The phase change actuators 24a, 24b do not move until they reach a predetermined temperature. This temperature is determined by the composition of the phase change working substance in each actuator 24a, 24b, as is known to the skilled person. [0091] At a predetermined temperature, the phase change working substance of the phase change actuators 24a, 24b is heated such that a liquid in the actuators 24a, 24b changes phase to a gas. This phase change causes the vortex generators 21a, 21b, which are connected to each phase change actuator 24a, 24b, to move to the second position.

[0092] The second position is shown in Figure 8B and 9B, in which the vane 23a, 23b extends from the side of the pylon 10 into the airflow at an angle to the line-of-flight of the aircraft 1, so as to redirect the airflow and mitigate any increase in temperature caused by the hot air 17.

[0093] Figure 10 shows a third example in which the flow control device 20 is positioned aft of the exhaust outlet 15. The third example functions substantially the same as the first and second examples.

[0094] The vortex generators 21a, 21b interact with an airflow. In this case the vortex generators 21a, 21b are positioned aft of the outlet 15 and so interact directly with at least a portion of the hot air 17 vented from the outlet 15 before the hot air 17 reaches the structure aft of the flow control device 20. In alternative examples, the vortex generators 21a, 21b may be positioned aft of the outlet but so positioned so that the hot air 17 from the outlet 15 does not interact directly with the vortex generators 21a, 21b, and instead the vortex generator 21a, 21b interact with an airflow that in turn interacts with the hot air 17.

[0095] In the previous examples, the vortex generators 21a, 21b lie flush with a surface of the pylon 10 in the first position and pivot about an axis so as to extend into the airflow in the second position.

[0096] For instance, Figure 11A shows an example of the vortex generators 21a, 21b in the first position, wherein the vane 23a, 23b is flush with the surface of the pylon 10 so that the interaction of the vortex generator 21a, 21b with the airflow is minimal. Figure 1 IB shows an example of the vortex generators 21a, 21b in the second position, wherein the vane 23a, 23b extends from the surface of the pylon 10 into the airflow so as to interact with the airflow and redirect it so as to mitigate any increase in temperature caused by the hot air 17. [0097] In an alternative example, the vortex generators 21a, 21b may be configured to minimise disturbance of the airflow in the first position, even if the vane 23a, 23b is not flush with a surface of the pylon 10.

[0098] For instance, Figure 12A shows the vortex generators 21a, 21b in the first position, wherein the vane 23a, 23b extends from the surface of the pylon 10 up into the airflow, however the vortex generators 21a, 21b are oriented in-line with the direction of the airflow to minimise any interaction of the flow control device 20 with the airflow.

[0099] The second position is shown in Figure 12B, in which the vane 23a, 23b extends from the surface of the pylon 10 into the airflow in a similar manner to the first position shown in Figure 11B. This results in the vortex generators 21a, 21b interacting significantly with the airflow in the second position, with respective to any interaction resulting from the position of the vortex generators 21a, 21b in the first position.

[00100] Figures 13A and 13B show the mechanism for moving the vortex generators 21a, 21b between the first position shown in Figure 12A and the second position shown in Figure 12B.

[00101] In this example, the vane 23a, 23b of each vortex generator 21a, 21b is fixed to its respective base 22a, 22b. The base 22a, 22b is able to rotate about a pivot axis relative to the surface of the pylon 10. Figure 13A shows the vortex generators 21a, 21b in the first position.

[00102] As the temperature of each phase change actuator 24a, 24b reaches the predetermined temperature, the phase change actuators 24a, 24b extend so as to press against each base 22a, 22b. The base 22a, 22b rotates about the pivot axis, causing the vane 23a, 23b of each vortex generator 21a, 21b to be oriented at an oblique angle to the direction of the airflow over the aircraft 1.

[00103] In the examples described above, the apparatus controlled a pair of vortex generators 21a, 21b so as to move between a first position and a second position, wherein the airflow 27 from the vortex generators 21a, 21b in the second position interacts with hot air 17 flowing from the outlet 15. [00104] In this second position, the airflow 27 from the vortex generators 21a, 21b may meet the hot air 17 as the hot air 17 strikes the structure of the aircraft 1, e.g. the leading edge 11 of the wing 2, or the airflow 27 from the vortex generators 21a, 21b may meet the hot air 17 at a location upstream of the structure, so as to cool the hot air 17 before it reaches the structure.

[00105] In alternative examples, the vortex generators 21a, 21b may be positioned adjacent to the outlet 15, or at the mouth of the outlet 15, so that the airflow 27 interacts with the hot air 17 as it leaves the outlet 15.

[00106] In an alternative example, rather than cooling the hot air 17 before it reaches any structure downstream of the outlet 15, the hot air 17 may instead be redirected whilst the apparatus is deployed in the second position, relative to the direction the hot air 17 would take with the apparatus in the first position. For example, in the second position, the vanes 23a, 23b may be oriented to deflect the hot air 17 in a predefined direction. In one example, the vane 23a, 23b extends at an oblique angle to the surface to which the vortex generators 21a, 21b attach. In doing so, the vortex generators 21a, 21b push the hot air 17 upwards, away from the leading edge 11 of the wing 2 or other structure that requires protection.

[00107] The hot air 17 may be directed away from a structure to be protected, and/or towards a target area. For instance, the hot air 17 may be directed to a downstream inlet.

[00108] In the previous examples, the hot air outlet 15 is a pre-cooler exhaust outlet of an engine 9.

[00109] In an alternative example, the hot air outlet 15 may be an air conditioning outlet from an air conditioning unit. For instance, Figure 14 shows an air conditioning outlet 15' positioned on the bottom of the fuselage 4 and having a pair of vortex generators 21a, 21b forward of the outlet 15' and configured to interact with the air upstream of the outlet 15. [00110] In this case, the predetermined temperature at which the phase change actuator 24a, 24b moves the flow control device 20 from the first position to the second position is typically lower than the predetermined temperature for a hot air outlet 15 from a pre cooler exhaust of an engine 9. For example, the predetermined temperature may be below 100 degrees, or below 60 degrees.

[00111] Below the predetermined temperature, the phase change actuators 24a, 24b will remain in the first position, such that the vortex generators 21a, 21b connected to each phase change actuator 24a, 24b do not interact significantly with any airflow.

[00112] When the air conditioning unit is turned on, and particularly when the demands placed on the system are high, the temperature of the airflow 17 from the outlet 15' will rise. If the temperature of the airflow 17 increases beyond an acceptable limit, the structure aft of the outlet 15' may be adversely affected.

[00113] To counter this increased temperature, a predetermined temperature can be set at which the phase change actuators 24a, 24b change phase so as to actuate the vortex generators 21a, 21b from the first position to the second position.

[00114] By reducing the temperatures outputted from the outlet 15', a greater flexibility in material selection may be provided for those parts of the structure downstream of the outlet 15'.

[00115] In yet another example, the hot air outlet 15 may be an auxiliary power unit outlet from an auxiliary power unit (APU). For instance, Figure 15 shows an APU supplementary cooling outlet 15" positioned near to the tail end 6 of an aircraft 1. The APU is typically used to assist in starting the main engines 9, and may be used to power electrical systems (not shown) on the aircraft 1. [00116] In this particular example, the APU supplementary cooling outlet 15" includes a protective barrier 30, made from titanium, attached to the outer surface surrounding the outlet 15", so that the surface is shielded from the high temperatures of the hot air outputted from the outlet 15". However, by positioning the flow control device 20, such as a pair of vortex generators 21a, 21b, adjacent to the outlet 15" the protective barrier 30 may be dispensed with, as shown in the example of Figure 16. This can reduce the weight of the aircraft 1, reduce complexity of manufacture, and reduce costs.

[00117] Whilst the protective barrier 30 is only shown in relation to the example shown in Figure 15, it will be known that aircraft 1 are often provided with protective barriers on other areas of the aircraft 1. For instance, aft of the pre-cooler exhaust outlet.

[00118] In relation to all the described examples, it will be understood by the skilled person that the flow control device 20 may be positioned in any suitable location from which it is able to interact with the hot air 17 from or within the outlet 15, 15', 15".

[00119] Similarly, the phase change actuator(s) 23 may be positioned in any suitable location, for instance directly on the structure that needs to be protected, or directly in the path of the hot air 17 so that the phase change actuator 20 reacts to the temperature of the hot air 17 rather than indirectly to the temperature of the structure heated by the hot air 17. The apparatus may include a heatsink 25 or other intermediary device between the hot air 15 and/or airflow 27, or may be placed directly in contact with the hot air 15 and/or airflow 27. The phase change actuator 23 may not be heated by the hot air 17 from the outlet 15, 15', 15", instead the phase change actuator 23 may be heated by the heat source heating the hot air 17, for example an engine, air conditioning unit, or auxiliary power unit.

[00120] In the previously described examples, the position of the flow control device 20 is different to the position of the phase change actuator 24. Whilst this may provide benefits in terms of individually optimising the position of each device, it will be understood that the flow control device 20 and phase change actuator 24 may be located in substantially the same location, such that they experience substantially the same temperature. [00121] The flow control device 20 may function as a heatsink 25, so as to transmit heat to an imbedded actuator 24.

[00122] In the examples shown, the engine 9 is an underwing engine 9 mounted below the wing 2. In alternative examples, the engine 9 is an overwing mounted engine 9 mounted on top of the wing 2, or the engine 9 is a rear fuselage mounted engine 9, or has any other position known in the art. The engine 9 may or may not be mounted by a pylon.

[00123] The number and position of the vortex generators 21 may vary. The apparatus may include one, two, three or more vortex generators 21.

[00124] A vortex generator is provided as an example of a flow control device. In alternative examples the flow control device may be, for example, a vane, a slat, a flap, a control surface, or any other aerodynamic surface able to suitably interact with an airflow. In some examples, the flow control device may be an orifice or nozzle configured to redirect an airflow.

[00125] The mechanical connection between the phase change actuator and the flow control device may comprise any suitable linkages to provide the connection between the devices, for example, rods, cables, cranks, or other suitable mechanisms known in the art. Each flow control device may be connected to a respective phase change actuator, or a common phase change actuator.

[00126] The apparatus is described in relation to its deployment during the landing and take-off phases of flight of an aircraft 1, however it will be understood that the apparatus is also suitable for deployment during any phase of flight, including cruise, or taxiing.

[00127] The invention has been described in relation to outlets located on an aircraft, however it will be apparent that the apparatus is applicable to other applications, for example automotive vehicles.

[00128] Where the word 'or' appears this is to be construed to mean 'and/or' such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination. [00129] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. An apparatus comprising: an outlet configured to output hot air, a flow control device movable between a first position and a second position; and a phase change actuator connected to the flow control device and configured to move the flow control device between the first position and the second position at a predetermined temperature where a change of phase of a working substance of the phase change actuator occurs; wherein, in the second position, the flow control device is configured to interact with an airflow and/or the hot air so as to protect a structure downstream of the outlet from overheating.

2. An apparatus according to claim 1, wherein the flow control device is a vortex generator.

3. An apparatus comprising: an outlet configured to output hot air, a flow control device movable between a first position and a second position, wherein the flow control device is a vortex generator; and a phase change actuator connected to the vortex generator and configured to move the vortex generator between the first position and the second position at a predetermined temperature where a change of phase of a working substance of the phase change actuator occurs; wherein, in the second position, the vortex generator is configured to interact with an airflow and/or the hot air from the outlet so as to redirect and/or reduce the temperature of the hot air.

4. An apparatus according to claim 3, further comprising a structure, wherein the vortex generator is configured to interact with the airflow and/or the hot air so as to protect the structure from overheating.

5. An apparatus according to any one of claims 1, 2 and 4, wherein the phase change actuator is arranged adjacent the structure.

6. An apparatus according to any one of claims 1, 2 and 4, wherein the flow control device is arranged upstream of the structure.

7. An apparatus according to any preceding claim, wherein movement of the flow control device by the phase change actuator is passively controlled.

8. An apparatus according to any preceding claim, wherein the phase change actuator is mechanically connected to the flow control device so as to move the flow control device between the first position and the second position.

9. An apparatus according to any preceding claim, wherein, in the second configuration, the flow control device is configured to be positioned in an airflow with a temperature lower than a temperature around the phase change actuator.

10. An apparatus according to any preceding claim, wherein, in the second configuration, the flow control device is configured to be positioned in an airflow with a temperature lower than a temperature of the airflow around the structure.

11. An apparatus according to claim 9 or 10, wherein the temperature difference is at least 50 degrees C, and preferably at least 100 degrees C.

12. An apparatus according to any preceding claim, wherein the phase change actuator is configured to be heated by the hot air from the outlet, or by heat from around the outlet, or by heat from a heat source which heats the hot air.

13. An apparatus according to any preceding claim, wherein the flow control device is arranged in the hot air outputted by the outlet.

14. An apparatus according to any preceding claim, wherein the flow control device is configured to attach to a surface, and wherein in the second position, the flow control device extends at an oblique angle to the surface.

15. An assembly according to any preceding claim, wherein the flow control device is configured to attach to a surface, and wherein in the first position, the flow control device extends at least substantially perpendicular to the surface.

16. An apparatus according to any preceding claim, wherein the phase change actuator is configured to change phase at temperatures above 50 degrees C, preferably above 150 degrees C, and more preferably above 190 degrees C.

17. An apparatus according to any preceding claim, wherein the working substance of the phase change actuator is configured to change phase between a solid in the first configuration and a liquid in the second configuration, or between a liquid in the first configuration and a gas in the second configuration.

18. An apparatus according to any preceding claim, wherein the apparatus is an aircraft apparatus for an aircraft.

19. An aircraft apparatus according to claim 18, wherein the outlet is one of a hot air exhaust outlet, an engine outlet, auxiliary power unit outlet, and an air conditioning unit outlet.

20. An aircraft apparatus according to claim 19, wherein the outputted hot air is heated by a heat source, and wherein the heat source is one of an engine, an auxiliary power unit, and an air conditioning unit.

21. An assembly according to claim 19 or claim 20, wherein the outlet is on an engine pylon.

22. An assembly according to any preceding claim, wherein the structure is a wing leading edge or a wing upper cover.

23. An aircraft comprising the apparatus of any preceding claim.

24. A method of controlling an airflow over the surface of a structure using the apparatus of any preceding claim, the method comprising: heating the working substance of the phase change actuator to the predetermined temperature to move the flow control device from the first configuration to the second configuration.

25. A method according to claim 24, further comprising the step of cooling the working substance of the phase change actuator below the predetermined temperature to move the flow control device from the second configuration back to the first configuration.

26. A method according to claim 24 or 25, wherein the apparatus is on an aircraft, and the step of heating the working substance of the phase change actuator to the predetermined temperature is performed during a take-off or a landing manoeuvre of the aircraft.