GB2337301A

GB2337301A - Aircraft run-up pens

Info

Publication number: GB2337301A
Application number: GB9910911A
Authority: GB
Inventors: Richard Adkins
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-05-14
Filing date: 1999-05-12
Publication date: 1999-11-17
Anticipated expiration: 2019-05-12
Also published as: GB9910911D0; GB2337301B

Abstract

An aircraft run-up pen includes:- a) cavities (23) for extracting energy from the engine exhaust jets (4), and/or b) ramps (44) for restricting the transmission of noise out through the front of the pen, and/or c) hollow pits (40) for reducing the generation of vortices on the ground in the vicinity of the engine intake, and/or d) castellations (50) for reducing or eliminating the formation of large airborne vortices by the action of the wind over the tops and front regions of the walls of the pen.

Description

2337301 IMPROVED AIRCRAFT RUN-UP PEN W_

Field of tM Invention

This invention relates to ant#nproved aircraft run-up pen, the primary purpose of which is to reduce the transmission of engine noise to the environment.

Run-up pens, sometimes retwed to as acoustic enclosures, are frequently used to reduce the transion of noise generated by the on wing testing of aircraft engines at ak. They normally include a large rectangular area, partially enclos- walls on three sides which are usually at least as high as the ai rM!n order to act as a barrier to the noise. The aircraft is manoeuvred #--rds to a position inside the pen and the wheels anchored to preven M--rther movement. The test engine is then started and its exhaust ga--lmpinge against a rear deflector wall which is set at an angle to the ^1 in order to guide the gases upwards into the atmosphere. In mty instances, it is necessary to run a 2 second engine simultaneously on the opposite side of the aircraft to the test engine in order to provide a counter torque to prevent the aircraft from rotating about a vertical axis.

Current run-up pens are not sufficiently successful in reducing the level of noise transmitted to the surroundings. Furthermore, problems of engine instability and subsequently of increased noise can occur due to the ingestion of vortices into the engine intakes. In some wind conditions, the level of engine instability is so severe that engine testing has to be postponed in order to avoid damage, and the subsequent delays caused to airline schedules can be very costly.

The vorticity encountered originates from three sources:a) from the ground below the engine intake - here the vortex strength is dependent upon the amount of air being entrained into the engine and upon the proximity of the ground to the engine, b) from the interaction of the wind on the walls of the pen, and c) from the interaction of the wind on nearby buildings.

The vortices which, are naturally transient and unstable, precipitate large scale flow separations inside parts of the engine fan and compressor which lead, in turn, to rapid changes in mass flow rate and pressure.

It is accordingly an object of the present invention to provide an improved aircraft run-up pen.

3 Summary of the Invention

According to the present invention there is provided an aircraft runup pen which includes means W reducing the level of noise transmitted to the atmosphere and for enabling testing to be conducted over a much wider range of ambient conditions than is currently possible, such means including:- a) means for extracting energy from the engine exhaust jets in order to reduce their velocity so that they,,1)enerate less noise and entrain less air into the pen from the atmospheM, andlor b) means for restricting the Cansmission of noise out through the front of the pen, andlor c) means for reducing the generation of vortices on the ground in the vicinity of the engine intake, andVor d) means for reducing or eliminating the formation of large airborne vortices by the action of the wind over the tops and front regions of the walls of the pen.

The optimum acoustic perfornwnce of the pen will be obtained if all the above features are incorporaM but it is not essential that every feature should be utilised.

Brief Descripti the Drawinggs Figure 1 shows in plan view an aircraft located inside a run-up pen, 4 Figure 2 shows a section taken through plane X - X as indicated in Figure 1, and Figure 3 shows a section through plane Y - Y as indicated in Figure 1.

Description of the Preferred Embodiment in the drawings, an aircraft 1 with engines 2, intakes 3 and exhaust jets 4 is shown located inside a run-up pen 10 which includes side walls 11, a rear wall 12 and a floor 14. Ambient air 5 is drawn into the run-up pen by the action of the engine intakes 3 and the exhaust jets. The exhaust jets 4 enter cavities 23 through openings 29. In some applications, these exhaust jets 4 are guided into the cavities 23 by a wall 16. The cavities 23 are formed in a space bordered by a front partition plate 26, a rear deflector ramp 13, a perforated diffuser plate 20, side walls 30 and the pen side walls 11.

The exhaust gases become entrained inside the cavities 23 by the cavity borders and by deflector plates 25 and 27 to form recirculations 24 before eventually exiting through a multiplicity of small holes 21 distributed over a large area in the perforated top diffuser plate 20 in the form of small jets 22. These jets 22 eventually coalesce to form a large slow-moving column of gas, which exhausts into the atmosphere without generating a high level of noise.

The total area of the small holes 21 is so determined that their flow resistance prevents large quantities of air from being entrained into the cavity by the motion of the exhaust jets 4. Preferably, the mass of ambient air entrained into each coft 23 should be less than one half of the mass flow of the gases flowinWin the exhaust jets 4.

The plates 25 are included to turn that part of the exhaust gases, which would normally recirculateIlrds along the side walls 11 in a direction towards the aircraft, bo the respective cavity 23. A plate 28, located against the perforate diffuser plate 20, is also included to assist recirculation of the exhausts back in the respective cavity 23.

The jets 22 will unavoidaWgenerate a loud noise directly above the top diffuser plate 20 but this wid be at a high frequency due to the small diameter of the holes 21, -end will be readily attenuated by the atmosphere. The side walls 11, w acoustic linings 15 attached to their surfaces, will reduce the transmissbn of noise generated by the jets 22 to the surroundings outside of the The closeness of the front pWftn plates 26 to the aircraft engines increases the angle through noise has to be refracted before returning to ground level behin n. The partition plates 26, together with the acoustic linings atta them, provide a more efficient acoustic barrier than the simple, wall ramp provided in previous acoustic pens.

6 Hollow pits 40 are located in the floor of the pen in a region underneath the aircraft engines and extend for a distance equivalent to at least one engine diameter upstream of the engine intakes. The depths of the pits 40 are preferably such that the height of the engine central axis above the floor of the pits is equivalent to at least 1.5 times the engine diameter.

Some of the air 43 which is ultimately entrained into the engine flows through the pits 40 and this improves the access of air from below the engine, so preventing or reducing the ingestion of vortices into the engine intake. Cover plates 41 with a multiplicity of holes 42 are located over the pits for safety purposes. In order to assist further in the reduction of vorticity, it is preferable that the holes 42 each have a length which is equivalent to at least half the hole diameter or, alternatively if the hole is not of circular horizontal section, equivalent to at least the square root of one third of the hole crosssectional area.

Ramps 44 are provided directly in front of the engines to reduce the transmission of noise from the front of the pen. The ramps 44 should preferably be at a distance equivalent to at least 1.5 times the engine intake diameter upstream of the intakes 3. The height of each ramp 44 should be at least as high as the upper part of the intake 3. The angle of inclination of each ramp 44 to the horizontal should be greater than 450 while testing is being carried out. Before and after engine testing, the angles of inclination of the ramps can be reduced by a mechanism 45 to 7 accommodate both the installation and removal of the aircraft into and out of the pen.

Vortex generation by the passage of air over the tops and front edges of the side walls 11 of the pm is either reduced or eliminated by vortex inhibiting devices which are shown here, by way of example, as castellations 50. The heights and widths of the castellations 50 will preferably be greater than one tenth of the diameter of the engine being tested, but less than the engine dimeter. Other vortex inhibiting devices (not shown) such as perforations 0"ats could be used to either assist or replace the castellations 50. If pmMed, the perforations or slats would extend for a distance down from the tops of the side walls 11 and for a distance along from the front edgm-of the side walls 11 which is at least one tenth of the engine diameter.

4 -k--- T J -- 1W 8

Claims

Claims:-

1. An aircraft run-up pen which includes means for reducing the level of noise transmitted to the atmosphere and for enabling testing to be conducted over a much wider range of ambient conditions than is currently possible, such means including:- a) means for extracting energy from the engine exhaust jets in order to reduce their velocity so that they generate less noise and entrain less air into the pen from the atmosphere, andlor b) means for restricting the transmission of noise out through the front of the pen, andlor c) means for reducing the generation of vortices on the ground in the vicinity of the engine intake, andlor d) means for reducing or eliminating the formation of large airborne vortices by the action of the wind over the tops and front regions of the walls of the pen.

2. An aircraft run-up pen as claimed in Claim 1, which includes feature a) which comprises cavities arranged in front of the rear wall of the pen.

3. An aircraft run-up pen as claimed in Claim 2, in which the cavities are each formed in a space defined by a front partition plate, a rear deflector ramp, a perforated diffuser plate, side walls and the side walls of the pen.

9

4. An aircraft run-up pen as claimed in Claim 3, in which deflector plates are provided so that the exhaust gases become entrained inside the cavities by the cavity borders and the deflector plates to form recirculations before exiting through the holes in the perforated diffuser plate.

5. An aircraft run-up pen as claimed in Claim 3, in which each front partition plate has an acoustic lining attached to it.

6. An aircraft run-up pen as claimed in Claim 1, which includes feature b) which comprises ramps located in front of the engines.

7. An aircraft run-up pen as cJaimed in Claim 6, in which means are provided for changing the angles of inclination of the ramps to the horizontal, each ramp being movable into a position in which it extends at at least 450 to the horizontal while testing is being carried out.

8. An aircraft run-up pen as claimed in Claim 1, which includes feature c) which comprises hollow pits in the floor of the pen in a region underneath the aircraft engines.

9. An aircraft run-up pen as cJaimed in Claim 8, in which each of the hollow pits extends for a distance equivalent to at least one engine diameter upstream of the engine intakes.

10. An aircraft run-up pen as claimed in Claim 9, in which the depth of each pit is such that the height of the engine central axis above the floor of the pit is equivalent to at least 1.5 times the engine diameter.

11. An aircraft run-up pen as claimed in any one of Claims 8 to 10, in which cover plates with a multiplicity of holes are located over the pits.

12. An aircraft run-up pen as claimed in Claim 11, in which the holes in the cover plates are of circular cross-section and have a length which is equivalent to at least half the hole diameter.

13. An aircraft run-up pen as claimed in Claim 11, in which the holes in the cover plates are not of circular cross-section and have a length equivalent to at least the square root of one third of the hole crosssectional area.

14. An aircraft run-up pen as claimed in Claim 1, which includes featured) which comprises castellations.

15. An aircraft run-up pen as claimed in Claim 14, in which the castellations have heights and widths greater than one tenth of the diameter of the engine being tested.

16. An aircraft run-up pen substantially as hereinbefore described with reference to and as shown in the accompanying drawings.