Patent Application
20060292002
The present invention relates to a duct casing structure within one end of which a stage of aerofoil blades is mounted for operational rotation. More particularly, the duct structure is of the kind that includes an aerofoil blade containment assembly downstream of the blade stage, whereby broken off root portions of a disintegrated blade that pass down the duct are prevented from exiting the outermost duct wall structure.
It is known from published European patent specification EP 1 245 791 A2, to include an annular metallic panel structure of honeycomb chambered form within and abutting a wall surface of a duct outer casing. EP 1 245 791 A2 further discloses that the metallic panel structure may be a one piece structure, or alternatively, may comprise a plurality of smaller panels arranged circumferentially of the inner surface of the outer casing. In either arrangement, the axes of the honeycomb chambers are all radial to the casing. The radially inner ends of the honeycomb chambers are closed by an inner casing.
Whilst the known arrangement has proved able to contain a broken off blade root portion i.e. it has prevented a blade root portion from completely exiting the outer casing, the rigidity of the assembly is such as to fail to absorb sufficient of the blow before the blade root portion reaches the outer casing, with consequent plastic deformation or even puncturing of the outer casing.
The present invention seeks to provide an improved fan duct broken blade portion containment assembly.
According to the present invention, a fan duct broken blade containment assembly comprises an outer casing having surrounding contact with outer ends of a circumferential array of honeycomb cells that are attached to and surround an inner casing, the respective axes of which cells are radial to an axis common to said casings, said cells being arranged in close spaced blocks, which spacing enables radially outward movement of only the block or blocks struck by a broken off blade portion, and cause said outer casing to flex and thus reduce the shock load thereon.
The invention will now be described, by way of example and with reference to the accompanying drawings, in which:
Referring to
Cowl 12 has an inner casing 22 consisting of an axially aligned assembly of casings that are more clearly seen in
Referring to
A second casing portion 30, the wall of which is thinner than that of casing 24, and therefor lighter, is connected to casing 24 via flanged joints 32. Casing portion 30 also has external circumferential stiffening flanges 34. A honeycomb cell structure 36 lies within casing 30. A plain metal liner 40, that is thinner than casing portion 30, lines honeycomb structure 36 and is fastened thereto by any suitable means, which for example, may be epoxy adhesives. A further, sound absorbing honeycomb structure 42, lines sheet metal liner 40, and an axial gap between honeycomb structure 26 and honeycomb structure 36 is bridged by a cylindrical piece 44. The assembly has radial fastenings in the form of nuts and bolts 38.
Referring now to
Blocks 36a are identically proportioned. Thus, by way of example, where the dimension between opposing walls of each cell in each block 36a is 3 mm to 6 mm, the dimensions “a” and “b”, of respective sides of each block is 25 mm to 75 mm respectively.
Where the dimension between opposing walls of each cell is 6 mm to 10 mm, the dimensions “a” and “b” of respective sides of each block 36a is 50 mm to 125 mm.
Where the dimension between opposing walls of each cell is 10 mm to 20 mm, the dimensions of “a” and “b” of respective sides of each block 36a is 75 mm to 200 mm.
The ratio of the dimension between the opposing walls of each cell in block to the dimensions of the sides of the block is between 1 to 3 and 1 to 30. Preferably the ratio is between 1 to 3 and 1 to 25, more preferably the ratio is between 1 to 4 and 1 to 20. Specific examples are 1 to 4, 1 to 5, 1 to 7, 1 to 8, 1 to 10, 1 to 12.5 and 1 to 20.
Utilising a honeycomb structure 36 having opposing wall spacing of 3 mm and a wall thickness of 0.1 mm, provides the structure with a stabilised crush strength of 4000 psi (27.6 MPa).
On honeycomb structure 36 being struck by a broken off portion of blade root 16 (
The assembly, as described so far, includes acoustic honeycomb liner 42. However, honeycomb liner 42 could be obviated, the lengths of the cells of honeycomb structure 36 extended, and the diameter of liner 40 reduced, so as to enable their use for absorbing noise. In such an arrangement, liner 40 would be perforated in alignment with each cell interior, so as to enable receipt and absorbtion of noise from the fan duct.
Honeycomb structure 36 can be manufactured from any one of steel, aluminium, magnesium, titanium, nickel or alloys of any thereof, that has weight and strength characteristics appropriate to the environment in which honeycomb structure 36 is used.
EP 1 245 791 A2 discloses honeycomb panels, the axially spaced ends of which are bounded by annular flanges. Also disclosed is the separation of panels by axially aligned ribs. Honeycomb blocks 36 of the present invention can be so bounded, (not shown), provided that any block or blocks 36 that receive a strike are not prevented from moving relative to the remainder, as described hereinbefore.
The cells of blocks 36 must be of identical form, which could be square, hexagonal, rectangular, or triangular.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0512758.4 | Jun 2005 | GB | national |
