Rotary kinetic fluid motors or pumps – Including destructible – fusible – or deformable non-reusable...
Reexamination Certificate
1999-06-03
2001-01-30
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Including destructible, fusible, or deformable non-reusable...
C415S173400, C415S197000
Reexamination Certificate
active
06179551
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally the design of gas turbine engine containment casings. In particular it relates to the design of containment casings which are provided to contain a fan blade, within the engine, during failure of a fan blade.
Turbo fan gas turbine engines are commonly provided with a fan rotor in the forward portion of the engine. The rotor assembly includes a rotor disc and a number of fan rotor blades. The fan rotor blades extend outwardly from the disc across a flow path for the working medium gases. These blades are more cambered and are considerably larger than the blades of the axial flow core compressors and turbines used in such engines.
The fan rotor blades are driven at high rotational speeds about an axis of rotation to provide the first stage of compression to the working medium gases, and propulsive thrust. Foreign objects, such as birds, hailstones or other objects, which are on occasion ingested into the engine with the working medium gases may strike and damage the blade to such an extent that the blade fails in the root region of the fan blade where it is attached to the rotor disc. The blade may also fail in the root region due to other causes. During such a failure a rotor blade may be hurled outwardly from the rotor assembly with considerable energy and at high speed.
Because of the size of the fan blades and the speeds at which they may be released in the event of failure, fan blades present a difficult containment problem. It being appreciated that it is desirable to contain a failed fan blade within the engine so that further damage to the aircraft or surrounding objects does not occur.
One known design of containment casing is described in U.S. Pat. No. 4,417,848. According to this patent an annular containment casing surrounds the outer portions of the fan blades. The thickness of this casing increases in an axially rearward direction such that the casing has a maximum thickness rearward of a plane passing through the mid-chord point of the rotor blades. This increase in thickness selectively reinforces the case against the predicted impact of blade fragments such that the blade does not penetrate the casing and is contained.
A problem with this design is that in order to withstand large fan blades and/or high impact velocities the casing thickness needs to be considerable and over a large area of the casing. This undesirably adds considerable weight to the engine casing. Furthermore such a containment casing design is not optimal and can be further improved.
It is therefore desirable to provide a containment casing that addresses the aforementioned problem and/or provides improvements to containment casings generally.
SUMMARY OF THE INVENTIONS
According to the present invention there is provided a containment casing for a gas turbine engine comprising a substantially rigid casing shell arranged in operation coaxially with an axis of rotation of the gas turbine engine, and extending circumferentially around an array of fan rotor blades arranged to rotate about the engine axis, and in a region of predicted blade impact in the event of a fan blade failure, there are at least two reinforcing ribs which extend substantially radially from the casing and circumscribe the outer periphery of the casing shell, wherein the ribs are of a generally T-shaped cross section comprising a substantially radially extending web portion and a rim portion, and wehrein the first rib is positioned axially about the casing between a plane perpendicular to the casing axis passing through the operational positions of the trailing edges of the fan blades, and a plane perpendicular to the casing axis passing through the operational positions of the mid chord points of the fan blades, and the second rib is positioned axially about the casing between the plane passing through the operational positions of the mid chord points of the fan blades and a plane perpendicular to the casing axis passing through the operational position of the leading edges of the fan blades.
The ribs selectively strengthen and stiffen the cylindrical shell of the containment casing thereby reinforcing the shell. The use of ribs is also more efficient than simply increasing the shell thickness. Consequently the shell can be of a thinner section than would be the case without the ribs producing a lighter, more optimal containment casing structure. In addition the ribs distribute the impact energy of a failed fan blade over a larger area of the containment casing thereby enabling the casing to better absorb the impact energy of a failed fan blade.
A third rib may also be provided, axially positioned forward of the plane passing through the operational positions of the leading edges of the fan blades.
The positioning of the ribs provides strengthening of the casing where it is required allowing the casing thickness in other areas to be reduced, thereby providing an improved lighter design.
The ratio of the axial width of the reinforcing rib rim portion, to the thickness of the casing shell radially adjacent to the operational positions of a trailing edge portions of the fan blades, is preferably in the range of 1 to 6. The ratio of the radial height of the reinforcing web portion from the casing, to the thickness of the casing shell radially adjacent to the operational positions of the trailing edges portions of the fan blades, is preferably in the ratio of 1 to 6.
Preferably the ratio of the thickness of the reinforcing rib rim portion, to the thickness of the casing shell radially adjacent to the operational positions of the trailing edge portions of the fan blades, is in the range 0.4 to 2.0; and the ratio of the axial thickness of the reinforcing rib web portion, to the thickness of the casing shell radially adjacent to the operational positions of the trailing edge portions of the fan blades, is in the range of 0.4 to 2.0.
Furthermore the ratio of the radial thickness of the casing in the region of the reinforcing ribs, to the thickness of the casing shell radially adjacent to the operational positions of the trailing edge portions of the fan blades, is may be in the range 0.4 to 2.0.
The ratio of the thickness of the casing shell axially rearward of the operational positions of the fan blades, to the thickness of the casing shell radially adjacent to the operational positions of the fan blades, is in the range 0.5 to 1.5.
Preferably the ratio of the thickness of the casing shell axially rearward of the operational position of the fan blades, to the thickness of the casing shell radially adjacent to the operational position of the fan blades, is in the range 0.4 to 1.5.
Preferably the ratio of the thickness of the casing shell axially rearward of a region of the casing shell or predicted main blade root impact in the event of fan blade failure, to the thickness of the casing shell radially adjacent to the operational position of the fan blades is in the range 0.3 to 1.5.
A fan catcher comprising a flange extending radially inwardly from an inner surface of the casing shell may be provided. The fan catcher positioned axially up to half a chord length of the fan blades forward of a plane perpendicular to the casing axis passing through the operational positions of the leading edges of the fan blades.
The ratio of the thickness of the casing shell forward of the fan catcher, to the radial thickness of the casing shell radially adjacent to the operational positions of the trailing edge portions of the fan blade, may be in the range 0.25 to 0.75.
Preferably the ratio of the thickness of the casing shell forward of the fan catcher, to the radial thickness of the casing shell radially adjacent to the operational position of the trailing edges portion of the fan blade, is in the range 0.1 to 0.75.
REFERENCES:
patent: 4417848 (1983-11-01), Dembeck
patent: 4598449 (1986-07-01), Monhardt
patent: 5259724 (1993-11-01), Liston
patent: 5403148 (1995-04-01), Forrester
patent: 5408826 (1995-04-01), Stewart
patent: 5413456 (1995-05-01), Kulak et al.
patent: 5485723 (1996-
Charadva Sunil V
Lawson Michael R
Sathianathan Sivasubramaniam K
Farkas & Manelli PLLC
Look Edward K.
Rolls-Royce plc
Taltavull W. Warren
Woo Richard
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