GB2108591A

GB2108591A - Casing of a gas turbine engine rotor

Info

Publication number: GB2108591A
Application number: GB08133086A
Authority: GB
Inventors: Wilfred Henry Wilkinson
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1981-11-03
Filing date: 1981-11-03
Publication date: 1983-05-18

Abstract

In gas turbine jet propulsion engines, the radial extension undergone by rotor blades, when engine acceleration is performed, can result in fouling of the casing surrounding the rotors, with consequent damage to the rotor tips and, reduction in efficiency through excessive clearances having been created, during consequent low pressure operation of the engine. In order to avoid this, the present invention provides a construction in which the casing portion surrounding the rotor blades (16) is formed into a number of rectangular arcuately curved members (28), groups of which are moveable by unison bars (30) in directions radially of the rotor blades (16). The movement of the rotor blades (16) themselves initiates the generation of signals, either by changes in fluid pressure or electrical capacitance, with which to bring about movement of the members (28). The casing (18) going out of round will also initiate generation of the signals. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a casing for a gas turbine engine rotor This invention relates to a casing construction for surrounding relatively rotatable parts.

The invention has particular efficacy in a gas turbine engine compressor.

A problem which exists in both compressors and turbines, is that heat generated therein during operation, plus centrifugal loads, brings about dimensional fluctuation of the rotating blades, in the radial sense. Clearances between rotating and static casing structures which surround them are thus lost or exceeded, with consequent detriment to performance.

Many solutions have been mooted, the majority of which call for the deliberate variable distortion of the fixed casing structure surrounding the rotor, to match the rotor dimensional fluctuation as and when it occurs.

The present invention seeks to provide an improved casing construction which in operation surrounds an array of rotary blades.

According to the present invention there is provided a casing structure which in operation surrounds an array of rotor blades and includes a ring of arcuate members, adjacent ones of which are directly interconnected by their edges such as to enable both relative and common movement thereof radially of the rotor blades, means interconnecting groups of the members for bringing about the relative or common movement at least of adjacent groups and moving means/actuating means adapted for operation by change in clearance between the rotor blades and members.

The moving means may comprise unison bars, each connected to a respective group of members such that on actuation, one or more bars move their respective group of members in unison radially of the rotor blades.

The actuation means may comprise sensing means for sensing change in clearance between rotor blades and members, signal generating means connected to the sensing means and adapted so as to generate a signal on a clearance change being sensed and power means to which the signal generating means is further connected, for operation thereby by a generated signal.

Preferably the sensing means comprises a fluid carrying conduit communicating with the annular space between rotor blades and casing and with the signal generating means, which may comprise a diaphragm which flexes on sensing a change in fluid pressure derived from a change in clearance and in flexing makes an electric circuit.

The electric circuit may include a solenoid connected to operate a valve connected between a fluid under pressure and a piston and cylinder arrangement, by means of which one or more unison bars are moved.

Alternatively, the sensing means may comprise a capacitor, the capacitance of which varies as the proximity of the rotor blades to the members.

The invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sketch of a gas turbine engine incorporating an embodiment of the invention.

Figure 2 is an enlaryed part view of figure 1 and Figure 3 is a view on line 3-3 of figure 2.

In figure 1, a gas turbine engine 10 includes an axial compressor rotor blades 1 6.

In the present example the inner casing 18 which surrounds the stator blades 1 4 and rotor blades 16, has an annular portion 20 which surrounds one row of rotor blades 1 6.

Referring now to figure 2. Annular portion 20 is defined by a pair of annular walls 22, 24, an outer casing 26 and a peripheral now of rectangular, arcuately curved members 28, only one of which is shown on figure 2 and which are movable relative to walls 22, 24, in a direction generally radially of rotor blades 1 6.

The means by which movement of member 28 is achieved, comprises a number of unison bars 30, supported in brackets 32 which are affixed to outer casing 26.

Unison bars 30 are arcuate in shape and are movable in directions peripherally of members 28 and to this end, are slidably supported in arcuately grooved portions 34 in brackets 32.

Interconnecting of unison bars 30 and members 28, is achieved via bell crank levers 36 which are more readily seen in figure 3, to which reference is now made.

Members 28 are arcuate in profile and interengage so as to form a ring, the diameter which during given operating conditions of engine 10, will just clear the outer tops of the rotor blades 1 6 the members surround.

Inter-engagement of members 28 is achieved by inserting one edge of each member 28, into a slot 40 in the adjacent edge of the next adjacent member 28. The fit of edge in slot is such that relative movement of adjacent members is enabled, at least in directions generally radially of rotor blades 1 6.

Each unison bar 30 spans a group of three members 28, though the number is purely illustrative. Each member 28 however, is connected via a respective bell crank lever 36, to that unison bar 30 which spans it.

Each bell crank lever 36 is pivotally mounted to either wall 22 or wall 24, so that its ends may move in arcuate manner about the pivot axis 42.

One end of each bell crank lever 36 is connected to its respective unison bar 30 via a radial slot 44, so that an arcuate movement of the unison bar occurring peripherally of members 28, the small radial component of movement of the lever end, is enabled.

The other end of each bell crank lever 36 has a pivotal connection 46 to a position adjacent an edge of a respective member 28.

One member of each group of members 28, includes a proximity sensing device 50 which in operation, senses the proximity of the tips of the rotor blades 1 6 to itself and therefore, to the member 28.

In the present example, the sensing device 50 is represented by an air jet which blows air onto the tips of rotor blades 1 6 as they rotate. Should the clearance between blade tips and member 28 reduce by virtue of the blades tips moving into close proximity to the outlet of air jet device 50, a back pressure will develop in the air conduit 52.

The back pressure is fed via conduit 52 to a signal generating device 54, which could be a diaphragm (not shown) on box 54, which flexes under the increased pressure and makes an electrical circuit. The electrical signal so generated is passed to the actuator (not shown) of a valve 56.

Valve 56 is actuated to allow fluid under pressure to pass from a ram 58, which is resiliently loaded to move the unison bar 30, to which it is attached for that purpose.

As viewed in Figure 3, unison bars 30 will move in a clockwise direction. Lever 36 will also pivot in a clockwise direction, about pivots 42, thus directly applying a force to the member edge to which it is connected and indirectly, via the slot engagement 40, to the adjacent edge of the adjacent member 28. Each member 28 will thus be moved radially outwardly and so retrieve the clearance, between them and rotor blades 1 6.

Contraction of rotor blades 16, will result in back pressure on the diaphragm being obviated.

The electrical circuit will break and valve 56 will load ram 58 against the resilient force and cause it to move unison bar 30 in an anticlockwise direction. Members 28 will thus be moved radially inwards by levers 36.

Each group of members 28 has its own sensing device 50, box 54, value 56 and cam 58. The arrangement thus enables appropriate movement of one or more groups of members, depending on whether the clearance is reduced concentrically or eccentrically.

One example of eccentric clearance variation, is the situation wherein casing 1 8 goes out of round, such distortion being brought about by working loads.

The air jet and diaphragm may be replaced by a capacitance device (not shown) i.e. a capacitor fitted flush with the inner surface of a member 28.

Change in proximity of rotor blades 1 6 to members 28 will change the capacitance of the capacitor and valve operating signal will be derived therefrom.

Claims

1. A casing structure including a ring of rectangular arcuately curved members which in operation surrounds an array of rotor blades and adjacent ones of which are directly interconnected by their edges such as to enable both relative and common movement thereof generally radially of the rotor blades, means interconnecting groups of the members for bringing about the relative and common movement at least of adjacent groups and moving means/actuating means, adapted for operation by change in clearance between rotor blades and members during said operation.

2. A casing structure as claimed in claim 1 wherein the moving means comprises unison bars, each connected to a respective group of members such that on actuation, one or more bars move their respective group of arcuate members in unison, radially of the rotor blades.

3. A casing structure as claimed in any previous claim wherein the actuation means comprises sensing means for sensing change in clearance between a said array of rotor blades and arcuate members, signal generating means connected to the sensing means and adapted so as to operate a signal on a clearance change being sensed and power means to which said signal generating means is further connected for operation by a generated signal.

4. A casing structure as claimed in claim 3 wherein the sensing means comprises a fluid carrying conduit communicating with the clearance space between rotor blades and arcuate members and with the signal generating means which comprises a diaphragm which flexes on sensing a change in fluid pressure derived from a change in said clearance and in flexing makes an electrical circuit to generate a said signal.

5. A casing structure as claimed in any of claims 1 to 3 wherein the sensing means comprises a capacitor, the capacitance of which varies as the proximity of the rotor blades to the arcuate members and so generates a said signal.

6. A casing structure substantially as described in this specification, with reference to the accompanying drawings.

7. A gas turbine engine including a casing structure substantially as described in this specification, with reference to the accompanying drawings.