Gas turbine engine havinga rotatable off-take passage in a compressor section

1. A gas turbine engine comprising:

a compressor section with rotational compressor components rotatable with respect to static compressor components;

a compressed air bleed arrangement that cools one or more other components of the gas turbine engine and that takes a flow of compressed air from the compressor section along an off-take passage,

wherein the off-take passage opens in the compressor section in a stepped arrangement at an off-take port and comprises a radially outer surface that is rotatable, in use, with the rotational compressor components, wherein the off-take passage includes one or more vanes shaped to increase a tangential velocity of a flow of compressed air in the off-take passage in comparison to a flow of compressed air at the off-take port, and

wherein the compressed air bleed arrangement is operable to provide the flow of compressed air along the off-take passage with higher static pressure than the flow of compressed air at the off-take port, and

wherein the one or more other components of the gas turbine engine includes at least one rotating component of a turbine section of the gas turbine engine and the compressed air bleed arrangement delivers the flow of compressed air from the compressor section to the at least one rotating component with a tangential velocity that is substantially matched to a tangential velocity of the at least one rotating component.

2. A gas turbine engine according to claim 1 wherein the compressor section has an inner annular periphery and an outer annular periphery,

the off-take port opens into the compressor section via the inner annular periphery.

3. A gas turbine engine according to claim 1 wherein the off-take passage provides an air flow path direction at an acute angle to an air flow path direction in the compressor section.

4. A gas turbine engine according to claim 1 wherein the off-take passage is shaped as a diffuser in order to reduce an axial velocity of the flow of compressed air in the off-take passage compared with the flow of compressed air at the off-take port.

5. A gas turbine engine according to claim 1 wherein the flow of compressed air in the off-take passage is provided with higher tangential velocity than the flow of compressed air at the off-take port.

6. A gas turbine engine according to claim 5 wherein the direction of the off-take passage is towards the principal rotational axis of the engine,

the off-take passage being operable to further increase the tangential velocity of the flow of compressed air in the off-take passage that would otherwise be provided due to conservation of angular momentum as the flow of compressed air in the off-take passage moves towards the principal rotational axis of the engine.

7. A gas turbine engine according to claim 1 wherein the off-take port is located upstream of a stator in the compressor section.

8. A gas turbine engine according to claim 1 wherein the off-take port is located upstream of a stator of a final stage of the compressor section and downstream of an adjacent rotor of the compressor section.

9. A method of operating a gas turbine engine, the gas turbine engine comprising a compressor section, the method comprising the steps of:

operating the gas turbine engine to rotate rotational compressor components with respect to static compressor components;

cooling one or more other components of the gas turbine engine with a compressed air bleed arrangement, the compressed air bleed arrangement taking a flow of compressed air from the compressor section along an off-take passage which opens in the compressor section in a stepped arrangement at an off-take port, the off-take passage comprising a radially outer surface that rotates with the rotational compressor components, wherein the off-take passage includes one or more vanes shaped to increase a tangential velocity of a flow of compressed air in the off-take passage in comparison to a flow of compressed air at the off-take port, and the flow of compressed air in the off-take passage is provided with higher static pressure than the flow of compressed air at the off-take port, wherein the one or more other components of the gas turbine engine includes at least one rotating component of a turbine section of the gas turbine engine and the flow of compressed air from the compressor section is delivered to the at least one rotating component with a tangential velocity that is substantially matched to a tangential velocity of the at least one rotating component.

10. A method according to claim 9 wherein the off-take passage is shaped as a diffuser and reduces an axial velocity of the flow of compressed air in the off-take passage compared with the flow of compressed air at the off-take port.

11. A method according to claim 9 wherein the direction of the off-take passage is towards the principal rotational axis of the engine, the off-take passage increasing the tangential velocity of the flow of compressed air in the off-take passage further than would be provided due only to conservation of angular momentum as the flow of compressed air in the off-take passage moves towards the principal rotational axis of the engine.

12. A method according to claim 9 wherein a swirl ratio of a flow of compressed air at an exit of the off-take passage is higher than a swirl ratio of the flow of compressed air at the off-take port.