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A swirler is provided for a fuel injector of a combustor of a gas turbine engine. The swirler is for directing an airflow into the combustor so as to atomize fuel exiting the fuel injector. The swirler has one or more passages for channelling the airflow. Each of the passages is configured to rotate

A swirler is provided for a fuel injector of a combustor of a gas turbine engine. The swirler is for directing an airflow into the combustor so as to atomize fuel exiting the fuel injector. The swirler has one or more passages for channelling the airflow. Each of the passages is configured to rotate the airflow channelled by that passage about a swirl axis of the swirler, such that on exiting the passage the airflow has an exit swirl angle and a direction of rotation relative to the swirl axis. The swirler is configured such that the exit swirl angle and/or the direction of rotation may be selectively varied.

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1. A swirler arrangement for a fuel injector of a gas turbine engine, the swirler arrangement comprising: a plurality of passages for channeling airflow through the swirler arrangement and into a combustor, each of the passages having an inlet, anda plug movable between a first position and a second

1. A swirler arrangement for a fuel injector of a gas turbine engine, the swirler arrangement comprising: a plurality of passages for channeling airflow through the swirler arrangement and into a combustor, each of the passages having an inlet, anda plug movable between a first position and a second position, wherein at the first position the inlet to a first passage of said plurality of passages is open and the inlet to a second passage of said plurality of passages is closed, and at the second position the inlet to the second passage of said plurality of passages is open and the inlet to the first passage of the plurality of passages is closed,the swirler arrangement has a pressurisable chamber for receiving a fluid, the pressure of the fluid in the chamber in use providing motive force to move the plug between the first and second position, andthe first passage of the plurality of passages is for channeling said airflow such that on exiting said first passage said airflow has a first exit swirl angle and a first direction of rotation relative to a swirl axis, and the second passage of the plurality of passages is for channeling said airflow such that on exiting said second passage said airflow has a second exit swirl angle and a second direction of rotation relative to said swirl axis. 2. A swirler arrangement according to claim 1, wherein said first passage rotates said airflow along a clockwise path and said second passage rotates said airflow along an anticlockwise path. 3. A swirler arrangement according to claim 1, wherein each passage is disposed along a helical path relative to the swirl axis of the swirler arrangement. 4. A swirler arrangement according to claim 1, in which said plug is positioned to block the entrance to said first passage of the plurality of passages and said airflow is channeled through said second passage of the plurality of passages. 5. A swirler arrangement according to claim 1, comprising a control mechanism for varying the exit swirl angle and/or the direction of rotation of said airflow in response to the power generated by said combustor. 6. A swirler arrangement according to claim 5, wherein said control mechanism controls the supply of fluid to the pressurisable chamber. 7. A swirler arrangement according to claim 1, wherein the fluid is fuel. 8. A swirler arrangement according to claim 1, wherein the plug is resiliently biased to the first position. 9. A swirler arrangement according to claim 1, wherein the plug is located within a bore with the inlet of each passage opening to the bore. 10. A swirler arrangement according to claim 9, wherein the bore has a closed end and the pressurisable chamber is defined between an end of the plug and the closed end of the bore. 11. A swirler arrangement according to claim 10, wherein a spring acts against an opposing end of the plug. 12. A swirler arrangement according to claim 1, wherein the plug has a channel defined therein. 13. A fuel injection system comprising a fuel injector and a swirler arrangement according to claim 1 for swirling air past said fuel injector. 14. A fuel injection system according to claim 13, wherein said fuel injector is an airblast fuel injector. 15. A fuel injection system according to claim 13, wherein said swirler arrangement is concentric with said fuel injector. 16. A fuel injection system according to claim 13, wherein said fuel injector is a pilot fuel injector, said fuel injection system further comprising a mains fuel injector. 17. A fuel injection system according to claim 13, wherein said swirler arrangement is disposed radially inwardly of said fuel injector. 18. A gas turbine engine having a fuel injection system according to claim 13. 19. A method of adjusting the exit swirl angle and/or direction of rotation of an air flow through a swirler arrangement in a fuel injector for a gas turbine engine, the swirler arrangement having a body concentrically disposed about a movable plug and having a plurality of passages for channeling airflow through the swirler arrangement and into a combustor, the plurality of passages including a first passage and a second passage disposed along a helical path relative to an axis of the swirler arrangement, the method comprising: supplying a fluid to a pressurisable chamber formed by the body and the plug, andmoving the plug, via pressure from the fluid, from a first position at which air flows through the first passage in the swirler arrangement to a second position at which air flows through the second passage in the swirler arrangement, whereinat the first position at least one inlet to the first passage is open and at least one inlet to the second passage is closed,at the second position the at least one inlet of the first passage is closed and the at least one inlet of the second passage is open, andthe exit swirl angle and/or direction of rotation of the air flow is adjusted in accordance with the first passage having a first exit swirl angle in a clockwise direction relative to the axis, and the second passage having a second exit swirl angle in an anticlockwise direction relative to the axis. 20. A method according to claim 19, wherein the fluid is a liquid hydrocarbon. 21. A swirler arrangement for a fuel injector of a gas turbine engine, the swirler arrangement having a body concentrically disposed about a movable plug, the body having a plurality of passages for channeling airflow through the swirler arrangement and into a combustor, each of the passages having an inlet, the plug being movable between a first position in which at least one inlet to a first of said passages is open and at least one inlet to a second of said passages is closed, and a second position in which the at least one inlet to the first of said passages is closed and the at least one inlet to the second of said passages is open,wherein the first and second of said passages are disposed along a helical path relative to an axis of the swirler arrangement, the first of said passages having a first exit swirl angle in a clockwise direction relative to the axis, and the second of said passages having a second exit swirl angle in an anticlockwise direction relative to the axis,wherein the body and plug form a pressurisable chamber for receiving a fluid, the pressure of the fluid in the chamber in use providing motive force to move the plug between the first and second positions.