GAS TURBINE ENGINE COOLING SYSTEM

A gas turbine engine (50) includes a nacelle (52) and an engine core (54) received within the nacelle. The engine core defines a principal rotational axis (56) along its length. The engine core and the nacelle define a bypass passage (58) therebetween. The gas turbine engine further includes a cooling system (100) including a cooling duct (102). The cooling duct defines an inlet (104) for receiving bypass air (D) from the bypass passage (58) at an upstream location and an outlet (106) for discharging the bypass air at a downstream location. The cooling duct extends, relative to the principal rotational axis, both axially and circumferentially around a section of the engine core (54). The cooling duct comprises: a first portion (108) that extends at least axially relative to the principal rotational axis; a second portion (110) downstream of the first portion that extends circumferentially around the engine core relative to the principal rotational axis; and a third portion (112) downstream of the second portion that extends at least axially relative to the principal rotational axis.