Abstract: A cooling air outlet duct for a heat exchanger of a gas turbine engine is provided with a rotatable wall portion. The rotatable wall portion is rotatable about a pivot positioned at its upstream end so that the total flow area between the downstream end of the rotatable wall portion and a first wall of the fluid outlet duct and the fluid flow rate may be varied to obtain relatively high exit velocities for the cooling air discharging from an exit nozzle in a fan casing to give good thrust recovery. This produces a lightweight and uncomplicated valve for the fluid outlet duct.

Abstract: An air bleed system for a compressor, particularly for gas turbine engines is provided with an air bleed from a portion of the compressor to an annular chamber through an annular opening in the casing; an annular passage is connected to the opening and terminates in the annular chamber surrounding the casing; a plurality of turning vanes change the direction of flow of the bleed air by 90.degree. to induce a circulating flow of air in the chamber; flush openings and ducts angle circumferentially in the direction of the circulating flow in the annular chambers supply air to the engine and aircraft accessories.

Abstract: The invention relates to fluid outlet ducts particularly cooling air outlet ducts of a gas turbine engine. A fluid outlet duct for a gas turbine engine is divided across its width into a plurality of second plenum chambers, each of the second plenum chambers has an associated exit nozzle located in the casing of the gas turbine engine for discharging cooling air. The cooling air from a heat exchanger is supplied through a first plenum chamber to each of the second plenum chambers. Each of the second plenum chambers has a valve to vary the flow of cooling into the second plenum chambers so that the total flow area of the fluid outlet duct may be varied to obtain relatively high exit velocities for the cooling air to give good thrust recovery.