GB871016A - Gas turbine jet propulsion engines - Google Patents

Abstract

871,016. Jet-propulsion plant. POWER JETS (RESEARCH & DEVELOPMENT) Ltd. Sept. 10, 1958 [June 12, 1957], No. 18547/57. Class 110 (3). In a gas-turbine jet-propulsion engine of either the by-pass or ducted fan-type, having concentric inner and outer passages for the turbine exhaust gas and air streams respectively leading into a common jet pipe, means are provided for varying the crosssectional area of the turbine exhaust passage at its outlet into the jet pipe. Fig. 1 illustrates an engine of the by-pass type and comprises a by-pass passage 12 between an inner casing 14 and an outer casing 13 and a turbine exhaust passage 16 with a mixing device 21, which facilitates the mixing of the two streams as they enter the jet pipe 18. The device 21, shown in greater detail in Figs. 2 and 3, comprises a corrugated member attached to the downstream extremity of the inner casing 14. The corrugated member comprises substantially radially extending walls 22 of triangular shape joined by circumferentially extending members 23. The outer crests 23a of some of the corrugations are formed as flaps operated by actuators 24 to vary the cross-sectional areas of the passages 12, 16. Alternatively some of the inner crests or some of both the inner and outer crests may be formed as flaps and some flaps may be movable independently of the others. In an alternative form (not shown) the mixing device is dispensed with and replaced by a ring of flaps, pivotally attached to the downstream end of casing 14, operated by actuators and movable radially inwards or outwards. In both embodiments the outlet cross-sectional areas of the two passages 12, 16 are varied simultaneously in opposite senses so that a relatively large change in the ratio of the areas can be achieved for a small movement of the flaps. For operation under supersonic flight conditions it may be desirable to close the outlet of the turbine exhaust passage completely and with fuel supplied to after burners 19, the engine would operate as a ram jet. In two further embodiments the turbine exhaust passage outlet can be completely closed. In the first, Fig. 6, the outlet from the turbine outlet passage 16 is rectangular in shape and is defined by a pair of fixed side walls 41 and a pair of pivotally mounted flaps 42 movable between the side walls and by jacks 43. In the other embodiment, Fig. 8, the wall 14 between the two passages 12, 16 terminates in a conical member 46 tapering to a point directed downstream and formed with longitudinally extending slots 46a, and a conical shutter 47 fitting outside the conical member 46 is also formed with longitudinal slots. To vary or close the outlet of the turbine exhaust passage the shutter is rotated relative to the conical member by an actuator 48. According to the Provisional Specification in one embodiment the outlet of the by-pass passage only is variable by means of an inflatable member forming part of the outer wall of the by-pass passage. For high air temperatures, the inflatable member is replaced by a series of longitudinally extending circumferentially overlapping flexible metal strips fixed at one end to the outer wall and encircled intermediate their ends by an expandable and contractable band which can be tightened to bow the strips inwardly and so coristrict the by-pass passage outlet. Specification 587,571 is referred to.