Patent GB-1401017-A (GB)
Title: Duct system
IPC: B64D27/16
Filed: 1972-10-30
Abstract: 1401017 Gas turbine ducted fan engines BOEING CO 30 Oct 1972 [8 Nov 1971 16 Feb 1972] 50000/72 Heading F1J The invention relates to a gas turbine engine of the ducted fan type in which means are provided to increase or to vary the by-pass ratio, in which first and second duct means are provided for inverting the spatial relationship of separate adjacent concentric annular flow patterns within the confines of an annular passageway having an area substantially equal to the combined area of the two separated flow patterns. The engine shown in Fig. 2 and 3 comprises a fan 26 with a valve assembly 20 disposed between the fan and the engine compressor, the valve comprising a fixed forward part 22 and an angularly rotatable rearward part 24, the parts adjoining at the plane 23. In the position shown in Fig. 2 air enters the outer annular duct B of the forward-part from inlet 28 and discharges from the inner annular duct B of the rearward part so passing to the engine compressor; air delivered by the fan passes into the inner annular duct A of the forward part and discharges from the outer annular duct A of the rearward part so discharging through the fan nozzle 30; this is the high by-pass ratio mode of operation. In Fig. 3 the rearward part 24 has been rotated whereby flow inversion does not occur, air discharged by the fan 26 entering and discharging from the inner annular ducts A to the engine compressor. Air-flow to the outer annular ducts B is closed off by valve-members 29, 31. The flow inversion valve is shown in detail in Fig. 4 with the cross-sections taken at lines 4a, 4b, 4c, 4d, 4e, 4f shown in the corresponding Figures. The inner and outer annular ducts A and B are defined by annular walls 62, 64, 60, the annular ducts being divided by radial walls 66, 68; an inner arcuate shaped passage A at the inlet Fig. 4a changes to a pentagonal shape at Fig. 4b, to a triangular shape with the apex outward Fig. 4c, to a narrow trapezium shape at Fig. 4d, then to a triangular shape with apex inward at Fig. 4e, and finally to an outer arcuate shaped passage A at the outlet Fig. 4f. Thus it is seen that flow inversion has occurred in passage through the flow inversion member. The flow inversion member may be fixed so that flow inversion always occurs. Alternatively the downstream portion 58 may be angularly movable with respect to the upstream portion 56 as shown in Fig. 5 with the shape of the passages shown at sections 5d, Se, 5f. The section at Fig. 5e now corresponds to that of Fig. 4c and that of the discharge plane Fig. 5f to that of the inlet  plane Fig. 4a, from which it may be seen that flow inversion has not taken place. The shape of a duct passage is indicated in Fig. 13 from which it may be seen that the passage is of constant area throughout its length even though the shape changes from horizontal rectangle, to triangular with apex outward, to vertical rectangle, to triangular with apex inward, to horizontal rectangle. Further applications are disclosed, in Fig. 15a, 15b for example an engine comprises forward and aft fans 156, 158 with the flow inversion member 150, 152, 154 disposed therebetween and surrounding the gas generator section 160 of the engine. In Fig. 15a, the member 150 is positioned for flow inversion this being the high by-pass ratio mode of operation; in Fig. 15b the member 150 is positioned for non-inverted flow, this being the low by-pass ratio mode. The engine shown in Figs. 17a, 17b comprises two front fans 176, 178; in the flow inversion position of the member 170, 172, 174, the air-flow B passes to the rearward fan 178 and air-flow A from the fan 176 passes to the outer fan nozzle, the fan nozzle being divided by a pivotable member 184. In Fig. 17b the member 170, 172, 174 is moved to the non-inverted flow position and the member 184 is moved about pivot point 180 to close off the fan nozzle. Air-flow A from the forward fan 176 now passes to the rearward fan 178, the air from which is directly forwardly by the member 184 as indicated by flow B and is discharged through a duct 186 for use in blown flaps for example; a valvemember 189 is moved so as to allow flow to the duct 186. In Fig. 19a the flow inversion member 190, 192, 194 is provided in an engine which may operate either as a turbo fan, a turbojet or a ram jet engine, a combustion apparatus 202 being disposed in the fan outlet duct 200. When the member 190 is positioned to provide flow inversion, Fig. 19a, the engine operates as a turbo fan; when the member is positioned to provide non-inverted or straight through flow, the engine operates either as a turbojet, as a turbojet with ramjet, or as a pure ramjet. Another embodiment is described which may operate either as a turbofan, as a turbofan with ramjet or as a pure ramjet.