GB814012A - Discharge nozzles for propulsive jets - Google Patents

Abstract

814,012. Jet propulsion plant. POWER JETS (RESEARCH & DEVELOPMENT) Ltd. May 29, 1957 [June 14, 1956], No. 18471/56. Class 110 (3). [Also in Group XXIX] A jet propulsion nozzle comprises a convergent nozzle portion, a first divergent nozzle portion, a second divergent nozzle portion the upstream end of which is outwardly stepped from the downstream end of the first divergent nozzle portion to form a peripheral gap between the divergent portions through which a fluid can enter the flow path and means operable on occasion to prevent fluid entering the flow path. The expression " outwardly stepped " is intended to imply that the conical surface on which the outlet of the first divergent portion and the inlet of the second divergent portion lie, has a greater divergence than the second nozzle portion adjacent its inlet. The propulsion nozzle shown comprises an entry member 8 which converges to a throat 11, a second member 9 attached to the member 8 which diverges in the downstream direction and a discharge member 10. The upstream end of the member 10 has a diameter about 10 per cent greater than the diameter of the adjacent end of the member 9 and is axially spaced therefrom by a distance equal to about 8 per cent of the diameter so as to form a peripheral slot 12. The members 9, 10 are connected by a number of beams 14. Flanges 15, 16 attached to the members 9, 10 support a number of guide rods 17 which carry an axially slidable ring 21 which may open or close the gap 12 to the flow of air from a casing 5. In the closed position the ring 21 engages seating flanges 18, 19. The flange 18 is mounted direct on the member 9 and the flange 19 is mounted on the member 10 by bellows 20. The seating surfaces are formed on a conical envelope. The ring 21 is actuated by jacks 25 controlled by a servo-mechanism 28 which operates when the pressure ratio or pressure difference between the pressure of the fluid entering the nozzle and the ambient atmospheric pressure at the nozzle outlet exceeds or falls below a particular value. In a modification, Fig. 5 (not shown), the duct 2 is extended to form a casing enclosing the members 8, 9 and 10. The flow through the gap 12 is controlled by a slidable ring opening or closing ports in the casing. In another modification, Fig. 6 (not shown), the member 10 is slidable axially to cooperate with a seating formed on the outside of the member 9. The member 10 also carries a sleeve which closes apertures in a casing surrounding the member 9 when it is retracted. In a further embodiment, Fig. 7 (not shown), the members 9, 10 are spaced apart by webs. The gap 12 is opened or closed by a ring which is slidable on flanges attached to the members 9, 10. More than one gap may be provided in the divergent portion of the nozzle. A gap may also be provided at the throat of the nozzle. This gap may be supplied with pressurized fluid from a chamber surrounding the gap. The throat of the nozzle may be varied by a pair of pivoted arms which move transversely to the jet. The arms or injection gap may be located slightly upstream of the throat. In another embodiment, the area of the nozzle throat is varied by means of interleaved members pivoted at their upstream ends. In one position the members meet the upstream end of the member 9 to form a continuous surface. In another position, the members are retracted to restrict the nozzle throat area to a minimum. A gap is formed around the retracted members which is associated with an outer step in the profile of the flow path. Specifications 606,176, 788,316 and 810,189 are referred to.