Patent GB-948067-A (GB)
Title: Improvements in fluid-flow diffusers and apparatus embodying such diffusers
IPC: F22D11/02
Filed: 1960-10-14
Abstract: 948,067. Propelling and lifting aircraft; wind tunnels; screw propellers. SOC. BERTIN & CIE. Oct. 14, 1960 [Oct. 16, 1959], No. 35343/60. Headings B7G, B7V and B7W. [Also in Divisions F1, F2 and F4] A diffuser, which may be incorporated in an aircraft lifting jet system, a ducted screw propeller, or a wind tunnel, comprises a portion of progressively increasing divergence bounded by a solid wall, the longitudinal section of which is of progressively increasing curvature going downstream, the downstream end of the portion having boundary layer control means whereby the marginal layers of the flow are maintained in contact with the wall while being accelerated by the increasing divergence, these layers being then slowed down and recompressed. In Fig. 1, the exhaust from a gas turbine engine nozzle 3 induces air flow through a vertical duct comprising a convergent portion 4 and divergent portion 5, to produce a lifting force on an aircraft. The radially outer parts of the flow are stated to have a higher velocity and lower pressure than the inner part, as a result of the divergence of portion 5, and to correct this, the end portion 6 of portion 5 has a high curvature, and a fluid screen shown by arrows f is ejected from a slot nozzle 9 leading from a manifold 7 fed from the gas turbine compressor 1, and thus prevents flow breakaway. Further annular guide vanes 10, 11 are provided, the former being solid, and the latter hollow, and receiving air from manifold 7 and discharging through a slot nozzle 12. In Fig. 2, a propeller 14 is situated at the throat of a convergent-divergent duct. Again, the outlet end of the divergent section has a high curvature, and boundary layer suction is applied at a slot 22 to prevent detachment of the airflow from the duct wall and to ensure diffusion of the radially outer part of the flow. Annular guide vanes 18, 19, 20, 21 define diverging annular channels, and may be extended upstream as shown for vanes 19 and 21. The outermost part of each propeller blade may have an increased angle of incidence. Further, the different parts of the blades which deliver air to the respective channels between vanes 18 ... 21 may have different angles of incidence. In a modification, Fig. 2a (not shown), boundary layer suction is replaced by boundary layer blowing over the inner wall of the duct and over the propeller hub. In this embodiment, the propeller blades extend radially outwardly and upstream from the hub. Struts supporting and upstream of the propeller hub impart a rotation to the flow, which is cancelled by the propeller blades. In Fig. 3, a propeller 25 is located within an annular wing of which the lower part 27 has a cross-section larger than that of the upper part 28, the whole forming a convergent-divergent duct. The rear part 27a is rounded, and a slot 29 extends round the lower half of the outer surface of the wing. The slot has a rounded leading edge 30, and a thin trailing edge 31, and air is blown through the slot to prevent separation of the airflow through the duct, and to increase the vertical component of the flow out of the duct to increase the lift. The wing and propeller are tiltable on the aircraft to vary the lifting and propulsive thrust components. Specifications 847,500 and 877,766 are referred to.