GB747705A - Improvements in and relating to aero-thermodynamic ducts adapted to operate at supersonic speeds - Google Patents

Abstract

747,705. Aircraft cabins; boundary layer control on jet-propelled aircraft. LEDUC, R. Feb. 5, 1954 [Feb. 6, 1953], No. 3453/54. Class 4. [Also in Group XXVI] An aero-thermodynamic duct for a ram-jet or a gas-turbine engine moving at supersonic speed has an annular diffuser entry defined by an outer tubular shell 11 and a central substantially coaxial core 4 which projects forwardly from the open leading end of the shell, in which the forwardly-facing portion of the core is of ogival section with its circumferential line of inflexion, at the point of maximum slope of the profile, situated near to and preferably slightly down-stream of the plane of the leading edge of the shell, and the surface of the concave portion 4a of the core, and optionally at least an adjacent part of the convex portion 4b, is provided with distributed perforations or porosity in communication by internal passage means with the exterior of the shell 11 at a region where the external fluid flow is least disturbed and the static pressure approximates to that of the undisturbed ambient fluid. In the embodiment shown, applied to an aircraft body, the core is provided with a skin 8 supported from the core in any known way and perforated at the portions stated, the space between the skin and the core being connected with the outside of the shell 11, in the region of the maximum diameter of the latter, through a duct 9 and apertures 10, whereby the boundary layer of fluid is drawn off from the surface of the core and discharged. The front portion 3a of the core is in the form of a cone of small angle housing the pilot's cabin, and the boundary layer formed along this portion is drawn into an annular slot 17 at the front end of the space between the core 4 and skin 8. In another embodiment the concave curve of the core and skin is continued forward to a sharp point. The arrangement is such that the single shock wave produced by the vertex of a cone is replaced by a series of smaller shock waves produced along the concave part 4a of the core, the envelope of these waves being of small or vanishing curvature and situated outside the leading edge of the shell 11 ; the effect is a substantial increase in the compression efficiency over a wide range of Mach number. The front portion of the shell 11 may be perforated, as shown at 12, for removal of the internal boundary layer at that portion, and the section 11a may be movable axially, for example by piston-rods 15, to vary the crosssection of the inlet.