The Busemann Air Intake for Hypersonic Speeds

A review and summary is presented of hypersonic air intake technology highlighting design objectives, basic flows, airframe integration, flowpath modification and intake flow startability. Taylor-Maccoll equations and Busemann flow are presented as the basis for constructing modular Busemann intakes. Wavecatching (streamline tracing), morphing and foreshortening are presented to show that (a) wavecatching is a useful technique to create modular startable intakes; (b) morphing is useful in integrating the intake shape with other geometric requirements of the airframe and combustor; and (c) foreshortening leads to minor gains in intake performance but large weight savings. A novel, strong shock method is presented, which uses strong-shock boundary conditions for designing spontaneously startable, modular Busemann intakes of high performance. This allows pre-determination of Busemann intake startability; offering great simplicity in the search for flowpath surface shapes that yield startable intakes with high compression, high efficiency and supersonic exit flows. Busemann flow contains unique fluid mechanical features: (a) a flow passage from a uniform, high Mach number flow, to another uniform, lower Mach number flow; (b) internal, convergent flow with an inflected surface; (c) conical flow where high gradients are near the center line and milder gradients are at the walls; (d) an axisymmetric and conically symmetric centered compression fan; (e) a free-standing conical shock, bounding irrotational flow. These are unique and fortuitous virtues, being significant in making the Busemann streamtube and its flow characteristics a suitable basis for designing high performance air intakes for hypersonic airbreathing engines