Hypersonic Air Intake Design for High Performance and Starting Sannu Mölder, Evgeny Timofeev Department of Mechanical Engineering, McGill University 817 Sherbrooke St. W. Montreal, P.Q. CANADA
[email protected] SUMMARY Hypersonic air intake performance is defined in terms of intake capability and efficiency. The propensity for intake flow starting is measured by the Startability Index – a parameter inversely related to capability that is shown to be a meaningful and convenient measure of the startability for a hypersonic air intake. It is shown that the basic Busemann flow is adaptable to the design of high-performance air intakes. Proper choice of the strength of the terminal shock yields high-performance, modular, intake shapes, with low internal contractions, that are capable of spontaneous starting with overboard mass spillage. Some practical designs and applications are presented. 1.0 INTRODUCTION Air-breathing aero-engines such as ramjets and scramjets, operating at supersonic and hypersonic speeds, ingest air through a converging air intake1. For both ramjets and scramjets at these speeds, convergence causes enough compression that no further mechanical compression is required before combustion. In a scramjet, the static temperature at combustor entry is high enough to cause the injected fuel to ignite spontaneously. The resulting lack of mechanical complexity, with practically no moving parts, puts the ramjet as well as the scramjet to overall advantage over the turbojet engine even at low Mach numbers where turbojet thermodynamic performance may exceed that of the ramjet/scramjet. For useful engine operation, at some flight conditions, the intake duct shape must be such that the required air mass flow in the duct is predictable, stable, properly conditioned (uniform in some sense) and thermodynamically efficient.