Designing high-performance air intakes is of crucial importance for the successful operation of hypersonic scramjet propulsion. This paper investigates the performance of axisymmetric intakes obtained by applying two shortening methods, namely, leadingedge truncation and stunting (longitudinal contraction), to the full Busemann intake in inviscid and viscous flowfields. The primary aim is to identify the key design factors and underlying flow physics in order to achieve the optimum performance

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... ith minimum weight by striking the balance between viscous and shock losses. The effects of intake shortening on performance are similar for the two methods for moderate length reduction (25%), conducing to considerable reduction in intake weight. Even reduced to half length, truncated intakes can produce reasonable compression (60% of the full Busemann intake) with the original level of total pressure recovery maintained in viscous flowfields. Stunted intakes, on the other hand, can enhance compression with considerable total pressure penalty, eventually leading to intake unstart at a certain point due to the emergence of Mach reflection, which makes this method potentially useful in situations where locally high pressure and temperature are desired near the centreline at the cost of total pressure recovery. cluding aerodynamic and combustion efficiency, aerothermal and structural management as well as manufacture, incorporated with innovative concepts including inlet fuel injection and radical-farming shock-induced combustion (6), (7) .