Inlets and Nozzles

Abstract

Inlets Introduction Air intakes for any air-breathing engine-equipped vehicles must capture the exact amount of air required by the engine, accomplish the deceleration to the required engine entrance air speed with minimum total pressure loss, deliver the air with tolerable flow distortion and contribute the least possible drag to the system (Mahoney, 1990). These general requirements for all air-breathing engine inlets would place particular emphasis on some of the stated functions or others, depending on the specific characteristics of the propulsion system used and the vehicle mission. Some of these requirements are of general applicability; minimum pressure losses and least possible drag induction fall into this category. Other inlet characteristics have more or less significant influence, depending on the particular engine used. For example, dynamic distortions induced by an inlet can create serious difficulties for a gas-turbine-engine compressor because they reduce the stall margin, thus limiting the operational range. The extent to which the dynamic distortions affect a scramjet engine operation, on the other hand, is not entirely clear because increased flow unsteadiness could accelerate mixing but may also have a negative effect on momentum losses. This is not the case for the steady-state flow nonuniformities that have been shown to cause significant effects on the scramjet flow field, as they do on other engines. Design considerations derived from mission requirements lead to specific inlet characteristics.