Reliable in-flight starting of the inlet is of critical importance for the successful operation of scramjet engines, particularly axisymmetric configurations with high-contraction inlets. The present research is undertaken to examine the capability of various inlet starting methods based on two principles: unsteady flow effects and variable geometries. Time-accurate viscous computations have been performed to investigate the transitional flowfields introduced by a variety of methods that are applicable to axisymmetric geometries. Parametric studies have been conducted for instantaneous rupture of conical diaphragms and addition of bleed slots, which induce highly unsteady flow phenomena. Several methods employing variable inlet geometries have been tested for the latter principle, including opening doors and sliding doors (or diaphragm erosion). Successful inlet starting has been achieved as a result of unsteady transition induced by diaphragm rupture and quasi-steady transition, due to the sliding-door opening process. In particular, a bleed addition to the diaphragm rupture method has been found to be highly effective and pronounced flow stability has been observed in the sliding-door process.
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