Analysis of transient thermal choking processes in a model scramjet engine

Shadowgraph flow visualisation and floor static pressure measurements have been used to examine the transient behaviour of a thermally choked combusting flow. Experiments were performed to examine the effect of varying inlet Mach number and fuel-air equivalence ratio on the nature and extent of the interaction. In all cases a sudden increase in static pressure was measured, followed by a highly turbulent region of sonic flow which was seen to propagate upstream along the duct. The nature of the dominant processes causing this pressure discontinuity are still not certain. Some mechanisms which may contribute to this phenomenon are presented. These include separation of the boundary layer in the duct, formation of a detonation and formation of a near-normal shock wave by the region of thermally choked flow.