Influences of Inlet Geometry Modification on Scramjet Flow and Combustion Dynamics

The influences of inlet geometry modification on flow and combustion dynamics are experimentally investigated in a model supersonic combustion ramjet (scramjet) installed in Mach 4.5 high-enthalpy air freestreams. The inlet upper-lip angle (6, 12, and 20 deg) and the intake contraction ratio (1.3 and 1.9) chosen as the generic inlet design parameters are varied. With the inlet geometries systematically modified, flowfields inside the model scramjet are visualized at cold conditions (room temperature) using a planar laser Rayleigh scattering method (wherein laser radiation is scattered by carbon dioxide particles). In addition, combustion dynamics and structures in the scramjet combustor are investigated in high-enthalpy flows with a total temperature of 2600 K capable of autoigniting injected fuels. High-frame-rate time-averaged chemiluminescence (broadband) imaging and hydroxyl planar laser-induced fluorescence are used for this investigation. Incident shock-wave strength, separated flow behavior, boundary-layer development, combustion structure/anchoring, and chemiluminescence intensity are found to be sensitive to the inlet geometry modifications.