Shock Boundary Layer Interactions in a Scramjet Inlet (037141)

Hypersonic air-breathing propulsion involving ramjet and scramjet technologies are evolving both in terms of their operational capabilities and performance targets. Scramjet engines, more than any other air-breathing engine, need to be integrated with the aircraft to efficiently compress air where the inlet achieves compression both externally and internally through a series of oblique shocks creating a shock train in the isolator. Maintaining supersonic flow at the exit of the isolator or at the entry of combustor is the desired conditions in order to achieve efficient combustion, continues to be a challenge that is yet to be adequately addressed. This is because there are a number of sources of instabilities that make the state flow properties less than optimal. The instabilities and transients can get initiated in the combustor e.g. due to fuel injection, atomization, mixing and thermoacoustic, or due to changes in the flight/operating conditions. Depending upon the source, the transients can range from the order of a few (-10) milliseconds in case of combustor driven instabilities, to O (Is), due to changes in flight conditions. Regardless of the source, their impact on scramjet perfonnance is significant, leading to flow unsteadiness, vibration and sometimes inlet unstart. The attraction of scramjet engines is their simplicity which makes the use of traditional, passive methods, such as long isolators unattractive and impractical. An effective scheme that maintains operation at (near) optimal condition must be active with the requisite sensitivity, responsiveness and co11trol authority to effect change at the range of time scales for scramjets. It must do while being robust and reliable in the harsh scram jet environment.