Physical insights into multi-point global optimum design of scramjet intakes for ascent flight

Scramjet propulsion offers promise for flexible and sustainable space transportation. Hypersonic airflow compression through the intake plays a major role in successful scramjet-powered ascent. It is thus of crucial importance to design high-performance intakes that can work efficiently and robustly throughout the ascent trajectory. The present research is conducted to gain physical insight into multi-point global optimum scramjet intake design and associated requirements by means of multi-point design optimization and analytical investigation in inviscid and viscous regimes. It has been found and verified theoretically that at any operating conditions, compression efficiency, drag, compression ratio, and mean exit temperature can theoretically be determined uniquely in an interrelated manner under calorically perfect and adiabatic flow assumptions, provided one of them is given or known except for compression efficiency. The multi-point optimization study in the inviscid regime has verified that the multi-point global optimum design can exist with respect to compression efficiency and drag. On the other hand, while the theoretical analysis also prescribes that the global optimum design can exist for a single operating condition in viscous flow, trade-off relations have been found to exist between two operating conditions in the viscous regime, where boundary layer is responsible for counteracting behaviors between compression efficiency and drag at different operating conditions. The insights gained contribute to the guiding principle for intake design of scramjet engines for access-to-space.