Experimental investigation of hypersonic 'directed-energy air spike' inlet at Mach 10-20

The use of thermal energy as a means of enhancing flight performance of blunt bodies at hypersonic speeds is investigated. The "DirectedEnergy Air Spike" (DBAS) inlet concept proposes the beamed transmission of concentrated energy forward of a moving vehicle in order to change the bow shock configuration from a detached normal (strong) shock wave to an oblique, parabolic-shaped (weak) shock wave. This new approach provides low aerodynamic drag and heating, or also deflects the oncoming air into an annular hypersonic inlet. The compressed inlet air can either be accelerated to produce thrust or decelerated to extract onboard electric power. A 6-in. diameter blunt body model was fabricated with pressure transducers at its surface and equipped with 6-in. long slender plasma torch at the stagnation point. This model has been installed in the RPI 24-in. diameter Hypersonic Shock Tunnel and used to test the Directed-Energy Air Spike concept. Pilot pressures have been measured at the maximum diameter annular region of the blunt body. Surface pressure and pilot rake pressure surveys are presented for Mach numbers of 10 to 20 for the blunt body with no spike, and for Mach numbers 10 to 15 for the spiked blunt body with spike but no power cases. Also, Schlieren photographs for all previous configurations at Mach number 10 flow are presented as well as for the spiked blunt body power on case at Mach number 10. § Graduate Student, AIAA Student Member. t Associate Professor of Aeronautical Engineering, AIAA Member. $ Active Professor Emeritus of Aeronautical Engineering, AIAA Fellow. Copyright © 1997 by L.N. Myrabo and P G. P. Toro. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. INTRODUCTION In an attempt to travel at ever increasing velocities in an efficient manner, Myrabo and Raizer have recently proposed the theoretical concept for an "Air Spike" inlet (see Fig. 1), now re-named the "Directed-Energy Air Spike" (DBAS). The DBAS inlet concept enables active control of external aerothermodynamics for an advanced hypersonic transalmospheric vehicle by replacing directed energy for mass, conventionally in the form of a sharp nosed structure. 'LASER SUPPORTED DETONATION (LSD) WAVE COMPRESSED INLET AIR OBLIQUE SHOCK WAVE ANNULAR MHD SLIPSTREAM JOR Figure 1. "Direct-Energy Air Spike" inlet concept. One major advantage of the directed-energy air spike over a solid mass spike is lhat it has no weight. In addition, the propulsion system design of a transatmospheric vehicle using the DBAS inlet presents two more advantages: 1) employs a detached parabolic bow shock wave to contain a rarefied, "hot air pocket" that substantially reduces the flow Mach number impacting the vehicle forebody; and 2) directs the incident hypersonic air flow toward the periphery of the craft where the annular inlet of the magnetohydrodynamic (MHD) slipstream accelerator is located. The directed-energy air spike in front of a craft may be created by a shock wave propagating from a weak laser-supported detonation (LSD) wave. The pressure at the LSD wave front, being higher than atmospheric pressure, deflects the incident air flow from the axial direction and forces it to flow over the spike to the periphery of the craft (Fig. 1). The feasibility of transatmospheric flight is limited by phenomena such as aerodynamic drag and heating, as well as related thermal management problems. Traditional blunt nosed hypersonic vehicles generate a strong detached, normal shock wave in the nose region, which produces a high drag coefficient. The temperature behind this strong shock wave escalates at hypersonic velocities (Fig. 2a), although the aerodynamic heating rates are reduced compared with that of an attached shock wave on a conical body.