JOURNAL OF SPACECRAFT AND ROCKETS Vol. 42, No. 1, January–February 2005 Laser-Supported Directed-Energy “Air Spike” in Hypersonic Flow M. A. S. Minucci, ∗ P. G. P. Toro, † A. C. Oliveira, ‡ A. G. Ramos, § J. B. Chanes Jr., ¶ and A. L. Pereira ∗∗ Instituto de Estudos Avanc ¸ados, 12228-840 S˜ ao Jos´ e dos Campos, Brazil and H. T. Nagamatsu †† and L. N. Myrabo ‡‡ Rensselaer Polytechnic Institute, Troy, New York 12180-3590 The experimental results on the laser-supported directed-energy “air spike” (DEAS) in hypersonic flow are presented. A CO 2 TEA laser has been used in conjunction with the IEAv 0.3-m Hypersonic Shock Tunnel to demonstrate the laser-supported DEAS concept. A single laser pulse generated during the tunnel useful test time was focused through a NaCl lens ahead of an aluminum hemisphere-cylinder model fitted with a piezoelectric pressure transducer at the stagnation point. In the more recent experiments, a double Apollo disk model fitted with seven piezoelectric pressure transducers substituted the simple hemisphere-cylinder model. The objective of the present research is to corroborate the past results as well as to obtain additional pressure distribution information. Introduction I T has been suggested by several authors 1−7 that aerodynamic drag and heating of a hypersonic trans-atmospheric vehicle (TAV) could be greatly reduced by adding energy to the air ahead of it. Such energy addition could be accomplished by a plasma torch mounted at the nose of the TAV, 8−12 by an electric break- down ahead of the TAV, 13−17 or by focusing a powerful laser (or microwave) beam ahead of the TAV flight path, as it has been originally suggested by Myrabo and Raizer 3 in 1994, and demonstrated by Minucci et al. 18−22 and Powell (a disclosure of the first successful directed-energy air spike by laser-energy deposi- tion tests by Minucci et al. in the IEAv Hypersonic Shock Tunnel, Brazil). 23 Knight et al. 24,25 provide very selective surveys of research in aerodynamic flow control at high speed using steady 24 and unsteady 25 energy deposition (e.g., plasma arcs, laser pulse, mi- crowave, electron beam, glow discharge.) not only for drag reduction applications but also for lift and moment enhancement, improved mixing, modification of shock structure, etc. The surveys review the effect of energy deposition, upstream of a blunt body in supersonic Received 27 May 2003; revision received 28 January 2004; accepted for publication 2 February 2004. Copyright c  2004 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with per- mission. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0022-4650/05 $10.00 in correspondence with the CCC. ∗ Lt. Col. Brazilian Air Force, Principal Research Engineer, Laboratory of Aerothermodynamics and Hypersonics, Centro T´ ecnico Aeroespacial; sala@ieav.cta.br. Senior Member AIAA. † Senior Research Engineer, Laboratory of Aerothermodynamics and Hy- personics, Centro T´ ecnico Aeroespacial; toro@ieav.cta.br. ‡ Graduate Student and Physicist, Centro T´ ecnico Aeroespacial. § Graduate Student and Research Assistant, Laboratory of Aerothermo- dynamics and Hypersonics, Centro T´ ecnico Aeroespacial; currently Oper- ational Engineer, Universidade do Vale do Para´ ıba, Av. Shishima Hifumi, 2911, 12244-000 S˜ ao Jos´ e dos Campos, S˜ ao Paulo, Brazil. ¶ Research Engineer, Laboratory of Aerothermodynamics and Hypersonics, Centro T´ ecnico Aeroespacial. ∗∗ Research Assistant, Centro T´ ecnico Aeroespacial. †† Active Professor Emeritus of Aeronautical Engineering, Department of Mechanical Engineering, Aeronautical Engineering, and Mechanics. Fellow AIAA. ‡‡ Assistant Professor of Aeronautical Engineering. Department of Mechanical Engineering, Aeronautical Engineering, and Mechanics; myrabl@rpi.edu. Senior Member AIAA. flow, on drag reduction (i.e., integrated frontal surface pressure) when sufficiently high levels of energy deposition were used. 26−30 Myrabo and Raizer called the effect of reducing aerodynamic drag and heating through the use of electromagnetic radiation (laser en- ergy addition) by directed-energy air spike (DEAS), effect. A laser- driven TAV, resembling two Apollo reentry heat shields mounted back to back, was even suggested by Myrabo. The experimental TAV, which makes use of the laser-supported DEAS effect, is de- picted in Fig. 1. The first experimental confirmation of such effect came in 1996 when a model of the proposed TAV, fitted with an electric arc plasma torch, was tested in the Rensselaer Polytechnic Institute (RPI) 0.6-m Hypersonic Shock Tunnel. 8,9 In these tests, the laser focus was represented by air plasma at the tip of the slender plasma torch mounted at the model center- line. It was observed that when the plasma torch was turned on at 35 kW the conical shock wave, originating at the tip of the plasma torch (without the electric arc), would assume a parabolic shape indicating a change in the hypersonic, Mach 10, flow, as a result of the energy addition. Continuing Marsh’s 8,9 exploratory work, Toro and coworkers 10−12 extended the DEAS investigation by measuring both the surface-pressure distribution and the surface heat-transfer distribution for several plasma torch power levels. The results once more corroborated Myrabo and Raizer 3 predictions, but the pres- ence of the torch itself would make it difficult to completely iso- late the torch assembly beneficial effects from those of the energy addition. To isolate the effects just mentioned and to more closely simulate the focusing of a laser beam (or a microwave beam) ahead of the model, the torch assembly had to be eliminated. To that end, Minucci et al. 13 and Bracken et al. 14 suggested that establishing an electric arc between two slender 1.5-mm-diam tungsten electrodes, mounted at the exit plane of the hypersonic shock tunnel conical nozzle, could perform the energy addition to the flow. In this way, the electrodes would be thin enough not to disturb the hypersonic flow and, at the same time, would eliminate the need to use the torch mounting. This experiment is still in progress 13,14 but has already produced some interesting results. 15−17 The next natural step, which constituted the motivation for the exploratory work 18−20 and the recent investigation carried out at Laboratory of Aerothermodynamics and Hypersonics (LAH), 21−23 was to use a laser beam to drive the DEAS, as suggested by Myrabo and Raizer. 3 In this situation, the DEAS in front of a vehicle is cre- ated by a shock wave propagating from a laser-supported detonation (LSD) wave (Fig. 2). The pressure at the wave front, being higher than atmospheric pressure, deflects the incident hypersonic airflow 51 Downloaded by UNIVERSITY OF OKLAHOMA on October 26, 2014 | http://arc.aiaa.org | DOI: 10.2514/1.2676