Experimental and computational investigation of an electric arc air-spike in hypersonic flow with drag measurements

Abstract

The effects of an arc discharge to create an Air-Spike in a hypersonic flow are currently being studied in the Rensselaer Polytechnic Institute 24-inch Hypersonic Shock Tunnel (RPI HST), modeled computationally, and compared to existing theory. The arc is a high current car battery array-driven, 75kilowatt peak, self-sustaining electrical discharge in a Mach 10, 260 psia stagnation pressure, and 560 K stagnation temperature flow. In this low enthalpy, ideal gas, condition, schlieren photographs are taken of the apparatus with and without a downstream blunt body, with varying arc powers. Blunt body drag measurements are also made with both hanging and sliding models with fast-response accelerometers, with and without the arc to establish a correlation between arc power and body drag. The computational effort employs the Euler gasdynamic equations to represent a heat source in flow conditions and geometries identical to those tested in the RPI HST. These two results are then compared to early Air-Spike theoretical predictions to qualitatively validate the CFD code and gain a better perspective on the loss mechanisms involved in the experiment. INTRODUCTION Among the most critical factors in the design of a hypersonic vehicle are aerodynamic drag and heating. To design for low aerodynamic drag would leave the body with sharp edges and a high fineness ratio. Heat transfer concerns would lead the design to a blunt body with a very low fineness ratio, which leads to a substantial increase in wave drag. It has been suggested by several authors (Myrabo, 1978, Tidman, 1990, Myrabo, et a/., 1994, Head, 1994, Seo, 1994, Gurijanov, et al.9 1996, and Co vault 1999) that both the drag and heating of a hypersonic Trans-Atmospheric Vehicle (TAV) could be greatly reduced by adding energy to the air ahead of the craft. This energy addition could be accomplished through the focusing of beamed electromagnetic radiation from a laser or microwave source. Figure 1 shows a diagram of this concept of focusing a laser beam to support the Directed-Energy Air-Spike (DEAS). Marsh, et al, (1996), have experimentally demonstrated that the strong bow shock wave normally produced by a blunt body would become a more benign conical shock wave when an electric arc torch is fired ahead of the body. Figure 2 is a schlieren photo from these tests. * Graduate Student, AIAA Student Member f Associate Professor of Engineering Physics, AIAA Senior Member : Active Professor Emeritus of Aeronautical Engineering, AIAA Fellow 5 Graduate Student, AIAA Student Member * Researcher, AIAA Member Copyright ©2001 by R.M. Bracken and L.N. Myrabo. Published by the American Institute of Aeronautics and Astronautics, Inc, with permission. $Annular inlet t Air Flow Shock Wave