Influence of differently organized microwave discharge on AD-body characteristics in supersonic flow

Abstract

The main idea of the present investigation was to examine the influence of MW discharge structure organization on the BSW behavior and other AD characteristics of a body in SS flow. All our previous investigations were fulfilled with MW discharge filaments oriented normally to the flow axis and, hence, parallel to the BSW front in near-axis spatial region. Now the electric vector of EM wave orientation was changed in respect of flow velocity vector and it became parallel to the last, and therefore, a spike-like plasma region pierced the BSW. Experiments were made not only in air but in argon and carbon dioxide as well. Introduction Activity in the area of applying microwaves in plasma aerodynamics has begun not so long ago but now is providing in several research centers. It includes creation of free localized and stimulated MW discharge in supersonic flow, MW discharge on the surface of AD body, as well as its application to the adjacent problems such as plasma-assisted combustion and MHD flow control [1]. The main goal of our activity is to understand the physical basis of the phenomena of drag reduction of AD-body in supersonic airflow caused by creation of free-localized MW discharge in front of a body. This problem taken in general has its history, as an anomalous features of plasma interactions with high speed bodies and air flows have been revealed far ago [2]. Two main reasons for such effect explanation were proposed gas heating (thermal mechanism) and/or direct plasma action (non-thermal mechanism). For a long time the activity of investigators was aimed at finding out the conditions for the last mechanism realization and rather often such kind of results seemed to be true. Our previous investigation [3] has revealed non-trivial behavior of the bow shock wave while its interaction with discharge regions. Therefore, two principle items were investigated and are the motivation of this work: the regime of MW energy input, including obtaining of its local values, and variation of MW discharge region organization in order to lighten the mechanism of discharge region bow shock wave (BSW) interaction. In all our previous experiments the electric field vector of electromagnetic (EM) wave was perpendicular both to the flow central axis (x-coordinate) and the main optic axis of the Schlieren device (z-coordinate), therefore, ypolarization has been realized. Present investigation was fulfilled under the two other possible electric field positions parallel to the main axis of Schlieren device (z-polarization), and parallel to the flow axis (x-polarization). It should be noted that x-, yand z-polarization designates only spatial orientation of electric field vector and in all three cases EM-wave itself was linearly polarized. Z-polarization is very efficient from the point of view of obtaining the detailed pictures of gas dynamic processes in discharge due to the increase of the total optic length. X-polarization should be more efficient for the process of discharge region BSW interaction. We provide fundamental investigations in plasma aerodynamic area at middle-class gas dynamic installation equipped by MW facility of moderate power [3]. This installation is a typical wind tunnel with operating time up to minutes (Mach up to 2) and is equipped by MW generator with pulse power up to 220kW and pulse duration up to 2jis. This complex is modernizing to provide better quality of the flow Copyright © 2001 by Yu.F.Kolesnichenko. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission 1 American Institute of Aeronautics and Astronautics (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.