Influence of structural electric discharges on parameters of streamlined bodies in airflow

Abstract

The paper analyses and discusses the results of recent experimental works on the influence of non-uniform plasma formations on streamlined bodies characteristics in a high-speed airflow. The widely recognized fact that the structure of these kinds of discharges is typically non-uniform is confirmed. New experimental results of the plasma influence on a boundary layer near plane and profiled plates along with the data on the plasma generation near the body surface and the discharge effects on the location and size of the separation zones are presented. The problem of the effectiveness of plasma aerodynamics methods is discussed. The conditions where/when non-thermal plasma properties can be observed, .are exampled. It is concluded that the local non-uniform plasma formations are, probably, most promising for the objectives of Advance Flow/Flight Control (AFFC). The recommendations on possible applications of plasma formations of different types are derived. Introduction. This paper analyses and discusses results of the last experimental works on influence of non-uniform plasma formations on characteristics of streamlined bodies in a high-speed airflow. At the present time there are a number of theoretical and experimental works demonstrating that the total drag of a body in the airflow can be reduced significantly by the energy release near/fore the body and the energetic effectiveness can be rather high (even higher than In the case of an aerodynamically optimized body with already provided low drag, the effective drag reduction is hardly possible. The chart in Fig.l shows the experimental dependence of counterblow plasma jet influence effectiveness on the initial drag factor under supersonic airflow conditions [4]. It is clearly seen that an optimal shape of streamlined body limits the effective enhancement. Effectiveness, % ^fjf' -1——I——I——I————I——I——J——,——I 0.00 0.20 0.40 0.60 0.80 1.00 Figure I The energetic effectiveness of a plasma jet vs initial drag factor of body. M=J. 7+2.0. Another type of plasma formation can demonstrate different values of the effect but the similar trend The vehicle designed for one of specific modes of flight conditions can spend a large part of the flight time at non-optimal aerodynamic situation. Probably, the most critical fraction of the trajectory lies under transonic mode of airflow-body interaction, especially, at the complex shape of the vehicle. The plasma technology can provide an effective influence on position and amplitude of local shocks and parameters of separation zones. Samples of such plasma effects are presented below. In general case the drag force of a vehicle at atmospheric flight is composed as the sum of the friction drag and the pressure drag. At the same time the pressure drag includes the wave drag, the base drag, the interference drag etc. The contributions of each component to the total drag at subsonic, transonic and supersonic flight modes are different. Usually the main attention is paid to pressure/wave shares of the total drag. Analysis of aerodynamic situation shows that the friction and interference effects can play an important role as well. Special advantages of plasma technology are anticipated for problem of internal flow enhancement. Plasma aerodynamics effects are associated with energy release and modification of gas-kinetic and electro-magnetic properties of media. Typically, inflow generated plasma appears as a non-uniform and unsteady formation. Utilization of a fully controllable electrical discharge could significantly decrease the required energy input to airflow. A special interest in electrodeless and single-electrode plasma generation has arisen due to its possibility to provide the energy deposition and gas property modifications at a predefined zone of the flowfield, prospectively, under the effective electronic control of plasma location. The mentioned above objectives of Plasma Aerodynamics for external flow applications could be now formulated as follows: (1) to compensate aerodynamic loses under non-optimal (off-design) flight conditions, (2) to stabilize the airflow structure at instabilities, (3) to decrease the effects of the aerodynamic interference, (4) to provide a fast flow/flight control etc. Copyright © 2001 The American Institute of Aeronautic and Astronautic Inc. All rights reserved.