The Features of Electro-Discharge Plasma Control of High-Speed Gas Flows

Abstract

The paper analyses and discusses the results of resent experimental works on influence of non-uniform plasma formation on characteristics of near-wall layers and separated areas in high-speed airflow. Experimental results are being presented, which are obtained at condition of small-scale model duct. Surface electrical discharge in different modes at variation of the input power is investigated. The discharge properties and structure are studied as well as the change of the gasdynamic structure of the flow due to electric discharge excitation. Images of the flow interaction with the plasma layer observed by the Schlieren method are shown. The effect of artificial flow separation by the plasma layer is demonstrated. The result of pressure redistribution in aerodynamic channel is presented. Application of the surface type of electric discharge for the flow modification in ducts and inlets is discussed. The work has been fulfilled in frames of Advance Flow/Flight Control (AFFC) concept. The Magneto-Plasma-Aerodynamics (MPA) technology promises the significant enhancement of characteristics of aerodynamic apparatus at atmospheric flight. Last several years there were numbers of papers which show that energy release to gas flows by means of electrical discharges leads to important change of the medium properties and therefore the bodies behavior in high speed airflow (1-6). Basically such a change is reflected in thermodynamic factors (temperatures, enthalpy…), dispersion factors (speed and damping of acoustic and shock waves), electromagnetic factors (conductivity and phase shift) and chemical activity. At the homogeneous and equilibrium state of the gas the properties can be defined by a few parameters, namely: species fractions, temperature, pressure and the gas velocity. In this case the plasma influence is reduced to a heat energy deposition to the flow. In other cases the attention should be fixed on important peculiarities of plasma-flow interaction process. The extra advantages of the discharge method of the flow modification are inertialess, electronically guided control of plasma and space predefined position of the energy release, prospectively. The experimental examples of such an approach can be found in recent papers (4-6). On the other side the problem of hypersonic flight requires additional methods of flow control in inlets and supersonic combustors. Several mechanisms related to the plasma assistance are supposed. Among of them are the following: shocks position control, friction decrease, instabilities damping, active particles injection/producing/deposition, mixing by artific ial un- steady separation, plasma ignition in separation areas, MHD mixing, non-homogeneous filamentary heating of the flow or air -fuel mixture (1, 6-8). Zones of flow separation are the most powerful sources of the turbulence that are equal to zones of the kinematical mixing. Besides of that the residence time of the fuel- oxidizer composition inside of such a zone is much more than in free stream. But the mechanical elements (steps, cavities, obstacles, etc.) for the separation processes are not positive, as a rule, for whole combustor performance. Such elements increase the flow loses. More justified decision could be local, programmable (in time and place) separation, especially, under the non-optimal operation modes. The main idea is using the artificial separation due to surface discharge plasma excitation for the duct-driven flow control. This paper presents the results of the last experimental works on influence of electro -discharge plasma formation on separation processes in high-speed airflow. The simple gasdynamic configuration has been tested. There was the duct with constant area of rectangular cross-section and flush-mounted electrodes. Two different modes of the surface discharge have been operated: longitudinal and transversal at the different level of the energy input. The condition of the artificial separation has been investigated. The study of such configuration is important for the duct-driven flows enhancement and can be related to the most aerodynamic situations.