Experiments on Control of Supersonic Flow Structure in Model Inlet by Electrical Discharge

Abstract

The paper considers an idea of shocks structure control in supersonic inlet in frames of the “Plasma Aerodynamics” approach. The method of the flow parameters steering is based on the reveal of main physical mechanisms of electrical discharges interaction with a gas: heating, electro-dynamic, magneto-dynamic, and chemical activation. The results of model experiments are discussed: shocks position control by near-surface discharge; efficiency enhancement by external magnetic field; and the effect augmentation by fuel injection. I. Introduction here are beyond doubts that the technique based on power deposition into a predefined zone of the flowfield have a practical potential for flow/flight control. The method for inertialess and effective energy release to the gas is the electrical discharges generation. Several topics are of the most interest in frames of “Plasma Aerodynamics”: drag/lift control, inlet/diffuser adjustment, supersonic combustion enhancement, etc. [1-3]. But in the most cases the magnitude of plasma influence on dense high-speed flow is not high enough, the impact is quite local, and its efficiency is rather low. The idea of this work is to analyze the conditions when the local plasma generation leads to notable modification of flow structure in relatively distant zone downstream of the discharge location. Three mechanisms of discharge interaction with gas flow are known: electrostatic, MHD, and thermal. The first mechanism is rather weak to be observable at M>1, and P0>1Bar. The second and the third methods may be much more intensive in dependence on conditions, of course. The abilities of plasma and MHD technique for highspeed inlets regulation are under intensive debates last years [4-12]. Previously the surface plasma effects on structure of duct-driven flow were demonstrated experimentally, and mechanisms of interaction were discussed [1314]. The effectiveness of thermal mechanism of flow control critically depends on spatial distribution of power deposition. The important feature of electrical discharge application is that the gas heating could occur not only at the place of electric current location but also downstream of this region due to both recombination and vibrationaltranslational (V-T) relaxation. This effect is especially substantial for nonequilibrium plasma with V-T relaxation time τVT being comparable or larger than characteristic gasdynamic time. The latter is usual for electrical discharge plasma generated in air flow. The Figs.1 and 2 show two main processes due to electrical discharge generation in flow: air excitation and relaxation length in supersonic M=2 flow. Well seen that under optimal conditions up to 90% of power deposition can be conserved in vibrational reservoir of molecular gas. From the second side this energy can be deposited later to provide more preferential profile of extrusive layer.