I. A. Znamenskaya

Development of gas-dynamic perturbations propagating from a distributed sliding surface discharge

Results are presented from experimental studies of the plasma layer structure of a distributed sliding surface discharge excited in quiescent air and in a uniform gas flow behind a plane shock wave at gas densities of 0.03–0.30 kg/m3. The dynamics of weak shock waves generated after discharge initiation was studied. According to the experimental and simulation results, 40% of the discharge energy transforms into heat within a surface gas layer in the energy input stage, which lasts up to 200 ns.

Energy deposition in boundary gas layer during initiation of nanosecond sliding surface discharge

The process of rapid gas heating in the region of distributed pulsed sliding surface gas discharge (plasma sheet) of nanosecond duration has been studied. The fraction of electric energy converted into heat during the passage of discharge current has been estimated from a detailed analysis of the dynamics of shock wave fields arising upon the initiation of discharge. Experiments are performed in quiescent gases (air, nitrogen, helium) and in supersonic airflows behind a plane shock wave in a shock tube at gas densities within 0.04–0.45 kg/m3 and flow velocities up to 1600 m/s.

Discontinuity breakdown on shock wave interaction with nanosecond discharge

Discontinuity breakdown conditions were experimentally realized by instant energy input in front of a plane shock wave. A shock tube and a special type of transversal nanosecond electric discharge with plasma electrodes were used for this research. A two-dimensional (2D) numerical simulation under experimental conditions has been undertaken. The pressure, density, temperature, and velocity fields have been examined. A comparison of numerical data and shadow images of a 2D flow after shock wave interaction with the discharge area was conducted. The geometry of the disturbed flowfield was found to be in good correspondence with one from numerical calculations. The results of the investigation also showed that, by using the described experimental setup, it is possible to achieve a special type of Richtmyer–Meshkov instability without applying an additional curved diaphragm.

On the Possibility of Controlling Transonic Profile Flow with Energy Deposition by Means of a Plasma-Sheet Nanosecond Discharge

A way of effectively affecting the gasdynamic structures of a transonic flow over a surface by means of instantaneous local directed energy deposition into a near-surface layer is proposed. Experimental investigations into the influence of a pulsed high-current nanosecond surface discharge of the “plasma sheet” type on gas fast flow with a shock wave near the surface are carried out. The self-localization of energy deposition into a low-pressure region in front of the shock wave is described. Based on this effect, a facility for automated energy deposition into a dynamic region bounded by the moving shock front can be designed. The limiting value of the specific energy deposition on the surface in front of the shock wave is found. With the help of the direct-shadow method, an unsteady quasi-two-dimensional discontinuous flow arising when a plasma sheet is initiated on the wall in a flow with a plane shock wave is studied. By numerically solving the two-dimensional nonstationary equations of gas dynamics, the influence of the energy of a pulsed nanosecond discharge, which is applied in the frequency regime, on the aerodynamic characteristics of a high-lift profile is investigated. It is ascertained that the energy delivered to the gas before the closing shock wave in a local supersonic region that is located in the neighborhood of the profile contour in zones extended along the profile considerably decreases the wave drag of the profile.

The surface energy deposited into gas during initiation of a pulsed plasma sheet discharge

Gasdynamic perturbations arising during the initiation of a pulsed surface (plasma sheet) discharge have been experimentally studied in a shock tube. The evolution of flow was also numerically simulated within the framework of a thermal energy deposition model. Experimental values of the velocity of perturbations well agree with the results of calculations obtained assuming that about 50% of the energy deposited in the surface layer is converted into heat in the stage of energy supply.

Two regimes of pulsed volume discharge action upon a shock wave

We have experimentally studied two qualitatively different regimes of nanosecond pulsed volume discharge action upon a plane shock wave with M = 2–3 in a channel. If the shock-wave front at the moment of discharge initiation is outside the gap, the mechanism of subsequent action is predominantly thermal. For a shock wave occurring inside the gap at the moment of discharge, the wave and flow behind it are subject to a predominantly shock-wave action whereby the flow in the channel exhibits irreversible transformation with the formation of three new discontinuities.

Localization of pulsed energy deposition in a transverse surface discharge initiated in a gas flow with shock wave

The localization of a nanosecond transverse surface discharge initiated in a plasma sheet sliding over a dielectric surface in a channel featuring gas flow with a plane shock wave has been studied by monitoring glow intensity distribution at the discharge-ionized channel surface in the presence of the shock wave. Judging from the glow pattern, the entire energy of discharge is usually localized in a low-pressure region in front of the propagating shock wave. The density of energy deposited in front of the shock wave can be varied (in particular, increased up to 12–15 eV per particle) by initiating the discharge at various positions of the shock wave. Transitions from the discharge with glow localized sharply in front of the shock wave to the regimes with glow extended behind the front or with a volume glow region ahead of the shock wave were observed for certain values of the Townsend parameter (E/P) and Mach number (M).

PIV analysis of the homogeneity of energy deposition during development of a plasma actuator channel

Nonstationary velocity fields that arise during the development of flows behind shock (blast) waves initiated by pulsed surface sliding discharge in air at a pressure of (2–4) × 104 Pa have been experimentally studied by the particle image velocimetry (PIV) technique. Plasma sheets (nanosecond discharges slipping over a dielectric surface) were initiated on walls of a rectangular chamber. Spatial analysis of the shape of shock-wave fronts and the distribution of flow velocities behind these waves showed that the pulsed energy deposition is homogeneous along discharge channels of a plasma sheet, while the integral visible plasma glow intensity decreases in the direction of channel propagation.

Thermographic study of turbulent water pulsations in nonisothermal mixing

The possibilities of using thermography for quantitative studies of the frequency characteristics of the nonisothermal water pulsations near the vessel walls transparent to infrared radiation are analyzed. Thermographic studies of the temperature dynamics in the contact zone of a nonisothermal liquid with the wall were performed using simple models. Frequencies of temperature fluctuations at the inner surface of the vessel through the wall transparent to infrared radiation were measured using a thermal imager with accurate focusing of the lens. Spectral curves of the fluctuations were constructed with the use of a Fourier transform. It is shown that Kolmogorov spectra (−5/3 law) are present in the nonisothermal flow in a T-junction channel, allowing the process to be characterized as developed turbulence of the water flow in the region of the boundary layer adjacent to the window.

Study of shock-wave flows in the channel by schlieren and background oriented schlieren methods

The results of recording gas flow in a shock tube by the schlieren and background oriented schlieren (BOS) methods after initiating a pulsed (surface or volume) discharge are presented. Simultaneous recording of the flow field by the two methods allows a complete qualitative and quantitative analysis of the shock-wave processes resulting from the interaction of a pulse discharge with high-velocity flow. The vector displacement field of the BOS method was determined by the cross-correlation method. The density field was obtained by solving the Poisson equation with special boundary conditions. It was shown that the BOS method yields a good quality map of the flow structure that corresponds to the classical schlieren method and provides reliable quantitative results except in areas of high gradients. A modification of the BOS method was proposed and tested to measure the density jump at the shock-wave front. Recording was performed at an angle to the plane of the wave front. Various Schemes of processing of digital flow images were tested. The proposed method provides a resolution of large density gradients at the shock-wave front. The obtained quantitative results are consistent with the calculated values.