N. N. Sysoev

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.

On autoionization and pH of liquid water

The ionization constant of water Kw is currently determined on the proton conductivity sigma1 which is measured at frequencies lower than 10^7 Hz. Here, we develop the idea that the high frequency conductivity sigma2 (~10^11 Hz), rather than sigma1 represents a net proton dynamics in water, to evaluate the actual concentration c of H3O+ and OH- ions from sigma2. We find c to be not dependent on temperature to conclude that i) water electrodynamics is due to a proton exchange between H3O+ (or OH-) ions and neutral H2O molecules rather than spontaneous ionization of H2O molecules, ii) the common Kw (or pH) reflects the thermoactivation of the H3O+ and OH- ions from the potential of their interaction, iii) the lifetime of a target water molecule does not exceed parts of nanosecond.The ionization constant of water Kw (or pH) is currently determined on the proton conductivity σ0 which is measured at frequencies lower than 107 Hz. We develop the idea that the high frequency conductivity σ∞ (~1011 Hz), rather than σ0 represents a net proton dynamics in water. We count the concentration c of the H3O+ and OH– ions from σ∞ to find c to be not dependent on temperature. We conclude that spontaneous ionization of H2O molecules is not essential in water electrodynamics; the common Kw reflects the thermoactivation of the H3O+ and OH– ions from the potential of their interaction; the lifetime of a target water molecule does not exceed parts of nanosecond.

Generation of intense x-rays during ejection of a fast water jet from a metal channel to atmosphere

The radiation processes associated with a supersonic water jet exhausting from a narrow channel are considered. It has been found for the first time that the output of the channel and the initial portion of the jet are sources of intense X-radiation, generation of which is related to cavitation processes in the water jet bulk and subsequent excitation of shock waves. The frequency of X-radiation depends on the types of atoms on a radiating surface (for a jet, it is water; for a channel, the metal atoms on the surface) and increases with the charge of atoms. The total X-ray activity of an experimental setup in the mode of jet exhaust reaches 0.1 Ci. It is found for the first time that the impact of shock acoustic waves, which are formed in the air as a result of cavitation jets of water, on distant screens leads to the generation of a quasi-coherent directional X-ray emission from the back side of these screens. The spatial parameters of this radiation depend on the shape and cross section of the screen and the spatial characteristics of the shock wave.

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.

Effect of Pb ions on the optical absorption in Gd3Ga5O12 epitaxial films

We have studied the effect of Pb2+ impurities and Pb2+-Pb4+ pairs on the optical absorption between 200 and 860 nm in single-crystal gadolinium gallium garnet films grown by liquid-phase epitaxy from supercooled PbO-B2O3 fluxed melts containing 0.1–0.5 mol% gadolinia.

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.

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.

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.

Dynamics of Domain Walls in Bismuth-Ytterbium-Containing Garnet Ferrite Films in the Vicinity of the Angular Momentum Compensation Point

The dependence of the domain-wall velocity V on the acting magnetic field H is investigated for (Bi,Yb)3(Fe,Ga)5O12 garnet ferrite single-crystal films in the vicinity of the angular momentum compensation point at different temperatures. The films are grown by liquid-phase epitaxy from a supercooled solution melt on Cd3Ga5O12 substrates with the (111) orientation. It is demonstrated that, in these films, the precessional mechanism is not responsible for the motion of domain walls but there arises an internal effective magnetic field that weakens the acting magnetic field.

Development of nanosecond combined volume discharge with plasma electrodes in an air flow

The space-time characteristics of a nanosecond combined volume discharge with preionization from a plasma sheet with a nanosecond duration in air (∼200 ns) are investigated. The integral discharge radiation, radiation spectrum, and discharge current under conditions within the discharge volume, including gas-dynamic flow with a planar shock wave, are analyzed. It is shown that the volume discharge glow is homogeneous in the master phase. The glow in the area of the shock-wave front increases and its duration may be more than 2 μs.