R. Sh. Tsvyk

Experimental study of thermal and fire tornados

In [1] various types of tornado-like flows arising above a heated rotating disk in the quiescent-air atmosphere were studied and an illustrating diagram was also presented. In what follows, we will refer to one of these types, namely a sole tornado-like vortex, as a thermal tornado. In [2], different methods for physically modeling fire tornados were proposed. It was shown that formation of fire tornados depends neither on the method of their production nor the nature of combustible material. This phenomenon is determined rather by both the density of heat flow arising as a result of combustion and the angular velocity (or frequency ω = 1.1‐1.3 Hz) of rotation of the cylinder into which the combustible substance is placed. The goals of the present paper are to present a comparative study of thermal and fire tornados, to understand conditions causing the appearance of fire tornados, to identify their types, and to analyze their stability as a function of both the level of combustible liquid in the cylinder and gas-flow properties. In this study, ethyl alcohol was used as a combustible liquid. Two methods were employed for swirling combustible liquid and combustion products. We implemented swirling from below by the rotation of a substrate (cylindrical vessel) and from above by means of a fan. Our setup consisted of an Mi-22 electric heater, a base, an electric-current voltage regulator, and a circular steel disk 0.4 m in diameter. The combustible liquid was placed on a cylindrical steel substrate fixed to the disk. In different experiments, the diameter and height of the cylinder were (6, 7, 10, 12, or 20) 〈 10 ‐2 m and (2, 6, or 12) 〈 10 ‐2 m, respectively. A thermocouple and a thermal-flux sensor, whose signals had been registered by a KSP-4 recorder, were used as measuring tools. The shaft rotation frequency of an electric motor with the disk was specified by the voltage regulator and varied within the limits of 0 - 20 Hz. In addition, as distinct from the experiment performed in [2], in a number of cases, an immobile steel circular plate 2 〈 10 ‐3 m thick and 0.5 m in diameter was placed at heights of 0.4, 0.45, and 0.5 m above the rotating substrate. In the experiments, the temperature of this plate remained almost invariable, which allowed us to model the action of the inversion layer of atmosphere temperature on a fire tornado.

Ignition of a layer of combustible forest materials

Theoretical and experimental studies of the ignition of forest combustible materials by real ignition sources, which are modeled by a reference source, are reported. The time of ignition by the reference source is determined. The critical ignition energy is estimated, and its variation under real conditions is analyzed.

Laser beam pointing based on the backscattered aerosol beam. A model experiment

We present the experimental results of studying the possibility of compensating the misalignment of the axes of a laser beam, focused in an aerosol volume, and a receiving telescope from the shift of an image formed by a laser beam backscattered by aerosol particles of 0.5–0.6 μm. It is shown that the compensation can be carried out accurate to a few microradians via control of the position of the intensity distribution centroid of the image of the beam formed by the scattering volume.

Intensity fluctuations of a laser beam propagating through a supersonic flooded jet

The results of experimental researches of intensity fluctuations of a laser beam propagating through a supersonic flooded jet are presented. The laser beam propagates across the jet at various distances from a Vitoshinskii nozzle. The experiment was carried out in an Eiffel chamber at pressure ratios from 1.7 to 7 at two modes of the outflow of the jet: with the use of chevrons on the outlet nozzle and without chevrons. Dependencies of the dispersion and fluctuation spectra on pressure and distances from the nozzle are determined. The inner scale of turbulence is estimated.

Mitigation of initial distortions of a laser beam when using radiation scattered at a screen to control for a flexible mirror

Results of atmospheric experiments on adaptive compensation of aberrations in the initial wavefront of laser beams of the visible and IR wavelength ranges are presented. The flexible mirror control signal was produced based on measurements of the average radiation power of a beam backscattered by a diffuse screen. It is shown that the compensation efficiency for initial aberrations of the wavefront increases with a decrease in the diaphragm of the scattered radiation receiver. The obtained experimental data agree with results of qualitative analysis of compensation efficiency achievable on the setup used in the experiments.

Laboratory modeling of laser radiation propagation in a turbulent atmosphere under thermal self-action conditions

The results of experimental investigations on the model conditions of fluctuations of the diameter and shift of the center of gravity of laser beams propagating under conditions of developed turbulence and thermal self-action, as well as the simultaneous influence of these factors, are presented.