Home – Home – Jornals – Avtometriya 2014 number 5

Basic technologies used to develop shadowgraphs, interference devices, and schlieren systems of the first and second generations failed to solve some problems of modern gas-dynamic experiments, first of all, creation of comparatively inexpensive and compact systems for optical and physical measurements of gas-dynamic fields (visualization fields) with sizes of 800–1000 mm and more. The demand for unique optical systems for wind tunnels and ballistic ranges is expected to increase in the near future: it is only these tools that can ensure adequate experimental investigations of flows around airplane, helicopter, future flying vehicle, car, and missile models whose scales are close to real ones. (In wind tunnels, the gas flow impinges onto a motionless model, e.g., of a flying vehicle; aeroballistic ranges allow direct modeling of the motion of examined bodies.) New capabilities of optical methods of gas flow research are implemented: a posteriori investigation of wave fields deformed after passing through the gas flow, increasing the sensitivity of optical measurements by one or two orders of magnitude, and manyfold increase in the amount of information obtained in a complex gas-dynamic experiment. Advanced optical technologies are used to solve these problems.

Formation of ordered structures from a large number (~10⁴) of charged diamagnetic macroparticles in a cusp magnetic trap under microgravity conditions is experimentally studied. The experiments are performed onboard the International Space Station. Dusty plasma structures in a cryogenic d.c. glow discharge (cryogenic dusty plasma) are examined. Ultrahigh charging of dust macroparticles under the action of an electron beam is experimentally obtained and studied. Results of an experimental investigation of various regimes of the Brownian motion of interacting dust particles in the plasma are presented. A method of determining particle interaction forces in nonideal systems with isotropic pair potentials is proposed. The method is based on solving an inverse problem that describes the motion of interacting particles by a system of the Langevin equations and allows reconstruction of parameters of the external confining potential without using a priori information about the friction coefficients of particles.

A modern method of velocity measurement in a flow volume on the basis of few-projections optical tomography and correlation of moving particles is considered. The method is used to measure instantaneous three-dimensional velocity distributions in non-swirling and swirling turbulent jet flows. In addition to measurement of three-dimensional velocity distributions, specific features of this experiment are a larger depth of the measurement region (up to 40 mm) and a higher resolution of cameras (up to 4 MP as compared to previous authors’ tomographic measurements). To verify the correctness of tomographic measurements, the velocity in the plane passing along the jet axis is measured by the Stereo PIV method. The difference between the stereoscopic and tomographic measurements of three components of the mean velocity for the flows considered in this study is smaller than 10 %. A three-dimensional vortex structure of the core of a swirling jet is visualized with a spatial resolution of 3 mm.

The structure and evolution of thermogravitational buoyant jets in a high-viscosity fluid above a linear source of heat suddenly switched on are studied by methods of the Hilbert optics and interferometry. Such jets can be considered as a model of an upward flow in the spreading zone in geodynamic problems associated with the behavior of the Earth’s mantle at large depths. Based on the interferogram structure, three-dimensional reconstruction of the temperature field in the jet is performed. The Hilbert image of the reconstructed three-dimensional temperature field is compared with the Hilbert image and interferogram of the jet.

This paper presents the results of theoretical and laboratory experimental studies of the image pattern correlation technique. It is shown that the obtained results depend on the observation angle. The possibility of applying the correlation method to flight tests is considered.

The effects of local interaction of light with a particle used for diagnostics of the dispersed phase of flows are usually well described by the laws of geometrical optics. For forward scattering, geometrical optics is complemented by Fraunhofer diffraction by an opaque disk. Accurate calculations using Mie theory reveal an additional intensity of the radiation scattered in a direction close to the the direction of illumination. This additional contribution is attributed to the edge wave. The components of forward scattered light, namely, diffraction, reflection, and edge wave are studies in order to refine the contribution to the scattered intensity and locality of the interaction with the particle. It is shown that localization of the interaction with the particle occurs for all of these components. The distributions of the intensity of the individual components in forward scattering are obtained.

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.

The statistical error of correlation measurement of the shift is estimated using the binary image model. The influence of image properties on the accuracy of subpixel measurements of the position of the maximum of the correlation peak is studied. Recommendations for the choice of parameters of the image and correlation algorithm are given.

This paper deals with the refractometry of optically inhomogeneous media under conditions of significant refraction of probing beams due to substantial gradients of the refractive index and the length of the test medium. For these conditions, wave and beam refraction models of laser beams in the presence of caustics are developed. The advantages of using structured beams to record caustics for the purpose of quantitative diagnostics of inhomogeneities of the refractive index are discussed. Based on the developed models, possible methods are proposed to solve the inverse refraction problem and reconstruct the refractive index values in inhomogeneity cross-sections.

The problem of quasioptimal nonlinear filtering of heterodyne laser Doppler vibrometer signals is solved in the Gaussian approximation of a posteriori probability density of the vector of estimated parameters. A filtering algorithm is synthesized for the case of monoharmonic vibrations with a fluctuating vibration displacement amplitude model in the form of a normal Markov random process. Mathematical simulation is used to show the efficiency of the algorithm of tracking the unknown parameters of the laser Doppler vibrometer signal in the presence of additive monitoring noise and the deterministic trend of the information parameter.

Optical study of the dynamics and deformation of erythrocytes in flow was performed by two methods. Cells were trapped and manipulated with laser tweezers. Laser tweezers allow observing the deformation of a single cell or a cell aggregate under various experimental conditions, such as at rest or in flow, and also studying the aggregation of erythrocytes, which is an important process that affects blood rheology. Another method — ektacytometry — is based on obtaining information about the microrheological parameters of erythrocytes from diffraction patterns of laser radiation on a diluted suspension of cells in a flow and at rest. This method makes it possible to determine the average shear strain of a whole ensemble that includes many thousands of particles from changes in the diffraction pattern depending on the shear stress applied to the cells. The forces of interaction between two erythrocytes in an aggregate are measured and the cell deformation parameters are determined. The data on erythrocyte deformation obtained by the two methods agree well with each other.

A method for videotaping micro-objects by means of overhead projection is described. This method allows recording microparticles, including rapidly moving ones, whose size is no less than 1 μm.

This paper presents the results of processing of the experimental data obtained in a study of cooling and crystallization of a thin boundary layer of distilled water by frustrated total internal reflection of a wide collimated laser beam in order to determine the dependence of the temperature of this layer on time.