Yu. N. Dubnishchev

Observation of large-scale hydrodynamic structures in a vortex tube and the Ranque effect

The existence of large-scale structures in the form of a vortical double helix in a swirling Ranque flow is observed for the first time. The structure of the vortical double helix is visualized in real time by the method of Hilbert bichromatic filtering. The experimental result is interpreted on the basis that the most probable physical mechanism for the spatial energy separation in the gas flow (i.e., for the so-called Ranque effect) is viscous heating of the gas in a thin boundary layer at the walls of the vortex chamber and the adiabatic cooling at the center owing to the formation of an intense vortex braid near the axis.

Polychromatic Hilbert diagnostics of the evolution of vortex rings induced by a pressure jump on a hole

The evolution of vortex structures induced by a pressure jump on the output hole of the chamber is experimentally studied by methods of the Hilbert diagnostics. Various types of optical filters that ensure the Hilbert and Foucault-Hilbert transforms are considered. Colored visualization of the fields of the phase optical density of the vortex structure in an air medium is performed by using a linear source of white light and a quadrature Hilbert filter.

Optical diagnostics of the structure and evolution of buoyant jets in a high-viscosity fluid

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.

Hilbert diagnostics of phase disturbances of the light field induced by a vortex flow

Methods of Hilbert filtration of phase disturbances of the light field in the spectral range of source emission are discussed. The evolution of complementary vortex rings induced in an air medium by a pressure pulse on the hole in the combustor wall under various boundary and initial conditions is experimentally studied.

Laser Doppler chromatic imaging of rotating structures

A method of the flow field velocity monitoring has been developed based on the laser Doppler imaging with chromatic selection of the velocity vector components in an orthogonal coordinate basis set.

Hilbert-diagnostics of vortex rings induced in air by a pressure pulse on a hole

Formation and evolution of complementary vortical rings induced in air by a pressure pulse on a hole under various boundary conditions are investigated by Hilbert-optics methods and computer modeling. It is experimentally demonstrated that reverse ring-shaped vortices inside the chamber after its depressurization are formed not only in the case with a reduced initial pressure in the chamber as compared with the ambient atmospheric pressure but also in the case with a higher gas pressure in the chamber than the atmospheric pressure. The complementary vortex rings propagating in forward and reverse directions might significantly affect the combustion process in the jets.

Optical control of the radius of a wheel rolling on a rail

An optical method for measuring the geometric radius and velocity of slip of a wheel rolling on a rail is discussed.

Optical Hilbert diagnostics of dynamic structures in gas flows

The possibility of visualizing the fine structure of optical inhomogeneities in gas and condensed fluids by Hilbert optics methods is discussed. Application of optical Hilbert filtering for investigating shock waves and dynamic perturbations induced by the waves in gas is described.

New Methods of Laser Anemometry in Investigations of Combined Gasdynamic Flows

New developments in laser anemometry which are based on digital technologies of input and processing of images using CCD chambers and personal computers are analyzed. The capabilities of digital dynamic speckle photography are illustrated by the intensity fields obtained for surface blood flow in biotissues. Two‐*;phase flows are investigated with the use of a new PIV technique. New developments in the field of laser anemometry which are based on the use of coherent optical Doppler processors and enable us to pass from the local diagnostics to the diagnostics of two‐dimensional fields of velocity and its visualization are described.

Photodynamic effects in laser Doppler anemometry

The first observations of photodynamic effects in laser Doppler anemometry are reported, consisting in the fact that the result of a measurement of the Doppler shift of the frequency of light scattered by a particle depends on the action of the probe light beams on the particle.