A visual study on flow pattern around the strip moving Uniformly in a continuously stratified fluid

The flow pattern around a thin strip horizontally towed at constant velocity in a continuously stratified liquid is visualized by conventional “Vertical slit-Foucault’s knife”, “Maksoutov’s slit-thread” and “horizontal slit-regular grating” methods. Using these sensitive high-resolution methods enables to reveal new kind of the streaky structure including a sequence of thin sloping interfaces both on the strip surface and inside its wake. When velocity or distance from the strip increases, the streaks may be turned into the sloping or nearly horizontal interfaces. Reconnections of outer edges of the streaks result in appearance of a set of symmetrical “butterfly-like” vortices, which are perturbed by a shear flow inside the downstream wake. Lift forces caused by a slope of the strip produce an asymmetry of the wake and lead to fast degeneration ofthe streaky structures.     

Investigation of the variability of the structure of a stratified wake behind a horizontal cylinder using optical and acoustic methods

The shadow flow pattern behind a horizontal cylinder uniformly towed in a stratified fluid with constant buoyancy frequency (in the imbedded vortex and turbulent wake regime) is recorded synchronously with acoustic echo sounding (basic frequency equal to 1 MHz) in a laboratory tank. Using computer processing, the illumination profiles in the schlieren pattern are constructed on scales comparable with the sounding acoustic ray width. Although the optical and acoustic profiles are not similar, nevertheless they enable the basic structural elements of the wake, including its high-gradient core to be identified, and their time variability traced. The features of the integral acoustic scattering characteristic, in particular, the volume scattering strength, allow this characteristic to be used, together with optical images of the flow pattern, to distinguish the flow regime identification criteria. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 5–17, May–June, 1998. The work was partly financed by the Russian Foundation for Basic Research (projects Nos. 96-05-64004 and 97-01-01013) and by INTAS Grant No. 93-1584.     

Fine structure of a stratified flow near a flat-plate surface

The pattern of disturbances arising during the motion of a strip along a horizontal surface in a continuously stratified fluid with identified upstream and attached internal waves, boundary layers, and edge singularities is calculated in the liner approximation. The flow pattern behind a flat plate moving with a constant velocity in a continuously stratified fluid is studied with the use of the optical schlieren technique; transformation of waves and finely structured elements of the flow with increasing plate velocity is analyzed. The calculated and experimentally observed patterns of internal waves at low velocities are demonstrated to be in good agreement. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 6, pp. 77–91, November–December, 2007.     

The aza-type-B photochemical rearrangement: the role of a second carbonyl in heterocyclic photochemistry. Mechanistic and exploratory organic photochemistry

In contrast to the photochemistry of monocyclic aza-cyclohexenones, their counterparts with a second carbonyl group undergo photochemical rearrangements which parallel those of the 4,4-disubstituted cyclohexenones.     

Suspended discontinuities in the field of two-dimensional internal waves

Using various shadow methods of visualization for a stratified flow near a horizontal cylinder towed with constant velocity, a new structural element of the flow, namely, the isolated high-gradient interlayers in the field of attached internal waves, is identified. In their basic characteristic features, these layers may be viewed as those belonging to the class of inner boundary layers which are the prevalent mechanism for formation of the fine structure of a continuously stratified medium. The data on optical visualization are confirmed by direct measurements of the electrical conductivity. Institute of Problems of Mechanics, Russian Academy of Sciences, Moscow 117526. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 5, pp. 40–50, September–October, 1999.     

Soaring interfaces, vortices and vortex systems inside the internal waves wake past the horizontally moving cylinder in a continuously stratified fluid

The flow pattern around a horizontal cylinder towed at constant velocity along isopycnic plane in a continuously stratified liquid is visualized by conventional techniques of “Vertical slit-Foucault’s knife”, “Maksoutov’s slit-thread” and “horizontal slit-regular grating”. Using sensitive high-resolution methods allows detail studying such component of stratified flow structures as soaring interfaces, singular soaring vortices and vortex systems, which arise directly inside the internal waves field past the cylinder. These flow elements having high level of vorticity are separated from the downstream wake by a strip of fluid without any small-scale inhomogeneities. Formation of singular vortex dipoles on leading edges of soaring interfaces is investigated in details in a wide range of flow parameters.     

A thermoanalyser for studies in an atmosphere of a gaseous fluorinating agent

A thermoanalyser for studies in an atmosphere of a strong fluorinating agent has been designed. A methodology for simultaneously obtaining DTA and TG/DTG curves of physicochemical processes over a wide range of temperatures in environments of gaseous fluorine, hydrogen fluoride and chlorine trifluoride, as well as under vacuum and hydrogen, has been developed. The construction of the thermoanalyser is described in detail. To illustrate the capabilities of the thermoanalyser a study of the thermal behaviour of M₂IrCl₆ complexes with gaseous fluorine is presented.     

Acoustic Sounding of Vortex Rings in a Continuously Stratified Fluid

The experimental simulation of solitary vortex rings in a stratified fluid performed using high-frequency echo-sounding and optical visualization methods shows that on the range from turbulent to laminar regimes the vortex is a volume inhomogeneity with a sound scattering cross-section m _vU ⁵, where U is the translational velocity. The absolute value of m _v is determined by the microscale component of the vortex microstructure, which is commensurable with the sounding sonic wave length.     

Transformation of hanging discontinuities into vortex systems in a stratified flow behind a cylinder

The mechanisms of formation of hanging discontinuities, vortex dipoles, and vortex arrays in the wave wake behind a cylinder moving at a constant velocity in a stratified fluid are investigated using various schlieren methods. The existence of discontinuities is attributable to the distortion of the internal-wave phase pattern in the shear flow and to the varying stratification and subsequent interaction of the waves with the appearing nonuniformities. Hanging discontinuities and vortex systems are low-velocity analogs of shock waves. An analysis of the internal-wave pattern indicates that the values of the normal velocity component differ on the upper and lower edges of the discontinuities. A regime diagram for flows of this kind is given.