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New information has been obtained on the mean flow, intensity, and spectral composition of fluctuations in the wake of semicircular cylinder placed at the angle of attack within the range (α=-20°... 20°) into a subsonic flow. It was found that as a result of the presence of a slit at low angles of attack there is a noticeable difference in the flow around semicircular cylinder with a slit in comparison with a semicircular cylinder without a slit. Especially intensive changes of the frequency and intensity of velocity fluctuations take place at small negative angle of attack. [ABSTRACT FROM AUTHOR]

New information has been obtained on the mean flow, intensity, and spectral composition of fluctuations in the wake of symmetrical drop-shaped airfoil exposed to a stream with substantially inhomogeneous properties. Some explanations are made for the formation and suppression of vortex evolution, and it is assumed that the vortex generation process is associated with temporarily unstable internal properties of the near-current flow field. [ABSTRACT FROM AUTHOR]

Modeling the Couette flow in a semicircular channel and experiments using hot-wires installed directly into the flow allowed to obtain new results on the flow structure, velocity fluctuations, Taylor-Görtler vortices for both laminar and turbulent regimes [1-3]. Data were also obtained for the distributed roughness created by two ways. For the first one a self-adhesive tape of 0.16 mm thickness and 15 mm width has been used along the generatrix of the rotating cylinder. It was possible to glue several layers so to increase the thickness of the protrusions up to 3 times. The number of the protrusions was 2 or 4. The second type of irregularities has been created with grooves. For this aim a 3D printer has been used to create inner rotating cylinder with 4 equispaced grooves. The depth of the grooves was varied up to 3.5 mm. The measurements were carried out at different flow Reynolds numbers, changed both by the cylinder rotation speed and by pressure inside the channel. The obtained from hot-wire measurement results contain the average velocity profiles, the velocity fluctuation profiles across the semicircular channel, the flow disturbance spectra and characteristic frequencies for many flow regimes. [ABSTRACT FROM AUTHOR]

With the help of the created facility for preparation of air-helium mixture of controlled composition experiments were conducted to simulate the flow in a semicircular channel in order to determine the influence of the composition of the gas mixture on the Couette flow characteristics. Data were obtained on the influence of the composition of the air-helium mixture on the dependence of the Nusselt number Nu on the Reynolds number Re for thin wires normally streamlined. It was found that the dependence Nu (Re) for helium is much lower than for air at almost the same Knudsen number. The results obtained supplement the previously determined dependences Nu (Re, Kn) given in [1]. The mean velocity profiles and profiles of the longitudinal component of velocity fluctuation were measured for both air and helium as working gases in a wide range of Reynolds and Taylor numbers. These experiments have demonstrated that the difference in the mean velocity profiles for helium and air with comparable parameters is maximum when approaching the stationary wall of the channel. It was founded that the previously discovered self-similarity of the dependence of the intensity of the flow velocity fluctuations on the Reynolds and Taylor numbers [2], remains within the measurement accuracy when using helium as the working gas. Some results of this work, together with previously published ones, allow to confirm the similarity of the Couette flow in a semicircular channel and in a completely annular channel. [ABSTRACT FROM AUTHOR]

A promising scientific direction in aerohydromechanics related to structure control is discussed. The combination of structural elements with generated jet-vortex structures makes it possible to intensify the transfer processes and sometimes radically improve the aerodynamic and thermophysical characteristics of technical and energy systems. As examples, we consider the control of the flow around thick bearing surfaces when changing the position of the vortex cell using the throttling effect to intensify the flow circulating in the cell, as well as anomalous intensification of the separated flow and heat transfer in dense single-row packets of oval-trench dimples on the wall with varying orientation angle dimples to a turbulent flow in a narrow channel. The stabilization of the flow around a thick 37% Göttingen airfoil with the location of the vortex cell in the trailing edge region is established. Turbulent heat transfer in a narrow rectangular channel 7 to 1 was calculated on a stabilized hydrodynamic section at Re = 3333 with a single-row OTL packet with a depth of 0.25 with a step between dimples 3. The influence of the oval-trench dimples inclination angle θ in the range from 30° to 56° was analyzed. The angle θ of about 55° is close to optimal, and the relative thermal efficiency approaches 100% with a 55% increase in hydraulic losses. The optimal angle θ corresponding to the highest thermohydraulic efficiency turned out to be close to 48°. The local maximum of the 4-fold increase in the relative heat transfer coincides with the local maximum of the static pressure inside the separation zone in the area of increasing relative friction after it reaches its minimum values, reaching -3.4. [ABSTRACT FROM AUTHOR]

Used the set-up with a semi-circular gap allows realization of different types of the Couette flow and to change the flow parameters (velocity, pressure, Reynolds and Knudsen numbers, etc.) over a wide range. Reynolds number can be varied both by the cylinder rotation speed and by changing pressure inside the facility. Obtaining high Knudsen numbers is possible at low pressures and using light gases, since the system is sealed. The nature of the flow varies from laminar to turbulent ones. Simulation of the properties of the flat Couette flow in the stand should be ensured by minimizing the influence of centrifugal forces on the flow, which are manifested by distortion of the linear velocity profile. Preliminary experiments have shown the possibility of modeling the formation of longitudinal vortices in a semicircular channel similar to the circular Couette flow. [ABSTRACT FROM AUTHOR]

Helium is an important substance for modern industry. The actual task is the development of effective methods for extracting helium. The membrane-sorption method, based on selective permeability of microspherical membranes (microspheres) to helium, stands out among such method. In this paper, an experimental determination of the permeability coeffcient for the binder material of granules of a composite sorbent based on MS-VP-A9 5 group microspheres had been carried out. The experiments had been conducted for air and helium. The air permeability coeffcient value was about 16.71 ± 11.70 darcy. [ABSTRACT FROM AUTHOR]

The motivation of this joint complex studies is related to the actual necessity of analyzing the strong wind impact in the coastline of the "sea-land" typical for Taiwan Island, as well as due to the long-established creative collaboration between partners from the Khristianovich Institute of Theoretical and Applied Mechanics SB RAS and National Cheng Kung University in Taiwan. Experimental studies were carried out in wind tunnels in Novosibirsk and Taiwan, in particular, in November this year, planned further experiments in wind tunnels in Taiwan. Numerical studies were carried out mainly in St. Petersburg, where for more than twenty years the package VP2/3 (velocity-pressure, 2D/3D) has been developing. Interest to the flow past a semicircular cylinder is high due to its phenomenal characteristics: ultra-low negative lift at zero angle of attack. In this paper, this effect is explained numerically, and this body is recommended for testing methods, models and packages. The influence of the Mach number on the flow past a semicircular cylinder at zero angle of attack is illustrated in the Mach number range M = 0 - 0.5. Turbulent regime with a throttling effect gave an exceptional result - the stabilization of the flow in the wake behind the circular cylinder when air is gone through the outlet channel from the zone of increased pressure in front of the body with the release of the jet inside the near wake. There is made a comparison of the experimental behavior of the resistance of a circular cylinder with an increase in the Reynolds number and the calculated dependence for a cylinder in a casing with holes. A three-fold decrease in drag on high Re numbers was detected. Completion of the test section of the T-325M wind tunnel of ITAM SB RAS allowed to increase (in several times) the Reynolds number of an incompressible flow. Design and manufacturing of circular and semicircular cylinders having the structured surface has been performed, for which some preliminary physical experiments in the test section of T-325M wind tunnel of ITAM SB RAS within the Reynolds and Mach numbers range citied above were carried out. [ABSTRACT FROM AUTHOR]

Used the set-up with a semi-circular gap allows the realization of different types of Couette flow and to change the flow parameters (velocity, pressure, Reynolds and Knudsen numbers, etc.) over a wide range. Reynolds number can be varied by the cylinder rotation speed and pressure inside the facility. Obtaining high Knudsen numbers is possible at low pressures and using light gases, since the system is sealed. The nature of the flow varies from laminar to turbulent ones. Simulation of the properties of the flat Couette flow in the stand should be ensured by minimizing the influence on the flow of centrifugal forces, which are manifested by distortion of the linear velocity profile. Preliminary experiments have shown the possibility of modeling the formation of longitudinal vortices in a semi-circular channel similar to the circular Couette flow. [ABSTRACT FROM AUTHOR]

One of the main tasks of experimental gas dynamics is to study the mechanisms of formation and evolution of fluctuations of flow parameters that arise when flowing around the studied bodies. The processing of the experimental data in this case is reduced to the extraction of the component from total signal due to the influence of the process under study. As a rule, pulsation processes are of non-stationary nature, and for the most effective analysis of such phenomena it is necessary to use special methods of time-frequency analysis. One such method proposed by N. Huang et al. is Hilbert-Huang transformation. This transformation recently finds more and more applications for the analysis of various processes. Hilbert-Huang transform consists of two main stages: an empirical mode decomposition and Hilbert transform. As a result of the decomposition, the signal is represented as a finite sum of so-called intrinsic mode functions. These modes are essentially a basis and unique for each signal. To each of the intrinsic modes, the Hilbert transform can be applied, with the result of which any can compute amplitudes and frequencies of these modes for each instant of time. Possibilities and features of empirical mode decomposition procedure and of the overall method are demonstrated. As an examples results of decomposition of the experimental signal of a thermoanemometer are considered. These signals are obtained in various flows characterized by a high level and a significant instability of flow fluctuations. [ABSTRACT FROM AUTHOR]

Experiments were made in a low-speed wind tunnel to study the effect of textile roughness on the critical transition phenomenon of flows over a 2D circular cylinder and a finite circular cylinder whose aspect ratio is 4, respectively. First, a comparison of the results of the two cylinder models without textile material fitted shows that the critical transition phenomenon takes place at higher Reynolds numbers for flow over the finite circular cylinder. Second, concerning the results obtained with the three kinds of textile materials fitted on the two cylinders, it is consistently shown that the critical transition Reynolds numbers for flows over the finite circular cylinder are lower than those for flows over the 2D circular cylinder. This finding is opposite to that of the smooth models. Moreover, discussion on the instantaneous flow characteristics in the critical transition range can be made with the plots showing the distributions of the instantaneous lift and drag forces measured. [ABSTRACT FROM AUTHOR]

The study of sorption and transport characteristics of a composite sorbent based on various types of glass microspheres is carried out. In order to carry out this research, an experimental stand has been prepared for measuring sorbent characteristics at specified pressure and temperature values. The technique of carrying out the experiment and processing the experimental data for the purpose of determining the helium permeability of composite sorbents with a filler made of different material: sodium borosilicate glass, silica microspheres, cenospheres has been worked out. The values of the helium permeability of the composite sorbent in the temperature range from 20 to 140 °C are determined. The transport characteristics of the medium formed by the granules of the composite sorbent, as well as the values of the characteristic time of helium sorption by the composite sorbent are found. [ABSTRACT FROM AUTHOR]

On the basis of discrete element method (DEM) several packing configurations of microspheres and granules (cylinders with round corners) are built. Collision model for granules is presented. The averaged parameters like volume ratio, the first and the second moments of particle distribution and pores linear sizes are calculated numerically using Monte-Carlo method. [ABSTRACT FROM AUTHOR]

On the basis of linear approximation of parameters of mixture additional relations describing interphase interactions are obtained for classical model of ideal and viscous gas and dispersed phase of spherical particles. [ABSTRACT FROM AUTHOR]

This work is devoted to determining of transport characteristics of a granular medium in an adsorber by the example of hollow glass microspheres and a composite sorbent on their basis. To carry out the research a special experimental stand was constructed to determine the transport characteristics for various gases at given pressure and temperature values in the adsorber. The technique of experiment and processing of experimental data for the purpose of determining transport characteristics of granular medium has been worked out. For microspheres of type MS-V-2L, MS-VP, MS-VP-A9 and composite sorbent based on microspheres MS-VP-A9 were determined the gas permeability of the granular medium, the propagation velocity of the pressure wave in a granular medium, the time of filling with gas of the adsorber containing microspheres or the composite sorbent. [ABSTRACT FROM AUTHOR]

Pulsed low-energy (about 100 eV) ion irradiation during Ge/Si heteroepitaxy was found to stimulate the nucleation of 3D Ge islands. This method provides the smaller average island’s size, increasing density of islands, narrower size distribution of 3D islands as compared to conventional molecular beam epitaxy (MBE). Perfect crystal Si cap layer above Ge irradiated film can be grown by Si MBE. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]