Visualization in the Ranque-Hilsch vortex tube using high-speed video recording

Visualisation via video recording was carryed out in a Ranque-Hilsch vortex tube with a square cross-section. Video files were captured at recording speeds from 1000 to 10 000 frames per second. The best video files were obtained at a shooting frequency of 7600 frames per second with an input pressure of 1 bar. The video confirmed the presence of a double helix in the flow core in the second section of the tube. The video files showed the presence of a circulation zone between the flow core and the periphery, which is constantly changing over time. It can be clearly seen the angle at which the particles move in the peripheral flow.

Vortex heat transfer enhancement in the separated flow near structured dimpled surfaces

The numerically discovered phenomena of abnormal enhancement of the separated flow in the inclined oval-trench dimple (OTD) and the flow acceleration in the dimpled narrow channel are substantiated experimentally. The analysis of turbulent flow around a deep OTD on the plate and on the channel wall show that within the inclination angle range from 25° to 85°, the pressure drop is seen between the zones of stagnation on the windward slope and of rarefaction in the place where a tornado-like vortex is generated. The velocity field measurements in the narrow channel with two rows of inclined OTDs at the inclination angles of ±45° and ±135° reveal that the shear flow with a maximum velocity in front of the dimple entrance is formed in the flow core. This maximum shear flow velocity exceeds the maximum velocity in the plane-parallel channel.

Flow approaches to community allocation in complex network systems

The paper investigates the problem of finding communities in complex network systems, the detec-tion of which allows a better understanding of the laws of their functioning. To solve this problem, two approaches are proposed based on the use of flows characteristics of complex network. The first of these approaches consists in calculating the parameters of influence of separate subsys-tems of the network system, distinguished by the principles of ordering or subordination, and the second, in using the concept of its flow core. Based on the proposed approaches, reliable criteria for finding communities have been formulated and efficient algorithms for their detection in com-plex network systems have been developed. It is shown that the proposed approaches make it pos-sible to single out communities in cases in which the existing numerical and visual methods turn out to be disabled.

Study of Oil Film Heat Transfer in Gas Turbine Engine Bearing Chamber

A clear understanding of the heat transfer processes in a gas turbine engine bearing chamber at the design stage makes it possible to properly design the lubrication and sealing systems and ensure the future bearing safe operation. The heat transfer coefficient (HTC) calculated based on the classical Newton-Richman equation is widely used to represent the heat transfer data and useful for the thermal resistance analysis. However, this approach is only formally applicable in the case of a two-phase medium. While there is a need to model a two-phase medium, setting the flow core temperature correctly in the Newton-Richman equation is an issue that is analyzed in this study. The heat from the flow core is transferred to the boundary of the oil film on the bearing chamber walls by an adjacent air and precipitating droplets. The analysis showed that droplet deposition plays a decisive role in this process and significantly intensifies the heat transfer. The main contribution to the thermal resistance of internal heat transfer is provided by the oil film. In this regard, the study considers the issues of the bearing chamber workflow modeling allowing to determine the hydrodynamic parameters of the oil film taking into account air and oil flow rates and shaft revolutions. The study also considers a possibility to apply the thermohydraulic analogy methods for the oil film thermal resistance determination. The study presents practical recommendations for process modeling in the bearing chamber.

Psychometric Analysis of the Flow Short Scale translated to Finnish

We report a psychometric scale validation study on a Finnish translation of the Flow Short Scale (FSS). Data from 200 Finnish speaking participants were collected via the Prolific Academic platform. To analyse the scale's factorial structure, we performed Mokken scale analysis, Parallel Analysis, Very Simple Structures analysis and a standard Confirmatory Factor Analysis. Then, we evaluated the correlations between FSS and two other flow scales, the Flow State Scale and Flow Core Scale. Finally, we evaluated the FSS's ability to distinguish flow-inducing experiences from boring (non-flow-inducing) experiences. Collectively the results showed that an 8-item, two-factor version of the scale was a justified instrument with good psychometric properties.

CENTRIFUGAL COMPRESSOR HEAD CHARACTERISTIC OF A MICRO TURBOJET ENGINE BASED ON NUMERICAL SIMULATION

Shown the possibility of using the standard ANSYS CFX hydrodynamic software package for calculating the gasdynamic characteristics of the centrifugal compressor impeller of micro turbojet engines with different options for profiling blades which based on physical and numerical modeling. Presented a methodology for designing the impeller of a centrifugal compressor based on solving the inverse problem of gas dynamics. As a result of a numerical study, the head coefficient of various forms of the impeller was obtained and presented the dependences of the head coefficient and efficiency on the blade back sweep angle 2 β . b The article discusses the effect of the blade back sweep angle 2 β b on the compressor efficiency and the head characteristic for three different values of the blade back sweep angle 2 β b for example, the impeller with the back sweep angle  2 β b and with the radial blades  2 β 90 b and with blades bent forward  2 β b The centrifugal compressor was designed using Vista CCD programs in one-dimensional computing and Fluid flow CFX in three-dimensional computing. For blade profiling, the BladeGend program was used with different profiling options in order to improve compressor efficiency. The computational grid and the construction of a structured hexahedral mesh for the impeller was carried out in Ansys Turbogrid and the SST model of turbulence was selected in the calculation, which, with sufficient grinding of the mesh at the walls, adequately simulates separated flows at the channel walls, as well as the flow in the flow core. When constructing a grid along the walls between the channel blades, the parameter y + was controlled, which should not exceed 2. It is permissible to use a coarser grid in the flow core compared to the grid near the walls. The design grid of the impeller consists of 350000 elements.

Apparatus for Intensification of Recycling Processes of Industrial Wastewater

The design of a high-technology apparatus has been developed with the purpose of intensification of interphase mass exchange and reaction processes occurring in heterogeneous systems. This apparatus generates hydrodynamic conditions that ensure a high degree of turbulence of the fluid flow core. Improved diffuse and kinetic characteristics of these processes leads to a reduction in time heterogeneous system stay in the reaction zone of the apparatus and increase its productivity.

MODELLING OF SHEAR AND SHEARLESS FLOW WITH PERIODIC VELOCITY NONSTATIONARITY

The results of experimental modeling of shear and shearless flow with periodic velocity nonstationarity, organized using a generator of periodic wakes such as the "squirrel" cage, are presented. The purpose of this paper is to compare the structure of the flow behind the "squirrel" cages, as well as the analysis of the characteristics of the transition boundary layer for two different ways of locating the working surfaces: in the zone of the shearless core and shear periphery zone. The physical modelling of turbulized flow with velocity periodic nonstationarity is carried out in two experimental installations. It is shown that behind rotating “squirrel” cages there are two regions in the distributions of mean time velocities: the shearless flow core located in the center of “squirrel” cage and peripheral shear part. The aim of this paper is to compare the flow structure behind “squirrel” cages as well as to analyze the features of transient boundary layer for two different installations of working surfaces. The latter were flat plates installed on the different distances from the center of the “squirrel” cages: in the shearless flow core and in shear zone. Total longitudinal fluctuations are characterized by peaks reason of which is intersections of wakes. Behind the “squirrel” cages the levels of fluctuations decrease along the plates at x~100-600 mm from ~12 to 4,5% (II) and from ~6 to 3,5% (I). Despite the development of boundary layer happens under different external conditions (in uniform (I) and shear (II) flows), wake-induced transition takes place in both installations. Transformation of velocity profiles from pseudolaminar to turbulent is similar to one taking place in bypass transition. Distributions of total longitudinal fluctuations across the boundary layer differ by quantity of peaks and their intensity. Today the physical modeling is one of the most perspective methods for studying transport processes under complex conditions. That is why the experimental investigations of periodic external flow structure are necessary for the further optimization of different equipment and their reliability enhancement.

Интенсификация ламинарного течения в узком микроканале с однорядными наклоненными овально-траншейными лунками

A fully developed laminar air flow in a plane-parallel channel of width 6 and height 1 with single-row inclined oval-trench dimples on the walls are calculated using multiblock computing technologies at Re = 10^3. A periodic channel section of length 4 with one dimple of length 4.5, width 1, an angle of inclination to the flow of 45°, and a depth varying from 0 to 0.375 is considered. Intensification of a laminar flow in the flow core in a channel supplied with trench dimples of depth more than 0.25, such that the maximum velocity is 1.5 times higher than the maximum flow velocity in a smooth channel, is found.