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In this paper, a new method using the experimental results is proposed to determine the rheological characteristics of glycerin purification by a vibrocentric machine. The experimental testings are reported based on the values of the unilateral deformation of the glycerin under different process modes. The Kelvin-Voight model is used for rheological modeling of the proposed vibrocentric purification of glycerin. A new compression device is presented for the experimental studies, which is useful to simulate different technological processing mods. The behavior of glycerin during the centrifugation and vibrationally separation could be simulated using the introduced compression device. Test results show that a 15 % increase in the deformation of the glycerin is achievable using the simultaneous vibration-based and centrifugation processes. The impacts of amplitude-frequency parameters of glycerin purification using the vibrocentric process on the stress, strain, and strain rate have been studies. The obtained test results illustrate that the specified rheological characteristics increase sharply due to the resonant mode of the vibrating machine’s operation.

This article shows the results of a study of the structure of turbulent flow behind a square profile ALUTEC 45 × 45 mm with T-slots. The angle of rotation of the profile relative to its axis varied α = 0 ° , 15 ° , 30 ° and 45 ° . During the experiment, the flow velocity was 5 m⋅s − 1 , Reynolds number was 7 . 7 ⋅ 1 0 4 . The Constant Temperature Anemometry technique was used for experimental studies. To avoid backflow, the measuring plane was positioned at the rear of the profile at a distance of x ⋅ d − 1 ≈ 2 . 2 . As a result of the studies, it was found that the highest Taylor microscale Reynolds number and standard deviation for turbulent flow was observed in the area behind the cylinder. The width of this area is 3.5 times the width of the cylinder. With the distance from the center of the cylinder in the spanwise direction to flow the Taylor microscale Reynolds number and standard deviation sharply decreases. The maximum values of the Taylor microscale Reynolds number are observed at α = 45 ° is 426 and 398. It has also been found that behind the cylinder there is some area in which the some parameters of the turbulent flow vary greatly with the change angle α . The lowest energy dissipation rate in this range is observed for α = 15 ° − 68 m 2 ⋅ s − 3 and the largest for α = 0 ° − 138 m 2 ⋅ s − 3 . We also found that the minimum value of the Kolmogorov scale and the Kolmogorov time is observed at α = 0 ° . The minimum values of the Kolmogorov scale η = 71 μ m and the Kolmogorov time τ η = 0 . 33 ms . The maximum values for previous parameters observed at α = 15 ° is η = 84 μ m and τ η = 0 . 47 ms . We also found that the flow rate and standard deviation distributions between the ALUTEC profile and the ordinary square cylinder different. This can be observed when the upper part of the profile is tightly closed and the lower part is open. In this case, along with the profile inside of the T-slot, there is a generation of internal flow. This reduces the total backflow area behind the ALUTEC profile by 20% compared to an ordinary square profile.

The airfoil NACA 64-618 is realized by using two levels of quality: first the theoretical profile is printed on a 3D printer in a direct, “naive” way, this geometry has been scanned by using 3D scanner and based on the deviations, a better model has been processed. The flow within the turbulent wake is measured by using Particle Image Velocimetry (PIV) technique at two velocities separated by one order of magnitude.

The feasibility study of Particle Image Velocimetry (PIV) measurements inside a test turbine at the University of West Bohemia. The current VT-400 turbine is not prepared for optical measurement with seeding particles, thus several technical issues had to be addressed until low-quality data were obtained only at low speed of 2000 RPM (rounds per minute). Even the low quality data are able to show the fluctuation anisotropy or the size of fluctuation structures, which are quantities not measurable by classical pressure methods.

By using the Stereo Particle Image Velocimetry (PIV) technique we observe the secondary flow of second kind in a corner of a channel of square cross-section. The boundary layer thickness is much lower than the channel size. Therefore, the flow is still developing, not filling the entire channel cross-section, which is the case more widely reported in literature studied in a very long channel. The non-linear secondary effects of interacting boundary layers are observed as a single stream-wise vortex close to the channel corner in case of laminar boundary layers. In the case of turbulent boundary layers, the secondary flow takes shape of a symmetric pair of counter-rotating vortices. This pattern is observable only in the average velocity field, while the instantaneous ones display large amount of vortices, whose spatial distribution close to the corner in dependence on their orientation leads to statistically emergent net vorticity. At the same time, this pattern is reproduced by using a numerical simulation.

A feasibility study of velocity field measurements using the Particle Image Velocimetry (PIV) method in an axial air turbine model is presented. The wakes past the blades of the rotor wheel were observed using the PIV technique. Data acquisition was synchronized with the shaft rotation, thus, the wakes were phase averaged for statistical analysis. The interaction of the rotor blade wakes with the stator ones was investigated by changing the stator wheel’s angle. The measurement planes were located just behind the rotor blades, covering approximately 3 cm × 3 cm in axial × tangential directions. The spatial correlation function suggests that the resolution used is sufficient for the large-scale flow-patterns only, but not for the small ones. The scales of fluctuations correspond to the shear layer thickness at the mid-span plane but, close to the end-wall, they contain larger structures caused by the secondary flows. The length-scales of the fluctuations under off-design conditions display a dependence on the area of the stator and rotor wakes cross-sections, which, in turn, depend on their angle. The obtained experimental data are to be used for the validation of mathematical simulation results in the future.

We measure the two dimensional instantaneous velocity fields inside an axial turbine by using the technique PIV (Particle Image Velocimetry). The measured plane is located just behind the rotor wheel and it is oriented in axial × tangential direction. We measured a single overloaded regime as well as the nominal one at tip radius. We discuss several technical difficulties appearing during this measurement, mainly with the seeding particles and with the optical access into a massive steel body. The glass dividing the channel past rotor and the empty space of diffusor has been dirtied by large oil droplets condensing at the blades and splashed to this window. We “solved” this trouble by removing the glass, because it anyway divides volumes with same static pressure. Best quality result was obtained without this glass, but its removal changes the geometry. In our contribution we focus to the effect of such rude change to the trustworthiness of the results.

In this article, we show the results of a study of the structure of a turbulent flow behind a square cylinder. Namely, for the series of points that have the highest standard deviation value. During the experiment, we were changing the position of the square cylinder relative to the total flow. Experimental data were obtained using Constant Temperature Anemometry. As a result of the analysis, we obtained graphical distributions of the main parameters of the turbulent flow. They revealed that the maximum value of the Reynolds number based on the Taylor micro-scale is observed exactly at the cylinder angle of 30° and 45°. It was also found that the distribution of the energy dissipation rate, depending on the angle of rotation of the cylinder, has a certain sinusoidal character with local peak values. The results of the analysis also showed that the distribution of values of dissipation scale and dissipation time at some distance from the cylinder has the largest range of their values.

This paper shows the results of a study of the turbulent structure behind the NACA 0012 airfoil. During the experiment, the flow velocity was 20 m·s−1. That corresponds the Reynolds number 1.3·105. The point behind the trailing edge was chosen for experimental studies. Measurements were performed at six angles of attack α = 0°, 15°, 30°, 45°, 60°, 75° and various cases of positioning the measuring section. Namely at a constant crosssection and a constant distance behind the airfoil. The NetScanner pressure system and hot-wire technique were used for experimental studies. The obtained data allowed us to investigate the wake topology. The average velocity and standard deviation distributions are clearly grouped depending on the angle of attack. Thus, flowing around the airfoil is better up to α ≤15°. Distributions by power density and dissipation spectra also have a similar grouping tendency. Finally, we investigated the turbulent structure according to the research program. We found that at α ≥45°, depending on the measurement case, there is a clear difference in the distribution of standard deviation, Eulerian length scale, Taylor micro-scale, and Reynolds number based on the Taylor micro-scale. The obtained values at the constant distance, in contrast to the constant cross-section, are reduced.

The air flow inside single-stage test turbine is studied experimentally by Particle Image Velocimetry (PIV). Here we report the measurements results at axial-tangential plane just behind the rotor wheel at middle blade radius. We studied one nominal state and two off-design states. We discuss the applicability of resolution of our PIV system to this flow – we can distinguish the largest vortical structures in the shear layers between blade wake and jet, but the bottom part of the cascade is invisible for us at this moment. Spatial distributions of statistical moments of vorticity show a non-classical behavior at the cross-points of stator and rotor jets. We use our previously published algorithm for calculating spatial energy spectrum and display the turbulent kinetic energy colored by different length-scales of the fluctuations.

Grid turbulence is considered to be a canonical case of turbulent flow. In the presented paper, the flow structure is analyzed from the point of view of mixing properties, where vortical structures and their properties play a significant role. That is why the effect of various length-scales in turbulence is studied separately. The experimental study uses the Particle Image Velocimetry (PIV) method. The original method for spatial spectrum evaluation is applied. Results on vortex spatial spectrum and isotropy are presented. The scaling of turbulent kinetic energy (TKE) is measured, furthermore, the TKE is decomposed according to the length-scales of the fluctuations. By this method, we found that the decay of TKE associated with the smallest length-scales is more sensitive to the Reynolds number than that at larger length-scales. The TKE at the largest investigated length-scales decays more slowly. The turbulence decay-law is studied for various Reynolds numbers. The second and fourth statistical moments of vorticity are evaluated at various Reynolds numbers and distances from the grid. The isotropy is investigated in the sense of ratio of fluctuations in stream-wise to span-wise directions as the used data are captured using the planar PIV method. The full 3D fluctuation invariants were investigated in a representative position by means of the Stereo-PIV method.

The scope of this paper is to perform a detailed experimental investigation of the shape error effect on the turbulence evolution behind NACA 64-618 airfoil. This airfoil is 3D-printed with predefined typical shape inaccuracies. A high-precision optical 3D scanner was used to assess the shape and surface quality of the manufactured models. The turbulent flow was studied using hot-wire anemometry. The developed force balance device was provided to measure the aerodynamic characteristics of the airfoil. Experimental studies were carried out for three angles of attack, +10∘, 0∘, −10∘, and different chord-based Reynolds numbers from 5.3×104 to 2.1×105. The obtained results show that the blunt trailing edge and rough surface decline the aerodynamic performance of the blades. In addition, the experimental results revealed a strong sensitivity of the Taylor microscale Reynolds number to the type of shape inaccuracy, especially at Re≈1.7×105. We also discuss the evolution of the Reynolds stress components, the degree of flow anisotropy, and the power spectrum distributions depending on the airfoil inaccuracies.

We studied the grid-generated turbulence by using Particle Image Velocimetry (PIV) technique. We test on this already well studied flow the new ways of analyzing spatially resolved PIV data, such as the spatial spectra and structure functions. We compare some of the turbulence characteristics with results of Laser Doppler Anemometry (LDA).

The grid turbulence past a grid made of row of prismatic circular rods (rod diameter = 10 mm, rod spacing = 20 mm) perpendicular to the flow is observed by using a pair of PIV cameras. The first one has field of view larger (81 mm), the second one smaller (31 mm), which increases the dynamical range, where the spectral turbulence properties can be explored. Energy spectra displays usual behavior approximately following k −5/3 law, the anisotropy originates at larger scales and the flatness describing strong rare events is connected with smaller scales. The spectral properties of vorticity do not collapse due to the different lengthscale of differentiation, which make questionable the previous research based on the vorticity statistics. Research background: Grid turbulence is the best experimentally accessible prototype of ideal homogenous and isotropic turbulence, although it is known, it is not exactly the ideal one. Purpose of the article: This contribution explores the possibility of expanding the limited dynamical range of PIV method. Methods: Particle Image Velocimetry is based on observing the motion of small particles carried by the flow. Findings & Value added: Anisotropy connected with large scales, flatness with small scales; it does not work for vorticity.

This paper presents the results of the drag coefficient estimations for different types of NREL airfoils based on the experimental data. Namely, it was S803, S807, S813, and S817 profiles with the same chord length. The investigations were conducted at three angles of attack α=0°, α=±5°, different chord-based Reynolds numbers 0.6×105, 1.3×105 and 2.6×105. While, measuring cross-sections were placed behind the trailing edge at x∙c−1≈0.2, 0.4 and 1.0. Experimental data were collected using a hot-wire split fiber probe 55R55, which allowed us to estimate the characteristics of turbulent flow in stream-wise and crosswise directions. According to the obtained results, the highest and lowest Cd values correspond to profiles S817 and S803, respectively. Moreover, the results show that more asymmetric profiles S803 and S807 have the lowest resistance at zero angles of attack. Research background: Application of Antonia and Rajagopalan methodology to drag assessment of various stream bodies. Purpose of the article: Comparative evaluation of the drag coefficients of the NREL airfoils based on instantaneous velocity distribution behind. Methods: Hot-wire anemometry with split fiber probe 55R55. Findings & Value added: The highest drag coefficient corresponds to the S817 profile. The asymmetry of the airfoil shape has a significant impact on its drag characteristics.

Aluminum construction profiles become a standard construction material for short-term stands in science and in industry as well. It has the shape of square prism with an groove in each side to easy connecting the nut or bolt in any location. We studied the wake past the profile of 45 mm side. We studied the topology of the wake in the dependence on the angle of attack by using the Particle Image Velocimetry technique.

This work aimed to investigate the turbulence characteristics behind different parts of the wind turbine blade. Airfoils S807, S813, S817, and S803, which characterize the shape of the blade at different lengths, were selected for estimation. During the experiment, the chord-based Reynolds number was 2.6×105, while the angle of attack was zero. Measuring crosssections were placed behind the trailing edge at x·c-1≈0.2, 0.4 and 1.0. For the determination flow topology, we used a Hotwire anemometry with a split fiber probe 55R55 and a miniature X-wire probe 55P64. The obtained data allowed us to determine and compare the evolution of the wake behind different types of airfoils in streamwise and spanwise directions. Thus, the largest and smallest velocity deficit located behind S817 and S803 airfoils, respectively. This trend is also evident in the Normalized Reynolds shear stress distributions. Finally, we determined the spectrum and calculated the Integral length scale, the Taylor and Kolmogorov microscale of turbulent flow. According to the results, profile S817 contributes to the formation of a flow with a large scale of turbulence, while the S803 is contrary.

Film downflow from captured liquid without wave formation and its destruction is one of the most important aspects in the development of separation equipment. Consequently, it is necessary to create well-organized liquid draining in areas of captured liquid. Thus, the proposed 3D mathematical model of film downflow allows for the determination of the hydrodynamic parameters of the liquid film flow and the interfacial surface. As a result, it was discovered that the interfacial surface depends on the proposed dimensionless criterion, which includes internal friction stress, channel length, and fluid density. Additionally, equations for determining the averaged film thickness, the averaged velocity vectors over the film thickness, the longitudinal and vertical velocity components, and the initial angle of streamline deviation from the vertical axis were analytically obtained.

Particle Image Velocimetry (PIV) is an experimental method of fluid research resulting into a spatially resolved two-dimensional velocity field. We measured the velocity inside a single-stage axial test turbine at the Czech Aerospace Research Centre. We studied the axial × tangential plane just behind the rotor wheel at the tip radius under three regimes: underloaded, designed and overloaded ones. We found individual vortices in the instantaneous snapshots and we analyze their properties statistically.

Analyses of trends increasing annual wind power plant capacity and power generation in the World and Europe are presented in this paper. Investigated main problems of increasing the power generation of renewable energy sources in distributed power grids. Proposed ways to decide them by taking into account the supply of power balance, reliability operating of the power grid, and electric power quality. Observed the daily power generation during the 2019 year for typical onshore wind power plant, which consists of 1 turbine type V-100/2.00 MW. The influence of the meteorological factors on the power generation of RESs was determined with usage Spearman's rank correlation coefficient.

We observe that decreasing the inner nozzle surface by adding longitudinal ribs increases the jet stability in terms of the amount of turbulent kinetic energy in the near shear layer. We try to explain our observation as a stabilization effect of secondary flow vortices emerging in the corners of the ribs. These stream-wise vortices damage the development of larger-scale structures in the near shear layer. This explanation is supported by autocorrelation function of the stream-wise velocity component, which displays slightly smaller integral length-scale in the case with ribs than in the case of smooth nozzle. The experiment is performed at Reynolds number 2.2 × 105 (based on the nozzle diameter 50 mm); the Stereo-PIV (Particle Image Velocimetry) measurement takes place at the plane perpendicular to the jet axis one diameter past the nozzle exit. Optical 3D scanner controls the real nozzle geometry. This article presents preliminary measurement at single position and single velocity only; further exploration of this problem is needed.

Wind tunnel is constructed. It is characterized by a high degree of airflow laminarization. The main constructive element of this aerodynamic tube is the laminarization module. It allows the destruction of turbulent fluxes by providing a homogeneous laminar flow. In order to evaluate the performance of the developed aerodynamic tube, a series of experimental studies was conducted in the range of air velocity of 10-50?m·s-1. To establish the laws of the distribution of flow parameters relative to the section the cross-sectional analysis method was used. It consists of forming a series of measuring planes that characterize the distribution of dynamic pressure and air flow velocity relative to the testing section. After that, the received experimental data are interpreted as three-dimensional graphic dependencies of the studied quantities. There is clearly observed a certain local area of stable values of dynamic pressure and flow velocity, after which they are sharply reduced in the direction of the walls of the section for testing. As a result of the analysis, a series of digital profiles of the distribution of dynamic pressure in the measuring planes of the testing section were obtained. Analysis of the obtained graphic dependencies allowed establishing of the uneven distribution of the dynamic pressure difference in the boundary layer zone along the inner perimeter of the test section is worth noting. Because of the side of the upper wall of the test section, the dynamic pressure difference is greater than the sidewall. This phenomenon is due to the difference in area of their blown air. Consequently, at a wall with a larger contact surface, a constant air stream experiences more loss of its kinetic energy than a wall with a smaller area. Especially this tendency is observed in the turbulent boundary layer.

The blown down wind tunnel tube has been developed. It provides a high degree of air flow laminarization. The uniqueness of this design is the presence of a system of air vortices destruction. This system contains a complex of metal grids, honeycomb straightener and contraction nozzle. The combination of these elements allows for low turbulence level and promote the air flow relative to its axis. The complex of measuring equipment for the establishment of operational characteristics in the test section has been performed. A four-channel probe has been developed to analyze the total pressure and air flow velocity in the measuring tunnel area. The design of this probe makes possible to analyze the boundary layers of air flow in a wind tunnel. The corrective algorithm of recombination for the obtained data and software for their analysis is developed. A prerequisite for developing an algorithm for the recombination of the obtained data and their subsequent visualization is the idea of sectoral analysis and averaging of the data of common areas of the measuring area. Besides the developed algorithm, the correction function for leveling the aerodynamic resistance of the design of the four-channel probe was included. Whereas it approaches the nozzle of static pressure, there is a distortion of the real data distribution on each of the probe tube. To confirm the adequacy of the developed algorithm and the correct functioning of the software developed on its basis, a series of experimental studies was conducted, which were based on the measurement of total pressure when placing objects that create aerodynamic resistance in the measuring section. A profile analysis of the data allowed to visualize correctly the distribution of total pressure around the investigated bodies, even in the place of its sharp difference.

We report observation of secondary flow in one corner of developing channel air flow. Length of the channel, i.e. length of boundary layer, is 400?mm, which is 3.2 times the channel cross-sectional size. Three components of velocity are measured by using a Stereo Particle Image Velocimetry (PIV) technique in the measurement area of size 24×22?mm, which is perpendicular to the direction of main flow in the channel. The Reynolds number based on the length of the channel ranged from 4·104 to 8·105 and has been controlled via imposed velocity. At low Reynolds number we observe a laminar corner vortex having at all velocities the same orientation. This symmetry breaking is probably caused by an imperfectness of the experimental device. At Reynolds number around 8·104 this vortex starts to slightly variate its strength and position causing transition of boundary layers into turbulence at Re = 1.1·105. At higher Re this laminar vortex disappears from the instantaneous velocity fields, but it is still apparent in the averaged ones. It gets smaller and another oppositely oriented vortex forms; note that the second vortex is not observed in the instantaneous velocity fields, only in the ensemble average. At even higher Re, this secondary flow structure is smaller than the turbulent boundary layers, but its shape of a pair of counter-rotating vortices is conserved probably being a seed for secondary flow between fully developed boundary layers reported in the literature for longer channels with fully developed flow.