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Turbulent swirling flow occupies attention of numerous researchers worldwide. In this paper are presented experimental results of the research of the self induced pre-swirl by the centrifugal impeller. Circumferential velocity was measured in two cross-sections by use of the one-component laser Doppler velocimetry (LDV) system. Flow visualization at the pump inlet, as well as at the pump outlet, was conducted by using the high speed camera Photron Fastcam SA1.1 and the LED light for illumination. Air bubbles were used for flow illumination, and silver coated particles for LDV measurements. Pump characteristics (head, volume flow rate and power) are, also, measured in the tested duty point. Pre-swirl is visualized, while almost developed uniform turbulent flow is documented at the pump casing outlet. By using LDV it was possible to identify almost solid body circumferential velocity profile at the pump inlet, only 0.5D upstream, where D is pipe inner diameter. So, the influence of the impeller suction is obvious. In paper is, also discussed statistics of the generated turbulence.

In a cavitating water jet, cavity clouds emerge and collapse with an unsteady, but periodic tendency where the frequencies depend on the working conditions. The presented work aims at examining and analyze the dynamic behavior and properties of the clouds under different circumstances. Computer vision and image processing were introduced as tools to define the cavitation clouds based on the Contour Recognition technique. A Canny operator and Otsu threshold fragmenting methods were used. The use of these methods allows for a better understanding of the cavitating jet clouds' behavior based on the pixel intensities and shows that for an arbitrary cloud the surface itself has a dynamic feature and depends on the cavity composition. The clouds' properties could be measured and correlated to the applied working conditions. Also, the oscillation frequencies of the area of the clouds could be determined. The analysis shows that the quality of the obtained results depends mainly on the input threshold values separating the foreground and background pixels. The difficulty of defining the threshold value is discussed in the paper, as well as the validity of using the Contour Recognition technique in this field.

Kolmogorov has formulated his two hypotheses of similarity in 1941 considering local-isotropic turbulence, and later has refined his theory [1, 2]. In this paper are discussed three turbulent swirl flows generated by the three various axial fan types in-built in the pipe. The spectral characteristics of the generated turbulent swirl flows are determined on the basis on the LDA (laser Doppler anemometry) experimental data for the circumferential velocity. In the inertial subranges these curves have the same tangent and obey the “- 5/3” Kolmogorov law. It is shown that in the generated turbulent swirl flows occur eddies of various scales, encompassing very wide spectra of wave numbers, i.e. frequencies.

У оквиру дисертацијe се истражује структура турбулентног вихорног струјања у млазу аксијалног вентилатора. Генерисано турбулентно струјање је тродимензионо, нехомогено и анизотропно. Примењени су сложени експериментални, нумерички и теоријски приступи. Експериментална инсталација је у раду детаљно описана, као и квантификација мерне несигурности трокомпонентног система за Ласер Доплер анемометрију (ЛДА). ЛДА систем је, при симултаном мерењу три компоненте брзине, захтевао прецизна подешавања мерне запремине у границама пречника до 100 μm. Остварено је прецизно померање ове запремине дуж млаза. Посебан изазов је представљала нумеричка обрада добијених, у времену неједнако распоређених, мерних резултата. Теоријским разматрањима, у оквиру дисертације, бачено је ново светло на класичне записе Навије-Стоксових и Рејнолдсових једначина у поларно-цилиндричним координатама. Детаљно су разматране емпиријске радијалноаксијалне расподеле укупне, аксијалне, радијалне и обимске брзине, измерене за две брзине обртања вентилатора и три угла лопатица. На овај начин је било могуће истражити утицај Рејнолдсовог броја, као и геометријских карактеристика вентилатора, тј. угла лопатица, на карактер дејства вихора на турбуленцију и еволуцију нивоа турбуленције, како у самом мерном пресеку, тако и у низструјном развоју млаза. Анализа генерисања турбуленције и продукције појединих Рејнолдсових напона указала је на битне карактеристике турбулентног преноса у слободном вихорном млазу. Уочено је да промена знака градијента брзине не изазива увек и промену знака припадајуће компоненте тензора турбулентног напона. У доменима струјног поља у којима се то дешава, механизам турбулентног преноса је нелокалног карактера, присутна је неградијентна турбулентна дифузија и јавља се негативна продукција кинетичке енергије турбуленције. Изложена је дискусија о утицају вихора на структуру турбуленције и механизам турбулентног преноса. Анализа је указала на сложена међудејства осредњених и флуктуационих пољ, The dissertation deals with the structure of the turbulent swirl flow in an axial fan jet. The generated turbulent flow is three-dimensional, inhomogeneous and anisotropic. Complex experimental, numerical and theoretical approaches were applied. The experimental setup is described in detail, as well as the quantification of the measurement uncertainty of a three-component Laser Doppler Anemometry (LDA) system. The LDA system, while measuring the three velocity components simultaneously, requires precise adjustments of the measuring volume up to 100 μm in diameter. A precise displacement of this volume along the jet was achieved. A particular challenge was the numerical processing of the obtained unequally spaced data. Theoretical considerations, in the framework of the dissertation, have brought new light on classical notations of Navier-Stokes and Reynolds equations in polar-cylindrical coordinates. The empirical radial-axial distributions of total, axial, radial, and circumferential velocities measured for two fan speeds and three vanes angles are thoroughly analyzed. In this way, it was possible to investigate the influence of the Reynolds number as well as the geometric characteristics of the fan, i.e. angles of the blades, on the character of the swirl influence on turbulence and the evolution of the turbulence level, both in the measuring cross section and in the downstream development of the jet. An analysis of the generation of turbulence and the production of individual Reynolds stresses indicated the essential characteristics of turbulent transfer in a free swirl jet. It has been observed that a change in the sign of the velocity gradient does not always cause a change in the sign of the corresponding component of the turbulent stress tensor. In the fluid flow domains where this occurs, the turbulent transfer mechanism has nonlocal character, non-gradient turbulent diffusion and negative production of turbulence kinetic energy occur. Discussion of the effe

In this paper is presented educational hydraulic pump test rig which has numerous applications. Some of them are: testing centrifugal pump after international standard ISO 9906:2012 (Rotodynamic pumps — Hydraulic performance acceptance tests — Grades 1, 2 and 3), calibration of the Venturi flow meter after international standard ISO 8316:1987 (Measurement of liquid flow in closed conduits — Method by collection of the liquid in a volumetric tank), energy efficiency issues like comparison of energy saving by adjusting the same flow rate by valve, using by-pass or by pump speed, determination of pump duty points, work in two pumps series mode, observation through the transparent walls of the cavitation and turbulent swirl phenomena, and etc (Nedeljković et al., Čantrak et al., 2019). Some experimentally obtained results are presented and discussed in this paper.

This part of the paper presents the relation between the working conditions, nozzle geometry, nozzle diameter, and jet behavior. Experimental work has been made by impinging the submerged jets on the copper specimen as a target for a period of time. The mass loss and erosion rate at various conditions were measured, calculated and analyzed. For the visualization, a high-speed camera was used and the obtained data were processed to measure parameters which are used to characterize the clouds. Correlations among the jet dynamic power, the cavity length, erosion rate, and the pertinent experimental parameters are apparent. In addition, formulas are proposed to conveniently compare the efficiency of jetting systems based on working conditions. Based on the mathematical analyses of the obtained results a new form for cavitation number calculation is proposed.

This paper presents the dependency of the jet power and the cavitation intensity on the working conditions of the cavitating and non-cavitating jet flow. This dependency is indicated by the cavitation erosion process and flow structure. The effects of working conditions on the cavitation erosion were experimentally investigated. The flow visualization was done using a high-speed photography recording system. The analysis shows that the erosion rate calculation and the visualization of the jet structure can be used as tools to estimate the jet strength, the jet actions, the jet power, and the performance of the jetting system.

This paper describes some pedagogical approaches of using electrical motors within engineering study programs. We are discussing the education of students who are without any electrical engineering background, and who only aim to use motors within different engineering applications like robots, hydro-mechanical or control engineering application. Laboratory support is typically expensive, especially for countries like Serbia, but laboratories are necessary for engineering education. The paper promotes problem-based learning approach which is based on affordable or as cheap as possible laboratory experiments.

Experimental investigation of the coherent vortex structure in pipe on the axial fan pressure side, by use of the velocity optical measurement techniques, is reported in this paper. Generated vortex structure, its velocity and turbulent statistical values are revealed and discussed.

In this paper is presented the educatioonal pump installation where students could demonstrate centrifugal pump testing after the international standard ISO 9906 and volumetric flow meter calibration. Fluid flow phenomenon, such as turbulent swirling flow and cavitation could be observed at the pump inlet and outlet due to the transparent piping. Students and engineers could observe and model various technical tasks, such as pump duty point regulation by use of the inverter, valve and by-pass. It is demonstrated how the pump head characteristic could be obtained for various pump speeds, as well as pump system hydraulic curves. LabVIEW applications are developed for all these tasks. In addition, is presented and discussed the concept of the installations in parallel and series modes.

High-speed visualization and subsequent statistical analysis of a high-speed cavitating water jet were performed with a custom image acquisition and processing system. In a cavitating water jet, cavity clouds form and collapse with an unsteady, periodic tendency where the frequency depends on the flow conditions. The aim of the presented investigations was to examine and analyse the dynamic behaviour of these cavity clouds to understand the effect of the influencing experimental working conditions, such as injection pressure, nozzle geometry and shape (convergent or divergent) on the size, integrity and life cycle of the clouds. The results show oscillation patterns in the geometry of the clouds (thickness, length, area, etc.), through shedding, growing, shrinking, which are related to upstream pressure fluctuations caused by the plunger pump and the interaction between the jet and the surroundings. The corresponding characteristic oscillation frequencies of the cavitating jets were also determined through cloud shape analysis.

Educational setup for demonstration of a pump operation and determination of full performance curves is presented. The upgrade of the setup has been done in order to implement electronic measurements, data acquisition, computer control, and for preparation of all necessary hardware elements for remote operation via Internet. Used equipment, rationale behind, characteristics and possibilities of the current status of the setup is discussed in detail.

This paper describes needs, possibilities, and implementation of open educational resources, which are supporting the problem-oriented engineering education based on realistic experimental results. Experimental results can partly substitute real experimentation which is necessary part of engineering education and research. Open educational resources and use of blended learning approach can improve relevancy and decrease costs of engineering education for the majority of engineering schools. These approaches include mobile learning concepts. Also, laboratories via the Internet are one way of sharing laboratory resources in order to increase the availability of experimental work. But there are many situations in which the use of Internet-mediated laboratories is nonrealistic. On the other hand, trained staff and hands-on laboratories and experimental installations are very limited resources at all engineering faculties in countries like Serbia. Because of that, the web portals for sharing experimental data (with defined experimental protocols and all relevant descriptions and tutorials) can be useful for mobile learning applications and engineering education and research.

Numerous students attend courses in hydraulic turbo pumps at the Faculty of Mechanical Engineering University of Belgrade, as well as from other faculties. They have oral lectures and exercises with numerical tasks, but also laboratory exercises. This easily driven upgraded installation is very convenient for laboratory exercises for various groups of students. In this paper is demonstrated upgrade of the present installation with transducers instead of U-tube analogue manometers, acquisition system and LabVIEW application for hydraulic pump diagnostics and flow meter calibration. Pressure transducers are also previously calibrated. This installation has three regulating valves and two for tanks emptying. In this way students could form two simple and one complex pipeline. Serious and parallel combinations of pipe lines could be demonstrated, as well as pump by-pass regulation. Hydraulic pipe curve could be formed for one position of the valve on the pump pressure side and various pump frequencies. This could be repeated for other valve positions. In addition pump head characteristic for one rotation number is formed by changing the valve position. Good overlapping with manufacturer's curve is demonstrated. Cavitation and turbulent swirling flow phenomena could be also visualized and demonstrated on this installation with transparent pump housing, as well as partly suction and pressure pipes.

A platform dedicated to the problems of engineering education (EngEdu) has been established by European Council of Academies of Applied Sciences, Technologies and Engineering (Euro-CASE). The renewed working group (WG) of this EngEdu Platform started to work in Sept. 2017 and now tries to establish a direct link with REV conference participants and organizers, and disseminate and exchange ideas and results. Current topics of interest are presented as well as one of the projects going on.

The paper presents research analysis of possible analytical relationships that could exist in pointwise data for four-quadrant performance curves of one radial pump and seven pump-turbines for which the authors collected the basic data and performed the calculation. All the performance curves are for different specific speeds. Additionally, the examples of transformation calculation from the four-quadrant curves into Suter form curves shown in [1] - Thorley (1996) and [2] - Stepanoff (1959) have been presented. A numerical model has been developed for the calculation of transient processes in hydropower plants with installed pumps and pump-turbines. As an input data, the analytical relationships found in the previous research analysis have been used, as well as the pointwise curves for various specific speeds. The multi comparison of the results has been made and comprehensive conclusions given.

Teaching in hydraulic machines at the University of Belgrade, Faculty of Mechanical Engineering, Chair for Hydraulic Machinery and Energy Systems has a long tradition starting back in the nineteenth century. Numerous experimental test rigs are designed and novel measurement techniques are applied. Students have an ability to design, perform computational fluid dynamics (CFD), manufacture, and test pump units with the supervision of lecturers. This practical work, with concept "do it yourself", attracts students to develop their abilities in 3D geometry modeling, computational fluid dynamics, computer-aided manufacturing (CAM), and application of novel acquisition and data processing softwares. Parallel to this, they develop a piping system, which will be coupled with the assembled centrifugal pump and run the first test. Afterward, they are stimulated to connect the acquisition system with LabView software. They are supported to develop their own application for pump and hydraulic components testing and to perform the tests. The final stage is to integrate this installation in Go-Lab Sharing platform repository or at the Hydraulic machinery and Energy Systems Department website. The purpose of this educational approach is to have well educated students, not only with good theoretical background, but also with practical skills and engineering way of thinking. They have to be able to develop the operational pump hydraulic system, and not only a component.

Educational setup for demonstration of a pump operation and determination of full performance curves is presented. The upgrade of the setup has been done in order to implement electronic measurements, data acquisition, computer control, and for preparation of all necessary hardware elements for remote operation via Internet. Used equipment, rationale behind, characteristics and possibilities of the current status of the setup is discussed in detail.

In this paper, analysis of valves and their influence on the hydraulic systems is being performed. Special attention is devoted to the analysis of the valve flow coefficient. Flow coefficient data from various manufacturers were collected and processed within Author’s Master Thesis and presented in a form of a manual. This manual serves as a support in selecting valves as well as in comparison of different types of valves as well as different manufacturers of the same type of valve. Additionally, suitable locations for the positioning of the pump within the system were considered. A simple example of a flow transient, caused by both sudden and gradual closing of the valve has been processed. The calculation has been performed analytically for the purpose of simplifying the approach as well as in order to ease the understanding of the problem. Finally, a comparison of the application of different valves in the transient process was performed in the calculation., U ovom radu izvršena je analiza zatvarača i njihov uticaj na hidrauličke sisteme. Posebna pažnja je posvećena analizi protočnog koeficijenta zatvarača. Prikupljeni su i obrađeni podaci o protočnim koeficijentima različitih proizvođača u master radu autora i prezentovani su u obliku priručnika. Ovaj priručnik služi kao pomoć u odabiru zatvarača, za poređenje različitih tipova zatvarača kao i različitih proizvođača istog tipa zatvarača. Takođe se razmatra i odgovarajuće mesto najpogodnije za postavljanje pumpe u sistemu. Obrađen je jednostavan primer prelaznog procesa izazvanog naglim ili postepenim zatvaranjem zatvarača. Analitičko izračunavanje je primenjeno u cilju pojednostavljenog pristupa kao i u cilju olakšanog razumevanja problema. Konačno, izvršeno je poređenje primene različitih zatvarača u prelaznom procesu.

Fluid machinery courses demand, besides theoretical approach, also good practice and laboratory exercises. After course completion, students should be aware of all aspects of good practice and possible problems. Focus of this paper is on hydraulic pumps and designed demonstrational-educational test rig. It is possible to demonstrate and educate students in following: Bernoulli equation, Euler equation for turbomachinery, hydraulic losses, Venturi flow meter - geometry and measurements, cavitation and swirling flow phenomena, as well as in practical issues such as pump testing after international standard ISO 9906, pump control and energy efficiency issues, determination of hydraulic system characteristics, volumetric calibration of the Venturi flow meter, and etc. Students are educated how to choose and connect pressure transmitters, as well as how to calibrate them, how to apply and upgrade developed LabVIEW application. In addition, many components of the installation are transparent, such as pipes at the pipe inlet and pressure side, Venturi flow meter, maul and calibration tank, as well as pump spiral casing. Flow visualization and application of modern measurement technique, such as particle image velocimetry are possible in this way. Following experiments of this test rig, students arc motivated to generate technical electronic report. In addition are presented virtual experiments, designed in LabVIEW for testing pumps in parallel and series modes.

Cyber-physical systems are an integration of physical and virtual reality. In this paper, we propose to design and use of one kind of cyber-physical systems in engineering education. In a limited condition of use physical plants for an experimental educational purpose, we can design and use virtual plants in real-time interaction with hardware for control, measurement,. conditioning and acquisition of signals, etc. In our case hardware part of the system is consisting of PLC/HMI devices with connected DC or AC motors with integrated gearboxes and encoders. Virtual part of the system is a controlled plant which is designed in Lab VIEW software package. Virtual part of the system is implemented on PC which is connected with PLC/HMI via NI USB 6008 AD/DA card and designed physical interface for signal conditioning. The proposed approach is tested in related to several control engineering educational examples which include designing of the experimental setup with virtual plant, and design, implementation and verification of control law The mentioned examples are concerning with three different types of control engineering problems: 1) discrete event system, 2) process control system, and 3) mechatronics system. These exercises are prepared for implementation in Go-Lab repository via local HER Laboratory and for educational materials. Our intention is that students can find on the Internet portal a detail tutorial how can produce and use cyber-physical system for educational needs.

This paper describes a study case of student production of laboratory model for engineering education and its integration in the local remote laboratory. Students guided by teaching staff are passing through all phases of development and testing of engineering product. In our case, student should produce and test a fan. This part of case study concerning with courses in Hydraulic and Pneumatic Machinery, which incorporates, besides fundamental courses, subjects related to the theory, construction, design and testing of the hydraulic machines (pumps, fans, turbines) and turbo-compressors. After this, students should produce fan and plate system, which is well-known a laboratory model for Control Engineering education. In this paper, are also described procedures and benefits of integration of a laboratory model in Go-Lab Portal as a remote controlled experimental setup with materials for teaching and learning.