Analysis of the vortex core and turbulence structure behind axial fans in a straight pipe using PIV, LDA and HWA methods

U disertaciji se istražuje struktura turbulentnog vihornog strujanja koje je generisano obrtnim kolom aksijalnog ventilatora. Kompleksnost trodimenzijskog nehomogenog anizotropnog turbulentnog brzinskog polja zahtevala je složen eksperimentalni i teorijski pristup, sjedinjen sa kompleksnim numeričkim postupcima. Primenom korelaciono-spektralne teorije turbulencije izložena je matematička interpretacija strukturalne analize turbulencije. Ovakvim teorijskim razmatranjem data su fizička tumačenja složenih međudejstava srednjeg i fluktuacionog brzinskog polja koja karakterišu procese turbulentnog prenosa. Analiza vrtložnog jezgra i statističkih karakteristika turbulentnog vihornog strujanja u cevi iza kola aksijalnih ventilatora zasniva se na najsavremenijim eksperimentalnim istraživanjima. U tom smislu primenjeni su savremeni merni sistemi koji obuhvataju klasične merne sonde, stereo PIV anemometriju, stereo PIV sa brzim kamerama i laserima (TR PIV), laser Dopler anemometriju (LDA) i to jednokomponentnu i dvokomponentnu, kao i originalne anemometarske sonde sa zagrejanim vlaknima (HWA). Merenja i principi merenja su zajedno razmatrani sa sofisticiranim merno-numeričkim metodama za akviziciju i statističku obradu merenih podataka, kao i za kalibraciju i analizu grešaka i merne nesigurnosti. Brojni eksperimenti su realizovani kako na instalaciji koja je dobijena modifikacijama postojećeg mernog štanda, tako i na celokupno novoj izgrađenoj eksperimentalnoj instalaciji.Na osnovu originalnih rezultata merenja u radu se detaljno istražuje uticaj tipa i režima rada aksijalnog ventilatora na strukturu turbulencije i mehanizam turbulentnog prenosa. Posebno se proučava fenomen precesije vrtložnog jezgra, kao i fenomeni nelokalnog turbulentnog prenosa i negradijentne turbulentne difuzije. Pri tome se analiziraju uticaji Rejnoldsovog i vihornog broja, kao i broja obrtaja i uglova lopatica kola na ove pojave. Fizička interpretacija eksperimentalnih podataka ukazuje na značajna strukturalna svojstva vrtložnog turbulentnog jezgra i smicajnog sloja. Eksperimentalno-korelacionom analizom istražuje se evolucija statističkih karakteristika i korelacionih momenata, na osnovu čega se zaključuje o izrazitoj nehomogenosti i anizotropnosti turbulencije. Izmerene raspodele turbulentnih napona omogućile su formiranje invarijantnih mapa anizotropnosti za različite uglove lopatica kola, tako da su dobijeni značajni zaključci o uticaju režima rada ventilatora na anizotropnost i strukturu turbulencije u jezgru, smicajnom sloju i osnovnom strujanju. Dodatne fizičke informacije o strukturi turbulencije dobijene su iz eksperimentalno određenih autokorelacionih funkcija i integralnih razmera turbulencije, kao i pomoću analize spektralne funkcije obimskih fluktuacionih brzina. Utvrđeni su uticaji vrste ventilatora na raspodelu statističkih momenata trećeg i četvrtog reda, kao i na generisanje polja vrtložnosti i precesiono kretanje vrtložnog jezgra.The dissertation investigates the structure of turbulent swirl flow generated by the axial fan impellers. The complexity of three-dimensional, non-homogeneous, anisotropic turbulent velocity fields required complex experimental and theoretical approach, associated with the complex numerical procedures. Mathematical interpretation of the structural analysis of turbulence is presented using the correlation-spectral theory of turbulence. This theoretical consideration provides adequate physical interpretation of complex interactions between the average and fluctuating velocity fields that characterize the processes of turbulent transfer. Analysis of the vortex core and the statistical characteristics of turbulent swirl flow in straight pipe behind axial fans is based on the latest experimental researches. In this sense, modern measurement systems that include classical probes, stereo particle image velocimetry (SPIV), high speed SPIV (TR PIV), laser Doppler anemometry (LDA) – one- and two-component and original hot-wire anemometers (HWA) were all applied. Measurements and measurement principles are discussed along with sophisticated numerical-measurement methods for data acquisition and statistical processing of measured data and together with calibration and error analysis and measurement uncertainty. Numerous experiments were carried out in the modified existing test rig and in the entire newly built experimental test rig. Based on the original measurement results, the PhD thesis examines in detail the influence of the type and operating regime of axial fan on turbulence structure and turbulent transfer mechanism. In particular, the phenomenon of the vortex core precession as well as the phenomenon of non-local turbulent transfer and non-gradient turbulent diffusion is studied. In addition, the effects of Reynolds and swirl number, and the effects of rotation speed and blade angle on these phenomena are investigated . The physical interpretation of experimental data indicates significant structural properties of a turbulent vortex core and a shear layer. Experimental and correlation analysis examines the evolution of statistical characteristics and correlation moments, which is the basis for drawing conclusions about the extreme turbulence non-homogeneity and anisotropy. The measured distributions of turbulent stresses enabled the formation of anisotropy invariant maps for various fan blade angles, so the important conclusions about the influence of fan duty point on anisotropy and turbulence structure in the core, shear layer and sound flow region were obtained. Additional pieces of information on turbulent structure physics were obtained on the basis of experimentally determined autocorrelation functions and turbulence integral scales, and also by the analysis of spectral functions of circumferential velocity fluctuations. Impacts of the fan types on the statistical moments of the third and fourth order, and on the generation of the vorticity field and vortex core precession movement, are determined

Analysis of the vortex core and turbulence structure behind axial fans in a straight pipe using PIV, LDA and HWA methods

U disertaciji se istražuje struktura turbulentnog vihornog strujanja koje je generisano obrtnim kolom aksijalnog ventilatora. Kompleksnost trodimenzijskog nehomogenog anizotropnog turbulentnog brzinskog polja zahtevala je složen eksperimentalni i teorijski pristup, sjedinjen sa kompleksnim numeričkim postupcima. Primenom korelaciono-spektralne teorije turbulencije izložena je matematička interpretacija strukturalne analize turbulencije. Ovakvim teorijskim razmatranjem data su fizička tumačenja složenih međudejstava srednjeg i fluktuacionog brzinskog polja koja karakterišu procese turbulentnog prenosa. Analiza vrtložnog jezgra i statističkih karakteristika turbulentnog vihornog strujanja u cevi iza kola aksijalnih ventilatora zasniva se na najsavremenijim eksperimentalnim istraživanjima. U tom smislu primenjeni su savremeni merni sistemi koji obuhvataju klasične merne sonde, stereo PIV anemometriju, stereo PIV sa brzim kamerama i laserima (TR PIV), laser Dopler anemometriju (LDA) i to jednokomponentnu i dvokomponentnu, kao i originalne anemometarske sonde sa zagrejanim vlaknima (HWA). Merenja i principi merenja su zajedno razmatrani sa sofisticiranim merno-numeričkim metodama za akviziciju i statističku obradu merenih podataka, kao i za kalibraciju i analizu grešaka i merne nesigurnosti. Brojni eksperimenti su realizovani kako na instalaciji koja je dobijena modifikacijama postojećeg mernog štanda, tako i na celokupno novoj izgrađenoj eksperimentalnoj instalaciji.Na osnovu originalnih rezultata merenja u radu se detaljno istražuje uticaj tipa i režima rada aksijalnog ventilatora na strukturu turbulencije i mehanizam turbulentnog prenosa. Posebno se proučava fenomen precesije vrtložnog jezgra, kao i fenomeni nelokalnog turbulentnog prenosa i negradijentne turbulentne difuzije. Pri tome se analiziraju uticaji Rejnoldsovog i vihornog broja, kao i broja obrtaja i uglova lopatica kola na ove pojave. Fizička interpretacija eksperimentalnih podataka ukazuje na značajna strukturalna svojstva vrtložnog turbulentnog jezgra i smicajnog sloja. Eksperimentalno-korelacionom analizom istražuje se evolucija statističkih karakteristika i korelacionih momenata, na osnovu čega se zaključuje o izrazitoj nehomogenosti i anizotropnosti turbulencije. Izmerene raspodele turbulentnih napona omogućile su formiranje invarijantnih mapa anizotropnosti za različite uglove lopatica kola, tako da su dobijeni značajni zaključci o uticaju režima rada ventilatora na anizotropnost i strukturu turbulencije u jezgru, smicajnom sloju i osnovnom strujanju. Dodatne fizičke informacije o strukturi turbulencije dobijene su iz eksperimentalno određenih autokorelacionih funkcija i integralnih razmera turbulencije, kao i pomoću analize spektralne funkcije obimskih fluktuacionih brzina. Utvrđeni su uticaji vrste ventilatora na raspodelu statističkih momenata trećeg i četvrtog reda, kao i na generisanje polja vrtložnosti i precesiono kretanje vrtložnog jezgra.The dissertation investigates the structure of turbulent swirl flow generated by the axial fan impellers. The complexity of three-dimensional, non-homogeneous, anisotropic turbulent velocity fields required complex experimental and theoretical approach, associated with the complex numerical procedures. Mathematical interpretation of the structural analysis of turbulence is presented using the correlation-spectral theory of turbulence. This theoretical consideration provides adequate physical interpretation of complex interactions between the average and fluctuating velocity fields that characterize the processes of turbulent transfer. Analysis of the vortex core and the statistical characteristics of turbulent swirl flow in straight pipe behind axial fans is based on the latest experimental researches. In this sense, modern measurement systems that include classical probes, stereo particle image velocimetry (SPIV), high speed SPIV (TR PIV), laser Doppler anemometry (LDA) – one- and two-component and original hot-wire anemometers (HWA) were all applied. Measurements and measurement principles are discussed along with sophisticated numerical-measurement methods for data acquisition and statistical processing of measured data and together with calibration and error analysis and measurement uncertainty. Numerous experiments were carried out in the modified existing test rig and in the entire newly built experimental test rig. Based on the original measurement results, the PhD thesis examines in detail the influence of the type and operating regime of axial fan on turbulence structure and turbulent transfer mechanism. In particular, the phenomenon of the vortex core precession as well as the phenomenon of non-local turbulent transfer and non-gradient turbulent diffusion is studied. In addition, the effects of Reynolds and swirl number, and the effects of rotation speed and blade angle on these phenomena are investigated . The physical interpretation of experimental data indicates significant structural properties of a turbulent vortex core and a shear layer. Experimental and correlation analysis examines the evolution of statistical characteristics and correlation moments, which is the basis for drawing conclusions about the extreme turbulence non-homogeneity and anisotropy. The measured distributions of turbulent stresses enabled the formation of anisotropy invariant maps for various fan blade angles, so the important conclusions about the influence of fan duty point on anisotropy and turbulence structure in the core, shear layer and sound flow region were obtained. Additional pieces of information on turbulent structure physics were obtained on the basis of experimentally determined autocorrelation functions and turbulence integral scales, and also by the analysis of spectral functions of circumferential velocity fluctuations. Impacts of the fan types on the statistical moments of the third and fourth order, and on the generation of the vorticity field and vortex core precession movement, are determined

PREDAVANJE PO POZIVU: THE NATIONAL STANDARD FOR VELOCIMETRY AND POSSIBILITIES FOR IT IN SERBIA

Velocimetry has a long tradition in Serbia. Anyhow, constant improvement of the laboratories calibration and measurement capabilities (CMC) is an ongoing effort. Serbia, although it has good capabilities in this field, still doesn’t have a national standard for velocimetry. Reliable velocimetry is a starting point in various sectors of energy production, numerous industrial branches, health, educational, business and sport centers, as well as in residential buildings, and etc. Realization of this national standard would influence and improve national industry capabilities, energy efficiency in general, health and environmental protection procedures, climate analysis, forecasts and hydrology. Various international and national standards treat velocimetry, especially, as a tool in determination of the flow rate in closed conduits and open channels. This opens a whole new area of validation of the volume flow rate calibration in laboratory, as well as in situ. In this paper will be presented novel velocimetry techniques and their capabilities implemented in the Laboratory for turbulence and velocimetry at the Faculty of Mechanical Engineering. Here are presented following measurement techniques: multihole probes, hot-wire anemometry, laser Doppler velocimetry (three-component) and image-based velocimetry techniques (particle image velocimetry (PIV) and micro PIV). In the Laboratory are implemented stereo PIV and high speed stereo PIV. In addition to this, constant upgrading of the existing systems is followed by the development of the new techniques and procedures. These complex measurement techniques are employed in research of various flow phenomena, what will be presented in short.Title: Programme & Full Papers Proceedings of IEEP 2022 Publisher: Society of Thermal Engineers of Serbia 11001 Belgrade, P.O. Box 522, Serbia For the publisher: Prof. Milan Radovanović, President of the Society of Thermal Engineers of Serbia Editors: Dr Dejan Cvetinović VINČA Institute of Nuclear Sciences, Belgrade, Serbia Prof. Goran Jankes and Assoc. Prof. Mirjana Stamenić Faculty of Mechanical Engineering, University of Belgrad

Scientific FabLab at the Faculty of Mechanical Engineering University of Belgrade - Support for Experimental Fluid Flow Research

Complex fluid flow phenomena, as well as energy and cavitation characteristics of hydraulic machinery and equipment are studied in the Laboratory for Hydraulic Machinery and Energy Systems, Faculty of Mechanical Engineering (FME), University of Belgrade (UB). Research in the Laboratory comprises micro to macro scales fluid flow research. In Laboratory exist installation for investigation of the energy and cavitation characteristics of turbine models (Francis, Kaplan, bulb), installation for research and visualization of the cavitation in pumps and on the hydroprofiles, installation for pump testing, educational-demonstrational set-up for testing hydraulic pump and Venturi flow meter calibration, installation for testing valves, four installations for volume flow calibrations: up to 10 l/min, 3 l/s, 50 l/s and 200 l/s, three installations for turbulent swirl flow investigations in air behind the axial fan impeller: in pipe, diffuser and jet, open wind tunnels for calibration of velocimetry probes: up to 10 m/s, 36 m/s and 60 m/s, and etc. In this lecture will be presented new results obtained in Laboratory, from idea, computer modelling and numerical simulation to realization of the experiments. In Laboratory exist various measuring and calibration devices, as well as machining systems. Novel measurement systems would be presented: three-components LDV (laser Doppler velocimetry) system, stereo particle image velocimetry (SPIV), high speed SPIV, micro PIV, calibration of pressure devices with air and oil, and etc. Some results of laser based turbulent swirl flow research are presented. Complex experiments seek thorough preparations, so production capacities must occur in such a big laboratory. This is organized in the Laboratory workshop. CAD (the computer-aided design) 3D models are designed in various softwares. Two CNC (computer numerical controlled) machines are fully operational: 3+1-axis vertical machining centre (1016 x 508 x 635 mm), 5-axis vertical machining centre (1270 x 660 x 635 mm). In Laboratory many other machines exist, like vertical drilling machine, another milling machine, one lathe machine, and etc. Other complex machines exist in the Department for Production Engineering at FME UB. In addition, Printrbot Simple Metal 3D printer is also applied in the Laboratory. For collaboration with students, researchers and sophisticated industry, these capacities are organized in Scientific FabLab [1, 2]. Realization of ideas is encouraged in the Scientific FabLab. In fact, 3D model and production simulation software reveal all important points in ideas realizations. Student project - axial compressor blade could be printed and they can study geometry in vivo, not only by computer 3D model [3]. They can also print designed centrifugal pump impeller [4]. Production on CNC 3-axis machine of radial centrifugal impeller in duraluminiun is presented in lecture, as well as designed mould for axial impeller blade [5]. Additional aspects of production of laboratory educational model and its integration in remote laboratory are also presented here [6]. In Laboratory is established procedure for repairing hot-wire anemometer (HWA) probes, with help of Prof. Dr Petar Vukoslavčević, University of Montenegro, Faculty of Mechanical Engineering. It is used for positioning and welding small sensors (2.5 microns or even lower in diameter) on the HWA probes prongs using stereo microscope and the original micro positioning device with fifteen degrees of freedom [7]. These HWA probes are afterwards used for turbulence measurements. In Laboratory are applied, as well as developed, novel measurement techniques. Technique and procedure for affordable and "do-it-yourself" PIV measurements are developed in Laboratory [8]. This technique is planned to be used for fluid flow research in micro channels [9]. Recent investigations are focused on micro channel manufacturing and some results will be presented [10-11]. In addition, acquired experience in knowledge dissemination through open access workshops will be introduced.invited by Dr. Dr Enrique Canessa, Second Workshop on "Science Dissemination for the Disabled" followed by workshop on "Scientific Fabrication Laboratories (SciFabLabs)", section: SciFabLabs, October 24, SciFabLab, ICT

Scientific FabLab at the Faculty of Mechanical Engineering University of Belgrade - Support for Experimental Fluid Flow Research

Complex fluid flow phenomena, as well as energy and cavitation characteristics of hydraulic machinery and equipment are studied in the Laboratory for Hydraulic Machinery and Energy Systems, Faculty of Mechanical Engineering (FME), University of Belgrade (UB). Research in the Laboratory comprises micro to macro scales fluid flow research. In Laboratory exist installation for investigation of the energy and cavitation characteristics of turbine models (Francis, Kaplan, bulb), installation for research and visualization of the cavitation in pumps and on the hydroprofiles, installation for pump testing, educational-demonstrational set-up for testing hydraulic pump and Venturi flow meter calibration, installation for testing valves, four installations for volume flow calibrations: up to 10 l/min, 3 l/s, 50 l/s and 200 l/s, three installations for turbulent swirl flow investigations in air behind the axial fan impeller: in pipe, diffuser and jet, open wind tunnels for calibration of velocimetry probes: up to 10 m/s, 36 m/s and 60 m/s, and etc. In this lecture will be presented new results obtained in Laboratory, from idea, computer modelling and numerical simulation to realization of the experiments. In Laboratory exist various measuring and calibration devices, as well as machining systems. Novel measurement systems would be presented: three-components LDV (laser Doppler velocimetry) system, stereo particle image velocimetry (SPIV), high speed SPIV, micro PIV, calibration of pressure devices with air and oil, and etc. Some results of laser based turbulent swirl flow research are presented. Complex experiments seek thorough preparations, so production capacities must occur in such a big laboratory. This is organized in the Laboratory workshop. CAD (the computer-aided design) 3D models are designed in various softwares. Two CNC (computer numerical controlled) machines are fully operational: 3+1-axis vertical machining centre (1016 x 508 x 635 mm), 5-axis vertical machining centre (1270 x 660 x 635 mm). In Laboratory many other machines exist, like vertical drilling machine, another milling machine, one lathe machine, and etc. Other complex machines exist in the Department for Production Engineering at FME UB. In addition, Printrbot Simple Metal 3D printer is also applied in the Laboratory. For collaboration with students, researchers and sophisticated industry, these capacities are organized in Scientific FabLab [1, 2]. Realization of ideas is encouraged in the Scientific FabLab. In fact, 3D model and production simulation software reveal all important points in ideas realizations. Student project - axial compressor blade could be printed and they can study geometry in vivo, not only by computer 3D model [3]. They can also print designed centrifugal pump impeller [4]. Production on CNC 3-axis machine of radial centrifugal impeller in duraluminiun is presented in lecture, as well as designed mould for axial impeller blade [5]. Additional aspects of production of laboratory educational model and its integration in remote laboratory are also presented here [6]. In Laboratory is established procedure for repairing hot-wire anemometer (HWA) probes, with help of Prof. Dr Petar Vukoslavčević, University of Montenegro, Faculty of Mechanical Engineering. It is used for positioning and welding small sensors (2.5 microns or even lower in diameter) on the HWA probes prongs using stereo microscope and the original micro positioning device with fifteen degrees of freedom [7]. These HWA probes are afterwards used for turbulence measurements. In Laboratory are applied, as well as developed, novel measurement techniques. Technique and procedure for affordable and "do-it-yourself" PIV measurements are developed in Laboratory [8]. This technique is planned to be used for fluid flow research in micro channels [9]. Recent investigations are focused on micro channel manufacturing and some results will be presented [10-11]. In addition, acquired experience in knowledge dissemination through open access workshops will be introduced.invited by Dr. Dr Enrique Canessa, Second Workshop on "Science Dissemination for the Disabled" followed by workshop on "Scientific Fabrication Laboratories (SciFabLabs)", section: SciFabLabs, October 24, SciFabLab, ICT

Integral and statistical characteristics of the turbulent swirl flow in a straight conical diffuser

The results of the experimental investigations of the turbulent swirl flow in a straight conical diffuser with inlet diameter 0.4 m and total divergence angle 8.6 degrees are presented in this paper. The incompressible swirl flow field is generated by the axial fan with outer diameter 0.397 m. The measurements were performed in one measuring section downstream the axial fan impeller in the conical diffuser in position (z/R-0 = 1) with original classical probes and an one-component laser Doppler anemometry (LDA) system, for four flow regimes. The comparative measurements of axial and circumferential velocities are presented. The Reynolds number, calculated on the basis of the average velocity, ranges from 149857 to 216916. Integral parameters, such as volume flow rate, average circulation and swirl number, are determined. Statistical characteristics, such as level of turbulence, skewness and flatness factors, are calculated. The highest levels of turbulence for axial velocity are reached in region 0.4 lt r/R lt 0.6, where D = 2R. The highest levels of turbulence for circumferential velocity are reached for the regimes with lower circulation in r/R approximate to 0.4, i.e., in the vortex core region for the cases with higher circulation

Laser sheet scattering and the cameras' positions in particle image velocimetry

Simulations of laser sheet scattering by microparticles, based on the generalized Lorenz-Mie theory for the case of numerous random spatial distributions of scattering particles, were done, using the novel computational time saving strategy. This type of scattering by particles immersed in a fluid flow and its recording on cameras, presents the essence of particle image velocimetry systems. The continuous and large change of the intensity of a scattered light failing on the camera causes the sequences of images of varying quality, which makes many of them useless. This paper shows how the problem could be alleviated by determining the angles of low relative standard deviation of scattered light intensity and using them for recording, as well as by avoiding the angles of high relative standard deviation of scattered light intensity

Experimental investigations of the turbulent swirl flow in straight conical diffusers with various angles

Results of experimental investigations of the turbulent swirl flow in three straight conical diffusers with various diffuser total angles are presented in this paper. All three diffusers have the inlet diameter 0.4 m and total divergence angles 8.6 degrees, 10.5 degrees, and 12.6 degrees. The incompressible swirl flow field is generated by the axial fan impeller, and for each diffuser several regimes were achieved by changing rotation number. Original classical probes were used for measurements. The distributions of the average main swirl flow characteristics along the diffuser are shown. Distributions of the inlet Boussinesq number, outlet Coriolis coefficient, ratio of the swirl and completely axial flow loss coefficients at conical diffuser on the inlet swirl flow parameter are also presented

Experimental investigations of the turbulent swirl flow in straight conical diffusers with various angles

Results of experimental investigations of the turbulent swirl flow in three straight conical diffusers with various diffuser total angles are presented in this paper. All three diffusers have the inlet diameter 0.4 m and total divergence angles 8.6 degrees, 10.5 degrees, and 12.6 degrees. The incompressible swirl flow field is generated by the axial fan impeller, and for each diffuser several regimes were achieved by changing rotation number. Original classical probes were used for measurements. The distributions of the average main swirl flow characteristics along the diffuser are shown. Distributions of the inlet Boussinesq number, outlet Coriolis coefficient, ratio of the swirl and completely axial flow loss coefficients at conical diffuser on the inlet swirl flow parameter are also presented

Fluid boundaries shaping using the method of kinetic balance

Fluid flow in curved channels with various cross-sections, as a common problem in theoretical and applied fluid mechanics, is a very complex and quite undiscovered phenomenon. Defining the optimum shape of the fluid flow boundaries, which would ensure minimum undesirable phenomena, like "dead water" zones, unsteady fluid flow, etc., is one of the crucial hydraulic engineering’s task. Method of kinetic balance is described and used for this purpose, what is illustrated with few examples