Laser doppler velocimetry and confined flows

Finding the mode, in which two component laser Doppler velocimetry can be applied to flows confined in cylindrical tubes or vessels, was the aim of this study. We have identified principle issues that influence the propagation of laser beams in laser Doppler velocimetry system, applied to flow confined in cylindrical tube. Among them, the most important are influences of fluid and wall refractive indices, wall thickness and internal radius ratio and beam intersection angle. In analysis of the degrees of these influences, we have applied mathematical model, based on geometrical optics. The separation of measurement volumes, that measure different velocity components, has been recognized as the main drawback. To overcome this, we propose a lens with dual focal length primary focal length for the measurement of one velocity component and secondary focal length for the measurement of the other velocity component. We present here the procedure for calculating the optimal value of secondary focal length, depending on experimental set-up parameters. The mathematical simulation of the application of the dual focal length lens, for chosen cases presented here, confirmed the accuracy of the proposed procedure

Numerical simulation of multiphase flow around suction plates of ventilation mill in the function of extending its remaining working life

Ovaj rad prestavlja mogućnost korišćenja rezltata numeričkih simulacija, za smanjenje habanja radnih delova ventilacionog mlina za mlevenje uglja u termoelektrani Kostolac B. Mogućnost revitalizacije usisnih ploča ventilacionog mlina je zasnovan na 3D numeričkoj simulaciji multifaznog strujanja u ventilacionom mlinu. Čvrste čestice smeše ugalj, mineralne materije, pesak tokom procesa mlevenja izazivaju veliko habanje usisnih ploča. Primenom softverskog paketa ANSYS FLUENT 12, dobiće se detaljniji prikaz multifaznog strujanja i brzine mešavine koja omogućuje da se na osnovu intenziteta i smera brzine, preciznije odrede kritične zone u kojima će se pojaviti oštećenja kod usisnih ploča ventilacionog mlina. Korišćen je Euler-Euler model mešavine. Rezultati dobijeni pomoću numeričke simulacije koristiće se za izbor optimalne tehnologije revitalizacije usisnih ploča ventilacionog mlina. Primenom ovog pristupa rešavanja problema smanjio bi se broj mogućih interventnih popravki i produžio bi se period između neophodnih kompletnih remonta postrojenja, čime bi se ostvarili značajni ekonomski efekti i ujedno povećala energetska efikasnost termoenergetskih agregata.This paper presents results of the analyses obtained by numerical simulation for the possibilities of increasing the wear resistance of the ventilation mill working parts for coal grinding in the Kostolac B power plant. The possibilities for modification are based on 3D numerical simulation of multiphase flow of ventilation mill. Mineral materials during the process of milling in the ventilation mill cause strong wear of the suction plates. The multiphase flow simulations are performed in order to obtain the mineral materials paths and velocity vectors. The mixture model of the Euler-Euler approach is used. The results obtained in the numerical simulation serve for the selection of an optimal redesign of the suction plates. The application of this approach can reduce the number of possible repairs and extends the period between them, resulting in significant economic effects

Numerical simulation of multiphase flow around suction plates of ventilation mill in the function of extending its remaining working life

Ovaj rad prestavlja mogućnost korišćenja rezltata numeričkih simulacija, za smanjenje habanja radnih delova ventilacionog mlina za mlevenje uglja u termoelektrani Kostolac B. Mogućnost revitalizacije usisnih ploča ventilacionog mlina je zasnovan na 3D numeričkoj simulaciji multifaznog strujanja u ventilacionom mlinu. Čvrste čestice smeše ugalj, mineralne materije, pesak tokom procesa mlevenja izazivaju veliko habanje usisnih ploča. Primenom softverskog paketa ANSYS FLUENT 12, dobiće se detaljniji prikaz multifaznog strujanja i brzine mešavine koja omogućuje da se na osnovu intenziteta i smera brzine, preciznije odrede kritične zone u kojima će se pojaviti oštećenja kod usisnih ploča ventilacionog mlina. Korišćen je Euler-Euler model mešavine. Rezultati dobijeni pomoću numeričke simulacije koristiće se za izbor optimalne tehnologije revitalizacije usisnih ploča ventilacionog mlina. Primenom ovog pristupa rešavanja problema smanjio bi se broj mogućih interventnih popravki i produžio bi se period između neophodnih kompletnih remonta postrojenja, čime bi se ostvarili značajni ekonomski efekti i ujedno povećala energetska efikasnost termoenergetskih agregata.This paper presents results of the analyses obtained by numerical simulation for the possibilities of increasing the wear resistance of the ventilation mill working parts for coal grinding in the Kostolac B power plant. The possibilities for modification are based on 3D numerical simulation of multiphase flow of ventilation mill. Mineral materials during the process of milling in the ventilation mill cause strong wear of the suction plates. The multiphase flow simulations are performed in order to obtain the mineral materials paths and velocity vectors. The mixture model of the Euler-Euler approach is used. The results obtained in the numerical simulation serve for the selection of an optimal redesign of the suction plates. The application of this approach can reduce the number of possible repairs and extends the period between them, resulting in significant economic effects

Hydro Turbine in a Venturi Tube

U radu su prikazani rezultati istraživanja hidroturbine u Venturijevoj cijevi za zadani broj okretaja i zadanom brzinom vode na ulazu u cijev. Rezultati su dobiveni komercijalnim softverom za numeričku dinamiku fluida. Ispitivanje je obuhvatilo usporedbu snage koju daju jedna i dvije suprotno smjerno rotirajuće hidroturbine u Venturijevoj cijevi. Numeričke simulacije za dvije turbine koje se okreću u suprotnim smjerovima s jednakim kutnim brzinama pokazale su da se javlja znatan pad snage na prednjoj turbini, dok je ukupna snaga nešto veća nego za jednu turbinu.This paper presents results of a research hydro turbine in a Venturi tube for given revolutions per minute and velocity of water at the entry of the tube. The results were obtained with commercial software for numerical fluid dynamics. The research was included comparison of power obtained with one and two contra-rotating hydro turbine in a Venturi tube. The numerical simulations, for two turbines rotating in opposite directions with equal angular velocities, showed that a considerable power drop occurred, whereas the total power is somewhat larger than for the one turbine

Uticaj ugla lopatice aksijalnog ventilatora na karakteristike turbulentnog vihornog strujanja

U ovom radu je prikazano istraživanje turbulentnog vihornog strujanja u cevi na potisu aksijalnog ventilatora sa devet podesivih lopatica za uglove 22°, 26° i 30° i istovetni broj obrtaja (1500 min-1). Brzine su merene laser Dopler anemometarskom tehnikom u mernom preseku 3.35·D od ulaska u instalaciju. Postignuti su Rejnoldsovi brojevi Re=236784, 259151 i 277018. Prikazana je nehomogenost i anizotropnost izučavanog turbulentnog brzinskog polja. Profili vremenski osrednjenih obimskih brzina imaju karakter Rankinovog vrtloga, dok se u slučaju aksijalnih brzina primećuje povratno strujanje u oblasti vrtložnog jezgra za uglove 26° i 30°. Eksperimentalno određeni momenti drugog i viših redova prikazuju kompleksnost turbulentnog vihornog strujanja. Vizualizacija turbulentnog vihornog strujanja je prikazana za ugao 22°.The paper presents the investigation of the turbulent swirl flow in a pipe behind the axial fan with adjustable nine blades for the angles of 22°, 26° and 30° for the same rotation number (1500 rpm). Velocities were measured with laser Doppler anemometry (LDA) in the measuring section 3.35·D from the test rig inlet. The achieved Reynolds numbers are Re=236784, 259151 and 277018. The non-homogeneity and anisotropy of the turbulent velocity field are shown. The time averaged circumferential velocity profiles have shown the Rankine vortex structure and revealed a reverse flow in the vortex core region for the blade angles of 26° and 30°. The experimentally determined moments of the second and higher orders reveal complex mechanisms in the turbulent swirl flow. In addition, the visualization of the turbulent swirl flow for an angle of 22° is presented

CFD Analysis of the Influence of Centrifugal Separator Geometry Modification on the Pulverized Coal Distribution at the Burners

This paper presents the results of 3D numerical flow simulation in the ventilation mill (VM) and air mixture channel (AMC) of Kostolac B power plant, where a centrifugal separator with adjustable blade angle is used. Numerical simulations of multiphase flow were performed using the Euler-Euler and the Euler-Lagrange approach of the ANSYS FLUENT software package. The geometry of the numerical model was almost identical to the VM and AMC of Kostolac B, except for the smallest details. An unstructured tetrahedral grid, consisted of almost three million cells, was generated. The main contribution of this paper is the original analysis of the influence of centrifugal separator (CFS) geometry modification on the coal powder distribution at the horizontal burners. The modification of the blade angle, blade shape, and vertical position of the separator and its effect on the coal powder distribution at the burners were analyzed and are published for the first time. Results of the numerical simulations were compared with the measurements and can be used in modifying the separator geometry and position to obtain optimal distribution of the pulverized coal at the burners. Application of these results, obtained by numerical methods, ensures significant savings in time and money, in the process of finding the optimal geometry of CFS

Influence of the axial fan blade angle on the turbulent swirl flow characteristics

U ovom radu je prikazano istraživanje turbulentnog vihornog strujanja u cevi na potisu aksijalnog ventilatora sa devet podesivih lopatica za uglove 22°, 26° i 30° i istovetni broj obrtaja (1500 min-1). Brzine su merene laser Dopler anemometarskom tehnikom u mernom preseku 3.35·D od ulaska u instalaciju. Postignuti su Rejnoldsovi brojevi Re=236784, 259151 i 277018. Prikazana je nehomogenost i anizotropnost izučavanog turbulentnog brzinskog polja. Profili vremenski osrednjenih obimskih brzina imaju karakter Rankinovog vrtloga, dok se u slučaju aksijalnih brzina primećuje povratno strujanje u oblasti vrtložnog jezgra za uglove 26° i 30°. Eksperimentalno određeni momenti drugog i viših redova prikazuju kompleksnost turbulentnog vihornog strujanja. Vizualizacija turbulentnog vihornog strujanja je prikazana za ugao 22°.The paper presents the investigation of the turbulent swirl flow in a pipe behind the axial fan with adjustable nine blades for the angles of 22°, 26° and 30° for the same rotation number (1500 rpm). Velocities were measured with laser Doppler anemometry (LDA) in the measuring section 3.35·D from the test rig inlet. The achieved Reynolds numbers are Re=236784, 259151 and 277018. The non-homogeneity and anisotropy of the turbulent velocity field are shown. The time averaged circumferential velocity profiles have shown the Rankine vortex structure and revealed a reverse flow in the vortex core region for the blade angles of 26° and 30°. The experimentally determined moments of the second and higher orders reveal complex mechanisms in the turbulent swirl flow. In addition, the visualization of the turbulent swirl flow for an angle of 22° is presented

Visualization of cortical speech areas by implementing of functional neuroimagining techniques

U radu su prikazani principi i savremene mogućnosti tehnika vizuelizacije moždanih funkcija – funkcionalnog neuroimidžinga, prvenstveno PET (pozitron emisiona tomografija) i fMRI (funkcionalni magnetski imidžing - BOLD) mozga, u identifikovanju kortikalnih područja uključenih u govorne funkcije. Tehnike funkcionalnog neuroimidžinga omogućavaju vizuelizaciju moždanih područja dok ispitanik obavlja određeni zadatak, pa spadaju u tzv. aktivacione studije. Neuronska aktivnost u regijama mozga uključenih u izvršenje određenog zadatka će se promijeniti, a time se mjenja i potrošnja energije kao i protok krvi u toj regiji, što obilježava aktiviranje ili deaktiviranje neurona u tom području. Opisan je klasični model neurobiološke osnove govorne funkcije poznat kao Broca-Wernicke-Lichtheim model. Takođe su opisani i noviji, znatno detaljniji neurobiološki modeli govornih funkcija koji uključuju i njihove kognitivne komponente i to model Price, model Friederici, Hickok i Poeppel model, Model Indefrey i Levelt i savremeni 6-to komponentni model. Prikazani su i rezultati novijih istraživanja vizuelizacije kortikalnih područja vezanih za govorne funkcije. Takođe su prikazani su i rezultati istraživanja hemisferne specijalizacije - dominacije govornih funkcija, budući da su procesi uključeni u govornu komunikaciju rijetko prisutni u obje moždane hemisfere, a leksičko i gramatičko znanje takođe pokazuje hemisfernu specijalizaciju.This paper aims at presenting the principles and possibilities of modern technology in visualization of brain function - functional neuroimaging, especially PET (positron emission tomography) and fMRI (functional magnetic imaginging) brain, in identifying cortical areas involved in speech function. Functional neuroimaging techniques take vizuelisation of brain areas while subject performs a certain task, then fall into activating brain studies. Neural activity in brain regions involved in the execution of certain tasks will change and thus changes and energy consumption as well as the flow of blood in the region, which marks the activation or deactivation of neurons in this area. We described the classic model of neurobiological basic of voice functions known as Broce-Wernicke-Lichtheim model. Also we described, new, much more detailed models of neurobiological basis of speech functions, including their cognitive components: model Price, model Friederici, Hickok and Poeppel model, Model Indefrey and Levelt and modern 6-component model. We shown some recent results of recent research of visualization of cortical areas related to speech function. Also we shown results of research in specialization or hemisferic-domination of speech functions, since the processes involved in oral communication is rarely present in both brain hemispheric, and lexical and grammatical knowledge also shows hemisfernu specialization to

Estimation of laser-Doppler anemometry measuring volume displacement in cylindrical pipe flow

Laser-Doppler anemometry application in measurements of the 3-D swirl turbulent flow velocity in the cylindrical pipe, behind the axial fan, have been analysed. This paper presents a brief overview of uncertainty sources in the laser-Doppler anemometry measurements. Special attention is paid to estimation of laser-Doppler anemometry measuring volume positioning in cylindrical pipe flow due to optical aberrations, caused by the pipe wall curvature. The hypothesis, that in the central part of the pipe (r/R < 0.6) exists a small, or negligible pipe wall influence on laser- -Doppler anemometry measuring position, is investigate. The required corrections, for measurements of axial, tangential, and radial velocity components such: shift of measuring volume and its orientation are analyzed and determined for used test rig and for some other pipe geometries. [Projekat Ministarstva nauke Republike Srbije, br. TR 35046