Anisotropy analysis of turbulent swirl flow

U radu su primenjene dve vrste invarijantnih mapa kako bi se procenio stepen anizotropnosti turbulentnog vihornog strujanja. Korišćene su invarijantna mapa, koju su predložili Lamli i Njuman, kao i baricentrična mapa. Analizirane su razlike u vizuelnom predstavljanju stanja anizotropnosti i izvedene su matematičke osnove za obe mape. Analizom eksperimentalnih podataka je pokazano da postoji značajan uticaj vihora na anizotropnost turbulencije. Korišćenje mapa anizotropnosti pokazuje da su različite oblasti strujnog polja u vihornom strujanju okarakterisane različitim stanjima anizotropnosti.Anisotropy invariant map proposed by Lumley and Newman and barycentric map proposed by Banerjee et al. were used in order to estimate the degree of anisotropy in turbulent swirl flow. The differences in visual interpretations of anisotropy states in these two maps were analyzed and mathematical basis of these two maps was derived. Experimental data reveal that there is significant influence of swirl on the anisotropy of turbulence. Anisotropy invariant mapping shows that different flow regions of swirl flow are characterized by different anisotropy states

On the non-local turbulent transport and non-gradient thermal diffusion phenomena in HVAC systems

Istraživanje strukture turbulencije je neophodno za razumevanje fizike strujno-termodinamičkih procesa u KGH sistemima. Analiza i proračun ovih sistema zasnovani su na poznavanju turbulentnog prenosa i njegovom modeliranju. S tim u vezi, u radu se analiziraju fenomeni nelokalnog prenosa impulsa i nelokalnog prenosa energije toplotom u zakrivljenim kanalima, asimetričnim mlazevima, vrtložnim tragovima i vihornom strujanju. Razmatra se fizika negradijentne turbulentne difuzije i negativne produkcije u brzinskim i temperaturskim poljima. Utvrđena je izvesna analogija između turbulentnih procesa u ovim klasama strujanja. Pomoću numeričke obrade sopstvenih eksperimentalnih rezultata izvršeno je modeliranje nelokalnog turbulentnog prenosa u vihornom strujanju.The turbulence structure investigation is essential for understanding the physics of flow-thermodynamic processes in Heating, Ventilation and Air conditioning (HVAC) systems. Analysis and calculation of these systems are based on the knowledge of turbulent transfer mechanism and its modeling. In this regard, the paper analyzes the phenomena of non-local momentum transfer and non-local transfer of energy by heat in curved channels, asymmetric jets, wakes and swirling flow. The physics of nongradient turbulent diffusion and negative production in velocity and temperature fields are analyzed. There was a certain analogy between the turbulent processes in these classes of flow. By means of numerical processing of experimental results, modeling of non-local transport in turbulent swirling flow was conducted

Numerical research of the compressible flow in a vortex tube using openfoam software

The work presented in this paper is dealing with numerical simulation of energy separation mechanism and flow phenomena within a Ranque-Hilsch vortex tube. Simulation of turbulent, compressible, highly swirling flow inside vortex tube is performed using RANS approach, with Favre averaged conservation equations. For turbulence closure, k-epsilon and k-omega shear-stress transport models are used It is assumed that the mean flow is axisymmetric, so the 2-D computational domain is used. Computations were performed using open-source CFD software Open FOAM All compressible solvers available within OpenFOAM were tested, and it was found that most of the solvers cannot predict energy separation. Code of two chosen solvers, which proved as the most robust, is modified in terms of mean energy equation implementation. Newly created solvers predict physically accepted behavior in vortex tube, with good agreement with experimental results. Comparison between performances of solvers is also presente

An experimental investigation and statistical analysis of turbulent swirl flow in a straight pipe

This paper presents results of our own velocity field measurements in a straight pipe swirl flow. These studies were conducted using an originally designed hot wire probe. Due to the specially tailored shape of the probe, it was possible to get four measurement points in the viscous sublayer. The time-averaged velocity field and the statistical moments of the second and third order are calculated based on the measured velocity components. Mathematical and physical interpretations of statistical characteristics and structures of turbulent swirl flow in the time domain are presented. On the basis of these results, deeper insight into turbulent transport processes can be obtained, as well as useful conclusions necessary for turbulent swirl flows modeling

Supplementary data for article: Grozdanović, M. M.; Burazer, L. M.; Gavrović-Jankulović, M. Kiwifruit (Actinidia Deliciosa) Extract Shows Potential as a Low-Cost and Efficient Milk-Clotting Agent. International Dairy Journal 2013, 32 (1), 46–52. https://doi.org/10.1016/j.idairyj.2013.03.001

Supplementary material for: [https://doi.org/10.1016/j.idairyj.2013.03.001]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/1589

Anisotropy analysis of turbulent swirl flow

U radu su primenjene dve vrste invarijantnih mapa kako bi se procenio stepen anizotropnosti turbulentnog vihornog strujanja. Korišćene su invarijantna mapa, koju su predložili Lamli i Njuman, kao i baricentrična mapa. Analizirane su razlike u vizuelnom predstavljanju stanja anizotropnosti i izvedene su matematičke osnove za obe mape. Analizom eksperimentalnih podataka je pokazano da postoji značajan uticaj vihora na anizotropnost turbulencije. Korišćenje mapa anizotropnosti pokazuje da su različite oblasti strujnog polja u vihornom strujanju okarakterisane različitim stanjima anizotropnosti.Anisotropy invariant map proposed by Lumley and Newman and barycentric map proposed by Banerjee et al. were used in order to estimate the degree of anisotropy in turbulent swirl flow. The differences in visual interpretations of anisotropy states in these two maps were analyzed and mathematical basis of these two maps was derived. Experimental data reveal that there is significant influence of swirl on the anisotropy of turbulence. Anisotropy invariant mapping shows that different flow regions of swirl flow are characterized by different anisotropy states

Comparison of different cfd software performances in the case of an incompressible air flow through a straight conical diffuser

Numerical flow simulations have been carried out in order to analyze the possibilities of numerical prediction of a steady-state incompressible air flow through a conical diffuser named Azad diffuser. The spreading angle of this diffuser is 8 degrees and it has cylindrical parts of the constant diameter in the inlet and outlet flow zones. Numerical analysis has been performed by the use of the standard k-epsilon turbulence model. The simulations have been performed using the Ansys CFX and the OpenFOAM software for cases of 2-D and 3-D computational domains. In both cases a Ally developed turbulent flow at the inlet section of diffuser is present. The numerical flow simulation in a 2-D computational domain has been performed under the assumption of an axisymmetric flow in the diffuser. Numerically obtained results have been compared with experimental data. Results obtained with these two softwares have also been mutually compared. At the end the results obtained by CFD for the cases of 2-D and 3-D computational domains have been mutually compared, and the advantages and disadvantages of performing numerical simulations under the assumption of an axisymmetric flow in the diffuser have been analyzed

Numerical research of compressible turbulent swirl flow with energy separation in a cylindrical tube

Cilj ovog rada je numerička analiza fenomena raslojavanja polja totalne temperature u turbulentnom stišljivom vihornom strujanju u cilindričnoj cevi. U tom smislu, raslojavanje polja totalne temperature u vrtložnoj cevi sa potpuno zatvorenim otvorom za izlaz ohlađenog gasa se analizira numeričkim putem primenom softverom otvorenog tipa - OpenFOAM. Validacija dobijenih numeričkih rezultata je vršena poređenjem sa vrednostima dobijenim eksperimentalnim putem. Za numeričke proračune koriste se dvojednačinski model (standardni k-ε) i puni naponski model turbulencije (LRR). Proračunski domen se smatra dvodimenzionalnim, a radni fluid - vazduh tretira se kao kalorički idealni gas. Uticaj broja ćelija u mreži je izvršen pomoću četiri različite veličine mreže. Raspodele jačine vihora, srednjeg vihora i ugaone brzine jasno ukazuju na uticaj prisustva vihora u strujnom polju. Sa druge strane, združeno sa njihovom vrednošću upućuju i na fiziku ovog izuzetno kompleksnog strujno-termodinamičkog fenomena kakav je fenomen raslojavanja polja totalne temperature. Na osnovu vrednosti i raspodela ovih strujnih veličina, izvršeno je i poređenje između stišljivog i nestišljivog turbulentnog vihornog strujanja.The aim of this paper is to numerically analyze the energy separation phenomenon in turbulent compressible swirling flow in a cylindrical tube. In that sense, the energy separation in a vortex tube with orifice at cold end closed completely is examined numerically using OpenFOAM software. Obtained results are validated with the experimental ones. For numerical calculations, both two-equation (standard k-ε) and full Reynolds stress turbulence models (LRR) are used. The computational domain is considered to be two-dimensional, and the working fluid - air is treated as calorically perfect gas. Mesh independence test is carried out for four different mesh sizes. Distributions of swirling flow intensity, average swirl and angular velocity clearly show the influence of the swirl presence in the flow. The values of these quantities point to the physics of this extremely complex flow-thermodynamic phenomenon, such is the energy separation. Based on values and distributions of these flow quantities a comparison between incompressible and compressible turbulent swirling flow is performed

Flow simulations in a small bulb turbine using two-equation turbulence models

U radu su urađene numeričke simulacije strujanja u maloj cevnoj turbini primenom softvera Ansys CFX. Simulacije su izvedene primenom tri različita modela turbulencije koji su bazirani na Rejnoldsovom osrednjavanju Navije-Stoksovih jednačina: k-ε , k-ω i SST. Za svaki od navedenih modela razmotreno je sedam različitih radnih režima turbine. Da bi se smanjilo korišćenje računarskih resursa izvedene su stacionarne simulacije strujanja. Za sve slučajeve dobijena je dobra numerička stabilnost i konvergencija rešenja. Radne krive turbine formirane su za svaki od izabranih modela turbulencije na osnovu rezultata izvedenih simulacija u različitim radnim režimima. Za optimalni radni režim turbine, u proizvoljno izabranom poprečnom preseku difuzora izračunati su profili brzina za svaki model turbulencije, kao i raspodela statičkog pritiska po konturama loptatica radnog kola turbine. Izvršeno je upoređivanje dobijenih performansi turbine i data je analiza dobijenih profila brzine i raspodele statičkog pritiska za izabrane modele turbulencije.Numerical flow simulations in a small bulb turbine by the use of Ansys CFX software were performed in this paper. Simulations were performed for three different RANS-based models: k-ε , k-ω and SST. For each of these models, seven different operating regimes were considered. In order to reduce computational effort, steady state simulations were performed. In all cases, good numerical stability and convergence of solution were obtained. Based on the obtained results, performance curves for each of selected turbulence models in different operating regimes are formed. In turbine's optimal operating regime, velocity profiles in a selected cross section of the draft tube were calculated, as well as the static pressure distribution on runner blades. Comparison of obtained performance curves was performed. Analysis of the velocity profiles and distribution of static pressure are given for each of the selected turbulence model

Numerical Study of the L/D Ratio and Turbulent Prandtl Number Effect on Energy Separation in a Counter-Flow Vortex Tube

Vortex tube is a device without moving parts with ability to separate pressurized gas into two streams: cold and hot. This is a consequence of the Eckert-Wiese effect, which is responsible for spontaneous redistribution of total energy within the flow domain. In order for vortex tubes to work properly, there are some constraints which have to be fulfilled. The most important constraint in that sense is the L/D ratio. One part of this paper is dedicated to the research of the influence of L/D ratio on the energy separation in a vortex tube, i.e. to the values of total temperatures on cold and hot outlets of the device. On the other hand, experimental research of the inner flow is quite challenging since vortex tube is a device of small dimensions. Hence, we are relaying on numerical computations. One of important quantities that has to be prescribed in these computations is the turbulent Prandtl number Pr-T. Because of that, the other part of this paper is dedicated to research of the influence of Pr-T on the results of numerical computations. The research is conducted using open-source software OpenFOAM. Turbulence is modelled using two-equation and RST models. For small L/D ratios there is a secondary circulation that acts as a refrigeration cycle, and for greater L/D ratios distribution of velocity and temperature inside the vortex tube remains the same, regardless of the stagnation point presence. It is not justified to increase the length of the vortex tube beyond 20D since the change in cold total temperature inside the vortex tube as well at the cold outlet is practically null. For L/D variation from 1.8 to 10, the cold outlet temperature changes from 270.9 K to 266.8 K, and then rises to its final value of 270.5 K. For L/D ratio from 20 to 60, the total temperature at cold end remains unchanged at 271.3 K. We obtained good results with the unit value of turbulent Prandtl number, and demonstrated that increasing the Pr-T beyond unit value is not necessary in order to numerically obtain the energy separation inside the vortex tube