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

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

Isolation of digoxin from secondary glycoside mixture of digitalis lanata ehrh. Using different liquid-liquid extraction techniques

The present doctoral dissertation deals with the fermentation of leaves of Digitalis lanata Ehrh. (woolly foxglove) causing the enzymatic transformation of lanatoside A, B and C (LA, LB and LC) into the secondary glycosides digitoxin (Dx), gitoxin (Gx) and digoxin (Dgx), the extraction of the secondary glycosides by percolation using the aqueous solutions of methanol and ethanol (10-50 % v/v), the purification of the percolates, the preparation of dry extracts of secondary glycosides using chloroform or trichlorethylene and the isolation of highly pure Dgx (>96 %) from the solution of the dry extracts by fractional dissolution employing either the batch liquid-liquid extraction or continuous countercurrent liquid-liquid extraction in a Karr’s extraction reciprocating plate column. Ground dried leaves cultivated of Digitalis lanata Ehrh. were used. The main goal was to develop the process for obtaining Dgx from the leaves of Digitalis lanata Ehrh. At first, the optimal operating conditions of the fermentation of leaves of Digitalis lanata Ehrh. under anaerobic conditions at 37 oC were determined to be as following: the mean size of plant particles of 7 mm and the water-to-plant material 1:2 g/cm3. Then, the optimal operating conditions of Dgx extraction from the fermented plant material by percolation ensuring the Dgx extraction degree higher than 95 % were found to be as follows: the mean size of plant particles of 7 mm, the depth of the plant material in the extractor of 30 cm, the 10 % vol. ethanol solution as the extracting solvent and the percolate flow rate of 4 dm3/h (i.e. the residence time of 4 h). Also the optimal conditions of purification of the liquid extract using chloroform or trichlorethylene. The obtained liquid extracts were evaporated under vacuum, treated by MgO, filtrated under vacuum and evaporated under vacuum (60 oC). The obtained dry extract contained about 80 % of the secondary glycosides. It was treated with a mixture of acetone and water (7:1 to 10:1 vol.) under reflux to get the Dgx product of high purity (>96 %). Further purification of iv Dgx was conducted by the batch and continuous processes. The first process was carried out using separating funnels (15 funnels for the light phase and 15 funnels for the heavy phase) and the extraction system EtOH:H2O:CHCl3:THE = 35:15:20:30 vol., having the saturated phases, at the concentration of secondary glycosides dissolved in the light phase of 15 g/dm3 and the volumetric ratio of light-to-heavy phase 1:1.1. The light phase was evaporated until the third of the initial volume. The Dgx crystals were separated by filtration under vacuum and dried. The Dgx yield was 98 %. The purification of Dgx was also carried out in the Karr’s extraction reciprocating plate column with countercurrent flows of the phases. The highest Dgx extraction degree (> 99 %) in the light phase was achieved when the solution of secondary glycosides (45 g/dm3 in the heavy phase) was fed in the middle of the column (4 h high) using the solvent system EtOH:H2O-CHCl3:THE = 35: 15:20: 30 vol. at the volumetric ratio of light-to-heavy phase 1:1.1, the spacing between the perforated plates 2.5 cm, the stroke 2 cm and the frequency 125 min-1. The Dgx product of high purity (99 %) was obtained, containing 98.6-100.2 % Dgx

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

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

On the influence of turbulent kinetic energy level on accuracy of k - epsilon and lrr turbulence models

This paper presents research regarding the influence of turbulent kinetic energy (TKE) level on accuracy of Reynolds averaged Navier-Stokes (RANS) based turbulence models. A theoretical analysis of influence TKE level on accuracy of the RANS turbulence models has been performed according to the Boussinesq hypothesis definition. After that, this theoretical analysis has been investigated by comparison of numerically and experimentally obtained results on the test case of a steady-state incompressible swirl-free flow in a straight conical diffuser named Azad diffuser. Numerical calculations have been performed using the OpenFOAM CFD software and first and second-order closure turbulence models. TKE level, velocity profiles and Reynolds stresses have been calculated downstream in four different cross sections of the diffuser. Certain conclusions about modeling turbulent flows by k - epsilon and LRR turbulence models have been made by comparing the velocity profiles, TKE distribution and Reynolds stresses on the selected cross sections

Reke Srbije kao putevi invazije - istočni koridor invazije Reynoutria spp.

Increasing levels of invasion worldwide have been the source of concern for scientists, due to significant costs and efforts required for managing them. The knowledge of invasion pathways, both those of initial introduction and subsequent spread, is of key importance, since further increase in the number of pathways and vectors of invasion is predicted for the 21st century. At regional scales habitat type has proven to be a reliable predictor of the level of invasion, as certain habitat types (i.e. frequently disturbed, under strong anthropogenic influence) is characterized by high invasion levels. Riparian habitats, as hotspots of alien species diversity and primary sources of their spread, represent some of the most important invasion corridors, where water acts as an effective dispersal mechanism. Some invasive plant species, like Reynoutria spp. show a strong tendency to invade riparian habitats. Preliminary findings of field surveys aimed to assess the level of riparian invasion by Reynoutria spp. in Serbia suggest that some river basins are significantly affected by the presence of these invasive species. Bearing in mind the principal means of their propagation, further spread of Reynoutria spp. along the rivers in Serbia is to be expected over the following years.Stepen invazija koji je u porastu širom sveta zabrinjava naučnike, zbog značajnih troškova i napora koji su neophodni u njihovom kontrolisanju. Poznavanje puteva invazije, kako početnog unosa tako i naknadnog širenja vrsta, od ključnog je značaja, jer je u 21. veku prognoziran dalji porast broja puteva i vektora invazije. Na regionalnom nivou tip staništa se pokazao kao pouzdani pokazatelj nivoa invazije, jer određene tipove staništa (često remećena, pod snažnim antropogenim uticajem) karakteriše visok nivo invazije. Riparijalna staništa, kao centri diverziteta alohtonih vrsta i primarni izvor njihovog širenja, predstavljaju neke od najznačajnijih koridora invazije, u kojima voda deluje kao uspešan mehanizam disperzije. Neke invazivne vrste biljaka, poput Reynoutria spp. pokazuju snažnu tendenciju ka invaziji riparijalnih staništa. Preliminarni rezultati terenskih istraživanja koji su za cilj imali procenu nivoa invazije riparijalnih staništa vrstama roda Reynoutria u Srbiji ukazuju na to da su slivovi nekih reka pod značajnim uticajem prisustva ovih invazivnih vrsta. Imajući u vidu osnovni vid njihove propagacije, dalje širenje Reynoutria spp. duž reka u Srbiji može se očekivati tokom narednih godina