Wyniki wyszukiwania - Biblioteka Nauki

1

Turbulent flow around circular cylinder in oscilatory inlet conditions

100%

Jarża A. , Tarnowski T.

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1999

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tom nr 105

3-16

EN

In the present paper the response of the flow around the stationary circular cylinder due to inlet stream oscillations has been discussed. The unsteady flow field was analysed on the base of complete set of mean velocity profiles, Reynolds and coherent stress components and spectral records in the near-wake region.

PL

Praca zawiera omówienie wpływu oscylacji strugi dolotowej na przepływ wokół sztywnego nieruchomego cylindra kołowego. Podstawę analizy stanowią eksperymentalne charakterystyki przepływowe obejmujące profile zarówno średnich jak i losowych i okresowych składowych pola prędkości i ciśnień. Rozważania dotyczą również udziałów energetycznych poszczególnych form ruchu w całkowitej energii kinetycznej fluktuacji przepływu. Szczególny nacisk położono na proces formowania się śladu zachodzący w warunkach rezonansu lock-on.

2

Analytical fluid film force in the turbulent journal bearings

80%

D'Agostino V. , Guida D. , Ruggiero A.

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1999

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tom Vol. 4, no spec.

25-31

EN

The aim of this paper is to illustrate a method to determine the analytical description of non-steady fluid film force and of the stiffness and damping coefficients for the "short" liquid-lubricated journal bearings in a fully developed turbulent flow regime. The equation goveming the distribution of pressure around the bearing has been solved analytically; the models has been developed assuming lubricant flow is isoviscous.

3

Symulacje numeryczne przepływu turbulentnego przez kanał silnie zakrzywiony z wykorzystaniem różnych modeli turbulencji RANS

80%

Kuczkowski M.

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2007

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tom nr 131

51-60

PL

Praca stanowi część przygotowywanej rozprawy doktorskiej dotyczącej zastosowania metody LES do symulacji numerycznej turbulentnego przepływu przez kanał silnie zakrzywiony. W celu wybrania najodpowiedniejszej metody symulacji przeprowadzono symulacje przepływu z wykorzystaniem różnych modeli turbulencji (k-ω, SST, SSG). Wyniki symulacji zostały zestawione z wynikami pomiarów dostępnymi w literaturze.

EN

The presented work is a part of the PhD dissertation which concerns an application of the LES method to simulate a turbulent flow through the strongly curved duct. For comparison, simulations of the turbulent flow with different RANS turbulence models (k-ω, SST, SSG) were conducted. The obtained simulation results are referred to the measurements reported in the literature.

4

Method of convective velocity determination from dissipative range of energy spectrum

80%

Kurasiński T. , Kuncewicz C. , Stelmach J.

Chemical and Process Engineering

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2012

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tom 33

|

nr 1

19-29

EN

In the study a new proposal of convective velocity determination necessary for eddy size determination from the dissipative range in a turbulent flow in a mixer was made. The proposed quantity depends on all the mean and fluctuating velocity components. By applying convective velocity one may determine the distribution of time and linear Taylor microscale in a stirred vessel.

5

Simulation of turbulent flow of a fine dispersive slurry

80%

Bartosik A.

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2010

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tom Vol. 31, z. 1

67-80

EN

Solid.liquid turbulent flow in a pipeline has been simulated for concentration of solids ranging from 0 to 45 % by volume. Water was the carrier liquid, the solid phase constituted fine particles with mean particle diameters of tens of microns. Mathematical model comprising the time averaged momentum equation, k-turbulence model with a modified turbulence damping function, Bingham rheological model has successfully been verified. The results of simulation indicate that concentration of solids affects strongly local velocity at the pipe wall while the pressure gradient and thickness of the viscous sublayer increase linearly for CV in the range 0.25%, and exponentially for CV > 25%.

PL

Symulowano turbulentny przepływ faza stała.faza ciekła w rurze w zakresie objętościowej koncentracji fazy stałej 0.45%. Ciecz nośną stanowiła woda, fazę stałą . drobnodyspersyjne cząstki o średniej średnicy kilkudziesięciu mikrometrów. Pozytywnie zweryfikowano model matematyczny, złożony z uśrednionego po czasie równania pędu, modelu turbulencji k-zmodyfikowanej funkcji tłumiącej turbulencję przy ścianie i modelu reologicznego Binghama. Wyniki symulacji wskazują, że prędkość lokalna przy ścianie zależy od koncentracji fazy stałej, jednostkowy spadek ciśnienia natomiast i grubość podwarstwy lepkiej zwiększają się liniowo dla CV w zakresie 0.25% i wykładniczo dla CV > 25%.

6

Transient CFD simulations of turbulent liquid - liquid flow in a Kenics static mixer. Radial and tangential velocities

80%

Murasiewicz H. , Jaworski Z.

Polish Journal of Chemical Technology

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2009

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tom 11

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nr 2

36-40

EN

The results of modelling of the two-phase turbulent flow of a two-phase, liquid-liquid mixture in a Kenics static mixer were reported. Advanced transient simulations were performed using the large eddy simulation (LES) approach and a broader analysis of the velocity field was carried out. The two-phase flow was modelled employing the Eulerian approach in the pseudo-homogeneous version of the mixture model. Three cases were again considered, which differed by the density of the two phases and the simulations were performed for Reynolds number of 10,000. The LES results for the tangential and radial components were compared with those obtained in the steady-state RANS approach.

7

LES of turbulent channel flow and heavy particle dispersion

80%

Pozorski J. , Wacławczyk T. , Łuniewski M. , Łuniewski M.

|

2007

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tom Vol. 45 nr 3

643-657

EN

The Eulerian-Lagrangian approach has been applied to two-phase turbulent flows with dispersed heavy particles. First, numerical computations of the continuous phase (fluid) have been performed using the Direct Numerical Simulations (DNS) and Large-Eddy Simulations (LES) for the case of a fully-developed channel flow. Parallelisation efficiency of flow and particle solvers has been estimated. Residual turbulent kinetic energy has been found from filtered DNS (also called a priori LES); a model for this quantity has been assessed. Then, heavy particles have been tracked in the LES velocity field. Statistics of particle motion (mean velocity, intensity of velocity fluctuations) and the profile of cross-stream number density as well as preliminary results for particle wall deposition have been obtained.

PL

W pracy zastosowano podejście Eulera-Lagrange'a do wyznaczenia ruchu fazy dyspersyjnej (cząstki, krople) w turbulentnym przepływie dwufazowym. Obliczenia ruchu fazy ciągłej (płynu) przeprowadzono za pomocą rozwiązania pełnych równań przepływu (DNS) oraz przy użyciu metody dużych wirów (LES) dla przypadku rozwiniętego przepływu w kanale płaskim. Oszacowano efektywność zrównoleglenia obliczeń numerycznych. Określono poziom energii kinetycznej skal podsiatkowych; porównano ją z wynikami uzyskanymi z modelu dynamicznego. Wyznaczono trajektorie cząstek fazy dyspersyjnej w polu prędkości LES. Określono statystyki ich ruchu: prędkość średnią, intensywność fluktuacji prędkości, profil koncentracji cząstek w poprzek kanału; uzyskano wstępne wyniki dla separacji cząstek na ściankach.

8

Methodology pertaining to component evaluation of turbulence energy balance in a premixed jet flame with dissipation

80%

Grodzki G.

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2012

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tom Vol. 11, nr 3

33-44

EN

This paper consists of an analysis of existing methods and their limitations pertaining to defining the dissipation rate as one of the components of the turbulent kinetic energy balance equation. Careful attention has been paid with reference to the method used during tests conducted in a burning round jet by means of laser Doppler anemometry. This paper covers the developed algorithms for digital signal processing of LDA, examples of output data sets for calculations and chosen profiles of energy balance components of dissipation and production.

9

Drop coalescence in a turbulent flow factors affecting film drainage

80%

Podgórska W.

|

2008

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tom Vol. 29, z. 1

257-269

EN

Coalescence of oil droplets in the system containing polyvinyl alcohol as a protective colloid was considered. Analysis of experimental results enables us to suppose that in the system containing 0.001% PVA drop interfaces remain partially mobile, while in the system containing 0.01% PVA droplets are immobilized. Coalescence models have been proposed taking into account intermittent character of turbulence and explain behaviour of droplets.

PL

Rozważono proces koalescencji kropel oleju w układzie zawierającym alkohol poliwinylowy działający jako koloid ochronny. Analiza wyników doświadczalnych pozwala przypuszczać, że w układzie zawierającym 0,001% PVA powierzchnie kropel pozostają częściowo ruchome, natomiast w układzie zawierającym 0,01% PVA powierzchnie kropel są unieruchomione. Zaproponowano modele koalescencji umożliwiające wyjaśnienie zachowania kropel i uwzględniające intermitentny charakter burzliwości.

10

Double-averaging methodology and its application to turbulent flow in and above vegetation canopies

80%

Finnigan J. , Shaw R.

Acta Geophysica

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2008

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tom Vol. 56, no. 3

534-561

EN

Double averaged equations for atmospheric boundary layer flows are introduced as natural extensions of single averaged Reynolds equations. We show that in circumstances where double averaged equations are needed, the two fundamental properties of Reynolds averaging are violated. First, we consider double-averaging in free air turbulence, where the aim is to separate coherent motions from background turbulence. We illustrate the different properties of the main operators that have been used and the physical meaning of the terms that result. Second, in canopy flows, the multiply connected nature of the canopy airspace leads to a different set of departures from the standard Reynolds equations. We establish the physical meaning of the extra terms that arise. Finally we briefly discuss the problems, both practical and theoretical, that arise when we use double averaged equations to interpret real data.

11

Analysis of turbulent flows in fixed and moving permeable media

80%

De Lemos M.

Acta Geophysica

|

2008

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tom Vol. 56, no. 3

562-583

EN

The ability to realistically model flows through heterogeneous domains, which contain both solid and fluid phases, can benefit the analysis and simulation of complex real-world systems. Environmental impact studies, as well as engineering equipment design, can both take advantage of reliable modelling of turbulent flow in permeable media. Turbulence models proposed for such flows depend on the order of application of volume- and time-average operators. Two methodologies, following the two orders of integration, lead to distinct governing equations for the statistical quantities. This paper reviews recently published methodologies to mathematically characterize turbulent transport in permeable media. A new concept, called double-decomposition, is here discussed and instantaneous local transport equations are reviewed for clear flow before the time and volume averaging procedures are applied to them. Equations for turbulent transport follow, including their detailed derivation and a proposed model for suitable numerical simulations. The case of a moving porous bed is also discussed and transport equations for the mean and turbulent flow fields are presented.

12

BLENDING CHARACTERISTICS OF HIGH-SPEED ROTARY IMPELLERS

70%

Fořt I. , Seichter P. , Pešl L. , Rieger F. , Jirout T.

Chemical and Process Engineering

|

2013

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tom 34

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nr 4

427-434

EN

This paper presents a comparison of the blending efficiency of eight high-speed rotary impellers in a fully baffled cylindrical vessel under the turbulent flow regime of agitated charge. Results of carried out experiments (blending time and impeller power input) confirm that the down pumping axial flow impellers exhibit better blending efficiency than the high-speed rotary impellers with prevailing radial discharge flow. It follows from presented results that, especially for large scale industrial realisations, the axial flow impellers with profiled blades bring maximum energy savings in comparison with the standard impellers with inclined flat blades (pitched blade impellers).

13

A study on blending characteristics of axial flow impellers

70%

Fořt I. , Jirout T.

Chemical and Process Engineering

|

2011

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tom 32

|

nr 4

311-319

EN

This paper presents an analysis of the blending characteristics of axial flow high-speed impellers under a turbulent regime of flow of an agitated low viscosity liquid. The conductivity method is used to determine the time course of blending (homogenisation) of miscible liquids in a pilot plant fully baffled mixing vessel, and a torquemeter is used for measuring the impeller power input in the same system. Four-blade and six-blade pitched blade impellers and three high efficiency axial flow impellers are tested for the given degree of homogeneity (98%).The experimental results and also the results of the authors' previous study, in accordance with the theoretical approach described in the literature, show that there is a universal relationship between the impeller power number and the dimensionless blending time, taking into consideration the impeller-to-vessel diameter ratio, independent of the geometry of the axial flow impeller but dependent on the degree of homogeneity. This relationship is found to be valid on a pilot plant scale under a turbulent flow regime of an agitated liquid.

14

Single phase pressure drop in minichannels

70%

Dutkowski K.

|

2008

|

tom nr 121

17-32

EN

This paper presents the results of experiential investigations of pressure drop in minichannels with use of water as the working fluid. The test section was made from stainless steel pipes with internal diameters of 0.55 mm, 0.64 mm and 1.10 mm respectively. A pressure drop was presented per a length unit as the function of Reynolds number both for laminar and turbulent flow. A comparison of the experimental friction factor with the results obtained from theoretical equations of Hagen-Poiseuille and Blasius are presented. The experiments were conducted in range of Reynolds number Re = 30 - 6 400. Contradictory reports concerning a sooner transition to the turbulent flow, or the friction factor values which diverge from those occurring in conventional channels, were not confirmed here. New experimental data presented in this paper constitute further contribution to the world's database of experimental results which constitute the basis for a verification of the existing theories or attempts to create new computational models.

15

Numerical simulation of turbulent flow through a square-sectioned duct with a 90-degree bend using FLUENT

70%

Rup K. , Gargula M. , Sarna P.

|

2008

|

tom nr 121

33-48

EN

The turbulent flow in a square-sectioned duct with an installed bend was investigated numerically. The calculations were based on two different turbulence models, namely the standard k-epsilon model and the k-omega SST model. The numerical computations were carried out using the commercial software package FLUENT 6.1. Numerical results for velocity, turbulent intensity and pressure distributions are presented. The obtained results of numerical calculations are compared with corresponding results of experimental studies available in references. The comparative analysis of the obtained numerical results and experimental ones, proved a high degree of their consistency.

16

Numeryczna symulacja turbulentnego przepływu przez kanał z wygięciem o 90° z wykorzystaniem metody LES i RANS

60%

Kuczkowski M.

|

2009

|

tom nr 136

43-56

PL

W pracy przedstawiono wyniki symulacji numerycznych turbulentnego (Re=40.000) przepływu nieściśliwego czynnika, bez wymiany ciepła na ściankach kanału, przez kanał o przekroju kwadratowym z wygięciem o kat 90°. Do przeprowadzenia symulacji użyto programu ANSYS CFX. Wykorzystano metody LES i RANS z modelowaniem naprężeń Reynoldsa SSG (Speziale, Sarkar, Gatski). Uzyskane rezultaty porównano z wynikami pomiarów dostępnymi w literaturze.

EN

An incompressible, isothermal turbulent water flow (Re = 40,000) in the square sectioned curved duct was investigated numerically. The duct had a 90-degree bend. The ANSYS CFX code was used for all computations. Numerical simulations were conducted with a LES and a RANS approach with Reynolds Stress SSG (Speziale, Sarkar, Gatski) turbulence model. The obtained results were compared with the measurements reported in the literature.

17

BLENDING CHARACTERISTICS OF HIGH-SPEED ROTARY IMPELLERS

60%

Fořt I. , Seichter P. , Pešl L. , Rieger F. , Jirout T.

|

18

Turbulence in mobile-bed streams

60%

Dey S. , Das R. , Gaudio R. , Bose S.

Acta Geophysica

|

2012

|

tom Vol. 60, no. 6

1547-1588

EN

This study is devoted to quantify the near-bed turbulence parameters in mobile-bed flows with bed-load transport. A reduction in near-bed velocity fluctuations due to the decrease of flow velocity relative to particle velocity of the transporting particles results in an excessive near-bed damping in Reynolds shear stress (RSS) distributions. The bed particles are associated with the momentum provided from the flow to maintain their motion overcoming the bed resistance. It leads to a reduction in RSS magnitude over the entire flow depth. In the logarithmic law, the von Karman coefficient decreases in presence of bed-load transport. The turbulent kinetic energy budget reveals that for the bed-load transport, the pressure energy diffusion rate near the bed changes sharply to a negative magnitude, implying a gain in turbulence production. According to the quadrant analysis, sweep events in mobile-bed flows are the principal mechanism of bed-load transport. The universal probability density functions for turbulence parameters given by Bose and Dey have been successfully applied in mobile-bed flows.

19

Simulation and numerical analysis of a rectangular pipe with transversal baffle – comparison between zigzag and plane baffles

60%

Zidani C. , Benyoucef B. , Didi F. , Guendouz N. , Zidani C. , Benyoucef B. , Didi F. , Guendouz N.

|

nr 4

20

Small-scale intermittency of turbulent flows

60%

Icha A.

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2001

|

tom z. 15

149-154

EN

The problem of internal intermittency in fully developed hydrodynamic turbulence is considered. A relatively simple phenomenological model for the energy-cascading process in the inertial range is proposed. The model is a combination of two models: the β-model and the log-stable distribution intermittency model. Results are in excellent agreement with experimental data when the intermittency exponent is μ = 0.17 (calculated) and the characteristic exponent of the distribution is α = 1.9 (free parameter, obtained by the least-squares method).

PL

W pracy rozważono zagadnienie wewnętrznej intermittencji rozwiniętego przepływu turbulentnego. Zaproponowano prosty, fenomenologiczny model procesu przenoszenia energii w przepływie przez kaskadę wirów, będący połączeniem tzw. β-modelu i logarytmicznie stabilnego modelu intermittencji. Uzyskano bardzo dobrą zgodność z istniejącymi danymi eksperymentalnymi przy wyborze wykładnika intermittencji μ = 0,17 (na podstawie obliczeń) i wykładnika charakterystycznego rozkładu α = 1,9 (metodą najmniejszych kwadratów).