Wyniki wyszukiwania - Biblioteka Nauki

1

Experimental research into turbulence field in combustion chamber of internal combustion engine

100%

Tutak W. , Jamrozik A. , Kociszewski A. , Sosnowski M.

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2006

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tom Vol. 13, No. 2

427-434

EN

The results of research into the velocity field in combustion chamber of piston engine are presented in the paper. The measurements of charge flow velocity in the cylinder axis and near the cylinder squeezing surface in several points were performed. The measurement results were used for analysis of turbulence field in examined combustion chamber. The turbulence field turned out to be inhomogeneous in the combustion chamber. The test stand, measurement system, measurement results, configuration of measurement points in combustion chamber of research engine, charge instantaneous velocity variation curve in the ignitron points of the research combustion chamber, turbulence intensity variation curve in ignitron points, mean velocity, mean velocity fluctuations and velocity random component variation curve, comparison of charge flow mean velocities, comparison of velocity fluctuations in research combustion chamber in four measurement points, velocity fluctuation for two perpendicular directions have been introduced in the paper. The thermoanemometric measurements showed that there exists significant inhomogeneity of turbulent flow field in the engine combustion chamber. Areas of considerably diversified turbulence exist in the engine cylinder. The biggest turbulence in the researched engine is observed in the area between 5 and 15 mm from the head surface. Higher values of turbulence parameters occur in the area localized near the squish surface of the piston.

2

Analysis of the fluctuations of a laser beam due to thermal turbulence

100%

Ndlovu S. , Chetty N.

Open Physics

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2014

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tom 12

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nr 7

466-472

EN

A laser beam propagating in air and passing through a point diffraction interferometer (PDI) produces stable interferograms that can be used to extract wavefront data such as major atmospheric characteristics: turbulence strength, inner scale and outer scale of the refractive index. These parameters need to be taken into consideration when developing defense laser weapons since they can be affected by thermal fluctuations that are due to the changes in temperature in close proximity to the propagating beam and results in phase shifts that can be used to calculate the temperature which causes wavefront perturbations on a propagating beam.

3

Metoda funkcji gęstości prawdopodobieństwa w problemie turbulencji

100%

Icha A.

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2012

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tom T. 12, nr 43

69-76

PL

W pracy rozważono statystyczny opis przepływów turbulentnych przy wykorzystaniu metody funkcji gęstości rozkładu prawdopodobieństwa charakterystyk przepływu. W szczególności otrzymano równanie ewolucyjne dla jednopunktowej funkcji gęstości prawdopodobieństwa pulsacji koncentracji dyfundującej substancji w zadanym polu prędkości cieczy. Rozważono bliżej przypadek statystycznie stacjonarnego i horyzontalnie jednorodnego przepływu turbulentnego, dla którego znaleziono ścisłe, zależne od dwóch parametrów, rozwiązanie zagadnienia dyfuzji, wyrażone przez 3-konfluentną funkcję Heuna.

EN

In the paper the use of probabiiity density functions metod to the statistical description of turbulent flows is considered. This formulation is less generał than the characteristic functionals approach, but primary in the relation to the Friedmann-Keller hierarchy equations. An evolution equation for single-point probability density function of pulsation of concentration of the diffusing substance in prescribed fluid velocity field, is derived. The case of statistical stationary and horizontal homogeneous turbulent flow is considered, for which an exact, new, two-parameter solution of diffusion problem in terms of Triconfluent Heun function, is obtained.

4

The impact of turbulence and phytoplankton dynamics on foam formation, seawater viscosity and chlorophyll concentration in the eastern English Channel

100%

Kesaulya I. , Leterme S. C. , Mitchell J. G. , Seuront L.

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2008

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tom No. 50 (2)

167-182

EN

The space-time dynamics of chlorophyll a concentration and seawater excess viscosity has been investigated in the hydrographically contrasting inshore and offshore water masses of the eastern English Channel. This was done during the phytoplankton spring bloom dominated by Phaeocystis globosa before and after the very large-scale formation of foam induced by an increase in wind-driven turbulence and the related wave breakings. The results suggest that the dynamics of chlorophyll a concentration and seawater excess viscosity are differentially controlled by the formation of foam through the intensity of the spring bloom and wind-generated turbulence.

5

Turbulence, from stochastic to deterministic approach

100%

Drobniak S.

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2002

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tom nr 110

103-114

EN

The paper presents contemporary development in the field of deterministic description of turbulence with a special reference to Large Eddy Simulation (LES) methods. The limitations of conventional turbulence modelling based on stochastic methodology have been discussed and reasons for the development of deterministic approach have been outlined. It has been shown that the computational power of the fastest available computers restrict the possible DNS (Direct Numerical Simulation) solutions to the range of small reynolds numbers. Finally, the basic assumptions have been formulated for the LES formalism, that seem to offer the reasonable compromise between the tendency towards the deterministic solution of Navier-Stokes equations and the existing computational resources.

6

Characteristics of the flow field in the combustion chamber of the internal combustion test engine

100%

Tutak W. , Jamrozik A.

Chemical and Process Engineering

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2011

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tom 32

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nr 3

203-214

EN

Results of a research study into the velocity field in combustion chamber of internal combustion engine are presented in the paper. Measurements of fresh charge flow velocity in the cylinder axis and near the cylinder squeezing surface were performed. The hot-wire anemometer was used. The measurement results were used for analysis of turbulence field in the examined combustion chamber. It turned out that in the axis of cylinder the maximum of velocity occurs 30 deg before TDC and achieves 6 m/s. In the studied combustion chamber, the maximum value of turbulence intensity was close to 0.2 and it was achieved 35 deg BTDC. Additionally, the maximal velocity dispersion in the following cycles of the researched engine was at the level of 2 m/s, which is 35% of the maximum value of flow velocity. At a point located near the squeezing surface of the piston, a similar level of turbulence, but a the smaller value of the average velocity was achieved. The turbulence field turned out to be inhomogeneous in the combustion chamber.

7

Prediction of Laminar-Turbulent Transition with the Low-Reynolds Model and Kinetic Energy Production Limiter

100%

Derevyanko A. , Yershov S.

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2012

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tom nr 141

7-14

EN

A bypass transition model has been implemented in the FlowER solver. The model is based on the Shear Stress Transport turbulence model and Low-Reynolds transition model with the kinetic energy production limiter. The modifications of transition model are implemented to enable fully turbulent flow beyond the transition region. Test cases include the classical flat-plate boundary flows and low-pressure compressor cascade. It is shown that proposed model allows an approximate simulation of some effects in a transitional flow.

8

Examination of air density fluctuations with the aid of laser beam

100%

Klemm K. , Pieszyński K. , Rożniakowski K.

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2007

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tom Vol. 37, nr 3

219-228

EN

The paper presents theoretical foundations and results of experimental verification of the possibility of laser beam application for registration of air density fluctuations caused either by mechanically forced air flow near obstacles which are not streamlined or by the presence of solid objects which produce thermal disturbance (temperature gradients).

9

Determination of turbulence and upper size limit in Jameson flotation cell by the use of computational fluid dynamic modelling

100%

Sahbaz O. , Ercetin U. , Oteyaka B.

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2012

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tom Vol. 48, iss. 2

533-544

EN

In the coarse particle flotation, turbulence which can be treated as energy dissipation rate, is one of the most significant parameters effecting the recovery and grade. Therefore, determination of energy dissipation rate is very beneficial for delineation of coarse particle flotation and determining the maximum floatable particle size in any cell. In this study, Computational Fluid Dynamic (CFD) modelling for the Jameson cell has been carried out to determine the high turbulent regions and the effect on the upper floatable size limit. The CFD modelling has been utilized for determining the flow characteristics and hydrodynamic behaviour of the Jameson flotation cell. In parallel with this purpose the turbulence map of the cell has been determined and energy dissipation rate determined by using the CFD modelling. According to the result acquired from the CFD modelling, there are two main turbulent regions which are mixing zone in the upper part of the downcomer and critical region at the separation tank. While the high turbulence at the mixing zone supplies fine bubbles and fast collection of particles, the turbulence at the separation tank causes the main detachment of the bubble-particle aggregate. Then, the increase in turbulence in the tank causes the decrease of the maximum floatable size of particles. In addition, the average energy dissipation rate in the critical region has been determined and used for estimation of the maximum floatable particle size in the Jameson cell. Moreover, the effect of hydrophobicity has been discussed.

10

New closure method for a simultaneous diazo coupling between 1- and 2-Naphthols and diazotized sulphanilic acid

100%

Bałdyga J. , Jasińska M.

Polish Journal of Chemical Technology

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2009

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tom 11

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nr 2

1-5

EN

This paper presents the effects of mixing on the course of complex chemical reactions in relation to the manufacturing of pure products at high reaction selectivity, and designing mixing strategies using complex, homogeneous test reaction systems. As an example, the competitive-consecutive and parallel reaction test system including a simultaneous diazo-coupling between 1- and 2-naphtols and diazotized sulphanilic acid is considered. The effect of mixing on the reaction selectivity is interpreted using mechanistic modeling and a new closure scheme. The new closure represents an extension of the conditional PDF closure applied before to simple reaction schemes.

11

The structure of average turbulent flow field

100%

Heinloo J.

Open Physics

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2010

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tom 8

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nr 1

17-24

EN

A mathematical formalism to reflect the turbulent hierarchic eddy structure in an average turbulence description is discussed. The formalism is founded on simultaneous application of turbulent flow field splitting procedures by the motion variability and by the motion order explained in the paper. It is shown that this formalism permits the outlining of different types of cascading processes in turbulent media within the turbulence average description.

12

Generalized theory of refraction and turbulence

100%

Moroz O. , Ostrovskyj A.

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2000

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tom z. 6/52

217-226

13

Estimation of the influence of inflow turbulence on heat convection from a sphere surface

100%

Bogusławski L.

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2007

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tom Vol. 45 nr 3

505-511

EN

In the paper, results of an experimental investigation of a heat transfer coefficient on a sphere for different inflow turbulence levels have been presented. The average heat transfer coefficient on the sphere surface appear to be dependent on the turbulence level of flow around the sphere. This effect of influence of the flow structure near the sphere surface on the heat transfer process have been presented. Distributions of heat transfer on spheres of different diameters for different turbulence levels of the inflow have been analyzed. It has been shown that an increase of the inflow turbulence level caused an increase of the average heat transfer coefficient on the sphere surface. The maximum increase of the heat transfer due to growing turbulence has been found to be about 30%.

PL

W pracy przedstawiono wyniki badań eksperymentalnych współczynników przejmowania ciepła na kuli przy różnych stopniach turbulencji napływającej strugi. Średni współczynnik przejmowania ciepła na powierzchni kuli jest zależny od stopnia turbulencji przepływu wokół kuli. Jest to rezultat zmiany struktury przepływu w pobliżu ścianki kuli wpływającej na procesy transportu ciepła. Przeprowadzono analizę wymiany ciepła na kulach o różnych średnicach przy zmianie stopnia turbulencji napływającej strugi. Wzrost stopnia turbulencji napływu powoduje wzrost średniego współczynnika przejmowania ciepła na powierzchni kuli. Maksymalny wzrost wymiany ciepła spowodowany wzrostem turbulencji przepływu był rzędu 30%.

14

PIV analysis of turbulent flow in a micro-channel

100%

Błoński S. , Kowalewski T. A.

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2007

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tom Vol. 45 nr 3

489-503

EN

Turbulent flow of water in a short 0.4 mm high micro-channel of an emulsifier is investigated experimentally using a micro-PIV technique and compared with numerical predictions. The micro-flow measurements are based on epi-fluorescence illumination and high-speed imaging. Velocity fields obtained from the measurements and direct numerical simulations indicate that flow turbulization is delayed and develops only at the outlet region of the micro-channel.

PL

W pracy przedstawiono analizę turbulentnego przepływu wody przez mikro-kanał emulsyfikatora. Wyniki uzyskane eksperymentalną techniką Cyfrowej Anemometrii Obrazowej (PIV - Particle Image Velocimetry) zaadoptowanej do pomiarów w mikroskali (micro-PIV) porównano z wynikami symulacji numerycznych przeprowadzonych zarówno poprzez bezpośrednie rozwiązanie równań Naviera-Stokesa (DNS - Direct Numerical Simulation), jak i wykorzystując hipotezę Reynoldsa uśredniającą fluktuacje prędkości i ciśnienia (model k-...). Część eksperymentalna pracy przeprowadzona została na unikalnym stanowisku pomiarowym bazującym na mikroskopii epifluorescencyjnej i szybkim obrazowaniu analizowanego przepływu. Charakterystyki przepływu wyznaczone eksperymentalnie i numerycznie symulacją DNS wykazały, że turbulizacja przepływu pojawia się dopiero w końcowym przekroju mikro-kanału, osiągając maksimum w kanale wylotowym emulsyfikatora.

15

Large-Eddy Simulations of Particle-laden Turbulent Jets

100%

Luniewski M. , Kotula P. , Pozorski J.

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2012

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tom Vol. 16, No 1-2

33-51

EN

The work presents an application of Large-Eddy Simulation (LES) for turbulent two-phase flows with dispersed particles. For the simulations of the continuous phase (fluid), an academic, finite volume LES solver was applied and customised. For comparison purposes, also a spectral solver was considered. The LES of fluid was used together with a Lagrangian module for the dispersed phase in the point-particle approximation, including the two-way momentum coupling between the phases. The particle solver has been further developed for parallel computations. The simulations of turbulent, particle-laden round jets were performed. The results for fluid and particle statistics were compared with available reference data.

16

Analysis of random cascade processes in the earth magnetospheric cusps

100%

Grzesiak M.

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2000

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tom Vol. 48, nr 2

241-261

EN

It is known that the invariance of a physical system subject to some groups of transformation may provide important information about dynamics of the system. This report deals with one of such invariances, namely the scaling invariance and its generalization - scale-similarity, which in the last few decades appeared to be very useful in the theory of fully developed turbulence. This concept is applied to turbulence in the high latitude magnetosphere.

17

Modeling of Rough Wall Boundary Layers with an Intermittency Transport Model

100%

Elsner W. , Warzecha P.

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2010

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tom Vol. 14, No 3

271-282

EN

The paper presents a new extension of the -Ret model to account for both the laminar-turbulent transition and the surface roughness. The new modeling approach takes into account the pressure gradient, turbulence intensity and roughness height and density. In the transition region both the intermittency transport equation and the momentum thickness Reynolds number Ret transport equation, supplemented by the correlation of Stripf et al. (2009) suitable for rough wall boundary layers are used. An additional modification of the SST turbulence model allows for modeling a full turbulent boundary layer over surfaces with sand roughness. A comprehensive validation of the new method using transitional and fully turbulent test cases was performed. Flat plate data with a zero and non-zero pressure gradient test case as well as a high pressure turbine blade case were used for this purpose The studies proved that the new modeling approach appeared to be sufficiently precise and enabled a qualitative prediction of the boundary layer development for the tested flow configurations.

18

Climate of long internal waves and resuspension on the coastal shelf

100%

Bogucki D. J. , Redekopp L. G.

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2008

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tom No. 50 (1)

5-21

EN

Observations of the shelf environment rarely associate internal solitary waves (ISWs) with the impact of their passage. An experiment observed during the Coastal Mixing and Optics 1996 (CMO '96), a sequence of long internal waves on a coastal shelf is reported, including both mode-1 and mode-2 waves, together with evidence related to the interaction of propagating ISWs and the benthic boundary layer. The observed ISW dynamics is shown to present a repetitive pattern or "climate cycle". The ISW-associated benthic signature described here occurs frequently (at least once a day) in the CMO '96 coastal area and suggests that ISWs under calm, summer-like conditions may have a decisive influence on the fate of near-bottom pollutants or biological processes in shelf regions.

19

Flow analysis in a channel with flexible vegetation using double-averaging method

100%

Righetti M.

Acta Geophysica

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2008

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tom Vol. 56, no. 3

801-823

EN

The paper addresses the problem of the resistance due to vegetation in an open channel flow, characterized by partially and fully submerged vegetation formed by colonies of bushes. The flow is characterized by significant spatial variations of velocity between vertical profiles that make the traditional approach based on time averaging of turbulent fluctuations inconvenient. A more useful procedure, based on time and spatial averaging (Double-Averaging Method) is applied for the flow field analysis and characterization. The vertical distribution of mean velocity and turbulent stresses at different spatial locations has been measured with a 3D Acoustic Doppler Velocimeter (ADV) for two different vegetation densities where fully submerged real bushes (salix pentandra) have been used. Velocity measurements were completed together with the measurements of drag exerted on the flow by bushes at different flow depths. The analysis of velocity measurements allows depicting the fundamental characteristics of both the mean flow field and turbulence. The experimental data show that the contribution of form-induced stresses to the momentum balance cannot be neglected. The mean velocity profiles and the spatially averaged turbulent intensity profiles allow inferring that the vegetation density is a driving parameter for the development of a mixing layer at the canopy top in the case of submerged vegetation. Moreover, the net upward turbulent momentum flux, evaluated with the methodology proposed by Lu and Willmarth (1973), appears to be damped for increased vegetation density; this finding can rationally explain the reduction of the suspended sediment transport capacity typically observed in free surface flows over a vegetated bed.

20

Turbulence in vegetated flows: Volume-average analysis and modelling aspects

100%

Souliotis D. , Prinos P.

Acta Geophysica

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2008

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tom Vol. 56, no. 3

894-917

EN

Two approaches for the modelling of turbulence in vegetated flows have been developed in the past. The “microscopic” approach which is straightforward but limited to simple cases and the “macroscopic” approach which is based on Volume Average Theory (VAT). In this study, aspects of Volume-Average (VA) analysis and modelling are investigated for turbulent vegetated flow using computed three-dimensional results from the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations around a representative vegetal element. In particular (a) the VA transport equations for k and ?, based on VAT, are properly derived, (b) the Boussinesq hypothesis for the VA quantities, employed in -<ε> turbulence models is tested, and (c) the values of the coefficients used in such turbulence models are assessed in comparison with those used in the classical turbulence models.