Temat: two-phase flow - Prolib Integro

Skocz do pozycji: 1.

Tytuł:: Numerical study of a polydisperse two-phase jet
Badania numeryczne polidyspersyjnej strugi dwufazowej
Autorzy:: Barata, J.
Perestrelo, N.
Tematy:: turbulent dispersion
two-phase flow; Pokaż więcej
Wydawca:: Sieć Badawcza Łukasiewicz. Przemysłowy Instytut Motoryzacji
Powiązania:: https://bibliotekanauki.pl/articles/263159.pdf Link otwiera się w nowym oknie
Opis:: Low emissions gas turbine combustors will demand fuel injection systems that are efficient in the accomplishment of the mixing of fuel and air in the shortest possible residence time. This paper describes a computational study of a polydisperse two-phase turbulent jet, which is the basic configuration to analyze how the various parameters influence the size distribution and the dispersion of the droplets in the injection process. An Eulerian frame for the for the gas phase was used in conjunction with a Lagrangian approach to describe both interphase slip and turbulence on particle motion. Good agreement of the computations with the experimental data is obtained for both the gas and the particles turbulence modulation and anisotropy effects were introduced and were found to be very important to the successful performance of the computational method. The exchange of monumentum and turbulence energy between the two phases was shown to play a decisive role on the flow development. The predictions confirmed the measurements and showed that the particles do not follow the turbulent gas flow, but they affect it significantly. Considerably high values of the radial velocity were detected around the centerline far from the jet exit where the velocity of the particles lags that of the fluid, that seems to be associated with the effect of shear induced lift forces.
Przedstawiono studium komputerowe polidyspersyjnej dwufazowej strugi turbulentnej, które jest bazą wyjściową do oceny wpływu różnych parametrów na rozkład średnicy kropel podczas wtrysku do ośrodka gazowego. Wykorzystano Eulerowską analizę do fazy gazowej oraz analizę Lagrange'a do obliczania drogi cząstek. Uzyskane wyniki obliczeniowe są zgodne z eksperymentalnymi. Turbulencja i niejednorodność średnic kropel mają istotny wpływ na rozwój strumienia. Stwierdzono także, że składowe promieniowe prędkości z daleka od otworu rozpylacza uzyskują wysokie wartości.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: CFD simulation as a tool for the identification of the manifold element reaction to pressure pulsations excitation (one- and two-phase flow)
Autorzy:: Cyklis, P.
Kantor, R.
Tematy:: pressure pulsations
two-phase flow
CFD; Pokaż więcej
Wydawca:: Politechnika Gdańska
Powiązania:: https://bibliotekanauki.pl/articles/1955745.pdf Link otwiera się w nowym oknie
Opis:: The periodicity of compressor operation is a source of pressure pulsations in volumetric compressor manifolds. An analysis of pressure pulsations is important for several reasons. The Helmholtz model, applied in all commercial programs offered by the companies professionally dealing with damping pressure pulsations, contains numerous simplifying assumptions; a straight pipe segment, with an ideal gas isentropic flow assumption, substitutes each element of the piping system. In many cases this model is insufficient. The existing experimental methods could not be used in the design of a muffler. The aim of this paper is to show a new method to identify an arbitrary fragment of a manifold, i.e. a method of identification of the appropriate complex transmittance matrix elements using CFD simulation. This method allows the liquid phase dispersed in the compressed gas and non ideal gas as a working medium to also be considered. The most important conclusion of this work is that identification of acoustic element parameters in the manifold, based on multi-dimensional simulation model, is feasible. The author obtained much better results from the developed method than those yielded by the classic Helmholtz model. A comparison between pure gas and gas with oil contamination is also shown in the paper.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Turbulent mixing of a cloud wit h the enviranment: two-phase evaporating flow. Numerical simulations, laboratory experiments and field measurements
Turbulencyjne mieszanie chmury z otoczeniem jako przepływ dwufazowy z parowaniem. Symulacje numeryczne, eksperymenty laboratyjne i pomiary in situ
Autorzy:: Malinowski, S. P.
Tematy:: two-phase flow
turbulent mixing
cloud interface; Pokaż więcej
Wydawca:: Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Powiązania:: https://bibliotekanauki.pl/articles/279222.pdf Link otwiera się w nowym oknie
Opis:: A brief overview of numerical simulations, laboratory experiments and in-situ measurements aimed at investigation of the cloud-clear air interfacial-mixing, conducted in recent years at the Institute of Geophysics, University of Warsaw is presented. The most interesting finding from these studies is that the evaporative cooling at the interface separating cloudy and clear filaments results in density differences in scale of centimeters. This effect influences smallest scales of turbulent motions through production of TKE by buoyancy forces and makes the small-scale turbulence anisotropic.
W artykule zawarto zwarty przegląd symulacji numerycznych, eksperymentów prowadzonych w laboratorium oraz pomiarów in situ, których celem było badanie mieszania turbulencyjnego na granicy chmury z nienasyconym otoczeniem. Badania te prowadzono w Instytucie Geofizyki Uniwersytetu Warszawskiego. Najciekawszym wynikiem tych prac jest pokazanie wpływu, jaki ma parowanie wody chmurowej na granicy chmury na dynamikę turbulencji w małych skalach. Parowanie powoduje powstanie lokalnych różnic gęstości o skali przestrzennej rzędu centymetrów. Działanie sił wyporu prowadzi do produkcji drobnoskalowej turbulencji. Ponieważ wyróżniony jest kierunek pionowy, turbulencja ta jest anizotropowa.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Impact of a discretization scheme on an autoignition time in LES of a reacting droplet-laden mixing layer
Autorzy:: Stempka, J.
Kuban, L.
Tyliszczak, A.
Tematy:: autoignition process
two-phase flow
mixing layer; Pokaż więcej
Wydawca:: Instytut Podstawowych Problemów Techniki PAN
Powiązania:: https://bibliotekanauki.pl/articles/38621390.pdf Link otwiera się w nowym oknie
Opis:: We analyse an autoignition process in a two-phase flow in a temporally evolving mixing layer formed between streams of a cold liquid fuel (heptane at 300 K) and a hot oxidizer (air at 1000 K) flowing in opposite directions. We focus on the influence of a discretization method on the prediction of the autoignition time and evolution of the flame in its early development phase. We use a high-order code based on the 6th order compact difference method for the Navier–Stokes and continuity equations combined with the 2nd order Total Variation Diminishing (TVD) and 5th order Weighted Essentially Non-Oscillatory (WENO) schemes applied for the discretization of the advection terms in the scalar transport equations. The obtained results show that the autoignition time is more dependent on the discretization method than on the flow initial conditions, i.e., the Reynolds number and the initial turbulence intensity. In terms of mean values, the autoignition occurs approximately 15% earlier when the TVD scheme is used. In this case, the ignition phase characterizes a sharp peak in the temporal evolution of the maximum temperature. The observed differences are attributed to a more dissipative character of the TVD scheme. Its usage leads to a higher mean level of the fuel in the gaseous form and a smoother distribution of species resulting in a lower level of the scalar dissipation rate, which facilitates the autoignition process.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: Formation of droplets in microfluidic cross-junctions at small Capillary numbers: breakdown of the classical squeezing regime
Autorzy:: Korczyk, Piotr
Kurniawian, Tetuko
Sahebdivani, Mahsa
Zaremba, Damian
Garstecki, Piotr
Van Steijn, Volkert
Błoński, Slawomir
Wydawca:: Elsevier
Cytata wydawnicza:: Tetuko Kurniawan, Mahsa Sahebdivani, Damian Zaremba, Slawomir Blonski, Piotr Garstecki, Volkert van Steijn, Piotr M. Korczyk, Formation of droplets in microfluidic cross-junctions at small capillary numbers: Breakdown of the classical squeezing regime, Chemical Engineering Journal, Volume 474, 2023, 145601,https://doi.org/10.1016/j.cej.2023.145601. (https://www.sciencedirect.com/science/article/pii/S1385894723043322)
Opis:: Two decades of research on droplet formation in microchannels have led to the widely accepted view that droplets form through the squeezing mechanism when interfacial forces dominate over viscous forces. The initially surprising finding that the volume of the droplets is insensitive to the relative importance of these two forces is nowadays well understood from the constrained deformation of the droplet interface during formation. In this work, we show a lower limit of the squeezing mechanism for droplets produced in microfluidic cross-junctions. Below this limit, in the leaking regime, which was recently discovered for droplets produced in T-junctions, the volume of the produced droplets strongly depends on the relative importance of interfacial and viscous forces, as captured by the capillary number. We reveal a fundamental difference in the mechanisms at play in the leaking regime between T- and cross-junctions. In cross-junctions, the droplet neck elongates substantially, and unlike the case of the T-junction, the magnitude of this elongation depends strongly on the value of the capillary number. This elongation significantly affects the final droplet volume in a low capillary number regime. Generalizing the classical squeezing law by lifting the original assumptions and incorporating both identified mechanisms of leaking through gutters and neck elongation, we derive a model for droplet formation and show that it agrees with our experiments.
First Team grant (POIR.04.04.00-00-3FEF/17-00) of the Foundation for Polish Science, co-financed by the EU under the Smart Growth Operational Program The European Union’s Horizon 2020 research and the innovation programme under the Marie Skłodowska-Curie grant agreement No. 711859 The financial resources for science in the years 2017-2022, awarded by the Polish Ministry of Science and Higher Education for implementing an international co-financed project The National Science Centre Poland, funding based on decision 2018/30/A/ST4/00036, Maestro 10 The National Science Centre Poland, 2019/34/H/NZ6/00699
Dostawca treści:: Repozytorium Centrum Otwartej Nauki

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Skocz do pozycji: 6.

Tytuł:: Spatial distribution and settling velocity of heavy particles in synthetic turbulent ﬁelds
Autorzy:: Łuniewski, M.
Pozorski, J.
Tematy:: two-phase ﬂow
heavy particles
turbulent dispersion; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Powiązania:: https://bibliotekanauki.pl/articles/175528.pdf Link otwiera się w nowym oknie
Opis:: We analyse numerically the motion of small inertial particles, subject to gravity, in two simple velocity ﬁelds: two-dimensional cellular ﬂow, and a three-dimensional ﬂow being the superposition of random Fourier velocity modes. The latter, also known as the kinematic simulation or synthetic turbulence, has often been applied in various studies, including those aiming to predict particle dispersion. The interplay of the particle inertia and the acceleration of gravity has non-trivial consequences for trajectories of particles and their spatial distribution, known as a preferential concentration. Also, we compute the average settling velocity of particles in function of their inertia and the number of ﬂuid velocity modes used in simulations. The present paper aims to study these efects, as the synthetic turbulence represents an interesting option for subﬁlter modeling in particle-laden large-eddy simulation.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Numerical Simulation of One-Dimensional Two-Phase Flow in Porous Media
Autorzy:: Szymkiewicz, A.
Tematy:: two-phase flow
porous media
numerical methods; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Instytut Budownictwa Wodnego PAN
Powiązania:: https://bibliotekanauki.pl/articles/241426.pdf Link otwiera się w nowym oknie
Opis:: The flow of two immiscible fluids in porous media is described by two coupled non-linear partial differential equations of the parabolic type. In this paper a numerical algorithm to simulate one-dimensional two-phase flow is presented. Cell-centered finite volume method and a generalized two-level scheme with weighting parameter are applied for the discretization in space and time, respectively. The performance of the algorithm is tested for different values of the weighting parameter in the time-discretization scheme and for various methods of approximation of the average conductivities between two adjacent gridblocks. The results are compared with an analytical solution for the horizontal flow and with a reference numerical solution performed on a dense grid for the vertical flow.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Modeling of selected phenomena governing surface icing
Autorzy:: Sznajder, J.
Tematy:: icing
transport
air transport
simulation
two-phase flow; Pokaż więcej
Wydawca:: Instytut Techniczny Wojsk Lotniczych
Powiązania:: https://bibliotekanauki.pl/articles/248155.pdf Link otwiera się w nowym oknie
Opis:: Atmospheric icing poses a threat for safety in many areas of transport, especially in air transport and exerts harmful impact on operation of external sensors and mechanisms of aircraft, ships and land vehicles. In order to investigate phenomena leading to ice accretion on sensitive parts of objects exposed to icing conditions numerical simulation models are in use. These models are typically composed of submodels dealing with a fragment of the complex phenomenon of ice accretion and its interaction with external flow. A practical approach to simulation of icing process is to divide it into three problems being solved interactively: 1) simulation of two-phase flow of air and dispersed supercooled water and determination of distribution of mass of water hitting the object’s surface, 2) determination of conditions on the surface collecting supercooled water from the external flow and simulation of freezing and water film flow, and 3) modification of computational grid as a consequence of change of shape of the surface with deposits of ice. A simulation system directed at investigation of atmospheric icing on moving object is being developed as an extension of capabilities of a commercial CFD code ANSYS FLUENT. Solutions of two-phase flow of air and dispersed water with specific boundary conditions enabling the determination of distribution of water hitting the surface, as well as results of modelling of water film flow on the surface will be presented. The system of equations describing the transport of the dispersed water consists of the continuity and momentum equations. It is assumed, that interactions between the phases are onedirectional, i.e. the air flow influences the water droplet flow and not vice-versa. It is also assumed that the water film velocity distribution is linear in direction normal to surface. This way, both phenomena are being described with first order partial differential equations with respect to space and time and the solution approaches may be similar.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 9.

Tytuł:: Application of stereology for assessment of two-phase flow structures
Autorzy:: Masiukiewicz, M.
Ulbrich, R.
Zając, D.
Tematy:: stereological analysis
two-phase flow pattern
pattern recognition; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Powiązania:: https://bibliotekanauki.pl/articles/175510.pdf Link otwiera się w nowym oknie
Opis:: This paper describes a method for two-phase flow structures evaluation of gas-liquid mixture based on theoretical assumptions for the stereology in materials science. This assessment is based on the analysis of digital images, obtained with a high-speed camera. The bright field technique was used for process visualization. The images obtained during the visualisation were, in fact, projections of the structures. For the given recording conditions, the stereological analysis applied was based on the linear method and on the method of random and directed secants. The new methods of determining important parameters of two-phase flow were proposed on the basis of collected data. The parameters are as follows: the volume fraction, the interfacial area, the number of objects in one of the phases of the mixture and two other structural parameters of the selected two-phase fluid obtained from the analysis of the two-dimensional image (average length of chords for projected objects, average free distance for convex shapes from the projection).
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 10.

Tytuł:: Complexity of two-phase flow dynamics using the recurrence and high speed video analysis
Autorzy:: Mosdorf, Romuald
Rafałko, Gabriela
Zaborowska, Iwona
Dzienis, Paweł
Grzybowski, Hubert
Tematy:: instabilities
two-phase flow
recurrence analysis
image analysis; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czasopisma i Monografie PAN
Powiązania:: https://bibliotekanauki.pl/articles/59111939.pdf Link otwiera się w nowym oknie
Opis:: During flow boiling in a system with small (mini/micro) channels, several instabilities may occur at the same time, which overlap each other such a phenomenon complicates the analysis of boiling dynamics. The above mentioned processes cause that the fluctuation of recorded signals occur on various time scales. Although many criteria for the stability of two-phase flows are available, their practical application is limited (they need many recorded parameter of two phase flow). Methods which we are looking for should allow flow pattern identification based on a small number (or single) recorded signals. The paper presents a new approach to the recurrence plot method combined with Principal Component Analysis and Self-Organizing Map analysis. The single signal of pressure drop oscillations has been analyzed and used for flow pattern identification. New method of correlation analysis of flow patterns on video frames has been presented and used for flow pattern identification. The obtained results show that pressure drop oscillations and high speed video contain enough information about flow pattern for flow pattern identification.
Dostawca treści:: Biblioteka Nauki

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