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1
Content available Nanovortex evolution in entrance part of the 2D open type long nanocavity
Kordos A., Kucaba-Piętal A.
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2018
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Vol. 66, nr 2
119--125
EN
Non-equilibrium molecular dynamics method (NEMD) is applied to investigate a formation process of water nanovortex in 7 nm wide nanocavity (aspect ratio of which was equal to 3.6). The flow in the nanocavity was induced by Poiseuille 2D water nanoflow in a main nanochannel, to which the nanocavity is situated perpendicularly. The wall of main channel and the nanocavity is made from quartz. Flow is induced by applying constant force to molecules inside the main channel. Based on NEMD simulation data, the sequence of images representing water velocity vector fields was obtained at constant time intervals equal to 1 ns, which shows vortex formation mechanism. Flow field images analysis indicates that the shape and centre position of the nanovortex vary slightly each nanosecond, nevertheless, the structure remains stable in the flow field at the entrance to the nanocavity.
2
Content available Influence of slim obstacle geometry on the flow and heat transfer in microchannels
Kmiotek M., Kucaba-Piętal A.
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2018
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Vol. 66, nr 2
111--118
EN
This paper presents a computational study on hydrodynamic and heat transfer characteristics of the laminar flow inside a rectangular 2D microchannel of height H, which includes a slim micro obstacle of height h and width w placed on the lower wall of the channel. The Reynolds number varies between 20 and 200. Three different values of height h and two different shapes of the slim obstacles: triangular and rectangular one, are considered. Thus, a total of 24 geometrical configurations of fluid flow are analyzed. Fluid flow equations are solved using the commercial CFD package of ADINA R&D, Inc. 9.1. Detailed analysis of the fluid velocity field and streamlines is carried out to investigate the flows in recirculation zone behind the obstacle. Results obtained show that the rectangular obstacle caused larger vortex formation in fluid flow. For flows with larger value of the (h/H) ratio, an increase in the value of loss coefficient factors is observed. Meanwhile, the increased Reynolds number causes the vortex zone behind the rectangular obstacle to be larger than behind the triangular one.
3
Content available Numerical investigation of local heat transfer distribution on surfaces with a non-uniform temperature under an array of impinging jets with various nozzle shapes
Marzec K., Kucaba-Piętal A.
Journal of Theoretical and Applied Mechanics
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2017
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Vol. 55 nr 4
1313--1324
EN
Numerical calculations of heat transfer characteristics of an impingement cooling system with a non-uniform temperature on a cooled surface using ANSYS CFX have been performed. The influence of a surface heat flux qw(x) and a nozzle shape on the Nusselt number distribution on the cooled surface has been studied. The setup consisted of a cylindrical plenum with an inline array of ten impingement jets. Cylindrical, convergent divergent shapes of nozzles and linear temperature distribution on the cooled surface have been considered for various heat fluxes qw (x). Results indicate that geometry of the cylindrical nozzles resulted in the highest Nusselt numbers along the cooled surface. The line of the averaged Nusselt number has a trend to increase in the direction of the flow for the cooling system with increasing values of the surface heat flux q(x). This tendency can be observed for all presented shapes of jets. On the other hand, for decreasing functions of the heat flux qw (x), the Nusselt number distribution is more uniform. It can be observed for all types of nozzles. Very similar values of the Nusselt number occur especially for the non-uniform heat flux 5000-2500W/m². For constant values of the heat flux q(x) = 5000W/m², the line of the average Nusselt number has a trend to increase slightly in the direction of the flow. Numerical analysis of different mesh density results in good convergence of the GCI index, what excludes mesh size dependency. The presented study is an extension of the paper (Marzec and Kucaba-Piętal, 2016) and aims at answering the question how the Nusselt number distribution on the cooled surface is affected by various geometries of nozzles for a non-uniform surface heat flux qw (x).
4
Content available Squeeze flow modeling with the use of micropolar fluid theory
Kucaba-Piętal A.
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2017
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Vol. 65, nr 6
927--933
EN
The aim of this paper is to study the applicability of micropolar fluid theory to modeling and to calculating tribological squeeze flow characteristics depending on the geometrical dimension of the flow field. Based on analytical solutions in the lubrication regime of squeeze flow between parallel plates, calculations of the load capacity and time required to squeeze the film are performed and compared – as a function of the distance between the plates – for both fluid models: the micropolar model and the Newtonian model. In particular, maximum distance between the plates for which the micropolar effects of the fluid become significant will be established. Values of rheological constants of the fluids, both those experimentally determined and predicted by means of using equilibrium molecular dynamics, have been used in the calculations. The same analysis was performed as a function of dimensionless microstructural parameters.
5
Fluid flows in narrow channels
Walenta Z. A., Kucaba-Piętal A., Peradzyński Z.
Journal of Technical Physics
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2009
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Vol. 50, no 1
65-70
EN
We present the results of some Direct Monte-Carlo Simulations of a simple, monoatomic gas flows and also some Molecular Dynamics simulations of the flows of water through very narrow channels (plane Poiseuille flows). The main conclusion from the results is that the roughness of the walls of such narrow channels, even if it is of molecular size, influences very strongly the flow of water, introducing large velocity fluctuations and sometimes even stopping the flow.
6
Content available remote Molecular dynamics computer simulation of water flows in nanochannels
Kucaba-Piętal A., Walenta Z.A., Peradzyński Z.
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2009
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Vol. 57, nr 1
55-61
EN
The work presents the results of the simulations of water flows through narrow channels (Poiseuille flows) performed using the molecular dynamics method, for two different channel widths (equal to 5 and 10 diameters of the water molecule) and for two different materials of the channel walls (copper and quartz). In the simulations, physical properties of the materials and their electrostatic interactions were considered. The obtained results are compared with the analytical solutions for a micropolar fluid flow taking account of the experimentally obtained rheological constants of water.
7
Wstępne obliczenia wpływu mikrostruktury mazi stawowej na trybologie biołożyska
Kucaba-Piętal A.
Systems : journal of transdisciplinary systems science
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2006
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Vol. 11, nr 1
197-203
EN
The micropolar fluid theory was applied to answer the question how the microstructure dependence of synovial fluid influences on tribological quantities of biobearing. The squeezing flow of micropolar fluid between two parallel circular plates was considered, as an approximation for the lubrication in the weight bearing synovial joint under conditions where the area of contact is maximum such as in standing and jumping. The generalised Reynolds equation to describe the flow fields was applied. The calculations show that the load bearing capacity and time of approach depend strongly on micrustucture of synovial fluid. Obtained results are in agreement with clinical observations, which indicates that proposed approach based on micropolar fluid mechanics can be applied to modeling of synovial fluid.
8
Content available remote Microchannels flow modelling with the micropolar fluid theory
Kucaba-Piętal A.
Bulletin of the Polish Academy of Sciences. Technical Sciences
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2004
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Vol. 52, nr 3
209-214
EN
The aim of this paper is to study the applicability of the theory of micropolar fluids to modelling and calculating flows in microchannels depending on the geometrical dimension of the flow field. First, it will be shown that if the characteristic linear dimension of the flow becomes appropriately large, the equations describing the micropolar fluid flow can be transformed into Navier-Stokes equations. Next, Poiseuille flows in a microchannel is studied in detail. In particular, the maximal cross-sectional size of the channel for which the micropolar effects of the fluid flow become important will be established. The experimentally determined values of rheological constants of the fluid have been used in calculations.
9
Content available Flows in microchannels
Kucaba-Piętal A., Walenta Z., Peradzyński Z.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2001
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Vol. 5, No 2
179-189
EN
The aim of this paper is to present a survey of the results for the flows of simple gases and liquids with substructure through narrow channels, obtained with the Direct Monte-Carlo and Molecular Dynamics Simulation methods.
10
Content available remote Liqiud crystalline properties of synovial fluid
Szwajczak E., Kucaba-Piętal A., Telega J. J.
Engineering Transactions
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2001
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Vol.49, iss.2/3
315-358
EN
The main aim of this paper is to discuss the liquid crystalline concept of synovial fluid. This new concept was proposed by Kupchinov [30] and was next developed in [31, 32, 58]. According to these papers, the crystalline structure of synovia ensures very low friction coefficient in human (and animal) joints. Experimental data in favour of crystalline structure of synovia have been discussed. Mathematical model of such fluid, based on Eringen's theory [14, 15], has been advanced.
11
Content available remote Analiza przepływu w mikroszczelinie na gruncie teorii płynów mikropolamych
Kucaba-Piętal A., Migoun N.
Zeszyty Naukowe. Cieplne Maszyny Przepływowe - Turbomachinery / Politechnika Łódzka
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2000
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nr 117, vol. 1
47-52
PL
W pracy przedstawiono wyniki numeryczne dotyczące przepływu płynu mikropolamego w wąskiej szczelinie między równoległymi płytkami, gdy jedna z nich zbliża się do drugiej (squeezing flow). Dzięki uzyskanej analitycznej postaci rozwiązania [3] przeprowadzono analizę wpływu wartości wektora mikrorotacji na ściankach na wielkości hydrodynamiczne i trybologiczne (nośność, czas zbliżenia) charakteryzujące przepływ w łożysku. Niezbędne obliczenia uzyskano za pomocą programu Mathcad 7.
EN
In the present paper we study the narrow squeeze film of micropolar fluid between two plates. Thanks the analytical solution obtained [3] we examine the effects of non-zero values of microrotation vector on the walls on hydrodynamic and tribological characteristics of the flow.
12
Content available remote Recent advances in solvers for nonlinear algebraic equations
Dent D., Paprzycki M., Kucaba-Piętal A.
Computer Assisted Mechanics and Engineering Sciences
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2000
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Vol. 7, No. 4
493-505
EN
In this paper the performance of four solvers for systems of nonlinear algebraic equations applied to a number of test problems with up to 250 equations is discussed. These problems have been collected from research papers and from the Internet and are often recognized as ``standard'' tests. Solver quality is assessed by studying their convergence and sensitivity to simple starting vectors. Experimental data is also used to categorize the test problems themselves. Future research directions are summarized.
13
Content available Modelling of lubrication mechanism in human joints using micropolar fluid theory
Kucaba-Piętal A.
Journal of Theoretical and Applied Mechanics
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1999
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nr 3
593-606
EN
The paper aims at presentation of modelling of human joints withinthe framework micropolar fluid theory. A mathematical model of two converging spheres represents the biobearings. In the model the boundaries of the spheres are considered to be rigid and the lubricant (synovial fluid) is represented by a micropolar fluid. Basing on the asymptotic solution obtained for squeezing motion of converging spheres (Kucaba-Piętal, 1999), the velocity vector in a gap is determined and asymptotic values of the forceare calculated. The effects or rheological constants variation on the flow field in a gap are disscussed.
PL
Przedmiotem pracy jest opis smarowania w stawach na bazie teorii płynów mikropolarnych. Rozpatrywany jest ruch ciśnieniowy (squeezing). Staw (biodrowy) modelowany jest za pomocą układu dwóch kul o twardych powierzchniach. Zakłada się, że przepływ opisany jest równaniem Stokesa. Na bazie rozwiązania asymptotycznego obliczono rozkład prędkości w szczelinie stawowej oraz wartość działającej asyptotycznie siły. Stałe reologiczne mazi stawowej oszacowano na podstawie danych eksperymentalnych.
14
Content available Flow past a sphere moving towards a wall in micropolar fluid
Kucaba-Piętal A.
Journal of Theoretical and Applied Mechanics
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1999
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nr 2
301-318
EN
The paper presents the first "exact" solution to the problem of creeping flow past a sphere mowing towards a wall in micropolar fluid. The analytical-numerical method is presented, that is a development of the boundary collocation technique previously used for solving many corresponding problems for a Newtonian fluid. The initial study of the method has been carried out and the results for a force acting on a sphere compared with their counterparts for a Newtonial fluid are presented. It is worth while to note that the drag force on a sphere depends on material constants of the micropolea fluid and the distance from the wall.
PL
Rozwiązane zostało zagadnienie wyznaczenia pola przepływu i działającej siły na cząstkę kulistą poruszającą się w kierunki ścianki w płynie mikropolarnym. Skonstruowano metodę analityczno-- --numeryczną w oparciu o metodę kolokacji. Rozpatrzono przepływ quasistacjonarny w przybliżeniu Stokesa.
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