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Wyszukujesz frazę "two-phase flow" wg kryterium: Temat


Wyświetlanie 1-5 z 5
Tytuł:
Modeling of selected phenomena governing surface icing
Autorzy:
Sznajder, J.
Powiązania:
https://bibliotekanauki.pl/articles/248155.pdf
Data publikacji:
2013
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
icing
transport
air transport
simulation
two-phase flow
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.
Źródło:
Journal of KONES; 2013, 20, 2; 377-384
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analysing the cavitation phenomena in in-nozzle flows
Autorzy:
Vajda, B.
Žunič, Z.
Kegl, B.
Powiązania:
https://bibliotekanauki.pl/articles/247508.pdf
Data publikacji:
2010
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
two-phase flow
cavitation
injector nozzle
CFD
nodalisation analysis
Opis:
The geometry of the diesel fuel injection nozzle and fuel flow characteristics in the nozzle significantly affects the processes of fuel atomization, combustion and formation of pollutant emissions in diesel engine. To improve the process of fuel injection, CFD packages are used. Since CPU times are often high, partial models are used for the analysis. In presented paper the influence ,of different density of mesh on the cavitation phenomena is being analysed. The theoretical backgrounds of the cavitation occurrence presented in the first part of the paper are followed by the numerical analyses of two-phase flow in same simplified nozzle models. The numerical analyses are made using computation fluid dynamic (CFD) program Fire. The numerical analysis is made for two different types of fluid, diesel (D2) and biodiesel (B 100). Numerical analysis also includes various densities of meshes and their influence on results. The two-phase flow is analysed using a two-equation approach, where all conservation equations are solved for every phase. Numerical analysis results are compared to the experimental observations of the two-phase flow available from the literature. The results are compared for various meshes and various fluid types. The results show that higher pressure yields mode cavitation and point out the importance of mesh densities.
Źródło:
Journal of KONES; 2010, 17, 2; 475-482
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Determination of ice deposit shape and ice accretion rate on airfoil in atmospheric icing conditions and its effects on airfoil characteristics
Autorzy:
Sznajder, J.
Sieradzki, A.
Stalewski, W.
Powiązania:
https://bibliotekanauki.pl/articles/242499.pdf
Data publikacji:
2017
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
aerodynamics
two-phase flow
simulation of ice accretion
aircraft engineering
transport
vehicle
Opis:
Simulations of ice accretion on airfoil in icing conditions were conducted using ice accretion model implemented by authors in ANSYS FLUENT CFD solver. The computational model includes several sub-models intended for simulations of two-phase flow, determination of zones of water droplets impinging on the investigated surface, flow of water in a thin film on airfoil surface and heat balance in air-water-ice contact zone. The method operates in an iterative loop, which enables determination of effects of gradual deformation of aircraft surface on airflow over the surface, which has impact on distribution of collected water, flow of water film over the surface and local freezing rates. The implementation of the method in CFD solver made it necessary to complement the mathematical model of determination of local rates of deformation of aircraft surface with modification of computational mesh around the surface, which must conform, to the deformed surface. Results of simulated ice accretion on NACA 0012 airfoil were compared with results of experiment conducted in icing wind tunnel for a 420 s long process of ice accretion in steady-flow, steady angle-of-attack conditions. Close agreement of values and location of maximum ice thickness obtained in experiment and in the flow, simulations can be observed. For the airfoil deformed with ice, contour determination of its aerodynamic characteristics at several other angles of attack was conducted proving dramatic degradation of its aerodynamic characteristics due to ice deformation.
Źródło:
Journal of KONES; 2017, 24, 2; 271-278
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Determination of water collection on two- and three-dimensional aerodynamic surfaces in external two-phase flow in atmospheric conditions
Autorzy:
Sznajder, R.
Powiązania:
https://bibliotekanauki.pl/articles/244126.pdf
Data publikacji:
2016
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
flow simulations
aerodynamics
two-phase flow
simulation of ice accretion
aircraft engineering
transport
vehicles
Opis:
Simulations of two-phase flow cases consisting of air and water dispersed in atmosphere were conducted using ANSYS FLUENT solver. The computational model was built with the aim of determination of zones of water droplets impinging on the investigated surface, which is a first step towards simulations of ice accretion in flow conditions where super cooled water is present as dispersed phase. It follows Eulerian approach, currently most effective approach for determination of distribution of water collection on two- and three-dimensional surfaces. Dispersed water is treated as continuous phase and its transport equations are being solved along with air flow equations in the whole computational domain. There are two specific factors of this two-phase flow problem. One of them is ratio of air and water density, which is a cause of existence of two time scales in obtaining a numerical solution of this problem: one for convergence of air flow solution and another for solution of flow of dispersed water in the computational domain. This required development of a specific strategy in obtaining a numerical solution in some circumstances important in aerodynamics, especially at high angle of attack with flow recirculation zones on the wing. The other factor is relatively low concentration of water droplets in conditions important for atmospheric icing. The consequence of this is possibility of uncoupling of solution for both phases and narrowing the solution of the phase of dispersed water to a small region of non-uniformity of velocities of the dispersed phase. Results for two objects: an airfoil and helicopter tail rotor blade, exploiting the developed computational strategy will be presented.
Źródło:
Journal of KONES; 2016, 23, 1; 369-376
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Simulation of rime icing and its effects on aerodynamic characteristics of an airfoil
Autorzy:
Sznajder, J.
Powiązania:
https://bibliotekanauki.pl/articles/243475.pdf
Data publikacji:
2018
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
computational fluid dynamics
aerodynamics
two-phase flow
simulation of ice accretion
heat exchange
aircraft engineering
transport
vehicle
Opis:
A mathematical model for simulation of icing dedicated to simulation of ice accretion and its effects on aircraft aerodynamic characteristics in conditions of rime icing is presented. Pure rime icing occurs at lower temperatures than glaze icing and results in higher roughness of the surface of deposited ice. The model accounts for increased surface roughness, in terms of equivalent sand grain roughness, caused by deposited rime ice, which influences generation and dispersion of heat in the boundary layer. Increase of surface roughness is determined by analytical models created upon experimental data obtained in icing wind tunnels. Increased generation of heat is a result of increased tangential stress on the surface and is quantified in the temperature recovery factor determined numerically by a CFD solver. Effects of surface roughness on the intensity of forced convection are quantified by application of Colburn analogy between heat and momentum transfer in the boundary layer, which allows assessment of heat transfer coefficient for known friction coefficient, determined by CFD. The computational method includes determination of the surface distribution of mass of captured water in icing conditions. The model of freezing of captured water accounts for generation of heat due to latent heat of captured water droplets, temperature recovery in boundary layer and kinetic energy of captured droplets. The sinks of heat include forced convection, heating of super cooled droplets, conduction of heat through the ice layer and sublimation. The mathematical model is implemented as user-defined function module in ANSYS Fluent solver. The results include effects of deposited ice, including increased surface roughness on aerodynamic characteristics of an airfoil.
Źródło:
Journal of KONES; 2018, 25, 3; 437-443
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-5 z 5

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