Wyniki wyszukiwania - BazTech

1

Simulation of rime icing and its effects on aerodynamic characteristics of an airfoil

Sznajder J.

Journal of KONES

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2018

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Vol. 25, No. 3

437--443

EN

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.

2

Determination of ice deposit shape and ice accretion rate on airfoil in atmospheric icing conditions and its effects on airfoil characteristics

Sznajder J., Sieradzki A., Stalewski W.

Journal of KONES

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2017

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Vol. 24, No. 2

271--278

EN

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.

3

Determination of water collection on two- and three-dimensional aerodynamic surfaces in external two-phase flow in atmospheric conditions

Sznajder R.

Journal of KONES

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2016

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Vol. 23, No. 1

369--376

EN

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.

4

Symulacja oblodzenia w strumieniu poddźwiękowym

Sierputowski P., Rewucki P.

Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska

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2000

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nr 13

305-310

PL

Badanie zjawiska oblodzenia skrzydeł samolotu oparto na odwrotnych założeniach. Zamiast modelować warunki zewnętrzne, symulowano zjawisko, schładzając model płata. Model z uzyskanymi formami oblodzenia zbadano w tunelu aerodynamicznym w celu wyznaczenia charakterystyk aerodynamicznych. Wyniki potwierdziły znaczny, negatywny wpływ oblodzenia na własności aerodynamiczne skrzydła, jak i zbieżność z wynikami drogich badań w tunelach stratyfikowanych termicznie.

EN

Studying ice accretion on airplane wings has been based on opposite assumptions. Instead of modeling atmospheric conditions, ice accretion has been simulated by freezing a wing model. The model with obtained ice forms has been then tested for aerodynamic characteristics. Results confirmed serious, negative influence of ice accretion on characteristics and also showed convergence with results of expensive test with the use of thermal wind tunnels.