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Rotating Rayleigh-Benard Convection

100%

Majchrowski W. , Tuliszka-Sznitko E.

tom Vol. 12, No 3-4

267-272

In the this paper our results on the natural convection in an enclosed rotating cavity are presented. We have focused our attention on the influence of the Rayleigh and Taylor numbers on the flow structure. DNS computations have been performed for the geometry of aspect ratio L=9 and curvature parameter Rm=1.5.

Some remarks on modelling and simulation of turbulence

85%

Drobniak S. , Bogusławski A. , Tyliszczak A.

tom Vol. 46 nr 2

243-256

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

Praca przedstawia współczesny stan wiedzy w dziedzinie numerycznego modelowania turbulencji ze szczególnym uwzględnieniem metody LES (ang. Large Eddy Simulation). Przedstawiono ograniczenia modeli turbulencji typu RANS, opartych o uśrednione w czasie równania Reynoldsa oraz wskazano perspektywy deterministycznego ujęcia turbulencji z użyciem metod DNS (ang. Direct Numerical Simulation). Wykazano również, że możliwości najszybszych dostępnych obecnie komputerów ograniczają możliwe obszary aplikacji DNS do przepływów o stosunkowo niskich liczbach Reynoldsa. Następnie sformułowano podstawowe zależności dla metod LES i wskazano ich perspektywiczne znaczenie dla inżynierskiego modelowania przepływów turbulentnych.

Numerical Investigations of Taylor-Couette Flow Using DNS/SVV Method

70%

Tuliszka-Sznitko E. , Kiełczewski K.

tom Vol. 21, No. 4

211--219

In the paper the authors present the results obtained during a numerical investigation (Direct Numerical Simulation/ Spectral Vanishing Viscosity method – DNS/SVV) of a Taylor-Couette flow, i.e. the flow between two concentric disks and two concentric cylinders. The Taylor-Couette flow is one of paradigmatical systems in hydrodynamics, widely used for studying the primary instability, pattern formation, transitional flows and fully turbulent flows. Simultaneously, the flows in rotating cavities appear in numerous machines in the field of mechanics and chemistry, e.g., in cooling systems of gas turbines and axial compressors. In the paper, attention is focused on the laminar-turbulent transition region of the Taylor-Couette flow. The main purpose of the computations is to investigate the influence of different parameters (the aspect ratio, the end-wall boundary conditions, temperature gradient) on the flow structure and on flow characteristics.

Large Eddy Simulation of transitional flows in rotor/stator cavity

51%

Tuliszka-Sznitko E. , Zielinski A. , Majchrowski W.

tom Vol. 61, nr 2

95-120

An algorithm for the Large Eddy Simulation, with subgrid modelling based on the spectral Chebyshev-Fourier approximation, is developed for the investigation of 3D turbulent and transitional non-isothermal flows within a rotor/stator cavity. In LES we use a version of the dynamic Smagorinsky eddy viscosity model in which the Smagorinsky coefficient at a given position x depends on the history of the flow along the fluid particle pathline. Computations are based on the efficient pseudo-spectral Chebyshev-Fourier method (S. HUGUES, A. RANDRIAMAMPIANINA, An improved projection scheme applied to pseudospectral methods for the incompressible Navier-Stokes equations, Int. J. Numer. Methods Fluids, 28, 501, 1998). To demonstrate the effectiveness of the proposed algorithm, computations were performed for the cavity of aspect ratio L = 5 and results were compared favorably with the experimental data taken from literature.