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Numerical experiments for turbulent flows
Trefilík, Jiří ; Kozel, Karel ; Příhoda, J.
The aim of the work is to explorethe possibilities of modelling transonic flowsin the internal and external aerodynamics. Several konfigurationswere analyzed and calculations were performed using both inviscid and viscous models of flow. Viscous turbulent flows have been simulated using either zero equation algebraic Baldwin-Lomax model and two equation k - w model in its basic version and improved TNT variant. The numerical solution was obtained using Lax-Wendroff scheme in the MAcCormack from on structured non-ortogonal grids. Artificial dissipation was added to improve the numerical stability. Achieved results are compared with experimental data.
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Unsteady flows in convergent channel with stationary walls
Pořízková, P. ; Kozel, Karel ; Horáček, Jaromír
A current challenging question is a mathematical and physical description of the mechanism for transforming the airflow energy in human vocal tract (convergent channel) into the acoustic energy representing the voice source in humans. Goal of this work is to describe mathematical model of flow in 2D convergent channel which involves attributes of real flow as is “Coanda phenomenon”, vortex convection and diffusion, jet flapping etc. along with lower call on computer time, due to later extension in 3D channel flow.
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Numerical comparison of unsteady compressible viscous flow in convergent channel
Pořízková, P. ; Kozel, Karel ; Horáček, Jaromír
This study deals with a numerical solution of a 2D flows a compressible viscous fluids in a convergent channel for low inlet airflow velocity. Three governing systems – Full system, Adiabatic system, Iso-energetic system based on the Navier-Stokes equations for laminar flow are tested. The numerical solution is realized by finite volume method and the predictor-corrector MacCormack scheme with Jameson artificial viscosity using a gird of quadrilateral cells. This unsteady grid of quadrilateral cells is considered in the form of conservation laws using Arbitrary Lagrangian-Eulerian method. The numerical results, acquired from a developed program. Are presented for inlet velocity ûĄ = 4,12ms-1 and Reynolds number Re = 4 x 103.
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Numerical experiment of compressible flow in convergent channel- pressure spectral analysis
Pořízková, P. ; Kozel, Karel ; Horáček, Jaromír
This study deals with a numerical solution of a 2D unsteady flow of a compressible viscous fluid in a channel for low inlet airflow velocity. The unsteadiness of the flow is caused by a prescribed periodic motion of a part of the channel wall with large amplitudes, nearly closing the channel during oscillations. The flow is described by the system of Navier-Stokes equations for laminar flows. The numerical solution is implemented using the finite volume method (FVM) and the predictor-corrector MacCormack scheme with Jameson artificial viscosity using a gird of quadrilateral cells. The numerical results of unsteady flows in the channel are presented for inlet velocity uĄ = 4.12m/s, inlet Reynolds number ReĄ = 4481 and wall motion frequency 100Hz.
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Boiling two phase flow in a coil-shaped duct combined with heat conduction in solid body
Novák, Aleš ; Hrubý, Jan ; Kozel, Karel
Forced-convection boiling in a coil-shaped duct heated from the outer side has an advantage of enhancing the heat transfer and reducing the risk of boiling crisis by pushing the liquid against the outer wall due to centrifugal force. Because of the large heat fluxes, the heat conduction in the solid walls is taken into account. The model is based on differential equations of mass, momentum and energy conservation. In the resulting quasi-1D model, the liquid and vapor phases are allowed to flow at different velocities. The model simulates a laboratory steam generator built in Institute of Thermomechanics AS CR.
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On the validation study devoted to stratified atmospheric flow over an isolated hill
Sládek, Ivo ; Kozel, Karel ; Jaňour, Zbyněk
The paper deals with description of the validation model, °ow conditions and mainly it presents some numerical results. Reference and input data for the validation study are based on work of Eidsvik [3]. The mathematical model is based on the system of RANS-equations closed by two-equation k ¡ " turbulence model together with wall functions. The thermal strati¯cation is modeled using transport equation for the potential temperature. The ¯nite volume method and the explicit Runge{Kutta time integration method are utilized for the numerics.
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Numerical simulation of turbulent compressible flows
Trefilík, J. ; Kozel, Karel ; Příhoda, Jaromír
The work deals with the development of numerical methods for simulation of subsonic and transonic turbulent flow over the DCA 20% profile in a cascade configuration with a zero stagger angle. Numerical results for compressible subsonic flow for Mach numbers M1 = 0.35 and 0.5 are compared with respekt to two different used turbulence models. A special attention was paid to modelling of the separation region near the trailing edge of profile.
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