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Modelling of subcritical free-surface flow over an inclined backward-facing step in a water channel
Příhoda, Jaromír ; Zubík, P. ; Šulc, J. ; Sedlář, M.
The contribution deals with the experimental and numerical modelling of subcritical turbulent flow in an open channel with an inclined backward-facing step. The step with the inclination angle 20 deg was placed in the water channel of the cross-section 200x200 mm. Experiments were carried out by means of the PIV and LDA measuring techniques. Numerical simulations were executed by means of the commercial software ANSYS CFX 12.0. Numerical results obtained for two-equation models and EARSM turbulence model completed by transport equations for turbulent energy and specific dissipation rate were compared with experimental data. The modelling was concentrated particularly on the development of the flow separation and on the corresponding changes of free surface.
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Numerical solution of flow over 2D backward facing step with different inclination angle
Louda, P. ; Sváček, P. ; Kozel, K. ; Příhoda, Jaromír
The finite-volume and finite-element techniques are used for the numerical simulation of the incompressible turbulent flows in a closed channel with a backward-facing step and with an inclined step under the angle 45 degree. A comparison of the finite-volume method based on the averaged Navier-Stokes equations closed by the explicit algebraic Reynolds stress model and the finite-element method using the Navier-Stokes equations with the two-equation k-eps model is presented. Numerical results are compared with experimental data of Makiola (1992).
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Prediction of turbulent flow over the inclined step by means of various two-equation turbulence models
Janeček, Vladislav ; Příhoda, Jaromír
The work deals with the numerical simulation of turbulent flow over an inclined step in a channel of the rectangular cross-section according to measurement of Makiola (1992). The simulation was carried out by means of the commercial software ANSYS FLUENT with users defined functions. Various two-equation turbulence models based on the k-eps formulation were tested with the aim to estimate their ability to predict the extent of the separation region and energy losses due to inclined step with the angle 15 deg. Numerical results were compared with experimental data from LDA measurements. Besides, determined energy losses were compared with losses in a channel with a backward-facing step.
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Simulace pohybu velkých vírů při volném proudu
Louda, Petr ; Kozel, K. ; Příhoda, Jaromír
The work deals with large eddy simulation (LES) of incompressible plane free jet issued from a slot nozzle. The mathematical model is based on filtered Navier-Stokes equations. The sub-grid turbulence is modelled by Smagorinsky eddy viscosity model. The numerical solution is carried out by a finite-difference method. The time discretization uses second order accurate 3-stage Runge Kutta scheme. The Poisson equation is used for the estimation of pressure. Various boundary conditions are tested for 2D free jet flow with the Reynolds number Re= 30000. The initial velocity field is randomly perturbed by divergence-free velocity field with maximum value of 0.03Uo.
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Numerical simulation of jet flow using LES
Louda, Petr ; Kozel, K. ; Příhoda, Jaromír
The work deals with the numerical method for the large eddy simulation (LES) of incompressible flow. Governing system of filtered Navier-Stokes equations is completed by the Smagorinsky turbulence model and the Poisson equation is used for pressure instead of the continuity equation. The numerical method is based on an explicit scheme with fourth order accurate central approximation for convection and resolved diffusion. Preliminary results for the plane turbulent free jet are shown. Problem of the prescription of boundary conditions is discussed in detail.
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Modelování nadkritického obtékání prahů na dně otevřeného kanálu
Příhoda, Jaromír ; Šulc, J. ; Zubík, P. ; Sedlář, M.
The contribution deals with the experimental and numerical modelling of turbulent supercritical flow over one or two bed sills of the cross-section 3030 mm placed in an open channel. Experiments were carried out in the water channel with the cross-section 200200 mm by means of PIV and LDA measuring methods. Optical methods were completed by the measurement of pressure distribution on rib surface in the channel centreline. Numerical simulation was carried out using the VOF method by means of the commercial software ANSYS CFX-11.0. Numerical results obtained for various two-equation turbulence models were compared with experimental data. The effect of the sill spacing on the extent of the separation region, the deformation of free surface and on the drag of individual sills was primarily investigated.
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Prediction of flow over a backward-facing step in the Star CD code using various turbulence models
Štěpaníková, D. ; Příhoda, Jaromír
The comparison of several turbulence models was carried out by the commercial software Star CD for turbulent flow over a backward-facing step with the aim to assess their ability to accurately predict separated flow. Presented simulation was focused on the two aspects, namely the effect of the inlet boundary conditions on the prediction and the relaxation of the shear layer behind the reattachment. Used modifications of two-equation models, especially the non-linear k-eps model and the v2-f model, show some advantages in comparison with the standard k-eps model, but none of used modifications gives positively a better agreement with experimental data than the SST model.
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