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Modelling of supercritical turbulent flow over an inclined backward-facing step in a open channel
Příhoda, Jaromír ; Zubík, P. ; Šulc, J. ; Sedlář, M.
The contribution deals with the experimental and numerical modelling of supercritical turbulent flow in an open channel with an inclined backward-facing step on its bottom. The step with the height 100 mm and 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 the commercial software ANSYS CFX 12.0. Numerical results obtained by the two-equation SST model and the EARSM model completed by transport equations for turbulent energy and specific dissipation rate were compared with experimental data. The modelling was concentrated particularly on the flow pattern near the step including the possible flow separation and the corresponding changes of free surface. The agreement of numerical results obtained by means of the EARSM model with experimental data is quite good.
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Experimental and numerical modelling of liquid flow with separation
Zubík, P. ; Šulc, J. ; Příhoda, Jaromír ; Sedlář, M.
The contribution deals with the experimental and numerical modelling of turbulent pressure, subcritical and supercritical flow with massive separation due to sudden expansion of the cross section (flow over an inclined step). Experiments were carried out in the water channel with the cross-section 200x200 mm by means of PIV and LDA measuring methods. Numerical simulation was carried out using the VOF (Volume-of-Fluid) method by means of the commercial software ANSYS CFX-12.0. Numerical results were compared with experimental data.
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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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Erozní potenciál bublinkové kavitace ve vodním čerpadle – numerická simulace a experiment
Zima, Patrik ; Sedlář, M. ; Müller, M.
A model assessing erosive potential of cavitation bubbles for 3D steady-state pump flow in the traveling cavitation mode is proposed. The 3D Navier-Stokes code for turbulent pump flow is coupled with the Rayleigh-Plesset equation by means of two-way coupling. The energy dissipated between two successive bubble rebounds is estimated to assess the erosive potential. The model is validated for a 2D hydrofoil in the cavitation tunnel and then employed for a 3D mixed-flow water pump impeller. The numerical results indicate the dominant effect of the first collapse and are in good agreement with the experiment.
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Výpočetní analýza potenciálu kavitační eroze v hydraulickém stroji
Sedlář, M. ; Zima, Patrik ; Müller, M.
The paper describes a new model for efficient modeling of water cavitation erosion potential in turbulent cavitating flow. The number and size of the cavitation nuclei in the inlet flow are predicted empirically or experimentally using the acoustic spectrometer. The bubble dynamics is described using the Rayleigh-Plesset equation along the flow streamlines obtained from the 3D RANS equations. The model of the erosion potential is based on the estimation of the energy dissipated by the collapses of the cavitating bubbles. The paper also describes the experiment carried out in the cavitation tunnel in the SIGMA R&D Institute. The CFD model is tested for 2D and 3D geometry. It is shown that the erosion potential of the first collapses is several orders higher than the potential of the subsequent collapses. The numerically determined location and magnitude of the first collapses are compared with the photographs of the erosion pattern. The agreement for the tested cases is very good.
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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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Vyšetřování turbulentního proudění v otevřeném kanálu s příčnými prahy
Příhoda, Jaromír ; Šulc, J. ; Sedlář, M. ; Zubík, P.
The contribution deals with the experimental and numerical modelling of turbulent supercritical flow over one and/or two transversal ribs with the cross-section 30x30 mm placed at the bottom of an open channel. Numerical simulation was carried out using the VOF (Volume-of-Fluid) method by means of the commercial software ANSYS CFX-11.0 for supercritical flow characterised by the Froudé number Fr = 2.2. The effect of the rib spacing on the extent of the separation region, the deformation of free surface and on the drag of individual ribs was primarily investigated. Numerical results were compared with experiments accomplished in the water channel with the cross-section 200x200 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.
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Experimentální a numerické modelování turbulentního obtékání příčných prahů v otevřeném kanálu
Příhoda, Jaromír ; Šulc, J. ; Sedlář, M. ; Zubík, P.
Modelling of turbulent flow in an open channel with transversal ribs on its bottom was concentrated particularly on the development of flow separation behind ribs and on the corresponding changes of free surface. Further, the pressure drag of individual ribs was investigated including their dependence on the rib spacing, as well as the origin of secondary flow near the side walls of the channel behind ribs. Numerical results obtained by the software ANSYS CFX 11.0 were compared with experiments carried out by means of LDA and PIV techniques in free-surface water channel 200x200 mm with one and/or two transversal ribs 10xl0 mm with various spacing.
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CFD analýza kavitačních jevů v hydraulických strojích
Sedlář, M. ; Zima, Patrik
The paper deals with the CFD analysis of cavitation phenomena in the hydraulic machinery. Both the ANSYS CFX 11.0 package and an in-house software developed in the SIGMA Research and Development Institute and the Institute of Thermomechanics, AS CR v.v.i. are used to study three types of cavitation problems: calculation of the NPSH3 curves, modelling of the cavitation instabilities and prediction of the cavitation erosion.
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