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Experimentální systém pro výzkum kavitačních jevů v hydraulických tlumičích rázů
Müller, M. ; Prášil, L. ; Zima, Patrik
The article describes the experimental system for investigation of growth, activity and collapse of cavitation bubbles or structures in a hydraulic shock absorber. The experimental chamber allows to insert a real shock absorber piston and install acoustic/optical measurement devices including bubble spectrometer, a PVDF hydrophone for the measurement of acoustic emission from the collapsing bubbles and a high-speed camera combined with laser sheet illumination. A specially designed high-resolution mirror lens can be installed in the chamber to investigate the bubbles in the micrometer range.
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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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Kavitační bublina v blízkosti pevné stěny
Müller, M. ; Zima, Patrik
The article presents the results of the calculation of the cavitation bubble collapse near a solid boundary. The solution is obtained using the FLUENT CFD software. The VOF (Volume Of Fluid) model is applied to study the behavior of the interphase between the liquid and the bubble content. The calculations were performed for three different distances of the bubble from the solid wall. The evolution of the bubble radius is obtained from the phase interface contours. The bubble jet velocity and its thickness are determined for all bubble positions.
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Experimentální výzkum kavitační bubliny ve vodě
Müller, M. ; Zima, Patrik
The article presents the results of experimental investigation of laser-induced cavitation bubble in water. The cavitation bubble is generated using the Q-switched Nd-YAG laser and recorded by a multi-exposure method, which allows to record the bubble at different phases into single frame.
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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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Kavitace a nukleace bublin ve vodě s příměsemi
Zima, Patrik ; Maršík, František ; Sedlář, M.
The latest advances in modeling of cavitation in water flows and experimental investigation of bubble nucleation in a cavitation nozzle will be presented. The emphasis will be put on presenting the results of the recent measurements with cavitation nozzle and the critical assessment of the applicability of the cavitation nozzle principle for determining the size of critical bubble radii. Some results of numerical modeling of cavitation in pumps will be summarized.
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Simulace kavitační nestability v induktoru se 3 lopatkami
Sedlář, M. ; Maršík, František ; Zima, Patrik
Axial-flow inducers are used to improve cavitation performance of radial-flow or mixed-flow pumps. There is a wide range of cavitation instabilities, which can be observed during inducer operation, even at the design flow rate. The type of cavitation instability is determined by the frequency analysis. Two cavitation models were used to determine the frequency range of four different types of cavitation instabilities – CEV and VOF built in the ANSYS CFX software – for a 3-blade inducer and suction impeller of a multistage pump. The calculated values of NPSH3 were compared with experimental data for SST, SST-SAS and RSM SSG turbulence models for fully unsteady solutions. It was found that the SST-SAS model provides the most realistic picture of the backflow vortices and their oscillations.
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