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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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Rozložení energie v kavitační bublině během jejího růstu a kolapsu
Müller, M. ; Maršík, František ; Garen, W.
Shock wave generation during the bubble growth and collapse and the corresponding energy separation were investigated experimentally. The calculation of the shock wave energy was based on the experimentally determined shock wave velocity profile. The possibility of using the similarity solution to determine the shock wave intensity is discussed. The velocity field around the collapsing bubble was visualized and compared with the numerical simulation using the commercial FLUENT code.
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Some possibilities of analytical description of strong non-adiabatic gas compression
Bayer, Zdeněk
Paper deals with modelling of the gas state- and thermodynamic behaviour in cavitation bubbles. After recent presentation of model M3 based on the more realistic idea of the heat transfer in the course of bubble compression, introduces its advanced version M4. The comparison of the polytropic and M4 model of process shows the results for high volume compression ratios may differ in tenths of percent. In a like range lies the discrepancy caused by using more accurate state equation and temperature dependence of the heat capacity.
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Dynamics of a bubble in variable pressure and temperature fields of a liquid
Zima, Patrik ; Maršík, František
A study of nucleation and growth of bubbles in a liquid by means of a method based on the nucleation pulse in a shock tube is proposed. The nucleation of bubbles in the shock tube is initiated by a sudden depressurization due to the expansion of the liquid. It is assumed that the nucleation is homogeneous and the nucleation rate and the growth of bubbles can be evaluated using the light scattering method. Description of the experimental setup and analytical solution of the expansion of water in a shock tube are given. The theory of radial dynamics of a spherical vapor/gas bubble in a liquid is then employed in the form of the Rayleigh-Plesset equation and some aspects of inertially controlled bubble growth are discussed. The governing equation and conditions for mass transfer across the bubble boundary due to diffusion of the contaminant gas are given.
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