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Numerické řešení dvoufázového proudění při interakci statoru a rotoru
Halama, Jan ; Fořt, Jaroslav
This work deals with a numerical solution of 2D unsteady compressible flow of mixture of vapor and condensed droplets in axial turbine stage. Governing equations consist of the Euler equations for the mixture and the transport equations for integral parameters of droplet spectra (Hill's approximation). The computational domain is created by several stator and rotor blade passages in order to get simple periodicity condition. The stator and the rotor parts are connected by 'interface cells', proposed originally by Giles. Numerical method is based on the Strang splitting method, convection part is solved by the finite volume cell-vertex method based on the Lax-Wendroff scheme with artificial viscosity term and condensation part is solved by two-stage explicit Runge-Kutta method. The first numerical results are discussed.
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Modelling of flow over one transversal rib in a channel with free surface
Sládek, Aleš ; Příhoda, Jaromír
Numerical simulation of flow over one transversal rib on the bottom of a channel with free surface was carried out. The VOF (Volume-of-Fluid) method implemented in the commercial software FLUENT 6.3 was used for the solution of supercritical flow in a channel with free surface. The two-equation turbulence model according to Shih et al. was applied. Profiles of mean velocity and velocity fluctuation obtained by numerical simulation were compared with experimental data from PIV measurements. Secondary flow and the length of separated region behind the rib were compared with experimental data as well.
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Mikrofluidika v řízení živých tvorů
Tesař, Václav
Microfluidics had recently interesting uses in biomedical sciences. Its development towards smaller scales has reached the stage making possible an interfacing with the brain cortex at the cellular level: reading and inputting the neural signals. The signals and their processing are mostly of electronic character, but fluidics plays in this application one of the key supporting roles. The contribution on the one hand lists therapeutical applications, but on the other hand notes current trend of military uses of insects or small rodents who can intrude into military establishments and gather there pictorial information.
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Výpočet hustotních profilů nano-kapiček použitím gradientní teorie: numerické řešení v transformovaných proměnných
Hrubý, Jan
The Cahn-Hilliard gradient theory extends the continuum fluid mechanics and thermodynamics to objects of typical dimensions of 1 nm. The present investigation concerns the computation of the density profile of a equilibrium spherical case (droplet, bubble). The solution for this case reduces to a single second-order ordinary differential equation (ODE) with boundary conditions. To overcome computational difficulties due to the tremendous difference of thermodynamic properties of the liquid and vapor phases at low temperatures, we suggest some mathematical transforms. Using these transforms, the right-hand side of the ODE becomes well-behaved and the numerical solution is converging.
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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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Numerické řešení proudění kolem profilu vibrujícího s dvěma stupni volnosti
Honzátko, R. ; Horáček, Jaromír ; Kozel, K.
The work deals with a numerical solution of two-dimensional inviscid incompressible flow over a profile NACA 0012 with two degrees of freedom. the profile can rotate around an elastic axis and oscillate in the vertical direction. The finite volume method in a form of a cell-centered scheme at qaudrilateral C-mesh is considered. The mathematical model of the fluid flow is represented by a modified system of unsteady Euler equations. The motion of the profile is described by a system of two ordinary differential equations. The numerical simulation of flow induced vibrations of the profile consists in a couling of the two systems of equations. An arbitrary Lagrangian-Eulerian method is employed to solve unsteady flows on a moving grid.
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Formation criterion for various synthetic jets: power and frequency characteristics
Kordík, Jozef ; Trávníček, Zdeněk ; Šafařík, P.
Synthetic jets are generated by periodic alternating flows. The jet parameters are: dimension, frequency, oscillation shape and amplitude. The Reynolds number (ReH) and Strouhal number (StH) (or Stokes number SH) are used as dimensionless paramers. The experiment was performed for the Reynolds number range of ReH = 500–10000 and Strouhal number range of StH = 0.2–8.9. Flow visualization and hot-wire measurement were performed. The present results focusing on the jet formation criterion agree quite well with the available literature (the criterion ReH crit = 0.16 SH2).
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Kalibrace clonkové tratě rotačním průtokoměrem a rezonance systému
Randa, Zdeněk ; Tesař, Václav ; Hrubý, Jan
Rotary piston flowmeters (RPF) are widely used for accurate measurement of gas flow rates. We used it to calibrate a Koennecke-type quadrant nozzle flowmeter. The evaluated discharge coefficient exhibited strange local maxima, even exceeding unity. The phenomenon was sensitive to the length of the tubes connecting the RPF with the calibrated quadrant nozzle. One possible explanation, discussed in the present paper, is the local maxima to be due to acoustic resonance in the system, excited by periodic character of the flow through the RPF. Another possibility is that the also the inertia of the pistons plays a role, the air providing the spring action.
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