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Neutrally stratified flow modelling over complex terrain at meso-scale: open-cut coal mine study
Nosek, Štěpán ; Jaňour, Zbyněk ; Jurčáková, Klára ; Kellnerová, Radka ; Kukačka, Libor
The objective of this case study was to determine the influence of the coal mine cavity and its vicinity on the main flow field with respect to prevailing wind direction. In order to model the neutrally stratified flow over extremely huge open-cut coal mine Libouš situated at north-west of Czech Republic the laminar flow analogy was applied. The model was scaled down to 1:9000 according to dimensions of wind-tunnel and selected coal mine surroundings. The measurements of longitudinal and lateral velocity components in selected vertical, resp. horizontal planes were performed by LDA. The measured data will be used for validation of CFD simulation and for selections of area of interest at bigger scales where turbulent flow modelling will be performed. The results revealed that not only of cavity shape and deepness but also the surroundings orography has influence on flow pattern, hence on ventilation, within the area of interest.
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Quadrant analysis of turbulent pollution flux above the modelled street intersection
Kukačka, Libor ; Nosek, Štěpán ; Kellnerová, Radka ; Jurčáková, Klára ; Jaňour, Zbyněk
The objective of this experimental study is to determine processes of a vertical turbulent pollution transport above the X-shaped street intersection in an idealised symmetric urban area for several approach flow directions. An experimental set-up for simultaneous measurement of the flow velocity and the tracer gas con-centration in a high temporal resolution is assembled. Vertical turbulent scalar fluxes are computed from the measured data in a horizontal plane above the street intersection. The quadrant analysis was applied to the vertical turbulent pollution fluxes data. Events with dominant contribution to vertical turbulent pollution flux were detected. The mean duration, repetition frequency and the duration percentage were computed for these events. A strong influence of the approach flow direction on the type of dominant events and their characteristics was resolved.
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Rotary slanted single wire CTA - a useful tool for 3D flows investigations
Jonáš, Pavel
The procedure is described of experimental investigation of a statistically stationary generally nonisothermal 3D flow by means of a constant temperature anemometer (CTA) using single slanted heated wire, rotary round the fixed axis. The principle of this procedure is quite clear. The change of the heated wire temperature modifies ratio of CTA sensitivities to temperature and velocity fluctuations. Turning the heated wire through a proper angle changes the sensitivity to components of the instantaneous velocity vector. Some recommendations are presented based on long time experiences, e.g. on the choice of probe, on the probe calibration, to the measurement organization and to the evaluation of results.
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Preliminary experimental investigation of boundary layer in decelerating flow
Hladík, Ondřej ; Jonáš, Pavel ; Příhoda, Jaromír
Investigations of characteristics of turbulence inside boundary layer under decelerating flow were studied by means of constant temperature anemometer. The decelerating flow was simulated in the closed circuit wind tunnel 0.9 m × 0.5 m at IT AS CR. The free stream turbulence was either natural or risen up by square mesh plane grid. The details of experimental settings and measurement procedures of the instantaneous longitudinal velocity component are described and the distributions of intensity, skewness and kurtosis of turbulent fluctuations are discussed in the contribution.
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Parametric study of vortex train generated by plasma actuator in dependency on input voltage waveform
Procházka, Pavel P. ; Uruba, Václav
This article is based on previous work of authors. The vortex train is created by a plasma DBD actuator after application of low-frequency amplitude modulation on high-frequency high-voltage carrier waveform. Data acquisition of flow field around actuators will be performed using time-resolved PIV measurement technique in plane parallel to flow and in cross-section. Phase-averaging will be used due to pseudo-periodical character of this process. The vortex behaviour dependency on modulation frequency, duty cycle, voltage value, electrode gap and other parameters will be shown. The generated flow patterns are to be applied for control of a boundary layer.
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Dynamics of flow behind backward-facing step in a narrow channel
Uruba, Václav
The results and their analysis from experiments obtained by TR-PIV are presented on the model of backward-facing step in a narrow channel. The recirculation zone is studied in details. Mean structures are evaluated from fluctuating velocity fields. Then dynamics of the flow is characterized with help of POD (BOD) technique. Substantial differences in high energy dynamical structures behaviour within the back-flow region and further downstream behind the flow reattachment have been found.
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Numerical simulations of the flow with the prescribed displacement of the airfoil and comparison with experiment
Řidký, Václav ; Šidlof, Petr ; Vlček, Václav
The work is devoted to comparing measured data with the results of numerical simulations. As mathematical model was used mathematical model whitout turbulence for incompressible flow In the experiment was observed the behavior of designed NACA0015 airfoil in airflow. For the numerical solution was used OpenFOAM computational package, this is open-source software based on finite volume method. In the numerical solution is prescribed displacement of the airfoil, which corresponds to the experiment. The velocity at a point close to the airfoil surface is compared with the experimental data obtained from interferographic measurements of the velocity field. Numerical solution is computed on a 3D mesh composed of about 1 million ortogonal hexahedron elements. The time step is limited by the Courant number. Parallel computations are run on supercomputers of the CIV at Technical University in Prague and on a computer cluster of the Faculty of Mechatronics of Liberec . Run time is fixed at five periods, the results from the fifth periods and average value for all periods are then be compared with experiment.
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Computational aeroacoustics of human phonation
Šidlof, Petr ; Zoerner, S.
The current paper presents a CFD model of flow past vibrating vocal folds coupled to an acoustic solver, which calculates the sound sources from the flow field in a hybrid approach. The CFD model is based on the numerical solution of 3D Navier-Stokes equations on a time-dependent domain, solved by cell-centered finite volume method. To capture the fine turbulent scales important for the acoustic source calculations, the equations are discretized and solved on large computational meshes up to 3.2M elements. The CFD simulations were run in parallel using domain decomposition method and OpenMPI implementation of the MPI standard. Aeroacoustic simulations are calculated in a separate step by Lighthill’s acoustic analogy, which determines the acoustic sources based on the fluid field. This is done with the research code CFS++ which employs the finite element method (FEM).
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Large-amplitude pulsatile nozzle flow
Tesař, Václav ; Kordík, Jozef
Flowfield inside a simply-shaped nozzle with periodic unsteadiness of so large amplitude that a flow reversal occurs during a part of the cycle was investigated. The range of frequencies was from 20 Hz to 320 Hz, and ratios of the pulsation amplitude to the steady flow were from 1.0 to 4.0. Anemometric velocity measurements were combined with numerical flowfield computations.
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