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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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Dynamics of flow around vibrating wing NACA 0012
Uruba, Václav
Flow around vibrating wing consisting of airfoil profile NACA 0012 has been studied experimentally using time resolved PIV technique. The unsteady velocity field close to the profile trailing edge is highly affected by the wing vibrations. The dynamic of the flow is analyzed using BOD technique of the flow-field for cases with and without vibrations. Comparison shows strong influence of the airfoil vibrations on the flow dynamics.
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Gas-Liquid Flows in Thin-Gap Electrochemical Microchannels – PIV Study
Záloha, Petr ; Křišťál, Jiří ; Jiřičný, Vladimír ; Aubin, J.
We focused on the study of the local hydrodynamics of liquid in gas-liquid flow in thingap microchannels (width 10 mm, depth 2 mm - 0.1 mm). Two-phase flow was obtained by injecting bubbles into the channel to mimic the gas generation during electrochemical reactions. The liquid flow velocity vectors were obtained by the PIV technique. Single phase measurements were used to verify our method by comparison with the theoretical velocity profiles. Local velocity fields around single bubble were evaluated.
Plný tet: SKMBT_C22012102413481 -  PDF
Plný text: content.csg - PDF
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Coherent turbulent structures in flow through the human vocal tract
Šidlof, Petr ; Doaré, O. ; Cadot, O. ; Čejka, J.
This paper presents experimental and computational data on the coherent turbulent structures in flow through the human vocal tract. The experimental results were obtained using a 4:1 scaled self-oscillating physical model of vocal folds. Flow velocity fields in the coronal plane were visualized and measured using a PIV system phase-synchronized with vocal fold vibration. Computational results originate from finite volume discretizations of viscous incompressible Navier-Stokes equations in 2D and 3D. The results reveal flow separation in the divergent part of glottis and formation of a planar jet. Vortex structures are shed from the shear layer of the jet and convected further downstream. The computational model helps to assess the influence of the ventricular folds on the flow patterns.
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DECOMPOSITION METHODS FOR A PIV DATA ANALYSIS WITH APPLICATION TO A BOUNDARY LAYER SEPARATION DYNAMICS
Uruba, Václav
Separation of the turbulent boundary layer (BL) on a flat plate under adverse pressure gradient was studied experimentally using Time-Resolved PIV technique. The results of spatio-temporal analysis of flow-field in the separation zone are presented. For this purpose, the POD (Proper Orthogonal Decomposition) and its extension BOD (Bi-Orthogonal Decomposition) techniques are applied as well as dynamical approach based on POPs (Principal Oscillation Patterns) method. The study contributes to understanding mechanisms of a boundary layer separation process. The acquired information could be used to improve strategies of a boundary layer separation control.
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High-Quality Vector Field and Direct Jacobian Estimation
Gronát, Petr
In this paper, a correlation method for direct vorticity computation of the fluid velocity field is introduced. The correlation method allows an affine transformation of a correlation window. It is shown that Lagrangian field of displacements, considering the linear terms only, satisfies the requirements for affine transformation and using the Normalized-Cross-Correlation (NCC) together with affine transformation and Newton-Raphson iterative method, six parameters defining this transformation can be estimated. Using these parameters, both displacement and vorticity can be computed directly without differentiation of the vector field.
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High-Quality Vector Field and Direct Vorticity Estimation Uusing the Affine Correlation Method
Gronát, Petr
We present a correlation method for direct vorticity computation of the fluid velocity field. The correlation method allows the affine transformation of a correlation window. It is shown that Lagrangian field of displacements is locally affine considering linear terms only. Using the Normalized-Cross-Correlation (NCC) combined with affine transformation and Newton-Raphson iterative method, six parameters defining this transformation are estimated. Subsequently, using these parameters, both displacement and vorticity can be computed, hence, these properties are being obtained for every single pixel directly during the correlation procedure.
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A New Method for Vector Fields Dynamic Analysis
Uruba, Václav
A method for analysis of spatio-temporal data is proposed. This is based on combination of Proper Orthogonal Decomposition and Principal Oscil-lation Patterns methods. The method provides dynamical characteristics of spatial modes evaluated either on both energetic or stability basis. Example on TR-PIV results on unsteady separation is shown.
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