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Dynamics of Flow-Field behind Backward-Facing Step in the Plane of Symmetry
Uruba, Václav
Dynamics of the flow-field behind a backward-facing step in a narrow channel is studied experimentally using time-resolved PIV technique in the measuring plane being the plane of symmetry in the streamwise direction. The channel width is 4 step heights, Reynolds number based on the step height was about 7 200. Instability of the free shear layer of Kelvin-Helmholtz type is observed. Dynamics of the flow is studied using the Bi-Orthogonal Decomposition (BOD) and Oscillation Pattern Decomposition (OPD) techniques. Typical time-mean structures of velocity statistics as well as dynamical structures are to be presented.
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3D Structure of the Flow-Field behind Backward-Facing Step in a Narrow Channel
Uruba, Václav
Time-mean flow-field structure behind the backward facing step in a narrow channel was studied in details using the PIV technique. The measuring cuboid was covered by systems of measuring planes in various orientations. The channel width to the step height ratio was 4, Reynolds number based on the step height was 34 400. Special attention has been paid to the region just behind the step forming the back-flow region.
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Dynamics of Recirculation Region Behind Backward-Facing Step
Uruba, Václav
Dynamics of the flow-field behind a backward-facing step in a narrow channel is studied experimentally using time-resolved PIV technique. Instability of the free shear layer of Kelvin-Helmholtz type is studied using simple averaging and Oscillation Pattern Decomposition (OPD) methods. Mean picture suggests existence of the classical recirculation zone. The OPD method reveals the structure of the instability consisting of a system of traveling vortical structures.
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Influence of Carrying Frequency Phase Shift of Synthetic Jet Generator on The Noise
Pick, P. ; Matějka, Milan ; Skála, V.
The main topic of this article is the influence of phase shift of neighbouring synthetic jet generators to the flow field past a hump and noise reduction. Syntheetic jet generators are placed in the hump in front of point of boundary layer separation. The carrying frequency of actuating signal, wich is driving the synthetic jet generator, is shifted for about 180°. The modulated frequency, which corresponds to the shading frequency of the flow, is superposed on the carrying signal. Finally, the benefits of phase shift signal of neighbouring synthetic jet generators are described, as far as the produced noise and the total loss coefficient decrease are concerned.
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Numerical Solution of 3D Airflow in Channel Representing a Vocal Tract
Pořízková, P. ; Kozel, Karel ; Horáček, Jaromír
This study deals with the numerical solution of a 3D compressible flow of a viscous fluid in a channel for low inlet airfloe velocity. the channel is a simplified model of the glottal space in the human vocal tract. The system of Navier-Stokes equations has been used as mathematical model of laminar flow of the compressible viscous fluid in a domain. The numerical solution is implemented using the finite volume method (FVM)and the predictor-corrector MacCormack scheme with artifical viscosity using a grid of quadrilateral cells.
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Dynamics of secondary flow behind backward-facing step in a narrow channel
Uruba, Václav
Dynamics of the flow-field behind a backward-facing step in a narrow channel is studied experimentally using time resolved PIV technique. Secondary flow represented by vortical structures is studied using Oscillation Pattern decomposition technique. The low-frequency quasi-periodical structures appearing in the region just behind the step close to the channel bottom are studied. Typical dynamics of vortex structures involving contra-rotating vortex pair train, vortices coalescence and splitting have been observed.
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Physical principle dealing with development of vortices formed by DBD actuator
Procházka, Pavel P. ; Uruba, Václav
Several configurations of vortex trains generated by plasma dielectric barrier discharge were measured by method of time-resolved PIV with application of phase-averaging of data. Mainly dynamics of vortical structures was studied in terms of vortex core trajectory, convective velocity, vortex diameter and vortex circulation. The generally valid physical mechanism of such vortices based on gained information will be introduced and presented. This mechanism will be considered with regards to the use for active flow control thus it could be very helpful in the future works dealing with plasma flow control.
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