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Coanda effect in valves
Uruba, Václav ; Procházka, Pavel P. ; Skála, Vladislav
Coanda effect takes place in flow within valves diffuser for certain conditions. The valve plug in\nhalf-closed position forms wall-jet, which could be stable or instable, depending on geometry and other\nconditions. This phenomenon was subject of experimental study using time-resolved PIV technique. For the acquired data analysis the special spatio-temporal methods have been used.
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On the recirculation zone suppression behind HUMP profile using the DBD actuator
Procházka, Pavel P. ; Uruba, Václav
Previously, the DBD (dielectric barrier discharge) plasma actuator was used in rectangular channel to modify the properties of the boundary layer in spanwise and in streamwise orientation. The actuator was redesigned for using on the surface of the Glauert-Goldschmied body in different position to influence the point of the separation and the reattachment point as well as the total extent of the separation bubble. The most intensive effect occurs when the actuator takes effect in the point of separation. Further downstream, the ionic wind produced by DBD causes complex coherent structures in the wake for spanwise orientation in both direction. The effect of streamwise orientation is studied also. Actuator is operated in steady regime to produces continuous ionic wind as well as in unsteady regime when the vortex street is generated. The properties of vortex street is given by modulation parameters (frequency and duty cycle). The effect of these parameters on the wake is evaluated. This experiment is realized in the perspex channel connected to the blow-down wind tunnel. The HUMP profile is flush-mounted to the bottom side. The wire electrode of the actuator is situated in x/L = 0.63, 0.66, 0.69 and 0.72 of the chord length. The time-resolved PIV (Particle Image Velocimetry) is used as a main measurement technique. The flow field behind the profile is captured in longitudinal plane as well as in cross-section planes using 3D PIV. The results based on statistical quantities will be presented in this paper. More, next part will be devoted to the decomposition analysis of the flow dynamics (BOD, OPD).
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A comment on the flat plate leading edge shape on laminar-turbulent transition
Antoš, Pavel ; Jonáš, Pavel ; Procházka, Pavel P.
Laminar-turbulent transition region is investigated in zero pressure gradient boundary layers developing on flat plates with different shapes of leading edges namely with the elliptical profile; the superelliptical one and with the thin circle profile. The mean flow field characteristics are presented and discussed. Near downstream from the leading edge are mean velocity profiles very similar to the Blasius solution in all compared configurations. The dramatic effect of the leading edge is ascertained in the beginning of the skin friction coefficient deflection from the course after Blasius solution. The start of deflection is moving downstream in sequence: elliptic – super-elliptic – circle shape. The length of the transitional region shortens in the opposed sequence.
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Stereoscopic PIV measurement of boundary layer affected by DBD actuator
Procházka, Pavel P. ; Uruba, Václav
The effect of ionic wind generated by plasma actuator on developed boundary layer inside a narrow channel was investigated recently. Since the main investigated plane was parallel to the channel axis, the description of flow field was not evaluated credibly. This paper is dealing with cross-section planes downstream the actuator measured via 3D time-resolved PIV. The actuator position is in spanwise or in streamwise orientation so that ionic wind is blown in the same direction as the main flow or in opposite direction or perpendicularly. The interaction between boundary layer and ionic wind is evaluated for three different velocities of main flow and several parameters of plasma actuation (steady and unsteady regime, frequency etc.). Statistical properties of the flow are shown as well as dynamical behaviour of arising longitudinal vortices are discussed via phase-locked measurement and decomposition method.
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The impact of plasma induced flow on the boundary layer in a narrow channel
Procházka, Pavel P. ; Uruba, Václav
The induced flow generated by dielectric barrier discharge (DBD) actuator working in steady and unsteady regime will be used to modify properties of naturally developer boundary layer (BL) in short and length rectangular perspex channel which is connected to the blow-down wind tunnel. The actuator is placed in spanwise configuration and the inlet velocities will range between 5 and 20 m•s-1. Previously, mean flow field and statistical quantities were subjugated to investigation. In this paper, there will be presented dynamical features of the BL as well as tracking of coherent structures using phase-averaging. Proper Orthogonal Decomposition (POD) of influenced flow field and frequency analysis will be presented. These results should be taken into account regarding to use in the flow around a bluff body.
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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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