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EXPERIMENTAL AND NUMERICAL STUDY OF A CONTROLLED PULSATING FLOW
Pírková, L. ; Kopecký, V. ; Trávníček, Zdeněk
A turbulent round air jet discharging into quiescent ambience was studied under circumferential excitation. Four synthetic jet actuators were distributed around the main nozzle exit; they were fed by an electronic control system with a chosen polarity and phase shift. This arrangement allowed to excite the main round jet in several modes, namely the (A) axisymmetric, (B) plane symmetric, (C) bifurcated, and (D) helical modes. The measurement of the excited jet flow fields A–D was performed using the PIV technique. Further, preliminary development of a numerical model of controlled pulsating jet flow is described. Relevant parameters in the numerical model and their effect on model accuracy were investigated. Emphasis is on the mesh density and time step size. This parametric study allowed us to clearly identify a regime of optimal mesh densities and time step sizes for the Reynolds number of interest. The simulations were calculated in Fluent.
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Systematické vyšetřování vzdáleného rychlostního pole syntetizovaných proudů
Tesař, Václav ; Kordík, Jozef
Paper presents results evaluated from anemometric data on a large number of synthetic jets. The results are based on a one-equation turbulence model solution of time-mean synthetic jets. This solution follows the classical concept of similarity transformation, but depends on a parameter the value of which varies along the jet axis. This is idea has been there before, but the scarcity of so far available experimental data made the previous attempt unreliable. This is now improved by the large number of new data that correct some previous coclusions.
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Dynamika odtržení řízené mezní vrstvy na válci
Uruba, Václav ; Matějka, Milan ; Procházka, Pavel
Dynamical aspects of the boundary layer separation on a circular cylinder in cross-flow are studied experimentally. Two cases are compared, the base case and the case with excitation using a synthetic jet actuator. The TR-PIV technique was used to catch both space and time velocity field correlations. Instantaneous velocity fields and skin friction distributions are evaluated. For dynamical structures study, the BOD method was applied based on energetic principle. Dynamical modes connected with vortex shedding process, dynamical excitation by synthetic jet and transition to turbulence are identified.
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Rezonanční frekvence generátorů syntetizovaných proudů
Kordík, Jozef ; Trávníček, Zdeněk ; Šafařík, P.
This contribution focuses on axisymmetric synthetic jet actuators from the theoretical point of view. In order to evaluate their resonance frequencies, four mathematical models were derived. The results were compared with experimental data, and analyzed. With respect to the theoretical and experimental results, the applicability and limits of the models were discussed. The results illustratively prove correctness of the previous derivation based on transformation of mechanical energy.
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Parametry modelu turbulence aplikovaného na syntetizované proudy
Tesař, Václav ; Kordík, Jozef
Anemometric data obtained on two synthetic jets issuing from 4 mm dia nozzle, differing in their frequency (25 Hz and 50 Hz), were applied to one-equation turbulence model solution of jets. It made possible evaluating spatial distributions of unsteady motion in the jets. The classical concept of similarity, however, ceased to be applicable and a concept of quasi-similarity was introduced. An important finding was the discontinuity found in the structure of the unsteady motions – the intial region dominated by large vortices is changed into a region of initially smaller/scale turbulent eddies.
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Dynamika řízené odtržené mezní vrstvy
Uruba, Václav ; Knob, Martin
The results of experimental study on a boundary layer separation control are given in the paper. The boundary layer on a flat wall is subjected to adverse pressure gradient. Three control strategies have been chosen for the study, both passive (rough wall, vortex generator) and active (synthetic jet). The separation process is investigated using TR-PIV method. Dynamical aspects of the phenomenon are analyzed in details. The strategy of application synthetic jet is shown to be the most efficient.
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Frekvenční charakteristika generátoru anulárního syntetizovaného proudu s velkým vnitřním průměrem
Krejčí, A. Petr ; Trávníček, Zdeněk ; Tesař, Václav ; Kordík, Jozef ; Pavelka, Miroslav
An annular synthetic jet actuator of large inner/outer diameter ratio of the nozzle has been developed, and four variants were designed, manufactured, and tested. The resonance frequency was estimated theoretically, based on the mechanical energy balance, and then measured by the pneumometric method. The resultant value was found to be 40 Hz. The nozzle geometry effect on the resonance frequency and on the velocity was quantified; both effects were concluded to be surprisingly small, less than 5%.
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