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Experimental investigation of turbulent flow in a channel with the backward-facing inclined step
Příhoda, Jaromír ; Kotek, M. ; Uruba, Václav ; Kopecký, V. ; Hladík, Ondřej
The work deals with the experimental investigation of turbulent flow in a closed channel with the backward-facing inclined step. Experiments were carried by means of the PIV optical measuring method in the channel of the rectangular cross-section in the inlet part and with inclined steps of the constant height and various inclination angles for a wide range of the Reynolds number. The attention was paid especially to the separation region behind the step and to the relaxation of the shear layer after the reattachment in the outlet part of the channel. The dependence of the length of the separation region on the inclination step angle. Optical measurements were completed by the measurement of static pressure distribution in the inlet and outlet part of the channel to estimate energy losses.
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Experimental investigation of a control synthetic jet
Němcová, L. ; Kordík, Jozef ; Trávníček, Zdeněk ; Kopecký, V.
Synthetic jets were used in previous studies to control a continuous round air jet. This study focuses on the single synthetic jet, which is measured using Constant Temperature Anemometry (CTA) and Particle Image Velocimetry (PIV). Velocity profiles and frequency characteristics of the single synthetic jet are discussed and the velocity maps at frequencies of 30 Hz, 81 Hz and 190 Hz are presented. Finally, velocity, flow rate and momentum coefficients featured the present flow control are evaluated, and examples of actively controlled round air jet are put on. The results confirm efficiency of the present flow control method.
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Měření piezoelektrického aktuátoru pro posun textilií metodou digitální holografie s frekvenčně posunutou referenční vlnou
Lédl, Vít ; Václavík, J. ; Rusín, L. ; Erhart, J. ; Kopecký, V.
Na pracovišti TUL je vyvíjen aktuátor pro po posun textilií. Při vývoji je nezbytné charakterizovat jeho vlastnosti pro čež se zdá být užitečná metoda časově průměrované digitální holografie. Ovšem s touto metodou je nemožné přímo měřit amplitudy kmitů s amplitudou desítek mikrometrů, které jsou charakteristické pro vyvíjený aktuátor. Místo ní musí být použita metoda časově průměrované digitální holografie s frekvenčně posunutou referenční vlnou. Bylo zaznamenáno několik interferogramů aktuátoru s rozdílnými posuny referenční vlny. Ze zaznamenaných intenzitních průběhů, odpovídající Besselovým funkcím, byly pomocí softwaru rekonstruovány amplitudy kmitů v celé ploše aktuátoru.
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Experimental study of a control synthetic jet's efficiency
Němcová, L. ; Kopecký, V. ; Trávníček, Zdeněk
The present paper deals with an active control of jet flows by means of a system of synthetic jets. The control synthetic jet in one segment of the main round nozzle was measured by means of PIV. The strength of the control synthetic jet was quantified, relatively to the main jet, in terms of the ratios of their velocities, flow rates, and momenta. The results confirm efficiency of the present flow control method.
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Prospects of digital holographic interferometry in heat transfer measurement
Doleček, R. ; Lédl, Vít ; Kopecký, V. ; Psota, P. ; Václavík, Jan ; Vít, Tomáš
In the measurement of heat transfer problem, a holographic interferometry (HI) is often used mainly because of its unique properties and very high adaptability to different sort of problems under investigation. Although in the area of vibration or deformation measurement of solid body the standard HI is replaced massively by digital holography in the case of refractive index distribution the situation is quite opposite. In this paper we present two different types of digital holographic interferometers. The interferometers with different sensitivities have been build and successfully tested.
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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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Studium řízených pulzních toků metodou PIV
Pírková, L. ; Kopecký, V. ; Trávníček, Zdeněk
Příspěvek se věnuje experimentálnímu výzkumu řízených pulzujících proudů s použitím PIV. Měření bylo synchronizováno s budícím signálem, což umožnilo získat vektorové mapy proudového pole s časovými rozestupy pod 1 ms. Princip metody a uspořádání experimentu jsou stručně vysvětleny. Hlavní část příspěvku se zabývá výsledky měření v podobě vektorových a skalárních map proudového pole.
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