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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.
The actuator for moving the fabric is under development. It is necessary to characterize its properties. Time average holographic interferometry seems to be suitable tool for this purpose. However it is impossible with standard technique to resolve amplitudes in tens of microns, which are characteristic for the operation of the actuator. Time average holographic interferometry with frequency shifted reference wave has to be applied to solve this problem. Few expositions of the vibrating actuator have been captured with different frequency shift of the reference wave. Bessel functions obtained from these interferograms were fitted together by the automated software. The shape and the amplitude of the movement were successfully measured in whole area of actuator.
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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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PIV study of the controlled pulsatile jets
Pírková, L. ; Kopecký, V. ; Trávníček, Zdeněk
The aim of this paper is to describe an experimental study of controlled pulsating jets using PIV method. The present synchronization of PIV data with the pulsating process enables to measure vector maps of the flow field with the time steps under 1ms. Principle of PIV method and the present experimental set up are described. Main part of the paper discusses vector and scalar maps of the flow.
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