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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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Zplyňování dřeva v plazmatu a produkce plynu s nízkým obsahem dehtů
Hlína, Michal ; Hrabovský, Milan ; Kopecký, Vladimír ; Konrád, Miloš ; Kavka, Tetyana ; Skoblja, S.
Tar content in gas produced by the gasification of biomass always plays an important role because high tar content disables some potentialities of the further treatment of the produced gas. There is a strong effort to produce gas with low tar content from this point of view. High concentrations of hydrogen and carbon monoxide also advance possibilities of the usage of the produced gas. Experiments were carried out in a reactor for plasma gasification equipped with hybrid gas-water stabilized DC torch. They confirmed that the reactor is absolutely suitable for this purpose mainly due to extremely low flow of plasma composed of argon, hydrogen and oxygen and its high inner temperature. The measurements of the tar content, using wood as a treated material, were based on SPE method and the determination of benzene and toluene in a gas phase revealed really low concentrations of tar, mostly below 10 mg/Nm3.
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Ofukování termického proudu plazmatu generovaného plazmatronem
Kavka, Tetyana ; Hrabovský, Milan ; Chumak, Oleksiy ; Kopecký, Vladimír
The ambient air is entrained intensively into atmospheric pressure thermal plasma jets. A system for shielding plasma jet has been used to improve jet characteristics and reduce oxygen content. Different gases have been applied as a shroud gas – argon, acetylene, methane, mixtures of acetylene-nitrogen and hydrogen-nitrogen. All shroud gases used in experiments affected plasma jet making the profiles of the jet characteristics flattened with higher temperatures and velocities and reduced amount of oxygen.
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Difuzní proud v hraniční oblasti oblouku měřený elektrickými sondami
Chumak, Oleksiy ; Hrabovský, Milan ; Kavka, Tetyana ; Kopecký, Vladimír
Electric probes were used for investigation of an intermediate layer between the arc and anode surface in regions outside the main current channel. Distributions of a diffuse current and the potential were measured. Resistance and heating of the intermediate layer by diffuse current were evaluated. It was found that not only the value of diffuse current strongly depends on distance from the arc but also the shape of the distribution and the position of the maximum of the current change with the distance. These trends can be explained by expanding of the plasma jet. Evaluated equivalent intermediate layer resistance shows widening of the conductive region in a stream wise direction. Variation of resistivity of the intermediate layer is much higher than variation of the potential drop on the layer. That means that distributed current as well as Joule heating of the layer are generally controlled by distributed resistance.
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