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Phase Coupling Between Core and Boundary Regions of a Thermal Plasma Jet
Hlína, Jan ; Šonský, Jiří
Time series of plasma jet radiation distributions in planes perpendicular to the jet axis were analyzed by the fast Fourier transform (FFT). Complex output yielded by FFT was used to study amplitudes and phase angles belonging to various frequencies occurring in the frequency spectra. The distributions of amplitudes and phase angles have shown the existence of characteristic core and boundary regions for various types of oscillations. Phase angle relations give evidence of coupling between the core and boundary of the jet at some frequencies.
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Dependence of Thermal Plasma Flow Velocity on Arc Current Determined by Correlation Analysis of Optical Records
Gruber, Jan ; Šonský, Jiří ; Hlína, Jan
Optical radiation of thermal plasma jet was recorded in two parallel cross-sections perpendicular to the jet axis and separated by 3.5 mm. Sufficient sampling rate was a prerequisite to obtain detectable shift between the time-series recorded in closer and farther cross-sections. We have determined time lags between the recorded signals both in the core and boundary regions by correlation analysis and subsequently determined associated velocities of plasma flow. Arc current was gradually increased in respective measurements, gas flow was fixed. Determined flow velocities are in the range 140 m/s - 280 m/s in the jet core and 110 m/s – 220 m/s in the boundary region. This is in agreement with the results obtained for similar plasma torches by other methods in the past. Velocity increases with arc current almost linearly and this dependence and velocity profile in the plasma jet cross-section are presented in this paper.
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Actuators for Flow Control Based on Plasma Principle
Procházka, Pavel P. ; Uruba, Václav ; Šonský, Jiří
One can distinguish between two types of flow control, passive and active. Active flow control has a few advantages. The biggest advantage is a possibility to influence the flow only if there is a need. By contrast, the passive control acts all the time and for all regimes and this is not good in terms of fuel consumption, for example. Active flow control provides the necessary momentum to the shear layer from an external source, as opposed to passive control which uses the momentum of free stream of fluid.
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Prostorové rozložení oscilací v modulovaném proudu plazmatu
Gruber, Jan ; Šonský, Jiří
Modulovali jsme stejnosměrný proud plazmatronu pracujícího ve vertikální konfiguraci. Frekvence modulace se pohybovala of 15 Hz do 7,5 kHz. Výsledné optické vyzařování proudu plazmatu jsme zaznamenávali vysokorychlostní CCD kamerou. Délka záznamu a časové rozlišení byly dostatečné pro aplikaci FFT, což nám poskytlo detailní pohled na oscilace v proudu plazmatu. Identifikovali jsme význačné oscilace a prozkoumali jsme jejich rozložení v rovině proudu plazmatu. V tomto článku ukazujeme vliv modulace proudu na dominantní frekvence oscilací a na jejich prostorové rozložení.
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EXTRACTING INFORMATION ABOUT COHERENCE IN JET FLOWS
Tesař, Václav ; Něnička, Václav ; Šonský, Jiří
Several alternative approaches to processing jet flow visualization images were recently introduced by the authors. Common feature is processing a sequence of 2D images to detect presence and evaluate development dynamics of 3D vortical structures, which are recognised as regions that differ from the uncorrelated turbulent background in the processed pictures by their high negative values of correlation coefficient.
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