The nonlinear dynamics of self-organising bubble departures from twin nozzles in engine oils was analysed. Air bubbles were generated from twin brass nozzles with an inner diameter equal to 1 mm. The flow of bubbles in bubble chains was recorded using high-speed camera. The time series of air pressure oscillations and signal from laser-phototransistor identifying the presence of bubbles over the nozzles outlet were recorded simultaneously. The self-organising bubble departures were observed and their stability was analysed. It was found that self-organising bubble departures become unstable because of successive (during subsequent bubble departures) decrease of the mean air pressure in one of the nozzle air supply system. It was shown that instability of selforganising bubble departures leads to equalization of pressures in both nozzles air supply systems which causes that simultaneous bubble departures appear. In the present experiment, this process was repeated in a cyclic and chaotic way. It was shown that stable selforganising bubble departures are accompanied by periodic air pressure oscillations in one of the nozzles and chaotic air pressure oscillations in the second one. Keywords Bubble Á Bubble chain Á Self-organising bubble departures Á Nonlinear data analysis
The bubble departures from two neighbouring brass nozzles (with inner
diameter of 1.1 mm) in three liquids: distilled water, mineral and synthetic
engine oils were investigated. The numerical simulations were used for
reconstruction of liquid flow around the departing bubbles. Bubble movements
in liquid have been recorded using a high speed camera. The 2D bubble paths
have been reconstructed using: Laplacian of Gaussian filters, algorithm of
detection of local extremes of image brightness and Kalman filter. It was
shown that during alternative bubble departures bubble paths become
repeatable. The dimensionless number (similar to Strouhal number) was
proposed to describe oscillating liquid flow generated by departing bubbles
over the nozzle outlet. Such number was used for defining the hydrodynamic
criterion of alternative bubble departures.
In the recent paper, non-linear methods of data analysis were used to study bubble departure synchronisation. In the experiment, bubbles were generated in engine oils from two neighbouring brass nozzles (with an inner diameter of 1 mm). During the experiment, the time series of air pressure oscillations in the air supply system and voltage changes on phototransistor were recorded. The analysis of bubble departure synchronisation was performed using a correlation coefficient. The following methods of non-linear data analysis are considered. Fast Fourier Transformation, autocorrelation, attractor reconstruction, correlation dimension, largest Lyapunov exponent and recurrence plot analysis were used to examine the correlation between bubbles behaviour and character of pressure fluctuations. Non-linear analysis of bubble departure synchronisation revealed that the way of bubble departures from two neighbouring nozzles does not depend simply on the character of pressure fluctuations in the nozzle air supply systems. The chaotic changes of the air pressure oscillations do not always determine the chaotic bubble departures.
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