Piv experimental study of single bubble rising behavior

A bubble observation test bench was built, and the high-speed camera, as well as particle image velocimetry (PIV), were used to explore the rising behavior of a single bubble in static water. The relationship between the change of bubble shape and the fluctuation of the rising speed was found: the flatter the bubble shape, the faster it rises. Besides, as the inner diameter of the needle increases, the size of the bubble generated increases, but the average rising speed decreases first and then increase. By comparing and analyzing the experimental data under different working conditions, it was found that the bubble has a minimum rising velocity of about 0.22 m/s when the radius is between 2.2 mm and 2.3 mm. By Fourier analysis of the bubble rising speed, the relationship between the fluctuation period and the bubble size was also found: the larger the bubble, the smaller the period. Through the frame-by-frame analysis of the bubble rising process by PIV technology, the annular flow field around the bubble in static water was found, and the relationship between the rising direction of the bubble and the change of the flow field was summarized. (authors)