Abstract
In the frictional drag reduction by using bubbles, fluctuations of void fraction take an important role to enhance the effect. We have investigated the mechanisms on formation of bubble clusters that provide the large fluctuation. The objective of this study is establishing a new measurement system of passing interval of bubbles with ultrasonic wave in order to find out the property of void fluctuation. We conducted synchronous measurement of ultrasonic pulse emission and video camera recording of bubble images in a horizontal bubbly channel flow. The present technique provided reasonable results on the passing interval in comparison with the estimates from the images. Probability distributions of the passing bubbles obtained at three different points in the downstream represent influence of bubble coalescence.
