Abstract
In the frictional drag reduction using bubbles, we proposed a periodic bubble injection technique to improve the performance and the new technique improved the performance 66% in Re 2200 at a horizontal channel flow. In this paper, the void fraction fluctuation in higher Reynolds number condition is investigated by visualization. The uncontrolled fluctuation of the void fraction fluctuation doesn't have any specific frequency, however the artificial fluctuation of void fraction maintain its frequency in streamwise. We indicate that it is possible to control density and shape of a swarm of bubbles by controlling the injection frequency and gas volume.
