Measurement of Reynolds Stress in Bubbly Flow Using Ultrasonic Doppler Method

Microscopic structure in bubbly flows is a topic of interest in the study of fluid flows. In the present paper, the Ultrasonic Doppler Method was applied to the measurement of bubbly flows from which Reynolds stress profiles were obtained. Experiments were carried out for an air-water dispersed bubbly flow in a 20mm x 100 mm vertical rectangular channel having a void fraction smaller than 3%. Two ultrasonic transducers were set on the outer surface of the test section with a contact angle of 45° off the vertical, one facing upward and the other facing downward. By applying statistical methods to the two directional velocity profiles, Reynolds stress profiles were calculated. By comparing the Reynolds stress in bubbly flow with that in single-phase flow, it was found that Reynolds stress profiles varied with the amount of bubbles present in the flow. Peak values of the Reynolds stress near the wall increased. This tendency was more pronounced as void fraction increased.