Abstract
The turbulent properties of the bubbly two-phase flow with sub-mm diameter bubbles are experimentally investigated in a rectangular channel for upward flows. Varied with the void fraction, the bubble size and the liquid phase velocity are measured by the image-processing method and the laser Doppler velocimetry, respectively. By adding the surfactant, the coalescence of bubbles is prevented and small bubbles less than 1mm in diameter are uniformly generated. The bubble size with the surfactant is independent of the void fraction less than 1%. In the case of the single phase flow, any influence of the surfactant on the turbulent statistics is not observed. In the case of the two-phase flow with sub-mm diameter bubbles, bubbles are strongly accumulated near the wall by the lift force and they slide up along the wall. Consequently, the mean velocity profile of the liquid phase is steepened near the wall due to the driving force of buoyant bubbles. The streamwise turbulent intensity in the vicinity of the wall, where corresponds to the dense bubble region, is enhanced due to the pseudo turbulence, while the turbulent intensity of the two-phase flow in almost same as one of the single phase flow at the center of the channel.
