Inverse energy cascade structure of turbulence in a bubbly flow (PIV measurement and results)

The inverse energy cascade, which is one of the important phenomena to enha nce the large-scale flow instability in bubbly flow, is investigated by mea suring a local two-phase flow structure driven by buoyant bubbles using par ticle imaging velocimetry (PIV). In PIV, the flow field of liquid phase is measured by separating an original image to respective phase images using a statistical thresholding method for separating image parameters of bubbles and particles. The present results obtained in the case where the bubble R eynolds number and average void fraction are less than 30 and 1.5%, respect ively, confirm the large energy decay with a slope index steeper than - 5/3 in the log-log diagram of energy spectrum in a high wavenumber region. An important relationship between the energy spectrum and the bubble-bubble in terval distance is also detected.