Ventilated cavities are characterized by the cavity shape, size, inception mechanism, cavity pressure with drag reduction, re-entrant jet and bubble breakoff from the cavity tip. All these characteristics are dependent upon each other. The aim of the present work is to study these aspects in an integrated way. Ventilated cavity formation was studied in a transparent acrylic channel by sparging gas behind straight blades. Clinging, partial, full and large cavity shapes were observed. Cavity transitions are correlated with the Froude and aeration numbers. Other cavities such as slug, and emulsion cavity were also observed. Bubble breakoff from the cavities is found to be dependent on the cavity type. Typically, large bubbles breakoff from slug cavities while smaller bubble sizes are observed breaking off from emulsion cavities. Other cavity shapes show a mixed breakoff pattern of varying proportion of large and small bubbles. Change in drag force on the blade is found to be dependent on the cavity shape and size. The cavity pressure is correlated with the liquid velocity over the blade and the superficial gas velocity. Negative and positive cavity pressure is found to be associated with the presence and absence of re-entrant jet. © 2006 Elsevier Ltd. All rights reserved.
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