Shape and terminal velocity

In contrast, additional complications arise when dealing with bubbles and drops as both their shape and terminal velocity are influenced by the bounding walls. The literature is less extensive on this aspect of bubble motion even in Newtonian liquids. Irrespective of the type of liquid, in narrow tubes, bubbles tend to assume an elongated bullet shape with a hemispherical fore end and nearly flat at the rear end. The limited experimental results of Coutanceau and Hajjam (1982) confirm this type of behavior in tubes such that rf/D> 0.5. 

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