Analytical and experimental studies of wakes behind circularly capped bubbles

The wakes behind circularly capped bubbles are examined by means of an experimental and analytical study. A single two-inch diameter bubble is injected into a six by three foot fluid column, one half inch thick, producing an essentially two-dimensional flow. Aspirin powder placed in the fluid column just prior to bubble release highlights the structure of the flow field before dissolving. High speed film and sequenced photographs are taken to document the observed results. Pressure-time measurements are made with sensitive capacitive transducers mounted in the rear column wall and are synchronized with photographs using a high speed clock. Experimental fluids, prepared by mixing water and glycerine in varying proportions, are used to study the effects of viscosity on bubble shape and wake structure. Testing is performed over a range of Reynolds numbers from 14 to 29,655 which includes the transition from circularly capped to ellipsoidal bubble shape. Experimental data is reduced and summarized in convenient dimensionless form to permit comparison with analytical predictions.