Physical modelling and similitude of air bubble entrainment at vertical circular plunging jets

When a plunging jet impinges into a pool of liquid, air bubble entrainment takes place if the inflow velocity exceeds a threshold velocity. This study investigates air entrainment and bubble dispersion in the developing flow region of vertical circular plunging jets. Three scale models were used and detailed air-water measurements (void fraction, bubble count rate, bubble sizes) were performed systematically for identical inflow Froude numbers. The results highlight that the modelling of plunging jet based upon a Froude similitude is affected by significant scale effects when the approach flow conditions satisfied We1 1E+3. Bubble chord time measurements showed pseudo-chord sizes of entrained bubbles ranging from less than 0.5 mm to more than 10 mm with an average pseudo-chord size were between 4 and 9 mm. However bubble size data could not be scaled properly.

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