Effects of Background Rotation on the Dynamics of Multiphase Plumes

We report laboratory results on bubble plumes released from a point source into a homogeneous liquid environment of depth H and rotation rate Omega. The gas phase is characterised by the non-dimensional slip velocity u(N) = u(s)/(BH-1)(1/3), where us is the slip velocity of the dominant bubble species and B is the source buoyancy flux. The effects of the background rotation are characterised by the Rossby number R-o = (B Omega(-3))(1/4)/H. We study the regimes 0.06 <= u(N) <= 0.36 and 0.03 less than or similar to Ro less than or similar to 0.3. We establish that, from Omega(t) approximate to 2.3, the growth of the maximum plume width bmax is slowed down compared to the non-rotating t(3/4) power law, where t is the time. At Omega t approximate to pi, the plume axis starts to tilt laterally and causes a slowdown of the rise of the height h(c) of the plume silhouette centroid from the t(3/4) power law. These critical times do not depend on u(N). After Omega t approximate to pi, the slip velocity counteracts the effects of rotation such that h(c) rises faster for larger u(N). The subsequent onset of the anticyclonic plume precession causes the disintegration of the rising plume front into vertical columnar structures for Ro less than or similar to 0.15. Once the plume reaches the free surface, the subsurface lateral dispersion of bubbles is increased compared to the non-rotating case. However, background rotation suppresses the lateral dispersion of bubbles at the free surface. We find that, asymptotically, the surface area A affected by the bubbles scales as (B Omega(-1))(1/2)t, and the proportionality factor reduces with an increasing u(N).