  Buoyancy-driven bubbly flows play pivotal roles in various scenarios, such as
the oxygenation and mixing in the upper ocean and the reaction kinetics in
chemical and bio-reactors. This work focuses on the convective flow induced by
the localized release of large air bubbles ($D_b=3.7$ mm, $\mathrm{Re}_b=950$)
in a water tank, exploring the resulting flow and the transition from laminar
to disturbed states as a function of the Rayleigh number in the range
$3\times10^3 \div 2\times10^5$. At low $\mathrm{Ra}$ the flow is smooth and
laminar with weak temporal oscillations, while a highly disturbed state appears
above a critical value $\mathrm{Ra}_c$. A theoretical analysis is presented
that links the mean flow circulation to the Rayleigh number. Through an
experimental investigation, utilizing 3D-particle tracking velocimetry and flow
visualization, we confirm the theory presented, and characterize the laminar to
disturbed transition in the system. The study offers insights into the
convective flow dynamics generated by bubbles, with implications for
applications such as bio-reactor soft mixer design.
