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We experimentally investigate the behaviour of instantaneous localisedreleases of heavy particles falling as turbulent clouds in quiescent water,both with and without background rotation. We present the results of 514systematic experiments for no rotation and for three rotation rates $\Omega =5,10,20$rpm, and for the size of particles in the range $5\mu m$ to $1mm$,exploring four decades of the Rouse number $\mathcal{R} \in [6\times10^{-4},4]$ which quantifies the inertia of particles. In the canonicalframework of turbulent thermals described by Morton \textit{et al.}, [Proc. R.Soc. A: Math. Phys. Sci. \textbf{234}, 1 (1956)], we compare particle cloudswith salt-water thermals to highlight specificities due to the particulatenature of the turbulence forcing. In the absence of rotation, particle cloudsinitially behave as salty thermals with a modulation of their entrainmentcapacity, which is optimally enhanced for a finite inertia $\mathcal{R}\simeq0.3$ due to particulate effects. However this regime of turbulence is limitedin time due to the inertial decoupling between turbulent eddies and particles.For the three values of $\Omega$ explored here, the particulate enhancement ofentrainment is inhibited. Moreover the cloud's expansion is interrupted whenthe Coriolis force overcomes its inertia, forcing the cloud to transform intovortical columnar flows which considerably increase the residence time ofparticles.

Effects of particle size and background rotation on the settling of particle clouds