Turbulence interactions with large bubbles

The dynamics of large and deformable bubbles in a turbulent channel flow is inves- tigated adopting the Phase Field Method (PFM) to define the distribution of the two phases (carrier and drops) inside the domain. The phase field variable is a marker func- tion defining the local concentration of each of the two phases; it is uniform in the bulk of the phases and it undergoes a smooth transition across the interface. All fluid properties are modelled as proportional to the phase field. A Cahn–Hilliard (CH) equation describes the transport of the phase variable in the entire domain. This CH equation is coupled to the Navier–Stokes (NS) equations via an interfacial term (Korteweg stress tensor). This CH–NS coupled system is solved using a pseudospectral technique based on a Fourier representation of variables in the periodic directions (streamwise and spanwise) and a Chebyshev representation in the wall-normal direction. We performed direct numerical simulations of a turbulent channel flow at a shear Reynolds number of Reτ = 300, laden with large and deformable bubbles (d+=120 w.u.) at a fixed Weber number (We = 0.75). The effect of different density ratios between the bubbles and the carrier fluid on turbulence has been investigated.