Wall drag modification by large deformable droplets in turbulent channel flow

• The wall drag modifications produced by large deformable droplets are investigated.
• The wall drag increases reducing the droplets deformability.
• The droplets average velocity reduces increasing the deformability.
• Vorticity fluctuations are increased in the wall region and in the channel center.
• The drag enhancement is due to the droplets slip velocity.

The role of deformability in the wall-drag modification produced by the dispersion of large deformable droplets in turbulence is investigated by Direct Numerical Simulations (DNS) of a turbulent channel flow (Reτ=150Reτ=150) coupled with the Phase Field Model (PFM) description of the droplets. The two fluids have the same density and viscosity, and a wide range of interface deformability is considered by changing the Weber number: We = 0.18–2.8. The results show wall-drag modifications that depend on the droplets deformability: when the deformability is low (small We), a significant Drag Enhancement (DE) is observed; increasing the deformability the DE is reduced and negligible effects are observed when the Weber number is sufficiently large. The DE is likely due to droplets velocity that reduces increasing the deformability, introducing an obstruction to the flow and increasing drag.