From breakup to coiling and buckling regimes in buoyant viscoplastic injections

We study the injection flow of a heavy viscoplastic fluid into light Newtonian fluid, via modelling and experiments. The is carried out downward, an eccentric inner pipe inside vertical closed-end outer pipe. This configuration results in core surrounded by annular fluid. structured mixing negligible. As rate increases typical experiment, we observe three distinct regimes, associated with behaviour, namely breakup, coiling buckling (bulging) regimes. In breakup regime, yielded due to extension caused buoyancy, while regime yielding occurs compression promoted pressure interfacial shear stress applied upward For remains largely unyielded until it exhibits behaviour. develop lubrication approximation model, using Herschel–Bulkley constitutive equation, dimensionless parameters including Bingham number, power-law index, buoyancy viscosity ratio, diameter eccentricity aspect ratio. Based on reasonable prediction onset, model allows us classify regimes versus elegant combination numbers.