An experimental study of low-Reynolds-number exchange flow of two Newtonian fluids in a vertical pipe

We present an experimental study of a buoyancy-driven, low-Reynolds-number ( Re J. Fluid Mech ., vol. 578, 2007, pp. 95–112). Experimental SBS velocity profiles are not well produced by the formulation of Kerswell ( J. Fluid Mech ., 10.1017/jfm.2011.190), possibly because the latter is restricted to flows whose cross-section has an interface of constant curvature. Despite the variations in flow regime, volume fluxes can be described by a power-law function of β, Q 1 = 0.059 β −0.74 . A comparison of experimental data with the theoretical approaches of Huppert Hallworth (2007) and Kerswell (2011) indicates that fluids are not arranged in the regime that maximises volume flux (e.g. SBS or CAF), nor do they adopt the geometry that maximises volume flux within that particular regime.