Buoyancy driven miscible front dynamics in tilted tubes -: art. no. 031702

The velocity V-f of the fronts of light and heavy fluids in a tilted tube, interpenetrating many diameters, is studied as a function of the fluid viscosity mu, Atwood number At<1 and tilt angle theta from vertical. Three flow regimes are observed: starting from vertical, V-f first increases with theta, reaches a plateau and then decreases again. In the first regime, V-f is controlled by segregation and mixing effects, respectively, increasing and decreasing with theta. On the plateau, V-f is independent of the fluid viscosity and proportional to (Atgd)(1/2), indicating a balance between inertia and buoyancy. In the third regime close to horizontal, the fluids separate into two parallel countercurrents controlled by viscosity. The variations of V-f with theta, At, and mu in the second and third regimes and the crossover from one to the other are described by scaling laws based on characteristic viscous and inertial velocities. (C) 2005 American Institute of Physics.