Buoyancy Profile Effects in Inclined Bubbly Shear Flow

Summary

We describe some studies of nominally two-dimensional fully turbulent and developed duct flows (breadth/depth B/D-5; overall length/depth L/D 60; D-based Reynolds number Re>10⁴) for inclination departures to 30 degrees from vertical at low voidages (<5% sectional average) representative of disperse regime using tap water bubbles (4mm) and smaller bubbles (2mm) stabilised in ionic solution. The bubbles were injected via a manifold located on the upper face at the entry station and turbulently dispersed transversely into the main body of flow. Pitot and static probe instrumentation, primitive but validated, provided adequate (10% local value) discrimination of main aspects of the mean velocity and voidage profiles at representative streamwise stations in L/D >30. Snapshot photography with axial slit-lighting was used to capture and characterise key features of buoyancy induced transverse layering and intermittent instability seen as Kelvin Helmoltz eddies responsible for sustaining dispersion at larger inclination departures of 10+ degrees.