A granular flow around an obstacle, and the shape of the static deposit it leaves behind, are sensitive to details of the granular friction. In particular, frictional hysteresis is a crucial part of the physics at the interface between flowing and static grains. Read more...
A symmetry breaking pattern switching phenomenon is observed in 2D granular media under compression. When the undeformed configuration on the left is compressed, rigid cylinders (white) form pairs, resulting from the buckling of columns of elastic cylinders (purple).
A semi-infinite air finger propagates into an elastic-walled channel initially filled by a viscous fluid. The influence of gravity causes asymmetries in the channel wall shapes and in the thicknesses of the fluid films above and below the finger, leading to a monotonic relationship between the air pressure and finger speed.
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Sinuous instability of a confined jet
Left: Passive tracers (shown as streaks) in a confined turbulent momentum jet; middle: corresponding velocity field (arrows) and vorticity field (background) measured using particle image velocimetry; right: schematic of the self-similar unstable sinuous core and alternating side vortices.
Numerical bifurcation tracking.
Contours of axial velocity for the flow past a cylindrical obstacle in a channel (top). A Hopf bifurcation occurs at Re ≈ 92, and the contours of the axial velocity for the critical eigenfunction (bottom) illustrate the complex downstream structure that must be resolved to accurately determine the location of the bifurcation.
Granular fingering and segregation-mobility feedback
A bidisperse granular avalanche exhibits a frontal instability which evolves into levee-channelised 'fingers'.
Granular shocks in shallow free-surface flows
Granular avalanches exhibit discontinuous shocks and bores with complex interaction dynamics.
Spin-over in a torus.
Snapshots of a simultaneous collisional boundary-layer breakdown in the cross section of a rotating fluid-filled torus following a change in the rotation rate.
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Pipe turbulence.
A turbulent puff in pipe at Re = 2200.
Pattern-switching in elastic media.
A pattern switch induced by the compression of a two-dimensional elastic foam. A square array of holes is transformed into an array of ellipses with their major axes arranged in orthogonal directions.
Vibration-driven segregation of grains.
Segregation of a thin layer of a mixture of polystyrene beads and '100's and 1000's' under vibration.
Attractors from Taylor-Couette flow.
The left one is from a quasiperiodic flow and the right one from a chaotic flow.
Bubbles propagating through expansions and contractions:
Semi-infinite and finite bubbles, propagating through a fluid filled channel of varying geometries. These have applications in microfl'>Read more...
Viscous fingering under a cellophane sheet.
Air is injected at constant flow rate into an oil-filled elastic cell, coupling a fingering instability to the wrinkling of the cellophane sheet.
Viscous fingering under an elastic membrane.
Above a critical flow rate of air injection into a oil-filled elastic cell, the interface becomes unstable and an unusual fingering pattern develops.
Airway reopening.
The reopening of pulmonary airways can occur through the propagation of long air finger. If the occluded elastic tube is initially very strongly collapsed, multiple reopening bubbles such as double-tipped (top) or pointed bubbles (bottom) can occur. Read more...
Bubble oscillation in a constricted tube.
The propagation of an air bubble into a constricted channel initially filled by a viscous fluid can lead to oscillations with a well defined spatial period. Read more...