Dr. Neil Balmforth

Roll waves:

Roll waves are the shock-like disturbances that ones typically sees on flowing films of fluids, whether they are laminar (as on gutters and windows on rainy days) or turbulent (in the case of streams and man-made water courses), or whether the fluid is water or some other kind of material (like mud). Analogues of roll waves may even perhaps be heard in stethoscopes (roll waves in flow down collapsible tubes have been suggested to lie at the origin of "Korotkov" sounds - the audible clicks heard when taking blood pressure) and seen in guinness (wave instabilities in two-phase flow).

My collaborators include Richard Craster, Alison Rust and Shreyas Mandre. And how could I possibly omit John Bush with his splendid webpage?

Click to enlarge
Turbulent roll waves
Roll waves in mud
Roll waves in a concrete channel in Lions Bay, B.C.

Roll waves in mud
(A clay slurry flowing   down an inclined chute develops intermittent surges; slower smooth roll waves, and faster "rippled" waves are seen)
Roll waves on a flowing layer of an aqueous suspension of cornstarch
(photographs from a flume in my basement)

Dynamics of roll waves

Erosive roll waves and cyclic steps

Roll waves in mud

Roll waves in custard

Department of Mathematics / Fluid Labs / Neil Balmforth / Research Interests