When a swarm of monodispersed air bubbles is injected into a stagnant Newtonian fluid, the disturbance caused by the motion of each bubble interacts with others, giving rise to velocity fluctuations in the continuous liquid phase. This phenomenon is referred to as bubble-induced turbulence, or more commonly, "Pseudoturbulence." A paramount attribute of pseudoturbulence is its departure from the homogeneous isotropic Kolmogorov's turbulence. When a small amount of polymer is dissolved into a Newtonian fluid, the dynamics of the flow can dramatically change. Because of the stretching property of the polymer molecules, efficient mixing can be achieved even in the absence of inertia (vanishing Reynolds number), referred to as "Elastic Turbulence''. When the Reynolds number is sufficiently high such that the inertial effects cannot be neglected, the modified turbulence due to the elasticity is referred to as "Elastoinertial Turbulence". 

For large bubbles rising in a viscous fluid, a thin layer of gas, commonly referred to as a “skirt,” can be observed issuing from the rim of bubbles. After its formation, a skirt can grow to a stable length or can become unstable and shed small fragments or large volumes. Recently, Legendre (2022) studied the motion of free-rising skirt bubbles using direct numerical simulation and identified two toroidal vortices in the skirt wake, a clear difference from the picture deduced from experimental observations from the 1970s.  The motivation of the current work is to experimentally identify the second toroidal vortex in the skirt bubble wake using particle image velocimetry.  Stay tuned to witness the results!

One of the most important fluid-mechanical concepts in an introductory class is the fluid viscosity. While other properties are more intuitive, such as density or surface tension, dynamic viscosity is hard to assimilate: its units do not offer an immediate physical measure of its meaning and its formal definition is more involved. Instead of the classical sedimenting-sphere experiment, we ask the students to "make pancakes": pour a known volume of a viscous fluid onto a horizontal surface to observe how it spreads. Using a phone to video-record the experiment, the time rate of change of the circular fluid blob radius can be determined with standard image processing techniques. By fitting the data to a viscous gravity current model, the value of  dynamic viscosity can be inferred in viscous-dominated flows, neglecting surface tension effects with notable accuracy and repeatability.

A single bubble rising in the viscoelastic fluid has a discontinuity in the bubble velocity as the bubble volume gradually increases. This is referred to as 'bubble velocity discontinuity' at the 'critical bubble volume'. Compared to the classical drafting-kissing-tumbling (DKT) behavior in Newtonian fluids, in the viscoelastic shear-thinning fluid, the subcritical bubble pair exhibit a drafting-kissing-coalescence (DKC) phenomenon, whereas the supercritical bubbles exhibit a drafting-kissing-dancing (DKD) phenomenon. In the so-called dancing phase, as the name implies, the bubble pair repeatedly interchange their relative leading and trailing positions as they rise to the free surface.