C. Palacios-Morales

Measurement of pseudoturbulence intensity in monodispersed bubbly liquids for 10<Re<500

Experiments were performed to measure the velocities of both phases in a monodispersed bubbly flow in a vertical column. Using water and water-glycerin mixtures, measurements were obtained for a range of Reynolds numbers from 10 to 500. For all cases, the Weber number was below 2. To generate a uniform stream of bubbles, an array of identical capillaries was used. To avoid coalescence, a small amount of salt was added to the interstitial fluid, which did not affect the fluid properties significantly. Measurements of the bubble phase velocity were obtained using a dual impedance probe and through high-speed digital video processing. A measurement of the vertical component of the fluctuating liquid velocity was obtained using a flying hotwire technique, which resolved the deficiency of this technique for flows with zero-mean velocity. To the best of our knowledge, this technique has not been used to study bubbly liquids in the past. It was found that for all cases, the bubble velocity decreases as the mean ...

Negative vortices: The formation of vortex rings with reversed rotation in viscoelastic liquids

The formation process of vortex rings in a viscoelastic liquid is studied experimentally considering a piston-cylinder arrangement. Initially, a vortex ring begins to form as fluid is injected from the cylinder into the tank in a manner similar to that observed for Newtonian liquids. For later times, when the piston ceases its motion, the flow changes dramatically. A secondary vortex with reversed spinning direction appears and grows to be as large in size as the original one. The formation process is studied by contrasting the evolution with that obtained for Newtonian liquids with equivalent Reynolds numbers and stroke ratios. We argue that the reversing flow, or negative vortex, results from the combined action of shear and extension rates produced during the vortex formation, in a process similar to that observed behind ascending bubbles and falling spheres in viscoelastic media.

Interaction of a vortex ring with a natural convective layer

We study the dynamics of the interaction of a vortex ring with a shear flow, generated by a natural convective layer. Laminar vortex rings were generated in water with a piston-cylinder arrangement. To generate the shear flow, a vertical wall was heated by a thermal bath held at constant temperature to produce a laminar and stable thermal boundary layer with a Grashof number of O(108). Measurements of the two-dimensional velocity field were obtained with a time resolved particle image velocimetry technique. Additionally, a 3D numerical model was used to simulate the experimental conditions. We mainly conducted experiments for the piston stroke L/D0 = 1 and Re of O(1000). The velocity ratio r = Uvi/Ush (where Uvi is the initial vortex velocity and Ush is the maximum velocity of the shear layer) was in the range 2.2 ⩽ r ⩽ 3.6. The results show that as the vortex approaches the shear layer, the ring expands and stretches mainly in the vertical direction and tilts slightly forming an angle between the wall an...