Bubble-to-Spiral Type Vortex Breakdown
The Vortex Breakdown movie shows iso-vorticity surfaces evolving in time (at a Reynolds number of 200). The early frames reveal an initially symmetric bubble-like structure which contains a region of reversed flow. An instability originates in the the “tail” emanating from the aft portion of the bubble. A transition to spiral-type breakdown then ensues.
Vortices Formed in Channel Heated From Below
Mixed convection in a horizontal rectangular duct of aspect ratio 4 heated from below, and with cold side walls, was studied numerically for a non-Boussinesq fluid. Results were computed for a Rayleigh number of 130,700, a reduced temperature of 2.33, and Reynolds numbers ranging from 5 to 20. The movie listed above reveals the time-dependent evolution of the flow at Re=5 in terms of contours of constant vorticity. (Flow from left to right, top view of the duct.) The sequence reveals that the inner vortex pair terminates upon itself, or form distinct ring vortices. The consequence of these coherent structures is a complex time-dependent distrubution of the Nusselt number on the lower wall.
Buoyant Pulsating Exchange Flow Through a Vent in a Horizontal Partition
Density contours of a buoyancy-driven exchange flow between compartments in a cylindrical take separated by a vented, horizontal partition of finite thickness (vent diameter to partition thickness ratio of L/D=0.3). Results were computed for water with density variation achieved through temperature differentials. At t=0, the temperature of the water in the lower and upper partitions was set to 320 and 295 K, respectively.