Dynamical Collapse of Interacting Two-Dimensional Buoyant Plumes

Buoyant plumes often exhibit pulsatile motion with a "puffing" frequency that depends on the Richardson number. This behavior has been well documented in both non-reacting plumes and pool fires. In this study, we investigate how this dynamical behavior is affected in two dimensions by the introduction of an adjacent plume. We expect that, at large spacing, the puffing frequency should be independent of the adjacent plume and, at small spacing, the frequency should approach the same frequency as if the two plumes were combined into one. The dynamical behavior between these two limits, however, depends on the competing effects of entrainment and vortex interaction along the inner shear layers. To investigate this regime, two-dimensional high-fidelity numerical simulations using adaptive mesh refinement are used to model the isothermal injection of helium into air from two adjacent plumes. Our results show that, as the spacing between the two plumes decreases, the plume interactions cause the puffing frequency to first increase, before decreasing to the expected combined frequency, comparable to reacting plume data. Further analysis is performed to extract phase information and to examine the collapse of the data using non-dimensional numbers.