On the highly unsteady dynamics of multiple thermal buoyant jets in cross flows

Abstract

Thermal plumes of small scale generated by spatially separated heat sources can form, like atoms in a chemical compound, complex structures of different kinds and with distinct behaviors. The situation becomes even more complex if plumes can interact with imposed vertical shear (a horizontal wind). In this analysis, a “minimal framework” based on the application of a filtering process to the governing balance equations for mass, momentum, and energy (falling under the general heading of “Large Eddy Simulation” approach) is used together with direct numerical simulation to inquiry about the relative importance of buoyancy and vertical shear effects in determining the patterning scenario when highly unsteady dynamics are established (turbulent flow). Emerging patterns range from the flow dominated by a static rising jet produced by the aggregation of plumes that are pushed by horizontal leftward and rightward winds toward the center of the physical domain to convective systems with disconnected thermal pillars of smaller scale, which travel in the same direction of the prevailing wind. The classical sheltering effect, which for flows that are steady “in mean” simply consists of an increased deflection of the leading buoyant jet with respect to the trailing ones, is taken over by a variety of new phenomena, including (but not limited to) fast plume removal-rebirth mechanisms (with local increase in the velocity frequency and shrinkage in the related amplitude), “bubble” formation-rupture, and local departure of the frequency spectrum from the Kolmogorov similarity law.