An examination of the high-order statistics of developing jets, lazy and forced plumes at various axial distances from their source

Abstract

In this study, direct numerical simulations of a turbulent free jet (Re = 2000), a lazy plume (), and a forced plume (Re = 1684, Ri = 0.025) are compared. The evolution of the various fluxes and the so-called source parameter, Γ, are examined as a function of distance from the source. The first-, second-, and third-order statistics of the flows are calculated and discussed. The radial profiles of such statistics, as well as that of the turbulent kinetic energy balance and other second-order transport equations are examined at two axial distances, one axial distance before the flows have adjusted to their similarity solution, and the other beyond the similarity adjustment length scale. Vortical structures are visualised and discussed along with entrainment. The source term Γ was not found to monotonically decrease with axial distance from the source as predicted by past researchers. While the mean flow and turbulent velocity statistics of the simulated lazy and forced plumes took on similar behaviour far from the sources turbulent statistics which involve buoyancy did not.

Keywords:

• direct numerical simulation
• environmental turbulent flows
• free shear layers

Acknowledgements

This research is funded by the National Science Foundation (NSF OISE-0968313) through the Partnership for International Research and Education (PIRE). The authors would also like to thank Prof. C.P. Caulfield of the University of Cambridge whose many helpful suggestions over the course of several enlightening conversations added immensely to the quality of this research.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Partnership for International Research and Education (PIRE): National Science Foundation [Grant Number NSF OISE-0968313].