On the effects of buoyancy on higher order moments in lazy plumes

ABSTRACT

Jets and plumes are shear flows created by momentum and buoyant sources. They can be classified as either pure jets, forced plumes, pure plumes, or lazy plumes. Lazy plumes are characterised as having a high source buoyancy flux relative to the momentum flux. We use direct numerical simulations to simulate lazy plumes to ascertain the effects of increasing plume ‘laziness’ on the higher order moments, such as Reynolds stresses, third order moments and turbulent kinetic energy budgets. The mildly lazy plumes behaved like most plumes in terms of higher order statistics: a self-similar collapse some distance downstream and peak values comparable to previous experiments and simulations. The highly lazy plumes did not show a self-similar collapse and, in most cases, had higher peak values in all moments. The highly lazy plumes had higher levels of turbulence intensities due to the high buoyancy flux, leading to significant buoyancy-induced turbulence production downstream.

KEYWORDS:

• Direct numerical simulation
• lazy plumes
• turbulent flows
• buoyancy
• free shear layers

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the U.S. Department of Energy, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement to the University of Florida under the Predictive Science Academic Alliance Program, under Grant DE-NA0002378. This research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Grant DE-AC02-06CH11357.