Applied Math Seminar
			  2-3pm, Feb. 13, Thursday
		         Mathematics Conference Room


  		     Large-eddy Simulation of Buoyant Jets

				Prof. Zhou Xu
		    Department of Mechanical Engineering
			     University of Vermont


Abstract: 

Spatially-evolving  circular buoyant jets (non-reacting and reacting) have 
been investigated using large-eddy simulation (LES) based on solving 
low-Mach-number Navier-Stokes equations. A second-order centre-difference 
scheme is used for the spatial discretization in Cartesian coordinates, 
an Adams-Bashforth scheme for the time marching, and Smagorinsky 
subgrid-scale model for the unresolved small scale turbulence. Buoyancy-driven
puffing phenomenon associated with self-excited large vortex structures  are  
well captured in the near-field, and the pulsation frequency of Strouhal 
number agrees well with the experimental correlation with Richardson number. 
The transition from laminar to turbulent flow  occurs further downstream with 
strong turbulent mixing by secondary instabilities. The plume-like behavior 
is characterized by a power law of -1/3 of the streamwise distance from the 
exit for the mean axial velocity in a fully-developed free plume. The 
energy-spectra for the scalar field show both -5/3 and -3 power laws, 
characteristic of buoyancy-dominated flows. The entrainment rate of buoyant 
jet is larger than isothermal jets. In addition, some results  are shown 
of premixed and diffusion jet flames using Reynolds-averaged Navier-Stokes 
(RANS) and detailed chemistry.