Dynamics of an Unsteady Diffusion Flame: Effects of Heat Release and Gravity
Abstract
This report presents time-dependent axisymmetric numerical simulations of an unsteady diffusion flame formed between a jet and a coflowing air stream. The computations include the effects of convection, molecular diffusion, thermal conduction, viscosity, gravitational forces, and chemical reactions with energy release. Previous work has shown that viscous effects are important in these flames and, therefore, all of the viscous terms in the compressible Navier-Stokes equations are included. In addition, the resolution is increased so that the large, vortical structures in the coflowing gas are resolved and the boundary conditions are improved so that the velocity field near the jet is more realistic. Computations with and without chemical reactions and heat release, and with and without gravity, are compared. Gravitational effects are insignificant in the nonreacting jet but in the reacting jet gravity produced the relatively low-frequency instabilities typically associated with flame flicker. Kelvin-Helmholtz instabilities develop in the region between the high-velocity and low-velocity fluid when there are no chemical reactions, but heat release dampens these instabilities to produce a mixing region which is almost steady in time.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 27, 1990
- Accession Number
- ADA227348
Entities
People
- Elaine Oran
- Janet L. Ellzey
Organizations
- United States Naval Research Laboratory