ISSN:
1573-1987
Keywords:
DNS
;
round jet
;
finite-rate reaction
;
spectral method
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The evolution of a reacting, circular mixing layer - a model of round-jet flow - in its transition to turbulence was studied by direct numerical simulation. An economical Fourier pseudospectral method was combined with the third-order Adams-Bashforth scheme to integrate Navier-Stokes and scalar transport equations. The Reynolds number based on initial mixing-layer diameter and velocity difference was 1600. The initially thin mixing layer encloses a cylindrical core of fuel that mixes and reacts with the surrounding oxidizer. Both fast and finite-rate reactions were examined. The stages in transition are characterized by roll-up of the mixing layer into a sequence of vortex rings, pairing of adjacent rings, azimuthal instability, and breakdown to a disordered (turbulent) state. Reaction surfaces in the fast reaction limit become extended, folded and pinched off at various times corresponding to the dynamics of the vortices observed in the simulations. When the equivalence ratio is O(1) or smaller,the progress of reaction is determined by the dynamics of vortex rings. For larger ratios there is a qualitative difference: Initially, the flame is located well outside the rings and is relatively unaffected. Following breakdown to turbulence, there is a steep increase in flame surface area resulting in a noticeable change in fuel consumption rate. At smaller reaction rates (small Damkohler numbers), the reaction zones are diffuse and fill the vortical (mixed) regions. Product accumulates in and its presence raises the temperature of vortex cores, but reaction rates remain low due to low reactant concentrations. Reaction rates are highest in the braids between vortex rings where scalar dissipation rates and compressive strain rates show the highest values.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1009955824402
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