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On unsteady reacting flow in a channel with a cavity

Published online by Cambridge University Press:  26 April 2006

Ivar ØYvind Sand
Ivar ØYvind Sand
Affiliation:
Chr. Michelsen Institute, Department of Science and Technology, N-5036 Fantoft, Bergen, Norway
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Abstract

The problem investigated is the stability of a flame anchored by recirculation within a channel with a cavity, acting as a two-dimensional approximation to a gas turbine combustion chamber. This is related to experiments of Vaneveld, Hom & Oppenheim (1982). The hypothesis studied is that hydrodynamic oscillations within the cavity can lead to flashback.

The method used is a semi-analytical-numerical technique where the conservation equations for enthalpy and fuel fraction are represented by the low-Mach-number combustion model of Ghoniem, Chorin & Oppenheim (1982). Burnt and unburnt gas are treated as incompressible fluids where the reaction zone acts as a source for volume expansion. The flame is modelled by a Lagrangian technique using a simple line interface calculation algorithm.

The turbulent flow field is determined using conformal mapping theory and the hybrid random vortex method. The vorticity generation takes place at the walls to achieve no slip, and is influenced by boundary-layer separation. To avoid locating the separation points a priori the numerical viscous sublayer is extended continuously past the corners, and their singularities are in effect cut off by using locally a corner rounding technique within the conformal mapping.

The computed unsteady boundary-layer separation and reattachment of the non-reacting flow field agrees with unsteady boundary-layer theory. On the basis of the numerical simulations of the flame stability problem it is concluded that hydrodynamic oscillations within the cavity, combined with unsteady boundary-layer separation and reattachment can cause a flashback.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 229 , August 1991 , pp. 339 - 364
Copyright
© 1991 Cambridge University Press

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