Basic Instability Mechanisms in Chemically Reacting Subsonic and Supersonic Flows.

Abstract

Abstract : This report summarizes the main results and conclusions of research on turbulent combustion. The main objective was to determine and elucidate the mechanisms governing turbulence-combustion interactions in different spectral regimes. Problems studied included: 1) Structure of disturbed flames; 2) Evolution of turbulence-combustion interactions; and 3) Thermal and flow structures of turbulent premixed V-flames at low Damkoehler numbers. In an experimental investigation, simultaneous measurements of velocity and temperature in premixed, rod-stabilized, lean methane-air V-flames demonstrated the presence of high-frequency fluctuations within slowly drifting flame brushes, leading to temporal changes in flame shapes, thicknesses and propagation speeds. Cross-correlation coefficients of these simultaneous signals assumed high values within the reaction zone, suggesting the possibility that these fluctuations might be induced by the same governing mechanism. A theoretical study showed the importance of 'wrinkling-like' effects as well as the effects of chemical reactions rate on the evolution of fluctuations in a reacting shear layer. The direct rate-augmentation effects due to reaction led to changes in phase relationships between the various fluctuations, resulting in turbulent energy and mass transport in a direction opposite to that suggested by the gradient model. Keywords: Reaction kinetics; Energy transport; Thermal and flow structures; Methane/ethane/air; High frequency fluctuations; Spectral density distributions; Probability density functions.