Potential of Direct Numerical Simulations to Investigate Flame/Acoustic Interactions

Abstract

The interaction between turbulent flames and isolated acoustic waves is a problem of fundamental interest with practical applications, for example for a better understanding of combustion instabilities. After developing a specific version of the well-known Rayleigh's criterion, allowing to investigate local amplification or damping of an acoustic pulse interacting with a reaction front, extensive investigations have been carried out on this subject. The present publication summarizes the main conclusions of all these studies. Premixed as well as non-premixed flames have been considered, using different fuels. All these investigations rely on high-fidelity models and high-accuracy methods, in order to reproduce quantitatively all important physical processes controlling this configuration. Direct Numerical Simulations (DNS) employing detailed physical models are best suited for this purpose, but lead to considerable requirements in terms of computing time. Due to these very high computational costs, first studies considered only two-dimensional flows. It is then questionable how general the obtained results can be for real turbulence. Therefore, the investigations have been later on extended to three-dimensional flows. A dedicated compressible DNS code has been developed for this purpose. For all DNS computations the developed Rayleigh's criterion then allows to quantify amplification or damping and to examine the reason for it. Strong focusing effects, highly local amplification and damping phenomena are observed. The influence of individual reactions and species on the damping process can also be quantified in this manner.