Extracting the Acoustic Pressure Field from Large Eddy Simulation of Confined Reactive Flows

Abstract

Today, much of the current effort in the field of combustion noise is the development of efficient numerical tools to calculate the noise radiated by flames. Although unsteady CFD methods such as LES or DNS can directly provide the acoustic field radiated by noise sources, this evaluation is limited to small domains due to high computational costs. Hybrid methods have been developed to overcome this limitation. In these schemes, the noise sources are decoupled from the radiated sound. The sources are still calculated by DNS or LES codes whereas the radiated sound is evaluated by acoustic codes. These two approaches (direct and hybrid) have been widely used to assess combustion noise radiated by open flames. On the contrary, not significative work has been done for evaluating noise radiated by confined flames. Moreover, several problems can arise when attempting to compare direct to hybrid methods results from confined combustors. While almost a pure acoustic pressure field is obtained from direct computations when considering an open flame, for confined flames this statement does not hold: hydrodynamic pressure fluctuations play an important role. In the present paper the assessment of combustion noise is conducted by both direct (LES) and hybrid computations in a premixed swirled combustor. A method to extract the acoustic field from the entire pressure field given by LES is proposed.