Sound Generation from Swirling, Premixed Flames Excited by Helical Flow Disturbances

Abstract

This article describes an analysis of the sound generated by swirling premixed flames when excited by helical disturbances, i.e., where the flow fluctuations have an azimuthal dependence of the form and denotes the helical mode number. These results illustrate the sensitivity of local and global sound generation characteristics to mode number, , swirl strength, and dimensionless frequency. An important result is the demonstration that specific mode numbers dominate particular aspects of the flame response. Specifically, particular helical modes dominate the magnitude of local flame wrinkling, , global heat release, , and sound generation, , and are generally not the same. For example, the helical mode that dominates the flame sound radiation, , is a function of flame compactness ratio, , while and are not. For compact, axisymmetric flames, , the axisymmetric, mode dominates the far-field sound radiation, both locally and in terms of global sound power. For and for , other helical modes dominate, generally those modes with closer to . Finally, the overall sound power scales as in the limit, while all modes scale equally as in the limit.