Coherence between the global heat release rate and acoustic pressure fluctuations of a turbulent flame*

In combustion noise studies, the coherence between temperature and pressure measurements are typically used to estimate the relative contribution of direct and indirect noise sources. In recent work, it was proposed that global chemiluminescence intensity could be used as an alternative or in conjunction. However, there has been no experimental evidence of unity coherence between global chemiluminescence and acoustic pressure fluctuations, even in direct noise dominant systems. It was discussed in previous work how nearfield and finite acoustic compactness could contribute to low coherence. Following this analysis, this work aims to present experimental measurements of coherence along with acoustic spectra of a turbulent Bunsen burner flame as a canonical baseline. The goal is to obtain explicit measurements of unity coherence in a direct noise dominant system and validate preceding theoretical studies. Results will deepen our understanding of combustion noise generation and serve as a basis for the use of chemiluminescence in combustion noise studies.