55 巻 (1989) 517 号 p. 2824-2829
Directional characteristics of the combustion noise are experimentally investigated on turbulent diffusion flames established in the plane shear layers of three different flow and turbulence conditions. The effects of a breakdown of the organized flame structure in the downstream direction on the spectral behavior of combustion noise are also examined by inspecting the coherence between the acoustic pressure perturbation and local temperature fluctuation. The results show that the combustion noise emitted from the objective flames bears a quadrupole nature, but not a monopole one, independent of the existence of organized structure. Also, the organized flame structure has stronger influences on the overall noise generation than the increased free stream turbulence intensity within 5-7% under the same flow conditions, which may provide a clue to the noise reduction in the industrial burner systems. It is expected that noise radiation due to organized eddies decreases relatively rapidly with their downstream disappearance.