Parametric study of the slope confinement for passive control in a centrally-staged swirl burner

Abstract

Lean premixed centrally-staged combustion holds the potential of meeting low-emission requirements, but it is known to be susceptible to thermoacoustic instabilities. A passive control method, using slope confinements has been demonstrated previously to be efficacy in suppressing thermoacoustic instabilities. Recognizing that the detailed flow features and the role of slope confinement structures associated with these thermoacoustic instabilities have not been well understood, the present study aims at revealing the suppressive mechanisms and assessing the suppressive efficacy of different slope confinements by measuring flow fields and conducting experiments with varying geometric parameters, including slope step height and slope angle. It is found that the slope confinements investigated have a general suppressive effect on thermoacoustic oscillations, which can be attributed to the limited vortex shedding from the dump plane. The slope confinement with smaller slope step height and slope angle is shown to have better performance on combustion stability. However, oscillations still occur in slope confinements with relatively large slope angle and step height. A qualitative relationship between the oscillation amplitude and the characteristic scale of corner recirculation zone is then established from the flow separation aspects. The present work provides insights into practical confinement design for passive control.