DOI: 10.1115/1.4064152 ISSN: 0742-4795

Effect of Insert Porosity on Combustion Instability In A Lean Premixed Combustor Analyzed By A Pod-Based Phase Reconstruction Technique

Mitchell Johnson, Ashley James, Ajay Agrawal
  • Mechanical Engineering
  • Energy Engineering and Power Technology
  • Aerospace Engineering
  • Fuel Technology
  • Nuclear Energy and Engineering

Abstract

Lean premixed (LPM) combustion is very effective at mitigating emissions but is vulnerable to strong thermoacoustic instabilities. A porous insert in the shape of an annular ring placed at the dump plane of the combustor has been proven to be an effective passive technique for mitigating these instabilities across a wide range of operating conditions. In this study, swirl-stabilized LPM combustion is investigated for three configurations - without any insert, with a porous insert, and with a geometrically similar solid insert. Acoustics, flow, and heat release rate behavior of the three test geometries are investigated using diagnostics including dynamic pressure and acoustic probes, particle image velocimetry (PIV), and OH* chemiluminescence (OH*CL) imaging. Synchronized measurements were acquired using sound probes, PIV, and OH*CL. Results include time-series and spectral measurements of pressure, velocity, and OH*CL, and mode analysis by proper orthogonal decomposition (POD). In addition, the dynamics of the instability are investigated by high-resolution phase reconstructions of velocity and OH*CL data using a novel implementation of POD introduced in this work. Results show two different instability modes: a longitudinal instability for the solid insert case and a helical, precessing vortex driven instability for the no insert case. In both cases, the flow field and heat release rate oscillations are coupled to produce the instability. No such coupling or oscillations are observed for the porous insert case. These results demonstrate that the insert porosity and flow dynamics associated with it are the primary mitigating factors.

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