Analysis of thermoacoustic instability with corresponding eigenfrequencies in a large scale industrial oil furnace

Abstract

It has been a serious concern to cope with noise and vibration problems due to thermoacoustic instability in design and operation of large industrial furnaces. In this work Reynolds-averaged Navier-Stokes (RANS) simulation was performed with resulting mean scalar fields provided as an input for acoustic analysis at the Maximum continuous rating (MCR) and 50 % MCR loads. Large Eddy simulation (LES) was performed for a single burner to investigate shear layer oscillations leading to vortex shedding which was suspected to be an excitation source. The Rayleigh parameter was estimated to check mutual correlation and any positive feedback of fluctuating pressure and heat release throughout the single burner domain. The flame transfer function in terms of n and τ was obtained for simplified network analysis from LES results. The peak frequency in turbulence energy spectrum was in good agreement with the measured resonant frequency with positive Rayleigh parameters around the region of shear layer oscillation at the MCR load. No instability was predicted at 50 % MCR load to be consistent with test results, with negative Rayleigh parameters throughout the domain. And the energy spectrum analysis confirms that there is mismatch between the peak frequency and the eigenfrequencies of the furnace at 50 % MCR load.