Suppression of Thermo-Acoustic Instabilities using Helhmoltz Resonator

Abstract

In combustion chambers due to coupling between unsteady heat release and pressure fluctuations the thermoacoustic instabilities are developed. These instabilities create structural vibration and damage. Therefore, there is a need to develop a technique which can effectively control these instabilities. The present work focuses on passive control using Helmholtz Resonator. The Rijke tube setup has been developed for characterization of thermos-acoustic instabilities. The study has been carried out with open-open ended steel Rijke tube of L/D ratio as 1. The preliminary results show that for LPG pre-mixed burner position at $x$ /L = 0.2, maximum thermos-acoustic instabilities were observed. The instability of 2nd and 3rd mode at a frequency of 500 Hz and 800 Hz respectively were observed for the different air-fuel ratio. The Helmholtz Resonator was designed and placed at the different position from one of the end. The maximum suppression of thermo-acoustic instabilities was observed at Helmholtz resonator position $x$ /L = 0.6. The experimental results show that approximately 10 dB reduction for the 2nd mode of instability was achieved whereas, the Helmholtz Resonator was not effective for 3rd mode as there is a change in heat source location and frequency of instability.