Suppression of Thermo-acoustic Instability inside a Rijke Tube using an Adaptive Passive Helmholtz Resonator

Thermo-acoustic instability (TAI) inside a lean premix combustor is a major hurdle towards operation of gas turbines for both aerospace and land based operations. It arises due to the coupling between heat release fluctuation and pressure fluctuation within the combustor. It is exhibited in longitudinal, radial, tangential and bulk mode. The Rijke Tube (RT) is a canonical example to study this phenomenon on a laboratory scale in which longitudinal modes of TAI are seen. In this work a passive approach of using Helmholtz Resonator (HR) as an acoustic damper is proposed for suppression of TAI inside the RT. An attempt has been made to suppress TAI corresponding to second mode of instabilities. To abate different modes using same HR, its tuning is proposed by changing cavity volume with a hinge and use of different neck orifice diameters. The designed HR is fixed at a certain longitudinal position on RT, to suppress TAI of multiple modes. To analyse effectiveness of HR for suppressing TAI, wall pressure is measured with pressure transducer. To acquire data and analyse it, data acquisition system from National Instruments and LabVIEW software is used. The obtained result shows around 16 dB reduction in sound pressure level with HR of 5 mm neck diameter at 150° angle of cavity. The designed HR will help to reduce TAI at the design stage.