Suppression of thermo-acoustic instabilities in horizontal Rijke tube using pulsating radial jets

Thermo-acoustic instability has been observed in gas turbines, rocket engines, and aero-engines. Acoustic perturbations grow and change the characteristics of the flow due to instability. The present work describes the use of pulsating air jets to suppress the thermo-acoustic instabilities. In present study pulsatile micro-jets are placed downstream of the burner radially which breaks the coupling between acoustic waves and unsteady heat release. A microphone connected to LIFA (LabVIEW Interface for Arduino) was used to detect the sound pressure levels. By controlling the airflow rate of the pulsatile jets, the sound pressure levels were suppressed down to the background noise level using minimum energy and time. A closed-loop control system is developed for this purpose, which works on the feedback signal acquired from microphone. To simulate the one dimensional combustion phenomenon, an experimental setup called Rijke tube was used. The suppression was most effective for the pulsatile jets of 27-33 Hz pulsation frequency range and at a flow rate of 6.8 LPM. This control strategy effectively controlled the combustion instability of around 35-42 dB.•The closed loop control method is built on DAQ and Arduino using the LabVIEW interface for Arduino (LIFA).•Developed closed loop active control method was observed to be effective for suppression of thermo-acoustic instability.•Optimum position of the radial planes of micro-jets with respect to the burner was decided to improve the efficacy of the pulsatile jets towards suppression of thermo-acoustic instability.

Experimental method for temperature measurement on lateral planes along a Rijke tube to assess efficacy of control method

The thermo-acoustic instabilities developed inside the combustor causes serious structural damage and reduces the life of power producing devices. The present work involves experimental investigation to assess effect of radial micro-jets air injection on thermo-acoustic instabilities and temperature in lateral planes. A co-axial pre-mixed gas burner used as the heat source inside the Rijke tube with variable location. Two types of Rijke tubes were used for experimental study, one is of steel with 75 mm internal diameter and 750 mm in length for the measurement of wall pressure, temperature and acoustics. •In the first part of the study, acoustic instability zone for different inlet mass flow rates was identified.•In the second part of study, the entire cross-sectional of Rijke tube was divided into 193 subzones and temperatures were measured at 193 locations when instability was present.•In third part, again temperatures were measured at 193 locations with implementation of control method with complete suppression of thermo-acoustic instabilities.

Predicting the secondary dynamic mode interference phenomenon in thermoacoustic instability control

This paper brings a novel mathematical perspective in assessing the rise of the secondary dynamic modes to prominence during the suppression of thermoacoustic instability. This phenomenon is observed by many earlier investigators; however, without a complete analytical reasoning. We consider a Rijke tube with both a passive Helmholtz resonator and an active feedback control to suppress instabilities. The core dynamics is represented as a linear time-invariant multiple time-delay system of neutral type. Parametric stability of the resulting infinite-dimensional dynamics is investigated using a recent analytical tool: cluster treatment of characteristic roots paradigm. This tool reveals the stability outlook of such systems exhaustively and non-conservatively in the parameter space of the system. First, we examine the stability with and without the Helmholtz resonator. We then select an unstable operation for the resonator-mounted Rijke tube, impose a time-delayed integral feedback control over it and reveal the stabilizing controller parameters using the cluster treatment of characteristic roots methodology. When high control gains are inappropriately selected, the new analytical procedure declares how the secondary dynamic modes of the system exhibit instability although the initially unstable mode is now stabilized. All of these stability assessments are cross-validated using experimental results from a laboratory-scale Rijke tube set-up.