Sensitivity of Combustion Driven Structural Dynamics and Damage to Thermo-Acoustic Instability: Combustion-Acoustics-Vibration

Abstract

The dynamic combustion process generates high amplitude pressure oscillations due to thermo-acoustic instabilities, which are excited within the gas turbine. The combustion instabilities have a significant destructive impact on the life of the liner material due to the high cyclic vibration amplitudes at elevated temperatures. This paper presents a methodology developed for mechanical integrity analysis relevant to gas turbine combustors and the results of an investigation of the combustion-acoustics-vibration interaction by means of structural dynamics. In this investigation, the combustion dynamics was found to be very sensitive to the thermal power of the system and the air-fuel ratio of the mixture fed into the combustor. The unstable combustion caused a dominant pressure peak at a characteristic frequency, which is the first acoustic eigenfrequency of the system. Besides, the higher-harmonics of this peak were generated over a wide frequency-band. The frequencies of the higher-harmonics were observed to be close to the structural eigenfrequencies of the system. The structural integrity of both the intact and damaged test specimens mounted on the combustor was monitored by vibration-based and thermal-based techniques during the combustion operation. The flexibility method was found to be accurate to detect, localize, and identify the damage. Furthermore, a temperature increase was observed around the damage due to hot gas leakage from the combustor that can induce detrimental thermal stresses enhancing the lifetime consumption.

Detecting deterministic nature of pressure measurements from a turbulent combustor

“…Thermo-acoustic instability is a dynamic phenomenon marked by the presence of large amplitude, self-excited pressure oscillations established in a confinement as a result of complex combustion acoustic interactions [1][2][3]. Such oscillations often lead to the failure of combustion systems due to excessive vibration of the hardware [4] and increased heat transfer to the walls of the chamber [5]. In many turbulent combustion systems, these thermo-acoustic oscillations are preceded by an intermittent regime.…”

Strongly Coupled Fluid–Structure Interaction in a Three-Dimensional Model Combustor During Limit Cycle Oscillations

“…Compared to the measurements performed by Altunlu [43], the predicted eigenfrequencies are acceptable except for the first torsional and the second bending mode in which 18% deviation can be observed. The deviation between the measurements and prediction can be caused by the effect of welds in the structure which is neglected in the FEM [3]. It can be also attributed to other simplifications made in the model such as neglecting the effect of thermocouples and pressure transducers.…”

“…These combustors can spontaneously exhibit significant flow and pressure oscillations. These oscillations may reach such high amplitudes that they cause flame extinction, structural vibration, flame flashback, and ultimately failure of the system [3,4]. Several coupled mechanisms are known to promote such interactions, for example, flame-acoustic wave interactions [5], flame vortex interactions [6], thermal-structure interactions [7,8], and fluid-structure interactions (FSI) [9,10], and all of them may be present in a system individually or simultaneously [11,12].…”

Impact of Oxygen Content on Flame Dynamics in a Non-Premixed Gas Turbine Model Combustor

“…With the increasing performance requirements of combustion chambers and increasingly stringent emission regulations [1][2][3][4], gas turbine combustion chambers are required to operate at high temperature and high pressure [5][6][7][8][9], which usually leads to the occurrence of combustion instability [10][11][12][13][14][15][16][17]. The combustion instability phenomenon will be accompanied by pressure pulsation and exothermic pulsation in the flow field inside the combustion chamber [18][19][20][21], which leads to vibration of the combustion chamber components and affects the safe operation of the engine [22][23][24]. In order to solve the adverse effects of combustion instability on the combustion chamber, it is necessary to study the combustion instability phenomenon to prevent the combustion instability phenomenon from leading to a decrease in the combustion chamber's stable operation time.…”