Date of Award

4-2016

Document Type

Thesis - Open Access

Degree Name

Master of Science in Engineering Physics

Department

Graduate Studies

Committee Chair

Dr. Mahmut Reyhanoglu

First Committee Member

Dr. John Hughes

Second Committee Member

Dr. William Mackunis

Abstract

Thermoacoustic instabilities can occur in thermal devices when unsteady heat release is coupled with pressure perturbations. This effect results in excitation of Eigen-acoustic modes of the system. These instabilities can lead to unpredictable behavior of the system. Gas-turbine combustion systems are especially prone to this phenomenon reducing their overall efficiency. Additionally, due to the nature of the combustion, the turbines end up releasing undesired amounts of harmful chemicals to the atmosphere, such as Nitrous Oxide (NOX).

A Rijke tube, representing a resonator with a mean flow and a concentrated heat source, is a convenient system to study the thermoacoustic phenomena. Under certain conditions of the main system, a loud sound is generated through a process similar to that in devices prone to thermoacoustic instabilities. Rijke devices have been extensively studied and several models which can provide accurate representation of the system, already exists. These models often assume that the system is comprised of a single heat source which drives the instability. This may not be the case as combustors which can use more than one flame are common for engines and industrial burners. By using the aforementioned models, a nonlinear feedback control scheme is developed for a Rijke-type combustor system with n actuators and m heat sources.

The performance of the controller is tested under different scenarios, assuring that is capable to exponentially stabilize the system despite any nonlinearities present in the heat release. Additionally, active control is studied in detail by analyzing the impact of the control parameters under different positioning of heat sources. The effect of the location for the actuators is also studied.

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