Ph.D. Thesis Defense: Yong Jea Kim

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  • Date/Time:
    • Monday November 6, 2017
      3:00 pm - 5:00 pm
  • Location: Montgomery Knight Room 325
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Summary Sentence: “Simulation of Full-Scale Combustion Instabilities in Small-Scale Rigs using Actively Controlled Boundary Conditions”

Full Summary: No summary paragraph submitted.

Ph.D. Thesis Defense by

Yong Jea Kim

(Advisor: Prof. Ben T. Zinn)

“Simulation of Full-Scale Combustion Instabilities in Small-Scale Rigs using Actively Controlled Boundary Conditions”

November 6, Monday @ 3 p.m.
Montgomery Knight Building, Room 325



            The onset of combustion instabilities (CIs) has hindered the development and performance of combustion systems employed in industrial, power generation and propulsion systems for many decades.   To Investigate CIs, actual “full-scale” engine tests are not practical because of the exorbitant cost of such tests, the large space required to house the full-sized engine, and the inability to equip full-scale engines with diagnostic systems that could measure, e.g., the temporal and spatial dependence of the mean and acoustic pressures, velocities, temperatures, compositions, and reaction rates.  Because of these difficulties, most studies of CIs to date were performed in “small-scale” setups that were geometrically similar to but smaller than the full-scale engines combustors.  While testing with these small-scale setups reduced the cost of testing and produced important results, the acoustic modes excited in the small-scale setups had considerably higher frequencies that did not simulate the lower frequency oscillations that are excited in the unstable full-scale engines. 

                The above discussion indicates that in order to study the driving of CIs in full-scale engines in small-scale rigs, the latter must simulate the acoustic environments, the combustion processes, and the interactions between these processes in the unstable full-scale engine.  This study developed a real time active acoustic boundary control approach to simulate the acoustic environment of the full-scale engine in the small-scale rig.  The proposed approach, for the study of the driving mechanism of longitudinal CIs, is described in the left figure below.  It describes the proposed approach for experimentally studying the processes taking place in region (I)~(II) of an unstable full-scale engine in a small-scale rig.  To attain this goal, the active control system (ACS) needs to generate an acoustic impedance at location (II) of the small-scale rig that equals to the acoustic impedance at the corresponding location in the full-scale unstable engine.  If this is accomplished, the acoustic oscillations in the region between locations (I) and (II) in the small-scale rig and the full-scale engine would be identical.

              This study has developed a real time ACS, which enables the small-scale tube rig to simulate the longitudinal acoustic oscillations in the full-scale tubes (or engine), with the one-dimensional cold flow setup.  In this setup, the speaker at the left end of the small-scale tube rig generated acoustic oscillations that simulate the driving by the combustion process, and the speaker at the right end was actively controlled to simulate the acoustic field of the full-scale system.  It was demonstrated that the developed, actively controlled, small-scale, rig can simulate travelling and standing waves oscillations that are encountered in longer full-scale tubes (or engines).  By modifying the ACS setup, the length of the “missing part” (see the left figure above), the simulations of the acoustic oscillations in various lengths’ full-scale tubes (or engines) were demonstrated in the same small-scale rig. 

                This study also developed a theoretical model that determines in real time the acoustic boundary condition (BC) that must be generated by the ACS at the boundaries of a small-scale rig that simulates transverse (tangential) CI in an annular combustor similar to those used in gas turbines and jet engines.  In this case, the small-scale rig consists of a small section of the annular combustor and the “missing part” of the full-scale engine consists of what has been “left over” after the small-scale sector-rig has been removed from the annular combustor (see the right figure above).  To determine the BCs that needed to be established at the boundaries of the actively controlled, small-scale rig, the developed model accounts for the effects of the combustion processes and flows through the reactants supply and exhaust nozzles in the “missing part” of the engine, and for the presence of a tangential mean flow in the annular combustor.  The developed model was numerically validated and used to investigate the effects of the exhaust nozzle, combustion process, and tangential mean flow component upon the characteristics of tangential CIs in an annular combustor. 

Committee Members 
Prof. Ben T. Zinn (advisor)
Prof. Jechiel Jagoda
Prof. Krishan K. Ahuja
Prof. Tim Lieuwen
Prof. Ari Glezer

Additional Information

In Campus Calendar

School of Aerospace Engineering

Invited Audience
Faculty/Staff, Public, Graduate students, Undergraduate students
aerospace engineering
  • Created By: Margaret Ojala
  • Workflow Status: Published
  • Created On: Oct 16, 2017 - 3:40pm
  • Last Updated: Oct 26, 2017 - 8:28am