Ph.D. Thesis Proposal

By

Travis E. Smith

(Advisor: Prof. Timothy C. Lieuwen)

(Committee Prof. Jerry Seitzman, Prof. Suresh Menon)

Experimental Investigation of Transverse Acoustic Instabilities

10:00 AM, Tuesday, August 2nd, 2016

Student Center

Room 320

ABSTRACT:

With the push towards reduced greenhouse gas emissions, the gas turbine industry is moving towards lean, premixed combustion systems to reduce NOx. A side effect of this change is that self-excited, combustion driven oscillations are becoming more prevalent. These instabilities pose significant operability challenges such as reduced hardware lifetimes and costly damage to combustor hardware. These instabilities are characterized by coupled heat release oscillations, velocity field oscillations, and acoustic oscillations Previous work on the subject has looked at the effects of either longitudinal acoustic oscillations or coupled transverse-to-longitudinal acoustic oscillations on the hydrodynamic response of the flow field and subsequently the heat release through flame wrinkling. This work proposes to first decouple the transverse acoustic field from the longitudinal acoustic field in a multi-nozzle swirl combustor in order to isolate the effects of the transverse acoustics. Next a new method will be developed for interpolating planar experimental data (Stereoscopic Planar Image Velocimetry and OH-Planar Laser Induced Fluoresence) to obtain volumetric phase-averaged data. The volumetric data will be decomposed into helical flow disturbances as previous studies have shown that the flame location in the acoustic field will give rise to either symmetric disturbances or asymmetric helical disturbances. Experimental data and results from a hydrodynamic stability analysis will be compared in order to identify mechanisms leading to growth of these modes. In addition, present theory says that only the symmetric disturbances contribute to heat release linearly while the asymmetric disturbances can interact non-linearly. Thus this work proposed to take heat release data experimentally and compare to the volumetric flow field data to either confirm or disprove this hypothesis. In summary, this work proposes to study the effects of pure transverse acoustics on a multi-nozzle swirling flame and flow field through the analysis of experimental data in order to better understand its role in the onset of combustion dynamics in modern low NOx combustors.