Experimental investigation of transverse acoustic instabilities

Smith, Travis Edward

Title:

Experimental investigation of transverse acoustic instabilities

dc.contributor.advisor	Lieuwen, Timothy C.
dc.contributor.author	Smith, Travis Edward
dc.contributor.committeeMember	Seitzman, Jerry M.
dc.contributor.committeeMember	Menon, Suresh
dc.contributor.committeeMember	Sun, Wenting
dc.contributor.committeeMember	Ranjan, Devesh
dc.contributor.department	Aerospace Engineering
dc.date.accessioned	2018-01-22T21:11:46Z
dc.date.available	2018-01-22T21:11:46Z
dc.date.created	2017-12
dc.date.issued	2017-11-09
dc.date.submitted	December 2017
dc.date.updated	2018-01-22T21:11:46Z
dc.description.abstract	This work presents 5 kHz stereo PIV and OH PLIF measurements as well as OH* and CH* chemiluminescence measurements of transversely forced swirl flames. The presence of transverse forcing on this naturally unstable flow both influences the natural instabilities, as well as amplifies disturbances that may not necessarily manifest themselves during natural oscillations. By manipulating the structure of the acoustic forcing field, both axisymmetric and helical modes are preferentially excited away from the frequency of natural instability. Additionally, forced and self-excited transverse acoustic instability studies to date have strong coupling between the transverse and axial acoustic fields near the flame. This is significant, as studies suggest that it is not the transverse disturbances themselves, but rather the induced axial acoustic disturbances, that control the bulk of the heat release response. The work first presents a method for spatially interpolating the phase locked r-z and r-θ planar velocity and flame position data, extracting the full three-dimensional structure of the helical disturbances. These helical disturbances are also decomposed into symmetric and antisymmetric disturbances about the jet core, showing the subsequent axial evolution (in magnitude and phase) of each of these underlying disturbances. Then experiments performed with essentially the same transverse acoustic wave field, but with and without axial acoustics, show that significant heat release oscillations are only excited in the former case. The results show that the axial disturbances at the nozzle exit are the dominant cause of the heat release oscillations. These observations support the theory that the key role of the transverse motions is to act as the “clock” for the instability, setting the frequency of the oscillations while having a negligible direct effect on the actual heat release fluctuations. They also show that transverse instabilities can be damped by either actively canceling the induced axial acoustics in the nozzle (rather than the much larger energy transverse combustor disturbances), or by passively tuning the nozzle impedance to drive an axial acoustic velocity node at the nozzle outlet.
dc.description.degree	Ph.D.
dc.format.mimetype	application/pdf
dc.identifier.uri	http://hdl.handle.net/1853/59252
dc.language.iso	en_US
dc.publisher	Georgia Institute of Technology
dc.subject	Combustion instabilities
dc.subject	Swirl flame
dc.subject	Transverse acoustics
dc.title	Experimental investigation of transverse acoustic instabilities
dc.type	Text
dc.type.genre	Dissertation
dspace.entity.type	Publication
local.contributor.advisor	Lieuwen, Timothy C.
local.contributor.corporatename	College of Engineering
local.contributor.corporatename	Daniel Guggenheim School of Aerospace Engineering
local.relation.ispartofseries	Doctor of Philosophy with a Major in Aerospace Engineering
relation.isAdvisorOfPublication	b612098b-d0e6-4ea2-a8d5-92d6d02fe6c4
relation.isOrgUnitOfPublication	7c022d60-21d5-497c-b552-95e489a06569
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thesis.degree.level	Doctoral