Dynamics of turbulent premixed flames in acoustic fields.
Degree: PhD, Aerospace Engineering, 2009, Georgia Tech
This thesis describes computational and theoretical studies of fundamental physical processes that influence the heat-release response of turbulent premixed flames to acoustic forcing. Attached turbulent flames, as found in many practical devices, have a non-zero mean velocity component tangential to the turbulent flame brush. Hence, flame surface wrinkles generated at a given location travel along the flame sheet while being continuously modified by local flow velocity disturbances, thereby, causing the flame sheet to respond in a non-local manner to upstream turbulence fluctuations. The correlation length and time scales of these flame sheet motions are significantly different from those of the upstream turbulence fluctuations. These correlation lengths and times increase with turbulence intensity, due to the influence of kinematic restoration. This non-local nature of flame sheet wrinkling (called 'non-locality') results in a spatially varying distribution of local consumption speed (i.e. local mass burning rate) even when the upstream flow statistics are isotropic and stationary.
Non-locality and kinematic restoration result in coupling between the responses of the flame surface to coherent acoustic forcing and random turbulent fluctuations respectively, thereby, causing the coherent ensemble averaged component of the global heat-release fluctuation to be different in magnitude and phase from its nominal (laminar) value even in the limit of small coherent forcing amplitudes (i.e. linear forcing limit). An expression for this correction, derived from an asymptotic analysis to leading order in turbulence intensity, shows that its magnitude decreases with increasing forcing frequency because kinematic restoration limits flame surface wrinkling amplitudes. Predictions of ensemble averaged heat release response from a different, generalized modeling approach using local consumption and displacement speed distributions from unforced analysis shows good agreement with the exact asymptotic result at low frequencies.
Advisors/Committee Members: Lieuwen, Tim (Committee Chair), Menon, Suresh (Committee Member), Peters, Norbert (Committee Member), Yang, Vigor (Committee Member), Zinn, Benjamin (Committee Member).
Subjects/Keywords: Heat release response; Turbulent flames; Level-set; Non-locality; Turbulent flame speed; Transfer function; Consumption speed; Turbulence; Combustion; Kinematics
to Zotero / EndNote / Reference
APA (6th Edition):
Hemchandra, S. (2009). Dynamics of turbulent premixed flames in acoustic fields. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/29615
Chicago Manual of Style (16th Edition):
Hemchandra, Santosh. “Dynamics of turbulent premixed flames in acoustic fields.” 2009. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021.
MLA Handbook (7th Edition):
Hemchandra, Santosh. “Dynamics of turbulent premixed flames in acoustic fields.” 2009. Web. 22 Jan 2021.
Hemchandra S. Dynamics of turbulent premixed flames in acoustic fields. [Internet] [Doctoral dissertation]. Georgia Tech; 2009. [cited 2021 Jan 22].
Available from: http://hdl.handle.net/1853/29615.
Council of Science Editors:
Hemchandra S. Dynamics of turbulent premixed flames in acoustic fields. [Doctoral Dissertation]. Georgia Tech; 2009. Available from: http://hdl.handle.net/1853/29615