PhD Thesis Proposal

Samuel K. Stoknes

(Faculty advisor: Dr. Ben Emerson)

"Forced Dynamics of the Reacting Jet in Crossflow"

Tuesday, July 21

11:30 a.m.

Montgomery Knight Conference Room 317

Abstract:

Modern gas turbines increasingly use axial fuel staging to limit NOx at the high inlet temperatures that efficient, fuel-flexible operation demands. In this architecture, a secondary fuel jet is injected into the hot, vitiated products of the primary combustor, forming a reacting jet in crossflow (RJICF). This secondary flame sits in an acoustically active environment, and its unsteady response to flow disturbances drives both thermoacoustic instability and pollutant emissions. Yet that forced response has never been characterized at the frequencies, amplitudes, and flame topologies relevant to staged combustion: prior studies are either confined to cold, non-vitiated crossflows that omit autoignition physics, or forced far too slowly to reach the jet’s natural timescales. Preliminary measurements reframe this gap as an opportunity: acoustic forcing can actually transform a wall-attached flame into a fully lifted, compacted one, providing direct control over flame position and shape that can benefit emissions and combustor design.

To more broadly investigate the forced response of reacting jets in crossflow, a new vitiated-crossflow combustor has been developed that can acoustically force the secondary injector independently through either the jet plenum or the crossflow, at Strouhal numbers reaching the jet’s natural shear-layer instabilities and across the full range of RJICF flame topologies—a combination of capabilities no prior facility has offered. Using this rig, the proposed work characterizes the forced RJICF along three connected fronts: its global heat-release response and mean flame structure as functions of forcing frequency and amplitude; the underlying flow-field and flame mechanisms, resolved with simultaneous high-speed particle image velocimetry and OH planar laser-induced fluorescence; and the distinct response to crossflow forcing, isolated from the jet-plenum coupling that has obscured it in earlier work. Together, these measurements will establish the baseline understanding of forced RJICF dynamics needed both to predict thermoacoustic behavior and to exploit acoustic forcing as a control input in next-generation staged combustors.

Committee:
Dr. Ben Emerson (advisor), School of Aerospace Engineering
Dr. Tim Lieuwen, School of Aerospace Engineering
Dr. Joseph Oefelein, School of Aerospace Engineering