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Ph.D. Thesis Proposal: Shear Layer Dynamics of a Reacting Jet in a Vitiated Crossflow
Presenter: Vedanth Nair
Committee: Prof. Tim Lieuwen (advisor), Prof. Suresh Menon, Prof. Adam Steinberg
When: Friday May 17th, from 11:00 – 12:00
Where: MK 317
Abstract
The jet in crossflow (JICF) is a canonical flow configuration, used extensively in a number of industrial applications like axially-staged gas turbine systems, industrial boilers and afterburners. Despite its simple implementation, incorporating this flow configuration in most high-performance systems requires an in-depth understanding of how the flow topology alters macro-phenomena like mixing and flame stabilization. Past studies analyzing the behavior of non-reacting jets have noted that the overall performance of JICF configurations can be tied to the behavior of the shear layer, which influences both near-field and far-field jet dynamics. As a result, techniques used to manipulate jet mixing and penetration, such as active jet modulation, require an understanding of the dominant instability characteristics of the shear layer. Although this configuration finds extensive use in reacting applications, the hydrodynamics of reacting flows are often fundamentally different from non-reacting flows, and few studies have analyzed the influence of heat release and reactions on JICF dynamics.
Analyzing shear layer behavior, primarily the shear layer vortices (SLV), is often challenging due to the high frequency of these instabilities as well as the complexities in employing non-intrusive flow diagnostics such as particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF). The preliminary work details techniques used to extract the growth rate of these vortices from PIV data using the swirling strength of these structures. Observations support the hypothesis that reactions have a stabilizing effect on shear layer instabilities. However, in the studied configuration, the position of the flame outside the shear layer has a minimal impact on vortical interactions, allowing vortex growth to proceed in a suppressed manner. Numerical investigations were conducted using large-eddy simulation (LES) to model a simple JICF and analyze the effect of the flame position on the shear layer. Early results provide qualitative evidence that the jet dynamics can dramatically change due to the complete suppression of vortex rollup in the near field by the crossflow. Thus, the simulations demonstrated that the flame position-shear layer offset can have a significant effect on the shear layer dynamics akin to the effects of the heat release rate and non-reacting jet parameters.
The proposed work seeks to extend this preliminary analysis by leveraging both experimental and computational techniques to study this JICF dynamics. High-speed time-resolved (with respect to the instabilities) and spatially-well-resolved PIV measurements will identify the characteristic frequencies and mode shapes of relevant high-frequency structures. Filtered chemiluminescence measurements will provide valuable information regarding the coupling between heat release and hydrodynamics by helping to identify the dominant heat release modes. Detailed velocity and thermodynamic fields, obtained by numerical simulation, will be used to develop a fundamental understanding of how physical mechanisms, such as baroclinic torque and dilatation, give rise to the characteristic differences between reacting and non-reacting JICF cases.
