Title:
Entrainment, Mixing, and Ignition in Single and Multiple Jets in a Supersonic Crossflow
Entrainment, Mixing, and Ignition in Single and Multiple Jets in a Supersonic Crossflow
Author(s)
Fries, Dan
Advisor(s)
Menon, Suresh
Ranjan, Devesh
Ranjan, Devesh
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Abstract
Jets in crossflow are a canonical example for three-dimensional turbulent mixing. Here, non-reacting and reacting sonic jets in a supersonic crossflow are studied. The influence of injectant properties on turbulent mixing is investigated. Using pure gases, the molecular weight and specific heat ratio is varied between 4-44 g/mol and 1.24-1.66, respectively. The jets are injected into a Mach 1.71 crossflow with a stagnation temperature ~600 K. Two single jet injectors and two staged jet injectors are designed to characterize potential enhancements in turbulent mixing and combustion processes. Mixture fraction and velocity fields are determined via Mie-scattering off solid particles. Velocity vectors are obtained by processing Mie-scattering image pairs with a correlation technique (particle image velocimetry). To ignite the flow field and enable systematic variation of the ignition location a traversable laser spark system is employed. The reacting flow is probed via CH* chemiluminescence and OH planar laser induced fluorescence visualizing regions containing hot combustion products. A new trajectory scaling improves correlation between all data sets considered, suggesting that the bow shock, boundary layer and momentum flux ratio are the dominant controlling factors. Turbulent mixing rates are highest for injectants with higher molecular weight and lower specific heat ratio. The larger of two jet spacings tested yields the greater enhancement of turbulent mixing rates. Ignition locations on the symmetry plane of the flow field are evaluated for their ability to sustain chemical reactions/heat release. Most favorable ignition locations lie in the windward jet shear layer away from the regions of highest flow strain. The smallest diameter single jet with presumably more boundary layer interaction and moderate strain rates provides the best results with regard to thermal energy release after spark deposition. Trends suggest that moderate compressible strain rates and no flow expansion are advantageous to sustain thermal energy release. Implications for future research directions and opportunities are discussed.
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Date Issued
2020-08-19
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Text
Resource Subtype
Dissertation