An experimental investigation of chemically-reacting, gas-phase turbulent jets

Citation

Gilbrech, Richard Joseph (1991) An experimental investigation of chemically-reacting, gas-phase turbulent jets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/p80s-h321. https://resolver.caltech.edu/CaltechETD:etd-06272007-091419

Abstract

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A new high pressure combustion facility was built to investigate mixing in axisymmetric, turbulent jets exiting into quiescent reservoirs. The facility uses fluorine and nitric oxide, diluted with nitrogen, for chemical product formation that is accompanied by heat release. The average temperature was measured by a set of long, thin, resistance wire thermometers stretched across the jet centerline at 16 downstream locations from x/d[subscript 0] = 30 to 240. Runs at several stoichiometric mixture ratios [phi], for Reynolds numbers ranging from 10,000 [...] Re [...] 150,000, were performed to determine any dependence of flame length on Reynolds number. The Reynolds number was varied through density, i.e., pressure, while the jet exit velocity and exit diameter were held constant. The time-averaged line integral of temperature, measured along the transverse axis of the jet by the wires, displays a logarithmic dependence on x/d* within the flame zone, and asymptotes to a constant value beyond the flame tip, as predicted from scaling and similarity arguments for a momentum-dominated, turbulent jet. The main result of the work is that the flame length, as estimated from the temperature measurements, varies with changes in Reynolds number, suggesting that the mixing process is not Reynolds number independent up to Re = 150,000. Specifically, the normalized flame length Lf/d* displays a linear dependence on [phi], with a slope that decreases from Re = 10,000 to 20,000, and then remains constant for Re > 20,000. Additionally, the measurements revealed a "mixing virtual origin," defined as the far-field flame length extrapolated to [phi] = 0, that increases with increasing Re for Re [...]20,000 and then decreases with increasing Re for Re > 20, 000. A separate set of experiments indicated that the runs described above were momentum dominated to the farthest measuring station and that the kinetics of the chemical reactions were fast compared to the characteristic mixing time. The transition of the jet flow from a momentum- dominated to a buoyancy-dominated regime was identified in another set of experiments.

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