A quasi-one-dimensional treatment of chemical reactions in turbulent wakes of hypersonic objects

Abstract

25 Langmuir, I., "The effect of space charge and initial velocities on the potential distribution and thermionic current between parallel plane electrodes," Phys.The effects of different mixing models on the chemical reaction histories in the turbulent wakes of hypersonic objects are investigated in a quasi-one-dimensional approximation. The radial propagation of the turbulent front is represented as a prescribed entrainment boundary and the chemical composition of the initial flow entering the boundary is calculated according to existing approximate methods for tracing chemical reactions in laminar flows. In the absence of a suitable chemical kinetics theory for turbulent flows, only the limiting cases of extremely slow and extremely fast viscous dissipation are considered for the subsequent turbulent mixing process. Specific examples are presented for the flow behind hypersonic spheres in air. In the slow-dissipation case, the high-entropy gas in the wake remains hot, and may even be reheated strongly by three-body atomic recombination. This gives rise to large amplitude fluctuations of the chemical species. In the fast dissipation case, the temperature generally falls off rapidly with distance behind the sphere, but moderately strong reheating may still take place due to sudden enhancement of the exothermic exchange reaction N + O2-*• NO -j-O. The mean electron density in the far wake is found to be extremely sensitive to the mixing model.

Nitric Oxide Production by Centimeter-Sized Meteoroids and the Role of Linear and Nonlinear Processes in the Shock Bound Flow Fields

“…The amount of NO produced in hypersonic flows depends strongly on the flow thermal evolution and history, but in general does not exceed several percent of the mole fraction [41]. An additional factor controlling the abundance of NO in high temperature flows is the Damköhler number (the ratio of the flow residence time to the chemical reaction time for reactions) [49]. The spatial and temporal importance of Reactions (1) and (2) in the context of the meteor generated shock waves, flow field evolution and diffusive processes are revisited in the next section.…”