Wake-temperature turbulent fluctuation decay rates deduced from O sub 2 radiation.

Abstract

The effects of temperature fluctuations in a hypersonic turbulent wake on a chemical reaction with a strong temperature dependence are analyzed to determine the appropriate turbulence parameters for several different turbulent wake models. The chemical reaction selected for its temperature sensitivity is the atomic-oxygen chemiluminescent recombination. This radiation has been measured behind nonablating spheres in air in the General Motors Ballistic Range by Reis. The wake turbulence models are: a) random inviscid convection (so-called marble cake), b) homogeneous mixing, c) partial dissipation or bimodal model, d) mixinglag models, and e) gaussian mean-temperature profile with superimposed fluctuations. The data are interpreted in terms of each model. It is shown that models a, b, and d are inconsistent with the data. The radiation is interpreted in terms of the unmixed volume fraction of the partial dissipation model to obtain the rms turbulent temperature and mass density fluctuations and the turbulent dissipation function, which is then applied to predict the rms fluctuations of electron density. It is found that the resulting predictions are consistent with other measurements. The dissipation function indicates that the mixing-lag length is equal to about 20 wake radii. The model involving the Gaussian mean-temperature profile and fluctuations is consistent with the data for a thermal half width equal to slightly less than ha]f the mean turbulent front wake radius, with the temperature fluctuation ratio on the axis between 0.3 and 0.5. This is consistent with the measured mean-temperature profiles and temperature fluctuations, but the results are very sensitive to the mean temperature in the wake.