Mean and Fluctuating Electron Density in Equilibrium Turbulent Boundary Layers

A simplified analysis is used to predict the mean and fluctuating electron density profiles in equilibrium high-speed turbulent boundary layers. The analysis is based on the application of nonlinear statistics to equilibrium chemistry and experimentally determined turbulence characteristics. Closed-form solutions of the electron density fluctuations are obtained for typical statistical distribution functions of the gas temperature fluctuations. The temperature dependence of the electron density is determined from complete thermochemical equilibrium calculations and the results are fit to a form of the Saha equation. Results are presented for reacting turbulent boundary layers consisting of clean air, Teflon/air mixtures, and phenolic carbon/air mixtures. It is shown that the true mean electron density can be orders-of-magnitude greater than the value computed at the local mean temperature. In addition, the root-mean-square electron density fluctuation can greatly exceed the true mean value.