A Parametric Study of Water Vapor Condensation in Supersonic Nozzle Flow Fields

Combustion driven hypersonic and supersonic wind tunnels are impaired in their flight simulation abilities by the condensation of water vapor introduced into the test stream by the burning byproducts of air and hydrocarbon fuels. The purpose of this study is to evaluate the abilities of a condensation model to predict the beginning axial locations of vapor changing into liquid droplets and study the correlations with initial combustion chamber conditions. A test matrix with different fuels, chamber pressure, and equivalence ratio was applied to the FIRACON model written by Erickson, et al. [7] using the dimensions of the NASA Langley eight-foot-high heated wind tunnel nozzle.

The results indicate higher chamber pressure and fuel-air equivalence ratio cause water vapor molecules to nucleate and condense further upstream of the nozzle, where as higher temperature delayed the condensation event in the expanding nozzle flow. At this time, FIRACON’s results can be considered qualitative in nature. General trends in the changes of the expanding flows due to varying initial chamber conditions can be seen, but the accuracy is unknown. A more thorough experimental and theoretical investigation of a condensing flow in a nozzle is needed to improve existing models before attaining results that could be considered relatively accurate or quantitative in nature.