Instability of stratified air-water flows in circular pipes

In this work, the results of a linear stability analysis of air-water stratified flows in horizontal circular pipes are presented. The computed stability boundaries are found to compare well with available experimental data. The stability analysis considered three-dimensional infinitesimal perturbations of all possible wavelengths and took into account deformations of the air-water interface. Comparing stability boundaries obtained in pipe, square duct, and two-plate geometries, it is shown that there are cases where the simplified geometry of two parallel plates can be useful to model the stability boundary in a realistic geometry reasonably well.