Two -phase flow through sudden area expansions

The objective of this research is to investigate, experimentally and analytically, the characteristics of two-phase flow across sudden area expansions. An analytical formulation for the pressure recovery was developed for two-phase flow across a sudden expansion that takes into account the change in void fraction across the expansion, the pressure difference between the upstream flow and the downstream face of the expansion and the wall shear stress. Experiments were performed to evaluate the existing models using air-oil flow through sudden expansions with different area ratios for various flow conditions. Flow visualizations along with time averaged local profiles of the void fraction, mean liquid velocity and the liquid turbulence intensity downstream of the expansion, obtained using hot-film anemometry, are presented to characterize the development of the two-phase flow downstream of the sudden expansion. The pressure recovery, void fraction change, and flow pattern change were used to characterize the two-phase flow through the sudden expansion. Based on the flow patterns, the contribution of the wall pressure and the wall shear stress terms to the pressure recovery formulation were evaluated. Including these terms in the pressure recovery formulation improved the accuracy of the pressure recovery prediction. In addition, correlations and an algorithm for predicting the pressure recovery were developed in terms of the upstream flow parameters.