On turbulence and interfacial momentum transfer in dispersed gas-liquid flows: Contribution of bubbly flow experiments under microgravity conditions

The major focus of the present work is to develop an adequate closure model for the turbulent contribution of the interfacial momentum transfer term in turbulent bubbly flow. For this purpose, numerical simulations have been conducted on bubbly pipe flows under microgravity conditions. With no buoyancy effect, the average interfacial forces are negligible due to the small interphase relative motion. In these conditions, the distribution and the dynamics of bubbles are mainly controlled by the turbulence effects. Based on a phenomenological approach, a new closure for the turbulent interfacial momentum transfer is developed within Eulerian two-fluid modelling based on the averaging of the added mass force. The turbulent terms thus obtained comprises a non-linear term and a convective acceleration term associated with the drift velocity. The two-fluid model with the proposed interfacial momentum transfer closure and an original three-equation turbulence model for bubbly flows has been implemented in a 3D CFD code and applied to pipe bubbly flow under microgravity conditions. When compared to conventional two-fluid closures, the turbulent contribution of the added mass force proved to be a relevant closure that provides a substantial improvement in predicting the void fraction distribution and the bubbles' dynamics.