Author(s): Zhiyi Yu; Shuliang Cao; Ying Liu
Linked Author(s): Ying Liu
Keywords: Multiphase rotodynamic pump; Two-fluid model; Virtual mass force; Unsteady flow; Gas-liquid two-phase flow
Abstract: The phase interaction is an important factor to affect the performance and the mixed transport process in a multiphase rotodynamic pump. As the density of dispersed gas phase (air) is much smaller than the continuous liquid phase (water), the virtual mass force cannot be ignored. To explore the effect of virtual mass force, the unsteady two -phase flow in a multiphase rotodynamic pump impeller was numerically simulated with two-fluid model based on the assumption of tiny bubbly flow. Because the wrap angle of the blade was large, the hybrid mesh was adopted to guarantee high mesh quality. In the working conditions, the liquid flow rates was kept constant, while the gas flow rate varies to get different IGVF (inlet gas void fraction) conditions, i. e. 4. 9% , 14. 9% and 25. 2% . In the simulation, the drag force and the virtual mass force were accounted for and the cases with and without the latter one were both analyzed for comparison. The results show that, the trajectories of the gas bubbles are influenced by the virtual mass force evidently in the inlet extended region. Due to the effect of virtual mass force, some gas will firstly move to the shroud before accumulating in the hub region of the impeller. The characteristic of the pump head was discussed and the results demonstrate that the virtual mass force can decrease the pump head and lead to its fluctuation. In addition, the comparison between the steady and unsteady simulation shows that the virtual mass effect can be found only by unsteady simulation, which demonstrates that the local relative acceleration is an important factor for the generation of virtual mass effect in the multiphase pump.
Year: 2013