Drag coefficient modification for turbulent gas-liquid two-phase flow in a rotodynamic pump

Abstract

An appropriate drag coefficient model is necessary for the simulation to better predict gas–liquid flow characteristics in a multiphase rotodynamic pump. However, most of the drag coefficient models are derived based on bubbles rising through a stagnant or laminar liquid, which are not applicable for turbulent flow in pumps. In this study, the drag coefficient in the quiescent flow is correlated with the drag coefficient in the turbulent flow through the Stokes number, and the drag coefficient model proposed by Ishii and Zuber (1979) is modified. By comparing the simulation results with experimental data of a rotodynamic pump, it is found that the pump performance predicted by the simulation with the modification is larger than without it, and has better accuracy. After the correction, the bubble accumulation near the suction side of the impeller blade is reduced, the gas volume fraction in the diffuser also decreases. When the rotational speed of the pump is 2350 r/min, the drag coefficient after the correction near the suction side of the impeller blade is much larger than before the correction. At the highest turbulent kinetic energy, the drag coefficient with the modification is more than 20 times greater than the corresponding ones without it. When the rotational speed increases to 2650 r/min or 2950 r/min, the frequency of the eddies are too high to affect the bubble motion, which makes the increasing degree of the drag coefficient decreases.