Flow field assessment under a plunging liquid jet

Within the current study, experimental investigations and computational fluid dynamics (CFD) simulations were performed to investigate the flow field structure developed under a turbulent liquid jet plunging into a quiescent pool of water. This topic is still challenging for CFD codes. Indeed, the study of turbulence in two-phase bubbly flows is one domain where experimental, numerical, and theoretical work is being extensively done nowadays. A correct description of closure laws for drag, lift, and interfacial forces is of great importance in numerical simulations.
Most critical with respect to CFD is the impact region between the jet and free surface of the liquid pool. Here, a complex interaction between surface waves and turbulence leads to the entrainment of air. These phenomena occur on very small scales. Up to now, it is not possible to resolve all relevant scales in one simulation due to limited computational resources. Therefore in this work, all phenomena above the pool surface and the impact region are excluded and the focus is set on the development of the flow field below the pool surface. The jet is modeled as a two-phase bubbly flow injecting into the pool.
For this purpose, the Particle Image Velocimetry (PIV) was utilized as measuring technique. Velocity fields for both impinging region and recirculation zone developed in the tank below the free surface were quantified and instantaneous and time-averaged velocity fields were obtained. For test cases where air entrainment occurred, only the recirculation region situated outside the bubble plume was quantified.On the other hand, the numerical simulations were performed using ANSYS-CFX 12.0, a commercial CFD package that solves the Navier-Stokes equations via a finite volume method and a coupled solver. The 2D as well as 3D simulation results are presented and compared with experimental results. Comparisons with the experimental data reveal satisfactory predictions of mean flow quantities, obtained by applying proper models of inter-phase momentum transfer.