Verification and Validation of Large Eddy Simulation for Tip Clearance Vortex Cavitating Flow in a Waterjet Pump

In this paper, large eddy simulation (LES) was adopted to simulate the cavitating flow in a waterjet pump with emphasis on the tip clearance flow. The numerical results agree well with the experimental observations, which indicates that the LES method can make good predictions of the unsteady cavitating flows around a rotor blade. The LES verification and validation (LES V&V) analysis was used to reveal the influence of cavitation on the flow structures. It can be found that the LES errors in cavitating region are larger than those in the non-cavitating area, which is mainly caused by more complicated cavitating and tip clearance flow structures. Further analysis of the interaction between the cavitating and vortex flow by the relative vorticity transport equation shows that the stretching, dilatation and baroclinic torque terms have major effects on the generation and transport of vortex structure. Meanwhile the Coriolis force term and viscosity term also exacerbate the vorticity transport in the cavitating region. In addition, the flow loss characteristics of this pump are also revealed by the entropy production theory. It is indicated that the tip clearance flow and trailing edge wake flow cause the viscous dissipation and turbulent dissipation, and the cavitation can further enhance the instability of the flow field in the tip clearance

Numerical Investigation of Unsteady Cavitation Flow around E779A Propeller in a Nonuniform Wake with an Insight on How Cavitation Influences Vortex

In the current study, the turbulent cavitation flow around a marine propeller in a nonuniform wake is simulated with the shear stress transport (k−ω SST) turbulence model combining Zwart–Gerber–Belamri (ZGB) cavitation model. The predicted cavity evolution shows a fairly well agreement with the available experimental results. Important mechanisms of propeller cavitation flow, including side-entrant jet and cavitation-vortex interaction, are analyzed in this paper. Vorticity is found to be mainly located in cavitation regions and the propeller wake during propeller rotating. The unsteady behavior of cavitation and side-entrant jet can both promote local vorticity generation and flow unsteadiness. In addition, it is indicated with the relative vorticity transport equation that the stretching term plays a major role in vorticity transportation, while baroclinic torque and Coriolis force term mainly influence the vorticity distribution along the liquid-vapor interface

Verification and validation of large eddy simulations of turbulent cavitating flow around two marine propellers with emphasis on the skew angle effects

Large eddy simulation (LES) was used to simulate turbulent cavitating flow around a conventional marine propeller (CP) and a highly skewed marine propeller (HSP) with emphasis on the skew angles effects. The LES verification and validation (V&V) analysis was carried out with cavitation influence on the flow structures. The current numerical results demonstrate that LES can give excellent predictions of the transient complex cavitating flows around a CP and a HSP with the numerical results agreeing well with experimental data. This study applies the LES V&V to the cavitating flow around two propellers with a simplified three-equation method. The results show that the LES errors for HSP are smaller than for CP, which is mainly resulted by more skewed blade of HSP than CP. In addition, the cavitation-vortex interactions around the propellers were studied using the relative vorticity transport equation. The results indicate that both the baroclinic torque term and the Coriolis force term have important influences on the vorticity generation and transport in the cavity closure region. Further analyses indicate that most of the important flow structures including the tip vortex, leading edge vortex, trailing vortex and internal jet are reproduced by the current LES simulations. Due to the different geometry features (less skewed blade of CP than HSP), significantly more intense and violent vortical structures and cavitation phenomena are observed on the CP than on the HSP