Experience using pressure-based CFD methods for Euler–Euler simulations of cavitating flows

Dynamics of unsteady compressible cavitating flows associated with the cavity shedding

Numerical investigation of cavitation vortex dynamics in unsteady cavitating flow with shock wave propagation

Comparative study between turbulence models in unsteady cavitating flow with special emphasis on shock wave propagation

Eulerian–Lagrangian multiscale numerical analysis of multimodal partial shedding dynamics

Numerical simulation unsteady cloud cavitating flow with a filter-based density correction model

We investigated the three-dimensional characteristics in the unsteady cavitating flow over an axisymmetric body with a blunt headform. A high-speed video camera was used to visualize the cavitating flow structures. A modified PANS (Partially-averaged Navier-Stokes) turbulence model coupled with Kubota cavitation model was used to simulate the time-evolution process of the unsteady cavitating flows. The finite-time Lyapunov exponent (FTLE) and Lagrangian coherent structures (LCS) methods are applied to investigate the three-dimensional flow patterns. The results show that the numerical method is capable of simulating the unsteady cavitating flow for capturing the attached cavity with maximum-length, the cavity break-off and U-type shedding, in accordance with the qualitative features observed in the experiment. Three-dimensional characteristics are extremely impressive in the unsteady cavitating flows. The re-entrant flows originate from different circumferential positions at the closure region of the attached cavity, and move upstream at different speeds. Moreover, substantial circumferential motions in the unsteady cavitating flow are found based on Lagrangian trajectories, and it is reasonably deduced that the U-type shedding cavity is primarily induced by the effect of re-entrant flow motions consisting of moving upstream and circumferential flows as well.

Numerical investigation of the shock wave propagation in cavitating flow around NACA66 hydrofoil based on a compressible method

In the present work, a cavitation model based on a new truncated form of the full Rayleigh-Plesset (R-P) equation for the source terms controlling vapor generation and destruction has been developed and implemented in the ANSYS FLUENT platform. Coupled with a Filter-based density corrected model (FBDCM), the cavitating flow over a 2-D Clark-Y hydrofoil is investigated numerically with particular emphasis on understanding the effect of cavitation structures and the shedding dynamics on the hydrodynamics coefficients and surrounding flow velocity structures. The hydrofoil has a fixed angle of attack of α = 8° with a moderate Reynolds number of Re = 7.0×105. Simulations have been carried out for various cavitation numbers ranging from non-cavitating flows to the cloud cavitation regime (σ = 0.80). In particular, we compared the lift and drag coefficients, the cavitation dynamics and the time-averaged velocity with available experimental data for two cavitation models, i.e. the proposed model and Schnerr-Sauer model. The comparisons between the numerical and experimental results show that the proposed model has a better capability than Schnerr-Sauer model to capture the characteristics of lift and drag coefficients under cavitation conditions. Meanwhile, the proposed model is sufficiently robust to predict the initiation of the sheet/cloud cavity, growth towards the trailing edge, and subsequent shedding downstream, which is in accordance with the experimental quantitative features in literature.

Hydrodynamic cavitation is a complex physical phenomenon that appeared in hydraulic systems (pumps, turbines, valves, Venturi tubes …etc.) when the fluid pressure decreases below the saturated vapor pressure. The works carried out in this study aimed to get a better understanding of the cavitating flow phenomenon. For this, we have numerically studied a cavitating bubbly flow through a venturi nozzle. The cavitation model is selected and solved using commercial code computational fluid dynamics (CFD). The numerical results are compared to the previous experimental and numerical data.The obtained results showed that the effect of the inlet pressure (10, 7, 5 and 2 bars) and outlet pressures (6.5, 6, 5, 4, 3.5, 1.5, and 1 bars) of the Venturi on pressure, velocity of the fluid flow and the vapor fraction formation. We found that the inlet and outlet pressures of the venturi are strongly affected on the evolution of the pressure, velocity and vapor fraction formation in the cavitating flow. The results presented in this study provide insight and useful guidance to the designer of hydrodynamic cavitation devices, identifying key geometrical and physical parameters of cavitation onset and intensification that can be manipulated to achieve the desired level of cavitation flow.

The unsteady cavitating flow and pressure fluctuation around the 3-D NACA66 hydrofoil were simulated and validated based on detached eddy simulation turbulence model and a homogeneous cavitation model. Numerical results show that detached eddy simulation can predict the evolution of cavity inception, sheet cavitation growth, cloud cavitation shedding, and breakup, as well as the pressure fluctuation on the surface of hydrofoil. The sheet cavitation growth, detachment, cloud cavitation shedding are responsible for the features of the pressure fluctuation.

A pressure-based algorithm for cavitating flow computations

In this paper, the cavitation and flow characteristics of the unsteady liquid nitrogen (LN2) cavitating flow in a submersible pump are investigated through both experimental and numerical approaches. The performance curve of the LN2 submersible pump is obtained via experimental measurement. Numerical simulations are performed using a modified shear stress transport k–ω turbulence model, incorporating corrections for rotation and thermal effects as per the Schnerr–Sauer cavitation model. The numerical framework is verified by comparing the cavitation morphology features with previously reported visual data of the LN2 inducer and aligning pump performance data with those obtained from experimental tests of the LN2 submersible pump. The results indicate that cavitation at the designed flow rate predominantly manifests as tip clearance vortex cavitation in the inducer. Increased flow rates exacerbate cavitation, potentially obstructing the flow passage of the impeller. The vortex identification method and the vorticity transport equation are employed to identify the vortex structures and analyze the interaction between cavitation and vortices in the unsteady LN2 cavitating flow. The vortex structures primarily concentrate at the outlet of the impeller flow passage, largely attributed to the vortex dilation term and baroclinic torque. The influence of thermal effects on the cavitation flow of submersible pumps is analyzed. An entropy production analysis model, comprehensively involving various contributing factors, is proposed and utilized to accurately predict the entropy production rate within the pump. This study not only offers an effective numerical approach but also provides valuable insight into the cavitation flow characteristics of the LN2 submersible pump.

Unsteady cavitating flow usually contains various vapor structures with different length scales and significant fluid compressibility, which poses great challenges to numerical simulation. In this work, we propose a compressible Eulerian–Lagrangian method to investigate cloud cavitation inside a nozzle, with particular emphasis on the effect of compressibility on multiscale structures. The macroscopic cavity evolution is dealt with using large eddy simulation and the volume of fluid method in a compressible Eulerian framework. Microscopic bubble dynamics are described using the equation of bubble motion and the compressible Rayleigh–Plesset equation. A two-way coupling algorithm is established to bridge the two frameworks. The calculated results are validated by comparison with available experimental data. The numerical results show that the compressibility exacerbates the instability of the cavitating flow field, generates more discrete bubbles, and promotes liquid–vapor mass exchange, which further increases the overall cavitation volume. Furthermore, two distinct power laws for bubble size distribution, with exponent −4/3 for small bubbles and −10/3 for large bubbles, are obtained. Owing to the influence of the high flow velocity and high ambient pressure in the nozzle, and the wall effects on bubble dynamics, the number of large-size bubbles calculated by the numerical simulation is greater than that obtained by theoretical analysis. The formation of these bubbles is affected by shear on the liquid–vapor interface, the presence of vortex structures, and turbulence, thus differing significantly from the case of cavitation flow around a hydrofoil.

Numerical study of the hydrofoil cavitation flow with thermodynamic effects

Cavitation is a phenomenon which occurs where the local pressure falls off under the vapor pressure. Over the past few years, numerical simulation models for cavitation have been developed significantly in order to investigate the mechanism of cavitation. In the paper, A local homogeneous cavitation model based on the theory of evaporation and condensation has been deduced, which is used to describe the phase change between water and vapor. The RNG k–ε turbulence model is used to simulate the turbulent flow and the finite volume method is employed to discrete the governing equations. The effects of surface tension of water, pressure fluctuations and non-condensable gases are included in the mass transfer cavitation model. Also in order to neglect the effects of the quantities such as the bubble number and bubble diameter, which is difficult to measure, the relations between the aerodynamic drag and surface tension forces is used to describe the bubble diameter. In order to evaluate the new cavitation model, the two phase cavitation flows around a NACA0015 hydrofoil at different attack angle and different cavitation number are simulated by the new cavitation model, and compared with references, which showed good agreement with the experiments.