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Notwithstanding the effectiveness of ventilated cavitation as a safe way to accelerate and achieve natural supercavitation, detailed physics of ventilated cavitating flows and hydrodynamic effects on underwater vehicles have been rarely explored. The present work deals with computational investigation on ventilated supercavitating flows around a high-speed underwater vehicle and its hydrodynamic characteristics. The homogeneous mixture model is adopted for describing the cavitating flow field composed of water, water vapor, and a ventilated gas. After extensively validating the flow solver with experiments of ventilated cavitating flows, we carry out a series of computations of supercavitating flows around a high-speed underwater vehicle with four control fins, and investigate the flow physics and the vehicle's hydrodynamic characteristics. The computations are performed under different freestream velocities, ventilation rates, and angles of attack. Furthermore, the unsteady effects of turbulence are examined by comparing the computed results based on unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation and Detached Eddy Simulation (DES). The computational results show that the cavitating flows cause substantial nonlinear characteristics in cavity shapes and hydrodynamic forces such as lift, drag, and pitching moment, due to the presence of natural and ventilated cavitations and their interaction. This can be beneficially exploited in understanding and predicting ventilated supercavitating flows around a high-speed underwater vehicle, and establishing an accurate dynamic model of the vehicle's motion. • Computations of ventilated cavitating flows around a vehicle are presented. • All the results exhibit non-linear hydrodynamic characteristics of the vehicle. • As a cavity passes through the fins, noticeable drag and lift changes are observed. • As the AOA increases, the pitching moment changes from nose-down to nose-up. • URANS and DES computations are compared for a specific flow condition. [ABSTRACT FROM AUTHOR]

• A new cavitation model is proposed by adopting physical bubble growth rates. • Empiricism inherent in the bubble number density is substantially reduced. • Smooth temperature recovery in cryogenic cavitation is well captured. • Existing characteristics under isothermal conditions are kept. Cavitation in thermosensitive fluids is accompanied by a noticeable temperature drop inside a cavity. Motivated by the fact that most popular cavitation models have been developed without considering thermodynamic effects, the present study proposes physics-based corrections to existing cavitation models. Two primary corrections are adopting the physical bubble growth rate and separating bubble number density in the vaporization and condensation terms. The bubble growth rate in the cavitation model is chosen as the limiting factor between the inertia-controlled rate and heat diffusion-controlled rate from the bubble growth theories. To implement the theoretical growth rate of the thermal regime into the computational framework based on the homogeneous mixture model, the bubble time and liquid temperature are newly modeled. Furthermore, the bubble number density, which is often set uniformly throughout the whole computational domain, is separated for the vaporization and condensation processes. The vaporization bubble number density is further modeled by experimental data to reduce the empiricism inherent in the user-defined coefficients. The relation between the remaining model coefficients and characteristic temperature drop (Δ T *) is developed and it is verified to be effective in various types of fluids and working conditions. The newly proposed model is validated by cryogenic cavitating tests and applied to the computations of the 3-D cryogenic cavitating flows around a turbopump inducer. Unlike the sudden temperature recovery by the previous inertial rate-based models, the proposed model predicts a gradual temperature recovery inside a non-isothermal cavity, which is consistent with the experimental observations. It is also confirmed that the new model chooses the physical inertial rate under isothermal conditions, and thus, the model can be used regardless of the flow conditions. [ABSTRACT FROM AUTHOR]

Underwater explosion (UNDEX) events involve complex physical phenomena and can be categorized into three stages: initial shock wave propagation, cavitation, and bubble pulsation. This study focuses on double UNDEX bubbles, elucidating their highly nonlinear interactions across these stages. Both synchronous and asynchronous explosion cases are examined, with a particular emphasis on assessing the influence of phase change. Employing the 3-D high-fidelity computational framework that incorporates the physics-based cavitation model and non-ideal equations of state for water and explosion gas properties, we conduct validations with field experimental data on single bubbles and extend our analysis to double bubbles. Our principal finding is the interaction between the cavity created by the shock wave and the bubble pulsations. Notably, we discern a significant phase change effect in asynchronous explosion, wherein the vapor cavity region delays the contraction of the previously-generated bubble. This delay is attributed to the low-density region created by the phase change, allowing the bubble to remain expanded for an extended period, thereby enhancing agreement with experimental data. To our knowledge, this study represents the pioneering effort to explore the critical role of phase change in accurately simulating the intricate interactions within double UNDEX scenarios. • Computational investigations on double UNDEX scenarios with thermodynamic cavitation process and non-ideal EOS. • Interactions between the cavity caused by the shock wave and the bubble pulsations are captured. • Phase change effect is more pronounced in asynchronous explosion. • Low-density cavity region delays the previously-generated bubble's contraction. • 3-D effect induced by the misalignment of gravity and bubble contraction direction. [ABSTRACT FROM AUTHOR]

To understand cavity dynamics, many experimental and computational studies have been conducted for many decades. As computational methods, incompressible, isothermal compressible, and fully compressible flow solvers were used for the purpose. In the present study, to understand the compressibility effect on cavity dynamics, both incompressible and fully compressible flow solvers were developed, respectively. Experiments were also carried out in a cavitation tunnel to compare with the computational results. The cavity shedding dynamics, re-entrant jet, transition from bounded shear layer vortices to Karman vortices, and pressure and velocity contours behind the two-dimensional wedge by the two developed solvers were compared at various cavitation numbers. [ABSTRACT FROM AUTHOR]

During cavitation bubble pulsations, a phase change intensively occurs near the collapsing moment due to high pressure and temperature inside bubbles, accompanying distinctive flow features: the rate of evaporation and condensation significantly changes according to the phase change regime. To account for this non-isothermal effect, the high-fidelity computational framework incorporating the physics-based cavitation model and a new fluid property model based on artificial neural network is proposed. The key finding of this study is the interplay between the thermal and inertial effects during multiple pulsations. At the early stages of bubble contraction, the phase change is primarily driven by fluid inertia. However, as the bubble continues to compress, the thermal effect becomes dominant and controls the entire phase change region at each moment of collapse. It is observed that the isothermal model relying on the inertial bubble growth rate only, does not capture this transition of dominance and eventually fails to predict multiple pulsations. The physics-based cavitation model successfully captures the bubble pulsation beyond the second collapse. These findings highlight that explicit consideration of the non-isothermal effect is essential for problems with varying phase change regimes, and a phase change model reflecting this effect is vital for accurate computations. • High-fidelity multi-phase computational framework ACTFlow_MP is proposed. • New fluid property model based on artificial neural network is constructed for water. • The thermal effect turns out to be dominant at the moment of each bubble collapse. • The physics-based model successfully captured bubble pulsations beyond 2nd period. [ABSTRACT FROM AUTHOR]