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In this study, we numerically examine the behavior of the NACA (National Advisory Committee for Aeronautics) 66 hydrofoil under combined oscillatory motion, considering different cavitation numbers. The large eddy simulation method is used for the turbulence modeling. The vertical oscillation (combined oscillation) creates an effective angle of attack, leading to reduced drag force. Our findings indicate that increasing the speed of hydrofoil oscillation leads to a delayed onset and increased production of cavity clouds. Moreover, an increase in the angle of attack during combined oscillatory motion decreases the detachment length of cavitation bubbles. Further investigations show that cavitation on the hydrofoil's surface can accelerate the shift from a laminar to turbulent boundary layer, reinforcing the turbulent boundary layer's strength and thereby delaying the onset of flow separation. Additionally, we accurately examine the terms of the vorticity transport equation in this research. It is evident that the vorticity dilatation term forms near the boundary layers close to the hydrofoil surface and correlates well with the vapor volume fraction. This term plays a vital role in the cavitation inception process. [ABSTRACT FROM AUTHOR]

The impetus of this study is to provide an in-depth insight into the unsteady hydrodynamic characteristics of the cavitating flow, effects of the wavy leading edge (WLE) on the noise suppression mechanism due to a cavity cloud formation, which contains condensation, detachment, collapse, spanwise flow, streamwise velocity fluctuation, and shedding phenomenon. NACA 634-021 hydrofoil was considered with WLE having a wavelength of 25% and an amplitude of 5% of the mean chord length and was compared to a straight-leading-edge (SLE) hydrofoil at cavitation numbers of σ = 0. 8 and a chord-based Reynolds number of 7. 2 × 1 0 5 . Counter-rotation vortices were produced between the peaks of the WLE hydrofoil by destroying the horseshoe vortex and delaying the tail vortex, changing the frequency. Here, the hydrodynamic forces have also been discussed in addition to the noise. The results showed that the leading-edge vortex formation and flow separation dynamics fundamentally differed between the SLE and the WLE hydrofoil. The main difference between the WLE and SLE hydrofoil turbulent flow is the formation of counter-rotating streamwise vortices pairs. We solved the cavitating flow using the large eddy simulation (LES) approach, as well as the Kunz mass transfer model, which is performed under the framework of the OpenFOAM package. [ABSTRACT FROM AUTHOR]

This numerical investigation employs advanced computational fluid dynamics techniques to examine the intricate physics of cavitating flows around a pitching NACA 66 hydrofoil. Unsteady simulations are conducted using both large eddy simulation (LES) and K-Omega SST turbulence models. The pitching motions range from 0 to 15°, encompassing four cavitation numbers (3.25, 3.5, 3.75, 4) and a Reynolds number of 750,000. The study comprehensively analyzes various flow field characteristics, including pressure distribution, velocity, vorticity, shear stress, vapor volume fraction, and turbulence kinetic energy. The kinematics of pitching significantly influence hydrodynamic loads and the surrounding flow structures in cavitating conditions. Flow visualizations illustrate the evolution of sheet/cloud cavitation, reentrant jet, and vortex dynamics throughout a pitching cycle. Notable findings demonstrate the impact of cavitation number on cavity shape and the relationship between angle of attack, reentrant jet location, and vortex size. Additionally, negative vorticity dilatation is observed to be correlated with cavity size. • The cavitation and supercavitation structure around a 2D, 3D pitching hydrofoil is studied using LES. • The impact of cavitation number on cavity shape and the relationship between angle of attack, reentrant jet location, and vortex size was studied. • Determination of the effect of pitching motion in cavitation flow on hydrodynamic coefficients and surrounding flow structure [ABSTRACT FROM AUTHOR]

In this paper, wavelet analysis of the cavitating flow over a sphere is reported. Unsteady and dynamic behaviors of cavitation were captured using large eddy simulation (LES) turbulence approach and Sauer mass transfer models. Numerical simulation is implemented under the framework of OpenFOAM within the interPhaseChangeFoam solver. The simulation is conducted over a wide range of cavitation numbers. Two more essential variations, pressures and kinetic energies, were considered at specific points in front and behind of the sphere's body for sufficient simulation period. The oscillations global frequency modes and spectral content of the cavity cloud are computed and analyzed using Fourier and continuous wavelet transformations. The computed results show that the flow fluctuations enhance by increasing the cavitation number. The low-frequency fluctuations play a pivotal role in the cavitating flow and possess almost the same magnitude in all investigated cavitation numbers. The frequencies enhance as the simulation time increases in all cases. One of the primary frequencies that happened in all cavitation numbers in the cavity cloud separation is due to a Strouhal number within the range of 0.046 and 0.05. Therefore, this Strouhal number can be used for the purpose of cloud cavitation detection. • LES simulation of cavitating flow around sphere in OpenFOAM. • Providing a thorough understanding of the wavelet analysis around a sphere for the first time. • Reporting the oscillations global frequency modes and spectral content of the sphere cavity cloud. [ABSTRACT FROM AUTHOR]

Here we examine partial and supercavitation over a sphere at a constant Reynolds number of 1.5 × 10 6 and a broad range of cavitation numbers (0.36 <σ< 1). Large eddy simulation (LES) and Sauer mass transfer model were used to simulate the dynamic and unsteady cavitation around the sphere. Also, the compressive volume of fluid (VOF) method is used to track the cavity interface. The two-phase flow solver of the OpenFOAM package, intephaseChangeFoam is employed. Large-eddy simulation of cavitating flow over the sphere is compared with the non-cavitating flow at the same Reynolds number. This work provides a thorough understanding of the fluid dynamic characteristics of the sphere cavitation such as vorticity field, turbulent kinetic energy, pressure, velocity, streamlines and boundary layer. Also, detailed analyses of the instantaneous cavity leading edge and separation point location, vortex shedding, streamwise velocity fluctuation and evolution of the cavity are reported. Characteristics of the wake of the cavitating flows are compared with the single-phase results. We report that cavitation suppresses instability in the near wake region and delays the three-dimensional breakdown of the vortices. The volume fraction contours of the cavity cloud obtained from the numerical simulations are compared with the experimental data at the same working condition with a suitable quantitative accuracy. [ABSTRACT FROM AUTHOR]

• Hybrid surfaces with contact angles ranging from superhydrophobic to superhydrophilic are used for controlling supercavitation flow. • ILES is employed to detect the exact structure of the supercavitation flow. • A specific pattern for contact angle distribution reduces the cavitation volume behind the hydrofoil and decreases the flow instability. Supercavitation flow is characterized by the presence of a supercavity, which can be unstable and cause unwanted motion or even loss of control of an object. To address this issue, flow control techniques are often employed. These techniques aim to manipulate the flow of liquid around the object and improve stability and control. Some of these methods include using control surfaces, injecting fluids, or more advanced techniques such as active flow control or smart materials. The aim of this study is to use computational methods to investigate the behaviour of supercavitation flow over a Clark-Y hydrofoil with different contact angle patterns (hybrid wettability) inspired by the Namib desert beetle. The hybrid wettability consists of six distinct patterns with a 160-degree contact angle for superhydrophobic surfaces and a five-degree contact angle for superhydrophilic surfaces. To predict the dynamic and unsteady behaviours of the supercavitation flow with a cavity number of 0.4, the implicit large eddy simulation (ILES) technique and Kunz mass transfer model are used. The compressive volume of fluid technique is used in conjunction with dynamic adaptive mesh refinement to track the interface between the vapour and liquid phases. The simulations are conducted using the interPhaseChangeFoam two-phase flow solver within the OpenFOAM framework. This study analyses the time-averaged and instantaneous fluid dynamic properties of the supercavitation flow of the hydrofoil with a hybrid surface, including pressure, velocity, vorticity fields, wake flow, recirculation zone, and liquid volume fraction. In addition, it examines the instantaneous cavity leading edge and flow separation, the vortical flow structure, vorticity stretching and dilatation, spanwise flow details, the creation of a low-pressure zone behind the hybrid hydrofoil, streamwise velocity fluctuations, and the cavity dynamics over an entire cycle. The results show that the contact angle has a significant effect on the structure of the supercavitation flow. Specifically, the use of a superhydrophobic surface on the pressure side and trailing edge of a hydrofoil, along with a superhydrophilic surface on the leading edge, can reduce the thickness of the wake zone, the length of the cloud cavity, and flow instability. Additionally, this approach can delay the onset of cavitation. [ABSTRACT FROM AUTHOR]

In this paper, cavitation and supercavitation around 3D hemispherical head-form body and a conical cavitator were simulated. Dynamic and unsteady behaviors of cavitation were solved using large eddy simulation (LES) and k-ω SST turbulence models, as well as Kunz and Sauer mass transfer models. In addition, the compressive volume of fluid (VOF) method is used to track the cavity interface. Simulation is performed under the framework of the OpenFOAM package. The main contribution of this work is to present a correlation between the cavity length and diameter for hemispherical head-form bodies for the first time. Moreover, we provide a detailed comparison between different turbulence and mass transfer models over a broad range of cavitation numbers, especially in small cavitation numbers, including σ =0.07, 0.05, 0.02 for two cases, which is not reported previously. Our numerical results are compared with the available experimental data and a broad set of analytic relations for the cavity characteristics such as cavity length and diameter with suitable accuracy. Discussions on boundary layer separation and re-entrant jet behavior, which play a significant role in the bubble shedding in the cavity closure region, are presented. [ABSTRACT FROM AUTHOR]

In this study, we performed numerical investigations of the cavitating and supercavitating flow behind a three-dimensional disk with a particular emphasis on detailed comparisons of various turbulence and mass transfer models. Simulations were performed using the OpenFOAM package and flows at three different cavitation numbers, ( σ = 0.2, 0.1, and 0.05) were considered. Large eddy simulation (LES) and k – ω shear stress transport turbulence approaches were coupled with various mass transfer model types (e.g., Kunz, Schnerr–Sauer, and Zwart models). The Zwart mass transfer model was added to the standard OpenFOAM package. A compressive volume of fluid method was used to track the interface between the liquid and vapor phases. Our numerical results in terms of the cavity length, diameter, and drag coefficient compared fairly well with experimental data and a broad set of analytical relations. Moreover, this study provides a better understanding of the cavitation dynamics behind disk cavitators. Our results indicate that the most accurate solutions will be obtained by applying an LES turbulence approach combined with the Kunz mass transfer model. [ABSTRACT FROM AUTHOR]

• Cavitating flow around a 3-D Hydrofoil with Wavy Leading Edges (WLE) is investigated using the LES approach in OpenFOAM. • Comparison of cavity features of wavy leading edges (WLE) hydrofoil with straight leading edge (SLE) one. • Force coefficients, re-entrant jet and separation are assessed during the cloud cavity evolution around WLE and SLE hydrofoils. • The mechanisms of the laminar separation bubble (LSB) and low-pressure zone behind the WLE hydrofoil are illustrated. • Role of vorticity stretching and vorticity dilatation with the presence of cavity for the WLE and SLE hydrofoils are investigated. The present study seeks to conduct numerical investigations of the cavitating flow characteristics around a sinusoidal wavy leading edge (WLE) 3-D hydrofoil underlying a NACA 63 4 –021 profile with an aspect ratio of 4.3. Cavitational and non-cavitational characteristics of hydrofoils are numerically examined at a chord-based Reynolds number of 7.2 × 105. The sinusoidal leading edge geometries include two WLE amplitudes of 5% and 25% and two WLE wavelengths of 25% and 50% of the mean chord length. We examined the cavitating flow around the hydrofoils in different cavitation numbers, namely σ = 0.8 and σ = 1.2. The flow over the protuberances of the WLE hydrofoil is considered at varying chord lengths and a constant angle of attack α = 6°, where significant spanwise variations in all flow properties, in contrast to the straight leading edge (SLE) hydrofoil, were observed. Large eddy simulation (LES) and Kunz mass transfer models are employed to simulate the dynamic and unsteady behavior of the cavitating flow. Besides, the compressive volume of fluid (VOF) method is used to track the cavity interface. Simulation is performed under the two-phase flow solver —interPhaseChangeFoam— of the OpenFOAM package. Compared to the SLE hydrofoil, we provided an exhaustive report of the time-averaged and instantaneous fluid dynamic characteristics of the cavitating flow around the sinusoidal leading edge hydrofoil, i.e., pressure, velocity, and vorticity fields, as well as lift and drag coefficients, and turbulent kinetic energy are reported. Furthermore, detailed analyses of the instantaneous cavity leading edge and flow separation treatment, vortical structure of the flow, vorticity stretching and dilatation, details of the spanwise flow, the formation of a low-pressure zone behind the WLE hydrofoil, streamwise velocity fluctuation, and evolution of the cavity dynamics through a complete cycle are reported. Results show that early development of the laminar separation bubble (LSBs) on the suction side of WLE hydrofoil prevents significant flow separation. Furthermore, the WLE cases exhibit a significantly reduced level of unsteady fluctuations in aerodynamic forces at the frequency of periodic vortex shedding. [ABSTRACT FROM AUTHOR]

In this paper, we sought to investigate unsteady cavitating turbulent flows around a twisted three-dimensional NACA 16012 hydrofoil using the large eddy simulation (LES) and volume of fluid (VOF) methods. The one-equation eddy viscosity model (OEEVM) was used to calculate the sub-grid scale (SGS) stress tensor. The compressive velocity VOF technique and the Kunz cavitation model were also employed. Numerical simulation was performed using the interPhaseChangeFoam solver within the OpenFOAM framework. Cavitation simulation was performed at three cavitation numbers within the cloud cavitation regime; that is to say, cavitation numbers: 0.95, 1.15, and 1.35. Afterwards, the details of flow predictions including the pressure, velocity, streamlines, volume fraction of water phase, and turbulent kinetic energy were reported. Cavity behaviours, including growth, shedding, and collapse of the cavity, were considered in detail. Three-dimensional cavity structures such as primary and secondary shedding and the shedding of the U-shaped horseshoe vortex were reported as well. The present work illustrated the side-entrant jets and the radially diverging re-entrant jet corresponding to the three-dimensional effect of the twisted wing. The cavity pattern and the shedding cycle frequency agreed well with the available experimental observations. • Cloud cavitation around a twisted wing with NACA16012 hydrofoil, Large Eddy Simulation (LES). • Detailed dynamic evolution of cavitation including growth, shedding and collapse in downstream at σ = 0.95, 1.15, 1.35. • Pressure fluctuations, turbulent kinetic energy, vapour volume of fraction. • Re-entrant jet and side jets. [ABSTRACT FROM AUTHOR]