Journal of Hydrodynamics最新文献

This study compares the “cavitation to no-cavitation” transition processes and the resulting pressure oscillation effects of water, liquid oxygen and liquid methane in an adjustable cavitation Venturi tube through back pressure experiments. The modal characteristics of cavitation images and the frequency domain characteristics of vibrations were analyzed using the proper orthogonal decomposition (POD) and fast Fourier transform (FFT). By observing with a transparent Venturi tube and high-speed photography, combined with one-dimensional homogeneous flow simulation, the evolution laws of cavitation length and downstream pressure oscillation during the processes of changing the pressure ratio p_r and the throat area A_t were studied. The evolution laws of cavitation length and flow pattern about working parameters were obtained, revealing the correlation between cavitation and vibration. Under low pressure ratios, the oscillation of bubble collapse dominated by the returning jet causes the tail of the cavitation area to be lengthened, resulting in an increase in downstream amplitude. Increasing the pressure ratio can effectively control the cavitation length and reduce the amplitude of downstream pressure oscillation. Reducing the throat area by moving the plug cone increases the cavitation length, and the downstream oscillation amplitude first increases and then decreases, with an oscillation maximum value existing.

This paper investigates the coupling characteristics of variable mass tank sloshing and ship motion. A full nonlinear numerical model of variable mass tank sloshing-external wave-ship motion coupling is established. Firstly, the coupled motion characteristics of tank sloshing and simplified hull in beam sea are compared, the time history of dimensionless roll angle agrees well with experimental results, and the accuracy of the numerical model is verified. Secondly, the effects of wave excitation and ship speed on the coupled characteristics of Korea Research Institute of Ships and Ocean Engineering very large crude carrier (KVLCC) tank sloshing and ship motion are discussed, and the influence of liquid filling rate on ship heave motion and pitch motion is discussed emphatically. The results show that during the tank filling, the sloshing pressure in the tank increases steadily, and the growth rate is positively correlated with the filling rate. At the same time, the ship pitch motion is less affected by tank sloshing, while the ship heave motion is evidently affected by tank sloshing.

Wake-induced vibration (WIV) is common in engineering and may cause structural damage. The application of bionic devices in vibration control has attracted much attention, but most studies focus on isolated system and pay insufficient attention to the response under wake interference, which limits their application in engineering. Therefore, it is crucial to better understand the interaction between flow and bionic devices under wake interference. Inspired by the tail fin structure of fish tail, this paper studies the hydrodynamic characteristics of an elastically mounted cylinder with a tail fin in the wake of an inverted D-section cylinder. By changing the distance between the two centers of the circle and the length of the tail fin, the amplitude, frequency response and the mechanism of wake-induced vibration are explored. The results indicate that as the spacing ratio (L / D) increases, the WIV of the cylinder with a longer tail fin is excited. When WIV occurs, the phase difference (Φ) between the hydrodynamic coefficient and the transverse displacement experiences two jumps, and the lock-in bandwidth is wider compared with the single cylinder. As the tail fin length increases, the transverse lock-in frequency ratio yosu (f_yosu / f_n) decreases. Additionally, vortex shedding from the upstream inverted D-section cylinder (UIDC) affects the surface pressure distribution and vortex shedding characteristics of the downstream cylinder with a tail fin (DCTF). An analysis of the energy transfer reveals that the direction of transmission between the energy transfer and cylinder motion affects the amplitude response.

This study examines the vortex-induced vibrations (VIV) and hydrodynamic characteristics of a rotating circular cylinder with two degrees of freedom (2DOF). The effects of varying mass ratios (M^*), rotation rates (α) and reduced velocities (U^*) on the cylinder’s vibration responses, hydrodynamic properties and near-wake structures are explored. The results indicate that the cylinder rotation significantly suppresses vibrations in the cross-flow direction, with the inhibitory effect intensifying with the increasing rotation ratio α. Additionally, contrary to the non-rotating cylinder, in which f ^*_x = 2f ^*_y , the rotating cylinder shows congruence in vibration frequencies in both the X - and Y - directions. In the motion trajectory, with the non-rotating cylinder exhibiting an “8” pattern, the rotating cylinder traces a single closed-loop shape. The mass ratio notably influences the displacement amplitude, trajectory, and phase portrait. Higher mass ratios (M^* = 6, 8) suppress the growth of time-averaged displacements in both the X - and Y - directions and the incidence of “lock-in” phenomena in the Y direction. Particularly, as M^* = 2, α = 1.0, 1.5, the displacement in the Y - direction is notably higher than that under other conditions. The higher mass ratio also modifies the motion trajectory of the cylinder, shifting it from a closed-loop droplet shape to a single closed loop, with the frequency ratio between lift force and cross-flow displacement transitioning from 3:1 to 1:1. Vortex structure analysis reveals patterns such as “2P”, “P+S”, and “2S”, with high mass ratios showing a U-shaped mode and an extended “2S” region in the wake structure.

Cavitation and cavitation erosion are prevalent phenomena in hydraulic machinery. In the present paper, a multiscale Eulerian-Lagrangian method in OpenFOAM is used to simulate cavitating flow in a Venturi tube. Additionally, a novel erosion prediction model is proposed, incorporating material hardening behavior under impact loads caused by asymmetric bubble collapse near walls. The model couples detailed bubble dynamics with the nonlinear plastic response of materials, enabling direct calculation of erosion pit depth. Simulation results show strong agreement with experimental erosion patterns, confirming the feasibility of this new method. The proposed method is pivotal for further studying how various materials respond to cavitation wear.

This study addresses the challenge by introducing a piezoelectric energy harvester based on vortex-induced vibration (VIV) and galloping interactions. Experiments on an elastically mounted circular cylinder equipped with two small square rods (SSR) in a DN100 pipe were conducted to examine how the circumferential angle of the SSR impacts the vibration response of cylinder, revealing distinct interaction modes (VIV-only and VIV-galloping interaction). The results show that placing the SSR toward the bluff body’s trailing edge accelerates the onset of galloping at lower velocities. In particular, as the SSR angle is in the range of θ = 160°–180°, the fluid-structure interaction behavior deviates from prior open-flow studies. This difference is attributed to the influence of the pipe wall and is analyzed using the shear layer interaction mode theory. The relationship between SSR placement angles and fluid-induced vibration (FIV) characteristics across various fluid velocities was also mapped, with dynamic influences assessed using the Strouhal number and stability parameter ΔS, helping to distinguish between interaction modes. Based on these findings, configurations with θ = 50°–70° and θ = 140°–150° are identified as preferable for enhanced power output, whereas θ = 170°–180° is better suited for optimizing efficiency and stability. These results provide good insights into the design and optimization of pipeline energy harvesting systems for industrial applications.

This paper introduces MultiPHydro, an in-house computational solver developed for simulating hydrodynamic and multiphase fluid—body interaction problems, with a specialized focus on multiphase flow dynamics. The solver employs the boundary data immersion method (BDIM) as its core numerical framework for handling fluid—solid interfaces. We briefly outline the governing equations and physical models integrated within MultiPHydro, including weakly-compressible flows, cavitation modeling, and the volume of fluid (VOF) method with piecewise-linear interface reconstruction. The solver’s accuracy and versatility are demonstrated through several numerical benchmarks: single-phase flow past a cylinder shows less than 10% error in vortex shedding frequency and under 4% error in hydrodynamic resistance; cavitating flows around a hydrofoil yield errors below 7% in maximum cavity length; water-entry cases exhibit under 5% error in displacement and velocity; and water-exit simulations predict cavity length within 7.2% deviation. These results confirm the solver’s capability to reliably model complex fluid-body interactions across various regimes. Future developments will focus on refining mathematical models, improving the modeling of phase-interaction mechanisms, and implementing GPU-accelerated parallel algorithms to enhance compatibility with domestically-developed operating systems and deep computing units (DCUs).

The precision in predicting cavitation noise critically depends on the accuracy of flow field simulations. In the present work, we employ the improved delayed detached eddy simulation (IDDES), coupled with Spalart-Allmaras (SA) turbulence model and Schnerr-Sauer cavitation model, to simulate the cavitating flow around a three-dimension twisted hydrofoil. The accuracy of simulation is accessed by examining the power spectral density of pressure fluctuations and the percentage of resolved turbulent kinetic energy. The simulated cavitation behavior is compared with experimental observation in terms of shedding patterns and frequencies. The cavitation-radiated noise, computed via the porous Ffowcs-Williams and Hawkings (PFWH) method, is subsequently calculated. Strategies for setting different integral surfaces are discussed. An analysis of sound pressure and cavity evolution patterns for a typical cycle elucidates the correlation between the dynamic characteristics of the cavity and the noise properties. The simulation addresses the lack of experimental data, which poses challenges due to the need for numerous hydrophones and the elimination of tunnel wall effects. The combination of the PFWH source surface and the original FW-H source surface facilitates the investigation of various noise sources. The results indicate that the pseudo-thickness term approximates a monopole noise associated with cavity volume acceleration, the loading term resembles a dipole, and the quadrupole term can be obtained by subtracting from the total sound pressure. The sound pressure levels at the monitoring points reveal that the monopole term predominates, followed by the quadrupole term, with the dipole term registering the lowest values.

A length scale refinement study is a standard practice to ensure the independence of a numerical model on spatial approximations. For smoothed particle hydrodynamics (SPH), the process of length scale refinement study tends to be conducted based on experience. A challenge of defining a universal length scale refinement strategy is the existence of two length scales–particle spacing and smoothing length. Despite the challenge, further investigations of the impact of different refinement strategies should be continually conducted to improve the reliability of practical SPH applications on 3-D free-surface flows. In this study, a conventional strategy and a novel coupled refinement strategy are used to investigate the convergence of SPH simulations for free-surface flows using a standard SPH scheme available in an open-source framework. The two case studies are a dam break flow and a lesser-known stable regime water flow inside a rotating drum with lifters. Validations are conducted using existing data from literature for the dam break flow and laser Doppler velocimetry (LDV) measurements for the rotating drum flow. The investigation shows that the proposed coupled length scale refinement strategy does not offer a significant improvement for the SPH model of the dam break flow comparing with the conventional strategy. On the other hand, the stable regime rotating drum fluid flow shows that both refinement strategies are not sufficient to tackle SPH’s on-going fundamental challenge of accurately predicting the flow field of complex 3-D turbulent flows with free surfaces.

Adaptive composites are widely employed in various hydraulic and marine applications, such as propulsors, turbines, and renewable energy-harvesting devices. This study investigates vortex-induced vibrations (VIV) in carbon fiber-reinforced plastic (CFRP) hydrofoils with different ply angles, focusing on the lock-in phenomenon. A multi-field synchronous measurement system was developed to simultaneously capture vortex dynamics and structural vibrations. The vibration spectrum under various flow velocities revealed distinct lock-in behaviors for the CFRP hydrofoils with different ply angles. The hydrofoil with 45° ply angle exhibited a “partial lock-in” behavior, characterized by dual lock-in peaks during secondary frequency lock-in. In contrast, the hydrofoil with −45° ply angle displayed a “double lock-in” phenomenon, marked by the simultaneous occurrence of two lock-in events. To elucidate the underlying mechanism, dynamic mode decomposition (DMD) was applied to identify the dominant vortex structures and their frequency characteristics in the wake during “partial lock-in”. This work provides methodological insights and engineering paradigms for the vibration suppression design of next-generation high-performance composite hydraulic equipment.