Journal of Hydrodynamics最新文献

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.

In open channels, floating vegetation canopies (e.g., E. crassipes) reduce the flow velocity within canopies and increase the velocity in the free-flow region below canopies. The variation in the flow structure below the canopies impacts both sediment resuspension and deposition onto the channel bed. Combining the random displacement model with the sediment deposition probability, a new model was proposed for predicting the longitudinal distribution of sediment deposition below floating vegetation canopies. The deposition distributions were measured below floating canopies of model vegetation (rigid cylinders) and real vegetation (E. crassipes). The measurements agreed well with the predictions of the proposed deposition model. With the use of the proposed model, the impacts of floating E. crassipes canopies on the deposition distribution were examined for different upstream mean flow velocities (U₀), relative flow depths (h_g/H), vegetation densities (a) and sediment sizes (d_s). The results suggested that net deposition below floating canopies decreased with increasing U₀ and a and with decreasing h_g/H. Under the same flow and vegetation conditions, smaller sediment particles were more likely to become resuspended, resulting in less net deposition below the floating canopies. These results can improve the fundamental understanding of vegetation-based river management and ecological restoration.

This study investigates cavitating swirling flow in a diffuser, i.e., a simplified model of a Francis turbine draft tube, using proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) applied to velocity and pressure field data. The interaction between vortex rope precession and cavitation surge under varying swirl and cavitation numbers is analyzed. The modal analysis results depicted the coherent structures correlated to the vortex rope precession near the diffuser inlet and the diffuser outlet, and cavitation surge in the diffuser. The POD analysis accurately revealed the flow features in the diffuser: The conical structure represents the flow diffusion with vortex rope precession and the reverse core indicates the backflow in the diffuser for the averaged flow, and the double helical structure near the diffuser inlet for the representative flow oscillation. The typical coherent structures obtained by the DMD for the cavitating swirling flow in the diffuser are the double helical structure concentrated near the diffuser inlet. The double helical structure also appears near the diffuser outlet where the breakdown of vortex rope occurs and the flow oscillation slows down. Once cavitation occurs, the mode induced by cavitation surge and its corresponding coherent structure may change according to the operating condition. The flow oscillation can be changed from the double helical mode to the axial oscillation caused by cavitation surge named breathing mode if cavitation surge becomes strong enough at a small cavitation number or large swirl number.

Research on the high maneuverability of fish swimming primarily involves addressing the batch processing of large experimental data, specifically how to simultaneously capture and rapidly process deformation-displacement information of fish bodies and related flow fields. The primary objective of this study is to integrate high-speed photography technology with deep learning methods to propose a set of data processing methods suitable for extracting fish swimming characteristic parameters. For the rapid movements of zebrafish (millisecond-level motion), this study utilized a high-speed camera for image acquisition, obtaining batches of swimming fish images and fluorescence particle information in the flow field. The geometric reconstruction of zebrafish under high-speed swimming was achieved by introducing deep learning algorithms and refining the U-Net model. To tackle the challenges of complex fish swimming scenes, we utilized a novel residual connection approach (path modification) and constructed a hybrid function model (module enhancement), resulting in a new neural network model tailored for zebrafish swimming image processing: Mod-UNet. Through testing, the improved Mod-UNet model effectively eliminated interference from fluorescence particles in the flow field on the extraction of fish body contours, achieving an overall IoU coefficient of 93%. The processing results demonstrated a kind of consistency compared to results obtained with traditional methods by previous researchers. By calculating the geometric morphology of zebrafish, we further derived the kinematic characteristics of zebrafish. Simultaneously, by applying cross-correlation algorithms to calculate the positions of fluorescence particles, the velocity characteristics of the flow field were obtained. The λ_ci method and the Ω method were used to identify vortex structures, providing the evolution patterns of corresponding flow field characteristic parameters. The experimental data processing method proposed in this paper provides technical support for establishing a zebrafish swimming information database.

Cloud cavitation that forms around a two-dimensional hydrofoil may exhibit three-dimensional characteristics. This study investigates the spanwise variations of cloud-cavitating flows through comprehensive analyses of both numerical results and experimental snapshots. Experiments were conducted in the cavitation tunnel, utilizing high-speed cameras to record the evolution of cavitation, while the cavitating flow of the same configuration was simulated using detached eddy simulation (DES). The three-dimensional shedding phenomena of cloud cavitation, characterized by spanwise variations, are observed in both numerical and experimental results, impacting on the oscillation of hydrodynamic forces. According to the investigation on the spatial-temporal evolution of flow field, two distinct patterns in terms of spanwise shedding of cloud cavitation, namely complete and incomplete shedding, are identified.