Surrounding Flow Field Research Articles

Reconfiguration and dynamics of clamped fibers under finite-amplitude surface gravity waves

We investigate the behavior of a flexible stem completely submerged under a surface gravity wave of finite amplitude using fully resolved direct numerical simulations. By varying the rigidity of the stem over ten orders of magnitude, we explore its motion in the drag-dominated regime with realistic air and water properties. Our findings reveal two distinct structural responses of the stem depending on the ratio between its natural frequency (fnat) and the wave frequency (fwave). For fnat/fwave≫1, the stem maintains on average a straight configuration and exhibits streamwise oscillations in phase opposition with the wave, moving symmetrically with respect to the vertical direction. Conversely, for fnat/fwave≪1, the stem reconfigures under the influence of the Stokes drift, bending forward and breaking the symmetry, and exhibits oscillations that are more coherent with the surrounding flow field. Resonance is observed when fnat≈fwave. These results provide insights into the dynamics of slender vegetation and manmade structures in wave fields, offering valuable implications for marine biology and engineering. Published by the American Physical Society 2025

The Interaction Mechanisms of Swimming Biomimetic Fish Aligned in Parallel Using the Immersed Boundary Method

In natural environments, fish almost always swim in groups. Investigating the coupled mechanism of biomimetic fish exhibiting autonomous swimming capabilities advances our understanding of fish schooling phenomena and simultaneously aids in refining the structural and formation configurations of underwater robotic vehicles. This work innovatively develops an algorithm based on the Direct-Forcing Immersed Boundary Method (DF-IBM) and implements it in an efficient, modular software program written in C++. The program accelerates the calculation process by using a multigrid method. Validation against a benchmark case of flow around a cylinder, with comparison to data from the existing literature, verifies the program’s precision with discrepancies of less than 3.6%. Based on this algorithm, the paper analyzes the incompressible viscous flow during the movement of parallel-aligned biomimetic fish. It uncovers the interaction between the fish’s motion and the surrounding flow field and also reveals the hydrodynamic mechanisms of the group motion of the parallel-aligned biomimetic fish. The flow field under varying spacing and phases between the parallel-aligned biomimetic fish proves that the interaction between the flow fields induced by the two fish bodies becomes increasingly significant when decreasing the lateral spacing from 1.4L to 0.6L. Notably, an initial lateral convergence of the fish bodies is observed, followed by a sideways swimming pattern at a particular pitch angle, accompanied by a decrement in their forward swimming velocity as they approach each other. Additionally, this study compares flow field alterations in parallel-aligned biomimetic fish with identical lateral spacing but opposing flapping phases. The findings indicate that, irrespective of the phase, the fish exhibit an initial convergence followed by a sideways motion at a specific pitch angle. However, due to disparities in the tail’s flow field, a larger pitch angle is generated when the fish swim in unison. All the findings above will provide a solid theoretical foundation for the design and optimization of underwater robotic vehicles.

On the threshold of bogie simplification for train crosswind testing

The bogie is a unique component exclusive to railway locomotives and rolling stock, and the simplified level of the bogie model directly influences the distortion and accuracy of the experimental results obtained. In this study, the effects of bogie simplified thresholds (T) are numerically investigated employing the improved delayed detached eddy simulation method. Three bogie configurations, comprising complex, moderate, and simple setups, were proposed for a 1/8th scale train model, each featuring different thresholds. The numerical algorithm was validated through a wind tunnel test, with a focus on aerodynamic loads and pressure distribution. The results indicate that as the bogie simplified threshold T increases, the drag and lift forces of each car increase. The head car exhibits a reduction in both lateral force and rolling moment coefficients, whereas the middle car sees a marginal increase, and the tail car maintains unchanged coefficients. As the bogie simplified threshold T increases, the blockage effects of the bogie cavity diminish under crosswinds, leading to decreased airflow impact on the bogie. However, the airflow impact on the vehicle bottom and the bogie cavity's end faces intensifies. The simple setup (T = 200 mm), due to neglecting significant geometric features, exhibits poorer agreement in surface and surrounding flow fields around the train, compared to the other two configurations. Therefore, to guarantee precise predictions accounting for both drag coefficients and detailed bottom flows, it is recommended to maintain the bogie simplified threshold at T = 100 mm at minimum. This study offers prospective insights into modeling detailed components for rail vehicles during wind tunnel experiments.

Effects of geometric and wake characteristics on vortex-induced vibrations of a seal-whisker cylinder

The unique wavy surface of harbor seal whiskers can alter the surrounding flow field, enabling drag reduction and vibration suppression. Investigating how surface undulation parameters and wake flow influence vortex-induced vibration (VIV) characteristics of these whiskers can enhance our understanding of their flow-sensing mechanism. In this work, the effects of geometric and wake features on the VIV characteristics of seal-whisker cylinders are numerically investigated. Specifically, two scenarios are considered: the first scenario examines the VIV of a whisker with different surface undulation amplitudes and wavelengths in uniform flow, while the second scenario explores the VIV of a whisker under various wake conditions generated by upstream circular, square, and diamond-shaped cylinders. For both scenarios, the hydrodynamic performance and the vibration response of the whisker are analyzed and compared. The results reveal significant differences in the wake flow patterns of whiskers with varying surface undulations, which in turn affect the drag reduction and vibration suppression of the whiskers. The results also demonstrate that, the primary frequency of the transverse vibration of the whisker is consistent with the vortex-shedding frequency of the upstream object, and there are notable disparities among different wakes regarding the flow patterns between the upstream object and the downstream whisker. Some findings of this study could provide valuable insights for the design and optimization of biomimetic structures.

Aerodynamic performance enhancement of a vertical-axis wind turbine by a biomimetic flap

We improve the aerodynamic performance of a simplified vertical-axis wind turbine (VAWT) using a biomimetic flap, inspired by the movement of secondary feathers of a bird's wing at landing (Liebe 1979Aerokurier1254). The VAWT considered has three NACA0018 straight blades at the Reynolds number of80000based on the turbine diameter and free-stream velocity. The biomimetic flap is made of a rigid rectangular curved plate, and its streamwise length is 0.2cand axial (spanwise) length is the same as that of blade, wherecis the blade chord length. This device is installed on the inner surface of each blade. Its one side is attached near the blade leading edge (pivot point), and the other side automatically rotates around the pivot point (without external power input) in response to the surrounding flow field during blade rotation. The flap increases the time-averaged power coefficient by 88% at the tip-speed ratio of 0.8, when its pivot point is at 0.1cdownstream from the blade leading edge. While the torque on the blade itself does not change even in the presence of the flap, the flap itself generates additional torque, thus increasing the overall power coefficient. The phase analysis indicates that the power coefficient of VAWT significantly increases during flap opening to full deployment through the interaction with vortices separated from the blade leading edge. When the pivot point of flap is farther downstream from the leading edge or the flap operates at a high tip-speed ratio, the performance of the flap diminishes due to its weaker interaction with the separating vortices.

Characterization of Particle Fluidization in a New Type of Fluidized Bed Flotation Unit

ABSTRACTUnderstanding the hydrodynamics of the bed layer in a fluidized bed is essential for optimizing and improving fluidized bed flotation units. This study proposes a fluidized bed flotation column that incorporates auxiliary particles into the gas–liquid two‐phase system to address the shortcomings of traditional flotation units. Stainless steel particles (glass beads), tap water, and compressed air were used as the solid, liquid, and gas phases, respectively. Key factors affecting the bed hydrodynamics (such as bed fluctuation, minimum fluidization velocity, bed expansion, and porosity) in the fluidized column include gas and liquid flow rates as well as the initial bed height. Experimental results show that selecting appropriate filling particles can effectively enhance the fluidization performance of the bed, while appropriately increasing the gas flow rate can achieve fluidization at lower liquid velocities, thus reducing energy consumption during the flotation mineralization process. Theoretical analysis combined with extensive data reveals that the expansion characteristics of the fluidized bed and the use of high‐density filling particles can effectively mitigate bed layer fluctuations and stabilize the flow field environment. Additionally, based on a wide range of data, this study employs model factor analysis, dimensionless analysis, and multiple linear regression analysis to propose a standard dimensionless parameter model for the fluidized bed flotation column, which can effectively predict bed layer fluctuations and expansion characteristics.

Simulation study of aerodynamic ablation characteristics of ballistic missile laser fuzes

Abstract When a ballistic missile re-enters the atmosphere at hypersonic speed, the warhead and the incoming flow have a violent effect, resulting in a rapid increase in the air temperature of the surrounding flow field, and the persistent high temperature will make the optical window of the ballistic laser fuzes appear ablation phenomenon, which seriously affects the ranging accuracy of the laser detection system. In this paper, the optical window of the laser fuze is taken as the research object, quartz glass is chosen as the optical window material, and the thermal response of the optical window of the laser fuze detection system is numerically simulated according to the heat flux density parameter of the ballistic missile when it re-enters the atmosphere. The simulation results show that the quartz glass as the optical window has good ablation resistance and thermal insulation performance.

Data-Driven Based Path Planning of Underwater Vehicles Under Local Flow Field

Navigating through complex flow fields, underwater vehicles often face insufficient thrust to traverse particularly strong current areas, necessitating consideration of the physical feasibility of paths during route planning. By constructing a flow field database through Computational Fluid Dynamics (CFD) simulations of the operational environment, we were able to analyze local uncertainties within the flow field. Our investigation into path planning using these flow field data has led to the proposal of a hierarchical planning strategy that integrates global sampling with local optimization, ensuring both completeness and optimality of the planner. Initially, we developed an improved global sampling algorithm derived from RRT to attain nearly optimal theoretical feasible solutions on a global scale. Subsequently, we implemented corrective measures using directed expansion to address locally infeasible sections. The algorithm’s efficacy was theoretically validated, and simulated results based on real flow field environments were provided.

A theoretical model for compressible bubble dynamics considering phase transition and migration

A novel theoretical model for bubble dynamics is established that simultaneously accounts for the liquid compressibility, phase transition, oscillation, migration, ambient flow field, etc. The bubble dynamics equations are presented in a unified and concise mathematical form, with clear physical meanings and extensibility. The bubble oscillation equation can be simplified to the Keller–Miksis equation by neglecting the effects of phase transition and bubble migration. The present theoretical model effectively captures the experimental results for bubbles generated in free fields, near free surfaces, adjacent to rigid walls, and in the vicinity of other bubbles. Based on the present theory, we explore the effect of the bubble content by changing the vapour proportion inside the cavitation bubble for an initial high-pressure bubble. It is found that the energy loss of the bubble shows a consistent increase with increasing Mach number and initial vapour proportion. However, the radiated pressure peak by the bubble at the collapse stage increases with decreasing Mach number and increasing vapour proportion. The energy analyses of the bubble reveal that the presence of vapour inside the bubble not only directly contributes to the energy loss of the bubble through phase transition but also intensifies the bubble collapse, which leads to greater radiation of energy into the surrounding flow field due to the fluid compressibility.

Preventing scour of monopile foundations using a vertical rotation device

Scour around monopile foundations is a major cause of offshore wind turbine failures, necessitating effective scour prevention measures to ensure the reliability of monopiles. This study investigates a new scour prevention strategy utilizing a vertical turbine rotor. This measure can not only effectively reduce scour around monopile foundations in complex flow field environments but also generate clean electricity, adding value. The effectiveness of the device in mitigating scour is evaluated through experiments. Subsequently, the impact of the flow field around the pile foundation and the seabed shear stress are examined using numerical simulations. The influence of the device’s installation position on seabed shear stress is also discussed. The results indicate that the vertical rotating device significantly reduce scour around the pile foundation, thereby enhancing the reliability of monopile foundations.

The mechanism of aerodynamic performance enhancement of flapping wings with spanwise active deformation

The single stiffness makes the micro-air vehicles (MAVs) only to show excellent flight performance in a specific flow field environment. The MAVs should have the ability to actively deform to adapt to different application scenarios. This study investigates the effects of spanwise active deformation amplitude (ψmax), phase difference (φP), and Strouhal number (St) on the aerodynamic loads and vortex of a wing through numerical simulations. Under the condition of Re= 1000, numerical simulations were conducted on a rectangular wing with an aspect ratio of 4 during the flapping process. The study reveals that moderate spanwise deformation can increase the thrust of the wing and improve propulsion efficiency (ηP). Within the study's scope, the thrust coefficient increases monotonically and linearly with the deformation, but the propulsion efficiency improves only within a limited parameter range. By observing the vortex under different spanwise deformations and monitoring the forces at different positions of the wing, it was found that active deformation can enhance the strength of the leading-edge vortex (LEV) and the wingtip vortex (TV), thereby enhancing the generation of thrust. The results also indicate that the enhancement of LEV is achieved through the coupling between LEV and secondary vortex. At different Strouhal numbers, improvements in ηP can only be achieved through the combined effects of increased vortex strength and optimal vortex residence time. Additionally, it was observed that at lower St, TV can switch from contributing thrust to causing drag.

Three-dimensional particulate volume fraction reconstruction in the fluid based on the Lambert–Beer physics information neural network

The measurement of particle volume fraction in flow fields is of great significance in scientific research and engineering applications. As one of the particle detection techniques, the light extinction method is widely used in measuring nano-particles volume fraction in flow fields due to its simplicity and non-contact nature. In particular, in complex reactive flow fields like combustion reactions, the volume fraction of soot particulate and other particles can be accurately measured and reconstructed via the light extinction method that based on the Beer–Lambert law. This is crucial for exploring combustion phenomena, understanding their internal mechanisms, and reducing pollutant emissions. However, due to the enormous computational burden, current algebra reconstruction techniques struggle to achieve high-precision three-dimensional (3D) reconstruction of particles. Therefore, this paper originally proposes a 3D reconstruction algorithm based on the Beer–Lambert law physical information neural networks (LB-PINNs). By incorporating physical information as constraints into the particle reconstruction process, it is possible to achieve high-precision 3D reconstruction of particles in complex flow field environments with low computational cost. Meanwhile, to address the trade-off issues of reconstruction accuracy and smooth noise resistance in previous reconstruction algorithms, i.e., Tikhonov regularization, this paper employs dynamically adjusted regularization parameters in the LB-PINN algorithm. This approach ensures smooth noise-resistant processing while maintaining reconstruction accuracy, significantly reducing computation time and resource consumption. According to the experimental results, LB-PINNs demonstrate superior performance compared to previous reconstruction algorithms when reconstructing the soot volume fraction in complex reacting flow fields, i.e., combustion flame scenarios.

Numerical Simulation of Spectral Radiation for Hypersonic Vehicles

The spectral radiation of hypersonic vehicles and surrounding flow fields is crucial for optical target detection. A novel approach combines Low-Discrepancy Sequences with the Reverse Monte Carlo Method to simulate the spectral radiation of hypersonic missiles. The effects of chemical non-equilibrium reactions and high-emissivity coating failures on the spectral radiation of a typical biconical hypersonic missile were investigated. Significant differences were found among chemical equilibrium, non-equilibrium, non-reactive, and catalytic wall models. High-emissivity coating failures occur mainly in the high-temperature regions of the nose cone and fins. The non-equilibrium model shows a transition peak distribution of NO in the head shock layer within the ultraviolet gamma band, with integrated ultraviolet radiation (200–300 nm) three times higher than the equilibrium model. In the 1–3 μm band, the non-equilibrium model’s radiation intensity at a 120° horizontal detection angle is about 1.46 times that of the equilibrium model. Using real coating emissivity, the 3–5 μm band radiation intensity is about 5% higher, and the 8–14 μm band is about 8.51% lower than the uniform emissivity model. When high-emissivity coating emissivity fails by 40%, the 3–5 μm band intensity decreases by about 15.38%, and the 8–14 μm band intensity decreases by about 12.67%.

Numerical Simulation and Experimental Research on Effect of Flow Regimes for Refrigeration Performance of Wave Rotor

Abstract Wave rotors exchange energy through the interaction of fluids with different pressures to produce a cooling effect without the application of mechanical parts, which makes them suitable for the complex flow field environments. But the flow situation inside the wave rotor is complex, and research on the impact of various flow regimes for the refrigeration efficiency is currently incomplete. This study deals with the numerical simulation and the experimental verification of a four-port fixed rotor gas wave refrigerator. Various typical flow regimes within the wave rotor were obtained through simulation to analyze their impact on the refrigeration efficiency. To further demonstrate the effectiveness of the simulation results, experimental verification was conducted. The simulation results indicate that separation bubbles and vortices will be respectively generated on the upper and lower walls of the wave rotor tube during the gradual opening stage. Vortex affects the airflow flow and causes detachment of separation bubbles as the airflow moves, which results in the loss of pressure energy and kinetic energy of the incident gas. As a result, the loss caused by the gradual opening process leads to a decrease in the self-expansion ability of high-pressure gas during the gradual closing stage, thereby affecting the refrigeration effect. Therefore, reducing the influence of vortices plays an important role in improving the cooling efficiency of wave rotors. Finally, this study analyzes the main factors that affect the cooling effect within the wave rotor through flow regime and provides new insights for improving refrigeration efficiency.

Deep‐Learning‐Assisted Triboelectric Whisker Sensor Array for Real‐Time Motion Sensing of Unmanned Underwater Vehicle

AbstractAquatic animals can perceive their surrounding flow fields through highly evolved sensory systems. For instance, a seal whisker array understands the hydrodynamic field that allows seals to forage and navigate in dark environments. In this work, a deep learning‐assisted underwater triboelectric whisker sensor array (TWSA) is designed for the 3D motion estimation and near‐field perception of unmanned underwater vehicles. Each sensor comprises a high aspect ratio elliptical whisker shaft, four sensing units at the root of the elliptical whisker shaft, and a flexible corrugated joint simulating the skin on the cheek surface of aquatic animals. The TWSA effectively identifies flow velocity and direction in the 3D underwater environments and exhibits a rapid response time of 19 ms, a high sensitivity of 0.2V/ms−1, and a signal‐to‐noise ratio of 58 dB. The device also locks onto the frequency of the upstream wake vortex, achieving a minimal detection accuracy of 81.2%. Moreover, when integrated with an unmanned underwater vehicle, the TWSA can estimate 3D trajectories assisted by a trained deep learning model, with a root mean square error of ≈0.02. Thus, the TWSA‐based assisted perception holds immense potential for enhancing unmanned underwater vehicle near‐field perception and navigation capabilities across a wide range of applications.

Stiffness Analysis of Cable-Driven Parallel Robot for UAV Aerial Recovery System

Unmanned Aerial Vehicle (UAV) aerial recovery is a challenging task due to the limited maneuverability of both the transport aircraft and the UAV, making it difficult to establish an effective capture connection in the airflow field. In previous studies, we proposed using a Cable-Driven Parallel Robot (CDPR) for active interception and recovery of UAVs. However, during the aerial recovery process, the CDPR is continuously subjected to aerodynamic loads, which significantly affect the stiffness characteristics of the CDPR. This paper conducts a stiffness analysis of a single cable and a CDPR in a flow field environment. Firstly, we derive the stiffness matrix of a single cable based on a model that considers aerodynamic loads. The CDPR is then divided into elements using the finite element method (FEM), and the stiffness matrix for each element is obtained. These element stiffness matrices are assembled to form the stiffness matrix of the CDPR system. Secondly, we analyze the stiffness distribution of a single cable at various equilibrium positions within a flow field environment. Aerodynamic loads were observed to alter the equilibrium position of the cable, thereby impacting its stiffness. The more the cable bends, the greater the reduction in its stiffness. We examine the stiffness distribution characteristics of the CDPR’s end-effector within its workspace and analyze the impact of varying flow velocities and different cable materials on the system’s stiffness. This research offers a methodology for analyzing the stiffness of CDPR systems operating in a flow field environment.

Effect of oyster shell filling in artificial reefs on flow field environment and assessing the potential of carbon fixation

Artificial reefs are basic fishery facilities for marine habitat conservation and construction. In order to enhance fishery resources and restore the ecological environment in Laizhou Bay, where is an important fishing ground in China, an assembly-type oyster reef was designed based on the biological community, water depth and sea current in Laizhou Bay. This paper studied the effect of filling oyster shell in the assembly-type oyster reef on the flow field distribution by computational fluid dynamics (CFD), optimized the structure of reef, and presented the construction deployment of reef habitat and assessed potential of carbon fixation of oyster reefs. Indexes of upwelling, slow flow and vortex were chosen to describe the flow field effect of oyster reefs. The distribution characteristics of flow field under three types of filling oyster shell were analyzed: filling no shell (UAR), filling shells with an 83.6 void ratio (OAR), and filling shells with a 0 void ratio (FAR). The results showed that the upwelling, vortex and slow flow efficiency indicators of the OAR had obvious advantages compared with the other two filling methods, and the efficiency indicators of OAR with the spacing between basic elements of 280 m and deployment angle of 0° were higher than the others. Finally, according to the study result of filling method, spacing and deployment of oyster reef, the assessment showed that reefs could fix 2178.9 t carbon by themselves on the basis of national marine ranching demonstration area regulations in China.

Optimization of wheel brow structures of a van considering rainwater pollutants based on discrete phase model

Four optimization models were proposed to reduce the impact of pollutants from vans on themselves and surrounding vehicles. The adsorption of pollutants on the body of the van in rainy conditions and the diffusion of pollutants into the external environment were numerically investigated using the Discrete Phase Model (DPM) for vans having different wheel brow structures. The pressure distribution on the surface of the van, the surrounding flow field, and the raindrop distributions of various external positions on and around the van were analyzed and compared. The results indicated that the van with externally covered wheel brow model was most effective in inhibiting the diffusion of rainwater pollutants from the van under rainy conditions. Compared with the original model, the reduction in the polluted area was 11.19%, the reduction in the influence of the visual field on the rear vehicle was 25.4%, and the reduction in the diffusion of pollutants on the bodies of the side vehicle was 20.7%.

Real-time digital twin of autonomous ships based on virtual-physical mapping model

The advancement of intelligent technology has propelled the development of smart unmanned vessels into a new phase. To address the urgent demands of current smart ship development, this paper develops a comprehensive ship digital twin system based on a virtual-real mapping algorithm, focusing on the fundamental elements of digital twin model construction. Using the smart unmanned experimental ship Dolphin 1 as a prototype, a digital twin virtual model is proposed. This system leverages real-time internal and external data from the entire vessel to track its navigational status, performance indicators, sailing trends, and surrounding flow field information, offering coordinated “human-machine” navigation assistance. Based on historical data collected from the vessel's long-term navigation, a real-time precise prediction of the vessel's navigational state and hydrodynamic performance is conducted using physics-informed neural network algorithm. This establishes a self-learning iterative virtual-physical mapping model that enables autonomous updates and evolution. As the real navigation data of the vessel continuously update, the virtual model can more accurately simulate the vessel's state in real time. The proposed digital twin model has been tested through sea trials under real sea conditions, demonstrating its high accuracy, robustness, and potential for enhancing navigational safety and efficiency. This system marks a significant step forward in the integration of digital twin technology with maritime navigation, providing a valuable tool for the future development of smart shipping.

CFD-based prediction of flow noise in offshore pipeline systems

Abstract The ship’s water injection system exhibits significant vibration and noise issues, necessitating the prompt implementation of targeted control measures. In this study, the simulation technique of computational fluid dynamics (CFD) combined with the finite element method and automatic matching layer method was applied to emulate the flow field environment of the outlet pipeline of a side valve in a seawater cooling system. Pulsating pressure data on the pipeline and valve’s wall were extracted from the flow field calculation and utilized as dipole noise sources and structural vibration excitations, enabling the prediction and separation of flow noise and flow-induced vibration noise in the water injection system. Leveraging the data from the flow field simulation, an analysis was conducted on the radiated noise at the side valve’s outlet, comparing the impact of different underwater depths and outlet pipe diameters on the underwater flow noise. The findings suggest that measures such as increasing the side valve’s diameter and lowering the discharge port’s underwater position can effectively reduce system flow noise, offering valuable insights for the design of noise reduction in seawater cooling systems for silent surface ships and submarines.