Fluid Method Research Articles

Prediction of hydrodynamic behavior of impinging Glycerin hollow droplet on a concave surface using jet counter and dynamic contact angle

PurposeThis study aims to study hollow droplet collisions for their hydrodynamic behavior and jet properties.Design/methodology/approachThe volume of fluid (VOF) method was used to simulate a hollow impact using OpenFoam software (VOF).FindingsThe height of the edge-jet decreased as the air diameter (d) and length of the concave surface (L) increased. Height is specific for case 1 at t = 4 ms and its value is 3 mm. The minimum height is 0.585 mm in case 5. Also, the length of the edge-jet changed with time and decreased with the increasing length of concave and air diameter. The maximum length observed in case 1 was 9.23 mm, and the minimum appeared in case 5, in which the length was 0.68 mm.Originality/valueThe impact of a hollow droplet on a solid concave surface was numerically analyzed in this paper at various lengths of surface and shell thicknesses.

Numerical and Experimental Study on the Hydrodynamic Performance of a Sloping OWC Wave Energy Converter Device Integrated into Breakwater

This study presents numerical and experimental investigations on an oscillating water column (OWC) wave energy device integrated into a sloping breakwater. Regular waves were generated in a physical wave tank to investigate the hydrodynamic performance and extraction efficiency of the small-scale nested OWC device. Simultaneously, to complement various scenarios, numerical simulations were conducted using the open-source computational fluid dynamics platform OpenFOAM. The volume of fluid (VOF) method was employed to capture the complex evolution of the air–water interface, and an artificial source term (Forchheimer flow region) was introduced into the Navier–Stokes equations to replace the power take-off (PTO) system. By analyzing wave reflection properties, energy absorption efficiency, and wave run-up, the hydrodynamic characteristics of the inclined OWC device were explored. The comparison between the numerical and experimental results indicate a good consistence. A smaller front wall draft broadens the high-efficiency frequency bandwidth. For relatively long waves, increasing the air chamber width enhances energy conversion efficiency and reduces wave run-up. The optimal configuration was achieved with the following dimensionless parameters: front wall draft a/h=1/3, air chamber width d1/h=2/9, and slope i=2. Due to the sloped structure, when compared with a vertical OWC, long waves can more easily enter the chamber. This causes the efficient frequency bandwidth to shift towards the low frequency range, allowing more wave energy to be converted into pneumatic energy. As a result, wave run-up is reduced, enhancing the protective function of the breakwater.

Research on Temperature Field Analysis Method of High-Speed Bearing Chamber–Bearing System

The analysis of the temperature field of a high-speed bearing chamber–bearing system is very complex. We used the temperature field analysis method on a 40,000 rpm bearing chamber–bearing system by simulation, which builds on the finite volume method and introduces a decoupling method that separates fluid dynamics from the thermal analysis of the solid temperature field. Firstly, according to bearing operating conditions, the characteristics of the oil–air two-phase distribution in the bearing chamber are determined using the Volume of Fluid (VOF) method. The convective heat transfer boundary conditions derived from this analysis serve as the thermal boundary conditions for the subsequent thermal analysis. Secondly, considering the heat generation of the bearings and the thermal boundary conditions, a temperature field analysis model is formulated. The calculated results are found to be in close agreement with the actual test data, with an error of less than 10% under three operational conditions. Thirdly, the presented method to evaluate the temperature field of the bearing chamber–bearing system has not been studied in other published literature. Additionally, compared with the thermal fluid–structure interaction method, the method described in this paper can save 90.75% of calculation time, which significantly improves efficiency. Therefore, the above method is reliable for evaluating the temperature field of the bearing chamber–bearing system.

Release of a finite volume of viscous fluid over rigid curvilinear surfaces

Viscous gravity currents play a fundamental role in many natural and industrial applications, where practical scenarios often involve the current propagating over rigid curvilinear surfaces. In this study, we employ lubrication theory to develop low-dimensional models for such two-dimensional and axisymmetric propagation, resulting from the release of a finite volume of viscous fluid. A key dimensionless parameter is identified, representing the volume ratio between the released fluid and the curvilinear surface, which governs the current evolution. By simplifying the curvilinear surface with linear–exponential and sinusoidal shapes, we observe distinct flow behaviours. Over linear–exponential surfaces, the current may become trapped, bypass the peak or flow downward, while over sinusoidal surfaces, the propagation is hindered compared with the behaviour over horizontal straight surfaces. The low-dimensional models are validated using the volume of fluid method in computational fluid dynamics, showing consistent predictions of the current evolution over rigid curvilinear surfaces.

Characterizing binary droplet collisions of power‐law fluids

AbstractThis study focuses on the dynamics of two equal‐sized droplets of non‐Newtonian liquids with simulations using the volume of fluid method and the local front reconstruction method. The non‐Newtonian behavior is implement via a power‐law model. The droplet interactions are performed for Weber numbers ranging from 20 to 300 and impact parameters from 0 to 0.6. Both methods produce similar results at low Weber numbers, while the disintegration of the droplets at high Weber numbers occurs via different mechanisms. Our results demonstrate that the boundaries of the collision maps are highly dependent on the power‐law index. Additionally, the diameter of the ring for head‐on collisions is increased with increasing Weber number and decreasing power‐law index, while the critical ligament length in off‐center collisions increases with Weber number and power‐law index.

Similarity Design Method for Fluid–Structure Models in Underwater Shaking Table and Wave Tests

Similarity Design Method for Fluid–Structure Models in Underwater Shaking Table and Wave Tests

Numerical study of vortex–bubble interaction mechanism in bubble breaker using the volume of fluid and large eddy simulation method

Effectively removing or reducing the number of bubbles doped in a material is of great significance to stabilize product characteristics and improve production safety. In this paper, the volume of fluid method and large eddy simulation method are used to numerically simulate the bubble dynamics in unsteady turbulence near a four-blade propeller in a bubble breaker at different speeds. The results show that the final rupture position of the bubble occurs in the main vortex region. The interaction mechanism between the vortex and the bubble involves not only the impact of the small vortex on the bubble but also the influence of the tail vortex pair, which exerts two strong torsional stresses in opposing directions. This interaction ultimately results in the breakup of the bubble. In addition, three different fracture modes were observed: Ring Broken Mode (RBM), Dented pull out Broken Mode (DBM), and Tear Broken Mode (TBM). The bubble breaking process is quantitatively described in terms of vorticity change rate and critical Weber number (We). It is found that DBM does not occur at high rotational speed, and TBM occurs faster and more violently with increase in vorticity change rate. After multiple cycles, the vorticity change in RBM is similar to that at medium speed, and when the change rate reaches its maximum, the size of the fragmentation bubble becomes smaller.

Phase-Controlled Construction of Copper-Leaf-like 2D NiS for Enhanced Supercapacitor Performance: A Supercritical Fluid Process

This study investigates a rapid and straightforward approach for constructing phase-controlled two-dimensional NiS nanosheets using the supercritical fluid (SCF) method. Through structural and morphological analyses, it is observed that the single-phase NiS nanosheets exhibit a rough and hierarchical surface, potentially offering a versatile electroactive area for energy storage. The electrochemical performance of fabricated single-phase NiS-based supercapacitors are measured in both three-electrode and two-electrode systems. In asymmetric supercapacitor (ASC) configuration with H2SO4 electrolyte, α-NiS demonstrated a remarkably high specific areal capacitance of 1664.61 mF.cm-2 at a current density of 1mA.cm-2. In asymmetric supercapacitor mode, NiS nanostructures achieved an exceptionally high volumetric energy density of 1953.61 mWh.cm-3 at a highest power density of 45.5W.cm-3. Furthermore, it showed an outstanding cycling performance of 95.77% retention after 5000 cycles at a high current density of 10mA.cm-2.

Numerical simulations of MHD effect on convective heat transfer characteristics in bubbles coalescence process

In this numerical study, the coalescence characteristic of a coaxial bubble pair and its influence on the liquid-to-wall convection heat transfer are investigated under different magnetic field intensities, magnetic field directions, and wall confinement ratios by adopting the volume of fluid (VOF) method. The results reveal that in the direction of heat flow, the toroidal vortices around the bubbles are dampened and even vanish completely after applying the spanwise magnetic fields, while the toroidal vortices only get away from the hot wall in the presence of the transverse magnetic fields. Correspondingly, the convective heat transfer on the hot wall is suppressed to varying degrees under the magnetic fields in different directions. The inhibitory action of the magnetic field on the heat transfer becomes stronger with the decreasing separation distance (s*) between the coaxial bubbles. The total increment of heat transfer (Nu*) is a decreased function of Hartmann number (Ha) and that decreased amplitude of Nu* under the spanwise magnetic field is nearly twice that of the transverse magnetic field. Additionally, the variations of Nu* are independent of the wall confinement ratio (Cr) for Ha < 400, while the Cr has an obvious effect on Nu* for Ha > 400 and the values of Nu* are considerably smaller at a larger Cr. The results about the effect of the magnetic field and wall confinement on the two-phase heat transfer can be referenced in the cooling system design of fusion reactor.

Interaction of a Taylor bubble with the liquid–liquid interface in a notched tube

Injection of air into stratified liquids for improved mixing and for the removal of oil droplets from water is some well-established applications for augmentation of heat and mass transfer and purification of water. The present study investigates the dynamics of a Taylor bubble passing through the liquid–liquid interface in a vertical tube provided with rounded notch of different radii using the Eulerian approach-based volume of fluid method. The complete bypass of the Taylor bubble across the liquid–liquid interface and the notch is observed for dimensionless notch radius, r* = 0.0388, whereas the Taylor bubble has bypassed in the form of smaller volumes periodically pinched-off near the notch for higher notch radius. The drag coefficient has significantly increased during the bypass of the bubble across the liquid–liquid interface, its peak has an order of magnitude ≅102 for r* = 0.0388, and it is ≅ 103 for a larger notch radius. This increase in the drag coefficient is also manifested in terms of significant increase in the wall shear stress and capillary pressure drop across the notch. The increase in liquid viscosity ratio has resulted in a slight increase in pinched-off bubble volumes and their surface oscillations.

A novel rigid-fluid method for landslide tsunami modeling

This study presents a three-dimensional numerical model with the novel rigid fluid method (RFM) to simulate slide-type landslides. RFM, coupled with the Navier–Stokes solver Splash3D, is developed to calculate the movement and rotation of a moving solid. With the pressure and shear stress data in each grid collected by the discrete element method, the moving solid is granted to be involved in the simulation. The model is validated against a three-dimensional experiment of a sphere entering water, demonstrating good agreement in terms of displacement and air column pinch-off time. Subsequently, the model is applied to simulate the process of a semispherical landslide tsunami, using a semispherical laboratory experiment as a benchmark. The numerical results show excellent agreement with the experimental data in terms of sliding track, velocity, dynamic pressure, and wave height. To investigate the applicability of the model to real-world scale events, the above-mentioned case is scaled up proportionally, and the time, flow velocity, dynamic pressure, and resultant force are compared to verify the Froude number similarity. The results indicate that the model can effectively capture the essential features of landslide-induce tsunamis and has the potential to be used for further studies on the impacts of such events.

Investigation of internal flow and mixing characteristics in dual-orifice atomizers

Dual-orifice atomizers have been developed to overcome the limitations of simplex atomizers—where “simplex” refers to having only a single flow channel—which cannot adjust flow rates over a wide range. This study explores the internal flow and mixing characteristics of dual-orifice atomizers using the Volume of Fluid method. The effects of four key parameters—primary post thickness, primary recess length, secondary swirl number, and mass flow rate ratio—on flow dynamics and atomizer performance, particularly exit film thickness and spray cone angle, are investigated. The results reveal that, before mixing, the low-pressure region created by the swirling flow inside the secondary nozzle increases the primary flow angle and reduces the thickness of the primary liquid film. After mixing, the velocity difference between the primary and secondary flows enhances atomization by promoting greater instability. The impingement position of the primary liquid film is influenced by recess and the low-pressure region inside the secondary nozzle, with longer recess lengths shifting the impingement point upstream. Increases in secondary swirl number, mass flow rate ratio, and primary post thickness further enlarge the low-pressure region, causing the impingement point to move upstream. The mixing regime is defined by the impingement position, with tip mixing creating velocity stratification that increases the instability. The performance of dual-orifice atomizers depends on the impingement position, resulting mixing regime, and secondary flow's swirl intensity. These findings provide valuable insights for optimizing atomizer design to improve performance.

Numerical Simulation on Flow and Heat Transfer Characteristics of a Single-loop Oscillating Heat Pipe with Variable Pipe Diameter Ratios

A three-dimensional numerical model, employing the Volume of Fluid (VOF) method, was developed for a single-loop oscillating heat pipe (OHP) with variable diameters. The investigation explored the impact of varying pipe diameter ratios on flow and heat transfer characteristics at different operational stages under a 40W heat power. The results reveal that the diameter ratio significantly affects the spatial arrangement of the evaporation, adiabatic, and condensation sections in the OHP. In the initial stage, the condensation section displays 15 liquid slugs when the diameter ratio is 1, but this number decreases to fewer than 10 in the same area when the diameter ratio exceeds 1. Comparative to a straight-pipe OHP, configurations with varying diameter ratios exhibit a marginal reduction in the average fluid velocity during the circulation of the working fluid inside the pipe, with the most pronounced velocity decrease occurring at a diameter ratio of 0.8. As the diameter ratio increases to 1.25 and 1.5, the turbulent disturbances in the region where the working fluid flows from the adiabatic section to the evaporation or condensation section intensify, facilitating the temperature exchange within the OHP. During stable operation of the OHP, the frequency of temperature oscillations increases with an increasing diameter ratio, while the amplitude decreases. Among all the cases, the OHP with a diameter ratio of 1.25 has the optimal heat resistance, 1.50K/W. The heat transfer performance of the OHP with a pipe diameter ratio of 0.8 deteriorated, and the thermal resistance increased by 27.6% compared with the straight-pipe OHP.

Numerical Analysis of the Effect of Tunnel Hydrofoil—Stern Flap on the Motion Stability of a Double M-Craft in Regular Waves

Abstract The double M-craft is a new type of high-performance multihull vessel that combines the gliding characteristics of a planing boat with the resistance-reducing characteristics of a hovercraft, but it also suffers from motion instability in regular waves. At present, there is scarce study on the effect of appendage on the motion stability of double M-craft in regular waves. By using the software star-ccm+ to numerically simulate the pitching and heaving motions of a double M-craft installed with tunnel hydrofoils and stern flaps in regular waves. Based on the overset mesh technology, the volume of fluid (VOF) method is used to capture the water–gas two-phase flow field. The 2-degree of freedom (2-DOF) motion of the rigid body is simulated by dynamic fluid-body interaction (DFBI). After investigating the effects of these combined appendages on the hydrodynamic performance, running attitude, and motion response of a double M-craft in regular waves, the optimal mounting parameters of the combined appendage have been obtained. The results have shown that all nine types of combined appendages can reduce the heave and pitch. The optimal combined appendage installation parameters include a hydrofoil longitudinal mounting position of 1/8L, an angle of attack of 3 deg, a stern flap length of 1.5%L, and a flap angle of 5 deg, which can effectively reduce the pitching response by about 8% and reduce the swaying response by about 2.6%, and enhance its longitudinal motion stability.

Investigation of Tool Cooling and Heat Transfer Using Computational Fluid Dynamics Simulations

Thermal errors remain one of the biggest challenges for the precision of cutting machine tools. Aside from optimizations in the machine tool design and behaviour, optimal cutting process parameters and targeted usage of cutting fluid or alternative methods of tool cooling are required for improved process efficiency with minimal energy demand and maximal tool life. A simulation-based study is presented which compares both different methods of tool cooling, specifically air cooling, flooded cooling and minimum quantity lubrication and also different simulation methods and models. Using a case study, which models an existing thermal test stand comprised of motor spindle, tool holder, tool and coolant nozzle, different cooling scenarios were tested and compared. The simulations were performed in ANSYS CFX. Comparisons were made between simulations with and without buoyancy, with and without tool rotation, transient and steady-state, with laminar flow and with different turbulence models and between the different cooling scenarios. Some insight on different time step sizes and the resulting increase in simulation time and precision was also gained. These results will make future studies on the thermal behaviour of both tool and cutting process easier by showing suitable simulation techniques and viable model simplifications.

Effect of multiple appendages on maritime surveillance ship resistance at various ship speeds

Resistance is a critical factor affecting the operational performance and economic efficiency of marine surveillance ships. To enhance the enforcement efficiency of marine surveillance ships, this study investigates the impact of five types of appendages on ship resistance performance. In this study, resistance experiments and numerical simulation calculation on the ship model were carried out. Based on Computational Fluid Dynamics (CFD) and the Volume of Fluid (VOF) method, the study captures the variations in ship resistance and the free surface Cases around the hull. A comparative analysis was then conducted on the resistance effects of different appendages installed on the ship model. It was found that the installation of stern shaft brackets, bilge keels, and ductkeel increased the ship's resistance. In contrast, the installation of spray rails reduced resistance by approximately 2.5%. However, the effectiveness of the spray rails diminished at high speeds due to their inability to prevent wave overtopping. Since stern flaps are commonly used drag-reducing appendages, this study improved the original design. Comparative analysis revealed that the modified curved structural design of the stern flaps exhibited enhanced drag reduction capabilities.

Numerical Study on the Influence of Drift Angle on Wave Properties in a Two-Layer Flow

This study examines the influence of drift angle on the wave and flow field generated by a submarine navigating through a density-stratified fluid. Employing a numerical methodology, this research computed the viscous flow field around the SUBOFF bare hull under conditions of oblique shipping maneuvers. The analytical framework relies on the Reynolds-Averaged Navier–Stokes (RANS) equations, supplemented by the Re-Normalization Group (RNG) k-ε turbulence model and the Volume of Fluid (VOF) method. The initial phases of this study involved verifying grid convergence and the accuracy of the numerical methods used. Subsequently, numerical simulations were performed across a spectrum of drift angles while maintaining a fixed Froude number of Fn = 0.5, with submergence depths set at 1.1 D and 2.0 D. The analysis focused on the wave profiles at both the free surface and the internal surface. The results indicate that the presence of a drift angle produces significant alterations in the characteristics of the free surface and internal surface when compared with straight-ahead motion. Specifically, the asymmetry in the flow field is enhanced, and the variability in the roughness of the free surface is pronounced.

Dynamic characteristics of wave entry for a deep-sea mining vehicle: Numerical and experimental studies

The deep-sea mining vehicle (DSMV) experiences complex impacts upon the wave entry, which directly affects the safety and reliability of the whole deployment system. In this paper, a computational fluid dynamics (CFD) method is proposed to investigate hydrodynamic properties and wave-entry effects of a DSMV with varying laying speeds. Firstly, a fifth-order Stokes surface gravity wave simulating Sea State 4 conditions is constructed based on the volume of fluid (VOF) method. Then, the overset mesh scheme is utilized to establish the multiple degree-of-freedom (DOF) model of DSMV which bears the traction loads of laying cable. Laboratory prototype tests are conducted, and the captured results of cavitation evolution and motion properties corroborate the present model. Numerical results indicate that the DSMV entering the wave danger point will experience hydrodynamic forces several to dozens of times greater, severely threatening structural safety. During the wave entry process, two phases of nonlinear deceleration occur, posing a risk to the umbilical cable. Surge and pitch motions caused by waves and structural asymmetry may lead to deployment position deviation. Based on the trends observed in the simulation data, guidance for deployment operations has been proposed.

Numerical investigation of fluid–structure interaction in a pilot-operated microfluidic valve

The present paper is concerned with numerical investigation of the performance of a pilot-operated control valve based on shape memory alloy actuation control. The valve under investigation can be integrated into miniaturized hydraulic systems and is developed to perform precise dispensing, mixing, or dosing tasks while being able to withstand relatively high pressure differences. The study evaluates the valve’s response under the current ON/OFF and the desired proportional control regimes using numerical methods for fluid–structure interaction. The computational model replicates the operation of the valve, which requires an understanding of the complex interactions between the fluid flow with the pressurized valve and the contact with the valve seat during the opening and closing processes. In addition, the model leverages advanced numerical techniques to overcome several complexities arising mainly from the geometrical, material, and contact nonlinearities, and to mitigate the shortcomings of the partitioned fluid–structure interaction approach. Several 3D fluid–structure-contact-interaction simulations are conducted to examine the valve’s structural and flow behavior under varying pressure conditions. Results indicate that the valve is adequate for ON/OFF actuation control but is susceptible to flow-induced vibrations during the proportional control regime that occurs due to the sharp pressure drop in the valve-seat gap and the ensuing Venturi effect, which counteract the opening of the main valve. The fluid–structure-interaction simulations provide insight into the mechanism underlying the flow-induced vibrations, which can serve to improve the design and enhance the performance of the valve in microfluidic applications.

Effect of liquid flux on wetting behavior in slender trickle bed reactors: A particle-resolved direct numerical simulation study

Slender trickle beds play a crucial role in various industrial processes involving gas-liquid-solid systems. Understanding the wetting characteristics is vital for optimizing their performance and efficiency. In this study, we employ a particle-resolved Computational Fluid Dynamics approach combining the Volume of Fluid (VoF) method for gas-liquid interactions and a second-order implicit Immersed Boundary Method (IBM) for fluid-solid interactions. The particle wettability is modeled by imposing a contact angle boundary condition at the gas-liquid-solid interface. The impact of the liquid flux on the wetting patterns and the rate of liquid penetration depth within the slender trickle bed is studied. The results show two main mechanisms of penetration through the bed: gravitation and inertia driven. The penetration of the liquid in the bed is driven by gravity when the liquid flux is low and the inertia is diminished in the top of the bed. This results in enhanced wetting from the onset of the penetration. If the inertia is high (high liquid flux), the initial liquid penetration is fast and spreading in the bed only occurs after full penetration of the bed.