Volume Of Fluid Technique Research Articles

Influence of hollow droplet impact and spreading characteristics on the cylindrical lateral surface

In this study, 3D model of a hollow glycerin droplet impacting on a cylindrical cross-section was numerically analyzed to coat the lateral surface of the cylinder. The hollow droplets had exterior diameters of 5.5 mm, 5.25 mm, and 5 mm, and the impact velocity was 1 m/s. To model, the influence of droplets on OpenFoam software, the Volume Of Fluid technique was utilized (VOF). The Newtonian, incompressible, and laminar fluid phase of a glycerin droplet was investigated using air with a diameter of 4 mm as the gas phase. The hydrodynamic behavior of droplet collisions as well as fluid properties were investigated. As a result, when can be observed in the simple cylinder, as the outer diameter increased, the spread diameter shrank. The least amount distributed diameter in Case 3 was 1.404, whereas the highest amount in Case 4 was 1.625. The situations with a simple lateral surface, uniform spread occurred, while in cases with a spiral lateral surface, non-uniform spread occurred. Observed the maximum length in Case 3 was 4.12 mm and the minimum was 1.83 mm in Case 4.

Fast droplets impacting liquid layer under a small angle: a numerical analysis of experimental observations

In presence of a strong wind above a liquid surface, liquid droplets get accelerated and eventually hit the interface with a high speed under a small angle. Experimental studies demonstrate that such droplets may escape the initial crater and either get broken into secondary droplets in the air, or protrude along the interface, leaving behind agitated surface with entrapped bubbles. Here we aim at reproducing the observed phenomena in a numerical model based on Volume of Fluid technique using Basilisk package. On a flat interface, the impacting droplets partially escape the crater and get broken in front of it within the range of impact angles from 15° to 45°, in agreement to the experiments and simple theoretical considerations. In presence of waves, the escaping droplets fly into the air but, being adhered to the crater, get stretched and broken into secondary droplets. For smaller angles, the droplets escape the crater and glide along the interface. The gliding droplet creates a chain of small craters in its wake. The rims between the craters may grow and get scattered into secondary droplets. Large liquid viscosity and small thickness of the liquid layer suppress the growth of the craters and secondary entrainment. Bubble entrapment during such impacts most likely occurs due to crater collapse with trapping air inside. However, such air pockets are not formed systematically in the present model. This discrepancy requires further investigation.

Numerical and experimental simulation on efficiency of air bubble barrier on various pollutants for preventing oil spill spread

This study conducts experimental and numerical simulations and analyzes the effects of the air bubble barrier (ABB) on the oil spill spread prevention efficiency regarding the varying aperture diameter, air discharge, and pollutant type. In a computational fluid dynamics simulation, a multiphase flow is studied using the finite volume method with the volume of fluid technique in the Star CCM+ software. The pipe generating air bubbles is fixed at the bottom of the tank at 1.8 m from the side of the experimental setup. The distinctive points of the study are the experiments conducted on different pollutants and the utilization of a novel adjustable air nozzle positioned on the air feed pipe. The effectiveness of the ABB in mitigating the spread of marine pollution is contingent on the aperture size, air discharge, and pollutant type. This study demonstrates that the ABB's feasibility for preventing the oil spill spread has improved.

Finite volume analysis of dam breaking subjected to earthquake accelerations

ABSTRACT Because of the complexity of the dam failure mechanism due to earthquakes that occur under the simultaneous influence of hydraulic and seismic forces, a single model has not been obtained so far and this study was conducted to achieve this model. In this paper, dam failure models including both sudden and gradual failure have been investigated using volume of fluid techniques (VOF) to simulate water fluxes, general moving object (GMO) to simulate moving bodies, and the fluid–structure interaction model for finite volume analysis. In order to be sure of the accuracy of the results, before examining the failure mechanisms, the verifications of utilized methods in the case of dam failure were proven using experimental and numerical studies from literature. The Koyna Dam earthquake of magnitude 6.5 (11 December 1967) is investigated as a test case. Comparison of the output discharges due to dam failure in the two failure models reveals that the peak discharge of sudden failure is recorded three times faster than the gradual failure mode. Another achievement that should be mentioned is that although large oscillating periods carry a higher risk of cracking of the dam’s body, smaller periods propagate the resulting cracks more rapidly.

CFD Investigation into Flow Characteristics of a Special Splash Lubrication in Light Helicopters

Lubricating oil flow characteristics are the primary concern in the main reducer of light helicopters. To improve the lubricating performance of the main reducer, a special lubrication system is innovatively constructed by adding two oil-guiding tubes to the hub of the output gear, and the influence of the oil-guiding tubes is investigated through CFD (computational fluid dynamics) techniques. A CFD model of the gearbox integrated with the VOF (volume of fluid) technique was established to explore the flow characteristics of the oil–air two-phase flow inside the gearing system. To validate the proposed CFD model, a specialized testing rig is devised and manufactured to examine the features of oil distribution. The effects of the structure parameters of the oil-guiding tubes and operating conditions on the lubrication performance are explored. Comparing experimental and numerical findings reveals that the inner diameter of the oil-guiding tube and the rotational speed of the driven gear have a significant influence on the lubrication performance. In contrast, the length of the installation end of the oil-guiding tube, its angle, and the oil-immersion depth show little impact.

Numerical Evaluation of Optimal Sizes of Wells Turbine and Chamber of a Cluster of Oscillating Water Columns Integrated into a Breakwater on the Southern Brazilian Coast

This paper describes a numerical evaluation of optimal sizes of a Wells turbine and chamber cross section to be used in a cluster of an oscillating water column (OWC) wave energy converter device. The FLUENT numerical model, based on the Reynolds–averaged Navier–Stokes equations and the volume of fluid technique, is used for modeling hydrodynamic and aerodynamic flows. Two new methods are developed for diminishing the computational cost: the generalized–TDO (turbine diameter optimization) model and the HAS (hydro-aerodynamic similarity) model. The generalized–TDO model is developed to determine the optimal turbine diameter for an OWC chamber with a square cross section. The analytical HAS model employs a similitude method to extend results obtained for a square cross section of the OWC chamber to a rectangular one. The optimal length, B, and width, W, of the chambers and turbine diameter, D, chosen by taking into account the southern Brazilian wave climate, were B × W = 15 × 15 m2 and D = 2.75 to 3.00 m and 20 × 20 m2 and D = 3.25 to 3.50 m, with efficiencies of 51% and 49%, respectively. Same optimal annual efficiency can be obtained for rectangular cross-section chambers 15 × W and 20 × W by using an adequate turbine diameter defined by the HAS model.

Computational Evaluation of Shock Wave Interaction with a Liquid Droplet

This article represents the natural continuation of the work by Rossano and De Stefano (2021), dealing with the computational fluid dynamics analysis of a shock wave interaction with a liquid droplet. Differently from our previous work, where a two-dimensional approach was followed, fully three-dimensional computations are performed to predict the aerodynamic breakup of a spherical water body due to the impact of a traveling shock wave. The present engineering analysis focuses on capturing the early stages of the breakup process under the shear-induced entrainment regime. The unsteady Reynolds-averaged Navier–Stokes approach is used to simulate the mean turbulent flow field in a virtual shock tube device with circular cross section. The compressible-flow-governing equations are numerically solved by means of a finite volume method, where the volume of fluid technique is employed to track the air–water interface. The proposed computational modeling approach for industrial gas dynamics applications is verified by making a comparison with reference numerical data and experimental findings, achieving acceptably accurate predictions of deformation and drift of the water body without being computationally cumbersome.

Numerical study of droplet impact on superhydrophobic vibrating surfaces with microstructures

The dynamic behavior characteristics of droplet impact on superhydrophobic microstructured surfaces vibrating in the vertical direction are evaluated with Computational Fluid Dynamics combined with Volume of Fluid technique. The effects of wall vibration amplitude, vibration frequency, phase angle and droplet velocity on contact time and maximum penetration depth are investigated. Results demonstrate that the phase angle affects the relative movement between droplet and vibrating surface, which causes changes of contact time and maximum penetration depth. The increase of vibration amplitude leads to larger fluctuation ranges of contact time and maximum penetration depth, compared with that on stationary surface. Moreover, the contact time decreases to the minimum values under nonresonant frequencies f* = 0.8, 1.2 at 270°, and the maximum values of maximum penetration depth curves are reduced along with the increase of vibration frequency. Furthermore, the contact time of droplet at dimensionless velocity 0.8 is shortened obviously in comparison with the results on stationary wall, while the maximum penetration depth of droplet at dimensionless velocity 1.5 is decreased the most. Finally, the surface vibration under dimensionless amplitude 0.2, and dimensionless nonresonant frequencies 0.8, 1.2 is obtained to improve dynamic behavior characteristics of droplet impact on superhydrophobic vibrating microstructured surfaces.

Wave loads on high-rise pile cap structures and mitigation approach

A novel type of foundation, a high-rise pile cap structure, was proposed to support offshore wind turbines in China. It is unique because the upper cap is now and then partially submerged or totally exposed in the air. The wave force of this unique structure is not well understood yet. In this paper, a fully nonlinear numerical wave tank is established to deal with this problem based on Navier-Stokes equations and volume of fluid technique. The wave impact loads on the structure and their mechanism are revealed. Modifications of the cap bottom elevation are considered to explore its influence on direct and indirect wave impact loads on the lower piles. The wave impact load on the most dangerous pile is detected high if the cap bottom is at the still water level or close to the wave crest level, and small impact load is found while the cap bottom is at the height of half wave crest. Attempts of structural improvement are considered to reduce the wave impact loads on the piles. The wave impact load can be notably reduced by opening air vents in the cap together with lifting the bottom of the inner part of the cap.

Experimental and numerical probe into the effects of adding one and two steps to a mono-hull planing vessel on its performance in calm water

In the current study, two different vessels with a single step and two steps are experimentally and numerically studied. The considered speeds are 8 and 9 m/s, equivalent to beam Froude numbers of 3.44 and 3.86. The experimentally measured parameters include bow rise-up, trim, and vessel’s resistance. On the other hand, numerical simulations of fluid flow around the vessel at 10 m/s and 12 m/s speeds are conducted using STAR-CCM+ software. Two-phase flow is analyzed using finite volume method and volume of fluid technique. Moving mesh approach through the Overset technique is applied for discretization of the domain. Based on the experimental results, it is observed that addition of the transverse step enhances the vessel’s stability and reduces its trim. It is also concluded that the resistance of a single stepped high-speed vessel reduces, compared to a vessel of without step. Meanwhile, numerical studies indicate that as the second step moves away from the transom, the resistance increases, and trim decreases. It is also concluded that both single-step and two-step models are stable at speeds up to 12 m/s.

Numerical simulation of interface tracking between two immiscible micropolar and dusty fluids

The development of the interfacetracking between two immiscible liquids is one of the most challenging problems in fluid dynamics. The simulation of the lubrication process, oil extraction, and the physicochemical mechanism that govern the behaviour of the uncertain conduct of interface is a key element in “gas-oil” or “oil–water” natural gas-oil reservoirs systems and should be tracked for optimal recovery. Motivated by the interface evolution process, in this article, an unsteady flow of two immiscible Eringen micropolar and Dusty (fluid-particle suspension) fluids is considered through a horizontal channel and the functioning of the interface is analysed. Although the channel wall is hyper-stick and no-slip, it is believed that the fluid–fluid interface is unsteady and can also be deformed from one location to another; thus, the single momentum equation is coupled for monitoring the interface profiles using the VOF (Volume of fluid) technique. The modelled coupled- partial differential equations are numerically solved by the modified B-spline differential quadrature method. The interface profile under the influence of different parameters, i.e., Froude, Capillary, wave and Reynolds number, amplitude, the ratio of viscosities, and time is analysed. Three applied pressure gradients namely constant Ge = 10, periodic Ge = 10Sin(t), and decaying Ge = e-t are considered with various constant values of other hydrodynamic parameters. It's been noted that thetopologydevelops with time asthe pulsing pattern repeats quicker for a longer period before becoming stable. The flow's qualitative characteristics remain preserved, the interface begins to move vertically as the amplitude is elevated. A higher interfacial drift is seen in the applied periodic pressure gradient case as compared to the constant and decaying pressure gradient scenario. The tracking does take high time to be stable in the presence of the micropolar parameter with all three applied pressure gradient cases.

On the dynamics of jet wiping: Numerical simulations and modal analysis

We analyze the flow of a planar gas jet impinging on a thin film dragged by a vertical moving wall. In the coating industry, this configuration is known as jet wiping, a process in which impinging jets control the thickness of liquid coatings on flat plates withdrawn vertically from a coating bath. We present three-dimensional (3D) two-phase flow simulations combining large eddy simulation (LES) and volume of fluid techniques. Three wiping configurations are simulated and the results are validated with experimental data from previous works. Multiscale modal analysis is used to analyze the dynamic interaction between the gas flow and the liquid film. In particular, we present a combination of multiscale Proper Orthogonal Decomposition (mPOD) and correlation analysis. The mPOD is used to identify the dominant traveling wave pattern in the liquid film flow, and the temporal structures are used to determine the most correlated flow features in the gas jet. This allows for revealing a two-dimensional mechanism for wave formation in the liquid coat. Finally, we use the numerical results to analyze the validity of some of the critical assumptions underpinning the derivation of integral film models of jet wiping.

Computational Evaluation of Shock Wave Interaction with a Cylindrical Water Column

Computational fluid dynamics was employed to predict the early stages of the aerodynamic breakup of a cylindrical water column, due to the impact of a traveling plane shock wave. The unsteady Reynolds-averaged Navier–Stokes approach was used to simulate the mean turbulent flow in a virtual shock tube device. The compressible flow governing equations were solved by means of a finite volume-based numerical method, where the volume of fluid technique was employed to track the air–water interface on the fixed numerical mesh. The present computational modeling approach for industrial gas dynamics applications was verified by making a comparison with reference experimental and numerical results for the same flow configuration. The engineering analysis of the shock–column interaction was performed in the shear-stripping regime, where an acceptably accurate prediction of the interface deformation was achieved. Both column flattening and sheet shearing at the column equator were correctly reproduced, along with the water body drift.

A RANS-VoF Numerical Model to Analyze the Output Power of An OWC-WEC Equipped with Wells and Impulse Turbines in A Hypothetical Sea-State

Wave energy is a renewable source with significant amount in relation to the global demand. A good concept of a device applied to extract this type of energy is the onshore oscillating water column wave energy converter (OWC-WEC). This study shows a numerical analysis of the diameter determination of two types of turbines, Wells and Impulse, installed in an onshore OWC device subjected to a hypothetical sea state. Commercial software FLUENT®, which is based on RANS-VoF (Reynolds-Averaged Navier-Stokes equations and Volume of Fluid technique), is employed. A methodology that imposes air pressure on the chamber, considering the air compressibility effect, is used. The mathematical domain consists of a 10 m deep flume with a 10 m long and 10 m wide OWC chamber at its end (geometry is similar to that of the Pico’s plant installed in Azores islands, Portugal). On the top of the chamber, a turbine works with air exhalation and inhalation induced by the water free surface which oscillates due to the incident wave. The hypothetical sea state, represented by a group of regular waves with periods from 6 to 12 s and heights from 1.00 to 2.00 m (each wave with an occurrence frequency), is considered to show the potential of the presented methodology. Maximum efficiency (relation between the average output and incident wave powers) of 46% was obtained by using a Wells turbine with the diameter of 2.25 m, whereas the efficiency was 44% by an Impulse turbine with the diameter of 1.70 m.

Hydrodynamics of a bordered collar as a countermeasure against pier scouring

An experimental campaign on long-term clear-water scour at bridge piers with different configurations was performed in a laboratory to investigate the effects of different countermeasures. Tests were performed in a flume with a movable sediment bed for an unprotected cylindrical pier, a cylindrical pier with a standard collar and a cylindrical pier with a bordered collar. The scoured beds at the equilibrium stage were acquired through the photogrammetry technique and the efficiencies of the tested countermeasures were measured. Results showed a reduction in the maximum scour depth as well as in the scour hole volume with respect to the unprotected pier. The maximum scour depth was reduced by 59.63% with the standard collar and by 63.51% with the bordered collar. The scoured volume was reduced by 43.80% with the standard collar and by 60.00% with the bordered collar. The three-dimensional Reynolds-averaged Navier–Stokes equations were solved numerically to reproduce the hydrodynamics of the experiments. The volume of fluid technique was used to reproduce the free surface. For each test, the results of the simulations were analysed to investigate the flow field around the pier both at the initial (flat-bed) and at the equilibrium stages, highlighting the changes in the velocity field owing to the presence of the standard collar and of the bordered collar.

Reviewing the Flow Film Condensation Parameters Inside Different Geometry Configuration

A literature survey on film condensation under various flow patterns such as annular, wavy, stratified and intermittent flow types numerically and experimentally for different fluids including refrigerants such as R141b, carbon dioxide, R134a, FC72, R290, R1234yf and ze(E) in addition to pure water vapor in tubes and mini-channels has been done between 2016-2020, taking into account variations in the geometry shaping characteristics used, including horizontal, vertical and inclined circular and twisted tubes for flat, finished and curved profiles and multiple cross-sectional mini-channels, including square, rectangular and triangular, with variations in their internal This survey includes shapes such as straight and convergent and/or divergent profiles, in addition to single and multi-port mini-channels. In addition, the effect of the surrounding cooling media type like stagnant air, natural gas flow (air and nitrogen), and immersed water are presented in this review. The survey focuses on the volume of fluid technique used in the numerical reviewed literature in order to solve the governing equations for laminar and turbulent flow conditions with great attention to the interface region characteristics between the vapor and the liquid phase for the above-mentioned flow types and their influence on the accuracy of the presented correlations on the evaluation of the condensate heat transfer coefficient.

A numerical model of an immiscible surfactant drop spreading over thin liquid layers using CFD/VOF approach

Numerical investigations of immiscible surfactant drops spreading over thin liquid substrates have been carried out. The CFD numerical model is based on a volume of fluid technique (VOF) coupled with piecewise linear interface calculations method (PLIC). This interface reconstruction is applied to simulate the time evolution of the dynamics of drop of surfactants spreading on thin water liquid substrates. In the model, the surfactant is considered as a separate phase instead of a solution of water containing the surfactant. This approach allows to avoid the parallel determination of the surfactant molecular diffusion coefficient, the maximum packing concentration, and the rate constants for adsorption and desorption prior to the simulations. Series of superspreader trisiloxane (M(D′EnOH)M surfactant are considered. The predictions of the CFD model agree remarkably well with the measurements from previously published experimental results. The simulations are used to predict and optimize the spreading behavior as a function of a range of well-defined parameters including the water/surfactant interfacial tension (28−35 mN/m), the volume of the drop of surfactant (0.61−38.79 mm3) and the thickness of the water layer (1−3 mm). The dewetting process of the thin water layer from the surface by the surfactant occurs for almost all the configurations. The formation of secondary drops and instable crown happen solely for the largest drop volume of 38.79 mm3. Only for the thicker films (h = 2 and 3 mm), a cavity on the liquid is generated after the impact. For all the thicknesses, instabilities appear at the surfactant/water interfaces and their numbers are larger for the thinner film (h = 1 mm). The kinetic analysis of the numerical data confirms the existence of two successive spreading regimes for all the drops of surfactants studied. The faster time evolution of the moving front proceeds for surfactant drops of low volume and high surface tension as well as a thick water underlayer.

Simulation of Partially Filled Liquid in A Moving Tank

Numerical simulations have been carried out on a rectangular tank filled partially with liquid using volume of fluid technique. The tank has been given to and fro motion in one direction. Numerical simulation has been carried for a two dimensional case having laminar and unsteady flow. The changes in free surface displacement and dynamic pressure at different times has been observed using ANSYS software. The study was conducted for two sec. It was observed that free surface displacement of fluid increases with velocity. Also, with an increase in volume of liquid the sloshing effect decreases.

Effect of Multiple Liquid Inlets on Mass Transfer in Rotating Packed Beds

This study deals with optimalization of rotating packed bed design using computational fluid dynamics approach. Comparison of three variants of liquid distributor were performed on 2D geometry. Turbulence was modelled using unsteady RANS approach and volume of fluid technique were used to simulate gas-liquid interphase. Results were compared on basis of liquid holdup evaluation.

LES investigation of sheet-cloud cavitation around a 3-D twisted wing with a NACA 16012 hydrofoil

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.