High Resolution Interface Capturing Research Articles

Numerical study on laser-induced cavitation bubble dynamics inside a millimetric droplet

In this study, complicated nonlinear interactions of a single laser-induced cavitation bubble inside a millimetric water droplet were numerically investigated using a fully compressible three-phase homogeneous model. A general condensation phase-change model and high-resolution interface-capturing schemes were adopted to accurately predict the bubble collapsing and rebound stages as well as strongly deformable droplet interface evolutions. The numerical model was validated using experimental data in terms of the equivalent bubble radius until the second collapse stage, and good quantitative agreement was achieved. The variation in the droplet surface velocity was detected and could better reveal the mechanism underlying the complicated bubbles and droplet interactions, particularly in droplet surface splash dynamics. Subsequently, the complex bubble–droplet interaction phenomena were studied by investigating the ratio of the maximum bubble radius to the initial droplet radius. The numerical results show that the bubble collapsing time decreases monotonically with an increase in the bubble–droplet radius ratio. The droplet surface instabilities became more dominant as the radius ratio increased. In addition, four distinct patterns of droplet motion, namely, stable, multi-spike, ventilating jet, and splashing phenomena, were captured. Finally, the specific mechanisms leading to droplet surface jetting were identified.

Experimental and CFD modeling of a progressive cavity pump (PCP) using overset unstructured mesh part 2: Two-phase flow.

In oil well operations, accurate modeling of two-phase liquid-gas flow in Progressive Cavity Pumps (PCPs) is vital. This study aimed to comprehensively analyze such flow in a metal-metal PCP using computational fluid dynamics (CFD) simulations validated by experimental data. The methodology applied to the High-Resolution Interface Capturing (HRIC) scheme is to compute the convective transport of phase fractions, yielding insights into the intricate dynamics of these flows. Validation was achieved using laboratory-acquired data and comparisons with extant publications. The findings confirmed the CFD simulations' alignment with field data for two-phase liquid-gas flows. Gas compression and effective viscosity gradient were crucial for accurate pump performance prediction. An investigation into the “gas seal” phenomenon using the Eulerian Multiphase Model elucidated the distinct separation of gas and liquid phases. The influence of the gas volume fraction on pump metrics like torque, power, and efficiency was explored, with CFD predictions exhibiting less than 8% error. The study underscores the pivotal role of CFD tools in predicting pump behavior under diverse conditions. It advances our understanding of two-phase flows in oil wells, especially regarding the gas's impact on pump components. This research offers the oil industry a refined modeling tool, enhancing the comprehension of oil well pump dynamics.

Superspreading metal–organic frameworks modified interface for high-performance tritiated wastewater separation: Experiments and CFD simulation studies

The tritiated water distillation method can inherently safely treat tritiated wastewater, but the separation efficiency is low, and there is limited understanding of the gas–liquid two-phase countercurrent distillation process that affects its separation performance. In this study, tritiated water distillation experiments with metal–organic frameworks (MOFs)-modified superspreading interface and computational fluid dynamic (CFD) simulations were conducted to investigate the influence of contact angle on gas–liquid two-phase interfaces and liquid holdup, as well as its impact on separation performance. A distillation column with a length of 1 m had a smaller height equal to a theoretical plate (HETP) of 3.0 cm, and higher separation performance than non-modified packing with HETP of 7.2 cm. The volume of fluid (VOF) method with the high-resolution interface capturing (HRIC) scheme was used to reconstruct the gas–liquid interface and the accuracy of CFD simulating was validated by droplet spreading experiment. CFD simulations demonstrated that the gas–liquid interface area increased from 34.9 m2/m−3(−|−) to 498.5 m2/m−3(−|−) with the contact angle decreasing from 90° to 0°. When the reflux rate increases from 85 kg m−2h−1 to 425 kg m−2h−1, the liquid holding capacity of the column remains stable at about 10 %, and the phase interface area remains stable at about 500 m2/m−3(−|−) for the MOFs-modified column. This research increased the understanding of the influence of surface wetting on the performance of tritiated water distillation and had potential applications for other gas–liquid two-phase flow separation processes.

Breaking wave simulations for a high-speed surface vessel with hybrid THINC and HRIC schemes

To simulate the ship-induced breaking waves with high-accuracy VOF (volume of fluid) schemes, the unstructured THINC (tangent of hyperbola for interface capturing) type scheme was selected as the main interface capturing method.Particularly, an extension version of THINC/QQ (THINC method with quadratic surface representation and Gaussian quadrature), namely THINC/QQ-SF (THINC/QQ extended for split-face unstructured cells) was used. The computational domain was discretized by the trimmed meshes of STAR-CCM+. The mesh cells were categorized into three groups, including regular unstructured (i.e. hexahedral, tetrahedral, prismatic and pyramidal) cells, split-face unstructured cells and polyhedral cells. THINC/QQ-SF was applied for the first two cell groups, which take up most of the space. The algebraic VOF scheme of HRIC (high-resolution interface capturing) which has the advantage of algorithm simplicity, was implemented for the third cell group. To validate the performance of THINC/QQ-SF and HRIC, a series of testing meshes were designed for the pure VOF advection cases. Additionally, the geometric VOF scheme of isoAdvector was also involved for comparisons. In terms of the accuracy, THINC/QQ-SF is similar with isoAdvector, both of which are much better than HRIC. For the efficiency, both THINC/QQ-SF and HRIC have obvious advantages over isoAdvector under the present conditions. Then, the hull form of DTMB (David Taylor model basin) 5415 was chosen for testing, under the Froude number of 0.35. By using the combination of THINC/QQ-SF and HRIC (i.e. THINC/QQ-SF & HRIC), the compactness of the interface can be maintained. Besides, the wave elevations are well agreed with the published experiment. For the averaged calm-water resistance, the present strategy can obtain more accurate results with fewer (or much fewer) cells, compared with the previous CFD studies. To better show the advantages of the hybrid method, the simulations with pure HRIC were also conducted. Compared with pure HRIC, THINC/QQ-SF & HRIC can better capture the wave breaking details with less numerical diffusion, and the reliability of the resistance prediction is higher.

LES investigation on cavitating flow structures and loads of water-exiting submerged vehicles using a uniform filter of octree-based grids

The water-exit course of a submerged vehicle launched underwater that moves into the atmosphere is one of the most important considerations in naval applications. In the present work, a large-eddy simulation with a uniform filter of an octree-based isotropic mesh and a high-resolution interface-capturing algorithm is employed to investigate this issue, with a special emphasis on the flow structures and pressure features. Various launch parameters, including the immersion depth, navigation speed, and angle of attack are discussed. The flow structures sensitive to adverse pressure relevant to the water-exit angle are captured and discussed. The flow experiences a laminar-turbulent transition and forms coherent turbulence structures, which develop a series of primary and secondary hairpin vortices. The distribution of pressure is more monotonic and regular on the pressure side of the vehicle as the angle increases, while a propagation of disturbance and a transition to turbulence can occur across the lateral side. Based on the clearly captured evolution of the water surface and cavitation, the cavity shedding induced by a pinch-off effect of the travelling liquid-vapor contact lines is found and investigated. The structural features of turbulence are greatly affected in this case, which contrasts with the noncavitating features. The structures are tuned due to the existence of cavitation, which blocks the hairpin-vortex generation mechanism. The cavity surface is full of Tollmien-Schlichting wave-like vortical structures caused by liquid-vapor interface shearing. Hundreds of monitors are intensively arranged on the vehicle's surface to capture the transient pressure signals, through which the crucial pressure features induced by the growth and collapse of the cavitation are captured.

Experimental and numerical investigation of cavitation in marine Diesel injectors

To further increase the efficiency and decrease emissions of large two-stroke marine Diesel engines, the understanding of the fuel injection, spray breakup and the resulting combustion plays a vital role. Investigations have shown that the strongly asymmetrically and eccentrically arranged nozzle bores of the fuel injectors can lead to undesirable spray deflections that provoke increased component temperatures, emissions and fuel consumption. In order to investigate the origin of these spray deviations, transparent nozzles have been used to qualitatively visualize the in-nozzle flow under realistic geometrical and fuel pressure conditions. Three different, 0.75 mm diameter, single-hole nozzle geometries that represent typical geometrical characteristics have been used in cavitating nozzle flow experiments. The optical measurement technique Shadowgraphy has been applied to visualize the in-nozzle flow over the complete fuel injection process. The experiments have been performed with Diesel fuel at a rail pressure of 50 MPa with ambient back-pressure and temperature. Impingement measurements have been executed to compare the nozzle performance and validate CFD simulations using URANS with cavitation modeling in order to provide qualitative and quantitative support to the experimental results. The volume of fluid (VOF) method has been applied to simulate the multiphase flow with High Resolution Interface Capturing (HRIC). The cavitation model is based on a flash-boiling method with rapid heat transfer between the liquid and vapor phases. A Homogeneous Relaxation Model (HRM) has been utilized to describe the rate at which the instantaneous quality, the mass fraction of vapor in a two-phase mixture, will approach its equilibrium value.The numerical modeling of the cavitation inside the nozzle bore and the evaluated momentum flux have been compared to the experimental findings and show good agreement for the qualitative comparison of the cavitation patterns and differences of less than 6% for the quantitative momentum flux comparison.

Modelling hydraulic jumps: IDDES versus experiments

The present paper analyses the advantages and limitations of using numerical modelling to simulate hydraulic jumps at high Froude numbers. Two hydraulic jumps of the same Froude number (7.5) but different Reynolds numbers were simulated using Improved Delayed Detached Eddy Simulation. The free surface was captured using the Volume of Fluid multiphase model with a High-Resolution Interface-Capturing technique. Flow properties including velocity, total pressure and air concentration profiles were compared with experimental results at different streamwise locations. It was observed that while the simulations were able to accurately capture the velocity and pressure fields, the air concentration values were over predicted, although the air concentration distribution was successfully reproduced. Since the simulations capture the complete three-dimensional flow field, further analysis of different physical mechanisms contributing to air entrainment are also carried out. The turbulent kinetic energy and the vorticity field were examined to understand the air–water flow dynamics. The coherent structures responsible for air entrainment were identified using vortex identification techniques. The influence of these structures on the air-entrainment mechanisms is presented with pertinent discussions.

Numerical simulation of bubble collapse between two parallel walls and saturated film boiling on a sphere

The present study aims at validating a computer simulation code for compressible interface flows with and without mass transfers. The numerical method was based on a dual-time fully compressible multiphase homogeneous mixture flow model. The interfaces with a large jump in density, pressure, velocity, and temperature were captured using a compressive high-resolution interface-capturing scheme. Lee’s boiling model was adopted for implementing the mass and energy transfers via interfaces. The bubble collapse between two parallel walls was first examined. The bubble profile during the collapse process was predicted and compared with experimental images. The numerical results showed good agreement. To evaluate the present model for multiphase flows, including the effects of heat and mass transfers, computations were performed for saturated film boiling on a sphere at atmospheric pressure. The evolution of the wavy liquid–vapor interface around the sphere during the film boiling process was observed. The time-averaged heat fluxes obtained from the numerical simulation were compared with those predicted from numerical data and analytical correlations. The effects of the superheated wall on heat fluxes were also investigated.

CFD modeling of air and highly viscous liquid two-phase slug flow in horizontal pipes

Computational Fluid Dynamics (CFD) approach, encoded on STAR-CCM+ was used to simulate air and highly viscous liquid two-phase slug flow in a 50.8-mm (2-in.) ID and 18.9-m (62ft.) long horizontal pipe. The Volume of Fluid (VOF) method, the Continuum Surface Force (CSF) model and the High Resolution Interface Capturing (HRIC) scheme were utilized. The liquid viscosity varied from 161 to 567mPas based on the experimental data. A sensitivity analysis of the sharpening factor, the angle factor, and the Interface Momentum Dissipation (IMD) model was carried out to obtain the best combination of parameters. Besides, comparison with experimental measurements concerning slug frequency, average liquid holdup and velocity profiles in the liquid region was carried out. The comparison shows a fair correspondence in terms of behavior and magnitude with the experimental results obtained by Particle Image Velocimetry (PIV). It was observed that the velocity profile is not fully developed near the bottom of slug body. Finally, extrapolation to the extended velocity conditions was performed. The reduction of translational velocity at higher mixture velocity conditions was investigated. A certain amount of gas passing from the tail to the front of the liquid slug body was visualized by three-dimensional velocity profiles. This phenomenon supports the reduction of translational velocity above the certain level of mixture velocity.

A compressive interface-capturing scheme for computation of compressible multi-fluid flows

Abstract In this paper, a compressive high-resolution interface-capturing scheme is presented for the computation of compressible multi-fluid flows with high-density ratios and strong shocks. The proposed scheme is coupled with a preconditioned dual-time compressible mixture solver for robust and accurate computations over a wide range of Mach numbers. The scheme is simple and relatively easy to implement. It does not require any calculations for the interface curvature and the normal vector. The numerical approximations were implemented on general, structured grids using an implicit MUSCL upwind approach. Validation tests were conducted for a single reversible vortex, advection of an air-water interface, dam-break flow, and air shock-helium bubble interaction. Finally, a three-dimensional gas-lift flow is presented to demonstrate the capability of the present scheme for handling an interface with large jumps in pressure, temperature, and density.

Submerged Hydraulic Jump Study Using DES

AbstractIn the present paper, three-dimensional, unsteady, detached eddy simulation (DES) of a submerged hydraulic jump with an inlet Froude number of 8.2 is performed. The volume of fluid (VOF) method with a high-resolution interface capturing (HRIC) scheme is used for free-surface tracking. The mean velocity and turbulence quantities including the Reynolds stresses are compared with available experimental data to validate the results. The three-dimensional nature of the flow in the developing and developed zone of the submerged hydraulic jump is evaluated by examining the coherent structures using the λ2 criteria. Additionally, proper orthogonal decomposition (POD) analysis reveals the dominance of smaller structures in the developed region of the submerged hydraulic jump. The presence of these smaller scales is directly responsible for the energy dissipation characteristic of the submerged hydraulic jump.

Numerical simulation of mold-filling capability for a thin- walled aluminum die casting

Mold-filling capability is an important property of casting materials. Especially in thin-walled die casting, fast cooling of the melt by contact to the die makes complete filling difficult to ensure. Simulation is an important tool enabling investigation of filling problems, even before the die is manufactured. However, the prediction of misruns is challenging. Flow and solidification have to be computed as closely coupled. The effects of surface tension, the wetting angle and reduced melt flow due to solidification must be modeled with high precision. To meet these requirements, a finite-volume method using arbitrary polyhedral control volumes is used to solve flow and solidification as closely coupled. The Volume-of-Fluid approach is used to capture the phase separation between gas, melt and solid in connection with a High-Resolution Interface-Capturing scheme to obtain sharp interfaces between phases. To model the resistance of the dendrite network to the melt flow, an additional source term in the momentum equation was implemented. The Bolt test was performed for A356 alloys at a range of different casting temperatures. Numerical prediction of incomplete filling in the bottleneck regions agreed well with experimental findings using 3D camera scanning. The simulation enables derivation of the dependence of critical wall-thickness, i.e. the thickness which is fillable, on casting temperature and metallostatic pressure. This could prove useful in predicting filling problems ahead of casting.

Simulation of jet impingement heat transfer onto a moving disc

A transient numerical investigation has been conducted to determine the thermal effects of an axisymmetric oil jet impinging on a high-speed reciprocating disc subjected to uniform heat flux and bounded by a cylindrical wall. The two-phase air–oil simulations are performed using the volume of fluid (VOF) method with a high-resolution interface-capturing scheme. The three-dimensional Navier–Stokes equations and energy equation are numerically solved using a finite volume discretization. The conjugate heat transfer (CHT) method is used to obtain a coupled heat transfer solution between the disc and fluid, yielding a more accurate prediction for the heat transfer coefficient. To overcome the high computational cost of such a simulation, a new methodology is presented to accelerate the solution. The simulation process involves several stages, including the simulation of the heat transfer of a stationary disc with a cooling jet at different impingement distances from the nozzle exit and simulation of a moving disc without the cooling jet and subjected to constant heat flux. Following this, the flow field and thermal characteristics of a reciprocating disc with constant heat flux and an impinging cooling jet is considered. For jet impingement onto the moving boundary, the maximum Nusselt number is achieved a short time after the relative velocity between the disc and the jet reaches its maximum.

Heat Transfer Due to an Impinging Jet in a Confined Space

A numerical investigation using unsteady three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations with the k-ω SST (shear stress transport) turbulent model was conducted to determine the flow and thermal characteristics of an unsubmerged axisymmetric oil jet in air, impinging normally on to a heated flat disk with finite radius, bounded by cylindrical walls kept at constant temperature. A 10 mm thick disk subjected to a high uniform heat flux was located at impingement distances ranging from 40 to 80 mm from the nozzle exit, for nozzle exit diameters of d = 1.0, 2.0, and 4.0 mm. The volume of fluid (VOF) method with a high-resolution interface-capturing (HRIC) scheme was implemented in STAR-CCM+. A new methodology was developed to predict the stagnation zone and local heat transfer coefficients. Contrary to previous research, it is shown that the radial extent of the stagnation zone is not fixed but depends on the gradient of radial velocity along the disk. The normalized local Nusselt number profile along the disk radius is found to be weakly dependent on Reynolds number for a given nozzle size. It is also shown that the local Nusselt number is not uniform in the stagnation region as reported by experimental studies but depends on the distribution of the near-wall radial velocity gradient. Using the computational results, new correlations to predict the dimensionless radial velocity gradient and Nusselt number have been developed. The present correlations are dimensionally balanced, eliminating a deficiency in earlier correlations noted in the literature.

An evaluation of interface capturing methods in a VOF based model for multiphase flow of a non-Newtonian ceramic in tape casting

The aim of the present study is to evaluate the different interface capturing methods as well as to find the best approach for flow modeling of the ceramic slurry in the tape casting process. The conventional volume of fluid (VOF) method with three different interpolation methods for interface capturing, i.e. the Geometric Reconstruction Scheme (GRS), High Resolution Interface Capturing (HRIC) and Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM), are investigated for the advection of the VOF, both for Newtonian and non-Newtonian cases. The main purpose is to find the best method for the free surface capturing during the flow of a ceramic slurry described by a constitutive power law equation in the tape casting process. First the developed model is tested against well-documented and relevant solutions from literature involving free surface tracking and subsequently it is used to investigate the flow of a La0.85Sr0.15MnO3 (LSM) ceramic slurry modeled with the Ostwald de Waele power law. Results of the modeling are compared with corresponding experimental data and good agreement is found.

Simulation of Cold Shuts and Misruns in Centrifugal Casting of TiAl Low Pressure Turbine Blades

In this work cold shuts and misruns in thin turbine blade test geometries are predicted using a three-phase mold filling and solidification simulation methodology applied to a centrifugal casting process of turbine blades. The methodology is based on a finite-volume method with arbitrary shaped polyhedral control volumes. The Volume-of-Fluid (VOF) approach has been used to capture the phase separation between gas, melt and solid. A High Resolution Interface Capturing (HRIC) scheme has been established to gain sharp interfaces between phases, mandatory for correct calculation of surface tension and wetting angle effects. An additional source term in the momentum equation based on Darcy-law for porous media and Kozeny-Carman relation for the permeability estimation was implemented to model the resistance of the dendrite network to the melt flow. A series of test blades with decreasing thickness has been simulated and cold shuts and misruns predicted at different locations, depending on the blade thickness. Casting trials show an excellent agreement between simulation prediction and experimental findings.

Predictions of misruns using three-phase coupled mold-filling and solidification simulations in low pressure turbine (LPT) blades

New alloy developments such as γ-TiAl aim at weight reduction and improvement of performance capabilities of aircraft engines. A drawback of TiAl is its low fluidity, which easily leads to misruns during the casting process.In this work a three-phase mold filling and solidification simulation methodology has been established and validated against casting trials. It uses the finite-volume method and arbitrary polyhedral control volumes to solve the governing equations. A High-Resolution Interface-Capturing (HRIC) scheme has been established as state-of-the-art for modeling multiphase flows with sharp interfaces using the so called Volume-of-Fluid (VOF) model. This multiphase model has been extended to casting processes to predict velocity, pressure and temperature distribution for all three phases, namely the gas, melt and solidified phase.Since LPT blades for aircraft engine applications are of widely differing in geometry with less than 1 mm thickness at the trailing edges, the effect of surface tension and wetting angle is dominant in these wall-bounded flows during the filling stage. These effects can only be calculated correctly if the interface between the phases is sharp and mesh quality is high. For the later automatically generated body-fitted polyhedral meshes with thin prism layers are used. In addition resistance of the dendrite network to melt flow must be adequately modeled. Here, an additional source term in the momentum equation based on Kozeny-Carman relation for permeability estimation is used.A detailed analysis of filling and solidification is presented to study the performance of the simulation method.

Three-Dimensional Numerical Study of Impinging Water Jets in Runout Table Cooling Processes

Cooling from impinging water jets in runout table (ROT) processing depends on the fluid flow and depth of water accumulated in the water pool that forms on the surface of the moving steel strip. This effect is investigated with a three-dimensional (3-D) computational model of fluid flow, pressure, and free surface motion for realistic banks of nozzles within the flow rate region of the ROT process (2400 to 9200 L/min m2). The volume of fluid (VOF) method with the high-resolution interface capturing (HRIC) scheme was implemented to handle the free surface flow of the water jet, and the k-e model was used for turbulence. The governing equations are discretized by a second-order accurate scheme and solved with the computational fluid dynamics (CFD) code Fluent. The model was validated with experimental measurements of free-surface shape and hydraulic jump position for a single water jet impinging onto a moving surface that included turbulent flow and multiphase regions of mixed bubbles and water. For banks of water jets impinging onto the surface of the moving strip in a realistic ROT, the free surface shape, velocity, and pressure distributions have been calculated for various flow rates and surface widths. A deeper water pool is expected on the moving surface with increasing water flow rate and with increasing width. In addition, as the water pool height increases, the pressure variations on the moving surface below the water jets decrease. A simple relation to predict the water pool height from the water flow rate per unit area and strip width has been derived. The predictions agree well with both the 3-D calculations and measurements from water model experiments.

Viscous waves and wave-structure interaction in a tank using adapting quadtree grids

Viscous waves and waves over a submerged cylinder in a stationary tank are simulated using a volume-of-fluid numerical scheme on adaptive hierarchical grids. A high resolution interface-capturing method is used to advect the free surface interface and the Navier–Stokes equations are discretised using finite volumes with collocated primitive variables and solved using a Pressure Implicit with Splitting of Operators (PISO) algorithm. The cylinder is modelled by using the technique of Cartesian cut cells. Results of flow of a single fluid past a cylinder at Reynolds number Re=100 are presented and found to agree well with experimental and other numerical data. Viscous free surface waves in a tank are simulated using uniform and quadtree grids for Reynolds numbers in the range from 2 to 2000, and the results compared against analytical solutions where available. The quadtree-based results are of the same accuracy as those on the equivalent uniform grids, and retain a sharp interface at the free surface while leading to considerable savings in both storage and CPU requirements. The nonlinearity in the wave is investigated for a selection of initial wave amplitudes. A submerged cylinder is positioned in the tank and its influence on the waves as well as the hydrodynamic loading on the cylinder is investigated.

A RANS-based technique for simulation of the flow near a rolling cylinder at the free surface

Accurate prediction of roll motion is very important in ship dynamics, particularly when the safety of the ship is in question. In this paper "COMET," a Reynolds averaged Navier–Stokes (RANS) solver, is used to simulate the flow in the vicinity of a rectangular cylinder rolling at the free surface and to demonstrate the potential of RANS-based techniques in complex flows with free surfaces. The method adopted is based on an unstructured collocated finite-volume technique, which uses a variation of the SIMPLE scheme for pressure correction. An advanced interface capturing technique known as high resolution interface capturing (HRIC) is used for tracking the free surface with reduced numerical diffusion. The results derived are compared with available numerical and experimental results, showing good agreement on added moment of inertia and damping coefficients, whilst accurately predicting other main features of the flow. However, further validation for other geometries and extension to 3-D hull forms are essential before applications to practical problems are realised.