Simulation Of Three-dimensional Flow Research Articles

Numerical Simulation of Cloud Cavitation in Hydrofoil and Orifice Flows With Analysis of Viscous and Nonviscous Separation

Three-dimensional (3D) numerical flow simulations with a mass transfer cavitation model are performed to analyze cloud cavitation at two different flow configurations, i.e., hydrofoil and orifice flows, focusing on the turbulence and cavitation model interaction, including a mixture eddy viscosity reduction and cavitation model parameter modification. For the cavitating flow around the hydrofoil with circular leading edge, a good agreement to the measured shedding frequencies as well as local cavitation structures is obtained over a wide range of operation points, even with a moderate boundary layer resolution, i.e., utilizing wall functions (WF), which are found to be adequate to capture the re-entrant jet reasonably in the absence of viscous separation. Simulations of the orifice flow, that exhibit significant viscous single-phase (SP) flow separation, are analyzed concerning the prediction of choking and cloud cavitation. A low-Reynolds number turbulence approach in the orifice wall vicinity is suggested to capture equally the mass flow rate, flow separation, and cloud shedding with satisfying accuracy in comparison to in-house measurements. Local cavitation structures are analyzed in a time-averaged manner for both cases, revealing a reasonable prediction of the spatial extent of the cavitation zones. However, different cavitation model parameters are utilized at hydrofoil and orifice for best agreement with measurement data.

Janus surface concept for three-dimensional turbulent flows

Three-dimensional numerical simulations of turbulent flow over a partial super-hydrophobic cylinder, hereinafter referred to as the “Janus cylinder”, are performed using large-eddy simulation (LES) with OpenFOAM solver. The slip-wall velocity at the super-hydrophobic surface is evaluated from a third-type (Robin) boundary condition whose coefficient is adjusted based on the available experimental data. Compared to no-slip smooth cylinder, the Janus cylinder has a lower drag coefficient and a lower root-mean-square (rms) lift coefficient, whereas its dominant vortex shedding frequency is higher. The power density distribution of the oscillations, obtained from the Fourier transform of the time-history of the lift coefficient, of the Janus cylinder has a less-sharp and broader distribution compared to the one of the smooth cylinder. No significant difference is observed between the wall shear stress distributions of a Janus cylinder, where super-hydrophobic surface covers only the frontal half of the cylinder, and a totally super-hydrophobic cylinder. This helps the potential manufacturers to reduce the manufacturing costs by partially processing the surface while achieving the highest possible drag reduction.

Numerical prediction of hydrodynamic forces on a moored ship due to a passing ship

The passing ship effect on berthed vessel is a well-known problem and is studied over many years. These interaction effects induce dynamic loads in the mooring system that can exceed the design values and lead to severe accidents. A study has been conducted to analyze the effect of various parameters such as passing ship speed, separation distance, depth to draft ratio and waterway geometry on the hydrodynamic interaction effects between berthed and a passing ship. Numerical simulation for three-dimensional unsteady viscous flow have been conducted using the overset mesh methodology and solving the Reynolds-averaged Navier–Stokes equations with k-ω shear-stress transport turbulence model for various cases, and interaction effect on berthed ship have been calculated. The method recommended in this study is validated by comparing the computational fluid dynamics (numerical) results with existing model scale experiments and mathematical curves from empirical formulas. The hydrodynamic interaction forces are computed for five types of waterway geometries. The magnitude and time histories of the forces and moment on the moored ship for various cases are analyzed to evaluate the effect of various parameters such as waterway geometries and separation distance. The results and conclusions made by this study can give definite guidance on safe maneuvering of a ship passing by a moored ship.

Electrohydrodynamic channeling effects in narrow fractures and pores.

In low-permeability rock, fluid and mineral transport occur in pores and fracture apertures at the scale of micrometers and below. At this scale, the presence of surface charge, and a resultant electrical double layer, may considerably alter transport properties. However, due to the inherent nonlinearity of the governing equations, numerical and theoretical studies of the coupling between electric double layers and flow have mostly been limited to two-dimensional or axisymmetric geometries. Here, we present comprehensive three-dimensional simulations of electrohydrodynamic flow in an idealized fracture geometry consisting of a sinusoidally undulated bottom surface and a flat top surface. We investigate the effects of varying the amplitude and the Debye length (relative to the fracture aperture) and quantify their impact on flow channeling. The results indicate that channeling can be significantly increased in the plane of flow. Local flow in the narrow regions can be slowed down by up to 5% compared to the same geometry without charge, for the highest amplitude considered. This indicates that electrohydrodynamics may have consequences for transport phenomena and surface growth in geophysical systems.

Proposal of fluid stirring by multi-layered trenches for liquid metal divertor

This study proposes ″multi-layered trenches″ as a new liquid metal flow stirring structure for the flowing-type liquid metal divertor to prevent the temperature stratification and the evaporation of liquid metal.Then it investigates the characteristics of the liquid metal flow induced by this structure experimentally and numerically. The proof-of-principal experiment using a torus channel simulating the trenches successfully demonstrated the liquid metal wavy flow where the ratio of meandering component to the main stream was 27% under the magnetic field up to 5 T. The experiment and three-dimensional magnetohydrodynamics flow simulation also proved that magnitudes of the wavy flow and the vorticity increased with a rise in the magnetic field. Moreover, two-dimensional heat transfer model simulation showed the heat transfer enhancement by the wavy flow. Maximum temperature was 26.6 K lower than that in the case without the wavy flow.

Developing transmission line equations of oxygen transport for predicting oxygen distribution in the arterial system

The oxygen content in the arterial system plays a significant role in determining the physiological status of a human body. Understanding the oxygen concentration distribution in the arterial system is beneficial for the prevention and intervention of vascular disease. However, the oxygen concentration in the arteries could not be noninvasively monitored in clinical research. Although the oxygen concentration distribution in a vessel could be obtained from a three-dimensional (3D) numerical simulation of blood flow coupled with oxygen transport, a 3D numerical simulation of the systemic arterial tree is complicated and requires considerable computational resources and time. However, the lumped parameter model of oxygen transport derived from transmission line equations of oxygen transport requires fewer computational resources and less time to numerically predict the oxygen concentration distribution in the systemic arterial tree. In this study, transmission line equations of oxygen transport are developed according to the theory of oxygen transport in the vessel, and fluid transmission line equations are used as the theoretical reference for the development. The transmission line equations of oxygen transport could also be regarded as the theoretical basis for developing lumped parameter models of other substances in blood.

Computations of Homogeneous Multiphase Real Fluid Flows at All Speeds

Computations of all-speed multiphase real fluid flows for aerospace launch vehicles are known to be very demanding, owing to several issues that include robust capturing of two-phase shock/phase discontinuity and proper scaling of numerical flux at steady/unsteady all-speed flows. This paper deals with the development of computational components to overcome difficulties arising from these issues. First, the shock-discontinuity-sensing term used in the two-phase and RoeM schemes is modified because the existing shock-discontinuity-sensing term is not suitable for complex equation of state of real fluids. The accuracy of the two-phase and RoeM schemes for unsteady low-Mach-number flows is then improveed through separate scaling of the velocity- and pressure-difference terms. It is demonstrated that the resulting schemes are capable of robustly and accurately capturing phenomena involving shock and phase discontinuities and interactions between them for numerous two-phase problems. Finally, numerical simulations of cryogenic cavitation and three-dimensional cavitating flows around the Korea Aerospace Research Institute turbopump are presented to confirm accurate and robust behavior of the proposed approaches in computations of multiphase real fluid flows at all speeds.

The Use of Biophysical Flow Models in the Surgical Management of Patients Affected by Chronic Thromboembolic Pulmonary Hypertension.

Introduction: Chronic Thromboembolic Pulmonary Hypertension (CTEPH) results from progressive thrombotic occlusion of the pulmonary arteries. It is treated by surgical removal of the occlusion, with success rates depending on the degree of microvascular remodeling. Surgical eligibility is influenced by the contributions of both the thrombus occlusion and microvasculature remodeling to the overall vascular resistance. Assessing this is challenging due to the high inter-individual variability in arterial morphology and physiology. We investigated the potential of patient-specific computational flow modeling to quantify pressure gradients in the pulmonary arteries of CTEPH patients to assist the decision-making process for surgical eligibility.Methods: Detailed segmentations of the pulmonary arteries were created from postoperative chest Computed Tomography scans of three CTEPH patients. A focal stenosis was included in the original geometry to compare the pre- and post-surgical hemodynamics. Three-dimensional flow simulations were performed on each morphology to quantify velocity-dependent pressure changes using a finite element solver coupled to terminal 2-element Windkessel models. In addition to transient flow simulations, a parametric modeling approach based on constant flow simulations is also proposed as faster technique to estimate relative pressure drops through the proximal pulmonary vasculature.Results: An asymmetrical flow split between left and right pulmonary arteries was observed in the stenosed models. Removing the proximal obstruction resulted in a reduction of the right-left pressure imbalance of up to 18%. Changes were also observed in the wall shear stresses and flow topology, where vortices developed in the stenosed model while the non-stenosed retained a helical flow. The predicted pressure gradients from constant flow simulations were consistent with the ones measured in the transient flow simulations.Conclusion: This study provides a proof of concept that patient-specific computational modeling can be used as a noninvasive tool for assisting surgical decisions in CTEPH based on hemodynamics metrics. Our technique enables determination of the proximal relative pressure, which could subsequently be compared to the total pressure drop to determine the degree of distal and proximal vascular resistance. In the longer term this approach has the potential to form the basis for a more quantitative classification system of CTEPH types.

Дослідження впливу інтерференції лопаткових вінців на втрати в ступені осьового компресора

Мета: дослідження втрат повного тиску у вхідному напрямному апараті, в робочому колесі й напрямному апараті ступеня осьового компресора з урахуванням їх газодинамічної інтерференції. Метод дослідження: дослідження виконано методом чисельного моделювання тривимірної течії в ступені осьового компресора. Побудовано неструктуровану адаптивну розрахункову сітку. Газодинамічний розрахунок течії в ступені осьового компресора виконано з використанням системи рівнянь Нав’є – Стокса, яка замикалася моделлю турбулентної в’язкості SST. Результати: було проведено серію газодинамічних розрахунків течії при різних значеннях осьової швидкості на вході в ступінь компресора. Колова швидкість на периферійному радіусі на розрахунковому режимі складала u=238.64 м/с. Коефіцієнт швидкості на вході в ступінь змінювався в діапазоні =0.35…0.7. За результатами розрахунку побудовано залежності коефіцієнтів втрат повного тиску від коефіцієнта швидкості на вході для вхідного напрямного апарату, робочого колеса і напрямного апарату. Аналіз результатів дослідження показує, що найбільший внесок у загальний баланс втрат повного тиску вносять втрати в напрямному апараті. Обговорення: унаслідок газодинамічної інтерференції робочого колеса і напрямного апарату відбувається збільшення втрат в напрямному апараті. Взаємний вплив лопаткових вінців робочого колеса і напрямного апарату призводить до суттєвої трансформації швидкостей і тисків в міжлопаткових каналах. Як наслідок, має місце перерозподілення втрат, обумовлених коловою і радіальною нерівномірністю потоку, кінцевими перетіканнями і дією відцентрових сил. Можна очікувати, що зменшення рівня втрат в ступені осьового компресора можна забезпечити шляхом впливу на пограничний шар в кінцевому зазорі робочого колеса.

Three-Dimensional Simulation of Turbulent Hot-Jet Ignition for Air-CH4-H2 Deflagration in a Confined Volume

This work describes essential aspects of the ignition and deflagration process initiated by the injection of a hot transient gas jet into a narrowly confined volume containing air-CH4-H2 mixture. Driven by the pressure difference between a prechamber and a long narrow constant-volume-combustion (CVC) chamber, the developing jet or puff involves complex processes of turbulent jet penetration and evolution of multi-scale vortices in the shear layer, jet tip, and adjacent confined spaces. The CVC chamber contains stoichiometric mixtures of air with gaseous fuel initially at atmospheric conditions. Fuel reactivity is varied using two different CH4/H2 blends. Jet momentum is varied using different pre-chamber pressures at jet initiation. The jet initiation and the subsequent ignition events generate pressure waves that interact with the mixing region and the propagating flame, depositing baroclinic vorticity. Transient three-dimensional flow simulations with detailed chemical kinetics are used to model CVC mixture ignition. Pre-ignition gas properties are then examined to develop and verify criteria to predict ignition delay time using lower-cost non-reacting flow simulations for this particular case of study.

Hydraulic performance prediction of a prototype four-nozzle Pelton turbine by entire flow path simulation

Abstract This paper presents entire flow path simulations in a prototype four-nozzle Pelton turbine under three water heads, from pipe flow to nozzle jet water sheet flow on rotating bucket and drop from bucket brim on the air. Different type flows in the Pelton turbine are analyzed by adopting the three-dimensional transient air-water two-phase flow simulation method. Hydraulic performance of stationary parts and rotating runner are evaluated along the entire flow path. Flow analyses indicate that the pressure pulsation is very low and the water flow could be regarded as steady flow in the stationary parts. The hydraulic loss in these parts drops as the water head increases due to a reduction of the frictional loss. Afterwards, the interactions between the jets and buckets in the rotating runner are discussed. The pressure pulse on the bucket surface pulsates with the spreading of the water sheet flow and takes up 10%–25% water energy. The hydraulic performance of the bucket is highest at optimal water head and decreases as the water head varies. Unsteady flow analyses show that there is a potential for interference between the two adjacent jets if the water head or the angle between the two jets decreases.

Three-dimensional simulation of transom stern flow at various Froude numbers and trim angles

Three-dimensional simulation of transom stern flow at various Froude numbers and trim angles

Three-dimensional numerical simulation of flow in trapezoidal cutthroat flumes based on FLOW-3D

Three-dimensional numerical simulation of flow in trapezoidal cutthroat flumes based on FLOW-3D

Application of Regularized Hydrodynamic Equations for Direct Numerical Simulation of Micro-Scale Flows in Core Samples

The paper is devoted to numerical simulation of three-dimensional isothermal two-phase two-component viscous fluid flows with surface effects in the pore space of core samples. The voxel representation of the flow domain is used suitable for digital rock physics applications. The flow is described by viscous compressible Navier-Stokes-Cahn-Hilliard equations. In order to use simple and computationally efficient explicit numerical algorithms with central difference approximations of spatial terms, a quasi-hydrodynamic regularization of equations is used. Simulation results of fluid displacement in pore space of realistic core sample (sandstone) are presented. The results demonstrate the applicability and good prospects of quasi-hydrodynamic regularization technique to solve the problem.

Aerodynamic design schemes of the inlet guide vane in a core-driven fan stage

A core-driven fan stage operates in both single bypass and double bypass modes. There are large differences in aerodynamic parameters between the two modes. To accommodate the differences, the inlet guide vanes must turn in a very large angle, which may cause significant flow losses. To reduce the flow losses, this article investigates three design schemes in detail using the flow field simulation method. The three schemes investigated include the inlet guide vanes adjusting entirely (Scheme 1), the rear part of the inlet guide vanes adjusting (Scheme 2), and both the front and rear part of the inlet guide vanes adjusting (Scheme 3). Comparisons of the three design schemes suggest that the flow losses in Scheme 1 are higher than those in the other two schemes and that the flow losses in Scheme 3 are not evidently lower than those in Scheme 2. The key geometrical parameters of Schemes 1 and 2 are determined for low flow losses and are used to design the inlet guide vanes. The inlet guide vanes are applied to a core-driven fan stage, and the flow fields are simulated by a three-dimensional flow simulation method to confirm the designs.

Numerical error analysis for three-dimensional CFD simulations in the two-room model containment THAI+: Grid convergence index, wall treatment error and scalability tests

This paper presents a step to define Best Practice Guidelines for CFD simulations in nuclear containment applications and other disciplines with similar complex geometries. For the two-room model containment THAI+, a three-dimensional natural convection flow simulation was performed using the CFD package Ansys CFX 16.1. For the quantification of the numerical error, the applicability of three versions of the Grid Convergence Index GCI to the complex flow field was tested. Those are the Standard method REM, the Blend Factor Method BFM and the Least Squares Method LSQ. Using these methods, the spatial discretization errors were quantified on six grids with different refinement levels up to 39.731·106 elements. Besides, the model error due to the different wall treatment approaches was also quantified. For this, the simulation results on grids with different y+ ranges were compared. Relative errors of approximately 58.40%, 7.2%, 8.43% and 0.96% were detected in the volume-integrated vorticity, temperature, mass flows and pressure between the simulations using the low-Reynolds approach (y+ < 1) and the wall function of the SST model (y+ > 30). The parallel performance of the calculations was also investigated on a CRAY XC-40 using four grids with different resolutions. The maximum speedup was achieved on approximately 1838 computational cores on the finest grid with 83·106 elements and 24·106 nodes and on 562 cores on the coarsest grid with 1.268·106 elements and 0.347·106 nodes. The insight and results of the GCI, wall treatment and scalability studies can be used as guidelines, on which future CFD containment simulations can be based. Finally, the comparison of the simulation results with the experimental data was carried out.

Effect of wind and buoyancy interaction on single-sided ventilation in a building

In this study, we performed numerical simulations of three-dimensional turbulent flows over an isolated building with a door-type opening by using a CFD model in order to investigate the combined effect of wind and buoyancy on windward single-sided ventilation. Positive and negative temperature differences between the inside and outside of the building were considered. The Archimedes number (Ar) was introduced as an index for evaluating the interaction between buoyancy and wind effects. The interaction between the two opposing forces under a positive temperature difference was found to be destructive, resulting in the combined effect reducing the volume flow rate. Furthermore, the wind effect was found to be dominant for Ar0.5<0.45, with the buoyancy effect beginning to increase at Ar0.5=0.2, and tending to be dominant for Ar0.5>0.45. The two effects were found to be fairly comparable at Ar0.5=0.45. The interaction between the two assisted forces under a negative temperature difference was always constructive, resulting in the combined effect reinforcing the ventilation for all the Archimedes numbers.

Simulation and Analysis of Three-Dimensional Electromagnetism, Heat Transfer, and Gas Flow for Flow-Levitation System

Magnetic levitation systems are influenced by an intense demand to gain greater feature sizes of metal nanoparticles and to increase the production efficiency for the flow-levitation (FL) method. This paper presents a systematic stability and temperature analysis of the process during the induction heating based on ANSYS. The comprehensive model was a liquid aluminum droplet levitated electromagnetically in an axisymmetric magnetic field induced by different sets of coaxial circular coils. First, we developed an optimized coil with a double helix structure to compare the force applied to the sample, electric field distribution, and temperature distribution in the eddy current field with an initial coil structure. The optimized coil has a more stable and efficient induction heating process for the FL method. We also utilized the optimized coil geometry to predict the maximum parameters of the electromagnetic induction system used to fabricate Al nanoparticles. The results from this approach shows that the turns = 2 + 3, D = 24 mm, I = ∼350 A, d = 1∼2 mm, with an equilibrium coefficient k of 0.30, are the maximum and optimal settings in the frequency of 400 kHz induction heating process.

Three-dimensional metal particle flow simulation during the whole rolling process for 60 kg/m heavy rail

Three-dimensional metal particle flow simulation during the whole rolling process for 60 kg/m heavy rail was accomplished by explicit dynamic finite element method and modified updating geometric m...

Research and development of asymmetrical heat transfer augmentation method in radial channels of blades for high temperature gas turbines

The serpentine-like one and half-pass cooling channel systems are primarily used in blades fabricated by the lost-wax casting process. The heat transfer turbulators like cross-sectional or angled ribs used in channels of the midchord region failed to eliminate the temperature irregularity from the suction and pressure sides, which is reaching 200°C for a first stage blade of the high-pressure turbine for an aircraft engine. This paper presents the results of a numerical and experimental test of an advanced heat transfer augmentation system in radial channels developed for alignment of the temperature field from the suction and pressure sides. A numerical simulation of three-dimensional coolant flow for a wide range of Reynolds numbers was carried out using ANSYS CFX software. Effect of geometrical parameters on the heat removal asymmetry was determined. The test results of a blade with the proposed intensification system conducted in a liquid-metal thermostat confirmed the accuracy of calculations. Based on the experimental data, the dependencies for calculation of heat transfer coefficients to the cooling air in the blade studied were obtained.