Software OpenFOAM Research Articles

Predictive Model and Optimization of Micromixers Geometry using Gaussian Process with Uncertainty Quantification and Genetic Algorithm

Abstract Microfluidic devices are gaining attention for their small size and ability to handle tiny fluid volumes. Mixing fluids efficiently at this scale, known as micromixing, is crucial. This article builds upon previous research by introducing a novel optimization approach in microfluidics, combining Computational Fluid Dynamics (CFD) with Machine Learning (ML) techniques. Our research focuses on enhancing global optimization techniques while minimizing computational costs. It draws inspiration from a Y-type micromixer, initially featuring cylindrical grooves on the main channel's surface and internal obstructions. Simulations, conducted using OpenFOAM software, evaluate the impact of circular obstructions on mixing percentage and pressure drop, considering variations in obstruction diameter and offset. A Gaussian Process (GP) was utilized to model the data, providing model uncertainty. This study optimizes geometries by using genetic algorithm (GA) based on the reduced order model provided by GP. Results align with previous research, showing that medium-sized obstructions (137 mm diameter, 10 mm offset) near the channel wall are optimal. This approach not only provides efficient microfluidic optimization with uncertainty quantification but also highlights the effectiveness of combining CFD and ML techniques in achieving desired outcomes.

Numerical Simulations for Calibration Setup for Dynamic Contrast-Enhanced Ultrasonography Imaging Protocol.

This study presents an investigation of an innovative microfluidic flow separator using both numerical and experimental approaches to calibrate contrast-enhanced ultrasound scanners. Numerical simulations were conducted using Lagrangian particles tracking and passive scalar transport methodologies using the OpenFOAM software. The experimental validation confirmed the accuracy of the numerical simulations, particularly at an imposed total pressure of , showing an excellent agreement in particle distributions. The study emphasizes the computational efficiency and modeling of passive scalar transport, providing valuable understanding into the behavior of scalar quantities in microfluidic systems. An optimized diffusion coefficient value of was identified, showing its critical role in achieving accurate simulation results and optimizing the performance of microfluidic flow separators for contrast-enhanced ultrasound scanner calibration.

Pseudosteady shock refractions over an air–water interface

Shock refraction in a gas–liquid interface is ubiquitous in nature and engineering. This study investigates the shock refraction phenomena in air–water interfaces for various inclination angles. The interface inclination angles are achieved using a tiltable vertical shock tube. The time-resolved schlieren images are compared with numerical simulations performed using the BlastFoam solver in the OpenFOAM software. The stiffened gas equation of state is used to model water in the simulations. The shock polar analysis using modified shock relations for a stiffened gas is used to elucidate the refraction patterns. A regular refraction pattern with a reflected shock wave and a bound precursor refraction with a regular reflection are observed experimentally for the first time in an air–water system. Further, a new free precursor refraction pattern with a Mach reflection is observed. The transition criteria and the corresponding boundaries for each refraction pattern are demarcated in the ( $M_S, \theta _w^c$ )-plane. The refraction sequence and the range for various incident shock strength regimes are also identified.

A comprehensive numerical model for aero-hydro-mooring analysis of a floating offshore wind turbine

This paper presents a comprehensive study of a Floating Offshore Wind Turbine (FOWT), requiring multidisciplinary expertise in floating platform hydrodynamics, mooring system dynamics, and wind turbine aerodynamics. We introduce a fully coupled numerical model, focusing specifically on the NREL's (National Renewable Energy Laboratory's) 5 MW OC4 FOWT. The model is validated through both numerical simulations using the Computational Fluid Dynamics (CFD) based software OpenFOAM and experimental results. Key findings demonstrate the model's accuracy in forecasting the aerodynamic behaviors of the turbine, the platform's response to motions, and the behavior of the mooring system across diverse wind and sea state scenarios. Furthermore, the study enhances the understanding of FOWT's stability and efficiency by examining the influence of different Center of gravity (COG) heights. Results show that reduction in COG height has a minor effect on heave and surge motion but significantly decreases pitch motion and mooring line tension, thereby improving static stability and reducing the impact of wave loads on dynamic responses. Additionally, the results show that this reduction in COG height enhances the aerodynamic power output, suggesting that optimized FOWT designs could achieve improved energy capture efficiency. These insights optimize FOWT design and efficiency, enhancing renewable energy performance.

Investigation on the wave focusing effects and energy capture of oscillating water column array

The study of OWC array hydrodynamic performance has been a focus of attention. However, due to the complex flow and strong nonlinearity generated during its interaction with waves, the main challenge and key focus in current research is how to simulate this process both quickly and accurately. A fast-numerical model of the OWC is developed using the open-source software package OpenFOAM. The numerical model replaces the orifice plate with Forchheimer-flow and the vertical walls with an immersed boundary. Compared to the traditional numerical model, the fast-numerical model can speed up the simulation by at least 10 times. The impact of row spacing and column spacing on the array gain is systematically investigated through the simulations of two-OWCs array, four-OWCs lattice array, and five-OWCs interlaced array. The results show that a two-OWCs array can generate a wave focusing area at its rear, and the location of this area changes with row spacings. For the four-OWCs lattice array, the row spacing increasing causes the wave focusing area to move closer to the array. The proximity of the wave focusing area enhances the power output of the second row of OWCs. After increasing the row and column spacing, the reflection of waves from the second row of OWCs to the first row is decreased, resulting in a reduction in the power output of the first row of OWCs. In contrast to the four-OWC lattice array, the five-OWCs interlaced array demonstrates a lower array gain in the first row of OWCs, with the second row displaying a higher array gain.

Numerical simulation of flow around a transversely oscillating square cylinder at Re=22000

The study utilized OpenFOAM software, combined with the k-ω shear stress transport (SST) turbulence model and Arbitrary Lagrangian-Eulerian (ALE) dynamic mesh method, to investigate the influence of the oscillation amplitude on the flow dynamics around a square cylinder at Re = 2.2 × 104. It was found that various oscillation amplitudes affect the non-Gaussian characteristics of fluctuating pressure differently along the cylinder's surface: diminishing at the leading edge while intensifying at the trailing-edge corner. Concurrently, secondary recirculation bubbles near the cylinder's leading and trailing edges gradually diminish and eventually disappear with increasing oscillation amplitudes. Analysis of the amplitude spectrum of transverse velocity indicates the exclusive presence of odd-order harmonics along the central axis, while both odd and even-order harmonics are observed on either side of the central axis. Additionally, heightened oscillation amplitudes result in increased energy transfer from the cylinder to the fluid, with the energy density function predominantly exhibiting negative values and periodic variations occurring at twice the frequency of cylinder displacement or lift coefficient. As the oscillation amplitude increases, the vortex in the wake region transitions from a single-row to a double-row configuration. The research results provide important theoretical guidance for deepening the understanding of the flow characteristics around the oscillating square cylinder.

Unlocking optimal performance and flow level control of three-phase separator based on reinforcement learning: A case study in Basra refinery

This research explores the application of a new reinforcement learning (RL-based) controller for a three-phase separator connected to a gas turbine. The control of flow levels within the separator directly impacts fluid flow turbulence, especially when the equipment is linked to waste heat gas from the turbine to improve gas quality. The study introduces the novel RL-based controller and validates its effectiveness in real-world conditions using three-phase separators in Basra, Iraq, and through a review of relevant literature. The controller can adapt to inlet conditions such as pressure, temperature, mass flow rate, and incoming heat from the gas turbine. Waste heat recovery from the gas can enhance gas purity but also increase turbulence in water and oil. Maintaining a calm flow while ensuring high-speed flow over the baffle in the middle of the separator is crucial for optimal performance. The study considers two geometrical configurations of the vessel for redesigning the separator at the Basra refinery. The controller was implemented using the groovyBC utility within the OpenFOAM software. This model was then utilized to simulate real-world scenarios at the Basra refinery, displaying faster convergence, more rapid response, and more accurate tracking of the target fluid level. This study marks the initial effort to apply the deep deterministic policy gradient (DDPG) controller in computational fluid dynamic (CFD) work. The findings demonstrated a significant enhancement in separation efficiency by more than 36%, as well as smoother streamlines through the control and maintenance of pressure and velocity over the baffle.

Assessment of the Influence of Input Parameters in CFD Simulation of Ventilation in an Experimental Chamber

Abstract The aim of this paper is to evaluate the impact of selected input parameters on the accuracy and usability of CFD simulations. This paper compares the achieved results of Computational Fluid Dynamics (hereinafter CFD) simulations of air age with the ventilation results of a specific experimental box. A total of 16 variants were simulated for different simulation settings, including various computational domains and meshes in OpenFOAM, Ansys Fluent, DesignBuilder, and BlueCFD-AIR software. The paper primarily focuses on the importance of meeting the suitability criterion for the yPlus parameter used in the wall function of turbulent models k-ε and k-ω SST, and the resulting air age. Simulation with the best yPlus parameter shows the best agreement in airflow velocity and air age with the experiment. Overall, this led to an improvement in accuracy by 41 % compared to original simulation and 56 % compared to the previous our best OpenFOAM simulation.

Comparison of Laminar and Turbulent K–Omega Shear Stress Transport Models Under Realistic Boundary Conditions Using Clinical Data for Arterial Stenosis

Abstract Early diagnosis of cardiovascular diseases (CVDs), including arterial stenosis, enables targeted treatments that reduce CVD mortality. It is vital to improve the accuracy of early diagnostic tools. Current computational studies of stenosis use mathematical models, such as laminar and k–omega shear stress transport (SST) models, available in ansys (Fluent and CFX), openfoam, and comsol software packages. Users can adjust boundary conditions, such as inlet velocity and outlet pressure using user-defined functions (UDFs) with different expressions and constant values. However, currently there is no rule over what to impose at these boundaries, and previous studies have used various assumptions, such as rigid artery wall, one-way fluid–structure interaction (FSI) or two-way FSI, and the blood's Newtonian or non-Newtonian material properties. This variety in construction has associated deviations of the models from the clinical data and lessens the value of the models as potential diagnostic or predictive tools for medical practitioners. In this study, we examine arterial stenosis models, with severities of 20%, 40%, and 50%, compared with the healthy artery analyzed in terms of strain energy to the artery wall. Additionally, we investigate elastic walls using one-way FSI, comparing with laminar and k–omega SST. These boundary conditions are based on clinical data. The results regarding the strain energy (mJ) behavior along the artery wall show that the k–omega SST model outperforms the laminar model for short arterial segments and under the Newtonian assumption with a no-slip boundary wall and turbulent flow.

Energy dissipation performance of labyrinth and harmonic stepped spillways

ABSTRACT Stepped spillways are structures that dissipate the energy on steps, especially in topography, where building the energy dissipate pool is impossible as long as required. For this reason, stepped spillways are one of the critical topics that have attracted the attention of researchers for many years. It has been the subject of many studies, especially because the step geometry is an effective parameter in the energy dissipation rate. In this study, the effect of the labyrinth and harmonic geometry on the plan on energy dissipation performance is examined using the open-source OpenFOAM software. The 11 different geometries were analyzed in detail and discussed with the literature results. For analysis, the k − ω SST turbulence model and the multi-phase solver interFoam were utilized. The results showed that the number of cycles is an effective parameter for energy dissipation performance; the energy dissipation rate increases when effective crest length increases, and labyrinth and harmonic models could dissipate about 20% more energy than the flat model.

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.

Exploiting Axisymmetry to Optimize CFD Simulations—Heave Motion and Wave Radiation of a Spherical Buoy

Simulating the free decay motion and wave radiation from a heaving semi-submerged sphere poses significant computational challenges due to its three-dimensional complexity. By leveraging axisymmetry, we reduce the problem to a two-dimensional simulation, significantly decreasing computational demands while maintaining accuracy. In this paper, we exploit axisymmetry to perform a large ensemble of Computational Fluid Dynamics (CFDs) simulations, aiming to evaluate and maximize both accuracy and efficiency, using the Reynolds Averaged Navier–Stokes (RANS) solver interFOAM, in the opensource finite volume CFD software OpenFOAM. Validated against highly accurate experimental data, extensive parametric studies are conducted, previously limited by computational constraints, which facilitate the refinement of simulation setups. More than 50 iterations of the same heaving sphere simulation are performed, informing efficient trade-offs between computational cost and accuracy across various simulation parameters and mesh configurations. Ultimately, by employing axisymmetry, this research contributes to the development of more accurate and efficient numerical modeling in ocean engineering.

Modeling of high-pressure transient gas-liquid flow in M-shaped jumpers of subsea gas production systems

Two-phase flow with low liquid loads is common in high-pressure natural gas offshore gathering and transmission pipelines. During gas production slowdowns or shutdowns, an accumulation of liquid in the lower sections of subsea pipelines may occur. This phenomenon is observed in jumpers that connect different units in deep-water subsea gas production facilities. The displacement of the accumulated liquid during production ramp-up induces temporal variations in pressure drop across the jumper and forces on its elbows, resulting in flow-induced vibrations (FIV) that pose potential risks to the structural integrity of the jumper. To bridge the gap between laboratory experiments and field conditions, transient 3D numerical simulations were conducted using the OpenFOAM software. These simulations facilitated the development of a mechanistic model to elucidate the factors contributing to increased pressure and forces during the liquid purging process. The study examined the influence of gas pressure level, pipe diameter, initially accumulated liquid amount, liquid properties, and gas mass flow rate on the transient pressure drop and the forces acting on the jumper's elbows. The critical gas production rate required for complete liquid removal of the accumulated liquid was determined, and scaling rules were proposed to predict the effects of gas pressure and pipe diameter on this critical value. The dominant frequencies of pressure and force fluctuations were identified, with low-pressure systems exhibiting frequencies associated with two-phase flow phenomena and high-pressure systems showing frequencies attributed to acoustic waves.

The application of the state-of-the-art turbulence models in the OpenFOAM CFD codes and the validation for different flow control cases in the continuous casting process

Computational fluid dynamics (CFD) is an established approach to study flow behaviour. Despite advances in mathematical numerical modelling in recent decades, accurately predicting the turbulent flow behaviour of steel using CFD remains a challenge. In the continuous casting process, two main flow control systems are employed to transfer liquid steel from the tundish to the mould, namely stopper control and slide gate control. In additional to these two main flow control systems, the casting nozzle geometries, casting rate, and casting mould dimensions vary considerably, and this complexity makes it difficult to precisely simulate turbulent flow in the casting channel. In this paper, examples are presented showing how different turbulence models influence the simulation results, using the latest version of the open source CFD simulation software OpenFOAM. Prior to the CFD modelling, RHI Magnesita's water modelling facilities in Leoben (Austria) were used to validate the state-of-the-art turbulence models selected for a particular casting nozzle geometry and flow control system.

Comparing Large-Eddy Simulation and Gaussian Plume Model to Sensor Measurements of an Urban Smoke Plume

The fast prediction of the extent and impact of accidental air pollution releases is important to enable a quick and informed response, especially in cities. Despite this importance, only a small number of case studies are available studying the dispersion of air pollutants from fires in a short distance (O(1 km)) in urban areas. While monitoring pollution levels in Southampton, UK, using low-cost sensors, a fire broke out from an outbuilding containing roughly 3000 reels of highly flammable cine nitrate film and movie equipment, which resulted in high values of PM2.5 being measured by the sensors approximately 1500 m downstream of the fire site. This provided a unique opportunity to evaluate urban air pollution dispersion models using observed data for PM2.5 and the meteorological conditions. Two numerical approaches were used to simulate the plume from the transient fire: a high-fidelity computational fluid dynamics model with large-eddy simulation (LES) embedded in the open-source package OpenFOAM, and a lower-fidelity Gaussian plume model implemented in a commercial software package: the Atmospheric Dispersion Modeling System (ADMS). Both numerical models were able to quantitatively reproduce consistent spatial and temporal profiles of the PM2.5 concentration at approximately 1500 m downstream of the fire site. Considering the unavoidable large uncertainties, a comparison between the sensor measurements and the numerical predictions was carried out, leading to an approximate estimation of the emission rate, temperature, and the start and duration of the fire. The estimation of the fire start time was consistent with the local authority report. The LES data showed that the fire lasted for at least 80 min at an emission rate of 50 g/s of PM2.5. The emission was significantly greater than a ‘normal’ house fire reported in the literature, suggesting the crucial importance of the emission estimation and monitoring of PM2.5 concentration in such incidents. Finally, we discuss the advantages and limitations of the two numerical approaches, aiming to suggest the selection of fast-response numerical models at various compromised levels of accuracy, efficiency and cost.

Comprehensive numerical modeling analysis and experimental validation of a multi-turn pulsating heat pipe

The aim of this paper is to present the results of the experimentally validated numerical code designed for thermal-fluid computations in pulsating heat pipes using CFD techniques. The analysis was carried out using the OpenFOAM software, where an algorithm was developed to simulate multiphase flow with phase change and coupled heat transfer between the fluid and solid domains. The article meticulously delineates the steps involved in implementing and validating the model, commencing from basic comparative tests like the Stefan problem, progressing through Scriven’'s bubble growth, and culminating in an experiment with single- and multi-turn pulsating heat pipes. The algorithm has been refined by including a convergence criterion based on the Galusinski-Vigneaux number, which allows faster results and reduces the likelihood of numerical anomalies. Finally, an experiment was carried out to evaluate the thermal efficiency of a two-loop heat pipe on a specially designed experimental set-up constructed by the authors. In the experiment, ethanol was utilized as the working fluid, operating within a temperature range of 20 to 90 °C. The experiment was carried out with three distinct filling ratios: 50 %, 62.5 %, and 75 %. The validated parameters included pressure and temperature at the measurement points and the experimentally derived thermal efficiency results were compared with the numerical results. The model showed an error of 7.06 ± 3.73 %.

Development of coupled fluid-flow/geomechanics model considering storage and transport mechanism in shale gas reservoirs with complex fracture morphology

Field observations frequently demonstrate stress fluctuations resulting from the reservoir depletion. The development of reservoirs, particularly the completion of infill wells and refracturing, can be significantly impacted by stress changes in and around drainage areas. Previous studies mainly focus on plane fractures and few studies consider the influence of complex transport and storage mechanism and irregular fracture geometry on stress evolution in shale gas reservoirs. Based on the embedded discrete fracture model (EDFM) and finite-volume method (FVM), a coupled geomechanics/fluid model has been successfully developed considering the adsorption, desorption, diffusion and slippage of shale gas. This model achieves coupling simulation of natural fractures, hydraulic fractures with complex geometry, storage and transport mechanism, reservoir stress, and pore-elastic effect. The open-source software OpenFOAM is used as the main solver for this model. The stress calculation and productivity simulation of the model are verified by the classical poroelasticity problem and the simulation results of published research and commercial simulator with EDFM respectively. The simulation results indicate that σxx, σyy, σxy and Δσ changes with time and space due to the time effect and anisotropy of formation pressure depletion; Due to the influence of different mechanisms on shale gas storage and transport, the reservoir pressure and stress distribution under different mechanisms are different; Among them, the stress with full mechanisms differs the most compared to the stress without any mechanism. The reservoir with stronger stress sensitivity (smaller Biot coefficient) is less sensitive to formation pressure depletion, and the stress variation range is smaller. For reservoirs with weak stress sensitivity, formation pressure depletion is more likely to lead to stress reversal. Under the influence of fracture geometry, the pressure depletion regions caused by the three types of fracture geometry are approximately rectangular, parallelogram and square, respectively. The corresponding σxx, σyy and Δσ also have great differences in spatial distribution and values. Therefore, the time effect, shale gas storage and transport mechanism and the influence of complex fracture geometry should be considered when predicting pressure depletion induced stress under the condition of simultaneous production. This study is of great significance for understanding the evolution law of stress induced by pressure consumption, as well as the design of infill wells and repeated fracturing.

A numerical simulation framework for wakes downstream of large wind farms based on equivalent roughness model

Accurate assessment of the wake effect of wind farm clusters is of great significance for the development of wind power bases, yet there is currently a deficiency in numerical simulation methods with high accuracy and simple modeling. To address this issue, a numerical simulation framework for large wind-farm wakes based on a wind farm parameterization model is proposed, and is then implemented based on the open-source CFD software OpenFOAM. In this framework, a newly proposed wind farm equivalent roughness model is adopted to parameterize wind farms and incorporated into the simulation via the wall stress model. To validate the method, the large-eddy simulation based on the actuator disk model resolving all the turbines in the wind farm is taken as a benchmark. Thirty two cases including spanwise infinite wind farms and finite wind farms with different streamwise turbine spacings, spanwise turbine spacings, wind turbine thrust coefficients, and roughness lengths of ground surface are set to analyze the sensitivity of the framework to different wind farm parameters. Results show that the proposed method predicts the velocity deficit and turbulence intensity downstream of the wind farm accurately. Compared to the classical wake superposition model, the prediction accuracy of the velocity deficit is improved by more than 30 %. Furthermore, without resolving the turbines using fine mesh, the framework shows a high potential to reduce computational costs compared with the turbine-resolved simulation.

Centrifugal failure mechanism analysis for ferrofluid seals based on a bidirectional coupled multi-physics model

In this paper, we propose a bidirectional coupled multi-physics (BCM) model to study the centrifugal failure mechanism of ferrofluid seals, employing a hybrid finite volume–finite element method. In this model, the evolution of the flow field is described by the two-phase incompressible Navier-Stokes (NS) equations with Kelvin force. The volume of fluid (VOF) method is used to capture the gas-ferrofluid interface. Magnetic scalar potential is introduced to solve for the magnetostatic field. We conducted secondary development on the OpenFOAM and Elmer software packages, which are based on the finite volume method (FVM) and finite element method (FEM), respectively, to calculate the flow field and magnetic field in ferrofluid seals. By developing interpolation methods between FEM and FVM grids based on the parallel bidirectional coupler EOF-Library[1], field information exchange between the flow field and magnetic field is achieved. The BCM model executes iterative computations on the flow and magnetic fields in an alternating way, continuously synchronizing the information of each, thus facilitating bidirectional coupling between the FVM and FEM frameworks. We employ the BCM model to investigate the failure mechanisms of ferrofluid seals under different conditions, including various load pressure and rotational velocity. The results indicate that the ferrofluid will leave the surface of the shaft along the pole teeth under the action of centrifugal forces, with the highest radial velocity occurring at the boundary of the liquid film. Under varying conditions of rotational velocity and pressure drop, the centrifugal failure modes of ferrofluid seals exhibit distinct differences. Moreover, two dimensionless numbers are proposed to quantitatively evaluate the effects of load pressure and centrifugal force, thereby augmenting the efficacy of seal design.

Optimizing the design of parallel busbars to suppress the Taylor Instability in large-scale liquid metal batteries

Abstract In this study, we utilize the open-source software OpenFOAM to numerically simulate the Tayler instability in liquid metal batteries. The simulation depicts the dynamic evolution of the electrolyte layer, fluid flow, and magnetic field distribution in the battery at different operating times. Special attention is paid to the influence of optimizing the parallel busbar configuration on Tayler instability and battery capacity. It is found that the additional magnetic field generated by the busbars can effectively alter the magnetic field distribution inside the battery, thereby significantly reducing the Lorentz force and suppressing the Tayler instability within the battery. Therefore, by optimizing the parallel busbar configuration, the stable operating time of the battery is prolonged, and the battery capacity is enhanced. This study provides theoretical support and practical guidance for the application of liquid metal batteries in large-scale grid-level energy storage systems and offers new insights into the development of energy storage technology.