OpenFOAM Simulations Research Articles

A workflow for the sustainable development of closure models for bubbly flows

Many years of research in developing closure models for polydisperse bubbly flows have produced a plethora of empirical and semi-empirical models. The continuous development and analysis of such models requires their constant validation with the steadily increasing number of validation cases in the literature.In this paper we present a pipeline for the fully-automated analysis of OpenFOAM simulations using the Snakemake workflow management system. The pipeline is applied to an extensive collection of well-established validation cases for bubbly flows and allows the fast and efficient production of large amounts of results that are summarized in well-structured reports. An optional post-processing step introduces a fuzzy logic controller developed for the detailed analysis of these results by quantifying the agreement of the simulation with the available experimental data. It is demonstrated how such quantification enables the systematic evaluation of new closure models and contributes to a more sustainable model development.

A combined experimental and numerical study on droplet-impact induced breakup and ejection behaviors in vertical electric field

Droplet impact on solid surface in the electric field is a fundamental process widely existing in our daily life and in engineering applications. Here, we investigated the dynamic behavior after droplet impact on the electrode plate in the electric field both experimentally and numerically. Particularly, the breakup or ejection behaviors were systematically studied. One key finding from the experiments is that the applied electric field can significantly affect the droplet stretching behavior, leading to two different breakup modes near the droplet top. We reproduced the two modes in the OpenFOAM simulation to reveal the intricate trade-off among the electrostatic force, surface tension and droplet gravity. Furthermore, the relationship between the impact Weber number, the applied electric field and the breakup modes was obtained. This work contributes to a thorough understanding of the droplet impact behavior and provides useful guidance for the development of modern droplet-related engineering applications.

Optimization and parallelization of the discrete ordinate method for radiation transport simulation in OpenFOAM: Hierarchical combination of shared and distributed memory approaches.

This paper describes the reduction in memory and computational time for the simulation of complex radiation transport problems with the discrete ordinate method (DOM) model in the open-source computational fluid dynamics platform OpenFOAM. Finite volume models require storage of vector variables in each spatial cell; DOM introduces two additional discretizations, in direction and wavelength, making memory a limiting factor. Using specific classes for radiation sources data, changing the store of fluxes and other minor changes allowed a reduction of 75% in memory requirements. Besides, a hierarchical parallelization was developed, where each node of the standard parallelization uses several computing threads, allowing higher speed and scalability of the problem. This architecture, combined with optimization of some parts of the code, allowed a global speedup of x15. This relevant reduction in time and memory of radiation transport opens a new horizon of applications previously unaffordable.

Numerical optimization of three-cavity magneto mercury reciprocating (MMR) micropump

The operation of the three-cavity magneto mercury reciprocating (MMR) micropump, whose prototype were presented in an earlier companion paper, was numerically explored. In the three-cavity MMR micropump, three mercury slugs are moved by a periodic Lorentz force with a phase difference in three separate cavities. A consecutive motion of the slugs in their cavities transfer air from the inlet to the outlet. Two-dimensional OpenFOAM simulations were carried out to explore the influence of electric current excitation phase difference and back-pressure. The numerical simulations predicted the MMR micropump (with no valve) with a phase difference of and produces a mean pumping flow rate of 2.7 and 6.1 mL/min at a back-pressure of 10 Pa and maintains a maximum back-pressure of 17.8 and 20 Pa, respectively. However, it was found that there was a reverse flow at large back-pressures with an excitation phase difference of . The numerical results showed that employing a diffuser/nozzle valve with a length of 5 mm and an angle of improves the mean flow rate of the micropump with a phase difference of at a back-pressure of 10 Pa by 140% from 2.7 to 6.5 mL/min, and its maximum back-pressure by 125% from 17.8 to 40 Pa.

OpenFOAM Simulations of Late Stage Container Draining in Microgravity

In the reduced acceleration environment aboard orbiting spacecraft, capillary forces are often exploited to access and control the location and stability of fuels, propellants, coolants, and biological liquids in containers (tanks) for life support. To access the ‘far reaches’ of such tanks, the passive capillary pumping mechanism of interior corner networks can be employed to achieve high levels of draining. With knowledge of maximal corner drain rates, gas ingestion can be avoided and accurate drain transients predicted. In this paper, we benchmark a numerical method for the symmetric draining of capillary liquids in simple interior corners. The free surface is modeled through a volume of fluid (VOF) algorithm via interFoam, a native OpenFOAM solver. The simulations are compared with rare space experiments conducted on the International Space Station. The results are also buttressed by simplified analytical predictions where practicable. The fact that the numerical model does well in all cases is encouraging for further spacecraft tank draining applications of significantly increased geometric complexity and fluid inertia.

Numerical simulation and experiments of multiple reflection and stratified absorption mechanism of pulsed laser in picosecond laser

Based on the combination of computational fluid dynamics (CFD), fluid–solid coupling theory, double-temperature model, C ++ programming and OpenFOAM simulation, this paper investigated the reflection and stratified absorption phenomenon of 10 ps pulsed laser on the surface of materials, calculated the laser reflectivity and stratified absorption coefficient as variables with electron and lattice temperature then innovatively added the calculating module of these variables to the laser processing simulation model. This paper also designed an functional module to simulate the multiple reflection and absorption phenomenon of deep-hole topography to pulsed laser and add it to the simulation model. Furthermore, the energy distribution algorithm in the model which aims at calculating the occupying ratio of energy used in Coulomb explosion and thermal effects has been also modified. The research results combined with experimental verification present that the modified simulation model has a higher accuracy than the original one, which proves that the laser-solid interactions mentioned above have large impacts on the precision of laser processing simulation. It is also proved that the modified energy distribution algorithm is more effective on improving the simulation accuracy than the original one. To sum up, a much more reliable simulation model which has the potential to guide the actual laser processing has been established.

Defocusing effect and energy absorption of plasma in picosecond laser drilling

Plasma is commonly existing in pulsed laser drilling and it has an important impact on drilling results. The effects include plasma absorption and defocusing effect caused by plasma. This paper studied the influence of plasma on laser drilling by a combination method of numerical simulation and experiment. Based on the combination of computational fluid dynamics (CFD), fluid–solid coupling theory, double-temperature model, C ++ programming and OpenFOAM simulation, this paper established and added the defocusing effect and energy absorption of plasma as sub-modules. Finally, this paper conducted a series of laser drilling experiments with different parameters such as repetition rate, laser power and pulse number. Comparison of the results of simulations and experiments were conducted to verify the accuracy of the improved model. The comparison results proved that plasma play a significant role in pulsed laser drilling and the accuracy of the modificated model is very high. There is another conclusion that the influence of defocusing effect on laser drilling is greater than that of energy absorption.

Modeling cross model non-Newtonian fluid flow in porous media

Fluids exhibiting non-Newtonian rheologies are used in a range of applications, including hydraulic fracturing, enhanced oil recovery, remediation, and industrial processes. Hydraulic fracturing in particular has received attention from environmental scientists, policy-makers, and the general public due in part to concerns about the possibility of contamination of groundwater resources by the complex and potentially harmful fluids used in the process. The non-Newtonian nature of many hydraulic fracturing fluids complicates the prediction of their movement, and precludes use of most traditional flow and transport models. To improve understanding of the flow of such fluids in porous media, a series of column experiments was conducted and a pore-scale lattice Boltzmann model (LBM) was developed, verified, and used to simulate analogous systems. Flow experiments were conducted with guar gum solutions of varying concentration and three porous media systems. The LBM was developed for transient, three-dimensional porous medium systems and included a shear rate-dependent dynamic viscosity based on the Cross rheological model. The LBM was verified using a semi-analytical solution for Cross model fluid flow, OpenFOAM simulations, and grid resolution inter-comparisons between two different solution approaches. Simulations were performed on synthetic porous medium systems produced with a sphere packing algorithm to approximate the properties of the experimental systems. The simulations were in good agreement with the experimental results, particularly for systems that exhibited the greatest non-Newtonian character. The modeling approach developed in this work provides a valuable tool for investigating relationships between pore-scale fluid flow and macroscale variables of interest for simulating movement of non-Newtonian fluids at larger scales.

Plasma density profile measurements for ultra-short high power laser beam guiding experiments at SPARC _LAB

External injection is a promising method to achieve high accelerating gradients and to control the beam properties. The energy gain of an electron via the wakefield is proportional to the product of the accelerating field multiplied by the effective propagation distance of the laser. Therefore, in order to bring the electron energy in the order of the GeV, a longer propagation length is required, which can be obtained by guiding the laser pulse in a wave-guide. In the case of SPARC_LAB, a 500 μτη diameter hydrogen-filled capillary discharge is used; to guide the laser beam it is necessary to act on the refractive index of the plasma, depending on its density. In this work measurements of the trend over time of the longitudinal profile of the plasma density within the capillary are presented, along with openFOAM simulations of the gas profile distribution. Preliminary test of laser guiding are also shown, detecting the behaviour of the laser beam at the exit of the capillary with respect to the discharge current value.

Numerical investigations on the flow over cubes with rounded corners and the noise emitted

The effect of corner rounding on the flow past a cube is investigated numerically at different Reynolds numbers ranging from 50,000 to 200,000 using delayed detached-eddy simulation in OpenFOAM. Different corner radii from 0 to 40% of the cube length have been considered. To validate the adopted methodology, a benchmark case on the flow over a sphere with the same characteristic length is first performed. Good agreement has been achieved between the results of the benchmark and available experimental and numerical data from literature. Subsequently, features of the flow around cubes with rounded corners are investigated, including the aerodynamic coefficients, mean flow patterns and the surface pressure distribution. The relation between flow features and the aerodynamic coefficients is also analysed. In addition, the far-field noise emitted from the rounded cube is predicted using the Ffowcs William-Hawkings acoustic analogy in FLUENT. It is found that corner rounding with carefully determined radius can be an effective way to reduce the emitted noise. The minimum noise is found for a radius 1/3 of the cube side length with the lowest surface pressure fluctuations, but the sound level increases again for a further increase in corner radius to R/L = 2/5 due to vortex shedding.

Numerical Simulation for The Forward Flight of the Tri-copter Using Virtual Blade Model

This paper presents the process of implementing numerical simulation for a tri-copter in forward flight using the open source code OpenFOAM with the library of Virtual Blade Model (VBM). The tri-copter has 0.75-meter radius and 15-Newton weight. Its propulsion system consists of three two-blade propellers typed XOAR PJP-T-L 1245 with12-inch diameter and 4.5-inch pitch. In the first part, the aerodynamic performance of the tri-copter’s frame (not including the propellers) is investigated at the range of angle of attack from -12 degree to 12 degree by simulation in OpenFOAM. Secondly, these force coefficients are exploited in the analytical approach based on the Blade Element Theory (BET) to determine the rotor disk plane angle and the tri-copter’s frame angle for steady, level, forward flight at 15-m/s. Finally, after obtaining the relative angle of -2 degree between the rotor tip-path-plane and the tri-copter’s frame, the simulation for the tri-copter in forward flight including three rotor disks rotating at 4732-RPM will be carried out through the rotorDisksource library of the open source code OpenFOAM. A steady, incompressible solver with k-ω SST turbulence model is applied in the simple Foam algorithm. The aerodynamic forces and the dynamic fields surrounding the tri-copter will be discussed in detail, while the effect of tri-copter’s frame on rotor operation will also be considered. Moreover, the results of thrust from each propeller from simulation are compared to that of analytical BET method and that of propeller performance provided by the manufacturer. This comparison proves rational of using virtual disk to replace real propeller in the CFD simulation.

An OpenFOAM simulation of the natural ventilation system in a university chemical laboratory

The indoor airflow with a natural ventilation system was numerically calculated using the laminar and turbulent approach. In the chemical laboratory of the Technical University of Ambato, the computational code OpenFoam demonstrated an ability to numerically predict flow patterns. The design contemplated the natural ventilation system considering the laboratories’ working conditions not only in summer, but also in a winter week. These two operating conditions are calculated on a fully open and closed environment. For a room with a capacity of 20 people, the climate data average values were recorded at 14.0 ° C, 81.7%, 1.7 m /s for temperature, relative humidity, and wind speed, respectively. Furthermore, the demonstration has shown that the homogeneous occupancy air speed average is was 0.7 m / s with a facade air intake of 1.0 m / s 0.6 m / s in the room valid for the exchange of air and evacuation of pollutants. The maximum pressures were found in the lower part of the laboratory. This prevents the modification of the thermo-hygrometric conditions.

Geometrical influence of the source/drains configuration on the flow interactions in a sandbox model: A three-dimensional OpenFOAM simulation

This paper explores the interaction of different flow paths in a porous medium by observing the effect of having more than one drain in a simple model domain with a single source. The work is based on three-dimensional numerical simulations of the flow of injected water in a sandbox domain with porous volume completely filled by water and oil. The calculation uses the OpenFOAM library to solve Darcy’s equations for the dynamics of a two-phase flow: water as the wetting, oil as the nonwetting fluid. We observe the interactions of flows in different paths under changes of number of drains and their relative positions.

Validation of Tidal Stream Turbine Wake Predictions and Analysis of Wake Recovery Mechanism

This paper documents the predictive capability of rotating blade-resolved unsteady Reynolds averaged Navier-Stokes (URANS) and Improved Delayed Detached Eddy Simulation (IDDES) computations for tidal stream turbine performance and intermediate wake characteristics. Ansys/Fluent and OpenFOAM simulations are performed using mixed-cell, unstructured grids consisting of up to 11 million cells. The thrust, power and intermediate wake predictions compare reasonably well within 10% of the experimental data. For the wake predictions, OpenFOAM performs better than Ansys/Fluent, and IDDES better than URANS when the resolved turbulence is triggered. The primary limitation of the simulations is under prediction of the wake diffusion towards the turbine axis, which in return is related to the prediction of turbulence in the tip-vortex shear layer. The shear-layer involves anisotropic turbulent structures; thus, hybrid RANS/LES models, such as IDDES, are preferred over URANS. Unfortunately, IDDES fails to accurately predict the resolved turbulence in the near-wake region due to the modeled stress depletion issue.

CFD Validation of a Model Wind Turbine by Means of Improved and Delayed Detached Eddy Simulation in OpenFOAM

With the ongoing increase in the size of wind turbines, experimental investigations have become more complicated and expensive. Therefore, computational models have proven to be a viable solution for design purposes. This article aims to validate CFD simulations of an experimental model wind turbine (MoWiTO 1.8) using Delayed Detached Eddy Simulation (DDES) and Improved DDES (IDDES) turbulence modelling approaches. For the purpose of validation, integral quantities (such as power, thrust, torque and blade-root bending moment in the flapwise direction) measured in the wind tunnel are compared with numerical results obtained with OpenFOAM. In general, the computational results show a very good agreement with the measurements for most of the monitored quantities. In particular, the blade-root bending moment presents the largest difference, taking into account that the simulation assumes the turbine blades are rigid. Nevertheless, the simulation does achieve in recreating the turbulent behavior as can be evidenced by the Power Spectral Density graphs, and the wake’s velocity measurements. In general, the IDDES turbulent model achieves a better agreement to the experimental results, while maintaining a very similar computational time as the DDES model.

Numerical based approach for predicting the response of flexible risers under oscillatory flows at Low Re and KC numbers

La predicción de respuesta en tuberías verticales flexibles se basa en modelos semiempíricos limitados por escasez de datos experimentales para modelados particulares. Este artículo presenta un enfoque numérico para predecir la respuesta de tuberías verticales flexibles en flujos oscilatorios. Se implementa un grado de libertad en un sistema de masa-resorte amortiguado, con la masa habilitada para moverse en la dirección transversal al flujo. Las ecuaciones de Navier-Stokes son discretizadas empleando el Método de Volúmenes Finitos. Los patrones de flujo en cada régimen son analizados en períodos de oscilación extensos. Se emplea un modelo bidimensional simulado en OpenFOAM. Se analiza el comportamiento del flujo, fuerzas hidrodinámicas y frecuencias para los valores de Reynolds entre 40 y 1000 utilizando 𝑲𝑪 𝟕, 𝟗. Para Reynolds, inferiores a 300, el comportamiento del modelo está de acuerdo con la literatura. Para valores de Reynolds 300 o más, algunas discrepancias aparecen en la dinámica del sistema. Los resultados numéricos obtenidos apartir del enfoque numérico propuesto concuerdan con los datos experimentales recopilados en un modelo de tubería vertical flexible

Mesh Twisting Technique for Swirl Induced Laminar Flow Used to Determine a Desired Blade Shape

Swirling flow has been shown to increase heat transfer in heat exchangers. However, producing swirl while not presenting a severe pressure drop can be a challenge. In this paper, a desired shape of guidance blades for laminar swirl flow is determined by numerical simulation in OpenFOAM. Emphasis is on the mesh technique, where a predefined blade shape is formed by mesh twisting, or morphing. The validity of numerical simulations on a twisted mesh is shown by comparing it to the theoretical solution of laminar flow in a pipe without swirl and guidance blades. A sensitivity study shows that a cell size ratio of 0.025 of diameter is sufficient and affects the solution minimally. To determine the desired shape of guidance blades previously found optimal swirl decay and velocity profile for laminar swirling flow are utilized. Three blade shapes are explored: (I) with a twist angle that varies with axial location only; (II) having a deviation angle matching the theoretical deviation angle for laminar swirling flow; (III) same as II but with a hollow center. Simulations are performed for Re = 100 and swirl number S = 0.2 . Case II is able to sustain swirl longest while maintaining a low pressure drop and is therefore a desired swirler shape profile as predicted theoretically.

Estimation of hydrodynamic derivatives of a container ship using PMM simulation in OpenFOAM

Static drift, pure sway and pure yaw simulation results are determined for a container ship. For simulation, open source RANS solver, OpenFOAM was used. The simulation results were compared with two sets of experimental data. Next, hydrodynamic derivatives were predicted from simulation results and compared with experimental ones. The results show good agreement with experimental data, except for some pure yaw cases. Overall, the paper concludes that OpenFOAM is well capable of estimating hydrodynamic derivatives maintaining reasonable accuracy and computational efficiency.

Results of the research project AssiSt

This article gives an overview of the results of the wind energy research project AssiSt. Results of the four work packages include flow in complex terrain, wind energy converters (WEC) in complex terrain subject to atmospheric inflow, laminar-turbulent transition, generator cooling, hub aerodynamics, and passive flow control devices. Four different flow solvers (PALM, FLOWer, THETA, OpenFOAM) are in use during the course of the project depending on the corresponding problem requiring specific solver features. Key achievements of the project are the coupling of atmospheric LES (PALM) and URANS simulations of the complete WEC (FLOWer as well as THETA) in order to impose the external turbulent flow fields to the inflow of the WEC for physics resolved load simulations, numerical replication of complex flows over blades with vortex generators using OpenFOAM and efficiency-augmented pressure loss simulations on very complex industrial geometries of ENERCON’s direct drive WEC generators for precise cooling analyses. Industrial validity of all methods, model and process developments were key objectives of this research project.

Numerical investigation of the impact of computational resolution on shedding cavity structures

In this paper, three-dimensional cavitation is analysed, and in particular how its dynamics is influenced by computational resolution. Cavitation-vorticity interactions are investigated in several spatial resolutions to address impact of the mesh resolution on cavitating vortical flow predictions. Three-dimensional, fully turbulent, cavitating flow around the Delft Twist11 foil is simulated and investigated numerically with particular focus on cavitation structures, shedding dynamics, and vorticity distribution. Implicit Large Eddy Simulation is employed along with the iso-thermal homogeneous two-phase mixture model to conduct the cavitation simulation in OpenFOAM. The paper clarifies the importance of capturing small scales of the flow, and their impact on the cavitation shedding behaviour, especially for flows where the shed cavity is affected significantly by flow vortices. It is shown that the mesh requirement for vortical cavitating flows is governed by the minimum spatial resolution needed to transport vorticity in the flow rather than the resolution needed to simulate the phase change. Better predictions of the mechanisms driving the shed cavity, and its collapse location, will provide a better control over nuisance behaviour in cavitating flows, which is a critical key for design improvements.