CFD Model Research Articles

Data-mining framework for in-depth quantitative study of influences on low-wind-velocity area from morphological parameters of cuboid-form buildings

Wind environment is important in architectural sustainable design, as existing studies show that it can be considerably influenced by building morphologies. This study aimed to develop a data-mining framework to quantitatively evaluate and compare influences on Low-Wind-Velocity Area (LWVA) of common cuboid-form buildings with typical morphological parameters. The data-mining framework was originally developed by integrating multiple computational methods for rapid in-depth iterative analyses, including the generation of building models using parametric modelling, the big data generation based on hybrid model, and the statistical metric analysis method. The hybrid model was created by combining the CFD model and machine learning model. The accuracy and efficiency of the framework were fully demonstrated through the comprehensive validation and analyses of different models. The data of more than fifty thousand building cases with different morphological parameters and relevant wind conditions were generated and analyzed. Influences on LWVA of morphological parameters of cuboid-form building was comprehensively evaluated, including the visualization of multiple parameters, calculation and comparison of several correlation coefficients. It suggested that the reduction of height and width on the windward side would significantly decrease the LWVA and promote the outdoor ventilation. The change of depth would have relatively limited influence on the LWVA. Multivariate regression model-fit and variance analyses were further implemented, and it was found that there was a relatively significant linear correlation between the LWVA and morphological parameters. The equation of multivariate regression model was provided for extra rapid prediction. The study outcome could contribute to efficient evaluation of LWVA and provide useful information for sustainable design.

Fluidized bed hydrodynamics under variable air inlet configurations to enhance gasification reactor efficiency: Computational study

This study employs diverse strategies to enhance motion dynamics within the reactor, with a specific focus on the critical geometric parameter of air nozzle configuration. Methodical analysis of various air nozzle angles, 0°, 45o, and 90° relative to the horizontal bottom line is undertaken to discern their influence on these key parameters throughout multiple stages during the recorded flow duration. A CFD model of the physical model is constructed and solved using ANSYS software. Parameters scrutinized include the longitudinal and lateral distribution of particle volume fraction, alongside radial and axial velocities of particles. The results emphasize the significant impact of air-feeding orientation on both radial and axial particle velocities. Notably, 45° air nozzle angle is the best orientation for the fluidized bed reactor displaying maximal values in particle volume fraction fluctuations and bed height. Furthermore, peak values for radial and axial velocity persist consistently throughout the entire flow duration.

CFD simulation of the inundation effect for saturated propane vapor condensation on the surface of a horizontal tube using the volume of fluid method

The inundation of the lower tubes in a tube bundle with condensate formed on the upper tubes is among the major causes of reduced condensation rate. Experimental methods can hardly be used to get detailed information on the inundation effect, since each factor that controls the condensation process should be considered individually. However, CFD modelling using direct interface-tracking methods is an effective tool for analyzing such processes. This paper reports the results of simulation of the saturated propane vapor condensation on the surface of a horizontal tube using the Volume of Fluid method with the modified Lee model. The study presents, for the first time, the characteristics of saturated vapor condensation including the effect of inundation predicted using a 3D model. The interphase surface and the distribution of instantaneous heat transfer coefficients over the surface of the inundated pipe are presented. It has been shown that increasing the temperature of the condensate flow can substantially affect the distribution of the heat transfer rate over the tube surface due to the formation of a thermal entrance region. These results may become a starting point for modelling condensation in a tube bundle that enjoys current interest in practice.

Research on Scavenging Flow Dynamics of Marine Two-Stroke Engines With a CFD-Derived Quasi-Dimensional Model

The complex in-cylinder gas state and flow significantly affect fuel-air mixture, combustion efficiency and emissions. However, the scavenging CFD model of large bore marine engines in digital twin system requires substantial computational resources. Therefore, a fast-run phenomenological model of the scavenging process is built in this study. The model simulates the thermal states and flow dynamics of inlet and exhaust gas based on the energy and momentum conservation principles, considering the ideal in-cylinder swirl velocity profile with effects of air mass loss, wall friction, and swirl shear. The model’s accuracy is confirmed by comparing it with CFD simulations on different engines, showing an average relative error less than 3.5%. It also analyzes the impacts of intake pressure. The model provides accurate boundary conditions for subsequent fuel spray, combustion, and emission simulations and can be combined with these models in the future, thereby applied to engine design, diagnostics, and control.

Computational simulation of the heat and mass transfer processes occurring in the containment of Novovoronezh NPP II’s units 1 and 2

The paper presents information on the key approaches to the design of the containment ventilation system for units 1 and 2 of Novovoronezh NPP II (NPP-2006 project). The authors have developed a CFD model for the containment of Novovoronezh NPP II’s units 1 and 2, which includes the key structural components and the basic equipment installed within the containment. A series of the containment air temperature measurements was undertaken during power operation of the units. Based on the measured temperature values, a series of calculations was undertaken to determine the air temperature field inside the containment. It is revealed that when ensuring the design characteristics of the cooling capacity of the ventilation system stages, the design parameters of the containment air, wall and equipment temperature are achieved. In addition, with proper mixing of the containment air, it is possible to significantly reduce the average air temperature in the most “hot” rooms. Based on the calculation results, causes have been identified for the low efficiency of the ventilation system, and specific measures have been proposed for increasing significantly the system capacity. The proposed approach to determining the characteristics of ventilation systems using modern methods of three-dimensional computational hydro-gas dynamics makes it possible to optimize and modernize existing ventilation systems, as well as to assess the efficiency of ventilation at the design stage of nuclear power plants. The developed and proposed CFD model makes it possible to do this at the modern level without resorting to bench/experimental modeling issues.

Numerical investigation and dynamics of pollutant dispersion in underground restroom ventilation

Urbanization is expanding in both surface and underground space, where the air quality in underground space restrooms in public transportation hubs is a huge challenge due to variations in passenger’ flow and specific features. The pollution in the underground restrooms mainly comes from the microorganisms and odors of human waste. This paper proposes a back-side air exhaust method for the restroom compartment to enhance pollutants removal efficiency, and an optimal design study is performed to determine the best device position, evacuation pressure, and air exchange rate. In response to research gaps, we introduced the influence of unsteady human breathing behavior and human obstacles coupled with the flow field and the pollutants diffusion in the CFD model. After model verification, we numerically investigated the effect of different ventilation modes. The results show that the top evacuation mode may accelerate the diffusion of pollutants. In contrast, the pollutant concentration around the mouth and the spillage outward from the door cracks are significantly reduced under the new ventilation mode. The standardized and actual concentrations of the pollutant and the normalized exposure index were used to assess the indoor air quality. Finally, we put forward a series of dynamical models to describe the variation of indoor pollutant concentrations over time. The study's results will provide reliable theoretical and numerical support to improve the air quality of public restrooms in urban underground spaces.

Экспериментальные исследования воспламенения и горения каменного угля с применением плазменной активации

This work presents experimental studies of a promising method of ignition and combustion of coal fuel using plasma activation. Experimental studies were carried out on a bench with a thermal power of up to 5 MW. As an experimental sample, hard coal of the GD grade was chosen selected after a ball drum mill with a sieve residue of R90 = 15%. The conditions were close to industrial ones used when lighting coal boilers. The operating range of pulverized coal flow velocities in the electric arc unit has been determined. It has been established that a stable process of ignition and further combustion of coal is possible at flow rates on the electric arc unit from 6 to 13 m/s. The experimental stand was kindled from a cold state to a temperature of 1000 °C at excess air coefficients a from 0.5 to 0.7, the kindling time did not exceed 200 seconds. Based on the experiments, CFD modeling determined whether the process conditions were met.

Enhancing blast mitigation in tunnels with expansion chamber subjected to high explosives detonations for protecting underground facilities

This paper presents a numerical investigation into the effect of expansion chamber in mitigating overpressures and impulses in protective tunnels subjected to detonation of high explosives. Blast shockwave propagation in a protective tunnel, with dimensions of 160 m in length, 8.9 m in width and 7.2 m in height, was simulated using a computational fluid dynamics code, Viper::Blast. The design parameters of the expansion chamber cover a broad spectrum chamber lengths between 6.1 and 12.1 m, widths spanning from 10.7 to 97 m, length-to-width ratios from 0.0 (indicating no chamber) to 5.0, heights of 8.0 and 14.9 m, and chamber-to-tunnel width ratios in the range of 1.2 to 10.9 m. Two charge weights of 1000 and 2000 kg of TNT were employed to assess their influences. To ensure the reliability of the CFD model, mesh sensitivity analysis, overpressure stability assessments, and validation studies were undertaken. A parametric analysis was then conducted using the validated model to derive an optimal design for the expansion chamber within the specified tunnel. Recommendations for incorporating an expansion chamber into protective tunnels under blast events are provided.

Thermal Performance of Earth Air Heat Exchanger for Geothermal Energy Application in Hot Climate using CFD Simulation

The Ground Air Heat Exchanger (GAHE) is a sustainable, environment friendly, and efficient device that can be used for both heating and cooling applications. Careful design of GAHE enables efficient exploit of the earth interior energy. The design of a GAHE relies on the constant temperature of the earth interior which allows consistent and reliable source of geothermal energy. By harnessing this renewable energy, a sustainable solution for heating and cooling needs is attained while minimizing the impact on environment. In this study, the performance of GAHE was examined using ANSYS Fluent 19 R1 and SOLID WORK 16.0 software. The efficiency and Coefficient of Performance (COP) of the ETHE have been investigated. The effect of air flow rate and operation conditions on the outlet air temperature have been studied. GAHE is made of Polyvinyl Chloride (PVC) pipe of 0.1 m diameter, 0.005 m thickness and 18 m horizontal length. Computer simulations were carried out for five different air velocities (1, 2, 3, 4, and 5 m/s) at various operation conditions. Results show that the 18 m pipe length is adequate to attain useful air outlet temperature giving COP values between 0.5 and 1.3. The length of the horizontal part of GAHE can be further increased for air velocities between 3 and 5 m/s. Comparison between the results obtained by the CFD model and experimental work demonstrated that the CFD model is capable of producing results with acceptable accuracy. This suggests that the CFD software can accurately model the performance of the GAHE under different operation conditions. Increasing the length of the horizontal part of the GAHE can improve its COP when higher air velocities are used.

CFD Analysis of a Latent Thermal Storage System (PCM) for Integration with an Air-Water Heat Pump

Heat pumps driven by sustainable electricity sources have been identified as a technology that can contribute to reduce carbon dioxide emissions. Furthermore, a heat pump can also provide energy savings when combined with a thermal energy storage system. Heat pumps can optimize their efficiency by accumulating thermal energy during periods of lower electricity demand, resulting in shorter operational durations and decreased overall energy consumption. In this work, the combination of a latent heat storage system with an air-water heat pump has been numerically analysed and experimentally tested. A phase change material (PCM) heat exchanger with an immersed plate was designed using a 3D CFD model (COMSOL Multiphysics®). The heat exchanger configuration with six steel plates immersed in the phase change material tank was proposed to enhance heat transfer in the storage system. The developed model is validated against experimental data from a real case study, demonstrating a maximum error of approximately 3% during the discharging phase. Additionally, the study explores the effects of different inlet heat transfer fluid temperatures and flow rates on the PCM solidification time.

An integrated 2D/3D numerical methodology to predict the thermal field of electric motors

The present work aims at providing a predictive numerical methodology for the thermal characterization of electric motors. The methodology relies on a 2D-FE simulation for the estimation of the electromagnetic (iron and joule) losses. The latter are then exploited in a 3D-CFD Conjugate Heat Transfer analysis for the evaluation of the thermal field.The CFD model includes both the solid components and the fluid domains. The main novelty of the paper is represented by the copper coil modelling. In fact, copper, air, epoxy resin and enamel are synthetized in a single homogeneous body able to reproduce the thermal behaviour without including the single components, to reduce the computational cost.The methodology is validated against experimental data on a three-phase squirrel-cage induction motor. As for the experimental data (available at three different operating conditions), temperature distributions are measured by thermocouples at the test bench for the validation of the 3D-CFD CHT model. In addition, experimental estimations of the losses are available for the validation of the 2D electromagnetic simulations.The numerical results in terms of motor performance, electromagnetic losses and thermal field are discussed and are proved to be close to the experimental counterparts, for all the investigated conditions.

A Novel CFD Model of SMX Static Mixer Used in Advanced Continuous Manufacturing of Active Pharmaceutical Ingredients (API)

A Novel CFD Model of SMX Static Mixer Used in Advanced Continuous Manufacturing of Active Pharmaceutical Ingredients (API)

Full-scale aerodynamic study on the effects of tower wind shields and road-sign gantries on passing high-sided vehicles in the tower region at the Queensferry Crossing

A novel investigation into the impact of the tower road-sign gantry and the tower shielding on double-decker buses and trucks passing by the bridge tower based on a previously validated full-scale CFD model. Two sets of simulations were conducted for comparison of aerodynamic force conditions of vehicles as they pass by the bridge tower: first group of simulations were performed including and excluding the road-sign gantry; and the second group include and exclude the tower shielding. Conditions in different traffic lanes (one on leeward side and two on windward side) considered. The effect of changes in wind yaw angle are also considered. Mechanism exploration on the variation of vehicle aerodynamic force conditions was made based on the numerical visualization of wind velocity field and pressure field. Novel results suggest that the road-sign gantry provides a sheltering effect in some circumstances, but a destabilizing effect in others. In addition, the tower shielding shows significant impact on reducing aerodynamic forces and sudden force changes of the high-sided vehicles while they are passing by the bridge tower.

CFD modeling for phase change materials integrated to building envelope

AbstractIntegrating thermal energy storage with thermal conversion systems is necessary to maximize their use. Phase change materials are the best media for storing and releasing thermal energy from various basic material types. Because the phase change materials have a high latent heat of fusion, it is often viable to use these characteristics and include the phase change materials in building envelopes to store thermal energy. The paper provides a thorough categorization of the phase change materials and thermal energy storage systems, in addition to an evaluation of their modeling using computational fluid dynamics. The purpose was to highlight computational fluid dynamics as a useful technique for advancing the engineering of thermal energy storage devices.

Prediction of heat and mass transfer inside 3D frost microstructure

In the present study, a CFD model based on 3D frost microstructure is developed. The desublimation phase change coupled with mass transfer of water vapor to ice surface and heat conduction through the tortuous ice crystals are calculated to predict accurate heat transfer process inside the frost microstructure. Air velocity and temperature inside the frost structure after 30 min operation are significantly lower than those inside 10 min operation, which are influenced by the structural change of the ice crystals. Vertical variations in ice crystal surface temperature and ice surface mass flux are also calculated, which varied between the frost structures operated for different periods. At 70 μm height of the frost, the mass flux at the ice crystal surface shows significant decrease from 7.48 × 10−5 kg/m2s for the frost structure at 10 min to 1.82 × 10−5 kg/m2s for that at 30 min. This study provides new and fundamental information to understand the mechanism of frost growth which is very important in refrigeration, cryogenics, and aerospace industry, etc.

Integrated Absorption–Adsorption Process for Waste-Free Decontamination of Gases from Sulfur Dioxide, Part 2: CFD Modeling and Experimental Investigation of a Bubble-Cap Tray

There are many technologies for removal of sulfur dioxide (SO2) from flue gases. They are intrinsic part of the efforts for sustainability of energy production as they reduce the harmful impact of fossil fuel combustion on the environment by minimizing one of the main air pollutants. A wide range of methods use alkaline absorbents. In most cases, the products obtained from the absorption process have to undergo further oxidation, which increases the cost of carrying out the process. As a final result, the sulfates obtained (Na2SO4 and CaSO4) have limited practical application and there is a problem with their disposal. Scientific and engineering efforts have been directed towards the development of a practically waste-free technology for gas purification from SO2. An absorption–adsorption method is proposed, which comprises absorption of SO2 in water with simultaneous adsorption of the resultant sulfurous acid (H2SO3) from the aqueous solution with a synthetic anion-exchange resin. Regeneration of the adsorbent is accomplished with a dilute solution of ammonia (NH3), followed by decomposition of the resulting ammonium sulfite ((NH4)2SO3) with nitric acid (HNO3). The products of the processes are pure gaseous (liquefied) SO2 and an aqueous solution of ammonium nitrate (NH4NO3). Sulfur dioxide has a wide range of applications in the chemical industry; ammonium nitrate is a product with a variety of commercial uses as well, the most common of which is as a soil fertilizer. The new absorption–adsorption method offers a practically waste-free technology. The basic unit of this technology is a bubble-cap tray column where the absorption–adsorption process is carried out in an aqueous suspension of a synthetic anion-exchange resin. This work presents a CFD simulation of the flow on the bubble-cap tray. A physical model of the column is constructed, which contains a bubble-cap tray fabricated by 3D printing. As a result of this experimental study, new data on the tray pressure drop, gas holdup, and the kinetics of the absorption–adsorption process were obtained.

Using dispersion models at microscale to assess long-term air pollution in urban hot spots: A FAIRMODE joint intercomparison exercise for a case study in Antwerp

In the framework of the Forum for Air Quality Modelling in Europe (FAIRMODE), a modelling intercomparison exercise for computing NO2 long-term average concentrations in urban districts with a very high spatial resolution was carried out. This exercise was undertaken for a district of Antwerp (Belgium). Air quality data includes data recorded in air quality monitoring stations and 73 passive samplers deployed during one-month period in 2016. The modelling domain was 800 × 800 m2. Nine modelling teams participated in this exercise providing results from fifteen different modelling applications based on different kinds of model approaches (CFD – Computational Fluid Dynamics-, Lagrangian, Gaussian, and Artificial Intelligence). Some approaches consisted of models running the complete one-month period on an hourly basis, but most others used a scenario approach, which relies on simulations of scenarios representative of wind conditions combined with post-processing to retrieve a one-month average of NO2 concentrations.The objective of this study is to evaluate what type of modelling system is better suited to get a good estimate of long-term averages in complex urban districts. This is very important for air quality assessment under the European ambient air quality directives. The time evolution of NO2 hourly concentrations during a day of relative high pollution was rather well estimated by all models. Relative to high resolution spatial distribution of one-month NO2 averaged concentrations, Gaussian models were not able to give detailed information, unless they include building data and street-canyon parameterizations. The models that account for complex urban geometries (i.e. CFD, Lagrangian, and AI models) appear to provide better estimates of the spatial distribution of one-month NO2 averages concentrations in the urban canopy. Approaches based on steady CFD-RANS (Reynolds Averaged Navier Stokes) model simulations of meteorological scenarios seem to provide good results with similar quality to those obtained with an unsteady one-month period CFD-RANS simulations.

CFD Analysis of Pressure Drop Reduction in PEMFC Flow Channels with Distinct Cross-Section Shapes

Proton exchange membrane fuel cells (PEMFCs) have great potential to produce renewable, sustainable and clean energy and reduce air pollutants to mitigate climate change. PEMFCs consist of distinct parts including anode and cathode bipolar plates having flow channels, gas diffusion layers, catalyst layers, and membrane. The flow channel geometry influences the flow and pressure drop characteristics of the channel and cell performance. In this work, a three-dimensional (3D) CFD model is built employing SOLIDWORKS and ANSYS Workbench. The innovative configurations are generated by changing the half of 0.2 x 0.2 mm square channel to 0.3 x 0.1 mm, 0.3 x 0.15 mm, 0.3 x 0.2 mm and 0.3 x 0.25 mm rectangular section at the top. The results showed that increasing rectangular section height significantly reduced pressure drop at the anode and cathode with a slight decrease in the current density at 0.4 and 0.6 V. The new configuration with 0.2 x 0.1 mm half square section at the bottom and 0.3 x 0.25 mm rectangular section at the top decreases the current density, anode and cathode pressure drop of 11%, 69% and 58%, respectively in comparison to 0.2 x 0.2 flow channel at 0.4 V. Taking into account pressure loss along the flow channels, this configuration is a good option to improve the cell performance.

From past to future: The role of computational fluid dynamics in advancing nuclear safety in Spain and Portugal

This document explores the role of CFD in nuclear safety studies, with a particular focus on advancements in Spain and Portugal. The field of nuclear safety has increasingly included CFD models to address complex safety–critical phenomena, given their ability to capture three-dimensional behavior with high resolution. While traditional one-dimensional codes remain very valuable, they often rely on conservative approximations, making 3D CFD approaches indispensable for accurate predictions across various nuclear scenarios. In the context of Spain and Portugal, this document shows the contribution to CFD applications for nuclear safety research. The topics covered include code development and validation, combustion studies, simulations of nuclear spent casks, fuel assembly analyses, and investigations into containment safety issues. These advances have mainly contributed to improving the predicting capabilities of CFD models for applications in various safety–critical domains. In addition to detailing the achievements and contributions in the field of CFD in Spain and Portugal, readers will find a comprehensive overview of the current challenges and future perspectives of CFD within the domain of nuclear fission technology.

Landslide-generated wave simulation using coupled multi-phase flow and Boussinesq-type models

The effect of landslide-generated tsunami waves on coastal areas can be initially understood through a numerical simulation. Moreover, an efficient numerical simulation would be beneficial for predicting tsunami waves. However, a single numerical model that can capture the landslide and wave propagation is still impractical, especially in a large-scale domain. A domain-partitioning technique or coupling model would be more practical. This paper reports a numerical study of a landslide-generated wave, which uses a multi-phase CFD model for the landslide phenomena and a surface wave model based on Boussinesq-type equations for wave propagation. The proposed coupling model that sits between the multi-phase CFD and wave models validated by laboratory experiments is shown to be effective. The computation domain of the CFD model can be defined as small as it covers the impacted area of the landslide. The rest of the domain can be handled by the wave model that propagates the wave accurately with a low computation cost.