CFD Simulation Research Articles

Coupled CFD modeling and thermal analysis of multi-layered insulation structures in liquid hydrogen storage tanks for various vapor-cooled shields

The present study aims to propose a coupled numerical model for analyzing the influence of the configuration of the vapor-cooled shield tubes on insulation performance. The numerical model is developed to calculate the effective thermal conductivity of multi-layer insulation (MLI) and rigorously evaluated. Specifically, the tank evaporation simulation software BoilFAST is manually coupled with the CFD commercial software of ANSYS FLUENT (2020 R2) to accurately determine the mass flow rate and temperature of boil-off gas in a tank, which is then used as inputs for the CFD simulations. This coupling methodology can be used for reliable calculations of boil-off losses for liquid hydrogen and heat transfer inside the MLI structures. Results demonstrate that the estimated effective thermal conductivity agrees with the earlier published data and that increasing the diameter and number of tubes enhances heat exchange between the VCS tubes and MLI structures. Also, the heat flux into the tank is relatively reduced by 32.04 % by increasing the diameter of the tube and 49.14 % by adding the number of tubes. Moreover, the maximum temperature difference of the VCS is estimated to be less than 1 K, indicating nearly uniform distributions of the VCS.

Novel flow field design for redox flow battery using algorithmic channel generation and self-adaptive network model and experimental verification

Flow fields play a vital role in redox flow batteries (RFBs) to increase the power density. Traditional design for flow field usually employs CFD simulations with substantial computational costs and adopts enumeration and trial-and-error methods based on designers’ subjectivity, which have become a bottleneck in flow field design. In this study, a novel research paradigm is employed for flow field design in vanadium redox flow battery (VRFB), i.e., an adaptive three-dimensional equivalent network model is developed and a self-developed flow channel generation algorithm is employed to obtain optimum flow field through comparison and screening. Firstly, a flow channel library consisting of 18,135 flow fields is generated by self-developed flow channel generation algorithm. Secondly, the electrolyte flow, species transport and charge transport with various flow fields is researched by the self-adaptive equivalent network model with low computational costs due to eliminated meshing. Thirdly, pressure drop and voltage efficiency are employed to evaluate different flow fields for the aim of obtaining high-performance flow field structures through comparison and screening. The obtained high-performance flow field is fabricated and its high performance is confirmed by comprehensive experimental validation. The energy efficiency of the high-performance flow field is 4 % higher than that of the serpentine flow field investigated at 100 mA cm−2. This work employs adaptive equivalent network model to generate and optimize flow channel for the first time, which provides a reference for flow channel selection and design.

Simulation and experimental analysis of fixed and rotating blades on the runner of Oryon Watermill applicable for head drops of the canal

Numerous sites for watermills exist in the world with shallow heads and are possible for power generation either mechanical or electrical. The prime mover required for the energy generation from such sites is in the developing phase with efficient, minimum components, and low cost as a modular unit. The Oryon Watermill (OWM) is one of them developed by Deepwater Energy applicable to water current directly. The working of OWM is used differently on the head drop of the canal with fixed and rotating blades using the NACA 6516 series of airfoil shapes as the novelty of this research. The research covers the CFD simulations with ANSYS Fluent 19.0 of two runners, fabrication, and conduction of tests on-site with a head drop of 1.2 m. The major variable was the water flow rate for both runners with the design discharge of 0.09 m3/s. The analysis of results showed the runner with rotating lamellas performed with 9% and 40% higher efficiency from the simulation and experiment respectively compared to the fixed type. The efficiency achieved from the research is at a low range indicating the availability of large space for future study on performance improvement.

Void drift in narrow rectangular channels for highly advective bubbly flows: A macroscopic drift-flux model derived from two-fluid local simulations

This article addresses the issue of reduced models to describe turbulent two-phase flows in industrial applications. This work is an application based on Bois (2021) theoretical derivations to connect the spatially-averaged drift-flux model (DFM) to the local Reynolds-averaged two-fluid model (TFM). It presents new opportunities to calibrate closure laws or propose new models based on finer-scale descriptions. Highly convective steady bubbly flows with wall-peaking void fraction profiles are considered. Dispersed bubbles are weakly deformable. A new model dedicated to void fraction dispersion in flat rectangular channels is developed for application into the DFM. The model is calibrated based on reference local Euler-Euler two-fluid simulations of pressurised water and steam mono-dispersed bubbles, in adiabatic conditions. 64 conditions are considered to cover regularly the 3D parameter space in void fraction, Reynolds and Eötvös numbers. The new formulation proposed shows a very good fit with the post-processed predictions of local CFD simulations along with a substantial reduction in grid requirement. The model contains sub-filter correlations between vapour concentration and mixture or relative velocities. This model derived from local simulations is validated a posteriori in an industrial component scale code where the full space-filtered DFM is implemented and resolved. This work proves the benefits and feasibility of one-by-one model development and calibration based on two-fluid simulations.

CFD simulation of liquid-liquid extraction mechanism and enhancement schemes in microchannels based on three mass transfer models

Microreactors are highly efficient devices with a large specific surface area to improve the mass transfer efficiency. In this paper, a comprehensive three-dimensional CFD model was constructed based on three mass transfer theories to simulate the liquid-liquid two-phase flow and mass transfer process in a microchannel reactor, and two enhancement schemes were proposed. The multiphase flow and mass transfer characteristics were investigated by visualization and extraction experiments. The results indicated that the extraction efficiencies (E) and overall mass transfer coefficients (KLa) calculated by the penetration model and surface renewal model were within ±15 % errors compared to the experimental values. Moreover, E primarily increases with the increase of fluid residence time, while KLa increases with increasing flow rate. As the flow rate increases from 0.3 ml/min to 1.5 ml/min, E decreases by 15 %, and KLa rises from 0.78 s⁻¹ to 2.65 s⁻¹. Whereas the channel width decreases from 0.8 mm to 0.3 mm, E decreases by 3 %, and KLa rises from 0.44 s⁻¹ to 2.77 s⁻¹. Finally, microchannel with necked structure and baffles in mixing zone both improve the mass transfer efficient to some extent.

Investigation of Dust Explosion in Food Silos: A Review

In this article, dust explosion phenomena and the status of research conducted on silos are reviewed. Dust explosions cause loss of life and property in many industrial facilities. There are many recorded dust explosion cases in our country as well as in the world. For example, in our country, in 2023, a dust explosion occurred in the TMO Kocaeli General Directorate (Derince Port Silo), in which 2 people died and great material damage occurred, as reflected in the national press. When we look at the various dust explosion cases that have occurred in the world, it is understood that they mostly occur in silos used for storage in the agricultural and food sectors. Licensed warehouses have been established in many regions of our country in order to store basic and processed agricultural products that can be standardized with the Agricultural Products Licensed Warehousing Law No. 5300, which came into force after being published in the Official Gazette on 17/02/2005, in safe and healthy conditions in warehouses belonging to licensed warehouse enterprise and continues to be established. It is important to understand the many factors affecting dust explosion, such as dust dispersion, properties, discharge, etc., and to design silos according to these factors. These effects are tried to be determined and understood through experimental or CFD simulations.

Machine learning-based surrogate models for fast impact assessment of a new building on urban local microclimate at design stage

The rapid urbanization introduces changes in the local urban microclimate. Many efforts have been paid on the impact assessment of building design on local microclimate. However, there is still a lack of efficient and accurate prediction method for assessing the impacts on local microclimate when making the design of individual buildings. Two complementary machine learning-based surrogate models are proposed, including an SVR-based local air temperature model and a LightGBM-based local wind velocity model. They are identified by evaluating and comparing eight alternative machine learning models, four for each model development. 200 sets of CFD simulation data corresponding to different building designs are used for the model training and validation. The results show that the developed surrogate models can dramatically reduce computation time (from over 5 h to less than a second for a single prediction) while keeping the same order of accuracy of CFD simulations for local microclimate prediction of individual buildings. It therefore facilitates the fast, comprehensive and accurate prediction of the impacts on the local microclimate at the early design stage of new construction and renovation of individual buildings, for designers to deliver preferred local microclimate and/or avoid unacceptable microclimate changes.

CFD Simulation of the Influence of the Type of Gas Distribution in the Burners on Thermal Aerodynamic Processes in the DKVR 10-13 Boiler

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power stations. However, in Asian countries, the ease of using natural gas as the main fuel and its environmental friendliness compared to coal made it possible to widely use natural gas in industry and energy sector. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion that it has the most attractive characteristics for its use in industry, including energy facilities, can be drawn. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy sector in the near future. The paper is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal one and at 60% capacity. The study was carried out using numerical methods with the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single-row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NOx generation in jet-niche systems was obtained. The authors of the paper believe that replacing the regular burners of the DKVR-10-13 water heating boiler with a jet-niche ones can contribute to better mixing of fuel and air and ensure more complete combustion. In this paper, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of combustion products spraying. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NOx. Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

Insights Into Turbocharger Centrifugal Compressor Stability Using High-Fidelity CFD and a Novel Impeller Diffusion Factor

Abstract Turbocharger technologies are widely applied in the modern automotive industry to meet increasingly stringent carbon emission standards. To support the continuous enhancement of these tactics, delivering improvement to the performance and stability of turbocharger compressors at low mass flow rate regimes is of paramount importance. The present paper investigated the stability of a turbocharger compressor stage equipped with a ported shroud, using high-fidelity CFD simulations. It was found that the recirculated flow passing through the ported shroud device had primary influence on the flow condition in the vicinity of the impeller tip region (80% to 100% span). This discovery facilitated the definition of a modified impeller diffusion factor (DF), which was applied to the CFD results for three different compressor geometry configurations to lead to the provision of quantitative metrics for impeller stability. Furthermore, the observed change in the limiting impeller DF along the compressor surge line indicated that the dominant components governing the instability of the entire stage had switched, i.e., the stalling behavior of the compressor stage had transitioned from impeller dominated stall to vaneless diffuser dominated stall. Additionally, the limiting impeller DF clearly showed that one of the compressor configurations with a change in the hub endwall recess around the rear of the impeller improved the impeller stability by 3%. By comparison, another configuration with a change to strut geometry in the ported shroud recirculation channel reduced the impeller stability by 10%.

Aerodynamic development of the BYD SEAL – Part 2: Overview

BYD SEAL is a new developed A+ class sedan by BYD Auto, based on third generation high-performance and high-safety electric platform for EVs. SEAL gives full play to the advantages of electric vehicles in terms of space, handling, NVH, etc., while striving to reach the same level of fuel vehicles in terms of cost and recharge mileage. Therefore it has been dedicated to minimizing energy consumption from all components since its inception, and an important one is to reduce the aerodynamic drag effectively. However, the “ocean aesthetics” styling design based on the original concept model and platform with short overhangs must be kept on this car, which brings great challenge to aerodynamic development. An adaptable aerodynamic development process is set up and correlation between CFD simulation and wind tunnel test are established. This paper depicts the features of the flow field determined in the aerodynamic development process of the BYD SEAL, and describes the key factors in aerodynamic drag reduction as a full model change in detail. Effective rear roofline angle, tail design, front bumper corners, underbody, wheel, detail management such as sealing loss are studied and optimized by Powerflow and Star-CCM+ simulation softwares, and verified in wind tunnel tests of full-scale clay models and prototype vehicles. Design fusion and development tool/efficiency improvement around the vehicle are established, and the inherent drag reduction mechanism is revealed. These findings are of great significance to the aerodynamic optimization with diverse aesthetic and engineering requirements under the background of EV platformization.

Assessment of Breakwater as a Protection System against Aerodynamic Loads Acting on the Floating PV System

Offshore floating photovoltaic (FPV) systems are subjected to significant aerodynamic forces, especially during extreme wind conditions. Accurate estimation of these forces is crucial for the proper design of mooring lines and connection systems. In this study, detailed CFD simulations were performed for various PV panel configurations, and using these CFD simulation correlations were developed to estimate lift and drag forces as a function of the number of panels. These correlations provide valuable tools for designing large-scale FPV systems with multiple PV modules. Additionally, this study investigates the potential of using breakwaters to reduce aerodynamic forces on FPV systems. Breakwaters, typically used to mitigate wave impacts, can also serve as wind barriers, significantly reducing wind forces before they reach the FPV array. Aerodynamic simulations with and without a breakwater were conducted using CFD to assess this effect. The results show a substantial reduction in lift and drag coefficients, especially for angles of attack up to 10 degrees, demonstrating the effectiveness of the breakwater in protecting the FPV system. However, beyond this threshold, the effectiveness of the breakwater of 2 m reduces. These findings highlight the importance of strategic breakwater placement and heights and their role in enhancing FPV system resilience. The insights gained from this study are critical for optimizing breakwater design and placement, ensuring the structural integrity and performance of FPV systems in varying environmental conditions. The data generated will also contribute to future design improvements for floating PV systems.

Spatial distribution of air pollutants in different urban functional zones based on mobile monitoring and CFD simulation

Spatial distribution of air pollutants in different urban functional zones based on mobile monitoring and CFD simulation

Flow memory effects on the nonlinear hydrodynamic load of an ROV in translational maneuvering

This paper describes experimental and numerical investigations of the flow memory effect on the nonlinear hydrodynamic load response of a work-class remotely operated vehicle (ROV) under surge, sway, and heave impulse motions. The hysteresis loops of the dynamic drag coefficients during impulse motion tests are analyzed by comparing them with those obtained in steady drag tests. The areas of the loops and differences between the maximum and minimum dynamic and steady coefficients are used to quantify the flow memory effect. A novel unsteady hydrodynamic model for ROVs in translational maneuvering is established. This model considers the flow memory effect in terms of the unsteady hydrodynamic load response obtained from impulse motion response tests. The results given by the unsteady model are found to be in good agreement with those from CFD simulations. The unsteady hydrodynamic characteristics (including the asymmetric forces, force magnitude, and phase delay), motion amplitude, and frequency effect on the hydrodynamic forces of the ROV are analyzed by comparing the unsteady model results with those obtained from the steady model, revealing the rules governing the flow memory effect.

High power target for the High Brilliance Neutron Source

The High Brilliance Neutron Source (HBS) is a High-Current Accelerator-driven Neutron Source (HiCANS) under development at Jülich Centre for Neutron Science - Forschungszentrum Jülich. The unique specifications of the HBS require a neutron target with a high neutron emission able to operate in vacuum with a 70MeV proton beam with 90mA peak current and 1.6% duty cycle leading to an average thermal load of 100kW. A tantalum target of 100cm2 irradiated area with an internal cooling structure which removes the heat quite homogeneously, provides a good compromise between low pressure and high heat transfer and ensures an homogeneous protons energy loss was designed and optimized by means of MCNP, CFD and FEM simulations. Such a target was successfully manufactured and its operational capability was demonstrated by operating it under a heat load of 1kWcm−2 from an electron gun.

Development of a Simulation Model for a New Rotary Engine to Optimize Port Location and Operating Conditions Using GT-POWER

The objective of this study is to develop a 1D CFD simulation model to identify the optimal design parameters, using GT-POWER prior to the optimization of a new rotary engine derived from a three-lobe gerotor pump (GP3 RTE) based on 3D CFD simulation. The models were compared based on their respective development stages (steps 1–4) to ascertain the impact of each parameter on performance. The step 4 model, which exhibited a similar trend to that observed in the 3D CFD results, was selected for further analysis and validation. The developed model accurately predicted GP3 RTE performance in terms of fuel consumption, indicated power, efficiency, and exhaust gas reticulation (EGR) behavior, approaching the accuracy of the CONVERGE model. Furthermore, the optimal intake/exhaust port locations and operating conditions of the GP3 RTE were derived using the developed step 4 model. The model provided a convenient and powerful tool for obtaining basic information regarding the unique behavior of the GP3 RTE, thereby enabling the optimization of the design parameters without the necessity for time-consuming three-dimensional design modifications.

Design perspectives of a system identification approach of the NATO AVT-316 multi-swept wing aerodynamics

Air supremacy requires enhanced maneuvering capabilities at high angles of attack and even beyond the stall angle. High angle-of-attack (high-α) maneuverability can be achieved using swept wings and tailored leading-edge shapes to replace local and disorganized flow separation with controlled separation-induced leading-edge vortices (LEV). Strong leading-edge vortices delay the stall to higher angles and generate a non-linear lift increment up to the angle of attack where the jet-type flow structure of LEV changes to a reversed-flow bubble (vortex breakdown phenomenon). A multi-swept wing configuration has the potential to delay the vortex breakdown to even higher angles as the vortices formed over the front wing can energize vortices formed over the main wing and lead to vortex merging. This article is focused on understanding the unsteady interactions between multiple leading edge vortices formed over multi-swept wing configurations in the subsonic speed regime. Specifically, this article investigates the aerodynamic characteristics of wings being evaluated under the initiative of the NATO STO AVT-316 Task Group. Highly refined meshes, and the use of hybrid turbulence models such as Detached Eddy Simulations (DES) and Delayed DES are required to accurately resolve the vortical flows over these wings. Simulating all flow conditions of interest is a computationally expensive approach. A system identification method was therefore proposed to rapidly and accurately generate aerodynamic models of these wings. The method uses a novel piece-wise chirp (constant amplitude and increasing frequency) motion as an input signal (training maneuver). The motion computational cost is equivalent to the cost of six static CFD simulations, however it can predict aerodynamic responses of the wings over a wide range of angles of attack. The method has been tested for double and triple delta wings. Some design considerations are provided based on predicted flow features and aerodynamic data. Prediction results with different turbulence models, sting geometries, grid resolutions and an adaptive mesh refinement approach are provided.

Modeling gas holdup in a multiphase oxygen slurry bubble column reactor for Cu-Cl hydrogen production using CFD

The hydrodynamics of the oxygen bubble column reactor is investigated numerically using CFD analyses to predict the values of the gas holdup using Eulerian model and k−ε turbulence method. It is shown that, at any given static liquid height and solid concentration, increasing the superficial gas velocity leads to a higher gas holdup. Also, the gas holdup reduces when the static liquid height increases and/or the solid concentration increases at any given superficial gas velocity. All gas holdup findings were verified by experimental results from prior literature, showing excellent agreement and validating the models' applicability to this kind of a slurry bubble column system. Profiles of gas holdup obtained from CFD simulations were shown to generally under-predict the experimental data. Also, it is shown that CFD models accurately anticipated the experimental effects of the superficial gas velocity, static liquid height, and solid concentration on gas holdup.

Advanced CFD simulation of two-phase anion exchange membrane water electrolysis

Anion exchange membrane (AEM) water electrolysis is a promising and inexpensive solution for hydrogen production and environmental problems. Owing to its low technical proficiency, AEM electrolysis necessitates high fidelity to improve its durability, reliability, and efficiency. Therefore, a CFD-based model for AEM electrolysis was developed to analyze the three-dimensional and two-phase phenomena inside the cell. The temperature, pressure, and gas generation profiles inside the cell were studied by combining electrochemical models with mass, momentum, and heat transfer models. Parameters were estimated using the experimental data from a high-accuracy model. The results showed that the applied voltage, which determined the exothermic/endothermic mode, significantly influenced the water electrolysis performance. Specifically, in the exothermic mode, with voltages exceeding the thermo-neutral voltage (1.48 V), the amount of hydrogen generated (15.53, 25.05, and 28.82 mol/m3 at 1.6, 1.8, and 2.0 V, respectively) was higher than that in the endothermic mode (4.78 mol/m3 at 1.45 V). However, the increased gas generation caused a rapid increase in the temperature and pressure drop inside the cell, which adversely affected durability. The model developed in this study can be used in experiments of various scales to optimize serpentine designs and commercial AEM electrolysis stack developments.

Influence of Water Vapor and Local Gas Velocity on the Oxidation Kinetics of In625 at 900 °C: Experimental Study and CFD Gas Phase Simulation

The effect of water vapor content on the oxidation behavior of In625 at 900 °C in synthetic air was reported. The higher the water vapor content, the greater the oxidation and volatilization rates were. Increasing the water vapor content led to an increase in the proportion of spinel and rutile-type oxides in the oxide scale compared to chromia, and the proportion of Al-rich oxides within the alloy. A kp-kv mass variation model was used to quantify the experimental results, and Fluent Ansys® CFD simulations of the gas phase were used to predict volatilization rates. CFD simulations were used to calculate local gas velocity, temperature and composition along with local volatilization rates at each point on the sample surface. It was possible to explain not only the variations in volatilization between upstream and downstream samples, but also the increased volatilization at sample corners. For longer durations, it was shown experimentally that the rate of volatilization decreases. This was explained by the enrichment of the oxide scale with spinel and rutile-type oxides.

Analysis of the Sustainable Cooperation between a Multi-Piped Impeller and a Concentric Casing Using Experimental Planning

Centrifugal pumps are one of the most commonly used devices in all branches of industry. Their application area is very broad and practically related to all sectors of the economy. Such pumps are widely applied in the chemicals industry, liquid gas technology, and machine lubrication systems, among others. On the basis of available data, it can be assumed that pumps consume approximately 27% of the world’s electricity. For this reason, their efficiency has a significant impact on the energy consumption of many technological processes. This article presents a summary of the research concerning the cooperation between a multi-piped impeller and a concentric casing. A multi-piped impeller is a completely new concept of a centrifugal impeller, which is characterized by the fact that the energy of the liquid is transferred as a result of the flow of media through the internal flow channels, and also the flow of media around it. The type and design of the casing, with regard to the flow in it and around the impeller’s pipes, plays an extremely important role. Numerical analysis was used as the main research method, which was based on a rotatable experimental plan. The CFD simulation results were validated on a test stand. Finally, the mathematical model and the rules for selecting the geometric features of such a stator were proposed in order to achieve the highest possible efficiency when cooperating with the multi-piped impeller, which constitutes a scientific novelty.