3D CFD Research Articles

Complete Workflow of Internal Nozzle Flow and Engine Simulation Using Multi-Component Fuel at Flash Boiling Conditions

Article Complete Workflow of Internal Nozzle Flow and Engine Simulation Using Multi-Component Fuel at Flash Boiling Conditions Bejoy Mandumpala Devassy 1, Yidan Zhang 2, * , Enyuan Zhang 2, and Long Zhou 2 1 AVL LIST GmbH, Hans-List-Platz 1, Graz 8020, Austria 2 AVL List Technical Center (Shanghai) Co., LTD. Shanghai 201206, China * Correspondence: yidan.zhang@avl.com Received: 17 May 2023 Accepted: 1 September 2023 Published: 14 September 2023 Abstract: At present 3D CFD simulation tools are getting more and more importance for addressing complex physical problems. This article presents a complete virtual analysis of the in-cylinder workflow in gasoline engine at flash boiling condition. Using the standard gasoline surrogate fuel PACE-20, properties of different fuel components was considered both the nozzle and in-cylinder flow. The flow, evaporation, spray jet interaction and spray collapse under flash boiling condition was studied. Molar density fraction was used to describe fuel component distribution for both gas phase and liquid phase. Based on nozzle flow simulation result, in-cylinder simulation has been done, the distribution of different fuel components and the influence on wall film, flame propagation, emission distribution has been studied. It shows that the simulation results have good agreement with testing data, and it proves the model validation for gasoline engine virtual development method under flash boiling conditions.

Experiments and CFD modelling of bubble formation at a lateral hole in a top-submerged nozzle

Top-submerged nozzles with lateral holes find applications as passive mixing devices in radiochemical/hazardous industries. We report the mechanism of bubble formation and detachment at a lateral hole in such a nozzle for the first time. Three distinct phases – a growth phase, an elongation phase and finally a rise/detachment phase – could be observed during bubble formation. Effect of gas flow rate, diameter of lateral hole (1, 2 and 3 mm) and physical properties of liquid-liquid system on bubble detachment time and bubble equivalent diameter are reported. Three different liquid-liquid systems (DM water, 2 N and 4 N nitric acid) have been considered. Bubble diameter first reduced, reached a minimum and then started to increase in an oscillatory manner with increase in air flow rate. Before the onset of oscillatory behaviour an increase in hole diameter was seen to reduce bubble diameter. Such a behaviour is typical to bubble formation at lateral hole and is not seen for top-submerged nozzles with central opening. A detailed analysis of the results was carried out and it was observed that inertial forces played a major role. The work also reports a fundamental criterion which must be achieved for onset of oscillations in bubble diameter with flow rate. We also report a 2D CFD model that can simulate bubble formation dynamics at a lateral hole. The model was validated qualitatively as well as quantitatively against the experimental data.

Frost prediction based on a 3D CFD model of heat and mass transfer in a counter-cross-flow parallel-plate liquid-to-air membrane energy exchanger

Frost prediction based on a 3D CFD model of heat and mass transfer in a counter-cross-flow parallel-plate liquid-to-air membrane energy exchanger

Understanding the Stability of Passenger Vehicles Exposed to Water Flows through 3D CFD Modelling

A vehicle exposed to flooding may lose its stability and wash away resulting in potential injuries and fatalities. Traffic disruption, infrastructure damage, and economic losses are also additional effects of the washed vehicles. Therefore, understanding the responses of passenger vehicles during flood events is of the utmost importance to reduce flood risks and develop accurate safety guidelines. Previously, flooded vehicle stability was investigated experimentally, theoretically, and numerically. However, numerical investigations are insufficient, of which only a few studies have been published since 1967. Furthermore, coupled motion simulations have not been employed to investigate the hydrodynamic forces on flooded vehicles. In this paper, a numerical framework was proposed to assess the response of a full-scale medium-size passenger vehicle exposed to floodwaters through three-dimensional computational fluid dynamic modelling. The vehicle was simulated under subcritical and supercritical flows with the Froude number ranging between 0.09 and 2.46. The results showed that the vehicle experienced the floating instability mode once the flow depth reached 0.38 m, while the sliding instability mode was observed once the depth×velocity threshold function exceeded 0.36 m2/s. In terms of hydrodynamic forces, it was noticed that the drag force decreased with the increment of the Froude number and flow velocity. On the other hand, the fraction and buoyancy forces are mainly governed by the flow depth at the vehicle vicinity. The drag coefficient was noticed to be less than 1 for supercritical flows and more than 1 for subcritical flows. The numerical results obtained through the framework introduced in this study demonstrate favorable agreement with three different previously published experimental outcomes.

Power Balance Strategies in Steady-State Simulation of the Micro Gas Turbine Engine by Component-Coupled 3D CFD Method

Currently, an increasing number of designers have begun to pay attention to a new paradigm for evaluating the performance with full engine 3-dimensional computational fluid dynamics (3D CFD) simulations. Compared with the traditional component-based performance simulation method component-based performance simulation method (‘component-matched’ method), this novel ‘component-coupled’ method can evaluate the overall performance of the engine more physically and obtain more detailed flow field parameters simultaneously. Importantly, the power balance iteration should be introduced to the novel method to satisfy the constraints of the coaxial components for the gas turbine engine at steady state. By carrying out the ‘component-matched’ simulation and the ‘component-coupled’ simulation for a micro turbojet engine, the necessity of introducing the power balance iteration was discussed in this paper. The influence of steady-state co-working constraints on the engine performance was analysed and strategies for power balance iteration were proposed. To verify the capability and feasibility of this method, not only the co-working state but also the windmill state of the gas turbine engine were simulated by using the 3D CFD method considering power balance iteration. The results show that the power balance strategy proposed in this paper can converge the aerodynamic parameters as well as the power residual in a robust way.

2D CFD simulations of flow and reaction during carbon dioxide methanation: A spatially resolved channel plate reactor study

Carbon dioxide methanation is a way of storing excess electrical energy as grid compatible gas. Spatially resolved channel plate reactor experiments were used to validate competing reactor (1D, 2Dx-z) models. Parallel exothermic carbon dioxide methanation and endothermic reverse water gas shift reactions were considered. The kinetic model, where the rate determining step is between an oxygenated complex (HCOO*) and an active site (*), was used in 2Dx-z CFD simulations for six laminar inflow conditions and variations in pressure, temperature, H2/CO2 ratio, methane, and steam co-feeds. The performance is improved by decreasing flowrate, and increasing H2/CO2 ratio, pressure, and temperature. Co-feeding methane has a negligible effect on reactor performance. However, co-feeding steam significantly reduces performance. At relatively high conversions, differential rates are obtained. This is due to the negligible dependence of the rate of carbon dioxide conversion with the equilibrium term of the reverse water gas shift reaction. With these studies, a link between the reaction mechanism and reactor performance is established at conditions relevant to power-to-gas applications.

3D CFD Simulation of a Bubble Column with Internals: Validation of Interfacial Forces and Internal Effects for Local Gas Holdup Predictions

3D CFD Simulation of a Bubble Column with Internals: Validation of Interfacial Forces and Internal Effects for Local Gas Holdup Predictions

Benchmark analysis of the FFTF LOSWOS test #13 with OpenMC and THACS

In order to support collaborative efforts within international partnerships on the development of sodium-cooled fast reactor (SFR), the International Atomic Energy Agency (IAEA) proposes a coordinated research project (CRP) about the unprotected loss-of-flow-without-scram test (LOSWOS) performed at Fast Flux Test Facility (FFTF) in 2018, which could validate simulation tool and numerical models for SFR. As one of the participants, the Nuclear THermal-hydraulic Laboratory at Xi’an Jiaotong University (NuTHeL) participates with the monte carol code OpenMC and system thermal hydraulic code THACS. This paperdeal with the standalone neutronic modeling by OpenMC and thermal hydraulic modelling by THACS. For neutronic part, the axial homogenous model was modeled to analyze the reactivity feedback coefficients and steady radial power distribution. For thermal hydraulic part, the system model, including 2D CFD outlet plenum model, subchannel model and inter-wrapper flow model, was modeled to analyze both system response and local phenomena during the LOSWOS. In general, both neutronic results and thermal hydraulic results agreed well with other participants or experiments, the reactivity feedback of GEM could provide major negative feedback, which could be used as a novel passive shutdown device. However, the remaining discrepancies were the underestimated peak temperature of PIOTA at the begin of transients, it may be caused by unknow heat transfer coefficients around hexagon tube, which has no correlation and should be further investigated by experiments. In addition, when considering IWF model, the maximum temperature of the outlet for the active fuel region was 10 K larger than the subassemblie’ outlet in the PIOTA, this phenomenon should be carefully treated in loss of flow accidents of SFR.

Development of a Numerical Approach for the CFD Simulation of a Gear Pump under Actual Operating Conditions

The geometric complexity and high-pressure gradients that characterize the design of the flow field of gear pumps make it very difficult to obtain an accurate CFD simulation of the component. Usually, assumptions are made both in terms of geometrical features and physics being included in the analysis. The contact between the teeth, which is a key factor for the correct functioning of these pumps, represents a critical challenge in 3D CFD simulations, mainly due to the intrinsic limits of the dynamic meshing techniques that can hardly effectively manage a zero or close to zero gap point forming during gear rotation. The geometric complexity and high-pressure gradients that characterize the gear pump flow field make a CFD analysis quite difficult, and the contact between the gear teeth is usually avoided, thus being an extremely important feature. In this paper, a gear pump composed of inlet and outlet pipes was considered, and the contact between the gear’s teeth was modeled in two different ways, one where it is effectively implemented and one where it is avoided using distancing and a proper casing modification. Herein, a new methodology is proposed for the application of the dynamic mesh method in the Simcenter STAR-CCM+ environment using an adaptive remeshing technique. The proposed methodology is compared with the alternative overset meshing method available in the software. The new meshing method is implemented using a user-routing that reproduces the real geometry of the gears while rotating during the pump operation, with teeth contact included. The routine is optimized in order to limit the additional computation and time needed for the remeshing process. The results that can be obtained using the two meshing approaches for the gear pump are compared in terms of computational effort and the accuracy of the results. The two methods showed opposite results in almost all the reported results, with the overset being more precise in the radial pressure evaluation and the dynamic being more reliable in the cavitation/aeration extension cloud.

Simulation study on proppant transport in a horizontal wellbore considering perforation erosion

Perforation erosion caused by pressure drop is widespread during a hydraulic-fracturing treatment. Perforation diameter can change proppant distribution between perforation clusters which affects proppant transport efficiency to fractures. Even though most of the relevant research on proppant transport in the wellbore focuses on the transport state and makes some sensitivity analysis, proppant transport law which considers the impact of perforation erosion is still unclear. 3D CFD wellbore models with a single cluster and double clusters are set in this paper. Simulations are conducted to investigate the proppant transport in the horizontal wellbore under the condition of different perforation erosion circumstances in clean water hydraulic fracturing. We combine the proppant transport and distribution when perforation erosion occurred and did not occur. The results also show that the factors including the location of perforation erosion, the angle of eroded perforations, the degree of perforation erosion, and the injection rate affect the proppant distribution and give some quantitative conclusions. This study provides useful insights into proppant transport in a horizontal wellbore.

Wind Resistance Evaluation of Existing Standing Buddha Statue Using 3D Laser Scanning and CFD

Wind Resistance Evaluation of Existing Standing Buddha Statue Using 3D Laser Scanning and CFD

Development of an ejector for passive hydrogen recirculation in PEM fuel cell systems by applying 2D CFD simulation

The anode subsystem is a major energy consumer of polymer-electrolyte-membrane (PEM) fuel cell systems. A passive hydrogen recirculation system, like an ejector, is an excellent solution to maximize hydrogen utilization while maintaining low parasitic losses. However, high development efforts are necessary to maximize the performance of the ejector for the entire operating range. This research paper provides part of a toolchain for ejector development, consisting in particular of a multi-parameter simulation based on rotational symmetric 2D CFD. The 2D CFD greatly helps optimize the design of the ejector, reducing development effort, and increasing accuracy. In addition, the main correlations between thermodynamic states and geometry on the entrainment ratio are evaluated. Subsequently, an ejector is designed for a PEM fuel cell application using 2D CFD and the results show in which operating range a single ejector can be applied. This toolchain enables rapid design and optimization of ejector geometry, saving development time and cost while increasing accuracy and extending the operating range.

Optical and thermal analysis of solar parabolic dish cavity receiver system for hydrogen production using deep learning

The solar thermochemical cycle, responsible for converting solar energy to chemical fuel, is an emerging clean hydrogen production technique. The distribution of the concentrated heat flux and temperature on the receiver is crucial in deciding solar-to-fuel conversion efficiency. Thus, the optimum configuration of a solar parabolic dish collector (PDC) is necessary for providing efficient thermal energy. The dish diameter, rim angle, and distance of the receiver aperture from the focal point of the dish characterize the optimization of the PDC. The non-uniform heat flux captured is coupled with a heat transfer model of a solar thermochemical reactor for a thermal dissociation of ZnO involved in a ZnO/Zn thermochemical cycle for hydrogen production. The directly irradiated rotating reactor comprises a cylindrical cavity packed with insulation layers and a quartz glass window. The rotating cavity is loaded with ZnO granular particles held by a centrifugal force. A 3D CFD numerical model is analyzed by coupling the Eulerian multiphase model for ZnO particle dynamics, fluid flow of gaseous mixture, RNG k-ԑ turbulence model, Energy and Discrete Ordinates (DO) radiation model, and Arrhenius reaction rate chemical reaction of ZnO dissociation. A numerical model with non-uniform heat flux input is validated for a cavity temperature, mass fraction of zinc and oxygen, and oxygen molar flow rate at the reactor outlet. An artificial neural network model is adopted to predict the heat flux and uniformity factor values of PDC. Correlation Coefficient (R2), Root Mean Square Error (RMSE), and Mean Absolute Percentage Error (MAPE) error metrices were used to evaluate the model's performance having the receiver diameter (d), the dish diameter (D), the rim angle (φ), and the distance between the focus and receiver (h) as input variables.

Assessment of fairing geometry effects on H-Darrieus hydro turbine performance using 2D URANS CFD simulations

This study aims to enhance the hydrodynamic efficiency of the fairing system and increase the power coefficient Cp of a three-bladed H-Darrieus turbine by investigating various geometries and configurations in comparison to the reference model. 2D CFD modeling and URANS calculations along with the k-ω SST turbulence model are employed for conducting parametric studies. The analysis focuses on assessing the geometric parameters of the fairing system that affect its behavior, such as the angle of incidence α and the chord length C of the fairing profile. It was found that at x/C=0.39934, the normalized power coefficient Cp/Cp,max of H-Darrieus equipped with the fairing amounts to 0.967581, whereas at x/C=0.750825, it attains Cp=0.486284. A power coefficient of Cp=0.621315 is achieved when an angle of attack α=10∘ and a tip speed ratio λ=2 are combined. In addition, the optimal operating point Cp for both fairing profiles is λ=2. In addition, maximum performance is reached at α=18∘ for the Eppler-420 profile, with a peak Cp=0.662, whereas the S1223-RTL profile demonstrates optimal performance at α=30∘ , with a peak Cp=0.728. Differences in the maximum and minimum ΔP∗ values between the Eppler-420 and S1223-RTL are also noted. It is observed that the S1223-RTL profile displays lower drag Cd and lift Cl coefficient values than the Eppler-420 profile up to α≈22∘. finally yet importantly, the highest Cp is observed at a chord length of C=4.0R, while the lowest occurs at a chord length of C=2.5R. Both Cd and Cl exhibit relative constancy for chord lengths shorter than C=4.0R.

Numerical analysis of transient heat and mass transfer for a water heat pipe under non-uniform heating conditions

Non-uniform loads are widely present in heat pipe applications and have significant effects on their performance. In this work, a transient 3D CFD model is developed to investigate the liquid–vapor flow and heat transfer for a water heat pipe under various non-uniform loads. The source terms are added to the governing equations using the User-Defined Function (UDF) to simulate the evaporation and condensation process. The model is verified using the experimental and simulated data under uniform and non-uniform loads in the literature. The effects of key parameters including adiabatic length, heating power, and heat distribution on the thermal performance of heat pipes are analyzed. The results show that the non-uniform conditions would shift the maximum axial velocity of vapor to the unheated side and induce a significant circumferential flow in the wick region, especially in the evaporator section. The short adiabatic length and high heating power could reduce the elapsed time of reaching the steady state. The heat distribution in the evaporator section exhibits little effect on the elapsed time reaching the steady-state and the average steady-state vapor temperature

Two-way Eulerian-Lagrangian coupling approach in GASFLOW code for containment spray modelling

Spray droplets are considered to have significant effects on the gas mixing and depressurization in the containment of nuclear power plants during hypothetical accident scenarios. The Eulerian-Lagrangian approach, which enables the two-way mass, momentum, and energy coupling of the continuous gas and the dispersed spray droplets, is promising to model the behaviours of spray droplets in 3D simulations of the full-scale containment. Two-way heat and mass transfer models have been developed in the 3D CFD code GASFLOW. The particle group method is applied in the Lagrangian approach to track the droplets. The ordinary differential equations which couple the local heat and mass exchanges between each droplet group and the surrounding gas mixtures have been solved using the Runge-Kutta method. The GASFLOW coupling this new approach is validated by TOSQAN water spray experiments, which demonstrate the good feasibility of implementing the approach. The analysis of the impact of the spray on containment atmosphere indicates that: 1) the droplet swarm entrains and mixes the surrounding gas, breaking up the gas stratification, with turbulent diffusion dominating momentum mixing in dead zones; 2) the thermal and mass exchanges between the spray droplet swarm and gas jointly determine the atmosphere depressurization, with the evaporation of the spray-formed film/sump on heat structures of great importance for the containment pressure development; and 3) these spray thermodynamic and dynamic effects highly depend on the droplet size distribution and the spray shape.

Structural and Environmental Safety Studies of the Holy Mosque Area Using CFD

A three-dimensional (3D) CFD model was developed, covering a square area of 3.64 km2 and comprising the Holy Mosque near its center, the actual terrain, and the main surrounding buildings. The gust wind effects on the existing cranes and the collapsed tower crane in 2015, the comfort of the pedestrians, and the air quality were studied for the first time in this area. The air quality was related to calm speed, accelerating the spreading of infectious diseases. The wind comfort levels were achieved in all selected locations. The wind speeds are generally low in the area. However, gusting wind currents appeared from limited directions, causing increments in wind speeds up to 30% and causing the tower crane to collapse. Therefore, finalizing work on some cranes is recommended soon, lowering the crane boom and stopping working on windy days or changing their places. The air quality in some sites may be relatively poor, such as at the lower terraces level. New tall buildings surrounding the mosque from the north and the east are not recommended unless studying their impacts on the air quality. Pruning north and east mounts can remarkably improve natural ventilation. Large-scale fans are another solution after a detailed simulation study.

Helical Gear Pump: A Comparison between a Lumped Parameter and a Computational Fluid Dynamics-Based Approaches

This research presents a comparison between two numerical approaches developed and later compared for studying External Gear Pumps (EGPs). Models have been developed for studying pumps with helical gears. Firstly, a three-dimensional (3D) CFD numerical model has been built using a commercial code. Then, a new tool called EgeMATor MP+, completely developed by the authors and capable of completely simulating this pump’s typologies is presented. Thanks to different subroutines developed in different interconnected environments, this tool can fully analyze those pumps, starting from the drawing. Both numerical approaches have been detailed, highlighting their strengths and weaknesses and the tweaking required to reach more accurate results. Both numerical models have been set up with the same boundary conditions to obtain a more accurate comparison. Comparisons have been performed using tests performed on a commercial pump taken as reference, focusing on steady-state volumetric performance as well as the transient features of the outlet port pressure oscillations. The comparison of the (Q,p) characteristics showed that the 3D CFD numerical model has a slightly better accuracy, but both models have errors that fall into the uncertainty range of the experimental measurements. In addition, the pressure ripples comparison verified good agreements, where also the double flank behavior of the pump is predicted. While comparing the two simulation approaches, the paper highlights the limits and strengths of each one of the two approaches. In particular, it is shown how both models can match the experimental results considering proper assumptions. The paper constitutes a unique contribution to the field of numerical simulation of EGPs and represents a useful reference to designers looking for suitable methods for simulating existing or novel design solutions.

Experimental and numerical investigation of an innovative complex piston with enhanced free spray length for the heavy-duty engine applications

The combustion and emission formation process in heavy-duty compression ignition engines are strongly influenced by the design of the piston bowl, the cylinder charge motion and the performance of the injection system. This paper proposes an innovative complex piston bowl design approach called as ’flower piston’ to improve the combustion process. It can be manufactured using the conventional machining approaches without use of still expensive additive manufacturing techniques. The flower piston features a scooped cavity with an intention of increasing the free fuel spray penetration. The potential of this innovative flower piston is evaluated using a validated 3D CFD model and compared with the results of single cylinder engine experiments at operating points with minimum fuel consumption. The results of the experimental investigations with the flower piston show an improvement in thermal efficiency in comparison to the conventional piston by up to 0.5%. This is due to a faster initial heat release and increased high pressure cycle work. However, the smoke emissions increased threefold due to fuel entrapment into the flower cavities, leading to formation of fuel-rich pockets. Also, the wall heat losses increased twofold with an increase in NOx raw emissions. With increased spray targeting angle, there was a drastic reduction in smoke emissions and an additional improvement in the thermal efficiency.

Photocatalytic degradation of ethylene in tubular microreactor coated with thin-film of TiO2: Mathematical modeling with experimental validation and geometry analysis using computational fluid dynamics simulations

The study aimed to establish a comprehensive understanding of the photocatalytic process and optimize the reactor design for efficient ethylene regulation to improve the shelf-life of fruits and vegetables. For this, it was performed 2D computational fluid dynamics modeling at two different reactor geometry (conventional cylindric reactor and annular cylindric reactor) using the conservation equations combined with Langmuir-Hinshelwood mechanism. A continuous single-phase multicomponent fluid flow with the reactor surface supported with a thin-film catalyst under UV-A light irradiation was simulated for initial ethylene concentration at 0.479–4.234 × 10−3 molC2H4 m−3 and inlet axial velocity at 0.0085–0.1019 m s−1. In the 2D CFD results, it was observed that the difference in ethylene concentration between the microreactor bulk and surface is only significant for high initial concentrations and axial velocities. Furthermore, it was found that the parabolic conversion profile remains unchanged for lengths greater than 10% of the reactor length across all geometries studied. The variation in reactor diameters resulted in a substantial reduction in ethylene conversion; however, the incorporation of an annular cylinder coated with a catalyst led to an enhancement in conversion rates, with improvements of approximately 28%, 17%, and 6% observed for diameters of 5 mm, 10 mm, and 20 mm, respectively. This reduction in improvement as diameter increase can be attributed to the laminar flow dynamics that impede the diffusion of ethylene molecules from the bulk to the catalytic surface. Consequently, the simulated data highlight the potential of employing a catalyst-doped annular cylinder as a promising strategy to increase ethylene conversion and extend the shelf life of fruits. However, it should be noted that the addition of an annular cylinder, while enhancing conversion, also introduces operational complexities and cost implications due to the significant increase in pressure drop associated with lower diameters.