Two-dimensional Computational Simulations Research Articles

Computational fluid dynamics analysis on performance assessment of Darrieus-type vertical axis wind turbine using NACA0016, NACA0019 and NACA0020 airfoil sections

The efficiency of a vertical-axis wind turbine is remarkably less than a horizontal-axis wind turbine and consequently, the most important challenge of the former one is to enhance its aerodynamic performance. An earlier study shows that the selection of an efficient airfoil shape is an important criterion for enhancing the overall performance of a wind turbine. The objective of the present work is to perform the two-dimensional Computational Fluid Dynamics simulation of Darrieus Vertical axis wind turbine using NACA0016, NACA0019 and NACA0020 airfoils which are neither too thick nor too thin. Furthermore, the performance of these three airfoils is compared with two established airfoils, namely NACA0015 and NACA0018. The result reveals that the overall power coefficient of NACA0019 airfoils resulting from the CFD simulation is significantly higher than that of NACA0015. Therefore, the NACA0019 airfoil may be considered one of the effective alternative airfoils for the Darrieus VAWT. Highlights Simulation of vertical axis wind turbine using NACA0016, NACA0019 and NACA0020 airfoils Unsteady URANS studies are carried out to investigate the performance of the airfoils Among the blade profiles studied in this work, NACA 0019 offers superior fluid mechanical performance

Quasi One-Dimensional characteristic analysis of ejector nozzle for turbofan propulsion system

To investigate the impact of the ejector characteristics of the exhaust system on the overall performance of a turbofan engine, this paper presents a study on the overall performance of the turbofan engine equipped with an ejector nozzle, focusing on its characteristics. Firstly, the design of the ejector exhaust system is presented and its ejector characteristics are analyzed through two-dimensional computational fluid dynamics simulations. Subsequently, a one-dimensional theoretical analysis of the ejector is conducted, and the pump suction and ejector nozzle’s thrust characteristics are determined based on the analysis results. Furthermore, a two-dimensional interpolation method is proposed to calculate the ejector coefficient, which utilizes the ejector's pump suction characteristics. By applying the matching principle of the ejector coefficient, a component-level model of the turbofan engine with an ejector nozzle is established. Based on this model, a method for predicting the backward infrared radiation intensity of the ejector exhaust system is proposed to investigate the influence of the ejector nozzle characteristics on the overall engine performance and infrared signature. The results demonstrate that the installation of the ejector exhaust system leads to a slight decrease in the overall engine performance, in which the average decrease of thrust is about 1.5%, and the average increase in fuel consumption is about 0.5%.but significantly reduces the infrared stealth characteristics, the average reduction is about 20%, which has good infrared stealth effect.

Numerical Simulation of Two-Dimensional Turbulent Dilatable Flows in a Fire

Numerical simulations, based on the theories of computational fluid dynamics and combustion, are currently a powerful tool in the field of fire engineering. Field models allow us to analyze key aspects such as the integrity of buildings and safety. However, it is fundamental to define strategies that allow engineers to obtain a balance between the precision of the results and the computational cost. One of the most relevant sub-models is the turbulence model. This paper presents the research carried out in the field of two-dimensional computational simulations of turbulent dilatable flows to evaluate the behavior of diffusion flames, hot gases, and smoke produced in accidental fires. Several computational simulations have been performed using direct numerical simulations and large eddy simulation turbulence models in the two-dimensional field, analyzing the ability of the models to correctly characterize the transport of hot gases and the behavior of the thermal plumes if the grid resolution is adequate to the physics of the problem. Additionally, several three-dimensional models have been developed to contrast and validate the results obtained in the two-dimensional simulations. In order to validate the capacity to develop a qualitative analysis of two-dimensional models in fire engineering, an evaluation criterion is presented based on the frequency spectral analysis to study the capacity of each type of turbulence model to accurately capture the vorticity of these dilatable flows.

Optimal configuration of oblique air curtains for heat loss suppression from vertical solar-thermal receiver surfaces

An external solar-thermal receiver is critical to the operation of a solar-thermal power plant because it converts concentrated solar radiation into useful heat. However, as these receivers are surrounded by relatively cold air, they suffer from significant convective heat loss that is detrimental to their thermal performance. Air curtains, in the form of air jets directed obliquely from the top of the receiver surface, have been shown to provide significant local reductions in receiver heat loss. This study presents, for the first time, a rigorous optimisation of air curtain operation to increase the mitigation of overall convective heat loss. Two-dimensional computational fluid dynamics simulations in OpenFOAM were used to optimise jet speed, angle, position, and thickness. Performance was measured based on global effectiveness, with a maximum of over 18% achieved for a jet with speed Uac=5.5ms−1, angle α=45°, thickness b=30mm, and gap G=30mm. Increasing jet thickness yielded the greatest gains in overall effectiveness. An equivalent air curtain effectiveness was defined, with the optimal case having an effectiveness of around 14%. The effect of jet outlet temperatures on effectiveness was also examined, with effectiveness gradually decreasing with increasing jet outlet temperature.

Computational fluid dynamics simulations of silicon μ-structure formation during excimer laser modification of silicon-nanoparticle layers

The laser modification of silicon-nanoparticle layers with a nanosecond pulsed excimer laser leads to the self-organized formation of crystalline, μ-cone-shaped silicon structures with good electronic properties, which have allowed the demonstration of their potential for printed flexible electronics. With the current nanosecond laser process, silicon exhibits only short melting times, resulting in a method-defined substrate contact angle, instead of this parameter being defined by the substrate surface energy as expected for equilibrium conditions. This substrate material-independent non-equilibrium contact angle of the silicon melt was experimentally determined in this study to be Θ = 68 ± 10°. To gain deeper insight into the process of the sequential melting and the formation of the silicon μ-cone structures during laser modification, a two-dimensional computational fluid dynamics simulation was performed in COMSOL Multiphysics® solving the Navier–Stokes equation for incompressible fluids. The simulation uses an effective medium approach by applying the conservative level set method to describe the porous silicon-nanoparticle layer. Its sequential melting during the pulsed laser modification is modeled using a newly developed simulation methodology, which uses a time- and depth-dependent dynamic viscosity of the molten silicon. The simulation was carried out for different laser energy densities and verified using scanning electron microscopy images of corresponding laser-modified samples. The simulation results agree well with the experiment and were subsequently used to optimize the laser process.

Performance enhancement of savonius wind turbine by multicurve blade shape

ABSTRACT This study proposes a novel blade configuration, made with a multicurve profile, to further maximize the advanced benefits and the performance of a Savonius turbine for energy harvesting applications. The advantages of the presently designed blade are proved by a detailed analysis of the flow mechanism and the performance through a sequence of two-dimensional (2D) unsteady computational fluid dynamics simulation. The remarkable finding states that the main blade section with a length ratio of 0.9 combined with an elliptical auxiliary section effectively enhances the positive wind flow phenomena around the blade, especially for the returning position, which either smooths the flow or reduces the pressure on the blade’s convex side. As a result, greater torque is obtained by the present configuration, responding to the improvement of the power generation to 0.24 – about 5.5% at the low TSR = 0.8 and up to 0.28 - about 185% at the high TSR = 1.5 over the conventional configurations. The effectiveness of the presently designed blade is further proved with more than 20% improvement in self-staring speed through six degrees of freedom analysis. The results above state a high potential application of the turbine with the presently designed blade for renewable energy applications and for supporting vulnerable communities without access to electricity.

Aerodynamic Exploration of Corrugated Airfoil Based on NACA0030 for Inflatable Wing Structure

The flow structures and surface pressure distributions on corrugated airfoils significantly differed from those on a conventional, smooth airfoil. An unsteady, two-dimensional computational simulation was carried out to investigate the flow behavior and associated aerodynamic performance of a group of corrugated airfoils with different levels of waviness at angles of attack from 0° to 20° with an interval of 2° at a low Reynolds number regime (Re = 1.2 × 105) and were quantitatively compared with those of its smooth counterpart. Time-averaged aerodynamic coefficients demonstrated that the corrugated airfoils have a lower lift and higher drag because of trapped vortices in the corrugations. The pressure drag of the corrugated airfoils was greater than that of the smooth airfoil. In contrast, the viscous drag of the corrugated airfoils was smaller than that of the smooth airfoil because the recirculation generated in the corrugation could reduce the viscous drag. The averaged velocity gradient in the boundary layer showed that the thickness of the boundary layer increased significantly for the corrugated airfoils because of recirculating flow caused by the small-standing vortices trapped in the valley of corrugations. The smoother the corrugated surface, the closer the aerodynamic characteristics are to those of the smooth airfoil.

Modelling of Tissue Invasion in Epithelial Monolayers

Mathematical and computational models are used to describe biomechanical processes in multicellular systems. Here, we develop a model to analyse how two types of epithelial cell layers interact during tissue invasion depending on their cellular properties, i.e., simulating cancer cells expanding into a region of normal cells. We model the tissue invasion process using the cellular Potts model and implement our two-dimensional computational simulations in the software package CompuCell3D. The model predicts that differences in mechanical properties of cells can lead to tissue invasion, even if the division rates and death rates of the two cell types are the same. We also show how the invasion speed varies depending on the cell division and death rates and the mechanical properties of the cells.

The impact of the wind attack angle on a typical bridge deck’s flutter behavior by the distributed aerodynamic characteristics method

To investigate the influence of the wind attack on a bridge deck’s flutter performance, the concept of “pressure flutter derivatives” was introduced as a part of the “distributed aerodynamic characteristics” method, which can be used to visualize the dominant fluctuations of the pressure field. The distributions of the aerodynamic damping and stiffness under different wind attack angles were visualized, instead of using an overall force perspective. The analysis was carried out through two-dimensional computational fluid dynamics simulations based on a typical box deck section. Necessary data were obtained through the forced vibrations of the deck. The dominant pressure fluctuations were demonstrated, around which the wind attack angles’ impact on the Scanlan flutter derivatives was discussed. For the deck section used in this study, the wind attack angle was found to most affect the windward parts of the deck. When wind attack angle ranged from − 1.5 ° to 3 ° , two regions contributed the most: one located behind the windward faring vertex and the other located behind the first vertex of the upper slab. When the wind attack angle decreased to − 3 ° , a new dominant region appeared behind the first vertex of the lower slab, which caused a sudden reduction of the flutter critical speed.

Effects of heave motion of an elastically supported floating oscillating water column device on wave energy harvesting efficiency

The main aim of this paper is to analyze the effects of the heave motion of an elastically supported floating oscillating water column device (OWC) on wave energy harvesting efficiency through two-dimensional computational fluid dynamics simulations. After the numerical model is validated using experimental data, it is used to analyze the effect of the natural frequency ratio on the hydrodynamic efficiency of the OWC. The natural frequency ratio is the ratio of the natural frequency to the wave frequency. The numerical results prove that the natural frequency ratio must be greater than 3 for achieving the best hydrodynamic efficiency. The best hydrodynamic efficiency decreases with the decrease in the natural frequency ratio when the latter is 3. If the natural frequency ratio is smaller than 3, both the amplitudes of wave surface elevation and the displacement of the OWC chamber increase but the harvested energy reduces because the relative motion of the wave surface and the OWC device is small. The energy dissipation due to vortices does not have a strong contribution to the reduction of energy at small natural frequencies.

Hydrodynamic Performance of a Floating Offshore Oscillating Water Column Wave Energy Converter

A floating oscillating water column (OWC) wave energy converter (WEC) supported by mooring lines can be modelled as an elastically supported OWC. The main objective of this paper is to investigate the effects of the frequency ratio on the performance of floating OWC (oscillating water column) devices that oscillate either vertically or horizontally at two different mass ratios (m = 2 and 3) through two-dimensional computational fluid dynamics simulations. The frequency ratio is the ratio of the natural frequency of the system to the wave frequency. Simulations are conducted for nine frequency ratios in the range between 1 and 10. The hydrodynamic efficiency achieves its maximum at the smallest frequency ratio of 1 if the OWC oscillates horizontally and at the largest frequency ratio of 10 if the OWC oscillates vertically. The frequency ratio affects the hydraulic efficiency of the vertical oscillating OWC significantly stronger than that of the horizontal oscillating OWC, especially when it is small. The air pressure and the volume oscillation in OWC is not affected much by the horizontal motion of the OWC but is significantly affected by the vertical motion, especially at small frequency ratios.

Heat transfer augmentation through rectangular cross section duct with one corrugated surface: An experimental and numerical study

One of the techniques utilized to enhance the heat transfer rate within air ducts is creating turbulence inducing designs. In this work, turbulent air flow through a rectangular cross-sectional duct with one corrugated surface was experimentally and numerically investigated. Hydraulic and thermal behaviors of the system were evaluated at different Reynolds numbers. A test rig was constructed to experimentally investigate the performance. Also, a two-dimensional computational fluid dynamics simulation was performed using k-ε model to simulate fluid flow within the duct. The model was validated against previous results as well as the experimental results from this research. The computational and experimental findings were in reasonable agreement with a maximum error of less than 10%. The results showed that the existence of the corrugated surface considerably enhanced the heat transfer rate in all the studied cases, while slightly increasing the pressure drop. Consequently, a parametric study was performed to investigate the effect of different design parameters on the performance. The best performance was observed at a rib height to width ratio of 0.2, and groove length to width ratio of three, with a thermal enhancement factor of about 1.5. an empirical relation between Nusselt number and Reynolds number was established using the obtained results with a relative error value less than 8%. The study proved the value of using a corrugated surface as a means to increase heat transfer rate within rectangular air ducts.

Numerical Simulation and Experimental Investigation of the Fixed Bed Gasification of Char With Focus on Pore Diffusion

Abstract Accurate modeling of the reaction rate of char particles is decisive for precise computational fluid dynamics simulations of gasifiers. Pore diffusion limits the reaction rate at medium temperatures and strongly depends on the pore size. In most of the present research, pore diffusion is either completely neglected or modeled with a single mean pore size. This work introduces a particle model with two pore sizes. Large pores transport the reactant gases into the particle and distribute them to small pores, in which the heterogeneous reactions take place. This approach is compared with a simpler model with a single mean pore size. The particle and the small pores are discretized by an appropriate number of elements, which allows an exact numerical calculation of the concentration profile for nth-order reactions. Both models are implemented into a two-dimensional computational fluid dynamics simulation of a lab-scale fixed bed gasifier. Simulations and experiments are carried out for 1.362 mm, 0.815 mm, and 0.458 mm sized particles, which are gasified with carbon dioxide and steam at 1200 °C and 1.1 bar total pressure. The reactant gases can penetrate smaller particles more easily. However, the measured product gas flow is independent of the particle size although the reactions take place under pore diffusion limitation. Only the proposed model with two pore sizes is able to reproduce the experiments adequately. However, it causes a significant extra computational effort.

Numerical investigation of offshore oscillating water column devices

The main objective of this paper is to analyse the hydrodynamic efficiency of offshore stationary OWC devices with different configurations through two-dimensional computational fluid dynamics simulations. The two-dimensional incompressible Reynolds-Averaged Navier-Stokes equations and the Shear Stress Transport (SST) k-ω turbulence model are solved for the simulation of water moetion under regular waves. The airflow through the turbine is calculated using a compressible aerodynamic model. After the numerical model is validated using the experimental data, it is used to analyse the effect of the submerged draught of rear vertical wall of the OWC on the hydrodynamic efficiency, and the improvement of hydrodynamic efficiency by a horizontal bottom plate attached to the back wall. The numerical results prove that increasing the rear wall draught improves the hydrodynamic efficiency if the front wall draught is 0.25 times water depth. If the draughts of the front and rear walls are the same, increasing them simultaneously causes a reduction in the hydrodynamic efficiency. Attaching a horizontal bottom plate on the deeper rear vertical wall improves efficiency. The best efficiency increases with the increase of the length of the bottom plate until the plate length is twice the chamber length. Further increase in the bottom plate length causes a reduction in the best efficiency.

2D SPH simulation of an anaerobic digester

Understanding the hydrodynamics within the anaerobic digester tank of a wastewater treatment plant is of high importance to ensure sufficient mixing and subsequently a homogeneous distribution of the substrates. In this paper, we demonstrate a two-dimensional computational fluid dynamics simulation of a real-world case study focusing on both, the methodology and the operation of mixing. For this work, DualSPHysics, a Lagrangian solver, has been explored as an alternative to the more commonly used Eulerian solvers in studying the slow-moving dynamics inside a digester tank. This choice of a Lagrangian solver is primarily due to the inherent accounting for advection within the formulation, thus allowing for subsequent modelling of anaerobic digestion processes. A comparison has been made between the simulations from the two methods (Eulerian and Lagrangian), highlighting the benefits and the shortcomings of using smoothed particle hydrodynamics. Concerning operational mixing, the case relies on a draft tube, the effect of which on the velocity profiles has been studied based on the presence of low-velocity zones and Lagrangian coherent structures. Removing the draft tube results in an increase in low-velocity zones by 21.38% while the amount of dead volume increases from 0.52 to 1.2%.

Flow dependent constriction-size distribution in gap-graded soils: a statistical inference

The clogging–unclogging process in gap-graded soils is a result of the migration of seepage-driven fines, which subsequently induces measurable changes in the local hydraulic gradients. This process can be temporally observed in the variations of Darcy's hydraulic conductivity (K). The current study proposes an integrated statistical Monte Carlo approach combining the discrete-element method and two-dimensional computational fluid dynamics simulations to estimate the flow-dependent constriction-size distribution (CSD) for a gap-graded soil. The computational inferences were supported with experimental results using an internally stable soil, which was subjected to one-dimensional flow stimulating desired hydraulic loadings: a hydraulic gradient lower than the critical gradient applied as a multi-staged loading pattern. The 35th percentile size of the flow-dependent CSD (Dc35) for both internally stable and unstable gap-graded soils becomes approximately equal to Dc35 at steady state. However, a greater variation of larger constrictions persists for the unstable soils. This pilot study has shown the applicability of the proposed method to estimate flow-dependent CSD for a wide range of experimentally observed K values.

Energy Efficiency Assessment of Pressure Losses in Horizontal Ground Heat Exchangers with Two-Dimensional Computational Simulations

Bu çalışmada yedi farklı geometrik tasarıma sahip yatay toprak ısı değiştiricilerin enerji verimini etkileyen basınç kayıpları bilgisayar destekli simülasyonlar aracılığı ile incelenmiştir. 30 m^2’lik (6mx5m) bir bahçe alanında kullanılmak üzere tasarlanan modeller, denklemlerin hesaplama kolaylığı açısından, iki boyutlu olarak oluşturulmuştur. Her bir tasarım ısı değişim yüzey alanları, basınç kayıpları ve enerji verimlilikleri açısından karşılaştırılmıştır. Enerji verimlilikleri açısından karşılaştırılmaları ısı değişim yüzey alanlarının basınç kayıplarına oranı olarak tabir edilen enerji kazanım oranı değerleri üzerinden yapılmıştır. Elde edilen sonuçlara bakıldığında Tasarım-6’nın en yüksek ısı değişim yüzey alanına (6,9681m^2), en düşük basınç kaybına (88,9790kPa) ve aynı zamanda en yüksek enerji kazanım oranına sahip olduğu (0,0783m^2 kPa^-1) görülmüştür. Her ne kadar diğer tasarımlara göre Tasarım-6 en enerji verimli gözükse de işletim ve bakım açısından değerlendirildiklerinde diğer tasarımlar yek pare olarak kullanılabileceklerken Tasarım-6’nın çok fazla bağlantı elemanı içermesinden dolayı pratik kullanımının riskli olduğu düşünülmektedir. Sonuçların projenin geliştirilmeye devam edilmesi açısından çok verimli olduğu görülmüştür.

Simulation of Hydrogen-Air-Diluents Mixture Combustion in an Acceleration Tube with FlameFoam Solver

During a severe accident in a nuclear power plant, hydrogen can be generated, leading to risks of possible deflagration and containment integrity failure. To manage severe accidents, great experimental, analytical, and benchmarking efforts are being made to understand combustible gas distribution, deflagration, and detonation processes. In one of the benchmarks—SARNET H2—flame acceleration due to obstacle-induced turbulence was investigated in the ENACCEF facility. The turbulent combustion problem is overly complex because it involves coupling between fluid dynamics, mass/heat transfer, and chemistry. There are still unknowns in understanding the mechanisms of turbulent flame propagation, therefore many methods in interpreting combustion and turbulent speed are present. Based on SARNET H2 benchmark results, a two-dimensional computational fluid dynamics simulation of turbulent hydrogen flame propagation in the ENACCEF facility was performed. Four combustible mixtures with different diluents concentrations were considered—13% H2 and 0%/10%/20%/30% of diluents in air. The aim of this numerical simulation was to validate the custom-built turbulent combustion OpenFOAM solver based on the progress variable model—flameFoam. Furthermore, another objective was to perform parametric analysis in relation to turbulent speed correlations and turbulence models and interpret the k-ω SST model blending function F1 behavior during the combustion process. The obtained results show that in the simulated case all three turbulent speed correlations behave similarly and can be used to reproduce observable flame speed; also, the k-ε model provides more accurate results than the k-ω SST turbulence model. It is shown in the paper that the k-ω SST model misinterprets the sudden parameter gradients resulting from turbulent combustion.

Power performance enhancement of vertical axis wind turbines by a novel gurney flap design

PurposeNowadays flaps and winglets are one of the main mechanisms to increase airfoil efficiency. This study aims to investigate the power performance of vertical axis wind turbines (VAWT) that are equipped with diverse gurney flaps. This study could play a crucial role in the design of the VAWT in the future.Design/methodology/approachIn this paper, the two-dimensional computational fluid dynamics simulation is used. The second-order finite volume method is used for the discretization of the governing equations.FindingsThe results show that the gurney flap enhances the power coefficient at the low range of tip speed ratio (TSR). When an angled and standard gurney flap case has the same aerodynamic performance, an angled gurney flap case has a lower hinge moment on the junction of airfoil and gurney flap which shows the structural excellence of this case. In all gurney flap cases, the power coefficient increases by an average of 20% at the TSR range of 0.6 to 1.8. The gurney flap cases do not perform well at the high TSR range and the results show a lower amount of power coefficient compare to the clean airfoil.Originality/valueThe angled gurney flap which has the structural advantage and is deployed to the pressure side of the airfoil improves the efficiency of VAWT at the low and medium range of TSR. This study recommends using a controllable gurney flap which could be deployed at a certain amount of TSR.

Computational Studies on the Effects of a Central Shaft and a Guiding Wall on the Savonius Hydrokinetic Turbine Performances

Most wetland rice production schemes have good networks of irrigation and drainage canals built for the benefit of the farmers to perform farming activities. The canals have ample volume of running water all year round and could be harnessed for hydropower. The Savonius hydrokinetic turbine has been generally used to generate electrical energy as the means of renewable source over fossil fuels. Numerous parameters have been studied to enhance the performance of the turbine. However, the turbine power performance is still low as compared to other types even though it is known to have excellent torque characteristics. Therefore, the objectives of this study are to evaluate the effects of a central shaft and a guiding wall on the performances of the Savonius hydrokinetic turbines by using two-dimensional computational simulations. ANSYS Fluent software with the standard k-ε turbulence model and dynamic mesh motion techniques were used to get the optimum central shaft and guiding wall configurations. The central shaft was studied in three cases; (I) with a full shaft, (II) with a shaft and space, and (III) without shaft between two end plates. Moreover, the turbine performances were also evaluated with and without the presence of a guiding wall. The turbine performances were computed. Simulation results e.g. velocity, pressure contours and flow structures across a SHKT model were analysed and discussed.