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14 pages, 6562 KiB

Open AccessArticle

Experimental and Numerical Analysis of a Seawall’s Effect on Wind Turbine Performance

by Hyun-Goo Kim and Wan-Ho Jeon

Energies 2019, 12(20), 3877; https://doi.org/10.3390/en12203877 - 14 Oct 2019

Cited by 2 | Viewed by 3720

Abstract

For the purposes of this study, a wind tunnel experiment and a numerical analysis during ebb and high tides were conducted to determine the positive and negative effects of wind flow influenced by a seawall structure on the performance of wind turbines installed [...] Read more.

For the purposes of this study, a wind tunnel experiment and a numerical analysis during ebb and high tides were conducted to determine the positive and negative effects of wind flow influenced by a seawall structure on the performance of wind turbines installed along a coastal seawall. The comparison of the wind flow field between a wind tunnel experiment performed with a 1/100 scale model and a computational fluid dynamics (CFD) analysis confirmed that the MP k-turbulence model estimated flow separation on the leeside of the seawall the most accurately. The CFD analysis verified that wind speed-up occurred due to the virtual hill effect caused by the seawall’s windward slope and the recirculation zone of its rear face, which created a positive effect by mitigating wind shear while increasing the mean wind speed in the wind turbine’s rotor plane. In contrast, the turbulence effect of flow separation on the seawall’s leeside was limited to the area below the wind turbine rotor, and had no negative effect. The use of the CFD verified with the comparison with the wind tunnel experiment was extended to the full-scale seawall, and the results of the analysis based on the wind turbine Supervisory Control and Data Acquisition (SCADA) data of a wind farm confirmed that the seawall effect was equivalent to a 1.5% increase in power generation as a result of a mitigation of the wind profile. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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18 pages, 5519 KiB

Open AccessArticle

CFD Simulation of an Industrial Spiral Refrigeration System

by A. Khenien, A. Benattayallah and G. Tabor

Energies 2019, 12(17), 3358; https://doi.org/10.3390/en12173358 - 30 Aug 2019

Cited by 1 | Viewed by 4596

Abstract

In the food industry, heating and cooling are key processes where CFD can play an important role in improving quality, productivity and reducing energy costs. Cooling products after baking is crucial for storage and transportation; the product has to be cooled efficiently to [...] Read more.

In the food industry, heating and cooling are key processes where CFD can play an important role in improving quality, productivity and reducing energy costs. Cooling products after baking is crucial for storage and transportation; the product has to be cooled efficiently to a specified temperature (often to fulfill regulatory requirements) whilst preserving its quality. This study involves the analysis of spiral cooling refrigerators used in cooling food products, in this case, Cornish Pasties. Three separate sets of CFD models were developed and validated against experimental data taken in the laboratory and measurements taken in use in industry. In the first set of models a full CFD model was developed of a refrigeration spiral including the pasties, and used to study the heat transfer from the products to the air. Further simulations were carried out on individual pasties to explore the pasty cooling and heat transfer to the air in more detail, with the pasty geometry being determined from MRI scans. In the final set of simulations, Image Based Meshing (IBM) was used to determine the interior structure of the pasty and develop a full heat conduction model of the interior, which was compared with separate laboratory experiments using jets of cold air to cool the pasty. In all cases, good agreement was obtained between the CFD results and experimental data, whilst the CFD simulations provide valuable information about the air flows and cooling in the industrial system. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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20 pages, 4344 KiB

Open AccessArticle

Flow Regime Analysis of the Pressure Build-Up during CO₂ Injection in Saturated Porous Rock Formations

by Ernestos Sarris and Elias Gravanis

Energies 2019, 12(15), 2972; https://doi.org/10.3390/en12152972 - 1 Aug 2019

Cited by 9 | Viewed by 3328

Abstract

In this work, we are concerned with the theoretical and numerical analysis of the pressure build-up on the cap of an aquifer during CO₂ injection in saturated porous rock formations in all flow regimes of the problem. The latter are specific regions [...] Read more.

In this work, we are concerned with the theoretical and numerical analysis of the pressure build-up on the cap of an aquifer during CO₂ injection in saturated porous rock formations in all flow regimes of the problem. The latter are specific regions of the parameter space of the plume flow, defined by the CO₂-to-brine relative mobility and the buoyancy parameter (injection pressure to buoyancy pressure scale ratio). In addition to the known asymptotic self-similar solutions for low buoyancy, we introduce two novel ones for the high buoyancy regimes via power series solutions of asymptotic self-similarity equations. The explicit results for the peak value of pressure on the cap, which arises in the vicinity of the well, are derived and discussed for all flow regimes. The analytical results derived in this work are applied for the purpose of cap integrity considerations in six test cases of CO₂ geological storage from the PCOR partnership, most of which correspond to high buoyancy conditions. The validity of the self-similar solutions (late time asymptotics) is verified with CFD numerical simulations performed with the software Ansys-Fluent. The result is that the self-similar solutions and the associated pressure estimations are valid in typical injection durations of interest, even for early times. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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20 pages, 10176 KiB

Open AccessArticle

Multi-Scale CFD Modeling of Plate Heat Exchangers Including Offset-Strip Fins and Dimple-Type Turbulators for Automotive Applications

by Augusto Della Torre, Gianluca Montenegro, Angelo Onorati, Sumit Khadilkar and Roberto Icarelli

Energies 2019, 12(15), 2965; https://doi.org/10.3390/en12152965 - 1 Aug 2019

Cited by 28 | Viewed by 8962

Abstract

Plate heat exchangers including offset-strip fins or dimple-type turbulators have a wide application in the automotive field as oil coolers for internal combustion engines and transmissions. Their optimization is a complex task since it requires targeting different objectives: High compactness, low pressure drop [...] Read more.

Plate heat exchangers including offset-strip fins or dimple-type turbulators have a wide application in the automotive field as oil coolers for internal combustion engines and transmissions. Their optimization is a complex task since it requires targeting different objectives: High compactness, low pressure drop and high heat-transfer efficiency. In this context, the availability of accurate Computational Fluid Dynamics (CFD) simulation models plays an important role during the design phase. In this work, the development of a computational framework for the CFD simulation of compact oil-to-liquid heat exchangers, including offset-strip fins and dimples, is presented. The paper addresses the modeling problem at different scales, ranging from the characteristic size of the turbulator geometry (typically µm–mm) to the full scale of the overall device (typically cm–dm). The simulation framework is based on multi-scale concept, which applies: (a) Detailed simulations for the characterization of the micro-scale properties of the turbulator, (b) an upscaling approach to derive suitable macro-scale models for the turbulators and (c) full-scale simulations of the entire cooler, including the porous models derived for the smaller scales. The model is validated comparing with experimental data under different operating conditions. Then, it is adopted to investigate the details of the fluid dynamics and heat-transfer process, providing guidelines for the optimization of the device. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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19 pages, 5388 KiB

Open AccessArticle

A Simple and Robust Shock-Capturing Approach for Discontinuous Galerkin Discretizations

by Jae Hwan Choi, Juan J. Alonso and Edwin van der Weide

Energies 2019, 12(14), 2651; https://doi.org/10.3390/en12142651 - 10 Jul 2019

Cited by 1 | Viewed by 3612

Abstract

The discontinuous Galerkin (DG) method has become popular in Computational Fluid Dynamics mainly due to its ability to achieve high-order solution accuracy on arbitrary grids, its high arithmetic intensity (measured as the ratio of the number of floating point operations to memory references), [...] Read more.

The discontinuous Galerkin (DG) method has become popular in Computational Fluid Dynamics mainly due to its ability to achieve high-order solution accuracy on arbitrary grids, its high arithmetic intensity (measured as the ratio of the number of floating point operations to memory references), and the use of a local stencil that makes scalable parallel solutions possible. Despite its advantages, several difficulties hinder widespread use of the DG method, especially in industrial applications. One of the major challenges remaining is the capturing of discontinuities in a robust and accurate way. In our previous work, we have proposed a simple shock detector to identify discontinuities within a flow solution. The detector only utilizes local information to sense a shock/discontinuity ensuring that one of the key advantages of DG methods, their data locality, is not lost in transonic and supersonic flows. In this work, we reexamine the shock detector capabilities to distinguish between smooth and discontinuous solutions. Furthermore, we optimize the functional relationships between the shock detector and the filter strength, and present it in detail for others to use. By utilizing the shock detector and the corresponding filtering-strength relationships, one can robustly and accurately capture discontinuities ranging from very weak to strong shocks. Our method is demonstrated in a number of two-dimensional canonical examples. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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18 pages, 47391 KiB

Open AccessArticle

CFD Simulation of Defogging Effectivity in Automotive Headlamp

by Michal Guzej and Martin Zachar

Energies 2019, 12(13), 2609; https://doi.org/10.3390/en12132609 - 7 Jul 2019

Cited by 7 | Viewed by 7028

Abstract

In the past decade, the condensation of internal air humidity in automotive headlamps has become more prevalent than ever due to the increased usage of a new light source—LEDs. LEDs emit far less heat than previously-used halogen lamps, which makes them far more [...] Read more.

In the past decade, the condensation of internal air humidity in automotive headlamps has become more prevalent than ever due to the increased usage of a new light source—LEDs. LEDs emit far less heat than previously-used halogen lamps, which makes them far more susceptible to fogging. This fogging occurs when the internal parts of the headlamp fall to a temperature below the dew point. The front glass is most vulnerable to condensation due to its direct exposure to ambient conditions. Headlamp fogging leads to a decrease in performance and the possibility of malfunctions, which has an impact not only on the functional aspect of the product’s use but also on traffic safety. There are currently several technical solutions available which can determine the effectivity of ventilation systems applied for headlamp defogging. Another approach to this problem may be to use a numerical simulation. This paper proposes a CFD (computational fluid dynamics) simulation with a slightly simplified 3D model of an actual headlamp, which allows simulation of all the phenomena closely connected with fluid flow and phase change. The results were validated by real experiments on a special fogging–defogging test rig. This paper compares three different simulations and their compliance with real experiments. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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17 pages, 11381 KiB

Open AccessArticle

The Use of CFD for the Design and Development of Innovative Configurations in Regenerative Glass Production Furnaces

by Carlo Cravero and Davide De Domenico

Energies 2019, 12(13), 2455; https://doi.org/10.3390/en12132455 - 26 Jun 2019

Cited by 9 | Viewed by 3651

Abstract

The limitation of nitrogen oxides emissions is nowadays a challenge in several engineering fields. Recent European regulations have reduced the maximum NO_x emissions and therefore forced the glass production sector to develop emission reduction strategies. Two different systems have been developed within [...] Read more.

The limitation of nitrogen oxides emissions is nowadays a challenge in several engineering fields. Recent European regulations have reduced the maximum NO_x emissions and therefore forced the glass production sector to develop emission reduction strategies. Two different systems have been developed within the framework of the European LIFE project and are currently applied to glass regenerative furnaces: the Waste Gas Recirculation (WGR) and the Hybrid Air Staging (HyAS). The above systems are primary NO_x reduction strategies because they both operate to control the combustion evolution. Both WGR and HyAS systems have been conceived with the extensive use of Computational Fluid Dynamics (CFD) models: design strategies for both systems have been developed based on the use of CFD and are currently under use by glass furnace designers. In the present work, the CFD procedures routinely used for the design of the above systems are described. The systems effectiveness, due to the harsh conditions in the industrial installation, can be tested with oxygen concentration measurements inside the regenerators. The oxygen concentration is correlated to the flame evolution and therefore to the nitrogen oxides formation. For the above reason, the models have been validated with experimental data from pilot furnaces using measured values of O₂ mole fraction. The CFD procedures are described in the paper together with their application to different configurations. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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16 pages, 7495 KiB

Open AccessArticle

Multiphase Flow Effects in a Horizontal Oil and Gas Separator

by Michael Frank, Robin Kamenicky, Dimitris Drikakis, Lee Thomas, Hans Ledin and Terry Wood

Energies 2019, 12(11), 2116; https://doi.org/10.3390/en12112116 - 3 Jun 2019

Cited by 14 | Viewed by 5435

Abstract

An oil and gas separator is a device used in the petroleum industry to separate a fluid mixture into its gaseous and liquid phases. A computational fluid dynamics (CFD) study aiming to identify key design features for optimising the performance of the device, [...] Read more.

An oil and gas separator is a device used in the petroleum industry to separate a fluid mixture into its gaseous and liquid phases. A computational fluid dynamics (CFD) study aiming to identify key design features for optimising the performance of the device, is presented. A multiphase turbulent model is employed to simulate the flow through the separator and identify flow patterns that can impinge on or improve its performance. To verify our assumptions, we consider three different geometries. Recommendations for the design of more cost- and energy-effective separators, are provided. The results are also relevant to broader oil and gas industry applications, as well as applications involving stratified flows through channels. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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24 pages, 13305 KiB

Open AccessArticle

The Effect of Wet Compression on a Centrifugal Compressor for a Compressed Air Energy Storage System

by Jianting Sun, Xin Zhou, Qi Liang, Zhitao Zuo and Haisheng Chen

Energies 2019, 12(5), 906; https://doi.org/10.3390/en12050906 - 8 Mar 2019

Cited by 11 | Viewed by 5163

Abstract

There is an urgent demand to reduce compression power consumption in Compressed Air Energy Storage (CAES) systems. Wet compression has been widely used in gas turbines to reduce compressor power consumption and improve thermal efficiency, but this technology has not been applied yet [...] Read more.

There is an urgent demand to reduce compression power consumption in Compressed Air Energy Storage (CAES) systems. Wet compression has been widely used in gas turbines to reduce compressor power consumption and improve thermal efficiency, but this technology has not been applied yet in the CAES field. In this paper, a centrifugal compressor for CAES was numerically studied to investigate the effect of wet compression on compressor and droplet motion. The results showed that wet compression makes the performance curve shift to a high-pressure ratio/efficiency. Meanwhile, wet compression lowers the stall margin and narrows the stable operation range, and the effect is enhanced with the increase of water injection ratio or the decrease of average droplet diameter. Wet compression can effectively save compressor power consumption during energy storage, and at the designed pressure ratio, the power consumption can be reduced by 1.47% with a water injection ratio of 3% and an average droplet diameter of 5 μm. Influenced by the inertia and secondary flow, the droplets migrate to the impeller pressure and shroud side, thus causing brake loss by impacting on blades. The migration of droplets strengthens with the increase in the average droplet diameter and flow coefficient. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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21 pages, 1367 KiB

Open AccessFeature PaperArticle

An Optimum Enthalpy Approach for Melting and Solidification with Volume Change

by Moritz Faden, Andreas König-Haagen and Dieter Brüggemann

Energies 2019, 12(5), 868; https://doi.org/10.3390/en12050868 - 5 Mar 2019

Cited by 42 | Viewed by 4500

Abstract

Classical numerical methods for solving solid–liquid phase change assume a constant density upon melting or solidification and are not efficient when applied to phase change with volume expansion or shrinkage. However, solid–liquid phase change is accompanied by a volume change and an appropriate [...] Read more.

Classical numerical methods for solving solid–liquid phase change assume a constant density upon melting or solidification and are not efficient when applied to phase change with volume expansion or shrinkage. However, solid–liquid phase change is accompanied by a volume change and an appropriate numerical method must take this into account. Therefore, an efficient algorithm for solid–liquid phase change with a density change is presented. Its performance for a one-dimensional solidification problem and for the quasi two-dimensional melting of octadecane in a cubic cavity was tested. The new algorithm requires less than 1/9 of the iterations compared to the source based method in one dimension and less than 1/7 in two dimensions. Moreover, the new method is validated against PIV measurements from the literature. A conjugate heat transfer simulation, which includes parts of the experimental setup, shows that parasitic heat fluxes can significantly alter the shape of the phase front near the bottom wall. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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23 pages, 22006 KiB

Open AccessArticle

Influence of Disc Tip Geometry on the Aerodynamic Performance and Flow Characteristics of Multichannel Tesla Turbines

by Wenjiao Qi, Qinghua Deng, Zhinan Chi, Lehao Hu, Qi Yuan and Zhenping Feng

Energies 2019, 12(3), 572; https://doi.org/10.3390/en12030572 - 12 Feb 2019

Cited by 17 | Viewed by 9222

Abstract

As a competitive small-scale turbomachinery option, Tesla turbines have wide potential in various fields, such as renewable energy generation systems and small power equipment. This paper investigates the influence of disc tip geometry, including its profile and relative height, on the aerodynamic performance [...] Read more.

As a competitive small-scale turbomachinery option, Tesla turbines have wide potential in various fields, such as renewable energy generation systems and small power equipment. This paper investigates the influence of disc tip geometry, including its profile and relative height, on the aerodynamic performance and flow characteristics of one-to-one and one-to-many multichannel Tesla turbines. The results indicate that compared to the turbine with blunt tips, the isentropic efficiency of the one-to-one turbine with sharp tips has a little decrease, which is because the relative tangential velocity gradient near the rotational disc walls decreases a little and additional vortices are generated at the rotor inlet, while that of the one-to-many turbine with sharp tips increases significantly, resulting from an increase in the relative tangential velocity in the disc channels and a decrease in the low Mach number and vortex area; for instance the turbine efficiency for the former relatively decreases by 3.6% and that for the latter increases by 13.5% at 30,000 r/min. In addition, the isentropic efficiency of the one-to-many turbine with sharp tips goes up with increasing relative height due to increasing improvement of flow status, and its increment rate slows down. A circular or elliptic tip performs better with lower relative height and a triangular tip behaves better with higher relative height. To sum up, a blunt disc tip is recommended for the one-to-one turbine, and a sharp disc tip is for the one-to-many turbine. The relative height and tip profile of the one-to-many turbine should be determined according to their effects on turbine performance, manufacturing difficulty and mechanical deformation. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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17 pages, 6546 KiB

Open AccessArticle

Numerical Analysis of Aerodynamic Characteristics of Hyperloop System

by Jae-Sung Oh, Taehak Kang, Seokgyun Ham, Kwan-Sup Lee, Yong-Jun Jang, Hong-Sun Ryou and Jaiyoung Ryu

Energies 2019, 12(3), 518; https://doi.org/10.3390/en12030518 - 6 Feb 2019

Cited by 93 | Viewed by 9545

Abstract

The Hyperloop system is a new concept that allows a train to travel through a near-vacuum tunnel at transonic speeds. Aerodynamic drag is one of the most important factors in analyzing such systems. The blockage ratio (BR), pod speed/length, tube pressure, and temperature [...] Read more.

The Hyperloop system is a new concept that allows a train to travel through a near-vacuum tunnel at transonic speeds. Aerodynamic drag is one of the most important factors in analyzing such systems. The blockage ratio (BR), pod speed/length, tube pressure, and temperature affect the aerodynamic drag, but the specific relationships between the drag and these parameters have not yet been comprehensively examined. In this study, we investigated the flow phenomena of a Hyperloop system, focusing on the effects of changes in the above parameters. Two-dimensional axisymmetric simulations were performed in a large parameter space covering various BR values (0.25, 0.36), pod lengths (10.75–86 m), pod speeds (50–350 m/s), tube pressures (~100–1000 Pa), and tube temperatures (275–325 K). As BR increased, the pressure drag was significantly affected. This is because of the smaller critical Mach number for a larger BR. As the pod length increased, the total drag and pressure drag did not change significantly, but there was a considerable influence on the friction drag. As the pod speed increased, strong shock waves occurred near the end of the pod. At this point, the flows around the pod were severely choked at both BR values, and the ratio of the pressure drag to the total drag converged to its saturation level. At tube pressures above 500 Pa, the friction drag increased significantly under the rapidly increased turbulence intensity near the pod surface. High tube temperatures increase the speed of sound, and this reduces the Mach number for the same pod speed, consequently delaying the onset of choking and reducing the aerodynamic drag. The results presented in this study are applicable to the fundamental design of the proposed Hyperloop system. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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25 pages, 46485 KiB

Open AccessArticle

Large Eddy Simulation with Energy-Conserving Schemes and the Smagorinsky Model: A Note on Accuracy and Computational Efficiency

by Dhruv Mehta, Ye Zhang, Alexander Van Zuijlen and Hester Bijl

Energies 2019, 12(1), 129; https://doi.org/10.3390/en12010129 - 31 Dec 2018

Cited by 5 | Viewed by 5179

Abstract

Despite advances in turbulence modelling, the Smagorinsky model remains a popular choice for large eddy simulation (LES) due to its simplicity and ease of use. The dissipation in turbulence energy that the model introduces, is proportional to the Smagorinsky constant, of which many [...] Read more.

Despite advances in turbulence modelling, the Smagorinsky model remains a popular choice for large eddy simulation (LES) due to its simplicity and ease of use. The dissipation in turbulence energy that the model introduces, is proportional to the Smagorinsky constant, of which many different values have been proposed. These values have been derived for certain simulated test-cases while using a specific set of numerical schemes, to obtain the correct dissipation in energy simply because an incorrect value of the Smagorinsky constant would lead to an incorrect dissipation. However, it is important to bear in mind that numerical codes may suffer from numerical or artificial dissipation, which occurs spuriously through a combination of spatio-temporal and iterative errors. The latter can be controlled through more iterations, the former however, depends on the grid resolution and the time step. Recent research suggests that a complete energy-conserving (EC) spatio-temporal discretisation guarantees zero numerical dissipation for any grid resolution and time step. Therefore, using an EC scheme would ensure that dissipation occurs primarily through the Smagorinsky model (and errors in its implementation) than through the discretisation of the Navier-Stokes (NS) equations. To evaluate the efficacy of these schemes for engineering applications, the article first discusses the use of an EC temporal discretisation as regards to accuracy and computational effort, to ascertain whether EC time advancement is advantageous or not. It was noticed that a simple non-EC explicit method with a smaller time step not only reduces the numerical dissipation to an acceptable level but is computationally cheaper than an implicit-EC scheme for wide range of time steps. Secondly, in terms of spatial discretisation on uniform grids (popular in LES), a simple central-difference scheme is as accurate as an EC spatial discretisation. Finally, following the removal of numerical dissipation with any of the methods mentioned above, one is able to choose a Smagorinsky constant that is nearly independent of the grid resolution (within realistic bounds, for OpenFOAM and an in-house code). This article provides impetus to the efficient use of the Smagorinsky model for LES in fields such as wind farm aerodynamics and atmospheric simulations, instead of more comprehensive and computationally demanding turbulence models. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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15 pages, 6795 KiB

Open AccessArticle

Experimental and Computational Demonstration of a Low-Temperature Waste to By-Product Conversion of U.S. Oil Shale Semi-Coke to a Flue Gas Sorbent

by Kathleen Dupre, Emily M. Ryan, Azat Suleimenov and Jillian L. Goldfarb

Energies 2018, 11(11), 3195; https://doi.org/10.3390/en11113195 - 17 Nov 2018

Cited by 12 | Viewed by 3361

Abstract

The volatility of crude oil prices incentivizes the use of domestic alternative fossil fuel sources such as oil shale. For ex situ oil shale retorting to be economically and environmentally viable, we must convert the copious amounts of semi-coke waste to an environmentally [...] Read more.

The volatility of crude oil prices incentivizes the use of domestic alternative fossil fuel sources such as oil shale. For ex situ oil shale retorting to be economically and environmentally viable, we must convert the copious amounts of semi-coke waste to an environmentally benign, useable by-product. Using acid and acid + base treatments, we increased the surface area of the semi-coke samples from 15 m²/g (pyrolyzed semi-coke) to upwards of 150 m²/g for hydrochloric acid washed semi-coke. This enhancement in porosity and surface area is accomplished without high temperature treatment, which lowers the overall energy required for such a conversion. XRD analysis confirms that chemical treatments removed the majority of dolomite while retaining other carbonate minerals and maintaining carbon contents of approximately 10%, which is greater than many fly ashes that are commonly used as sorbent materials. SO₂ gas adsorption isotherm analysis determined that a double HCl treatment of semi-coke produces sorbents for flue gas treatment with higher SO₂ capacities than commonly used fly ash adsorbents. Computational fluid dynamics modeling indicates that the sorbent material could be used in a fixed bed reactor to efficiently remove SO₂ from the gas stream. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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21 pages, 5568 KiB

Open AccessFeature PaperArticle

Numerical Investigation of an OxyfuelNon-Premixed CombustionUsing a Hybrid Eulerian Stochastic Field/Flamelet Progress Variable Approach: Effects of H₂/CO₂ Enrichment and Reynolds Number

by Rihab Mahmoud, Mehdi Jangi, Benoit Fiorina, Michael Pfitzner and Amsini Sadiki

Energies 2018, 11(11), 3158; https://doi.org/10.3390/en11113158 - 14 Nov 2018

Cited by 7 | Viewed by 4006

Abstract

In the present paper, the behaviour of an oxy-fuel non-premixed jet flame is numerically investigated by using a novel approach which combines a transported joint scalar probability density function (T-PDF) following the Eulerian Stochastic Field methodology (ESF) and a Flamelet Progress Variable (FPV) [...] Read more.

In the present paper, the behaviour of an oxy-fuel non-premixed jet flame is numerically investigated by using a novel approach which combines a transported joint scalar probability density function (T-PDF) following the Eulerian Stochastic Field methodology (ESF) and a Flamelet Progress Variable (FPV) turbulent combustion model under consideration of detailed chemical reaction mechanism. This hybrid ESF/FPV approach overcomes the limitations of the presumed- probability density function (P-PDF) based FPV modelling along with the solving of associated additional modelled transport equations while rendering the T-PDF computationally less demanding. In Reynolds Averaged Navier-Stokes (RANS) context, the suggested approach is first validated by assessing its general prediction capability in reproducing the flame and flow properties of a simple piloted jet flame configuration known as Sandia Flame D. Second, its feasibility in capturing CO₂ addition effect on the flame behaviour is demonstrated while studying a non-premixed oxy-flame configuration. This consists of an oxy-methane flame characterized by a high CO₂ amount in the oxidizer and a significant content of H₂ in the fuel stream, making it challenging for combustion modelling. Comparisons of numerical results with experimental data show that the complete model reproduces the major properties of the flame cases investigated and allows achieving the best agreement for the temperature and different species mass fractions once compared to the classical presumed PDF approach. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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28 pages, 9579 KiB

Open AccessArticle

Analysis of the Impact of Auxiliary Ventilation Equipment on the Distribution and Concentration of Methane in the Tailgate

by Magdalena Tutak and Jarosław Brodny

Energies 2018, 11(11), 3076; https://doi.org/10.3390/en11113076 - 8 Nov 2018

Cited by 52 | Viewed by 4370

Abstract

Methane, which is commonly found in hard coal deposits, represents a considerable threat to the safety of mining operations in these deposits. The paper presents the results of tests, aiming to limit the negative impact of methane on hard coal exploitation and improve [...] Read more.

Methane, which is commonly found in hard coal deposits, represents a considerable threat to the safety of mining operations in these deposits. The paper presents the results of tests, aiming to limit the negative impact of methane on hard coal exploitation and improve work safety. The tests encompassed an analysis of methane concentration distributions in the tailgate (in the intersection area with the longwall), with account being taken of auxiliary ventilation equipment. This equipment is responsible for reducing methane concentration levels in the intersection area between the longwall and the tailgate. The analyses presented in the article were conducted for a spatial model of a longwall area, using the Computational Fluid Dynamics (CFD) method. Account was taken of the real-world measurements of the headings as well as the measurement data concerning methane concentration and ventilation parameters. The tests took into account methane emissions from the mined coal and from the goaf with caving. The analyses were performed for the system with and without auxiliary equipment, for different velocities of the additional air stream. This made it possible to compare both systems and determine the impact of auxiliary equipment on the distribution and concentration of methane in the most vulnerable area of exploitation. The distributions of the air and gas mixture were also determined in the analysed headings and goaf with caving. The results obtained clearly demonstrate that using auxiliary equipment has a significant effect on the ventilation parameters of the air stream and leads to reduction in methane concentrations in the most vulnerable section of the longwall. These results also confirmed the advantages of auxiliary ventilation equipment, which should contribute to their wider application in underground hard coal exploitation. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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22 pages, 5110 KiB

Open AccessArticle

Prediction of the Maximum Erosion Rate of Gas–Solid Two-Phase Flow Pipelines

by Jingyuan Xu, Zhanghua Lian, Jian Hu and Min Luo

Energies 2018, 11(10), 2773; https://doi.org/10.3390/en11102773 - 16 Oct 2018

Cited by 17 | Viewed by 4686

Abstract

Erosion is one of the important reasons for the thickness decrease and perforation of the pipe walls. Understanding the gas–solid two-phase flow pipe erosion mechanism is the basis for monitoring pipe erosion. According to the structural characteristics and working conditions of the gas–solid [...] Read more.

Erosion is one of the important reasons for the thickness decrease and perforation of the pipe walls. Understanding the gas–solid two-phase flow pipe erosion mechanism is the basis for monitoring pipe erosion. According to the structural characteristics and working conditions of the gas–solid two-phase flow pipeline in a gas transmission station, a gas–solid two-phase flow pipe erosion finite element model was established and validated by combining it with field test data. Then, the gas–solid two-phase flow pipeline erosion characteristics under different pressures, solid contents, throttle valve openings, and pipe diameters were studied. On this basis, a maximum erosion rate prediction equation was put forward after verification by using actual wall thickness detection data. Results show the following: (1) The absolute error of the maximum erosion rate between the model results and the test datum is ≤10.75%. (2) The outer cambered surface of the bend after the throttle valve is the most seriously eroded areas. (3) The maximum erosion rate increases with pressure, solid content and throttle valve opening increasing, but, along with the change of the pipe diameter, the maximum erosion rate increases at first and then decreases with pipe diameter increasing for throttle valve openings of 20% and 30%, and it decreases with pipe diameter increasing for a throttle valve opening of 50%. (4) A maximum erosion rate prediction equation, involving pressure, solid content, opening of the throttle valve, and pipe diameter, is proposed and is verified that the absolute percentage error between the prediction equation calculation results and the field test datum is ≤11.11%. It would seem that this maximum erosion rate prediction equation effectively improves the accuracy of predicting the gas–solid two-phase flow pipe erosion rate in a gas transmission station. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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16 pages, 7119 KiB

Open AccessArticle

Influence of Blade Leading-Edge Shape on Cavitation in a Centrifugal Pump Impeller

by Ran Tao, Ruofu Xiao and Zhengwei Wang

Energies 2018, 11(10), 2588; https://doi.org/10.3390/en11102588 - 28 Sep 2018

Cited by 36 | Viewed by 8106

Abstract

Cavitation is an important issue in pumps and usually starts on the blade leading-edge. For fixed blades with constant rotational speeds and specific flow rates, the incident angle, which is between the flow direction and the blade installing direction, on the blade leading-edge [...] Read more.

Cavitation is an important issue in pumps and usually starts on the blade leading-edge. For fixed blades with constant rotational speeds and specific flow rates, the incident angle, which is between the flow direction and the blade installing direction, on the blade leading-edge plays the key role in the cavitation process. The leading-edge shape is crucial on the local flow separation, pressure distribution, and cavitation. Hence, the influence of the leading-edge shape on cavitation has been studied in the current work in a centrifugal pump impeller. The blunt, sharp, ellipse and round leading-edge cases were compared using numerical simulation and verified by experimental data. Results show different features of cavitation. The round and ellipse leading-edge impellers have higher inception cavitation coefficient. It was caused by the sudden pressure drop on leading-edge arc or elliptical arc. The sharp and blunt leading-edge impellers have a wide flow-separation region on leading-edge with a wide low-pressure region. This is because of the sudden turn in geometry on the leading-edge corner. Cavitation grew quickly after inception and caused rapid head-drop in the sharp and blunt leading-edge impellers. Results suggest the critical cavitation performance is dominated by the leading-edge low-pressure area while the inception cavitation is mostly affected by the minimum pressure value on the leading-edge. The critical cavitation performance can be evaluated by checking the leading-edge low-pressure area. The inception cavitation can be evaluated by checking the minimum pressure value on the leading-edge. These strategies can be used in the further leading-edge designs. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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20 pages, 6418 KiB

Open AccessArticle

Prediction of Combustion and Heat Release Rates in Non-Premixed Syngas Jet Flames Using Finite-Rate Scale Similarity Based Combustion Models

by Ali Shamooni, Alberto Cuoci, Tiziano Faravelli and Amsini Sadiki

Energies 2018, 11(9), 2464; https://doi.org/10.3390/en11092464 - 17 Sep 2018

Cited by 7 | Viewed by 4812

Abstract

Generating energy from combustion is prone to pollutant formation. In energy systems working under non-premixed combustion mode, rapid mixing is required to increase the heat release rates. However, local extinction and re-ignition may occur, resulting from strong turbulence–chemistry interaction, especially when rates of [...] Read more.

Generating energy from combustion is prone to pollutant formation. In energy systems working under non-premixed combustion mode, rapid mixing is required to increase the heat release rates. However, local extinction and re-ignition may occur, resulting from strong turbulence–chemistry interaction, especially when rates of mixing exceed combustion rates, causing harmful emissions and flame instability. Since the physical mechanisms for such processes are not well understood, there are not yet combustion models in large eddy simulation (LES) context capable of accurately predicting them. In the present study, finite-rate scale similarity (SS) combustion models were applied to evaluate both heat release and combustion rates. The performance of three SS models was a priori assessed based on the direct numerical simulation of a temporally evolving syngas jet flame experiencing high level of local extinction and re-ignition. The results show that SS models following the Bardina’s “grid filtering” approach (A and B) have lower errors than the model based on the Germano’s “test filtering” approach (C), in terms of mean, root mean square (RMS), and local errors. In mean, both Bardina’s based models capture well the filtered combustion and heat release rates. Locally, Model A captures better major species, while Model B retrieves radicals more accurately. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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18 pages, 4067 KiB

Open AccessArticle

Numerical Study of the Respirable Coal Dust Removal Performance of a Vortex Ventilation System at an Excavation Face

by Xiaofei Liu, Ping Chang, Enyuan Wang, Zhenguo Zhang and Shuai Yang

Energies 2018, 11(9), 2449; https://doi.org/10.3390/en11092449 - 14 Sep 2018

Cited by 18 | Viewed by 3685

Abstract

Coal dust is one of the most serious issues in coal mines. The miners at an excavation face have a high potential for exposure to high concentrations of coal dust. The main method for removing coal dust is by ventilation. To better control [...] Read more.

Coal dust is one of the most serious issues in coal mines. The miners at an excavation face have a high potential for exposure to high concentrations of coal dust. The main method for removing coal dust is by ventilation. To better control the coal dust at the excavation face, it is important to understand the coal dust movement patterns and distribution characteristics. This paper used the computational fluid dynamics (CFD) approach to simulate coal dust movement under two different ventilation systems. The Eulerian-Lagrange method was used to study the gas‒solid two-phase fluid behavior. The coal dust concentration distributions under the two ventilation systems are presented and further compared. From the comparison results, it is found that a vortex ventilation system has better coal dust removal performance. This ventilation system is recommended for excavation for better coal dust control and miners’ health protection. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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Review

Jump to: Research

17 pages, 1802 KiB

Open AccessFeature PaperReview

Multiscale Computational Fluid Dynamics

by Dimitris Drikakis, Michael Frank and Gavin Tabor

Energies 2019, 12(17), 3272; https://doi.org/10.3390/en12173272 - 25 Aug 2019

Cited by 39 | Viewed by 6582

Abstract

Computational Fluid Dynamics (CFD) has numerous applications in the field of energy research, in modelling the basic physics of combustion, multiphase flow and heat transfer; and in the simulation of mechanical devices such as turbines, wind wave and tidal devices, and other devices [...] Read more.

Computational Fluid Dynamics (CFD) has numerous applications in the field of energy research, in modelling the basic physics of combustion, multiphase flow and heat transfer; and in the simulation of mechanical devices such as turbines, wind wave and tidal devices, and other devices for energy generation. With the constant increase in available computing power, the fidelity and accuracy of CFD simulations have constantly improved, and the technique is now an integral part of research and development. In the past few years, the development of multiscale methods has emerged as a topic of intensive research. The variable scales may be associated with scales of turbulence, or other physical processes which operate across a range of different scales, and often lead to spatial and temporal scales crossing the boundaries of continuum and molecular mechanics. In this paper, we present a short review of multiscale CFD frameworks with potential applications to energy problems. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)

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