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3 pages, 179 KiB

Open AccessEditorial

Special Issue on “Advancement in Computational Fluid Mechanics and Optimization Methods”

by Krzysztof Rogowski and Piotr Lichota

Processes 2022, 10(6), 1100; https://doi.org/10.3390/pr10061100 - 01 Jun 2022

Viewed by 1091

Abstract

In recent years, CFD methods have become a universal engineering tool for modeling many classes of flows [...] Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

Research

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25 pages, 8696 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Numerical Study of the Effect of the Reynolds Number and the Turbulence Intensity on the Performance of the NACA 0018 Airfoil at the Low Reynolds Number Regime

by Jan Michna and Krzysztof Rogowski

Processes 2022, 10(5), 1004; https://doi.org/10.3390/pr10051004 - 18 May 2022

Cited by 11 | Viewed by 4869

Abstract

In recent years, there has been an increased interest in the old NACA four-digit series when designing wind turbines or small aircraft. One of the airfoils frequently used for this purpose is the NACA 0018 profile. However, since 1933, for over 70 years, [...] Read more.

In recent years, there has been an increased interest in the old NACA four-digit series when designing wind turbines or small aircraft. One of the airfoils frequently used for this purpose is the NACA 0018 profile. However, since 1933, for over 70 years, almost no new experimental studies of this profile have been carried out to investigate its performance in the regime of small and medium Reynolds numbers as well as for various turbulence parameters. This paper discusses the effect of the Reynolds number and the turbulence intensity on the lift and drag coefficients of the NACA 0018 airfoil under the low Reynolds number regime. The research was carried out for the range of Reynolds numbers from 50,000 to 200,000 and for the range of turbulence intensity on the airfoil from 0.01% to 0.5%. Moreover, the tests were carried out for the range of angles of attack from 0 to 10 degrees. The uncalibrated

γ - R e_{θ}

transition turbulence model was used for the analysis. Our research has shown that airfoil performance is largely dependent on the Reynolds number and less on the turbulence intensity. For this range of Reynolds numbers, the characteristic of the lift coefficient is not linear and cannot be analyzed using a single aerodynamic derivative as for large Reynolds numbers. The largest differences in both aerodynamic coefficients are observed for the Reynolds number of 50,000. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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12 pages, 1567 KiB

Open AccessFeature PaperArticle

CFD Modeling of Flame Jump across Air Gap between Evasé and Capture Duct for Ventilation Air Methane Abatement

by Zhengbiao Peng, Jafar Zanganeh and Behdad Moghtaderi

Processes 2021, 9(12), 2278; https://doi.org/10.3390/pr9122278 - 19 Dec 2021

Cited by 2 | Viewed by 2268

Abstract

The ventilation air–methane (VAM) released from underground mines is often transported into regenerative thermal oxidizer (RTO) devices and burnt into heat energy. This study numerically investigates the scenarios where explosion occurs inside the RTO and the flame and pressure waves propagate back quickly [...] Read more.

The ventilation air–methane (VAM) released from underground mines is often transported into regenerative thermal oxidizer (RTO) devices and burnt into heat energy. This study numerically investigates the scenarios where explosion occurs inside the RTO and the flame and pressure waves propagate back quickly towards the VAM discharge duct. Possibilities of secondary explosion in the discharge duct, hence in the downstream underground mines, are examined. The results critically showed that when the methane concentration accumulated in the RTO reached 7.5% or above, the flame generated from the explosion jumped to the evasé of the discharge section (over a distance of 29.4 m) and could induce explosions in underground mines. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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20 pages, 1501 KiB

Open AccessArticle

Comparison of Different Numerical Interface Capturing Methods for the Simulation of Faraday Waves

by Armando Blanco, Richard Oliva, Daniel Machado and Dominique Legendre

Processes 2021, 9(6), 948; https://doi.org/10.3390/pr9060948 - 27 May 2021

Cited by 1 | Viewed by 1890

Abstract

Faraday instability is a classic problem that occurs due to the relative displacement of the interface that separates two immiscible fluids placed in a closed container under oscillating acceleration parallel to gravity. The interface deformation and the induced flow patterns of this two-phase [...] Read more.

Faraday instability is a classic problem that occurs due to the relative displacement of the interface that separates two immiscible fluids placed in a closed container under oscillating acceleration parallel to gravity. The interface deformation and the induced flow patterns of this two-phase flow are very complex and numerical simulations could allow a deeper understanding of the dynamics of these systems. Some tests have been performed to establish a reference solution, but further validation is needed in order to ensure the validity of these solutions. In this work, we compare some numerical solutions for the linear and nonlinear regimes using the phase field scheme with predictions obtained using different numerical schemes such as Front Tracking, Volume of Fluid, and Element-based Finite Volume Method. The results show that, in both linear and nonlinear regimes, some important differences in the prediction of the interface dynamics between the methods are observed, and the need to provide a reference numerical solution for future benchmarks is highlighted. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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26 pages, 7456 KiB

Open AccessArticle

Numerical Study on the Aerodynamic Characteristics of the NACA 0018 Airfoil at Low Reynolds Number for Darrieus Wind Turbines Using the Transition SST Model

by Krzysztof Rogowski, Grzegorz Królak and Galih Bangga

Processes 2021, 9(3), 477; https://doi.org/10.3390/pr9030477 - 07 Mar 2021

Cited by 26 | Viewed by 7696

Abstract

A symmetrical NACA 0018 airfoil is often used in such applications as small-to-medium scale vertical-axis wind turbines and aerial vehicles. A review of the literature indicates a large gap in experimental studies of this airfoil at low and moderate Reynolds numbers in the [...] Read more.

A symmetrical NACA 0018 airfoil is often used in such applications as small-to-medium scale vertical-axis wind turbines and aerial vehicles. A review of the literature indicates a large gap in experimental studies of this airfoil at low and moderate Reynolds numbers in the previous century. This gap has limited the potential development of classical turbulence models, which in this range of Reynolds numbers predict the lift coefficients with insufficiently accurate results in comparison to contemporary experimental studies. Therefore, this paper validates the aerodynamic performance of the NACA 0018 airfoil and the characteristics of the laminar separation bubble formed on its suction side using the standard uncalibrated four-equation Transition SST turbulence model and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations. A numerical study was conducted for the chord Reynolds number of 160,000, angles of attack between 0 and 11 degrees, as well as for the free-stream turbulence intensity of 0.05%. The calculated lift and drag coefficients, aerodynamic derivatives, as well as the location and length of the laminar bubble quite well agree with the results of experimental measurements taken from the literature for validation. A sensitivity study of the numerical model was performed in this paper to examine the effects of the time-step size, geometrical parameters and mesh distribution around the airfoil on the simulation results. The airfoil data sets obtained in this work using the Transition SST and the k-ω SST turbulence models were used in the improved double multiple streamtube (IDMS) to calculate aerodynamic blade loads of a vertical-axis wind turbine. The characteristics of the normal component of the aerodynamic blade load obtained by the Transition SST approach are much better suited to the experimental data compared to the k-ω SST turbulence model. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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12 pages, 6655 KiB

Open AccessArticle

Comparative Study on CFD Turbulence Models for the Flow Field in Air Cooled Radiator

by Chao Yu, Xiangyao Xue, Kui Shi, Mingzhen Shao and Yang Liu

Processes 2020, 8(12), 1687; https://doi.org/10.3390/pr8121687 - 21 Dec 2020

Cited by 8 | Viewed by 2085

Abstract

This paper compares the performances of three Computational Fluid Dynamics (CFD) turbulence models, Reynolds Average Navier-Stokes (RANS), Detached Eddy Simulation (DES), and Large Eddy Simulation (LES), for simulating the flow field of a wheel loader engine compartment. The distributions of pressure fields, velocity [...] Read more.

This paper compares the performances of three Computational Fluid Dynamics (CFD) turbulence models, Reynolds Average Navier-Stokes (RANS), Detached Eddy Simulation (DES), and Large Eddy Simulation (LES), for simulating the flow field of a wheel loader engine compartment. The distributions of pressure fields, velocity fields, and vortex structures in a hybrid-grided engine compartment model are analyzed. The result reveals that the LES and DES can capture the detachment and breakage of the trailing edge more abundantly and meticulously than RANS. Additionally, by comparing the relevant calculation time, the feasibility of the DES model is proved to simulate the three-dimensional unsteady flow of engine compartment efficiently and accurately. This paper aims to provide a guiding idea for simulating the transient flow field in the engine compartment, which could serve as a theoretical basis for optimizing and improving the layout of the components of the engine compartment. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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16 pages, 6751 KiB

Open AccessArticle

Numerical Analysis of the Flow around Two Square Cylinders in a Tandem Arrangement with Different Spacing Ratios Based on POD and DMD Methods

by Feng Wang, Xiaodong Zheng, Jianming Hao and Hua Bai

Processes 2020, 8(8), 903; https://doi.org/10.3390/pr8080903 - 30 Jul 2020

Cited by 8 | Viewed by 3057

Abstract

To more clearly understand the changes in flow characteristics around two square cylinders with different spacing ratios, the main mode of the flow field was extracted by using the Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) methods. The changes in the [...] Read more.

To more clearly understand the changes in flow characteristics around two square cylinders with different spacing ratios, the main mode of the flow field was extracted by using the Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) methods. The changes in the main mode of the flow field at different spacing ratios and the difference of the time series were analyzed and compared. This processing can separate the mixed information in the flow field and obtain the dominant modes in the flow field. These main modes can clearly reflect the dominant flow characteristics in the flow field. The analysis results show that when L/D = 2, the flow field structure is consistent with the flow field around a single square cylinder. When L/D = 2.5–3.5, the vortex shedding from upstream cylinders combines with the vortex near the downstream cylinders. This mutual coupling causes a significant change in the drag coefficient value of the downstream cylinder. When L/D = 4, the main vortex from the upstream cylinder can be completely shed, which means that the upstream and downstream square cylinder vortices start to become independent. The main focus of this paper is to use the advantages of POD and DMD to obtain several modes with higher energy in the flow field. Furthermore, it can be considered that these main modes can fully reflect the flow characteristics of the flow field. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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17 pages, 873 KiB

Open AccessArticle

Lattice Boltzmann Simulation of Ferrofluids Film Boiling

by Mohammad Yaghoub Abdollahzadeh Jamalabadi

Processes 2020, 8(8), 881; https://doi.org/10.3390/pr8080881 - 22 Jul 2020

Cited by 3 | Viewed by 2417

Abstract

In the present investigation, two phase film boiling of ferrofluids under an external field delivered around a two-dimensional square cross-section heater was investigated using the lattice Boltzmann technique. The purpose of this work is to find the effect of magnetic field magnitude and [...] Read more.

In the present investigation, two phase film boiling of ferrofluids under an external field delivered around a two-dimensional square cross-section heater was investigated using the lattice Boltzmann technique. The purpose of this work is to find the effect of magnetic field magnitude and direction on the Nusselt number in single and double heater geometry. The improving thermal efficiency in the horizontal and vertical placement of heaters is also presented. The governing equations of mass conservation, momentum conservation, and energy conservation are solved by using a central-moments-based Lattice Boltzmann scheme. The air pocket generated around heater raised incorporating magnetic effects. The heat transfer through this advancement has been explored quantitatively and abstractly. The results shows that with the development in the volumetric applied force at the bubble-fluid interface, the bubble boundary layer thickness around the square heater lessened which cause the Nusselt number augmented. Through the parameter study it found that the Nusselt number can be essentially extended by altering the course of magnet shafts, and that film rising outwardly of the bubble. The improvement and advancement of vapour phase in various heater arrangement made two column of bubble rises at the same time, which rose above each heater and in the end changed into one column of bubble. A correlation considering magnitude and angle of the magnetic field on time-averaged Nusselt number is presented. Finally, the Nusselt number can be controlled with the help of the incorporation of other heaters. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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22 pages, 7089 KiB

Open AccessArticle

The Effect of Geometrical, Operational, Mixing Methods, and Rheological Parameters on Discharge Coefficients of Internal-Mixing Twin-Fluid Atomizers

by Farid A. Hammad, Kai Sun, Jan Jedelsky and Tianyou Wang

Processes 2020, 8(5), 563; https://doi.org/10.3390/pr8050563 - 11 May 2020

Cited by 9 | Viewed by 3879

Abstract

Accurate prediction of the discharge coefficient (C_D) for internal-mixing twin-fluid (IMTF) atomizers is challenging, the effect of control factors remains inadequately understood, and comparative data on the C_D of IMTF atomizers are unavailable. This work presents an experimental study on [...] Read more.

Accurate prediction of the discharge coefficient (C_D) for internal-mixing twin-fluid (IMTF) atomizers is challenging, the effect of control factors remains inadequately understood, and comparative data on the C_D of IMTF atomizers are unavailable. This work presents an experimental study on C_D for different IMTF atomizers with a wide range of factors, including the gas-to-liquid ratio (GLR), the inlet-overpressure ratio (∆p_mix/p_amb), the orifice length-to-diameter ratio (L_o/d_o), and the liquid viscosity (µ_L). Five atomizers with different internal-mixing principles were probed on a cold test rig, including the frequently studied outside-in-gas (OIG) and inside-out-gas (IOG) effervescent types, the recently-introduced outside-in-liquid (OIL) and air-core-liquid-ring (ACLR) atomizers, and our new design named the swirling-air-core-liquid-ring (SACLR) atomizer. The results demonstrate that C_D is governed mainly by GLR, and reduces if GLR, L_o/d_o, or µ_L is increased. An increase in ∆p_mix/p_amb causes a C_D reduction up to ∆p_mix/p_amb = 0.98, and C_D increases for a higher ∆p_mix/p_amb. Surprisingly, differences in C_D amid examined atomizers were found negligible, although the flow visualization inside the orifice showed a significantly different flow character for each one of the atomizers. Finally, a general C_D correlation fitting with an R² ≥0.99 for all the tested nozzles was proposed. The results amend the present knowledge, allow design optimization, and provide flow rate prediction for a variety of IMTF atomizers. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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17 pages, 5600 KiB

Open AccessFeature PaperArticle

Thermally Optimum Spacing between Inner Plates in Natural Convection Flows in Cavities by Numerical Investigation

by Blas Zamora

Processes 2020, 8(5), 554; https://doi.org/10.3390/pr8050554 - 09 May 2020

Cited by 5 | Viewed by 2249

Abstract

Buoyancy-driven airflow that included two isothermal inner plates established in a vented cavity is investigated numerically. The thermally optimum wall-to-wall spacing of the immersed channel, as well as its dependence with respect to the relevant governing parameters, are determined. Results are presented as [...] Read more.

Buoyancy-driven airflow that included two isothermal inner plates established in a vented cavity is investigated numerically. The thermally optimum wall-to-wall spacing of the immersed channel, as well as its dependence with respect to the relevant governing parameters, are determined. Results are presented as a function of the aspect ratio b/H for a wide range of Rayleigh numbers Ra_H. A logarithmic correlation for the optimum (b/H)_opt as a function of Ra_H is presented. In addition, since the outlined configuration might be subject to intense heating conditions, the influence of considering variable thermophysical properties is also included in the analysis. In fact, an appreciable influence of the variation of properties on (b/H)_opt is also detected for a representative value of Ra_H = 10⁹. Obtained results can be directly applied to the optimization of electronic equipment cooling, or even to thermal passive devices in buildings. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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16 pages, 7963 KiB

Open AccessArticle

Cavitating Flow Suppression in the Draft Tube of a Cryogenic Turbine Expander through Runner Optimization

by Ning Huang, Zhenlin Li and Baoshan Zhu

Processes 2020, 8(3), 270; https://doi.org/10.3390/pr8030270 - 27 Feb 2020

Cited by 7 | Viewed by 2838

Abstract

The application of a cryogenic liquefied natural gas expander can reduce the production of flash steam and improve the efficiency of natural gas liquefaction. Like traditional hydraulic machinery, cavitation will occur during the operation of a liquefied natural gas expander, in particular, there [...] Read more.

The application of a cryogenic liquefied natural gas expander can reduce the production of flash steam and improve the efficiency of natural gas liquefaction. Like traditional hydraulic machinery, cavitation will occur during the operation of a liquefied natural gas expander, in particular, there is a strong vortex flow in the draft tube, and the cavitation phenomenon is serious. In this paper, the energy loss coefficient of the draft tube is used to describe the cavitation flow in the draft tube, and the goal of reducing the cavitation in the draft tube is achieved through the optimization design of the runner. Different runner models within the range of design parameters were obtained using the Latin hypercube test, and the relationship between design parameters and objective functions is constructed by a second-order response surface model. Finally, the optimized runners were obtained using a genetic algorithm. The effects of blade loading distribution and blade lean angles on the cavitation in the draft tube were studied. According to the optimization results, the blade loading distribution and blade lean angles are recommended in the end. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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14 pages, 4454 KiB

Open AccessArticle

Research on Rotordynamic Characteristics of Pump Annular Seals Based on a New Transient CFD Method

by Fengqin Li, Baoling Cui and Lulu Zhai

Processes 2020, 8(2), 227; https://doi.org/10.3390/pr8020227 - 15 Feb 2020

Cited by 8 | Viewed by 3277

Abstract

Pump annular seals can cause fluid reaction forces that have great effects on the vibration characteristic and stability of a pump system. For this reason, it is important to study rotordynamic characteristics of annular seals. In this paper, a new transient computational fluid [...] Read more.

Pump annular seals can cause fluid reaction forces that have great effects on the vibration characteristic and stability of a pump system. For this reason, it is important to study rotordynamic characteristics of annular seals. In this paper, a new transient computational fluid dynamics (CFD) method with dynamic mesh is proposed to investigate rotordynamic characteristics of the pump annular seal. The reliability of the transient CFD method is validated by comparison with the results from the experiment and the bulk-flow method, and the relationship between the seal length and rotordynamic characteristics is investigated by the transient CFD method. The results indicate that direct stiffness decreases sharply even turns to negative as the seal length increases, this phenomenon may change the direction of fluid force on the rotor surface and affect supporting condition of the pump rotor. With the increasing seal length, the whirl frequency ratio gradually increases, which would weaken the stability of the pump rotor system. Full article

(This article belongs to the Special Issue Advancement in Computational Fluid Mechanics and Optimization Methods)

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