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Fluids, Volume 7, Issue 8 (August 2022) – 33 articles

Cover Story (view full-size image): Cerebral aneurysms are pathological dilatations of the vessels supplying the brain. They carry a certain risk of rupture, which, in turn, results in a high risk of mortality and morbidity. Flow diverters are high-density meshed stents which are implanted in the vessel segment harboring an intracranial aneurysm to cover the entrance of the aneurysm, thus reducing the intra-aneurysmal blood flow, promoting thrombosis formation and stable occlusion, which prevent the rupture or growth of the aneurysm. In this study, CFD aneurysm blood flow treated with stents was modeled and analyzed considering its design and flow reduction to investigate the quantitative and qualitative effect of the stent on intra-aneurysmal hemodynamics. It may lead to a better understanding of failed aneurysm occlusions treated with stents. View this paper
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Article
Field Study of Three–Parameter Flow Resistance Model in Rivers with Vegetation Patch
Fluids 2022, 7(8), 284; https://doi.org/10.3390/fluids7080284 - 22 Aug 2022
Viewed by 344
Abstract
Bed shear stress in coarse–bed rivers with vegetation patches is one of the challenging parameters in hydraulic engineering, mechanical engineering, fluvial morphology, and environmental studies. Based on this necessity, in this study, the values of bed shear stress in four reaches of rivers [...] Read more.
Bed shear stress in coarse–bed rivers with vegetation patches is one of the challenging parameters in hydraulic engineering, mechanical engineering, fluvial morphology, and environmental studies. Based on this necessity, in this study, the values of bed shear stress in four reaches of rivers in Iran were estimated and compared using the methods of boundary layer characteristics, logarithmic law, and Darcy–Weisbach. Data collection in this study started in February 2021 and ended in April 2021. Estimation of flow resistance is a key factor in many numerical and physical models. In order to obtain a reasonable evaluation of this factor, it is necessary to measure and calculate the key variables of resistance to flow. Accordingly, the experimental design in this study includes surveying operations, velocity measurement, and sampling of bed sediments. The results show that due to bed forms, vegetation patches, and variations of flow depth and grain size in the river, the universal velocity distribution law (the log law) may not be suitable to estimate the shear velocity, which is a key parameter of flow resistance. This calls for more justifiable methods which are not affected by near–the–bed conditions. Accordingly, a three–parameter flow resistance model is presented, which shows an average error of 17%, indicating the accuracy of the model. The investigation of 71 measured velocity profiles shows the occurrence of the Dip phenomenon in the velocity profiles near the vegetation patches. However, by moving away from the vegetation patches, the effect of this phenomenon is decreased, and the profiles illustrate an S–shaped distribution. The results show that the relative differences between the logarithmic law and Darcy–Weisbach methods compared to the boundary layer characteristics method (BLCM) are equal to 87% and 39%, respectively, indicating a more reasonable agreement between the Darcy–Weisbach method and the boundary layer characteristics method. This is due to the application of key parameters of the boundary layer theory to calculate shear velocity by BLCM. However, to simplify data collection in the field, the application of the Darcy–Weisbach method is suggested. Full article
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Article
Aerodynamic Drag Reduction of Railroad Tank Wagons
Fluids 2022, 7(8), 283; https://doi.org/10.3390/fluids7080283 - 19 Aug 2022
Viewed by 421
Abstract
Several geometrical modifications for passive flow control applied to a railroad tank wagon were investigated for the purpose of assessing the potential for the aerodynamic optimization of freight trains. The modifications were designed in accordance with applicable requirements and regulations. Four different modifications [...] Read more.
Several geometrical modifications for passive flow control applied to a railroad tank wagon were investigated for the purpose of assessing the potential for the aerodynamic optimization of freight trains. The modifications were designed in accordance with applicable requirements and regulations. Four different modifications were investigated in the wind tunnel of the TU Berlin with 1:25 scaled wagon models: face radius, side skirts, fairing of the roof platform, and the newly introduced inter-wagon discs. In order to simulate the positions of the tested wagon at the end of a long train, the boundary layer on the train model setup was artificially thickened by spires. The Reynolds number was in the range of 0.4 × 106. The results of the experiments show that the proposed measures can reduce the aerodynamic drag of the individual wagon by up to 29%, depending on the location in the train consist. It was also shown that by combining different measures, the individual drag reductions add up. The device with the highest drag reduction was found to be the inter-wagon disc. Three different diameters of the inter-wagon disc were investigated. The largest diameter performed best and was less sensitive to the moving direction of the wagon in comparison to the smaller diameters. Full article
(This article belongs to the Special Issue Aerodynamics of Road Vehicles and Trains)
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Article
Numerical Simulations of the Flow Dynamics in a Tube with Inclined Fins Using Open-Source Software
Fluids 2022, 7(8), 282; https://doi.org/10.3390/fluids7080282 - 18 Aug 2022
Cited by 1 | Viewed by 419
Abstract
Finned tubes increase the convective heat transfer in heat exchangers, reducing the total energy consumption of integrated industrial processes. Due to its stability and robustness, Computational Fluid Dynamics (CFD) commercial software is generally utilized for analyzing complex systems; however, its licensing is expensive. [...] Read more.
Finned tubes increase the convective heat transfer in heat exchangers, reducing the total energy consumption of integrated industrial processes. Due to its stability and robustness, Computational Fluid Dynamics (CFD) commercial software is generally utilized for analyzing complex systems; however, its licensing is expensive. Nowadays, open-source software is a viable substitute for proprietary software. This work presents a CFD analysis of the hydrodynamics of a finned tube using the OpenFOAM and SALOME Meca platforms. The results are compared with experimental data and CFD using the commercial software Fluent, both previously reported in the open literature. This work studies the fluid flow pattern around a tube with six 45-degree-angled fins, and the working fluid, air, is considered as an incompressible fluid. Special attention is paid to calculating the pressure coefficient distribution for the internal and external surfaces of the inclined fins. Open-source platforms allow researchers to visualize how the airflow interacts with the cylinder and the fin surfaces to form a fluid structure, formerly known as a horseshoe vortex system. The findings of the analysis of flow dynamics in the channel between inclined fins and in the wake help explain the results obtained in experimental tests and are relevant for the configuration of a bank of tubes with inclined fins. Full article
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Article
Effect of Plasma Actuator on Velocity and Temperature Profiles of High Aspect Ratio Rectangular Jet
Fluids 2022, 7(8), 281; https://doi.org/10.3390/fluids7080281 - 16 Aug 2022
Viewed by 327
Abstract
The turbulence jet centerline velocity and temperature decay intensely along the centerline flow direction. Thus, improving it could benefit engineering applications, such as air conditioners. However, active flow control techniques with high-aspect-ratio jets, especially for controlling the temperature, have not been widely investigated. [...] Read more.
The turbulence jet centerline velocity and temperature decay intensely along the centerline flow direction. Thus, improving it could benefit engineering applications, such as air conditioners. However, active flow control techniques with high-aspect-ratio jets, especially for controlling the temperature, have not been widely investigated. This paper presents the velocity and temperature performance of a high-aspect-ratio rectangular jet controlled by two dielectric barrier discharge plasma actuators located on the longer sides of the nozzle and controlled by high-voltage and high-frequency pulse-width modulation sinusoidal waves. The scanning method was used to cover 362 cases as combinations of working parameters (modular frequency vs. duty vs. phase difference) for the velocity and temperature performances of the jets. Results show that plasma actuators can control both velocity and temperature distribution with minor input power compared with the rectangular jet’s kinetic energy and heat flux. The velocity increased up to 4% and decreased to 11%, measured at the interest position where x/h = 70 on the centerline. There were a 5% increase and a 4% decrease compared to the temperature-based case. Distinctive velocity and temperature distributions were observed under noteworthy cases, indicating the potential of the actuator to create various flow features without installing new hardware on the flow. Full article
(This article belongs to the Special Issue Turbulent Flow)
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Article
Wind Turbine Blade Design Optimization for Reduced LCoE, Focusing on Design-Driving Loads Due to Storm Conditions
Fluids 2022, 7(8), 280; https://doi.org/10.3390/fluids7080280 - 16 Aug 2022
Viewed by 331
Abstract
Design modifications of the blade inner structure, targeted at reducing design-driving extreme loads due to storm conditions, are assessed in the present paper. Under survival wind speeds, the lack of sufficient aerodynamic damping in the edgewise direction is responsible for excessive stall-induced vibrations [...] Read more.
Design modifications of the blade inner structure, targeted at reducing design-driving extreme loads due to storm conditions, are assessed in the present paper. Under survival wind speeds, the lack of sufficient aerodynamic damping in the edgewise direction is responsible for excessive stall-induced vibrations that usually drive wind turbine blade design loads. The modifications considered in the work are (i) a non-symmetric increase in the thickness of the uniaxial and tri-axial material on the suction and pressure side of the blade sections, (ii) a shift in the spar caps in opposite directions and (iii) the ply-angle re-orientation of the laminates on the spar caps. The first two design interventions aim at increasing the damping of the low-damped edgewise modes in the idling rotor, while the third aims at reducing the fatigue and ultimate loads in normal operation. The design parameters in the problem are determined on the basis of a multidisciplinary optimization (MDAO) process, which minimizes the levelized cost of energy (LCoE). The in-house integrated optimization tool employed in the present study combines: (i) a servo-aero-elastic analysis tool for calculating ultimate loads and power yield, (ii) a cross-sectional analysis tool for obtaining structural properties and stress distributions in the modified blades and (iii) a cost model of the overall wind turbine to evaluate the LCoE. Full article
(This article belongs to the Special Issue Wind and Wave Renewable Energy Systems, Volume II)
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Review
Small-Scale Rotor Aeroacoustics for Drone Propulsion: A Review of Noise Sources and Control Strategies
Fluids 2022, 7(8), 279; https://doi.org/10.3390/fluids7080279 - 15 Aug 2022
Viewed by 383
Abstract
In the last decade, the drone market has grown rapidly for both civil and military purposes. Due to their versatility, the demand for drones is constantly increasing, with several industrial players joining the venture to transfer urban mobility to the air. This has [...] Read more.
In the last decade, the drone market has grown rapidly for both civil and military purposes. Due to their versatility, the demand for drones is constantly increasing, with several industrial players joining the venture to transfer urban mobility to the air. This has exacerbated the problem of noise pollution, mainly due to the relatively lower altitude of these vehicles and the proximity of their routes to extremely densely populated areas. In particular, both the aerodynamic and aeroacoustic optimization of the propulsive system and of its interaction with the airframe are key aspects of unmanned aerial vehicle design that can signify the success or the failure of their mission. The industrial challenge involves finding the best performance in terms of loading, efficiency and weight, and, at the same time, the most silent configuration. For these reasons, research has focused on an initial localization of the noise sources and, on further analysis, of the noise generation mechanism, focusing particularly on directivity and scattering. The aim of the present study is to review the noise source mechanisms and the state-of-the-art control strategies, available in the literature, for its suppression, focusing especially on the fluid-dynamic aspects of low Reynolds numbers of the propulsive system and on the interaction of the propulsive system flow with the airframe. Full article
(This article belongs to the Special Issue Aeroacoustics of Drones)
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Article
The Static Analysis of the Gas Content and the Gas-Dynamic Characteristics at the Second Potash Bed in the Starobinsk Potassium Salts Deposit
Fluids 2022, 7(8), 278; https://doi.org/10.3390/fluids7080278 - 15 Aug 2022
Viewed by 342
Abstract
The use of the new mining technology on the Third potash bed at the Starobinsk potash salt deposit is accompanied by the displacement of the undermined rocks. The displacement is accompanied by the foliation. The gas accumulates in the resulting foliation. The gas [...] Read more.
The use of the new mining technology on the Third potash bed at the Starobinsk potash salt deposit is accompanied by the displacement of the undermined rocks. The displacement is accompanied by the foliation. The gas accumulates in the resulting foliation. The gas accumulations in the roof or the floor rocks can be the cause of a rockburst. A rockburst poses a threat to the miners’ lives, breaks driving and wide equipment and stops the working activity of the mines. Therefore, the study of the underworking effect on the gas content and the gas-dynamic characteristics are relevant problems in mining science. Thus, the purpose of this work is the study of the underworking effect on the gas content and the gas-dynamic characteristics. The τ criterion was used for testing the data samples. At the second stage of the comparative statistical analysis, two hypotheses H0 and H1 were accepted which were later subjected to verification using Student’s t-test. The gas parameters are changed by the camera floor and are not changed by other places. Therefore, the effect of the rock underworking leads to the formation of the additional foliation of the floor and, accordingly, to the free gases’ redistribution along the stratigraphic section and, ultimately, to the significant changes of the free gas content, the starting gas release and the gas pressure. The validity of the effect of the undermining can be the intensive gas releases repeatedly recorded in the process of drilling research holes into the soil with the ejection of a piece of the rock. Full article
(This article belongs to the Special Issue Fluid Flows in Geotechnical Engineering)
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Technical Note
Sediment Transport Patterns of Channels on Tidal Lowland
Fluids 2022, 7(8), 277; https://doi.org/10.3390/fluids7080277 - 15 Aug 2022
Viewed by 421
Abstract
Many reclaimed areas in Indonesia have abandoned swampland or idle land which is attributed to various factors. One of the main factors is the unsuitability of the exiting flow system in this area since the condition of the canals and water structures in [...] Read more.
Many reclaimed areas in Indonesia have abandoned swampland or idle land which is attributed to various factors. One of the main factors is the unsuitability of the exiting flow system in this area since the condition of the canals and water structures in this area has not been rehabilitated for a long time. No study has been carried out to investigate the suitable model for simulating the appropriate criteria for assessment of erosion within the channel on Tidal lowland in Indonesia. This study focuses on the investigation of erosion occurring within the Rural Channel and Main Drainage Channel on Tidal lowland in Palembang, Indonesia which becomes the originality of this manuscript. The erosion was attributed to the accumulation of sediment transport within the channel of the reclaimed tidal delta region Telang I. The results of the research on the P8-13S scheme show that equilibrium on the accumulation of sediment transport in the channel was observed in the Rural Channel and Main Drainage Channel on average ranging from 3,301,859 m3 to 3,349,103 m3 while the average sedimentation ranged from 809,232–898,467 m3. This study is very important in minimizing the possible erosion near riverbank. Full article
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Article
Limits on the Rate of Conversion of Potential to Kinetic Energy in Quasigeostrophic Turbulence
Fluids 2022, 7(8), 276; https://doi.org/10.3390/fluids7080276 - 13 Aug 2022
Viewed by 306
Abstract
Flow configurations that maximize the instantaneous rate of conversion from potential to kinetic energy are sought using a combination of analytical and numerical methods. A hydrostatic model is briefly investigated, but the presence of unrealistic ageostrophic flow configurations renders the results unrealistic. In [...] Read more.
Flow configurations that maximize the instantaneous rate of conversion from potential to kinetic energy are sought using a combination of analytical and numerical methods. A hydrostatic model is briefly investigated, but the presence of unrealistic ageostrophic flow configurations renders the results unrealistic. In the quasigeostrophic (QG) model, flow configurations that locally optimize the conversion rate are found, but it remains unclear if these flow configurations produce the global maximum conversion rate. The difficulty is associated with the fact that in the QG model, the vertical velocity is a quadratic function of the QG streamfunction, which renders the conversion rate a cubic function of the QG streamfunction. For these locally maximal conversion rates, the rate of conversion depends on the horizontal length scale of the flow: for scales larger than the deformation radius, the maximal rates are small and decrease as the horizontal scale increases; for scales smaller than the deformation radius, the maximal conversion rate rises until it becomes comparable to the maximal rate at which potential energy can be extracted from the mean flow. Full article
(This article belongs to the Collection Geophysical Fluid Dynamics)
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Article
Phase Convergence and Crest Enhancement of Modulated Wave Trains
Fluids 2022, 7(8), 275; https://doi.org/10.3390/fluids7080275 - 11 Aug 2022
Viewed by 440
Abstract
The Akhmediev breather (AB) solution of the nonlinear Schrödinger equation (NLSE) shows that the maximum crest height of modulated wave trains reaches triple the initial amplitude as a consequence of nonlinear long-term evolution. Several fully nonlinear numerical studies have indicated that the amplification [...] Read more.
The Akhmediev breather (AB) solution of the nonlinear Schrödinger equation (NLSE) shows that the maximum crest height of modulated wave trains reaches triple the initial amplitude as a consequence of nonlinear long-term evolution. Several fully nonlinear numerical studies have indicated that the amplification can exceed 3, but its physical mechanism has not been clarified. This study shows that spectral broadening, bound-wave production, and phase convergence are essential to crest enhancement beyond the AB solution. The free-wave spectrum of modulated wave trains broadens owing to nonlinear quasi-resonant interaction. This enhances bound-wave production at high wavenumbers. The phases of all the wave components nearly coincide at peak modulation and enhance amplification. This study found that the phase convergence observed in linear-focusing waves can also occur due to nonlinear wave evolution. These findings are obtained by numerically investigating the modulated wave trains using the higher-order spectral method (HOSM) up to the fifth order, which allows investigations of nonlinearity and spectral bandwidth beyond the NLSE framework. Moreover, the crest enhancement is confirmed through a tank experiment wherein waves are generated in the transition region from non-breaking to breaking. Owing to strong nonlinearity, the maximum crest height observed in the tank begins to exceed the HOSM prediction at an initial wave steepness of 0.10. Full article
(This article belongs to the Special Issue Nonlinear Wave Hydrodynamics, Volume II)
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Article
Probability Distribution of Extreme Events in a Baroclinic Wave Laboratory Experiment
Fluids 2022, 7(8), 274; https://doi.org/10.3390/fluids7080274 - 11 Aug 2022
Viewed by 329
Abstract
Atmospheric westerly jet streams are driven by temperature differences between low and high latitudes and the rotation of the Earth. Meandering jet streams and propagating Rossby waves are responsible for the variable weather in the mid-latitudes. Moreover, extreme weather events such as heat [...] Read more.
Atmospheric westerly jet streams are driven by temperature differences between low and high latitudes and the rotation of the Earth. Meandering jet streams and propagating Rossby waves are responsible for the variable weather in the mid-latitudes. Moreover, extreme weather events such as heat waves and cold spells are part of the jet stream dynamics. For many years, a simple analog in the form of a simplified laboratory experiment, the differentially heated rotating annulus, has provided insight into the dynamics of the meandering jet stream. In the present study, probability density distributions of extreme events from a long-term laboratory experiment are studied and compared to the atmospheric probability density distributions. Empirical distributions of extreme value monthly block data are derived for the experimental and atmospheric cases. Generalized extreme value distributions are adjusted to the empirical distributions, and the distribution parameters are compared. Good agreement was found, but the distributions of the experimental data showed a shift toward larger extreme values, and some explanations for this shift are suggested. The results indicate that the laboratory model might be a useful tool for investigating changes in extreme event distributions due to climate change. In the laboratory context, the change can be modeled by an increase in total temperature accompanied by a reduction in the radial heat contrast. Full article
(This article belongs to the Collection Geophysical Fluid Dynamics)
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Article
A 3D CFD-Based Workflow for Analyses of a Wide Range of Flow and Heat Transfer Conditions in Air Gaps of Electric Machines
Fluids 2022, 7(8), 273; https://doi.org/10.3390/fluids7080273 - 10 Aug 2022
Viewed by 415
Abstract
Increasing power densities of electric machines in e-vehicles in addition to the resulting quest for enhanced cooling concepts are bringing forward the importance of defining adequate heat transfer correlations in air gaps. This is a highly challenging topic, as there exist no generally [...] Read more.
Increasing power densities of electric machines in e-vehicles in addition to the resulting quest for enhanced cooling concepts are bringing forward the importance of defining adequate heat transfer correlations in air gaps. This is a highly challenging topic, as there exist no generally applicable flow and heat transfer phenomena descriptions for air gaps due to their highly variable geometrical properties and operating conditions. As an answer to this challenge, this paper presents a workflow that defines an adequate 3D CFD model for an arbitrary air-gap design that includes its system-dependent boundary conditions. The workflow is built on the recognition of underlying air-gap flow phenomena, which are used to steer the subsequent design of the 3D CFD model in a systematic step-by-step manner. Consequently, the complexity of the 3D CFD model gradually increases to the point where it provides an adequate flow and heat transfer description. Validation of the workflow is presented for a wide range of air-gap designs and flow conditions. It is demonstrated that the 3D CFD models obtained with the workflow match the experimentally obtained data from various flow cases that have been documented in the literature. Considerable optimization of computational costs, offering potentially an order-of-magnitude reduction in computational time, is achieved as a result of computational domain span optimization and transient simulations being applied only when required. The validation confirms that this workflow facilitates construction of valid 3D CFD models without the prior knowledge of flow and heat transfer phenomena in a specific air gap. This workflow thus provides a reliable and computationally efficient tool for valorization of convective heat transfer, and opens up prospects for time- and cost-efficient optimizations of electric machines’ cooling system designs. Full article
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Article
Comparison of FLACS and BASiL Model for Ro-Pax Ferry LNG Bunkering Leak Analysis
Fluids 2022, 7(8), 272; https://doi.org/10.3390/fluids7080272 - 08 Aug 2022
Viewed by 396
Abstract
Performing liquefied natural gas (LNG) bunkering involves the risk of accidental leakage. When released from containment, LNG rapidly vaporizes into flammable natural gas and could lead to flash fire and explosion. Hence, LNG bunkering needs to take place in an area without an [...] Read more.
Performing liquefied natural gas (LNG) bunkering involves the risk of accidental leakage. When released from containment, LNG rapidly vaporizes into flammable natural gas and could lead to flash fire and explosion. Hence, LNG bunkering needs to take place in an area without an ignition source called a safety zone. This study compares the safety zone estimated by the Bunkering Area Safety Information for LNG (BASiL) model with that of the computational fluid dynamic (CFD) software FLACS, for Ro-Pax ferry bunkering. Horizontal leaks covering different wind speeds in eight wind directions were compared between the two models. Additionally, a grid refinement study was performed systematically to quantify the discretization error uncertainty in the CFD. Of 24 leak cases, FLACS and the BASiL model results agreed on 18 cases. In three cases validation was inconclusive due to the CFD error uncertainty. The BASiL model underestimated the safety zone distance in three cases compared with FLACS. Future work would be to perform a higher grid refinement study to confirm inconclusive comparison and examine ways to reduce gas dispersion spread for the worst result. Full article
(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering)
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Article
Dynamical Filtering Highlights the Seasonality of Surface-Balanced Motions at Diurnal Scales in the Eastern Boundary Currents
Fluids 2022, 7(8), 271; https://doi.org/10.3390/fluids7080271 - 08 Aug 2022
Viewed by 489
Abstract
Balanced motions (BM) and internal gravity waves (IGW) account for most of the kinetic energy budget and capture most of the vertical velocity in the ocean. However, estimating the contribution of BM to both issues at time scales of less than a day [...] Read more.
Balanced motions (BM) and internal gravity waves (IGW) account for most of the kinetic energy budget and capture most of the vertical velocity in the ocean. However, estimating the contribution of BM to both issues at time scales of less than a day is a challenge because BM are obscured by IGW. To study the BM regime, we outlined the implementation of a dynamical filter that separates both classes of motion. This study used a high-resolution global simulation to analyze the Eastern Boundary Currents during the winter and summer months. Our results confirm the feasibility of recovering BM dynamics at short time scales, emphasizing the diurnal cycle in winter and its dampening in summer due to local stratification that prevents large vertical excursion of the surface boundary layer. Our filter opens up new possibilities for more accurate estimation of the vertical exchanges of any tracers at any vertical level in the water column. Moreover, it could be a valuable tool for studies focused on wave–turbulence interactions in ocean simulations. Full article
(This article belongs to the Special Issue Boundary Layer Processes in Geophysical/Environmental Flows)
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Article
Taichi-LBM3D: A Single-Phase and Multiphase Lattice Boltzmann Solver on Cross-Platform Multicore CPU/GPUs
Fluids 2022, 7(8), 270; https://doi.org/10.3390/fluids7080270 - 08 Aug 2022
Viewed by 669
Abstract
The success of the lattice Boltzmann method requires efficient parallel programming and computing power. Here, we present a new lattice Boltzmann solver implemented in Taichi programming language, named Taichi-LBM3D. It can be employed on cross-platform shared-memory many-core CPUs or massively parallel GPUs (OpenGL [...] Read more.
The success of the lattice Boltzmann method requires efficient parallel programming and computing power. Here, we present a new lattice Boltzmann solver implemented in Taichi programming language, named Taichi-LBM3D. It can be employed on cross-platform shared-memory many-core CPUs or massively parallel GPUs (OpenGL and CUDA). Taichi-LBM3D includes the single- and two-phase porous medium flow simulation with a D3Q19 lattice model, Multi-Relaxation-Time (MRT) collision scheme and sparse data storage. It is open source, intuitive to understand, and easily extensible for scientists and researchers. Full article
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Article
Image-Based Numerical Investigation in an Impending Abdominal Aneurysm Rupture
Fluids 2022, 7(8), 269; https://doi.org/10.3390/fluids7080269 - 05 Aug 2022
Viewed by 374
Abstract
Blood flow dynamics plays a crucial role in the growth and rupture of abdominal aortic aneurysms. The aim of this study was to analyze the possibility of predicting aneurysmal rupture by numerical investigations based on diagnostic images. The blood flow dynamics was analyzed [...] Read more.
Blood flow dynamics plays a crucial role in the growth and rupture of abdominal aortic aneurysms. The aim of this study was to analyze the possibility of predicting aneurysmal rupture by numerical investigations based on diagnostic images. The blood flow dynamics was analyzed in a patient-specific abdominal aortic aneurysm, reconstructed from CT images of an aneurysm while it was rupturing. The patient-specific geometry was virtually repaired in order to obtain a non-ruptured model representative of the geometry immediately preceding the rupture. To reproduce physiological conditions, numerical simulations were performed under pulsatile flow conditions, and blood was modelled as a non-Newtonian fluid, using the Carreau rheological model. Hemodynamic parameters that influence the rupture of the aneurysm were investigated, and their possible association with vascular disease was discussed. The results of the numerical simulations indicated regions of slow recirculation and low values of Time Averaged Wall Shear Stress (TAWSS) in the region of rupture. Unlike literature results, a high Oscillatory Shear Index (OSI) was not clearly found in this region. Nevertheless, just in the region where the rupture will occur, high values of Endothelial Cell Activation Potential index (ECAP) were found. This index is therefore extremely significant for assessing the vulnerability of the aortic wall and locating the critical rupture region. Full article
(This article belongs to the Special Issue Image-Based Computational and Experimental Biomedical Flows)
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Article
Barite-Free Muds for Drilling-in the Formations with Abnormally High Pressure
Fluids 2022, 7(8), 268; https://doi.org/10.3390/fluids7080268 - 04 Aug 2022
Viewed by 455
Abstract
This paper discusses problems associated with water-based drilling fluids used for drilling formations with abnormally high pressure. The available solutions are suitable for a narrow range of applications, especially when weighted muds should be used. This paper reviews the experience of searching and [...] Read more.
This paper discusses problems associated with water-based drilling fluids used for drilling formations with abnormally high pressure. The available solutions are suitable for a narrow range of applications, especially when weighted muds should be used. This paper reviews the experience of searching and developing a new type of drilling mud based on saturated brines. With the referenced papers as the basis, the authors developed compositions of such brine-based drilling muds. A distinctive feature of the considered compositions is the absence of barite, which is often used as a weighting agent. The paper presents a methodology for creating and investigating the proposed drilling fluids. The rheological properties and thermal stability of the muds at various temperatures were studied. The results show that proposed drilling fluids can be efficiently used for drilling formations with abnormally high pressure. It is assumed that the developed muds have greater versatility than analogues. Full article
(This article belongs to the Special Issue Fluid Flows in Geotechnical Engineering)
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Article
Comparison of Two Hydrological Models, HEC-HMS and SWAT in Runoff Estimation: Application to Huai Bang Sai Tropical Watershed, Thailand
Fluids 2022, 7(8), 267; https://doi.org/10.3390/fluids7080267 - 04 Aug 2022
Viewed by 555
Abstract
In the present study, the streamflow simulation capacities between the Soil and Water Assessment Tool (SWAT) and the Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS) were compared for the Huai Bang Sai (HBS) watershed in northeastern Thailand. During calibration (2007–2010) and validation (2011–2014), the [...] Read more.
In the present study, the streamflow simulation capacities between the Soil and Water Assessment Tool (SWAT) and the Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS) were compared for the Huai Bang Sai (HBS) watershed in northeastern Thailand. During calibration (2007–2010) and validation (2011–2014), the SWAT model demonstrated a Coefficient of Determination (R2) and a Nash Sutcliffe Efficiency (NSE) of 0.83 and 0.82, and 0.78 and 0.77, respectively. During the same periods, the HEC-HMS model demonstrated values of 0.80 and 0.79, and 0.84 and 0.82. The exceedance probabilities at 10%, 40%, and 90% were 144.5, 14.5, and 0.9 mm in the flow duration curves (FDCs) obtained for observed flow. From the HEC-HMS and SWAT models, these indices yielded 109.0, 15.0, and 0.02 mm, and 123.5, 16.95, and 0.02 mm. These results inferred those high flows were captured well by the SWAT model, while medium flows were captured well by the HEC-HMS model. It is noteworthy that the low flows were accurately simulated by both models. Furthermore, dry and wet seasonal flows were simulated reasonably well by the SWAT model with slight under-predictions of 2.12% and 13.52% compared to the observed values. The HEC-HMS model under-predicted the dry and wet seasonal flows by 10.76% and 18.54% compared to observed flows. The results of the present study will provide valuable recommendations for the stakeholders of the HBS watershed to improve water usage policies. In addition, the present study will be helpful to select the most appropriate hydrologic model for humid tropical watersheds in Thailand and elsewhere in the world. Full article
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Article
Serre-Green-Naghdi Dynamics under the Action of the Jeffreys’ Wind-Wave Interaction
Fluids 2022, 7(8), 266; https://doi.org/10.3390/fluids7080266 - 04 Aug 2022
Viewed by 321
Abstract
We derive the anti dissipative Serre-Green-Naghdi (SGN) equations in the context of nonlinear dynamics of surface water waves under wind forcing, in finite depth. The anti-dissipation occurs du to the continuos transfer of wind energy to water surface wave. We find the solitary [...] Read more.
We derive the anti dissipative Serre-Green-Naghdi (SGN) equations in the context of nonlinear dynamics of surface water waves under wind forcing, in finite depth. The anti-dissipation occurs du to the continuos transfer of wind energy to water surface wave. We find the solitary wave solution of the system, with an increasing amplitude under the wind action. This leads to the blow-up of surface wave in finite time for infinitely large asymptotic space. This dispersive, anti-dissipative and fully nonlinear phenomenon is equivalent to the linear instability at infinite time. The theoretical blow-up time is calculated based on real experimental data. Naturally, the wave breaking takes place before the blow-up time. However, the amplitude’s growth resulting in the blow-up could be observed. Our results show that, based on the particular type of wind-wave tank data used in this paper, for h=0.14m, the amplitude growth rate is of order 0.1 which experimentally, is at the measurability limit. But we think that by gradually increasing the wind speed U10, up to 10 m/s, it is possible to have the experimental confirmation of the present theory in existing experimental facilities. Full article
(This article belongs to the Special Issue Nonlinear Wave Hydrodynamics, Volume II)
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Article
Conformal Satellite Tanks—Printed Plastics and Fluid Interactions
Fluids 2022, 7(8), 265; https://doi.org/10.3390/fluids7080265 - 03 Aug 2022
Viewed by 441
Abstract
Initial experiments in the design process of a novel 3D printed conformal propellant tank for small satellites are conducted. Contact angle measurements of static colored water droplets on printed PLA, PMMA, and PETG sample plates are performed. Additionally, the optical characteristics of transparent [...] Read more.
Initial experiments in the design process of a novel 3D printed conformal propellant tank for small satellites are conducted. Contact angle measurements of static colored water droplets on printed PLA, PMMA, and PETG sample plates are performed. Additionally, the optical characteristics of transparent printed tanks of two to five millimeter wall thickness and with three illumination setups are evaluated. The results indicate that the influence of fluorescein as a colorant in the useful concentration only slightly affects the contact angle measurements. The combination of well scattered UV light and use the smallest possible wall thicknesses, on the order of two millimeters, made out of PLA provides the best visibility. These findings enable the development of a printed conformal tank design with an integrated PMD. Full article
(This article belongs to the Special Issue Fluids in Space)
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Article
On Energy Redistribution for the Nonlinear Parabolized Stability Equations Method
Fluids 2022, 7(8), 264; https://doi.org/10.3390/fluids7080264 - 03 Aug 2022
Viewed by 387
Abstract
We identify and quantify a seemingly overlook mechanism for energy transfer between adjacent frequency disturbances in the Nonlinear Parabolized Stability Equations method. Physically, this energy transfer results from the finite-bandwidth nature of actual disturbance spectrums versus the common numerical assumption of a discrete [...] Read more.
We identify and quantify a seemingly overlook mechanism for energy transfer between adjacent frequency disturbances in the Nonlinear Parabolized Stability Equations method. Physically, this energy transfer results from the finite-bandwidth nature of actual disturbance spectrums versus the common numerical assumption of a discrete spectrum representation. Both quiet wind tunnel and flight conditions are considered and it is found that, for Mack’s second-mode instability, the mechanism is most significant in the 0.1–1% disturbance amplitude range (based on normalized pressure) and is responsible for a 15–30% increase in predicted disturbance amplitude. Full article
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Article
Analysis of Temperature Field in the Dielectrophoresis-Based Microfluidic Cell Separation Device
Fluids 2022, 7(8), 263; https://doi.org/10.3390/fluids7080263 - 02 Aug 2022
Viewed by 348
Abstract
Cell separation techniques based on dielectrophoresis are of high interest as an effective method of performing cell separation non-invasively on cells. However, dielectrophoresis devices have the problem that cells in the device are exposed to a high-temperature environment due to the generation of [...] Read more.
Cell separation techniques based on dielectrophoresis are of high interest as an effective method of performing cell separation non-invasively on cells. However, dielectrophoresis devices have the problem that cells in the device are exposed to a high-temperature environment due to the generation of Joule heat caused by high-voltage application and dielectric-loss heat when the applied voltage is AC voltage. There is concern that the heat generated in the device may affect cell viability, cell cycle and apoptosis induction. In this study, the temperature field inside the dielectrophoretic cell separation device was experimentally and numerically investigated. The temperature rise at the bottom of the flow channel in the device was measured using the LIF method, and the thermofluidal behavior of the device was numerically simulated by adopting a heat generation model that takes the Joule and dielectric-loss heating into account in the energy equation. The temperature rise in the device was evaluated and the effect of the heat generation on cells in the device is discussed. Full article
(This article belongs to the Section Heat and Mass transfer)
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Article
Suitability of the VOF Approach to Model an Electrogenerated Bubble with Marangoni Micro-Convection Flow
Fluids 2022, 7(8), 262; https://doi.org/10.3390/fluids7080262 - 02 Aug 2022
Viewed by 497
Abstract
When a hydrogen or oxygen bubble is created on the surface of an electrode, a micro-convective vortex flow due to the Marangoni effect is generated at the bottom of the bubble in contact with the electrode. In order to study such a phenomenon [...] Read more.
When a hydrogen or oxygen bubble is created on the surface of an electrode, a micro-convective vortex flow due to the Marangoni effect is generated at the bottom of the bubble in contact with the electrode. In order to study such a phenomenon numerically, it is necessary to be able to simulate the surface tension variations along with a liquid-gas interface, to integrate the mass transfer across the interface from the dissolved species present in the electrolyte to the gas phase, and to take into account the moving contact line. Eulerian methods seem to have the potential to solve this modeling. However, the use of the continuous surface force (CSF) model in the volume of fluid (VOF) framework is known to introduce non-physical velocities, called spurious currents. This paper presents an alternative model based on the height function (HF) approach. The use of this method limits spurious currents and makes the VOF methodology suitable for studying Marangoni currents along with the interface of an electrogenerated bubble. Full article
(This article belongs to the Special Issue Dynamics of Droplets and Bubbles)
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Article
Inclusive Hyper- to Dilute-Concentrated Suspended Sediment Transport Study Using Modified Rouse Model: Parametrized Power-Linear Coupled Approach Using Machine Learning
Fluids 2022, 7(8), 261; https://doi.org/10.3390/fluids7080261 - 30 Jul 2022
Viewed by 515
Abstract
The transfer of suspended sediment can range widely from being diluted to being hyper-concentrated, depending on the local flow and ground conditions. Using the Rouse model and the Kundu and Ghoshal (2017) model, it is possible to look at the sediment distribution for [...] Read more.
The transfer of suspended sediment can range widely from being diluted to being hyper-concentrated, depending on the local flow and ground conditions. Using the Rouse model and the Kundu and Ghoshal (2017) model, it is possible to look at the sediment distribution for a range of hyper-concentrated and diluted flows. According to the Kundu and Ghoshal model, the sediment flow follows a linear profile for the hyper-concentrated flow regime and a power law applies for the dilute concentrated flow regime. This paper describes these models and how the Kundu and Ghoshal parameters (linear-law coefficients and power-law coefficients) are dependent on sediment flow parameters using machine-learning techniques. The machine-learning models used are XGboost Classifier, Linear Regressor (Ridge), Linear Regressor (Bayesian), K Nearest Neighbours, Decision Tree Regressor, and Support Vector Machines (Regressor). The models were implemented on Google Colab and the models have been applied to determine the relationship between every Kundu and Ghoshal parameter with each sediment flow parameter (mean concentration, Rouse number, and size parameter) for both a linear profile and a power-law profile. The models correctly calculated the suspended sediment profile for a range of flow conditions (0.268 mmd502.29 mm,  0.00105gmm3particle density2.65gmm3, 0.197mmsvs96mms,  7.16mmsu*63.3mms,  0.00042c¯0.54), including a range of Rouse numbers (0.0076P23.5). The models showed particularly good accuracy for testing at low and extremely high concentrations for type I to III profiles. Full article
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Article
Mechanisms for CH4/CO2 Swapping in Natural Sediments
Fluids 2022, 7(8), 260; https://doi.org/10.3390/fluids7080260 - 30 Jul 2022
Cited by 1 | Viewed by 343
Abstract
Production of natural gas from hydrates involves multiple complex competing phase transitions, which are rarely analyzed thermodynamically. Hydrates in sediments are typically examined in terms of the local conditions of indirect thermodynamic variables, such as temperature and pressure. This can be very misleading [...] Read more.
Production of natural gas from hydrates involves multiple complex competing phase transitions, which are rarely analyzed thermodynamically. Hydrates in sediments are typically examined in terms of the local conditions of indirect thermodynamic variables, such as temperature and pressure. This can be very misleading in the evaluation of hydrate production methods. Any hydrate production method is governed by the thermodynamic laws. The combined first and second laws determine phase distributions in terms of Gibbs free energy minimum. This minimum is constrained by the first law of thermodynamics through enthalpy. The entropy changes during a specific action for hydrate production need to be sufficient to overcome the bottlenecks of breaking hydrogen bonds. In this work, I point out some important drawbacks of the pressure reduction method. The main focus is, however, on combined safe long-term storage of CO2 and release of CH4. It is demonstrated that CO2 hydrate is more stable than CH4 hydrate, in contrast to interpretations of pressure temperature diagrams, which are frequently used in discussions. Pressure and temperature are independent thermodynamic variables and merely determine at which conditions of these independent variables specific hydrates can exist. Gibbs free energy is the dependent thermodynamic variable that determines the level of phase stability. The first law determines the need for supply of thermodynamic driving forces for hydrate dissociation. Unlike in conventional analysis, it is pointed out that chemical work is also a driving force in the pressure reduction method. The release of heat from the formation of a new CO2 hydrate from injection gas is the primary source for CH4 hydrate dissociation in the CO2 method. Increased salinity due to consumption of pure water for new hydrate could potentially also assist in dissociation of in situ CH4 hydrate. Based on thermodynamic calculations, it is argued that this effect may not be significant. Full article
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Article
Stability Analysis of Concrete Block Anchor on Steep-Slope Floating Breakwater
Fluids 2022, 7(8), 259; https://doi.org/10.3390/fluids7080259 - 29 Jul 2022
Viewed by 319
Abstract
The floating breakwater is a protective structure that can absorb waves and can be used effectively in coastal areas with moderate wave environmental conditions. The stability of the floating breakwater is affected by the tension of the mooring line and the weight of [...] Read more.
The floating breakwater is a protective structure that can absorb waves and can be used effectively in coastal areas with moderate wave environmental conditions. The stability of the floating breakwater is affected by the tension of the mooring line and the weight of the anchor. This research was conducted experimentally with a model scale of 1:10 on a floating breakwater with mooring systems and concrete anchor blocks with three types of configurations. The experiment was carried out on irregular waves with the following variations: wave height and period, mooring angle, structure width, and anchor weight. The results of this study indicate that at a wave steepness of 0.02–0.025 floating breakwater, which is installed with a mooring angle of 45 deg, configuration 3 has the largest stability parameter among other configurations. However, if the structure is installed at a mooring angle of 90 deg and cross, configurations 2 and 3 have almost the same stability. The test results also show that the relative width will affect the stability parameters. Configuration 3 (B = 30 cm) has the largest stability-parameter value among other configurations (B = 10 cm and 20 cm). Full article
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Article
Experimental Investigation on the Impact of Dam-Break Induced Surges on a Vertical Wall
Fluids 2022, 7(8), 258; https://doi.org/10.3390/fluids7080258 - 29 Jul 2022
Viewed by 330
Abstract
This paper presents the results of an experimental investigation on the impact of dam-break-induced surges on a vertical wall. The instantaneous surge height and dynamic pressure on a vertical wall were measured for surges with different reservoir depths of H = 200 mm, [...] Read more.
This paper presents the results of an experimental investigation on the impact of dam-break-induced surges on a vertical wall. The instantaneous surge height and dynamic pressure on a vertical wall were measured for surges with different reservoir depths of H = 200 mm, 250 mm, and 300 mm. The time-histories of horizontal pressure on the wall were measured using the miniaturized pressure transducers, and the surge heights were recorded with an ultrasonic sensor. The relationships between dynamic pressure and surge height on the vertical wall and during the impact were obtained from recorded raw data. The experimental results highlighted detailed processes on the variation of impact pressure during the surge propagation, impact on the wall, runup, falling, and breakup of the turbulent flow. The time-histories of surge height and dynamic pressure were analyzed, and the results were compared with the hydrostatic pressure on the wall to study wave breaking mechanism of tsunami waves on the wall. Dynamic pressures at the impact instant were found to be approximately three times the corresponding static pressure in the bed, in good agreement with previous research Moreover, the maximum surge runup heights on the wall were between 2.1 and 2.3 times the corresponding initial reservoir depths. The vertical distributions of impact pressure were divided into two hydrodynamic regimes. Based on the impact duration, the first regime occurred less than 0.1 s after the impact with highly non-linear pressure distributions, and the second regime showed a semi-hydrostatic pressure distribution from 0.5 s to 0.7 s. The results presented in this study are suitable for the design of coastal infrastructures and can be used to validate numerical models. Full article
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Article
Performance of a Helical Microswimmer Traversing a Discrete Viscoelastic Network with Dynamic Remodeling
Fluids 2022, 7(8), 257; https://doi.org/10.3390/fluids7080257 - 29 Jul 2022
Viewed by 362
Abstract
Microorganisms often navigate a complex environment composed of a viscous fluid with suspended microstructures such as elastic polymers and filamentous networks. These microstructures can have similar length scales to the microorganisms, leading to complex swimming dynamics. Some microorganisms secrete enzymes that dynamically change [...] Read more.
Microorganisms often navigate a complex environment composed of a viscous fluid with suspended microstructures such as elastic polymers and filamentous networks. These microstructures can have similar length scales to the microorganisms, leading to complex swimming dynamics. Some microorganisms secrete enzymes that dynamically change the elastic properties of the viscoelastic networks through which they move. In addition to biological organisms, microrobots have been engineered with the goals of mucin gel penetration or dissolving blood clots. In order to gain insight into the coupling between swimming performance and network remodeling, we used a regularized Stokeslet boundary element method to compute the motion of a microswimmer consisting of a rotating spherical body and counter-rotating helical flagellum. The viscoelastic network is represented by a network of points connected by virtual elastic linkages immersed in a viscous fluid. Here, we model the enzymatic dissolution of the network by bacteria or microrobots by dynamically breaking elastic linkages when the cell body of the swimmer falls within a given distance from the link. We investigate the swimming performance of the microbes as they penetrate and move through networks of different material properties, and also examine the effect of network remodeling. Full article
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Article
Examination of Haines Jump in Microfluidic Experiments via Evolution Graphs and Interface Tracking
Fluids 2022, 7(8), 256; https://doi.org/10.3390/fluids7080256 - 29 Jul 2022
Viewed by 361
Abstract
This work examines a type of rapid pore-filling event in multiphase flow through permeable media that is better known as Haines Jump. While existing microfluidic experiments on Haines Jump mostly seek to maintain quasi-steady states through very low bulk flow rates over long [...] Read more.
This work examines a type of rapid pore-filling event in multiphase flow through permeable media that is better known as Haines Jump. While existing microfluidic experiments on Haines Jump mostly seek to maintain quasi-steady states through very low bulk flow rates over long periods of time, this work explores the combined use of a highly structured microscale transport network, high-speed fluorescent microscopy, displacement front segmentation algorithms, and a tracking algorithm to build evolution graphs that track displacement fronts as they evolve through high-speed video recording. The resulting evolution graph allows the segmentation of a high-speed recording in both space and time, potentially facilitating topology-cognitive computation on the transport network. Occurrences of Haines Jump are identified in the microfluidic displacement experiments and their significance in bulk flow rates is qualitatively analyzed. The bulk flow rate has little effect on the significance of Haines Jump during merging and splitting, but large bulk flow rates may obscure small bursts at the narrowest part of the throat. Full article
(This article belongs to the Collection Advances in Flow of Multiphase Fluids and Granular Materials)
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Article
Turbulence Modulation by Slender Fibers
Fluids 2022, 7(8), 255; https://doi.org/10.3390/fluids7080255 - 28 Jul 2022
Viewed by 341
Abstract
In this paper, we numerically investigate the turbulence modulation produced by long flexible fibres in channel flow. The simulations are based on an Euler–Lagrangian approach, where fibres are modelled as chains of constrained, sub-Kolmogorov rods. A novel algorithm is deployed to make the [...] Read more.
In this paper, we numerically investigate the turbulence modulation produced by long flexible fibres in channel flow. The simulations are based on an Euler–Lagrangian approach, where fibres are modelled as chains of constrained, sub-Kolmogorov rods. A novel algorithm is deployed to make the resolution of dispersed systems of constraint equations, which represent the fibres, compatible with a state-of-the-art, Graphics Processing Units-accelerated flow-solver for direct numerical simulations in the two-way coupling regime on High Performance Computing architectures. Two-way coupling is accounted for using the Exact Regularized Point Particle method, which allows to calculate the disturbance generated by the fibers on the flow considering progressively refined grids, down to a quasi-viscous length-scale. The bending stiffness of the fibers is also modelled, while collisions are neglected. Results of fluid velocity statistics for friction Reynolds number of the flow Reτ=150 and fibers with Stokes number St = 0.01 (nearly tracers) and 10 (inertial) are presented, with special regard to turbulence modulation and its dependence on fiber inertia and volume fraction (equal to ϕ=2.12·105 and 2.12·104). The non-Newtonian stresses determined by the carried phase are also displayed, determined by long and slender fibers with fixed aspect ratio λtot=200, which extend up to the inertial range of the turbulent flow. Full article
(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)
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