Journal Description
Fluids
Fluids
is an international, peer-reviewed, open access journal on all aspects of fluids, published monthly online by MDPI. The Portuguese Society of Rheology (SPR) is affiliated with Fluids and its members receive discounts on the article processing charges.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, ESCI (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
- Journal Rank: CiteScore - Q2 (Mechanical Engineering)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 20.7 days after submission; acceptance to publication is undertaken in 3.6 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Impact Factor:
1.9 (2022);
5-Year Impact Factor:
1.8 (2022)
Latest Articles
Experimental Analysis of the Effect of Limescale on the Wettability of Indirect Evaporative Cooling System Plates
Fluids 2024, 9(3), 76; https://doi.org/10.3390/fluids9030076 - 17 Mar 2024
Abstract
Indirect evaporative cooling systems have attracted much interest in recent years as they guarantee good cooling effectiveness, with lower energy demand with respect to traditional systems, thus helping to address the issue of climate change. Many studies have shown that an increase in
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Indirect evaporative cooling systems have attracted much interest in recent years as they guarantee good cooling effectiveness, with lower energy demand with respect to traditional systems, thus helping to address the issue of climate change. Many studies have shown that an increase in the wettability of recuperator plates results in an improvement in the system performance. However, if the water injected into the system comes from the city water supply, it will contain calcium carbonate residuals, which will form limescale layers on the plates, thus possibly changing their wetting behavior. Therefore, the wettability of three surfaces (an aluminum uncoated surface, AL, a standard epoxy coating, STD, and a hydrophilic lacquer, HPHI) was analyzed in the presence of limescale formations, and compared with that obtained in a previous study for corresponding clean surfaces. The results showed that the HPHI contact angle was reduced in the presence of limescale (median: 50°), that for STD was slightly increased (median: 81°), and that for AL was again reduced (median: 75°). Consequently, HPHI was confirmed to be the most wettable surface in both clean and limescale conditions. Finally, an analysis was undertaken evaluating the spreading factor and the reversible work of adhesion, which were in good agreement with the qualitative visual observations of the plates covered with limescale.
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(This article belongs to the Special Issue Fluids and Surfaces, 2nd Edition)
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The Effect of Varying the Air Flow in a Solar Collector on the Quality of Arabica Coffee Beans
by
Parulian Siagian, Farel Hasiholan Napitupulu, Himsar Ambarita, Hendrik Voice Sihombing, Yogie Probo Sibagariang and Horas Sotardodo Siagian
Fluids 2024, 9(3), 75; https://doi.org/10.3390/fluids9030075 - 15 Mar 2024
Abstract
Agricultural commodity drying technology aims to maintain and improve the quality of agricultural products. Coffee quality is important for the welfare of coffee farmers, and drying technology plays an important role in determining the quality of coffee. Various drying models can be applied,
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Agricultural commodity drying technology aims to maintain and improve the quality of agricultural products. Coffee quality is important for the welfare of coffee farmers, and drying technology plays an important role in determining the quality of coffee. Various drying models can be applied, including the traditional model that is still applied today: drying directly under solar radiation. One drying technology that can accelerate the drying time is varying the air velocity in the drying chamber. In this study, the air velocity was varied by 1–3 m/s over coffee bean samples with an initial weight of 1500 g that were dried in parallel simultaneously. The time required was 25 h, with a maximum radiation of 586.9 w/m2 and total solar energy over 3 days of 16.6 MJ/m2. It was found that good quality coffee was achieved using drying box 1, with a drying air velocity of 1.0 m/s, with which a final mass of 732.24 g was obtained with coffee moisture content of 12.0%, protein content of 11.7%, carbohydrate content of 21.7%, and free fatty acid content of 0.05%. Higher air velocities resulted in almost the same protein and carbohydrate content, as well as a fatty acid content of less than 0.1%, but a higher moisture content.
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(This article belongs to the Topic Applied Heat Transfer)
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Open AccessArticle
Fly by Feel: Flow Event Detection via Bioinspired Wind-Hairs
by
Alecsandra Court and Christoph Bruecker
Fluids 2024, 9(3), 74; https://doi.org/10.3390/fluids9030074 - 15 Mar 2024
Abstract
Bio-inspired flexible pillar-like wind-hairs show promise for the future of flying by feel by detecting critical flow events on an aerofoil during flight. To be able to characterise specific flow disturbances from the response of such sensors, quantitative PIV measurements of such flow-disturbance
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Bio-inspired flexible pillar-like wind-hairs show promise for the future of flying by feel by detecting critical flow events on an aerofoil during flight. To be able to characterise specific flow disturbances from the response of such sensors, quantitative PIV measurements of such flow-disturbance patterns were compared with sensor outputs under controlled conditions. Experiments were performed in a flow channel with an aerofoil equipped with a 2D array of such sensors when in uniform inflow conditions compared to when a well-defined gust was introduced upstream and was passing by. The gust was generated through the sudden deployment of a row of flaps on the suction side of a symmetric wing that was placed upstream of the aerofoil with the sensors. The resulting flow disturbance generated a starting vortex with two legs, which resembled a horseshoe-type vortex shed into the wake. Under the same tunnel conditions, PIV measurements were taken downstream of the gust generator to characterise the starting vortex, while further measurements were taken with the sensing pillars on the aerofoil in the same location. The disturbance pattern was compared to the pillar response to demonstrate the potential of flow-sensing pillars. It was found that the pillars could detect the arrival time and structural pattern of the flow disturbance, showing the characteristics of the induced flow field of the starting vortex when passing by. Therefore, such sensor arrays can detect the “footprint” of disturbances as temporal and spatial signatures, allowing us to distinguish those from others or noise.
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(This article belongs to the Special Issue Fluid Dynamics in Biological, Bio-Inspired, and Environmental Systems)
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Open AccessArticle
Hydromechanical Transmission IC2OC: Component Sizing and Optimization
by
Nicola Andretta, Antonio Rossetti and Alarico Macor
Fluids 2024, 9(3), 73; https://doi.org/10.3390/fluids9030073 - 12 Mar 2024
Abstract
The IC2OC transmission is a continuous transmission whose layout can change from simple IC to simple OC configuration and vice versa. It was proposed to cover a wider range of vehicle speeds without adding gears. Its sizing can lead to higher efficiencies than
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The IC2OC transmission is a continuous transmission whose layout can change from simple IC to simple OC configuration and vice versa. It was proposed to cover a wider range of vehicle speeds without adding gears. Its sizing can lead to higher efficiencies than those of the IC and OC layouts. Therefore, this work deals with the sizing methodologies of this transmission. Two methodologies are proposed and discussed: the first uses the functional and constitutive equations of the transmission; the second is based on a mathematical programming problem. Both methodologies start from the choice of the full mechanical point speeds. The comparison between the two methods is carried out on the transmission of a commercially available 230 kW reach stacker. The comparison shows that the functional method, leaner and faster, can provide results very close to those obtained with the heavy and time-consuming optimization, provided that the values of the two full mechanical point speeds are the optimal ones for the two basic transmissions taken individually.
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(This article belongs to the Special Issue Selected Papers from the 2022 IEEE Global Fluid Power Society PhD Symposium (GFPS 2022))
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Transition to the Fluid Dynamic Limit: Mathematical Models and Simulation Results
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Hans Babovsky
Fluids 2024, 9(3), 72; https://doi.org/10.3390/fluids9030072 - 11 Mar 2024
Abstract
Numerical simulations of standard situations in the transition region from gas kinetics to fluid dynamics at small Mach numbers indicate a clear dependence of the simulation results on the underlying kinetic model (here: nonlinear and linearized Boltzmann collision operator vs. BGK relaxation model).
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Numerical simulations of standard situations in the transition region from gas kinetics to fluid dynamics at small Mach numbers indicate a clear dependence of the simulation results on the underlying kinetic model (here: nonlinear and linearized Boltzmann collision operator vs. BGK relaxation model). We develop an improved mathematical framework (trace theory) to explain these differences. In particular we reveal certain deficiencies for the classical BKG system as well as for the standard Navier Stokes approach.
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(This article belongs to the Special Issue Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime)
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Open AccessArticle
CFD Turbulence Models Assessment for the Cavitation Phenomenon in a Rectangular Profile Venturi Tube
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Mauricio De la Cruz-Ávila, Jorge E. De León-Ruiz, Ignacio Carvajal-Mariscal and Jaime Klapp
Fluids 2024, 9(3), 71; https://doi.org/10.3390/fluids9030071 - 07 Mar 2024
Abstract
This study investigates cavitation in a rectangular-profile Venturi tube using numerical simulations and four turbulence models. The unsteady Reynolds-averaged Navier–Stokes technique is employed to simulate vapor cloud formation and compared against experimental data. κ-ε realizable, κ-ε RNG, κ-ω SST, and κ-ω GEKO models
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This study investigates cavitation in a rectangular-profile Venturi tube using numerical simulations and four turbulence models. The unsteady Reynolds-averaged Navier–Stokes technique is employed to simulate vapor cloud formation and compared against experimental data. κ-ε realizable, κ-ε RNG, κ-ω SST, and κ-ω GEKO models are evaluated. The simulation results are analyzed for pressure, turbulence, and vapor cloud formation. Discrepancies in cavitation cloud formation among turbulence models are attributed to turbulence and vapor cloud interactions. RNG and SST models exhibit closer alignment with the experimental data, with RNG showing a superior performance. Key findings include significant vapor cloud shape differences across turbulence models. The RNG model best predicts velocity at the throat exit with an error of 4.145%. Static pressure predictions include an error of 4.47%. The vapor cloud length predictions show variation among models, with the RNG model having a 0.386% error for the minimum length and 4.9845% for the maximum length. The SST model exhibits 4.907% and 13.33% errors for minimum and maximum lengths, respectively. Analysis of the cavitation number reveals agreement with the experimental data and sensitivity to cavitation onset. Different turbulence models yield diverse cloud shapes and detachment points. Weber number contours illustrate the variation in the cavitation cloud behavior under different turbulence models.
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(This article belongs to the Special Issue Pipe Flow: Research and Applications)
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Influence of Nozzle Geometry and Scale-Up on Oil Droplet Breakup in the Atomization Step during Spray Drying of Emulsions
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Sebastian Höhne, Martha L. Taboada, Jewe Schröder, Carolina Gomez, Heike P. Karbstein and Volker Gaukel
Fluids 2024, 9(3), 70; https://doi.org/10.3390/fluids9030070 - 07 Mar 2024
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Spray drying of oil-in-water emulsions is a widespread encapsulation technique. The oil droplet size (ODS) significantly impacts encapsulation efficiency and other powder properties. The ODS is commonly set to a specific value during homogenization, assuming that it remains unchanged throughout the process, which
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Spray drying of oil-in-water emulsions is a widespread encapsulation technique. The oil droplet size (ODS) significantly impacts encapsulation efficiency and other powder properties. The ODS is commonly set to a specific value during homogenization, assuming that it remains unchanged throughout the process, which is often inaccurate. This study investigated the impact of atomizer geometry and nozzle dimensions on oil droplet breakup during atomization using pressure-swirl atomizers. Subject of the investigation were nozzles that differ in the way the liquid is set in motion, as well as different inlet port and outlet orifice dimensions. The results indicate that nozzle inlet port area may have a significant impact on oil droplet breakup, with x90,3 values of the oil droplet size distribution decreasing from 5.29 to 2.30 µm with a decrease of the inlet area from 2.0 to 0.6 mm. Good scalability of the findings from pilot to industrial-scale was shown using larger nozzles. A simplified theoretical model, aiming to predict the ODS as a function of calculated shear rates, showed reasonable agreement to the experimental data for different atomization pressures with coefficients of determination of up to 0.99. However, it was not able to predict the impact of different nozzle dimensions, most likely due to changes in flow characteristics. These results suggest that the stress history of the oil droplets might have a larger influence than expected. Further studies will need to consider other zones of high stress in addition to the outlet orifice.
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Open AccessArticle
Effects of Nozzle Pitch Adaptation in Micro-Scale Liquid Jet Impingement
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Georg Elsinger, Herman Oprins, Vladimir Cherman, Geert Van der Plas, Eric Beyne and Ingrid De Wolf
Fluids 2024, 9(3), 69; https://doi.org/10.3390/fluids9030069 - 07 Mar 2024
Abstract
With ever increasing integration density of electronic components, the demand for cooling solutions capable of removing the heat generated by such systems grows along with it. It has been shown that a viable answer to this demand is the use of direct liquid
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With ever increasing integration density of electronic components, the demand for cooling solutions capable of removing the heat generated by such systems grows along with it. It has been shown that a viable answer to this demand is the use of direct liquid jet impingement. While this method can generally be scaled to the cooling of large areas, this is restricted by the necessity of coolant flow rate scaling. In this study, the benefits and restrictions of using increased nozzle pitch to remedy the increasing demand for overall flow rate are investigated. To this end, a model is validated against experimental findings and then used for computational fluid dynamics simulations, exploring effects of the pitch change for micro-scale nozzle diameters and nozzle-to-target spacings. It is found that while this method is efficient in adjusting the tradeoff between total coolant flow rate and pressure drop up to a certain pint, the occurrence of a hydraulic jump in the cavity causes a deterioration of its effect for large nozzle pitches.
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(This article belongs to the Special Issue Heat Transfer Enhancement Mechanisms and Techniques)
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Unsteady Multiphase Simulation of Oleo-Pneumatic Shock Absorber Flow
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Ahmed A. Sheikh Al-Shabab, Bojan Grenko, Paulo A. S. F. Silva, Antonis F. Antoniadis, Panagiotis Tsoutsanis and Martin Skote
Fluids 2024, 9(3), 68; https://doi.org/10.3390/fluids9030068 - 07 Mar 2024
Abstract
The internal flow in oleo-pneumatic shock absorbers is a complex multiphysics problem combining the interaction between highly unsteady turbulent flow and multiphase mixing, among other effects. The aim is to present a validated simulation methodology that facilitates shock absorber performance prediction by capturing
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The internal flow in oleo-pneumatic shock absorbers is a complex multiphysics problem combining the interaction between highly unsteady turbulent flow and multiphase mixing, among other effects. The aim is to present a validated simulation methodology that facilitates shock absorber performance prediction by capturing the dominant internal flow physics. This is achieved by simulating a drop test of approximately 1 tonne with an initial contact vertical speed of 2.7 m/s, corresponding to a light jet. The flow field solver is ANSYS Fluent, using an unsteady two-dimensional axisymmetric multiphase setup with a time-varying inlet velocity boundary condition corresponding to the stroke rate of the shock absorber piston. The stroke rate is calculated using a two-equation dynamic system model of the shock absorber under the applied loading. The simulation is validated against experimental measurements of the total force on the shock absorber during the stroke, in addition to standard physical checks. The flow field analysis focuses on multiphase mixing and its influence on the turbulent free shear layer and recirculating flow. A mixing index approach is suggested to facilitate systematically quantifying the mixing process and identifying the distinct stages of the interaction. It is found that gas–oil interaction has a significant impact on the flow development in the shock absorber’s upper chamber, where strong mixing leads to a periodic stream of small gas bubbles being fed into the jet’s shear layer from larger bubbles in recirculation zones, most notably in the corner between the orifice plate and outer shock absorber wall.
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(This article belongs to the Special Issue Turbulent Flow, 2nd Edition)
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Comparative Study of Air–Water and Air–Oil Frictional Pressure Drops in Horizontal Pipe Flow
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Enrique Guzmán, Valente Hernández Pérez, Fernando Aragón Rivera, Jaime Klapp and Leonardo Sigalotti
Fluids 2024, 9(3), 67; https://doi.org/10.3390/fluids9030067 - 07 Mar 2024
Abstract
Experimental data for frictional pressure drop using both air–water and air–oil mixtures are reported, compared and used to evaluate predictive methods. The data were gathered using the 2-inch (54.8 mm) flow loop of the multiphase flow facility at the National University of Singapore.
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Experimental data for frictional pressure drop using both air–water and air–oil mixtures are reported, compared and used to evaluate predictive methods. The data were gathered using the 2-inch (54.8 mm) flow loop of the multiphase flow facility at the National University of Singapore. Experiments were carried out over a wide range of flow conditions of superficial liquid and gas velocities that were varied from 0.05 to 1.5 m/s and 2 to 23 m/s, respectively. Pressure drops were measured using pressure transducers and a differential pressure (DP) cell. A hitherto unreported finding was achieved, as the pressure drop in air–oil flow can be lower than that in air–water flow for the higher range of flow conditions. Using flow visualization to explain this phenomenon, it was found that it is related to the higher liquid holdup that occurs in the case of air–oil around the annular flow transition and the resulting interfacial friction. This additional key finding can have applications in flow assurance to improve the efficiency of oil and gas transportation in pipelines. Models and correlations from the open literature were tested against the present data.
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(This article belongs to the Special Issue Pipe Flow: Research and Applications)
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Pipe Formation by Fluid Focalization in Bilayered Sediments
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Aurélien Gay, Ganesh Tangavelou and Valérie Vidal
Fluids 2024, 9(3), 66; https://doi.org/10.3390/fluids9030066 - 06 Mar 2024
Abstract
Pipe structures are commonly encountered in the geophysical context, and in particular in sedimentary basins, where they are associated with fluid migration structures. We investigate pipe formation through laboratory experiments by injecting water locally at a constant flow rate at the base of
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Pipe structures are commonly encountered in the geophysical context, and in particular in sedimentary basins, where they are associated with fluid migration structures. We investigate pipe formation through laboratory experiments by injecting water locally at a constant flow rate at the base of water-saturated sands in a Hele–Shaw cell (30 cm high, 35 cm wide, gap 2.3 mm). The originality of this work is to quantify the effect of a discontinuity. More precisely, bilayered structures are considered, where a layer of fine grains overlaps a layer of coarser grains. Different invasion structures are reported, with fluidization of the bilayered sediment over its whole height or over the finer grains only. The height and area of the region affected by the fluidization display a non-monotonous evolution, which can be interpreted in terms of fluid focusing vs. scattering. Theoretical considerations can predict the critical coarse grains height for the invasion pattern transition, as well as the maximum topography at the sediment free surface in the regime in which only the overlapping finer grains fluidize. These results have crucial geophysical implications, as they demonstrate that invasion patterns and pipe formation dynamics may control the fluid expulsion extent and localization at the seafloor.
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(This article belongs to the Special Issue Pipe Flow: Research and Applications)
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Characteristics of a Particle’s Incipient Motion from a Rough Wall in Shear Flow of Herschel–Bulkley Fluid
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Alexander Seryakov, Yaroslav Ignatenko and Oleg B. Bocharov
Fluids 2024, 9(3), 65; https://doi.org/10.3390/fluids9030065 - 05 Mar 2024
Abstract
A numerical simulation of the Herschel–Bulkley laminar steady state shear flow around a stationary particle located on a sedimentation layer was carried out. The surface of the sedimentation layer was formed by hemispheres of the same radius as the particle. The drag force,
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A numerical simulation of the Herschel–Bulkley laminar steady state shear flow around a stationary particle located on a sedimentation layer was carried out. The surface of the sedimentation layer was formed by hemispheres of the same radius as the particle. The drag force, lift force, and torque values were obtained in the following ranges: shear Reynolds numbers for a particle , corresponding to laminar flow; power law index ; and Bingham number . A significant difference in the forces and torque acting on a particle in shear flow in comparison to the case of a smooth wall is shown. It is shown that the drag coefficient is on average 6% higher compared to a smooth wall for a Newtonian fluid but decreases with the increase in non-Newtonian properties. At the edge values of and , the drag is on average 25% lower compared to the smooth wall. For a Newtonian fluid, the lift coefficient is on average 30% higher compared to a smooth wall. It also decreases with the increase in non-Newtonian properties of the fluid, but at the edge values of and , it is on average only 3% lower compared to the smooth wall. Approximation functions for the drag, lift force, and torque coefficient are constructed. A reduction in the drag force and lifting force leads to an increase in critical stresses (Shields number) on the wall on average by 10% for incipient motion (rolling) and by 12% for particle detachment from the sedimentation bed.
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(This article belongs to the Special Issue Multiphase Flow and Granular Mechanics)
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V Flow Measurements of Pulsatile Flow in Femoral-Popliteal Bypass Proximal Anastomosis Compared with CFD Simulation
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Andrey Yukhnev, Ludmila Tikhomolova, Yakov Gataulin, Alexandra Marinova, Evgueni Smirnov, Andrey Vrabiy, Andrey Suprunovich and Gennady Khubulava
Fluids 2024, 9(3), 64; https://doi.org/10.3390/fluids9030064 - 04 Mar 2024
Abstract
This paper presents the experience of using the V Flow high-frame-rate ultrasound vector imaging method to study the pulsatile velocity fields in the area of the proximal anastomosis for femoral popliteal bypass surgery in vitro and in vivo. A representative (average) anastomosis model
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This paper presents the experience of using the V Flow high-frame-rate ultrasound vector imaging method to study the pulsatile velocity fields in the area of the proximal anastomosis for femoral popliteal bypass surgery in vitro and in vivo. A representative (average) anastomosis model and the experimental setup designed for in vitro studies covering forward and reverse flow phases throughout the cycle are described. The results of the measurements are presented for areas with a relatively uniform velocity distribution and for areas with pronounced spatial inhomogeneities due to the jet or recirculating nature of the flow. The results of ultrasonic studies of the velocity field of the three-dimensional pulsatile flow in vitro and in vivo are compared with the data of numerical simulations carried out for the average and personalized models based on the Navier–Stokes equations. Acceptable consistency between the results of experimental and numerical studies is demonstrated.
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(This article belongs to the Special Issue Image-Based Computational and Experimental Biomedical Flows)
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The Law of the Wall and von Kármán Constant: An Ongoing Controversial Debate
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Stefan Heinz
Fluids 2024, 9(3), 63; https://doi.org/10.3390/fluids9030063 - 04 Mar 2024
Abstract
The discovery of the law of the wall, the log-law including the von Kármán constant, is seen to be one of the biggest accomplishments of fluid mechanics. However, after more than ninety years, there is still a controversial debate about the validity and
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The discovery of the law of the wall, the log-law including the von Kármán constant, is seen to be one of the biggest accomplishments of fluid mechanics. However, after more than ninety years, there is still a controversial debate about the validity and universality of the law of the wall. In particular, evidence in favor of a universal log-law was recently questioned by data analyses of the majority of existing direct numerical simulation (DNS) and experimental results, arguing in favor of nonuniversality of the law of the wall. Future progress requires it to resolve this discrepancy: in absence of alternatives, a reliable and universal theory involving the law of the wall is needed to provide essential guideline for the validation of theory, computational methods, and experimental studies of very high Reynolds number flows. This paper presents an analysis of concepts used to derive controversial conclusions. Similar to the analysis of observed variations of the Kolmogorov constant, it is shown that nonuniversality is a consequence of simplified modeling concepts, leading to unrealizable models. Realizability implies universality: there is no need to adjust simplified models to different flows.
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(This article belongs to the Special Issue Turbulent Flow, 2nd Edition)
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Turbulent Channel Flow: Direct Numerical Simulation-Data-Driven Modeling
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Antonios Liakopoulos and Apostolos Palasis
Fluids 2024, 9(3), 62; https://doi.org/10.3390/fluids9030062 - 03 Mar 2024
Abstract
Data obtained using direct numerical simulations (DNS) of pressure-driven turbulent channel flow are studied in the range 180 10,000. Reynolds number effects on the mean velocity profile (MVP) and second order statistics are analyzed with a view of
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Data obtained using direct numerical simulations (DNS) of pressure-driven turbulent channel flow are studied in the range 180 10,000. Reynolds number effects on the mean velocity profile (MVP) and second order statistics are analyzed with a view of finding logarithmic behavior in the overlap region or even further from the wall, well in the boundary layer’s outer region. The values of the von Kármán constant for the MVPs and the Townsend–Perry constants for the streamwise and spanwise fluctuation variances are determined for the Reynolds numbers considered. A data-driven model of the MVP, proposed and validated for zero pressure-gradient flow over a flat plate, is employed for pressure-driven channel flow by appropriately adjusting Coles’ strength of the wake function parameter, Π. There is excellent agreement between the analytic model predictions of MVP and the DNS-computed MVP as well as of the Reynolds shear stress profile. The skin friction coefficient Cf is calculated analytically. The agreement between the analytical model predictions and the DNS-based computed discrete values of Cf is excellent.
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(This article belongs to the Special Issue Future Trends and Challenges in High Performance Computing for Turbulence)
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Investigating Heat Transfer in Whole-Body Cryotherapy: A 3D Thermodynamic Modeling Approach with Participant Variability
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Rim Elfahem, Bastien Bouchet, Boussad Abbes, Fabien Legrand, Guillaume Polidori and Fabien Beaumont
Fluids 2024, 9(3), 61; https://doi.org/10.3390/fluids9030061 - 01 Mar 2024
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Whole-body cryotherapy (WBC) is a therapeutic practice involving brief exposure to extreme cold, typically lasting one to four minutes. Given that WBC sessions often occur in groups, there is a hypothesis that cumulative heat dissipation from the group significantly affects the thermo-aerodynamic conditions
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Whole-body cryotherapy (WBC) is a therapeutic practice involving brief exposure to extreme cold, typically lasting one to four minutes. Given that WBC sessions often occur in groups, there is a hypothesis that cumulative heat dissipation from the group significantly affects the thermo-aerodynamic conditions of the cryotherapy chamber. Computational fluid dynamics (CFD) is employed to investigate thermal exchanges between three subjects (one man, two women) and a cryotherapy chamber at −92 °C during a 3-minute session. The investigation reveals that collective body heat loss significantly influences temperature fields within the cabin, causing global modifications in aerodynamic and thermal conditions. For example, a temperature difference of 6.7 °C was calculated between the average temperature in a cryotherapy chamber with a single subject and that with three subjects. A notable finding is that, under an identical protocol, the thermal response varies among individuals based on their position in the chamber. The aerodynamic and thermal characteristics of the cryotherapy chamber impact the heat released at the body’s surface and the skin-cooling rate needed to achieve recommended analgesic thresholds. This study highlights the complexity of physiological responses in WBC and emphasizes the importance of considering individual positions within the chamber for optimizing therapeutic benefits.
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Open AccessArticle
Grid Turbulence Measurements with an Acoustic Doppler Current Profiler
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Trygve K. Løken, David Lande-Sudall, Atle Jensen and Jean Rabault
Fluids 2024, 9(3), 60; https://doi.org/10.3390/fluids9030060 - 01 Mar 2024
Abstract
The motivation for this study is to investigate the abilities and limitations of a Nortek Signature1000 acoustic Doppler current profiler (ADCP) regarding fine-scale turbulence measurements. Current profilers offer the advantage of gaining more coherent measurement data than available with point acoustic measurements, and
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The motivation for this study is to investigate the abilities and limitations of a Nortek Signature1000 acoustic Doppler current profiler (ADCP) regarding fine-scale turbulence measurements. Current profilers offer the advantage of gaining more coherent measurement data than available with point acoustic measurements, and it is desirable to exploit this property in laboratory and field applications. The ADCP was tested in a towing tank, where turbulence was generated from a grid towed under controlled conditions. Grid-induced turbulence is a well-studied phenomenon and a good approximation for isotropic turbulence. Several previous experiments are available for comparison and there are developed theories within the topic. In the present experiments, a Nortek Vectrino acoustic Doppler velocimeter (ADV), which is an established instrument for turbulence measurements, was applied to validate the ADCP. It was found that the mean flow measured with the ADCP was accurate within 4% of the ADV. The turbulent variance was reasonably well resolved by the ADCP when large grid bars were towed at a high speed, but largely overestimated for lower towing speed and smaller grid bars. The effective cutoff frequency and turbulent eddy size were characterized experimentally, which provides detailed guidelines for when the ADCP data can be trusted and will allow future experimentalists to decide a priori if the Nortek Signature can be used in their setup. We conclude that the ADCP is not suitable for resolving turbulent spectra in a small-scale grid-induced flow due to the intrinsic Doppler noise and the low spatial and temporal sample resolution relative to the turbulent scales.
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(This article belongs to the Collection Advances in Turbulence)
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Application of Deep Learning in Predicting Particle Concentration of Gas–Solid Two-Phase Flow
by
Zhiyong Wang, Bing Yan and Haoquan Wang
Fluids 2024, 9(3), 59; https://doi.org/10.3390/fluids9030059 - 27 Feb 2024
Abstract
Particle concentration is an important parameter for describing the state of gas–solid two-phase flow. This study compares the performance of three methods, namely, Back-Propagation Neural Networks (BPNNs), Recurrent Neural Networks (RNNs), and Long Short-Term Memory (LSTM), in handling gas–solid two-phase flow data. The
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Particle concentration is an important parameter for describing the state of gas–solid two-phase flow. This study compares the performance of three methods, namely, Back-Propagation Neural Networks (BPNNs), Recurrent Neural Networks (RNNs), and Long Short-Term Memory (LSTM), in handling gas–solid two-phase flow data. The experiment utilized seven parameters, including temperature, humidity, upstream and downstream sensor signals, delay, pressure difference, and particle concentration, as the dataset. The evaluation metrics, such as prediction accuracy, were used for comparative analysis by the experimenters. The experiment results indicate that the prediction accuracies of the RNN, LSTM, and BPNN experiments were 92.4%, 92.7%, and 92.5%, respectively. Future research can focus on further optimizing the performance of the BPNN, RNN, and LSTM to enhance the accuracy and efficiency of gas–solid two-phase flow data processing.
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(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows)
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Open AccessArticle
Visualizing and Evaluating Microbubbles in Multiphase Flow Applications
by
Safa A. Najim, Deepak Meerakaviyad, Kul Pun, Paul Russell, Poo Balan Ganesan, David Hughes and Faik A. Hamad
Fluids 2024, 9(3), 58; https://doi.org/10.3390/fluids9030058 - 27 Feb 2024
Abstract
Accurate visualization of bubbles in multiphase flow is a crucial aspect of modeling heat transfer, mixing, and turbulence processes. It has many applications, including chemical processes, wastewater treatment, and aquaculture. A new software, Flow_Vis, based on experimental data visualization, has been developed to
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Accurate visualization of bubbles in multiphase flow is a crucial aspect of modeling heat transfer, mixing, and turbulence processes. It has many applications, including chemical processes, wastewater treatment, and aquaculture. A new software, Flow_Vis, based on experimental data visualization, has been developed to visualize the movement and size distribution of bubbles within multiphase flow. Images and videos recorded from an experimental rig designed to generate microbubbles were analyzed using the new software. The bubbles in the fluid were examined and found to move with different velocities due to their varying sizes. The software was used to measure bubble size distributions, and the obtained results were compared with experimental measurements, showing reasonable accuracy. The velocity measurements were also compared with literature values and found to be equally accurate.
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(This article belongs to the Special Issue Multiphase Flow for Industry Applications)
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Open AccessReview
Ten Years of Passion: I.S. Gromeka’s Contribution to Science
by
Kamil Urbanowicz and Arris S. Tijsseling
Fluids 2024, 9(3), 57; https://doi.org/10.3390/fluids9030057 - 23 Feb 2024
Abstract
The work and life of Ippolit Stepanovich Gromeka is reviewed. Gromeka authored a classical set of eleven papers on fluid dynamics in just ten years before a tragic illness ended his life. Sadly, he is not well known to the western scientific community
[...] Read more.
The work and life of Ippolit Stepanovich Gromeka is reviewed. Gromeka authored a classical set of eleven papers on fluid dynamics in just ten years before a tragic illness ended his life. Sadly, he is not well known to the western scientific community because all his publications were written in Russian. He is one of the three authors who independently derived an analytical solution for accelerating laminar pipe flow. He was the first to eliminate the contradiction between the theories of Young and Laplace on capillary phenomena. He initiated the theoretical basis of helical (Beltrami) flow, and he studied the movement of cyclones and anticyclones seventeen years before Zermelo (whose work is considered as pioneering). He is also the first to analyse wave propagation in liquid-filled hoses, thereby including fluid–structure interaction.
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(This article belongs to the Special Issue Vortical Flows in Memory of Professor Ippolit Stepanovich Gromeka)
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