Fluids

19 pages, 7406 KiB

Open AccessArticle

Effect of Serpentine Flow Field Channel Dimensions and Electrode Intrusion on Flow Hydrodynamics in an All-Iron Redox Flow Battery

by Rakesh Basavegowda Krishnappa, S. Gowreesh Subramanya, Abhijit Deshpande and Bharatesh Chakravarthi

Fluids 2023, 8(8), 237; https://doi.org/10.3390/fluids8080237 - 21 Aug 2023

Viewed by 1244

Abstract

This paper presents a study on flow hydrodynamics for single-channel serpentine flow field (SCSFF) and cross-split serpentine flow field configurations (CSSFF) for different geometric dimensions of channel and rib width ratios with electrode intrusion over varying compression ratios (CRs) in an all-iron redox [...] Read more.

This paper presents a study on flow hydrodynamics for single-channel serpentine flow field (SCSFF) and cross-split serpentine flow field configurations (CSSFF) for different geometric dimensions of channel and rib width ratios with electrode intrusion over varying compression ratios (CRs) in an all-iron redox flow battery. Pressure drops

(Δ p)

measured experimentally across a cell active area of 131 cm² for different electrolyte flow rates were numerically validated. A computational fluid dynamics study was conducted for detailed flow analyses, velocity magnitude contours, flow distribution, and uniformity index for the intrusion effect of a graphite felt electrode bearing a thickness of 6 mm with a channel compressed to varying percentages of 50%, 60%, and 70%. Experimental pressure drops

(Δ p)

over the numerical value resulted in the maximum error approximated to 4%, showing good agreement. It was also reported that the modified version of the cross-split serpentine flow field, model D, had the lowest pressure drop,

Δ p

, of 2223.4 pa, with a maximum uniformity index at the electrode midplane of 0.827 for CR 50%, across the active cell area. The pressure drop

(Δ p)

was predominantly higher for increased compression ratios, wherein intrusion phenomena led to changes in electrochemical activity; it was found that the velocity distribution was quite uniform for a volumetric uniformity index greater than 80% in the felt. Full article

(This article belongs to the Special Issue Pipe Flow: Research and Applications)

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21 pages, 5023 KiB

Open AccessArticle

Hybrid Computation of the Aerodynamic Noise Radiated by the Wake of a Subsonic Cylinder

by Benet Eiximeno, Carlos Tur-Mongé, Oriol Lehmkuhl and Ivette Rodríguez

Fluids 2023, 8(8), 236; https://doi.org/10.3390/fluids8080236 - 21 Aug 2023

Cited by 1 | Viewed by 1189

Abstract

The noise radiated by the flow around a cylinder in the subcritical regime at

R e_{D} = 1 \times 10^{4}

and at a subsonic Mach number of

M = 0.5

is here studied. The aerodynamic sound radiated by a cylinder has [...] Read more.

The noise radiated by the flow around a cylinder in the subcritical regime at

R e_{D} = 1 \times 10^{4}

and at a subsonic Mach number of

M = 0.5

is here studied. The aerodynamic sound radiated by a cylinder has been studied with a wide range of Reynolds numbers, but there are no studies about how the Mach number affects the acoustic field in the subsonic regime. The flow field is resolved by means of large-eddy simulations of the compressible Navier–Stokes equations. For the study of the noise propagation, formulation 1C of the Ffowcs Williams–Hawkings analogy is used. The fluid flow results show good agreement when comparing the surface pressure coefficient, the recirculation length, the vortex shedding frequency and the force coefficients against other studies performed under similar conditions. The dynamic mode decomposition of the pressure fluctuations is used to relate them with the far-field noise. It is shown that, in contrast to what happens for low Mach numbers, quadrupoles have a significant impact mainly in the observers located in the streamwise direction. This effect leads to a global monopole directivity pattern as the shear fluctuations compensate for the lower value of the aeolian tone away from the cross-stream direction. Full article

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18 pages, 3854 KiB

Open AccessArticle

Sill Role Effect on the Flow Characteristics (Experimental and Regression Model Analytical)

by Hamidreza Abbaszadeh, Reza Norouzi, Veli Sume, Alban Kuriqi, Rasoul Daneshfaraz and John Abraham

Fluids 2023, 8(8), 235; https://doi.org/10.3390/fluids8080235 - 21 Aug 2023

Cited by 3 | Viewed by 1093

Abstract

This study investigates the effects of gate openings and different sill widths on the sluice gate’s energy dissipation and discharge coefficient (C_d). The physical model of the sills includes rectangular sills of different dimensions. The results show that the gate [...] Read more.

This study investigates the effects of gate openings and different sill widths on the sluice gate’s energy dissipation and discharge coefficient (C_d). The physical model of the sills includes rectangular sills of different dimensions. The results show that the gate opening size is inversely related to the C_d for a gate without a sill. In addition, increasing the gate opening size for a given discharge decreases the relative energy dissipation, and increasing the Froude number increases the relative energy dissipation. The results also show that the C_d and relative energy dissipation decrease when the width of the sill is decreased, thus increasing the total area of the flux flowing through the sluice gate and vice versa. According to the experimental results, the relative energy dissipation and the C_d of the sluice gate are larger for all sill widths than without the sill. Finally, non-linear polynomial relationships are presented based on dimensionless parameters for predicting the relative energy dissipation and outflow coefficient. Full article

(This article belongs to the Special Issue Pipe Flow: Research and Applications)

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22 pages, 7571 KiB

Open AccessArticle

A Parametric Design Study of Natural-Convection-Cooled Heat Sinks

by Oisín McCay, Rajesh Nimmagadda, Syed Mughees Ali and Tim Persoons

Fluids 2023, 8(8), 234; https://doi.org/10.3390/fluids8080234 - 21 Aug 2023

Viewed by 2207

Abstract

Effective natural-convection-cooled heat sinks are vital to the future of electronics cooling due to their low energy demand in the absence of an external pumping agency in comparison to other cooling methods. The present numerical study was carried out with ANSYS Fluent and [...] Read more.

Effective natural-convection-cooled heat sinks are vital to the future of electronics cooling due to their low energy demand in the absence of an external pumping agency in comparison to other cooling methods. The present numerical study was carried out with ANSYS Fluent and aimed at identifying a more-effective fin design for enhancing heat transfer in natural convection applications for a fixed base-plate size of 100 mm × 100 mm under an applied heat flux of 4000 W/m². The Rayleigh number used in the present study lied within the range of 2.6 × 10⁶ to 4.5 × 10⁶. Initially, a baseline case with rectangular fins was considered in the present study, and it was optimized with respect to fin spacing. This optimized baseline case was then validated against the semi-empirical correlation from the scientific literature. Upon good agreement, the validated model was used for comparative analysis of different heat sink configurations with rectangular, trapezoidal, curved, and angled fins by constraining the surface area of the heat transfer. The optimized fin spacing obtained for the baseline case was also used for the other heat sink configurations, and then, the fin designs were further optimized for better performance. However, for the angled fin case, the optimized configuration found in the scientific literature was adopted in the present study. The proposed novel curved fin design with a shroud showed a 4.1% decrease in the system’s thermal resistance with an increase in the heat transfer coefficient of 4.4% when compared to the optimized baseline fin case. The obtained results were further non-dimensionalized with the proposed scaling in terms of the baseline case for the two novel heat sink cases (trapezoidal, curved). Full article

(This article belongs to the Collection Challenges and Advances in Heat and Mass Transfer)

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37 pages, 1889 KiB

Open AccessArticle

A Vaporization Model for Continuous Surface Force Approaches and Subcooled Configurations

by Charles Brissot, Léa Cailly-Brandstäter, Elie Hachem and Rudy Valette

Fluids 2023, 8(8), 233; https://doi.org/10.3390/fluids8080233 - 19 Aug 2023

Viewed by 725

Abstract

The integration of phase change phenomena through an interface is a numerical challenge that requires proper attention. Solutions to properly ensure mass and energy conservation were developed for finite difference and finite volume methods, but not for Finite Element methods. We propose a [...] Read more.

The integration of phase change phenomena through an interface is a numerical challenge that requires proper attention. Solutions to properly ensure mass and energy conservation were developed for finite difference and finite volume methods, but not for Finite Element methods. We propose a Finite Element phase change model based on an Eulerian framework with a Continuous Surface Force (CSF) approach. It handles both momentum and energy conservation at the interface for anisotropic meshes in a light an efficient way. To do so, a model based on the Level Set method is developed. A thick interface is considered to fit with the CSF approach. To properly compute the energy conservation, heat fluxes are extended through this interface thanks to the resolution of a transport equation. A dedicated pseudo compressible Navier–Stokes solver is added to compute velocity jumps with a source term at the interface in the velocity divergence equation. Several 1D and 2D benchmarks are considered with increasing complexity to highlight the performances of each feature of the framework. This stresses the capacity of the model to properly tackle phase change problems. Full article

(This article belongs to the Special Issue Stochastic Equations in Fluid Dynamics, 2nd Edition)

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41 pages, 29991 KiB

Open AccessArticle

A Stabilized Finite Element Framework for Anisotropic Adaptive Topology Optimization of Incompressible Fluid Flows

by Wassim Abdel Nour, Joseph Jabbour, Damien Serret, Philippe Meliga and Elie Hachem

Fluids 2023, 8(8), 232; https://doi.org/10.3390/fluids8080232 - 19 Aug 2023

Viewed by 960

Abstract

This paper assesses the feasibility of performing topology optimization of laminar incompressible flows governed by the steady-state Navier–Stokes equations using anisotropic mesh adaptation to achieve a high-fidelity description of all fluid–solid interfaces. The present implementation combines an immersed volume method solving stabilized finite [...] Read more.

This paper assesses the feasibility of performing topology optimization of laminar incompressible flows governed by the steady-state Navier–Stokes equations using anisotropic mesh adaptation to achieve a high-fidelity description of all fluid–solid interfaces. The present implementation combines an immersed volume method solving stabilized finite element formulations cast in the variational multiscale (VMS) framework and level-set representations of the fluid–solid interfaces, which are used as an a posteriori anisotropic error estimator to minimize interpolation errors under the constraint of a prescribed number of nodes in the mesh. Numerical results obtained for several two-dimensional problems of power dissipation minimization show that the optimal designs are mesh-independent (although the convergence rate does decreases as the number of nodes increases), agree well with reference results from the literature, and provide superior accuracy over prior studies solved on isotropic meshes (fixed or adaptively refined). Full article

(This article belongs to the Section Mathematical and Computational Fluid Mechanics)

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13 pages, 541 KiB

Open AccessArticle

Korteweg–De Vries–Burger Equation with Jeffreys’ Wind–Wave Interaction: Blow-Up and Breaking of Soliton-like Solutions in Finite Time

by Miguel Alberto Manna and Anouchah Latifi

Fluids 2023, 8(8), 231; https://doi.org/10.3390/fluids8080231 - 19 Aug 2023

Viewed by 679

Abstract

In this study, the evolution of surface water solitary waves under the action of Jeffreys’ wind–wave amplification mechanism in shallow water is analytically investigated. The analytic approach is essential for numerical investigations due to the scale of energy dissipation near coasts. Although many [...] Read more.

In this study, the evolution of surface water solitary waves under the action of Jeffreys’ wind–wave amplification mechanism in shallow water is analytically investigated. The analytic approach is essential for numerical investigations due to the scale of energy dissipation near coasts. Although many works have been conducted based on the Jeffreys’ approach, only some studies have been carried out on finite depth. We show that nonlinearity, dispersion, and anti-dissipation are the dominating phenomena, obeying an anti-diffusive and fully nonlinear Serre–Green–Naghdi (SGN) equation. Applying an appropriate perturbation method, the current research yields a Korteweg–de Vries–Burger-type equation (KdV-B), combining weak nonlinearity, dispersion, and anti-dissipation. This derivation is novel. We show that the continuous transfer of energy from wind to water results in the growth over time of the KdV-B soliton’s amplitude, velocity, acceleration, and energy, while its effective wavelength decreases. This phenomenon differs from the classical results of Jeffreys’ approach and is due to finite depth. In this study, it is shown that expansion and breaking occur in finite time. These times are calculated and expressed with respect to soliton- and wind-appropriate parameters and values. The obtained values are measurable in experimental facilities. A detailed analysis of the breaking time is conducted with regard to various criteria. By comparing these times to the experimental results, the validity of these criteria are examined. Full article

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15 pages, 1280 KiB

Open AccessArticle

Modeling of Local Hematocrit for Blood Flow in Stenotic Coronary Vessels

by Ilya Starodumov, Ksenia Makhaeva, Andrey Zubarev, Ivan Bessonov, Sergey Sokolov, Pavel Mikushin, Dmitri Alexandrov, Vasiliy Chestukhin and Felix Blyakhman

Fluids 2023, 8(8), 230; https://doi.org/10.3390/fluids8080230 - 18 Aug 2023

Cited by 1 | Viewed by 1045

Abstract

This mainly theoretical work is devoted to the study of the contribution of the cell-free layer (CFL) near the vessel wall to hemodynamics in a large coronary artery with stenosis to assess the relevance of CFL modeling to the needs of interventional cardiology. [...] Read more.

This mainly theoretical work is devoted to the study of the contribution of the cell-free layer (CFL) near the vessel wall to hemodynamics in a large coronary artery with stenosis to assess the relevance of CFL modeling to the needs of interventional cardiology. An Euler–Euler model considering blood as a two-component fluid with a discrete phase of erythrocytes and a liquid plasma phase was applied to a simple 2d vessel with 65% stenosis. It was found that both the CFL thickness and the local contribution of the CFL thickness to hemodynamics are inhomogeneous along the vessel. The effects of CFL on the velocity profiles, vortex formation, hematocrit, viscosity, and wall shear stresses in the area of stenosis were determined. To demonstrate the significance of CFL modeling for prognostic purposes, the same hemodynamic conditions, analyzed using a one-component model, were also considered. A comparison analysis showed that the existence of CFL resulted in a significant overestimation (up to over 100%) of the main hemodynamic characteristics of the flow obtained using the model based on the Carreau equation. Full article

(This article belongs to the Section Non-Newtonian and Complex Fluids)

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17 pages, 9231 KiB

Open AccessArticle

An Interface-Fitted Fictitious Domain Finite Element Method for the Simulation of Neutrally Buoyant Particles in Plane Shear Flow

by Yi Liang, Cheng Wang and Pengtao Sun

Fluids 2023, 8(8), 229; https://doi.org/10.3390/fluids8080229 - 12 Aug 2023

Viewed by 915

Abstract

In this paper, an interface-fitted fictitious domain finite element method is developed for the simulation of fluid–rigid particle interaction problems in cases of rotated particles with small displacement, where an interface-fitted mesh is employed for the discrete scheme to capture the fluid–rigid particle [...] Read more.

In this paper, an interface-fitted fictitious domain finite element method is developed for the simulation of fluid–rigid particle interaction problems in cases of rotated particles with small displacement, where an interface-fitted mesh is employed for the discrete scheme to capture the fluid–rigid particle interface accurately, thereby improving the solution accuracy near the interface. Moreover, a linearization and decoupling process is presented to release the constraint between velocities of fluid and rigid particles in the finite element space, and to make the developed numerical method easy to be implemented. Our numerical experiments are carried out using two different moving interface-fitted meshes; one is obtained by a rotational arbitrary Lagrangian–Eulerian (ALE) mapping, and the other one through a local smoothing process among interface-cut elements. A unified velocity is defined in the entire domain based on the fictitious domain method, making it easier to develop an interface-fitted mesh generation algorithm in a fixed domain. Both show that the proposed method has a good performance in accuracy for simulating a neutrally buoyant particle in plane shear flow. This approach can be easily extended to fluid–structure interaction problems involving fluids in different states and structures in different shapes with large displacements or deformations. Full article

(This article belongs to the Special Issue Challenges and Directions in Fluid Structure Interaction)

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14 pages, 6710 KiB

Open AccessArticle

The Heat Transfer in Plate Fin Heat Exchanger for Adsorption Energy Storage: Theoretical Estimation and Experimental Verification of the Methodology for Heat Accumulation Process

by Alexandra Grekova, Svetlana Strelova, Anton Lysikov and Mikhail Tokarev

Fluids 2023, 8(8), 228; https://doi.org/10.3390/fluids8080228 - 10 Aug 2023

Cited by 1 | Viewed by 1065

Abstract

Adsorption energy storage is a promising resource-saving technology that allows the rational use of alternative heat sources. One of the most important parts of the adsorption heat accumulator is the adsorber heat exchanger. The parameters of heat transfer in this unit determine how [...] Read more.

Adsorption energy storage is a promising resource-saving technology that allows the rational use of alternative heat sources. One of the most important parts of the adsorption heat accumulator is the adsorber heat exchanger. The parameters of heat transfer in this unit determine how fast heat from an alternative energy source, such as the Sun, will be stored. For the design of adsorption heat accumulators, plate fin heat exchangers are mainly used. In this paper, the procedure for the estimation of the global heat transfer coefficient for the adsorber heat exchanger depending on its geometry is considered. The heat transfer coefficient for a LiCl/SiO₂ sorbent flat layer under conditions of heat storage stage was measured. Based on these data, the global heat transfer coefficients for a number of industrial heat exchangers were theoretically estimated and experimentally measured for the adsorption cycle of daily heat storage. It was shown that theoretically obtained values are in good agreement with the values of the global heat transfer coefficients measured experimentally. Thus, the considered technique makes it possible to determine the most promising geometry of the plate fin heat exchanger for a given adsorption heat storage cycle without complicated experiments. Full article

(This article belongs to the Collection Challenges and Advances in Heat and Mass Transfer)

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18 pages, 15091 KiB

Open AccessArticle

Efficient Scale-Resolving Simulations of Open Cavity Flows for Straight and Sideslip Conditions

by Karthick Rajkumar, Eike Tangermann and Markus Klein

Fluids 2023, 8(8), 227; https://doi.org/10.3390/fluids8080227 - 08 Aug 2023

Viewed by 1334

Abstract

This study aims to facilitate a physical understanding of resonating cavity flows with efficient numerical treatments of turbulence. It reinforces the efficiency and affordability of scale-adaptive numerical techniques for simulating open cavity flows with a separated shear layer consisting of a wide range [...] Read more.

This study aims to facilitate a physical understanding of resonating cavity flows with efficient numerical treatments of turbulence. It reinforces the efficiency and affordability of scale-adaptive numerical techniques for simulating open cavity flows with a separated shear layer consisting of a wide range of flow scales. Visualization of the resonant modes occurring due to the acoustic feedback loop aids in a better understanding of large-scale flow oscillations. Under this scope, scale-adaptive simulation (SAS) based on the k-

ω

SST RANS model with different turbulence treatments has been studied for an open cavity configuration with a length-to-depth

(L / D)

ratio of

5.7

featuring Mach number (

M a

)

0.8

and Reynolds number (

R e

)

12 \times 10^{6}

. It is shown that the essential cavity flow physics has been captured using the SAS approach with more than

90 %

improved computational efficiency compared to commonly used hybrid RANS-LES approaches. In addition, wall-modeled SAS when supplemented with an artificial forcing concept to trigger the model provides very good spectral estimates comparable with hybrid RANS-LES results. Following the validation of numerical approaches, the directional dependence of the cavity resonance is investigated under asymmetric flow conditions, and spanwise interference of waves due to the lateral walls of the cavity has been observed. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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21 pages, 5656 KiB

Open AccessArticle

Rapid Hydrate Formation Conditions Prediction in Acid Gas Streams

by Anna Samnioti, Eirini Maria Kanakaki, Sofianos Panagiotis Fotias and Vassilis Gaganis

Fluids 2023, 8(8), 226; https://doi.org/10.3390/fluids8080226 - 05 Aug 2023

Cited by 2 | Viewed by 1433

Abstract

Sour gas in hydrocarbon reservoirs contains significant amounts of H₂S and smaller amounts of CO₂. To minimize operational costs, meet air emission standards and increase oil recovery, operators revert to acid gas (re-)injection into the reservoir rather than treating [...] Read more.

Sour gas in hydrocarbon reservoirs contains significant amounts of H₂S and smaller amounts of CO₂. To minimize operational costs, meet air emission standards and increase oil recovery, operators revert to acid gas (re-)injection into the reservoir rather than treating H₂S in Claus units. This process requires the pressurization of the acid gas, which, when combined with low-temperature conditions prevailing in subsurface pipelines, often leads to the formation of hydrates that can potentially block the fluid flow. Therefore, hydrates formation must be checked at each pipeline segment and for each timestep during a flow simulation, for any varying composition, pressure and temperature, leading to millions of calculations that become more intense when transience is considered. Such calculations are time-consuming as they incorporate the van der Walls–Platteeuw and Langmuir adsorption theory, combined with complex EoS models to account for the polarity of the fluid phases (water, inhibitors). The formation pressure is obtained by solving an iterative multiphase equilibrium problem, which takes a considerable amount of CPU time only to provide a binary answer (hydrates/no hydrates). To accelerate such calculations, a set of classifiers is developed to answer whether the prevailing conditions lie to the left (hydrates) or the right-hand (no hydrates) side of the P-T phase envelope. Results are provided in a fast, direct, non-iterative way, for any possible conditions. A set of hydrate formation “yes/no” points, generated offline using conventional approaches, are utilized for the classifier’s training. The model is applicable to any acid gas flow problem and for any prevailing conditions to eliminate the CPU time of multiphase equilibrium calculations. Full article

(This article belongs to the Special Issue Multiphase Flow and Granular Mechanics)

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25 pages, 5348 KiB

Open AccessArticle

The Emptying of a Perforated Bottle: Influence of Perforation Size on Emptying Time and the Physical Nature of the Process

by Callen Schwefler, Peyton Nienaber and Hans C. Mayer

Fluids 2023, 8(8), 225; https://doi.org/10.3390/fluids8080225 - 04 Aug 2023

Viewed by 861

Abstract

An inverted bottle empties in a time

T_{e, 0}

through a process called “glugging”, whereby gas and liquid compete at the neck (of diameter

D_{N}

). In contrast, an open-top container empties in a much shorter time

T_{e}

through [...] Read more.

An inverted bottle empties in a time

T_{e, 0}

through a process called “glugging”, whereby gas and liquid compete at the neck (of diameter

D_{N}

). In contrast, an open-top container empties in a much shorter time

T_{e}

through “jetting” due to the lack of gas–liquid competition. Experiments and theory demonstrate that, by introducing a perforation (diameter

d_{p}

), a bottle empties through glugging, jetting, or a combination of the two. For a certain range of

d_{p} / D_{N}

, the perforation increases the emptying time, and a particular value of

d_{p} / D_{N}

is associated with a maximum emptying time

T_{e, m a x}

. We show that the transition from jetting to glugging is initiated by the jet velocity reaching a low threshold, thereby allowing a slug of air entry into the neck that stops jetting and starts the glugging. Once initiated, the glugging proceeds as though there is no perforation. Experimental results covered a range of Eötvös numbers from Eo∼ 20–200 (equivalent to a range of

D_{N} / L_{c} \sim

4–15, where

L_{c}

is the capillary length). The phenomenon of bottle emptying with a perforation adds to the body of bottle literature, which has already considered the influence of shape, inclination, liquid properties, etc. Full article

(This article belongs to the Special Issue Advances in Multiphase Flow Science and Technology, 2nd Edition)

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20 pages, 2356 KiB

Open AccessReview

Wavelet Transforms and Machine Learning Methods for the Study of Turbulence

by Jahrul M Alam

Fluids 2023, 8(8), 224; https://doi.org/10.3390/fluids8080224 - 03 Aug 2023

Cited by 1 | Viewed by 2374

Abstract

This article investigates the applications of wavelet transforms and machine learning methods in studying turbulent flows. The wavelet-based hierarchical eddy-capturing framework is built upon first principle physical models. Specifically, the coherent vortex simulation method is based on the Taylor hypothesis, which suggests that [...] Read more.

This article investigates the applications of wavelet transforms and machine learning methods in studying turbulent flows. The wavelet-based hierarchical eddy-capturing framework is built upon first principle physical models. Specifically, the coherent vortex simulation method is based on the Taylor hypothesis, which suggests that the energy cascade occurs through vortex stretching. In contrast, the adaptive wavelet collocation method relies on the Richardson hypothesis, where the self-amplification of the strain field and a hierarchical breakdown of large eddies drive the energy cascade. Wavelet transforms are computational learning architectures that propagate the input data across a sequence of linear operators to learn the underlying nonlinearity and coherent structure. Machine learning offers a wealth of data-driven algorithms that can heavily use statistical concepts to extract valuable insights into turbulent flows. Supervised machine learning needs “perfect” turbulent flow data to train data-driven turbulence models. The current advancement of artificial intelligence in turbulence modeling primarily focuses on accelerating turbulent flow simulations by learning the underlying coherence over a low-dimensional manifold. Physics-informed neural networks offer a fertile ground for augmenting first principle physics to automate specific learning tasks, e.g., via wavelet transforms. Besides machine learning, there is room for developing a common computational framework to provide a rich cross-fertilization between learning the data coherence and the first principles of multiscale physics. Full article

(This article belongs to the Special Issue Wavelets and Fluids)

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11 pages, 5815 KiB

Open AccessArticle

Trapped Solitary Waves in a Periodic External Force: A Numerical Investigation Using the Whitham Equation and the Sponge Layer Method

by Marcelo V. Flamarion, Roberto Ribeiro-Jr, Diogo L. S. S. Vianna and Alex M. Sato

Fluids 2023, 8(8), 223; https://doi.org/10.3390/fluids8080223 - 01 Aug 2023

Cited by 1 | Viewed by 684

Abstract

This paper concerns the interaction between solitary waves on the surface of an ideal fluid and a localized external force, which models a moving disturbance on the free surface or an obstacle moving at the bottom of a channel. Previous works have investigated [...] Read more.

This paper concerns the interaction between solitary waves on the surface of an ideal fluid and a localized external force, which models a moving disturbance on the free surface or an obstacle moving at the bottom of a channel. Previous works have investigated this interaction under the assumption that the external force moves with variable speed and constant acceleration. However, in this paper we adopt a different approach and consider the scenario in which the external force moves with variable speed and non-constant acceleration. Using the Whitham equation framework, we investigate numerically trapped waves excited by a periodic external force. Our experiments reveal regimes in which solitary waves are spontaneously generated and trapped for large times at the external force. In addition, we compare the results predicted by the Whitham equation with those of the Korteweg–de Vries equation. Full article

(This article belongs to the Section Mathematical and Computational Fluid Mechanics)

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25 pages, 13801 KiB

Open AccessArticle

Numerical Assessment of Flow Energy Harvesting Potential in a Micro-Channel

by Dimitrios G. Koubogiannis and Marios Vasileios N. Benetatos

Fluids 2023, 8(8), 222; https://doi.org/10.3390/fluids8080222 - 30 Jul 2023

Viewed by 862

Abstract

A micro-energy harvesting device proposed in the literature was numerically studied. It consists of two bluff bodies in a micro-channel and a flexible diaphragm at its upper wall. Vortex shedding behind bodies induces pressure fluctuation causing vibration of the diaphragm that converts mechanical [...] Read more.

A micro-energy harvesting device proposed in the literature was numerically studied. It consists of two bluff bodies in a micro-channel and a flexible diaphragm at its upper wall. Vortex shedding behind bodies induces pressure fluctuation causing vibration of the diaphragm that converts mechanical energy to electrical by means of a piezoelectric membrane. Research on enhancing vortex shedding was justified due to the low power output of the device. The amplitude and frequency of the unsteady pressure fluctuation on the diaphragm were numerically predicted. The vortex shedding severity was mainly assessed in terms of pressure amplitude. The CFD model set-up was described in detail, and appropriate metrics to assess the energy harvesting potential were defined. Several 2D cases were simulated to study the effect of the inlet Reynolds number and channel blockage ratio on the prospective performance of the device. Furthermore, the critical blockage ratio leading to the vortex shedding suppression was sought. A higher inlet velocity for a constant blockage ratio was found to enhance vortex shedding and the pressure drop. Great blockage ratio values but lower than the critical ones seemed to provide great pressure amplitudes at the expense of a moderate pressure drop. There is evidence that the field is fruitful for further research and relevant directions were provided. Full article

(This article belongs to the Section Mathematical and Computational Fluid Mechanics)

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18 pages, 5239 KiB

Open AccessArticle

Numerical Evaluation of the Flow within a Rhomboid Tessellated Pipe Network with a 3 × 3 Allometric Branch Pattern for the Inlet and Outlet

by René Rodríguez-Rivera, Ignacio Carvajal-Mariscal, Hilario Terres-Peña, Mauricio De la Cruz-Ávila and Jorge E. De León-Ruiz

Fluids 2023, 8(8), 221; https://doi.org/10.3390/fluids8080221 - 30 Jul 2023

Viewed by 831

Abstract

This study presents a comprehensive assessment of the hydrodynamic performance of a novel pipe network with tessellated geometry and allometric scales. Numerical simulations were used to evaluate flow behaviour and pressure drop. The comparison geometry featured a Parallel Pipe Pattern (PPP), while the [...] Read more.

This study presents a comprehensive assessment of the hydrodynamic performance of a novel pipe network with tessellated geometry and allometric scales. Numerical simulations were used to evaluate flow behaviour and pressure drop. The comparison geometry featured a Parallel Pipe Pattern (PPP), while the proposed design employed a Rhombic Tessellation Pattern (RTP). Steady-state simulations were conducted under identical boundary conditions, examining water mass flows ranging from 0.01 to 0.06 kg/s. The results revealed RTP significant advantages over the PPP. The RTP, integrated with a fractal tree pattern, demonstrated remarkable capabilities in achieving uniform flow distribution and maintaining laminar flow regimes across the mass flow rates. Additionally, exhibited an average reduction in pressure drop of 92% resulting in improved efficiency. The Reynolds number at PPP inlet was 5.4 times higher than in the RTP, explaining the considerably higher pressure drop. At a mass flow rate of 0.06 kg/s, the PPP experienced a pressure drop of up to 3.43 kPa, while the RTP’s pressure drop was only 0.350 kPa, highlighting a remarkable decrease of 91.5%. These findings underscore the RTP superior performance in minimizing pressure drop, making it suitable for accommodating higher mass flow rates, thus highlighting its exceptional engineering potential. Full article

(This article belongs to the Special Issue Pipe Flow: Research and Applications)

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21 pages, 8709 KiB

Open AccessArticle

Dynamics of a Laser-Induced Cavitation Bubble near a Cone: An Experimental and Numerical Study

by Jianyong Yin, Yongxue Zhang, Dehong Gong, Lei Tian and Xianrong Du

Fluids 2023, 8(8), 220; https://doi.org/10.3390/fluids8080220 - 29 Jul 2023

Cited by 1 | Viewed by 1187

Abstract

A bubble’s motion is strongly influenced by the boundaries of tip structures, which correspond to the bubble’s size. In the present study, the dynamic behaviors of a cavitation bubble near a conical tip structure are investigated experimentally and numerically. A series of experiments [...] Read more.

A bubble’s motion is strongly influenced by the boundaries of tip structures, which correspond to the bubble’s size. In the present study, the dynamic behaviors of a cavitation bubble near a conical tip structure are investigated experimentally and numerically. A series of experiments were carried out to analyze the bubble’s shape at different relative cone distances quantitatively. Due to the crucial influence of the phase change on the cavitation bubble’s dynamics over multiple cycles, a compressible two-phase model taking into account the phase change and heat transfer implemented in OpenFOAM was employed in this study. The simulation results regarding the bubble’s radius and shape were validated with corresponding experimental photos, and a good agreement was achieved. The bubble’s primary physical features (e.g., shock waves, liquid jets, high-pressure zones) were well reproduced, which helps us understand the underlying mechanisms. Meanwhile, the latent damage was quantified by the pressure load at the cone apex. The effects of the relative distance γ and cone angle θ on the maximum temperature, pressure peaks, and bubble position are discussed and summarized. The results show that the pressure peaks during the bubble’s collapse increase with the decrease in γ. For a larger γ, the first minimum bubble radius increases while the maximum temperature decreases as θ increases; the pressure peak at the second final collapse is first less than that at the first final collapse and then much greater than that one. For a smaller γ, the pressure peaks at different θ values do not vary very much. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows)

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13 pages, 21929 KiB

Open AccessArticle

Dynamic Mixed Modeling in Large Eddy Simulation Using the Concept of a Subgrid Activity Sensor

by Josef Hasslberger

Fluids 2023, 8(8), 219; https://doi.org/10.3390/fluids8080219 - 28 Jul 2023

Viewed by 841

Abstract

Following the relative success of mixed models in the Large Eddy Simulation of complex turbulent flow configurations, an alternative formulation is suggested here which incorporates the concept of a local subgrid activity sensor. The general idea of mixed models is to combine the [...] Read more.

Following the relative success of mixed models in the Large Eddy Simulation of complex turbulent flow configurations, an alternative formulation is suggested here which incorporates the concept of a local subgrid activity sensor. The general idea of mixed models is to combine the advantages of structural models (superior alignment properties), usually of the scale similarity type, and functional models (superior stability), usually of the eddy viscosity type, while avoiding their disadvantages. However, the key question is the mathematical realization of this combination, and the formulation in this work accounts for the local level of underresolution of the flow. The justification and evaluation of the newly proposed mixed model is based on a priori and a posteriori analysis of homogeneous isotropic turbulence and laminar–turbulent transition in the Taylor–Green vortex, respectively. The suggested model shows a robust and accurate behavior for the cases investigated. In particular, it outperforms the separate structural and functional base models as well as the simulation without an explicit subgrid-scale model. Full article

(This article belongs to the Collection Feature Paper for Mathematical and Computational Fluid Mechanics)

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19 pages, 3849 KiB

Open AccessArticle

Comprehensive Perturbation Approach to Nonlinear Viscous Gravity–Capillary Surface Waves at Arbitrary Wavelengths in Finite Depth

by Arash Ghahraman and Gyula Bene

Fluids 2023, 8(8), 218; https://doi.org/10.3390/fluids8080218 - 27 Jul 2023

Viewed by 765

Abstract

This study presents a comprehensive analysis of the second-order perturbation theory applied to the Navier–Stokes equations governing free surface flows. We focus on gravity–capillary surface waves in incompressible viscous fluids of finite depth over a flat bottom. The amplitude of these waves is [...] Read more.

This study presents a comprehensive analysis of the second-order perturbation theory applied to the Navier–Stokes equations governing free surface flows. We focus on gravity–capillary surface waves in incompressible viscous fluids of finite depth over a flat bottom. The amplitude of these waves is regarded as the perturbation parameter. A systematic derivation of a nonlinear-surface-wave equation is presented that fully takes into account dispersion, while nonlinearity is included in the leading order. However, the presence of infinitely many over-damped modes has been neglected and only the two least-damped modes are considered. The new surface-wave equation is formulated in wave-number space rather than real space and nonlinear terms contain convolutions making the equation an integro-differential equation. Some preliminary numerical results are compared with computational-modelling data obtained via open source CFD software OpenFOAM. Full article

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26 pages, 14053 KiB

Open AccessArticle

Improving Pump Characteristics through Double Curvature Impellers: Experimental Measurements and 3D CFD Analysis

by Alfredo M. Abuchar-Curi, Oscar E. Coronado-Hernández, Jairo Useche, Verónica J. Abuchar-Soto, Argemiro Palencia-Díaz, Duban A. Paternina-Verona and Helena M. Ramos

Fluids 2023, 8(8), 217; https://doi.org/10.3390/fluids8080217 - 27 Jul 2023

Viewed by 1244

Abstract

The outlet angle and shape of impeller blades are important parameters in centrifugal pump design. There is a lack of detailed studies related to double curvature impellers in centrifugal pumps in the current literature; therefore, an experimental and numerical analysis of double curvature [...] Read more.

The outlet angle and shape of impeller blades are important parameters in centrifugal pump design. There is a lack of detailed studies related to double curvature impellers in centrifugal pumps in the current literature; therefore, an experimental and numerical analysis of double curvature impellers was performed. Six impellers were made and then assessed in a centrifugal pump test bed and simulated via 3D CFD simulation. The original impeller was also tested and simulated. One of the manufactured impellers had the same design as the original, and the other five impellers had a double curvature. Laboratory tests and simulations were conducted with three rotation speeds: 1400, 1700, and 1900 RPM. Head and performance curve equations were obtained for the pump–engine unit based on the flow of each impeller for the three rotation speeds. The results showed that a double curvature impeller improved pump head by approximately 1 m for the range of the study and performance by about 2% when compared to basic impeller. On the other hand, it was observed that turbulence models such as k-ε and SST k-ω reproduced similar physical and numerical results. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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28 pages, 8270 KiB

Open AccessArticle

CFD Simulation of SCR Systems Using a Mass-Fraction-Based Impingement Model

by Max Quissek, Uladzimir Budziankou, Sebastian Pollak and Thomas Lauer

Fluids 2023, 8(8), 216; https://doi.org/10.3390/fluids8080216 - 25 Jul 2023

Viewed by 1143

Abstract

Computational fluid dynamics (CFD) are an essential tool for the development of diesel engine aftertreatment systems using selective catalytic reduction (SCR) to reduce nitrous oxides (

{NO}_{x}

). In urea-based SCR, liquid urea–water solution (UWS) is injected into the hot exhaust gas, [...] Read more.

Computational fluid dynamics (CFD) are an essential tool for the development of diesel engine aftertreatment systems using selective catalytic reduction (SCR) to reduce nitrous oxides (

{NO}_{x}

). In urea-based SCR, liquid urea–water solution (UWS) is injected into the hot exhaust gas, where it transforms into gaseous ammonia. This ammonia serves as a reducing agent for

{NO}_{x}

. CFD simulations are used to predict the ammonia distribution in the exhaust gas at the catalyst inlet. The goal is to achieve the highest possible uniformity to realize homogeneous

{NO}_{x}

reduction across the catalyst cross section. The current work focuses on the interaction of UWS droplets with the hot walls of the exhaust system. This is a crucial part of the preparation of gaseous ammonia from the injected liquid UWS. Following experimental investigations, a new impingement model is described based on the superposition of four basic impingement behaviors, each featuring individual secondary droplet characteristics. The droplet–wall heat transfer, depending on surface temperature and impingement behavior, is also calculated using a newly parameterized model. Applying the presented approach, the cooling of a steel plate from intermittent spray impingement is simulated and compared to measurements. The second validation case is the distribution of ammonia at the catalyst inlet of an automotive SCR system. Both applications show good agreement and demonstrate the quality of the new model. Full article

(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering)

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Fluids, Volume 8, Issue 8 (August 2023) – 22 articles

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