Fluids

18 pages, 948 KiB

Open AccessArticle

Universal Scaling Laws for Propulsive Performance of Thrust Producing Foils Undergoing Continuous or Intermittent Pitching

by Anil Das, Ratnesh K. Shukla and Raghuraman N. Govardhan

Fluids 2022, 7(4), 142; https://doi.org/10.3390/fluids7040142 - 14 Apr 2022

Cited by 1 | Viewed by 2368

Abstract

High efficiency thrust generating foils are extensively being researched for potential use as thrusters in micro air vehicles and biomimetic autonomous underwater vehicles. Here, we propose a simple reduced order model for prediction of thrust generation attributes of foils that are pitched either [...] Read more.

High efficiency thrust generating foils are extensively being researched for potential use as thrusters in micro air vehicles and biomimetic autonomous underwater vehicles. Here, we propose a simple reduced order model for prediction of thrust generation attributes of foils that are pitched either continuously or intermittently in a periodic and possibly asymmetric fashion. Our model accounts for the distinct thrust contributions from added mass, leading edge suction, quasi steady and wake terms, all deduced from a rigorous generalization of linearized potential theory to foils undergoing small amplitude multimodal flapping motion. Additionally, the model relies on Bone-Lighthill boundary layer thinning hypothesis to account for the pitching motion induced increase in the drag force exerted on the foil. We derive generic forms of the thrust coefficient for prescribed multimodal pitching motions and specifically in the limit of large reduced frequencies, demonstrate a convergence to rather simplified scaling laws that are functions of just the Reynolds number and Strouhal number based on root mean square of the foil’s trailing edge velocity. Comparisons with previously reported experimental and simulation-based investigations demonstrate that the scaling laws capture the influence of imposed pitch on thrust generation characteristics over a range of pitching waveforms ranging from sinusoidal to square or triangular-shaped waveforms and also waveforms corresponding to intermittent pitching. The generalized relations derived in our work and the asymptotic scaling laws deduced from them are applicable to a wide spectrum of self-propulsion enabling and thrust producing waveforms including the ones that can potentially be employed in burst and coast swimming. Full article

(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)

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Graphical abstract

23 pages, 2053 KiB

Open AccessReview

On the Thermodynamics of Self-Organization in Dissipative Systems: Reflections on the Unification of Physics and Biology

by Bong Jae Chung, Benjamin De Bari, James Dixon, Dilip Kondepudi, Joseph Pateras and Ashwin Vaidya

Fluids 2022, 7(4), 141; https://doi.org/10.3390/fluids7040141 - 14 Apr 2022

Cited by 7 | Viewed by 3511

Abstract

In this paper, we discuss some well-known experimental observations on self-organization in dissipative systems. The examples range from pure fluid flow, pattern selection in fluid–solid systems to chemical-reaction-induced flocking and aggregation in fluid systems. In each case, self-organization can be seen to be [...] Read more.

In this paper, we discuss some well-known experimental observations on self-organization in dissipative systems. The examples range from pure fluid flow, pattern selection in fluid–solid systems to chemical-reaction-induced flocking and aggregation in fluid systems. In each case, self-organization can be seen to be a function of a persistent internal gradient. One goal of this article is to hint at a common theory to explain such phenomena, which often takes the form of the extremum of some thermodynamic quantity, for instance the rate of entropy production. Such variational theories are not new; they have been in existence for decades and gained popularity through the Nobel Prize-winning work of theorists such as Lars Onsager and Ilya Prigogine. The arguments have evolved since then to include systems of higher complexity and for nonlinear systems, though a comprehensive theory remains elusive. The overall attempt is to bring out examples from physics, chemistry, engineering, and biology that reveal deep connections between variational principles in physics and biological, or living systems. There is sufficient evidence to at least raise suspicion that there exists an organization principle common to both living and non-living systems, which deserves deep attention. Full article

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21 pages, 3081 KiB

Open AccessArticle

Calculation of the Pressure Field for Turbulent Flow around a Surface-Mounted Cube Using the SIMPLE Algorithm and PIV Data

by Nikolaos-Petros Pallas and Demetri Bouris

Fluids 2022, 7(4), 140; https://doi.org/10.3390/fluids7040140 - 14 Apr 2022

Cited by 4 | Viewed by 3062

Abstract

The calculation of the pressure field on and around solid bodies exposed to external flow is of paramount importance to a number of engineering applications. However, conventional pressure measurement techniques are inherently linked to problems principally caused by their point-wise and/or intrusive nature. [...] Read more.

The calculation of the pressure field on and around solid bodies exposed to external flow is of paramount importance to a number of engineering applications. However, conventional pressure measurement techniques are inherently linked to problems principally caused by their point-wise and/or intrusive nature. In the present paper, we attempt to calculate a time-averaged two-dimensional pressure field by integrating PIV (particle image velocimetry) velocity measurements into a CFD code and modifying them by the respective correction step of the SIMPLE algorithm. Boundary conditions are applied from the PIV data as a three-layer area of constant velocities adjacent to the boundaries. A novel characteristic of the approach is the straightforward inclusion of the Reynolds stresses into the source terms of the momentum equations, calculated directly from the PIV statistics. The methodology is applied to three regions of the symmetry plane parallel to the main boundary layer flow past a surface-mounted cube. In spite of findings of deviations from the planar 2D flow assumption, the derived pressure fields and the adjusted velocity fields are found to be reliable, while the intrinsic turbulent nature of the flow is considered without modelling the Reynolds stresses. Full article

(This article belongs to the Special Issue Modelling and Simulation of Turbulent Flows)

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14 pages, 2360 KiB

Open AccessArticle

Impact of Porous Media on Boundary Layer Turbulence

by Sutharsan Satcunanathan, Matthias Meinke and Wolfgang Schröder

Fluids 2022, 7(4), 139; https://doi.org/10.3390/fluids7040139 - 13 Apr 2022

Cited by 4 | Viewed by 3217

Abstract

The subsonic flows around NACA 0012 aerofoils with a solid, a porous, and a poro-serrated trailing edge (TE) at a Reynolds number of 1 × 10⁶ are investigated by a hybrid Reynolds-averaged Navier–Stokes (RANS)/large-eddy simulation (LES) approach. The porosity is treated by [...] Read more.

The subsonic flows around NACA 0012 aerofoils with a solid, a porous, and a poro-serrated trailing edge (TE) at a Reynolds number of 1 × 10⁶ are investigated by a hybrid Reynolds-averaged Navier–Stokes (RANS)/large-eddy simulation (LES) approach. The porosity is treated by the method-of-volume averaging. In the RANS, a two-equation low Reynolds number k-ε turbulence model is modified to include the porous treatment. Similarly the equations in the LES are extended by the Darcy–Forchheimer model. The simulation is set up with the broadband turbulent boundary layer trailing edge (TBL-TE) noise prediction as a future objective in mind, i.e., the noise sources in the trailing edge region are captured by the LES. To enforce a physically realistic transition from an averaged RANS solution towards a resolved turbulent flow field, at the inflow of the LES coherent structures are generated by means of the reformulated synthetic turbulence generation (RSTG) method. For the poro-serrated TE, turbulence statistics vary in the spanwise direction between the two extremes of a pure solid and a rectangular porous TE, where porosity locally increases the level of turbulence intensity and alters the near wall turbulence anisotropy. Full article

(This article belongs to the Special Issue Turbulent Flow)

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11 pages, 2965 KiB

Open AccessArticle

Blood Flow Simulation to Determine the Risk of Thrombosis in the Fontan Circulation: Comparison between Atriopulmonary and Total Cavopulmonary Connections

by Ken-ichi Tsubota, Hidetaka Sonobe, Koichi Sughimoto and Hao Liu

Fluids 2022, 7(4), 138; https://doi.org/10.3390/fluids7040138 - 13 Apr 2022

Viewed by 2458

Abstract

Three-dimensional computational fluid dynamics (CFD) simulations were performed in the anastomotic region of the Fontan route between the venae cava and pulmonary arteries to investigate the risk of thrombosis due to blood stasis in the Fontan circulation. The finite volume method based on [...] Read more.

Three-dimensional computational fluid dynamics (CFD) simulations were performed in the anastomotic region of the Fontan route between the venae cava and pulmonary arteries to investigate the risk of thrombosis due to blood stasis in the Fontan circulation. The finite volume method based on the time-averaged continuity and Navier–Stokes equations combined with the k-ω SST turbulent model was used in the CFD simulations. Low shear rate (SR) and SR on the wall (WSR) of <10 s⁻¹ were used as markers to assess blood stasis as a cause of blood coagulation. Simulated blood flow velocity and both SR and WSR were reduced in the right atrium (RA) as the cavity of a flow channel in the atriopulmonary connection (APC) Fontan model, whereas the values increased in the total cavopulmonary connection (TCPC) Fontan model, which has no cavity. The volume of SR <10 s⁻¹ and wall surface area of WSR <10 s⁻¹ were, respectively, 4.6–261.8 cm³ and 1.2–38.3 cm² in the APC Fontan model, and 0.1–0.3 cm³ and 0.1–0.6 cm² in the TCPC Fontan model. The SR and WSR increased in the APC model with a normal-sized RA and the TCPC model as the flow rate of blood from the inferior vena cava increased with exercise; however, the SR and WSR in the RA decreased in the APC model with a dilated RA owing to the development of a recirculating flow. These findings suggest that the APC Fontan has a higher risk of thrombosis due to blood stasis than the TCPC Fontan and a higher RA dilation is associated with a higher risk of thrombosis from a fluid mechanics perspective. Full article

(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)

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39 pages, 5611 KiB

Open AccessFeature PaperReview

Impact of the Dissipation on the Nonlinear Interactions and Turbulence of Gravity-Capillary Waves

by Michael Berhanu

Fluids 2022, 7(4), 137; https://doi.org/10.3390/fluids7040137 - 12 Apr 2022

Cited by 5 | Viewed by 2940

Abstract

Gravity-capillary waves at the water surface are an obvious example illustrating wave propagation in the laboratory, and also nonlinear wave phenomena such as wave interactions or wave turbulence. However, at high-enough frequencies or small scales (i.e., the frequencies typically above 4 Hz or [...] Read more.

Gravity-capillary waves at the water surface are an obvious example illustrating wave propagation in the laboratory, and also nonlinear wave phenomena such as wave interactions or wave turbulence. However, at high-enough frequencies or small scales (i.e., the frequencies typically above 4 Hz or wavelengths below 10 cm), the viscous dissipation cannot be neglected, which complicates experimental, theoretical, and numerical approaches. In this review, we first derive, from the fundamental principles, the features of the gravity-capillary waves. We then discuss the origin and the magnitude of the viscous wave. dissipation in the laboratory and under field conditions. We then show that the significant level of dissipation has important consequences on nonlinear effects involving waves. The nonlinearity level quantified by the wave steepness must be large enough to overcome the viscous dissipation. Specifically, using water as fluid in the field and in the laboratory, nonlinear wave interactions and wave turbulence occur most of the time in a non-weakly nonlinear regime, when the waves are in the capillary or gravity-capillary range. Full article

(This article belongs to the Special Issue Nonlinear Wave Hydrodynamics, Volume II)

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Graphical abstract

17 pages, 12904 KiB

Open AccessArticle

Two Methods to Improve the Efficiency of Supersonic Flow Simulation on Unstructured Grids

by Andrei S. Kozelkov, Andrei V. Struchkov and Dmitry Y. Strelets

Fluids 2022, 7(4), 136; https://doi.org/10.3390/fluids7040136 - 12 Apr 2022

Cited by 5 | Viewed by 2311

Abstract

The paper presents two methods to improve the efficiency of supersonic flow simulation using arbitrarily shaped unstructured grids. The first method promotes increasing the numerical solution convergence rate and is based on the geometric multigrid method for initialization of the flow field. The [...] Read more.

The paper presents two methods to improve the efficiency of supersonic flow simulation using arbitrarily shaped unstructured grids. The first method promotes increasing the numerical solution convergence rate and is based on the geometric multigrid method for initialization of the flow field. The method is used to obtain the initial field of distributed physical quantity values, which maximally corresponds to the converged solution. For this purpose, the problem simulation is performed on a series of coarse grids beginning from the coarsest one in this series. Upon completion of simulations, the solution obtained is interpolated to a finer grid and used for initialization of simulations on this grid. The second method allows increasing the numerical solution accuracy and is based on statically adapting the computational grid to the flow specifics. The static adaptation algorithm provides automatic refinement of the computational grid in the region of specific features of flow, such as shock waves typical for supersonic flows. This algorithm provides a better description of the shock-wave front owing to the local grid refinement, with the local refinement region being automatically selected. Results of using these methods are demonstrated for the two supersonic aerodynamics problems: the simulation of the bow shock strength at a given distance under axially symmetric body Seeb-ALR and a mock-up aircraft Lockheed Martin 1021. It is shown that in both cases, the numerical solution convergence rate is increased owing to the use of the geometric multigrid method for initialization and a higher quality and a higher accuracy of solution is gained owing to the local grid refinement (using static adaptation means) near the shock-wave front. Full article

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17 pages, 5140 KiB

Open AccessArticle

Mathematical Modeling and Pilot Test Validation of Nanoparticles Injection in Heavy Hydrocarbon Reservoirs

by Juan D. Valencia, Juan M. Mejía, Matteo Icardi and Richard Zabala

Fluids 2022, 7(4), 135; https://doi.org/10.3390/fluids7040135 - 12 Apr 2022

Viewed by 2338

Abstract

Heavy-oil mobility in reservoir rocks can be improved, using nanotechnology, by reducing the viscosity of the oil and improving the rock wettability to a water-wet condition. Previous pilot studies in Colombian heavy oil fields reported that nanoparticles dispersed in an oleic carrier fluid [...] Read more.

Heavy-oil mobility in reservoir rocks can be improved, using nanotechnology, by reducing the viscosity of the oil and improving the rock wettability to a water-wet condition. Previous pilot studies in Colombian heavy oil fields reported that nanoparticles dispersed in an oleic carrier fluid (diesel) increased oil production rates between 120–150% higher than before the interventions. However, to optimally deploy a massive nanofluid intervention campaign in heavy oil fields, it is valuable to implement simulation tools that can help to understand the role of operational parameters, to design the operations and to monitor the performance. The simulator must account for nanoparticle transport, transfer, and retention dynamics, as well as their impact on viscosity reduction and wettability restoration. In this paper, we developed and solved, numerically, a 3D mathematical model describing the multiphase flow and interaction of the nanoparticles with oil, brine, and rock surface, leading to viscosity reduction and wettability restoration. The model is based on a multiphase pseudo-compositional formulation, coupled with mass balance equations, of nanoparticles dispersed in water, nanoparticles dispersed in oil, and nanoparticles retained on the rock surface. We simulated a pilot test study of a nanofluid stimulation done in a Colombian heavy oil field. The injection, soaking, and production stages were simulated using a 3D single-well formulation of the mathematical model. The comparison of simulation results with the pilot test results shows that the model reproduced the field observations before and after the stimulation. Simulations showed that viscosity reduction during the post-stimulation period is strongly related to the detachment rate of nanoparticles. Simulation indicates that the recovery mechanism of the nanofluid stimulation is initially governed by viscosity reduction and wettability alteration. At latter times, wettability alteration is the main recovery mechanism. The nanoparticles transferred to the residual water promote the wettability alteration to a water wet condition. The model can be used to design field deployments of nanofluid interventions in heavy oil reservoirs. Full article

(This article belongs to the Collection Advances in Flow of Multiphase Fluids and Granular Materials)

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15 pages, 7053 KiB

Open AccessArticle

Simulation of Winter Deep Slope Convection in Peter the Great Bay (Japan Sea)

by Sergey V. Prants, Pavel A. Fayman, Maxim V. Budyansky and Michael Yu. Uleysky

Fluids 2022, 7(4), 134; https://doi.org/10.3390/fluids7040134 - 12 Apr 2022

Cited by 7 | Viewed by 2137

Abstract

In wintertime, a high-density water forms on the shallow shelf in the vast Peter the Great Bay (Japan Sea). The steep continental slope with deep canyons and cold winters in the area provide suitable conditions for the implementation of deep slope convection—an important [...] Read more.

In wintertime, a high-density water forms on the shallow shelf in the vast Peter the Great Bay (Japan Sea). The steep continental slope with deep canyons and cold winters in the area provide suitable conditions for the implementation of deep slope convection—an important phenomenon in the formation of intermediate and bottom waters that occurs at a few locations in some semi-enclosed seas, including the Japan Sea. The descent of dense shelf water down the continental slope of Peter the Great Bay usually occurs to 1000–1200 m; however, in anomalously cold winters, it has been observed at greater than 2000 m depth supporting renewal and deep ventilation of intermediate and bottom waters in the Japan Sea. The deep slope convection is a rare episodic phenomenon with durations ranging from several hours to several days, that has never been simulated in Peter the Great Bay with a realistic numerical model of circulation. We apply the Regional Ocean Modeling System (ROMS) with a 600 m horizontal resolution to simulate the deep slope convection in the anomalously cold winter of 2001 when it has been observed in cruises. The results are compared with propagation of deep shelf water in the regular winter of 2010 when hydrological characteristics of this water were recorded by a profiler “Aqualog” installed at the shelf break. Using Lagrangian methods, we track and analyze the formation of dense shelf water, its advection to the slope edge in the bottom layer and descent down the slope. Special attention is payed to the role of coastal eddies arising due to a symmetric instability. These eddies promote the cross-shelf transport of the dense shelf water towards the continental slope edge. The simulation results are compared with rare observations of the deep slope convection in Peter the Great Bay. Full article

(This article belongs to the Special Issue Instabilities and Nonlinear Dynamics in Oceanic Flows)

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15 pages, 3522 KiB

Open AccessArticle

The Radiation Problem of a Submerged Oblate Spheroid in Finite Water Depth Using the Method of the Image Singularities System

by Eirini I. Anastasiou and Ioannis K. Chatjigeorgiou

Fluids 2022, 7(4), 133; https://doi.org/10.3390/fluids7040133 - 8 Apr 2022

Viewed by 2014

Abstract

This study examines the hydrodynamic parameters of a unique geometry that could be used effectively for wave energy extraction applications. In particular, we are concerned with the oblate spheroidal geometry that provides the advantage of a wider impact area on waves, closer to [...] Read more.

This study examines the hydrodynamic parameters of a unique geometry that could be used effectively for wave energy extraction applications. In particular, we are concerned with the oblate spheroidal geometry that provides the advantage of a wider impact area on waves, closer to the free surface where the hydrodynamic pressure is higher. In addition, the problem is formulated and solved analytically via a method that is robust and most importantly very fast. In particular, we develop an analytical formulation for the radiation problem of a fully submerged oblate spheroid in a liquid field of finite water depth. The axisymmetric configuration of the spheroid is considered, i.e., the axis of symmetry is perpendicular to the undisturbed free surface. In order to solve the problem, the method of the image singularities system is employed. This method allows for the expansion of the velocity potential in a series of oblate spheroidal harmonics and the derivation of analytical expressions for the hydrodynamic coefficients for the translational degrees of freedom of the body. Numerical simulations and validations are presented taking into account the slenderness ratio of the spheroid, the immersion below the free surface and the water depth. The validations ensure the correctness and the accuracy of the proposed method. Utilizing the same approach, the whole process is implemented for a disc as well, given that a disc is the limiting case of an oblate spheroid since its semi-minor axis approaches zero. Full article

(This article belongs to the Special Issue Wind and Wave Renewable Energy Systems, Volume II)

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13 pages, 4818 KiB

Open AccessArticle

Experimental and Analytical Studies of Reciprocating Flow Heat Transfer in a Reciprocating Loop Device for Electronics Cooling

by Mohammad Didarul Alam, Majid Almas, Soheil Soleimanikutanaei and Yiding Cao

Fluids 2022, 7(4), 132; https://doi.org/10.3390/fluids7040132 - 8 Apr 2022

Cited by 1 | Viewed by 2050

Abstract

The thermal management of electronics is essential, since their lifetime and reliability are highly dependent on their operating temperature and temperature uniformity. Regarding that, Reciprocating-Mechanism Driven Heat Loop (RMDHL) technology has been invented and shows potentiality to become an effective high heat flux [...] Read more.

The thermal management of electronics is essential, since their lifetime and reliability are highly dependent on their operating temperature and temperature uniformity. Regarding that, Reciprocating-Mechanism Driven Heat Loop (RMDHL) technology has been invented and shows potentiality to become an effective high heat flux cooling system. In this paper, the performance of a reciprocating cooling loop, in terms of heat transfer and temperature distribution, is studied experimentally and analytically. The experimental results showed that, as the reciprocating flow amplitude increases, the loop surface temperature decreases, and the temperature uniformity along the loop improves. However, in contrast to the amplitude effect, a higher frequency may not necessarily improve the temperature uniformity, although the condenser section temperature may be lower. Further, adiabatic section temperature appears to be insensitive to the reciprocating frequency. The experimental results were then summarized in a semi-empirical correlation that demonstrates a useful design tool for the thermal engineer community. Additionally, the analytical results provide critical design requirements that should be considered during Reciprocating-Mechanism Driven Heat Loop (RMDHL) system design. Full article

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16 pages, 10810 KiB

Open AccessArticle

Numerical Simulation of Turbulent Flow in Eccentric Co-Rotating Heat Transfer

by Mongkol Kaewbumrung and Akapak Charoenloedmongkhon

Fluids 2022, 7(4), 131; https://doi.org/10.3390/fluids7040131 - 7 Apr 2022

Cited by 6 | Viewed by 3065

Abstract

Heat transfer engineering is significant in many applications, especially in buoyancy natural convection in concentric and eccentric cavities. The biggest practical challenges, in this context, are capturing the self-natural flow, estimating the mixing performance, and determining what parameters affect the temperature distribution in [...] Read more.

Heat transfer engineering is significant in many applications, especially in buoyancy natural convection in concentric and eccentric cavities. The biggest practical challenges, in this context, are capturing the self-natural flow, estimating the mixing performance, and determining what parameters affect the temperature distribution in the cavity. In this paper, we focus on the improvement of a mathematical model, in order to enhance the accuracy of the solution, by investigating a new source term in the SST

k - ω

turbulence model based on the finite volume technique. The commercial numerical simulation software ANSYS Fluent 2021R1 is implemented to validate the accuracy. A concentric cavity was chosen for validation, the obtained temperature profiles at

θ = 0^{°}

,

θ = 30^{°}

,

θ = 60^{°}

,

θ = 90^{°}

,

θ = 120^{°}

,

θ = 150^{°}

, and

θ = 180^{°}

were compared with previous experimental data. We applied this model to four eccentric rotating scenarios, including inner counterclockwise rotation, outer counterclockwise rotation, inner–outer clockwise rotation, and inner clockwise–outer counterclockwise rotation. The numerical simulation results reveal that the new source term in the momentum equation can produce superior results in the concentric test-case. The proposed mathematical model can describe the heat transfer under the eccentric co-rotation scenario well. Furthermore, the results for eccentric cases confirm that the rotational direction affects the mixing temperature by generating a large vortex in the cavity, which increases the temperature mixing performance. Full article

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30 pages, 34456 KiB

Open AccessArticle

Adaptive Data-Driven Model Order Reduction for Unsteady Aerodynamics

by Peter Nagy and Marco Fossati

Fluids 2022, 7(4), 130; https://doi.org/10.3390/fluids7040130 - 6 Apr 2022

Cited by 3 | Viewed by 2486

Abstract

A data-driven adaptive reduced order modelling approach is presented for the reconstruction of impulsively started and vortex-dominated flows. A residual-based error metric is presented for the first time in the framework of the adaptive approach. The residual-based adaptive Reduced Order Modelling selects locally [...] Read more.

A data-driven adaptive reduced order modelling approach is presented for the reconstruction of impulsively started and vortex-dominated flows. A residual-based error metric is presented for the first time in the framework of the adaptive approach. The residual-based adaptive Reduced Order Modelling selects locally in time the most accurate reduced model approach on the basis of the lowest residual produced by substituting the reconstructed flow field into a finite volume discretisation of the Navier–Stokes equations. A study of such an error metric was performed to assess the performance of the resulting residual-based adaptive framework with respect to a single-ROM approach based on the classical proper orthogonal decomposition, as the number of modes is varied. Two- and three-dimensional unsteady flows were considered to demonstrate the key features of the method and its performance. Full article

(This article belongs to the Special Issue Reduced Order Models for Computational Fluid Dynamics)

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27 pages, 1732 KiB

Open AccessArticle

Aeroelastic Response of Wind Turbine Rotors under Rapid Actuation of Flap-Based Flow Control Devices

by Muraleekrishnan Menon and Fernando Ponta

Fluids 2022, 7(4), 129; https://doi.org/10.3390/fluids7040129 - 6 Apr 2022

Cited by 4 | Viewed by 2734

Abstract

The largest commercial wind turbines today are rated at powers between 12 MW to 16 MW, with rotor diameters between 220 m to 242 m, which are expected to grow beyond 250 m in the near future. Economies-of-scale factors suggest the advantages of [...] Read more.

The largest commercial wind turbines today are rated at powers between 12 MW to 16 MW, with rotor diameters between 220 m to 242 m, which are expected to grow beyond 250 m in the near future. Economies-of-scale factors suggest the advantages of upscaling in rotor size to effectively harvest the wind potential. An increased emphasis on studies related to improvements and innovations in aerodynamic load-control methodologies has led researchers to focus on overcoming the bottlenecks in size upscaling. Though conventional pitch control is an effective approach for long-term load variations, their application to mitigate short-term fluctuations has limitations. This is directly associated with the cubical dependence on the weight of the rotor with increasing diameter. Alternatively, active flow-control devices (FCDs) have the potential to alleviate load fluctuations through rapid aerodynamic trimming. Fractional light-weight attachments such as trailing-edge flaps promise the swift response of such rapid fluctuations and require low power of actuation. The current study investigates the performance of active in dynamic load control for utility-scale wind turbines through an aeroelastic evaluation of the turbine response to control actions in short time-scales relevant to rapid load fluctuations. The numerical platform used in the analysis is designed to consider the complex multi-physics dynamics of the wind turbine through a self-adaptive Ordinary Differential Equation (ODE) algorithm that integrates the dynamics presented by control system in to the coupled response of aerodynamics and structural deformations of the rotor. The benchmark case in consideration is the use of fractional trailing-edge flaps used on blades designed for the NREL-5MW Reference Wind Turbine, originally designed by the National Renewable Energy Laboratory. Full article

(This article belongs to the Special Issue Wind and Wave Renewable Energy Systems, Volume II)

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20 pages, 3967 KiB

Open AccessArticle

Evaluation and Improvements to Interfacial Curvature Predictions in interFoam

by Arpit Agarwal, Mohan Ananth and Mario F. Trujillo

Fluids 2022, 7(4), 128; https://doi.org/10.3390/fluids7040128 - 1 Apr 2022

Cited by 2 | Viewed by 3124

Abstract

Improvements to the interfacial curvature of interFoam based on (i) the smoothing of the liquid fraction field and (ii) the creation of a signed distance function (

ϕ

-based) are implemented. While previous work in this area has focused on evaluating spurious currents [...] Read more.

Improvements to the interfacial curvature of interFoam based on (i) the smoothing of the liquid fraction field and (ii) the creation of a signed distance function (

ϕ

-based) are implemented. While previous work in this area has focused on evaluating spurious currents and similar configurations, the tests implemented in this work are more applicable to sprays and hydrodynamic breakup problems. For the

ϕ

-based method, a dual approach is developed based on a geometric reconstruction of the interface at interfacial cells and the solution of the Hamilton-Jacobi equation away from these cells. The more promising results are from this method, where the lack of convergence of Laplace pressure predictions existing in the standard version of interFoam is fixed, resulting in second-order convergence. Similar but less drastic improvements are observed for other exercises consisting of the oscillation of a droplet, a 2-phase Orr–Sommerfeld problem, the Rayleigh–Plateau instability, and the retraction of a liquid column. It is only when the dynamics are either entirely governed by surface tension or are heavily influenced by it that we see the need to substitute the standard interFoam curvature approach with a more accurate scheme. For more realistic problems, which naturally include more complicated dynamics, the difference between the standard approach and the

ϕ

-based approach is minimal. Full article

(This article belongs to the Special Issue Advances in Numerical Methods for Computational Fluid Dynamics With Open-Source Software)

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10 pages, 3218 KiB

Open AccessArticle

Depolymerization of Waste Plastic Using Bubble Column for Nano Alumina Blended Coating

by Mohammed Alzuhairi, Hanaa Al-Kaisy and Mena Khdheer

Fluids 2022, 7(4), 127; https://doi.org/10.3390/fluids7040127 - 28 Mar 2022

Cited by 3 | Viewed by 2774

Abstract

In this study, we aimed to figure out how the depolymerization of polyethylene terephthalate produces monomers, dimers, trimers, and other oligomers of bis (2-hydroxyethyl) terephthalate. Polymerization was achieved in a bubble column reactor with 0.05 wt% 40–50 nm magnesium oxide nanoparticle as a [...] Read more.

In this study, we aimed to figure out how the depolymerization of polyethylene terephthalate produces monomers, dimers, trimers, and other oligomers of bis (2-hydroxyethyl) terephthalate. Polymerization was achieved in a bubble column reactor with 0.05 wt% 40–50 nm magnesium oxide nanoparticle as a catalyst. A bubble column reactor was used to perform the recycling process at the boiling point of ethylene glycol and atmospheric pressure. Depolymerized polyethylene terephthalate (DPET) was mixed with poly(methyl methacrylate) and reinforced with 1% Nano Al₂O₃. The nanoparticles acted as a composite coating in low carbon steel protection. Adhesion strength and mechanical and structural properties were investigated for the composite, and the average coating thickness was 28.39 µm. The results showed that the hardness and adhesion forces between the substrate and composite coating increased with an increase in the amounts of DPET and nano-Al₂O₃ per polymer resin. On the other hand, the thermal conductivity of the composite coating decreased with the addition of DPET because of an increase in the end chain movement in the composite coating induced by the retardant and an increase in cross-linking force. Furthermore, the bubble column demonstrated outstanding heat and mass transfer phenomena that reduced the reaction time to just 40 min for complete depolymerzation and also reduced energy consumption. Full article

(This article belongs to the Section Flow of Multi-Phase Fluids and Granular Materials)

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13 pages, 1956 KiB

Open AccessArticle

A Comparative Analysis of In-Situ Optical Velocimetries for Oil Spill Flow Rate Estimation

by Osman Abu Bkar, Mark Ovinis and Abdalellah O. Mohmmed

Fluids 2022, 7(4), 126; https://doi.org/10.3390/fluids7040126 - 28 Mar 2022

Viewed by 2075

Abstract

In the Deepwater Horizon oil spill, optical plume velocimetry (OPV), a flow measurement technique for use in seafloor hydrothermal systems, was found to have the least uncertainty in estimating the rate at which oil was escaping from the well in the deep sea. [...] Read more.

In the Deepwater Horizon oil spill, optical plume velocimetry (OPV), a flow measurement technique for use in seafloor hydrothermal systems, was found to have the least uncertainty in estimating the rate at which oil was escaping from the well in the deep sea. However, OPV still had a high uncertainty of 21%, partly due to the limited accuracy of the temporal cross-correlation algorithm used. In this work, the accuracy of several in-situ optical velocimetries, namely wavelet-based optical velocimetry (WOV), OPV, and two classical correlation-based algorithms, namely fast Fourier transform (FFT) and normalized cross-correlation (NCC), for a plume flow with Reynolds numbers varying from 1847 to 11,656 was investigated. WOV, FFT, and NCC resulted in flow rates closer to the expected turbulent plume flow rate as compared to OPV. Moreover, a noisy velocity field was found using OPV. The accuracy of wavelet-based algorithm outperformed all cross-correlation based algorithms. The flow rate was measured with an error of 8.5% using WOV, whereas errors of 18.2%, 19.7%, to 21.1% were obtained when applying FFT, OPV, and NCC, respectively. There was a statistically significant difference between wavelet-based and correlation-based algorithms, but no statistically significant difference between the estimation of the three cross-correlation based velocimetries. WOV outperformed the other velocimetries and estimated flow rates with an error of 8.5%, whereas the OPV, FFT, and NCC were estimated with errors of 19.7%, 18.2%, and 50.8%, respectively. Full article

(This article belongs to the Special Issue Wavelets and Fluid Dynamics)

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14 pages, 2599 KiB

Open AccessArticle

Evaluation of Turbulent Jet Characteristic Scales Using Joint Statistical Moments and an Adaptive Time-Frequency Analysis

by Anderson R. Proença and Stefano Meloni

Fluids 2022, 7(4), 125; https://doi.org/10.3390/fluids7040125 - 25 Mar 2022

Cited by 1 | Viewed by 2775

Abstract

This paper presents an analysis of turbulence characteristic scales and eddy convection velocity of jet flows computed using joint statistical moments, digital filters, and a modified version of the empirical mode decomposition (EMD). The ongoing aim of this study is to develop semi-empirical [...] Read more.

This paper presents an analysis of turbulence characteristic scales and eddy convection velocity of jet flows computed using joint statistical moments, digital filters, and a modified version of the empirical mode decomposition (EMD). The ongoing aim of this study is to develop semi-empirical space-time cross-correlation models based on stationary statistics and jet physical lengths. Multivariate statistics are used to correlate jet properties to one-dimensional time series. The data available to this study were recorded from single-point and two-point hot-wire anemometry experiments carried out for a range of jet Mach numbers (

0.2 \leq M \leq 0.8

). Firstly, the jet eddy convection velocity, turbulence length, and time scales are computed using space-time cross-correlation functions. Isotropic flow and frozen turbulence hypothesis are then used to estimate the joint moments from single-point statistics in the fully developed turbulence region. An EMD-based decomposition method is presented and assessed in both the Gaussian and non-Gaussian signal regions. It is demonstrated that the artificially filtered signal reconstructs the physical properties of single and multi-point jet statistics. The relationship between central moments and joint moments presented here focuses on the region of high turbulence levels, which generates the vast majority of jet mixing noise produced by turbofan engines. Further analysis is required to extend this investigation to intermittent zones and other jet noise sources, such as jet-surface installation noise. Full article

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

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17 pages, 12023 KiB

Open AccessArticle

Modeling Conjugate Heat Transfer in an Anode Baking Furnace Using OpenFoam

by Domenico Lahaye, Prajakta Nakate, Kees Vuik, Franjo Juretić and Marco Talice

Fluids 2022, 7(4), 124; https://doi.org/10.3390/fluids7040124 - 23 Mar 2022

Cited by 7 | Viewed by 2722

Abstract

The operation of large industrial furnaces will continue to rely on hydrocarbon fuels in the near foreseeable future. Mathematical modeling and numerical simulation is expected to deliver key insights to implement measures to further reduce pollutant emissions. These measures include the design optimization [...] Read more.

The operation of large industrial furnaces will continue to rely on hydrocarbon fuels in the near foreseeable future. Mathematical modeling and numerical simulation is expected to deliver key insights to implement measures to further reduce pollutant emissions. These measures include the design optimization of the burners, the dilution of oxidizer with exhaust gasses, and the mixing of natural gas with hydrogen. In this paper, we target the numerical simulation of non-premixed turbulent combustion of natural gas in a single heating section of a ring pit anode baking furnace. In previous work, we performed combustion simulations using a commercial flow simulator combined with an open-source package for the three-dimensional mesh generation. This motivates switching to a fully open-source software stack. In this paper, we develop a Reynolds-Averaged Navier-Stokes model for the turbulent flow combined with an infinitely fast mixed-is-burnt model for the non-premixed combustion and a participating media model for the radiative heat transfer in OpenFoam. The heat transfer to the refractory brick lining is taken into account by a conjugate heat transfer model. Numerical simulations provide valuable insight into the heat release and chemical species distribution in the staged combustion process using two burners. Results show that at the operating conditions implemented, higher peak temperatures are formed at the burner closest to the air inlet. This results in a larger thermal nitric-oxide concentration. The inclusion of the heat absorption in the refractory bricks results in a more uniform temperature on the symmetry plane at the center of the section. The peak in thermal nitric-oxides is reduced by a factor of four compared to the model with adiabatic walls. Full article

(This article belongs to the Special Issue Modeling and Experimental Techniques to Combat Pollutant Emissions from Combustion Systems)

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18 pages, 8406 KiB

Open AccessArticle

Comparison of Flow Behavior in Saccular Aneurysm Models Using Proper Orthogonal Decomposition

by Paulo Yu and Vibhav Durgesh

Fluids 2022, 7(4), 123; https://doi.org/10.3390/fluids7040123 - 23 Mar 2022

Cited by 1 | Viewed by 2289

Abstract

Aneurysms are abnormal ballooning of a blood vessel. Previous studies have shown presence of complex flow structures in aneurysms. The objective of this study was to quantify the flow features observed in two selected saccular aneurysm geometries over a range of inflow conditions [...] Read more.

Aneurysms are abnormal ballooning of a blood vessel. Previous studies have shown presence of complex flow structures in aneurysms. The objective of this study was to quantify the flow features observed in two selected saccular aneurysm geometries over a range of inflow conditions using Proper Orthogonal Decomposition (POD). For this purpose, two rigid-wall saccular aneurysm models geometries were used (i.e., the bottleneck factor of 1 and 1.6), and the inflow conditions were varied using a peak Reynolds number (

R e_{p}

) from 50 and 270 and Womersley number (

α

) from 2 and 5. The velocity flow field data for the studied aneurysm geometries were acquired using Particle Image Velocimetry (PIV). The average flow field from the PIV measurement showed that the model geometry and

R e_{p}

have more significant impact on the average flow field than the variations in

α

. The POD results showed that the method was able to quantify the flow field characteristics between the two model geometries. The mode shapes obtained showed different spatial structures for each inflow scenarios and models. The POD energy results showed that more than

80 %

of the fluctuating kinetic energy were captured within five POD modes for

B F = 1.0

flow scenarios, while they were captured within ten modes for

B F = 1.6

. The time varying coefficient results showed the complex interplay of POD modes at different inflow scenarios, highlighting important modes at different phases of the flow cycle. The low-order reconstruction results showed that the vortical structure either proceeded outward or stayed within the aneurysm, and this behavior was highly dependent on

α

,

R e_{p}

, and model geometry that were not evident in average PIV results. Full article

(This article belongs to the Special Issue Recent Advances in Computational Methods in Fluid Dynamics and Applications, Volume II)

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13 pages, 332 KiB

Open AccessArticle

Generalized Clebsch Variables for Compressible Ideal Fluids: Initial Conditions and Approximations of the Hamiltonian

by Benno Rumpf and Yuri V. Lvov

Fluids 2022, 7(4), 122; https://doi.org/10.3390/fluids7040122 - 23 Mar 2022

Viewed by 2244

Abstract

Clebsch variables provide a canonical representation of ideal flows that is, in practice, difficult to handle: while the velocity field is a function of the Clebsch variables and their gradients, constructing the Clebsch variables from the velocity field is not trivial. We introduce [...] Read more.

Clebsch variables provide a canonical representation of ideal flows that is, in practice, difficult to handle: while the velocity field is a function of the Clebsch variables and their gradients, constructing the Clebsch variables from the velocity field is not trivial. We introduce an extended set of Clebsch variables that circumvents this problem. We apply this method to a compressible, chemically inhomogeneous, and rotating ideal fluid in a gravity field. A second difficulty, the secular growth of canonical variables even for stationary states of stratified fluids, makes expansions of the Hamiltonian in Clebsch variables problematic. We give a canonical transformation that associates a stationary state of the canonical variables with the stationary state of the fluid; the new set of variables permits canonical approximations of the dynamics. We apply this to a compressible stratified ideal fluid with the aim to facilitate forthcoming studies of wave turbulence of internal waves. Full article

(This article belongs to the Special Issue Internal Waves in the Ocean)

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15 pages, 4917 KiB

Open AccessArticle

Spanwise-Discontinuous Grooves for Separation Delay and Drag Reduction of Bodies with Vortex Shedding

by Elena Pasqualetto, Gianmarco Lunghi, Alessandro Mariotti and Maria Vittoria Salvetti

Fluids 2022, 7(4), 121; https://doi.org/10.3390/fluids7040121 - 23 Mar 2022

Cited by 7 | Viewed by 2335

Abstract

Suitably shaped grooves, placed transverse to the flow, can delay flow separation over curved surfaces. When grooves are fully extruded in the spanwise direction, they may reduce the drag of boat-tailed bodies with vortex shedding, but with the drawback of increasing the spanwise [...] Read more.

Suitably shaped grooves, placed transverse to the flow, can delay flow separation over curved surfaces. When grooves are fully extruded in the spanwise direction, they may reduce the drag of boat-tailed bodies with vortex shedding, but with the drawback of increasing the spanwise correlation of the vortex shedding. We investigate herein the effect of spanwise-discontinuous grooves through Large Eddy Simulations. A systematic analysis is carried out on the effect of the number, N, of grooves that are present for N equally long portions of the total spanwise length of the boat-tail. Discontinuous grooves further reduce the drag compared with the full-spanwise-extruded groove. Increasing N produces an improvement of the flow-control-device performance, whose maximum value is reached for

N = 3

, corresponding to a spanwise extension of the groove roughly equal to the body crossflow dimension. Above this value, no further improvements are found. The maximum drag reduction is equal to

25.7 %

of the drag of the boat-tail without grooves and to

17.7 %

of the one of the boat-tail with the full-spanwise-extruded groove. The lowest drag value occurs for the least correlated vortex-shedding in the spanwise direction. The reduction in the correlation is mainly related to a flow separation line that is less regular in the spanwise direction. Full article

(This article belongs to the Special Issue Bluff Body Aerodynamics)

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11 pages, 375 KiB

Open AccessArticle

From Darcy Equation to Darcy Paradox

by Carmine Di Nucci and Daniele Celli

Fluids 2022, 7(4), 120; https://doi.org/10.3390/fluids7040120 - 22 Mar 2022

Cited by 1 | Viewed by 2191

Abstract

This theoretical paper focuses on the single-phase fluid flow through a granular porous medium. The emphasis is on the Darcy flow regime (without free boundary) of a linear viscous fluid in a saturated, deformable, homogeneous porous medium. The approach is developed at the [...] Read more.

This theoretical paper focuses on the single-phase fluid flow through a granular porous medium. The emphasis is on the Darcy flow regime (without free boundary) of a linear viscous fluid in a saturated, deformable, homogeneous porous medium. The approach is developed at the Darcy scale (also referred to as macroscale or phenomenological scale). Within this framework, some discrete aspects of the flow model are highlighted, the governing equations are revisited, the thermodynamic state functions are reconsidered, and the Darcy paradox is presented. The Darcy paradox is illustrated for the isoshoric-isothermal flow of a viscous fluid in the liquid state, in a homogenous porous medium. After some remarks about the intrinsic assumption of this kind of flow, the governing equations are reduced to a well-known parabolic equation. According to this equation, infinitesimal pressure disturbances diffuse at an infinite speed. To remove this paradox, a mathematical model, based on the elementary scales method, is employed. Full article

(This article belongs to the Section Geophysical and Environmental Fluid Mechanics)

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