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Fluids, Volume 6, Issue 3 (March 2021) – 41 articles

Cover Story (view full-size image): Sensing of critical events or flow signatures in nature often presents itself as a coupled interaction between a fluid and arrays of slender flexible beams, such a wind hairs or whiskers. A model of a sea lion is built with artificial whiskers on the head in the form of optical fibres. Motion tracking is used to analyse the correlation of the bending deformations of the pairs of fibres. Coherent vortical structures can be detected from cross-correlation of their signals, even in highly turbulent flows. Such vortices carry important information within the environment, e.g., underlying convection velocity. More importantly, in nature, these vortices are characteristic elementary signals left by prey and predators. The present work can help to further develop flow, or critical event, sensory systems that can overcome high noise levels due to the proposed correlation principle. View this paper.
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17 pages, 57616 KiB  
Article
Micropolar Blood Flow in a Magnetic Field
by George C. Bourantas
Fluids 2021, 6(3), 133; https://doi.org/10.3390/fluids6030133 - 23 Mar 2021
Cited by 1 | Viewed by 2269
Abstract
In this paper we numerically solve a flow model for the micropolar biomagnetic flow (blood flow) in a magnetic field. In the proposed model we account for both electrical and magnetic properties of the biofluid and we investigate the role of microrotation on [...] Read more.
In this paper we numerically solve a flow model for the micropolar biomagnetic flow (blood flow) in a magnetic field. In the proposed model we account for both electrical and magnetic properties of the biofluid and we investigate the role of microrotation on the flow regime. The flow domain is in a channel with an unsymmetrical single stenosis, and in a channel with irregular multi-stenoses. The mathematical flow model consists of the Navier–Stokes (N–S) equations expressed in their velocity–vorticity (uω) variables including the energy and microrotation transport equation. The governing equations are solved by using the strong form meshless point collocation method. We compute the spatial derivatives of the unknown field functions using the discretization correction particle strength exchange (DC PSE) method. We demonstrate the accuracy of the proposed scheme by comparing the numerical results obtained with those computed using the finite element method. Full article
(This article belongs to the Special Issue Fluids in Magnetic/Electric Fields)
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11 pages, 2593 KiB  
Article
Aspects Concerning the Fabrication of Magnetorheological Fluids Containing High Magnetization FeCo Nanoparticles
by Jon Gutiérrez, Virginia Vadillo, Ainara Gómez, Joanes Berasategi, Maite Insausti, Izaskun Gil de Muro and M. Mounir Bou-Ali
Fluids 2021, 6(3), 132; https://doi.org/10.3390/fluids6030132 - 23 Mar 2021
Cited by 6 | Viewed by 1953
Abstract
Recently, our collaborative work in the fabrication of a magnetorheological fluid (MRF) containing high magnetization FeCo nanoparticles (NPs, fabricated in our laboratories using the chemical reduction technique; MS = 212 Am2/kg) as magnetic fillers have resulted in a new MRF [...] Read more.
Recently, our collaborative work in the fabrication of a magnetorheological fluid (MRF) containing high magnetization FeCo nanoparticles (NPs, fabricated in our laboratories using the chemical reduction technique; MS = 212 Am2/kg) as magnetic fillers have resulted in a new MRF with superior performance up to 616.7 kA/m. The MRF had a yield stress value of 2729 Pa and good reversibility after a demagnetization process. This value competes with the best ones reported in the most recent literature. Nevertheless, the fabrication process of this type of fluid is not an easy task since there is a strong trend to the aggregation of the FeCo NPs due to the strong magnetic dipolar interaction among them. Thus, now we present the analysis of some aspects concerning the fabrication process of our FeCo NPs containing MRF, mainly the type of surfactant used to cover those NPs (oleic acid or aluminium stearate) and its concentration, and the procedure followed (mechanical and/or ultrasound stirring) to achieve a good dispersion of those magnetic fillers within the fluid. Full article
(This article belongs to the Special Issue Fluids in Magnetic/Electric Fields)
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29 pages, 468 KiB  
Article
Implicit Type Constitutive Relations for Elastic Solids and Their Use in the Development of Mathematical Models for Viscoelastic Fluids
by Vít Průša and K. R. Rajagopal
Fluids 2021, 6(3), 131; https://doi.org/10.3390/fluids6030131 - 22 Mar 2021
Cited by 3 | Viewed by 2263
Abstract
Viscoelastic fluids are non-Newtonian fluids that exhibit both “viscous” and “elastic” characteristics in virtue of the mechanisms used to store energy and produce entropy. Usually, the energy storage properties of such fluids are modeled using the same concepts as in the classical theory [...] Read more.
Viscoelastic fluids are non-Newtonian fluids that exhibit both “viscous” and “elastic” characteristics in virtue of the mechanisms used to store energy and produce entropy. Usually, the energy storage properties of such fluids are modeled using the same concepts as in the classical theory of nonlinear solids. Recently, new models for elastic solids have been successfully developed by appealing to implicit constitutive relations, and these new models offer a different perspective to the old topic of the elastic response of materials. In particular, a sub-class of implicit constitutive relations, namely relations wherein the left Cauchy–Green tensor is expressed as a function of stress, is of interest. We show how to use this new perspective in the development of mathematical models for viscoelastic fluids, and we provide a discussion of the thermodynamic underpinnings of such models. We focus on the use of Gibbs free energy instead of Helmholtz free energy, and using the standard Giesekus/Oldroyd-B models, we show how the alternative approach works in the case of well-known models. The proposed approach is straightforward to generalize to more complex settings wherein the classical approach might be impractical or even inapplicable. Full article
(This article belongs to the Collection Non-Newtonian Fluid Mechanics)
17 pages, 3558 KiB  
Article
Frequency and Amplitude Modulations of a Moving Structure in Unsteady Non-Homogeneous Density Fluid Flow
by Tolotra Emerry Rajaomazava III, Mustapha Benaouicha, Jacques-André Astolfi and Abdel-Ouahab Boudraa
Fluids 2021, 6(3), 130; https://doi.org/10.3390/fluids6030130 - 21 Mar 2021
Cited by 4 | Viewed by 2019
Abstract
A fluid-structure interaction’s effects on the dynamics of a hydrofoil immersed in a fluid flow of non-homogeneous density is presented and analyzed. A linearized model is applied to solve the fluid-structure coupled problem. Fluid density variations along the hydrofoil upper surface, based on [...] Read more.
A fluid-structure interaction’s effects on the dynamics of a hydrofoil immersed in a fluid flow of non-homogeneous density is presented and analyzed. A linearized model is applied to solve the fluid-structure coupled problem. Fluid density variations along the hydrofoil upper surface, based on the sinusoidal cavity oscillations, are used. It is shown that for the steady cavity case, the value of cavity length Lp does not affect the amplitude of the hydrofoil displacements. However, the natural frequency of the structure increases according to Lp. In the unsteady cavity case, the variations of the added mass and added damping (induced by the fluid density rate of change) generate frequency and amplitude modulations in the hydrofoil dynamics. To analyse this phenomena, the empirical mode decomposition, a well established data-driven method to handle such modulations, is used. Full article
(This article belongs to the Special Issue Fluid Structure Interaction: Methods and Applications)
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20 pages, 5461 KiB  
Article
Integration of Fluidic Nozzles in the New Low Emission Dual Fuel Combustion System for MGT Gas Turbines
by Bernhard Ćosić, Dominik Waßmer and Franklin Genin
Fluids 2021, 6(3), 129; https://doi.org/10.3390/fluids6030129 - 21 Mar 2021
Cited by 6 | Viewed by 7654
Abstract
Fluidic oscillators have proven their capabilities and advantages in terms of the generation of oscillating jets without moving parts for many years, mainly in experimental studies. In this paper, the design, development, and integration of fluidic atomizers into the liquid-fuel system of the [...] Read more.
Fluidic oscillators have proven their capabilities and advantages in terms of the generation of oscillating jets without moving parts for many years, mainly in experimental studies. In this paper, the design, development, and integration of fluidic atomizers into the liquid-fuel system of the dual-fuel low NOX Advanced Can Combustion (ACC) system of the MAN Gas Turbines (MGT) are presented. The two-stage system comprises a pressure-swirl nozzle as a pilot stage and an assembly of four main premixed nozzles, based on fluidic technology. The design and the features of the pilot nozzle are briefly presented, whereas the focus lies on the functionality and layout of the fluidic nozzles. The complete integration, validation, and verification of this innovative liquid-fuel injection unit are presented. The final system features fast fuel-switchovers, low complexity, high reliability, and dry low emissions in liquid-fuel operation. Full article
(This article belongs to the Special Issue Fluidic Oscillators-Devices and Applications)
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16 pages, 20888 KiB  
Article
Design of a Fluidic Actuator with Independent Frequency and Amplitude Modulation for Control of Swirl Flame Dynamics
by Amrit Adhikari, Thorge Schweitzer, Finn Lückoff and Kilian Oberleithner
Fluids 2021, 6(3), 128; https://doi.org/10.3390/fluids6030128 - 20 Mar 2021
Cited by 5 | Viewed by 2701
Abstract
Fluidic actuators are designed to control the oscillatory helical mode, called a precessing vortex core (PVC), which is often observed in gas turbine combustors. The PVC induces large-scale hydrodynamic coherent structures, which can considerably affect flow and flame dynamics. Therefore, appropriate control of [...] Read more.
Fluidic actuators are designed to control the oscillatory helical mode, called a precessing vortex core (PVC), which is often observed in gas turbine combustors. The PVC induces large-scale hydrodynamic coherent structures, which can considerably affect flow and flame dynamics. Therefore, appropriate control of this structure can lead to a more stable and efficient combustion process. Currently available flow control systems are designed to control the PVC in laboratory-scale setups. To further develop these systems and find an approach applicable to the industrial scale, a new actuator design based on fluidic oscillators is presented and studied in this paper. This actuator allows for independently adjusting forcing frequency and amplitude, which is necessary to effectively target the dynamics of the PVC. The functionality and flow control of this actuator design are studied based on numerical simulations and experimental measurements. To verify the flow control authority, the actuator is built into a prototype combustor test rig, which allows for investigating the impact of the actuator’s forcing on the PVC at isothermal conditions. The studies conducted in this work prove the desired functionality and flow control authority of the 3D-printed actuator. Accordingly, a two-part stainless steel design is derived for future test conditions with flame. Full article
(This article belongs to the Special Issue Fluidic Oscillators-Devices and Applications)
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17 pages, 2410 KiB  
Article
Anguilliform Locomotion across a Natural Range of Swimming Speeds
by Nils B. Tack, Kevin T. Du Clos and Brad J. Gemmell
Fluids 2021, 6(3), 127; https://doi.org/10.3390/fluids6030127 - 20 Mar 2021
Cited by 12 | Viewed by 4363
Abstract
Eel-like fish can exhibit efficient swimming with comparatively low metabolic cost by utilizing sub-ambient pressure areas in the trough of body waves to generate thrust, effectively pulling themselves through the surrounding water. While this is understood at the fish’s preferred swimming speed, little [...] Read more.
Eel-like fish can exhibit efficient swimming with comparatively low metabolic cost by utilizing sub-ambient pressure areas in the trough of body waves to generate thrust, effectively pulling themselves through the surrounding water. While this is understood at the fish’s preferred swimming speed, little is known about the mechanism over a full range of natural swimming speeds. We compared the swimming kinematics, hydrodynamics, and metabolic activity of juvenile coral catfish (Plotosus lineatus) across relative swimming speeds spanning two orders of magnitude from 0.2 to 2.0 body lengths (BL) per second. We used experimentally derived velocity fields to compute pressure fields and components of thrust along the body. At low speeds, thrust was primarily generated through positive pressure pushing forces. In contrast, increasing swimming speeds caused a shift in the recruitment of push and pull propulsive forces whereby sub-ambient pressure gradients contributed up to 87% of the total thrust produced during one tail-beat cycle past 0.5 BL s−1. This shift in thrust production corresponded to a sharp decline in the overall cost of transport and suggests that pull-dominated thrust in anguilliform swimmers is subject to a minimum threshold below which drag-based mechanisms are less effective. Full article
(This article belongs to the Special Issue Ecological Fluid Dynamics)
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22 pages, 27222 KiB  
Article
Heat and Mass Transfer Analysis on Magneto Micropolar Fluid Flow with Heat Absorption in Induced Magnetic Field
by Md. Mohidul Haque
Fluids 2021, 6(3), 126; https://doi.org/10.3390/fluids6030126 - 19 Mar 2021
Cited by 6 | Viewed by 2459
Abstract
Heat and mass transfer due to a magneto micropolar fluid flow along a semi-infinite vertical plate bounded by a porous medium are investigated in presence of induced magnetic field. In case of cooling flow, heat and mass fluxes from the plate are subjected [...] Read more.
Heat and mass transfer due to a magneto micropolar fluid flow along a semi-infinite vertical plate bounded by a porous medium are investigated in presence of induced magnetic field. In case of cooling flow, heat and mass fluxes from the plate are subjected to be constant under the action of a constant heat sink. Mathematical model related to the problem is developed from the basis of studying magnetohydrodynamics (MHD) for both lighter and heavier particles. Dimensionless model of momentum, microrotation, induction, energy and concentration equations are solved simultaneously by the explicit scheme of finite difference technique. According to the obtained stability and convergence criteria of this transient flow, very negligible time step (Δt = 0.002) compared to the existing works has been taken to perform the numerical computation. Quantities of chief physical interest of the flow as shear stress, couple stress, current density, Nusselt number and Sherwood number are also studied here. The numerically computed results are compared with published results of available research works. Interestingly an excellent agreement is found with finite difference solutions in both explicit and implicit schemes. In order to discuss the physical aspects of the problem, the flow variables for different values of associated parameters are illustrated in graphs. Finally, important findings of the study are listed as concluding remarks. Full article
(This article belongs to the Special Issue Fluids in Magnetic/Electric Fields)
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10 pages, 4010 KiB  
Article
Chaotic Dynamics of the Interface between Dielectric Liquids at the Regime of Stabilized Kelvin-Helmholtz Instability by a Tangential Electric Field
by Evgeny A. Kochurin and Nikolay M. Zubarev
Fluids 2021, 6(3), 125; https://doi.org/10.3390/fluids6030125 - 19 Mar 2021
Cited by 1 | Viewed by 1896
Abstract
The nonlinear dynamics of the interface between two immiscible dielectric liquids at the regime of suppressed Kelvin-Helmholtz instability by external horizontal electric field is studied theoretically. The initial equations of the fluids motion are reduced to a single weakly nonlinear integro-differential equation that [...] Read more.
The nonlinear dynamics of the interface between two immiscible dielectric liquids at the regime of suppressed Kelvin-Helmholtz instability by external horizontal electric field is studied theoretically. The initial equations of the fluids motion are reduced to a single weakly nonlinear integro-differential equation that describes the interaction of solitary waves (rational solitons) propagating along the interface. The dynamics of two interacting solitons is regular and integrable; they can combine into a stable wave packet (breather). It is shown that the interaction of three solitons becomes complex and, for a wide rang of initial conditions, chaotic. The numerically obtained Poincaré sections demonstrate the destruction of toroidal trajectories in the phase space during the transition of the system to a chaotic regime of fluid motion. Such a behaviour is consistent with the Kolmogorov-Arnold-Moser theory describing quasi-periodic chaotic motion in Hamiltonian systems. At the developed chaotic state, the system fast loses the information on its initial state; the corresponding estimate for Lyapunov exponent is obtained. From the physical point of view, the chaotic behavior of the system is related with structural instability of the soliton triplet. The triplet can decay into a solitary wave and stable breather consisting of two interacting solitons. Full article
(This article belongs to the Special Issue Recent Advances in Free Surface Hydrodynamics)
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9 pages, 3119 KiB  
Case Report
Sediment Deposition within Rainwater: Case Study Comparison of Four Different Sites in Ikorodu, Nigeria
by Chukwuemeka K. John, Jaan H. Pu, Manish Pandey and Prashanth R. Hanmaiahgari
Fluids 2021, 6(3), 124; https://doi.org/10.3390/fluids6030124 - 19 Mar 2021
Cited by 14 | Viewed by 2239
Abstract
Building roofs represents a critical pathway for sediment mixing with rainwater. This study aims to explore the correlation between roof-top deposited sediment matter in the different areas of the Ikorodu Local Government Area in Lagos, Nigeria. The deposition rate on the roof was [...] Read more.
Building roofs represents a critical pathway for sediment mixing with rainwater. This study aims to explore the correlation between roof-top deposited sediment matter in the different areas of the Ikorodu Local Government Area in Lagos, Nigeria. The deposition rate on the roof was studied for 34 weeks in total (i.e., 17 weekly analyses in the rainy season and 17 weekly analyses in the dry season). The total deposition was collected by a 10 inch funnel and directed into a 5 L container, which was partially filled with sterilised water. The roof-top deposition in four different areas was inspected and analysed. The four areas were selected based on the levels of sanitation and vegetation. The experimental results showed that the enumerated total depositions in different areas were higher in the dry season than the rainy season, with the highest deposition occurring in the Harmattan period. The data obtained from this study have evidenced that the contamination from roof-harvested rainwater can mainly be attributed to atmospheric deposition. Another key factor was the hygiene and sanitation of the harvesting areas, including the gutter, pipes and proximity to animal faeces. Full article
(This article belongs to the Special Issue Environmental Sediment Transport: Methods and Applications)
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26 pages, 10318 KiB  
Article
Wind-Forced Submesoscale Symmetric Instability around Deep Convection in the Northwestern Mediterranean Sea
by Anthony Bosse, Pierre Testor, Pierre Damien, Claude Estournel, Patrick Marsaleix, Laurent Mortier, Louis Prieur and Vincent Taillandier
Fluids 2021, 6(3), 123; https://doi.org/10.3390/fluids6030123 - 17 Mar 2021
Cited by 11 | Viewed by 3419
Abstract
During the winter from 2009 to 2013, the mixed layer reached the seafloor at about 2500 m in the northwestern Mediterranean Sea. Intense fronts around the deep convection area were repeatedly sampled by autonomous gliders. Subduction down to 200–300 m, sometimes deeper, below [...] Read more.
During the winter from 2009 to 2013, the mixed layer reached the seafloor at about 2500 m in the northwestern Mediterranean Sea. Intense fronts around the deep convection area were repeatedly sampled by autonomous gliders. Subduction down to 200–300 m, sometimes deeper, below the mixed layer was regularly observed testifying of important frontal vertical movements. Potential Vorticity dynamics was diagnosed using glider observations and a high resolution realistic model at 1-km resolution. During down-front wind events in winter, remarkable layers of negative PV were observed in the upper 100 m on the dense side of fronts surrounding the deep convection area and successfully reproduced by the numerical model. Under such conditions, symmetric instability can grow and overturn water along isopycnals within typically 1–5 km cross-frontal slanted cells. Two important hotpspots for the destruction of PV along the topographically-steered Northern Current undergoing frequent down-front winds have been identified in the western part of Gulf of Lion and Ligurian Sea. Fronts were there symmetrically unstable for up to 30 days per winter in the model, whereas localized instability events were found in the open sea, mostly influenced by mesoscale variability. The associated vertical circulations also had an important signature on oxygen and fluorescence, highlighting their under important role for the ventilation of intermediate layers, phytoplankton growth and carbon export. Full article
(This article belongs to the Special Issue Submesoscale Processes in the Ocean)
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31 pages, 473 KiB  
Article
Wind-Driven Waves on the Air-Water Interface
by Harvey Segur and Soroush Khadem
Fluids 2021, 6(3), 122; https://doi.org/10.3390/fluids6030122 - 16 Mar 2021
Viewed by 2038
Abstract
An ocean swell refers to a train of periodic or nearly periodic waves. The wave train can propagate on the free surface of a body of water over very long distances. A great deal of the current study in the dynamics of water [...] Read more.
An ocean swell refers to a train of periodic or nearly periodic waves. The wave train can propagate on the free surface of a body of water over very long distances. A great deal of the current study in the dynamics of water waves is focused on ocean swells. These swells are typically created initially in the neighborhood of an ocean storm, and then the swell propagates away from the storm in all directions. We consider a different kind of wave, called seas, which are created by and driven entirely by wind. These waves typically have no periodicity, and can rise and fall with changes in the wind. Specifically, this is a two-fluid problem, with air above a moveable interface, and water below it. We focus on the local dynamics at the air-water interface. Various properties at this locality have implications on the waves as a whole, such as pressure differentials and velocity profiles. The following analysis provides insight into the dynamics of seas, and some of the features of these intriguing waves, including a process known as white-capping. Full article
(This article belongs to the Special Issue Recent Advances in Free Surface Hydrodynamics)
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13 pages, 1702 KiB  
Article
An Analytical Investigation of Natural Convection of a Van Der Waals Gas over a Vertical Plate
by Andriy A. Avramenko, Igor V. Shevchuk and Margarita M. Kovetskaya
Fluids 2021, 6(3), 121; https://doi.org/10.3390/fluids6030121 - 15 Mar 2021
Cited by 7 | Viewed by 2417
Abstract
The study focused on a theoretical study of natural convection in a van der Waals gas near a vertical plate. A novel simplified form of the van der Waals equation derived in the study enabled analytical modeling of fluid flow and heat transfer. [...] Read more.
The study focused on a theoretical study of natural convection in a van der Waals gas near a vertical plate. A novel simplified form of the van der Waals equation derived in the study enabled analytical modeling of fluid flow and heat transfer. Analytical solutions were obtained for the velocity and temperature profiles, as well as the Nusselt numbers. It was revealed that nonlinear effects considered by the van der Waals equation of state contribute to acceleration or deceleration of the flow. This caused respective enhancement or deterioration of heat transfer. Results for a van der Waals gas were compared with respective computations using an ideal gas model. Limits of the applicability of the simplified van der Waals equations were pinpointed. Full article
(This article belongs to the Special Issue Thin Liquid Films: From Theory to Applications)
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11 pages, 10026 KiB  
Article
Heat Transfer Study of the Ferrofluid Flow in a Vertical Annular Cylindrical Duct under the Influence of a Transverse Magnetic Field
by Panteleimon A. Bakalis, Polycarpos K. Papadopoulos and Panayiotis Vafeas
Fluids 2021, 6(3), 120; https://doi.org/10.3390/fluids6030120 - 15 Mar 2021
Cited by 7 | Viewed by 2428
Abstract
We studied the laminar fully developed ferrofluid flow and heat transfer phenomena of an otherwise magnetic fluid into a vertical annular duct of circular cross-section and uniform temperatures on walls which were subjected to a transverse external magnetic field. A computational algorithm was [...] Read more.
We studied the laminar fully developed ferrofluid flow and heat transfer phenomena of an otherwise magnetic fluid into a vertical annular duct of circular cross-section and uniform temperatures on walls which were subjected to a transverse external magnetic field. A computational algorithm was used, which coupled the continuity, momentum, energy, magnetization and Maxwell’s equations, accompanied by the appropriate conditions, using the continuity–vorticity–pressure (C.V.P.) method and a non-uniform grid. The results were obtained for different values of field strength and particles’ volumetric concentration, wherein the effects of the magnetic field on the ferrofluid flow and the temperature are revealed. It is shown that the axial velocity distribution is highly affected by the field strength and the volumetric concentration, the axial pressure gradient depends almost linearly on the field strength, while the heat transfer significantly increases due to the generated secondary flow. Full article
(This article belongs to the Special Issue Fluids in Magnetic/Electric Fields)
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14 pages, 19656 KiB  
Article
Aerodynamic Dispersion of Respiratory Droplets and Aerosols by Turbulent Airflow
by Pablo Cornejo, Nicolás Guerrero and Vicente Sandoval
Fluids 2021, 6(3), 119; https://doi.org/10.3390/fluids6030119 - 13 Mar 2021
Cited by 3 | Viewed by 3119
Abstract
The precautionary measures recommended during the current COVID-19 pandemic do not consider the effect of turbulent airflow. We found the propagation of droplets and aerosols highly affected by this condition. The spread of respiratory droplets by the action of sneezing is characterized by [...] Read more.
The precautionary measures recommended during the current COVID-19 pandemic do not consider the effect of turbulent airflow. We found the propagation of droplets and aerosols highly affected by this condition. The spread of respiratory droplets by the action of sneezing is characterized by the dynamics of two groups of droplets of different sizes: Larger droplets (300–900 μm) have a ballistic trajectory and can be spread up to 5 m, while a cloud of smaller droplets (100–200 μm) can be transported and dispersed at longer distances up to 18 m by the action of the turbulent airflow. In relation to the spread of exhaled aerosols during respiration, these remain in the air for long periods of time. In the presence of intense or moderate airflow, this set of particles follow airflow streamlines, and thus their propagation is directly determined by the air velocity field. Given the scientific evidence, these results should be considered in public debate about the aerodynamic dispersion characteristics of scenarios where social interactions occur and about the measures to mitigate the spread of the virus. Full article
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26 pages, 1523 KiB  
Article
Double-Multiple Streamtube Analysis of a Flexible Vertical Axis Wind Turbine
by Lalit Roy, Kellis Kincaid, Roohany Mahmud and David W. MacPhee
Fluids 2021, 6(3), 118; https://doi.org/10.3390/fluids6030118 - 13 Mar 2021
Cited by 8 | Viewed by 3872
Abstract
Vertical-axis wind turbines (VAWTs) have drawn increased attention for off-grid and off-shore power generation due to inherent advantages over the more popular horizontal-axis wind turbines (HAWTs). Among these advantages are generator locale, omni-directionality and simplistic design. However, one major disadvantage is lower efficiency, [...] Read more.
Vertical-axis wind turbines (VAWTs) have drawn increased attention for off-grid and off-shore power generation due to inherent advantages over the more popular horizontal-axis wind turbines (HAWTs). Among these advantages are generator locale, omni-directionality and simplistic design. However, one major disadvantage is lower efficiency, which can be alleviated through blade pitching. Since each blade must transit both up- and down-stream each revolution, VAWT blade pitching techniques are not yet commonplace due to increased complexity and cost. Utilizing passively-morphing flexible blades can offer similar results as active pitching, requiring no sensors or actuators, and has shown promise in increasing VAWT performance in select cases. In this study, wind tunnel tests have been conducted with flexible and rigid-bladed NACA 0012 airfoils, in order to provide necessary input data for a Double-Multiple Stream-Tube (DMST) model. The results from this study indicate that a passively-morphing VAWT can achieve a maximum power coefficient (Cp) far exceeding that for a rigid-bladed VAWT CP (18.9% vs. 10%) with reduced normal force fluctuations as much as 6.9%. Operational range of tip-speed ratio also is observed to increase by a maximum of 40.3%. Full article
(This article belongs to the Special Issue Wind and Wave Renewable Energy Systems)
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14 pages, 1223 KiB  
Article
HVDC Converter Cooling System with a Phase Change Dispersion
by Ludger Fischer, Ernesto Mura, Geng Qiao, Poppy O’Neill, Silvan von Arx, Qi Li and Yulong Ding
Fluids 2021, 6(3), 117; https://doi.org/10.3390/fluids6030117 - 12 Mar 2021
Cited by 4 | Viewed by 6027
Abstract
High voltage direct current converters require efficient cooling of thyristors via heat sinks. Currently, infrastructures use deionised water as a means of cooling the high voltage direct current converters; however, recent research has shown that other fluids have potential to offer more efficient [...] Read more.
High voltage direct current converters require efficient cooling of thyristors via heat sinks. Currently, infrastructures use deionised water as a means of cooling the high voltage direct current converters; however, recent research has shown that other fluids have potential to offer more efficient cooling. Phase change dispersions are a new class of heat transfer fluids that employ the latent heat of phase change, thus offering isothermal cooling during melting. For cooling applications, the temperature increase during operation is thus lowered when using phase change dispersions (compared to water) and consequently, the heat sink and thyristors surface temperatures are reduced. In this investigation, a phase change dispersion with non-conductive components, high stability, high capacity and low viscosity has been developed and tested. An experimental setup of a real size heat sink has been installed and the heat transfer behaviour of both the formulated phase change dispersion and water have been investigated and a comparison has been presented. Using water as the heat transfer fluid, the temperature increase from inlet to outlet of the heat sink was 4 K and with the formulated phase change dispersion (at the same mass flow rate and heat input) the temperature increase was 2 K. The phase change dispersion caused a 50% reduction in the heat sink surface temperature. Furthermore, the global heat transfer coefficients obtained for the phase change dispersion were found to be independent of the heating input applied, unlike the trend found for water, additionally, the global heat transfer coefficients were found to be similar to those obtained for water at the same mass flow rates and reached a maximum value of 6100 W m2 K1. Despite this, the pressure drops and viscosities obtained for the phase change dispersion were higher than for water. Overall, the current investigation demonstrates the ability of using a phase change dispersion as a cooling fluid for the cooling of electronic components, which thus far is limited to using air and water cooling and cannot reach the cooling capacity achieved by phase change dispersions. Full article
(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)
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28 pages, 9305 KiB  
Article
Thermal Conductivity of Ionic Liquids and IoNanofluids. Can Molecular Theory Help?
by Xavier Paredes, Maria José Lourenço, Carlos Nieto de Castro and William Wakeham
Fluids 2021, 6(3), 116; https://doi.org/10.3390/fluids6030116 - 12 Mar 2021
Cited by 11 | Viewed by 3352
Abstract
Ionic liquids have been suggested as new engineering fluids, specifically in the area of heat transfer, and as alternatives to current biphenyl and diphenyl oxide, alkylated aromatics and dimethyl polysiloxane oils, which degrade above 200 °C, posing some environmental problems. Addition of nanoparticles [...] Read more.
Ionic liquids have been suggested as new engineering fluids, specifically in the area of heat transfer, and as alternatives to current biphenyl and diphenyl oxide, alkylated aromatics and dimethyl polysiloxane oils, which degrade above 200 °C, posing some environmental problems. Addition of nanoparticles to produce stable dispersions/gels of ionic liquids has proved to increase the thermal conductivity of the base ionic liquid, potentially contributing to better efficiency of heat transfer fluids. It is the purpose of this paper to analyze the prediction and estimation of the thermal conductivity of ionic liquids and IoNanofluids as a function of temperature, using the molecular theory of Bridgman and estimation methods previously developed for the base fluid. In addition, we consider methods that emphasize the importance of the interfacial area IL-NM in modelling the thermal conductivity enhancement. Results obtained show that it is not currently possible to predict or estimate the thermal conductivity of ionic liquids with an uncertainty commensurate with the best experimental values. The models of Maxwell and Hamilton are not capable of estimating the thermal conductivity enhancement of IoNanofluids, and it is clear that the Murshed, Leong and Yang model is not practical, if no additional information, either using imaging techniques at nanoscale or molecular dynamics simulations, is available. Full article
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10 pages, 692 KiB  
Article
Bound Coherent Structures Propagating on the Free Surface of Deep Water
by Dmitry Kachulin, Sergey Dremov and Alexander Dyachenko
Fluids 2021, 6(3), 115; https://doi.org/10.3390/fluids6030115 - 12 Mar 2021
Cited by 2 | Viewed by 1777
Abstract
This article presents a study of bound periodically oscillating coherent structures arising on the free surface of deep water. Such structures resemble the well known bi-soliton solution of the nonlinear Schrödinger equation. The research was carried out in the super-compact Dyachenko-Zakharov equation model [...] Read more.
This article presents a study of bound periodically oscillating coherent structures arising on the free surface of deep water. Such structures resemble the well known bi-soliton solution of the nonlinear Schrödinger equation. The research was carried out in the super-compact Dyachenko-Zakharov equation model for unidirectional deep water waves and the full system of nonlinear equations for potential flows of an ideal incompressible fluid written in conformal variables. The special numerical algorithm that includes a damping procedure of radiation and velocity adjusting was used for obtaining such bound structures. The results showed that in both nonlinear models for deep water waves after the damping is turned off, a periodically oscillating bound structure remains on the fluid surface and propagates stably over hundreds of thousands of characteristic wave periods without losing energy. Full article
(This article belongs to the Special Issue Recent Advances in Free Surface Hydrodynamics)
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15 pages, 8937 KiB  
Article
On the Origin of the Magnetic Concentration Gradient Force and Its Interaction Mechanisms with Mass Transfer in Paramagnetic Electrolytes
by Magne Waskaas
Fluids 2021, 6(3), 114; https://doi.org/10.3390/fluids6030114 - 11 Mar 2021
Cited by 4 | Viewed by 2544
Abstract
The objective of this work is to analyze the origin of the magnetic concentration gradient force. The force will be studied in a diffusion system where a paramagnetic electrolyte diffuses through a thin, inert membrane under the influence of a homogeneous magnetic field. [...] Read more.
The objective of this work is to analyze the origin of the magnetic concentration gradient force. The force will be studied in a diffusion system where a paramagnetic electrolyte diffuses through a thin, inert membrane under the influence of a homogeneous magnetic field. The force will be analyzed using the theory of magnetic circuits, i.e., by the concept of minimum reluctance principles. In addition, based on some previous studies, it will be discussed whether the minimum reluctance principle can be applied to mass transfer into and out of the diffusion layer at electrode/electrolyte interfaces. The results show that the magnetic concentration gradient force arises as a consequence of the minimum reluctance principle. Applied to the diffusion system, the magnetic concentration gradient force arises in the membrane as a consequence of the concentration gradient and hence, the reluctance gradient. The force acts on the flow in such a way that the reluctance in the membrane is minimized. The force implies two interaction mechanisms: attraction of the paramagnetic electrolyte flowing into the membrane in order to decrease the reluctance, and hindrance of the paramagnetic electrolyte flowing out of the membrane in order to hinder an increase in the reluctance. Based on previous studies, it is shown that the minimum reluctance principle can be applied to mass transfer into or out of the diffusion layer at electrode/electrolyte interfaces as well. Full article
(This article belongs to the Special Issue Fluids in Magnetic/Electric Fields)
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19 pages, 7215 KiB  
Article
Biomagnetic Fluid Flow and Heat Transfer Study of Blood with Gold Nanoparticles over a Stretching Sheet in the Presence of Magnetic Dipole
by Jahangir Alam, Ghulam Murtaza, Efstratios Tzirtzilakis and Mohammad Ferdows
Fluids 2021, 6(3), 113; https://doi.org/10.3390/fluids6030113 - 10 Mar 2021
Cited by 23 | Viewed by 2982
Abstract
In this study, we examined the biomagnetic flow and heat transfer of an incompressible electrically conductive fluid (blood) containing gold nanoparticles over a stretching sheet in the presence of a magnetic dipole. In this problem, both principles of magnetohydrodynamics (MHD) and ferrohydrodynamics (FHD) [...] Read more.
In this study, we examined the biomagnetic flow and heat transfer of an incompressible electrically conductive fluid (blood) containing gold nanoparticles over a stretching sheet in the presence of a magnetic dipole. In this problem, both principles of magnetohydrodynamics (MHD) and ferrohydrodynamics (FHD) were adopted. Biot number and slip and suction parameters were taken into consideration. The nonlinear partial differential equations were transformed into ordinary differential equations by implementing similarity transformations. The numerical solution was attained by utilizing the bvp4c function technique in MATLAB R2018b software. The influence of pertinent parameters involved in this model, such as ferromagnetic parameter, magnetic field parameter, Grashof number, Eckert number, suction parameter, Biot number, slip parameter and Prandtl number, on the dimensionless velocity, temperature, skin friction and heat transfer rate were analyzed numerically and are represented graphically. Among the numerous results, it was observed that increment in ferromagnetic parameter and Prandtl number results in decrement of the velocity and temperature, respectively. For some values of the parameters, a comparison with the results of other documents in the literature is also made. Full article
(This article belongs to the Special Issue Fluids in Magnetic/Electric Fields)
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12 pages, 555 KiB  
Article
Effect of Wall Boundary Conditions on a Wall-Modeled Large-Eddy Simulation in a Finite-Difference Framework
by H. Jane Bae and Adrián Lozano-Durán
Fluids 2021, 6(3), 112; https://doi.org/10.3390/fluids6030112 - 10 Mar 2021
Cited by 21 | Viewed by 3164
Abstract
We studied the effect of wall boundary conditions on the statistics in a wall-modeled large-eddy simulation (WMLES) of turbulent channel flows. Three different forms of the boundary condition based on the mean stress-balance equations were used to supply the correct mean wall shear [...] Read more.
We studied the effect of wall boundary conditions on the statistics in a wall-modeled large-eddy simulation (WMLES) of turbulent channel flows. Three different forms of the boundary condition based on the mean stress-balance equations were used to supply the correct mean wall shear stress for a wide range of Reynolds numbers and grid resolutions applicable to WMLES. In addition to the widely used Neumann boundary condition at the wall, we considered a case with a no-slip condition at the wall in which the wall stress was imposed by adjusting the value of the eddy viscosity at the wall. The results showed that the type of boundary condition utilized had an impact on the statistics (e.g., mean velocity profile and turbulence intensities) in the vicinity of the wall, especially at the first off-wall grid point. Augmenting the eddy viscosity at the wall resulted in improved predictions of statistics in the near-wall region, which should allow the use of information from the first off-wall grid point for wall models without additional spatial or temporal filtering. This boundary condition is easy to implement and provides a simple solution to the well-known log-layer mismatch in WMLES. Full article
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15 pages, 3495 KiB  
Article
Reconstruction of Diffusion Coefficients and Power Exponents from Single Lagrangian Trajectories
by Leonid M. Ivanov, Collins A. Collins and Tetyana Margolina
Fluids 2021, 6(3), 111; https://doi.org/10.3390/fluids6030111 - 9 Mar 2021
Cited by 2 | Viewed by 1530
Abstract
Using discrete wavelets, a novel technique is developed to estimate turbulent diffusion coefficients and power exponents from single Lagrangian particle trajectories. The technique differs from the classical approach (Davis (1991)’s technique) because averaging over a statistical ensemble of the mean square displacement (< [...] Read more.
Using discrete wavelets, a novel technique is developed to estimate turbulent diffusion coefficients and power exponents from single Lagrangian particle trajectories. The technique differs from the classical approach (Davis (1991)’s technique) because averaging over a statistical ensemble of the mean square displacement (<X2>) is replaced by averaging along a single Lagrangian trajectory X(t) = {X(t), Y(t)}. Metzler et al. (2014) have demonstrated that for an ergodic (for example, normal diffusion) flow, the mean square displacement is <X2> = limTτX2(T,s), where τX2 (T, s) = 1/(T − s) 0Ts(X(t+Δt)X(t))2 dt, T and s are observational and lag times but for weak non-ergodic (such as super-diffusion and sub-diffusion) flows <X2> = limTτX2(T,s), where is some additional averaging. Numerical calculations for surface drifters in the Black Sea and isobaric RAFOS floats deployed at mid depths in the California Current system demonstrated that the reconstructed diffusion coefficients were smaller than those calculated by Davis (1991)’s technique. This difference is caused by the choice of the Lagrangian mean. The technique proposed here is applied to the analysis of Lagrangian motions in the Black Sea (horizontal diffusion coefficients varied from 105 to 106 cm2/s) and for the sub-diffusion of two RAFOS floats in the California Current system where power exponents varied from 0.65 to 0.72. RAFOS float motions were found to be strongly non-ergodic and non-Gaussian. Full article
(This article belongs to the Special Issue Lagrangian Transport in Geophysical Fluid Flows)
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44 pages, 8408 KiB  
Review
Physical Background, Computations and Practical Issues of the Magnetohydrodynamic Pressure Drop in a Fusion Liquid Metal Blanket
by Sergey Smolentsev
Fluids 2021, 6(3), 110; https://doi.org/10.3390/fluids6030110 - 8 Mar 2021
Cited by 38 | Viewed by 4142
Abstract
In blankets of a fusion power reactor, liquid metal (LM) breeders, such as pure lithium or lead-lithium alloy, circulate in complex shape blanket conduits for power conversion and tritium breeding in the presence of a strong plasma-confining magnetic field. The interaction of the [...] Read more.
In blankets of a fusion power reactor, liquid metal (LM) breeders, such as pure lithium or lead-lithium alloy, circulate in complex shape blanket conduits for power conversion and tritium breeding in the presence of a strong plasma-confining magnetic field. The interaction of the magnetic field with induced electric currents in the breeder results in various magnetohydrodynamic (MHD) effects on the flow. Of them, high MHD pressure losses in the LM breeder flows is one of the most important feasibility issues. To design new feasible LM breeding blankets or to improve the existing blanket concepts and designs, one needs to identify and characterize sources of high MHD pressure drop, to understand the underlying physics of MHD flows and to eventually define ways of mitigating high MHD pressure drop in the entire blanket and its sub-components. This article is a comprehensive review of earlier and recent studies of MHD pressure drop in LM blankets with a special focus on: (1) physics of LM MHD flows in typical blanket configurations, (2) development and testing of computational tools for LM MHD flows, (3) practical aspects associated with pumping of a conducting liquid breeder through a strong magnetic field, and (4) approaches to mitigation of the MHD pressure drop in a LM blanket. Full article
(This article belongs to the Special Issue Fluids in Magnetic/Electric Fields)
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17 pages, 5174 KiB  
Article
Magneto-Bioconvection Flow of Williamson Nanofluid over an Inclined Plate with Gyrotactic Microorganisms and Entropy Generation
by Tunde A. Yusuf, Fazle Mabood, B. C. Prasannakumara and Ioannis E. Sarris
Fluids 2021, 6(3), 109; https://doi.org/10.3390/fluids6030109 - 8 Mar 2021
Cited by 100 | Viewed by 3285
Abstract
The fluid flow through inclined plates has several applications in magneto-aerodynamics, materials processing and magnetohydrodynamic propulsion thermo-fluid dynamics. Inspired by these applications, the rate of entropy production in a bio-convective flow of a magnetohydrodynamic Williamson nanoliquid over an inclined convectively heated stretchy plate [...] Read more.
The fluid flow through inclined plates has several applications in magneto-aerodynamics, materials processing and magnetohydrodynamic propulsion thermo-fluid dynamics. Inspired by these applications, the rate of entropy production in a bio-convective flow of a magnetohydrodynamic Williamson nanoliquid over an inclined convectively heated stretchy plate with the influence of thermal radiation, porous materials and chemical reaction has been deliberated in this paper. The presence of microorganisms aids in stabilizing the suspended nanoparticles through a bioconvection process. Also, the thermal radiation assumed an optically thick limit approximation. With the help of similarity transformations, the coupled partial differential equations are converted to nonlinear ordinary differential equations and the resulting model is numerically tackled using the shooting method. The influences of the determining thermo-physical parameters on the flow field are incorporated and extensively discussed. The major relevant outcomes of the present analysis are that the upsurge in values of Schmidt number decays the mass transfer characteristics, but the converse trend is depicted for boost up values of the thermophoresis parameter. Enhancement in bioconvection Peclet and Schmidt numbers deteriorates the microorganism density characteristics. Further, the upsurge in the Williamson parameter declines the Bejan number and irreversibility ratio. Full article
(This article belongs to the Special Issue Fluid Flows at the Nanoscale)
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12 pages, 2929 KiB  
Article
Vibroconvective Patterns in a Layer under Translational Vibrations of Circular Polarization
by Victor Kozlov, Kirill Rysin and Aleksei Vjatkin
Fluids 2021, 6(3), 108; https://doi.org/10.3390/fluids6030108 - 6 Mar 2021
Cited by 4 | Viewed by 1498
Abstract
This article experimentally investigates thermal vibrational convection in horizontal layers, subject to circular translational oscillations in the horizontal plane. The definite direction of translational vibrations lacks investigation, and the case of a layer heated from above is considered. At large negative values of [...] Read more.
This article experimentally investigates thermal vibrational convection in horizontal layers, subject to circular translational oscillations in the horizontal plane. The definite direction of translational vibrations lacks investigation, and the case of a layer heated from above is considered. At large negative values of the gravitational Rayleigh number, the thermovibrational convection appears in a threshold manner with an increase in the vibration intensity. Our results show that in the case of strong gravitational stabilization, thermovibrational convection develops in the form of patterns with strong anisotropy of spatial periods in orthogonal directions. The vibroconvective patterns have the form of parallel rolls divided along their length into relatively short segments. The layer thickness determines the distance between the rolls, and the longitudinal wavelength, depends on the Rayleigh number. Convective cells are studied using the noninvasive thermohromic methodic. It is found that when using the tracers for flow visualization, the concentration and type of the visualizer particles have a serious impact on the shape of the observed vibroconvective structures. In particular, the presence of even a small number of tracers (used in the study of velocity fields by the PIV method) generates flows and intensifies the heat transfer below the threshold of thermovibrational convection excitation. Full article
(This article belongs to the Special Issue Thermal Flows)
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22 pages, 13690 KiB  
Article
Computational Study of Three-Dimensional Flow Past an Oscillating Cylinder Following a Figure Eight Trajectory
by Sofia Peppa, Lambros Kaiktsis, Christos E. Frouzakis and George S. Triantafyllou
Fluids 2021, 6(3), 107; https://doi.org/10.3390/fluids6030107 - 5 Mar 2021
Cited by 2 | Viewed by 2480
Abstract
The paper presents a computational study of three-dimensional flow past a cylinder forced to oscillate in a uniform stream, following a figure-eight trajectory. Flow simulations were performed for Re = 400, for different cases, defined in terms of the oscillation mode (‘counter-clockwise’ or [...] Read more.
The paper presents a computational study of three-dimensional flow past a cylinder forced to oscillate in a uniform stream, following a figure-eight trajectory. Flow simulations were performed for Re = 400, for different cases, defined in terms of the oscillation mode (‘counter-clockwise’ or ‘clockwise’), for values of the ratio, F, of the transverse oscillation frequency to the Strouhal frequency close to 1.0. The results demonstrate that, for F ≤ 1.0, counter-clockwise cylinder motion is associated with positive power transfer from the flow to the cylinder, corresponding to excitation; for the clockwise motion, power transfer is negative at intermediate to high amplitudes, corresponding to damping. For the clockwise mode, in the range F = 0.9–1.1, a transition to two-dimensional vortex street is identified for transverse oscillation amplitude exceeding a critical value. This results from the induced suction of vortices, which moves vortex formation and shedding closer to the cylinder surface, thus resulting in a narrower wake, characterized by an effective lower Reynolds number. Both oscillation modes are characterized by higher harmonics in the lift force spectrum, with the third harmonic being very pronounced, while even harmonics are present for the case of clockwise mode, resulting from a wake transition to a “S + P” mode. Full article
(This article belongs to the Special Issue Turbulent Flow)
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16 pages, 3661 KiB  
Article
On an Exact Step Length in Gradient-Based Aerodynamic Shape Optimization—Part II: Viscous Flows
by Farzad Mohebbi, Ben Evans and Mathieu Sellier
Fluids 2021, 6(3), 106; https://doi.org/10.3390/fluids6030106 - 4 Mar 2021
Cited by 4 | Viewed by 2941
Abstract
This study presents an extension of a previous study (On an Exact Step Length in Gradient-Based Aerodynamic Shape Optimization) to viscous transonic flows. In this work, we showed that the same procedure to derive an explicit expression for an exact step length β [...] Read more.
This study presents an extension of a previous study (On an Exact Step Length in Gradient-Based Aerodynamic Shape Optimization) to viscous transonic flows. In this work, we showed that the same procedure to derive an explicit expression for an exact step length βexact in a gradient-based optimization method for inviscid transonic flows can be employed for viscous transonic flows. The extended numerical method was evaluated for the viscous flows over the transonic RAE 2822 airfoil at two common flow conditions in the transonic regime. To do so, the RAE 2822 airfoil was reconstructed by a Bezier curve of degree 16. The numerical solution of the transonic turbulent flow over the airfoil was performed using the solver ANSYS Fluent (using the Spalart–Allmaras turbulence model). Using the proposed step length, a gradient-based optimization method was employed to minimize the drag-to-lift ratio of the airfoil. The gradient of the objective function with respect to design variables was calculated by the finite-difference method. Efficiency and accuracy of the proposed method were investigated through two test cases. Full article
(This article belongs to the Special Issue Recent Numerical Advances in Fluid Mechanics, Volume II)
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16 pages, 5619 KiB  
Article
Experimental Study on Coherent Structures by Particles Suspended in Half-Zone Thermocapillary Liquid Bridges: Review
by Ichiro Ueno
Fluids 2021, 6(3), 105; https://doi.org/10.3390/fluids6030105 - 4 Mar 2021
Cited by 9 | Viewed by 2075
Abstract
Coherent structures by the particles suspended in the half-zone thermocapillary liquid bridges via experimental approaches are introduced. General knowledge on the particle accumulation structures (PAS) is described, and then the spatial–temporal behaviours of the particles forming the PAS are illustrated with the results [...] Read more.
Coherent structures by the particles suspended in the half-zone thermocapillary liquid bridges via experimental approaches are introduced. General knowledge on the particle accumulation structures (PAS) is described, and then the spatial–temporal behaviours of the particles forming the PAS are illustrated with the results of the two- and three-dimensional particle tracking. Variations of the coherent structures as functions of the intensity of the thermocapillary effect and the particle size are introduced by focusing on the PAS of the azimuthal wave number m=3. Correlation between the particle behaviour and the ordered flow structures known as the Kolmogorov–Arnold—Moser tori is discussed. Recent works on the PAS of m=1 are briefly introduced. Full article
(This article belongs to the Special Issue Thermal Flows)
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18 pages, 8052 KiB  
Article
Numerical Investigation of Spray Collapse in GDI with OpenFOAM
by Jan Wilhelm Gärtner, Ye Feng, Andreas Kronenburg and Oliver T. Stein
Fluids 2021, 6(3), 104; https://doi.org/10.3390/fluids6030104 - 4 Mar 2021
Cited by 13 | Viewed by 3451
Abstract
During certain operating conditions in spark-ignited direct injection engines (GDI), the injected fuel will be superheated and begin to rapidly vaporize. Fast vaporization can be beneficial for fuel–oxidizer mixing and subsequent combustion, but it poses the risk of spray collapse. In this work, [...] Read more.
During certain operating conditions in spark-ignited direct injection engines (GDI), the injected fuel will be superheated and begin to rapidly vaporize. Fast vaporization can be beneficial for fuel–oxidizer mixing and subsequent combustion, but it poses the risk of spray collapse. In this work, spray collapse is numerically investigated for a single hole and the spray G eight-hole injector of an engine combustion network (ECN). Results from a new OpenFOAM solver are first compared against results of the commercial CONVERGE software for single-hole injectors and validated. The results corroborate the perception that the superheat ratio Rp, which is typically used for the classification of flashing regimes, cannot describe spray collapse behavior. Three cases using the eight-hole spray G injector geometry are compared with experimental data. The first case is the standard G2 test case, with iso-octane as an injected fluid, which is only slightly superheated, whereas the two other cases use propane and show spray collapse behavior in the experiment. The numerical results support the assumption that the interaction of shocks due to the underexpanded vapor jet causes spray collapse. Further, the spray structures match well with experimental data, and shock interactions that provide an explanation for the observed phenomenon are discussed. Full article
(This article belongs to the Special Issue Modelling of Reactive and Non-reactive Multiphase Flows)
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