Fluids

10 pages, 2244 KiB

Open AccessArticle

Hydrodynamics of Direct Contact Condensation Process in Desuperheater

by Hassan A. Ghazwani, Afrasyab Khan, Pavel Alexanrovich Taranenko, Vladimir Vladimirovich Sinitsin, Mofareh H. H. Ghazwani, Ali H. Alnujaie, Khairuddin Sanaullah, Atta Ullah and Andrew R. H. Rigit

Fluids 2022, 7(9), 313; https://doi.org/10.3390/fluids7090313 - 19 Sep 2022

Cited by 1 | Viewed by 2087

Abstract

Due to global environmental conditions, the focus of household heating has shifted from fossil fuels towards environmentally friendly and renewable energy sources. Desuperheaters have attracted attention as a domestic provision involving steam-induced direct contact condensation (DCC)to warm the water. The present study is [...] Read more.

Due to global environmental conditions, the focus of household heating has shifted from fossil fuels towards environmentally friendly and renewable energy sources. Desuperheaters have attracted attention as a domestic provision involving steam-induced direct contact condensation (DCC)to warm the water. The present study is an attempt to investigate the hydrodynamics in the desuperheater vessel experimentally, namely, when the pressurized pulsating steam is injected into the vessel, where the steam jet interacts co-currently with the slow-moving water. Flow visualization showed a circulation region when the pulsating steam was injected into the slow-moving water, and the peaked vorticity corresponded to the steam injection duration of 10–60 s. Sevenhot film anemometers (HFAs) were traversed axially and radially to determine the velocity fluctuations at 0–20 cm from the steam’s nozzle exit. Vortical structures indicated the entrainment of the steam with the surrounding moving water. The circulation regions were thus exhibited in relation to the steam’s injection durations as well as the downstream axial distances of 2 and 15 cm from the nozzle exit, which showed that the core local circulation at 2 cm downstream of the nozzle exit lost 75–79% of its circulation at 15 cm downstream of the nozzle exit. Full article

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28 pages, 6947 KiB

Open AccessArticle

Design of a Pyroacuotubular (Mixed) Boiler for the Reduction of Flue Gas Emissions through the Simultaneous Generation of Hot Water and Water Steam

by Duilio Aguilar Vizcarra, Doris Esenarro and Ciro Rodriguez

Fluids 2022, 7(9), 312; https://doi.org/10.3390/fluids7090312 - 18 Sep 2022

Cited by 1 | Viewed by 3188

Abstract

Environmental protection is a continuous challenge that requires innovating the combustion process of boilers that emit polluting gases. This research proposes a novel pyroacuotubular (mixed) boiler design that reduces the emission of combustion gases by hot water and steam. The applied methodology considers [...] Read more.

Environmental protection is a continuous challenge that requires innovating the combustion process of boilers that emit polluting gases. This research proposes a novel pyroacuotubular (mixed) boiler design that reduces the emission of combustion gases by hot water and steam. The applied methodology considers the dimensioning-construction, modification, and analytical calculation of water volume, metallic masses, heat for hot water and steam generation, and combustion gases. The Ganapaty method of heat transfer is applied to prioritize the velocity of gas displacement, the pressure drop along the pipe, and its application on surfaces. In the parallel generation of hot water and steam, a mass of CO₂ (1782.72 kg/h) and CO (5.48 kg/h) was obtained; these masses were compared with the results of the proposed design, obtaining a reduction in the mass of gases emitted to the environment in hot water CO₂ (44.35%) and CO (44.27%); steam CO₂ (55.65%) and CO (55.66%). A significant reduction was achieved in the simultaneous generation of hot water and steam compared to the individual generation, which shows that the simultaneous generation of the pyroacuotubular (mixed) boiler reduces the emission of combustion gases. Full article

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16 pages, 6813 KiB

Open AccessArticle

Development and Testing of a Mathematical Model for Dynamic Network Simulation of the Oil Displacement Process

by Sergey A. Filimonov, Maxim I. Pryazhnikov, Andrey I. Pryazhnikov and Andrey V. Minakov

Fluids 2022, 7(9), 311; https://doi.org/10.3390/fluids7090311 - 16 Sep 2022

Cited by 2 | Viewed by 1585

Abstract

Multiphase flows in porous media are widespread in nature and various technologies. One of the most common examples of this kind of task is the task of recovering oil from the rock. This article describes a mathematical model of the flow of a [...] Read more.

Multiphase flows in porous media are widespread in nature and various technologies. One of the most common examples of this kind of task is the task of recovering oil from the rock. This article describes a mathematical model of the flow of a two-phase (immiscible) liquid based on a new approach of network hydrodynamics for a highly branched microchannel medium (simulating a porous space in the rock). The coupling of the flow and pressure fields in the network is performed using a well-proven SIMPLE algorithm in CFD problems; this approach allows us to use effective approaches to modeling 3D tasks. Phase transfer over the network is carried out by an explicit method with an adaptive time step. The article presents the results of verification of the model, with analytical calculations and in comparison with the results of experimental studies. As an experiment, the displacement of oil from a microchip (Dolomite: 3200284) simulating a porous medium was simulated. The good qualitative and quantitative compliance with the results calculated and the results of the experiment show the correct functioning of the model. Full article

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17 pages, 5663 KiB

Open AccessArticle

Integration within Fluid Dynamic Solvers of an Advanced Geometric Parameterization Based on Mesh Morphing

by Ubaldo Cella, Daniele Patrizi, Stefano Porziani, Torbjörn Virdung and Marco Evangelos Biancolini

Fluids 2022, 7(9), 310; https://doi.org/10.3390/fluids7090310 - 16 Sep 2022

Cited by 1 | Viewed by 2113

Abstract

Numerical optimization procedures are one of the most powerful approaches with which to support design processes. Their implementation, nevertheless, involves several conceptual and practical complexities. One of the key points relates to the geometric parameterization technique to be adopted and its coupling with [...] Read more.

Numerical optimization procedures are one of the most powerful approaches with which to support design processes. Their implementation, nevertheless, involves several conceptual and practical complexities. One of the key points relates to the geometric parameterization technique to be adopted and its coupling with the numerical solver. This paper describes the setup of a procedure in which the shape parameterization, based on mesh morphing, is integrated into the analysis tool, accessing the grid nodes directly within the solver environment. Such a coupling offers several advantages in terms of robustness and computational time. Furthermore, the ability to morph the mesh “on the fly” during the computation, without heavy Input/Output operations, extends the solver’s capability to evaluate multidisciplinary phenomena. The procedure was preliminary tested on a simple typical shape optimization problem and then applied to a complex setup of an industrial case: the identification of the shape of a Volvo side-view mirror that minimizes the accumulation of water on the lens of a camera mounted beneath. Full article

(This article belongs to the Special Issue Aerodynamics and Aeroacoustics of Vehicles, Volume II)

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12 pages, 3073 KiB

Open AccessArticle

Aerodynamic Study of a Drag Reduction System and Its Actuation System for a Formula Student Competition Car

by Ricardo Loução, Gonçalo O. Duarte and Mário J. G. C. Mendes

Fluids 2022, 7(9), 309; https://doi.org/10.3390/fluids7090309 - 16 Sep 2022

Cited by 3 | Viewed by 8472

Abstract

This work presents a computational fluid dynamic (CFD) analysis of a drag reduction system (DRS) used in a Formula Student competition vehicle, focusing on the interaction between the triple wing elements, as well as on the electrical actuators used to provide movement to [...] Read more.

This work presents a computational fluid dynamic (CFD) analysis of a drag reduction system (DRS) used in a Formula Student competition vehicle, focusing on the interaction between the triple wing elements, as well as on the electrical actuators used to provide movement to the upper two flaps. The S1123 wing profile was chosen, and a 2D analysis of the wing profile was made. The trailing edge was rounded off to conform to Formula Student competition safety rules, resulting in around a 4% decrease in the lift coefficient and around a 12% increase in the drag coefficient for an angle of attack of 12°, compared to the original wing profile. The multi-element profile characteristics are: wing main plate with 4°, first flap 28°, and second flap 60°. To evaluate the wing operation, end plates and electrical linear actuators were added, generating a maximum lift coefficient of 1.160 and drag coefficient of 0.397, which provides around a 10% reduction in lift and a 9% increase in drag compared to the absence of the linear actuators. When activating the DRS, the flap rotation generates about a 78% decrease in the aerodynamic drag coefficient and 53% in the lift coefficient for the minimum aerodynamic drag setting. Full article

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10 pages, 2522 KiB

Open AccessArticle

Computational Inertial Microfluidics: Optimal Design for Particle Separation

by Suvash C. Saha, Isabella Francis and Tanya Nassir

Fluids 2022, 7(9), 308; https://doi.org/10.3390/fluids7090308 - 16 Sep 2022

Cited by 6 | Viewed by 3213

Abstract

Following the emergence of many blood transfusion-associated diseases, novel passive cell separation technologies, such as microfluidic devices, are increasingly designed and optimized to separate red blood cells (RBCs) and white blood cells (WBCs) from whole blood. These systems allow for the rapid diagnosis [...] Read more.

Following the emergence of many blood transfusion-associated diseases, novel passive cell separation technologies, such as microfluidic devices, are increasingly designed and optimized to separate red blood cells (RBCs) and white blood cells (WBCs) from whole blood. These systems allow for the rapid diagnosis of diseases without relying on complicated and expensive hematology instruments such as flow microscopes, coagulation analyzers, and cytometers. The inertia effect and the impact of intrinsic hydrodynamic forces, the Dean drag force (F_D), and the inertial lift force (F_L) on the migration of particles within curved and complex confined channels have been explored theoretically, computationally, and experimentally. This study aimed to optimize the dimensions of a microfluidic channel for fast particle propagation and separation. Several spiral geometries with different cross-sections were tested using computational fluid dynamics (CFD) to separate two particle types representing RBCs and WBCs. The chosen three geometries consist of a single inlet, two outlets, and three spiral turns, each having a different cross-sectional height (120, 135, and 150 µm). Particle separation was successfully achieved in the 135 µm-height microchannel, while other microchannels demonstrated mixed particle types at the outlets. Full article

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

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14 pages, 1963 KiB

Open AccessArticle

Pressure Fluctuation near the Limiting Characteristics in a Sonic Flow around NACA0012 Airfoil

by Lei Zhang and Zi-Niu Wu

Fluids 2022, 7(9), 307; https://doi.org/10.3390/fluids7090307 - 16 Sep 2022

Viewed by 1666

Abstract

Pressure fluctuation for flow around an airfoil has been well studied for subsonic, transonic and supersonic flows. In this paper, the sonic flow case is studied using a NACA0012 airfoil. It is known that such a flow has a limiting characteristic line which [...] Read more.

Pressure fluctuation for flow around an airfoil has been well studied for subsonic, transonic and supersonic flows. In this paper, the sonic flow case is studied using a NACA0012 airfoil. It is known that such a flow has a limiting characteristic line which is known to separate the supersonic region into an upstream zone(U-zone) and a downstream zone(D-zone) where the pressure waves propagate into different directions, thus it is interesting to investigate whether the pressure fluctuation also exhibits special behavior along the limiting characteristic line. From an analysis of the pressure fluctuation properties by detached eddy simulation and method of characteristics, it is found that the pressure fluctuation exhibits different behavior in these two zones, and displays interesting properties along the limiting characteristic line. The fluctuation pressure is the largest along the limiting characteristic line, while the correlation coefficient between two adjacent points is the smallest along the limiting characteristic line. Away from the limiting characteristic line, the fluctuation pressure decays. Moreover, there is a spatial variation of the pressure fluctuation across the boundary layer. This spatial variation is in the mid-frequency band in the U-zone, in the high-frequency band in the D-zone, and in the entire-frequency band along the limiting characteristics line.The special behavior of the pressure fluctuation along the limiting characteristic line revealed by this study enriches our knowledge about transonic flow. Full article

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19 pages, 5660 KiB

Open AccessArticle

Frequency Specificity of Liquid-Fountain Swinging with Mist Generation: Effects of Ultrasonic Irradiation Angle

by Xiaolu Wang and Katsumi Tsuchiya

Fluids 2022, 7(9), 306; https://doi.org/10.3390/fluids7090306 - 16 Sep 2022

Cited by 1 | Viewed by 1774

Abstract

Atomization of liquid into the air attained through submerged ultrasound irradiation will involve the formation of liquid fountain, which exhibits a sequence of oscillating and/or intermittent characteristics/events: its vertical/axial growth and breakup; its lateral “compound swinging”; and its associated dynamics of mist [...] Read more.

Atomization of liquid into the air attained through submerged ultrasound irradiation will involve the formation of liquid fountain, which exhibits a sequence of oscillating and/or intermittent characteristics/events: its vertical/axial growth and breakup; its lateral “compound swinging”; and its associated dynamics of mist formation and spreading. This study attempts to provide a mechanistic view of ultrasonic atomization (UsA) process in terms of the swinging periodicity of water fountain and to specifically examine the influence of ultrasonic irradiation (i.e., transducer installation) angle on the liquid-fountain oscillations with mist generated intermittently. Through high-speed visualization, it was qualitatively found that as the extent of tilt (from the vertical direction) in the irradiation angle was increased, the degree of occurrence of mist generation and the amount of identifiable mist being generated tended to decrease. This trend was associated with reductions in both the growth rate and breakup frequency of the fountain on the tilt. It was further found, through the analysis of time variation in the resulting angle of liquid-fountain inclination, that the swinging fountain fluctuated periodically in an asymmetric manner and its periodicity could be fairly predicted based on a proposed simple “pendulum” model. An optimum value of the transducer installation angle was observed and judged to be 2° from the viewpoint of effective mist generation as well as fluid dynamic stability of the UsA liquid fountain. Full article

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13 pages, 450 KiB

Open AccessArticle

Nucleus-Acoustic Solitary Waves in Warm Degenerate Magneto-Rotating Quantum Plasmas

by Jhorna Akter and A A Mamun

Fluids 2022, 7(9), 305; https://doi.org/10.3390/fluids7090305 - 16 Sep 2022

Cited by 2 | Viewed by 1902

Abstract

A warm degenerate magneto-rotating quantum plasma (WDMRQP) model consisting of a static heavy nucleus, inertial non-degenerate light nucleus, and warm non-relativistic or ultra-relativistic electrons has been considered to observe the generation of nucleus-acoustic (NA) solitary waves (NASWs). A Korteweg–de-Vries-type equation is derived by [...] Read more.

A warm degenerate magneto-rotating quantum plasma (WDMRQP) model consisting of a static heavy nucleus, inertial non-degenerate light nucleus, and warm non-relativistic or ultra-relativistic electrons has been considered to observe the generation of nucleus-acoustic (NA) solitary waves (NASWs). A Korteweg–de-Vries-type equation is derived by using the reductive perturbation method to describe the characteristics of the NASWs. It has been observed that the temperature of warm degenerate species, rotational speed of the plasma system, and the presence of heavy nucleus species modify the basic features (height and width) of NASWs in the WDMRQP system and support the existence of positive NA wave potential only. The applications of the present investigation have been briefly discussed. Full article

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

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14 pages, 7764 KiB

Open AccessArticle

Improvement of Gas–Liquid Separation Performance of Engine Oil Using Swirling

by Shinji Kajiwara

Fluids 2022, 7(9), 304; https://doi.org/10.3390/fluids7090304 - 15 Sep 2022

Cited by 1 | Viewed by 1844

Abstract

The purpose of this study is to improve the gas–liquid separation performance of an oil tank and to establish a design method to enable gas–liquid separation only in an oil tank. Since it is difficult for conventional oil tanks to completely remove bubbles [...] Read more.

The purpose of this study is to improve the gas–liquid separation performance of an oil tank and to establish a design method to enable gas–liquid separation only in an oil tank. Since it is difficult for conventional oil tanks to completely remove bubbles remaining in the hydraulic oil, it is essential to introduce a technology to actively separate and remove bubbles from the oil. Therefore, the bubble removal performance was improved even under the condition of added lateral acceleration by appropriately generating a swirl flow. First, an acrylic model of an oil tank was used to verify the accuracy by performing numerical analysis using various turbulence models. Then, the parameters of the bubble remover, such as the size of the oil tank, were studied. In addition, the bubble removal performance under the condition of added lateral acceleration was examined. Full article

(This article belongs to the Special Issue Multiphase Flows in Engineering Applications)

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19 pages, 9441 KiB

Open AccessArticle

Numerical Simulation of the Effect of a Single Gust on the Flow Past a Square Cylinder

by Maria Kotsiopoulou and Demetri Bouris

Fluids 2022, 7(9), 303; https://doi.org/10.3390/fluids7090303 - 15 Sep 2022

Cited by 2 | Viewed by 2119

Abstract

The flow past a square cylinder under the influence of a one dimensional gust was investigated using computational fluid dynamics (CFD). The effect of upstream wind gusts of the same amplitude but different duration was investigated with respect to their effect on the [...] Read more.

The flow past a square cylinder under the influence of a one dimensional gust was investigated using computational fluid dynamics (CFD). The effect of upstream wind gusts of the same amplitude but different duration was investigated with respect to their effect on the flow, the vortex-shedding, and the pressure distribution around the square cylinder. For the computations, a very large eddy simulation (VLES) model was implemented in an in-house code and validated against numerical and experimental results from the literature. The gusts of different duration were found to have a distinctly different effect. The short-duration gust causes a lock-on behavior with cessation of the alternating vortex shedding, and a symmetric pair-vortex was created above and below the square cylinder. It was observed that the pressure distribution on the lateral sides of the cylinder has the same magnitude and phase, which resulted in a zero total lift coefficient. In terms of a free-standing structures, such as a building, this would lead to zero instantaneous forces and pressure difference in the lateral direction with obvious implications for dynamic response and cross ventilation. Full article

(This article belongs to the Special Issue Fluid Flows at the Interface between the Environment, Technology and Human Development)

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23 pages, 25584 KiB

Open AccessArticle

CFD Modeling of Wind Turbine Blades with Eroded Leading Edge

by Michael Carraro, Francesco De Vanna, Feras Zweiri, Ernesto Benini, Ali Heidari and Homayoun Hadavinia

Fluids 2022, 7(9), 302; https://doi.org/10.3390/fluids7090302 - 14 Sep 2022

Cited by 17 | Viewed by 5188

Abstract

The present work compares 2D and 3D CFD modeling of wind turbine blades to define reduced-order models of eroded leading edge arrangements. In particular, following an extensive validation campaign of the adopted numerical models, an initially qualitative comparison is carried out on the [...] Read more.

The present work compares 2D and 3D CFD modeling of wind turbine blades to define reduced-order models of eroded leading edge arrangements. In particular, following an extensive validation campaign of the adopted numerical models, an initially qualitative comparison is carried out on the 2D and 3D flow fields by looking at turbulent kinetic energy color maps. Promising similarities push the analysis to consequent quantitative comparisons. Thus, the differences and shared points between pressure, friction coefficients, and polar diagrams of the 3D blade and the simplified eroded 2D setup are highlighted. The analysis revealed that the inviscid characteristics of the system (i.e., pressure field and lift coefficients) are precisely described by the reduced-order 2D setup. On the other hand, discrepancies in the wall friction and the drag coefficients are systematically observed with the 2D model consistently underestimating the drag contribution by around 17% and triggering flow separation over different streamwise locations. Nevertheless, the proposed 2D model is very accurate in dealing with the more significant aerodynamics performance of the blade and 30 times faster than the 3D assessment in providing the same information. Therefore the proposed 2D CFD setup is of fundamental importance for use in a digital twin of any physical wind turbine with the aim of carefully and accurately planning maintenance, also accounting for leading edge erosion. Full article

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

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21 pages, 8861 KiB

Open AccessArticle

Experimental Investigation on the Spray Behaviour of Bluff Body Air-Assisted Atomizer Designs

by Raghav Sikka, Knut Vågsæther, Dag Bjerketvedt and Joachim Lundberg

Fluids 2022, 7(9), 301; https://doi.org/10.3390/fluids7090301 - 14 Sep 2022

Cited by 1 | Viewed by 1933

Abstract

This study investigates the gas dynamic effects and atomization behavior of a novel sonic bluff body-assisted two-fluid atomizer with three different geometric configurations based on airflow orifice diameters (d) of 2.0 mm, 3.0 mm, and 4.0 mm. Along with a 280 µm annular [...] Read more.

This study investigates the gas dynamic effects and atomization behavior of a novel sonic bluff body-assisted two-fluid atomizer with three different geometric configurations based on airflow orifice diameters (d) of 2.0 mm, 3.0 mm, and 4.0 mm. Along with a 280 µm annular liquid sheet, atomizers that employed a central bluff body (cone) with 6.0 mm cone distance (L_c) are compared based on the range of different air and liquid (water) flow rates. The spray-bluff body-impacted secondary atomization was characterized through volume-normalized droplet size distribution (DSD) and cumulative droplet distribution, excentricity plots, Sauter mean diameter (SMD), and relative span factor (Δ). Droplet number density decreases with the increase in radial location, with lesser droplet density for the 3.0 mm atomizer. DSD and cumulative droplet distribution become less uniform with the increase in the radial locations with wider distribution for larger diameter atomizers (4.0 mm). Droplet excentricity follows an inverse relationship with the droplet diameter such that high diameter droplets have low excentricity (%) and vice versa. SMD and relative span factor (RSF) showed opposite trends when plotted (line plots) against the air-to-liquid ratio (ALR) with larger fluctuation in the SMD than the RSF (Δ) value. The spray pattern spread increases gradually with increasing liquid loading and with decreases in the ALR value for all atomizers. Full article

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10 pages, 2208 KiB

Open AccessArticle

Experimental Validation of a Test Apparatus for the Evaluation of Hydrogen Permeation in Silane-Modified Sealants on Fuel-Cell-Powered Vehicles

by Patrizio Tiziano Locatelli Quacchia, Lorenzo Sisca, Pietro Ripa, Noemi Giorcelli and Alessandro Inferrera

Fluids 2022, 7(9), 300; https://doi.org/10.3390/fluids7090300 - 10 Sep 2022

Cited by 1 | Viewed by 2344

Abstract

Silane-modified sealants are widely used for the construction of railway vehicles and have several advantages in the production of elastic structural joints and seals featuring high bond thickness. The use of hydrogen fuel cells to power newly developed rolling stock places further safety [...] Read more.

Silane-modified sealants are widely used for the construction of railway vehicles and have several advantages in the production of elastic structural joints and seals featuring high bond thickness. The use of hydrogen fuel cells to power newly developed rolling stock places further safety constraints on the design of the sealing elements of those technical compartments that contain the storage tanks of the propulsion system. Given the lack of solutions based on the use of silane-modified sealants validated for operating environments in which leaks of gaseous hydrogen may occur, an experimental test was carried out to characterize the permeability of some adhesive products according to the requirements of the BS ISO 15105-2:2003 standard, and a specific test bench was developed for this. Two different sealants were subjected to the hydrogen permeability test. The processing of the results provided by the apparatus designed specifically for the execution of the test made it possible to determine a permeability rate dependent on the thickness of the adhesive in the order of ng/(min × cm²). The results of the test were subsequently contextualized within the technical application to rolling stock, with the ultimate aim of verifying that the permeability rate determined experimentally is compatible with the design safety criteria. The developed test bench allowed the correct execution of the permeability test. In general, the two sealants showed hydrogen permeability values compatible with the application. In particular, the hydrogen permeation rate (Rp) was lower than 0.25 ng/min for both sealants. Full article

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18 pages, 5526 KiB

Open AccessArticle

Utilization of Geogrid and Water Cushion to Reduce the Impact of Nappe Flow and Scouring on the Downstream Side of a Levee

by Fakhar Muhammad Abbas and Norio Tanaka

Fluids 2022, 7(9), 299; https://doi.org/10.3390/fluids7090299 - 10 Sep 2022

Cited by 4 | Viewed by 2119

Abstract

Water overflowing from a levee generates scour holes on the toe, which progresses towards the backward crest of the levee and results in nappe flow generation. The direct collision of nappe flow on the downstream area causes levee failure. It is important to [...] Read more.

Water overflowing from a levee generates scour holes on the toe, which progresses towards the backward crest of the levee and results in nappe flow generation. The direct collision of nappe flow on the downstream area causes levee failure. It is important to introduce a novel countermeasure against scouring caused by nappe flow. Hence, the present study utilized a new technique to reduce scouring due to nappe flow by introducing a combination of pooled water and geogrids. Herein, laboratory experiments were conducted with the three cases for rigid bed (R), named as NR, G1R, G2R (N, G1 and G2 represent no geogrid, geogrid 1 and geogrid 2, respectively), and moveable bed (M), named as NM (nothing moveable), G1M (geogrid 1 moveable), G2M (geogrid 2 moveable), to elucidate the effect of dimensionless pooled water depth (D_P*), overtopping depth (D_C*) and the aperture size of geogrids (d*) on flow structure and scouring. The results showed that the scour depth was reduced by around 17–31% during the NM cases, 57–78% during the G1M cases and 100% during the G2M cases by increasing the D_P* from 0.3 to 0.45. Hence, the combination of geogrids with pooled water (G1M, G2M) performed a vital role in suppressing the scouring, but the results of G2M were more advantageous in terms of scouring countermeasures. Full article

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11 pages, 4036 KiB

Open AccessArticle

Study of the Influence of Thermal Convection on Temperature Measurement in Thermal Control Boreholes during Artificial Ground Freezing

by Mikhail Semin and Lev Levin

Fluids 2022, 7(9), 298; https://doi.org/10.3390/fluids7090298 - 9 Sep 2022

Cited by 2 | Viewed by 1374

Abstract

This paper considers the problem of thermal convection of a calcium chloride solution in a vertical borehole. A non-uniform temperature distribution with a given vertical gradient is set at the walls of the borehole. The non-stationary temperature distribution along the borehole axis was [...] Read more.

This paper considers the problem of thermal convection of a calcium chloride solution in a vertical borehole. A non-uniform temperature distribution with a given vertical gradient is set at the walls of the borehole. The non-stationary temperature distribution along the borehole axis was analyzed, and its deviations from the temperature at the walls were investigated. From a practical point of view, this problem is important for estimating the error in distributed temperature measurements over the depth of thermal control boreholes during artificial ground freezing. In this study, an area near the bottom of the borehole was identified where the fluid temperature at the borehole axis deviates significantly from the temperature at the wall. The maximum deviations of the fluid temperature from the temperature at the walls, as well as the length of the temperature deviation sections, were determined. Full article

(This article belongs to the Special Issue Fluid Flows in Geotechnical Engineering)

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12 pages, 3537 KiB

Open AccessArticle

Detuned Resonances

by Greg Colyer, Yuuichi Asahi and Elena Tobisch

Fluids 2022, 7(9), 297; https://doi.org/10.3390/fluids7090297 - 9 Sep 2022

Viewed by 1221

Abstract

Detuned resonance, that is, resonance with some nonzero frequency mismatch, is a topic of widespread multidisciplinary interest describing many physical, mechanical, biological, and other evolutionary dispersive PDE systems. In this paper, we attempt to introduce some systematic terminology to the field, and we [...] Read more.

Detuned resonance, that is, resonance with some nonzero frequency mismatch, is a topic of widespread multidisciplinary interest describing many physical, mechanical, biological, and other evolutionary dispersive PDE systems. In this paper, we attempt to introduce some systematic terminology to the field, and we also point out some counter-intuitive features: for instance, that a resonant mismatch, if nonzero, cannot be arbitrarily small (in some well-defined sense); and that zero-frequency modes, which may be omitted by studying only exact resonances, should be considered. We illustrate these points with specific examples of nonlinear wave systems. Our main goal is to lay down the common language and foundations for a subsequent study of detuned resonances in various application areas. Full article

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

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21 pages, 7178 KiB

Open AccessArticle

Assessment of a Hybrid Eulerian–Lagrangian CFD Solver for Wind Turbine Applications and Comparison with the New MEXICO Experiment

by Nikos Spyropoulos, George Papadakis, John M. Prospathopoulos and Vasilis A. Riziotis

Fluids 2022, 7(9), 296; https://doi.org/10.3390/fluids7090296 - 8 Sep 2022

Cited by 1 | Viewed by 1949

Abstract

In this paper, the hybrid Lagrangian–Eulerian solver HoPFlow is presented and evaluated against wind tunnel measurements from the New MEXICO experiment. In the paper, the distinct solvers that assemble the HoPFlow solver are presented, alongside with details on their mutual coupling and interaction. [...] Read more.

In this paper, the hybrid Lagrangian–Eulerian solver HoPFlow is presented and evaluated against wind tunnel measurements from the New MEXICO experiment. In the paper, the distinct solvers that assemble the HoPFlow solver are presented, alongside with details on their mutual coupling and interaction. The Eulerian solver, MaPFlow, solves the compressible Navier–Stokes equations under a cell-centered finite-volume discretization scheme, while the Lagrangian solver uses numerical particles that carry mass, pressure, dilatation and vorticity as flow markers in order to represent the flow-field by following their trajectories. The velocity field is calculated with the use of the decomposition theorem introduced by Helmholtz. Computational performance is enhanced by utilizing the particle mesh (PM) methodology in order to solve the Poisson equations for the scalar potential

ϕ

and the stream function

\vec{ψ}

. The hybrid solver is tested in 3-D unsteady simulations concerning the axial flow around the wind turbine (WT) model rotor tested in the New MEXICO experimental campaign. Simulation results are presented as integrated rotor loads, radial distribution of aerodynamic forces and moments and pressure distributions at various span-wise positions along the rotor blades. Comparison is made against experimental data and computational results produced by the pure Eulerian solver. A total of 5 PM nodes per chord length of the blade section at

75 %

have been found to be sufficient to predict the loading at the tip region of the blade with great accuracy. Discrepancies with respect to measurements, observed at the root and middle sections of the blade, are attributed to the omission of the spinner geometry in the simulations. Full article

(This article belongs to the Special Issue Fluid Flows at the Interface between the Environment, Technology and Human Development)

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16 pages, 2153 KiB

Open AccessArticle

Numerical Investigation on Wave-Overtopping at a Double-Dike Defence Structure in Response to Climate Change-Induced Sea Level Rise

by Yueyuan Jin, Weizhi Wang, Arun Kamath and Hans Bihs

Fluids 2022, 7(9), 295; https://doi.org/10.3390/fluids7090295 - 8 Sep 2022

Cited by 1 | Viewed by 1814

Abstract

Climate change has tremendous economic and environmental impacts on coastal areas and threatens human lives and livelihoods in generally densely populated coastal communities. Climate change-induced sea level rise (SLR) is a particular risk factor for coastal and low-lying areas. Therefore, the study on [...] Read more.

Climate change has tremendous economic and environmental impacts on coastal areas and threatens human lives and livelihoods in generally densely populated coastal communities. Climate change-induced sea level rise (SLR) is a particular risk factor for coastal and low-lying areas. Therefore, the study on the overtopping of coastal structures in a changing climate is a critical topic for coastal protection and adaptation. As most coastal areas have shallow water conditions, the open-source nonhydrostatic shallow water equation-based model REEF3D::SFLOW is applied for the numerical investigation of overtopping over a coastal structure. Validation is performed by comparing the numerical estimations with the existing experiment presented by previous studies. The time evolution of overtopping can be predicted well by the numerical model in comparison to the experimental data. The computational speed is seen to be approximately 1500 times as fast as the Navier–Stokes equation-based counterparts. Thereafter, a comprehensive study on overtopping that takes into account different climate scenarios is presented with regard to the chosen coastal structure; this offers insights for future adaptations. The numerical approach provides an efficient alternative for the coastal protection structure adaptations in the changing climate. Full article

(This article belongs to the Special Issue Modelling and Observation of Water Waves)

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11 pages, 2960 KiB

Open AccessArticle

Rational Solitons in the Gardner-Like Models

by Efim Pelinovsky, Tatiana Talipova and Ekaterina Didenkulova

Fluids 2022, 7(9), 294; https://doi.org/10.3390/fluids7090294 - 6 Sep 2022

Cited by 4 | Viewed by 1629

Abstract

Rational solutions of nonlinear evolution equations are considered in the literature as a mathematical image of rogue waves, which are anomalously large waves that occur for a short time. In this work, bounded rational solutions of Gardner-type equations (the extended Korteweg-de Vries equation), [...] Read more.

Rational solutions of nonlinear evolution equations are considered in the literature as a mathematical image of rogue waves, which are anomalously large waves that occur for a short time. In this work, bounded rational solutions of Gardner-type equations (the extended Korteweg-de Vries equation), when a nonlinear term can be represented as a sum of several terms with arbitrary powers (not necessarily integer ones), are found. It is shown that such solutions describe first-order algebraic solitons, kinks, and pyramidal and table-top solitons. Analytical solutions are obtained for the Gardner equation with two nonlinear terms, the powers of which differ by a factor of 2. In other cases, the solutions are obtained numerically. Gardner-type equations occur in the description of nonlinear wave dynamics in a fluid layer with continuous or multilayer stratification, as well as in multicomponent plasma, and their solutions are used for the interpretation of rogue waves. Full article

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

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12 pages, 1816 KiB

Open AccessArticle

The Influence of Mitral Valve Asymmetry for an Improved Choice of Valve Repair or Replacement

by Dario Collia and Gianni Pedrizzetti

Fluids 2022, 7(9), 293; https://doi.org/10.3390/fluids7090293 - 5 Sep 2022

Cited by 2 | Viewed by 1735

Abstract

The study of valve asymmetry represents an important avenue for modern cardiac surgery. The correct choice of leaflet reconstruction may indicate a new path in the quality and long-term survival of patients. A systematic investigation was performed with a total of 25 numerical [...] Read more.

The study of valve asymmetry represents an important avenue for modern cardiac surgery. The correct choice of leaflet reconstruction may indicate a new path in the quality and long-term survival of patients. A systematic investigation was performed with a total of 25 numerical simulations using a healthy ventricle and an ideal valve with varying degrees of valve asymmetry. An overall assessment is made in terms of vorticity, kinetic energy, dissipated energy, and hemodynamic forces. The results indicate that the optimal asymmetry to consider for a valve repair or prosthetic design is between 0.2 and 0.4 with an optimal point of about 0.3. Out of this range, the heart is subjected to an excessive workload, which can only worsen the patient’s state of health. Full article

(This article belongs to the Special Issue Recent Advances in Fluid Mechanics: Feature Papers, 2022)

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23 pages, 44891 KiB

Open AccessFeature PaperArticle

On the Wake Dynamics of an Oscillating Cylinder via Proper Orthogonal Decomposition

by Benet Eiximeno, Arnau Miró, Juan Carlos Cajas, Oriol Lehmkuhl and Ivette Rodriguez

Fluids 2022, 7(9), 292; https://doi.org/10.3390/fluids7090292 - 2 Sep 2022

Cited by 4 | Viewed by 2618

Abstract

The coherent structures and wake dynamics of a two-degree-of-freedom vibrating cylinder with a low mass ratio at

R e = 5300

are investigated by means of proper orthogonal decomposition (POD) of a numerical database generated using large-eddy simulations. Two different reduced velocities of [...] Read more.

The coherent structures and wake dynamics of a two-degree-of-freedom vibrating cylinder with a low mass ratio at

R e = 5300

are investigated by means of proper orthogonal decomposition (POD) of a numerical database generated using large-eddy simulations. Two different reduced velocities of

U^{*} = 3.0

and

U^{*} = 5.5

, which correspond with the initial and super-upper branches, are considered. This is the first time that this kind of analysis is performed in this kind of system in order to understand the role of large coherent motions on the amplification of the forces. In both branches of response, almost 1000 non-correlated in-time velocity fields have been decomposed using the snapshot method. It is seen that a large number of modes is required to represent 95% of the turbulent kinetic energy of the flow, but the first two modes contain a large percentage of the energy as they represent the wake large-scale vortex tubes. The energy dispersion of the high-order modes is attributed to the cylinder movement in the inline and cross-stream directions. Substantially different POD modes have been found in the two branches. While the first six modes resemble those observed in the static cylinder or in the initial branch of a one-degree of freedom cylinder in the initial branch, the modes not only contain information about the wake vortexes in the super-upper branch but also about the formation of the 2T vortex pattern and the Taylor–Görtler structures. It is shown that the 2T vortex pattern is formed by the interplay between the Taylor–Görtler stream-wise vortical structures and the cylinder movement and is responsible for the increase in the lift force and larger elongation in the super-upper branch. Full article

(This article belongs to the Special Issue External Aerodynamics)

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6 pages, 1091 KiB

Open AccessCommunication

Heat Flux Measurement in Shock Heated Combustible Gases and Clarification of Ignition Delay Time

by Mikhail A. Kotov, Pavel V. Kozlov, Gennady Ya. Gerasimov, Vladimir Yu. Levashov, Andrey N. Shemyakin, Nikolay G. Solovyov, Mikhail Yu. Yakimov, Vladislav N. Glebov, Galina A. Dubrova and Andrey M. Malyutin

Fluids 2022, 7(9), 291; https://doi.org/10.3390/fluids7090291 - 2 Sep 2022

Viewed by 1341

Abstract

Correct understanding of the ignition and combustion processes in the combustion chambers are critical for modeling advanced schemes of engines of high-speed aircraft and promising spacecraft. Moreover, experimental data on the ignition delay time are a universal basis for the development and testing [...] Read more.

Correct understanding of the ignition and combustion processes in the combustion chambers are critical for modeling advanced schemes of engines of high-speed aircraft and promising spacecraft. Moreover, experimental data on the ignition delay time are a universal basis for the development and testing of combustion kinetic models. Moreover, the higher the temperature of the fuel mixture, the smaller this time value and the more important its correct determination. The use of a thermoelectric detector allows to measure ignition delay times and record heat fluxes with a high time resolution (to tenths of μs) during ignition in propane–air mixtures. Due to the faster response time, the use of it allows refining the ignition delay time of the combustible mixture, and the detector itself can serve as a useful device that allows a more detailed study of the ignition processes. Full article

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13 pages, 3491 KiB

Open AccessArticle

Velocity Distribution in Channels with Submerged Vegetation

by Aristotelis Mavrommatis and George Christodoulou

Fluids 2022, 7(9), 290; https://doi.org/10.3390/fluids7090290 - 31 Aug 2022

Cited by 3 | Viewed by 1878

Abstract

An experimental study is presented for investigating the effect of vegetation element geometry on the velocity distribution within and above the canopy. Three types of artificial submerged vegetation elements with common parts and different foliage are used, with two density patterns each. Detailed [...] Read more.

An experimental study is presented for investigating the effect of vegetation element geometry on the velocity distribution within and above the canopy. Three types of artificial submerged vegetation elements with common parts and different foliage are used, with two density patterns each. Detailed velocity profiles are obtained and compared at nine locations in the vegetation array. The velocity distribution above the canopy is found to closely follow a logarithmic law and its parameters, namely the shear velocity u*, zero-plane displacement height d and roughness height z₀ are determined. These depend on the vegetation density and type of element, but also on the particular position in the array. A unified velocity distribution over the water column is found appropriate for the case of stems with no foliage and also for the cases of compound elements at certain positions in the vegetation array but not at those where locally minimum velocity values occur at the foliage level. Moreover, the logarithmic profile obtained for the upper layer is seen to also fit well the measured velocities to a certain extent below the top of the canopy. Full article

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

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25 pages, 10151 KiB

Open AccessArticle

Toward the Simulation of Flashing Cryogenic Liquids by a Fully Compressible Volume of Fluid Solver

by Daniel Angel Palomino Solis and Federico Piscaglia

Fluids 2022, 7(9), 289; https://doi.org/10.3390/fluids7090289 - 30 Aug 2022

Cited by 1 | Viewed by 2791

Abstract

We present a fully compressible single-fluid volume of fluid (VOF) solver with phase change for high-speed flows, where the atomization of the liquid can occur either by the aerodynamics or by the effect of the local pressure. The VOF approximation among a non-miscible [...] Read more.

We present a fully compressible single-fluid volume of fluid (VOF) solver with phase change for high-speed flows, where the atomization of the liquid can occur either by the aerodynamics or by the effect of the local pressure. The VOF approximation among a non-miscible phase (non-condensable gas) and a mixture of two fluids (liquid and vapor) represents the liquid core of the jet and its atomization. A barotropic model is used in combination with the equation of state (EoS) to link the mixture density to pressure and temperature. The solver is written with the aim to simulate high-pressure injection in gas–liquid systems, where the pressure of the liquid is great enough to cause significant compression of the surrounding gas. Being designed in an C++ object-oriented fashion, the solver is able to support any kind of EoS; the aim is to apply it to the simulation of the injection of liquid propellant in rocket engines. The present work includes the base development; a verification assessment of the code is provided by the solution of a set of numerical experiments to prove the boundedness, convergence and accuracy of the method. Experimental measurements of a cavitating microscopic in-nozzle flow, available in the literature, are finally used for a first validation with phase change. Full article

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25 pages, 13992 KiB

Open AccessArticle

Unsteady Fluid Flows in the Slab Mold Using Anticlogging Nozzles

by María Guadalupe González-Solórzano, Rodolfo Morales Dávila, Javier Guarneros, Ismael Calderón-Ramos, Carlos Rodrigo Muñiz-Valdés and Alfonso Nájera-Bastida

Fluids 2022, 7(9), 288; https://doi.org/10.3390/fluids7090288 - 30 Aug 2022

Cited by 2 | Viewed by 1663

Abstract

The characterization of the fluid flow of liquid steel in a slab mold, using two nozzle designs under unclogged and clogged conditions, is performed using physical and mathematical simulations. Nozzle A, with an expanding and contracting geometry, yields larger sub-meniscus experimental velocities than [...] Read more.

The characterization of the fluid flow of liquid steel in a slab mold, using two nozzle designs under unclogged and clogged conditions, is performed using physical and mathematical simulations. Nozzle A, with an expanding and contracting geometry, yields larger sub-meniscus experimental velocities than nozzle B, with internal flow deflectors. The numerical predictions indicate quick time-changing velocity profiles in the submeniscus region between the mold’s narrow face and the nozzles. The flow deflectors in nozzle B have two effects; the high dissipation rate of kinetic energy in the upper-half length induces lower velocities in the ports than nozzle A. The neutralization of the biased flow caused by the sliding gate allows a balanced fluid through the ports. According to the results, nozzle A yields velocity profiles in the sub-meniscus region with larger standard deviations than nozzle B, leading to an unstable bath surface. The clogged nozzles produced biased-asymmetrical flow patterns in the mold, finding approximated matchings between numerical predictions and experimental measurements. The internal protrusions of the deposits lead to covariance losses of the bath surface wave heights. The use of internal deflectors helped to decrease the amount of clog material in nozzle B. Full article

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

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14 pages, 4871 KiB

Open AccessArticle

Hydrodynamic Characteristics of Two Side-by-Side Cylinders at a Pitch Ratio of 2 at Low Subcritical Reynolds Numbers

by Thiago Gomes, Jhon Goulart and Carla Anflor

Fluids 2022, 7(9), 287; https://doi.org/10.3390/fluids7090287 - 30 Aug 2022

Cited by 1 | Viewed by 1946

Abstract

Isothermal turbulent flow around circular cylinders arranged side-by-side was numerically simulated on a commercial finite-volumes platform, ANSYS^® CFX, version 2020 R2. The turbulence was modeled by using k-ω shear stress transport (k-ω SST). Three different Reynolds numbers were computed, Re_d [...] Read more.

Isothermal turbulent flow around circular cylinders arranged side-by-side was numerically simulated on a commercial finite-volumes platform, ANSYS^® CFX, version 2020 R2. The turbulence was modeled by using k-ω shear stress transport (k-ω SST). Three different Reynolds numbers were computed, Re_d = 200, 1000, and 3000, which were based on the cylinder diameter, d, the free stream velocity, U∞, and the kinematic viscosity of the fluid, ν. Sided cylinders were spaced apart from each other, forming a p/d ratio equal to 2, which was kept constant throughout the computations regardless of changes in the Reynolds number. The drag coefficient, C_d, as well as its time traces, was evaluated along with the different wake topologies experienced by the cylinders (wide wake WW and narrow wake NW). The simulations were able to predict the bistable flow over the cylinders and the Cd changes associated with the wakes. Whenever a new wake topology was identified, the shape drag changed in accordance with the instantaneous pressure distribution. A laminar simulation was carried out for the lowest Reynolds number case, showing that the adopted turbulence model did not affect the dynamic response of the flow. The Re_d = 3000 case was compared to Afgan’s outcomes, whose simulations were carried out in a 3-D mesh using LES (Large Eddy Simulation), showing great agreement with their results. Full article

(This article belongs to the Topic Fluid Mechanics)

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15 pages, 6031 KiB

Open AccessArticle

Effects of Surface Roughness on Shock-Wave/Turbulent Boundary-Layer Interaction at Mach 4 over a Hollow Cylinder Flare Model

by Matt Garcia, Eugene N. A. Hoffman, Elijah J. LaLonde, Christopher S. Combs, Mason Pohlman, Cary Smith, Mark T. Gragston and John D. Schmisseur

Fluids 2022, 7(9), 286; https://doi.org/10.3390/fluids7090286 - 23 Aug 2022

Cited by 6 | Viewed by 2780

Abstract

Although it is understood that surface roughness can impact boundary layer physics in high-speed flows, there has been little research aimed at understanding the potential impact of surface roughness on high-speed shock-wave/boundary-layer interactions. Here, a hollow cylinder flare model was used to study [...] Read more.

Although it is understood that surface roughness can impact boundary layer physics in high-speed flows, there has been little research aimed at understanding the potential impact of surface roughness on high-speed shock-wave/boundary-layer interactions. Here, a hollow cylinder flare model was used to study the potential impact of distributed surface roughness on shock-wave/boundary-layer interaction unsteadiness. Two surface conditions were tested—a smooth steel finish with an average roughness of 0.85 μm and a rough surface (3K carbon fiber) with an average roughness value of 9.22 μm. The separation shock foot from the shock-wave/boundary-layer interaction on the hollow cylinder flare was tracked by analyzing schlieren images with a shock tracking algorithm. The rough surface increased boundary layer thickness by approximately a factor of 10 compared to the smooth case, significantly altering the interaction scaling. Despite normalizing results, based on this boundary layer scaling, the rough surface case still exhibited mean shock foot positions further upstream more than the smooth surface case. Power spectra of the unsteady shock foot location data demonstrated that the rough surface case exhibited unsteady motion with attenuated energy relative to the smooth-wall case. Full article

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16 pages, 9180 KiB

Open AccessArticle

Study on the Sensitivity of the Streamwise Location of MVG on SWBLI in MVG-Based Supersonic Flow Control

by Yonghua Yan, Demetric L. Baines, Yong Yang, Caixia Chen and Tor A. Kwembe

Fluids 2022, 7(9), 285; https://doi.org/10.3390/fluids7090285 - 23 Aug 2022

Viewed by 1632

Abstract

Micro vortex generator (MVG) is a currently facile, robust, and feasible device for supersonic and hypersonic flow control. The purpose of this study is to investigate the impact on SWBLI from the streamwise location of MVG. Large eddy simulation (LES) was conducted on [...] Read more.

Micro vortex generator (MVG) is a currently facile, robust, and feasible device for supersonic and hypersonic flow control. The purpose of this study is to investigate the impact on SWBLI from the streamwise location of MVG. Large eddy simulation (LES) was conducted on MVG controlled supersonic ramp flow to reveal the sensitivity of MVG streamwise position on shock-wave boundary-layer interaction (SWBLI) control. Numerical cases with minor different distances between MVG and ramp corner are carried out. The results are analyzed in time-averaged and instantaneous view, respectively. The results show that streamwise position has a significant effect on SWBLI in some aspects. With minor changes on the streamwise position, the ring-like vortices generated by MVG were very similar, with only small changes in height and intensity. However, the small changes made on the ring-like vortices produced relatively significant changes to the separation region in front of the ramp. In terms of the time-averaged solution, the farther the MVG is from the ramp, the higher the ring-like vortices are lifted, and the shock wave is also disturbed/reduced more strongly. Further, the flow separation zone on the wall also appears smaller. The results of this study play a guiding role for further optimal configuration of MVG in flow control. Full article

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

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