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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Mechanical Engineering".

Deadline for manuscript submissions: closed (31 July 2021) | Viewed by 32732

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Prof. Dr. Rüdiger Schwarze

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Institute of Mechanics & Fluid Dynamics, TU Bergakademie Freiberg, Lampadiusstr 4, D-09599 Freiberg, Germany
Interests: fluid mechanics; process engineering; metallurgy; granular materials; turbomachinery

Special Issue Information

Dear Colleagues,

Fluid dynamics is often related to complex flow conditions and systems, either in the context of fundamental research or in the context of industrial processes. Typically, the study of such flows requires experimental or numerical models which capture their complex, e. g. multiphase and turbulent, nature. Although such models have been state of the art for years or decades in areas like aerodynamics or weather simulation, the field of the application of experimental and numerical flow models is constantly expanding. The goal of this Special Issue is to present an overview of applied experimental and numerical flow models, with a focus on advanced models and new application areas.

This Special Issue will consider contributions which give an overview of applied experimental and numerical flow models, with a strong focus on the following topics:

New application areas
Advanced experimental or numerical models
Innovative modeling approaches
Challenges in modeling techniques

Prof. Dr. Rüdiger Schwarze
Guest Editor

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Keywords

fluid flow
modeling
model experiments
CFD
applied fluid dynamics
multi-physics

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Published Papers (11 papers)

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Editorial

Jump to: Research

3 pages, 170 KiB

Open AccessEditorial

Experimental and Numerical Modeling of Fluid Flow

by Rüdiger Schwarze

Appl. Sci. 2022, 12(18), 9042; https://doi.org/10.3390/app12189042 - 8 Sep 2022

Cited by 1 | Viewed by 960

Abstract

Fluid dynamics is often related to complex flow conditions and systems, either in the context of fundamental research or in the context of industrial processes [...] Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

Research

Jump to: Editorial

18 pages, 5209 KiB

Open AccessArticle

Numerical Simulation of a Fire Accident in a Longitudinally Ventilated Railway Tunnel and Tenability Analysis

by Thomas Zisis, Konstantinos Vasilopoulos and Ioannis Sarris

Appl. Sci. 2022, 12(11), 5667; https://doi.org/10.3390/app12115667 - 2 Jun 2022

Cited by 11 | Viewed by 2703

Abstract

The present study examines the prevailing conditions in a railway tunnel after a train fire accident and the ability of the ventilation system to create the proper conditions for a safe passenger evacuation. The examined scenario included an event of a 20-MW diesel pool fire on a suburban train, immobilized in the middle of a 1.5-Km long, linear shaped rectangular tunnel ventilated by a longitudinal jet fan system, and the people’s movement during the evacuation was effectuated along walking platforms. More specifically, three scenarios with different fan activation times and different evacuation processes were examined. A Large Eddy simulation model (LES) was used for the simulation of the air flow in the railway tunnel. The evaluation of the ventilation system criteria considered the achievement of the air critical velocity inside the railway tunnel, and for the people’s safe evacuation, the Fractional Effective Dose (FED) value was examined. It was found that the most important action in a tunnel fire is the time, after the start of a fire, the ventilation system is activated. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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27 pages, 6555 KiB

Open AccessArticle

Air Flow Study around Isolated Cubical Building in the City of Athens under Various Climate Conditions

by Chariton L. Pavlidis, Anargyros V. Palampigik, Konstantinos Vasilopoulos, Ioannis C. Lekakis and Ioannis E. Sarris

Appl. Sci. 2022, 12(7), 3410; https://doi.org/10.3390/app12073410 - 27 Mar 2022

Cited by 5 | Viewed by 2359

Abstract

This study focuses on the airflow and pollutant dispersion around an isolated cubical building located in a warm Mediterranean climate, taking into account the local microclimate conditions (of airflow, albedo of building and soil, and air humidity) using a large-eddy simulation (LES) numerical approach. To test the reliability of computations, comparisons are made against the SILSOE cube experimental data. Three different scenarios are examined: (a) Scenario A with adiabatic walls, (b) Scenario B with the same constant temperature on all the surfaces of the building, and (c) Scenario C using convective and radiative conditions imposed by the local microclimate. For the first two cases the velocity and temperature fields resulting are almost identical. In the third case, the resulting temperature on the surfaces of the building is increased by 19.5%, the center (eye) of the wake zone is raised from the ground and the maximum pollutant concentration is drastically reduced (89%). Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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22 pages, 9160 KiB

Open AccessArticle

Thermal Performance Enhancement Using Absorber Tube with Inner Helical Axial Fins in a Parabolic Trough Solar Collector

by Mohammad Zaboli, Seyed Soheil Mousavi Ajarostaghi, Seyfolah Saedodin and Mohsen Saffari Pour

Appl. Sci. 2021, 11(16), 7423; https://doi.org/10.3390/app11167423 - 12 Aug 2021

Cited by 33 | Viewed by 3509

Abstract

In the present work, a parabolic trough solar (PTC) collector with inner helical axial fins as swirl generator or turbulator is considered and analyzed numerically. The three-dimensional numerical simulations have been done by finite volume method (FVM) using a commercial CFD code, ANSYS FLUENT 18.2. The spatial discretization of mass, momentum, energy equations, and turbulence kinetic energy has been obtained by a second-order upwind scheme. To compute gradients, Green-Gauss cell-based method has been employed. This work consists of two sections where, first, four various geometries are appraised, and in the following, the selected schematic of the collector from the previous part is selected, and four various pitches of inner helical fins including 250, 500, 750 and 1000 mm are studied. All the numerical results are obtained by utilizing the FVM. Results show that the thermal performance improvement by 23.1% could be achieved by using one of the proposed innovative parabolic trough solar collectors compare to the simple one. Additionally, the minimum and maximum thermal performance improvement (compare to the case without fins) belong to the case with P = 250 mm by 14.1% and, to the case with P = 1000 mm by 21.53%, respectively. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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24 pages, 11120 KiB

Open AccessArticle

Experimental and CFD Investigation into Using Inverted U-Tube for Gas Entrainment

by Khaled Yousef, Ahmed Hegazy and Abraham Engeda

Appl. Sci. 2020, 10(24), 9056; https://doi.org/10.3390/app10249056 - 18 Dec 2020

Cited by 1 | Viewed by 2854

Abstract

An experimental and numerical study is presented in the current work for gas entrainment using an inverted vertical U-tube. Water flows vertically up in an inverted U-tube which creates a low-pressure region in the tube upper portion. This low-pressure region can be used to extract gases by connecting it to a branch pipe. The extracted gases considered in this work are a mixture of air and water vapor. The water vapor from the side branch pipe is mixed with the flowing water under the siphon effect. This results in a progressive water vapor condensation as the mixture proceeds towards the exit due to an increase in vapor partial pressure. The air is drawn by inertia to be released out at the tube lower exit of the inverted U-pipe. The current study deals with these complicated flow behaviors due to the mixing undergoing condensation. A test rig is designed for experimentally studying the behavior of water flow in an inverted U-tube where the air is mixed with the flowing water at the top region of this tube. The CFD computations are accomplished for a side gas mixture with volume fractions up to 0.7 with water vapor mass fractions in this mixture to be 0.1–0.5. The tested water mass flow rates in the main tube are 2, 4, 6, 8 kg/s to account for all possible flow mass ratios. The CFD computations are validated with water and air two phase flow with the measurements of both the experiments of the current research and the literature. The present results reveal that slightly raising the water mass flow rate at a constant side mixture mass ratio produces a reduced generated pressure in the upper tube part. This is attributed to extra water vapor condensation taking place rapidly by increasing the water flow rate in the tube upper part. Furthermore, the turbulence quantities begin to break down at a side mixture volume fraction of 0.55 with water and air mass flow rates of 2 kg/s and 0.002 kg/s, respectively. On the other side, raising the air mass flow rate at the higher values of water vapor and water mass flow rates breaks the generated vacuum pressure and turbulence due to entrainment. Moreover, this proposed framework can produce a lower static pressure, reaching 55.1 kPa, which makes it attractive for gas extraction. This new technique presents innovative usage with less consumable energy for extracting gases in engineering equipment. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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14 pages, 3425 KiB

Open AccessArticle

In-Vitro Experimental Modeling of Oscillatory Respiratory Flow in a CT-Scanned OSAHS Tract

by Zhenshan Zhu, Yaping Ju and Chuhua Zhang

Appl. Sci. 2020, 10(22), 7979; https://doi.org/10.3390/app10227979 - 10 Nov 2020

Cited by 2 | Viewed by 2328

Abstract

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is a highly prevalent respiratory disorder. The knowledge of respiratory flow is an essential prerequisite for the establishment and development of OSAHS physiology, pathology, and clinical medicine. We made the first in-vitro experimental attempt to measure the oscillatory flow velocity in a computed tomography (CT) scanned extra-thoracic airway (ETA) model with OSAHS by using the particle image velocimetry (PIV) technique. In order to mimic respiration flow, three techniques were adopted to address difficulties in in-vitro experimental modeling: (1) fabricating the obstructive ETA measurement section with the CT-scanned data of an OSAHS patient airway; (2) maintaining the measurement accuracy by using the optical index-matching technique; (3) reproducing the oscillatory respiratory flow rates with the compiled clinical data of transient tidal volumes. The in-vitro measurements of oscillatory respiratory flow velocity manifested the time evolution of the complex OSAHS flow patterns, and the potential wall collapse of the ETA model with OSAHS. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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19 pages, 12475 KiB

Open AccessArticle

Experimental and Numerical Study on Performance Enhancement by Modifying the Flow Channel in the Mechanical Chamber Room of a Home Refrigerator

by Dong Kyun Kim

Appl. Sci. 2020, 10(18), 6284; https://doi.org/10.3390/app10186284 - 9 Sep 2020

Cited by 2 | Viewed by 4552

Abstract

Recently, many refrigerators of high have been designed so as to improve the performance of the refrigerator and to economize on energy. There are many methods of improving the total efficiency of the refrigerators using a methodological approach. In this experimental and numerical study, three methods—namely, modifying the flow channel and the operating conditions and changing the positions of the fan at the mechanical chamber room (MCR)—are used to analyze the performance improvement of the refrigerator. These methods of changing the flow channel in an MCR of a refrigerator are, in many ways, used as a regulation of the upper flow region of the condenser, especially in this research. Modifying the refrigerators’ MCR is carried out by changing the shape of the cover back machine (CBM). We compute the fluid flow in a refrigerator MCR by computational fluid dynamics (CFD) techniques. The commercial code ANSYS CFX 16.2 is used for this computation. The regulation flow region shows a reduction in power consumption of about 0.75% per month. The result of the operating conditions of the fan at MCR is relative to the flow rate for reducing power consumption. The changing positions are also relative to the length of the reducing power consumption. Moreover, with the results obtained by CFD, we understand the flow structure in a refrigerators’ MCR for various types of CBM. The results also show that the efficiency of the refrigerator is improved by 1.2%. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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19 pages, 5182 KiB

Open AccessArticle

Investigation of Fluid-Structure Interaction Induced Bending for Elastic Flaps in a Cross Flow

by Tayyaba Bano, Franziska Hegner, Martin Heinrich and Ruediger Schwarze

Appl. Sci. 2020, 10(18), 6177; https://doi.org/10.3390/app10186177 - 5 Sep 2020

Cited by 16 | Viewed by 4201

Abstract

With the recent increase in the design of light and flexible structures, numerical investigations of fluid and structure together play a significant role in most engineering applications. Therefore, the current study presents an examination of fluid-structure interaction involving flexible structures. The problem is numerically solved by a commercial software ANSYS-Workbench. Two-way coupled three-dimensional transient simulations are carried out for the flexible flaps of different thicknesses in glycerin for a laminar flow and Reynolds number ranging from 3 < Re < 12. The bending line of the flaps is compared with experimental data for different alignments of the flaps relative to the fluid flow. The study reports the computation of the maximum tip-deflection and deformation of flaps fixed at the bottom and mounted normal to the flow. Additionally, drag coefficients for flexible flaps are computed and flow regimes in the wake of the flaps are presented. As well, the study gives an understanding on how the fluid response changes as the structure deforms and the model is appropriate to predict the behavior of thick and comparatively thinner flaps. The results are sufficiently encouraging to consider the present model for analyzing turbulent flow processes against flexible objects. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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18 pages, 6555 KiB

Open AccessArticle

Numerical Simulation of the Oil Droplet Size Distribution Considering Coalescence and Breakup in Aero-Engine Bearing Chamber

by Fei Wang, Lin Wang, Guoding Chen and Donglei Zhu

Appl. Sci. 2020, 10(16), 5648; https://doi.org/10.3390/app10165648 - 14 Aug 2020

Cited by 7 | Viewed by 2892

Abstract

In order to improve the inadequacy of the current research on oil droplet size distribution in aero-engine bearing chamber, the influence of oil droplet size distribution with the oil droplets coalescence and breakup is analyzed by using the computational fluid dynamics-population balance model (CFD-PBM). The Euler–Euler equation and population balance equation are solved in Fluent software. The distribution of the gas phase velocity field and the volume fraction of different oil droplet diameter at different time are obtained in the bearing chamber. Then, the influence of different initial oil droplet diameter, air, and oil mass flow on oil droplet size distribution is discussed. The result of numerical analysis is compared with the experiment in the literature to verify the feasibility and validity. The main results provide the following conclusions. At the initial stage, the coalescence of oil droplets plays a dominant role. Then, the breakup of larger diameter oil droplet appears. Finally, the oil droplet size distribution tends to be stable. The coalescence and breakup of oil droplet increases with the initial diameter of oil droplet and the air mass flow increasing, and the oil droplet size distribution changes significantly. With the oil mass flow increasing, the coalescence and breakup of oil droplet has little change and the variation of oil droplet size distribution is not obvious. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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20 pages, 4633 KiB

Open AccessArticle

A New Vector-Based Signal Processing Method of Four-Sensor Probe for Measuring Local Gas–Liquid Two-Phase Flow Parameters Together with Its Assessment against One Bubbly Flow

by Xiaohang Qu, Qianjian Guo, Yi Zhang, Xiaoni Qi and Lei Liu

Appl. Sci. 2020, 10(16), 5463; https://doi.org/10.3390/app10165463 - 7 Aug 2020

Cited by 6 | Viewed by 2204

Abstract

A multiphase flow measurement technique plays a critical role in the studies of heat and mass transfer characteristics and mechanism of the gas–liquid two-phase, the practical measurement of the gas–liquid flow and the improvement of multiphase theoretical models. The four-sensor electrical probe as an emerging measurement method has been proved to be able to get the local flow parameters of multi-dimensional two-phase flow. However, few studies have been reported using the four-sensor probe to obtain the interface information (e.g., the interface direction and velocity). This paper presents a new signal processing method by which the interface direction and velocity can be obtained, besides void fraction, interfacial area concentration (IAC) and bubble chord length. The key solution is to employ the vector-based calculating method, which possesses the merits of simplicity and efficiency, to gain the interface velocity vector through legitimately assuming a direction of the interface velocity. A miniaturized four-sensor electrical probe was made and a gas–liquid two-phase flow experiment was performed to test the proposed signal process scheme. The two-phase flow was controlled to be in cap-bubble flow regime. To validate the availability and reliability of the proposed method, the local flow parameters obtained by the probe measurement were compared with the results from visual measurement technique in the same flow conditions. The comparison indicates that the above local flow parameters from four-sensor probe measurement are in good agreement with the visual measurement results, with maximum deviations of chord length of 8.7%, thereby proving the correctness of the proposed method. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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17 pages, 9765 KiB

Open AccessArticle

CFD Analysis of Subcooled Flow Boiling in 4 × 4 Rod Bundle

by Ye-Bon Seo, SalaiSargunan S Paramanantham, Jin-Yeong Bak, Byongjo Yun and Warn-Gyu Park

Appl. Sci. 2020, 10(13), 4559; https://doi.org/10.3390/app10134559 - 30 Jun 2020

Cited by 5 | Viewed by 3106

Abstract

Rod bundle flow is an important research field related to reactor cooling in nuclear power plants. Owing to the rapid development of computerized performance assessments, interest in coolant flow analysis using computational fluid dynamics has garnered research interest. Rod bundle flow research data compared with experimental results under various conditions are thus needed. To address this, a boiling model verification study was conducted with reference to experiments. This study adopts the Reynolds-averaged Navier–Stokes equation, a practical analysis method compared to direct numerical simulation and large eddy simulation, including turbulence modeling, to predict the flow of coolant inside a rod bundle. This study also investigates void behavior in low-pressure subcooled flow boiling using a Eulerian approach (two-fluid model). The rod bundle has a length of 0.59 m and a hydraulic diameter of approximately 14.01 mm. At the cross-section at a height of 0.58 m, near the exit, numerical results were compared with the experimental values of the volume fraction of vapor and interfacial area concentration. The simulation results showed good agreement with the experimental data for six different initial conditions with constant density. Full article

(This article belongs to the Special Issue Experimental and Numerical Modeling of Fluid Flow)

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