bluuebunny/crossref_metadata_2025_split huggingface dataset:
PIV Visualization of Flow Around Airfoil Controlled by Synthetic Jet Actuators at Shear-Layer and Wake Instability Frequencies
Authors: Yang Eric , Sullivan Pierre E. 
Published: October 2021

Abstract
The response of a separated boundary layer to synthetic jet flow control at the global wake instability (F+ ≈ 𝒪(1)) and the shear-layer instability (F+ ≈ 𝒪(10)) measured by particle image velocimetry are presented. The visualization shows that in each of the control cases, coherent vorticity develops and breaks down into a turbulent wake. When the jets are actuated by burst-modulation at the wake instability frequency, they induce regular formation and detachment of large-scale vorticity to form a wide turbulent wake. Excitation at the shear-layer instability frequency, on the other hand, produces a train of alternating velocity fluctuations in the boundary layer which dissipate to a narrower wake. Proper orthogonal decomposition of the velocity fields show that the physical extent of the jet-induced coherent structures is decreased with increasing addition of momentum for both excitation frequencies.
Modeling of Cube Array Roughness: RANS, LES, and DNS
Authors: Altland Samuel , Xu Haosen H. A. , Yang Xiang I. A. , Kunz Robert 
Published: October 2021

Abstract
Flow over arrays of cubes is an extensively studied model problem for rough wall turbulent boundary layers. While considerable research has been performed in computationally investigating these topologies using DNS and LES, the ability of sublayer-resolved RANS to predict the bulk flow phenomena of these systems is relatively unexplored, especially at low and high packing densities. Here, RANS simulations are conducted on six different packing densities of cubes in aligned and staggered configurations. The packing densities investigated span from what would classically be defined as isolated, up to those in the d-type roughness regime, filling in the gap in the present literature. Three different sublayer-resolved turbulence closure models were tested for each case; a low Reynolds number k-ε model, the Menter k-ω SST model, and a full Reynolds stress model. Comparisons of the velocity fields, secondary flow features, and drag coefficients are made between the RANS results and existing LES and DNS results. There is a significant degree of variability in the performance of the various RANS models across all comparison metrics. However, the Reynolds stress model demonstrated the best accuracy in terms of the mean velocity profile as well as drag partition across the range of packing densities.
Flow Characterization of an Industrial Size Francis Turbine Operating at Ultra-Low Load – The Effect of Water Injection
Authors: Altimemy Muhannad , Caspar Justin , Watheq Saif , Oztekin Alparslan 
Published: October 2021

Abstract
Large Eddy Simulations (LES) are carried out for a Francis turbine operating at an ultra-low load with and without injection. The flow rate of the turbine is 40% of the design value. The injection aims to improve turbine operation for the already unstable base case away from the design flow rate. Tangential water injection was introduced through the draft tube wall in the same and opposite runner rotation direction. The injection angle was varied (15°, 30°, 45° and 60°). Two water injection rates were applied at 4% and 8 % of the optimal design flowrate. While injection with the 4% rate and 30° in the opposite runner rotation direction helped reduce pressure fluctuations downstream of the injection inlets; no injection configuration could completely mitigate the power and pressure fluctuations. The injection was found to increase the amplitude of pressure fluctuations close to the injection inlets by 2 to 20 times the magnitude of fluctuations without injection. There was a slight reduction in mean power production (4–10% loss) by injection. The high amplitude fluctuations were observed in power signals with and without the injection.
Detailed Analysis of Fiber Motion in Human Nasal Airways
Authors: Li Jiang , Ma J. W. , Tu J. Y. , Tian L. , Ahmadi G. 
Published: October 2021

Abstract
Information on the fiber particle transport and deposition in human nasal airways is of great importance in inhalation toxicology study. Due to the complex interactions between the inhaled aerosol particles and human respiratory airways, the particles’ toxicity varies with their chemical composition, size, and shape. In the earlier computational study of fiber particle motion in human nasal cavities, overall deposition efficiency curves were evaluated and compared with the available experimental data. The majority of investigations were on micron-scale fiber particles, and the observed deposition fraction is strongly affected by fiber inertial impaction and the geometry of the cavity. The fiber characterization by its equivalent spheres is still not entirely fully understood. Limited existing evidence indicated that, when benchmarked by the impaction parameter, spherical particles tend to have a higher deposition fraction than that of the elongated fiber particles in the nasal cavity. More data is needed to elaborate on these observations and reveal the underlying physics. A more profound understanding of fiber transport in human airways may be obtained by comparing the fibrous particle deposition to that of the spherical particles.
In this study, simulations of transport and deposition of elongated particles in a realistic human nasal cavity model for a steady laminar airflow rate were performed. FLUENT 19.2 was used to solve the airflow conditions. The elongated ellipsoidal particle transport and deposition were simulated using the coupled translational and rotational equations of motion. The hydrodynamic drag and torque, shear-induced lift, and gravitational force were included in the analysis. One-way coupling was assumed, and an in-house User Defined Function (UDF) was developed and was implemented into the ANSYS-FLUENT code for analyzing the fiber transport and deposition. The airflow field, the particle deposition efficiency, particle deposition pattern, and single-particle trajectories of fiber and sphere were analyzed and presented. The simulation results were compared with available experimental data and simulation results in the literature.
Impact of Urban Microclimate on Air Conditioning Energy Consumption Using Different Convective Heat Transfer Coefficient Correlations Available in Building Energy Simulation Tools
Authors: Kadam Sambhaji T. , Hassan Ibrahim , Wang Liangzhu (Leon) , Rahman Mohammad Azizur 
Published: October 2021

Abstract
Rapid urbanization resulted in the drastic expansion of the built infrastructure in urban areas. This eventually led to an increase in energy consumption in the residential and commercial sectors. An appropriate selection of the convective heat transfer coefficient correlation at the design stage is of vital importance as it directly affects the cooling load of the building and consequently buildings’ energy demand. In this context, the comparative analysis of existing convective heat transfer coefficient correlations (CHTCs) used in building simulation programs such as EnergyPlus, ESP-r, IES, IDA, and TAS, are assessed. These correlations are tested against the data of Liu et al.’s [1]. It is observed that some of CHTCs correlations show lower error and others exhibit a significant deviation. In the case of the CHTCs used EnergyPlus, it is observed that the TARP algorithm shows overall better prediction ability for windward, leeward, and roof surface. On the other hand, in the case of the ESP-r, different correlations show a good prediction ability for different surfaces. For windward surface: MoWiTT; for leeward surface: MoWiTT and McAdams; and for roof surface: Liu and Harris show closer prediction with an error of less than 30% among other correlations. The correlation used in IES, IDA, and TAS shows a large deviation for windward, leeward, and roof surfaces under considered input. Based on this analysis, it can be concluded that the choice of such CHTCs uses in the BES tool can lead to the significantly higher energy consumption of the building and hence need the expertise to make the appropriate selection.
Fluid Dynamics and Contact Stress on Hard Sealing Surface Analysis of LNG Cryogenic Ball Valve
Authors: Lin Zhen-Hao , Lu Jia-Jie , Li Jun-Ye , Qian Jin-Yuan 
Published: October 2021

Abstract
LNG (liquefied natural gas) cryogenic ball valve (CBV) is an important flow control device in LNG receiving stations. Its reliability directly affects the stability of the pipeline system, especially its damage or leak in the seat seal will seriously threaten the normal operation and the safety of LNG receiving stations. When LNG flows through the CBV, due to the interaction between fluid pressure and the valve structure, the hard sealing at the valve seat is not only subjected to the pre-tightening force of saucer spring, but also affected by the fluid pressure of the complex flow. Therefore, it is necessary to study the flow characteristics in the CBV and the hard sealing performance affected by the LNG. In this paper, the fluid dynamics and the contact stress on hard sealing performance in the CBV are analyzed. The pressure drop, pressure, and velocity distributions were analyzed, respectively. The contact stress on the hard sealing surfaces of the CBV with fluid pressure was analyzed by the fluid-structure coupling method. This work has a certain reference value for researching and mastering the hard sealing performance of cryogenic ball valves.
Wall Bounded Flows and a General Proof of the Validity of the Universal Logarithmic Law of the Wall
Authors: Epple Philipp , Steppert Michael , Malcherek Andreas 
Published: October 2021

Abstract
The logarithmic law of the wall is usually derived for the flat plate assuming stationary, two-dimensional fully developed flow with no external pressure gradient. The Prandtl mixing length model for the turbulence is applied, which assumes homogeneous turbulence and two empirical constants, and the logarithmic wall law is derived. It is than stated in the textbooks that it is universally valid without a proof. As a justification experimental evidence is shown. First this proof will be shown in detail. Than a more general approach based on similarity considerations is made to show the universal validity of the logarithmic law of the wall.
Starting from the Navier-Stokes equation a general non dimensional form of this equation is derived showing its dependency from four non-dimensional numbers, the Strouhal, Euler, Reynolds and the Froude number.
Then wall bounded laminar flows are analyzed by dimensional analysis. The laminar boundary length and time scales are derived and used to non-dimensionalize the Navier-Stokes equation. With this specific non-dimensionalization for the laminar boundary layer a more specific non dimensional Navier-Stokes equation is derived. Then the high Reynolds limit is taken with considerations of orders of magnitude and the boundary layer equations are derived.
Finally, for turbulent near wall flows a dimensional analysis is made and the corresponding near wall non-dimensional velocities and coordinates y+ and u+ are derived from the Buckingham-Π theorem. Using these variables to non-dimensionalize the Navier-Stokes equations in the near wall turbulent region the third author Malcherek showed that the so derived non-dimensional Navier-Stokes equations do not depend on any non-dimensional number and has a unique solution. Hence, the logarithmic law of the wall must be universally valid, without any simplification, any turbulence model, empirical constant or further assumptions.
In such a way the students do not have to believe anymore in the universality of the logarithmic law of the wall based on empirical evidence only, now this fact has been proven by the third author Malcherek and the larger context has been elaborated by all authors for an advanced teaching of wall bounded flows.
Flow Field Investigation in Draft Tube of Francis Turbine at Off-Design Operation Using a Vortex Identification Algorithm
Authors: Kumar Sandeep , Khullar Subodh , Gandhi Bhupendra K. 
Published: October 2021

Abstract
At off-design operations, flow instabilities such as vortex breakdown, reverse flows, and stagnant regions are observed in Francis turbines. The present work shows the numerical flow field investigations of a Francis turbine at two different part loads (PL) by employing a vortex identification algorithm. The analysis has been performed at various locations in the draft tube by extracting the velocity fields at different time steps of the simulation. The first operating point involves a fully developed rotating vortex rope (RVR) in the draft tube, which precesses at a frequency of 0.28 times of the runner rotation. The present algorithm is able to identify the regions along with the eccentric local rotation center. The second operating regime shows characteristics of deep part load with central solid body rotation in the draft tube flow field. The results show highly swirling flows with very low axial velocity. The flow is confined primarily near the walls. The analysis shows that the extent of stagnation region at deep part load is more and no inner shear layer is present as compared to the part-load operation. The spatial harmonic decomposition (SHD) of the pressure data is also performed to evaluate the synchronous and asynchronous components of pressure pulsations.
Secondary Flow Loss Reduction Method by Use of Endwall Contouring in Gas Turbine Cascade Using Optimization Method
Authors: Yamamoto Kazuki , Uehara Ryota , Mizuguchi Shohei , Miyabe Masahiro 
Published: October 2021

Abstract
High efficiency is strongly demanded for gas turbines to reduce CO2 emissions. In order to improve the efficiency of gas turbines, the turbine inlet temperature is being raised higher. In that case, the turbine blade loading is higher and secondary flow loss becomes a major source of aerodynamic losses due to the interaction between the horseshoe vortex and the strong endwall cross flow. One of the authors have optimized a boundary layer fence which is a partial vane to prevent cross-flow from pressure-side to suction-side between blade to blade. However, it was also found that installing the fence leads to increase another loss due to tip vortex, wake and viscosity. Therefore, in this paper, we focused on the endwall contouring and the positive effect findings from the boundary layer fence were used to study its optimal shape. Firstly, the relationship between the location of the endwall contouring and the internal flow within the turbine cascade was investigated. Two patterns of contouring were made, one is only convex and another is just concave, and the secondary flow behavior of the turbine cascade was investigated respectively. Secondly, the shape was designed and the loss reduction effect was investigated by using optimization method. The optimized shape was manufactured by 3D-printer and experiment was conducted using cascade wind tunnel. The total pressure distributions were measured and compared with CFD results. Furthermore, flow near the endwall and the internal flow of the turbine cascade was experimentally visualized. The internal flow in the case of a flat wall (without contouring), with a fence, and with optimized endwall contouring were compared by experiment and CFD to extract the each feature.
A Versatile IBM-Based AMR Method for Studying Human Snoring
Authors: Zhang Wei , Pan Yu , Gong Yuchen , Dong Haibo , Xi Jinxiang 
Published: October 2021

Abstract
In this work, a local adaptive mesh refinement (AMR) embedded incompressible flow solver is developed for biomedical flows. This AMR technique is based on the block-structured mesh and adapted from an in-house numerical solver for the Navier-Stokes equations with immersed-boundary method embedded, which is suitable for flows with complex and moving boundaries in biomedical applications. Flow behavior of the human upper airway under various head-neck postures is evaluated using the developed AMR technique, where the head-neck posture is hypothesized to change the cross-sectional area of the airway, therefore the airflow and aerodynamic behavior. The anatomically accurate three-dimensional human upper airway model is reconstructed from human magnetic resonance images (MRI) with measurements from the literature. Analyses were performed on vortex dynamics and pressure fluctuations in the pharyngeal airway. It was found that the vortex formation and aerodynamic pressure were affected by the airway bending. The sniffing position or the head-neck junction extension posture tend to facilitate the airflow through the upper human airway.
Fractal and Convolutional Analysis for Deep Atmospheric Turbulence Using Machine Learning
Authors: Dudu Nicholas , Rodriguez Arturo , Moran Gael , Terrazas Jose , Adansi Richard , Kotteda V. M. Krushnarao , Harris Christopher , Kumar Vinod 
Published: October 2021

Abstract
Atmospheric turbulence studies indicate the presence of self-similar scaling structures over a range of scales from the inertial outer scale to the dissipative inner scale. A measure of this self-similar structure has been obtained by computing the fractal dimension of images visualizing the turbulence using the widely used box-counting method. If applied blindly, the box-counting method can lead to misleading results in which the edges of the scaling range, corresponding to the upper and lower length scales referred to above are incorporated in an incorrect way. Furthermore, certain structures arising in turbulent flows that are not self-similar can deliver spurious contributions to the box-counting dimension. An appropriately trained Convolutional Neural Network can take account of both the above features in an appropriate way, using as inputs more detailed information than just the number of boxes covering the putative fractal set. To give a particular example, how the shape of clusters of covering boxes covering the object changes with box size could be analyzed. We will create a data set of decaying isotropic turbulence scenarios for atmospheric turbulence using Large-Eddy Simulations (LES) and analyze characteristic structures arising from these. These could include contours of velocity magnitude, as well as of levels of a passive scalar introduced into the simulated flows. We will then identify features of the structures that can be used to train the networks to obtain the most appropriate fractal dimension describing the scaling range, even when this range is of limited extent, down to a minimum of one order of magnitude.
Investigation of Particle Size Effects on Solid Particle Erosion of Elbows in Series for Liquid-Solid Flows
Authors: Rajkumar Yeshwanthraj , Karimi Soroor , Shirazi Siamack A. 
Published: October 2021

Abstract
The entrainment of solid particles within the produced fluids can cause solid particle erosion by impacting the piping of production and transportation facilities. Liquid dominated flows are commonly encountered in deep water subsea pipelines while producing oil and gas fluids. It is of great importance to predict the erosion pattern and magnitude for elbows in series in liquid-solid flows as in the oil and gas productions, liquids tends to produce more solid particles compared to gas-solid flows. In the current work, erosion of elbows in series for different particle sizes are investigated by using computational fluid dynamics (CFD) and compare the erosion pattern results with the results of paint removal experiments using a 76.2 mm diameter acrylic elbows, qualitatively. CFD simulations have been performed to study the particle size effects on erosion using Reynolds stress turbulence model (RSM) and Low-Reynolds number K-ε model. Grid refinement studies have been performed and particles are rebounded at the particle radius to accurately examine the effects of particle sizes on solid particle erosion of these elbows. The CFD results shows that significant erosion is observed at the inner wall of the first elbow for larger particles, and the maximum erosion can be seen towards the end of the second elbow for 300 μm particle size.
A Comprehensive Review of 4D Flow MRI and CFD in Cardiovascular and Congenital Heart Disease
Authors: El Nihum Lamees , Chinnadurai Ponraj , Lin C. Huie , Banerjee Debjyoti 
Published: October 2021

Abstract
A growing population of adults with congenital heart disease (CHD) has spurred increased study in recent decades into the complex anatomical vasculature of congenital heart patients and the resulting hemodynamic changes that progressively affect the heart and great vessels. To this end, assessment of flow dynamics using advanced imaging technology and computational simulations have paved a path toward greater understanding of the patterns and implications of flow alterations in complex and changing vasculature, and offer promise for diagnostic and therapeutic intervention in the future. The focus of this review is to describe past studies of four-dimensional (4D) magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) in the literature as related to pathophysiology of the heart in structural and CHD. This review will highlight the importance of working with both imaging and simulation technology to co-validate experimental (4D MRI) and simulation (CFD) models, allowing for more accurate depiction of flow dynamics within human vasculature and ultimately toward improvement of the tools and methodologies used in analysis, simulation and prediction of cardiovascular hemodynamics toward enhanced diagnostics and therapeutic intervention.
Design, Microfabrication and Testing of Brain-on-a-Chip (BOC) Platform Using Neural Organoids (Spheroids)
Authors: Shettigar Nandan , El Nihum Lamees , Thyagarajan Ashok , Banerjee Debjyoti , Krencik Robert 
Published: October 2021

Abstract
Three-dimensional (3D) organoid engineering aims to steer cell aggregates toward physiological mimicking of human tissue and organ systems at the cellular level, essentially serving as tissue and organ proxies that recapitulate biological parameters (e.g., spatial organization of heterogenous tissue-specific cells, cell-cell interactions, etc.). Currently, attempts at generation of brain organoids do not mature beyond the prenatal brain equivalent, the major obstacle being the lack of vascularization in the initial embryoid bodies that ultimately limit the growth and maturation of the organoids. Thus, attention is turned toward generation of a brain-on-a-chip model that can serve as a relevant model of the human brain in its recapitulation of the neuronal circuit (i.e., organoid-on-chip or “OOC”; brain-on-chip or “BOC”). In this study, soft lithography techniques using polydimethylsiloxane (PDMS) elastomers were implemented to fabricate a microfluidic chip to serve as a BOC/OOC. A mold was fabricated using 3D printing for performing soft lithography of the BOC (followed by bonding on to a glass slide). Neural organoids (spheroids) were dispensed into the BOC using a pipette. The BOC was designed for the organoids to be captured at specific locations using micro-pillars that are located strategically within the microchannel network. Copper microelectrodes were manually inserted into the device through specially designed ports to serve as probes (as electrical sensors) and were mounted strategically for detection of electrical response from the organoids. Experiments were conducted to acquire and analyze the electrical response of the organoids when subjected to a variety of conditions (and stimuli). Two sets of organoids were tested in these experiments: organoids that are light responsive (LR) and organoids that are not light responsive (NLR). The set of experiments performed in this study include: control experiments using pure media (exposed to light), control experiments performed using media decanted from organoid suspensions (with and without exposure to light for both LR and NLR), baseline tests using organoids not exposed to light (control experiments for both LR and NLR), and experiments involving organoids exposed to variety of stimuli (light exposure, saline solution, etc. for both LR and NLR).