bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigation of a Vertical-Axis Wind Turbine Using a Three-Dimensional Panel Method
Authors: Nicola Yannick , Thümmler René , Kassera Volker , Böhle Martin 
Published: September 2024

Abstract
Vertical-axis wind turbines (VAWTs) have their rotor blades oriented vertically around a central axis of rotation. Unlike horizontal axis wind turbines (HAWTs), they do not require a mechanism to orient their blades into the wind, enabling them to capture wind from any direction. The absence of this directional adjustments makes VAWTs easier to install and to maintain. Furthermore, VAWTs can operate at a lower rotational speed, resulting in reduced noise emissions. This is one advantage making them more suitable for urban environments. The present paper discusses the procedure for calculating the aerodynamic loads on VAWTs using a three-dimensional panel method. Panel methods are based on potential theory and consider incompressible, non-viscous, irrotational flows. However, they do not account for flow separation effects but due to their fast computation time, they are primarily used for the initial aerodynamic design, such as the design of wind turbines. The paper first introduces the theoretical foundations of the numerical panel method, followed by an explanation of its application to vertical-axis wind turbines. By incorporating a rigid body motion, the rotation of the blades can be considered. Furthermore, to accurately reproduce the aerodynamics on the blades, a wake roll-up algorithm for the wingtips is utilized. The study focuses on a three-bladed vertical-axis wind turbine with NACA 0021 airfoils. For comparative purposes, transient numerical 2D simulations based on Computational Fluid Dynamics (CFD) were performed, using the OpenFOAM software. For the CFD simulations, the two-equation k-ϵ turbulence model was used. In order to minimize the effects of the VAWTs start-up process, multiple revolutions were examined in the simulations. The results obtained from the panel method and the CFD are compared, considering variations in forces and the rotor torque over the last revolution. The paper concludes by assessing the agreement between the results obtained from both methods and suggests how the panel method can be further developed with regard to accuracy and efficiency.
Sparse Reduced-Order Modeling of a Hovering Hawkmoth’s Wake
Authors: Lionetti Seth , Hedrick Tyson L. , Li Chengyu 
Published: September 2024

Abstract
As insects fly, their wings generate complex wake structures that play a crucial role in their aerodynamic force production. This study focuses on utilizing reduced order modeling techniques to gain valuable insights into the fluid dynamic principles underlying insect flight. Specifically, we used an immersed-boundary-method-based computational fluid dynamics (CFD) solver to simulate a hovering hawkmoth’s wake, and then identified the most energetic modes of the wake using proper orthogonal decomposition (POD). Furthermore, we employed a sparse identification of nonlinear dynamics (SINDy) approach to find a simple reduced order model that relates the most energetic POD modes. Through this process, we formulated multiple different models incorporating varying numbers of POD modes. To compare the accuracy of these models, we utilized a force survey method to estimate the aerodynamic forces produced by the hawkmoth’s wings. This force survey method uses an impulse-based approach to calculate the aerodynamic lift and drag based solely on the velocity and vorticity information provided by the model. By comparing the estimated aerodynamic force with the actual force production calculated by the CFD solver, we were able to find the simplest model that still provides an accurate representation of the complex wake produced by the hovering hawkmoth wings. We also evaluated the stability and accuracy of this model as the number of flapping cycles increases with time. The reduced order modeling of insect flight has important implications for the design and control of bio-inspired micro-aerial vehicles. In addition, it holds the potential to reduce the computational cost associated with high-fidelity CFD simulations of complex flows.
Optimizing Ventilation Strategy for Enhanced Airborne Disease Control in the Intensive Care Unit
Authors: Amininan Koorosh , Salmanzadeh Mazyar , Ahmadi Goodarz 
Published: September 2024

Abstract
Humans have been struggling with various infectious diseases that can spread through the air. Plague, SARS, smallpox, and influenza epidemics are a few examples of serious concerns. At the end of 2019, a new acute respiratory disease caused by the SARS-CoV-2 virus started the COVID-19 global pandemic. Recent studies have emphasized the importance of breathing and talking in the spread of airborne diseases. In this study, the chance of cross-infection in an Intensive Care Unit (ICU) in a hospital was studied numerically under different air distribution system strategies. We assumed 1 μm droplets, which carry viruses, were released from the patient’s mouth during speaking and breathing. The simulated environment was a segment of a hospital’s intensive care unit (ICU) with two nurses and two patients. Eulerian and Lagrangian approaches were used to simulate droplet movement using ANSYS-FLUENT software. The study examined two ventilation strategies, all operating at a similar ventilation rate of 12 ACH but distinguished by different inlet and outlet configurations. The purpose of the study was to understand the distribution of particles in this environment at 300-second intervals. Validation of the computational model included a comparative analysis of simulated velocity flows over a single heated humanoid manikin’s head with the experimental data. The results showed that having a downward vertical inlet airflow and air exhaust register at the top of the patient bed has the most effective droplet removal strategy.
Bubble Dynamics in Accelerating Flow Through Axisymmetric Nozzle
Authors: Shepard Thomas , Law Deify , Cunningham Connor , Churchill Will , Selvamani Arun Sriniwas , Robles Emmanuel Fernandez 
Published: September 2024

Abstract
A gas bubble traveling in a liquid flow through a convergent nozzle will experience a rapidly decreasing pressure on the leading edge of the bubble. Thus, the bubble will dynamically deform while passing through the nozzle showing an elongation of the front of the bubble. This work reports on experimental studies with high-speed imaging in a refractive index matched axisymmetric nozzle and complementary volume of fluid numerical simulations conducted via ANSYS Fluent. In these studies, an individual bubble is tracked as it flows downward approaching and then passing through the nozzle. A digital image processing algorithm is used to obtain quantitative information about the bubbles from high-speed images. Experimental results are provided that detail the bubble leading and trailing edge trajectory and bubble deformation. Under certain conditions the bubble deformation can lead to the bubble pinching apart near the leading edge, a phenomenon that was found in both the experiments and simulations. Simulation results are compared with experimental data and additionally provide information on the time-varying exit void fraction and exit velocity as the bubble accelerates through the contraction. This study examines two different bubble diameters and two different liquid flow rates to identify their role in the deforming bubble dynamics.
A Comparison Between a New Blade Design Model for Side Channel Pumps and Standard Side Channel Pump Blade Design in Terms of Performance and Flow Topology
Authors: Fleder Annika , Hassert Frank , Böhle Martin 
Published: September 2024

Abstract
Side channel pumps are low specific speed pumps with high head and low flows. The ability to process high amounts of gas in the fluid as well as the self-priming makes them a perfect match for oil and gas applications. In recent years, more attention is paid to side channel pumps especially due to their benefits in LNG (liquid natural gas) applications, e.g. as fuel pump to fulfill the increasing emission limits of cargo vessels by dual fuel or LNG propulsion.
To increase the performance of side channel pumps by increasing head and efficiency, the blade shape is investigated more in detail. Common side channel pump impeller blades have a triangular or straight cross section.
Based on earlier investigations on the flow phenomena in side channel pumps we are able to adapt the shape of the blades to the flow angle inside the pump, resulting in a new impeller blade design with a curved cross section.
As the flow angle differs from inner to outer diameter and from pressure to suction side of the blade, the blade shape was optimized to maintain the flow rate of the best efficiency point.
The new design is investigated in numerical simulation with ANSYS CFX and measurements on a water test rig at the manufacturer. A comparison with former measurements and simulations of traditional designs highlights the benefits of the new design by describing the internal flow.
Experimental and Numerical Investigations of Deformation in the Impeller of a Boiler Feed Pump at Design and Off-Design Conditions
Authors: Baum Andreas , Schneider Andreas , Knapp Axel , Grunenberg Matthias , Böhle Martin 
Published: September 2024

Abstract
Pump impellers have to be designed from two separate points of view. From a hydraulic aspect the impeller has to fulfill the specified operating conditions for flow rate, head at the speed of rotation. Additionally, from the structural point of view, the impeller must be capable to resist mechanical loads. To fulfill nowadays requirements of flexible operating conditions, the mechanical design becomes more crucial, because of increased loads at part-load operation. Consequently, trustworthy information about deformation and stress are mandatory.
The present paper deals with the comparison of mechanical deformation of a pump impeller at design and off-design operation. The full loading on the impeller caused by fluid pressure and centrifugal forces is considered in experimental and numerical investigations. Therefore, an experimental model pump, representing a repeating stage of a multistage boiler feed pump has been developed. Besides performance values, transient pressure and strain measurements at the back side of the impeller rear shroud are evaluated. For the strain measurements, strain gauges are used in Wheatstone bridges to evaluate transient data. For numerical simulations a one-way coupled Fluid Structure Interaction (FSI) model has been used. Transient Computational Fluid Dynamics (CFD) simulations have been performed for the complete model pump. For the turbulence modeling Menter’s SST model was used. In subsequent quasi-stationary Finite Elements (FE) simulations, the pressure loading on the impeller is taken from the CFD simulations for one impeller revolution.
Evaluating the Role of Ejector Nozzle Angle Deviation on the Performance of an Industrial Stack Ejector System
Authors: Ghateii Mohammad Hosein , Darbandi Masoud , Jalali Ramin , Schneider Gerry E. 
Published: September 2024

Abstract
Stack ejectors are considered as an essential component in numerous industries, serving as a pivotal mechanism for efficiently eliminating flue gas by inducing a draft. This research delves into the intricacies of stack ejector design and performance, emphasizing evaluating the consequences of deviations in ejector nozzle angles on flue gas flow. Within the stack ejector system, an air fan propels air into the stack to encourage flue gas to exit. The correct design and alignment of the ejector nozzle are paramount in maximizing flue gas flow. The computational fluid dynamics (CFD) simulations were carried out to gauge the impact of deviations in the ejector nozzle angle on flue gas flow. The results revealed that the deviations of 2, 4, and 6 degrees in the ejector nozzle angle would reduce the flue gas flow by 25%, 50%, and 60%, respectively. These findings underscore the substantial influence of ejector nozzle variations on flue gas flow within the stack ejector system. By comprehending the ramifications of nozzle angle deviation, engineers can enhance the design and alignment of stack ejectors to elevate their performances and overall efficiencies within their industrial setups.
Application of POD and DMD to Study Flow in Porous Media
Authors: Basnet Piyush , Durgesh Vibhav 
Published: September 2024

Abstract
Fluid flows in porous media exhibit diverse spatially and temporally complex structures arising from intricate interactions between fluid motion and solid interfaces/flow paths. While numerous experimental studies have aimed to quantify these complex flow structures, recent technological advancements have facilitated the widespread adoption of data-driven analysis approaches. These approaches offer invaluable insights into flow physics and can also be used for low-order modeling. The two primary objectives of this study are to apply Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) to velocity flow field data to predict the flow phenomena, develop low-order models, and apply DMD onflow visualization Planar Laser-Induced Fluorescence (PLIF) data to identify the temporal evolution of flow structures for recirculation region in porous media. An in-house refractive index-matched flow loop system was designed for the experiments, where a gear pump was used for fluid circulation, and a syringe pump was used for dye injection. The Reynolds numbers (Re) and the average porosity for the experiment were 42 and 0.39. Irregularly shaped 3 mm Tetrafluoroethylene hexafluoropropylene vinylidene fluoride (THV) beads were used as the porous media. 2D-PIV measurements were made at the center plane of the models to obtain a velocity flow field, which revealed a recirculation region. Applying POD in the PIV dataset, the energy distribution in the first twenty-five POD modes revealed key insights at Re. First twenty-five POD modes captured 74% of the recirculation region’s total energy. DMD provided dynamic insights into the velocity flow field, including frequency and growth rate associated with the frequencies in the recirculation region. Dominant frequencies were obtained using DMD, which were related to the occurrence of vortex in velocity flow field data. Low-order models were created using twenty-five POD modes and three DMD with modes with mean flow mode. The reconstructed velocity flow field data was compared with PIV velocity flow field data, resulting in an average Root Mean Square Error (RMSE) of 0.06% for POD across all regions and 1.37% for DMD low-order models for the recirculation region. Additionally, PLIF measurements using Rhodamine-B dye were used for flow visualization in the recirculation region. PLIF data offered qualitative information complementary to PIV. DMD results from flow visualization provided information about the flow dynamics of dye at Re = 42 in the recirculation region. The frequencies associated with the growth rate closer to zero in the frequency trend could capture the diffusion of dye, and the remaining frequencies captured the advection of dye. In conclusion, this study highlights the applicability of POD and DMD in unraveling the intricate dynamics of fluid flow in porous media, paving the way for future advancements in understanding and modeling these complex systems.
Expansion Ratio and the Heat Transfer Characteristics of Suddenly Expanding Viscoplastic Flows
Authors: Hammad Khaled J. 
Published: September 2024

Abstract
The impact of the expansion ratio on heat transfer from Bingham viscoplastic non-Newtonian flows through axisymmetric sudden expansions has been studied numerically by solving the mass, momentum, and energy conservation equations. Two expansion ratios 1:5 and 1:2 have been investigated. The expansion ratio has a dramatic impact on the reattachment length, in the case of Newtonian flows, and the recirculation intensity, in the case of Newtonian and viscoplastic non-Newtonian flows. In general, a more intense recirculation is associated with higher expansion ratios. The non-dimensional yield stress, i.e., yield number, is found to have a significant impact on the flow and heat transfer behavior. The relative recirculation intensity substantially diminishes with the yield number for both expansion ratios. For a given Reynolds number, increasing the yield number, results in transitioning from a recirculating to a non-recirculating viscoplastic flow regime downstream of the expansion plane. Substantial heat transfer enhancement exists downstream the expansion. A single wall heat transfer peak is observed for Newtonian and non-separating viscoplastic flows, immediately downstream of the reattachment point and corner unyielded region, respectively. However, two local peaks are observed in the case of recirculating viscoplastic flow fields. The first is close to the center of the weak corner vortex and the second is downstream of the stagnant impingement region. Peak heat transfer rates were found to substantially increase with the yield number, Prandtl number, and, to a lesser extent, with the expansion ratio.
Validating the Nonlinear Slip Boundary Conditions for Water TIP3P Using Molecular Dynamics Simulations
Authors: Islam Hafizul , Thalakkottor Joseph John 
Published: September 2024

Abstract
Studying the movement of fluid requires some assumptions about how fluid flows (the boundary condition) at the solid-fluid interface. The boundary condition, commonly known as the no-slip condition, states that fluid elements adjacent to a surface assume its velocity. Despite its remarkable success in replicating the characteristics of many flow types, this condition can produce unusual or singular behavior when applied to the spreading of a fluid on a solid substrate, corner flow, and forcing molten polymers out of a narrow tube. Maxwell and Navier’s slip model resolved these difficulties by allowing finite slip at liquid-solid interfaces. However, these phenomenological models cannot provide a universal perception of momentum transfer at liquid-solid interfaces. Thompson and Troian showed that for high shear rates, the slip is no longer a constant rather, it is a function of the shear rate. This was further extended by Thalakkottor and Mohseni, who showed slip length is more generally a function of the principal strain rate. Both these models were validated using molecular dynamics simulations of a monoatomic liquid similar to liquid Argon, which is rarely encountered in real-world applications. In this study, we simulate water instead, using the TIP3P model. Three different liquid-solid interfaces with varying degrees of hydrophobicity are studied. The study demonstrates that the nonlinear slip model, especially Thompson and Troian’s slip model, is valid for water flows as well.
Investigation of Low-High Fidelity Turbulent Models in Scramjet Engines
Authors: En-Nali Mohamed , Palakurthy Seshendra , Zope Anup , Bhushan Shanti , Collins Eric M. , Luke Edward 
Published: September 2024

Abstract
In the present work, we aim to investigate the predictive capabilities of low and high-fidelity turbulence models and understand how they perform in complex conditions in a scramjet engine. In this study, we use the DLR experiments [1] to present a comparative performance assessment of low to high fidelity turbulence models. The DLR case is interesting since it exhibits turbulence due to wall effects as well as due to shear layer. Results show relatively good agreement when compared against the validation data set from the experiment. DHRL was able to resolve more turbulence structures compared to all other models. HRL showed better prediction of the momentum deficit in the wake of the strut than all other models. Additionally, results for reacting case show that choice of turbulence models affects the intensity and lift-off distance of the flame where RANS and DHRL show the most rigorous flame and a smooth peak in temperature profile near the base of the strut at the centerline while IDDES and HRL show no combustion at the same location. Comparison against computational results shows an underprediction of the flame lift-off distance.
Testosterone treatment impacts the intestinal microbiome of transgender individuals
Authors: Harris Rebecca M. , Pace Fernanda , Kuntz Thomas M. , Morgan Xochitl C. , Hyland Phoebe , Summers Kiana , McDermott Em , Blumen Kai , Watnick Paula I. 
Published: September 2024

ABSTRACT

Medical modulation of sex hormone levels is a cornerstone of treatment for many conditions that impact well-being, including cancer, fertility/infertility, gender dysphoria, and chronic metabolic diseases such as diabetes and obesity. The microbial residents of the intestine, known as the microbiota, interact with sex hormones in the intestine, and there is correlative evidence that this interaction is bidirectional. Based on these published findings, we hypothesized that transgender individuals receiving exogenous testosterone as part of their gender-affirming medical treatment might undergo changes in their intestinal microbiome. To test this, we collected 26 stool samples from nine individuals before and up to 8 months after initiation of treatment with exogenous testosterone and subjected these samples to metagenomic analysis. While no species were significantly associated with the duration of testosterone therapy, pathways that generate glutamate increased in abundance, while those that consume glutamate decreased. Glutamate is a precursor of arginine, and testosterone is known to increase levels of arginine and its metabolites in the plasma. We hypothesize that testosterone increases the uptake of glutamate by enterocytes, thus decreasing access of the microbiota to this amino acid. While this pilot study establishes the impact of testosterone therapy on the intestinal microbiome, a more comprehensive study is necessary to establish the impact of testosterone-driven metagenomic shifts on the stool metatranscriptome, the stool metabolome, and the plasma metabolome.

IMPORTANCE
The human intestine is inhabited by a large community of microbes known as the microbiome. Members of the microbiome consume the diet along with their human host. Thus, the metabolomes of the host and microbe are intricately linked. Testosterone alters the plasma metabolome. In particular, plasma levels of arginine and its metabolites and testosterone are positively correlated. To investigate the impact of exogenous testosterone on the microbiome, we analyzed the stool metagenomes of transgender individuals before and after the initiation of testosterone treatment. In this pilot project, we found a modest impact on the microbiome community structure but an increase in the abundance of metabolic pathways that generate glutamate and spare glutamate consumption. We propose that the host uses glutamate to generate arginine, decreasing the amount available for the microbiome.