bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigation of Supercritical N-Dodecane Flows in a Heated Circular Pipe With Thermal Cracking
Authors: Yatsuyanagi Shuto , Furusawa Takashi , Yamamoto Satoru , Onodera Takuo , Tomioka Sadatake 
Published: October 2021

Abstract
Supercritical n-dodecane (C12H26) flows in heated circular pipes with thermal cracking were numerically investigated using a numerical preconditioning method for solving the compressible Navier–Stokes equations. The reaction rate constants for thermal cracking of n-dodecane were determined using Cantera. The thermophysical properties of pure n-dodecane and its decomposed components were calculated using the Helmholtz free-energy equation of state. The outlet temperatures agreed well with experimental results, and the maximum error was 3.2%. The outlet temperature increased with the wall temperature condition, although the rate of increase became slightly smaller when the wall temperature was high. We discussed the relationship between the wall temperature condition and heat transfer in terms of thermal diffusivity in the radial direction. We also compared the radial distributions with those of n-octane (C8H18) in terms of temperature, thermal diffusivity, and mass fraction of unreacted fed hydrocarbons. Thermal cracking mainly occurred in a high-temperature region near the heated wall. The density of the decomposed components was much lower than that of n-dodecane and n-octane, resulting in a significant decrease in the mixture’s density near the heating wall. The decomposed components affected the supercritical hydrocarbon flows owing to changes in their thermophysical properties. The thermal diffusivity due to the decomposed components and turbulence affects the temperature distributions and mass fraction in n-dodecane and n-octane flows. Finally, we compared the outlet conversion rates of n-dodecane and n-octane flows.
Numerical Study of Aerodynamic Forces of Two Airfoils in Tandem Configuration at Low Reynolds Number
Authors: Hosseini N. , Tadjfar M. , Abba A. 
Published: October 2021

Abstract
For a tandem airfoil configuration, an airfoil is placed in the wake of an upstream airfoil. This interaction affects the aerodynamic forces of the airfoils, especially the downstream one. In the present study a tandem configuration consists of an upstream pitching airfoil and a downstream stationary airfoil is investigated. This study aims to investigate the role of reduced frequency and pitch amplitude of the upstream airfoil’s motion on lift and drag coefficients of two airfoils. These two parameters play an important role in the formation of vortices. The investigation is done for Selig-Donovan 7003 (SD7003) airfoils at low Reynolds number of 30,000 using a computational fluid dynamics. Incompressible URANS equations were employed for solving the flow field. It was found that for a fixed reduced frequency of 0.5 thrust is produced on the hindfoil for a part of cycle for different pitch amplitudes from light to deep stall while for a fixed pitch amplitude at different reduced frequencies high level of thrust or drag can be produced. The reason is related to the type and intensity of vortex-blade interaction.
Stereographic Backlit Imaging and Bubble Identification From a Plunging Jet With Floor Interactions
Authors: Pillers Roy A. , Heindel Theodore J. 
Published: October 2021

Abstract
Plunging jets have been extensively studied for their relatively simple set-up but complex multiphase interactions. This phenomenon includes gas carry-under and mixing, which occurs when shear effects between the plunging liquid jet and surrounding gas are sufficient to entrain gas at the impact site. Previous investigations typically assume the floor has an infinite depth and neglect compressive effects caused by the jet interacting with the catch tank floor. While this assumption is ideal for breaking waves in the middle of the ocean, many other applications have to contend with floor effects. These include waterfalls, wastewater treatment, dams, fish farms, mineral separation, and molten metal pouring. It is hypothesized that floor interactions will significantly affect the multiphase flow hydrodynamics, especially in places where the uninhibited jet would approach or pass the floor region.
Using a large catch tank with an adjustable floor region designed to hold a constant water level, data were collected using high-speed backlit stereographic imaging to capture and compare the effects of three separate tank depths with those found using an infinite pool assumption. To identify bubbles in each stereographic projection, a uniform bubble recognition procedure was developed that was used across all data sets. This allowed for the automated identification of bubble entrainment regions, which could be compared with different flow conditions. Preliminary results are inconclusive as to the effects of the floor region on the bubble plume dynamics; however, the results showed consistent measurements between trials and the two stereographic cameras, implying the time variation of the jet dynamics was the primary source of uncertainty in the results and not the identification procedure. Therefore, the identification methods have provided a method for plume volume and shape estimation, which will be used in future studies using 3D imaging techniques.
Multiphysics Modeling and Simulation of an Arc-Jet Sprayer
Authors: Campos Manzo Juan J. , Wagner Nicole , Anderson Kevin R. 
Published: October 2021

Abstract
Twin wire arc spraying (TWAS) is a plasma spraying process that offers low workpiece heating and high deposition rates at a lower cost. Variations in TWAS process conditions cause the substrate temperature to fluctuate and even melt. Therefore, the motivation of this project was to simulate the heat transfer from the TWAS torch to the substrate during spraying and layer formation of a coating. Simulations using ANSYS FLUENT Computational Fluid Dynamics (CFD) software were used to model the heat transfer in a TWAS system. The results of this paper are meant to augment and improve the database of TWAS technology. A CFD numerical heat transfer model is presented that was used to investigate the substrate surface temperature during the TWAS process. The results for the different pressure models showed that for a 3 second simulation, substrate surface temperatures increased as nozzle inlet pressure was decreased. For the upper and lower bound pressures of 75 psia and 29 psia, substrate surface temperature resulted in 946 °C and 1010 °C, respectively.
CFD Analysis and Wind Tunnel Testing of Human Powered Vehicle Drag Coefficients
Authors: Estrada Tony , Anderson Kevin R. , Gundersen Ivan , Johnston Chuck 
Published: October 2021

Abstract
This paper presents results of Computational Fluid Dynamics (CFD) modeling and experimental wind tunnel testing to predict the drag coefficient for a Human Powered Vehicle (HPV) entered in the World Human Powered Speed Challenge (WHPSC). Herein, a comparison of CFD to wind tunnel test data is presented for ten different HPV designs. The current study reveals that streamlining the nose cone, tail cone, and wheel housing allows for a reduction of drag forces in critical areas, and a reduced drag coefficient. This allows for a selection to be made during the design phase, prior to manufacturing. Drag coefficients were found to be in the range of 0.133 &lt; CD &lt; 0.273, depending on the type of HPV considered. Wind tunnel testing was performed on scale models of the HPV showing agreement to the CFD results on average to within 16%. The wind tunnel testing showed a 7.7% decrease in drag coefficient from the baseline HPV of 2019 to the baseline HPV of 2020. Thus, the wind tunnel data supported by CFD analysis was used to assist in the design of the HPV.
Research on Formation Mechanism and Suppression Method of Surface Force Caused by Pump Jet Propeller
Authors: Zhang Yu , Wu Dazhuan 
Published: October 2021

Abstract
Propeller exciting force is divided into bearing force and surface force according to the transfer path, and they are essential for radiated noise of the underwater vehicle. Surface force is an increasingly important issue in radiated noise because of the appearance of guide vanes and ducts. But the related questions about surface force are not thoroughly considered. Here we show spectral characteristics of surface force and its formation mechanism. Computational Fluid Dynamics is used in this paper. One of the important results is that there is a significant blade passing frequency (BPF) line spectrum in the radial component of surface force which does not appear in the axial direction; Another one is that the frequency amplitude at BPF of the duct is ten times that of the stator blades, which shows that the duct mainly contributes to the surface force. We also found that the amplitude of the duct surface force is equivalent to the rotor bearing force, which illustrates the importance of surface force research. It is demonstrated that the tip leakage vortex is the reason for the duct surface force by the analysis of the flow field. By adjusting the size of the tip clearance to control the tip leakage vortex, we found that the uniformity of the flow field has a significant effect on the surface force of the duct. The result obtained by this study can be used to reduce the radiated noise of underwater vehicles.
Interactions Between the Shear Layer Emanating From Rectangular Cylinders and the Near Wake Region
Authors: Kumahor Sedem , Addai Samuel , Tachie Mark F. 
Published: October 2021

Abstract
The interactions between the separated shear layer and the near wake region of rectangular cylinders of varying streamwise extents in a uniform flow are investigated using time resolved particle image velocimetry. The streamwise aspect ratios (AR) tested were 1 and 5, and the Reynolds number based on the oncoming flow velocity and cylinder height is 16200. The effects of varying AR on the mean flow, turbulent kinetic energy and Reynolds shear stresses are studied. Furthermore, the unsteady characteristics of the separation bubbles are examined in terms of frequency spectra analysis. The mean flow topology shows flow separation at the leading edge is not affected by the streamwise aspect ratios. However, the primary, secondary and wake vortexes show significant differences. Mean flow reattaches over the cylinder at 4.30 cylinder heights in the AR5 case while there is no mean reattachment in the AR1 case. The magnitudes of turbulent kinetic energy and Reynolds shear stress in the wake region are an order of magnitude higher in AR1 compared to AR5. Depending on the streamwise location, the vortex shedding motions in the near wake region reflect the dominant and second harmonic of the shear layer shedding frequency measured near the leading edge.
Significance of Vocal Tract Geometrical Variations and Loudness on Airflow and Droplet Dispersion in a Two-Dimensional Representation of [F]
Authors: Mofakham Amir A. , Helenbrook Brian T. , Ahmed Tanvir , Erath Byron D. , Ferro Andrea R. , Brown Deborah M. , Ahmadi Goodarz 
Published: October 2021

Abstract
The significance of respiratory droplet transmission in spreading respiratory diseases such as COVID-19 has been identified by researchers. Although one cough or sneeze generates a large number of respiratory droplets, they are usually infrequent. In comparison, speaking and singing generate fewer droplets, but occur much more often, highlighting their potential as a vector for airborne transmission. However, the flow dynamics of speech and the transmission of speech droplets have not been fully investigated. To shed light on this topic, two-dimensional geometries of a vocal tract for a labiodental fricative [f] were generated based on real-time MRI of a subject during pronouncing [f]. In these models, two different curvatures were considered for the tip tongue shape and the lower lip to highlight the effects of the articulator geometries on transmission dynamics. The commercial ANSYS-Fluent CFD software was used to solve the complex expiratory speech airflow trajectories. Simultaneously, the discrete phase model of the software was used to track submicron and large size respiratory droplets exhaled during [f] utterance. The simulations were performed for high, normal, and low lung pressures to explore the influence of loud, normal, and soft utterances, respectively, on the airflow dynamics. The presented results demonstrate the variability of the airflow and droplet propagation as a function of the vocal tract geometrical characteristics and loudness.
Automated Mini-Channel Platform for Studying Plant Root Environments
Authors: Kreis Kevin F. , Ryu Sangjin 
Published: October 2021

Abstract
Plants are crucial to our lives because they provide us with building materials, oxygen, and food. A season’s crop yield can be significantly affected by local environmental factors. In particular, improving fundamental understanding of plant root interactions with their local soil environment, or rhizosphere, will help improve crop yield. Studying such interactions is challenging because roots are underground, making it difficult to observe interactions and to manipulate the local soil environment. The goal of this study was to develop an automated mini-channel platform to investigate how plant roots respond to changes in their environment using corn as a model plant. Considering the size of corn seedling roots, mini-channel devices were fabricated in soft lithography using master molds produced with a 3D printer and polydimethylsiloxane (PDMS). Our use of a 3D printer instead of photolithography allowed for a broader range of PDMS mold designs, such as including embedded rubber gaskets built into the mold. Then, corn seedlings were grown inside the transparent mini-channel devices, and they were found to consume an observable amount of nitrate over time. Image processing was employed to measure the contour length of the roots for quantitative characterization of root growth. Then, an automated platform was developed to measure the growth rate of the corn seedling roots and the consumed nitrate over time. The automated platform maintained the level of growth medium in the channel device, and was equipped with a digital camera to image the root growing in the channel, electrochemical sensors to measure changes in nitrate concentration in the channel, and sensors to measure temperature and humidity. Therefore, the platform could automatically measure root growth while simultaneously measuring root environment. The platform’s adaptable design, simple fabrication, and low cost make it simple to replicate and use to study different plants and environmental stimuli.
Wall-Pressure Fluctuations Inside Attached Cavitation
Authors: Wang Changchang , Wang Guoyu , Zhang Mindi , Wu Qin 
Published: October 2021

Abstract
This study experimentally investigates the statistics of wall-pressure fluctuations and their source inside attached cavitation under different cavity regimes. Experiments were conducted in the divergent section of a convergent-divergent channel at a constant Reynolds number of Re = 7.8 × 105 based on throat height, and different cavitation numbers σ = 1.18, 0.92, 0.82 and 0.78. Four high-frequency unsteady pressure transducers were flushed-mounted in the divergent section downstream the throat where cavitation develops to sample the unsteady pressure signals induced by cavity behaviors. Flow visualization and wall-pressure measurement in high frequency on the order of MHz were employed using a synchronizing sampling technique. Results are presented for sheet/cloud cavitating flows. Specifically, sheet cavitation with both inception shear layer and fully cavitated shear layer and cloud cavitation under re-entrant jet dominated shedding and shock wave dominated shedding are studied. Compared with re-entrant jet, the interactions between shock wave and cavity could induce pressure peaks with high magnitude within cavity, which will collapse the local vapor along its propagating path and reduce local void fraction. Furthermore, statistics analysis shows that within the cavity, wall-pressure fluctuations increase with the distance to cavity leading edge increase in the first half of cavity length, and the moments of the probability density distribution skewness and kurtosis factor decrease, indicating the asymmetry and intermittency of wall-pressure fluctuation signals decrease. In shock wave dominated cavity shedding condition, the skewness and kurtosis factor increase. These results can provide data to improve the accuracy of turbulence modeling in numerical simulation of turbulent cavitating flow.
Comparison of Axial Water and Air Injections in the Draft Tube of a Francis Turbine for RVR Mitigation
Authors: Khullar Subodh , Singh Krishna M. , Cervantes Michel J. , Gandhi Bhupendra K. 
Published: October 2021

Abstract
The presence of excessive swirl at the runner outlet in Francis turbines operating at part load leads to the development of flow instabilities such as the rotating vortex rope (RVR). The presence of RVR causes severe pressure pulsations, power swings, and fatigue damage in the turbine unit. Air and water injection in the draft tube have been reported to reduce the detrimental effects of RVR formation in the Francis turbines. Air injection is one of the oldest and most widely used methods. In contrast, water jet injection is a relatively new methodology. The present work reports the numerical simulations performed to compare the respective effectiveness of these methods to mitigate the RVR and the related flow instabilities. The efficacy of the two methods has been compared based on the pressure pulsations and pressure recovery in the draft tube cone. The results show that the air and water injection influence the draft tube flow field in different ways. Both air and water injection led to a reduction in pressure pulsation magnitudes in the draft tube cone. However, the air injection led to a negative pressure recovery while the water injection improved the draft tube action.
An LBM Study of the Sedimentation Behaviors of Double Particles With Non-Identical Sizes
Authors: Dai Wentao , Tang Jun , Zhang Shengyuan , Wu Huiying 
Published: October 2021

Abstract
In this work, the size effects on the sedimentation behaviors of two non-identical particles are investigated through the lattice Boltzmann method (LBM). The method is first validated by simulating the settling process of single and double particles, which agrees well with analytical and previous results. Then the hydrodynamic behaviors of double non-identical-size particles settling in an infinite-long narrow channel are investigated, in which the larger particle is initially placed above the smaller one. Different sedimentation behaviors are observed with different diameter ratios in the present work. In the first Draft-Kiss-Tumble (DKT) cycle, it is observed that the time durations of both drafting state and kissing state are shortened by the increase of the diameter ratio γ . Considering a longer sedimentation time, three different settling modes are observed with different diameter ratios, which can be summarized as: (1). Repeated DKT cycle (1.0 ≤ γ ≤ 1.13); (2). Repeated DT-DKT after the first DKT cycle (1.14 ≤ γ ≤ 1.22); (3). Separation after the first DKT cycle (1.23 ≤ γ). It should be noted that Mode 2 is first defined in this work, which helps explain the divergence in the threshold diameter ratios of the recurrence of DKT cycles proposed in the previous literatures. In addition, the periodical length of the repeated cycles experiences instant increase and decrease against the diameter ratio near the transition from Mode 1 to Mode 2, while an instant increase is also observed near the threshold diameter ratio between Mode 2 and Mode 3.
Effect of Speed Variation on Clogging of Sewage Pumps
Authors: Müller Enrico , Pensler Thomas , Thamsen Paul Uwe 
Published: October 2021

Abstract
Pump clogging is a well-known problem due to the increasing amount of nonwoven wet wipes in the wastewater system. In addition, the usage of water decreases which causes higher concentration of solids in the wastewater. Based on the high variation of sewage flow many operators of sewer systems and sewage pumping stations were motivated to act that the wastewater is pumped as needed. It means that with reducing costs of frequency-controlled drives the usage of pumps with speed variation became a more state of the art application.
The current operation mode when speed variation in wastewater pumps are used, affects the pumping of sewage water depending on inflow and the minimum velocity in the pipes. Until now, there is no answer which functionality and clogging occurs in the pump when speed changes.
The study investigates how speed influences the clogging phenomena of wastewater pumps. The pumps have been approved at a test stand in a laboratory that is designed for proving wastewater pumps. The test includes several speeds with different quantities of wipes in a short-time and long-time functional performance test. The effects on the pumps and their clogging behavior are very different.
Suppression of Diffuser Rotating Stall in a Centrifugal Pump by Use of Slit Vane
Authors: Takao Shunya , Konno Shinichi , Ejiri Shinichiro , Miyabe Masahiro 
Published: October 2021

Abstract
The objective of this research is to suppress pressure fluctuation by machining slits to the diffuser vanes and clarify its effect on the diffuser rotating stall from the hydrodynamics point of view.
In order to investigate pressure fluctuations due to the diffuser rotating stall, both experiment and CFD (Computational Fluid Dynamics) calculations were conducted. In the experiment, two kinds of pump (one is original and another is with slit vanes) characteristics and time history of static pressure were measured. Then, data processing of wave form were conducted by FFT (Fast Fourier Transform) analysis. The static pressure transducers were mounted at casing-side of diffuser inlet in two passages.
On the other hand, the CFD calculations were carried out to investigate the behavior of the diffuser rotating stall and the effect of slit vanes using a commercial CFD software, ANSYS CFX.
A positive slope of head-flow characteristics is confirmed around at ϕ = 0.036 in the case of original pump. On the other hand, it has been shifted to lower flow rate, ϕ = 0.020 in the case of slit vanes. The periodic pressure fluctuations were observed for both cases at those flow rate, respectively. Then, it was confirmed that the diffuser rotating stall occurs and the number of cell is one from the co-relation between pressure wave form of two flow passages. The unsteady RANS (Reynolds-averaged Navier-Stokes) calculations were conducted for two kinds of pump. Then the internal flow within the diffuser were compared and the differences were clarified.
Effects of Aerodynamics on Line Sail During Parachute Deployment
Authors: Tang Mingzhang , Wang Liwu , Liu Yu , Zhang Sijun 
Published: October 2021

Abstract
This paper presents a dynamic model to numerically simulate the parachute deployment for space vehicle recovery system. In the proposed dynamic model, the deployment bag and the space vehicle are treated as a six-degree-of-freedom rigid body with mass varied and a regular six-degree-of-freedom rigid body, respectively. The parachute system is considered as the mass spring damper model, in which the canopy, suspension lines, risers and bridles are discretized into some three-degree-of-freedom segments with their centralized mass on the end points. During the deployment a notable phenomenon can be observed and so-called line sail. The line sail generally occurs during a deployment in which the relative wind is not parallel to the deployment direction. The line sail has been known to cause or contribute to the following problems: increased deployment times, changes in snatch load, asymmetrical deployment, friction damage, and unpredictable canopy inflation. To understand its mechanisms, the effects of aerodynamics such as angle of flight path, deployment bag ejection velocity, Mach number, air density and wind velocity are numerically investigated.