bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamics and Breakup Regime of a Vapor Bubble Traveling Through a Heated T-Shaped Branching Microchannel
Authors: Yan Zhe , Li Shanshan , Li Lichun , Deng Bili , Pan Zhenhai 
Published: October 2020

Abstract
Dynamics and breakup characteristics of a vapor bubble when traveling through the T-junction of a heated branching microchannel are numerically investigated with the Volume of Fluid-Continuum-Surface-Force (VOF-CSF) method. The moving reference frame method, which has been demonstrated to help suppressing the unphysical spurious velocity around the liquid-vapor interface (Numer. Heat Trans. 67, 1–12), is employed and coupled to the VOF-CSF model. In order to evaluate the influence of the wall heating on the growth and breakup of vapor bubble, the saturated-interface-volume phase change model is further coupled to account for the phase change on the bubble interface. The numerical model is first validated against experimental results in literature. Then the effect of wall superheat on bubble dynamics and heat transfer coefficient is investigated. Bubble motion, growth, breakup and heat transfer characteristics at different wall superheats are analyzed in detail. Four bubble breakup regimes are observed, namely non-breakup (NB), breakup with tunnel (TB), combined breakup (CB) and breakup with permanent obstruction (OB). The present study reveals the transport details around an evaporating vapor bubble and helps understanding the underlying physics of bubble behaviors when traveling through a T-shaped branching microchannel.
Length Reduction of a Compressor Multi-Spool Transition Annular S-Duct
Authors: Agrawal M. , Sinha D. , Das S. P. , Vidhyashankar N. , Abbas R. 
Published: October 2020

Abstract
Increasing interest in improving the efficiency of the turbo-fan engine results in a large low pressure compressor and small high pressure core. The consequence of the increment in radial offset is that the importance of the transition duct is growing. Shortening this transition duct length can effectively reduce the weight of the engine. However, it conflicts with the need to avoid flow separation within the duct. Further, radial struts are also present in duct passage for support. In present work, numerical investigations were performed on an annular S-duct with bypass suitable for connecting the compressor spools of a small turbofan engine. The length of S-duct was reduced by 6%, 12%, and 18% from the original S-duct length. The wall contour was selected based on the optimum value of the total pressure loss coefficient for the particular length. It was found that the loss coefficient is a weak function of duct length as long as the flow is attached. Further, the effect of the radial strut on the selected contour for two different lengths was studied. The increase in loss for 100% and 88% length in the presence of all struts was 17% and 27%.
Attached Jet Velocity Profiles in Mixing Tanks
Authors: Pease Leonard F. , Bamberger Judith Ann 
Published: October 2020

Abstract
Free jets have been studied in detail over much of the last century, but the theory for offset and attached jets remains incomplete. Attached jets differ from free jets in that they lose momentum to nearby surfaces, attenuating their velocities. The velocity profiles of free circular jets are nearly Gaussian, with quantitative mathematical descriptions derived from first principles by Goertler and Tollmien (Rajaratnam, 1976). In contrast, mathematical descriptions of three-dimensional attached jets from circular nozzles remain much less mature. Agelin-Chaab and Tachie (2011) used particle imaging velocimetry of a three-dimensional attached jet to show that the scaled velocity decays with scaled distance from the nozzle with a power law exponent between −1.15 and −1.20, which is larger in magnitude than that of a free jet. However, quantitative analytical expressions for the velocity profiles of attached jets similar to those of free jets remain elusive. This paper addresses this critical gap.
Here we evaluate the velocity profiles of three-dimensional offset jets emerging from circular nozzles that become attached jets. These jets lose momentum due to interactions with nearby surfaces and are important to evaluating flows in mixing vessels and to suspending solids and trapped gases in radioactive waste tanks. Despite the importance of attached jets, prior insight has been purely experimental, limited to overly simplistic analytical models, or restricted to computationally expensive computational fluid dynamics case studies. We compare the expression of Verhoff (1963) to experimental results to find reasonable quantitative agreement.
As stated by Agelin-Chaab and Tachie (2011), “detailed velocity measurements of 3D offset jets are rare.” Such remains the case. This study adds to the literature by providing information at two additional Reynolds numbers (1.43 · 106 and 1.87 · 106) and evaluating simple but accurate expressions for velocity profiles. These Reynolds numbers and corresponding velocities are higher, typically orders of magnitude higher, than other reports. The semi-empirical stream wise velocity profile perpendicular to the surface proposed by Verhoff (1963) is in approximate agreement with these velocity profiles, which is surprising because these attached jets are three-dimensional instead of two-dimensional as evaluated by Verhoff. However, additional work is necessary to fully describe these profiles quantitatively.
Experimental Comparison of Newtonian and Non-Newtonian Multiphase Flow in Horizontal Pipes
Authors: Ben Rajeb Faraj , Odan Mohamed , Aborig Amer , Imtiaz Syed , Zhang Yan , Awad Mohamed M. , Rahman Mohammad Azizur 
Published: October 2020

Abstract
Two-phase flow of gas/Newtonian and gas/non-Newtonian fluid through pipes occurs frequently in the chemical industry as well as in petroleum refining. Extensive experimental and theoretical research has been carried out on these systems in order to better understand their behaviour under different conditions regarding pressure, temperature and mixture concentrations. In this study, experimental apparatuses are used to investigate two-phase flow of gas/liquid systems through pipes. Air is used as the gas in the experiments, while water is used as the Newtonian fluid and Xanthan gum as the non-Newtonian fluid. The objectives of the study are to compare pressure drops when the same gas flows simultaneously with Newtonian and non-Newtonian fluids through tubes. The comparison here is between experimental pressure drops and estimated pressure drops, based on available empirical correlations for gas/Newtonian and gas/non-Newtonian flow. The trend exhibited by the pressure drops in both systems helps us to better understand the relationship between mixture flow pressure drops in Newtonian and non-Newtonian fluids and thereby develop a new experimental model. The tube diameter for the flow loop is 3/4 inch and the flow type ranges from transient to turbulent.
Disruption Behavior of Aggregates in a Rotating/Oscillating Cylindrical Tank and Implications for Particle Transport in the Ocean
Authors: Song Yixuan , Rau Matthew J. 
Published: October 2020

Abstract
Particle size and settling speed determine the rate of particulate mass transfer from the ocean surface to the sea bed. Turbulent shear in the ocean can act on large, faster-settling flocculated particles to break them into slower-settling primary particles or sub-aggregates. However, it is difficult to understand the disruption behavior of aggregates and their response to varying shear forces due to the complex ocean environment. A study was conducted to simulate the disruption behavior of marine aggregates in the mixed layer of the ocean. The breakup process was investigated by aggregating and disrupting flocs of bentonite clay particles in a rotating and oscillating cylindrical tank 10 cm in diameter filled with salt water. This laboratory tank, which operated based on an extension of Stokes’ second problem inside a cylinder, created laminar oscillating flow superimposed on a constant rotation. This motion allowed the bentonite particles to aggregate near the center of the tank but also exposed large aggregates to high shear forces near the wall. A high-speed camera system was used, along with particle tracking measurements and image processing techniques, to capture the breakup of the large particle aggregates and locate their radial position. The breakup response of large aggregates and the sizes of their daughter particles after breakup were quantified using the facility. The disruption strength of the aggregated particles is presented and discussed relative to their exposure to varying amounts of laminar shear.
Evaporative Emissions From Automotive Gasoline Fuel Tank Refueling: Experimental Activity and Numerical Simulation
Authors: Romagnuolo Luca , Frosina Emma , Andreozzi Assunta , Senatore Adolfo , Fortunato Francesco , Mirante Vincenzo 
Published: October 2020

Abstract
Vehicle evaporative emission is one of the most important sources of pollution from a gasoline-fueled vehicle. Since international regulations on Volatile Organic Compounds (VOC) emission are becoming increasingly stringent every year, the study of the VOC generation has become of fundamental importance.
It is known that VOC generation is particularly high during the refueling phase: fresh fuel coming from the refueling nozzle impacts on the filling pipe wall and it is a source for sloshing in the fuel tank. Fuel vapor generated can be collected by a vapor recovery nozzle and stored in the gas station tank (Stage II vapor recovery system, European normative) or trapped by the vehicle carbon canister (On-board Refueling Vapor Recovery system, U.S. normative).
In this activity, an automotive gasoline fuel tank for U.S. applications has been used for both experimental and numerical analyses, provided by FCA. Experiments were performed in FCA laboratories, in a sealed and thermal controlled environment (mini-SHED): vapor flow exiting the fuel tank during refueling has been measured, and fuel vapor mass has been evaluated by dynamically measuring the weight variation of a carbon canister filter connected to the fuel tank vent system. A CFD model was built based on CAD geometries provided by FCA, and numerical analysis of the refueling process has then been executed by using a commercial 3D CFD software. Results were then compared with experimental data.
This activity is a part of a collaboration between University of Naples Federico II and FCA Italy about fuel vapor emissions control and prediction.
Large Eddy Simulation of Active Flow Control Over SD7003 at Reynolds Number of 60,000
Authors: Kamari Djavad , Tadjfar Mehran , Tarokh Ali 
Published: October 2020

Abstract
Large Eddy Simulation for active flow control (AFC) by employing synthetic and continuous blowing is done to investigate their effects on resizing separation. The flow around an SD7003 airfoil at Reynolds number of 60,000 and angles of attack of 13° is considered where a widespread separation occurs at post stall. In this work, the Dynamic Smagorinsky model is used as to calculate the turbulent viscosity.
Impact of Print Parameters on Pressure Drop in Turbulent Flow Through 3-D Printed Pipes
Authors: Shepard Thomas G. , Wentz John , Bender Tucker , Olmschenk Derek , Gutenberg Alex 
Published: October 2020

Abstract
Flow conduits made via additive manufacturing, commonly referred to as 3-D printing, are of increasing interest for a variety of industrial applications due to the ability to create unique and conformal flow paths that would not be possible with other fabrication techniques. Fused filament fabrication (FFF) is an additive manufacturing technique that is seeing new interest in the creation of internal flow channels with its ability to print high-temperature polymers and soluble supports. Printing parameter choices in the FFF printing process result in surfaces that can have significant profile differences that may significantly impact the flow characteristics within the conduits. In this study, two print parameters were experimentally studied for turbulent water flow through circular pipes created by fused filament fabrication out of acrylonitrile butadiene styrene (ABS). The print layer orientation relative to the flow was investigated for printing layers parallel, perpendicular, and at 45 degrees from the flow axis. Layer thickness were varied from 0.254 mm to 0.330 mm and all channels were created using soluble support structures. Pressure drops were measured for fully developed flow through pipes with an inside diameter of 5 mm and Reynolds numbers up to 62,000. Results are presented in terms of relative pressure drops as well as the wall surface roughness that would lead to such impacts. These flow-determined grain surface roughnesses are then compared against measurements of print surface roughness.
Parameter Sensitivity and Statistical Correlation Found in Atmospheric Turbulence Studies
Authors: Rodriguez Luis F. , Kumar Vinod , Rodriguez Arturo , Kotteda V. M. Krushnarao , Gudimetla V. S. Rao , Munoz Jorge A. 
Published: October 2020

Abstract
We have simulated atmospheric turbulence at several instances of possible laser propagation paths and turbulent flow regime regions within the area of interest. At a control volume that is in between two Hawaii mountains. We have applied statistical correlations between Large-Eddy Simulations results using CFD modeling and parametrizing optical variables of interest, such as refractive index structure function. By comparing our Large-Eddy Simulations with specified parameters against other Large-Eddy Simulations with almost all same parameters except for one allows us to perform a sensitivity study. To study the changes on how a parameter can affect other scenarios of Large-Eddy Simulations parametric studies. With the end goal of validating the capacity of a sensitivity analysis study using Large-Eddy Simulations versus other Large-Eddy Simulations by a way of simulating and parametrizing turbulent flow studies found in the field of CFD modeling. Allowing us to achieve our stochastic analysis by applying sensitivity studies to see how our distributions change as a function of different parameters, but one at a time. After a comparison between CFD modelling simulations we have found that after a complete parametric study, a correlation was formed between turbulent flow parameters and optical parameters of interest.
Evaluation of Erosion Equations in Submerged Impinging Jets
Authors: Wang Qiuchen , Huang Qiyu , Sun Xu , Zhang Jun , Karimi Soroor , Shirazi Siamack A. 
Published: October 2020

Abstract
During petroleum production, small sand particles can be entrained with the transported carrier fluid despite of any sand exclusion process and these sand particles can erode inner walls of pipelines. Therefore, the ability to accurately predict erosion rate caused by particles in oil and water is important to pipeline safety. There are erosion equations available in the literature to predict this phenomenon. However, most of the widely used erosion equations are derived by analyzing gas-solid erosion process, which were later validated and shown to be less accurate in predicting slurry erosion. Modified slurry erosion equations are then proposed to improve the prediction accuracy, while overpredictions occur when particle sizes vary. In this study, the available mechanistic and empirical equations are evaluated by experimental and numerical study. Computational Fluid Dynamics (CFD) is used to simulate the fluid flow and track particles to obtain impact information. Erosion equations then connect the particles’ impact information with erosion rate. The slurry erosion experiments are conducted using quartz silica particles with similar shapes and different sizes ranging from 25 micrometers to 600 micrometers in oil and water as carrier fluids. Finally, the erosion models are evaluated by comparing predicted erosion profile with experimental data.
The Effects of Upstream Wall Roughness on Separated and Reattached Flows Over a Forward-Facing Step
Authors: Kumahor Sedem , Fang Xingjun , Ediger William , Tachie Mark F. 
Published: October 2020

Abstract
Separating and reattaching turbulent flows induced by a forward-facing step submerged in thick oncoming turbulent boundary layers developed over smooth and rough walls were investigated using time-resolved particle image velocimetry. Both smooth and fully rough upstream bottom wall conditions were examined and the resultant oncoming boundary layer thickness were 4.3 and 6.7 times the step height, respectively. The Reynolds number based on the step height and free-stream velocity was 7800. The mean velocities, Reynolds stresses analyzed in both Cartesian and curvilinear coordinate systems, eddy viscosity, correlation coefficient and third order moments are discussed. The results indicate that, due to the enhanced turbulence intensity and shear rate in the fully rough case, distinct elevated regions of vertical and shear Reynolds stresses are consistent upstream of the leading edge of the step while the magnitude of the Reynolds stresses are consistently higher than observed in the smooth case. The correlation coefficient, eddy viscosity and third order moments also show distinct elevated regions upstream of the leading edge of the step in the fully rough case. Above the step, distinct elevated regions of the Reynolds stresses, eddy viscosity and correlation coefficient are observed in both cases with the peak values at a vertical location corresponding to the maximum elevation of the mean separating streamline.
The Effects of Upstream Wall Roughness on the Spatio-Temporal Characteristics of Flow Separations Induced by a Forward-Facing Step
Authors: Kumahor Sedem , Fang Xingjun , Nematollahi Ali , Tachie Mark F. 
Published: October 2020

Abstract
The unsteady characteristics of flow separations induced by a forward-facing step immersed in thick oncoming turbulent boundary layers developed over smooth and fully rough upstream walls were experimentally studied using time-resolved particle image velocimetry. The upstream boundary layer thicknesses were 4.3 and 6.7 times the step height in the smooth and fully rough wall cases, respectively. The Reynolds number based on the step height and free-stream velocity was 7800. The effects of upstream wall roughness on the instantaneous separated shear layer, frequency spectra and two-point correlations are critically examined. Proper orthogonal decomposition (POD) is employed to investigate the mechanism underlying the unsteadiness of turbulent separation bubbles over the step. The first two POD modes exhibit the same topology in both cases. The energy fraction of the first mode is significantly larger in the rough wall case, signifying the enhanced large-scale motion residing in the incoming turbulent boundary layer. The correlation between the reverse flow area over the step and the first POD mode coefficient is much stronger in the rough wall case than in the smooth wall case. High levels of vertical fluctuating velocity immediately upstream of the leading edge of the step is mostly associated with the first POD mode in the rough wall case, but is further influenced by the higher POD modes in the smooth wall case. Irrespective of the upstream wall roughness, the vertical fluctuating velocity over the step are mostly induced by vortex shedding motion from the leading edge of the step.
On How the Generation of Lift Can Be Explained in a Closed Form Based on the Fundamental Conservation Equations
Authors: Epple Philipp , Babinsky Holger , Steppert Michael , Fritsche Manuel 
Published: October 2020

Abstract
The generation of lift is a fundamental problem in aerodynamics and in general in fluid mechanics. The explanations on how lift is generated are often very incomplete or even not correct. Perhaps the most popular explanation of lift is the one with the Bernoulli equation and with the longer path over an airfoil as compared to the path below the airfoil, assuming the flow arrives at the same time at the trailing edge on both paths. This is an intuitive assumption, but no equation is derived from this assumption. In some explanations the Bernoulli equation is also complemented with Newton’s laws of motion. In other explanations Newton’s law is said to be the only explanation. Other explanations mention the Venturi suction effect to explain the generation of lift. In books of aerodynamics and on the homepage of well-known research institutes the explanations are, although better and partially correct, still very often incomplete. In this contribution the generation of lift is explained in a scientific way based on the conservation principles of mass, momentum and energy and how they have to be applied to close the system of equations in order to explain the generation of lift. The most common incomplete or incorrect explanations of lift are also analysed and it is explained why they are incomplete or wrong. In this work the generation of lift is explained based on the conservation equations. It is shown how and when they apply to the problem of lift generation and how the system of equations has to be closed.
Cavitation in Hydraulic Machines: Measurement, Numerical Simulation and Damage Patterns
Authors: Benigni Helmut 
Published: October 2020

Abstract
Cavitation is a phenomenon that occurs in liquid media when the pressure drops below the vapor pressure. Cavitation is accompanied by damage when the imploding vapor bubbles implode in the vicinity of components. Cavitation is known in all hydraulic machines, be it a pump or a turbine, and it can occur within all components that are flowed through and have a low-pressure side or area.
In the last 100 years, a lot has been done to understand the damage caused by cavitation, and cavitation has been classified within the entire range of component-damaging mechanisms. Nevertheless, users are now interested in the behavior of different machine types and different specific speeds and need information for a particular installation situation, while hydraulic developers are interested in a methodology for the rapid assessment of CFD results.
This paper presents examples of damage to all kinds of hydraulic machines as well as numerical simulations of cavitation. Cross-comparisons between single-phase numerical calculations are realized with the histogram method, and multi-phase calculations are carried out and then compared with test rig investigations.
Often, it is not possible or economically feasible to completely avoid cavitation. With the help of dimensionless values and the assumption of complete cavitation, a generally valid physical limit curve can be specified for turbines.