bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Numerical Simulation of Radial Convection in a Cylindrical Annulus With and Without Rotation
Authors: Pitz Diogo B. , Wolf William R. 
Published: November 2019

Abstract
In rotating systems with temperature gradients, convection may occur due to gravitational or centrifugal effects. In cases where rotation is strong enough so that the centrifugal acceleration is higher than gravity, the flow is induced by centrifugal buoyancy and gravitational effects can be neglected. The problem of flow induced by centrifugal buoyancy in a cylindrical annulus has been used as a canonical setup to investigate industrial configurations, such as buoyancy-driven flows occurring in gas turbine secondary air systems, as well as geophysical flows, such as convection in the core of planets and the global circulation of the atmosphere. Due to the constraints imposed by the Taylor-Proudman theorem, such flows are quasi-homogeneous along the axial direction, and heat transfer as well as turbulent fluctuations tend to be suppressed by the action of the Coriolis force. Previous work has demonstrated that when the annulus is bounded by parallel disks, boundary layers scaling consistently with laminar Ekman layers are formed near each of the disks, even though the flow is purely buoyancy-induced. Also, the Nusselt number measured on the outer cylindrical surface has been shown to scale with the Rayleigh number as in natural convection between horizontal plates. In the present work we use direct numerical simulation (DNS) to investigate buoyancy-induced flow in an air-filled cylindrical annulus bounded by two adiabatic parallel disks, with and without rotation around the axis. In both cases the outer cylindrical surface is at a higher temperature than the inner one, so that a radial acceleration directed outwards induces an unstable stratification. In the case with rotation, the flow is induced by the centrifugal acceleration in the radial direction, and Coriolis forces are considered. For the case without rotation, the Coriolis terms are suppressed in the calculations, whereas the radial acceleration is the same as in the rotating case. Statistics are obtained and compared in the two cases, including the time-averaged Nusselt number, mean temperature profiles, velocity and temperature fluctuations, as well as terms of the turbulent kinetic energy equation. By analysing such statistics, the extent to which rotation suppresses heat transfer and turbulent fluctuations, as well as the contribution of each term to the turbulent kinetic energy budget, can be assessed.
Numerical Investigation on Multiphase Reacting/Combusting Turbulent Flows: Aerodynamics, Kinetics, Heat and Mass Transfer Inside a Cement Kiln Precalciner
Authors: Cristea Eugen-Dan , Conti Pierangelo 
Published: November 2019

Abstract
This paper reports the modeling work to develop a computational fluid dynamics (CFD) engineering application, based on an appropriate 3D mathematical model able to perform the thermo-fluid dynamic numerical simulation of multiphase reacting/ combusting turbulent flows within a precalciner of an industrial four-stage cyclone preheater/precalciner cement kiln. In the precalciner furnace the hot micron-sized limestone (calcite/dolomite) meal, held in suspension, is quiet completely converted to quicklime (CaO(s)), and the CO2(g) by-product is driven-off during calcination process. Since, the thermal decomposition mechanism is a very endothermic reaction, the necessary heat is balanced by pulverized petcoke combustion.
These major physical and chemical processes inside the precalciner are properly described by the 3-D Favre-averaged Navier-Stokes equations with the species transport equations, the energy equation and the state equation, to be solved by an Eulerian-Lagrange approach. The CFD solver employed in this study is the commercial CFD code ANSYS Fluent R18.2. The used built-in models/sub-models include turbulence models and near-wall treatment, model of traditional air-pulverized petcoke combustion, pulverized-limestone calcination model, as well as the sub-models for radiation heat transfer and turbulence-chemistry interaction. They are used to formulate the closures of the unclosed terms in the PDEs system.
In summary, the trends of predicted results of limestone calcination and petcoke/TDF combustion processes in an industrial precalciner furnace are reasonable fair in confront to operation data measurable in the harsh environment conditions, typical for the pyroprocessing systems. The developed CFD engineering application can be used as an effective design tool for preliminary examination of the global effect of thermal-flow aerodynamics and turbulence on the precalciner processes.
Characteristics of Swirl Angle in Pump Intake Flow Near the Minimum Inlet Submergence
Authors: Norizan Tajul Ariffin , Harun Zambri , Wan Mohtar Wan Hanna Melini , Abdullah Shahrir 
Published: November 2019

Abstract
Swirling flow in pump sump intake has been the subject of discussion for the past decades due to the detrimental effects brought about by its existence. Among the effects of swirling flow are reduced pump efficiency, cavitation, excessive vibration and load imbalance at the pump impeller which are caused by hydraulic problems associated to swirling flow such as swirls and vortices. One of the remedial measures for preventing such occasion is by keeping the pump inlet submerged above a defined value known as the minimum inlet submergence. It is the minimum submergence required to reduce the probability of the occurrence of free surface vortices. However, this requirement may not be fulfilled in some situations due to on site conditions or operational restrictions. In this paper, an experimental study was conducted to investigate the characteristics of swirl angle in the pump intake flow when the pump inlet is submerged near the value of minimum inlet submergence. The ratio of pump submergence to the minimum submergence was varied between 0.8 to 1.2 with constant inlet Froude Number which referred to as submergence ratio. The strength of the swirl in the intake flow was determined by measuring the swirl angle which was accomplished using a swirl meter attached in the suction pipe. Measurements using Acoustic Doppler Velocimeter (ADV) was performed to capture the velocity profile in the intake sump. The swirl angle distribution across the range of submergence ratios was dominated by a subsurface vortex formed at the sump floor. As soon as the submergence was reduced below the minimum submergence, a free surface vortex emerged near the pump inlet and brought a swirl retardation effect to the swirl meter rotation resulting in a bigger fluctuation of the swirl meter reading. An anti vortex device (AVD) called the floor splitter commonly used to reduce vorticity at pump inlet was installed and its effect on the reduction of swirls and vortices was evaluated.
Data-Driven Reduced Order Modeling of Flows Around Two-Dimensional Bluff Bodies of Various Shapes
Authors: Hasegawa Kazuto , Fukami Kai , Murata Takaaki , Fukagata Koji 
Published: November 2019

Abstract
We propose a reduced order model for predicting unsteady flows using a data-driven method. As preliminary tests, we use two-dimensional unsteady flow around bluff bodies with different shapes as the training datasets obtained by direct numerical simulation (DNS). Our machine-learned architecture consists of two parts: Convolutional Neural Network-based AutoEncoder (CNN-AE) and Long Short Term Memory (LSTM), respectively. First, CNN-AE is used to map into a low-dimensional space from the flow field data. Then, LSTM is employed to predict the temporal evolution of the low-dimensional data generated by CNN-AE. Proposed machine-learned reduced order model is applied to two-dimensional circular cylinder flows at various Reynolds numbers and flows around bluff bodies of various shapes. The flow fields reconstructed by the machine-learned architecture show reasonable agreement with the reference DNS data. Furthermore, it can be seen that our machine-learned reduced order model can successfully map the high-dimensional flow data into low-dimensional field and predict the flow fields against unknown Reynolds number fields and shapes of bluff body. As concluding remarks, we discuss the extension study of machine-learned reduced order modeling for various applications in experimental and computational fluid dynamics.
A Study on Improvement of Aerodynamic Performance for 100HP Axial Fan Blade and Guide Vane Using Response Surface Method
Authors: Choi Young-Seok , Kim Yong-In , Kim Sung , Lee Seul-Gi , Yang Hyeon-Mo , Lee Kyoung-Yong 
Published: November 2019

Abstract
This paper describes the numerical optimization of an axial fan focused on the blade and guide vane (GV). For numerical analysis, three-dimensional (3D) steady-state Reynolds-averaged Navier-Stokes (RANS) equations with the shear stress transport (SST) turbulence model are discretized by the finite volume method (FVM). The objective function is enhancement of aerodynamic performance with specified total pressure. To select the design variables which have main effect to the objective function, 2k factorial design is employed as a method for design of experiment (DOE). In addition, response surface method (RSM) based on the central composite design applied to carry out the single-objective optimization. Effects on the components such as bell mouth and hub cap are considered with previous analysis. The internal flow characteristics between base and optimized model are analyzed and discussed.
Visualization of Oil Droplets Distribution in a Rotary Compressor
Authors: Wu Puyuan , Chen Jun , Sojka Paul E. 
Published: November 2019

Abstract
A rotary compressor relies on an eccentric rolling piston, which rotates at high speed, to compress gas in the compression chamber. The oil in the rotary compressor is used for lubricating the bearing and sealing the clearance of sliding parts. However, the oil can exhaust from the rotary compressor by the refrigerant flow and reduce the reliability of the compressor as a result. Thus, studying the behavior of oil droplets distribution in a rotary compressor is a major challenge for manufacturers who rely on CFD tools to predict the multiphase flow. By modifying a rotary compressor, the oil behavior inside the cylinder is observed and recorded by a high-speed imaging system. In the current phase, multiple targeted locations, including the space between the bearing housing and the stator, and the space above the stator are measured in different conditions. The number, size, velocity, and morphology of oil droplets are analyzed based on multiple snapshots. The result can assist designers in improving the CFD analysis of compressors and ultimately reducing the oil discharge rate (ODR).
Detailed Numerical Simulation of Two Impinging Jets With Moderate Injection Velocities
Authors: Ling Yue , Shang Weixiao , Chen Jun 
Published: November 2019

Abstract
Impinging-jet injectors are commonly used in liquid propellant rocket engines. Two cylindrical liquid jets impinge at a certain angle and form a liquid sheet in the plane normal to the jets. When the Reynolds and Weber numbers are large, the liquid sheet becomes unstable and disintegrates into liquid ligaments and droplets. In the present study, we focus on cases with moderate injection velocities so that the liquid sheet remains unbroken. Detailed numerical simulations are performed using the adaptive multiphase flow solver, Basilisk. The volume-of-fluid method is used to resolve the gas-liquid interface. Grid-refinement studies are conducted to verify the formation of the liquid sheet is accurately captured in simulation. The numerical results are compared to the recent experimental measurement of the sheet thickness distribution by partial coherent interferometry and a good agreement is achieved.
The Influence of Flexible Strip Height on Convective Heat Transfer Enhancement
Authors: Yang Yang , Ting David S.-K. , Ray Steve 
Published: November 2019

Abstract
A 12.7 mm wide flexible rectangular strip, made from 0.1 mm-thick aluminum sheet, is experimentally explored as a vortical flow generator for promoting heat convection from a flat plate in a wind tunnel. The strip is positioned normal to the freestream with an incoming velocity of 10 m/s, resulting in a Reynolds number, based on the strip width, of 8,500. The influence of the height of the flexible strip on the convective heat transfer enhancement is of interest. Three strip heights, 25.4 mm, 38.1 mm and 50.8 mm, were investigated. The heat transfer results are expressed in terms of Nusselt number, Nu, normalized by the unperturbed reference Nu0. The shortest, 25.4 mm high flexible strip resulted in the highest peak and overall heat transfer enhancement. The distribution of the local heat transfer enhancement is found to correlate well with the turbulent flow motion detailed using a triple-sensor hot-wire anemometer. Pointedly, the heat transfer rate is most elevated when the local flow is moving toward the hot plate, sweeping across a stretch of the surface before moving away from it. These effective convective motions are most effectively generated by the vortices produced by the shortest strip.
Theoretical Model of a Flow in a Tube With a Slit
Authors: Toda Yuki , Morimatsu Masataka , Nishio Yu , Ogawa Takanobu 
Published: November 2019

Abstract
A tube-type gas burner consists of a straight tube with a slit along it and discharges an air-gas mixture through the slit to produce a flame. The flow velocity from the slit depends on the pressure in the tube and the pressure loss at the slit, and it varies in the longitudinal direction of the tube. The resulting uneven flame degrades the quality of the burner.
In this study, we develop a one-dimensional theoretical model of the flow in a tube with a slit. To validate the result of the theoretical model, we also conduct experiments and numerical simulations for the same flow field. We applied this theoretical model to a flow in a tube, 1 m length, 40 mm in diameter, with a slit 2.5 mm wide. The end of the tube is closed. We also discuss the effect of the length of the burner on the unevenness.
Optimal Design for Impeller of a Sludge Pump Using Design of Experiment
Authors: Jin Jeong-Min , Ji Hyo-Geun , Kim Youn-Jea 
Published: November 2019

Abstract
Recently, many studies carried out to improve the performance of the pump with shape changes. In this paper, impeller optimization is performed to improve the pump performance. Design optimization techniques for the sludge pump impellers have been developed by using computational fluid dynamics (CFD) and optimal design theory. This paper describes the design optimization of a sludge pump impeller based on Response Surface Method (RSM) coupled with Navier-Stokes flow analysis. In particular, RSM which was based on the results of the design of experiment (DOE) helps to achieve the optimum point. In order to optimize the shape of the impeller, the thickness and the height of the blade were set as design factors. As a result, it was confirmed that the efficiency and the head were improved by 11.2% and 6.67%, respectively, compared to the referenced model.
Large Scale Wettability Quantification in Porous Media Using Tracers
Authors: Singh Deepshikha , Pant Harish J. , Phirani Jyoti , Roy Shantanu 
Published: November 2019

Abstract
Tracers are widely used to study physical phenomena taking place inside the porous medium such as hydrodynamics of the reactor by residence time distribution, and characterizing the oil reservoirs for heterogeneity and residual oil saturation. In this work, we use tracer techniques to characterize oil phase tracers to quantify the wettability of a fluid in a multi-phase flow in a porous medium. The wetting fluid will have more contact area with the sediments. The quantification of contact area of a fluid with sediments during flow will give us insights into the wettability and wettability alteration. A two tracer method is used to quantify the wetted area by one fluid in the porous medium. We first find the adsorption characteristics of the tracers for non-aqueous-phase tracers on the sediments. Subsequently flow experiments are performed to conduct residence time distribution (RTD) analysis using single phase flow. The adsorption characteristics during flow are identified for various flow rates. The difference in RTD curves of the two tracers of a phase is used to estimate the area in contact with the fluids with the sediment surface.
Development of Rotating Stall Cell Under Coexisting Phenomena of Surge and Rotating Stall in an Axial-Flow Compressor
Authors: Sakata Yuu , Ando Shuji , Fujisawa Nobumichi , Ohta Yutaka 
Published: November 2019

Abstract
The relationship between the growth of the stall cell and variation in the surge behavior was experimentally investigated. The aim of this study was to reveal the effect of the stall cell on the surge behavior from the viewpoint of the inner flow structure. In the experiment, the unsteady compressor characteristics during the surge and rotating stall were obtained by using a precision pressure transducer and a one-dimensional single hotwire anemometer. Under the coexisting states of surge and rotating stall, various surge behaviors were observed by throttling the mass flow rate. When the flow rate was set such that the surge behavior switched, an irregular surge was observed. During the irregular cycle, two different cycles were selected randomly corresponding to the stall behavior. When the amplitude of the plenum pressure is relatively large among the measurement results, the absolute value of the time-change rate in the flow coefficient and the static pressure-rise coefficient tend to be high. This shows that the flow field during stable operation near the peak point of the unsteady characteristics changes rapidly. In this case, an auto-correlation function of the wall-pressure fluctuation data showed that the stall inception of the compressor was induced earlier in the large cycle compared with the case of the top cycle. When studying the growth of the stall cell during the stalling process of the large cycle, the wall-pressure fluctuation data showed that the stall cell rapidly grew by gathering more than one spike-type disturbance into one stall cell. In this case, the stall cell fully expanded along the circumferential direction and developed into a deep stall. Therefore, the key factors that determine the surge behavior are the sudden change in the flow field near the peak point of the unsteady characteristics and the rapid growth in the stall cell during the stalling process.
Experimental Study on the Effects of Radial Dispersion of Spherical Particles on the Suspension Rheology
Authors: Kawaguchi Misa , Fukui Tomohiro , Funamoto Kenichi , Miyauchi Suguru , Hayase Toshiyuki 
Published: November 2019

Abstract
Experimental studies were performed to characterize the effects of the microstructure on the rheology of suspension. We focused on the change in the dispersion of the suspended particles under different particle Reynolds number conditions. Suspension flow through a microchannel with a circular cross-section was measured, and the radial dispersion of suspended particles and the velocity profiles were obtained. It was suggested that the particle dispersion could be changed owing to the difference in inertial force acting on the particles.
Inducer Design Optimization to Improve its Suction Performance
Authors: Nakamura Yushi , Lubieniecki Marek , Hayashi Kentarou , Kawata Yutaka , Miyabe Masahiro , Lettieri Claudio 
Published: November 2019

Abstract
The purpose of this paper is to present optimization method of an inducer blade shape to improve its suction performance and clarify the relationship between pump performance and design parameters. In order to conduct the optimization process a response surface based optimization framework was established. Baseline was designed in previous research [1]. The inducers were 3Dprinted in ABS plastic and their wetted and cavitating characteristics were measured. It was confirmed that the optimized inducer can maintain its wetted performance at lower cavitation numbers. A response surface is a mathematical model that approximates the relationship between the input parameters and the objective function from a finite number of learning points within the design space. The design space was defined by four parameters: sweep angle, sweep radius, incidence angle and blade solidity at the tip that controlled the blade shape. The performance of each design was evaluated with a CFD simulation established in a commercial solver. The optimization goal was to minimize the critical cavitation number that corresponds to a 5% drop of pressure increase through the pump due to cavitation.
A starting point of the optimization was the industrial pump designed by a Japanese company Teral [1]. The results of the numerical optimization show that the critical cavitation number was decreased by 17.6% with respect to the baseline design. In the experimental results, an average improvement of 15.4% was achieved.
Deposition of Ellipsoidal Fibers in Nasal Cavity: Influence of Non-Creeping Flow Conditions
Authors: Tash Mehdi Aboulhasan , Tavakol Mohammad Mehdi , Abouali Omid , Ahmadi Goodarz 
Published: November 2019

Abstract
In this study, deposition fraction of ellipsoidal particles in a 3D-Model of the nasal cavity (right airway) of a 24-year-old healthy woman was simulated for laminar and turbulent inhalation flow rates. The geometry used included the main nasal cavity from the nostril to the beginning of nasopharynx and was constructed in the Ansys-ICEM software from a CT scan image. The numerical simulations of governing equations were obtained using the Ansys-Fluent software. The mean airflow was assumed to be incompressible and steady. For turbulence modeling, the Realizable k-ε model was employed and the Lagrangian trajectory analysis method was used for particle tracking. For evaluating the ellipsoidal particle motions, several user-defined functions (UDFs) were developed and linked to the discrete phase model of the Ansys-Fluent code. The developed UDFs solve for the coupled translational and rotational equations of motion for ellipsoidal fibers and also accounts for the stochastic modeling of turbulence velocity fluctuations. The hydrodynamic forces and torques were calculated based on the non-creeping formulations for various ellipsoidal fibers. Laminar flow condition was assumed for breathing rate of 5.0 lit/min for the rest or light physical activities and turbulent flow condition was assumed for airflow rate of 20 lit/min for high physical activities. To investigate the dispersion and deposition of particles in the model of the human nasal cavity, various fibers with a semi-minor axis of 1, 3, 5 and 10 μm and various aspect ratios were considered.
Using the non-creeping flow formulation for hydrodynamic forces and torques, the simulation results showed slight differences in the total deposition fraction of ellipsoidal fibers compared with the corresponding creeping flow model. Small fibers deposit roughly uniformly in the nasal cavity with no hotspot region. For the large inertial fibers, however, the nasal valve is a hot spot region, where the deposition rate reaches to its peak.