bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow and Heat Transfer Characteristics of Multi-Armed Impinging Jet Using DNS
Authors: Echigo Kentaro , Tsujimoto Koichi , Shakouchi Toshihiko , Ando Toshitake 
Published: November 2019

Abstract
A single impinging jet (SIJ) produces a high heat transfer rate around an impinging position on an impinging wall, while the heat transfer performance (HTP) decays increasing the distance from the impinging position. Thus in order to overcome the shortcoming of SIJ: the occurrence of both inhomogeneous heat distribution on the wall and the narrow heating area, multiple impinging jets (MIJ) are generally introduced, however, nonuniformity of heat transfer still occurs. Therefore, the viewpoint of new jet control is required in order to further improvement of the uniformity of heat transfer. On the other hand, blooming jets occur with superimposition of axial and helical excitations on the inlet velocity profile. Blooming jets are characterized by vortex rings moving along branches of separate streams. In previous studies, it is observed that blooming jets change its flow pattern with different frequency ratio of axial to helical, and its mixing and diffusion characteristics. However, there are no studies that observe heat transfer performance of the blooming jet. In this study, we conduct a direct numerical simulation of blooming jet that impinges upon the wall, and investigate its flow characteristics and heat transfer performance. As a control parameter, the distance from the wall is varied. From the view of vortex structures and velocity magnitude, it reveals how the generation of flow phenomena are modulated through the blooming control. Further in order to quantify the heat transfer of the blooming, distributions of mean local Nusselt Number are examined. Compared to the uncontrolled jet, it is confirmed that the uniformity of heat transfer is improved, suggesting that the blooming jets can be expected to be useful for the improvement of uniform heat transfer performance of impinging jets.
Coupled Blowing and Suction for Flow Separation Control
Authors: Tadjfar M. , Kamari D. J. 
Published: November 2019

Abstract
The effects of applying a coupled unsteady blowing and suction combination over SD7003 airfoil at Reynolds number of 60,000 at an angle of attack of 13°, where a large separation on the suction side of the airfoil existed, was considered to investigate active flow control (AFC) mechanism. URANS equations were employed to solve the flow field and k–ω SST was used as the turbulence model. The unsteady blowing and suction were implemented at an angle to the surface crossing the boundary layer (CBL). The influence of location and frequency of the blowing/suction jets were examined.
Dynamic Characteristics of Blade Surface Cavitation on Various Types of Hydrofoils
Authors: Horiguchi Hironori , Toyoshima Masakazu , Matsuda Takuya , Sugiyama Kazuyasu 
Published: November 2019

Abstract
In high speed turbopumps, various types of cavitation such as blade surface cavitation, tip leakage vortex cavitation, and backflow vortex cavitation occurs. When cavitation responses to encourage fluctuation of pressure and flow rate, the oscillation of flow rate called cavitation surge can occur. Therefore, clarification of dynamic characteristics of cavitation is desired to obtain higher reliability of turbopumps. Focusing on blade surface cavitation as one of fundamental cavitation, we investigated dynamic characteristics of blade surface cavitation on Clark-Y 11.7% hydrofoil and NACA0015 hydrofoil in addition to a flat plate hydrofoil in experiments. Several interesting characteristics of blade surface cavitation were clarified.
Curvature Estimation Modeling Using Machine Learning for CLSVOF Method: Comparison With Conventional Methods
Authors: Haghshenas Majid , Kumar Ranganathan 
Published: November 2019

Abstract
Despite extensive progress in recent decades, curvature estimation in two-phase models remains a challenge. Well-established curvature computing techniques such as distance function, smoothed volume fraction and height-function directly estimate the interface curvature from the implicit representation of the interface. Most recently, machine learning approach has been incorporated in computational physics simulation. Machine learning is a set of algorithms that can be utilized for training a system which allows predicting the output in the future. In this work, we train a curvature estimation model using machine learning approach for Coupled Level Set Volume of Fluid (CLSVOF) method in which both distance function and volume fraction implicitly represent the interface. Three datasets for the curvature are generated: a) curvature as a function of volume fraction (nine inputs), b) curvature as a function of distance function (nine inputs), and c) curvature as a function of both volume fraction and distance function (eighteen inputs). For each interfacial cell, curvature and input parameters (nine volume fraction and nine distance function values) at nine grid points across the interface are stored. Datasets are utilized to train different curvature computing models using neural network (NN) learning algorithm. Comparison of different datasets reveals that the distance function dataset is the best input for curvature function training. Different available learning algorithms on built-in NN toolbox in Matlab are examined. The curvature estimation function is examined for a dimensional 2D well-defined droplet on different grid resolution. In addition, the curvature estimation model by machine learning approach is compared with conventional methods such as the level set method and height function method for couple of cases. First, the case of elliptical droplet is used to evaluate curvature estimation of different methods in comparison with the analytical solution. Then, the standard case of equilibrium droplet is simulated by CLSVOF solver using different curvature estimation methods to evaluate parasitic currents generation and droplet pressure prediction. The results show that the machine learning curvature function outperforms conventional methods even on coarse grids. Finally, the curvature estimation methods are is utilized to solve a practical case of rising bubble. We observed that the terminal velocity of capped bubble reported by curvature function simulation has the lowest error.
Can Natural Convection on Smooth Vertical Plates in the Laminar Regime Be Improved by Adding Forward Facing Triangular Roughness Elements?
Authors: Hærvig Jakob , Jensen Anna Lyhne , Sørensen Henrik 
Published: November 2019

Abstract
Vertical smooth surfaces are commonly used for transferring heat by natural convection. Many studies have tried altering smooth surfaces in various ways to increase heat transfer. Many of these studies fail to increase global heat transfer. The problem commonly reported is dead zones appearing just upstream and downstream obstructions that effectively decrease wall temperature gradients normal to the surface. In this study, we simulate how changes geometry of forward facing triangular roughness elements affect local and global heat transfer for isothermal plates.
We change the aspect ratio of the triangular elements from L/h = 5 to L/h = 40 at Grashof numbers of GrL = 8.0 · 104 and GrL = 6.4 · 105. In all cases the flow remains laminar. Even when accounting for the increase in surface area, we keep observing a decrease in global heat transfer compared to the smooth vertical plate. However, the results show by carefully selecting the aspect ratio and pitch distance of the triangular elements based on the Grashof number, the dead zone behind the horizontal part can be eliminated thereby significantly increasing local heat transfer. This observation could help to improve cooling of electronics with high localised heat fluxes.
Two-Phase Flow Simulation of High-Pressure Gas Atomization: Effect of Molten Metal and Atomizing Gas Properties on Droplet Size Distribution
Authors: Hanthanan Arachchilage Kalpana , Haghshenas Majid , Kumar Ranganathan 
Published: November 2019

Abstract
Numerical simulations of high-pressure gas atomization are performed by varying the molten metal and the atomizing gas to understand the physics behind high-pressure gas atomization and the effects of the melt and the atomizing gas on droplet size distributions. The Volume of Fluid method is used in the OpenFoam platform. The three melt-gas combinations used in these simulations are aluminum-nitrogen, aluminum-argon, and low carbon steel-nitrogen. Three interfacial instabilities have been identified in the early stages of all three atomization processes. Comparison of aluminum and steel as the molten metal indicates that steel atomizes more effectively and provides a higher yield than aluminum. However, changing the atomizing gas does not result in a significant change in the atomization process.
Air Entrainment and Bubble Generation by a Hydrofoil in a Turbulent Channel Flow
Authors: Kumagai Ichiro , Taguchi Kakeru , Kawakita Chiharu , Hamada Tatsuya , Murai Yuichi 
Published: November 2019

Abstract
Air entrainment and bubble generation by a hydrofoil bubble generator for ship drag reduction have been investigated using a small high-speed channel tunnel with the gap of 20 mm in National Maritime Research Institute (NMRI). A hydrofoil (NACA4412, chord length = 40 mm) was installed in the channel and an air induction pipe was placed above the hydrofoil. The flow rate of the entrained air was quantitatively measured by thermal air flow sensors at the inlet of the air induction pipe. The gas-liquid flow around the hydrofoil was visualized by a backlight method and recorded by a high-speed video camera. As the flow velocity in the channel increased, the negative pressure generated above the suction side of the hydrofoil lowered the hydrostatic pressure in the channel, then the atmospheric air was entrained into the channel flow. The entrained air was broken into small air bubbles by the turbulent flow in the channel. The threshold of air entrainment, the air flow rate, and gas-liquid flow pattern depends on Reynolds number, angle of attack (AOA), and hydrofoil type. We identified at least three modes of air entrainment behavior: intermittent air entrainment, stable air entrainment, and air entrainment with a ventilated cavity. At high flow speed in our experimental condition (9 m/s), a large volume of air bubbles was generated by this hydrofoil system (e.g. air flow rate was 50 l/min for NACA4412 at AOA 16 degrees), which has a high potential to reduce ship drag.
A Transient Approach for Estimating Concentration of Water Droplets in Oil and Corrosion Assessment in the Oil and Gas Industry
Authors: Darihaki Farzin , Shirazi Siamack A. , Feng Qingshan 
Published: November 2019

Abstract
Water-in-oil dispersion modeling is critical to assess the internal corrosion in pipelines, specifically for the oil and gas industry applications. In many oil transportation facilities, a small amount of water could be entrained in production fluids. Turbulence can break out the water into the form of tiny droplets. Under certain conditions in horizontal or inclined pipelines, water droplets can settle and contact the wall which may lead to CO2 and/or O2 or other forms of corrosion and damage the transport system integrity.
In the present study, a novel transient approach has been developed that provides water concentrations across the pipe section. A one-dimensional transient finite-difference computational model has been used to determine concentration distribution in a vertical direction across the pipe. Calculated water fractions using the transient model is compared to experimental data and more comprehensive 3-D Computational Fluid Dynamics (CFD) approach for various flow conditions and watercuts that shows the viability of the simplified one-dimensional approach. The proposed model is capable of predicting water dispersion at different locations and could be utilized for various pipe-flow systems.
Furthermore, water in the form of droplets or liquid film can result in corrosion when it wets the pipeline surface. Consequently, the calculated water concentration at the bottom of the pipe assists in determining wettability of the pipe surface by water and evaluating the corrosion risk along the pipeline.
Experimental Analysis of Water Flow in Aquaponics Fish Tanks
Authors: Thomas Hannah , Coombs Danielle , Nedyalkov Ivaylo , Guerdat Todd 
Published: November 2019

Abstract
Aquaponic systems are a combination of hydroponics, growing plants in water, and aquaculture, growing of fish. The two subsystems are connected so that the water circulating between the two, transfers the waste from the fish tank to the plants, where the plants take in nutrients. The water is filtered by the plants and is recirculated back into the fish tank. Small-scale aquaponic systems are of particular interest, as they are appropriate for rural and developing locations to harvest both plants and fish for a local community. To improve the level of sustainability, the flow within the fish tank needs to be better understood since most of the power required to operate an aquaponic system is used by the fish-tank pump. The shape of the fish tank is of importance for the flow in the tank and the initial cost of the tank. In this work, the flow in a 2 m × 2 m square fish tank with curved corners was studied experimentally with a Vectrino Acoustic Doppler Velocimeter. Two inlet configurations were studied and compared to each other — inlets at each corner of the tank, and inlets at two of the corners of the tank. The results suggest that good recirculation can be achieved with the two inlet locations. The present work can be used for evaluating numerical simulations of the flow in the tank. The ultimate goal of the study is to develop an inlet-design configuration which minimizes initial and operational costs of the small-scale aquaponic system.
A TomoPIV Flow Field Study of NACA 63-215 Hydrofoil With CFD Comparison
Authors: Sheikhshahrokhdehkordi Mohammadamin , Goudarzi Navid , Saffaraval Farhad , Mousavi sani Seyedmohammad , Tkacik Peter 
Published: November 2019

Abstract
This paper investigates the unsteady flow field around the NACA 63-215 hydrofoil. Computational fluid dynamics (CFD) study is followed by tomographic particle image velocimetry (TomoPIV) experiments in a closed-loop water channel at Reynolds number of approximately 2.9 × 104. The k-ω SST turbulence model results, namely the performance metrics such as lift and drag coefficients, are within 2% of the published values in the literature. There is also a good agreement between the numerical and experimental flow filed characteristics (i.e. average total velocity) around the studied NACA 63-215 hydrofoil; a maximum difference of 2% is observed. The difference in the results is mainly from the implemented boundary condition constraints in the CFD model. Longitudinal variations of streamwise velocity (i.e. u component) deficit from CFD are within 5% of the experimental values. In contrast with 2D measurements, the TomoPIV captures the 3D phenomena such as out of the plane velocity gradients. The results from this work supports both fundamental and applied research areas such as studying the development of high-performance and cost-effective ocean current turbine array models.
Concentration Distribution of Photosensitive Liquid in a Droplet Under UV Light
Authors: Li Tianyi , Kar Aravinda , Kumar Ranganathan 
Published: November 2019

Abstract
A semi-analytical solution for the concentration of photosensitive suspension is developed in a hemispherical droplet illuminated with UV laser. A biharmonic equation in stream function is analytically solved using toroidal coordinates and the velocity is then used to solve the mass transport equation for concentration. Flow pattern and photosensitive material concentration are affected by the peak location of the UV light intensity, which corresponds to a surface tension profile. When the laser beam is moved from the droplet center to its edge, a rotationally symmetric flow pattern changes from a single counter clockwise circulation to a circulation pair and finally to a single clockwise circulation. This modulation in the orientation of circulation modifies the concentration distribution of the photosensitive material. The distribution depends on both diffusion from the droplet surface as well as Marangoni convection. The region beneath the droplet surface away from the UV light intensity peak has low concentration, while the region near the downward dividing streamline has the highest concentration. When the UV light peak reaches the droplet edge, the concentration is high everywhere in the droplet.
Impact of Combustion Models on Emissions Predictions From a Piloted Methane-Air Diffusion Flame
Authors: Naik Chitralkumar V. , Elasrag Hossam , Yadav Rakesh , Validi Ahad , Meeks Ellen 
Published: November 2019

Abstract
Combustion models can have a significant impact on flame simulations. While solving finite rate chemistry typically yields more accurate predictions, they depend significantly on the detailed kinetics mechanism used. To demonstrate the effect, Large Eddy Simulation (LES) of Sandia Flame D [1] has been performed using various combustion models. Four different detailed kinetics mechanisms have been considered. They include DRM mechanism with 22 species, GRI-mech 2.11 with 49 species, GRI-mech 3.0 with 53 species [2], and Model Fuel Library (MFL) mechanism with 29 species [3]. In addition to the mechanisms, two modeling approaches considered are direct integration of finite rate kinetics (FR) and Flamelet Generated Manifold (FGM). The performance is compared between combinations of the mechanisms and combustion-modeling approaches for prediction of the flame structure and pollutants, including NO and CO. The mesh contains about half a million hexahedral cells and LES statistics were collected over ten flow throughs. Advanced solvers including dynamic cell clustering using the Chemkin-CFD solver in Fluent have been used for faster simulation time. Based on comparison of simulation results to the measurements at various axial and radial positions, we find that the results using the FGM approach were comparable to those using direct integration of FR chemistry, except for NO. In general, the simulation results are in good agreement with the experiment in terms of aerodynamics, mixture fraction and temperature profiles. However, kinetics mechanisms were found to have the most pronounced effect on emissions predictions. NO was especially more sensitive to the kinetics mechanism. Both versions of the GRI-mech fell short in predicting emissions. Overall, the MFL mechanism was found to yield the closest match with the data for flame structure, CO, and NO.
CFD Simulations of Oil-Water Flow Behavior in Horizontal Pipe Separator
Authors: Kolla Srinivas Swaroop , Mohan Ram S. , Shoham Ovadia 
Published: November 2019

Abstract
Horizontal Pipe Separators (HPS©) are used for separation of oil and water especially in subsea environment owing to its simplicity, installation, and operation. In the present work, the flow phenomena in the HPS with 0.0762m ID and 10.3 m long separating oil and water with specific gravities of 1 and 0.857 is simulated and analyzed using ANSYS Fluent 16. Hexahedral mesh with boundary layers has been done utilizing ANSYS design modeler for this analysis. A grid independence study is performed on 3 different mesh grids using grid convergence index. 3-D simulations are carried out using a Hybrid Eulerian-Eulerian Multifluid VOF model for watercuts ranging from 20 to 80% and a mixture velocity of 0.08 m/s. The CFD simulations analyzed the effect of watercut on the oil-water mixture flow behavior and the entry region required for the oil and water to separate in the HPS. These simulation results are validated against acquired experimental data by Othman in 2010. These simulations provide an insight to understand the effects of diameter, watercut, and mixture velocities on the performance of HPS to aid in its design and scale up/down studies.
Dynamic Characteristics of Unshrouded Impellers Equipped With Balance Piston Systems for Rocket Turbo Pumps
Authors: Hayashi Tomoyuki , Yoshimura Mamiko , Matsumoto Keisuke , Miyagawa Kazuyoshi , Kawasaki Satoshi , Takida Junya , Hiraki Hiromichi , Suwa Naohito 
Published: November 2019

Abstract
Turbo pumps for rocket engines often equipped balance piston (BP) systems at the back-shroud of the impellers for cancelling their axial thrust. The BP system is self-balancing and stable under quasi-static conditions, but it is known that the BP systems can be unstable under certain dynamic conditions. The performance characteristics of turbo pumps equipped with unshrouded impellers might be affected by the axial position of the rotor. Thus it is necessary to consider this effect when calculating the balance of axial thrust. Few experiments have determined the characteristics of unshrouded impellers equipped with BP systems yet.
In this research, an experimental study of a model turbo pump for rocket engines was carried out. This pump had an unshrouded impeller, a BP system, a vaned diffuser, and a volute. Axial forced oscillations were applied on the rotor of the pump by an active magnetic bearing (AMB) test facility. This setup can oscillate with freely-selected amplitude and frequency applying thrust to the rotor. During the oscillations, the fluctuation of axial thrust under the operating conditions was monitored using strain gauges. The axial thrust compensation ability and the response of the BP system were evaluated by analyzing the magnitude, amplitude and phase delay of the axial position of the rotor. Moreover, 3D simulations and 1D simulations were carried out for the model pump. In the 3D simulations, computational fluid dynamics (CFD) was used to calculate the internal flow of the model pumps. The BP system was equipped with an impeller on which were applied forced oscillations. The impeller movement was modeled using a mesh morphing method. The 1D simulation predicted the axial thrust by calculating the mass flow balance using the geometry of the model pump.
The phase lag between the axial position and the thrust was dominated by the pressure fluctuation at the BP chamber caused by the mass flow balance. The 3D simulations well predicted the fluctuation, but the characteristics of the BP system estimated by the 3D simulations were more stable than those determined by the experiments. On the other hand, the characteristics estimated by the 1D simulation was less stable than those by the experiments. However, these simulations grasped the tendency of the BP system to become unstable as the oscillation frequency increases, and are effective in predicting the characteristics.
Numerical Simulation of Proppant Transportation in Hydraulic Fracture Based on DDPM-KTGF Model
Authors: Zhang Yan , Lu Xiaobing , Zhang Xuhui , Li Peng 
Published: November 2019

Abstract
Hydraulic fracturing is an efficient way to improve the conductivity of the tight oil or gas reservoirs. Proppant transportation in hydraulic fractures need to be investigated because the proppant distribution directly affects the oil or gas production. In this paper, the dense discrete particle model (DDPM) combined with the kinetic theory of granular flow (KTGF) are used to investigate the proppant transportation in a single fracture. In this model, the effects of proppant volume fraction, proppant-water interaction, proppant-proppant collision, and proppant size distribution are considered. The proppant-proppant collision is derived from the proppant stress tensor. This model is applicable from dilute to dense particulate flows. The simulated results are similar to the experimental data from other researchers. In further study, the two-phase flow in the cross fractures will be considered for engineering application.