bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Influences of the Body’s Presence on Flow Around the Wings in Insect Flapping Flight
Authors: Yamauchi Kohei , Fukui Tomohiro , Morinishi Koji
Published: November 2019

In this research, we numerically investigated the influences of the body’s presence on flow around the hovering fruit fly with regularized lattice Boltzmann method. In recent years, insect’s flapping flight system has been investigated because their superior flight mechanisms are expected to improve the flight abilities of micro air vehicles. Because of the simplification of experimental equipment and computational simulation, the insect model without body is often used to investigate the flow around the hovering flight insect. However, the gap between the wing and body can significantly change the flow around the wing root. Thus, we conducted investigations of the influences of the body’s presence on the vortical flow structure and cycle-averaged lift coefficient. As a result, the aerodynamic forces on the wings were enhanced by the body’s presence. The flow at the gap between wing and body enhanced the vortex strength and aerodynamic forces on the wing root region. Also, the cycle-averaged lift coefficient of the with body model was slightly higher than that of the without body model. If the wing’s flapping motion or the shape of the wing is changed, the effects of the body’s presence will cause different flow around the wing root. Therefore, it is necessary to take body’s presence into consideration.
Optimization of a Cyclone Using Multiphase Flow Computational Fluid Dynamics
Authors: Weber Justin , Fullmer William , Gel Aytekin , Musser Jordan
Published: November 2019

The US Department of Energy (DOE) National Energy Technology Laboratory’s (NETL) 50 kWth chemical looping reactor has an underperforming cyclone, designed using empirical correlations. To improve the performance of this cyclone, the vortex tube radius and length, barrel radius, and the inlet width and height are optimized using computational fluid dynamics (CFD). For this work, NETL’s open source Multiphase Flow with Interphase eXchange (MFiX) CFD code has been used to model a series of cyclones with varying geometric differences. To perform the optimization process, the surrogate modeling and analysis toolset inside Nodeworks was used. The basic methodology for the process is to use a design of experiments method (optimal Latin Hypercube) to generate samples that fill the design space. CFD models are then created, executed, and post-processed. A response surface (Gaussian process model) is created to characterize the relationship between input parameters and the Quantities of interest (QoI). Finally, the CFD-surrogate is used by an optimization method (differential evolution) to find the optimal design condition. The resulting optimal cyclone has a larger diameter and longer vortex tube, a larger diameter barrel, and a taller and narrower solids inlet. The improved design has a predicted pressure drop 11-times lower than the original design while reducing the mass loss by a factor of 2.3.
Numerical Simulation of Mixed Flow Past an Inclined Square Cylinder Using a Local Radial Basis Function Method
Authors: Wang Tongsheng , Huang Zhu , Sun Zhongguo , Xi Guang
Published: November 2019

Unsteady mixed convective heat transfer flow past an inclined square cylinder is numerically investigated using a local multi-quadric radial basis function (MQRBF) interpolation. The blockage parameter (ratio of square cylinder length d to height of the computational domain H) varies from 0.025 to 0.2. Air is considered as the working fluid and Prandtl number is fixed at 0.71. Richardson number generally affects the heat transfer efficiency ranging from 0 to 20. Inclined angle of square cylinder ranges from 0° to 45°. The inlet flow is assumed to be laminar and uniform. At the outlet of the computational domain, a convective boundary condition is compared with a traditional Neumann condition. A study of the shape parameter of MQRBF which is sensitive to the distribution of inhomogeneous supporting nodes is provided. The representative streamlines, vortex structures and isotherm patterns are presented and discussed. In addition, the overall lift and drag coefficients, average Nusselt number and Strouhal number for unsteady flow are analyzed for various Reynolds number and Richardson number.
Bubble Measurement via Hough Transform in Highly Overlapping Conditions
Authors: Shepard Thomas , Höft Thomas
Published: November 2019

Accurate measurement of bubble size in digital images can prove challenging in conditions that involve significant overlapping of bubbles and/or images with a combination of in and out of focus bubbles. The method employed in the current study uses the circular Hough transform to identify circular features in the image. This method can handle mildly non-circular (i.e. non-spherical) bubbles as well as non-trivial overlapping. Several image pre-processing steps are employed to improve the method’s accuracy in detecting in-focus bubbles along with their radii, reduce both spurious detection of out-of-focus bubbles and non-bubble features, and reduce non-detection of in-focus bubbles. Pre-processing steps include histogram equalization and illumination variation reduction via filtering. In this paper, results from the algorithm are compared against a manual detection of bubbles in digital images under conditions of varying bubble diameter and bubble number density.
Effect of Diameter Size on the Unsteady Characteristics of Pulsatile Flow in Curved Human Blood Vessel
Authors: Tang Ruixuan , Zhao Xuanming , Wang Junshi , Hyde Justin , Kesser Bradley , Dong Haibo
Published: November 2019

Pulse-synchronous tinnitus (PST) has been linked to multiple anatomical variants of the venous outflow tract, including transverse sinus (TS) stenosis and sigmoid sinus (SS) dehiscence. It is unknown if the size of diameter in the TS part at the symptomatic side will result in PST. In this study, a combined experimental and computational approach is adopted to study the blood flow during PST. A parametric study is performed on the diameter size of one PST patient at the symptomatic side. A Reynold-averaged-Navier-Stokes (RANS) flow solver is employed in ANSYS Fluent to simulate the symptomatic side at different TS diameter sizes. Results have shown distinct differences in the flow characteristics (including pressure, turbulent kinetic energy (TKE), velocity and shear stress) between the symptomatic side at different TS diameter sizes. The result provides evidence to the hypothesis that anatomic differences can be an important element in affecting blood flow in the venous outflow tract. Resulted findings reveal the strong connection between the flow characteristics of a dehiscent SS and resultant PST. The findings help to understand the flow physics of PST and provide insightful guidance for surgical interventions.
CFD Study of Implanted-Stent Impacts on Blood Flows in Left Coronary Artery Branch Models
Authors: Fujimoto Kazushi , Tsukahara Takahiro , Yamamoto Ken , Motosuke Masahiro , Kawamoto Hiroyoshi , Tahara Satoko , Tanaka Kentaro , Nakamura Sunao
Published: November 2019

Percutaneous coronary intervention (PCI) is widely used as a treatment for ischemic heart disease. In particular, a high procedural precision of PCI for the left main coronary artery (LMCA), which supplies coronary artery blood to large amount of myocardium, is required. The restenosis after stent placement and target lesion revascularization of side branches (SB) is still a clinical issue. Regarding the stent implantation for bifurcation or trifurcation lesion, the stent struts should jail the inlets of SB. In such a situation, we clinically do the kissing balloon technique (KBT) to remove the struts existing at the opening of SB. As well as KBT, the proximal optimization technique (POT), which presses the stent against the wall, is also commonly used. However, merits of therapeutic strategies of KBT and POT for the branch are not confirmed from the fluid-dynamical viewpoint. In this study, we examined the influence of a stent in left main coronary artery on blood flow by employing CFD simulations. We investigated the influence of membrane position on the flow in bifurcation as well as of the stent position and shift on the flow in trifurcation. we confirmed that the effect of the stent position on the flow was bigger than that of the area occupied by the stent and that of KBT which moves the stent from the flow peak may be useful. However, it was also suggested that the intimal lining after KBT may cause serious flow inhibition.
Effects of Volute Cross-Sectional Area Distribution on Performance of Double-Suction Volute Pump
Authors: Chen Szu Yung , Zhang Lu , Sekino Yumiko , Watanabe Hiroyoshi
Published: November 2019

The following study describes the optimization design procedure of a double-suction pump. BASELINE pump is designed as inlet nozzle diameter 800 mm and impeller outlet diameter 740 mm. Each component of a BASELINE pump, impeller configurations, discharge volute, and the suction casing were determined by DOE (Design of Experiments) and sensitivity analysis. However, finite selected design parameters for each component are mostly restricted to the free surface design of the pump casing. In this study, the optimization method approach along with steady Computational Fluid Dynamics (CFD) is introduced to achieve the high efficiency request of a double-suction pump. To investigate the matching optimization of the impeller and discharge volute at design point, the full parametric geometry of discharge volute was developed referred to the BASELINE shape and Multi-Objective Genetic Algorithm NSGA-II (Non-dominated Sorting Genetic Algorithm II) was used. Optimization result shows that by increasing the volute cross-sectional area from the volute tongue till the circumferential angle 180 deg. provides lower loss. This is due to the improvement achieved for the better distribution of the velocity gradient within the volute. A validated unsteady computational fluid dynamics (CFD) was also employed to investigate the performance difference between optimized volute design and the BASELINE which correlated to the pressure fluctuation and secondary flow behavior inside the cross-sections from 80% to 120% of nominal flow rate. The result shows that the flow distortion in the streamwise direction is stronger with the BASELINE and sensitively affects the operation stability. This is due to the different secondary flow pattern in the cross-sections, hence demonstrating a design direction of desired volute cross-sectional shape for high-performance can be used in a double-suction volute pump.
Numerical Investigation of Flow and Heat Transfer Characteristics for Attached and Separated Low-Pr Flows
Authors: Bhushan S. , Elmellouki M. , Jock W. D. , Walters D. K. , Lai J. K. , Hassan Y. A. , Obabko A. , Merzari E.
Published: November 2019

This study performs a comprehensive analysis of the effect of flow separation and reattachment, convective conditions and Pr to understand their effect on heat transfer characteristics and the predictive capability of low- and hig-fidelity turbulence models are assessed. To achieve the objective DNS is performed for plane channel flow at Reτ = 640, Pr = 0.71 and 0.025 involving mixed forced and natural convection condition, and RANS, hybrid RANS/LES, and LES calculations are performed for backward backing step with expansion ratio 1.5, Pr = 0.71 and 0.0088 and Ri = 0 and 0.338. Channel flow simulations reveal that the convective conditions affect the near-wall turbulent structures and thermal diffusion more significantly in high-Re flows that in low-Re flows. Thus, the generated DNS database provides a challenging test case for turbulence model validation. For backward facing step case, all the turbulence models predict the overall flow characteristics, and Ri = 0 case is a more challenging validation test case than Ri = 0.338, as the former involves complex turbulent diffusion, whereas the latter is dominated by large scale buoyancy driven convection. Results show that well resolved PANS and LES predictions can help in improve understanding of turbulent diffusion under complex convection and flow separation/ reattachment regimes. RANS results are also quite encouraging and indicates that they may represent a reasonable compromise between computational expense and accuracy for cases in which high resolution simulations are not feasible.
Effect of Stator Geometry on the Performance of a Positive Displacement Hydraulic Turbine
Authors: Sonawat Arihant , Kim Jin-Hyuk , Kim Seung-Jun , Choi Young-Seok , Yang Hyeon-Mo , Lee Yong-Kab , Kim Kyung-Min
Published: November 2019

Positive displacement turbine (PDT) is a special class of hydraulic turbine which finds its usage in the applications involving very low flow rates with high heads and very low specific speeds. In the present case, a PDT was designed and developed to replace the pressure differential control valve (PDCV) and to harness the unused differential pressure energy from the water supply pipeline system. The turbine was designed considering the on-site available head and flowrate. The rotors were twisted to damp the fluctuations in pressure, flow rate and torque. The primary objective of the present study was to analyze the effect of the stator shape on the performance of PDT using Computational Fluid Dynamics approach. The governing equations of the fluid flow were solved using an unsteady approach to capture accurately the pulsating nature of the flow using ANSYS CFX v17.1. Initially a circular stator turbine was used for transporting the working fluid to and from the turbine rotors and later the effects of square and rectangular shaped stator designs were also checked. It was observed that the performance of the PDT slightly improved with rectangular and square stators in terms of hydraulic efficiency than with circular stator with low flow fluctuations.
A Computational Estimation of Velocity Distribution of Boundary Layer on a Spherical Bubble
Authors: Kusuno Hiroaki , Sanada Toshiyuki
Published: November 2019

The aim of this study is to investigate a velocity distribution of velocity boundary layer on a spherical bubble using numerical simulation and to compare the results with the theoretical model. In this study, we calculated the axisymmetric flow around a spherical bubble, the Reynolds number ranged from 50–1000. We selected Navier-Stokes equations written in the vorticitystream function to capture small vorticity generated on the bubble surface. We described bubble surface with boundary-fitted coordinate system.

As a preliminary test, we guaranteed the accuracy of calculation method adopted in this study. Previous study showed that it needs three calculation points in the theoretical boundary layer to describe the boundary layer with second order accuracy. Our study, however, shows that the it needs seven points to describe the boundary layer even if forth order accuracy.

We compared the velocity distribution of numerical result to that of theoretical model. The velocity in the vicinity of bubble is divided into potential solution and perturbed velocity component. At bubble side, the absolute value of the perturbation velocity estimated by numerical result is slightly larger than that of the theoretical model in any Reynolds numbers. When we defined bubble boundary layer thickness as the region below to 99% velocity of the potential solution, we find that value of the boundary layer thickness proposed in this study is two to three times larger than that of theoretical model. In the vicinity of the rear stagnant region (i.e. in the wake of bubble), numerical and the theoretical velocity distribution does not match at all.
Polynomial Chaos Based Solution to Inverse Problems in Petroleum Reservoir Engineering
Authors: Khatoon Sufia , Phirani Jyoti , Bahga Supreet Singh
Published: November 2019

In reservoir simulations, model parameters such as porosity and permeability are often uncertain and therefore better estimates of these parameters are obtained by matching the simulation predictions with the production history. Bayesian inference provides a convenient way of estimating parameters of a mathematical model, starting from a probable range of parameter values and knowing the production history. Bayesian inference techniques for history matching require computationally expensive Monte Carlo simulations, which limit their use in petroleum reservoir engineering. To overcome this limitation, we perform accelerated Bayesian inference based history matching by employing polynomial chaos (PC) expansions to represent random variables and stochastic processes. As a substitute to computationally expensive Monte Carlo simulations, we use a stochastic technique based on PC expansions for propagation of uncertainty from model parameters to model predictions. The PC expansions of the stochastic variables are obtained using relatively few deterministic simulations, which are then used to calculate the probability density of the model predictions. These results are used along with the measured data to obtain a better estimate (posterior distribution) of the model parameters using the Bayes rule. We demonstrate this method for history matching using an example case of SPE1CASE2 problem of SPEs Comparative Solution Projects. We estimate the porosity and permeability of the reservoir from limited and noisy production data.
Study of a Microfluidic System Based One-Step Blood Cell-Free Region for Biomarker Detection
Authors: Kanjirakat Anoop , Sadr Reza
Published: November 2019

Microfluidic systems are becoming common in the development of point-of-care (PoC) diagnostic systems where various methods are used to efficiently separate blood cells from whole blood. The goal of this research is to develop a passive plasma separator that can easily be integrated into an entire blood-based diagnosis microfluidic platform. In the present work, a one-step process of creating a cell-free region in the flow without the plasma being actively extracted from the whole blood is discussed. Centrifugal force together with a backward facing step is utilized to create a blood cell-free zone. Sensors (typically less than 10 micrometers in size) are proposed to be placed in the cell-free zones for biomarker detection. A detailed numerical study for the design of the microfluidic platform is reported. The two-phase nature of the blood is modeled using a discrete element method (DEM) where blood cells are modeled as spherical constituents with the inclusion of inter-particular interactions. The sizes of the cell-free zones in the microfluidic system are measured for various geometric and flow conditions. An expansion chamber with a larger aspect ratio together with a low Reynold number flow entering it is observed to create a larger cell-free zone.
Numerical Simulation of a Pouring Flow From a Beverage Can
Authors: Nishio Yu , Niwa Keiji , Ogawa Takanobu
Published: November 2019

Motion of liquid pouring from a beverage can is numerically studied. A liquid is poured from a can which is rotated at a prescribed angular speed. The flow is simulated by solving the unsteady three-dimensional Navier-Stokes equations. An experiment under the same condition is also carried out to validate the computational result. The result shows that, when the can is tipped, the liquid flows over the lid of the can and is once obstructed by the rim of the lid. The numerical result is in good agreement with the experimental result. The effect of condensation formed on a can surface is also considered. The effect of condensation is taken into account by adjusting a contact angle. The liquid pouring from a can trickles down along the can body. The computation reproduces these experimental observations.
Numerical Analysis of Contraction Geometry Effects on Cavitation Choking in a Piping System
Authors: Nohmi Motohiko , Kagawa Shusaku , Tsuneda Tomoki , Tsuru Wakana , Yokota Kazuhiko
Published: November 2019

There is a contraction portion in the water supply pipe line system, and cavitation may occur in the contraction when the flow velocity is increased. Such a situation occurs widely in the throat of the fluid machineries and in the vicinity of the valve body of the valve. In operation of the valve, it is well known that a phenomenon occurs in which the flow rate does not increase even if the static pressure difference upstream and downstream of the valve is increased due to the growth of cavitation in the contraction, which is well known as choking . It is not clear what phenomena occurs when cavitation surge occurs in the pipe system in the situation where choking is occurring in the contraction. In this study, cavitation CFD was performed on pipes those have three different geometry contractions. It was revealed that choking occurred when cavitation occurred in any shape. Also, in the case with the sharp contraction part and the sudden expansion, the flow fluctuation at the upstream of the contraction is much weaker than that at the downstream, but in the contraction with the bent part where the centrifugal force acts on the flow, the flow fluctuation at the upstream was found to be strong.
Flow and Heat Transfer Characteristics of Multi-Armed Impinging Jet Using DNS
Authors: Echigo Kentaro , Tsujimoto Koichi , Shakouchi Toshihiko , Ando Toshitake
Published: November 2019

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Effect of Diffuser Vane Solidity on Performance of a Multistage Bowl Pump
Authors: Cooper Paul , Hosangadi Ashvin
Published: November 2019

The performance of a mixed-flow three-stage pump having a stage specific speed Ns = 2630 (rpm, gpm, ft) or nq = 53 (rpm, m3/s, m) — commonly known as a “bowl” pump — was improved by nearly five (5) percentage points by substantially increasing the number of vanes in the bowl-type diffuser. analysis showed a large field of unintended swirling flow emerging from the exit of the original diffuser. The solidity of the improved diffuser was much greater than conventional design practice would indicate. Yet this was needed to eliminate separation of the radially inward diffusing flow from the vanes as they effectively guide the fluid into the axial direction, thereby enabling the following stage(s) to generate the intended head and so achieve the intended efficiency. This apparently radical approach appears to be necessary in order to overcome the tendency of the circumferential velocity component of the flow from the impeller to increase as it is transported to the smaller radii of this radial inflow diffuser configuration.
Numerical and Experimental Investigation on the Influence of Blades Gap Flow on Axial Blood Pump Performance
Authors: Liu Guangmao , Jin Donghai , Wang Mengyu , Gui Xingmin
Published: November 2019

The axial blood pump body primarily contains the Inlet Guide Vane (IGV), Rotor Impeller (RI), Outlet Guide Vane (OGV) and pump casing. There must be gaps between rotor blade tip and pump casing or between OGV blade root and rotor hub for the impeller rotating in the pump. The flow characteristics inside an axial blood pump with different blade gaps were numerically simulated and analyzed. Hydraulics experiments were conducted to verify the numerical results. The results show that the pump efficiency decreased slowly when the OGV blade gap increased from 0.1 mm to 0.3 mm, but quickly when the rotor blade gap increased from 0.1 mm to 0.3 mm. The hydraulics characteristic results indicate that the pressure rise and efficiency are mainly influenced by the rotor blade gap. The OGV blade root gaps have little influence on the decrease of pressure rise and efficiency. The novel configuration with uneven blade gaps inside the pump result in improved hydraulics and hemolytic performance compared with the similarly sized configuration with even blade gaps.
IBM POWER9 Systems, Shock Simulation and Testing Validation
Authors: Alfoqaha Arshad , O’Connell Kevin , Campbell Eric
Published: November 2019

At IBM Systems, developing reliable and robust designs of supercomputers is critical to IBM’s vision and continuing its leadership in our industry. Shorter development cycle time, increasingly dense product designs, along with advanced design features create real challenges in predicting structural performance of servers, such as the recently refreshed IBM Cognitive Systems’ POWER9 portfolio of servers. Both 4U and 2U versions have DDR4 RDIMM’s, POWER9 HLGA processor modules, PCIe Gen3 and Gen4 slots, blowers, hard drives, and internal storage controller slots.

To meet IBM shipping standards to ensure POWER9 system’s reliability and design robustness, ANSYS Mechanical and LS-Dyna FEA models were developed and physical tests were conducted. The ability to apply accurate predictive engineering methods using simulation early in the design cycle predicted the structural performance of the servers and shortened its development time, reduced number of physical builds, and therefore, reduced development cost.