bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design Optimization of Splitter Blade Impeller in a Centrifugal Pump
Authors: Takao Shunya , Hayashi Kentarou , Miyabe Masahiro 
Published: October 2020

Abstract
In order to improve suction performance, centrifugal pumps with an inducer are used for rocket pumps, liquid gas transport such as LNG, and general-purpose pumps. Since a higher suction performance than conventional pump is required, a splitter blade that consists of a long blade and a short blade is sometimes adopted. However, the design becomes more difficult due to the increased number of parameters. The stable operation over a wide flow rate range are required in the general-purpose pumps. Therefore it is necessary to design them so that unstable flow phenomena such as surges do not occur. However, the design method to avoid them is not well understood yet.
In this study, we focused on the splitter blade impeller in a general-purpose low-speed centrifugal pump with an inducer. Six parameters such as leading edge position and trailing edge position of the short blade for both hub-side and tip-side were set as design ones. A multi-objective optimization method using a commercial software was applied to improve suction performance while maintaining high efficiency. Then obtained optimal shape were analyzed by CFD calculation and extracted the feature. Furthermore, optimized impellers were manufactured and confirmed the performance over a wide flow rate range by experiments. In addition, a optimizing design method that improves pump performance at lower cost was studied.
A Computational Study of a Biomass Cookstove With Forced Secondary Air Injection
Authors: Cassidy Liam , MacCarty Nordica 
Published: October 2020

Abstract
The use of solid biomass as a primary energy source for cooking is common to nearly half of the world’s population. Household air pollution as a byproduct of biomass combustion creates powerful negative health impacts related to air quality and a strong influence on our global radiative balance. Despite efforts to improve biomass-fueled cooking technology, many current designs still fail to meet WHO guidelines for air quality and consume excessive fuel. One promising method to improve in both of these areas is through introduction of forced primary or secondary air to the combustion process to increase turbulence, mixing, and velocity. Incorporating computational fluid dynamics to the design process for this forced draft air flow can provide insights into the complex and interconnected thermophysical relationships which, otherwise, would require extensive experimentation. The objective of this work is to provide a preliminary computational fluid dynamics study of a secondary air forced draft biomass cookstove. Thermal efficiency and emissions concentrations are investigated relative to various combinations of secondary air flow rates and injection angles. The results from the case study suggest that thermal efficiency of the cookstove is a function of secondary air injection angle, with optimal angle being a function of the specific air-fuel ratio. Additionally, a design trade-off is evident when comparing the pollutant concentration data and thermal efficiency data. Lastly, analysis of the computational results suggests that large pressure gradients about secondary air vortices in the combustion chamber lead to improved thermal efficiency and more complete combustion. The continued development of this work into an open-source computational fluid dynamics tool is underway.
Simulation of Ventilation Flow Through a Room Fitted With a Windcatcher Incorporating Phase Change Materials
Authors: Abdo Peter , Reyes-Cubas Angel 
Published: October 2020

Abstract
Natural ventilation is the process of supplying and removing air through an indoor space by natural means. Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment by decreasing moisture content in the air and reducing pollutants concentration effectively. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Materials that change phase at certain temperature are frequently referred to as Phase Change Materials (PCMs). PCMs change from solid to liquid and vice versa. PCMs could be used in passive cooling systems and they are directly related to building energy efficiency. In this study air flow through a two-dimensional room fitted with a windcatcher and incorporated with phase change materials (PCMs) is simulated. The temperature change in the room implementing PCM is analyzed to monitor the PCMs’ performance. To achieve this, Ansys Fluent is used to simulate the temperature changes inside the room as well as the melting process of PCM. PCM is placed at the right and left walls of the room and at its bottom. Two cases have been considered (with and without PCM) and the average temperatures at three locations have been compared for an inlet velocity of 1 m/s and an inlet temperature of 302 K. The average temperature at 1.2 m high inside the room with PCM dropped by about 1–2 °C compared to that without PCM.
Measurements of Morphology and Locomotion of Caenorhabditis Elegans With Digital Holographic Microscopy
Authors: Wang Yijie , Chen Jun , Zhang Yuan , Kim Kee-Hong 
Published: October 2020

Abstract
Digital holographic microscopy (DHM) enables 3D volumetric measurements of small objects with high magnification. DHM has been applied to measure a variety of experimental studies, including turbulent boundary layer, spray droplets, individual cells, development of zebrafish embryo, etc. In this study, a DHM system is applied to measure the morphology and locomotion of two groups of Caenorhabditis Elegans (C. Elegans) with different development conditions (ATGL-1 group and n2 group) in an 8-day time period from their hatching to the adult stage, whose body lengths range from hundreds of micrometers to one millimeter. The length and volume are determined to describe the morphology of the C. Elegans at different development stages. The locomotion of the C. Elegans is divided into linear motion and curl motion. The kinetic energy derived from the two types of motion describes the extent of how active the C. Elegans is. The statistics of morphology and locomotion of the two groups of C. Elegans are compared at different development stages to illustrate the influence of the applied development conditions.
Vortex-Induced Rotations of a Pair of Laterally Arranged Square Cylinder in a Two-Dimensional Microchannel
Authors: Li Lichun , Li Shanshan , Yan Zhe , Pan Zhenhai 
Published: October 2020

Abstract
This paper investigates the dynamic response of two freely rotatable rigid square cylinders to two-dimensional laminar flow in a microchannel. The square cylinders are laterally pinned side-by-side in the microchannel with a single freedom of rotation. Finite volume method coupled with a dynamic mesh technique is developed and validated to reveal the detailed motion characteristics of the cylinders and nearby flow structures. Under small Reynolds number (Re = 50), both cylinders oscillate periodically. The oscillate curves (rotating angle v.s. time) are symmetrical with each other but with a certain phase difference. At Re = 150, both cylinders oscillate randomly. Under high Reynolds number (Re = 300), the two cylinders both keep rotating in the opposite direction with the velocity magnitude fluctuating drastically around 1.75. Important motion details are presented to understand the Fluid-Structure interaction mechanism under different Reynolds number, including the time history of rotating angles and rotating velocities, lift and drag coefficients on the cylinders, distribution of pressure around the cylinder sides. Both pressure-induced torque and the shear induced one are obtained and their contributions to both cylinders’ rotation characteristics are quantitatively evaluated. Vortex structures and streamlines around the cylinders at specific moments are also revealed in this paper to help understanding the fluid-structure interaction phenomenon.
Recommendations for Long-Term Operation of High-Performance Submersible Motor Pumps in Mine Dewatering
Authors: Beck David , Wulff Sebastian , Thamsen Paul Uwe , Reich Morris , Worringer Jean Pierre 
Published: October 2020

Abstract
Modern submersible pumps are high performance aggregates for long-term operation, which find application in open-pit mining. Dewatering of groundwater to run an open-pit mine with various conditions for submersible pumps often leads to short-term performance based on different circumstances in the well as well as in the general operation. These result in high maintenance and energy costs and decreases the drawdown in open-pit mining.
To ensure a long-time performance, a proper selection of submersible pump and motor is required.
It is also necessary to consider the geometry of different deep wells in order to take into account the initial conditions of the pumps.
This paper shows recommendations for long-term operation of high-performance submersible pumps due to the conditions of the mining industry. Therefore, a holistic consideration of the aggregate takes place to receive recommendations, which minimize the rate of pump failures and increase the efficiency of the dewatering process. These recommendations are based on various failures found during an investigation. Furthermore, this paper recommends different methods to prevent these failures, for instance clogging and erosion through particles in the well. These recommendations are linked to the research of different submersible motor pumps from various manufacturers in different wells in German open-pit mines with short-term operation caused by several circumstances.
Trilinos Solvers Scalability on a MFiX-Trilinos Framework Applied to Fluidized Bed Simulations
Authors: Rodriguez Arturo , Kotteda V. M. Krushnarao , Rodriguez Luis F. , Kumar Vinod , Munoz Jorge A. 
Published: October 2020

Abstract
MFiX is a multiphase open-source suite that is developed at the National Energy Technology Laboratories. It is widely used by fossil fuel reactor communities to simulate flow in a fluidized bed reactor. It does not have advanced linear iterative solvers even though it spends 70% of the run time in solving the linear system. Trilinos contains algorithms and enabling technologies for the solution of large-scale, sophisticated multi-physics engineering and scientific problems. The library developed at Sandia National Laboratories has more than 60 packages. It consists of state-of-the-art preconditioners, nonlinear solvers, direct solvers, and iterative solvers. The packages are performant and portable on various hybrid computing architectures. To improve the capabilities of MFiX, we developed a framework, MFiX-Trilinos, to integrate the advanced linear solvers in Trilinos with the FORTRAN based multiphase flow solver, MFiX. The framework changes the semantics of the array in FORTRAN and C++ and solve the linear system with packages in Trilinos and returns the solution to MFiX. The preconditioned iterative solvers considered for the analysis are BiCGStab and GMRES. The framework is verified on various fluidized bed problems. The performance of the framework is tested on the Stampede supercomputer. The wall time for multiple sizes of fluidized beds is compared.
Analysis of Coupled CFD-DEM Simulations in Dense Particle-Laden Turbulent Jet Flow
Authors: Weaver Dustin , Miskovic Sanja 
Published: October 2020

Abstract
In this paper, coupled CFD-DEM simulations of dense particle-laden jet flow are performed using CFDEM® coupling interface that couples LAMMPS-based LIGGGHTS® DEM engine with OpenFOAM CFD framework. Suspensions of mono-sized spherical glass particles with 80 microns diameter and a mass loading of 0.23 and 0.86 are considered. Three different CFD meshes are used with an average mesh resolution dimension of 3.06, 2.67, and 1.86 particle diameters and it is determined that mesh resolution does not change results for void fraction calculation (using the divided model) of the CFD-DEM equations. Samples of particle flux are taken at 0.1, 10, and 20 nozzle diameters along the axial direction of the jet region. The numerical results for particle flux are compared with a well cited experimental data found in literature. The CFD-DEM simulations in turbulent jet flow are found to be highly sensitive to initial particle velocity inputs but the experimental data provide sufficient information to produce comparable results.
Investigation of the Flow Instabilities of a Low Specific Speed Pump-Turbine: Part 2 — Flow Control With Fluid Injection
Authors: Deniz Sabri , von Burg Martin , Tiefenthaler Manuel 
Published: October 2020

Abstract
This the second part of a two-part paper focusing on the flow instabilities of low-specific pump turbines. In this part, results of the flow control application with fluid injection (using both water and air) in the vaneless space in order to suppress the flow instabilities of a low specific speed model pump-turbine in turbine mode operation at HSLU (Lucerne University of Applied Sciences) Switzerland are presented.
Based on the analysis of the experimental data, flow visualization, and CFD results focusing especially on the flow features in the vaneless space and at the runner inlet, the onset and development of the flow instabilities are explored as presented in the first part of this paper. Based on these analyses, the flow control technology by injecting air and water as well as suction of the fluid in the vaneless space of the model pump-turbine is implemented for suppressing the flow instabilities and thus extending the operating range of the pump-turbine. Both air- and water-injection are applied by using an external energy source (compressor and pump) and discrete nozzles circumferentially distributed in the vaneless space. The S-shaped pump-turbine characteristics in turbine operating mode are modified so that the slope at speed no load conditions is no more positive meaning an improvement in the stability behavior. To the best of our knowledge, this is the first successful application of flow control with fluid injection in the vaneless space of pump-turbines. Fluid injection is applied at two different guide vane openings, i.e. at 6° and 18°. The analysis of the unsteady pressure data indicates the suppression of flow instability such as rotating stall with fluid injection in the vaneless space. The water injection is more effective than the air injection for modifying the slope of the pump-turbine characteristics.
Two-Phase Wakes in Adiabatic Liquid-Gas Flow Around a Cylinder
Authors: Kim Dohwan , Rau Matthew J. 
Published: October 2020

Abstract
Small tubes and fins have long been used as methods to increase surface area for convective heat transfer in single-phase flow applications. As demands for high heat transfer effectiveness has increased, implementing evaporative phase-change heat transfer in conjunction with small fins, tubes, and surface structures in advanced heat exchanger and heat sink designs has become increasingly attractive. The complex two-phase flow that results from these configurations is poorly understood, particularly in how the gas phase interacts with the flow structure of the wake created by these bluff bodies. An experimental study of liquid-gas bubbly flow around a cylinder was performed to understand these complex flow physics. A 9.5 mm diameter cylinder was installed horizontally within a vertical water channel facility. A high-speed camera captured the movement of the liquid-gas mixture around the cylinder for a range of bubble sizes. Liquid Reynolds number, calculated based on the cylinder diameter, was varied approximately from 100 to 3000. Time-averaged probability of bubble presence was calculated to characterize the cylinder wake and its effects on the bubble motion. The influence of the liquid Reynolds number, superficial air velocity, and bubble size is discussed in the context of the observed two-phase flow patterns.
Comparative Analysis of Shell and Tube Type Heat Exchanger Based on Bell Delaware, Flow Stream and Numerical Methods
Authors: Khan Tariq S. , Fawad Hasan , Nawaz Kashif 
Published: October 2020

Abstract
An optimized heat exchanger design is always a challenge to designers. This study presents a simplified simulation study on thermal-hydraulic of a small heat exchanger. Both the heat transfer coefficient and pressure drop are simulated for a nine tube shell and tube heat exchanger. A detailed mesh sensitivity analysis is performed to arrive at numerically converged solution. The results of the study are compared with Bell Delaware (BD) and Flow Stream (FS) analytical methods. Results obtained using all three methods show similar trends. Heat transfer coefficient determined using Bell Delaware method is found to be in good agreement with that of ANSYS CFX, whereas pressure drop calculated using Flow stream method is within small percentage difference with CFX results. Overall, the simulation results are verified by the results obtained using analytical methods.
Particle Concentration Variation for Inflow Profiles in High Reynolds Number Turbulent Boundary Layer
Authors: Rahman Mustafa M. , Samtaney Ravi 
Published: October 2020

Abstract
Large-eddy simulations (LES) of incompressible turbulent boundary-layer flows can simulate a fundamental unsteady turbulent flow, including time-variant streamwise and wall-normal velocity as well as the near-wall locations of significant turbulence intensities. A typical illustration of turbulent flows with such high Reynolds numbers can be roughly approximated to atmospheric boundary-layer flows. To bypass the demanding mesh criteria of near-ground field and direct numerical simulations, we adopt a virtual-wall model with a stretched-vortex subgrid-scale model. We simulate the dynamics of solid particles in this wall-modeled LES approach toward incompressible flow. The particles considered are both charged and uncharged, and have a fixed concentration profile with no fluctuations at the inflow. An extended streamwise simulation domain is implemented as an alternative to rerunning the simulation with a turbulent inflow profile from the simulation of the previous downstream profile. By extending the streamwise domain, the fluctuation dynamics of the particles reach a steady state far downstream from the inflow. The streamwise and altitude variation of the particle parameters are compared for various particle-concentration inflow profiles. Furthermore, an estimate of the streamwise variation of parameters is also observed. This study is the first step towards enhancing our understanding of the particle dynamics in turbulent flows.
Wake Comparison of Open and Ducted Wind Turbines Using Actuator Disc Simulations
Authors: Bagheri-Sadeghi Nojan , Helenbrook Brian T. , Visser Kenneth D. 
Published: October 2020

Abstract
Shrouding a wind turbine inside a duct can significantly augment its power and energy output by increasing the mass flow rate through the rotor and decreasing the cut-in speed. Whether this is an advantage in a turbine array depends on the wake recovery behavior and how this compares to open wind turbines. Axisymmetric CFD simulations using the Reynolds-Averaged Navier-Stokes equations with a k–ω SST turbulence closure were used to compare the wake behavior of open and ducted wind turbines. For both cases, the rotor blades were modeled using an actuator disc. Simulations of open wind turbines revealed significant sensitivity of the wake behavior to the mean turbulence intensity at the rotor. Better agreement with experimental data for the far wake was obtained when the turbulence intensity at the rotor was comparable to values measured experimentally. It was observed that compared to an open wind turbine with similar power output, a DWT has a significantly slower wake recovery. This was attributed to the extra momentum deficit of the wake due to the drag force on the duct.
On the Potential for Low-Frequency Control Valve Vibrations Being Caused by Upstream Oscillating Dean Vortexes
Authors: Lozowy Richard , Forcinito Mario 
Published: October 2020

Abstract
At several natural gas compressor stations control valves have experienced low-frequency vibrations when placed directly downstream of pipe bends. It is know that at pipe bends a pair of counter-rotating vortexes form and extend several diameters downstream. These vortexes are not symmetric and instead oscillate back and forth at a low-frequency phenomenon referred to as swirl-switching. It is suspected that these upstream flow oscillations enter the valve and are the cause of the valve vibrations. Large-eddy simulations have been performed on pipe bends with two different bend radius at a Reynolds number of 80,000. The simulations showed that the frequency of the vortexes decreased as the bend radius increased. When non-dimensionalized the frequency obtained from the simulation is comparable to the field measurement from the compressor station. This consistency provides support to the argument that upstream flow-induced oscillations are the cause of the low-frequency valve vibrations. The velocity fluctuations due to swirl-switching dissipate downstream of the bend and by placing several diameter lengths of straight pipe between a control valve and a pipe bend, the issue of low-frequency vibrations induced at the valve could be avoided. The objective of this study is to provide evidence that low-frequency valve vibrations can be linked to upstream pipe geometry and put forward a plausible explanation of why.
Turbulent Flow Measurements and Visualizations of Supersonic Jets Impinging on a Flat Plate and an Inclined Plate
Authors: Nguyen Thien D. , Maher Blake , Hassan Yassin A. 
Published: October 2020

Abstract
This study experimentally investigates the flow characteristics of a high-pressure air jets impinging on a flat plate and an inclined plate with various nozzle-to-plane gaps of 10 mm, 20 mm, and 30 mm. Full-field measurements of flow characteristics in the central plane of the nozzle and near the impinging surface are performed using two-dimensional two-component (2D2C) particle image velocimetry (PIV) technique. This paper presents results from the nozzle pressure ratio (NPR) of 2.77, approximately yielding the sonic jet with Mach number of 1.2. Flow characteristics obtained from the 2D2C-PIV measurements with various spatial gaps are compared and presented. Results including the first- and second-order flow statistics, such as mean velocity and turbulent kinetic energy, and effects of the impinging surface to the flow patterns are investigated. Finally, proper orthogonal decomposition (POD) analysis is applied to reveal the statistically dominant flow structures that capture the highest amount flow kinetic energy and play important roles to the flow dynamics and heat transfers.