bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Water pH in Calcasieu Lake Area Using Regional Scale Hydrodynamic Models
Authors: Zhang Ning , Wang Weihao
Published: October 2017

In Southwest Louisiana, the Calcasieu Lake and surrounding water systems are the major fresh water sources to the nearby coastal wetlands and agricultural areas. There are two national wide life refuges located in both east and west sides of Calcasieu Lake. Both refuges are covered by coastal wetlands. The health of the wetland vegetation is essential to the wetland losses in the area. One of the major problems related to the health of marshes is the nutrient deficiency. In addition, the surface water system is a possible source for agriculture use that requires sufficient nutrient components in water. Understanding the transport and distribution of various nutrients in the coastal water system is very important to the above-mentioned issues. In this study, a regional scale hydrodynamic model was utilized to simulate the hydrodynamics, salinity transport and sediment transport in this major water system in Southwest Louisiana. The pH distribution in water is a good indication of many nutrient components, such as phosphorous, and is essential to understand the nutrient distributions in the target area. A pH calculation procedure was implemented in the model to determine pH values based on the salinity and other water properties. The model results can be used to indicate the dynamic change of nutrient distributions and the areas of nutrient deficiency.
Open-Ended Curiosity-Driven Fluids Lab Project
Authors: Shepard Thomas G. , Haas Christopher , Menon Rajagopala
Published: October 2017

The lab component of a fluid mechanics course permits a great opportunity for students to engage with course material. These labs can take many forms including field trips, guided inquiry exercises, formulaic lab exercises, practical/hands-on skill development, CFD and design-build-test projects to name a few. Previous literature on self-determination theory suggests that many positive results can be gained by giving students a choice in their studies. Related literature on the importance of curiosity in students suggests similar benefits. This paper describes a multi-week lab experience where students were given the opportunity to study anything remotely related to fluid mechanics with very few restrictions on implementation. The project goals were proposed by a student, or a team of two students, and then refined with the assistance of the course instructor to ensure proper scope. Pre-project surveys were used to gage the importance students place on studying material which is of personal interest and to determine how other parts of the undergraduate curriculum match up with student interest. Post-project surveys were used to gather input on the student experience of completing the curiosity project. This paper details the results from the various assessments and discusses feedback from the course instructor, lab instructors and students relating to project implementation, opportunities for improvement and some of the advantages of such a lab experience.
Pressure Oscillations in Piva Hydro Power Plant Draft Tube: Case Studies
Authors: Giljen Z.
Published: October 2017

In this paper performed the analysis and comparison the measured values of pressure oscillations in the draft tube of Francis units obtained in tests from 1976 and 2009. HPP “Piva” has been operating since 1976. In July 1976, September 1976 and in October 1976, performed tests on Francis units HPP “Piva”, at different levels of head water elevations, reason for which measurements are repeated complexity of the observed problems, the excessive pressures oscillations in the unit’s draft tube. Also during 2009 performed measurements the pressure oscillations on the rim of the draft tube and at turbine head cover Francis units HPP “Piva”, as a supervising engineer I worked on these measurements.

During 1976, team from Litostroj-Ljubljana performed the measurements and recording of pressures oscillations in the middle of draft tube (in direction of the unit’s axis), at 0.25 Ds distance from the draft tube’s rim, and at the mere rim of the draft tube. The most unfavourable results were obtained, on the measuring point at 0.25 Ds from the rim the draft tube. In order improve the performances of Francis turbines installed in the HPP “Piva” units, it is very important thoroughly investigate and eliminate the causes of increased pressure oscillations in the draft tube HPP “Piva” units.
Experimental Study of Separation Control Over a Wide Range of Reynolds Numbers Using Dielectric Barrier Discharge Plasma Actuator on Airfoil
Authors: Sekimoto Satoshi , Fujii Kozo , Anyoji Masayuki , Miyakawa Yuma , Ito Shinichiro , Shimomura Satoshi , Nishida Hiroyuki , Nonomura Taku , Matsuno Takashi
Published: October 2017

This study proposes separation control investigation using a Dielectric Barrier Discharge (DBD) plasma actuator on a NACA0015 airfoil over a wide range of Reynolds numbers. The airfoil was a two dimensional NACA0015 wing model with chord length of 200mm. Reynolds numbers based on the chord length were ranged from 252,000 to 1,008,000. A plasma actuator was installed at the leading edge and driven with AC voltage. Burst mode (duty cycle) actuations, in which nondimensional burst frequency F+ was ranged in 0.1–30, were applied. Time-averaged pressure measurements were conducted with angles of attack from 14deg to 22deg. The results show that initial flow fields without an actuation can be classified into three types; 1) leading edge separation, 2) trailing edge separation, and 3) hysteresis condition between 1) and 2), and the effect of burst actuation is different for each above initial condition.
Large Eddy Simulation of a Helical Coil Steam Generator Test Section
Authors: Lai Jonathan K. , Merzari Elia , Delgado Marilyn , Lee Samuel J. , Lee Saya , Hassan Yassin A.
Published: October 2017

The helical coil steam generator (HCSG) is a compact heat exchanger that can have high heat transfer even when the pressure drop is low. This makes it advantageous in small modular reactors and high-temperature reactor designs. In order to investigate the fluid phenomena around these helical banked tubes, a test section was built at Texas A&M University to represent flow across two half-rods within HCSG. This study focuses on the validation of large eddy simulation (LES) for this particular geometry. Pressure tap and particle image velocimetry (PIV) measurements have been recorded at an inlet Reynolds number of 8643, and both mean and fluctuating data is compared with the numerical results.

The highly scalable spectral-element code Nek5000 has been used to produce the LES calculations. First, simulations of varying polynomial order expansions are made to determine the spatial resolution required to capture the turbulent scales. Then, simulations with different inlet conditions are compared with experimental data. The pressure drop shows good agreement with pressure tap measurements while velocity shows similar characteristics with PIV. Furthermore, the components of the Reynolds stresses and modes from proper orthogonal decomposition have been developed to validate the physics captured.
Flow Energy Harvesting of an Oscillating Foil With Rigid and Passive Surface Flexibility
Authors: Totpal Alexander D. , Siala Firas F. , Liburdy James A.
Published: October 2017

The aerodynamic performance of an oscillating pitching and plunging foil operating in the energy harvesting mode is experimentally investigated. Experiments are conducted in a closed-loop recirculating wind tunnel at Re of 24,000 to 48,000, and reduced frequencies (k) of 0.04 to 0.08. Foil kinematics are varied through the following parameter space: heaving amplitude of 0.3c, pitching amplitudes of θ0 = 45° to 75°, as well as phase lag between sinusoidal pitching and heaving motions of Φ = 30° to 120°. Aerodynamic force measurements are collected to show the energy extraction performance (power coefficient and efficiency) of the foil. Coupled with the force measurements, flow fields are collected using particle image velocimetry. The flow field characteristics are used to supplement the force results, shedding light into flow features that contribute to increased energy extraction at these k values. In addition, inertia-induced passive chord-wise flexibility at the leading edge (LE) of the foil is investigated in order to assess its feasibility in this application. Results indicate that favorable performance occurs near θ0 = 45°, Φ = 90° and k = 0.08. When k is decreased (through increased U∞) to 0.04, overall extraction performance becomes insensitive to θ0 and Φ. This is supported by the flow field measurements, which show premature leading edge vortex (LEV) evolution and detachment from the foil surface. Although overall performance was reduced with the passive LE flexibility, these results indicate that a proper tuning of the LE may result in a delay of the LEV detachment time, yielding increased energy harvesting at this otherwise inefficient operating parameter space.
STRUCT: A Second-Generation URANS Approach for Effective Design of Advanced Systems
Authors: Baglietto Emilio , Lenci Giancarlo , Concu Davide
Published: October 2017

This work presents the recently developed STRUCT hybrid turbulence model and assesses its potential to address the poor grid consistency and limited engineering applicability typical of hybrid models. Renouncing the ability to consistently bridge RANS, LES and DNS based on the computational grid size, we aim at addressing the engineering design needs with a different mindset. We opt to leverage the robustness and computational efficiency of URANS in all nearly homogeneous flow regions while extending it to locally resolve complex flow structures, where the concept of Reynolds averaging is poorly applicable. The proposed approach is best characterized as a second generation URANS closure, which triggers controlled resolution of turbulence inside selected flow regions. The resolution is controlled by a single-point parameter representing the turbulent timescale separation, which quantitatively identifies topological flow structures of interest. The STRUCT approach demonstrates LES-like capabilities on much coarser grids, and consistently increases the accuracy of the predictions from the baseline URANS at increasing grid finesse. The encouraging results show the potential to support effective design application through resolution of complex flow structures while controlling the computational cost. The ultimate objective is to continue improving the robustness and computational efficiency while further assessing the accuracy and range of applicability.
Consistent Evaluation of Wear Coefficients From the Experiments for Use in CFD Simulations
Authors: Pagalthivarthi Krishnan V. , Furlan John M. , Visintainer Robert J.
Published: October 2017

Coriolis and impact wear testers are commonly used in the slurry industry to determine the sliding and impact wear coefficients (respectively) for a given combination of slurry and wear substrate material. In these experiments, the mass loss of wear specimens, and the easily-measured bulk concentration, flow rate and angle of the impact wedge are correlated to determine estimates of wear coefficients. In CFD-based wear prediction in slurry pump casings and impellers, these experimentally determined coefficients are used in combination with such near-wall computed quantities as particle concentration, velocity, and angle of impact, with a potential inconsistency between the bulk quantities of the wear experiments and the local CFD-based flow field.

This paper uses finite element CFD to obtain the slurry flow field in the Coriolis and impact wear testers. The ratio of the wear-related bulk quantities to the local quantities is evaluated for both impact and sliding wear. It is observed that this ratio for the impact wear coefficient is of the order of 2.0 for the flow conditions studied. In the Coriolis wear tester experiment, it turns out fortuitously that for certain operating conditions, the wear coefficient determined using bulk flow quantities would be nearly the same as the wear coefficient determined using local quantities.
Feasibility Study of Centrifugal Compressor Performance Under Wet Gas Conditions
Authors: Kawaguchi Daisuke , Sakamoto Kiyohide , Kobayashi Katsutoshi
Published: October 2017

In this study, we developed a new centrifugal compressor test facility that can produce wet gas conditions (up to 15% liquid mass fraction (LMF)) and analyzed the effect of the wet gas flow on the fluid performance of a centrifugal compressor. As a result, we found that adiabatic efficiency decreased as LMF increased due to an increase in the shaft power. Moreover, we assumed that the liquid film on the inner wall of the impeller was discharged from the trailing edge at a peripheral-speed by the centrifugal force. Then we found that the shaft power increase ratio at a maximum LMF of 15% could be predicted within 3.7% error on the basis of the assumption.
Improvement of Suction Performance Using Splitter Impeller and Inducer
Authors: Hayashi K. , Konno S. , Hayakawa M. , Kawata Y.
Published: October 2017

Suction performance is one of the most important characteristics of the industrial pump to keep the pump capability against the cavitation under the low suction pressure condition. Inducers have been developed to improve the suction performance of pumps. They are used for rocket turbo pumps and recently for many industrial applications. It is one of the competitiveness of the industrial pumps to downsize the scale with higher rotational speed by adopting inducer.

The authors had proved that pump with splitter impeller with inducer can further improve the suction performance. The splitter impeller was specially designed to be resistant to the cavitation choke. The other very important requirement for the pump against cavitation is that it does not occur cavitation surge. The cavitation surge arises at the partial flow rate of the pump. In contrast to this the suction performance become better at the partial flow rate. So the precise compromise is necessary to satisfy these requirements.

This paper presents the experimental and CFD results to improve and optimize the suction performance without generating cavitation surge. The many design and combination of splitter impeller and inducer are tested to get the better performance. The test results of pumps with different inlet flow coefficient are compared not only suction performance but also the onset of cavitation surge.
CFD Prediction of Gas-Liquid Separation Efficiency of Geothermal Steam-Water Cyclone Separator Using a Verified Turbulence Model
Authors: Hu Xidong , Qian Shaoxiang , Yamauchi Kaori , Okochi Haruo
Published: October 2017

The present paper aims to predict the separation efficiency and pressure drop of a vertical geothermal cyclone type separator using CFD (Computational Fluid Dynamics) simulations, for optimizing the design of such separator. A benchmark study was firstly performed for a single phase flow in a Stairmand design cyclone using four different turbulence models, in order to verify the prediction accuracy of flow velocity distribution by comparison with experimental data in literature. The investigated turbulence models include (1) Renormalization Group (RNG) k-ε, (2) Realizable k-ε, (3) Reynolds stress turbulence model (RSM) and (4) Large eddy simulation (LES). Results show that RNG k-ε and Realizable k-ε models are not capable of reproducing the experimental data while the RSM and LES models reproduce the flow velocity distribution very well. Then, CFD simulations of two-phase flow in a steam-water cyclone separator were carried out for different stream inlet velocities applying the RSM model. This is based on the consideration that steady state analysis can be done for the RSM model, and however, transient analysis is needed for the LES model, and hence, more expensive and time-consuming for engineering applications. The CFD results for outlet steam quality and pressure drop were obtained under different stream inlet velocities. The separation efficiency and outlet steam quality decreases a little when the inlet velocity increases from 34.5m/s to 72m/s. However, the outlet steam quality predicted in the present CFD analysis is close to that of Lazalde-Crabtree.
Visualization of Internal Flow Field of Propeller Fan
Authors: Onishi Takaya , Sato H. , Hayakawa M. , Kawata Y.
Published: October 2017

Propeller fans are required not only to have high performance but also to be extremely quiet. The internal flow field of ventilation propeller fans is even more complicated because they usually have a very peculiar configuration with protruding blades upstream. Thus, many kinds of internal vortices yield which cause noise and their cause and countermeasures are needed to be clarified.

The purposes of this paper are to visualize the internal flow of the propeller fan from the static and rotating frame of reference. The internal flow visualization measured from the static frame gives approximately the scale of the tip vortex. The visualization from the rotating coordinate system yields a better understanding of the flow phenomena occurring at the specific blade. The experiment is implemented by using a small camera mounted on the shaft of the fan and rotated it to capture the behavior of the vortices using a laser light sheet to irradiate the blade surface. Hence, the flow field of the specific blade could be understood to some extent. The visualized results are compared with the CFD results and these results show a similar tendency about the generation point and developing process of the tip vortex. In addition, it is found that the noise measurement result is relevant to the effect of tip vortex from the visualization result.
Investigation of Obstacle Effects on the Aerodynamic Performance of Flapping Wings
Authors: Yin Bo , Yang Guowei
Published: October 2017

The study of highly unsteady wing flapping includes the large scale vortices, complicated locomotion/dynamics and deformable wing structures. When flapping insects/birds approach or perch on some objects, such as ground, wall or obstacle, the solid boundary dissipates, absorbs and bounces the leading edge, trailing edge and wing tip vortices, which are generated and shed during the flapping flight. Such phenomenon creates a high pressure area, leads to cushion effect and influences the aerodynamics, stability and maneuverability significantly. This paper uses immersed boundary method (IBM) to numerically study the aerodynamic performance of flapping wing in proximity of obstacles, investigate the distance, flapping motion and wing flexibility effects and relevant symmetric/asymmetric flow patterns, research the influence of vortex generating and shedding to the lift/drag change, explore the key distance and reveal the mechanism how insects/birds adjust the flapping motion to achieve ideal flight. Such research could theoretically support the development of micro-bionic flapping wing vehicle.
Machine Learning Control for Experimental Turbulent Flow Targeting the Reduction of a Recirculation Bubble
Authors: Chovet Camila , Lippert Marc , Keirsbulck Laurent , Noack Bernd R. , Foucaut Jean-Marc
Published: October 2017

We experimentally control the turbulent flow over backward-facing step (ReH = 31500). The goal is to modify the internal (Xr) and external (Lr) recirculation points and consequently the recirculation zone (Ar). A model-free machine learning control (MLC) is used as control logic. As benchmark, an optimized periodic forcing is employed. MLC generalizes periodic forcing by a multi-frequency actuation. In addition, a sensor-based control and a non-autonomous feedback, open- and closed-loop laws, were use to optimize the control. The MLC multi-frequency forcing outperforms, as expected, periodic forcing. The non-autonomous feedback brings a further improvement. The unforced and actuated flows have been investigated in real-time with a TSI particle image velocimetry (PIV) system. The current study shows that a generalization of multi-frequency forcing and sensor feedback significantly reduces the turbulent recirculation zone, far beyond optimized periodic forcing. The study suggests that MLC can effectively explore and optimize new feedback actuation mechanisms and we anticipate MLC to be a game changer in turbulence control.
Traceable Flow Rate Measurements With a Very Low Uncertainty Using Laser Doppler Anemometry
Authors: Juling Markus , Steinbock Jonas , Weissenbrunner Andreas
Published: October 2017

Precise volume flow rate measurements are very important for various industrial applications. Here, one problem is that the service conditions of a flow meter used in the field differ significantly from the conditions present during calibration. The working conditions such as the pressure, the temperature and the flow profile greatly increase the uncertainty of the flow rate measurement.

To address this problem, a new laser-optical flow rate standard (LFS) was developed at the Physikalisch-Technische Bundesanstalt (PTB) that allows flow meters to be calibrated on site, thus greatly reducing the uncertainty of the flow rate measurement.

For the LFS, the velocity profile within the pipe is measured with laser Doppler anemometry (LDA). The profile is then integrated to calculate the volume flow rate. Various improvements to LDA have made it possible to measure the flow rate with an uncertainty of less than 0.15 % (k = 2).

A comparison of the LFS with the primary standard for thermal energy at PTB, which has an uncertainty of less than 0.04 % (k = 2), revealed a maximum deviation of 0.07 % for Reynolds numbers from 105 to 106, thus verifying the uncertainty of the LFS.
Inflow Conditions and Suddenly Expanding Annular Shear-Thinning Flows
Authors: Hammad Khaled J.
Published: October 2017

The impact of inflow conditions on the flow structure and evolution characteristics of annular flows of Newtonian and shear-thinning fluids through a sudden pipe expansion are studied. Numerical solutions to the elliptic form of the governing equations along with the power-law constitutive equation were obtained using a finite-difference scheme. A parametric study is performed to reveal the influence of inflow velocity profiles, annular diameter ratio, k, and power-law index, n, over the following range of parameters: inflow velocity profile = {fully-developed, uniform}, k = {0, 0.5, 0.7} and n = {1, 0.8, 0.6}. Flow separation and entrainment, downstream of the expansion plane, creates central and a much larger outer recirculation regions. The results demonstrate the influence of inflow conditions, annular diameter ratio, and rheology on the extent and intensity of both flow recirculation regions, the wall shear stress distribution, and the evolution and redevelopment characteristics of the flow downstream the expansion plane. Fully-developed inflows result in larger reattachment and redevelopment lengths as well as more intense recirculation, within the central and corner regions, in comparison with uniform inflow conditions.
Noise Reduction Measures for an Axial Fan
Authors: Swienty Andreas , Palamarchuk Evgenii , Abou Ackl Raja , Thamsen Paul Uwe
Published: October 2017

The aim of this work is to investigate how a reduction of the noise emissions can be achieved by means of an irregular arrangement of the blades of the fan impeller and an additional blade skewing.

For this purpose a fan impeller with a defined operating point is designed. Preliminary investigations have shown that a volumetric flow rate of 18 m3/h at a pressure of 200 Pa is required for cooling. Due to structural restrictions, only one axial impeller with a diameter of 68 mm can be used. The rotational speed of the electric motor is 10000 rpm. In a further step, the influences of the blade skewing and irregular arrangement of the blades are examined. These impellers are manufactured in a rapid prototyping process, which is a cost-effective and fast process. Thus, various variants can be examined to find the most suitable impeller. The study of the impellers is divided into two phases. Firstly, the fluid mechanical data of the impeller is measured. For this purpose, a chamber test stand is used to measure the characteristic curves of fan impellers. Thus, on the one hand, it can be examined whether the designed impeller reaches the operating point and, on the other hand, the influence of the noise reduction measures on the characteristic curves can also be evaluated. It is, of course, not desired that the noise reduction measures result in a deterioration of the pressure increase or in the volumetric flow rate. In the second phase, the noise generation of the impeller is measured in an installed state on an acoustic test stand. For this purpose, the impellers are installed in the electric motor and then acoustically examined in enveloping surface method according to DIN 45635.

It can be seen that the sound load can be reduced by 5.6 dB by a sufficient design of the impeller compared to a reference impeller. The further measures taken, such as the irregular arrangement of the blades and the blade skewing, have shown a further improvement of 1.6 dB. The influence of the implemented measures on the characteristic curve lies in a small area. It is measured that the pressure increase has fallen due to the irregular arrangement of the blades and the blade skewing by 10 Pa with a constant remaining flow rate.
Physics-Based Reconstruction of Interfacial Jump Conditions in All-Speed Multi-Fluid Dynamics
Authors: Nourgaliev Robert , Greene Patrick T. , Schofield Samuel P.
Published: October 2017

A new high-order sharp treatment of mixed cell solutions is introduced. The method is based on the reconstructed discontinuous Galerkin (rDG) scheme, in which we embed the known interfacial jump conditions as additional (physics-based) constraints in the least-squares reconstruction of the high-order degrees of freedom for multiple solution fields in the interfacial (mixed) cells. The approach allows us to avoid direct differentiation across multi-material interfaces, thus providing a robust and high-order accurate solution procedure. To track the interface dynamics, the method is combined with a hybrid of the level set (LS) and the front tracking (FT) methods — the so-called “Marker-Re-Distancing” (MRD) approach. As a fluid solver, we utilize the recently developed fully-implicit reconstructed discontinuous Galerkin method, developed for efficient and high-order resolution of all-speed compressible fluid dynamics. The new sharp physics-based reconstruction is incorporated into the overall Newton-Krylov-based solution procedure, with the residual of the mixed cell representing conservation of the mass, momentum and energy for the mixture. Thus, upon a convergence of the non-linear iterations, our treatment of interfacial cells is conservative.
Numerical Simulation of Two-Phase Slug Flow From Horizontal to Downward Inclined Pipe Using a Hybrid Code Based on Slug Tracking and Two-Fluid Methodologies
Authors: Almeida Vinicius R. , Conte Marco G. , Barbuto Fausto A. A. , Cozin Cristiane , Morales Rigoberto E. M.
Published: October 2017

The slug flow regime is probably the prevailing pattern in the oil and gas industry, appearing in the nuclear industry as well. As a consequence, several studies have been conducted in order to understand the physics of this flow regime and to obtain a model to predict its properties. This work presents a transient hybrid methodology to simulate the gas-liquid slug regime in pipes with a change of direction from horizontal to downward inclined flow. The simulation initiates with a slug tracking model assuming the pipe to be filled with liquid, and follow the unit cells while they flow through the horizontal section; the information about the unit cells entering the pipe are obtained from experimental data. Near the elbow and beyond, the unit cells are simulated by a simplified two-fluid Lagrangian model, capable of providing flow details with the change of direction, and the dissipation of the slug flow to the stratified regime in a descendent slope. Simulations for a 4.862-m pipe were carried out, with the change of direction from horizontal to −3° and −5°. The results were compared to experimental data, showing that the model can successfully predict the flow behaviour for the given conditions.
Investigation of the Dynamics of Incompressible Flow in Domains of Multiple Close-Packed Spheres
Authors: Fick Lambert H. , Merzari Elia , Marin Oana , Hassan Yassin A.
Published: October 2017

The study of flows over spherical bluff bodies is relevant in engineering systems such as nuclear power reactors. These flows exhibit complex spatial and temporal behavior due to the presence of significant streamwise curvature that leads to boundary layer separation and reattachment, and the turbulence phenomena associated with these effects. In this study, we present results for flow over one and two spheres in free-stream conditions at Reynolds number 1,000, which corresponds to a turbulent-flow regime. The goal of the study was to verify our simulation methodology and develop an initial understanding regarding the spatial and temporal effects of additional spheres in close proximity to the canonical single-sphere case. Based on our results, we find that additional spheres significantly alter the behavior of the flow. The addition of a second sphere suppresses vortex formation, while the temporal correlation between points in the wake is also reduced.
Uncertainty Analysis in a Scale Model Wind Turbine Array Boundary Layer
Authors: Turner John J. , Wosnik Martin
Published: October 2017

Uncertainty estimates from an experimental investigation of a scale model wind turbine array, conducted with (on the order of) 100 0.25 meter diameter model wind turbines in a high Reynolds number turbulent boundary layer facility, are reported. An expanded uncertainty analysis using the Taylor series method is executed to predict uncertainty for the system of interest in the mean flow. A workable comprise has been found for data acquisition time mitigating changing initial conditions due to exposure to atmospheric conditions and temperature drift. The study was conducted in the University of New Hampshire (UNH) Flow Physics Facility (FPF) which is the worlds largest flow physics quality turbulent boundary layer wind tunnel, with test section dimensions of 6 m wide, 2.7 m tall and 72 m long. Naturally grown turbulent boundary layers with scale ratios of energy-containing to dissipative scales (Karman number) of up to 20,000 can be generated, and are on the order of 1 m thick near the downstream end of the test section. The long fetch of the facility offers unique opportunities to study the downstream evolution of the wake of single wind turbines, and the flow through model wind turbine arrays over long distances. Far downstream within a wind farm it is proposed that the farm reaches a fully developed state where the flow field becomes similar from one row to the next. The goal of this work is to accurately determine the uncertainty associated with open to atmosphere wind tunnel data for use in validation of numerical models regarding the fully developed wind turbine array boundary layer.
Direct Measurement of Heat Flux Partitioning in Boiling Heat Transfer
Authors: Richenderfer A. , Kossolapov A. , Seong J. H. , Saccone G. , Bucci M. , Buongiorno J.
Published: October 2017

The development and validation of mechanistic boiling heat transfer models has been a focal point in the efforts to improve the efficiency and profitability of power generation systems, e.g. nuclear reactors. The primary goal of these models is improving the accuracy of boiling heat transfer simulations and reducing the uncertainty margins that affect both the design and the safety of a system. However, the emergence of these models has also stimulated the need for high-fidelity experiments and experimental data for validation and verification.

In this work we present first-of-a-kind data of heat flux partitioning in boiling heat transfer, obtained using cutting-edge diagnostics and post-processing techniques. A HSV camera was used to visualize the boiling surface at 10,000 frames per second with simultaneous front and side views of the two-phase flow. A high-speed IR camera was used to capture the 2-D radiative signal from the boiling surface to visualize bubble nucleation, growth and detachment at a 115 μm/pixel resolution at 2,500 frames per second. A coupled radiation-conduction calibration model was used to calibrate the IR data and extract the full local temperature and heat flux distributions on the boiling surface, which enable a direct measurement of the partitioned heat fluxes.

Here we report the results of investigations performed in flow boiling conditions with a mass flux of 500 kg/m2/s, at atmospheric pressure and 10 K of subcooling. These data will be leveraged to inform the development and validation of the next generation of mechanistic boiling heat transfer models, to be used in Computational Fluid Dynamics (CFD) codes for the design and the safety analysis of nuclear reactors.
The Influence of Surface Patterning on the Thermal Properties of Textured Thrust Bearings
Authors: Fu Gen , Untaroiu Alexandrina
Published: October 2017

Contact performance can be enhanced by using textured surfaces. These are also found to have influences on lubricated contacts. The effects of textured surface on lubricated contacts has been widely investigated over the past twenty years. The property of lubricated contacts has been found to play an important role on the performance of fluid film bearings. According to the previous study, the introduction of dimples on the inner surfaces of parallel thrust bearings can improve the load capacity and reduce the friction. Since the friction loss is mostly converted to thermal energy and then increase the temperature, textured surface is expected to have a positive effect on the thermal property of the thrust bearings. A procedure to find the optimal partially texture geometry, which minimize the temperature inside the bearing film, is presented in this study. A parallel sector-pad thrust bearing is simulated by a 3D computational fluid dynamics model. The stationary surface of the bearing is textured with dimples while the rotor surface is flat. The results of the baseline model have been validated by the experimental data from the literature. The temperature and pressure distribution on the bearing pad are presented. In this study, two types of dimples, including rectangular and elliptical, are compared together. A parametric study is conducted to investigate the influence of the texture geometries. In this study, the length of the major axis (width), the length of the minor axis (length), dimple depth, circumferential space between two dimples, radial space between two dimples, radial extend and circumferential extend are selected as design parameters. A surrogate model is used to reduce the computing time of CFD analysis. Based on the surrogate model, a multi-objective optimization scheme is used to navigate the design space and find the optimal texture structure that provides a lower maximal temperature inside the fluid film, higher load capacity, and lower friction torque. The optimal radial extent of the texture is around 80% of the pad radial length for both cases. The optimal length of the elliptical dimples in the circumferential direction is about 30% larger than the value of the rectangular dimples. In the final optimal design, the maximal temperature reduces 1.1% and 1.3% for rectangular and elliptical dimples while the load capacities are maintained at the same level.
Metal Foam Microchannel Heat Exchangers for Cooling of Fuel Cells and Flow Batteries
Authors: Santamaria Anthony , Zhang Jingru
Published: October 2017

A metal foam filled microchannel cooling device for polymer-electrolyte-membrane fuel cell (PEFC) and flow batteries was investigated experimentally and numerically in this study. Nickel foam was selected due to its high conductivity, large surface area, low density and low cost. The properties of the nickel foam were determined analytically and experimentally. Experiments were conducted to obtain pressure drop at various Reynolds numbers for metal foams of varying porosities. The experimental data was used to provide inputs for the numerical model. A modeling approach for flow in a metal foam filled channel was validated with the available data. The validated model was then used to analyze the heat transfer and fluid flow characteristics of the metal foam microchannel. Two different locations of the cooling device with respect to the PEF C stack were investigated. The thermal resistance and pressure drop change with Reynolds number are presented. Significant temperature drop was observed with the metal foam microchannel design. The modeling results can be used to guide the direction of future experiments.
Simulation of Fluid-Structure Interaction of Crossflow Through a Tube Bundle and Experimental Validation
Authors: Brockmeyer Landon , Solberg Jerome , Merzari Elia , Hassan Yassin
Published: October 2017

Fluid-structure interactions are complex, multi-physics phenomena of consequence for many fluid-flow domains. Modern multi-physics codes are becoming capable of simulating with great accuracy the interaction between fluid and structure dynamics. While fluid-structure interactions can occur in many forms, flow-induced vibrations are of particular interest. Such vibrations can result in the fatigue and even failure of a vibrating geometry. The prediction and minimization of flow induced vibrations are of particular importance for heat exchangers, which commonly contain bundles of tubes experiencing high-velocity crossflow. The present study simulates the fluid-structure interaction for flexibly mounted tube bundles undergoing crossflow and compares the results with experiment. The simulation code consists of a spectral-element fluid solver directly coupled with a finite-element solid mechanics solver. The fluid solver locally adapts the fluid mesh to accommodate the moving solids. In order to minimize computational expense, low Reynolds number flows are considered, allowing for a thin, pseudo 2-D domain. The flow remains laminar for the majority of the domain, with local areas of turbulence. The pins are connected to springs that supply a restorative force equivalent to the flexible mounts of the corresponding experiment. Fluid-only simulations are performed for flow spanning low to moderate velocities and compared visually with experimental flow visualizations. Coupled fluid-structure interactions are simulated with low velocity and vibration amplitudes. The measured vibration amplitudes of the simulation agree well with those of the experiment.
An Improved CFD Approach for Ice-Accretion Prediction Using the Discrete Element Roughness Method
Authors: Hanson David , Kinzel Michael
Published: October 2017

Ice-shape prediction results are shown wherein Discrete-Element Roughness Method (DERM)-based CFD solutions are coupled with LEWICE to supplement the built-in heat transfer prediction module. This coupling produces multi-step ice-shape predictions. The effect of using the newer roughness-height distribution model of Han and Palacios rather than the roughness-height prediction of LEWICE is also gauged. DERM is used in an attempt to improve heat transfer predictions beyond the capability of a sand-grain-roughness model while only slightly increasing the computation time. LEWICE is the industry-standard ice growth prediction tool maintained by NASA. LEWICE is known to predict ice shapes very accurately within its validation envelope, but suffers lowered accuracy for icing conditions in the glaze regime. The predictions that result from the DERM-LEWICE coupling are compared with ice shapes generated in experiments from the Penn State Adverse Environment Rotor Test Stand (AERTS). It is observed that ice-shape predictions in the glaze-icing regime can be highly sensitive to the convective heat-transfer predictions.
Artificially Ventilated Cavities: Evaluating the Constant-Pressure Approximation
Authors: Fronzeo Melissa A. , Kinzel Michael , Lindau Jules
Published: October 2017

Computational Fluid Dynamics (CFD) is employed to study the fundamental aspects of the internal pressure within artificially ventilated, gaseous cavities in both twin- and toroidal-vortex closure modes. The results show that several pressure regions develop within the cavities, indicating that the common assumption that the cavity has a constant pressure breaks down when evaluated in high detail. The internal cavity pressure is evaluated using a probability density function (PDF). The resulting PDF plots show a clusters with multiple peaks. A mixture-of-Gaussians (MOG) method is employed to better understand the distributions of these peaks. These peaks are then mapped to the simulation results, where it is observed that these peaks correlate to distinct cavity regions (which vary depending on cavity type). Moreover, these varying pressure regions appear to align with cavity-radius growth and reduction and appear to be the driving force of the internal, circulatory flow. Lastly, the importance of these pressure regions are investigated with respect to predictions from semi-empirical theory of the cavity shape, showing a moderate impact depending on where the cavity is probed. Overall, these results provide physical insight into ventilated cavity flow behavior that is often ignored.
Numerical Simulations of Electric Field Driven Self-Assembly of Monolayers of Mixtures of Nanoparticles
Authors: Amah E. , Musunuri N. , Fischer Ian S. , Singh Pushpendra
Published: October 2017

We numerically study the process of self-assembly of particle mixtures on fluid-liquid interfaces when an electric field is applied in the direction normal to the interface. The force law for the dependence of the electric field induced dipole-dipole and capillary forces on the distance between the particles and their physical properties obtained in an earlier study by performing direct numerical simulations is used for conducting simulations. The inter-particle forces cause mixtures of nanoparticles to self-assemble into molecular-like hierarchical arrangements consisting of composite particles which are organized in a pattern. However, there is a critical electric intensity value below which particles move under the influence of Brownian forces and do not self-assemble. Above the critical value, when the particles sizes differed by a factor of two or more, the composite particle has a larger particle at its core and several smaller particles forming a ring around it. Approximately same sized particles, when their concentrations are approximately equal, form binary particles or chains (analogous to polymeric molecules) in which positively and negatively polarized particles alternate, but when their concentrations differ the particles whose concentration is larger form rings around the particles with smaller concentration.
Solids Erosion Patterns Developed by Pulse Jet Mixers
Authors: Bamberger Judith Ann , Pease Leonard F. , Minette Michael J.
Published: October 2017

Millions of gallons of radioactive waste are stored in underground tanks at the Hanford Site in Washington State. This waste will be vitrified at the Waste Treatment and Immobilization Plant that is under construction. Vessels in the pretreatment portion of the plant are being configured for processing waste slurries with challenging physical and rheological properties that range from Newtonian slurries to non-Newtonian sludge. Pulse jet mixing (PJM) technology has been selected for mobilizing and mixing this waste. In the pulse jet mixing process, slurry is expelled from pulse tube nozzles directed towards the vessel floor. The expelled fluid forms a radial jet that erodes the settled layer of solids. The pulse tubes are configured in a ring or multiple rings and operate concurrently. The expelled fluid and mobilized solids traverse toward the center of the tank. At the tank center, the jets from pulse tubes in the ring collide and lift solids upward in a central plume. At the end of the pulse, when the desired fluid volume has been expelled from the pulse tube, the applied pressure switches to suction and the pulse tubes are refilled. This cycle is used to mobilize and mix the tank contents.

An initial step of the process is the erosion of solids from the vessel floor by the radial jets that form on the vessel floor beneath each pulse tube. Experiments have been conducted using simulants to evaluate the ability of the pulse jet mixing system radial jets to combine to develop the central upwell and lift solids in the vessel. These experiments were conducted at three scales using a range of granular simulants over a range of concentrations in vessels with elliptical, spherical, or flanged and dished bottoms. Process parameters evaluated experimentally include the velocity of fluid expelled from the pulse tube, the duration of the pulse and the ratio of pulse duration to cycle time. Videos taken from beneath the vessel show the growth of the cleared area beneath each pulse tube as a function of time during the pulse. The focus of this paper is to describe measurement techniques and compare and contrast erosion patterns developed from different simulants and pulse tube configurations. The cases are evaluated to determine how changes in process parameters affect the PJM’s ability to mobilize solids from the vessel floor.
Mixing Control in an Isobaric Energy Recovery Device of Seawater Reverse Osmosis Desalination System
Authors: Goto Akira , Shinoda Masao , Takemura Takashi
Published: October 2017

Mixing phenomena in an isobaric energy recovery device (ERD) of a seawater reverse osmosis (SWRO) desalination system are investigated experimentally and numerically using Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD). The ERD, which recovers energy from high-pressure brine discharged from RO membranes, is one of the most important mechanical devices in a SWRO desalination system. In this ERD, seawater is introduced into a vertical chamber from the top, and then high-pressure brine is introduced into the chamber from the bottom. The high-pressure brine pressurizes the seawater through direct liquid-to-liquid contact, transferring high-pressure energy of the brine to the seawater. This enables a sharp reduction in the electric energy consumption, typically 50%, of high-pressure pumps used to elevate seawater pressure for RO membranes. The energy recovery efficiency of the present ERD is over 98%, which is extremely high compared to a conventional turbine-type energy recovery device, such as a Pelton turbine, which has a system energy recovery efficiency of 60 to 80%. The possible weakness of the present ERD is the amount of mixing between brine and seawater around the direct contact surface, because mixing phenomena increase the salinity of seawater supplied to RO membranes. A higher pressure is required to keep the same amount of permeate from the membrane, which results in an energy loss in the system. To minimize mixing, a set of unique flow distributors was invented and placed at both ends of the pressure exchange chamber, which stabilizes the contact surfaces and suppresses excessive mixing. Mixing phenomena in the pressure-exchange chamber are investigated experimentally in detail with PIV and numerically with CFD, and the effectiveness of the flow distributors is clarified.