bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on Application of 500MPa Water Cutting Composite Material
Authors: Xue Shengxiong , Chen Zhengwen , Ren Qile , Han Caihong , Chen Bo , Wu Ziquan , Li Yuefeng
Published: October 2017

For large scale curved composite components cutting process engineering application, high precision and high speed are basic cutting requirements. This paper proposed to improve the working pressures up to 500MPa as high-end water cutting working condition. Mathematical model was established based on lots of complicated tests, and cutting mechanism with the aim of ultra-high pressure water cutting processing center equipment reliability was designed. Through the test application examples, it is showed that high precision and high speed water cutting composite components are corresponding to reliable water cutting processing operation. The theoretical research, structural design, test application of the project in this paper was well adapted to the high technical requirements for composite craft wing processing. It can be seen that it is very important to improve the working pressure to reach high precision and high speed composite components processing under the premise of reliable operation.
Numerical and Experimental Investigation of Flow in Fish Tanks for Small-Scale Aquaponic Systems
Authors: Nedyalkov Ivaylo , Guerdat Todd , Seksinsky Drue , Romero Sylvia , Stickney Justin , Pirie Ethan
Published: October 2017

Aquaponic systems combine recirculating aquaculture (growing of fish) with hydroponics (growing of plants in water). The fish in the recirculating aquaculture systems provide nutrients for the plants and the plants remove excess nutrients from the water, making these systems more efficient than traditional farming methods in terms of nutrient utilization. Small, recirculating aquaponic systems may provide a more sustainable and cost-effective alternative for securing food supply in both developing and developed nations. Recirculating aquaculture systems tend to be capital-intensive and require significant power to circulate the water in the fish tanks, which helps with the removal of waste and the distribution of oxygen. To reduce capital costs, alternative, culture vessels made from locally available materials were investigated (i.e. square-shaped tanks, and international bulk containers - IBC). These non-standard shaped culture tanks, pose an additional challenge for proper circulation of the water as compared to traditional round tanks. To address the issue of circulation, numerical and experimental data were obtained for rectangular containers. The numerical results were obtained using OpenFoam models of the experimental setup. The experimental data were obtained by measuring flow velocities in an IBC tank using Acoustic Doppler Velocimetry. Currently the experimental data show good repeatability when data are taken for at least five minutes at each position in the tank. The focus of the continuing work is to establish a good agreement between numerical and experimental results. Ultimately the study will contribute to the design of cost-effective recirculating aquaponic fish and plant systems which require lower capital expenditures and achieve energy-efficient circulation of water in the fish culture tanks.
Fluid-Structure Interaction Study of GLCC© Inlet Modifications
Authors: Kolla Srinivas Swaroop , Mohan Ram S. , Shoham Ovadia
Published: October 2017

The Gas-Liquid Cylindrical Cyclone (GLCC©1) is a simple, compact and low-cost separator, which provides an economically attractive alternative to conventional gravity based separators over a wide range of applications. The GLCC© inlet section design is a key parameter, which is crucial for its performance and proper operation. An in-depth evaluation of specific design modifications and their effectiveness on safety and structural robustness are carried out in this study using Finite Element Analysis. Fluid-Structure Interaction (FSI) analysis is also carried out utilizing the results of Computational Fluid Dynamics (CFD) aimed at investigating the effect of fluid flow on the inlet section structural integrity. The selected design modifications are based on feasibility of GLCC© manufacturing and assembly for field applications. Different case studies incorporating sustained GLCC© internal pressure, dead weight loading, forces generated because of slug flow and high temperatures are evaluated and presented. The concept of holes cutout in baffle have been proven effective with no stresses or deformation in the baffle area. FSI simulation of slug flow have proved that FEA direct loading case studies are far more conservative.
Experimental-Numerical Analysis of Turbulent Incompressible Isothermal Jets
Authors: Aleyasin Seyed Sobhan , Fathi Nima , Tachie Mark Francis , Vorobieff Peter , Koupriyanov Mikhail
Published: October 2017

An experimental investigation was conducted to study the effects of Reynolds number on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free equilateral triangular and round jets issuing from modified contoured nozzles (nozzles with sharp linear contractions). Detailed velocity measurements were made using a particle image velocimetry at Reynolds numbers of 6000, 10000, 13800 and 20000. Computational fluid dynamics (CFD) was also applied to understand the flow behaviors in different Reynolds numbers. We applied standard k-ε turbulence model in an axisymmetric domain to conduct the numerical simulation of the round jet cases. The potential core length was the system response quantity to evaluate our simulation against the experimental results. The geometrical comparative study shows enhanced mixing in the near field of the triangular jets compared to the round jets, regardless of Reynolds number. This conclusion is supported by shorter potential core length and faster growth of turbulence intensity on the centerline of the triangular jets. The obtained data in the round jets exhibit that the jet at the lowest Reynolds number has the most effective mixing with the ambient fluid, while increase in Reynolds number reduces the mixing performance. In the triangular jets almost there is no Reynolds number effect on the measured quantities including the length of the potential core, the decay rate and the axis-switching locations. The results revealed that the asymptotic values of the turbulence intensities on the jet centerline are not only independent of the Reynolds number but also they are the same for both the round and triangular jets. Due to the specific shape of the triangular nozzle, a skewed flow pattern is observed in the near field region in the major plane while the jet is absolutely symmetric in the minor plane. The turbulence structures in all the jets studied become larger as streamwise distance increases, while there is no considerable Reynolds number or nozzle geometry effects on the size of the structures on the jet centerline.
Thermal and Fluid Dynamic Model for Capillary-Driven Heat Pipe With Closed-Form Solution
Authors: Maxwell Jesse
Published: October 2017

A model is derived for the steady state performance of capillary-driven heat pipes on the basis treating fluid flow through miniature- and micro-channels and applied as bulk properties to a large aspect ratio quasi-one-dimensional two-phase system. Surface tension provides the driving force based on an equivalent bulk capillary radius while laminar flow through micro-channels and the vapor core are treated. Heat conduction is accounted for radially while isothermal advection is treated along the axis. A closed-form solution is derived for a steady state heat pipe with a constant heat flux boundary condition on the evaporator as well as a constant heat flux or a convective boundary condition along the condenser. Two solution methods are proposed, and the result is compared to empirical data for a copper-water heat pipe. The components of the closed-form solution are discussed as contributors to driving or frictional forces, and the existence of an optimal pore radius is demonstrated.
Modeling Jet Erosion of Particle Beds
Authors: Pease Leonard F. , Bamberger Judith Ann , Minette Michael J.
Published: October 2017

Here we present and benchmark an analytical model to describe the radial extent of erosion of settled particle beds by radial wall jets as a function of time. The extent of erosion is an essential measure of the performance of vessels mixed by arrays of radial wall jets because portions of vessel floors not cleared of settled particles may accumulate undesirable constituents. We derive a model of the cleared radius as a function of time scaled so that fits may be described using only two free parameters. We find remarkably good agreement between experimental data and the model upon fitting. Extracted fitting parameters are shown to be reasonable. The influence of nozzle transience on erosion transience has also been evaluated. We find that nozzle transience explains the initially slower rate of erosion and decreases the final extent of erosion by one to three nozzle diameters for the cases considered. Future work remains to evaluate the dimensionless groups from conservation laws and account for vessel curvature.
Surface Tension Capability Within an Adaptively Refined Compressible Flow Code
Authors: Jibben Z. , Velechovsky J. , Masser T. , Francois M.
Published: October 2017

We present a method to simulate surface tension between immiscible materials within an inviscid compressible flow solver. The material interface is represented using the volume of fluid technique with piecewise-linear interface reconstruction. We employ the continuum surface force model for surface tension, implemented in the context of the MUSCL-Hancock finite volume method for the Euler equations on an adaptively refined Eulerian mesh. We show results for droplet verification test cases.
A Vertical Axis Rotor for Wave Energy Conversion
Authors: Yang Yingchen , Soto Joab , Salazar Francisco
Published: October 2017

The present work augments vertical-axis unidirectional wave energy converter (WEC) designs with a new approach. The enabling technique is the hydrodynamic design of a special rotor, which consists of a series of uniquely shaped blades in a certain formation. Specifically, individual blades are realized by revolving a two-dimensional symmetric hydrofoil about its chord line. Then the blades are arranged around a vertical shaft in a desired formation to form the rotor. When driven by an approaching flow through interaction, the rotor naturally rotates about the vertical shaft in a predefined direction. The approaching flow could be from any spatial direction, and could have changing speed and direction in any fashion, but the unidirectional behavior of the rotor never changes. Such a behavior guarantees a unidirectional performance of the rotor in waves, where the water flow is omnidirectional and constantly evolving. In validating the proof of concept and characterizing the rotor’s unidirectional performance, experiments were carried out under various flow conditions. Specifically, three types of flows were employed: horizontally oscillating flow, vertically oscillating flow, and orbital flow along a circular path in a vertical plane. The three flows were actually created by translating the rotor in still water, with the first two to characterize the rotor’s responsiveness to the flow direction and the third one to simulate rotor interaction with deep waves. For each flow type, different rotor configurations/blade formations were examined under various testing parameters. For all the cases, the rotor shaft was kept vertically all the time. The experimental results are discussed in details in the paper.
Performance of Supercritical Slurry Jet Drilling System
Authors: Padsalgikar Ashwin , Dabirian Ramin , Oglesby Ken , Mohan Ram S. , Shoham Ovadia
Published: October 2017

A slurry jet driller is a novel drilling method, which delivers an abrasive slurry and supercritical gas mixture, to an expander nozzle. The expanded fluids flowing out of the nozzle, energize the particles, which hit the target material and erode it, achieving drilling. The expansion of the gas from a super critical state to in situ pressure and temperature conditions is the driving mechanism of the drilling operation. The primary objective of this paper is to evaluate the feasibility of the novel slurry jet drilling system.

An experimental program is carried out for testing the performance of a slurry jet driller. The slurry is formed by mixing water with garnet particles, and a super critical carbon dioxide as the gas phase. The purpose of experiments is to evaluate the erosive nature of garnet rocks and to test the cutting efficiency of the nozzle. The acquired data show that the material removal rate increases with increase in the gas-slurry flow ratio, until a ratio of 1.5. A further increase in the flow ratio results in a reduction of the rate of material removal.

Improved nozzle geometry was obtained using a program written in MATLAB. Criteria used for geometry improvement was the force applied to the bottom of the drilled bore. A rudimentary model is developed for the prediction of material removal rate utilizing a slurry jet driller, which is presented in a dimensionless form. The model incorporates the important variables affecting the jet driller system performance, including fluid and target material properties, and particle velocity. A fair agreement is observed between model predictions and experimental data, exhibiting a 20% deviation.
A Low Cost Fabrication Method for Electrowetting Assisted Desiccation of Colloidal Droplets
Authors: Li Xi , Maki Kara L. , Schertzer Michael J.
Published: October 2017

When colloidal droplets evaporate, material is often deposited at the periphery in a coffee-ring pattern. An understanding of colloidal transport and deposition in evaporating droplets is critical for optimization of many medical diagnostic devices and printing processes. This phenomenon can also be used for nanoparticle self-assembly, containerless materials processing, and manufacturing of flexible electronics. The forces affecting colloidal transport can be categorized as (i) convective effects, (ii) particle diffusion, and (iii) boundary effects. Knowledge of fluid flow in an evaporating droplet is required to understand particle transport when convection effects dominate over particle diffusion. The evaporative radial flow identified by Deegan et al. [1] is the result of contact line pinning and high evaporation flux at the contact line. Hu and Larson later identified that dominance of thermal Marangoni recirculation within the droplet can suppress ring formations by convecting particles to the center of the deposition.

Bhardwaj et al. [2] demonstrated that van der Walls and electrostatic forces can dominate colloidal transport and capture particles on the substrate to form uniform depositions. These effects are represented by the Derjaguin, Verwey, and Overbeek (DLVO) force. This force can attract or repel particles from the surface or other particles when they are separated by less than the Debye length. Attractive DLVO forces result in uniform depositions when they dominate over the evaporative and Marangoni flows in evaporating droplets. Particle capture on the substrate has also been achieved by antibodies-antigen reactions, or by leveraging magnetic and electrophoretic forces.

Particles can also be captured on the interface of evaporating droplets. Li et al. [3] observed uniform colloidal monolayers when water droplets were evaporated at elevated temperatures. They argued that particles were being captured on the interface in these cases as the particle diffusion rate was smaller than the velocity of the collapsing interface.

This work will find a low cost method for electrowetting assisted deposition and examine how electric fields can disrupt the interplay between convection, diffusion, and interface trapping in evaporating colloidal droplets. Application of AC and DC electric fields has the potential to suppress the coffee-ring effect by independently controlling the shape of the fluid interface, the contact angle hysteresis, and the motion of particles suspended in the droplet. This investigation will compare the interfacial evolution and deposition patterns left by evaporating protein laden droplets under AC and DC fields to examine their suitability for medical diagnostic applications.
Flow and Mixing in Rotating Zigzag Microchannel
Authors: Ren Yong , Leung Wallace Woon-Fong
Published: October 2017

The flow and mixing in rotating zigzag microchannel is investigated experimentally and numerically with objective of improving mixing, which is largely due to secondary or cross-flow in the cross-sectional plane of the channel and the bend connecting non-radial angled channel segments. Unlike the conventional stationary zigzag channel, crossflow in the zigzag channel is highly intensified from a combination of (a) centrifugal acceleration component in the cross-sectional plane due to the angled channel segments, (b) centrifugal acceleration generating Görtler vortices at “channel bends”, and (c) Coriolis acceleration. When the channel segment in the zigzag channel is inclined towards rotation direction (prograde), all three accelerations are aligned intensifying the crossflow; however, when it is inclined opposite to rotation (retrograde), Coriolis acceleration negates the other two accelerations reducing mixing. A numerical model has been developed accurately accounting for the interactions of throughflow, crossflow and material dispersion by diffusion and convection in a rotational platform. An experimental microfluidic platform with rotating zigzag microchannel has also been developed. Experimental results on mixing quality carried out at two rotation speeds compared well with prediction from the numerical model. The overall mixing quality of a rotating zigzag channel is much improved compared with that of a stationary zigzag channel.
Investigation of Internal Flow Velocity Distribution and Gas Loss of High-Speed Supercavitating Flows
Authors: Zou Wang , Xue Lei-Ping , Jin Wei-Wei , Xiang Xin-Tao
Published: October 2017

Internal velocity distribution is an important content of flow structure and reveals the gas loss mechanism for supercavitating flows. Considering the three-phase momentum interactions and the water-vapor mass transport, the water-gas-vapor multi-fluid model is established to simulate ventilated supercavitating flows at high speed in the frame of the nonhomogeneous multiphase flows theory. Based on the model, the gas velocity field inside supercavity is studied. In the case of supercavitating flows around disk cavitator, two vortex cores are formed in the longitudinal plane under the actions of the adverse pressure gradient in the tail and the viscous friction on cavity surface, and are symmetrically distributed about the longitudinal axis. Most inner regions in the cavity cross section are occupied by circulation flows, where the velocity is in the opposite direction of incoming flows and decreases in the radial direction. When passing the vortex center, the velocity changes direction and increases in the radial direction. Part of gas departs to wake flows from the outermost regions close to the section boundary. The results confirm Spurk’s assumption for gas entrainment in detail. It is also found that the gas velocity distribution in the cross section through vortex cores does not depend on cavitation number. Supercavitating vehicle has the similar internal velocity distribution and gas loss mechanism. Due to the added viscous effect of the enveloped body, there are multiple axisymmetrical distributed vortices inside the cavity. The relative distance between the vortex core and the cavity wall increases downstream. Computations of ventilated supercavitating flows at different Reynolds numbers show that the gas leakage is decreasing with increasing Reynolds number for a given cavitation number. This study deepens the understanding of gas loss for ventilated supercavity at high speed, and lays a foundation for further refinement of the dynamic model of the maneuvering ventilated supercavity and the control of ventilated supercavitating flows.
Flow Inertia and Heat Transfer in Suddenly Expanding Annular Shear-Thinning Flows
Authors: Hammad Khaled J.
Published: October 2017

The impact of flow inertia on flow and heat transfer in suddenly expanding annular pipe flows of a shear-thinning non-Newtonian fluid is studied within the steady laminar flow regime. The equations governing conservation of mass, momentum, and energy, along with the power-law constitutive model are numerically solved using a finite-difference numerical scheme. The influence of inflow inertia, annular-nozzle-diameter-ratio, k, power-law index, n, and Prandtl numbers, is reported for: Re = {50, 100}, k = {0, 0.5}; n = {1, 0.6}; and Pr = {1, 10, 100}. Heat transfer augmentation, downstream the plane of expansion, is only observed for Pr = 10 and 100. The extent and intensity of recirculation in the corner region, increases with inflow inertia. Higher Reynolds and Prandtl numbers, power-law index values, and annular diameter ratios, in general, reflect a more dramatic heat transfer augmentation downstream of the expansion plane.
Modeling Interfacial Instabilities With a Modal Model
Authors: Canfield Jesse M. , Denissen Nicholas A. , Reisner Jon M.
Published: October 2017

The well-known Rayleigh-Taylor (RTI) and Richtmyer-Meshkov (RMI) instabilities occur at the interface between two fluids. Though the two problems have been researched extensively, accurate modeling of the growth of an interface into a mixing layer is exceedingly difficult. A pseudospectral modal model was developed to predict early-time, sub-grid, growth of the mixing layer for RTI and RMI; in the multi-physics code xRage. The modal model couples a weakly nonlinear single mode growth model (Goncharov) to a weakly nonlinear multi-mode model (Haan). Both approaches are semi-analytical derivations that are solved to completion through numerical integration. The complete modal model (Goncharov-Haan) evolves the interfacial surface into a mixing layer. By integrating the displacement of the surface along the interface, turbulence closure variables, such as turbulent kinetic energy and length scale, are calculated which are used to dynamically initialize the BHR turbulence model in xRage. As the mixing layer grows, individual modes interact producing new modes that result in a non-locally determined mixing layer. The modal model is demonstrated for a few cases of interest. Results and their implications will be discussed.
Numerical and Experimental Study of the Rotational Behaviour of Flat Plates Falling Freely With Periodic Oscillating Motion
Authors: Hærvig Jakob , Jensen Anna L. , Pedersen Marie C. , Sørensen Henrik
Published: October 2017

When a flat plate falls freely in periodic oscillating motion regime, unsteady fluid forces create additional lift force contributions due to the rotational behaviour. Computational fluid dynamics is used to simulate the free fall behaviour of a flat plate with aspect ratio β = 20 falling in two-dimensional flow with Reynolds number Re ≈ 10,000 and non-dimensional moment of inertia I* = 0.115. To validate the free fall trajectory obtained by computational fluid dynamics, video recordings are used. Based on the validated free fall computational fluid dynamics simulation, the instantaneous fluid forces and torques on the plate are obtained.

The validated simulations show significant deviations in per-pendicular and tangential force coefficients at the same angle of attack depending on the trajectory history of the plate. At low angles of attack below 5 deg, the tangential force differs significantly. Oppositely, the difference in the perpendicular force is most pronounced at high angles of attack. During a free fall, the angle of attack is below 5 deg in 70 % of the time. Furthermore, the angle of attack is only above 45 deg in less than 5 % of the time. Therefore, effort must be put into a more detailed description of the tangential force component, in order to improve the existing modelling framework for non-spherical particles.
A Theoretical Study of Saline Droplet Evaporation in Solar-Thermal Driven Full Separation Multi Effect Distillation (FS-MED) System
Authors: Wei Yan , Guo Penghua , Xu Ben , Rodriguez Thomas , Escobar Luis , Chirino Hermes
Published: October 2017

The significant changes of population, environment and climate have led to the increased need for freshwater. However, the shortage of naturally available freshwater is becoming more frequent than ever. Desalination, removal of salt and other minerals from seawater, brackish water, and wastewater, is a promising solution to provide the increasing need of freshwater. Multi stage flashing (MSF) and multi effect distillation (MED) can be classified as conventional thermal-driven desalination technologies. Nevertheless, the disposal of high concentrated brine is a big environmental concern. Despite the tremendous improvements in conventional desalination technology, the desalination process is very energy consuming. Due to high expenses of the conventional energy resources, renewable energy sources can provide alternatives.

Considering the fact that Concentrated Solar Power (CSP) has been significantly developed during the past two decades, inorganic salts are the perfect candidates as Heat Transfer Fluid (HTF) for high temperature applications in solar thermal energy storage, fully separating water and salts in the desalination process arises naturally, since the leftover salts can be collected instead of disposing them to the environment. A full separation multi effect distillation (FSMED) system was proposed by other researchers, where the air fed to the full separation tank (FST) is preheated by a heat source, and the highly concentrated brine from the last effect is sprayed in the FST, so that the brine droplets can be completely evaporated by leaving behind inorganic salts. Obviously, the full separation process of salts and water involves multiphase heat and mass transfer. However, a key question is the characterization of the lifetime of brine droplets inside the FST during its entire evaporation process, and the effects from the internal circulation to droplet evaporation. If the droplet has strong internal circulation, the definition of two stages of evaporation becomes inaccurate, it has to be corrected based on the detailed calculation of time scale at each stage. In the current study, a 1D quasi-steady evaporation model was developed to characterize the effects from internal circulation to the life cycle of droplets in the FST, compared with the results using the dynamic evaporation model. To simplify the analysis, water droplet with impurity particles was considered, and a case study was also provided to compare the life cycle of water droplets without internal circulation. Finally, a correction to the definition of two-stage of water droplet evaporation was provided. It is expected that the computation results will be beneficial for thermal driven desalination community.
Effect of Surfactant (Foamer) Delivery Location on Horizontal Wells Deliquification
Authors: Barreto Carolina V. , Karami Hamidreza , Pereyra Eduardo , Sarica Cem
Published: October 2017

One of the methods to unload liquid from gas wells is foam-assisted lift. The applied surfactant reduces the liquid surface tension facilitating foam stability, and consequently, reducing mixture density and gas slippage. In this experimental study, a 2-in ID facility consisting of a 64-ft lateral section followed by a 41-ft vertical section is used to determine the optimum surfactant delivery location in horizontal wells. Water and compressed air are the liquid and gas phases, and an anionic surfactant is applied continuously with fixed concentration. Lateral section inclination is varied between ±1°, and four injection points are tested, including one with a static mixer, used as an external source of agitation. Recorded parameters are flow pattern, pressure gradient, liquid holdup, and foam quality.

In the lateral section, the highest efficiency is obtained by using a static mixer causing significant drop in liquid holdup and increase in pressure drop due to frictional losses. All other injection points show similar behavior to the air-water case, due to negligible generated foam amid the existing flow pattern agitation. In the vertical section, all injection points show similar and significant drops in liquid holdup and delays in liquid loading onset compared to air-water case, and foam quality decreases as gas flow rate is reduced. Increasing the liquid flow rate causes increases in liquid holdup and pressure drop and shifts liquid loading onset to higher gas flow rates. The experimentally observed liquid loading onset is compared to the predictions of Turner et al. (1969), and a modification is proposed in this correlation to consider the effects of surfactant injection.

The number of experimental studies investigating foam effects on liquid loading is limited especially for off-vertical configurations. The results of this study provide an experimental source to optimize foam lift in deviated wells.
On the Test Setting at Condenser in Thermal Performance Tests of Heat Pipes
Authors: Wong S.-C. , Hsu Z.-J. , Hsu L.-C.
Published: October 2017

This work compares the heat pipe test results using different test settings at the condenser under an identical evaporator setting and operating temperature of 45°C at the adiabatic section. The first test setting, considered as the standard, adopts a pair of water-cooled cold plates in which the heat pipe condenser is embedded, with a number of thermocouple beads attached to the condenser wall. In the second setting, the condenser resistances are determined based on the wall temperatures measured outside either end of the cold plate. The third setting adopts a water jacket with a number of thermocouples attached to the condenser wall but exposed to the cooling water. These three test settings have been applied in the literature. The second setting fails to count in the thermal resistances across the wick and pipe wall, and thereby seriously under-estimated the condenser resistances. For the third setting, the temperature readings are lowered by the cooling water so that the condenser resistances are greatly over-estimated. However, a fourth setting with the cooling-protected thermocouples yields similar results obtained using the standard setting. These results suggest that thermocouples be suitably arranged to ensure reliable performance measurements for the heat pipe condenser.
Modification of Near-Wall Turbulent Structure in Channel Flow by Dosing a Small Amount of Polymer Solution
Authors: Okamura Yushi , Kurose Tomohiro , Kawaguchi Yasuo
Published: October 2017

The phenomenon known as Toms effect can impart viscoelasticity to a water flow when a small amount of water-soluble polymer is added. The resulting viscoelastic fluid generates viscoelastic stress in the flow, dramatically reducing the turbulent stress.

In this study, the spatial distribution of velocity is measured using a stereo-PIV method in the streamwise-spanwise plane parallel to the wall. Modification of the near wall turbulence by the polymer solution blown slowly from a permeable wall was investigated by analyzing the velocity distribution acquired by stereo-PIV measurements.

Experimental results reveal that streamwise local mean velocity decreases as the dosed polymer concentration increases. The skewness factor at this height shifts from 0 to positive by adding the polymer, which indicates intensified turbulent coherent structure. Moreover, the spatial two-point correlation function calculated from streamwise velocity fluctuations maintains its high correlation with the streamwise direction. It is consistent with the finding from the instantaneous velocity distribution, which shows that the flection of low-speed streaks is suppressed. Next, it is revealed that the normal velocity at the wall for low-speed fluid is decreased dramatically by polymer additives. Moreover, applying the quadrant analysis, it is confirmed that ejection events are suppressed with decreasing normal velocity at the wall. Suppression of ejection motion affects to the turbulence in the log law layer. We conclude that this is one reason that turbulence is suppressed in a wide range of the shear layer by polymer additives present only in the vicinity of the wall.
A General Frictional Pressure Drop Correlation for Condensation in Microfin Tubes
Authors: Sun Zhichuan , Li Wei
Published: October 2017

Experimental pressure drop data of condensation from the previous literature were collected to develop a general frictional pressure drop correlation for horizontal micro-fin tubes. The collected database contained 481 data points, covering nine working fluids at average saturated condensing temperatures ranging between 14 and 65°C, with mass velocities ranging from 50 to 800 kg/m2s, and average vapor qualities from 0.11 to 0.91. The hydraulic diameter of micro-fin tubes varied from 2.16 to 5.67 mm and was employed in the calculation of Reynolds number. The Fanning frictional factor was calculated by adopting the Churchill model with the empirically fitted relative roughness. Four existing pressure drop correlations developed for micro-fin tubes were evaluated by the database for condensation in micro-fin tubes. The correlation proposed by Cavallini et al. was the best prediction model among them, predicting 85.6% of the collected data points within the 30% error band. In addition, a new correlation based on the Martnelli parameter Xtt modified by incorporating the reduced pressure was proposed to predict the present database, which showed a good agreement.
CFD Analysis and Experimental Comparison of a Large Centrifugal Pump
Authors: Rocco Giuseppe , Schiavello Bruno , Pirola Davide , Cicatelli Giancarlo
Published: October 2017

The design of a large size centrifugal pump with conflictual requirements from customized specifications is a hard engineering challenge. Centrifugal pumps are the most commonly used in different industrial fields like power generation, oil & gas, chemical plants, desalination, pipeline, water treatment, agriculture, automotive, aerospace, and domestic applications. On the other hand, centrifugal pumps are a very complex type of turbomachines in which mechanical energy is converted into pressure energy by means of blades action and angular momentum change. To design and develop a centrifugal pump, it is very important to have a long experience and ability to predict the final performance with good accuracy. The design can be very complex because the flow in a centrifugal pump is a very complex turbulent, three dimensional and time-dependent flows. The primary purpose of this paper is to show a comparison between numerical analysis performed by means of a commercial code and the experimental results obtained during the testing phase of a very large in-line centrifugal pump, including suction casing - double suction impeller - double volute - discharge branch diffuser. The key focus will be in the comparison between test measurements and numerical results in term of overall performance (head, power and efficiency) as verification and validation of the CFD simulation for future applications.
Experimental Investigation of the Influence of Inflow Conditions on the Flow Over an Extended Edge Escarpment
Authors: LoTufo J. , Siddiqui K. , Hangan H.
Published: October 2017

Mean and turbulent flow behavior over a 1:50 scale model of a wind turbine site containing a local escarpment was investigated from wind directions of 230°, 270° and 300°. Flow from each direction contained vastly different local geometry at the same elevation.

Results showed separation regions are formed immediately downstream of the escarpment at each wind direction. It is observed that turbulence within the first 3 meters from the escarpment edge is strongest for inflow from 230° while flow from 300° shows similar trends with lower turbulence magnitude. Inflow from 270° had the most impactful effect on the flow behavior showing the largest wake region increasing in height with the distance from the leading edge. The results also show that the flow field below 55 m was effected by the local geometry of the escarpment leading up to and likely beyond the turbine location. It is concluded that the effects induced from local geometry may cause changes to dynamic loading and fatigue on both the turbine blades and tower.
Geometry Effects on Thermal Striping in Nuclear Reactors: POD Analysis of Large-Eddy Simulations and Experiments
Authors: Marin Oana , Merzari Elia , Obabko Aleks , Alvarez Andres , Lomperski Stephen , Fischer Paul
Published: October 2017

Thermal striping is of particular significance in nuclear reactor applications, primarily in sodium cooled fast reactors. The mixing chamber of the upper plenum of a nuclear reactor can be subjected to thermal striping unless designed such that the coolant is sufficiently mixed prior to reaching the top wall of the upper plenum. In order to conduct a systematic analysis of this phenomenon a simplified experimental set-up was designed and built at Argonne National Laboratory. In a parallel effort a similar simulation was conducted using the spectral-element code Nek5000. The set-up consists of two turbulent jets entering a rectangular tank via two hexagonal inlets, the interesting phenomena being the mixing within the tank. Two different inlet geometries were studied previously, both experimentally and via high-fidelity large-eddy simulations reporting various turbulent statistical quantities. To further assess the flow behavior we hereby perform a Proper Orthogonal Decomposition (POD) to identify the most dominant energetic modes and quantify their impact on the top wall of the upper plenum. The POD analysis of the experimental data in both inlet geometrical configurations is compared with LES and presented to highlight the impact of geometry on the velocity and thermal fields. We find a qualitative coherence between both simulation and experiment, characterized by a strong backflow in the weakly stable geometry, as indicated by the first mode, and the presence of three stagnation points in the strongly stable geometry setup. Also we identify a pairing of modes 1 and 3 with higher frequency than the second mode. This pairing is opposite in the two flow configurations leading to a faster decay of one of the jets in one case and a stable flow in the other.
Turbulent Flow Behaviour in a Pipe Fully Submerged in a Hot Fluid
Authors: Steen Benjamin , Siddiqui Kamran
Published: October 2017

We report on an experimental study conducted to investigate the flow behaviour in a heat exchanger pipe submerged in a hot stagnant fluid. Particle Image Velocimetry (PIV) was used to measure the two-dimensional velocity field in the mid-vertical plane of the tube. Fluid temperatures in the cross-sectional plane were also measured using thermocouples. The mode of heat transfer into the pipe was mixed convection where both inertia and buoyancy contributed to the convection. The results show that when the contribution of buoyancy-driven flow (natural convection) was smaller than that of the inertia-driven flow (forced convection), in an originally turbulent flow, the shear-induced turbulence dominated the flow and the turbulent velocity profile was not influenced by the heat input. In an originally laminar flow, the role of buoyancy was primarily limited to the initiation of instabilities in the laminar flow to trigger the turbulence transition. The temperature profiles indicate the presence of stably stratified layer inside the pipe in originally laminar flow regime that suppressed the heat transfer rate. In originally turbulent regime, the fluid temperature field was nearly uniform indicating efficient flow mixing.
Effect of Drip Line Hydrocyclone Design on Head Loss for Agricultural Irrigation
Authors: Ramirez Christian , Law Deify
Published: October 2017

In the present work, computational fluid dynamics (CFD) analysis of an existing drip line hydrocyclone is performed in order to improve the current design for agricultural irrigation by understanding the effect of water flow rate on pressure drop and head loss. When water flows through a pipe, the pressure continuously drops in the stream-wise direction because of friction along the walls of the pipe. It is common to express this pressure drop in terms of an irreversible head loss. Numerical simulations are performed using the commercial CFD code ANSYS FLUENT with the finite volume method. The pressure drops of the hydrocyclone are computed numerically and they are in reasonable agreement with the experimental data provided by the Center for Irrigation Technology at Fresno State. For example, the measured pressure drop across the part is approximately 2.76 × 104 Pa at 1.89 × 10−4 m3/s inlet flow rate whereas the numerical pressure drop is roughly 2.62 × 104 Pa at 1.89 × 10−4 m3/s. Additionally, the present work shows head loss reduction by making changes to the existing hydrocyclone design including the length and diameter of the cavity as well as length of the outlet tube.
Next-Generation Multiphase Flow Solver for Fluidized Bed Applications
Authors: Kotteda V. M. Krushnarao , Chattopadhyay Ashesh , Kumar Vinod , Spotz William
Published: October 2017

A framework is developed to integrate MFiX (Multiphase Flow with Interphase eXchanges) with advanced linear solvers in Trilinos. MFiX is a widely used open source general purpose multiphase solver developed by National Energy Technology Laboratories and written in Fortran. Trilinos is an objected-oriented open source software development platform from Sandia National Laboratories for solving large scale multiphysics problems. The framework handles the different data structures in Fortran and C++ and exchanges the information from MFiX to Trilinos and vice versa. The integrated solver, called MFiX-Trilinos hereafter, provides next-generation computational capabilities including scalable linear solvers for distributed memory massively parallel computers. In this paper, the solution from the standard linear solvers in MFiX-Trilinos is validated against the same from MFiX for 2D and 3D fluidized bed problems. The standard iterative solvers considered in this work are Bi-Conjugate Gradient Stabilized (BiCGStab) and Generalized minimal residual methods (GMRES) as the matrix is non-symmetric in nature. The stopping criterion set for the iterative solvers is same. It is observed that the solution from the integrated solver and MFiX is in good agreement.
Numerical Study of Hydrodynamic Instabilities in Converging Geometry
Authors: Proano Erik S. , Rollin Bertrand
Published: October 2017

This work presents simulations of a heavy gas, SF6, immersed within a light gas, air, under the effect of a converging shock wave. Upon interaction of the shock wave with the perturbed interface between air and SF6, Richtmyer-Meshkov instability (RMI) and, later, Rayleigh-Taylor instability (RTI) take place. More precisely, a succession of RMI and RTI occurs due to multiple shock and rarefaction waves, and gives rise to mixing between the heavy and light fluids. The problem of hydrodynamic instability-induced mixing in converging geometry is particularly relevant to engineering applications such as the process of nuclear fusion by the inertial confinement approach. This study is motivated by the need to better understand the relation between the initial perturbations at the interface between the fluids and the development of the instabilities and mixing in a converging geometry. Using the Flash Code, a PPM hydrodynamic solver developed by the ASC center at the University of Chicago [1], this study focuses on the growth rate of instabilities and the subsequent mixing associated with various carefully designed initial interfacial perturbations in the implosion configuration described above. In cylindrical geometry, comparisons between the growth of high and low frequency single mode perturbations are presented. It is found that at later times, after RMI and RTI take place, the width of the mixing layer is the largest for the low-wavenumber initial interface perturbation. Also, simulations show that the SF6 target with the highest wavenumber perturbation presents the most mixing at the later times but the lowest wavenumber initial interface perturbation presents the most mixing before reshock.
Large Eddy Structure Appearing in Meandering Motion of High Reynolds Number Viscoelastic Flow Past a Backward-Facing Step
Authors: Onishi Shohei , Ii Ryusuke , Hara Shumpei , Tsukahara Takahiro , Kawaguchi Yasuo
Published: October 2017

The addition of a small amount of surfactant into water induces viscoelasticity. In turbulent channel and pipe flows, the wall friction significantly decreases with the surfactant additive, but a heat-transfer reduction also occurs. On the other hand, a phenomenon is reported that the instantaneous main flow broadly meanders in space and time under a certain condition in the surfactant solution flow past a backward-facing step (BFS); thus, the mean Reynolds shear stress remarkably increases. The influence of such a phenomenon cannot be neglected in thermal fluid equipment with usually complicated configurations. Therefore, understanding this phenomenon in detail is important both academically and industrially. In this study, particle image velocimetry measurements were carried out in a viscoelastic BFS flow with meandering phenomenon at high Reynolds number. We focused on the turbulent structures in the flow fields and investigated the interrelationship among the spatial scales of the eddy structures, Reynolds shear stress, and meandering motion using a spatial two-point correlation function or conditional averaging. In the meandering condition, we revealed that the Reynolds shear stress due to the low-speed fluid that departs from the upper wall opposite the step across the main flow contributes the largest to the mean Reynolds shear stress value. Then, a secondary recirculation region appears near the upper wall, in addition to the primary recirculation region. A reverse flow is apt to occur when rapid deceleration and pressure rise happens due to the sudden expansion of the channel cross section. Therefore, flow separation occurs at the upper wall, and a large-scale circulation appears there. Such flow is caused by the relationship between the pressure rise and the momentum transfer between the flow and the wall. We can conclude that the condition where an unstable motion occurs is influenced by the concentration of the surfactant solution because the surfactant additive acts on the shear stress.
The Two-Dimensional Aerodynamic Analysis of Various Cross-Sections of a Morphologically Accurate Bee Wing in Forward Flight
Authors: Feaster Jeffrey , Battaglia Francine , Bayandor Javid
Published: October 2017

Bees sustain flight at extremely low Reynolds Numbers (500<Re<10,000) using three degrees of freedom and a flap frequency between 100 and 200 Hz. These combined mechanics create a complex vortex field that results in extraordinary agility and flight efficiency. In addition to agility and efficiency, bees are able to carry loads up to 80% of their body weight for miles making bee flight a very interesting subject area for drone and UAV related development. In order to better understand these complex fluid dynamics, Fluent is utilized to resolve the flow fields during forward flight for 4 anatomically accurate cross-sections of the bee wing at a speed of 1 m/s in two-dimensional flow. Each of the four cross-sections are taken at regular 1/6th wingspan intervals from the anatomically accurate bee wing model. The bee wing model was generated from a μCT scan of Bombus pensylvanicus with generalized bee kinematics presented in the literature. The kinematics applied to each cross-section are adjusted for the change in radial distance from the wing base. The presented analysis and discussion investigates the effects of the variation in cross-section and kinematics over the wing on vortex-shedding dynamics, and instantaneous aerodynamic forces.