bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Mode Repulsion of Ultrasonic-Guided Waves in Pipe Bends
Authors: Wu Wenjun , Zhu Longxiang , Wang Yuemin
Published: November 2019

The wave motion of guided waves in pipe bends is still veiled in some mystery, which hinders the application of guided-wave techniques in the inspection of pipelines with bends. Mode repulsion, which exists in the wavenumber versus frequency dispersion curves of guided waves in pipe bends, is an intriguing phenomenon deserving in depth study. The governing equation of wave motion in pipe bends, deduced by the semi-analytical finite element (SAFE) method, can be regarded as an eigenvalue problem. The eigenvalue derivatives, with respect to the wavenumber, are investigated to determine whether mode repulsion will occur or not. A term in the second derivative of the eigenvalue is identified to determine the mode repulsions. With respect to symmetry, it is found that mode repulsion only occurs between modes of one and the same type, such as symmetric or antisymmetric modes, and does not occur between modes of different type, like between symmetric and antisymmetric modes. A specific case of mode repulsion in a small-bore thin-walled pipe in the low-frequency range, where relatively fewer modes exist, is further studied, and the interactions between these modes are clarified. The evolutions of mode shapes before and after mode repulsion are further illustrated.
Estimating Laminar Flame Speed and Ignition Delay for a Series of Natural Gas Mixtures at IC Engine-Relevant Conditions
Authors: Fieseler Kelsey , Linker Taylor , Patterson Mark , Rem Daniel , Jacobs Timothy J.
Published: November 2019

Two equations are developed to estimate laminar flame speed and ignition delay for different alkane mixtures at a range of engine-relevant conditions. Fuel mixtures of methane, ethane, propane, butane, and pentane were selected by analyzing the natural gas composition in a natural gas pipeline located in the Midwestern United States. The laminar flame speed and ignition delay were calculated for each mixture at each set of conditions using Cantera, a chemical kinetics solver. The range of initial conditions for laminar flame speed includes temperatures from 300 to 700 K, pressures from 1 to 40 bar, equivalence ratios from 0.4 to 1.2, and residual fractions from 0% to 20%. These data were then fit to a non-linear regression. The range of initial conditions for the ignition delay equation includes temperatures from 1100 to 2000 K, pressures from 1 to 40 bar, equivalence ratios from 0.4 to 1.15, and residual fractions from 0% to 20%. These data were fit to a previously developed equation. Sensitivity studies were conducted on each equation to quantify the impact of the independent variables on the target variable. This showed that, for laminar flame speed, the initial pressure, temperature, and equivalence ratio had the largest impact, with fuel composition having a lesser impact. For ignition delay, the temperature and pressure were shown to have the largest impact. There is a room for improvement, namely, increasing the fuel mixture variability and range of initial conditions, and developing a better fit to the data.
Passive Pitching Mechanism of Three-Dimensional Flapping Wings in Hovering Flight
Authors: Li Chengyu , Wang Junshi , Liu Geng , Deng Xiaolong , Dong Haibo
Published: November 2019

Flapping wings of insects can passively maintain a high angle of attack due to the torsional flexibility of wing basal region without the aid of the active pitching motion. However, the lift force generated by such passive pitching motion has not been well explored in the literature. Consequently, there is no clear understanding of how torsional wing flexibility should be designed for optimal performance. In this work, a computational study was conducted to investigate the passive pitching mechanism of flapping wings in hovering flight using a torsional spring model. The torsional wing flexibility was characterized by Cauchy number. The impacts of the inertial effect of wings were evaluated using the mass ratio. The aerodynamic forces and associated unsteady flow structures were simulated by an in-house immersed-boundary-method based computational fluid dynamic solver. A parametric study on the Cauchy number was performed with a Reynolds number of 300 at a mass ratio of 1.0, which covers a wide range of species of insect wings. According to the analysis of the aerodynamic performance, we found that the optimal lift can be achieved at a Cauchy number around 0.16, while the optimal efficiency in terms of lift-to-power ratio was reached at a Cauchy number around 0.3. All the corresponding wing pitching kinematics had a pitching magnitude around 60 degrees with slightly advanced rotation. In addition, 3D wake structures generated by the passive flapping wings were analyzed in detail. The findings of this work could provide important implications for designing more efficient flapping-wing micro air vehicles.
Investigation on the Characteristic of Bubbles in Horizontal Channel Flow by Fiber Optic Sensor
Authors: Hiroi Takamichi , Hamada Tatsuya , Kawakita Chiharu
Published: November 2019

Friction drag and characteristic of bubbles in horizontal water channel are investigated at bulk liquid velocity Um = 1 ∼ 5 m/s (Reynolds number Rem = 16,000 ∼ 120,000 (based on the channel height)) and mean void fraction α = 0.5, 1, 2 %. Firstly, shear stress sensor is applied to investigate the relation between friction drag with bubbles and bulk liquid velocity. Friction drag in the bubbly flow is larger than it in the single-phase flow at Um = 1 ∼ 2 m/s. It in the bubbly flow, however, decreases with the mean liquid velocity. Furthermore, it in bubbly flow is smaller than it in the single-phase flow at Um ≥ 3 m/s. Secondly, fiber optic sensor is applied to investigate the void fraction distribution, bubble diameter distribution and streamwise velocity of bubbles. The peak value of the void fraction decreases with increasing of the bulk liquid velocity at Um = 2 ∼ 5 m/s. Bubbles exist in only y/δ = 0 ∼ 0.5 at Um = 1, 2 m/s. The mean bubble velocity increases with the bulk liquid velocity. The mean Sauter diameter decreases with increasing of the bulk liquid velocity. It appears that the high void ratio near the wall causes the increasing of drag and friction drag decreases when bubbles exist in whole of upper half of channel.
Cryogenic Pumps Monitoring, Diagnostics and Expert Systems Using Motor Current Signature Analyses and Vibration Analyses
Authors: Popaleny Peter , Péton Nicolas
Published: November 2019

The paper discusses the Cryogenic Pumps Condition Monitoring and Machinery Diagnostics Systems, including the automated Expert Diagnostics Systems. The Cryogenic Pump construction differs by design, failure modes and criticality and no single solution will suit all designs. Therefore, two approaches are discussed: Motor Current Signature Analyses and Vibration Analyses. The paper further shows the real case studies, diagnostics and findings on Cryogenic Pumps using both analyses.

The article addresses common failure types and proposes applicable solutions. The Cryogenic Pumps mechanical and electrical malfunctions are discussed, their reflection on the dynamic current spectrum using improved Motor Current Signature Analysis (MCSA), aka. Model-Based Voltage and Current (MBVI) Analyses and vibration spectrum using Vibration Analyses (VA). The article contrasts the similarities vs. differences and advantages vs. disadvantages of both methods and may be of value for field engineers to understand the pros. and cons. of each technology.

The paper outlines the Expert Diagnostics System based on MBVI, able to distinguish automatically among different malfunctions. The Expert System uses the power spectral density of the difference between the expected current obtained from the model and the actual current. These differences include only abnormalities generated by the motor anomaly. Therefore, they are immune to the noise or harmonics present in the supply voltages.

The presented results, using both approaches: Model-Based Voltage and Current Analyses and Vibration Analyses, prove the potential of both techniques and the advantages of their combined use for reaching a maximum reliable Condition Monitoring and Diagnostics of Cryogenic Pumps.
Effect of Reactor Thickness on Gas-Solid Flow and Heat Transfer of Thin Rectangular Fluidized Bed Reactors for CO2 Capture
Authors: Choi Seungyeong , Bang Minho , Kim Kiwoong , Park Yong-Ki , Cho Hyung Hee
Published: November 2019

Thermal design of dual circulating fluidized bed reactors for carbon dioxide (CO2) capture was carried out. To handle large heat duties for regeneration, a thin rectangular reactor was proposed. For feasible thermal design, the effect of varying reactor thickness on the gas-solid flow and heat transfer of the thin rectangular fluidized bed was investigated. Reactor thickness of 10, 30, and 60 mm was tested. Numerical simulations were conducted to analyze the pressure difference, solid particle hold-up distribution, particle velocity, granular temperature, and heat transfer in detail. According to our results, when the reactor is between 10 mm and 30 mm thick, a large solid hold-up occurs adjacent to the narrow wall. This causes a large pressure difference due to the wall effect. Furthermore, the particle velocities were analyzed to evaluate that there is the two-dimensional (2D) particle mixing behaviors. On the other hand, in the case of reactors with a thickness of 60 mm, tuning flows occur adjacent to the narrow wall. This reduced the pressure difference and the three-dimensional (3D) particle mixing behaviors. This difference in particle behavior affected heat transfer. In the case of reactor thicknesses between 10 mm and 30 mm, the heat transfer increased with the reactor thickness. In particular, the heat transfer at the narrow wall of the reactor with a thickness of 10 mm was extremely low due to the low particle mixing. On the other hand, there was more heat transfer with a thickness at the 60 mm wall, despite the low solid hold-up.
Assessment of Compressible RANS and LES Methods for Organic Vapor Flows Past a NACA4412 Airfoil
Authors: Hasselmann Karsten , aus der Wiesche Stefan , Kenig Eugeny Y.
Published: November 2019

In this contribution, an assessment of compressible Reynolds Averaged Navier Stokes equations (RANS) and Large Eddy Simulation (LES) is presented using transonic organic vapor flow past a NACA4412 airfoil as a case study. The NACA4412 represents a canonical geometry, which, in case of air, has been well investigated numerically and experimentally. The results of the real gas simulations are compared with those of air simulations. For the real gas, the organic vapor Novec 649® is chosen as a representative fluid. The thermodynamic behavior of Novec 649® is modeled with the Peng-Robinson equation of state. Different inlet Mach numbers are applied, namely, a sub-critical, the critical, and a super-critical Mach number. It turns out, that the critical Mach number of the NACA4412 airfoil increases when Novec 649® is used as working fluid. Furthermore, it is shown that real gas flow simulations cause additional difficulties for the computational fluid dynamics (CFD) analysis. Although the speed of sound of Novec 649® is lower than the speed of sound of air, a finer grid resolution is required for the real gas simulations due to its high density. Based on an extensive simulation study, an assessment of different numerical modelling strategies and methods is given.
Simulation-Based Approach to Science, Technology, Engineering, and Math Challenges
Authors: Milanovic Ivana , Eppes Tom , Wright Kamau
Published: November 2019

This paper discusses an undergraduate mechanical engineering (ME) curricular sequence of four required and four elective courses (4+4) in the area of modeling, simulation, and application development with the focus on the thermo-fluids topics. The purpose is early and consistent integration of knowledge and modern computational skills across curriculum. This approach facilitates a deeper understanding of complex theoretical concepts and engineering solutions by embedding modeling and simulations in required courses from the freshmen to the junior year. Professional electives provide an additional opportunity to apply the same strategy either in the concentration format or in one-off courses that individual students may decide to take.

The sequence starts with four courses that are required for all ME majors: Graphic Communication, Computer-Aided Design and Analysis, Fluid Mechanics, and Heat Transfer. Four additional courses are technical electives and a part of an undergraduate Computational Mechanical Engineering (Comp ME) concentration: Applied CFD, Multidisciplinary Modeling, Finite Element Analysis, and Convective Heat and Momentum Transfer. The first two required courses, Graphic Communication and Computer-Aided Design and Analysis, provide the foundation in model development. There can also be opportunities to embed simulations as a part select sophomore level courses, such as Thermo-dynamics. In the third year thermo-fluids sequence, as well as in the Comp ME technical electives, students gain experience creating models of new and existing systems, visualizing simulation results, going through the process of verification and validation, optimizing solutions, and building applications.

We will first present the rationale for adopting a simulation-based approach to Science, Technology, Engineering, and Math (STEM) challenges. Second, we will show how this high-impact approach can be implemented without additional labor-intensive work on the part of faculty members. Finally, special attention will be devoted to the required and elective thermo-fluids courses that use COMSOL Multiphysics® as the software platform. In each course, a series of models are created and documented in technical reports. Applications are also built based on the underlying models to complete the experience. The paper provides a detailed description of the technical content in each course, learning strategies, expected outcomes, and assessment criteria. Several examples illustrating student work are presented. How and why the courses evolved and were improved over time is included. Lastly, the importance and value of this approach in view of changes coming to the ABET criteria is discussed.
Redesign and Performance Analysis of Medium Flow Coefficient Centrifugal Compressor
Authors: Yousef Khaled , Engeda Abraham , Hegazy Ahmed
Published: November 2019

In-house design/analysis program is used in this study to redesign and predict the entire performance of an existing centrifugal compressor. The centrifugal compressor experimental data from a cooperative company is validated first with the 3D CFD simulation for a single passage flow. The validation shows an acceptable performance discrepancy between experimental data and CFD for the existing impeller. Then, a redesign procedure by the in-house program is carried out to get more efficient impeller based on the experimental data. This redesigned impeller is re-implemented in the CFD simulation to be compared with in-house program analysis data. The validation shows a good performance comparison between CFD and in-house program for the redesigned impeller. Moreover, this procedure succeeds to improve the redesigned stage efficiency and work coefficient with 6.79%, and 10.55% compared to the experimental impeller, respectively.
Experimental Tests With Centrifugal Pumps: Degradation of Performance, Instability and Dynamic Phenomena With Non-Newtonian Suspensions of Kaolin in Water
Authors: Occari Matteo , Munari Enrico , Mazzanti Valentina , Pinelli Michele , Mollica Francesco , Suman Alessio
Published: November 2019

The performance of pumps when working with non-Newtonian fluids significantly change with respect to water. In several experimental tests with non-Newtonian fluids, significant deration of head and the presence of head instability were observed. The present work aims to better understand this phenomenon since the reasons that originate it are not clear. Two small size centrifugal pumps were experimentally tested with different mixtures of kaolin-in-water, which showed a verified non-Newtonian behavior. The rheology of the mixtures and the particle size distribution of kaolin powder were measured to characterize the fluids. Similar to previous tests, a strong reduction of head and the appearance of instability were observed at low flow rates and, in some cases, also at higher flow rates. This behavior was related to the presence of air trapped into the fluid that, within the pump, generated a phenomenon known as gas-locking, which in literature it has been studied in detail with water but not with non-Newtonian fluids. Moreover, in some working conditions, non-stable time-varying phenomena are observed and their consequence on performance commented. Comparing the two pumps, characterized by a similar specific speed but by a different geometry, the head drop manifested itself with different intensity.
Recapitulation of Trophoblast Invasion During Pregnancy in a Physiological Hypoxia Induced Microfluidic Device
Authors: Woo Jin Hyuk , Lee Insu , Kim Sun Min , Jeon Tae-Joon
Published: November 2019

Trophoblast invasion and remodeling of uterine spiral artery is closely related to the healthy pregnancy and normal development of fetus. However, if the trophoblast invasion is inhibited and the spiral artery remodeling process is not sufficiently done, this promotes grave pregnancy diseases such as pre-eclampsia.

In this research we focused on one of the major factors that affect trophoblast invasion, oxygen concentration. We designed a microfluidic device fabricated with Polydimethylsiloxane (PDMS) which can mimic the microenvironment of the placenta and control physiological oxygen concentration. Human umbilical vessel cells (HUVEC) and trophoblasts (HTR-8) were cultured inside the microfluidic device to recapitulate the placental microenvironment. HUVECs and trophoblasts were co-cultured under normoxic and hypoxic condition to recapitulated trophoblast invasion. We anticipate this device to be utilized as a research model for improve our understandings on mechanisms of trophoblast invasion and a possible platform for developing treatment methods and medicines for pregnancy disorders.
Phenomenological Prediction of Convective Heat and Mass Transfer to Taylor Bubbles Rising in Vertical Pipes
Authors: Kendoush Abdullah Abbas
Published: November 2019

Phenomenological equations derived for the convective heat and mass transfer to Taylor bubbles (TB) rising in vertical cylindrical pipes. Three models presented; first for the bubble thin liquid layer region, second for the rounded nose region, and third for the wake region. The solution is confined to flat-ended Taylor bubbles under laminar flow and constant heat flux conditions. The results compared reasonably well with the experimental data of other investigators.
Experimental Investigations on Friction Drag Reduction on an Airfoil by Passive Blowing
Authors: Hirokawa Shiho , Eto Kaoruko , Fukagata Koji , Tokugawa Naoko
Published: November 2019

Friction drag reduction effect of a passive blowing on a Clark-Y airfoil is investigated. The passive blowing is conducted by the pressure difference on a wing surface between suction and blowing regions. The suction and the blowing regions are respectively set around the leading edge and the rear part of the upper surface. The Reynolds number based on the chord length is 0.65 × 106 and 1.54 × 106. The angle of attack is set to 0° and 6°. The mean velocity profiles on the blowing region and the downstream are shifted away from the wall by the passive blowing. This behavior qualitatively suggests local reduction of skin friction on the wing surface. As a result of the quantitative assessment, which takes into account the effects of pressure gradient and the roughness of the wall, the local friction drag reduction effect of passive blowing is estimated to reach 4%–23%.
Effects of Curvature Radius of Volute Profile on Aerodynamic Performance of Squirrel Cage Fan
Authors: Wang Ke , Ju Yaping , Zhang Chuhua
Published: November 2019

Volute profile exerts great influences on flow losses and aerodynamic performance of squirrel cage fan. In practical, equilateral- or inequilateral-element method is usually applied to design the volute profile for convenient manufacture. This kind of volute profile consists of several arc segments, however, is discontinuous for curvature radius at the junctions of adjacent arc segments. To overcome this issue, we propose a new volute profiling method to guarantee the continuity of curvature radius along the whole volute profile. By means of three-dimensional computation fluid dynamic simulations, the proposed method is validated through comprehensive comparisons of aerodynamic performances and flow fields of squirrel cage fans with and without continuous curvature radius of volute profile. The results show that the continuous curvature radius of volute profile is of benefit to the aerodynamic performance increase of squirrel cage fan. The velocity downstream the volute tongue is improved. The local sudden diffusion-expansion around the junctions of volute arc segments nearly disappears with continuous increase of static pressure along the volute wall.
Multiple Shock Waves and its Unsteady Characteristics in Internal Flows
Authors: James Jintu K. , Kim Heuy Dong
Published: November 2019

Shock wave turbulent boundary layer interaction is a fundamental phenomenon observed in most of the gas dynamics applications such as wind tunnels, supersonic air intakes, transonic airfoil, nozzle flows, etc. The flow field and shock wave pattern in a constant area duct are analyzed experimentally. The focus of the present study is to present the time-resolved flow characteristics of the multiple shock waves and its oscillations. High-speed Schlieren flow visualization is used to capture the transient shock structure in the wind tunnel constant area test section. A gradient-based image processing was incorporated to capture the shock excursion details. Results indicate that the shock pattern is unsymmetrical in the flow field. The foot of the lambda shock wave in the upper and lower exhibit a difference in axial location and there is a large difference in this value at the mean position when the shock moves in the upstream direction compared to the downstream movement.
Vortical Structure Characteristics of Transitional Flow Through Porous Media
Authors: Ziazi Reza M. , Liburdy James A.
Published: November 2019

The flow characteristics in the inertial Reynolds number regime are investigated in a mono-dispersed random pack porous media. Time-resolved particle image velocimetry (PIV) is used to visualize the velocity field in a low aspect ratio bed with 15 mm glass beads. An aqueous solution of Ammunium Thiocynante is used as the working fluid to facilitate matching the solid-fluid refractiveindices. In order to illuminate the inertial regime characteristics, two pore Reynolds number of 100 and 270 are examined. Also, due to the random nature of the packing several pore geometries are compared to identify local scaling used to define the inertial regime effects. Discrete vortical flow structures are evaluated using LES (lowpass filtering) decomposition, in conjunction with criticalpoint analysis of the local velocity gradient tensor. The identified scales associated with the vortical elements are compared based on Reynolds number and pore geometry. Implementing circulation as an integral measure of all vortical structures locally at the pore-scale level demonstrated a linear attitude over the range of Reynolds numbers. Evolution of inertial effects within pore-regions are indicated to be the primary driving mechanism for the emergence of swirling structures passing through the PIV field of view at the onset of turbulence.
Development of a New Exhaust Air System for Combined Air Compressor and Dryer System
Authors: Steppert Michael , Epple Philipp , Steber Michael , Florschuetz Michael , Schneider Felix , Habrock Kevin , Ruppelt Erwin , Eideloth Sebastian , Seitz Anja
Published: November 2019

In this work a new exhaust air system for rotary screw compressors with integrated refrigeration dryers has been developed. The new system unites both, the exhaust air flow out of the compressor and out of the refrigeration drier and in such a way the overall exhaust air and hence the overall heat are exhausted through one single air duct. For the development of the system, the ASD 50 T SFC compressor system from KAESER Kompressoren SE [1] was used. Because of the slight overpressure in the exhaust air duct due to the cooling radial fan in the compressor, a jet pump was designed and placed into the main exhaust air duct to reduce the static pressure in the main duct. In such a way, after the jet pump the exhaust air of the refrigeration drier is sucked into the main exhaust air duct through an intake fitting. The nozzle and the intake fitting of the exhaust air duct were first designed by using the commercial CFD solver CFX from ANSYS. The nozzle length, angle and diameter were varied to determine the best geometry. In order to validate the components designed by CFD simulations, three of the designs were manufactured and measured in the compressor laboratory at Coburg University. Therefor heat and velocity measurements in the exhaust air ducts have been done. Also the flow of the exhaust air was visualized using smoke and laser sheets. The simulation and experimental results are shown in detail in this work.
Computational Studies of Droplet Motion Near a Rough Surface via 3D Spectral Boundary Elements
Authors: Wang Yechun , Wang Xinnan
Published: November 2019

A plethora of studies have investigated the motion of a liquid droplet in the vicinity of a smooth surface, incurred by shear flow, parabolic flow or gravity. However, there are few studies that consider the roughness of the surface that could affect the droplet motion. In this study, we employ a 3D spectral boundary element method for interfacial dynamics to examine the droplet translation, migration, and deformation in the vicinity of a rough surface due to shear flow. The roughness feature of the surface is comparable to the size of the droplet and is simulated with sinusoidal functions. Topologies of epoxy coating surfaces are also considered in the computations. The roughness and profile of the coating surface is obtained by atomic force microscopy. The computational results show that the surface roughness affects significantly the behavior of a deformable droplet near the surface, including its deformation and migration speed. In return, the dynamics of the droplet also influences the stress distribution on the rough surface. The results of this study could provide theoretical foundation in the prediction of particle induced erosion corrosion of organic coatings.
Effects of Liquid Viscosity on Laser-Induced Shock Dynamics
Authors: Kurahara Hiroki , Ando Keita
Published: November 2019

We experimentally study the effects of viscosity on laser-induced shockwave in glycerol-water solution. A shockwave is generated through rapid expansion of plasma, which is induced by focusing a 6 ns pulse laser (532 nm) of energy fixed at 1.66 ± 0.22 mJ into 80, 90, 100 wt% glycerol-water solution. The shockwave propagation is recorded by an ultra-high-speed camera taken at 100 Mfps together with a pulse laser stroboscope. The photographs are used to determine the shock front position as a function of time, which allows for calculating the shock pressure according to the stiffened-gas type Rankine-Hugoniot relation. It turns out that the initial plasma pressure is reduced by having higher glycerol concentration (i.e., higher viscosity); therefore, wave steepening effect is deemphasized, resulting in a smaller decay rate.
Dynamics of Forced Imbibition in Interacting Pores
Authors: Ambekar Aniket S. , Ashraf Shabina , Phirani Jyoti
Published: November 2019

Imbibition of viscous fluids in capillaries is important in diagnostics, design of microfluidic devices and enhanced oil recovery. The imbibition of a viscous wetting fluid in a capillary follows Lucas-Washburn law. The Lucas-Washburn regime is only observed when the viscous forces are balanced by the capillary forces. This has been previously described for capillary driven flow as a function of the Ohnesorge number (Oh), the length imbibed by the fluid (x) and the radius (r), for a capillary initially filled with fluid of negligible viscosity, i.e., Ohxr∼1. We show using VOF simulations that, in a capillary of length L initially filled with a viscous fluid, the modified Lucas-Washburn law is observed only if the criterion OhLr∼1 is fulfilled. We use VOF simulations to show the deviation of capillary driven flow from the classical Lucas-Washburn behavior for OhLr∼0.1. VOF simulations for forced imbibition in the regime preceding the Lucas-Washburn regime for a single capillary show that with increase in the applied pressure, the advancement of the meniscus is faster. Forced imbibition dynamics in the interacting capillary geometry are also investigated in this study using VOF simulations. We observe that the leading meniscus in the interacting capillaries is significantly dependent on the applied pressures. We also show using VOF simulations that the wettability of the imbibing fluid plays a crucial role in determining the dynamics in an interacting capillary system.
Influence of Geometric Parameters on Aerodynamic and Acoustic Performances of Bladeless Fans
Authors: Li Ang , Chen Jun , Liu Yangfan , Bolton Stuart , Davies Patricia
Published: November 2019

In recent years, the bladeless fan that does not have visible impellers have been widely applied in household appliances. Since the customers are particularly sensitive to noise and the strength of wind generated by the fan, the aerodynamic and acoustic performances of the fan need to be accurately characterized in the design stage. In this study, computational fluid dynamic (CFD) and computational aeroacoustics (CAA) are applied to investigate the performances of different designs of a bladeless fan model. The influence of four parameters, namely the airfoil selection for cross-section of the wind channel, the slit width, the height of cross-section and the location of the slit, is investigated. The results indicate the streamwise air velocity increases significantly by narrowing the outlet, but the noise level increases simultaneously. In addition, the generated noise increases while the height of fan cross-section increases, and a 4mm height of the cross section is optimal for aerodynamic performance. When the slit is closer to the location of maximum thickness, the performances of the bladeless fan increases. Moreover, the performance is not changed significantly by changing the cross-sectional profile. Finally, the optimal geometric parameters are identified to guide the future design of the bladeless fan.
Investigation of Magnetic Journal Bearing Instability Issues in Supercritical CO2 Turbomachinery
Authors: Kim Dokyu , Baik SeungJoon , Lee Jeong Ik
Published: November 2019

With the increasing emphasis on reducing the CO2 emission while improving power generation efficiency, new power cycles are being developed. One of those promising power cycles is a supercritical CO2 (S-CO2) power cycle. To generate over 10MW electricity with S-CO2 power cycle, a magnetic bearing can be a good option for the hermetic type turbomachinery. However, from several studies on the magnetic bearing, the instability issues under high density fluid and high speed operating conditions were repeatedly mentioned. The instability in the magnetic bearing was observed to be related to the fluid conditions, mostly pressure and density. Because of this issue, the magnetic bearing sometimes cannot maintain enough clearance for the rotor leading to physical contact and consequently damaging the system. Thus, these instability issues should be thoroughly studied and be resolved for the successful and steady operation of the power system. The instability due to fluid force around the rotating shaft can be modeled with the Reynolds lubrication equation. The steady lubrication force analysis model is developed based on this equation. The model results imply that the lubrication performance is quite sensitive to the thermal condition of the CO2 especially density gradient around the shaft. Based on the modeling results, an experimental system is designed to investigate the issue. To study the instability issues experimentally, an impeller of the operating S-CO2 compressor is removed and the discharge line is blocked. Therefore, the main instability factor in this experiment will be the interaction between the rotor and the bearing only. The shaft position can be measured with inductive sensors. The forces exerted from the electromagnet is calculated from the electric current data which is applied by the controller. From these experimental data, the lubrication force is calculated. These results are compared with the analytical lubrication model to verify the model. From this study, it is expected that it will be possible to define the unstable operating conditions and suggest the required magnetic bearing performance for S-CO2 conditions.
Rapid and Versatile Micromold Fabrication Using Micromilling and Nanopolishing for Microfluidic Devices
Authors: Nguyen Thanh-Qua , Mah Jeongmin , Park Woo-Tae , Lee Sangyoup
Published: November 2019

In an effort to make microfluidic research more attractive and cost-effective, micromilled polymethyl methacrylate (PMMA) has gained interests as an alternative method to the conventional cleanroom-based micromolds fabrication technologies. The most enabling aspects of micromilling are flexibility on the design changes and the ability to fabricate three-dimensional structures. However, the major drawback of micromilling based micromold fabrication is the presence of burrs and tool marks on the surface after machining. High surface roughness on replicated polymer results in poor bonding strength and optical clarity. The roughness of micromilled surface strongly depends on the machining parameters such as tool size, spindle speed, feed rate, width of cut, and depth of cut. Thus, it is crucial to optimize the machining parameters to obtain a good surface finish. Although the optimal fabrication parameters are used to machine the micromold, the surface roughness of micromilled mold is still relative high compared to the surface of unprocessed PMMA.

In this paper, we first optimize the micromilling parameters of Computer Numerical Control (CNC) milling machine to achieve the best possible of surface roughness. We have optimized the machining parameters for a flat endmill with 100 μm, 200 μm, and 400 μm in diameter of spindle speed, feed rate, width of cut, and the depth of cut respectively at 18000 rpm, 20 mm/min, 30 μm, and 20 μm. Then, a method to polish the structured surface of the micromilled mold was developed using the rotary magnetic field. By modifying the CNC program language G-code, we were able to control the polishing path, polishing force and time precisely. Consequently, the burrs and tool marks are completely removed, such that the roughness of the surface is decreased from 350 nm Ra to 30 nm Ra, and 1200 nm Rz to 300 nm Rz while the profile of microstructures is not deteriorated. Finally, we demonstrate our mold fabrication scheme by building a microfluidic immunoassay device with four Quake’s valves and showed the sequential assay process successfully.
Evaluation of Pressure-Strain Correlation As a Basis for Development of a Physics-Based Transition Onset Marker
Authors: Muthu Satish , Bhushan Shanti , Walters D. Keith
Published: November 2019

Temporally developing direct numerical simulations (T-DNS) are performed for bypass transition of a zero pressure gradient flat plate boundary layer to understand the interplay between pressure-strain terms and flow instability mechanisms, and to propose and validate a phenomenological hypothesis for the identification of a robust transition onset marker for use in transition-sensitive Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) simulations. Results show that transition initiates at a location where the slow pressure-strain term becomes more dominant than the rapid term in the pre-transitional boundary layer region. The slow term is responsible for the transfer of turbulence energy from the streamwise component to other components, most importantly the wall-normal. The relative magnitudes of the slow and rapid terms can potentially provide a basis for the development of physically meaningful large-scale parameters that can be used as transition onset markers for Reynolds averaged Navier-Stokes (RANS) simulations.
Leakage Rate Performance Mapping of Smooth Stator/Grooved Rotor Labyrinth Seals Using Statistical Tools
Authors: Jin Hanxiang , Untaroiu Alexandrina
Published: November 2019

As one of the most widely used annular pressure seals, labyrinth seals are used to reduce the fluid leakage between different pressure stages. They are multi-toothed seals with circumferential grooves located on the rotor surfaces and/or stator surfaces, which are distributed along the axial direction. The intricacy of the surface geometry and directionality of the seal pattern assist in converting pressure into dissipated kinetic energy without rotor-stator rub effects. The majority of previous studies focused on annular labyrinth liquid seals with smooth rotor/grooved stator (SR/GS) case, whereas this paper attempts to elucidate the effects of geometric variables modification for smooth stator/grooved rotor (SS/GR) case using Computational Fluid Dynamics (CFD) and design of experiments (DOE) techniques. In this study, a smooth stator/grooved rotor liquid seal was modeled and validated against experimental data. The model was then used as a baseline case for a sensitivity analysis of its geometry variations. Simulation results under different pressures/rotor speeds were used to validate the CFD setup. Four geometric parameters of the seal were then selected as design variables to adapt the baseline geometry for potential performance improvements. The design space was discretized using the DOE technique. Similar mesh/simulation setups were automatically generated for each design point. Regression analysis was applied based on the CFD results for a better understanding of the effects associated with different design variables. These results can be used to improve the current design of smooth stator/grooved rotor annular pressure seals in order to achieve lower leakage rates.
Modeling and CFD Analyses of Gear Pump in OpenFOAM
Authors: Shoukat G. , Siddique Kamran , Sajid M.
Published: November 2019

Turbomachinery plays a key role in process and manufacturing industries. The interplay between power, flow rates and pressure output remain an interesting research area. To support specific processes in the industry, each pump or compressor must be fine-tuned for peak performance. As trend shifts from large organizations to entrepreneurial startups, spending significant costs on licensing of commercially available CFD softwares becomes unfeasible. This paper investigates the use of OpenFOAM – open source CFD package towards the analysis of gear pumps. The solution employs dynamic meshing and snappyHexMesh library in a single study. To validate the numerical model developed under OpenFoam’s environment, experimental studies were carried out. The pressure output of the pump was measured at four different RPMs — 200, 250, 300 and 400. An excellent agreement between experimental and numerical studies was seen at relatively higher RPMs. The numerical studies further explored the pulsating flow, recorded the variation between a constant maximum and minimum pressure value for each RPM. The variation in pressure was observed to increase at higher RPMs. The agreement between experimental and numerical findings established the utility of OpenFoam in investigating pump action.
Design of a New Type of Balance Drum to Reduce Axial Loading in Centrifugal Pumps
Authors: Bruurs K. A. J. , van Esch B. P. M. , van der Schoot M. S. , van der Zijden E. J. J.
Published: November 2019

In centrifugal pumps, axial thrust bearings are required to compensate for the axial loading on the pump impeller(s). These forces are mainly the result of unequal distributions of pressure on projected areas at both sides of the impeller(s). Axial loading tends to be highest in multistage pumps in which all impellers face the same direction. Balancing devices are often used to reduce the loading of the axial bearings. Common types of balancing devices are the balance drum and the balance disc. Both of them have their advantages and disadvantages. A stepped balance drum is a new concept for a balancing device that can be used in any type of turbomachinery. It combines the benefits of the balance drum and the balance disk without the drawbacks of both. In this paper, the new concept is presented along with a semi-empirical model of its performance. A CFD analysis is also presented which serves to verify the analytical model. An optimization procedure of a stepped balance drum is given using a multistage centrifugal pump as an example.
Effect of Mass Distribution on Falling Cylindrical Particles at Intermediate Reynolds Numbers
Authors: Angle Brandon R. , Rau Matthew J. , Byron Margaret L.
Published: November 2019

In natural sedimentation, many particles of interest are both large and nonspherical. Some common particle types (e.g. naturally occurring aggregates) do not have a uniform mass distribution. As a result, the centers of mass and buoyancy are not co-located, leading to more complex settling dynamics. Here we investigated the orientation and terminal velocity of freely falling cylinders, in which the mass distribution was either constant (uniform-density, UD) or bipartite, undergoing a step function halfway along the length (compound-density, CD). Cylinders had relatively low aspect ratios (1 < AR < 4), and fell at intermediate Reynolds numbers (of order 100). The cylinders, initially horizontal, were released at the top of a tall hexagonal still-water tank, and imaged by a high-speed camera. Two low-speed cameras simultaneously captured 1) full cylinder trajectory and 2) landing position. We recorded the terminal velocity, fall orientation, and landing site of each cylinder. Results showed significant differences in the settling characteristics of uniform- vs. compound-density cylinders. UD cylinders of AR = 1 fell broadside initially, whereas AR = 1 CD cylinders fell vertically. However, both cases showed oscillation in cylinder orientation upon descent. UD cylinders with AR = 2 and AR = 4 consistently fell broadside, with minimal cylinder axis oscillation. CD cylinders with AR = 2 fell with two different modes. In mode 1, cylinders rotated 90° from their initial orientation before beginning to oscillate about the vertical axis. In mode 2, cylinder orientation remained constant at a slight angle from the horizontal. This mode was also observed in the CD AR = 4 cylinders, which fell at a constant (tilted) orientation angle and moved horizontally as they fell. The landing sites for all CD cylinders were biased toward the side of the target where the denser end of the cylinder was initially oriented, whereas UD cylinders landed in a uniform distribution around the tank center. In general, cylinders with the smallest vertical projected area fell with the greatest terminal velocity; however, the mechanisms controlling orientation remain unclear. Our results have important implications for predicting the settling behavior of naturally-occurring particles, and lay the groundwork for further study of particles settling in complex flows such as turbulence. Given our results in still water, the interplay between the buoyant torques created by the offset between the center of mass and center of volume are likely to strongly impact particle motion in turbulence.
Hydrodynamics and Flow Characterization of Tuna-Inspired Propulsion in Forward Swimming
Authors: Wang Junshi , Tran Huy , Christino Martha , White Carl , Zhu Joseph , Lauder George , Bart-Smith Hilary , Dong Haibo
Published: November 2019

A combined experimental and numerical approach is employed to study the hydrodynamic performance and characterize the flow features of thunniform swimming by using a tuna-inspired underwater vehicle in forward swimming. The three-dimensional, time-dependent kinematics of the body-fin system of the underwater vehicle is obtained via a stereo-videographic technique. A high-fidelity computational model is then directly reconstructed based on the experimental data. A sharp-interface immersed-boundary-method (IBM) based incompressible flow solver is employed to compute the flow. The primary objective of the computational effort is to quantify the thrust performance of the model. The body kinematics and hydrodynamic performances are quantified and the dynamics of the vortex wake are analyzed. Results have shown significant leading-edge vortex at the caudal fin and unique vortex ring structures in the wake. The results from this work help to bring insight into understanding the thrust producing mechanism of thunniform swimming and to provide potential suggestions in improving the hydrodynamic performance of swimming underwater vehicles.
Characterization of Aggregate Disruption Using Organic Marine Particles and Particle Tracking Measurements in Rotating/Oscillating Aggregation Tanks
Authors: Song Yixuan , Rau Matthew J.
Published: November 2019

The fate of particulate matter in the ocean is determined in large part by its size and settling rate. Disaggregation, caused by turbulence-induced shear, acts to fracture or erode large particles into slower-settling sub-aggregates and primary particles. The strength and breakup response of organic marine aggregates (i.e. marine snow particles consisting of phytoplankton) is poorly understood, limiting our ability to accurately predict marine particle transport effects on the global carbon cycle. A study was conducted to enable the investigation of disaggregation effects on these organic marine particle aggregates. Due to the fragile nature of the Phytoplankton cells and their resulting aggregates, test facilities that do not rely on external sampling or pumps are required. A novel rolling aggregation tank was developed that can both aggregate phytoplankton cells under varying hydrodynamic conditions and then expose them to calibrated shear forces using laminar oscillating flow. The theory behind the operation of this tank is presented along with the necessary operating conditions to create stable regions within the tank where particle settling effects are minimal but shear is still representative of values expected in the open ocean. Phytoplankton was cultured in the laboratory to create simulated marine snow particles in the open ocean for disaggregation experiments. The procedure to calculate and track the shear-history of each aggregate is described and how the data generated from this facility will be used to quantify disaggregation parameters relevant for population balance modeling is discussed.
An Analytical and Modular Software Workbench for Solving Kinematics and Dynamics of Series-Parallel Hybrid Robots
Authors: Kumar Shivesh , Mueller Andreas
Published: November 2019

Parallel mechanisms are increasingly being used as modular subsystem units in various robots and man-machine interfaces for their superior stiffness, payload-to-weight ratio and dynamic properties. This leads to series-parallel hybrid robotic systems which are difficult to model and control due to the presence of various closed loops. Most model based kinematic and dynamic modeling tools resolve loop closure constraints numerically and hence suffer from inefficiency and accuracy issues. Also, they do not exploit the modularity in robot design. In this paper, we present a modular and analytical approach towards kinematic and dynamic modeling of series-parallel hybrid robots. This approach has been implemented in a software framework called Hybrid Robot Dynamics (HyRoDyn) and its application is demonstrated with the help of a series-parallel hybrid humanoid robot recently developed at DFKI-RIC.