bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Investigations on Friction Drag Reduction on an Airfoil by Passive Blowing
Authors: Hirokawa Shiho , Eto Kaoruko , Fukagata Koji , Tokugawa Naoko 
Published: November 2019

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.