bluuebunny/crossref_metadata_2025 huggingface dataset:
Return Migration in Africa and the Relationship between Educational Attainment and Labor Market Success: Evidence from Uganda
Authors: Thomas Kevin J. A.
Published: September 2008

The return migration of skilled professionals has been suggested as a policy instrument suitable for reversing the large-scale emigration of skilled professionals from African countries. However, there are no empirical studies showing how migrant professionals from Africa are reintegrated into the labor market after they return. This study examines the relationship between educational attainment and the likelihood of employment among native-born African migrants returning home from abroad. The study focuses on the evidence from Uganda since this country has one of the longest histories of skilled migration in Africa. The results show that returning migrants with university degrees and vocational credentials are more likely to be employed than their nonmigrant and immigrant counterparts. However, this employment advantage was not observed among returning migrants with secondary schooling or below. Furthermore, the results show that returning migrants are generally more likely to be employed as district employment rates increase.
Mexican Migration Networks in the United States, 1980–2000
Authors: Light Ivan , von Scheven Elsa
Published: September 2008

Between 1980 and 2000, about 1.2 million Mexican immigrants settled in 47 new settlement states. In the past, these immigrants would have settled in California, Texas, or Illinois, the three traditional states for Mexican settlement. Explaining this dispersion, the network saturation theory claims that high-volume migration of Mexicans finally saturated the housing and job opportunities of Mexicans in traditional states and especially in Los Angeles. High rents and low wages then encouraged Mexican immigrants to select new states for settlement. This article subjects the network saturation theory to a rigorous reanalysis using new evidence. The empirical results tend to confirm the network saturation theory.
Ametor scabrosus(Horn) (Coleoptera: Hydrophilidae: Hydrophilinae) new to Korea
Authors: LEE Dae‐Hyun , AHN Kee‐Jeong
Published: September 2008

Ametor scabrosus(Horn) is identified for the first time in Korea. A habitus photo, a description, and illustrations of the diagnostic characters of species are provided.
First record of the genus Adelphocorisella Miyamoto and Yasunaga (Hemiptera: Miridae) from Korea
Authors: CHO Young Jae , KWON Yong Jung , SUH Sang Jae
Published: September 2008

Adelphocorisella lespedezae
Miyamoto and Yasunaga, 1993, which was previously known only from Japan, is reported from Korea for the first time and diagnosed. An image of its dorsal habitus as well as illustrations of the male genitalia are provided. The discovery of the mirid species also represents the first distributional record in Korea as well as the continental Palaearctic Region for the genus Adelphocorisella Miyamoto and Yasunaga, 1993.
Characterization of Australian fur seal vocalizations during the breeding season
Authors: Tripovich Joy S. , Canfield Rhondda , Rogers Tracey L. , Arnould John P. Y.
Published: September 2008

Abstract

The vocal repertoire, structure, and behavioral context of airborne vocalizations produced by Australian fur seals (Arctocephalus pusillus doriferus) are described using recordings made at a breeding colony on Kanowna Island, Bass Strait, Australia. The study identified six different call types: three produced by males (bark, guttural threat, and submissive call); five produced by females (bark, guttural threat, submissive call, growl, and pup attraction call) and the female attraction call produced by pups and yearlings. Vocalizations were compared according to age and sex classes. The overall structure and function of the pup attraction and female attraction call produced by females, yearlings, and pups, was similar. However, while similar in their overall appearance, certain call types have a lower fundamental frequency when compared with other fur seals. In addition, the male bark call alters in rate of production according to the context used, where calls are slower when males are stationary and advertising their territorial status and faster when males are involved in confrontations with other males or actively herding females. Further research is required to investigate changes in environmental conditions and their effects on shaping the call structure and communication in Australian fur seals.
The Kenneth S. Norris Lifetime Achievement Award Lecture
Authors: Kasuya Toshio
Published: September 2008

Abstract

Since the early 20th century, Japanese cetacean biology relied heavily on fisheries for their materials. The work environment was challenging because research activities were controlled by industries and the fishery administration. I became a cetacean scientist in 1961 and worked mainly in the western North Pacific. There I witnessed the collapse of coastal populations of striped dolphins and sperm whales as a result of over‐hunting. Nonetheless, my research revealed fascinating aspects of cetacean biology, which still await explanation, such as the following: neighboring populations of the same species having different breeding seasons, the role of reproductively senescent females in some toothed whales, the role of “social sex” in short‐finned pilot whales, and the selective benefit of male Baird's beaked whales living longer than the females. New methodologies are required to address these questions. I propose to include the following aims for the conservation biology of cetaceans: to identify a community as a conservation unit, and to focus on conserving the cultural diversity and variability of such communities, and henceforth to focus increased research on understanding the contribution of individuals within a community. Today, marine mammal biologists of all fields need to pay more attention to conservation.
Evaluation of eosin‐5‐maleimide flow cytometric test in diagnosis of hereditary spherocytosis
Authors: KAR R. , MISHRA P. , PATI H. P.
Published: September 2008

A flow cytometry‐based test using eosin‐5‐maleimide (EMA) dye was used for diagnosis of hereditary spherocytosis (HS). The mean fluorescence intensiy (MFI) of EMA tagged erythrocytes is lower in HS than that in other hemolytic and nonhemolytic anemias. We enrolled 114 subjects comprising 20 confirmed HS, 20 suspected HS/hemolytic anemia (HA), 20 normal controls, 20 other hemolytic anemias [13 autoimmune hemolytic anemia, three congenital dyserythropoietic anemia (CDA), one pyruvate kinase deficiency, two microangiopathic hemolytic anemia], 18 microcytic anemia and 16 macrocytic anemia cases. All samples were subjected to flow cytometry as per standard protocol. The mean MFI of normal control subjects was 11 861.5 (SD 883.5) and of confirmed HS was 7949.3 (SD 1304.1). Using this test, of 20 patients suspected to be HS/HA but with no confirmatory diagnosis, eight patients were diagnosed as HS. Using logistic regression analysis, the optimum cut‐off MFI value between HS and normal controls was 10126. The area under the ROC curve was 0.99. The statistical significance of MFI values was obtained by t‐test or Wilcoxon rank sum test as applicable. Compared with normal controls, the MFI values in HS were lower and in megaloblastic anemia were higher which was statistically highly significant (P < 0.01), and the MFI values in CDA were lower which was statistically significant (P < 0.05). False‐positive values were obtained in three cases of AIHA and two cases of CDA. The sensitivity and specificity was 96.4% and 94.2% respectively. The EMA‐based flow cytometry test is a highly sensitive and specific method for the diagnosis of HS.
Intravitreal bevacizumab for treatment‐naïve subfoveal occult choroidal neovascularization in age‐related macular degeneration
Authors: Furino Claudio , Boscia Francesco , Recchimurzo Nicola , Besozzi Gianluca , Cardascia Nicola , Sborgia Luigi , Niro Alfredo , Sborgia Carlo
Published: September 2008

Purpose:  This study aimed to evaluate the efficacy of multiple injections of intravitreal bevacizumab for treatment‐naïve subfoveal occult choroidal neovascularization (CNV) in age‐related macular degeneration (AMD).

Methods:  Twelve eyes of 12 patients (mean age 76 ± 6 years) with mean best corrected visual acuity (BCVA) of 20/100 and occult subfoveal CNV at fluorescein angiography (FA), indocyanine‐green (ICG) angiography and optical coherence tomography (OCT), showing intra‐ or subretinal fluid with or without retinal pigment epithelial detachment (PED), underwent multiple intravitreal injections (mean 2.4 ± 0.7) of 1.25 mg (0.05 ml) bevacizumab. Visual acuity and OCT findings were assessed at the end of follow‐up.

Results:  After a mean follow‐up of 5.7 ± 2 months, BCVA improved from 20/100 (range 20/50–20/303) to 20/60 (range 20/28–20/200) (p = 0.038). Five eyes (42%) increased BCVA by ≥ 3 lines, six eyes (50%) increased BCVA by < 3 lines and one eye (8%) remained stable. Macular thickness decreased from 298 ± 71 μm to 223 ± 72 μm (p = 0.017). No ocular or systemic side‐effects were observed.

Conclusions:  Short‐term results suggest that multiple intravitreal injections of 1.25 mg bevacizumab are well tolerated and associated with significant improvements in BCVA and decreased retinal thickness by OCT in most patients with treatment‐naïve occult CNV. Further evaluation of intravitreal bevacizumab for the treatment of occult CNV is warranted.
Analysis of Flow in Fractal Porous Media
Authors: Yu Boming
Published: September 2008

The flow in porous media has received a great deal of attention due to its importance and many unresolved problems in science and engineering such as geophysics, soil science, underground water resources, petroleum engineering, fibrous composite manufacturing, biophysics (tissues and organs), etc. It has been shown that natural and some synthetic porous media are fractals, and these media may be called fractal porous media. The flow and transport properties such as flow resistance and permeability for fractal porous media have steadily attracted much attention in the past decades. This review article intends to summarize the theories, methods, mathematical models, achievements, and open questions in the area of flow in fractal porous media by applying the fractal geometry theory and technique. The emphases are placed on the theoretical analysis based on the fractal geometry applied to fractal porous media. This review article shows that fractal geometry and technique have the potentials in analysis of flow and transport properties in fractal porous media. A few remarks are made with respect to the theoretical studies that should further be made in this area in the future. This article contains 220 references.
A CFD Study of the Flow Field, Resultant Force, and Aerodynamic Torque on a Symmetric Disc Butterfly Valve in a Compressible Fluid
Authors: Leutwyler Zachary , Dalton Charles
Published: September 2008

The flow field, resultant force, and aerodynamic torque on a butterfly valve with a symmetric disc are studied computationally at disc positions 45° and 70° over a range of operating pressure ratios that include subsonic and supersonic flow states. The aerodynamic torque coefficients were predicted using a k-ε RNG turbulence model and were compared to test data at both 45° and 70° over a range of operating pressure ratios. The numerical results were generally in good agreement with test data, although a few disparities existed. The computational results were obtained using Fluent 6.0 and were performed on a Dell Precision workstation with dual Xeon processors.
The Effect of a Modified Downcomer on the Hydrodynamics in an External Loop Airlift Reactor
Authors: Jones Samuel T. , Heindel Theodore J.
Published: September 2008

Gas holdup and superficial liquid velocity in the downcomer and riser are studied for an external loop airlift reactor with an area ratio of 1:16. Two downcomer configurations are investigated consisting of the downcomer open or closed to the atmosphere. Experiments for these two configurations are carried out over a range of superficial gas velocities from UG = 0.5 to 20 cm/s using three aeration plates with open area ratios of 0.62, 0.99 and 2.22%. These results are compared to a bubble column operated with similar operating conditions. Experimental results show that the gas holdup in the riser does not vary significantly with a change in the downcomer configuration or bubble column operation, while a considerable variation is observed in the downcomer gas holdup. Gas holdup in both the riser and downcomer are found to increase with increasing superficial gas velocity. Test results also show that the maximum gas holdup for the three aerator plates is similar, but the gas holdup trends are different. The superficial liquid velocity is found to vary considerably for the two downcomer configurations. However, for both cases the superficial liquid velocity is a function of the superficial gas velocity and/or the flow condition in the downcomer. These observed variations are independent of the aerator plate open area ratio. When the downcomer vent is open to the atmosphere, the superficial liquid velocity is initially observed to increase with increasing superficial gas velocity until the onset of choking occurs in the downcomer. Increasing the superficial gas velocity beyond the onset of choking increases the effect of choking and decreases the superficial liquid velocity. Once maximum choking is reached, the superficial liquid velocity becomes independent of the superficial gas velocity. When the downcomer vent is closed to the atmosphere, the superficial liquid velocity is initially observed to decrease with increasing superficial gas velocity as choking in the downcomer is immediately present. Once maximum choking occurs, the superficial liquid velocity once again becomes independent of the superficial gas velocity.
Translating Equations Into Their Physical Meaning as an Effective Tool of Engineering
Authors: Yedidiah S.
Published: September 2008

This paper is an extension of the discussion pertaining the need for, and the benefits of the capability to translate a mathematical expression into a description of a relevant physical event, respectively of a physical situation. It shows, how such a translation has made it possible to recognize the shortcomings of the deeply-rooted conception, that the outlet angle of the impeller blades is the most significant design parameter of a rotodynamic pump. The awareness of these shortcomings, in turn, has led already to the development of a more reliable approach for calculating the heads generated by a rotodynamic impeller, (Compare Fig. 2.). It has also made possible to solve to a number of additional problems which, in the past, could be solved only by the costly and time consuming method of trial and error. This paper also discusses the physical meaning of the Navier-Stokes equations. It shows how the translation of these equations into their physical meaning made it possible to explain several seemingly enigmatic results of tests. In addition to the above, this paper also discusses a number of problems which need yet to be explored in the future, in order to be able to turn CFD into a useful tool for the design of rotodynamic pumps.
A Numerical Method for Gas-Particle Flows With Accumulation
Authors: Zhao Xiang , Zhang Sijun
Published: September 2008

A mathematical model is proposed to describe the gas-particle flow in a bed packed with particles. The model is in essence the same as the two fluid model developed on the basis of the space-averaged theorem but extended to consider the interactions among the gas, powder and packed particles and the static and dynamic holdups of powder. In particular, a method is proposed to determine the boundary between powder mobile and non-mobile zones, i.e. the profile of powder accumulation zone. The validity of the numerical modelling is examined by comparing the predicted and measured distributions of powder accumulation under various flow conditions.
A Mean-Field Free-Energy Lattice Boltzmann Model for Liquid-Vapor Interfaces
Authors: Li Shi-Ming , Tafti Danesh K.
Published: September 2008

A nonlocal pressure equation is proposed for liquid-vapor interfaces based on mean-field theory. The new nonlocal pressure equation is shown to be a generalized form of the nonlocal pressure equation of the van der Waals theory or the “square-gradient theory”. The proposed nonlocal pressure is implemented in the mean-field free-energy lattice Boltzmann method (LBM) proposed by Zhang et al (2004). The modified LBM is applied to simulate equilibrium interface properties and the interface dynamics of capillary waves. Computed results are validated with Maxwell constructions of liquid-vapor coexistence densities, theoretical relationship of variation of surface tension with temperature, theoretical planar interface density profiles, and the dispersion relation between frequency and wave number describing the dynamics of capillary waves. It is shown that the modified LBM gives very good agreement with the theories. In addition, preliminary calculations of phase transition and binary droplet coalescence are also presented.
Numerical Study of Fluid Flow in an Enclosed Electrical Motor
Authors: Fasquelle A. , Saury D. , Harmand S. , Randria A. , Boualem B.
Published: September 2008

Nowadays, design of electrical motors runs up more and more against the problems of heatings during operation. These excessive heatings result from a weak heat dissipation. The improvement of cooling system passes thought the improvement of convective heat transfers within the motors. However, these heat transfers strongly depend on the flow structure. This structure is particularly significant for the enclosed motors. The air is completely enclosed inside the machine and consequently, it is never renewed. Indeed, for this kind of configuration, the flow structure is only regulated by the geometry. It is thus not possible to modify it from the outside as for the open motors. That is why, the numerical study presented below analyzes the flow structure in an enclosed induction motor of railway traction. The sliding mesh method has been carried out in order to keep a significant accuracy on the flow nature. Then, some air spaces in the motor have been proved to be particularly sensitive for this kind of enclosed motor.
Experimental and Numerical Research of the Effects of a Perturbed Inflow of a Centrifugal Pump
Authors: Roth M. , Stoffel B. , Ludwig G.
Published: September 2008

The influence of a disturbed inflow condition on a single-stage, end suction volute casing pump, as they are frequently found e.g. in water supply plants, was analyzed experimentally in a test bench and numerically using CDF simulation. The analyzed pump operates with water and has a specific speed (ns) of 42 (metric units), an outside impeller diameter (D2) of 188 mm and an operating speed (n) of 2300 rpm. The measurements were carried out in a closed test loop where the operating conditions and the inlet piping can be varied to analyze the influence of bend and valve over the pump performance. For the 3-D numerical analysis two configurations were simulated. First the combination bend and butterfly valve was calculated and second the complete pump. Different coupling methods between fixed and rotating parts and some turbulence models were analyzed. For the comparison between experiment and simulation the characteristic curves of the pump are used. Also the calculated flow distribution directly upstream of the suction branch of the pump was compared with the velocity profile measured non-intrusively with a Laser Doppler Velocimeter (LDV). The aim of the study is to determine the effects of a disturbed flow at the inlet of a pump on its performance and to analyze the causes of these effects using CFD.
Thermal Gradient Determination Inside Vaporizing Droplets by Combining Rainbow and Laser Induced Fluorescence Measurements
Authors: Laurent C. , Biscos Y. , Doue´ N. , Maqua C. , Lemoine F. , Grehan G. , Lavergne G.
Published: September 2008

This paper describes the setting of two measuring techniques on a rectilinear monosized droplets stream allowing the validation of droplet vaporizing models for internal spatial temperature distribution. Indeed, the vaporizing rate depends strongly on droplet surface temperature and consequently on physical phenomena inside droplets. However, the measurement of temperature in small droplets whose diameter is about 100μm is not easy. To determine the thermal gradient, two experimental techniques have to be coupled: the first must be sensitive to the thermal gradient and the second to the mean temperature. The two chosen experimental techniques, the rainbow refractometry and the Laser Induced Fluorescence (LIF) in liquid phase, agree with these criteria. Some experiments have been done on ethyl alcohol and acetone droplet streams with different injection temperatures and in vaporizing or burning conditions. Then, the results have been compared to numerical predictions.
The RANS, PDF and TBL Simulations of Turbulent Gas-Solid Particle Flow in Vertical Pipe
Authors: Kartushinsky Alexander I. , Michaelides Efstathios E. , Zaichik Leonid I.
Published: September 2008

The numerical simulation of turbulent gas-solid particle flow in vertical round pipe is performed & analyzed by three different approaches: RANS 2D modeling, PDF approach (Zaichik’s model 2001) & by two-phase TBL (turbulent boundary layer approach). The given performances include all relevant force factors imposed on the motion of solid phase (two-fluid model is considered): particle-turbulence, particle-particle, particle-wall interactions, two-lift the Magnus & Saffman forces and buoyancy (gravitational) force. The dispersed phase is considered as a polydispersed phase composed of finite number of particle fractions and the mass & momentum equations are closed with the help of implementation of original “collision” model (Kartushinsky & Michaelides, 2004). The two/four-way coupling model of Gillandt & Crowe (1998) is accounted for turbulence modulation. The numerical results show that retaining of second diffusion terms in both directions (in streamwise & transverse directions) aligns the average x-velocity components of gas and dispersed phases as well as the particle mass concentration and k-profiles across the flow in case of both PDF and RANS 2D approaches that versus the distributions of parameters obtained by two-phase TBL approach. This is reasonable due to additional effect of fluxes diffusion of the carrier fluid & solid phase in the main direction derived from turbulence fluctuation and inter-particle collision which smoothes the profile shapes.
Simulations of Particle-Wall-Turbulence Interactions, Particle Motion and Erosion in With a Commercial CFD Code
Authors: Zhang Yongli , McLaury Brenton S. , Shirazi Siamack A. , Russell Ronnie D.
Published: September 2008

Calculation of a representative particle impacting velocity is an important component in calculating solid particle erosion inside a pipe geometry. Experiences in calculating erosion for solid-gas systems indicate that gases normally do not affect particle motion near a solid wall. However, solid particles that are entrained in a liquid system tend to undergo a considerable momentum exchange before impacting the solid wall. Currently, most commercial CFD codes allow the user to calculate particle trajectories using a Lagrangian approach. Additionally, the CFD codes calculate particle impact velocities with the pipe walls. However, these commercial CFD codes normally use a wall function to simulate the turbulent velocity field in the near wall region. This wall-function velocity field near the wall can affect the small particle motion in the near wall region. Furthermore, the CFD codes assume particles have zero volume when particle impact information is being calculated. In this investigation, particle motions that are simulated using a commercially available CFD code are examined in the near wall region. Calculated solid particle erosion patterns are compared with experimental data to investigate the accuracy of the models that are being used to calculate particle impacting velocities. While not considered in particle tracking routines in most CFD codes, the turbulent velocity profile in the near-wall region is taken into account in this investigation and the effect on particle impact velocity is investigated. The simulation results show that the particle impact velocity is affected significantly when near wall velocity profile is implemented. In addition, effects of particle size are investigated in the near wall region of a turbulent flow in a 90 degree sharp bend. A CFD code is modified to account for particle size effects in the near wall region before and after the particle impact. It is found from the simulations that accounting for the rebound at the particle radius helps avoid non-physical impacts and reduces the number of impacts by more than one order-of-magnitude for small particles (25 μm) due to turbulent velocity fluctuations. For large particles (256 μm), however, non-physical impacts were not observed in the simulations. Solid particle erosion is predicted before and after introducing these modifications and the results are compared with experimental data. It is shown that the near wall modification and turbulent particle interactions significantly affect the simulation results. Modifications can significantly improve the current CFD-based solid particle erosion modeling.
Fluid Dynamics Around an Inclined Cylinder With Running Water Rivulets
Authors: Alam Md. Mahbub , Zhou Y.
Published: September 2008

This paper presents the experimental study of fluid dynamics around an inclined circular cylinder with and without water running over its surface, covering the water rivulet formation, the fluid forces on the cylinder, the near-wake structure and their interrelationships. Two cylinder inclination angles (α) were investigated, i.e., 80° and 55°, respectively, with respect to incident flow. It has been found that water running over the cylinder surface may behave quite differently, depending on the incident flow velocity (U∞), which has subsequently a great impact upon fluid dynamics around the cylinder. As such, five flow categories are classified. Category A: one water rivulet was observed, irrespective of α, at the leading stagnation point at a small U∞. Category B: the rivulet splits into two, symmetrically arranged about the leading stagnation line, once U∞ exceeds a α-dependent critical value. The two rivulets may further switch back to one, and vice versa. Category C: two symmetrical straight rivulets occur constantly. Category D: the two rivulets shift towards the flow separation line with increasing U∞ and oscillate circumferentially. The oscillation reaches significant amplitude when the rivulets occur at about 70° from the leading stagnation point. This increased amplitude is coupled with a rapid climb in the mean and fluctuating drag and lift, fluctuating lift rising by a factor of near 5 at α = 80°. Meanwhile, the flow structure exhibits a marked variation, including a declining Strouhal number, reduced vortex formation length, velocity fluctuation and velocity deficit, improved two-dimensionality of the flow, increased coherence between vortex shedding and fluctuating lift, and dipped fluid damping at the vortex shedding frequency. All these observations point to the occurrence of a ‘lock-in’ phenomenon, i.e. the rivulet oscillation synchronizing with flow separation. Category E: the two rivulets shift further downstream just beyond the separation line; the shear layers behind the rivulets become highly turbulent, resulting in weakened vortex shedding, fluctuating fluid forces and fluctuating wake velocity. Based on the equilibrium of water rivulet weight, aerodynamic pressure and friction force between fluid and surface, analysis is developed to predict the rivulet position on the cylinder, which agrees well with measurements.
Simulating the Dynamics of Entangled Polymers Using the Kinetic Theory Description of the Doi-Edwards Model
Authors: Mokdad B. , Ammar A. , Chinesta F.
Published: September 2008

In this work, the model of Doi-Edwards with independant alignment approximation describing the dynamics of polymer melts is simulated. The main aim of this work is the analysis of some new simulation techniques operating on the Fokker-Planck equation related to that model. For this purpose we consider the kinetic theory description of the Doi-Edwards model, implemented in the 2D and 3D cases under shear and elongational flows. The Fokker Planck equation which governs the evolution of the distribution function involves two variables: the tube orientation (described by a unit vector defining the unit surface in 3D and the unit circle in 2D) and the coordinate that locates the segment tube on the molecular chain, taking values in the unit interval. To separate both variables during the problem resolution we make use of the Alternating Direction Implicit method (ADI) which allows reducing the computation time and efforts. A model reduction technique is also proposed and analyzed. It consists of considering an optimal representation basis which is constructed during the problem resolution. Thus, a reduced number of approximation functions, now defined in the whole domain, are enough to describe the solution evolution during the entire time interval considered in the simulation, with significant CPU time savings.
Centrifugal Compressor Design Considerations
Authors: Xu C.
Published: September 2008

Initial design considerations of centrifugal compressor are commonly performed with experience base, although computer technology and numerical methods had made significantly progress. Three-dimensional Computational Fluid Dynamics (CFD) codes are still not major design tools for centrifugal compressors. Major design systems for industrial centrifugal compressor design are largely based on one-dimensional meanline and two-dimensional through flow tools. The experience of designers is one of the key factors to drive design success. The impeller is one of the key components of a centrifugal compressor stage. Design of the impeller is critical to the success of compressor stage design. Basic sizing information to establish the initial parameters can save development time for industrial centrifugal compressor development. The diffuser plays an important role in the compressor operating range. A poorly designed diffuser reduces compressor operating range and stage efficiency. The volute design impacts the compressor performance and bearing life. For successful design all compressor components, the design experience is one of a key factor to make design success. This paper presents author’s design experience for centrifugal compressors. The discussions and information on compressor design considerations in open literature are also reviewed. The purpose of the paper is to serve as a part of compressor design experience database for young engineers and college students in order to reduce their training time to become compressor designers.
Analysis of Flow Physics and Jet-Mainstream Interaction in Leading Edge Filmcooling Using Large Eddy Simulation
Authors: Rozati Ali , Tafti Danesh K.
Published: September 2008

A numerical investigation is conducted to study leading edge film cooling at a compound angle with Large Eddy Simulation (LES). The domain geometry is adopted from an experimental set-up (Ekkad et al. [14]) where turbine blade leading edge is represented by a semi-cylindrical blunt body. The leading edge has two rows of coolant holes located at ±15° of the stagnation line. Coolant jets are injected into the flow field at 30° (spanwise) and 90° (streamwise). Reynolds number of the mainstream is 100,000 and jet to mainstream velocity and density ratios are 0.4 and 1.0, respectively. The results show the existence of an asymmetric counter-rotating vortex pair in the immediate wake of the coolant jet. In addition to these primary structures, vortex tubes on the windward side of the jet are convected downstream over and to the aft- and fore-side of the counter-rotating vortex pair. All these structures play a role in the mixing of mainstream fluid with the coolant. A turbulent boundary layer forms within 2 jet diameters downstream of the jet. A characteristic low frequency interaction between the jet and the mainstream is identified at a non-dimensional frequency between 0.79 and 0.95 based on jet diameter and velocity. The spanwise averaged adiabatic effectiveness agrees well with the experiments when fully-developed turbulence is used to provide time-dependent boundary conditions at the jet inlet, without which the calculated effectiveness is overpredicted.
Simulation and Experimental Investigation of Variable Swirl Intake Port in DI Diesel Engine Using CFD
Authors: Rathnaraj J. David , Raja Bose B. Jefferson , Kumar Michael N.
Published: September 2008

Knowledge of the flow phenomena inside the cylinder is necessary for optimum design of the intake port and the piston cavity configurations. Recent trends in direct injection diesel engines have increased the need for clear understanding of the flow field, especially the swirl characteristics. The swirl flow is an essential parameter which affects the air fuel mixing, combustion efficiency and therefore the engine performance. The purpose of this study is to investigate the combustion, emission, spray and flow field phenomena of a D I diesel engine and to come up with a geometrical shape for a port and valve or valves that produce the optimum swirl ratio. The percentage opening of a helical port for the DI diesel engine is simulated and studied using Computational Fluid Dynamics with experimental validation. Steady flow rig experiments are most widely used to evaluate the swirl ratio of an intake port design. The three dimensional developing flow patterns are needed throughout the compression and combustion stroke to understand the various experimental results. Flow is simulated by solving governing equations, viz., conservation of mass and momentum using the simple-algorithm. Turbulence has been modeled by standard kφ–φ∈ model with standard wall treatment. The predictive accuracy of the calculation method is compared with detailed mass flow rate and paddle rpm measurements. The results are in good agreement with experimental results and clearly predict the under predictability of the paddle swirl meter in lower lifts. Emission standards, which demand large reduction in NOx and PM emission, require a more comprehensive study of all elements that contribute to emission formulation. The combustion chamber is subject of research and development in an effort to achieve optimized combustion system. The intake port fluid dynamics contribute to the fuel air mixing which in turn is the most important parameter for the control of fuel burning rate for diesel engines. The intake port fluid dynamics also significantly affects ignition delay, the magnitude and timing of the diffusion burn, the magnitude of the premixed burn and emission of nitrous oxide and soot. According to the Modulated Kinetics (MK) concept, which improves the emission performance of diesel engines, a D I Diesel engine requires higher intake swirl in the part-load region. The computations are used to optimize the swirl flow characteristics of an intake port system over a wide range of operating conditions. In this study, the numerical simulation of the helical intake port and variable swirl intake port for two-valve DI Diesel engines are discussed with experimental validation. The improvement of swirl generation capacity of the port design according to the stringent emission norms are also studied.
Vorticity Dynamics Analysis on Flow in Francis Hydraulic Turbine
Authors: Zhang Liang , Liu Shuhong , Wu Yulin , Zhang Lefu
Published: September 2008

In this research, moment expression of Francis runner is derived in vorticity dynamics type firstly, diagnose method based on vorticity dynamics is also introduced. Then, numerical simulation is applied to turbine flow passage with all blades (from inlet of wicket gate to outlet of draft) using RNG k-ε turbulence model with RANS method. With computational results, BVF (Boundary Vorticity Flux) and skin friction distributions on blades and draft tube walls are worked out; flow in Francis hydraulic turbine is estimated by vorticity dynamics method. Compared with traditional analysis method and experimental data, practicability of vorticity dynamics is confirmed.
PDF Approach for the Collision Modeling in Binary Mixture of Particles
Authors: Fede Pascal , Simonin Olivier , Zaichik Leonid
Published: September 2008

The purpose of the paper is to introduce the formalism of the joint fluid-particle PDF approach for polydisperse gas-particle flow and to focus on the derivation of the collision terms. The originality of this work is that our model takes into account the correlation between colliding particles and also the effect of a large drift. A discussion is performed on the model.
Development and Application of LED Illumination Color PIV
Authors: Jaw Shenq-Yuh , Hwang Robert R. , Shyu K. L.
Published: September 2008

In this study, red, green, and blue light-emitting diodes (LED) are adopted as the light source to illuminate sequentially a two-dimensional soap film channel flow. Triple-exposure particle image is recorded on the same image frame by a 3-ccd color camera. Since the particles illuminated by the R, G, B LED will only be recorded on the R, G, B ccd-chip of the digital camera, three sequential exposure, R, G, B particle images can be obtained from separating the triple-exposure particle image. Two sequential velocity fields can be determined from the correlation analysis of the R-G and G-B sequential particle images. Time derivative of the velocity fields, and hence the evolution of the unsteady flow or the characteristics of turbulent flows can be analyzed from the two velocity fields determined. The color PIV method incorporated with the LED light has proven to be a cheap, safe, and powerful tool for the full-field flow measurements. Results of the flow past circular cylinder in the confined soap film channel flow are presented.
Nanoparticle Precipitation in a T-Mixer: Coupling Experimental and Numerical Investigations of the Fluid Dynamics With the Solid Formation Processes
Authors: Gradl Johannes , Schwertfirm Florian , Schwarzer Hans-Christoph , Schmid Hans-Joachim , Manhart Michael , Peukert Wolfgang
Published: September 2008

Mixing and consequently fluid dynamic is a key parameter to tailor the particle size distribution (PSD) in nanoparticle precipitation. Due to fast and intensive mixing a static T-mixer configuration is capable for synthesizing continuously nanoparticles. The flow and concentration field of the applied mixer is investigated experimentally at different flow rates by Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF). Due to the PIV measurements the flow field in the mixer was characterized qualitatively and the mixing process itself is quantified by the subsequent LIF-measurements. A special feature of the LIF set up is to detect structures in the flow field, which are smaller than the Batchelor length. Thereby a detailed insight into the mixing process in a static T-Mixer is given. In this study a CFD-based approach using Direct Numerical Simulation (DNS) in combination with the solid formation kinetics solving population balance equations (PBE) is applied, using barium sulfate as modeling material. A Lagrangian Particle Tracking strategy is used to couple the flow field information with a micro mixing model and with the classical theory of nucleation. We found that the DNS-PBE approach including macro and micro mixing, combined with the population balance is capable of predicting the full PSD in nanoparticle precipitation for different operating parameters. Additionally to the resulting PSD, this approach delivers a 3D-information about all running subprocesses in the mixer, i.e. supersaturation built-up or nucleation, which is visualized for different process variables.
Exploratory Experiments on Machined Riblets on Compressor Blades
Authors: Oehlert Karsten , Seume Joerg R.
Published: September 2008

During the last decades, riblets have shown a potential for viscous drag reduction. Several investigations and measurements of skin-friction have been completed in the boundary layer over a flat plate carrying riblets, mostly on thin foils. The purpose of the present study is to investigate machined riblet structures which are fabricated by grinding and laser machining. First tests dealing with machined riblets on flat plates are presented in this paper. Future investigations will examine the aerodynamic behaviour of machined riblets on NACA compressor blades. The specimens, flat plates and compressor blades, are tested in a linear cascade wind tunnel. Perfect trapezoidal riblets have been designed specifically to the flow parameters in this wind tunnel. Foils carrying the ideal riblets provide a basis for comparison with the riblets created by grinding and by laser machining. Parameters describing the geometry and the deviation from ideal riblets have been developed. It turned out that it is quite difficult to produce riblets satisfying the ideal geometrical requirements by machining. However, measurements in the wake of flat plates show that the laser shaped riblets as well as the ground riblets reduce pressure loss coefficients by up to 3.6%.
On the Dynamics of Active Flow Control Over a Separated Airfoil Using Leading Edge Unsteady Blowing
Authors: Charonko John J. , Vlachos Pavlos P.
Published: September 2008

Flow control has become universally accepted as an important technology that can potentially be implemented in future air and naval vehicles. It has been shown that flow control strategies can be effective in increasing lift, reducing or increasing drag, delaying or controlling separation, or even reattaching separated flows. However, there is still a need for better understanding of the physics that govern these processes. In order to address this, Time-Resolved Digital Particle Image Velocimetry (TRDPIV) was used in this experiment to quantitatively image the velocity field around a NACA-0015 airfoil at an angle of attack of 25 degrees and a Reynolds number of about 38,000. A slot was located approximately 0.1 chord lengths behind the leading edge and was used for pulsed flow injection at the natural shedding frequency of the wing. Ten cases with varying momentum ratios and pulse duty cycles were tested. A spatio-temporal analysis of the resulting flow fields was conducted. Reattachment and flow turning were observed, and the important features of the flow and their interactions with the wing are described. Analysis showed that the cycle-averaged momentum coefficient may govern flow behavior more than its peak value, and that the primary influence of flow control may be limited to the area within the pre-blowing separation region.
Aerosol Generation and Entrainment Model for Cough Simulations
Authors: Ersahin C. , Celik I. B. , Lindsley W. G. , Frazer D. G.
Published: September 2008

Coughing produces aerosols comprised of components of fluid that line the respiratory tract. These aerosols have been implicated in the transmission of many infectious diseases. Important factors that must be considered in aerosol transport include its physical size distribution, the shape and density of its components, as well as its chemical and biological composition. This study represents the initial phase of a larger project whose goal is to investigate the relationship between the generation of infectious aerosols and the dissemination of diseases in the workplace. The objective of this study was to develop a computational model representative of the generation and entrainment of an aerosol during cough. This model is composed of two sub-models; the first describes the formation of “mother” droplets and their entrainment in an air-stream and the second simulates the fragmentation of these droplets into smaller size distributions. The first sub-model is used to calculate the amount of fluid entrained in the droplets which is a function of the physical properties of the airway lining fluid and airflow patterns in the airway. The second sub-model describes the fragmentation of the droplets as a function of the physical properties of the fluid composition and a description of the flow field surrounding the droplet. Preliminary results show that, with the proper choice of model constants, it is possible to obtain relatively good agreement between model predictions and experimental measurements.
Visualization of Macro- and Micromixing Using Two-Color Laser Induced Fluorescence and Particle Image Velocimetry
Authors: Faes M. , Mewes D.
Published: September 2008

The progress in mixing on macro- and microscale is visualized by means of optical measurement systems. The Particle Image Velocimetry (PIV) is used to measure the velocity field inside the mixing system. The source term of the local energy dissipation is calculated by the information of the gradients of velocity. The Laser Induced Fluorescence (LIF) Technique is further developed for the simultaneous application of two different colors. A mixture of an inert and a reacting fluorescent dye is injected into a vessel. The macromixing is reflected by the inert dye serving as a tracer. Mixing on molecular scale is required for the progress of chemical reactions. Therefore the reacting dye indirectly visualizes the micromixing by changing its fluorescent characteristics during the reaction. The concentration fields of the two dyes are determined from measured fluorescence intensities. Based on these the local degree of deviation is calculated for detecting the areas of micromixing. Measurements are performed in a mixing system equipped with two glass cylinders. The working fluid is a mixture of glycerol and some adittional chemicals. The experiments are conducted in the laminar region. The injected dyes are stretched and folded in the flow field of the mixing system creating lamellar structures. The two optical measurement systems are prepared for the analysis of interrelation of macro- and micromixing subject to the local dissipation of energy.
A Numerical Model for Gaseous Cavitation Flow in Liquid Transmission Lines
Authors: Freitas Rachid Felipe Bastos
Published: September 2008

This work presents a numerical model for predicting the isothermal transient two-phase flow of liquid-gas homogeneous mixtures in rigid pipelines. The resulting mathematical problem is governed by a system of non-linear hyperbolic partial differential equations which is solved by means of an operator splitting technique, combined with the Glimm’s method. To implement Glimm’s method, it is presented the closed-form analytical solution of the associated Riemann problem. Uniqueness of this solution is demonstrated for a general set of equations of state for the liquid and the gas. Preliminary numerical results are presented in order to illustrated the model performance.
Modification of Blade Vortex Interactions Using Leading Edge Blowing
Authors: Weiland C. J. , Vlachos P. P.
Published: September 2008

This paper investigates the effectiveness of leading-edge blowing (LEB) active flow control for modifying the vortex induced vibrations induced on an airfoil by the wake of a circular cylinder. The airfoil was allowed to oscillate perpendicular to the fluid flow direction in response to the impinging Von-Karman street. The flow field was simultaneously captured using Digital Particle Image Velocimetry (DPIV) and accelerometer measurements in a time-resolved sense. The results indicate that LEB can significantly reduce the degree of unsteady loading due to the blade vortex interaction (BVI). In some cases, the LEB jet appears to break the coherency of a vortex incident on the airfoil, and in other cases it appears to increase the mean standoff distance of the vortex as it convects over the airfoil surface.