bluuebunny/crossref_metadata_2025 huggingface dataset:
SDSS J084539.17+225728.0: the first DBZ white dwarf with a metal-rich gaseous debris disc
Authors: Gänsicke B. T. , Koester D. , Marsh T. R. , Rebassa-Mansergas A. , Southworth J.
Published: October 2008

We report the discovery of a third white dwarf hosting a gaseous debris disc, SDSS J084539.17+225728.0. The typical double-peaked Ca ii 8498,8542,8662 Å emission lines can be modelled in terms of a Keplerian gas disc with a radial extent from ∼0.5 to ∼1.0 R⊙. The effective temperature of SDSS 0845+2257, Teff≃ 18 600 ± 500 K, is comparable to the two other white dwarfs with gaseous discs, SDSS 1043+0855 and SDSS 1228+1040, and hence substantially hotter than the bulk of white dwarfs where dusty debris discs were identified through the presence of infrared excess flux. This may suggest that the conditions to produce emission lines from debris discs in the optical wavelength range are only met for a relatively narrow range in Teff. The observed asymmetry in the line profiles indicates a substantial eccentricity in the disc. Two spectra obtained four years apart reveal a significant change in the shapes and equivalent widths of the line profiles, implying that the circumstellar disc evolves on relatively short time-scales. In contrast to SDSS 1043+0855 and SDSS 1228+1040, SDSS 0845+2257 has a helium-dominated atmosphere. We detect photospheric absorption lines of He, Ca, Mg and Si in the Sloan Digital Sky Survey spectrum, and hence classify SDSS 0845+2257 as DBZ white dwarf. The abundances for the three metals determined from model atmosphere fits are Ca/He ≃ 1.3 × 10−7, Mg/He ≃ 6.0 × 10−6 and Si/He ≃ 8.0 × 10−6. From the non-detection of Hα, we derive H/He < 3 × 10−5, which implies that the hydrogen-to-metal abundance ratio of the circumstellar material is ≳1000 times lower than in the Sun. This lends strong support to the hypothesis that the gaseous and dusty debris discs found around roughly a dozen white dwarfs originate from the disruption of rocky planetary material.
Self‐Reported Substance Use and Sexual Behaviors Among Adolescents in a Rural State
Authors: Dunn Michael S , Ilapogu Varaprasad , Taylor LaShan , Naney C. , Blackwell Roger , Wilder Regina , Givens C.
Published: October 2008

Background:  Research finds a strong association between substance use and risky sexual behavior but more needs to be known about this relationship. Few studies have examined this relationship among rural sixth‐ to eighth‐grade students. As such, the purposes of this study were to provide a descriptive profile of rural sixth‐ to eighth‐grade students’ substance use behavior and sexual activity and to examine the relationship between substance use behaviors and sexual activity.

Methods:  Participants consisted of a convenience sample of 10,273 middle school students (sixth to eighth grade) attending 10 public schools in rural Tennessee. The middle school Youth Risk Behavior Survey was administered to these students during April and May 2004.

Results:  Analysis found that a large percentage of students had tried cigarettes, alcohol, and inhalants. Additionally, it was found that sexual intercourse had been initiated by 18.8% of females and 25.4% of males. Of those students who reported ever having had sexual intercourse, 75% had reported the use of cigarettes and alcohol. In addition, approximately 50% of those students reported marijuana and inhalant use.

Conclusions:  The results suggest that substance use behavior has a relationship with the likelihood of initiating sexual activity. Additional longitudinal research with this population will be needed for explaining whether these select substance use behaviors are probable risk factors predisposing young rural adolescents to report engaging in sexual behaviors or a result of other factors.
Sexual Harassment Policies in K‐12 Schools: Examining Accessibility to Students and Content
Authors: Lichty Lauren F. , Torres Jennifer M.C. , Valenti Maria T. , Buchanan NiCole T.
Published: October 2008

Background:  Peer sexual harassment is a significant social problem with consequences for both students and schools. Four out of 5 students report experiencing sexual harassment. These experiences have been linked to poor psychological health and academic withdrawal. Recognizing the seriousness of sexual harassment in schools, Supreme Court rulings have established school liability for known instances of sexual harassment under Title IX of the Education Amendments of 1972. Federal guidelines established by the Office for Civil Rights of the US Department of Education mandate schools to develop sexual harassment policies; however, the implementation of these guidelines has not been examined. Therefore, this study assessed the degree to which sexual harassment policies in primary and secondary schools adhered to said guidelines.

Methods:  This study evaluated 784 primary and secondary school sexual harassment policies across 4 states on 3 key factors: accessibility to students (ie, via the Internet), consistency with federal guidelines regarding their content and the inclusion of 10 key components, and consistency of content across educational levels.

Results:  Only 14% of sexual harassment policies were available online; the majority of policies incorporated only 5 of the 10 critical components, and elementary school policies contained significantly fewer components than all other educational levels.

Conclusions:  The Internet is an underused resource for disseminating school sexual harassment policies to students. When policies are available, they rarely incorporate the key elements specified in the federal guidelines. Particularly troubling are the inaccessibility and incompleteness of elementary school policies. Greater attention to policy accessibility and comprehensiveness is needed.
Continuous Flow Microwave‐Assisted Processing and Aseptic Packaging of Purple‐Fleshed Sweetpotato Purees
Authors: Steed L.E. , Truong V.‐D. , Simunovic J. , Sandeep K.P. , Kumar P. , Cartwright G.D. , Swartzel K.R.
Published: October 2008

ABSTRACT:  Pumpable purees from purple‐flesh sweetpotatoes (PFSP) were subjected to microwave heating using a 60 kW, 915 MHz continuous flow system, followed by aseptic packaging in flexible containers to obtain a shelf‐stable product. Initial test runs were conducted using a 5 kW 915 MHz microwave system to measure dielectric in‐line properties and examine the puree temperature profiles. The results demonstrated uniformity in heating of the puree at sterilization temperatures (>121 °C), and the dielectric constants and loss factors were within the range of published values for orange‐fleshed sweetpotato purees. The pilot‐scale test runs in a 60 kW microwave unit produced shelf‐stable puree packages stable at room temperature. Polyphenolic content of the PFSP purees were evaluated and the results showed that while total phenolics increased (5.9%) and total monomeric anthocyanins slightly decreased (14.5%) with microwave application, antioxidant activity determined by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging activity and oxygen radical absorbance capacity (ORAC) assays did not significantly change as a result of microwave processing. Color values showed that microwave‐processed samples differed from fresh puree in saturation and hue angle, but not in overall color change. PFSP purees increased in gel strength when microwave processed, packaged, and stored, but the gel could be easily disrupted into flowable purees. Overall, high‐quality retention can be obtained by microwave processing and aseptic packaging of PFSP purees so that they can be used as functional food ingredients.
Efficacy of a Pharmacist‐Led Cardiovascular Risk Reduction Clinic for Diabetic Patients With and Without Mental Health Conditions
Authors: Taveira Tracey H. , Pirraglia Paul A. , Cohen Lisa B. , Wu Wen‐Chih
Published: October 2008

Coexisting mental health conditions (MHCs) attenuate treatment effects in diabetes. A retrospective analysis was performed of a pharmacist‐led cardiovascular risk reduction clinic (CRRC) targeting hypertension, diabetes, hyperlipidemia, and tobacco use in patients with at least one CRRC visit between January 2001 and January 2002. The United Kingdom Prospective Diabetes Study (UKPDS) risk change (after/before CRRC) for those with and without MHCs was compared. Of the 297 with diabetes and complete UKPDS data, 40.7% had at least 1 MHC (22.3% had a severe MHC). Patients with MHCs had a similar number of CRRC visits (4.7±2.6 vs 4.4±2.6) but had a lower baseline UKPDS score (0.31±0.18 vs 0.40±0.20; P=.001) compared with non‐MHC patients. The risk change after CRRC was similar for those with and without MHCs (0.10±0.13 vs 0.10±0.14; P=.82), but patients with MHCs had a longer CRRC enrollment (245±152 vs 205±161 days; P<.03). The efficacy of the CRRC model to reduce cardiovascular risk is not attenuated by a concomitant MHC.
Transitory Behavior of Synthetic Jets
Authors: Amitay Michael , Cannelle Florine
Published: October 2008

The transitory behavior of an isolated synthetic (zero net mass flux) jet was investigated experimentally using PIV and hot-wire anemometry. In the present work, the synthetic jet was produced over a broad range of length- and time-scales, where three formation frequencies, f = 300, 917, and 3100Hz, several stroke lengths (between 5 and 50 times the slit width) and Reynolds numbers (between 85 and 408) were tested. The transitory behavior, following the onset of the input signal, in planes along and across the slit was measured. It was found that the time it takes the synthetic jet to become fully developed depends on the stroke length, formation frequency and Reynolds number. In general, the transients consist of four stages associated with the merging of vortices in both cross-stream and spanwise planes that grow in size, which lead to the pinch off of the leading vortex before the jet reaches its steady-state.
Effect of Particulate Diffusion on the Free Turbulent Flow Based on Two-Fluid
Authors: Fesanghari R. , Basirat Tabrizi H. , Hamdullahpur F.
Published: October 2008

This paper is concerned with the two-dimensional gas-solid turbulent plane-mixing layer. The solid phase is considered a continuum and a two-fluid model, which is coupled by source terms due to particle drag and diffusion. Finite volume scheme has been employed for the governing equations. The simulation results show that the ratio of particle diffusion coefficient and kinematics viscosity of the carrier gas, have significant influence on the prediction of particles trend. In addition, it is observed that the loading ratio has no significant effect on the gas-solid flow prediction. The results are compared with the existed experimental data’s of others. This kind of modeling will ease the time consuming, stochastic approach of the Eulearian-Lagrangian methods but needs further investigation on the particle diffusivity term.
Numerical Analysis of Flow Phenomena Related to the Unstable Energy-Discharge Characteristic of a Pump-Turbine in Pump Mode
Authors: Braun O. , Kueny J.-L. , Avellan F.
Published: October 2008

Regions of positive slope in the pressure-discharge characteristics are one of the major concerns in design and operation of centrifugal pumps, as they are limiting the admissible operating range to values above the critical discharge. The industrial pump turbine of specific speed ν = 0.42 (nq = 66 min−1) proposed as QNET-CFD test case TA6-04 shows a marked saddle in the energy-discharge characteristic associated to a sudden drop of efficiency versus discharge at part load. The pump-turbine consists of a shrouded impeller with five blades, a diffuser with 22 guide and stay vanes and a spiral casing. CFD flow simulations on a reduced model were carried out with a finite volume Navier-Stokes code (CFX-5.7) using block-structured hexahedral meshes and the Menter-SST Turbulence model. Control of numerical quality has been performed. Reduced models with relatively low computational effort (mixing plane interface) already permit to capture the drop in efficiency and energy coefficient to analyze the flow phenomena inducing the drop of the energy coefficient Ψ that occurs at partial discharge. Analysis of local flow patterns and energy and velocity distributions at the rotor-stator interface that are related to the onset of recirculation are presented.
A Lagrangian Vortex Method for Simulating Flow Over 3-D Objects
Authors: Gharakhani A. , Sitaraman J. , Stock M. J.
Published: October 2008

A grid-free method for the simulation of incompressible flow over complex 3-D objects is presented. The algorithm is based on the Lagrangian Vortex Element and the Vorticity Redistribution methods to account for vorticity dynamics and diffusion, respectively. The wall velocity boundary conditions are imposed by solving a Petrov-Galerkin discretization of the Fredholm boundary integral equation of the second kind for the vector-valued vortex sheets at the wall. Computations are accelerated using a MPI-parallel adaptive Fast Multipole Method (oct-tree code). In this paper, the computational algorithm is described briefly, and the first in a series of benchmark results presented using the example of flow over a sphere at low Reynolds numbers. Preliminary diagnostics of the present simulations show very good agreement with previously published data.
Rotor-Stator Interactions in a Vaned Diffuser Radial Flow Pump
Authors: Dupont P. , Caignaert G. , Bois G. , Schneider T.
Published: October 2008

The paper presents an analysis of unsteady effects associated with rotor stator interactions in a vaned diffuser radial flow pump. The experimental data have been obtained by 2D Particle Image Velocimetry at mid height between hub and shroud, in the impeller outlet zone and within a vaned diffuser passage. Unsteadiness is discussed first in the impeller outlet zone and then along a passage of the vaned diffuser.
Numerical Torque Converter Performance Predictions: Validation and Application to a Rapid One Dimensional Approach
Authors: Bois G. , Bayeul A. C. , Leclerc C. , Meredith B. , Lebouvier Y.
Published: October 2008

The flow field in an automotive torque converter was analysed using the munerical results given by a commercially available package CFD code: FLUENT 5 TM. Calculations are performed for different speed ratio between pump and turbine in order to cover the total range of operation assuming no transient effects. The different number of blades of the torque converter components (pump, turbine and stator) are taken into account. The use of a close loop domain allows the circulating mass flow rate to be adjust itself depending on the computed flow. Local flow patters and evolutions with speed ratio are analysed and discussed. Overall numerical results are compared with experimental standard performances like torque ratio K, pump Y factor and efficiency. Results of these numerical analysis are taken into account in order to improve an existing one dimensional approach. The resulting modifications have been applied in a complete set of different converter geometries with good results.
Certain Effects of Blade-Geometry and of Inlet-Recirculation on the Distribution of the Meridian Velocities at the Impeller-Outlet
Authors: Yedidiah S.
Published: October 2008

This study discusses certain causes of the differences in the distribution of the meridian velocity-components of the pumped liquid, at the outlet of a rotodynamic impeller. In particular, it explains the seemingly enigmatic fact that, at design-flow, there have been observed very large differences in the shroud-to-shroud distribution of the meridian velocity-components of the liquid at the outlet of the impeller. Against this, below a certain partial flow-rate, the shroud-to-shroud distribution of these velocity-components became much more uniform.
Formulation and Numerical Performance of an Adaptive Algorithm for Efficient Collision Detection
Authors: Melheim Jens A. , Chiesa Matteo , Gjelsvik Anders
Published: October 2008

The ‘Discrete Particle Method’ (DPM) is a versatile numerical tool for improving the understanding of particle flows behavior on a meso-scopic level. A crucial point when using the DPM is the CPU-time consumption for detection of particle collisions. An adaptive algorithm for efficient particle-particle and particle-wall collision detection in a two-dimensional case is presented. The physical domain is hierarchically divided and structured as a quadtree. The algorithm ensures an efficient computation of colliding particle flows by splitting and merging the cells between each time step to keep the number of particles within a proposed range. The numerical performance of the adaptive algorithm is studied by simulating a flow particle in a 90° bend. The computational time of the adaptive algorithm is compared with the simulations performed with a uniform fixed cell structure with optimal size. The adaptive algorithm seems to be mostly advantageous in flows where the particles are not uniformly distributed, in complex geometries, and otherwise where information about the optimal cell size is not known a priori.
Invariance of CDST in the Turbulent Wake of Bluff Bodies
Authors: Hu J. C. , Zhou Y. , Huang J. F.
Published: October 2008

The inter-relationship of drag coefficient Cd and Strouhal number St in a turbulent wake was experimentally investigated for ten cylinders of the same characteristic height d but of different cross-sections at Re = 2600 and 6000, based on the freestream velocity U∞ and d. It is found that, although Cd and St depend strongly on the geometric cross-section of the cylinder, the product of CdSt is invariant, about 0.25, under present experimental conditions. This invariance of CdSt is further confirmed with respect to Re and angle of attack of a square cylinder based on a collection of data in the literature. It is further found that CdSt is actually the ratio of the dimensionless work done upon the fluid by the cylinder to the dimensionless wavelength.
Basic Considerations for Evaluating Hydraulic Power Recovery of Fluid Streams Expanding With or Without Gas or Vapor Evolution
Authors: Visser Frank C.
Published: October 2008

A review of status is presented, discussing hydraulic power recovery of fluid streams expanding with or without gas evolution. Point of departure for the treatise given, is embedded in basic thermodynamics and fluid mechanics. Formulae for estimating isentropic power recovery are derived, which hold asymptotically for low gas to liquid mass fraction. These formulae provide simple means for calculating power recovery with gas evolution, given a certain vapor void fraction. The key element in the entire approach is to attribute the extra power recovery due to gas evolution to the change in density of the fluid stream. The formulae and discussions presented in the paper may assist the (application) engineer in evaluating the effect of vapor evolution with regard to hydraulic performance of hydraulic power recovery turbines. The paper further also discusses the condition of (runaway) overspeed, as this should not be omitted from a review on basic considerations for hydraulic power recovery turbines. Formulae and calculation methods are given for calculating runaway speed, choke flow and time to runaway speed.
Numerical Investigations of the Flow Characteristics in the Straight-Through Honeycomb Seal
Authors: Li Jun , Deng Qinghua , Feng Zhenping
Published: October 2008

Investigation of the flow characteristics in the straight-through honeycomb seal installed in the diagram for steam turbines using the numerical simulation method is presented in this paper. To illustrate the leakage flow performance of the straight-through honeycomb seal, the straight-through labyrinth seal with the same sealing clearance and pressure difference is also calculated. The flow fields are predicted using a commercial finite volume code with the standard k-ε turbulence model. The computational grids include the basic sealing geometries as well as the three-dimensional honeycomb seal and labyrinth seal structures. The obtained results demonstrate that the dimensionless discharge coefficient of the honeycomb seal is smaller than that of the labyrinth seal at the same sealing clearance and pressure difference. The leakage flows of the honeycomb seal are divided into much more smaller recirculation flows than that of the labyrinth seal due to its honeycomb structures. The honeycomb structure of the honeycomb seal leads to decrease the leakage mass flow rate. The flow characteristics of the honeycomb seal and labyrinth seal are also illustrated. This study can be able to supply the theoretical foundation and technical support for the engineering application of the honeycomb seal in steam turbines.
Numerical Investigation on Wavy Streak Formation Due to Sand Erosion
Authors: Suzuki Masaya , Toda Kazuyuki , Yamamoto Makoto
Published: October 2008

It is well known that sand erosion is a typical multi-physic problem, that is, the interactions among flow field, particle motions and wall deformation are important. To simulate this phenomenon, turbulent flow field, particle trajectories and amount of erosion on an eroded wall are calculated repeatedly. In the computations of the flow field, compressible Navier-Stokes equations and low-Reynolds-number type k-ε turbulence model are adopted. Assuming that the concentration of suspended particles is dilute, particle-particle collision and the influence of particle motions on the flow field are neglected. The Neilson-Gilchrist erosion model is used to estimate the weight loss due to erosion. Based on this numerical procedure, the gas-particle two-phase turbulent flow field in 90-degree bend with a square cross-section is simulated, in order to clarify erosion pattern formation by fluid/particle/wall interaction.
Large Eddy Simulation of Confined Swirling Coaxial Jets
Authors: Kim Sung-Eun , Zhu Xuelei , Orsino Stefano
Published: October 2008

Large eddy simulations (LES) have been carried out for confined swirling coaxial jets discharged into a suddenly expanded pipe, which was studied experimentally by Roback and Johnson [1, 2]. The computations were made using a parallelized finite-volume-based Navier-Stokes solver that is second-order accurate in time and space, and permits use of unstructured meshes. The computational domain starts from an inlet placed upstream of the swirl generator, which makes the inlet boundary condition easy to specify. Subgrid-scale turbulent stresses were modeled using a dynamic Smagorinsky model applicable to complex three-dimensional flows without any statistically homogeneous directions. Subgrid-scale turbulent scalar flux is modeled using a constant Schmidt number in conjunction with the dynamically computed subgrid-scale turbulent viscosity. The LES predictions were found to closely reproduce the salient features of the flow and the species concentration downstream of the expansion. One of the conclusions was that a good resolution of the mean flow and turbulence in the upstream region is crucial in accurately predicting the mixing downstream of the expansion.
Particle Deposition in a Room-Scale Chamber With Particle Injection
Authors: Zhang N. , Zheng Z. Charlie , Glasgow L. , Braley B.
Published: October 2008

A model simulating the deposition of small particles with turbulent transport, sedimentation, and coagulation, is presented. Experimental measurements were conducted in a room-scale chamber using a specially designed sequential sampler. The measured deposition-rate data are compared with the simulation results. Distributions of particle-number density at different times are plotted in several viewing planes to facilitate discussion of the particle distribution patterns.
A Novel Mirror-Image Technique for Wheel and Ground Simulation in Automotive Wind-Tunnels
Authors: Mavuri Satya P. , Watkins Simon , Watmuff Jon
Published: October 2008

A novel method for simulating the relative motions of the wheels and moving ground for road vehicle aerodynamics is presented. The method revisits an old concept where two identical vehicles are used and positioned so that they are mirror images, with the ground being represented by the horizontal plane of symmetry. The method involves double symmetry, where two half models (e.g. a car split down the vertical centerline) contact at the rotating wheel contact patches and the resulting (opened) vehicle halves lie on a reflection plane. This can either be the tunnel floor or the equivalent CFD plane. For some forms of physical testing this offers advantages (such as easy access to wheel cavities and requiring only one vehicle) but sealing the gap between the tunnel floor and the vehicle halves can interfere with the force balance accuracy and problems can arise with time-varying flows crossing the time averaged zero flow boundary. This paper describes the concept and CFD and model-scale EFD evaluations which were found to compare well.
An Integrated Experimental/Numerical Study of the Bubbly Wake Behind a Cavitating Hydrofoil
Authors: Qin Qiao , Wang Hong , Arndt Roger E. A.
Published: October 2008

Since cavitation is often unavoidable, it is crucial to understand how fluid-handling machinery operates under cavitating conditions. The purpose of this research is to investigate two-phase flow structure in the wake of a hydrofoil undergoing unsteady partial cavitation using an integrated experimental and numerical approach. Experiments were conducted systematically in the high-speed water tunnel at the St. Anthony Falls Laboratory to capture the characteristics of the bubbly wake induced by unsteady partial cavitation. The velocity and bubble information were obtained using a TSI color burst LDA/PDA system with a beam splitter and IFA processor. A nominal sampling period of 30 seconds per coordinate point was chosen for the collection of all data sets of LDV measurements. Since the LDV data rate changes with position, the collection period was also controlled by the upper limit of samples, which were 3,000 samples per point. In order to get enough samples, a nominal sampling period of 180 seconds per coordinate point was selected for PDA measurements and 10,000 samples were used as the upper limit. The actual number of samples for each PDA measurement location was between 5,000 and 10,000 with an average data rate of 40 Hz. The averaged bubble size measured in the wake is obtained to be 240 ∼ 300 microns and the estimated maximum void fraction in the wake being in the order of one percent. A virtual single-phase natural cavitation model with the effect of incondensable gas was developed and implemented to better understand the cavitating wake physics. A number of parameters, such as time-averaged velocity distributions both on suction side of the hydrofoil and in the wake, spectral characteristics of unsteady lift oscillations etc., were computed and found in very good agreement with experimental data (Qin 2004), indicating this model can capture the main physics of unsteady cavitating flow. It was also found that the peak of time-averaged incondensable gas in the wake is in the order of one percent, indicating that the majority of vapor bubbles were condensed to water in the wake and hence the bubbles in the wake of unsteady cavitation are mainly gas bubbles.
Application of a Perturbated Two-Maxwellian Approach for the Modelling of Kinetic Stress Transfer by Collision in Non-Equilibrium Binary Mixture of Inelastic Particles
Authors: Fede Pascal , Simonin Olivier
Published: October 2008

This paper introduce a model for the kinetic stress transfer by collision in binary mixture of inelastic particles. The derived model is based on a perturbated two-Maxwellian approach allowing to described non-equilibrium particulate flows. The model is validated by comparison with numerical results carried out using a deterministic Discrete Particle Simulation (DPS).
Sedimentation of 1,024 Particles
Authors: Zhang Zhongzhen , Prosperetti Andrea
Published: October 2008

This paper demonstrates the performance of PHYSALIS, a numerical method for the direct numerical simulation of Navier-Stokes flows with many solid spheres. The particles may be fixed or mobile, and they may have different radii. The basic idea of the method stems from the observation that, due to the no-slip condition, the fluid velocity in the immediate neighborhood of the particle differs little from a rigid-body velocity field so that it is legitimate to neglect the square of this difference. With the aid of a suitable transformation, it is possible to exploit this observation to introduce an auxiliary velocity field that satisfies the Stokes equations in a thin layer of cells adjacent to the particle. The known general solution of the Stokes equations can then be used to bridge the gap between a finite-difference solution on a regular grid and the particle surface. After a brief summary of the method, the paper presents the results of validation studies for the flow past a stationary sphere and the motion of a sphere settling in a container under gravity. The main motivation for the development of the method was however its ability to deal with a large number of particles. To demonstrate this point, some results of the simulation of the gravitational settling of 1,024 spheres are shown. The time evolution of the spatial arrangement of the particles is investigated by means of the two-particle distribution function.
A Numerical Study on the Aeroacoustic of a Vaned Centrifugal Fan
Authors: Khelladi S. , Kouidri S. , Bakir F. , Rey R.
Published: October 2008

High speed vaned centrifugal fans are widely used in several manufacturing and home appliances. For the designers the noise generated by these machines is one of the most important parameters to be reduced. The centrifugal fan used for this study is made up of an impeller, a diffuser and a return channel. The impeller turns at a relatively high speed about 35000 rpm. The objective of this study is to understand the mechanism of the noise generation within this type of machines. The contribution of the tangential and radial forces is highlighted. These fluctuating forces are due to the unsteady flow at the impeller-diffuser interface. The obtained result shows the effect of monopole and dipole sources on the overall noise.
Pump Performance Improvement by Restraining Back Flow in Screw-Type Centrifugal Pump
Authors: Tatebayashi Yasushi , Tanaka Kazuhiro , Kobayashi Toshio
Published: October 2008

The authors have been investigating the various characteristics of screw-type centrifugal pumps, such as pressure fluctuations in impellers, flow patterns in volute casings, and pump performance in air-water two-phase flow conditions. During these investigations, numerical results of our investigations made it clear that three back flow regions existed in this type of pump. Among these, the back flow from the volute casing toward the impeller outlet was the most influential on the pump performance. Thus the most important factor to achieve higher pump performance was to reduce the influence of this back flow. One simple method was proposed to obtain the restraint of back flow and so as to improve the pump performance. This method was to set up a Ring-like wall at the suction cover casing between the impeller outlet and the volute casing. Its effects on the flow pattern and the pump performance have been discussed and clarified to compare the calculated results with experimental results done under two conditions — namely, one with and one without this Ring-type wall. The influence of wall’s height on the pump head was investigated by numerical simulations. In addition, the difference due to the wall’s effect was clarified to compare its effects on two kinds of volute casing. From the results obtained it can be said that restraining the back flow of such pumps was very important to achieve higher pump performance. Furthermore, another method was suggested to restrain back-flow effectively. This method was to attach a wall at the trailing edge of impeller. This method was very useful for avoiding the congestion of solids because this wall was smaller than that used in the first method. The influence of these factors on the pump performance was also discussed by comparing simulated calculations with actual experiments.
Experimental Investigation of Statistically Steady Rayleigh-Taylor Mixing at High Atwood Numbers
Authors: Banerjee Arindam , Andrews Malcolm J.
Published: October 2008

In the present work, a novel gas channel experiment was used to study the non-equilibrium development of high Atwood number Rayleigh-Taylor mixing. Two gas streams, one containing air and the other containing a Helium-Air mixture, flow parallel to each other separated by a thin splitter plate. The streams meet at the end of the splitter plate leading to the formation of an unstable interface and initiation of buoyancy driven mixing. This buoyancy driven mixing experiment allows for long data collection times, short transients and was statistically steady. The facility was capable of large Atwood number studies (At ∼ 0.75). Here, we describe recent work to measure the self similar evolution of mixing at large density differences (At ∼ 0.1). Diagnostics include a constant temperature Hot Wire anemometer, and high resolution thermocouple measurements. The Hot Wire probe gives velocity statistics of the mixing layer. A multi-position single-wire technique was used to measure the velocity fluctuations in three mutually perpendicular directions. Analysis of the measured data was used to explain the structure of mixing as it develops to a self-similar regime in this flow.
Interfacial Area and Number Density Transport Equations for Modeling Multiphase Flows With Cavitation
Authors: Wang De Ming , Han Jaehoon , Greif David , Zun Iztok , Perpar Matjaz
Published: October 2008

In this paper we report progress toward developing advanced cavitation models with Eulerian multifluid method. The bubble number density and the interfacial area equations are introduced into the general framework of multifluid method for multiphase cavitating flows in order to account for the variable size nature of the bubble distribution. The physical models for bubble breakup and coalescence are based on the work by Ishii group’s work in recent years. Simulation results of a cavitating flow are compared with the corresponding experimental data, which include the bubble size distribution, bubble volume fraction and bubble number density. The ability of predicting bubble distribution characteristics is particularly useful as an input for cavitation erosion analysis.
A Novel Approach for Modeling Material Bed in a Rotary Kiln
Authors: Jaanu Keijo , Vanhanen Jarkko , Zamankhan Piroz
Published: October 2008

Handling and processing contaminated, as well as environmentally hazardous materials, requires a deeper understanding of their physics of deformation and flow. In industrial scale, a sampling procedure can be applied at the end of the large reactor aperture such as a rotary kiln. In order to predict the processes involved in systems such as a rotary kiln, in the present study computational models are used to develop a useful tool to guide the refinement of the design process. Employing hydrodynamic continuum equations for describing the deformation and flow of dense gas-particle mixtures, the behavior of the materials within the bed and the release process of the contaminants are modeled during the handling process. The present model assumes a thin active layer at the bed surface with the rest of the bed material deforming plastically like a solid under weak shear. Material transport properties are defined in order to describe the mixing processes in the above-mentioned system. The numerical results obtained elucidate the physics of movement of the bed material, opening the possibility for developing a meaningful numerical model for the heat and mass transfer in a rotary kiln that may be of industrial use.
The Effect of Inlet and Exit Pressure-Drop on the Determination of Porous Media Permeability and Form Coefficient
Authors: Naaktgeboren Christian , Krueger Paul S. , Lage Jose´ L.
Published: October 2008

The determination of permeability and form coefficient, defined by the Hazen-Dupuit-Darcy (HDD) equation of flow through a porous medium, requires the measurement of the pressure-drop per unit length caused by the medium. The pressure-drop emerging from flow adjustment effects between the porous medium and the surrounding clear fluid, however, is not related to the porous medium length. Hence, for situations in which the entrance and exit pressure-drops are not negligible, as one would expect for short porous media, the determination of the hydraulic parameters using the HDD equation is hindered. A criterion for determining the relative importance of entrance and exit pressure-drop effects, as compared to core effect, is then of practical and fundamental interest. This aspect is investigated analytically and numerically considering flow through a thin planar restriction placed in a circular pipe. Once the pressure-drop across the restriction is found, the results are then compared to the pressure-drop imposed by an obstructive section having the same dimension as the restriction but finite length, playing the role of the least restrictive porous medium core. This comparison yields a conservative estimate of the porous medium length necessary for neglecting entrance and exit pressure-drop effects. Results show that inlet and exit pressure-drop effects become increasingly important compared to core effects as the porosity decreases and Reynolds number increases for both laminar and turbulent flow regimes. (Correlations based on experimental results available in the literature are employed for turbulent pipe flow). The analysis also shows why the HDD equation breaks down when considering flow through porous media where the entrance and exit pressure-drop effects are not negligible, and how modified permeability and form coefficients become necessary to characterize this type of porous media. Curve-fits accurate to within 2.5% were obtained for the modified permeability and form coefficients of the planar restriction with Reynolds number ranging from 0.01 to 100 and porosity from 0.0625 to 0.909.
Unsteady Aerodynamic Performance of a Centrifugal Compressor With Oscillating Downstream Static Pressure
Authors: Eum H. J. , Kang S. H.
Published: October 2008

In many applications, centrifugal compressors experience various kinds of downstream pressure disturbances which can lead to unstable operation even at the design operating condition. In this paper, 3-D numerical simulations have been carried out to understand the dynamic behaviors of the centrifugal compressor for the pulsation of downstream pressure disturbances and 1-D model using the method of characteristics has been developed to predict the behaviors more effectively. Static pressure disturbances with a frequency range from 25Hz to 1300 Hz and constant amplitude have been introduced at the diffuser exit. Static pressure rise and mass flow rate deviated from the quasi-steady characteristic as the frequency increased. The fluctuation of mass flow rate at the diffuser exit was amplified or attenuated depending on the disturbance frequency. The fluctuation was severely amplified at a specific frequency which seemed to be an acoustic resonance of the present compressor model including an inlet duct, a blade passage and a diffuser. The result of 1-D model showed good agreements with that of 3-D numerical simulation.
Explicit vs. Implicit Particle-Liquid Coupling in Fixed-Grid Computations at Moderate Particle Reynolds Number
Authors: Truong Hung V. , Wells John C. , Tryggvason Gretar
Published: October 2008

In an attempt to develop a reliable numerical method that can deal economically with a large number of rigid particles moving in an incompressible Newtonian fluid at a reasonable cost, we consider two fictitious-domain methods: a Constant-density Explicit Volumetric forcing method (CEV) and a Variable-density Implicit Volumetric forcing method (VIV). In both methods, the mutual interaction between the solid and the fluid phase is taken into account by an additional body force term to the Navier-Stokes equations, but the physical meaning of the forcing is different for the two methods. In the CEV method, which is built on a constant-density Navier-Stokes solver, the net forcing added to the fluid is generally not zero, and must be cancelled by applying Newton’s first law to a rigid particle template which has the same shape as the rigid particle and carries the “excess mass” of the rigid particle, i.e. the excess over the mass of the displaced fluid. The “target velocity” to which one forces the velocity within the particle is evaluated through the equation of motion for the rigid particle template. In the VIV method, built on a variable-density incompressible flow solver, the rigid particle (angular) velocity is determined by averaging the (angular) momentum, within the particle domain, of the fractional-step velocity field, and the net forcing is zero. By design, this method does not require any rigid particle template equations, so it can be applied for both neutral and non-neutral density ratios without any difficulties. We consider two test problems with single freely moving circular disks: a disk falling in quiescent fluid, and a disk in Poiseuille channel flow. At near-neutral density ratios, the CEV method is found to perform better, while the VIV method yields more accurate results at higher relative density ratios.
A New Approach to Heat and Mass Transfer in a Rotary Dehumidifier: Modeling and Simulation
Authors: Esfandiarinia Fatemeh , van Paassen Dolf , Saidi Mohamad Hassan
Published: October 2008

In this paper the analytical and simulation modelling of the combined heat and mass transfer processes that occur in a solid desiccant wheel is carried out. Using the numerical method, the performance of an adiabatic rotary dehumidifier is parametrically studied, and the optimal rotational speed is determined by examining the outlet adsorption-side humidity profiles. An approach to compare the solutions for different conditions used in air dehumidifier has been investigated according to the previous published studies. Comparing the simulated results with the published actual values of an experimental work substantiates the validity of model. The model accuracy with respect to the key variables (outlet and inlet temperatures and humidity) is optimized to minimize margin of error. This method is useful to study and modelling of solid desiccant dehumidification and cooling system.
Computational Analysis of Various Factors on the Edgetone Mechanism Using High Order Schemes
Authors: Nonomura Taku , Muranaka Hiroko , Fujii Kozo
Published: October 2008

Flow fields of two dimensional jets impinging on the sharp edge are computationally simulated and the effect of various parameters on the edgetone that is created by the flow interaction is investigated. Compressible Navier-Stokes equations are used so that acoustic waves are captured accurately as a part of feedback-loop. For numerical accuracy, Pade type compact finite difference scheme are used. First parameter is the jet velocity. Computational result shows good qualitative agreement with the experiment. Edgetone frequencies obtained by the computation also show good correspondence with those of experimental study in the past. Second parameter is the nozzle lip thickness. Although not considered in the computational study in the past, the nozzle lip thickness influences to the results. Amplitude of acoustics of larger nozzle lip is greater than that of smaller ones. This effect may comes from the fact that acoustic wave as a part of feedback loop is emphasized by nozzle lip. Third parameter is the jet-profile. Four different jet-profiles with the same maximum velocity (from top-hat profile to parabolic profile) and four different jet-profiles with the same mean velocity are computed. The mean jet velocity appears to have strong influence on the stage. The results also indicated that the mean jet velocity and the jet-profile have influence on edgetone frequencies.
Prediction of Flow Behavior on Diffuser Angle in an Enclosure
Authors: Tripathi B. , Arora R. C. , Moulic S. G.
Published: October 2008

The present investigation deals with numerical prediction of airflow pattern in a room (enclosure) with a specific location of inlet and outlet with different values of Gr/Re2. Two-dimensional, steady, incompressible, laminar flow under Boussinesq’s approximation has been considered. The velocity and temperature distributions in a room have been found by solving Navier Stokes equations and energy equation numerically by SIMPLE and SIMPLEC algorithms.
Cavitation Experiments on Turbopump Inducers and Hydrofoils at Alta/Centrospazio: Overview and Future Activities
Authors: Cervone Angelo , Bramanti Cristina , Rapposelli Emilio , d’Agostino Luca
Published: October 2008

The aim of the present paper is to provide some highlights about the most interesting experimental activities carried out during the years 2000–2004 through the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Centrospazio/Alta S.p.A. After a brief description of the facility, the experimental activities carried out on a NACA 0015 hydrofoil for the characterization of the pressure coefficient on the suction side and evaluation the cavity length and oscillations are presented. Then, the results obtained to characterize the performance and the cavitation instabilities on three different axial inducers are showed: in particular, a commercial three-bladed inducer, the four-bladed inducer installed in the LOX turbopump of the Ariane Vulcain MK1 rocket engine and the “FAST2”, a two-bladed one manufactured by Avio S.p.A. using the criteria followed for the VINCI180 LOX inducer. The most interesting results are related to the effects of the temperature on the cavitation instabilities on hydrofoils and inducers. Experiments showed that some instabilities, like the cloud cavitation on hydrofoils and the surge on inducers, are strongly affected by the temperature, while others seem not to be influenced by the thermal effects. In the final part of this paper, some indications of the main experimental activities scheduled for the next future are provided.
An Analytic and Experimental Investigation of the Aerodynamic Performance Enhancements of Multiple Winglet Configurations
Authors: Miklosovic D. S. , Bookey P. M.
Published: October 2008

An experimental effort was undertaken to assess the effectiveness and efficiency of three winglets mounted chordwise to the tip of a rectangular wing (NACA 0018 section). The winglets, with an aspect ratio of 3.6, were mounted on a half-span wing having an aspect ratio of 3.1. Twenty configurations of varying dihedral arrangements were analyzed with a vortex lattice method and tested in a low-speed wind tunnel at a Reynolds number of 600,000. In general, the arrangements involving high dihedral angles had lower performance increments, due to lower lift and higher interference drag. More specifically, the results showed that the winglets placed at 60, 45, and 30 degrees, respectively, produced nominal 4% higher lift and 46% lower drag. The most dramatic findings from this study show that positioning the winglet dihedral angles had the result of adjusting the point of maximum L/D and the magnitude of the pitching moment coefficient. These observations suggest that multiple winglet dihedral changes affect the lift, drag, and pitching moment in such a way that they are feasible for use as actively-controlled surfaces to improve the performance of aircraft at various flight conditions and to “tune” the longitudinal stability characteristics of the wing.