bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFICIENCY OF LIABILITY RULES WITH MULTIPLE VICTIMS
Authors: Jain Satish K.
Published: March 2009

Abstract. This paper investigates the structure of liability rules from the efficiency perspective when there are multiple victims. It is shown that, when there is one injurer and multiple victims, there is no liability rule with the property of invariably yielding efficient outcomes. The fact that there is no rule which is efficient for all applications of course does not in any way preclude the possibility of a rule being efficient with respect to some subclass of applications which may be of interest. We consider in this paper the important subclass of applications (′) which are such that the expected loss of a victim depends only on the care level taken by that victim and the care level taken by the injurer. It is shown that a sufficient condition for a one‐injurer multiple‐victim liability rule to be efficient with respect to the above subclass of applications ′ is that its structure be such that: (i) whenever the injurer is negligent and a particular victim is non‐negligent, the entire loss incurred by that victim must be borne by the injurer; and (ii) whenever a particular victim is negligent and the injurer is non‐negligent, the entire loss incurred by that victim must be borne by the victim himself. In fact, for an important subclass of one‐injurer multiple‐victim liability rules, characterized by the condition that the proportions in which the loss incurred by a particular victim is to be borne by the injurer and that victim must depend only on the non‐negligence proportions of the injurer and that victim, the above condition is both necessary and sufficient for efficiency with respect to the restricted subclass of applications ′.
Cognitive and emotional associations to positive schizotypy during adolescence
Authors: Debbané Martin , Van der Linden Martial , Gex‐Fabry Marianne , Eliez Stephan
Published: March 2009

Background:  Sub‐clinical symptoms of psychosis such as hallucinations and delusions, known as positive schizotypy, constitute one of the strongest predictive factors for adult psychotic disorders. Recent cognitive models suggest that the expression of positive schizotypy is associated with depression, anxiety, metacognitive beliefs and self‐monitoring deficits. In this study, we present empirical data on the relationships positive schizotypy hold with both emotional and cognitive factors.

Methods:  A sample of 163 adolescents (77 females) participated in this study (mean age 15.3, 12–18 years). Subjects filled out self‐report questionnaires assessing the emotional dimensions of depression and anxiety, as well as metacognitive beliefs. Self‐monitoring skills were assessed using an action monitoring paradigm sensitive to dysfunctions associated with psychosis‐proneness. Multivariate regression models were employed to examine emotional and cognitive contributions to positive schizotypy during adolescence.

Results:  Analyses revealed that dimensions of depression, anxiety, and metacognitive beliefs significantly correlated with the expression of positive schizotypy. When accounting for the effects of depression and metacognitive beliefs in adolescents reporting hallucinations, self‐monitoring dysfunctions seemed to represent a significant factor in the expression of positive schizotypy.

Conclusion:  The present results suggest that the expression of positive schizotypy during adolescence is modulated by emotional factors of depression and anxiety, as well as metacognitive beliefs and self‐monitoring dysfunctions. The current data lend some evidence that supports the cognitive‐developmental account of positive symptom formation before the onset of a psychotic disorder.
Biomechanical and histological behavior of zirconia implants: an experiment in the rat
Authors: Kohal Ralf J. , Wolkewitz Martin , Hinze Marc , Han Jung‐Suk , Bächle Maria , Butz Frank
Published: March 2009

Objective: This study aimed at evaluating the integration of zirconia implants in a rat femur model.

Material and methods: Zirconia implants with two distinct surface topographies were compared with titanium implants with similar topographies. Titanium and zirconia implants were placed into the femurs of 42 male Sprague–Dawley rats. Four groups of implants were utilized: machined zirconia implants, zirconia implants with a rough surface, machined titanium implants, and titanium implants with an electrochemically roughened surface. After a healing period of 28 days, the load‐bearing capacity between the bone and the implant surface was evaluated by a push‐in test. Additionally, after a healing period of 14 and 28 days, respectively, bone tissue specimens containing the implants were processed and histologically analyzed.

Results: The mean mineralized bone‐to‐implant contact showed the highest values after 14 and 28 days for the rough surfaces (titanium: 36%/45%; zirconia: 45%/59%). Also, the push‐in test showed higher values for the textured implant surfaces, with no statistical significance between titanium (34 N) and zirconia (45.8 N).

Conclusions: Within the limits of the animal investigation presented, it was concluded that all tested zirconia and titanium implant surfaces were biocompatible and osseoconductive. The presented surface modification of zirconia implants showed no difference regarding the histological and biomechanical results compared with an established electrochemically modified titanium implant surface.
Association of glucocorticoid receptor polymorphisms with the susceptibility to major depressive disorder and treatment responses in Korean depressive patients
Authors: Lee Hwa-Young , Kang Rhee-Hun , Han Sang-Woo , Paik Jong-Woo , Chang Hun Soo , Jeong Yoo Jung , Lee Min-Soo
Published: March 2009

Objective:

Major depressive disorder (MDD) is closely related to stress reactions and serotonin probably underpins the pathophysiology of MDD. Alterations of the hypothalamic-pituitary-adrenal axis at the gene level have reciprocal consequences on serotonin neurotransmission. Glucocorticoid receptor (GR) polymorphisms affect glucocorticoid sensitivity, which is associated with cortisol feedback effects. Therefore, we hypothesised that GR polymorphisms are associated with the susceptibility to MDD and predict the treatment response.

Method:

Ninety-six subjects with a minimum score of 17 on the 21-item Hamilton Depression Scale (HAMD) at baseline were enrolled into the present study. The genotypes of GR (N363S, ER22/23EK, Bcl1, and TthIII1 polymorphisms) were analysed. The HAMD score was again measured after 1, 2, 4 and 8 weeks of antidepressant treatment to detect whether the therapeutic effects differed with the GR genotype.

Results:

Our subjects carried no N363S or ER22/23EK genetic polymorphisms and three types of Bcl1 and TthIII1 genetic polymorphisms. The C/C genotype and C allele at Bcl1 polymorphism were more frequent in MDD patients than in normal controls (p < 0.01 and p = 0.01, respectively). The genotype distributions did not differ significantly between responders and non-responders.

Conclusion:

These results suggest that GR polymorphism cannot predict the therapeutic response after antidepressant administration. However, GR polymorphism (Bcl1) might play a role in the pathophysiology of MDD. Future studies should check this finding in larger populations with different characteristics.
Cichlid fish visual systems: mechanisms of spectral tuning
Authors: CARLETON Karen
Published: March 2009

Hundreds of species of cichlid fishes have evolved in the Great Lakes of Africa. These colorful fishes are known for their ecological diversity. Here, we discuss the diversity of their visual systems. Cichlids have seven unique cone opsin genes, which produce visual pigments sensitive from the ultraviolet to the red end of the spectrum. Different species typically express three visual pigments to produce a trichromatic visual system. Because species differ in which sets of opsin genes they express, visual sensitivities can differ widely. In addition to the large visual pigment shifts from changing gene expression, cichlids can also more finely tune visual pigments through alterations in opsin amino acid sequence. Both of these tuning mechanisms likely play an important role in cichlid ecology and could contribute to the evolution of cichlid diversity through speciation.
Investigation of the Cavitation in High Pressure Diesel Injection Nozzles
Authors: Baz Ihab , Champoussin Jean-Claude , Lance Michel , Marie´ Jean-Louis
Published: March 2009

Laser light sheet and shadowgraphy techniques have been applied to investigate cavitation phenomena in the spray hole of Diesel injection nozzles. The nozzles were operated on a test-bench based on a Common Rail injection system. Rail pressures up to 50 MPa were used. The diesel test oil was injected into a chamber which could be pressurized up to 8 MPa. The local position and range of cavitation films, lying between the flow and the nozzle wall, as well as single bubbles could be observed at different instants of the injection process. The pictures of the light sheet experiment were compared with photographs taken by the shadowgraphy technique under the same injection conditions. Cavitation number estimates were obtained by direct measurements of nozzle sac pressures.
Experimental Control of Vortex Breakdown by Pulsed Blowing Over a Delta Wing With Rounded Leading-Edge
Authors: Florent Renac , Pascal Molton , Didier Barberis
Published: March 2009

The purpose of this study is to construct and test an experimental device to control vortex on a delta wing. The model has a root chord of c = 690mm and a sweep angle of Λ = 60°. The control system is based on four rectangular slits 50 mm long and 0.2 mm wide running along the leading edge. This configuration produces jets normal to the leading edge. The mass flow rates and frequencies of injection can be varied independently. The results are shown in the form of surface flow visualizations, with the skin friction pattern exhibited by oil flow visualization, and the laminar-to-turbulent transition by acenaphthene. Mean and instantaneous surface pressure distributions were determined with Kulite™ sensors and the velocity field was determined by 3D laser Doppler velocimetry (LDV) measurements. Control device efficiencies were evaluated by laser sheet visualization.
Robust Control of Non-Periodic Channel Flow
Authors: Tutty Owen R. , Baramov Lubomir , Rogers Eric , O’Dea Enda
Published: March 2009

In this paper we consider the control of disturbances in a channel where surface sensing and actuation (blowing/suction) are used. Unlike in many other studies, the flow is not assumed to be periodic. As a result disturbances are allowed over the full range of unstable wave numbers/frequencies, and spatially growing disturbances can be studied explicitly. However, a major drawback is that, even for two-dimensional flow, the order of the numerical model is extremely large. Model order reduction based on a non-linear least squares fit is used to generate a model plus an uncertainty bound that are suitable for control design purposes. These are used to produce a robustly stable H∞ controller. The behaviour of this controller is compared with those designed assuming periodic flow. It is shown that a non-periodic controller can perform satisfactorily in cases where a periodic one will not.
A Numerically Tractable Global Framework for the Feedback Control of Boundary-Layer Perturbations
Authors: Cathalifaud Patricia , Bewley Thomas R.
Published: March 2009

We present a global framework for the feedback control of a large class of spatially-developing boundary-layer flow systems. The systems considered are (approximately) parabolic in the spatial coordinate x. This facilitates the application of a range of established feedback control theories which are based on the solution of differential Riccati equations which march over a finite horizon in x (rather than marching in t, as customary). However, unlike systems which are parabolic in time, there is no causality constraint for the feedback control of systems which are parabolic in space; that is, downstream information may be used to update the controls upstream. Thus, a particular actuator may be used to neutralize the effects of a disturbance which actually enters the system downstream of the actuator location. In the present study, a numerically-tractable feedback control strategy is proposed which takes advantage of this special capability of feedback control rules in the spatially-parabolic setting in order to minimize a globally-defined cost function in an effort to maintain laminar boundary-layer flow.
An Experimental Study of a Free-Surface Shear Layer With and Without the Presence of Surfactants
Authors: Lang Amy Wamcke , Manglano Carlos E.
Published: March 2009

A free-surface shear layer was studied to ascertain the effects due to the presence of surface tension gradients on the directional shift of the shear layer and turbulence intensities in the vicinity of the water free-surface. It was found that the presence of surfactants altered the direction of the shear layer in the vicinity of the free surface, with the shear layer being pulled to the higher surface tension side. In addition, the turbulence intensity in the plane of the free surface was dramatically reduced, also leading to damped surface deformations. These results show conclusively that the role surfactants play in turbulent free-surface shear flows needs to be considered.
Deformation of a Droplet Passing Through a Contraction
Authors: Whyte David S. , Cooper-White Justin , Davidson Malcolm , Lundqvist Amanda , Schaerringer Peter
Published: March 2009

Deformation of a droplet passing through a contraction and expansion at intermediate to large Reynolds number is predicted numerically and compared with experimental observations. The effects of fluid properties, contraction geometry and flow behaviour is considered. The experiments were performed for silicon oil droplets in water moving through a contraction. Orifice and droplet diameter were of the order of millimetres. Contraction length and flow rate were varied, while the contraction ratio was kept constant (1:4). The droplets are stretched by the contraction, after which oscillations are observed on the interface. Observation of the systems indicated that a disintegration zone exists for droplets above a critical size. Numerical simulations were carried out using an axisymmetric Volume-of-Fluid (VOF) code. Simulations were carried out to match the experimental conditions as well as for a few different Reynolds and Weber numbers. Results showed qualitative agreement with experiments. The predictions indicate that vortices within the contraction are responsible for the capillary-like waves on the stretched droplet.
Control of Ink Transportation in Electrostatic Inkjet Printer
Authors: Sou Akira , Sasai Kosuke , Nakajima Tsuyoshi
Published: March 2009

In order to develop and realize a new electrostatic printer, the ways to reduce the switching voltage were examined by the numerical simulation in the present study. Furthermore, the possibility of the control of the volume of transported ink was numerically investigated. As a result, it was clarified that by charging about 1.0kV of bias voltage, by changing the shape of projection, and by decreasing the ink viscosity, the surface tension and the contact angle, switching voltage can be reduced. As for the volume of transported ink, linearity between pulse width and transported volume was observed, which show us a large possibility to realize a high quality inkjet printer.
A Computational Evaluation of Impeller Blade Moment
Authors: Kaupert Kevin A.
Published: March 2009

A computational evaluation of impeller blade moment during the impeller-diffuser interaction is performed. The moment calculated is based on the axial moment generated by fluid forces acting on a control volume surrounding an impeller blade passage. Included in the computations are unsteady flow field contributions to the unsteady impeller moment. Results are compared to numerical predictions of the impeller blade moment based on pressure and shear stress terms integrated over the blade surface. A comparison is also made to the Euler turbomachinery equation often used for calculating blade moment and energy transfer in simplified design procedures.
Compressor Volute Design System: Part I — Volute Design by Bezier Application
Authors: Phuong Guy , Abanteriba Sylvester , Haley Paul
Published: March 2009

This is Part I of a two-part paper describing a new compressor volute design system, which is applied to an interactive program that completely describes volute geometry and its interactions with CFD. Part I goes into the theory behind the program and the design of the volute geometry by application of Bezier polynomials while Part II fully describes the actual design system approach and its application to the program. Based on the developed mathematics of B-spline and Bezier polynomials, the present paper further develops the extent of Bezier polynomials by application of Bezier to volute design. Bezier polynomials will be used to describe and define volute geometry for centrifugal compressors with the objective of serving as an aid for volute design and performance analysis. The current research aims to develop an algorithm for volute design that will enable the volute geometry, to be fully described and viewed, in two-dimensional (2D) and three-dimensional (3D) modes. A program based on this algorithm will deliver output data for grid generation and CFD flow simulation and eventual manufacture of the volute. These procedures will be developed for a family of centrifugal compressors.
Inprovement of the ε Transport Equation for High- and Low-Reynolds Turbulence Models
Authors: Merci Bart , De Langhe Chris , Dick Erik
Published: March 2009

A common weak spot of RANS turbulence models is that one turbulence scale is determined from the dissipation rate ε (or some other turbulence quantity). An improved transport equation for ε is presented. It is valid in both high and low Reynolds number flow regions. The new ε-equation is combined with a cubic eddy-viscosity model. The complete model is applied to fully developed channel and pipe flows, the turbulent plane and round jet, a backward-facing step flow and to heat transfer predictions with turbulent impinging jets. The presented model yields accurate results for all these test cases (in particular the plane jet–round jet anomaly is resolved).
Mapping of Hydraulic Model Dynamics Using Transient Operating Conditions
Authors: Lysaker Henning , Kjeldsen Morten , Arndt Roger E. A.
Published: March 2009

This paper reviews the issue of making unsteady measurements involving cavitating flow in traditional test loops. Transients were applied to a model turbine, including both ramping in time of wicket gate movement and time dependent variations of model test loop system pressure. These actions allowed a continuous change of parameters such as reduced flow rate and cavitation index as a function of time. By the use of Joint Time Frequency Analysis (JTFA) techniques mappings of the dynamics of stationary hydrofoils and rotating machinery can be compared. The objective of this study to investigate whether transient operation would allow a rapid mapping of dynamic for different operation points. Special attention was given to the requirements for controlling the machinery in a manner that allows such experiments to be possible. This paper reports results of so-called ramping tests and compares the results with data obtained by traditional means.
Development of the Change-Resisting Mechanical Seal in Changing Condition
Authors: Lu Liu , Ying Shenqi
Published: March 2009

Based on the experiment of the motion of mechanical seal face in changing work condition, the change of the phase-changing radius in mechanical seal in changing work condition is discussed. And the method to deal with the unstable mechanical seal caused by the change of the radius is shown. Based on the mechanical seal theory on vapor-liquid two phases in changing condition, the change-resisting mechanical seal is developed, which is applied to industry successfully.
A Study on the Unstable Coupling Between Pumps and Hydraulic Circuits With Entrapped Gas Pockets
Authors: Parrondo-Gayo Jorge L. , Antun˜a-Schu¨tze Juan , Gonza´lez-Pe´rez Jose´ , Ferna´ndez-Francos Joaqui´n
Published: March 2009

A theoretical and experimental study has been conducted on the mass oscillation instability in hydraulic systems with entrapped gas pockets and pumps with positive slope in the head curve. The theoretical study was composed of an analysis of the critical conditions for the instability to develop, followed by the numerical resolution of the fundamental equations that govern the phenomenon, assuming unsteady one-dimensional flow, in order to simulate the limit cycle oscillations of the unstable system. Additionally a series of laboratory tests was conducted on a conventional centrifugal pump, with variation of the initial volume of an entrapped air pocket in the circuit. As expected from the predictions of the theoretical model, instability was found to developed with pressure amplitude oscillations and frequency dependent on the amount of entrapped air.
Vorticity Dynamics in the Wake of a Yawed Cylinder
Authors: Marshall J. S.
Published: March 2009

A theoretical and computational study is reported of the effect of cylinder yaw angle on the vorticity and velocity field in the cylinder wake. Previous experimental studies for yawed cylinder flows conclude that, sufficiently far away from the cylinder ends and for small and moderate values of the yaw angle, the near-wake region is dominated by vortex structures aligned parallel to the cylinder. Associated with this observation, experimentalists have proposed the so-called Independence Principle, which asserts that the forces and vortex shedding frequency of a yawed cylinder are the same as for a cylinder with no yaw using only the component of the free-stream flow oriented normal to the cylinder axis. The current paper examines the structure and consequences for yawed cylinder flows of a quasi-two-dimensional (Q2D) approximation in which the velocity and vorticity have three nonzero components, but have vanishing gradient in the direction of the cylinder axis. In this approximation, the cross-stream velocity field is independent of the axial velocity component, thus reproducing the Independence Principle. Both the axial vorticity and axial velocity components are governed by an advection-diffusion equation. The governing equations for vorticity and velocity in the Q2D theory can be nondimensionalized to eliminate dependence on yaw angle, such that the cross-stream Reynolds number is the only dimensionless parameter. Computations using the Q2D theory are performed to examine the evolution of the cross-stream vorticity and associated axial velocity field. The cross-stream vorticity is observed to shed from the cylinder as thin sheets and to wrap around the Ka´rman vortex structures, which in turn induces an axial velocity deficit within the wake vortex cores. The computational results indicate two physical mechanisms, associated with instability of the Q2D flow, that might explain the experimentally observed breakdown of the Independence Principle for large yaw angles.
Experimental Study of a High Speed Flow Inside a Dual Research Ducted Rocket Combustor Using Laser Doppler Velocimetry
Authors: Gicquel Pierre , Brossard Christophe , Barat Mireille , Ristori Arnaud
Published: March 2009

As part of a research program initiated at ONERA with the aim to improve methodology for ramjet combustion chamber design and tuning by using validated CFD codes, an experimental study of the high speed flow inside the duct section of a 3D research ducted rocket combustor was conducted. A 2D Laser Doppler Velocimeter was used to deduce velocity profiles and turbulence characteristics in the horizontal and vertical mid-sections of the combustor duct. Based upon these data, the flow field structure, and in particular the recirculation zone in the dome region, was characterized. Comparison between the results obtained in non-reacting and reacting flow cases is discussed. Comparison between seeding particles velocities and soot particles velocities produced by the flame is also discussed here. An image sampled from one of the flame movies recorded using a high speed digital video camera (1,000 and 4,000 i/s) is briefly presented.
Identification of Gas-Liquid Flow Regimes From a Space-Frequency Representation by Use of an Impedance Probe and a Neural Network
Authors: Hervieu Eric
Published: March 2009

The identification of two-phase flow patterns has been widely studied, and the diagnostic procedures are traditionally based on statistical or spectral signal analysis, while the spatial information related with the geometrical topology of the phase distribution in the pipe is never taken into account. The aim of this study is to demonstrate how the exploitation of both spectral and spatial information leads to an unambiguous identification of the flow patterns. Experiments are performed on a 30 meters long horizontal air-water loop. By simultaneously analyzing the power spectral density of the signals delivered by a multi-electrode impedance sensor, we obtain a space-frequency representation which exhibits particular features of the different flow regimes. They can be characterized by a set of 3 scalar parameters, quantifying respectively the localization in space, in frequency and the shape of the spectral content. The final demonstration of this space-frequency characterization is provided by the use of a multi-layer neural network, trained on a 80 tests database. This net exhibits a successful identification rate above 80% when used in blind real-time tests.
An Insight Into the Methodology of the Hydro Wankel Cell
Authors: Jandhyala Aditya Srujan , Varun G. S. , Paliwal Richa
Published: March 2009

The fusion of a wankel engine and a fuel cell gives a wonderful new dimension. The net output given by the engine is both mechanical and electrical. The requirement of an engine is paramount which voids the conversion of mechanical power to electrical power, due to the losses in energy. It would be thrilling to note that a major space occupier and trouble maker like a battery can be done away with. When compared to an IC engine the power given by this engine is large and with hydrogen being used as the fuel, it turns into a zero emission engine. The vibration factor is also cut down, as a Wankel engine has far less number of moving parts when compared to an IC engine.
Computational Optimization of a Subsonic Compressible Gas Venturi’s Ejector
Authors: Cristea E. D. , Savini M. , Conti P.
Published: March 2009

The paper deals with a 3-D numerical simulation and validation against industrial measurements of turbulent frozen reacting flow in a subsonic compressible gas Venturi’s ejector used as “fluid dynamic engine” for external flue gas recirculation in a state-of-the-art “annular shaft” lime kiln. Higher stagnation thermodynamics parameters of the ejector hot gas primary stream permit the avoidance of the condensing temperature window of compounds such as K2O and Na2O, and KCl and NaCl that produce sticky builds-up on the ejector’s internal wall. An improved gas dynamics effectiveness allows the maximization of the amount of secondary flue gas stream using much less primary stream mass flow rate. The commercial Fluent™ UNS/5 software was used to predict all flow behavior characteristics inside the original and new Venturi’s ejectors. A reasonable agreement has been found between the computed and experimental flow rate figures of the secondary flue gas stream of the actual functioning kiln.
Performance Evaluation of Liquid Flow With NPCM in Microchannels
Authors: Xing K. Q. , Tao Y.-X. , Hao Y. L.
Published: March 2009

A two-phase, non-thermal-equilibrium based model is applied to the numerical simulation of laminar flow and heat-transfer characteristics of suspension with nano-size phase change material (NPCM) particles in a microchannel. The model solves the conservation of mass, momentum and thermal energy equations for liquid and particle phases separately. The study focuses on the parametric study of optimal conditions where heat transfer is enhanced with an increase in fluid power necessary for pumping the two-phase flow. The main contribution of NPCM particles to the enhancement of heat transfer in a micro-size tube is to increase the effective thermal capacity and utilize the latent heat effect under the laminar flow condition. An effectiveness factor εeff is defined to evaluate the heat transfer enhancement compared to the single phase flow heat transfer and is calculated under different wall heat fluxes and different Reynolds numbers. The comparison is also made to evaluate the performance index (PI); i.e., the ratio of total heat transfer rate to fluid flow power (pressure drop multiplied by volume flow rate) between NPCM suspension flow and pure water single-phase flow. The results show that for a given Reynolds number, there exists an optimal heat flux under which the εeff value is the greatest. In general, the NPCM suspension flow with phase change has a significantly higher performance index than the pure-fluid flow.
Laminar Entropy Generation Over a Flat Plate With Isothermal and Constant Heat Flux Boundary Conditions Using the Von Ka´rma´n Integral Method
Authors: Ratts Eric B. , Brown J. Steven
Published: March 2009

This paper is a fundamental study on the irreversibility of single-phase laminar convective heat transfer over a flat plate with isothermal and constant heat flux boundary conditions. It quantifies the losses due to viscous momentum transfer losses and heat transfer losses and presents the irreversibility of the convective flow based on the entropy generation (EG) method. This paper determines the entropy generation for incompressible, single phase, laminar flow for large and small Prandtl numbers over a flat plate with isothermal and constant heat flux boundary conditions using von Ka´rma´n’s integral theory.
Three-Dimensional Simulation of Turbulent Rectangular and Square Impinging Jet Flows
Authors: Chen Qingguang , Xu Zhong , Wu Yulin , Zhang Yongjian
Published: March 2009

Flow characteristics of turbulent impinging jets issuing, respectively, from a rectangular and a square nozzles have been investigated numerically through the solution of three-dimensional Navier-Strokes equations in steady state. Two geometries with two nozzle-to-plate spacings of four and eight times of hydraulic diameters of the jet pipes, and two Reynolds numbers of 20000 and 30000 have been considered with fully developed inlet boundary conditions. An RNG based k–ε turbulence model and a deferred correction QUICK scheme in conjunction with the wall function method have been applied to the prediction of the flow fields within semi-confined spaces. A common feature revealed by the computational results is the presence of a toroidal recirculation zone around the jet. An adverse pressure gradient is found at the impingement surface downstream the stagnation point. Boundary layer separation will occur if the gradient is strong enough, and the separation manifests itself as a secondary recirculation zone at the surface. In addition, three-dimensional simulations reveal the existence of two and four pronounced streamwise velocity off-center peaks at the cross-planes near to the impingement plate, respectively, in the rectangular and square impinging jet flows. These peaks are found forming at the horizontal planes where the wall jets start forming accompanied by two or four pairs of counter-rotating vortex rings. It is believed that the formation of the off-center velocity peaks is due to the vorticity diffusion along the wall jet as the jet impinges on the target plate.
Heating Thermal/Structural Analysis of a Thin Beam Window of Ultra Cold Neutron Test Facility
Authors: Chen Zukun , Bultman Nathan K.
Published: March 2009

This paper is an analytical investigation of a proposed vacuum barrier window that isolates the proton beam transport vacuum envelope from the Ultra Cold Neutron (UCN) experimental target system at atmospheric pressure. The window is subjected to static pressure and cyclic thermal stresses as the accelerated particle beam passes through it and deposits a small amount of energy in the window. The analysis investigates various beam rms sizes for two beam delivery time structures. The 0.1-mm thick, 52 mm diameter window is made of inconel alloy 718 and is welded to the beamline tube at its outer edge. For some combinations of delivery time structure and beam size, the window under differential pressure and proton beam heating experiences stress that is well above yield and possibly large enough to break the inconel foil. In order to analyze the induced temperature and stress, a finite element model has been developed. The model has been written parametrically to allow the beam characteristics, window material properties, dimensions and mesh densities to be easily adjusted. The heat load is applied to the model through the use of a 3-dimentional table containing the calculated volumetric heat rates. The heat load is based on a radial distribution for a circular Gaussian beam under both normal and extensional operation cases. In this analysis, a radial-centered, circular beam is assumed. The results of several analyses are presented in this paper.
Prediction of Developing Turbulent Flow in a Rectangular-Sectioned Curved Duct
Authors: Etemad Sassan , Sunde´n Bengt
Published: March 2009

The developing turbulent flow in a rectangular-sectioned curved duct with an aspect-ratio of 6 was explored using linear and non-linear high- and low-Re k-ε turbulence models. The impact of the inlet flow conditions and grid density was also studied. It was found that the boundary layer thickness upstream the bend has fundamental influence on the secondary flow, velocity profile and turbulence level. The flow in the straight inlet duct was nearly 2-dimensional. The predicted data using Chen’s model and the quadratic high-Re model agreed well with the experimental data from Kim and Patel [1]. Also Suga’s cubic low-Re model performed well. The quadratic low-Re model, however, predicted thicker boundary layer which gave magnified secondary flow with high levels of shear and turbulence. It is not certain that the used high-Re models would perform well in a fully three-dimensional flow. Suga’s model, however, might perform well in other more complex flows.
Wavelet Cross-Correlation Analysis of the Unsteady Signals of the Flow in the Open Sump
Authors: Kante Mansa , Wu Yulin , Li Yong , Liu Shuhong , Zhou Daqing
Published: March 2009

The wavelet cross-correlation method was used to analyze the unsteady signals of the flow of the model open pump sump, which include pressure signal, vibration signal and acoustic signal. The continuous wavelet transform was done first to find the signal distribution at various periods and at any time, then the wavelet cross-correlation was used to find the relationship between the signals taken two a two. Through comparing the result of wavelet cross-correlation and the result of classic cross-correlation, one can find the correlation scale of any two unsteady signals (pressure-vibration, pressure-noise, and vibration-noise). The signal on the correlation scale was reconstruct and its characteristics were obtained using classical signal analysis method same as the structural similarity of a arbitrary two signals.
Experimental Study on Skin Friction Reduction With Micro-Blowing
Authors: Liu Song , Li Hongmin , Braun Minel J.
Published: March 2009

Reducing skin friction, such as friction on a car hood or a plane wing, can significantly reduce the drag force and decrease specific fuel consumption. Many techniques and methods have been tried. The Micro-blowing Technique (MBT) is an innovative way to reduce skin friction. Suggested by early research in boundary layer injection in 1950s, MBT was actually brought to effective use in 1994 by Hwang [1]. The basic idea is that by blowing fluid, same as or different from the mainstream flow, at an angle with that of the main flow, a decrease in the velocity gradient at the wall can be achieved, and thus the shear stress on the surface is reduced. Although the experimental data on boundary layer with micro blowing show a significant friction reduction, the mechanism of MBT is still not well understood and thus its full range of application is not yet established. In this paper, we further the understanding of the MBT mechanism. An experimental system is set up to visualize the flow structure on a plate with and without micro blowing in a tunnel. A long distance microscope is combined with a Full Field Flow Tracking visualization method in order to elucidate the nature of the flow interaction and mixing between the blowing flow and the main flow. The flow above the porous plates is visualized and velocities both in the blowing layer immediately adjacent to the plate and in the main flow are quantified using the PIV procedure. The flow and shear stress analysis shows that MTB has significantly different effects on a flow with a boundary layer and fully developed internal flows.
Accurate Time-Dependent Computations and Reduced-Order Modeling for Multiphase Flows
Authors: Utturkar Yogen , Thakur Siddharth , Shyy Wei
Published: March 2009

In the present study, we initiate development of a non-iterative multiphase algorithm by enhancing the Pressure Implicit with Splitting of Operators (PISO) algorithm. The Gallium fusion problem, which is characterized by a solid-liquid phase front and natural convection effects, is employed as a test case for validation. The problem poses serious computational issues in form of a non-linear energy equation and a strong pressure-velocity-temperature coupling. The single-fluid modeling approach is adopted in conjunction with the enthalpy-based formulation for the temperature equation. The current algorithm computes the solution through a series of predictor-corrector steps with special treatment to achieve rapid convergence of the energy equation. The algorithm demonstrates an enhanced performance for the highly unsteady, chosen test problem. A reduced-order analysis of the simulated data is also performed by Proper Orthogonal Decomposition (POD). Specifically, impact of the constantly changing flow domain, and flow scales, on the POD implementation is highlighted.
Numerical Investigation on the Conjugate Heat Transfer in Double-Pipe Heat Exchangers With Propane Flow Boiling
Authors: Chen Xuelei , Sa´nchez Mauricio A. , Sutton William H.
Published: March 2009

This investigation is part of the composite fuel project in the University of Oklahoma [1]. The composite fuel is a mixture resulted from natural gas resolving in liquid propane, which has a relatively lower storage pressure compared with that of compressed natural gas. Here in this paper, a numerical investigation of conjugate heat transfer among convection, wall conduction and flow boiling in a double-pipe heat exchanger is presented. The heat exchanger has hot fluid flowing in the annular section and propane boiling in the inside tube. A computer program is developed to calculate the conjugate heat transfer of convection, conduction and boiling. In computing the convection and conduction, control volume method and SIMPLE algorithm are used to solve momentum equations and the energy equation of conjugate heat transfer. The contribution of this work is to combine the third kind (Neuman) of boundary condition with the boiling correlations for flow boiling in horizontal tubes in order to calculate the conjugate heat transfer of the whole problem. Two boiling correlations have been selected to give inside tube boiling heat transfer coefficient. Because the boiling coefficient depends on the wall temperature and local propane quality, so we have to solve the boiling correlation, the conduction and the convection governing equations simultaneously. The iteration method and TDMA are used to solve these coupled equations. The two boiling correlations are Chen’s (1966) correlation [2] and Kandlikar’s (1990) correlation [3]. Finally the results are compared with the experiment data. It has been found in low quality range, Kandlikar’s result is close to the experiment data. Because very few data of propane flow boiling can be found in literature, we use propane pool boiling data by Shen, Spindler and Hahne (1997) [4] to estimate parameter Ffl in Kandlikar’s correlation. The influence of simultaneously developing velocity and temperature field at entrance length in annular passage is considered and discussed in detail. The wall conduction resistance is also compared with convection and boiling resistance in the whole length of the heat exchanger. The completed computer program can be used to the design of shell and tube heat exchangers.
Computational Model for Predicting the Location of Glass Solidification in Optic Fiber Drawing
Authors: Wei Zhiyong , Lee Kok-Meng , Zhou Zhi , Hong Siu-Ping
Published: March 2009

This paper presents a computational model for predicting the location at which the glass fiber solidifies during a high-speed drawing process. Although modeling of the optic fiber drawing process has been of interest for the past two decades, traditional fiber drawing process uses small diameter preforms and low draw speeds, where the glass usually solidifies and turns into fiber inside the furnace. Much larger preforms drawn at higher speeds have been used in the state-of-the-art fiber drawing systems to improve production efficiency and reduce cost. Insulated post-chambers are often added below the furnace to reduce the glass cooling rate so that the optical loss in the fiber is low. To provide a basis for design optimization of the post-chamber, we have solved the conjugate problem of the glass free surface flow and the air convection to determine the location where the glass solidifies. As radiation is the dominant mode of heat transfer in the glass, the radiative transfer equation (RTE) is solved directly by discrete ordinate method (DOM). The heat flux due to the mixed convection of the air is also numerically calculated along the glass free surface, which involves the boundary layer flow around a continuously moving fiber and the buoyancy driven flow through the open-ended channel. The calculated free shapes are compared against the experimentally measured data to verify the computational model.
In Situ ESEM Study of Liquid Interactions With Carbon Nanopipes
Authors: Rossi M. Pi´a , Ye Haihui , Gogotsi Yury
Published: March 2009

The wetting and fluidic properties of various types of carbon nanotubes (CNT) are currently being studied for various applications, including their use as nanopipes for the controlled transport of fluids to well-defined locations, such as a cell. While numerous studies on the modeling of the behavior of liquids in nanotubes and nanopores have already been reported, very few experimental observations have been published. In this research, the field emission Environmental Scanning Electron Microscope (ESEM) has proved to be a powerful tool in the in situ analysis of the wetting of CNT with diverse liquids at high magnification. Additionally, the ability of the ESEM to condense and evaporate liquids within the chamber has enabled the dynamic study of CNT/liquid interactions. As a result, hydrophilic and hydrophobic behavior of diverse types of commercial carbon nanofibers (CNF) and CNT has been observed. The fluidic behavior of CNF depends largely on surface chemistry and structure. The presence of defects and end groups may cause partial wetting, while graphitized CNF are extremely hydrophobic. Nevertheless, water still becomes drawn into hydrophobic CNF due to surface tension and capillary forces. CNT fabricated by chemical vapor deposition (CVD) with straight, thin walls appear transparent under the electron beam of the ESEM. When studying the interaction of these CNT with water, it was possible to see liquid menisci inside the CNT. From the measured contact angles, it is clear that these CNT are hydrophilic. Furthermore, the wetting behavior observed is very similar to that of closed hydrothermal CNT under high pressures in TEM. Finally, rupture of these thin-walled CNT was observed inside the ESEM chamber as a result of rapid changes in pressure at constant temperatures.
Control of Vortex Breakdown in a Torsionally Driven Closed Cylinder by Addition of Swirl Using a Small Disk
Authors: Mununga L. , Thompson M. C. , Hourigan K. , Leweke T.
Published: March 2009

This paper discusses results of a new experimental approach to control vortex breakdown in a confined cylindrical vessel with a rotating top endwall. The aim was to determine the effectiveness of adding co-rotating and counter rotating swirl near the axis of rotation using a small disk located in the bottom endwall. Initial results, with only the top end rotating, were satisfactorily validated against classical data from the literature. Results of the vortex breakdown onset, using this new non-intrusive approach, have revealed that co-rotation of the smaller disk precipitates vortex breakdown formation while counter rotation delays the onset of the breakdown phenomenon. It has also been shown that co-rotation increases the bubble radial and axial dimensions while shifting the bubble in the upstream direction. By contrast, counter rotation tends to reduce the size of the bubble, or completely suppress it, while shifting the bubble in the downstream direction.
CHF in Vertical Round Tubes With Uniform Heat Flux
Authors: Shim W. Jaewoo , Lee Ji-Su
Published: March 2009

In recent years it is well known that models based on the local condition hypothesis give significant correlations for the prediction of CHF (Critical Heat Flux), using only few local variables. In this work, a study was carried out to develop a generalized CHF correlation in vertical round tubes with uniform heat flux. For this analysis, a CHF database that composed of over 10,000 CHF data points, which were collected from 12 different sources, was used. The actual data used in the development of this correlation, after the elimination of some questionable data, consisted of 8,951 data points with the following parameter ranges: 0.101 ≤ P (pressure) ≤ 20.679 MPa, 9.92 ≤ G (mass flux) ≤ 18,619.39 kg/m2s, 0.00102 ≤ D (diameter) ≤ 0.04468 m, 0.03 ≤ L (length) ≤ 4.97 m, 0.11 ≤ qc (CHF) ≤ 21.42 MW/m2, and −0.87 ≤ Xe (exit qualities) ≤ 1.58. The result of this work showed that regardless of various flow patterns and regimes that exist in the wide flow conditions, the prediction of CHF can be made accurately with few major local variables: the system pressure (P), tube diameter (D), mass flux of water (G), and true mass flux of vapor (GXt). The new correlation was compared with 5 well-known CHF correlations published in world literature. The new correlation can predict CHF within the root mean square error of 13.44% using the heat balance method with average error of −1.34%.
Large Eddy Simulation of the Flow Around an Ahmed Body
Authors: Krajnovic´ Sinisˇa , Davidson Lars
Published: March 2009

A new approach for large eddy simulation (LES) of the flows around ground vehicles is demonstrated. It is based on the character of the flow with large regions of recirculations rather than on traditional resolution requirements for the LES of wall bounded flows. Recommendations for preparing and realization of LES for vehicle flows are presented and validated on a test case of the flow around an Ahmed body with the 25° angle of the rear slanted surface. Comparison of the LES results with the experimental data proved the validity of this new method.