bluuebunny/crossref_metadata_2025 huggingface dataset:
Tribute to Richard E. Zody
Authors: MARTELL CHRISTINE R. , DOUGHERTY MICHAEL , SMITH JAMES FIELDING
Published: March 2009

Public budgeting is multifaceted. It draws from areas of study and practice ranging from management to administration to planning. Guided by analysis—enhanced by computational and technical advances—and political systems, it overlays the public sector at every level of government, including local, state, national, and international. It is also the domain of both academics and practitioners. This tribute honors Richard E. Zody by focusing on the multifaceted nature of public budgeting to reflect the career of a man committed to many of these dimensions. The central focus of his career was on improving public budgetary and management systems, and in doing so, he deftly drew from the many dimensions of budgeting. Dick demonstrated in his study, writing, teaching, and application an intellectual interest in two particular themes: the relationship between academics and practitioners; and budgeting and management, which includes the use of analytical skill and strategic planning. Through these interests, Dick impacted many lives.
Now You See It, Now You Don't: The Mysterious Case of the Vanishing Split Bond Rating in States
Authors: WALKER ROBERT W. , KRUEGER SKIP
Published: March 2009

Bond ratings on state‐issued debt provide a signal to credit markets that help them charge an appropriate interest rate, based on the risk of payment default. Though actual default may occur only in extreme circumstances, observed differences in ratings and interest costs across states and time demonstrate that a sound economy, strong financials, and stable policies matter. When data on the factors that presumably affect ratings is public and easily accessible, making sense of differences of opinion between bond rating agencies is difficult. We suggest that such differences—observed as so‐called split bond ratings—are often ephemeral. Utilizing a simulation method to uncover the latent credit risk presented by each state, we show that split ratings on state bonds are often due to the fact that presumed category overlap between rating agencies is absent when evaluated on a common latent scale. Most observed state bond rating splits from 1997 through 2006 can be explained by this category mismatch. Our approach has broad implications for pricing state debt, as well as pricing rated debt in other capital market sectors.
A Multilevel Model of the Impact of Farm‐Level Best Management Practices on Phosphorus Runoff1
Authors: Reckhow K.H. , Qian S.S. , Harmel R.D.
Published: March 2009

Abstract:  Multilevel or hierarchical models have been applied for a number of years in the social sciences but only relatively recently in the environmental sciences. These models can be developed in either a frequentist or Bayesian context and have similarities to other methods such as empirical Bayes analysis and random coefficients regression. In essence, multilevel models take advantage of the hierarchical structure that exists in many multivariate datasets; for example, water quality measurements may be taken from individual lakes, lakes are located in various climatic zones, lakes may be natural or man‐made, and so on. The groups, or levels, may effectively yield different responses or behaviors (e.g., nutrient load response in lakes) that often make retaining group membership more effective when developing a predictive model than when working with either all of the data together or working separately with the individuals. Here, we develop a multilevel model of the impact of farm level best management practices (BMPs) on phosphorus runoff. The result of this research is a model with parameters which vary with key practice categories and thus may be used to evaluate the effectiveness of these practices on phosphorus runoff. For example, it was found that the effect of fertilizer application rate on farm‐scale phosphorus loss is a function of the application method, the hydrologic soil group, and the land use (crop type). Further, results indicate that the most effective method for controlling fertilizer loss is through soil injection. In summary, the resultant multilevel model can be used to estimate phosphorus loss from farms and hence serve as a useful tool for BMP selection.
Similitude of Air Entrainment at Vertical Circular Plunging Jets
Authors: Chanson Hubert , Aoki Shin-Ichi , Hoque Ashabul
Published: March 2009

Air bubble entrainment at plunging jet takes place when the jet impact velocity exceeds a critical velocity function of the inflow conditions. This study investigates scale effects affecting air entrainment and bubble dispersion at vertical circular plunging jets. Three scale models were used and detailed air-water measurements were performed systematically for identical Froude numbers. The results highlight significant scale effects when We1 < 1E+3 or V1/ur < 10. Bubble chord times were also measured and presented in terms of pseudo-bubble chord length which was found to overestimate real bubble chords by 10 to 30%. The data show pseudo-bubble chord sizes ranging from less than 0.5 mm to more than 10 mm. The average pseudo-chord sizes were between 5 and 7 mm.
Mean Rise-Rate of Droplets in Isotropic Turbulence
Authors: Friedman P. D. , Katz J.
Published: March 2009

This paper investigates the rise-rate of droplets that are slightly lighter than the surrounding fluid. We experimentally investigate the effect of three parameters: Stokes number, turbulence intensity and droplet Reynolds number. Droplets were injected into a chamber with nearly isotropic turbulence and little mean flow. The results show that at high turbulence intensity, the mean droplet rise-rate is 25% of the rms velocity regardless of the Stokes number, while at low turbulence intensity, the droplets rise at a rate equal to the rise-rate in a quiescent fluid. At intermediate turbulence intensity, the rise-rate is strongly dependent on the Stokes number.
A Study of Active Control of Vortex Shedding and Wake From a Cylinder
Authors: Nigim Hani H. , Shiino Kohta , Koyama Hide S. , Sung Hyung Jin
Published: March 2009

The control of vortex shedding and wake from a circular cylinder was studied experimentally at Reynolds numbers, ranging from 160 to 400, using an acoustic active control system. The investigation has been carried by, quantitatively, hot-wire to measure the mean and fluctuating velocities and, qualitatively, by using smoke-wire flow visualization technique to examine the formation of the flow field downstream of the cylinder. The present active control method is able to influence the rate of entrainment from main flow into the wake flow. When the Reynolds number is relatively small, it is the size of the cylinder and the induced sound field velocity rather than Reynolds number which are the significant parameters in determining the controlling reverse and optimum phase lag angels.
A 3-D Thin Layer Navier-Stokes Code for Supersonic Laminar and Turbulent Flows
Authors: Abouali Omid , Alishahi Mohammad M. , Emdad Homayoon , Ahmadi Goodarz
Published: March 2009

A 3-D Thin Layer Navier-Stokes (TLNS) code for solving viscous supersonic flows is developed. The new code uses several numerical algorithms for space and time discretization together with appropriate turbulence modeling. Roe’s method is used for discretizing the convective terms and the central differencing scheme is employed for the viscous terms. An explicit time marching technique and a finite volume space discretization are used. The developed computational model can handle both laminar and turbulent flows. The Baldwin-Lomax model and Degani-Schiff modifications are used for turbulence modeling. The computational model is applied to a hypersonic laminar flow at Mach 7.95 around a cone at different incidence angles. The circumferential pressure distribution is compared with the experimental data. The cross-sectional Mach number contours are also presented. It is shown that in addition to the outer shock, a cross-flow shock wave is also present in the flow field. The cases of supersonic turbulent flows with Mach number 3 around a tangent-ogive with incidence angles of 6° and a secant-ogive with incidence angles of 10° are also studied. The circumferential pressure distributions are compared with the experimental data and the Euler code results and good agreement is obtained. The cross-sectional Mach number contours are also presented. It is shown that in this case also in addition to the outer shock, a cross-flow shock wave is also present at the incidence angle of 10°.
The Measurement of Three-Dimensional Flow Field in an Axial Flow Fan Using PDA
Authors: Du Zhaohui , Lin Wanlai , Zhu Xiaocheng , Zhao Yan
Published: March 2009

In this paper, a three-color dual-beam PDA (Particle Dynamic Analyzer) system (made by DANTEC Measurement Technology) is used to measure the three-dimensional velocity of an axial flow fan. Due to the geometrical limit of fan rotor, non-orthogonal velocity components are measured first, from which the orthogonal three-dimensional components of the velocity field are computed through transformation equations. The detailed flow fields at 15 axial locations upstream, inside and at the exit of the rotor are measured, respectively. On each cross section perpendicular to the rotating axis, the flow field measurement at 15 different radial locations from 50% of the blade span to the region inside the tip clearance (between the tip blade and the casing wall) are taken. The experimental technique is described, and the three dimensional flow fields (including the tip clearance flow) are presented and analyzed.
Pneumotransport of Grains Through a Pipeline
Authors: Shrivastava Kaushal K.
Published: March 2009

Determination of pressure drop correlation using experimental techniques has been a central topic of research in the area of pneumotransport. However, the objective of the present investigation is to apply the mathematical model (SK model) developed by the author [1,2] along with other correlations [3–5] to estimate pressure drops for conveying varieties of grains through horizontal pipe and compare the values with the experimental results of Siegel [6]. The SK model has also been utilized to calculate pressure drops for conveying mustard seeds pneumatically through horizontal, inclined and vertical pipes and compare the values with the experimental results of Rose and Barnacle [7]. It is evident from various comparisons shown in this paper that the SK model predicts the values of pressure drop accurately as compared to the experimental results in all the cases of grains transport through horizontal, inclined, and vertical pipes, whereas, other correlations do not predict accurate results consistently in all cases.
Wavelet Multi-Resolution Analysis of Coherent Structure in a Jet Issuing From Rotating Circular Pipe With Inclined Section
Authors: Nakashima Masahiro , Li Hui , Tabata Takahide , Nozaki Tsutomu
Published: March 2009

The flow feature of the jet issuing from the circular pipe with the rotating inclined section has been investigated by the method of the flow visualization and the image processing. It has been found that the jet diffusion is affected by the inclined angle and the rotating speed. The coherent structure of the jet has been also studied by using the wavelet multi-resolution analysis. The multi-scale turbulent structures were visualized and the core and edge of the vortex were identified at different broad scales.
A Computational Model for the Formation of Turbulent Liquid Sprays
Authors: Schmidt David J. , Ahmadi Goodarz
Published: March 2009

The motions of deformable liquid droplets in a turbulent spray are simulated numerically using a three-dimensional joint, one-way coupled Lagrangian-Eulerian simulation technique. The instantaneous fluid velocity and velocity gradient of the continuous phase is simulated with the use of an advanced Navier-Stokes based Lagrangian PDF (probability density function) stochastic model. This model is used to simulate the turbulent structures known to exist within the shear layers of a plane and axisymmetric jet. The mean fluid velocity field is obtained with the use of the FLUENT computer code, using the Reynolds stress transport turbulence model. The dilute phase is modeled as a series of continuously injected spheres, with no particle-particle interactions. Forces on the particles include nonlinear Stokes drag and Saffman lift. Multiple particle trajectories are then numerically evaluated by integrating the equations of motion using the computed fluid velocity field as input. Ensembles of particle trajectories are generated for a point and line source emanating near the inlet to the spray chamber. Test cases for an axisymmetric jet are considered. Results show agreement in the instantaneous flow field for all lower statistical moments. For a turbulent spray consisting of nonevaporating spherical droplets, good qualitative agreement is seen in the overall dispersion of droplets as well as the corresponding spray angle.
Integrated Micro- and Nanofluidics: Silicon Revisited (Keynote Paper)
Authors: Gardeniers Han J. G. E. , van den Berg Albert
Published: March 2009

Although silicon may generally not be the material of first choice for applications in the field of fluidics for (bio)chemistry and medicine, the extended toolbox of fabrication methods makes it a very attractive material for the demonstration of microfluidic principles for these fields. In particular, the monocrystalline nature of silicon substrates in combination with anisotropic etching processes, the precise dry-etching techniques and sophisticated thin-film surface micromachining processes, can be used to create a large variety of innovative microstructures. Several examples of such micro- and nanofluidic structures for (bio)chemical and medical analysis will be presented and discussed.
Cavitation Studies on a Model of Primary Sodium Pump
Authors: Joshi S. G. , Pujari A. S. , Kale R. D. , Sreedhar B. K.
Published: March 2009

Indira Gandhi Centre for Atomic Research for their Fast Breeder Reactor had a requirement of two primary sodium pumps, with relatively medium head and comparatively large flow rate. The pumps had to be vertical bowl type, with inverted suction, drawing the relatively cold liquid sodium from the reactor pool, and forcing it over the fuel rods. The flow involved was 4.3 M3/sec. per pump and the head involved was 75 m. The available NPSH was 16.02m. The choice of the right speed was the first hurdle to be overcome. The size of the pump governed the cost of the reactor. Hence it was essential to make the pump as compact as practicable, by designing it to run at the highest possible speed. On the other hand the required NPSH of the pump increased with speed, there by reducing the safety cushion between required NPSH and available NPSH. Increasing the available NPSH beyond 15.55 m to accommodate higher speeds also increased the cost of the reactor phenomenally. Coupled with the requirement of head, flow rate, efficiency, the application demanded a certain erosion life of the pump impeller. Concluding from the previous experience and available literature on the subject, it was necessary to limit the size of the cavitation bubble patch, during operation under available NPSH, to meet erosion life requirement. The paper describes how the choice of speed was made and what were the criteria applied for deciding the value of 3% head drop NPSH. It also describes how a closed circuit test rig was installed for the purpose of testing a model pump and how the usual performance and NPSHR tests paint erosion tests and visual cavitation tests were carried out on a geometrically similar, smaller model pump, to decide that the prototype pump built from the model will meet all the requirements of head, flow rate, efficiency, 3% head drop NPSHR, 0% head drop NPSHR, Paint erosion NPSHR, and the cavitation patch size to meet desired erosion life criteria, in the laboratories of Kirloskar Brothers Limited.
Modelling of Incompressible Three-Dimensional Flow in Rotating Turbomachinery Passages
Authors: Cravero C. , Satta A. , Marini M.
Published: March 2009

A CFD method, previously developed by the authors for compressible flows, has been modified through a preconditioning technique to account for purely incompressible flows. Such a code is used to compute three-dimensional flows in a mixed flow pump impeller at design and off-design conditions. The results of the inviscid flow approach are critically discussed by comparison to available experimental data.
The Interaction Between the Impeller and Casing in a Small-Size Turbo-Compressor
Authors: Kim D.-W. , Kim Youn J.
Published: March 2009

The effects of casing shape on the performance and the interaction between the impeller and casing in a small-size turbo-compressor are investigated. Numerical analysis is conducted for the compressor with circular and single volute casings from inlet to discharge nozzle. In order to predict the flow pattern inside the entire impeller, vaneless diffuer and casing, calculations with multiple frames of reference method between the rotating and stationery parts of the domain are carried out. For compressible turbulent flow fields, the continuity and three-dimensional time-averaged Navier-Stokes equations are employed. To evaluate the performance of two types of casings, the static pressure and loss coefficients are obtained with various flow rates. Also, static pressure distributions around casings are studied for different casing shapes, which are very important to predict the distribution of radial load. To prove the accuracy of numerical results, measurements of static pressure around casing and pressure difference between the inlet and outlet of the compressor are performed for the circular casing. Comparison of these results between the experimental and numerical analyses are conducted, and reasonable agreement is obtained.
A Study of Flow Analysis for a Double-Suction Centrifugal Pump
Authors: Chung Kyung-Nam , Park Pyun-Gu , Cho Hyun-Joon , Lee Sang-Gu
Published: March 2009

Flow analysis was carried out for a double-suction centrifugal pump. An impeller-only model and a full pump model were used to simulate the velocity and the pressure field of the pump. Pump head and efficiency were calculated with flow rate in order to obtain general performance of the pump. The calculation results were compared to the experimental data, and satisfactory results were obtained. Also, the velocity and the pressure field of this pump were analyzed for the rated point and off-design points. Changes of the velocity and the pressure field with flow rate were investigated at impeller eye and impeller exit.
A Study on the Flow Characteristics in a Plug Valve With Various Port Shapes
Authors: Kim T.-A. , Ahn B.-J. , Kim Youn J.
Published: March 2009

Analyses on the characteristics of flow fields in the plug valve are required to improve performance and safety at severe operating conditions such as high-pressure and high-temperature. In this study, numerical and experimental analyses are carried out with various opening rates of the valve and the shapes of the plug port: circular, triangle, and modified triangle shapes. Especially, the distributions of the static pressure, velocity vector and streamlines are investigated to calculate the flow coefficient (Cv) and the resistance coefficient (K) in each opening rate and shape. For the case of full open, the static pressure passed through the valve port has almost been recovered. However, in case of other opening rates, pressure has not permanently recovered due to pressure drop leading to loss. This phenomenon in each shape of the valve shows the different behaviors. Result of calculation show that the modified triangle shape is good on flow characteristics and the triangle one is good for the flow rate control.
Parameter Studies on the Effect of Boundary Conditions in Three-Dimensional Calculations of Bubble Column
Authors: Bourloutski E. , Sommerfeld M.
Published: March 2009

This paper describes an extension and validation of the Euler/Lagrange approach for three-dimensional time-dependent calculations of the flow in a bubble column. The fluid phase was calculated based on the Euler approach solving the unsteady Reynolds-averaged Navier-Stokes equations in a time-dependent way. The conservation equations were closed using the standard k-ε turbulence model. The coupling between the phases is considered through the momentum source terms and source terms in the k- and ε-equations. The usage of the Consistent term for the k-equation and taking into account an additional dissipation due to the presence of small bubbles yielded a reasonable agreement of the predicted turbulent kinetic energy level with measurements. Bubble motion was calculated by solving the equations of motion taking into account drag force, pressure, added mass force, transverse lift force, buoyancy and gravity. Numerical calculations are presented providing information on the sensitivity of the results on several boundary conditions, such as disturbed aeration. The computational results are validated based on available measurements in a laboratory-scale bubble column.
The Next Generation Feedback Controlled Propulsive System
Authors: Bayandor Javid
Published: March 2009

A short synopsis pertaining to the concept, analysis and development of the new advanced zero head HYdro-Propulsive System (HYPS) has been drawn. Within this system, of particular importance are the implemented revolutionary feedback control systems. These systems provide the HYPS with a unique ability to efficiently receive and capture the kinetic energy embedded in multi-directional, random and turbulent fluid flow motions. The system is equipped with specially designed bladings (propulsors) that are attached through the feedback controllers to the extending radial arms, allowing the blades to adjust their orientations according to the oncoming flow. It has been demonstrated, through implicit analysis and extensive tests, that this system can effectively maximise the favourable aero-hydrodynamic forces on its impellers and, in turn, achieve a much higher energy conversion rate compare to those of the conventional devices.
Control of Transition in Supersonic Boundary Layers: Experiments and Computations (Keynote)
Authors: Saric William S. , Reed Helen L.
Published: March 2009

The present work addresses a technique that can lead to drag reduction on supersonic wings by means of passive laminar flow control. Recent developments in the stability and transition in swept-wing flows in low-disturbance environments have offered the promise of controlling transition without suction. It has been demonstrated in low-speed experiments that distributed roughness near the attachment line can control the crossflow instability provided the roughness spacing is below a critical value. This is extended to supersonic flow over highly swept wings where the combined computational and experimental work gives design criteria for airfoils swept beyond the characteristic Mach angle.
Application of a CFD-Based Erosion Prediction Procedure for Sudden Expansions
Authors: Nugroho Sekti S. , McLaury Brenton S. , Shirazi Siamack A.
Published: March 2009

Pipe fittings used in the production of oil and gas can experience erosion damage from solid particles such as sand present in the produced fluid. The fittings disturb the flow, which often results in erosion. Certain geometries are more susceptible to erosion damage than others; for example, a sudden expansion can experience severe erosion under certain operating conditions. A sudden expansion can promote erosion for two reasons. First, a radial velocity develops downstream of the expansion. This velocity component drives particles toward the wall. Second, the sudden expansion causes a zone of elevated turbulent kinetic energy. The high level of turbulent kinetic energy results in large turbulent fluctuations, and these fluctuations can also force particles to the wall. A comprehensive model for predicting sand erosion has been developed by utilizing a commercially available computational fluid dynamics (CFD) code. This procedure involves flow modeling, particle tracking, and applying erosion equations. Due to the low sand concentrations a one-way coupling is used between the fluid and the particles. The goal of this study is to use the procedure to calculate erosion in sudden expansions and determine if modifications to the existing procedure are necessary. Simulation results for sand in air flowing through sudden expansions with different diameter ratios (1.25 to 2.00) are compared with experimental data. Both the simulations and data show that the maximum erosion rate evaluated in thickness loss per mass of sand passing through the geometry decrease with increasing expansion ratio.
A 3D Computational Fluid Dynamics Analysis of the Wells Turbine
Authors: Daly John , Bajeet Elvis Sheik , Thakker Ajit , Frawley Patrick
Published: March 2009

This paper deals with the application of Computational Fluid Dynamics (CFD) to the performance comparison of some proposed blade designs for the Well’s Turbine. The turbines were modelled at typical Reynolds numbers for full scale rigs and the results were found to correlate well with scale predictions from experimental data. Three different turbine designs were analysed, one a 4-bladed rotor and the other two 8-bladed rotors. The only difference between the two 8-bladed rotors was the addition of forward sweep to one. The addition of forward sweep was shown to have little effect on the overall performance of the 8-bladed rotor. The 4-bladed rotor was shown to have the highest efficiency and pressure drop at low flow rates, however it was also shown to have a much smaller operating range than the 8-bladed rotors.
The Influences of Gap Clearance and Surface Roughness on Leakage Loss and Disc Friction of Centrifugal Pumps
Authors: Tamm Alberto , Stoffel Bernd
Published: March 2009

Among the losses arising in low specific speed pumps, the disc friction and leakage losses are especially important. These losses arise due to the flow through unavoidable gaps and side spaces (SS) between impeller and casing. To predict these losses, normally simple correlations and empirical formulas are used. The following analysis was intended to study the effects of the radial clearance of the sealing gaps as well as of the surface roughness of the wetted surfaces within the SS, which may have an essential impact on the losses of centrifugal pumps.
Numerical Simulation of a Spatial Turbo-Pump Stage
Authors: Maruzewski Pierre , Leboeuf Francis
Published: March 2009

The aim of this paper is to present the analysis of numerical results of the unsteady flow in a spatial turbo-pump stage. This stage includes an axial part with an inducer, and a centrifugal part with a shrouded impeller and a vaned diffuser. The numerical results are obtained with two different softwares that use two different numerical models: a structured model used by Fine/Turbo Euranus solver and an unstructured model used by N3S/Natur solver. Comparisons are performed between the results obtained with these two codes and measurements for steady and unsteady cases. These steady and unsteady studies underline the effects of unsteadiness.
Microstructure of a Bidisperse Swarm of Spherical Bubbles
Authors: Go¨z Manfred F. , Sommerfeld Martin , Bunner Bernard , Tryggvason Gretar
Published: March 2009

Three-dimensional simulations of bidisperse bubble swarms rising in a liquid have been carried out. This article describes the microstructure of a swarm of mostly spherical bubbles representing 6% void fraction. The swarm consists of an equal number of large and small bubbles with volume ratio 2. While the behavior of the large bubbles is similar to that in a comparable monodisperse system, the behavior of the small bubbles is different.
Numerical Simulation of Direct Injection of Carbon Dioxide in the Ocean
Authors: Sato Toru , Sato Kei , Ishikawa Atsuhiro
Published: March 2009

It is important to predict biological impacts caused by the ocean sequestration of carbon dioxide (CO2). For this purpose, the dilution processes of CO2 should be understood in the deep ocean. A two-phase computational fluid dynamics (CFD) method with mass transfer was developed in order to predict droplet plume flow, the dissolution of CO2 from droplets into seawater, and the advection-diffusion of dissolved CO2 (DCO2). Change of pH due to the concentration of DCO2 is also calculated. In addition, a new mortality model was installed to predict the lethal damage of DCO2 to marine organisms. The simulation results suggest that the biological impacts of the CO2 sequestration can be insignificant in terms of mortality in business cases we proposed.
Analysis of 3-D Braided Composite Ablative Rocket Nozzle
Authors: Shivakumar Kunigal N. , Cozart Aaron
Published: March 2009

Aerodynamic flow, thermal flow, and stress analyses of a proposed 2.5-in braided composite ablative nozzle were conducted. The nozzle was made up of PAN based carbon fiber and Primaset Cyanate Ester resin. The designed thermal and structural layers’ thicknesses were 0.62-in and 0.42-in, respectively. The objective of this paper is to establish the thermal stability and structural integrity of the nozzle. A ballistic profile of 17 seconds burn at 740 psi maximum pressure was used in the analysis. The combustion gas flow was subsonic, sonic, and supersonic, respectively, in the inlet, throat, and exit sections of the nozzle. The exit plane Mach number was 2.32. Three thermochemical states were considered: 100% efficiency, 72% efficiency and no aluminum combustion and 72% efficiency and 100% aluminum combustion. Flow analysis was conducted by NAT92 Code, thermal analysis by CMAFLOW92 Code, and structural analysis by ANSYS. Ablation rates for the three cases were 0.023, 0.047, and 0.01-in/sec, respectively. The recession life of thermal layer was 27, 13, and 62 sec for the three cases. Stress analysis of the nozzle due to aerodynamic pressure and temperature resulted in low strains and presents no concern.
Predicting Performance of an Electro-Rheological Fluid Clutch for Power Transmission
Authors: Truong Tam D. , Semercigil S. Eren , Turan O¨zden F.
Published: March 2009

A clutch has the duty of interrupting power transmission without shutting off the source. As expected from any friction dependent operation, a traditional clutch suffers from wear and dynamic instability. What is proposed in this paper is to employ a liquid with a controllable apparent viscosity to avoid the inherent problems of friction. Electro-Rheological (ER) fluids can reversibly change between the liquid phase and a solid-like gel phase in response to electric potential fields in the order of a few kV/mm. Therefore, it is possible to use ER fluids as power transmission agents. If the level of power transmission is the result of the phase change of an ER fluid, then such a design has no moving components, smooth operation, low power consumption and a fast reaction time. This paper details experiments to quantify the variation of the shear strength of an ER fluid as a function of its important parameters. Then, these values are used to predict the amount of power transmission. Although ER fluids have attracted significant attention in the literature, published works deal with investigations either in the molecular level or in pure application. To the best of the authors’ knowledge, this paper reports the necessary information to predict performance in a practical format for the first time.
Calculation of Debris Trajectories During High-Speed Snowplowing
Authors: Nakhla H. K. , Thompson B. E.
Published: March 2009

An engineering model is presented to calculate the trajectory of airborne debris that adversely affects visibility during high-speed snow plowing. Reynolds-averaged Navier-Stokes equations are solved numerically with turbulence-modeling, particle-tracking, and cutting-edge approximations. Results suggest snow can be divided into splash and snow-cloud when designing treatments to improve visibility for snowplow drivers and following traffic. Calculated results confirm the findings of windtunnel and road tests, specifically that the trap angle of overplow deflectors should be less than 50 degrees to eliminate snow debris blowing over top of the plow onto the windscreen.
Fluid Flow Effect in Electrical Conductivity Measurements of Molten Metals by Inductive Technique
Authors: Bakhtiyarov Sayavur I. , Dupac Mihai , Overfelt Ruel A. , Teodorescu Sorin G.
Published: March 2009

In this paper we propose a new relationship between the opposing mechanical torque and the electric conductivity of a rotating liquid specimen in a permanent external magnetic field of constant induction, which includes the effect of fluid flow. The proposed relationship was applied to describe the experimental data for a conductive specimen rotating in a permanent magnetic field.
Entrainment Correlations Based on a Fuel/Water Stratified Shear Flow
Authors: Chang Peter A. , Wilson Wesley , Atsavapranee Paisan , Wu Xiongjun , Katz Joseph
Published: March 2009

The purpose of this work was twofold: first, to develop correlations for the entrainment of small fuel droplets into water in a stratified fuel/water shear flow; second, to implement the correlations in a CFD code and validate it with experimental effluent fuel concentration data. It is assumed that the droplets act as passive scalars and are advected far from their generation regions where they may cause fuel contamination problems far down-stream. This work relied upon extensive experimental data obtained from a stably stratified shear flow: droplet number, droplet PDF, fluid fraction and velocity field data. The droplet data was expressed as a nondimensional entrainment velocity (E) for the volume flux of fuel due to small droplets. The fluid fraction and velocity fields at the interface were expressed in terms of Richardson numbers (Ri). It was found that E = CeRi−n where n = 1 and Ce is a constant, gives a good fit for the two experimental velocity cases. The best correlation was implemented in a computational simulation of the stably stratified shear flow, and the results show that the simulation can predict the entrainment quite well. A second simulation was performed for a flow with energetic vertical buoyant jets (“buoyant flow events”) and stably stratified shear flows with very large Richardson numbers. In this case, the simulations underpredicted effluent fuel concentrations by two orders of magnitude. Ad hoc corrections to the entrainment correlations show marked improvements.
Leakage Flow of Labyrinth Seals in Hydraulic Components
Authors: Cheng Minter
Published: March 2009

Leakage flow plays an important role on the performance evaluation of hydraulic components. Leakage flow induces adverse influences on many practical industrial applications. For the sake of reducing friction and/or abrasion, most of the high-speed hydraulic components install some kind of non-contact seals to minimize leakage flow, the labyrinth seal is the most popular one. This research is to investigate the leakage flow of labyrinth seals in hydraulic components by using numerical analysis technique. The parameters investigated in this study are cavity number, cavity width, cavity depth, cavity gap, and Reynolds number. The traditional rectangular cavity is considered in this research. It shows that cavity width is about 20∼30 times of clearance, cavity depth is about 3∼5 times of clearance, cavity gap is greater than 50 times of clearance, cavity depth to width ratio is about 0.15∼0.25, and cavity gap to width ratio is greater than 2.5 have better sealing capability.
CFD Calculation and Experiments of Unsteady Flow on Control Valve
Authors: Morita Ryo , Inada Fumio , Mori Michitsugu , Tezuka Kenichi , Tsujimoto Yoshinobu
Published: March 2009

A steam control valve causes vibrations of piping when the opening is in the middle condition. For the rationalization of maintenance and management in a plant, valves should be improved, but it is difficult to understand the flow characteristics in detail experimentally because the flow around the valve has a complex 3D structure and becomes supersonic (M>1). Therefore, it is necessary to clarify the cause of vibration and to develop improvements both experimentally and through CFD (Computational Fluid Dynamics) calculation. First, small-scale air experiments are performed. In this experiment, a spike-type pressure fluctuation that rotates circumferentially is observed in a middle valve opening. This fluctuation sometimes changes its rotation direction suddenly, or sometimes stays at the same position. Because of this randomness, FFT analysis cannot reproduce this peak frequency. However, another peak caused by the 1st-mode resonance in the pipe-diameter direction can be seen. After some experiments, a high-precision 3D CFD code for compressible flow, “MATIS”, was developed. This code can calculate an unsteady 3D compressible flow steadily and accurately, with TVD scheme, LU-SGS implicit scheme and inner iterative calculation. This code also includes LES turbulence model for compressible fluid in order to reproduce turbulence flow accurately. To validate this code, first, some benchmark tests such as karman vortex calculation and the calculation of a detached shock position on a sphere are performed. After benchmark tests, CFD calculation of the valve is performed under several valve opening conditions. The mesh number is about 600 thousand and y+ is about 3. CFD results agree well with those of the experiment qualitatively and quantitatively. Therefore, the validation of MATIS is confirmed. Detailed flow characteristics around the valve in a middle valve opening are investigated. Under this condition, the jet after the throat travels the valve (named “attached flow”) and strikes the jet coming from the opposite side. This phenomenon generates a high-pressure region and a pair of vortices; this region rotates circumferentially and causes cyclic side load on the valve body. CFD calculation clarifies that a circumferentially propagating spike-type pressure fluctuation is caused by attached flow along the valve, and this is though to be the cause of vibration.
Theory Analysis and Experimental Investigation of Liquid Droplets Evaporization in High Speed Flow
Authors: Zhang Kunpeng , Zou Song , Wang Haigui , Pan Weiming , Xue Fei
Published: March 2009

Experimental study of spray cooling system with wet compression has been carried out on a small hot wind tunnel. A mathematical model is established for liquid droplets evaporization and a set of experiments have been carried out to study the inherent law of liquid spray with evaporization. The experiment result is accord with the theory analysis. The result of this paper will be good reference for spray system design for a wet compression system. And the detail information of the experiment and the mathematical model take us further understanding of the real wet compression process.
Experimental and Computational Studies of the Effect of ‘Casing Eye Rib’ on the Swirl Flow at the Exit of a Pump as Turbine
Authors: Singh Punit , Kshirsagar J. T. , Caglar Saban , Nestmann Franz , Natanasabapathi
Published: March 2009

This paper presents a detailed hydraulic analysis of the effects of the casing eye rib on a pump operating as a turbine. It describes a flow-zone approach within a pump as turbine and lays out the build up for the experimental and numerical techniques applied. The pump as turbine exhibits very good characteristics with a maximum operating efficiency over 82%. The similitude between experimental and numerical results has been satisfactory. The two stages namely the ‘casing rib present’ and the ‘casing rib absent’ stage are compared at 6 different load points encompassing the entire characteristics. Both methods reveal that the performance of the PAT has enhanced without the presence of the rib. However the two methods show different causes for this behaviour. The comparison of the swirl profiles reveal that the fluid in the ‘casing rib absent’ stage has greater rotational momentum in the part-load and overload region compared to the ‘casing rib present’ stage. However the ‘casing rib absent stage’ displays more symmetric swirl profiles. At the end of the paper, an uncertainly analysis for the experimental efficiency is carried out.
Prediction of Aeroacoustic Noise Levels in Cross-Flow Fans for Air Conditioners
Authors: Funabashi Shigehisa , Shigenaga Yasushi , Watanabe Masatoshi , Takada Yoshihiro
Published: March 2009

We have developed a prediction model for the overall level of aeroacoustic noise generated by cross-flow fans. It is based on two assumptions: the velocities along the outside edge of the impeller have an especially close relation to the noise levels, and the noise levels are in proportion to the sixth power of the relative velocities at the edge of the blade. A computational fluid dynamics is used to obtain the necessary velocity-field data for this prediction model. The predicted noise levels of a test impeller for different flow coefficients are in good agreement with the measured results. This means that variations in noise levels with the flow coefficient can be described accurately by the prediction model, which should prove to be a useful tool for speeding up the development of silent cross-flow fans.
Development of Thermal Flow Simulation Method for Electronic Equipment Integrated With Electric Circuit Design: Application to the Thermal Design of a Natural Convection Air Cooling SMPS
Authors: Koizumi Katsuhiro , Ishizuka Masaru
Published: March 2009

This paper describes the development of a thermal flow simulation method for the design of electronic equipment. In the proposed sequence of analyses the first step is the estimation of heat generation rate from electric circuit. The method was applied to the thermal design of a new switch mode power supply (SMPS). The analysis was carried out using a computational fluid dynamics (CFD) code (Icepak: trademark of Fluent Inc.). In reducing the actual structural organizations of the printed circuit board (PCB) and the power semiconductor devices to simpler models the method of experimental design (MED) was employed. Following the prescription of MED the PCB was modeled as a simple plate having a thermal conductivity of epoxy resin. The power semiconductor devices were modeled by hexahedral resistance network. The heat sources are a field effect transistor (FET) and a diode, and computation of the power loss from them is described. The difference between measured and calculated temperatures on the power semiconductor devices was found to be within approximately 10 K.
Inertia Effects on the Modulated Air Layer Heat and Moisture Transport From Clothing With Open Aperture
Authors: Ghaddar Nesreen , Ghali Kamel , Harathani Jihad
Published: March 2009

A two-dimensional model is developed of the modulated internal airflow in the gap between clothing and skin surface due to walking and in presence of clothing end apertures. The normal airflow renewing the air layer through the fabric is conducted in an oscillatory way during body motion without gross environmental air movement using fabric-three node model [1]. The parallel flow is induced by periodic pressure difference between environment pressure at the aperture of the clothing system and trapped air layer pressure. The parallel flow is assumed locally governed by Womersley solution of time-periodic laminar flow in a plane channel. The three-node fabric ventilation model has been modified to include the diffusion-dominated transport processes in the fabric at low normal flow rates. The low flow rates occurred near the opening and during the periodic ventilation cycle when the airflow rate approaches zero before changing direction in and out of the fabric. The fabric ventilation model and the diffusion model completely overlap at the normal airflow rate of 0.00777 kg/m2·s. The new modified-model has been used in the 1-D steady periodic normal flow model and results have shown good agreement with published experimental data. The 2-D model using Womersley-flow model in the parallel direction has predicted significantly lower flow rates than Poisueille flow model. In addition, the 2-D model predicted the sensible and latent heat loss from the sweating skin in presence of openings in the clothing system. The reported results showed that under walking conditions, a clothing system with an open aperture reduced heat loss from the skin when compared to 1-D normal ventilation model (closed aperture). These results were consistent with previously published empirical data of Lotens [2] and Danielsson [3] on air layer resistance for open and closed aperture of high air permeable fabric.
A Lattice Boltzmann Dynamic Subgrid Model for Lid-Driven Cavity Flow
Authors: Yang Fan , Wu Yulin , Liu Shuhong
Published: March 2009

In recent years, the lattice Boltzmann method (LBM) has developed into an alternative and promising numerical scheme for simulating fluid flows and modeling physics in fluids. In order to proposing lattice Boltzmann method for high Reynolds number fluid flow applications, as well as conforming the value of Smagorinsky coefficient of subgrid model appropriately, a dynamic subgrid turbulence model for lattice Boltzmann method was proposed on the base of dynamic Smagorinsky subgrid model and LBGK model. Then the subgrid LBGK model was used to simulate the two-dimensional driven cavity flow at some high Reynolds numbers. The simulation results including distribution of stream lines, dimensionless velocities distribution, stream function, as well as location of vertex center, were compared with benchmark solution. Both simulation results and benchmark solution are agreed with each other.
Two Numerical Models for Optimization of the Foundry Technology of the Ceramics EUCOR
Authors: Dobrovska Jana , Kavicka Frantisek , Stransky Karel , Dobrovska Vera , Stetina Josef , Heger Jaromir
Published: March 2009

Corundo-baddeleyit material — EUCOR — is a heat- and wear-resistant material even at extreme temperatures. This article introduces a numerical model of solidification and cooling of this material in a non-metallic mould. The model is capable of determining the total solidification time of the casting and also the place of the casting which solidifies last. Furthermore, it is possible to calculate the temperature gradient in any point and time, and also determine the local solidification time and the solidification interval of any point. The local solidification time is one of the input parameters for the cooperating model of chemical heterogeneity. This second model and its application on samples of EUCOR prove that the applied method of measurement of chemical heterogeneity provides detailed quantitative information on the material structure and makes it possible to analyse the solidification process. The analysis of this process entails statistical processing of the results of the measurements of the heterogeneity of the components of EUCOR and performs correlation of individual components during solidification. The crystallisation process seems to be very complicated, where the macro- and microscopic segregations differ significantly. The verification of both numerical models was conducted on a real cast 350 × 200 × 400 mm block.