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In recent years, additive manufacturing (AM) has begun to displace traditional manufacturing techniques for specific applications. Notable benefits of AM include reduced times from design to product, an improved buy-tofly [...]

Three-dimensional, non-isothermal, transient computational fluid dynamics simulations are conducted for rubber mixing with a set of two-wing rotors in a partially filled chamber. The main objective is to analyze the effect of different fill factors of rubber on dispersive and distributive mixing characteristics by simulating 15 revolutions of the rotors rotating at 20 rpm. 60%, 70%, 75%, and 80% are the four different fill factors chosen for the study. An Eulerian multiphase model is employed to simulate two different phases, rubber and air, and the volume of fluid technique is used to calculate the free surface between two phases, in addition to the continuity, momentum and Energy equations. To characterize non-Newtonian, highly viscous rubber, shear rate and temperature dependent Carreau-Yasuda model has been used. A set of more than 3,600 massless particles are injected after a certain period of time to calculate several quantities in terms of dispersive and distributive mixing. Both the Eulerian and Lagrangian results showed that, fill factors between 70% and 80% presented the most reasonable and efficient mixing scenario, thus exhibiting the best dispersive and distributive mixing characteristics combined., INTRODUCTION Rubber is the basic raw material for tire manufacturing process, which is mainly synthesized from petroleum byproducts [1]. Rubber can also be harvested naturally as a form of latex, [...]

Aerosol deposition (AD) is a thick-film deposition process that can produce films tens to hundreds of micrometers thick with densities greater than 95% of the bulk at room temperature. However, [...]

In this paper, a 3-D computational fluid dynamics (CFD) model of a circular sedimentation tank is presented, where the interfacial momentum transfers, buoyant forces, and the effect of sediment-induced density currents were included in the model. A convection-dispersion equation governed the mass transfer in the clarifier, and the double-exponential law was used to describe the settling velocity dependence on the concentration. The predicted values in the radial and axial directions and the solids distribution were in satisfactory agreement with experimental results from Deininger. The results showed that the tangential velocity distribution was not uniform, and the surface return flow was identified. The turbulent kinetic energy was relatively large and decreased drastically in the inlet zone, whereas the turbulent kinetic energy was relatively small in the settling zone. A density current was also formed. Furthermore, the influence of the inlet baffle length and location on suspended solids settling is discussed. Key words: circular sedimentation tank, 3-D CFD simulation, suspended solids concentration, process of sludge settling, density current. Un modele informatique tridimensionnel de dynamique des fluides dans une cuve de sedimentation cylindrique est presente dans cet article; le modele tient compte des transports de la quantite de mouvement a l'interface, des forces de flottabilite et de l'effet des courants de densite induits par les sediments. Une equation de convection-dispersion regit le transfert de masse dans le clarificateur et la loi exponentielle double est utilisee pour decrire comment la vitesse de sedimentation depend dela concentration. Les valeurs prevues dans les directions radiales et axiales ainsi que la distribution des matieres concordaient raisonnablement bien avec les resultats experimentaux de Deininger. Les resultats montrent que la distribution de vitesse d'ecoulement tangentiel n'etait pas uniforme et l'ecoulement de retour a la surface a ete identifie. L'energie cinetique turbulente etait relativement importante et chutait de maniere draconienne dans la zone de la prise d' entree, alors que l'energie cinetique turbulente etait relativement petite dans la zone de sedimentation. Un courant de densite s'est egalement forme. De plus, l' influence de la longueur du deflecteur a l' entree et de son emplacement sur la sedimentation des matieres en suspension est examinee. Mots-cles : cuve de sedimentation cylindrique, simulation tridimensionnelle dynamique des fluides, concentration de matieres en suspension, processus de sedimentation des boues, courant de densite. [Traduit par la Redaction], 1. Introduction Sedimentation is the most common method of solid-liquid separation in wastewater treatment plants, where settling tanks are of vital importance. Previous experience has shown that the secondary clarifier [...]

This study was led in collaboration with the French Space Agency ( CNES) and the Rocket Engine Division of Snecma. The main aims were the simulations and the analyses of cavitating flows in the rocket engine turbopump inducers, where the operating fluids are LH2 and LOx under cryogenic conditions. A [rho](P, T) state law modeling the cavitation phenomenon was integrated by the laboratory LEGI in the commercial computational fluid dynamics (CFD) code FINE/TURBO[TM], developed by Numeca International. Various 3D numerical results are given for an inducer geometry and comparisons are made with experimental data (head drop curves) obtained by NASA. [DOI: 10.1115/1.4002886]

A spring-loaded pressure safety valve (PSV) is a key device used to protect pressure vessels and systems. This paper developed a three-dimensional computational fluid dynamics (CFD) model in combination with a dynamics equation to study the fluid characteristics and dynamic behavior of a spring-loaded PSV. The CFD model, which includes unsteady analysis and a moving mesh technique, was developed to predict the flow field through the valve and calculate the flow force acting on the disk versus time. To overcome the limitation that the moving mesh technique in the commercial software program ANSYS CFX (Version 11.0, ANSYS, Inc., USA) cannot handle complex configurations in most applications, some novel techniques of mesh generation and modeling were used to ensure that the valve disk can move upward and downward successfully without negative mesh error. Subsequently, several constant inlet pressure loads were applied to the developed model. Response parameters, including the displacement of the disk, mass flow through the valve, and fluid force applied on the disk, were obtained and compared with the study of the behavior of the PSV under different overpressure conditions. In addition, the modeling approach could be useful for valve designers attempting to optimize spring-loaded PSVs. [DOI: 10.1115/1.4001428]

A major concern in drilling operations is the proper determination of frictional pressure loss in order to select a mud pump and avoid any serious problems. In this study, a mechanistic model is proposed for predicting the frictional pressure losses of light drilling fluid, which can be used for concentric annuli. The experimental data that were available in the literature and conducted at the Middle East Technical University-Petroleum Engineering (METU-PETE) flow loop as well as computational fluid dynamics (CFD) software are used to verify the results from the proposed mechanistic model. The results showed that the proposed model can estimate frictional pressure losses within a [+ or -] 10% error interval when compared with the experimental data. Additionally, the effect of the pipe eccentricity on frictional pressure loss and tangential velocity using CFD for laminar and turbulent flow is also examined. It has been observed that pipe eccentricity drastically increases the tangential velocity inside the annulus; especially, the flow regime is turbulent and frictional pressure loss decreases as the pipe eccentricity increases. [DOI: 10.1115/1.4002243] Keywords: light drilling fluid, frictional pressure loss, concentric, eccentric, CFD, annulus, finite difference approximation

This work extends and improves a one-dimensional shallow flow model to two-dimensional (2D) for real-world flood simulations. The model solves a prebalanced formulation of the fully 2D shallow water equations, including friction source terms using a finite volume Godunov-type numerical scheme. A reconstruction method ensuring nonnegative depth is used along with a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored for calculation of interface fluxes. A local bed modification method is proposed to maintain the well-balanced property of the algorithm for simulations involving wetting and drying. Second-order accurate scheme is achieved by using the slope limited linear reconstruction together with a Runge-Kutta time integration method. The model is applicable to calculate different types of flood wave ranging from slow-varying inundations to extreme and violent floods, propagating over complex domains including natural terrains and dense urban areas. After validating against an analytical case of flow sloshing in a domain with a parabolic bed profile, the model is applied to simulate an inundation event in a 36 [km.sup.2] floodplain in Thamesmead near London. The numerical predictions are compared with analytical solutions and alternative numerical results. DOI: 10.1061/(ASCE)HY.1943-7900.0000219 CE Database subject headings: Floods; Simulation; Shallow water; Friction; Topography; Hydraulic models. Author keywords: Flood simulation; Shallow water equations; Well-balanced scheme; Riemann solver; Friction terms; Complex topography.

In the present, a steady laminar of two dimensional and incompressible fluid flow induces from wall injection in a circular chamber has been studied experimentally and numerically. The water is injected from injection system into the chamber through the wall jets. The centerline static pressure variation with the distance along the chamber length is measured and calculated at different Reynolds numbers and inlet flow angles. The average heat transfer with Reynolds number at different values of the inlet flow angle is obtained. The velocity vectors are presented and Reynolds number is varied between 433 and 910 with inlet flow angle of 0 deg, 15 deg, 30 deg, 45 deg, and 60 deg. The results indicate that the pressure recovery coefficient decreases as both Reynolds number and flow angle increase. The average heat transfer coefficient increases with increasing both Reynolds number and flow angle. The results showed that two recirculation zones occur in the sides of centerline of the chamber behind the step. The size of these recirculation zones decreases by increasing the inlet flow angle. At high value of the inlet flow angle, other recirculation zone occurs on the wall chamber. [DOI: 10.1115/1.4001394] Keywords: annular injection, laminar flow, two dimensional, pressure coefficient, heat transfer

In this work, the effect of the second-order term to the velocity-slip/temperature-jump boundary conditions on the solution of four cases in which the driving force is fluctuating harmonically was studied. The study aims to establish criteria that secure the use of the first order velocity-slip/temperature-jump model boundary conditions instead of the second-order ones. The four cases studied were the transient Couette flow, the pulsating Poiseuille flow, Stoke's second problem, and the transient natural convection flow. It was found that at any given Kn number, increasing the driving force frequency, increases the difference between the first and second-order models. Assuming that a difference between the two models of over 5% is significant enough to justify the use of the more complex second-order model the critical frequencies for the four different cases were found. For the cases for which the flow is induced by the fluctuating wall as in cases 1 and 3, we found that critical frequency at Kn=0.1 to be [omega]=8. For the cases of flow driven by a fluctuating pressure gradient as in case 2, this frequency was found to be [omega]=1, at the same Kn number. In case 4, for the temperature-jump model the critical frequency was found to be [omega]=7 and for the velocity-slip model the critical frequency at the same Kn number was found to be [omega]=1.35. [DOI: 10.1115/1.4001970]

A 3D computational fluid dynamics model with a reduced detailed chemical kinetics of the combustion of diesel and methane fuels is developed while considering turbulence during combustion to simulate the mixture flow, formation, and combustion processes within diesel and diesel/methane dual fuel engines having swirl chambers. The combustion characteristics of the pilot injection into a small prechamber are also investigated. Modeled results were validated by a group of corresponding experimental data. The spatial and temporal distributions of the mixture temperature, pressure, and velocity under conditions with and without liquid fuel injection and combustion are compared. The effects of engine speed, injection timing, and the addition of carbon dioxide on the combustion process of dual fuel engines are investigated. It is found that in the absence of any fuel injection and combustion, the swirl center is initially formed at the bottom-left of the swirl chamber, and then moved up with continued compression in the top-right direction toward the highest point. The swirling motion within the swirl and main combustion chambers promotes the evaporation of the liquid pilot and the combustion processes of diesel and dual fuel engines. It was observed that an earlier autoignition can be obtained through injecting the pilot fuel into the small prechamber compared with the corresponding swirl chamber operation. It is to be shown that reduced engine emissions and improved thermal efficiency can be achieved by a two-stage homogenous charge compression ignition combustion. [DOI: 10.1115/1.2981175] Keywords: dual fuel engine, swirl chamber, small prechamber, autoignition

This paper deals with the utilization of the dynamic characteristics of laminar flow in circular pipes for the indirect measurement of flow rates. A discrete-time state space realization of the transmission line dynamics is computed via inverse Laplace transform and an identification and model reduction method based on the singular value decomposition. This dynamic system is used for the computation of the flow rate at one end of a pipe section. Special attention is paid to the identification of the speed of sound and the dimensionless dissipation number of the pipe section, since exact knowledge of these parameters is crucial for the reliability of the measurement results. First, experimental validation results are given in a limited range of operating frequencies between 100 Hz. and 2000 Hz. Flow rate variations within [+ or -] 1.2 1/min have been measured with an uncertainty of [+ or -] 0.07 1/min at the 95% confidence level. The test fluid was mineral oil. [DOI: 10.1115/1.2969464]

An eddy-viscosity turbulence model employing three additional transport equations is presented and applied to a number of transitional flow test cases. The model is based on the k-[omega] framework and represents a substantial refinement to a transition-sensitive model that has been previously documented in the open literature. The third transport equation is included to predict the magnitude of low-frequency velocity fluctuations in the pretransitional boundary layer that have been identified as the precursors to transition. The closure of model terms is based on a phenomenological (i.e., physics-based) rather than a purely empirical approach and the rationale for the forms of these terms is discussed. The model has been implemented into a commercial computational fluid dynamics code and applied to a number of relevant test cases, including flat plate boundary layers with and without applied pressure gradients, as well as a variety of airfoil test cases with different geometries, Reynolds numbers, freestream turbulence conditions, and angles of attack. The test cases demonstrate the ability of the model to successfully reproduce transitional flow behavior with a reasonable degree of accuracy, particularly in comparison with commonly used models that exhibit no capability of predicting laminar-to-turbulent boundary layer development. While it is impossible to resolve all of the complex features of transitional and turbulent flows with a relatively simple Reynolds-averaged modeling approach, the results shown here demonstrate that the new model can provide a useful and practical tool for engineers addressing the simulation and prediction of transitional flow behavior in fluid systems. [DOI: 10.111511.2979230]

Thermal management as a method of heightening performance in miniaturized electronic devices using microchannel heat sinks has recently become of interest to researchers and the industry. One of the current challenges is to design heat sinks with uniform flow distribution. A number of experimental studies have been conducted to seek appropriate designs for microchannel heat sinks. However, pursuing this goal experimentally can be an expensive endeavor. The present work investigates the effect of cross-links on adiabatic two-phase flow in an array of parallel channels. It is carried out using the three-dimensional mixture model from the computational fluid dynamics software, FLUENT 6.3. A straight channel and two cross-linked channel models were simulated. The cross-links were located at 1/3 and 2/3 of the channel length, and their widths were one and two times larger than the channel width. All test models had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm. The results showed that the trend of flow distribution agrees with experimental results. A new design, with cross-links incorporated, was proposed and the results showed a significant improvement of up to 55% on flow distribution compared with the standard straight channel configuration without a penalty in the pressure drop. Further discussion about the effect of cross-links on flow distribution, flow structure, and pressure drop was also documented. [DOI: 10.1115/1.3001093] Keywords: two-phase flow, cross-links, CFD, flow distribution, pressure drop, microchannel heat sinks

A 3D computational fluid dynamics model for describing the water flow and suspended solids (SS) concentration distribution in a rectangular sedimentation tank is presented. The interfacial momentum transfer, buoyant forces, and the effect of sediment-induced density currents are considered. A convection-diffusion equation, which is extended to incorporate the sedimentation of activated sludge in the field of gravity, governed the mass transfer in the clarifier. The double-exponential law is used to describe the dependence of the settling velocity on the concentration. The results show that during the dynamic settling process of the sludge, the mud surface rose slowly, and a period of time later, the mud surface kept stability and reached dynamic equilibrium in the tank. The distribution of velocity along the z axis in the rectangular tank is not uniform, and the surface return flow is found. The turbulent kinetic energy is larger and dropped drastically in the inlet zone, while in the settling zone the turbulent kinetic energy is relatively small. Density current is formed, and the clear water zone, flocculation zone, lamella zone, and compression zone are found. Furthermore, under certain operational conditions, the influence of inlet baffle length on SS settling in the rectangular sedimentation tank is discussed. The prediction by the present model for liquid flow and SS concentration is confirmed by the experimental measurement in a rectangular sedimentation tank in Sweden reported by Larsen in 1977. DOI: 10.1061/(ASCE)0733-9372(2008)134:11(902) CE Database subject headings: Sedimentation tanks; Three-dimensional models; Simulation; Water flow; Suspended solids; Sludge settling; Density current.

The analysis of residence time distribution functions originating from tracer studies is one of the main tools for the assessment of hydraulic performance in water and wastewater treatment units. In order to simplify the analysis, hydraulic indexes extracted from these functions are normally used. In general, these indexes are divided into two categories: short circuit and mixing indicators. However, some indexes may be related to more than one physical phenomenon (i.e., short circuit, mixing, recirculation, dead zones), leading to erroneous interpretation. In this work their capability to evaluate short-circuit and mixing levels in water and wastewater treatment units is assessed. Among the indexes analyzed, [t.sub.l0], which is the time necessary for 10% of the tracer to leave the unit, is recommended as a short-circuit indicator and the dispersion index ([[sigma].sup.2]) and the Morril index as mixing indicators, depending on the mixing level. DOI: 10.1061/(ASCE)0733-9372(2008)134:10(851) CE Database subject headings: Hydrodynamics; Water treatment plants; Wastewater management; Tracers.

The ability to understand and manage the performance of hydraulic control valves is important in many automatic and manual industrial processes. The use of computational fluid dynamics (CFD) aids in the design of such valves by inexpensively providing insight into flow patterns, potential noise sources, and cavitation. Applications of CFD to study the performance of complex three-dimensional (3D) valves, such as poppet, spool, and butterfly valves, are becoming more common. Still validation and accuracy remain an issue. The Reynolds-averaged Navier-Stokes equations were solved numerically using the commercial CFD package FLUENT V6.2 to assess the effect of geometry on the performance of a 3D control valve. The influence of the turbulence model and of a cavitation model was also investigated. Comparisons were made to experimental data when available. The 3D model of the valve was constructed by decomposing the valve into several subdomains. Agreement between the numerical predictions and measurements of flow pressure was less than 6% for all cases studied. Passive flow control, designed to minimize vortical structures at the piston exit and reduce potential cavitation, noise, and vibrations, was achieved by geometric smoothing. In addition, these changes helped to increase [C.sub.v] and reduce the area affected by cavitation as it is related to the jet shape originated at the valve throat. The importance of accounting for full 3D geometry effects in modeling and optimizing control valve performance was demonstrated via CFD. This is particularly important in the vicinity of the piston. It is worth noting that the original geometry resulted in a lower [C.sub.v] with higher velocity magnitude within the valve, whereas after smoothing [C.sub.v] increased and served to delay cavitation inception. [DOI: 10.1115/1.2813131] Keywords: CFD, modeling, control valve, cavitation

The design of trickle irrigation systems is crucial to optimize profitability and to warrant high values for the emission uniformity (EU) coefficient. EU depends on variation of the pressure head due to head losses along the lines and elevation changes, as well as the water temperature, and other parameters related to the emitters (manufacturer's coefficient of variation, number of emitters per plants, emitter spacing). Trickle irrigation plants are usually designed using small diameter plastic pipes (polyethylene or polyvinyl chloride). The design problem, therefore, needs to consider head losses along the lines as well as emitter discharge variations due to the manufacturer's variability. Variations in the hydraulic head are a consequence of both friction losses along the pipe and local losses due to the emitters' connections, whose importance has been recently emphasized. Since each local loss depends on the emitter type (in-line or on-line) as well as on its shape and dimensions, the morphological variability of the commercially available emitter requires experimental investigations to determine local losses in drip laterals. On the other hand, local losses can be estimated by the mean of computational fluid dynamics (CFD) models, allowing analysis of velocity profiles and the turbulence caused by the emitters' connections. FLUENT software can be considered a powerful tool to evaluate friction and local losses in drip irrigation laterals, after the necessary validation has been carried out by means of experimental data. The main objective of this study was to assess a CFD technique to evaluate friction and local losses in laterals with in-line coextruded emitters. The model was initially used to choose the turbulence model allowing the most accurate estimation of friction losses in small diameter polyethylene pipes, characterized by low Reynolds number. Second, the possibility of using CFD to predict local losses in drip irrigation laterals with a commercially available coextruded emitter was investigated. Simulated local losses were obtained as difference of the total and friction losses along a trunk of pipe, where one single emitter was installed, not considering the emitter outflow. The proposed procedure allows to evaluate local losses for other different emitter models, avoiding tedious and time-consuming experiments. DOI: 10.1061/(ASCE)0733-9437(2007) 133:6(520) CE Database subject headings: Irrigation; Head loss; Computational fluid dynamics technique; Turbulence; Water management.

This paper discusses the use of 3-D computational fluid dynamics (CFD) software for simulation of explosive detonations against the wearer of a typical bomb suit. The focus is to demonstrate the utility of the model to assess the differential overpressure loads on the various bomb suit components protecting critical body parts. Since overpressures can vary significantly depending on the position and orientation of the wearer, simulations are performed for a range of orientations including kneeling and standing at common standoff distances. Overpressure loads on the head, neck, and torso regions are predicted for each orientation, capturing ground and other surface reflections that can enhance effects of the blast. This is not normally observed during tests of individual bomb suit components. Direct correlations between the suit orientation and environmental factors to load enhancements are documented, and an effort to address probable injury is made.

The use of in-line static mixers has been widely advocated for an important variety of applications, such as continuous mixing, heat and mass transfer processes, and chemical reactions. This paper extends previous studies by the authors on industrial static mixers and illustrates how static mixing processes of single-phase viscous liquids can be numericallysimulated. Mixing of Newtonian, shear-thinning, and shear-thickening fluids through static mixer, as well as thermal enhancement by static mixer is studied. Using different measuring tools, the global performance and costs of SMX (Sulzer mixer X) and helical static mixers are studied. It is shown that the SMX mixer manifests a higher performance; however, the required energy to maintain the flow across a SMX mixer is significantly higher. [DOI: 10.1115/1.2427082] Keywords: helical static mixer, SMX static mixer, particles distribution uniformity, residence time distribution, shear-thinning fluids, shear-thickening fluids

This paper presents results of the simulation of two vehicles overtaking each other at highways conditions (30 m/s). The simulation was fully unsteady and tracks the maneuver for several body lengths from downstream to upstream. Different mesh strategies have been investigated and assessed. Structured methods with sliding planes have been found the most feasible. The results shown include the effects of relative speed and lateral separation. The passing maneuver is described in detail and a number of physical phenomena are identified. In particular, the rapid fluid compression and acceleration at the nose passing situation yields a pulse in the drag of the overtaken vehicle. The high pressure bow wave followed swiftly by the low-pressure wake affects the side force and lateral stability at positions slightly different than the nose passing. [DOI: 10.1115/1.2427085]

This paper presents comparisons between two-dimensional (2D) CFD simulations and experimental investigations of the cavitating flow around a symmetrical 2D hydrofoil. This configuration was proposed as a test case in the 'Workshop on physical models and CFD tools for computation of cavitating flows' at the 5th International Symposium on cavitation, which was held in Osaka in November 2003. The calculations were carried out in the ENSTA laboratory (Palaiseau, France), and the experimental visualizations and measurements were performed in the IRENav cavitation tunnel (Brest, France). The calculations are based on a single-fluid approach of the cavitating flow: the liquid/vapor mixture is treated as a homogeneous fluid whose density is controlled by a barotropic state law. Results presented in the paper focus on cavitation inception, the shape and the general behavior of the sheet cavity, lift and drag forces without and with cavitation, wall pressure signals around the foil, and the frequency of the oscillations in the case of unsteady sheet cavitation. The ability of the numerical model to predict successively the noncavitating flow field, nearly steady sheet cavitation, unsteady cloud cavitation, and finally nearly supercavitating flow is discussed. It is shown that the unsteady features of the flow are correctly predicted by the model, while some subtle arrangements of the two-phase flow during the condensation process are not reproduced. A comparison between the peer numerical results obtained by several authors in the same flow configuration is also performed. Not only the cavitation model and the turbulence model, but also the numerical treatment of the equations, are found to have a strong influence on the results. [DOI: 10.1115/1.2427079]

Jet-crossflow experiments were performed in a water channel to determine the Reynolds number effects on the plume trajectory and entrainment coefficient. The purpose was to establish a lower limit down to which small scale laboratory experiments are accurate models of large scale atmospheric scenarios. Two models of a turbulent vertical surface jet (diameters 3.175 mm and 12.7 mm) were designed and tested over a range of jet exit Reynolds numbers up to [10.sup.4]. The results show that from Reynolds number 200-4000 there is about a 40% increase in the entrainment coefficient, whereas from Reynolds number 4000-10,000, the increase in entrainment coefficient is only 2%. The conclusion is that Reynolds numbers significantly affect plume trajectories when the model Reynolds numbers are below 4000. Changing the initial turbulence in the exit flow from 12% to 2% without changing its mean velocity profile caused a less than one source diameter increase in the final plume rise. [DOI: 10.1115/1.2427084] Keywords: jet-crossflow, plume-rise, LIF, PLIF, downwash entrainment

To study the drag reduction effect of a bubbly fluid, a pin-disk experiment is performed on the Universal Micro Tribotester system. Bubbles are generated by water electrolysis in holes that are specially designed on the disk surface. Experiment result shows that the drag force experiences a dynamic process, both drag reduction and drag increment effects appear in the process depending on the bubble behavior. This process is numerically simulated using computational fluid dynamics (CFD), and the explanations for the drag variation are given based on the analysis of drag forces on each wall of the disk surface. The drag reduction occurs when the bubble fills the hole, as the viscous drag on the air-liquid surface is small, and the pressure drag is reduced as the side wall of the hole is covered by the bubble. The drag increment is thought to be caused by the increment of the fluid viscosity when the bubble leaves the hole and flows in the fluid. [DOI: 10.1115/1.2354531] Keywords: bubble, drag reduction, lubrication, surface roughness

Computational fluid dynamics calculations of flow in a straight flume for sediment erodibility testing were conducted. The calculations allowed improved postprocessing of the erosion data collected and better understanding of scour pit formation that is sometimes found in the flume's test section. The flume is a 3-m-long, rectangular (13-cm-wide by 10-cm-high) water conduit, which is placed on the sediment water interface during the sediment transport tests. The flume consists of a 1.6-m inlet section, followed by a 1.1-m test section, where the flowing water contacts the sediment. After erosion has occurred in the test section, the flow entering from the inlet section is an expanding flow. It generates a circulation cell and nonuniform bottom stress and pressure. Flow calculations were conducted for four different erosion depths (0, 1, 2, and 4 cm) and for two different flow velocities (1 and 0.5 m/s). After erosion had occurred, the effective stress in the test section was within 15% of the bottom stress calculated with the Schlichting equation, as long as the increased cross-sectional area was accounted for. DOI: 10.1061/(ASCE)0733-950X(2006) 132:6(457) CE Database subject headings: Flumes; Cohesive sediment; Computational fluid dynamics technique; Shear strength; Shear stress; Erosion.

A miniaturized nebulizer chip for vaporization of liquid samples for mass spectrometry has been designed, fabricated, and characterized for fluidic and thermal performance. Silicon/glass chip has a liquid sample channel placed centrally between symmetric nebulizer gas channels. The liquid sample is nebulized and vaporised by an integrated platinum heater. The vaporized sample exits through an etched nozzle, and is ionized by an external corona needle. The ions are analysed by a mass spectrometer. The chip has been fabricated in both anisotropically wet etched and DRIE versions in silicon, with an anodically bonded Pyrex glass cover plate. Three different fluidic inlet designs are presented, with both through-wafer and edge insert versions. The shape of the erupting gas jet has been visualized by infrared thermography by using a low-diffusivity imaging screen and high heat capacity helium as a test gas. Dimensions of the jet's thermal footprint on the screen show that the jet is very narrow and confined, and this is confirmed in mass spectrometry results. This confined jet supplies the sample to the ionization region near corona tip, enabling efficient use of very small sample amounts and submicroliter flows. [1591] Index Terms--Fluidics, infrared imaging, mass spectrometry, micromachining, silicon.

The theory behind ideal sedimentation tanks assumes that the fluid moves in uniform flow. Numerous studies have shown numerous nonuniform flow patterns, which explains why the solids removal efficiency of real clarifiers does not match theory predictions. This problem gets worse when the influent flow rate exceeds what the clarifier was designed to handle. This research shows that introducing a highly porous bed of 'dendrite' fibers into clarifiers designed for the pulp and paper industry removed some of the nonuniformities as shown in a residence time distribution (RTD). These clarifiers have RTDs that are similar to their waste treatment counterparts. So, it is expected that the new technology will have similar effects in waste treatment systems. The bed acts as a resistor to nonaxial flow, reducing radial and angular components of velocity. It is also shown that the greatest effect on the bulk flow patterns occurs when the bed is positioned such that all of the overflow passes through it. Increasing the bed thickness also increases the effect. Analysis of these results was performed with a new model for RTDs based on the Weibull distribution, which is mathematically similar to the equation for a mixed flow RTD. DOI: 10.1061/(ASCE)0733-9372(2006) 132:10(1249) CE Database subject headings: Fluid flow; Porous media; Uniform flow; Sedimentation.

This paper analyzes the effect of groove dimensions (width, depth, and spacing) of transversely grooved pavement surface on hydroplaning using a three-dimensional finite-volume hydroplaning simulation model. Groove widths varying from 2 to 10 ram, groove depths from 1 to 10 ram, and center-to-center spacings from 5 to 25 mm are examined. The effectiveness of a pavement groove design against hydroplaning can be assessed by its ability to raise the hydroplaning speed, which is the vehicle speed at which hydroplaning occurs. It is found that the hydroplaning speed can be raised by increasing the groove depth and width, and decreasing the groove spacing, thereby reducing the risk of hydroplaning occurrence. Among the three groove dimensions (i.e., width, depth, and spacing), changes in groove width is found to have the most significant effect, followed by groove spacing and groove depth. This paper next proposes an analytical procedure for the design of transverse pavement grooving using the simulation model based on the concept of risks of hydroplaning. An illustration of the proposed design procedure is presented in this paper, using a wet-weather freeway vehicle speed distribution, to determine the transverse pavement grooving designs for different risk levels from 0.001% upward. The design concept also allows one to assess the hydroplaning risk level of an existing transversely grooved pavement surface or a proposed groove design, with known wet-weather traffic speed distribution and water film thickness. DOI: 10.1061/(ASCE)0733-947X(2006) 132:6(449) CE Database subject headings: Computational fluid dynamics technique; Pavements; Hydrodynamic pressure; Design.

The time-dependent fluid flow in a square cavity was studied using model fluids of glycerol-water solution at different frequencies and amplitudes of motion of the top plate. The range of Reynolds numbers in our investigation varied from 5 to 3700. The experiments were carried out in a square cavity with a periodically driven lid, and planar velocity measurements were obtained using particle image velocimetry. The flow was driven by moving the top surface of the cavity in a simple harmonic motion. The aspect ratio, defined as the ratio of cavity length to the cavity height, is unity. The ratio of cavity spanwise width to the length of the cavity is 0.2. The temporal variation of velocity at fixed locations in the cavity exhibits a periodic variation. The basic frequency of the fluid motion at a point in the flow domain was observed to be the same as that of plate motion for low Reynolds number Re. However, existence of dominant secondary frequencies was observed along the central vertical plane. The velocity variation as a function of time at a fixed position and the velocity profiles along horizontal and vertical planes are also quantitatively described. These were compared to computational fluid dynamics (CFD) simulations based on the finite volume technique. Comprehensive details of the flow as a function of Reynolds number are analyzed. The evolution of secondary vortices at different plate positions as a function of Reynolds number is also presented. The planar velocity measurements acquired are indicative of the flow behavior in a periodically driven cavity with a narrow span width even at high Re. At very low Re, the flow throughout the periodically driven cavity qualitatively resembles the classical steady lid-driven cavity flow. At high Re, the entire cavity is occupied with multiple vortices. The qualitative features of the bulk flow observed are valid even for cavities with infinite span width. [DOI: 10.1115/1.2173289] Keywords: periodically driven cavity, particle image velocimetry, periodicity, secondary vortex, CFD simulations

A new and generalized lattice Boltzmann model for simulating thermal two-phase flow is described. In this model the single component multi-phase lattice Boltzmann model proposed by Shan and Chen is used to simulate the fluid dynamics. The temperature field is simulated using the passive-scalar approach, i.e., through modeling the density field of an extra component, which evolves according to the advection-diffusion equation. By coupling the fluid dynamics and temperature field through a suitably defined body force term, the thermal two-phase lattice Boltzmann model is obtained. In this paper, the theoretical foundations of the model and the validity of the thermal lattice Boltzmann equation method are laid out, illustrated by analytical and numerical examples. In a companion paper (P. Yuan and L. Schaefer, 2006, ASME J. Fluids Eng., 128, pp. 151156), the numerical results of the new model are reported. Keywords: lattice Boltzmann equation (LBE) method, two-phase flow, interparticle potential, passive-scalar

We perform molecular dynamics (MD) simulations (based on the soft-sphere model) of a model dry. granular system consisting of two types of spherical particles differing in size and/or density to characterize particle-particle momentum transfer (solid drag). The velocity difference between two types of particles is specified in the initial conditions, and the evolution of relative mean velocity and the velocity fluctuations in terms of granular temperature are quantified. The dependence of the momentum transfer is studied as a function of volume fraction, size and density ratio of the two types of particles, inelasticity, and friction coefficient. An existing continuum model of particle-particle momentum transfer is compared to the MD simulations. A modified continuum solid drag model is suggested for a limited range of parameters.

Using computational fluid dynamics as the key tool for analysis, this paper looks into the generic designs of two popular types of breakwater, i.e., V-shape breakwater and vane-type breakwater. These are common practices to prevent the intrusion of green water deep into the deck and to protect deck structures and containers from direct impact loading. A hydrodynamic model to present green water flow on deck is also summarized together with brief validation for its appropriateness. The geometrical parameters of these two breakwaters are systematically varied and the effects on their performance against green water are evaluated. The effectiveness of coping with green water loading of each type of breakwater is also analyzed and compared. DOI: 10.1061/(ASCE)0733-950X(2006)132:1(57) CE Database subject headings: Breakwaters; Design; Computational fluid dynamics technique; Velocity; Waterfront structures; Ships.

We present computational fluid dynamic (CFD) simulation of aggregation of two deformable cells in a shear flow. This work is motivated by an attempt to develop computational models of aggregation of red blood cells (RBCs). Aggregation of RBCs is a major determinant of blood viscosity in microcirculation under physiological and pathological conditions. Deformability of the RBCs plays a major role in determining their aggregability. Deformability depends on the viscosity of the cytoplasmic fluid and on the rigidity of the cell membrane, in a macroscopic sense. This paper presents a computational study of RBC aggregation that takes into account the rheology of the cells as well as cell-cell adhesion kinetics. The simulation technique considered here is two dimensional and based on the front tracking/immersed boundary method for multiple fluids. Results presented here are on the dynamic events of aggregate formation between two cells, and its subsequent motion, rolling, deformation, and breakage. We show that the rheological properties of the cells have significant effects on the dynamics of the aggregate. A stable aggregate is formed at higher cytoplasmic viscosity and membrane rigidity. We also show that the bonds formed between the cells change in a cyclic manner as the aggregate rolls in a shear flow. The cyclic behavior is related to the rolling orientation of the aggregate. The frequency and amplitude of oscillation in the number of bonds also depend on the rheological properties.

Federal regulations (IOCFR71) require radioactive material transport packages to safely withstand a 30 min fully engulfing fire. The three-dimensional Container Analysis Fire Environment (CAFE-3D) computer code was developed at Sandia National Laboratories to simulate the response of massive packages to large fires for design and risk studies. These studies require rapid and accurate estimates of the package temperature distribution for a variety of package designs and fire environments. To meet these needs CAFE-3D links a finite element model that calculates the package response to the Isis-3D CFD fire model. 1SIS-3D combines computational fluid dynamics with reaction chemistry and thermal radiation models to rapidly estimate the heat transfer from a fire. In the current work, parameters used in the fire model were determined. Simulations were then performed of a test that modeled the conditions of a truck-sized nuclear waste package in a regulatory fire under light wind conditions. CAFE-3D underestimated the ability of the wind to tilt the fire and deliver oxygen to the region above the fuel pool However, it accurately and rapidly estimated the total heat transfer to the test object. CAFE-3D will become a more useful tool for estimating the response of transport packages to large fires once it has been benchmarked against a larger range of fire conditions.

Current suggestions for estimating the numerical uncertainty in solutions by the Large-Eddy Simulation (LES) methodology require either a posteriori input or reflect global assessments. In most practical applications, this approach is rather costly for the user and especially time consuming due to the CPU effort needed to reach the statistical steady state. Herein, we demonstrate two alternate a priori graphical exercises. An evaluation of the numerical uncertainty uses the turbulent quantities given by the area under the wave number spectra profiles. These profiles are easily constructed along any grid line in the flow domain prior to the collection of the turbulent statistics. One exercise involves a completion of the spectrum profile beyond the cutoff wave number to the inverse of Kolmorgorov's length scale by a model of isotropic turbulence. The other extends Richardson Extrapolation acting on multiple solutions. Sample test cases of both LES solutions and direct numerical simulations as well as published experimental data show excellent agreement between the integrated matched spectra and the respective turbulent statistics. Thus, the resultant uncertainties themselves provide a useful measure of accumulated statistical error in the resolved turbulent properties. [DOI: 10.1115/1.2060735]

In this paper, the kinetics of the outflow in a microporous particle infiltrated by a nonwetting liquid is analyzed in context of effective phase transformation. The 'dewetting' process is considered as the nucleation, growth, and coalescence of empty pore dusters (EPCs) that starts from the interior and eventually involves the whole particle. Initially, the EPC nucleation is dominant while the influence of EPC coalescence becomes increasingly important as the EPC volume fraction increases. The dependence of the dewetting time on the pore size distribution is discussed in detail. [DOI: 10.1115/1.2060734]

A numerical method is developed for modeling the violent motion and fragmentation of an interface between two fluids. The flow field is described through the solution of the Navier-Stokes equations for both fluids (in this case water and air), and the interface is captured by a Level-Set function. Particular attention is given to modeling the interface, where most of the numerical approximations are made. Novel features are that the reintialization procedure has been redefined in cells crossed by the interface; the density has been smoothed across the interface using an exponential function to obtain an equally stiff variation of the density and of its inverse; and we have used an essentially nonoscillatory scheme with a limiter whose coefficients depend on the distance function at the interface. The results of the refined scheme have been compared with those of the basic scheme and with other numerical solvers, with favorable results. Besides the case of the vertical surface-piercing plate (for which new laboratory measurements were carried out) the numerical method is applied to problems involving a dam-break and wall-impact, the interaction of a vortex with a free surface, and the deformation of a cylindrical bubble. Promising agreement with other sources of data is found in every case. [DOI: 10.1115/1.2062707]

Labyrinth seals are used in various kinds of turbo machines to reduce internal leakage flow. The working fluid, or the gas passing through the rotor shaft labyrinth seals, often generates driving force components that may increase the unstable vibration of the rotor. It is important to know the accurate rotordynamic force components for predicting the instability of the rotor-bearing-seal system. The major goals of this research were to calculate the rotordynamic force of a labyrinth seals utilizing a commercial CFD program and to further compare those results to an existing bulk flow computer program currently used by major US machinery manufacturers. The labyrinth seals of a steam turbine and a compressor eye seal are taken as objects of analysis. For each case, a 3D model with eccentric rotor was solved to obtain the rotordynamic force components. The leakage flow and rotor dynamics force predicted by CFX TASCFlow are compared with the results of the existing bulk flow analysis program DYNLAB. The results show that the bulk flow program gives a pessimistic prediction of the destabilizing forces for the conditions under investigation. Further research work will be required to fully understand the complex leakage flows in turbo machinery. [DOI: 10.1115/1.1808426]

The cavitating flow around a marine propeller is studied using an unstructured grid based Reynolds-averaged Navier-Stokes computational fluid dynamics method. A cavitation model based on a single-fluid multi-phase flow method is implemented in the Navier-Stokes solver. The proposed computational approach for cavitation is validated against a benchmark database for a cavitating hydrofoil as well as measured data for a cavitating marine propeller. The leading edge and mid-chord cavitation on the hydrofoil is reproduced well and shows good comparison with the well-known experimental data. The predicted noncavitating open water performance of the marine propeller geometry agrees well with the measured one. Finally, the cavitating propeller performance as well as cavitation inception and cavity shape are in good agreement with experimental measurements and observation. The overall results suggest that the present approach is practicable for actual cavitating propeller design procedures without lengthy preprocessing and significant preliminary knowledge of the flow field. [DOI: 10.1115/1.1989370]

An innovative methodology is presented for th purpose of analyzing fluid flow and heat transfer in a porous-fluid composite system, where the porous medium is assumed to have a periodic structure. The analytical solutions are validated by comparing them with the corresponding numerical solutions for the case of the ideal composite channel, and with existing experimental data.

Throughout the history of turbomachines investigators have tried to develop reliable methods for prediction of centrifugal pump behavior. Among the parameters available to estimate the performance of this kind of machine is the slip factor. In spite of being regarded as a variable of great significance in the analysis of turbomachinery, there seem to be a misconception regarding its concept and application. Indeed, empirical correlations have been widely used to estimate the slip factor, even in the case of two-phase flow applications, where it has not been investigated. Moreover, these correlations provide a constant value of the slip factor for a given impeller only at the best efficiency point, which is an important restriction to the pump performance prediction, considering that slip factor varies with the pump flow rate. In this study, three-dimensional computational fluid dynamics simulations were carried out on an impeller of known geometry ([N.sub.s] = 1960) from which values of slip factor were calculated for both single- and two-phase flow (water and water-air). These results include curves of the slip factor as a function of the specific capacity and the gas-void fraction. Additionally, results for the slip factor in the case of single-phase flow (water) are given for various centrifugal impellers ([N.sub.s] = 157, 1447, 1612, and 3513) in order to illustrate the influence of the flow rate on this parameter. Finally, based on the numerical results, a methodology for prediction of the pump head is presented. Excellent agreement with experimental results has been found. This paper attempts to contribute to a better understanding of the fluid dynamics within centrifugal pump impellers and to shed more light on the path that prediction models should follow in the future. [DOI: 10.1115/1.1891153]

Numerical simulations of cavitation in liquid nitrogen and liquid hydrogen are presented; they represent a broader class of problems where the fluid is operating close to its critical temperature and thermal effects of cavitation are important. A compressible, multi-phase formulation that accounts for the energy balance and variable thermodynamic properties of the fluid is described. Fundamental changes in the physical characteristics of the cavity when thermal effects become significant are identified; the cavity becomes more porous, the interface less distinct, and it shows increased spreading while getting shorter in length. The heat transfer model postulated in variants of the B-factor theory, where viscous thermal diffusion at the vapor-liquid interface governs the vaporization, is shown to be a poor approximation for cryogenic fluids. In contrast the results presented here indicate that the cavity is sustained by mass directly convecting into it and vaporization occurring as the liquid crosses the cavity interface. Parametric studies for flow over a hydrofoil are presented and compared with experimental data of Hord (1973, 'Cavitation in Liquid Cryogens II--Hydrofoil,' NASA CR-2156); free-stream velocity is shown to be an independent parameter that affects the level of thermal depression. [DOI: 10.1115/1.1883238]

The conservation element and solution element (CE/SE) method, an accurate and efficient explicit numerical method for resolving moving discontinuities in fluid mechanics problems is used to solve three-dimensional phase-change problems. Several isothermal phase-change cases are studied and comparisons are made to existing analytical solutions and the method is found to be accurate, robust and efficient for the numerical modeling of phase-change problems.

A model for predicting sand erosion in 90 degree elbows and bends has been developed based on computational fluid dynamics (CFD), panicle tracking and erosion data. After the flow field was obtained from the flow (CFD) model, particles were introduced into the flow and particle trajectories were computed using a Lagrangian approach. A model was also implemented that accounts for the interaction between the particles and the target material. Based on predicted particle impingement velocities, erosion rates and penetration rates were predicted using the empirical equations for erosion ratio. The predicted penetration rates are compared with available experimental data for several different elbows. The agreement between the predicted penetration rates and the experimental data is good. In addition, based on many predictions and erosion rate results, a new CFD based correlation is developed that can be used for an approximate engineering calculation to account for effects of elbow radius on erosion in long-radius elbows. This equation is for computing the ratio of the wall thickness loss (or the penetration rate) in a long-radius elbow to the penetration rate of a standard (short-radius) elbow. The results from the correlation agree well with the trend of available data in the literature.

Numerical computations and laboratory experiments are carried out to investigate the three-dimensional structure of large-scale (coherent) vortices induced by bridge abutments on a flat bed. A finite-volume numerical method is developed for solving the unsteady, three-dimensional Reynolds-averaged Navier-Stokes equations, closed with the k-[omega] turbulence model, in generalized curvilinear coordinates and applied to study the flow in the vicinity of a typical abutment geometry with a fixed, flat bed. The computed flowfields reveal the presence of multiple, large-scale, unsteady vortices both in the upstream, 'quiescent,' region of recirculating fluid and the shear-layer emanating from the edge of the foundation. These computational findings motivated the development of a novel experimental technique for visualizing the footprints of large-scale coherent structures at the free surface. The technique relies on digital photography and employs averaging of instantaneous images over finite-size windows to extract coherent eddies from the chaotic turbulent flow. Application of this technique to several abutment configurations yielded results that support the numerical findings. CE Database keywords: Scour; Bridge abutments; Turbulence; Models; River beds.