bluuebunny/crossref_metadata_2025 huggingface dataset:
Large-Eddy Turbulent Flow Simulation of an Industrial Helical Static Mixer
Authors: Rahmani Ramin K. , Keith Theo G. , Ayasoufi Anahita
Published: March 2009

Viscous liquids have to be homogenized in continuous operations in many branches of processing industries; and therefore, fluid mixing plays a critical role in the success or failure of many industrial processes. Consequences of improper mixing include non-reproducible processing conditions and lowered product quality, resulting in the need for more elaborate downstream purification processes and increased waste disposal costs. The range of practical flow Reynolds numbers for helical static mixers in industry is usually from very small (Re ≈ 0) to moderate values (e.g. Re = 5,000). However, it has been found that the flow regime within helical static mixers is turbulent for relatively low Reynolds numbers, compared to the flow inside a pipe with no mixing elements present. This paper extends previous studies by the authors on the industrial helical static mixer. Its purpose is to present an improved understanding of the turbulent flow pattern for single-phase liquids through the mixer. Three-dimensional finite volume simulations are used to study the performance of the mixer using different turbulent models. Large-Eddy Simulation (LES) model is applied to the flow in an industrial helical static mixer to calculate the flow velocities, pressure drops, etc. Using a variety of predictive tools, the mixing results are obtained. Also, the accuracy and global performance of several different turbulent models are compared against the LES model.
Stefan Number-Insensitive Numerical Simulation of the Enthalpy Method for Stefan Problems Using the Space-Time Conservation Element and Solution Element Method
Authors: Ayasoufi Anahita , Keith Theo G. , Rahmani Ramin K.
Published: March 2009

An improvement is introduced to the conservation element and solution element (CE/SE) phase change scheme presented previously. The improvement addresses a well known weakness in numerical simulations of the enthalpy method when the Stefan number, (the ratio of sensible to latent heat) is small (less than 0.1). Behavior of the improved scheme, at the limit of small Stefan numbers, is studied and compared with that of the original scheme. It is shown that high dissipative errors, associated with small Stefan numbers, do not occur using the new scheme.
Relation of the Formation of Secondary Flow Between Atmospheric Flow and Turbomachinery Flow
Authors: Hamrick Joseph T.
Published: March 2009

Researchers at Iowa State University instituted a research program in which they built a vortex generator in an effort to simulate atmospheric mesocyclones and to determine their relationship to tornado formation. In their research it was observed that when a vortex touched down on a ground surface there was a build up of a concentrated vortex at the center of the parent vortex. It was also observed that the concentrated vortex cannot be formed without contact with a ground surface. They attributed the build up of the concentrated vortex to radially inward flows in the boundary layer adjacent to the ground plane but provided no analysis of the flow in the boundary layer. To perform the analysis provided herein an attempt was made to apply a transfer of technology developed at the National Advisory Committee for Aeronautics (NACA), Lewis Flight Propulsion Laboratory at Cleveland, Ohio. In the NACA research the mechanisms of radially inward flows in boundary layers were evaluated. The transfer of that technology to atmospheric flows is presented herein. In this paper it is illustrated that the transfer of technology can be an effective tool in attempts to resolve issues in related fields of endeavor.
Measurement of Permeability and Slip Coefficient of Porous Tubes
Authors: Brown N. M. , Lai F. C.
Published: March 2009

Experiments have been conducted to measure the permeability and slip coefficient of seven porous tubes. These tubes are to be used in a liquid storage tank to enhance thermal stratification. They were made from fiberglass and nylon nettings with various wall thicknesses. Six tubes had an outer diameter of 1.9 cm and a thickness ranging from 0.158 cm to 0.635 cm, and the seventh tube had an outer diameter of 10 cm and a thickness of 0.635 cm. Tests show that these tubes have a distinct permeability in the longitudinal and radial directions. As such, both permeabilities of the tubes were measured. In addition, the slip coefficient which is an important parameter in the Beaver-Joseph interface condition was determined. From the results obtained, one can conclude that both permeabilities depend on the material, but the radial permeability also depends on the wall thickness. The slip coefficient depends not only on the material but also on the Reynolds number, permeabilities and porous wall thickness.
Development of CFD Capability for Airbag Out-of-Position Applications
Authors: Lian Wenyu , Olovsson Lars , Bhalsod Dilip
Published: March 2009

The need for Out-Of-Position (OOP) simulation capabilities in crash safety software has risen in importance in the automotive industry after the final ruling of FMVSS 208 by the National Highway Transportation Safety Administration (NHTSA) in 2000. However, because of current technical challenges, the thermodynamics airbag models are not capable of either accurately simulating the flow-bag interactions under OOP conditions, or differentiating the effect of some important design changes, such as vent locations, inflator configuration, and flow diverging devices. The development of these capabilities entails overcoming tremendous technical challenges and numerical difficulties in computational fluid dynamics (CFD) and crash simulations due to the complexity and extreme conditions of OOP. This paper summarizes the developments of algorithms used in the context of an Arbitrary Lagrangian-Eulerian (ALE) formulation. The main developments of this study include the gas dynamic model for mixing gases, the special treatment of inflator gas flows, a penalty based fluid-structure coupling algorithm, and a permeability algorithm for porous fabrics. To expedite the developments and resolve the technical difficulties, a set of benchmark problems was used in this study. Each of the benchmark problems addresses specific technical difficulties of airbag OOP simulations by comparing simulation results to analytical solutions, well-known numerical solutions, or test results. The benchmark set was designed to start from simple CFD problems and progress to the most complicated OOP applications such that the weakness and algorithmic errors of the simulation code can be easily identified. Simulation results of the benchmark problems and the issues addressed by them are discussed in this paper. The simulation results have demonstrated that LS-DYNA now has the capabilities to simulate certain OOP problems.
Numerical Simulation of Fluid Slip at a Hydrophobic Surface
Authors: Fujita Takao , Watanabe Keizo
Published: March 2009

Laminar drag reduction is achieved by using a hydrophobic surface. In this method, fluid slip is applied at the hydrophobic surface. An initial experiment to clarify for a laminar skin friction reduction was conducted using ducts with a highly water-repellent surface. The surface has a fractal-type structure with many fine grooves. Fluid slip at a hydrophobic surface has been analyzed by applying a new wet boundary condition. In this simulation, an internal flow is assumed to be a two-dimensional laminar flow in a rectangular duct and an external flow is assumed to be a two-dimensional laminar flow past a circular cylinder. The VOF technique has been used as the method for tracking gas-liquid interfaces, and the CSF model has been used as the method for modeling surface tension effects. The wet boundary condition for the hydrophobic property on the surface has been determined from the volume ratio in contact with water near the surface. The model with a stable gas-liquid interface and the experimental results of flow past a circular cylinder at Re = 250 without growing the Karman vortex street are made, and these results show that laminar drag reduction occurring due to fluid slip can be explained in this model.
Numerical Simulation of Fires in Ventilated Compartment
Authors: Kameel Ramiz , Khalil Essam E.
Published: March 2009

This study is the analytical investigation of transient flow characteristics in a ventilated compartment fire. This study aims at enhancing the understanding of fire propagation in the compartment and its influence on the air flow characteristics. The present paper discusses the results of different ventilation scenarios for a single fire scenario. It is recommended to use the smoke extract fans in designated locations in the spaces that could be exposed to the fire hazards. Corridor smoke extract fan provides the safe escape for the occupancy. Quantitative parametric studies are carried out for various situations, to enhance our knowledge about the fire behavior. The critical time for the safe escaping of occupancy from the fire starting is discussed in the present work. Also, it is found that, the fire field models based on CFD are useful tools that can greatly support this target.
Heat and Moisture Flow Simulation With MULTIFLUX
Authors: Danko G. , Bahrami D.
Published: March 2009

The paper describes the results of a ventilation study involving subsurface heat and moisture flow at Yucca Mountain (YM), Nevada. MULTIFLUX (MF), a fully-coupled, hydrothermal-ventilation model and software code is used to model the flow of heat, moisture, and air in a subsurface airway within the conceptual, high-level nuclear waste repository proposed to be built at YM. The hydrothermal-ventilation/heat flow model and software MF is a universal coupler that connects the heat and moisture transport calculations in two different domains: (1) the rockmass, with a NUFT-based NTCF model, and (2) the airway with the heat-generating nuclear waste packages, using a CFD model. Temperature, relative humidity and water condensate variations are analyzed in the emplacement drift, assuming air movement, to determine the conditions of the psychometric corrosion environment in the emplacement area. The calculation results show condensate formation in the cold drift section, and are found to be sensitive to choosing from two different CFD model configurations.
Numerical Transport Code Functionalization Procedure and Software Functions
Authors: Danko G.
Published: March 2009

A numerical–computational procedure is described to determine a multi-dimensional functional or an operator for the representation of the computational results of a numerical transport code. The procedure is called Numerical Transport Code Functionalization (NTCF). Numerical transport codes represent a family of engineering software to solve, for example, heat conduction problems in solids using ANSYS; heat and moisture transport problems in porous media using NUFT; or laminar or turbulent flow and transport problems using FLUENT, a computational fluid dynamic (CFD) model. The NTCF procedure is developed to determine a model for the representation of the code for a variety of input functions. Couple solution of multiphysics problems often require repeated, iterative calculations for the same model domain and with the same code, but with different boundary condition values. The NTCF technique allows for reducing the number of runs with the original numerical code to the number of runs necessary for NTCF model identification. The NTCF procedure is applied for the solution of coupled heat and moisture transport problems at Yucca Mountain, Nevada. The NTCF method and the supporting software is a key element of MULTIFLUX, a coupled thermohydrologic-ventilation model and software. Numerical tests as well as applications for Yucca Mountain, Nevada are presented using both linear and nonlinear NTCF models. The performance of the NTCF method is demonstrated both in accuracy and modeling acceleration.
Improved Lumped Model for Transient Heat Conduction in a Heat Generating Cylinder With Temperature-Dependent Thermophysical Properties
Authors: Pontedeiro Auro C. , Cotta Renato M. , Su Jian
Published: March 2009

This paper presents improved lumped-differential formulations for one dimensional transient heat conduction in a heat generating cylinder with temperature-dependent thermo-physical properties. Two points Hermite approximations for integrals (H1,1/H1,1) are used to approximate the average temperature and the heat flux in the radial direction. As a testing case, transient heat conduction in a nuclear fuel rod was computed with the thermo-physical properties represented by correlations from MATPRO — a Library of Materials Properties for Light-Water-Reactor Accident Analysis. The problem was formulated and solved using the symbolic/numerical computation software system MATHEMATICA. The solution of the proposed improved lumped models is validated by a numerical solution of the original distributed parameter formulation.
Effect of Interfacial Heat Transfer on Molten Tin Jet Breakup in an Oil Tank
Authors: Mehdi-Nejad Vala , Mostaghimi Javad , Chandra Sanjeev
Published: March 2009

This paper presents the effect of interfacial heat transfer on the breakup of an annular jet surrounded by another viscous liquid. Specifically, we consider the breakup of a molten tin jet in eicosane. One-field volume tracking is used which involves solving one set of equations for conservation of mass, momentum and energy. The original idea behind volume tracking methods has been used not only to advect mass and momentum but also energy across cell boundaries. The van Leer method is used to approximate advection temperatures across the sharp temperature gradients existing at fluid/fluid interface. To study the effect of heat transfer on the hydrodynamics of the flow, all fluid properties except density are modelled as temperature dependent. Results show a direct correlation between interfacial heat transfer and the location of the breakup. For tin, results show that the temperature dependency of viscosity is the major factor in dictating the location and time of the breakup.
Laminar Flow and Heat Transfer in Spiral Ducts of Rectangular Cross Section
Authors: Egner Michael W. , Burmeister Louis C.
Published: March 2009

Laminar flow and heat transfer in three-dimensional spiral ducts of rectangular cross section with aspect ratios of 1, 4, and 8 were determined with the aide of the FLUENT computational fluid dynamics program. Peripherally-averaged coefficients of friction and Nusselt numbers are presented as a function of distance from the inlet and of the Dean number. Fully-developed values of friction coefficient and Nusselt number for a constant-radius-of-curvature duct, either toroidal or helical with small pitch, can be used to predict those quantities for the spiral duct in post-entry regions. These results are applicable to spiral-plate heat exchangers.
Heat Transfer in a Narrow Channel Roughened by 45° Ribs With Twin-Blow Entrances
Authors: Chang Shyy Woei , Chiang Kuei Feng , Sung Kuei Chih
Published: March 2009

This experimental study investigates the heat transfer in a narrow, rib-roughened, rectangular channel with the width-to-height ratio of 10 for its cross-sectional shape. Two flow entrances with equal areas are respectively opened at the upper and side ends of this channel that allows for increasing the coolant-flow fed into the enhanced channel without increasing the height of cooling device. At a fixed total coolant mass flow rate, three test scenarios, namely the single-blow from the side or upper entrance and the twin-blow with the coolant mass flow ratio of 2:1 between the side and upper blows are performed. A selection of detailed heat transfer measurements, evaluated from infrared thermal images over the rib-roughened surface, illustrates the manner by which the flow entry direction and the twin-blow condition affect the local and spatially averaged heat transfers. Relative to the heat transfer results acquired from the single-blow tests, the present twin-blow entry condition could augment the spatially averaged heat transfers to the levels of 150–180% of the single-blow reference levels. A regression-type analysis is subsequently performed to develop the correlation of spatially-averaged Nusselt numbers over rib-roughened surface, which permits the effect of Reynolds number, evaluated from the total amount of coolant consumption, on heat transfer to be determined for three test scenarios.
CFD Studies on a Large Diameter Jet Impingement Flow
Authors: Zhang Zhiguo , Ibrahim Mounir
Published: March 2009

This paper presents computational study for a large diameter (216 mm) and small space ratios (S/D = 0.25 and 0.5) jet impingement flow. CFD-ACE code was used as the computational tools; the code was first validated by comparing its predictions with both CFD and experimental data from the literature. Then, the study was performed for two different Reynolds numbers: 7600, 17700 and two different space ratios: 0.25 and 0.5. Also two different turbulence models were utilized in this study: low Reynolds number turbulent k-ε and k-ω. The CFD results were compared with flow visualization results conducted at the University of Minnesota for the same configurations. The impact of choosing different inlet conditions on the CFD flow field was examined. The k-ε model showed greater sensitivity to the selection of the inlet conditions. Moreover, the k-ω model showed much better agreement with the experimental data than the k-ε model.
Case Study of Impeller Profile Considering Additional Parameters
Authors: Tsugawa Takuji
Published: March 2009

In the previous paper, the optimum meridian profile of impeller was obtained for various specific speed by means of five shape factors. In this paper, the optimum meridian profile of impeller is obtained by means of eight shape factors. The basic five shape factors are inlet relative flow angle β1, turning angle Δβ, axial velocity ratio kc = Cm2/Cm1 impeller diameter ratio kd = D1c/D2c and outlet hub-tip ratio ν2 (β1 and Δβ are in mid span stream surface). The additional three parameters are three stream lines solidity (tip solidity σt, mid span solidity σc, and hub solidity σh). The blade length of impeller meridian profile is able to obtain by additional three parameters. The method of optimization is the calculation of hydraulic efficiency and suction specific speed in all combinations of eight shape parameters. The number of five shape factors are expressed by Nβ1, NΔβ, Nkc, Nkd, Nν2. The number of calculations is expressed by Nβ1 × NΔβ × Nkc × Nkd × Nν2. For example, Nβ1 = NΔβ = Nkc = Nkd = Nν2 = 40, the number of calculations is about 100000000. The calculation time is about 2 hours. The best parameters are selected in 100000000 cases. In case of eight shape factors, the number of calculation is Nβ1 × NΔβ × Nkc × Nkd × Nν2 × Nσt × Nσc × Nσh. Nβ1 = NΔβ = Nkc = Nkd = Nν2 = Nσt = Nσc = Nσh = 10, the number of calculation is 100000000. In this case, the calculation time of eight shape factors is as same as that of five shape factors. By means of this method, the more detailed optimum mixed flow impeller meridian shape is obtained. In case study, the best 1000 optimum meridian profiles and the best design parameter are selected for few kinds of specific speed using eight dimensional optimum method. In the previous paper, the mixed flow angle on tip meridian stream line isn’t able to be decided by this optimization using diffusion factor. But, in this paper, the mixed flow angle is able to be decided by the number of blade and optimum solidity. As the best solidity of three stream lines is obtained, the axial coordinates of impeller inlet and outlet are obtained. The more detailed optimum mixed flow impeller meridian shape is drawn.
Parametric Study of MMC Solidification in the Presence of Cooled Fibers: Numerical Simulation and Experimental Validation
Authors: Lee E. K. , Amano R. S. , Xie J. , Rohatgi P. K.
Published: March 2009

A new experimental configuration for the casting of metal matrix composites (MMCs) using Al-4.5 wt pct Cu has been used to obtain finer microstructures around the fiber reinforcement. The new configuration allows fibers to be extended out of the mold and cooled by a heat sink. By doing so, solidification can be sped up and more primary alpha-aluminum phase can be formed on the surface of the fibers. It is believed that this can lead to improved material properties of the composite. A simulation study of the solidification process has been carried out to examine the effects of different processing parameters on the cooling rate during the casting of MMC. Among these parameters include the pouring temperature of the liquid melt, sink temperature, fiber length extended out of the mold, fiber conductivity, mold initial temperature, mold conductivity, applied pressure, mold wall thickness, and fiber bundle diameter. Selected simulation results are compared with the available experimental data obtained from the UWM Center for Composites.
Performance Analysis of an Ultrahigh Performance, 3-D Micro Convective Heat Sink With a Nearly Fractal Plumbing System
Authors: Moreno R. , Tao Y.-X.
Published: March 2009

This paper presents the design and CFD analysis of a 3-D, active micro convective heat sink having high surface-to-volume ratio geometry. The heat sink consists of an array of elemental units arranged in parallel. Each unit is constructed as a network of nearly fractal geometry. The design of each unit uses the constructal method to minimize the point-to-point temperature difference within the heat sink and Murray’s Law to minimize pressure drop across the device. The heat sink is designed for the tape casting fabrication method using thick silver film techniques and co–fired with low temperature co-fired ceramic substrate. To analyze fluid flow and heat transfer characteristics of the design, we use the Fluent CFD software. The numerical results are presented to validate the theoretical optimization and outline the ultra-high performance characteristics of the heat sink such as the overall thermal resistance, pumping power and effectiveness.
Flow and Pressure Measurement in a Selective Laser Sintered Human Tracheobronchial Airway Model Under Cyclic Flow Conditions
Authors: Pulat O. , Parthasarathy R. N.
Published: March 2009

A selectively laser sintered human tracheobronchial airway model was used to study periodic flows at different frequencies corresponding to inhalation and exhalation. The model was fabricated from a 3-d point could based on the Visible Human Male Project. The objective was to document the volumetric flow rate and pressure drop under periodic flow conditions and compare these values with those obtained in steady flow. The flow was cycled via a Programmable Logic computer (PLC) at a specified breathing frequency of 12 breaths per minute. The tracheal flows rate studied were 30, 50, and 120 liters per minute. The results indicated that significant differences existed between flow measurements made under steady conditions and periodic conditions; these differences became significant at high flow rates. The flow distribution in the right and left side of the airway model was asymmetric. The results also indicated the existence of both turbulent and laminar flow regimes at all tracheal flow rates.
Comparison of CFD Natural Convection and Conduction-Only Models for Heat Transfer in the Yucca Mountain Drifts
Authors: Hadgu Teklu , Webb Stephen W. , Itamura Michael T. , Francis Nicholas D.
Published: March 2009

A CFD analysis was conducted comparing turbulent natural convection and conduction-only models used for heat and fluid flow simulations in the drifts of the Yucca Mountain Project. The conduction-only model represents open spaces in the drifts using effective air thermal conductivities. The FLUENT code was used for both simulations with heat generation boundary condition at the waste package and constant temperature boundary condition 5 meters into the host rock formation. Comparisons were made of temperature contours in the drift air and temperature profiles at surfaces of the different engineered components using the two approaches. The results show that for the two-dimensional YMP geometry considered, the average surface temperatures of the CFD natural convection and conduction-only using the equivalent thermal conductivity are similar and the maximum local temperature differences for the different surfaces were within two 2°C. The differences in temperature profiles reflect the use of a single average equivalent thermal conductivity. The effect of the differences on repository performance is discussed.
A Parallel Domain Decomposition Boundary Element Method Technique for Large-Scale Transient Heat Conduction Problems
Authors: Erhart Kevin , Divo Eduardo , Kassab Alain J.
Published: March 2009

In this paper, we develop a parallel domain decomposition Laplace transform BEM algorithm for the solution of transient heat conduction problems. The original domain is decomposed into a number of sub-domains, a procedure is described to provide a good initial guess for the domain interface temperatures, and an iteration is carried out to satisfy continuity of temperature and heat flux at the domain interfaces. The decomposition procedure significantly reduces the size of any single problem to be tackled by the BEM, significantly reduces the overall storage and computational burden, and renders the application of the BEM to modeling large transient conduction problem feasible on modest computational platforms. The procedure is readily implemented in parallel and applicable to 3D problems. Moreover, as the approach described herein readily allows adaptation and integration of traditional BEM codes, it is expected that the domain decomposition approach coupled to parallel implementation should prove very competitive to alternatives proposed in the literature such as fast multipole acceleration methods that require a complete re-write of traditional BEM codes.
Thermal and Mass Modeling of the Laser-Point Sealing Process in MEMS Packaging
Authors: Alaeddine Marios , Zou Jin , Ranganathan Rajesh , Doumanidis Charalabos C. , Ando Teiichi , Wong Peter Y.
Published: March 2009

This article addresses the reactive thermal processing of locally heated intermetallic seals for micro-electro-mechanical systems (MEMS) packaging. Traditional post-packaging of MEMS involves high temperature brazing or soldering which results in degrading the quality of the thermally sensitive device. Focused laser heating of multilayer metals, therefore, serves as an attractive alternative due to a decrease in heat affected/degraded area. In this work a model is presented to decipher the dynamics of the thermal reaction and to serve as a tool for optimization and control of the multilayer sealing process. The analytical model is based on three-dimensional space- and time-dependent temperature and concentration Green’s fields and is solved numerically. The laser heat distribution is represented as a spatially varying Gaussian heat source to simulate the temperature and concentration evolution that occurs during the thermal process. The rapid heating induced by the laser source results in melting the sealing layer of lowest melting temperature, and then dissolves the layer in contact with the molten region to facilitate the nucleation and growth of an intermetallic compound. The simulation results show the model can successfully predict the temperature of the layers as well as the amount of barrier layer dissolution, which consequently determines the extent of the intermetallic compound growth in the bonding/sealing process.
Influence of Drag-Reducing Surfactant Additives on Vortex Structures and Turbulent Events in a Channel Flow
Authors: Li Feng-Chen , Kawaguchi Yasuo , Segawa Takehiko , Hishida Koichi
Published: March 2009

The characteristics of vortex structures and turbulent events of drag-reducing surfactant (CTAC) solution flows in a two-dimensional channel have been studied using particle image velocimetry (PIV) to measure the instantaneous velocity fields in a streamwise-wall-normal plane. Through visualizing the instantaneous velocity field, contour maps of the swirling strength and instantaneous value of uv, the characteristic angle of vortex packets was quantified, and it was shown that the drag-reducing CTAC additive reduced both the strength and frequency of turbulent bursts near the wall, and that the characteristics of vortex structures and bursts were not only dependent on drag-reduction level but also on concentration of additive. Based on the quantified parameters characterizing turbulent events in a wall-bounded turbulent flow, a model of turbulent contribution to the friction factor, fT, was proposed. It was obtained that fT was linearly proportional to the product of frequency and strength of turbulent events.
The Flow Research in an Open Type Pump Sump by PIV Experiments
Authors: Li Yong , Wu Yulin , Mansa Kante , Liu Shuhong , Okamura Tomoyoshi , Nagahara Takahide
Published: March 2009

Pump sump is an important part of pump station its performance influences the flow condition in the pump and even the total performance of the pumping system. In order to study the flow in an open pump sump the Two-dimension PIV system was used. Flow velocity, flow streamlines, turbulence intensity and vorticity can be obtained from the PIV data. The critical velocities for vortex inception have also been measured in this paper. Analyzing those parameters, the flow performance of the sump with special structure was found then the best condition could be chosen basing on the experiments.
Rotor Boundary Layer Response to an Impinging Wake
Authors: Soranna Francesco , Chow Yi-Chih , Uzol Oguz , Katz Joseph
Published: March 2009

This paper presents results of an experimental investigation on the response of a rotor boundary layer to an impinging Inlet Guide Vane (IGV) wake. High resolution two-dimensional Particle Image Velocimetry (PIV) measurements are conducted in a refractive index matched facility that provides an unobstructed view of the entire flow field. Data obtained at four different rotor phases, as the wake is chopped and passes by the rotor blade, allows us to examine the response of the rotor boundary layer to the mean flow and turbulence associated with the impinging wake. We focus on the suction side boundary layer in regions with adverse pressure gradients, from mid chord to the trailing edge. The phase-averaged velocity profiles are used for calculating the momentum and displacement thicknesses of the boundary layer, and for estimating the pressure gradients along the wall. Distributions of Reynolds stresses are also provided. The phase-averaged velocity profiles in the rotor boundary layer vary significantly with phase. During wake impingement the boundary layer becomes significantly thinner and more stable compared to other phases at the same location. Analysis of the possible causes for this trend suggests that the dominant contributors are unsteady, phase-dependent variation in pressure gradients along the wall.
Comparison of Four Eddy-Viscosity SGS Models in Large-Eddy Simulation of Flows Over Rough Walls
Authors: Bou-Zeid Elie , Meneveau Charles , Parlange Marc B.
Published: March 2009

Large Eddy Simulation (LES) has become an increasingly attractive option for turbulence modeling due to the rise in computing power and the improvement in sub-grid scale (SGS) parameterizations. This study tests the improvements in simulations of wall-bounded flows over heterogeneous surfaces attained by the implementation of three improvements in the eddy-viscosity SGS closure: the dynamic model by Germano et al. [1], the Lagrangian model by Meneveau et al. [2], and the scale-dependent approach by Porte´-Agel et al. [3]. The dynamic model consists of using the resolved scales to ‘measure’ the model coefficient during the simulation; therefore, no a-priori knowledge of the coefficient or the flow physics is needed. The traditional dynamic approach averages the coefficient over statistically homogeneous directions to numerically stabilize the simulations. The Lagrangian model relaxes the need for homogeneous directions by averaging the coefficient over pathlines, hence allowing local determination of the coefficient and facilitating applications to complex-geometry flows. The scale-dependent approach uses the dynamic formulation but does not assume that the SGS coefficients are scale-invariant, as is the case in traditional dynamic formulations. The deficiencies of the traditional Smagorinsky model are confirmed. Implementation of a dynamic model treats some of these deficiencies but is found to be under-dissipative close to the wall in high Reynolds number LES that does not resolve the viscous layer. The sensitivity of the model coefficient to the wall roughness is demonstrated thus confirming the need for a local SGS model such as the Lagrangian model used here. Finally, when the Lagrangian-dynamic model is implemented with the scale-dependent formulation, the results improve significantly.
Significance of Thermal Conductivity of Molten Polyethylene in Cable Extrusion Process
Authors: Ka¨llstrand Birgitta , Olsson Carl-Olof
Published: March 2009

The dominating parameter for heat transfer during continuous curing of extruded high voltage cables is the thermal conductivity of molten polyethylene. Literature on thermal conductivity has been reviewed, and it is found that there are differences of order 50% between different investigations. From numerical simulations it is found that 20% increase in thermal conductivity corresponds to 8 °C increase in maximum conductor temperature for constant line speed or 16% increase in line speed for optimized crosslinking. The calculated conductor temperature profile is compared with experimental data from the cable manufacturing. The conductor temperature was measured continuously, using an optical fiber embedded in the outer layer of the conductor, while the conductor passed through the extrusion line. The comparison between measured and simulated conductor temperature profiles show good agreement provided that an appropriate value of the thermal conductivity is chosen.
N-Phase Interface Tracking Method Based on Prime Enumeration of Microcells
Authors: Clarke Mary Ann D. , Freitas Christopher J.
Published: March 2009

This paper presents a general method for tracking N incompressible materials and their associated interfaces, where N may be an integer greater than 2. Two key components are fundamental to the method. First, is the concept of a microgrid element or cell, which is uniquely identified or associated with a fluid material. Second, is a method for uniquely identifying a microcell through the use of prime numbers. The approach implements a microcell methodology embedded on a regular grid to further subdivide and then tag the material components of the computational system via a prime numbering algorithm. The microcells motion are then tracked, driven by local velocity conditions computed at the macrogrid level, and rectifying small anomalies by a coupled evaluation of local volume fraction fields and global mass conservation. Volume fractions can be calculated at any time step by an evaluation of the prime number distribution so that average cellular density and viscosity values can be regularly updated at the macrogrid level. This paper, then, presents the details of the microgrid method and illustrates its capabilities through two-dimensional, N-component, problem simulations.
A Simple Model for Fluid Flow and Particle Motion Inside the Human Larynx
Authors: Ersahin C. , Celik I. B. , Elci O. C. , Yavuz I. , Li J. , Hu G.
Published: March 2009

This study aims to develop a simple and quick, but sufficiently accurate solution method for calculating the air flow and tracking the particles in a complex tubular system, where the flow changes its magnitude and direction in a periodic manner. The flow field is assumed to be quasi-two-dimensional and a pressure-correction method is employed to calculate the spetio-temporal variation of the air velocity inside the larynx. Then, the calculated one-dimensional flow distribution is used to reconstruct a two-dimensional flow field is constructed based on the average velocity along the axial direction. The system geometry is taken as close as possible to the actual larynx for an average person with an average glottis opening. For the current study the walls of the larynx is approximated as rigid walls, but different ways to account for compliant walls are proposed within the context of the one-dimensional mode. The 1-D transient model is validated against a two-dimensional model using a verified commercial code. Particles are introduced into the system and tracked during every time fraction of the respiratory cycle. Then, the histograms of particles that come into contact with the larynx are calculated, and regions with a higher probability for particle deposition are identified.
LES of Turbulent Separated Flow and Heat Transfer in a Symmetric Expansion Plane Channel
Authors: Sugawara Kazuaki , Yoshikawa Hiroyuki , Ota Terukazu
Published: March 2009

LES method is applied to simulate numerically a turbulent separated and reattached flow and heat transfer in a symmetric expansion plane channel of expansion ratio 2.0. Smagorinsky model is used in the analysis and fundamental equations are discretized by means of the finite difference method, and their resulting finite difference equations are solved using SMAC method. The calculations are conducted for Re = 15000. It is found that the present numerical results, in general, agree well with the previous experimental ones. The complicated vortical flow structures in the channel and their correlations with heat transfer characteristics are visualized through various fields of flow quantities.
Numerical Modeling of Coupled VSTOL-Ship Airwake Flowfields
Authors: Arunajatesan S. , Shipman J. , Sinha N.
Published: March 2009

Validation of CRUNCH CFD® for problems of relevance to modeling coupled VSTOL-Ship Airwake flow fields is presented. The basic numerical framework consists of an edge based multi-element unstructured Navier-Stokes solver. The governing equations are solved using an upwind biased MUSCL scheme and an implicit scheme is used for time marching. Validation of the spatial and temporal aspects of the numerical framework are presented here, with a special emphasis on bluff body shedding problems as these are of particular relevance to the VSTOL-Ship airwake problem. Results from simulations of several unit problems are presented.
A Charge-Diffusion-Filtration Model for Endothelial Surface Glycocalyx
Authors: Chen Bin , Fu Bingmei
Published: March 2009

Endothelial surface glycocalyx plays an important role in the regulation of microvessel permeability by possibly changing its charge and configuration. To investigate the mechanisms of how surface properties of the endothelial cells control the changes in microvessel permeability, we extended the electrodiffusion model developed by Fu et al. (Am. J. Physiol. 284:H1240-1250, 2003), which is for the interendothelial cleft with a negatively charged surface glycocalyx layer, to include the filtration due to hydrostatic and oncotic pressures across the microvessel wall as well as the electrical potential across the glycocalyx layer. On the basis of the hypotheses proposed by Curry (Microcirculation 1(1): 11–26, 1994), the predictions from this electrodiffusion-filtration model provide a remarkably good agreement with experimental data for permeability of negatively charged α-lactalbumin summarized in Curry (Microcirculation 1(1): 11–26, 1994) under various conditions. In addition, we applied this new model to describe the transport of negatively charged macromolecules, bovine serum albumin (BSA), across venular microvessels in frog mesentery. A very interesting prediction is that the convective component of albumin transport is greatly diminished by the presence of a negatively charged glycocalyx under both normal and increased permeability conditions.
Numerical Modeling of Hot Metal Flow and Heat Transfer in a Blast Furnace
Authors: Yan Fang , Zhou Chenn Q. , Huang D. , Chaubal Pinakin
Published: March 2009

Hearth wearing is the key limit of a blast furnace campaign life. Hot metal flow pattern and temperature distributions are the two key variables to determine the rate and style of the hearth wearing. And the shape, structure and position of the deadman are the three major variables to assign the fluid flow pattern and temperature profile in the hearth. In this paper, a new method for deadman description was put forward and a comprehensive computational fluid dynamics (CFD) code was described, which was developed specifically for the simulation of blast furnace hearth. That program can predict the liquid flow patterns and temperature distributions of the hot metal as well as temperature profiles in the hearth refractory materials under different conditions. The results predicted by the CFD code were evaluated by comparing with actual industrial operation data.
Enhancement of Heat Transfer to an Air Jet Impinging on a Flat Plate
Authors: Mishra D. P. , Mishra D.
Published: March 2009

An experimental investigation of the impinging jet cooling from a heated flat plate has been carried out for several Reynolds numbers (Re) and nozzle to plate distances. The present results indicate that the maximum heat transfer occurs from the heated plate at stagnation point and decreases with radial distances for all cases. The maximum value of the stagnation as well as average Nusselt number is found to occur at separation distance, H/D = 6.0 for Re = 55000. An attempt is also made to study effects of nozzle exit configuration on the heat transfer using a sharp edged orifice for same set of Reynolds numbers and nozzle to plate distance. The stagnation Nusselt numbers of sharp orifice jets are found to be enhanced by around 16–21.4% in comparison to that of square edged orifice. However, the enhancement in the average Nusselt number of sharp orifice is found to be in the range of 7–18.9% as compared to the square edged orifice. The maximum enhancement of 18.9% in average Nu is achieved for Re = 55 000 at H/D = 6. Two separate correlations in terms of Nuo, Re, H/D for both square and sharp edged orifice are obtained which will be useful for designing impinging cooling system.
Solute Transport in Porous Medium Under External Loads
Authors: Lu Yiling , Wang Wen
Published: March 2009

Dynamic compression of soft tissues affects tissue mechanical properties and metabolic activities. The effect is attributed, in part, to the movement of water and solutes in extracellular matrix, which alters the mechanical (e.g. fluid shear stress) and chemical (e.g. growth factors, cytokines and hormones) microenvironments for cells in the tissue. To quantify contributions of external dynamic loads on solute transport in extracellular matrix, we have applied a poroelastic theory to calculate the deformation of the matrix and the movement of the fluid. In the simplified two-dimensional model, the solid phase represented the matrix of collagens and proteoglycans and the liquid phase represented the interstitial fluid. Deformable matrix embedded with cells was immersed in a solution inside a well with rigid, impermeable walls. On top of the matrix, solution with known solute concentration existed. Solute moved into the matrix and was consumed by cells. Mechanical cyclic loads were applied over a central area on the top surface of the matrix, causing its deformation and extracellular fluid movement. Resulting cell density in the matrix changed with the time during the loading cycle and it varied with the location in the matrix as well. Movement of the extracellular fluid coupled with solute diffusion contributed to the overall solute transport in the matrix. Effects of different loading frequencies and amplitudes were investigated. Different sized molecules were also considered in the study. Results from the model confirmed experimental findings that cyclic loads facilitated solute transport in soft tissues. The effect was more significant for large sized molecules. Special attention was given to regions of the matrix where cells would initially remain metabolically inactive due to lower than the critical value of the solute concentration. Quantitative analysis of solute concentration distribution in the matrix made it possible to predict regions where cells became activated by the improved solute supply. The fact that more cells in tissues became metabolically active under dynamic loads exemplified most directly the effect of external dynamic loads on solute transport in soft tissues.
Spray Cooling Using Multiple Nozzles: Visualization and Wall Heat Transfer Measurements
Authors: Horacek Bohumil , Kim Jungho , Kiger Kenneth T.
Published: March 2009

Time and space resolved heat transfer data on a nominally isothermal surface cooled by two spray nozzles was obtained using an array of individually controlled microheaters. Visualization and measurements of the liquid-solid contact area and three-phase contact line length were made using a total internal reflectance technique. The spacing between the nozzles and the heated surface was varied between 7 mm and 17 mm. Little interaction between the two sprays was observed for the tested conditions, with the heat flux produced by a single nozzle remaining comparable to that produced by two nozzles, provided the areas considered were limited to the regions impacted by the sprays. Variations in the heat transfer across the surface, however, increased significantly with decreasing spacing. The phase change heat transfer was strongly correlated with the length of the three-phase contact line.
Analysis of Fired-Heater Fouling in a Refinery Coking Unit
Authors: Barkat Omar , Nyberg Richard J.
Published: March 2009

Delayed Coking is a principal thermal cracking process utilized by petroleum refineries to decrease residual output. Fired heater performance is critical to coker unit profitability. Adversely affecting heater performance, coke deposits inside heater tubes must be removed periodically (decoked). There are three main methods of decoking fired heaters: online spalling, steam-air decoke, and pigging. For each decoking technique, the most widely-used procedures are described. Also, the merits and drawbacks of each method are discussed. A survey of industry decoking practice has been attempted as part of this study. Fire-side tube metal temperature (TMT) and heater inlet pressure (PIN) are the critical parameters used to analyze heater tube fouling. However, changes in flow rate, density, process temperature, and steam injection can cause a pass to have higher TMT or PIN than one with greater fouling. This study suggests approximation of coke deposit thickness to obtain a parameter normalized against changes in process variables. When used in conjunction with TMT and PIN, such a parameter can help in evaluating decoke effectiveness and identify the pass with least economically efficient operation. Economic analysis of fired-heater fouling considers direct costs and opportunity costs. Direct costs, such as plant utilities, fuel, in-house manpower, and outside contractor expense are assessed for each decoking method. This study also evaluates opportunity costs associated with reduction of throughput during decoking procedures. An example economic case is presented to illustrate the potential benefit of using estimated coke deposit thickness to schedule decokes.