bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of the Coke-Free Layer Height on the Wear of the Bottom Wall of a Blast Furnace Hearth
Authors: Elsaadawy E. A. , Lu W.-K.
Published: October 2008

The blast furnace is a huge counter-flow heat exchanger, lined with refractory brick, which is used to chemically reduce and physically convert iron oxides into liquid iron called “hot metal”. In the blast furnace, iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom. The raw materials require 6 to 8 hours to descend to the bottom of the furnace, called the hearth, where they become the final product of liquid slag and liquid iron. The liquid products are drained (tapped) from the hearth at regular intervals. The hearth is a crucial region of the blast furnace, since the life of its refractory determines to a great extend the life span of the furnace. Therefore, it is necessary to understand the process of erosion and the wear mechanisms. The wear of the hearth lining (refractory) arises from a combination of hydrodynamic, chemical, and thermomechanical phenomena. Due to the very hostile environment inside the furnace, direct measurements of flow and temperature distributions that impact hearth wear is fundamentally precluded. Consequently, one resorts to physical and mathematical modeling of the process. In the current study, a mathematical model of the tapping process is presented. This model, in the current stage of an ongoing program in McMaster University, is two-dimensional and unsteady. The coke bed (packed bed or deadman) is assumed of uniform permeability. The effect of the coke-free layer height on the flow pattern and bottom wall shear stress distributions is investigated. Also, the effect of the taphole height is considered in other wards, the effect of the sump ratio is studied. The study is performed using Fluent which is a commercial computational fluid dynamics software package. From the study it was shown that, for a sitting bed, the flow resistance is uniform every where and liquid flows directly to the taphole along the shortest path which offers the least resistance in this case. When the packed bed (deadman) floats at a low height the liquid now has a region with much less resistance to flow in. Therefore, the liquid rushes into the coke-free layer putting higher stress on the hearth floor which means higher heat transfer rates and more erosion of the bottom wall of the hearth. The higher the floating is the weaker this effect. Changing the sump ratio also affects the stress load on the hearth floor. Deeper pool, higher taphole, has a less shear stress on the floor compared to a shallow one, lower taphole.
Modeling of the Vortex-Structure in a Particle-Laden Mixing-Layer
Authors: Melheim Jens A. , Horender Stefan , Sommerfeld Martin
Published: October 2008

Numerical calculations of a particle-laden turbulent horizontal mixing-layer based on the Eulerian-Lagrangian approach are presented. Emphasis is given to the determination of the stochastic fluctuating fluid velocity seen by the particles in anisotropic turbulence. The stochastic process for the fluctuating velocity is a “Particle Langevin equation Model”, based on the Simplified Langevin Model. The Reynolds averaged Navier-Stokes equations are closed by the standard k-epsilon turbulence model. The calculated concentration profile and the mean, the root-mean-square (rms) and the cross-correlation terms of the particle velocities are compared with particle image velocimetry (PIV) measurements. The numerical results agree reasonably well with the PIV data for all of the mentioned quantities. The importance of the modeled vortex structure “seen” by the particles is discussed.
Gas Holdup in Opaque Cellulose Fiber Slurries
Authors: Talcott Sarah M. , Heindel Theodore J.
Published: October 2008

Three different cellulose fiber types are used to study their effect on gas holdup and flow regime transition in a 10.2 cm semi-batch bubble column. The three natural fiber types include bleached softwood chemical pulp (softwood), bleached hardwood chemical pulp (hardwood), and bleached softwood chemithermomechanical pulp (BCTMP). Gas holdup is recorded over a range of fiber mass fractions (0 ≤ C ≤ 1.6%) and superficial gas velocities (Ug ≤ 23 cm/s). Experimental results show that gas holdup decreases with increasing fiber mass fraction. Homogeneous, transitional, and heterogeneous flow is observed for all three fiber types at low fiber mass fractions. All three fiber types produce similar results in the homogeneous flow regime while significant differences are recorded in the heterogeneous flow regime; those being low mass fraction hardwood (softwood) fiber slurries produce the highest (lowest) gas holdup. At higher fiber mass fractions, only pure heterogeneous flow is observed and softwood fiber slurries still produce the lowest gas holdup, although the differences in gas holdup between fiber types are small. The Zuber-Findlay drift flux model is used to describe the gas holdup results in cellulose fiber slurries when the flow conditions are heterogeneous. The Zuber-Findlay drift flux model is also used to identify the superficial gas velocity at which homogeneous flow is no longer observed with some success. Generally, the superficial gas velocity at which the flow deviates from homogeneous flow decreases with increasing fiber mass fraction.
Investigation on Performance Conversion of Centrifugal Oil Pumps Used in China
Authors: Xue Dun-Song , Cao Guang-Jun , Chen Xiao-Ling
Published: October 2008

A series of performance tests with different specific speeds (40, 50, 80, 90 and 130) were carried out on centrifugal oil pumps used in China’s oil industry under different conditions of liquid viscosities (1–300mm2/s) and pump rotating speeds (1000–3000rpm). The effect of viscosity on centrifugal oil pump performance and cavitations characteristic has been investigated. By considering the effects of flow rate viscosity and pump design parametric such as impeller outlet diameter and outlet width on the pump cavitations characteristics, a new performance and cavitations conversion correction factor diagram was plotted.
A CFD Analysis of Easterly Wind Flow Impacting the Vehicle Assembly Building
Authors: Vu B. T. , Zysko J. A.
Published: October 2008

In an attempt to explain the high loss of panels from the south face of the Vehicle Assembly Building (VAB) during Hurricane Frances, a three-dimensional computational fluid dynamics (3-D CFD) model was developed to simulate local velocity and pressure distributions resulting from such a storm. A preconditioned compressible Navier-Stokes flow solver1 was used to compute the flow field around the VAB complex, including the Launch Control Center, the Low and High Bays of the VAB, and several outbuildings in the immediate LC-39 area. The mapping of the forces and velocities on and along the affected faces of the VAB correlated surprisingly well with the extensive damage areas realized on both on the south face and on the southeast section of the roof. The model results were also consistent with the minimal damage seen on the east, north, and west faces of the structure.
Self-Preserving Mixing Properties of Steady Round Buoyant Turbulent Plumes in Uniform Crossflows
Authors: Diez F. J. , Bernal L. P. , Faeth G. M.
Published: October 2008

The self-preserving mixing properties of steady round buoyant turbulent plumes in uniform crossflows were investigated experimentally. The experiments involved salt water sources injected into fresh water crossflows within the windowed test section of a water channel. Mean and fluctuating concentrations of source fluid were measured over cross sections of the flow using Planar-Laser-Induced-Fluorescence (PLIF) which involved seeding the source fluid with Rhodamine 6G dye and adding small concentrations of ethanol to the crossflowing fluid in order to match the refractive indices of the source flow and the crossflow. The self-preserving penetration properties of the flow were correlated successfully based on the scaling analysis of Diez et al. (2003) whereas the self-preserving structure properties of the flow were correlated successfully based on the scaling analysis of Fischer et al. (1979); both approaches involved assumptions of no-slip convection in the cross stream (horizontal) direction (parallel to the crossflow) and a self-preserving line thermal having a conserved source specific buoyancy flux per unit length that moves in the streamwise (vertical) direction (parallel to the direction of both the initial source flow and the gravity vector). The resulting self-preserving structure consisted of two counter-rotating vortices having their axes nearly aligned with the crossflow direction that move away from the source in the streamwise (vertical) direction due to the action of buoyancy. Present measurements extended up to 202 and 620 source diameters from the source in the streamwise and cross stream directions, respectively. The onset of self-preserving behavior required that the axes of the counter-rotating vortex system be nearly aligned with the crossflow direction. This alignment, in turn, was a strong function of the source/crossflow velocity ratio, uo/v∞. The net result was that the onset of self-preserving behavior was observed at streamwise distances of 10–20 source diameters from the source for uo/v∞ = 4 (the smallest value of uo/v∞ considered), increasing to streamwise distances of 160–170 source diameters from the source for uo/v∞ = 100 (the largest value of uo/v∞ considered). Finally, the counter-rotating vortex system was responsible for substantial increases in the rate of mixing of the source fluid with the ambient fluid compared to axisymmetric round buoyant turbulent plumes in still environments, e.g., transverse dimensions in the presence of the self-preserving counter-rotating vortex system were 2–3 times larger than the transverse dimensions of self-preserving axisymmetric plumes at similar streamwise distances from the source.
Determination of Optimum Particle Size for Economical Hydrotransport
Authors: Shrivastava Kaushal Kishore
Published: October 2008

In the present work the generalized mathematical model (SK model) developed by Shrivastava and Kar [1, 2] has been utilized to determine the optimum size of the solid particles (sand, coal, pvc- granules, and lead shot), which offers the minimum frictional resistance to flow and results into the minimum head loss when transported through horizontal pipes under the conditions identical to those achieved by the investigators [3- 6] in their experiments. On the basis of the present investigation it has been observed that for the transport of solid through horizontal pipe at constant throughput the head loss does not depend directly on the size of the particles rather it depends on the values of the critical velocity (fluid velocity at which the head loss is minimum in the characteristic curve) calculated for solids of different sizes. Whereas for the transport of solid particles at constant volumetric concentration the head loss depends directly on the size of the particle and it is minimum for the largest size of the particle. Thus, it is possible to determine the optimum size of the particles for economical hydrotransport through horizontal pipe at constant throughput from the energy consumption point of view by utilizing the expressions of SK model.
Low Reynolds Number Flow Computations of a Sphere With Slip
Authors: Pulat O. , Parthasarathy R. N.
Published: October 2008

A computational fluid dynamics package (FLUENT) was used to simulate the conditions of a falling sphere through a water medium with a zero shear stress condition (full slip) for Reynolds numbers in the range. Comparisons of the results were made with simulations of the flow past a sphere with no slip. Specific differences were observed in the drag coefficient, drag forces, axial velocity, radial velocity, and wake characteristics. A significant reduction in the drag coefficient was observed with the presence of slip on the surface. With a decrease in the Reynolds number the decreases in the wake structure became negligible, however, the differences in drag coefficient became significant. At high Reynolds numbers, the wake was skewed towards the rear of the sphere, under the full slip condition.
Three-Phase Liquid-Gas-Solid Flows in a Bubble Column
Authors: Ahmadi Goodarz , Zhang Xinyu
Published: October 2008

An Eulerian-Lagrangian computational model for simulations of gas-liquid-solid flows in three-phase slurry reactors is developed. In this approach, the liquid flow is modeled using a volume-averaged system of governing equations, whereas motions of bubbles and particles are evaluated by Lagrangian trajectory analysis procedure. It is assumed that the bubbles remain spherical and their shape variations are neglected. The two-way interactions between bubble-liquid and particle-liquid are included in the analysis. The discrete phase equations include drag, lift, buoyancy, and virtual mass forces. Particle-particle interactions and bubble-bubble interactions are accounted for by the hard sphere model approach. The bubble coalescence is also included in the model. The predicted results are compared with the experimental data, and good agreement is obtained. The transient flow characteristics of the three-phase flow are studied and the effects of bubble size on variation of flow characteristics are discussed. The simulations show that the transient characteristics of the three-phase flow in a column are dominated by time-dependent staggered vortices. The bubble plume moves along the S-shape path and exhibits an oscillatory behavior. While particles are mainly located outside the vortices, some bubbles and particles are retained in the vortices. Bubble upward velocities are much larger than both liquid and particle velocities. In the lower part of the column, particle upward velocities are slightly smaller than the liquid velocities, while in the upper part of the column, particle upward velocities are slightly larger. The bubble size significantly affects the characteristics of the three-phase flows and flows with larger bubbles appear to evolve faster.
SPH Simulations for Turbulence Control of Magnetohydrodynamic Poiseuille Flow
Authors: Jiang Fangming , Oliveira Mo´nica S. A. , Sousa Antonio C. M.
Published: October 2008

A new magnetohydrodynamic (MHD) turbulence control methodology is proposed, in which the applied stationary magnetic field is not simply aligned along the streamwise or transverse flow direction, but along a direction that forms an angle within the range of 0° (i.e. streamwise flow direction) to 90° (transverse flow direction) to the main fluid flow. For planar Poiseuille flow, the magnitude of this angle is optimized by using the smoothed particle hydrodynamic (SPH) methodology. The best results in what concerns turbulence control are obtained when this angle falls in the range of 20° to 50°, for the cases studied, which consider an electrically conducting flow of Reynolds number 104 with an electrical conductivity of σ = 1.0×106 (Ω m)−1, and an applied magnetic field B = 0.2 Tesla, there is no onset of turbulence up to the end of the simulation time (6.79 s).
Velocity Measurements in Metallic Melts
Authors: Eckert S. , Gerbeth G. , Gundrum T. , Stefani F.
Published: October 2008

Various developments of velocity measuring techniques, their tests in different liquid metals, and applications in hot melts are reported. A Mechano-Optical Probe (MOP) performing local measurements up to temperatures of about 700°C has been developed and successfully tested. The Ultrasound Doppler Velocimetry (UDV) can be considered as another attractive technique to get velocity data from opaque flows. To extend the application range to higher temperatures and to abrasive liquids a new integrated ultrasonic sensor with an acoustic wave guide has been designed. First successful measurements in a CuSn melt of about 620°C and in liquid Al of about 750°C were carried out. A fully contactless investigation of the mean velocity field is possible by magnetic tomography. Local measurements of the induced magnetic field and the application of inverse reconstruction techniques allow an analysis of the flow structure. A first demonstration experiment showing the feasibility of this approach for the reconstruction of the three-dimensional mean velocity structure is presented.
A Computational and Experimental Investigation of Flow in an Intracranial Side-Wall Aneurysm
Authors: Miller Ross , Battaglia Francine , Olsen Michael G.
Published: October 2008

Pulsatile flow patterns in an intracranial side-wall aneurysm of a human carotid artery were investigated experimentally using microscopic particle image velocimetry on a flexible wall model. Numerical calculations were performed on a stiff-walled artery with the same geometry and flow conditions. Experimental results showed cyclical vortex formation and decay within the aneurysm. Numerical simulations agreed well with the experimental results and indicate that vortex position and magnitude are due to pulsatile flow conditions rather than wall elasticity. However, the present results suggest that wall compliance plays a role in sustaining the pressure gradients needed for vortex development.
Bifurcation Characteristics of Flows in Rectangular Sudden Expansion Channels
Authors: Battaglia Francine , Papadopoulos George
Published: October 2008

The effect of three-dimensionality on low Reynolds number flows past a symmetric sudden expansion in a channel was investigated. The geometric expansion ratio of in the current study was 2:1 and the aspect ratio was 6:1. Both experimental velocity measurements and two- and three-dimensional simulations for the flow along the centerplane of the rectangular duct are presented for Reynolds numbers in the range of 150 to 600. Comparison of the two-dimensional simulations with the experiments revealed that the simulations fail to capture completely the total expansion effect on the flow, which couples both geometric and hydrodynamic effects. To properly do so requires the definition of an effective expansion ratio, which is the ratio of the downstream and upstream hydraulic diameters and is therefore a function of both the expansion and aspect ratios. When the two-dimensional geometry was consistent with the effective expansion ratio, the new results agreed well with the three-dimensional simulations and the experiments. Furthermore, in the range of Reynolds numbers investigated, the laminar flow through the expansion underwent a symmetry-breaking bifurcation. The critical Reynolds number evaluated from the experiments and the simulations was compared to other values reported in the literature. Overall, side-wall proximity was found to enhance flow stability, helping to sustain laminar flow symmetry to higher Reynolds numbers in comparison to nominally two-dimensional double-expansion geometries. Lastly, and most importantly, when the logarithm of the critical Reynolds number from all these studies was plotted against the reciprocal of the effective expansion ratio, a linear trend emerged that uniquely captured the bifurcation dynamics of all symmetric double-sided planar expansions.
Turbulent Flow and Heat Transfer in a Symmetric Expansion Plane Channel
Authors: Ota Terukazu , Suzuki Takuma , Yoshikawa Hiroyuki
Published: October 2008

Experimental results of turbulent flow and heat transfer in the separated and reattached flow in a symmetric expansion plane channel are presented. Experiments were conducted using a low speed open circuit wind tunnel, the expansion ratio of channel was 2.0 and the Reynolds number 15000, respectively. The flow and temperature fields were measured using split film probes and a cold wire. The conditional sampling techniques were employed in order to investigate the large scale vortex structure shed from the reattachment flow region and its correlation with the heat transfer behavior. It is found that the local Nusselt number profile is considerably different on the upper and lower walls due to the Coanda effect. Two large scale vortices shed from the reattachment regions on two walls are combined into one large vortex in the redeveloping region, whose configuration is estimated to be an ellipse inclined to the main flow.
Water Quality and the Periodicity of Sheet/Cloud Cavitation
Authors: Kawakami Damien T. , Qin Qiao , Arndt Roger
Published: October 2008

Cloud cavitation is the rapid formation and shedding of vaporous clouds from a cavitating hydrofoil. This type of cavitation occurs under certain conditions that are characterized by the cavitation number [σ] and the angle of attack [α]. Associated with cloud cavitation are large, abrupt changes in surface pressure caused by the shedding of the attached cavity. Our experimental data display trends that are contained in the linearized flat plate theories of Acosta and Tulin. Near values of σ/2α equal to 4, a singularity exists in the flat plate theory. Experimental results and numerical simulations indicate that in this region a transition between competing mechanisms of cavity shedding occurs. A new finding is that water quality appears to have a significant effect on cavitation behavior. It is well known that nuclei content plays an important role in cavitation inception. However, a recent investigation made possible by high-speed video reveals that the cloud shedding is periodic and that, for each cycle, the cavitating surface becomes fully wetted. Thus, inception physics come into play for a fraction of each cycle. Experimental data shows that the fraction of time in each period that the hydrofoil is fully wetted varies with gas content. In addition, the spectral characteristics of lift and surface pressure measurements show a strong dependence on gas content. Numerical simulations made to incorporate gas content effects show surprisingly close agreement with experimental data. This is also factor that may be of importance in comparing the results from different experimental facilities since comparisons are often made without considering gas content as a factor.
Stratified Flow and Free Surface of an Uncovered Reactor Pressure Vessel Cold Leg: Water-Air Experimental Results
Authors: Bichet Thierry , Martin Alain , Beaud Fre´de´ric
Published: October 2008

Within the Reactor Pressure Vessel (RPV) plant life time project, Electricite´ de France (EDF) must carry out studies showing the RPV integrity during severe loading conditions as the Small Break Loss Of Coolant Accidents (SBLOCA) scenarios. A recent thermal-hydraulic SBCLOCA scenario study, concerning a certain RPV geometry, showed two-phase-flow conditions appears in the cold leg. The single phase flow CFD tools, usually used in these cases, are unsuitable to carry out such studies. That is the reason why EDF is developing a new CFD code (called Neptune_Code) implementing two-phase flow models. In order to improve the physical phenomena knowledge and the existent experimental data for Neptune_Code development, EDF carried out an experimental study concerning the stratified flow (salt water) and free surface (water air) behavior during a representative ECC scenario with partial uncovered cold leg. This paper focuses mainly on the experimental method and the measurements obtained in three tests showing the effects of the uncovered cold leg level on the stratified flow and the free surface behavior.
A Controllable Microbubble Emitter
Authors: Brown Neal A. , Wosnik Martin
Published: October 2008

Controlled emission of microbubbles into a water flow boundary layer appears to be a promising means to significant reduction of frictional drag on ships. Theoretical analyses and hypotheses require that particularly small (∼ 100 micrometers or less) gas bubbles be emitted and retained in particular laminae close to the wetted surface. Drag reduction economy requires that the quantity of gas emitted be very small. Here a design of a controllable microbubble emitter which meets both demands above is put forth. The two key requirements governing the design are pulsed operation, which expels a known volume of air during each cycle, and a known number of uniformly-sized micro-holes, which determines bubble number and therefore bubble diameter. A first, proof-of-concept experiment with a modified pulsed-pressure design of the proposed microbubble emitter was carried out and shows promise.
Modeling of Pressure Undershoot and Heat and Mass Transfer at Negative Pressures
Authors: Gale Janez , Tiselj Iztok
Published: October 2008

This paper addresses preliminary study of the behavior of the cold liquid exposed to the significant rapid pressure changes, performed with recently developed Waha computer code. The goal of the study is to develop semi-empirical model, able to describe heat and mass transfer in cold liquids exposed to negative pressure loads. Negative pressure in liquid can appear after sudden depressurization and the amount of pressure undershoot encountered is highly correlated to density of the nucleation sites i.e. properties defined at molecular level. Therefore, raw model is proposed and discussed and the conclusion is that the results are in particularly good agreement comparing to the uncertainty of the phenomenon itself.
Estimation of Time Dependent Flow Properties in an Open Cavity
Authors: Ukeiley Lawrence , Murray Nathan
Published: October 2008

Experiments have been performed to measure the velocity field and surface pressure synchronously for flow over an open cavity. Specifically, an l/d = 6 full span cavity with a Mach 0.6 free stream flow and a turbulent boundary layer at the cavities leading edge was studied. The study focuses on using these measurements in a mean-square estimation technique to study the time dependence of a low-dimensional formulation of the velocity field. Utilizing select modes from the Proper Orthogonal Decomposition in the estimation technique, flow features associated with select Rossiter modes were reconstructed. The time dependent estimated flow field demonstrates how the shear layer structures and free stream velocity interact with the aft wall of the cavity to form the source of the intense areoacoustic environment known to exist in cavity flows.
A Critical Review of Classical Force Estimation Methods for Streamlined Underwater Vehicles Using Experimental and CFD Data
Authors: Jeans T. L. , Baker C. R. , Holloway A. G. L. , Gerber A. G. , Watt G. D.
Published: October 2008

Classical hydrodynamic force estimation methods are widely used by industrial designers of underwater vehicles for whom captive model experiments and CFD based simulations are uneconomical. They are also used in the preliminary design of submarines and when real time submarine simulations are required. These methods poorly estimate the contribution of the hull to the forces, especially at moderate to high incidence angles. This paper critically reviews the classical hull force estimation methods developed by Munk, Allen, Perkins and Jorgensen, and Sarpkaya. It compares the methods with experimentally validated CFD predictions of a streamlined body at incidence angles up to 30 degrees and for Reynolds numbers from 2.3 to 230 million. The comparison shows that inadequately modeled flow separation and leeside body vortices explain the poor force and moment predictions. This is partly due, at least, to the lack of a streamlined tail on the truncated missile shapes for which the estimation methods were developed.
An Experimental Investigation of the Effect of Walls on Gas-Liquid Flows Through Fixed Particle Beds
Authors: Cooper Marcia A. , Cote Raymond O. , O’Hern Timothy J. , Torczynski John R. , Evans Lindsey R. , Cross William M.
Published: October 2008

The effect of particle diameter on downward co-current gas-liquid flow through a fixed bed of particles confined within a cylindrical column is investigated. Several hydrodynamic regimes that depend strongly on the properties of the gas stream, the liquid stream, and the packed particle bed are known to exist within these systems. This experimental study focuses on characterizing the effect of wall confinement on these hydrodynamic regimes as the diameter d of the spherical particles becomes comparable to the column diameter D (or D/d becomes order-unity). The packed bed consists of polished, solid, spherical, monodisperse particles (beads) with mean diameter in the range of 0.64–2.54 cm. These diameters yield D/d values between 15 and 3.75, so this range overlaps and extends the previously investigated range for two-phase flow. Measurements of the pressure drop across the bed and across the pulses are obtained for varying gas and liquid flow rates.
Gas Flow in Microchannels: An Experimental Study
Authors: Skudarnov P. V. , Lin C. X.
Published: October 2008

In this paper preliminary results are presented for gas flow velocity measurements in microscale via Image Correlation Velocimetry (ICV). Nitrogen flow in a microchannel of square 500 μm × 500 μm cross section was studies for Reynolds numbers in the range of 50 to 180. The flow was seeded with acetone vapor to obtain Laser Induced Fluorescence images that are subsequently used for ICV analysis. Controlled gas flow is produced in the test cell and associated flow loop. Pressures at the channel entrance and exit are measured, as well as, gas mass flow rate. These measurements allow gas flow velocity estimation for comparison with ICV measurements. Measurements in the parameter range studied so far agree well with conventional scale correlations for square channel flows.
Large Eddy Simulation and PIV Experiments of a Two Phase Air-Water Mixer
Authors: Honkanen Markus , Koohestany Akbar , Hatunen Tarmo , Saarenrinne Pentti , Zamankhan Piroz
Published: October 2008

The simulations and experiments of a turbulent bubbly flow are carried out in a cylindrical mixing vessel. Dynamics of the turbulent bubbly flow is visualized using a novel two-phase Particle Image Velocimetry (PIV) with a combination of back lighting, digital masking and fluorescent tracer particles. Using an advanced technique, Mie’s scattering at surfaces of bubbles is totally filtered out and, henceforth, images of tracer particles and of bubbles are obtained with high quality. In parallel to the comprehensive experimental studies, numerical results are obtained from large eddy simulations (LES) of the two-phase air-water mixer. The impeller-induced flow at the blade tip radius is modeled by using sliding mesh method. The results demonstrate the existence of large structures such as tip-vortex tips, and also some finer details. In addition, the stability of the jet is found to be connected with the fluctuations of the tip votices whose dynamics are affected by the presence of bubbles. Numerical results are used to interpret the measurement data and to guide the refinement of consistent theoretical analyses. Such information is invaluable in the development of advanced theories capable of describing bubbly flows in the presence of complex liquid flow. This detailed information is of real significance in facilitating the design and scale-up of practical stirred tanks.
Motion of a Deformed Sphere With Slip in Creeping Flows
Authors: Jia Liping , Be´nard Andre´ , Petty Charles A.
Published: October 2008

The motion of a rigid particle whose surface is a slightly deformed sphere is studied for creeping flows with the assumption of slip on the particle. Expressions are obtained for the hydrodynamic force and torque exerted by the fluid on a deformed sphere using an asymptotic method introduced by H. Brenner, wherein the normalized amplitude of the deviation from sphericity is assumed to be a small parameter. The Stokes’ resistance calculated by this method is validated by comparing with existing solutions the limiting cases of no slip and perfect slip. The equations describing the motion of a deformed sphere with a slip surface in a simple shear flow are also derived and solved. The motion of the deformed sphere is shown to differ significantly from the no-slip case for low values of a dimensionless parameter that incorporates the slip coefficient. The period of rotation of the deformed sphere is longer, and for cases where the slip coefficient is low, the spheroid rotates to a fixed angle and reaches a quasi-steady orientation.
A Simple Device for Wind Tunnel Performance Testing of Small Scale Powered Propellers
Authors: Beck B. Terry , Pratt Nelson A.
Published: October 2008

Propellers represent an interesting application of the principles of aerodynamics. The basic physics of propeller operation can be modeled as a rotating wing section using classical blade element analysis procedure, which can also include flows induced by the propeller motion itself. Performance testing of small-scale powered propellers in modest size educational wind tunnels could yield important verification of these analysis tools, and also provide valuable experimental insight into important aspects of propeller design for the engineering laboratory. To provide useful data, measurements of propeller performance must include not only rotation speed and thrust, but also torque. These variables need to be investigated as a function of the imposed wind tunnel airspeed, which represents the forward speed of a powered propeller in flight. Rotation speed is easily measured using a variety of simple optical (including stroboscopic) techniques and thrust simply corresponds to the axial force measurement obtained directly from the typical “sting” balance used with educational wind tunnels. However, commercial devices for practical torque measurement can be quite expensive and are also typically of much higher torque range than that achieved by small-scale propellers designed for model airplane use, which limits their usefulness in the educational engineering wind tunnel laboratory. This paper presents a simple and inexpensive strain gage based device designed for measurement of low level torque developed by small-scale powered propellers. The operating principles of the torque measurement device are described, along with static calibration test results and experimental measurements of the performance characteristics of a small-scale electric motor driven powered propeller using our educational wind tunnel test facility. The torque sensor can be combined with rapid prototyping propeller design to allow investigation of a wide variety of propeller design features. Additional planned improvements and other wind tunnel applications for the torque measurement device are also discussed in the paper.
Resonance in Flow-Induced Cable Vibration: Analytical Prediction and Numerical Simulation
Authors: Kwan M. K. , Hwang R. R. , Hsu C. T.
Published: October 2008

Flow-induced resonance for a two-end hinged cable under uniform incoming flows is investigated using analytical prediction and numerical simulation. In this study, the fundamental mode is analyzed for simplicity. First, based on a series of physical judgments, the approximate cable trajectory is predicted — the whole cable vibrates as a standing wave, with its locus on the transverse cross-section having a convex “8”-like shape. To find the exact path, however, experiment or numerical simulation is necessary. Hence, a bronze cable at aspect ratio (length/diameter) of 100 under water flows at Reynolds number (based on cable diameter and incoming velocity) of 200 is computed. The result confirms our predictions. Moreover, it is found that the amplitude of the cross-flow displacement is much higher than that of the streamwise displacement, despite the higher streamwise fluid force. As a consequence, energy transfer from fluid to solid is maximized in the cross-flow direction.
Review of Thrust Prediction Method Based on Momentum Balance for Ducted Propellers and Waterjets
Authors: Bulten Norbert , van Esch Bart
Published: October 2008

Equations for thrust calculation of ducted propellers and waterjet propulsion systems are derived from the theory of open propellers. The streamtube of an open propeller shows contraction upstream and downstream of the propeller, with a strength depending on the propeller loading. The contraction of the streamtube in a waterjet propulsion unit is governed by the geometry of the installation. This paper presents the analyses of the development of the streamtube of a waterjet and a ducted propeller. Determination and visualization of the streamtubes is accomplished with a commercial CFD method. Development of the streamtube is analyzed in streamwise direction and as a function of the loading of the waterjet or the ducted propeller. It is proven that the ducted propeller has a fixed ratio between the velocity through the nozzle and the velocity downstream. This is comparable to the behavior of a waterjet, and consequently different from an open propeller. Thrust of the propulsion unit can be determined from a direct summation of all wall forces or from summation of the different terms of a momentum balance. The pressure, which acts on the streamtube surface, is neglected in this calculation, according to generally accepted theory. Comparison of both methods shows deviations for some operating conditions, which is attributed to the neglect of the pressure forces. It is concluded that the pressure forces on the streamtube of both ducted propellers and waterjet propulsion systems should not be neglected a priori.
Time-Dependent Simulation of a Swirling Two Phase Flow Using an Anisotropic Turbulent Dispersion Model
Authors: Lipowsky Justus , Sommerfeld Martin
Published: October 2008

Time-dependent simulations of a particle-laden swirl flow in a pipe expansion based on the Euler-Lagrange approach are presented. Two equation and Reynolds Stress Models were used in the calculation of turbulent quantities in the continuous phase. Additional attention was payed to the influence of particle dispersion. The instantaneous fluid velocities seen by the particles was reconstructed by different dispersion models. To come to a time dependant solution for the Euler-Lagrange approach, a quasi-unsteady approach is taken. This results in a calculational scheme where one Eulerian time-step is divided in a number of Lagrangian steps. Particle source term are sampled which represent the influence of the disperse phase on the flow field. which call for additional coupling within one Eulerian time step. The effect of inter-particle collisions on the movement of the disperse phase is accounted for using a stochastic inter-particle collision model. Special interest of this study was the formation of dust ropes which are observed in such flows.
Investigations of Dust Separation in a Gasturbine Pre-Swirl Cooling Air System Using New, Enhanced Simulation Methods
Authors: Schneider O. , Dohmen H. J. , Benra F. K. , Jarzombek K.
Published: October 2008

In the last years the leading manufacturers enhanced the performance of heavy-duty gas turbines rapidly. With the increasing amount of cooling air passing the internal air system, a rising amount of air borne particles are transported to the film cooling holes at the turbine blade surface. Due to the size, these holes are critical for blockage. Experience with gas turbines during operation showed a complex interaction of cooling air under different flow conditions and its particle load. In this paper the results of a new Lagrange-Tracking simulation algorithm based on 3D-Navier-Stokes flow solution are shown for the first time. Compared to previously shown simulations the algorithm is enhanced by models, taking additional, relevant physical effects into account. The new simulation results are compared to experimental results and former simulations.
Analysis on Microfluids Squeeze Film Damping of Perforated Disks With a Centre Hole
Authors: Wang Weidong , Jia Jianyuan
Published: October 2008

Based on the equations of gap flow and squeezed flow, the solution for viscosity amendment with slip-flow boundary condition is presented for microfluids damping force on perforated disks with one centre hole, moving along its axial direction in microfluids. The correlation between the kinetic damping of the perforated disk and the parameters, such as the gap height, the radius of the center hole and the thickness of disk, is investigated and obtained. Also an analytical expression of the damping composed of slide film damping and squeezed film damping is given for this kind of perforated disks. Having compared with the numerical solution from FEM method, the analytical solutions match well with those from FEM method. It shows that the microfluids damping on micro-disk has relationship with the surface characteristics of solid wall. Through amending the momentum accommodation coefficient, the accurate effective viscosity can be obtained. Thereby the microfluids damping force on the moving object can be calculated correctly. A simple computation method is presented for analysis and design on microfluids damping of a perforated disk with one centre hole.
Instantaneous Measurement of Unsteady Three-Dimensional Velocity Fields With Photogrammetric PIV
Authors: Schimpf A. , Thamsen P. U.
Published: October 2008

Knowledge about the three-dimensional structure of a velocity field is important for understanding multiple flow phenomena associated with off design operation of pumps and turbines, acoustic emissions or two phase flow to name but a few. The measurement of three-dimensional unsteady velocity fields in industrial applications requires a robust, easy to use and universal measurement system. Existing 3D-3C-Particle-Image Velocimetry (PIV) Systems like Holographic PIV (HPIV) or Defocus-PIV suffer from restrictions to the optical accessibility of the volume to be investigated and a sophisticated optical set up. Hence the objective of this paper is to present the advanced Photogrammetric PIV (PPIV), a robust and easy to use 3D-3C-PIV system applicable to flows in areas with limited optical accessibility like in housings of rotary machines.
A Numerical Study on Mixing In Turbulent Flow Behind a Backward-Facing Step
Authors: Veturi R. , Aung K.
Published: October 2008

Present work studies the mixing in turbulent flow behind a backward-facing step, which is a classical example of mixing of jet in cross flow. In this study the cross flow was an unconfined cross flow flowing through a duct, which has geometry of backward-facing step with varying cross section. Three jet geometries, a slot jet, a single circular jet and three circular jets with different injection angles were studied. Spatial unmixedness based on helium mass concentration was used as an indicator for determining the degree of mixing. Velocity ratio, defined as ratio of jet velocity to the cross flow velocity, was varied during the analysis. Three different values of velocity ratio were considered during the study. Computational fluid dynamics analysis was performed using commercial CFD software CFX 5.6. Results were extracted in the form of helium mass concentration fields, concentration profiles, concentration contour plots and velocity vector plots. From the results obtained it can be concluded that, angle of jet inclination is the important controlling parameter in mixing in flow behind a backward-facing step. Single jet geometry gives better mixing for the given conditions.
A Comprehensive Erosion Prediction Method for Gas/Liquid/Sand Multiphase Flow
Authors: Chen Xianghui , McLaury Brenton S. , Shirazi Siamack A.
Published: October 2008

Sand particles induced erosion of the piping system and fittings is a concern for many industrial practices. The local flow behavior is one of the primary factors that determine the severity of erosion as well as the location where the erosion occurs. Extensive research has been conducted experimentally and numerically to study the erosion phenomena in single-phase (i.e. gas or liquid) flow systems and a variety of erosion prediction models have been developed. Nevertheless, very limited work has been done to investigate the erosion in multiphase (i.e. gas/liquid) flow systems, which is mainly due to the extreme complexity of the phenomena. A comprehensive procedure is proposed to estimate the erosion for sand particles entrained in gas/liquid multiphase flow systems. This procedure combines the mechanistic analysis approach and numerical simulation approach. In this procedure, the dominant flow characteristics of a given flow pattern are analyzed and the corresponding representative single-phase flow is proposed. Such that the erosion problem in this multiphase flow is simplified as one in the representative single-phase to which a single-phase Computational Fluid Dynamics (CFD) based erosion prediction model is applied. Meanwhile, the effective sand mass ratio is introduced to reflect the influence of individual flow patterns on the erosion process by applying a unified mechanistic multiphase flow prediction model. The calculated erosion from the single-phase flow weighted by the effective sand mass ratio yields the estimated erosion for the multiphase flow. Applying this approach, the erosion in elbows is calculated for bubbly flow, annular and annular-mist flow and slug flow and compared with the experimental data in literature. Agreement between the simulations and the data is reasonable, which indicates that the proposed method is an effective tool to estimate the erosion in multiphase flow.
Determination of Time Optimal Diafiltration for an Ultrafiltration Process
Authors: Foust Henry , Bakeer Reda , Drakunov Sergey
Published: October 2008

An ultrafiltration process (UFP) associated with the Hanford Department of Energy facility separates sodium solution from radioactive solids, which are then individually immobilized. An oversight of the UFP design and operation has identified several areas to improve the capacity of the UFP. This paper presents the development of a time optimal controller for an ultrafiltration process (UFP). The current mode of operation is a form of diafiltration where feed rates into the UFP are matched with the permeate rates (permeate matching diafiltration). Another approach advocated in this paper is to allow the control parameters into the UFP to vary with time and is termed time optimal diafiltration. It will be shown that permeate matching diafiltration and time optimal diafiltration are equivalent in terms of dewatering times, but not in terms of feedback. An empirical model for optimal time was then developed.
Navier-Stokes Simulation of Air-Conditioning Facility of a Large Modern Computer Room
Authors: Ahmad Jasim U. , Pandya Shishir A. , Chan William M. , Chaderjian Neal M.
Published: October 2008

A 3-D full Navier-Stokes simulation of a large scale computing facility at NASA Ames Research center was carried out to assess the adequacy of the existing air handling and conditioning system. The flow simulation of this modern facility was modeled with a viscous, compressible flow solver code OVERFLOW-2 with low Mach number pre-conditioning. A script was created to automate geometry modeling, grid generation, and flow solver input preparation. A new set of air-conditioning boundary conditions was developed and added to the flow solver. Detailed flow visualization was performed to show temperature distribution, air-flow streamlines and velocities in the computer room.
Numerical Simulation of Flow and Electric Field in a Corotron Over a Moving Substrate
Authors: Zamankhan Parsa , Ahmadi Goodarz , Fan Fa-Gung
Published: October 2008

The steady state airflow and electric field distributions in a corona device (corotron) during charging of a moving dielectric substrate (photoreceptor) for different operating conditions are studied. The set of two-way, fully-coupled electro-hydrodynamics governing equations is used in the analysis and parametric studies are performed. The effects of wire voltage, photoreceptor speed on photoreceptor charging, airflow, charge density and electrical potential are studied. It is shown that the charging is strongly affected by the wire voltage and the substrate speed. The results also show the importance of corona effect on the flow structure in the device.