bluuebunny/crossref_metadata_2025 huggingface dataset:
CFD Performance Analysis of a Stirred Tank Flowmaker
Authors: Rosendahl Lasse A. , Wang Xiaopeng , Jacobsen Christian B.
Published: September 2008

In the present work, the mean flow field in a stirred tank equipped with a commercially available Grundfos AFG.40.230.35 flowmaker is investigated using both steady-state and transient CFD simulation, in order to provide information on the interaction between flow, propeller and wall proximity as well as information on aspects of using numerical tools for this type of fluid machinery. The simulations, carried out with Ansys CFX 10, used a multiple frame of reference (MFR) approach to include a full representation of the flowmaker blade and motor geometry, in order to fully include the effects of the blade shape and variable pitch for both stationary and transient simulations. The influence of grid type, turbulence model and steady vs transient setup on solution quality has been investigated, and the steady state calculations are compared with LDA measurements. The results show that for the steady state calculations, the choice of grid type is decisive in terms of quality of results, and that the transient simulations using the SST turbulence model yields a superior prediction of flow characteristics; however, the computational expenses for transient simulation is around 10 times than steady-state simulation.
A CFD Study of the Flow of a Power-Law Fluid in Annuli With Variable Eccentricity
Authors: Nun˜ez Oswaldo , Blanco Armando J.
Published: September 2008

Some industrials processes are associated with flow of non-Newtonian fluids in annular spaces. Examples are found in oil industry and food industrial processing. In some cases, gravitational forces cause internal pipe deflection and, consequently, the eccentricity changes along of axis of the annular space. So, flow patterns are modified respect to those found in constant eccentricity annular spaces. Current industrial practice consists on extrapolate predictions based on flow patterns from the constant eccentricity critical scenario, corresponding to the critical region where both boundaries are closer, to the variable eccentricity actual scenario. In practice, using this approach, flow pattern predictions could significantly deviate from the actual profile, and variables such as shear stress at walls or pressure gradient could not be estimated with adequate accuracy. This work consists of a Computational Fluid Dynamics study, aimed to state the implications of evaluating flow patterns, assuming constant eccentricity, in opposition to a more realistic scenario, considering deflection path along the annular space, using a commercial code. A particular application is made to mud removal during well cementing operations in oil industry. For the casing in the hole, the deflection equation is solved and eccentricity along of the system axis is found. Flow of a non-Newtonian fluid described by Power Law model is considered. Oil industry typical conditions are considered for fluid density, rheological parameters, flow rates, casing and hole sizes, and annulus eccentricity. The flow regime was considered laminar. Numerical model capability to reproduce accurately flow patterns in these conditions was assured by comparison with others analytical-numerical solutions for concentric systems. Results show that local Reynolds number Re, shear stress τw and pressure gradient predictions G, under local eccentricity variations, differ from those under constant eccentricity. Differences in Re and τw show a maximum for eccentricity ranging from 60% to 80%, for all flow conditions whereas for G, this difference increases as casing deflection does it. When variable eccentricity models are compared to constant eccentricity one, the latter approach underestimates Re and τw along the narrowest section of the annuli, whereas overestimates the same features along the widest clearance. Additionally, considerably higher variations between these two models are taking place along the narrowest section compared to the variations arising on the widest annular section. When applied to well cementing processes, these results show that considering the most realistic scenario may impact significantly the flow pattern prediction on the annulus during primary cementing operations. Therefore, the quality of the cement job may be greatly compromised.
Effects on Topology of a Turbulent Channel Flow Subject to Blowing Through a Porous Strip
Authors: Labraga L. , Keirsbulck L. , Haddad M. , Elhassan M.
Published: September 2008

An experimental investigation is performed on a fully developed turbulent channel flow with local injection through a porous strip. The Reynolds number based on the channel half-width was set to 5000. In addition to the no blowing data, measurements are made for three different blowing rates σ = 0.22, 0.36 and 0.58 (where σ is the ratio of momentum flux gain due to the blowing and momentum flux of the incoming channel flow). Measurements carried out with hot-wire anemometry reveal that injection strongly affects both the velocity profiles and the turbulence characteristics. The injection decreases the skin friction coefficient and increases all the Reynolds stresses downstream the blowing strip. Moreover, the anisotropic invariant map (A.I.M.) for the Reynolds stress tensor revealed that blowing decreased the anisotropy of the turbulent structure in the near wall region and a decrease in the longitudinal integral length scale was observed when the blowing rate increased. The space time correlation measurements show that injection increases the inclination of the coherent structures in both (x,y) and (x,z) plan.
Theoretical Parameter Study of Aerodynamic Vectoring Particle Sorting
Authors: Jackson Dane N. , Smith Barton L.
Published: September 2008

A new particle sorting technique called Aerodynamic Vectoring Particle Separation (AVPS) has recently been shown to be effective at sorting particles without particles contacting surfaces. The technique relies on turning a free jet sharply without extended control surfaces. The flow turning results in a balance of particle inertia and several forces (pressure, drag, added mass, body) that depend on particle size and density. The present paper describes a theoretical study of particle sorting in a turning flow. The purpose of this study is to extend AVPS to parameter spaces other than those that are currently under study, including liquid jets and nano-particles. Spherical particles are introduced into a turning flow in which the velocity magnitude decreases like 1/r. The trajectory of each particle is calculated using the particle equation of motion with drag laws that are appropriate for various Knudsen number regimes. Large data sets can be collected rapidly for various particle sizes, densities, turning radii, flow speeds and fluid properties. Ranges of particle sizes that can be sorted are determined by finding an upper bound (where particles move in a straight line) and a lower bound (where particles follow flow streamlines). It is found that the size-range of particles that can be sorted is larger for smaller turning radii, and that the range moves toward smaller particles as the flow speed and the particle-to fluid density ratio are increased. Since this flow is laminar and 2-D, the results represent a “best case” scenario.
Alternative Modeling for Turbulent Flow in Porous Media
Authors: Teruel F. E. , Uddin Rizwan
Published: September 2008

The development of models for turbulent flows in porous media is an active area of research with diverse and practical applications. Following the steps to model turbulence in clear flows, porous media models have appeared in the last three decades to capture the turbulence phenomenon at macroscopic scales. The fact that, in the porous media approximation, we are representing a region of the space with single values, obligate us to introduce space-fluctuating quantities in addition to the time decomposition or Reynolds decomposition. This issue has yielded some controversies in the way that turbulence quantities are defined and therefore, in the resulting turbulence models for porous media that have been already developed following the well known k-ε model. In this paper an alternative model is developed to address turbulent flows in porous media. This new set of k-ε equations for rigid and isotropic porous media is developed treating spatial and time fluctuations as a unique identity. This feature leads to a natural construction of the k and ε equations with the same terms found in the corresponding equations for clear flow plus additional terms resulting from the interaction between solid walls of the porous media and the fluid. These extra terms arise in an integral form allowing their evaluation from microscopic or clear flow calculations. Assuming the eddy viscosity approximation and simple models to represent the interaction between solid walls and fluid, the model is closed. The resulting equations are simplified and numerically solved for fully developed flow in one dimensional porous media. Results are compared with those obtained using existing models.
Computational Aerodynamics of the Ahmed Model Car Body
Authors: Demuren Ayodeji , Trehan Rajat
Published: September 2008

This study reports aerodynamic computations of a model car body using various turbulence models. Simulation results were compared with data from wind tunnel tests, for two rear slant angles. The results indicate that RSM simulations gave slightly better predictions of the drag coefficient in both cases. All turbulence models performed reasonable well for the 25° case. However, none of the models could predict observed separation on the rear slant in the 35° case. Consequently, they all failed to predict the massive recirculation zone in the wake.
Numerical Modeling of Flow Over a Dam Spillway
Authors: Saeedpanah Iraj , Shayanfar M. , Jabbari E. , Haji Mohammadi Mohammad
Published: September 2008

Free surface flows are frequently encountered in hydraulic engineering problems including water jets, weirs and around gates. An iterative solution to the incompressible two-dimensional vertical steady Navier-Stokes equations, comprising momentum and continuity equations, is used to solve for the priori unknown free surface, the velocity and the pressure fields. The entire water body is covered by a unstructured finite element grid which is locally refined. The dynamic boundary condition is imposed for the free surface where the pressure vanishes. This procedure is done continuously until the normal velocities components vanish. To overcome numerical errors and oscillations encountering in convection terms, the SUPG (streamline upwinding Petrov-Galerkin) method is applied. The solution method is tested for different discharges onto a standard spillway geometries. The results shows good agreement with available experimental data.
Two-Dimensional Numerical Solution of Steady Withdrawal From the Lens of Freshwater in a Tropical Island
Authors: Jabbari E. , Haji Mohammadi Mohammad , Saeedpanah Iraj
Published: September 2008

The work presented here is a study of the steady withdrawal of water from the lens of freshwater situated above the ocean’s salt water and within the island. It is the aim of this paper to investigate the process of withdrawal from the lens of freshwater with a view to establishing the critical flow values for withdrawal and the effects of sink location and density differences on these values, and also to determine the effects of relative density differences. Steady solutions are found for the shape of the interface between salt and freshwater beneath a tropical island. A Green_s function approach is used and proves to be much more robust than spectral methods. Computations of the surface shape during withdrawal through a line sink are described and the maximum pumping rate before critical breakthrough of the salt water is found for a range of different sink locations. The effects of density ratio, withdrawal depth and horizontal location are also calculated and found to be significant. Decreasing the density ratio between the layers, or increasing withdrawal height is shown to make a significant difference to the critical flow rate. Further, it is shown that for realistic densities, the island width can be a factor for quite substantial widths, whereas for higher, unrealistic density differences an increase in width quickly becomes irrelevant to the interface shape.
Large Eddy Simulation and Acoustical Analysis for Prediction of Aeroacoustics Noise Radiated From an Axial-Flow Fan
Authors: Yamade Yoshinobu , Kato Chisachi , Shimizu Hayato , Nishioka Takahiro
Published: September 2008

A final objective of this study is to develop a tool to predict aeroacoustics noise radiated from a low-speed fan, and its reduction. Aeroacoustics noise that is radiated from a low-speed axial flow fan, with a six-blades rotor installed in a casing duct, is predicted by an one-way coupled analysis of the computation of the unsteady flow in the ducted fan and computation of the sound radiated to the ambient air. The former is performed by our original code, FrontFlow/blue, which is based on Large Eddy Simulation (LES). The latter is performed by using a commercial code, SYSNOISE, which computes the sound fields in the frequency domain. The following three cases of computations are performed for LES with different flow field configurations and/or grid resolutions: a coarse mesh without the struts located, in the actual fan, upstream of the rotor blades, a fine mesh without the struts, and a coarse mesh with the struts. The first two test cases are intended to investigate the effects of the mesh resolution on the prediction accuracy of the unsteady flow field, especially we intended to capture unsteadiness in turbulent boundary layer (TBL) in the second test case with the computational mesh composed of about 30 millions hexahedral elements. The fine mesh LES successfully reproduced the transition to TBL on the suction surface of the rotor blades and gives better, when compared with the results from the coarse mesh LES, agreements with measurements in terms of Euler’s. The final case is used for providing acoustical input data of the sound source. A reasonable agreement is obtained between the predicted and measured sound pressure level evaluated at 1.5 m upstream of the blade center.
A Numerical Model for Brownian Motions of Nano-Particles in Supersonic and Hypersonic Impactors
Authors: Zare Azam , Abouali Omid , Ahmadi Goodarz
Published: September 2008

In this paper, transport and deposition processes of nano-particles in supersonic and hypersonic impactors were investigated using a computational modeling approach. Axisymmetric forms of the compressible Navier-Stokes and energy equations were solved and the airflow and thermal condition in the impactor including the upstream nozzle were evaluated. A computer simulation model for solving the Lagrangian particle equation of motion including all the relevant forces was developed. The importance of the accurate modeling of the Brownian motion of nano-particles was further emphasized. The motion of nano- and micro-particles in the supersonic and hypersonic impactors were then simulated and the impactor capture efficiencies under various operating conditions were studied. For dilute particle concentrations, the assumption of one-way interaction was used. Particular attention was given to proper evaluation of the Brownian motion of the nano-particles in the upstream nozzle and in the body of impactor. The simulation results for collection efficiency were found to be in good agreement with experimental data. In particular, the model accurately predicted the loss of the nano-particles in the upstream nozzle due to their Brownian motion.
Characterization and Thrust Optimization of Synthetic Jets
Authors: Loayza Yury , Mohseni Kamran
Published: September 2008

A synthetic jet is a zero-mass pulsatile jet. A common approach in creating a synthetic jet is to use a cavity with an orifice on one side and an oscillating membrane on another side. In this study the dynamics of a piezoelectrically driven synthetic jet is investigated using a laser nano sensor to capture the temporal and spatial deflection of the membrane. The frequency and voltage response of the piezoelectric membrane for different cavity dimensions are presented, while the velocity field of the resulted jet is characterized by hotwire anemometry. Subsequently, the volume of the expelled jet for any given exit diameter is correlated to the resulting jet velocity. It is found that at a formation number around 3 the nature of the average jet velocity changes and the resulting jet velocity shows less sensitivity to the formation number.
Electrowetting Droplet Manipulation for Application in Thermal Management of Compact Microsystems
Authors: Mohseni Kamran , Baird Eric
Published: September 2008

Digitized heat transfer (DHT), a novel active management technique for high power density electronic and integrated micro systems in which heat is transported by a discrete array of electrostatically activated microdroplets, is proposed. Liquids, especially liquid metals or alloys, support significantly higher heat transfer rates than classical air-cooled heat sinks; in addition, discrete microdroplets are shown to be actuated and controlled with a high degree of precision and programmability. As a consequence, DHT is a viable new alternative for achieving the most important objectives of electronic cooling, i.e., minimization of the maximum substrate temperature, reduction of the substrate temperature gradient and removal of substrate hot spots. Three methods of microdroplet actuation, electrowetting on dielectric (EWOD), dielectrophoresis (DEP), and continuous electrowetting (CEW), are described, with simple results for steady state velocities in terms of known parameters. The use of EWOD to transport a droplet of commercially available liquid metal is reported. In addition, preliminary considerations on the heat transfer rates of such droplets are presented, with a simple analysis leading to a generalization of the continuous Nusselt number to a discretized flow.
Large-Eddy Simulation of Transitional Flow Through a Low-Pressure Turbine Cascade
Authors: Poondru Shirdish , Ghia Urmila , Ghia Karman
Published: September 2008

Subsonic, transitional flow through a low-pressure turbine (LPT) cascade is investigated using high-order compact difference scheme in conjunction with large-eddy simulation (LES). Three-dimensional simulations are performed at chord inlet Reynolds numbers (Re) of 25,000 and 50,000. The inlet Mach number is approximately 0.06. An MPI-based higher-order accurate, Chimera version of the FDL3DI flow solver developed by the Air Force Research Laboratory at Wright Patterson Air Force base, is extended for the present turbomachinery application. The implicit solver is based on an approximate factored time-integration method of Beam and Warming. Fourth-order compact-difference formulations are used for discretizing spatial derivatives in conjunction with sixth-order non-dispersive filtering. Solutions are obtained both with and without a sub-grid scale (SGS) model. A dual topology, 16-block, structured grid generated using GridPro is utilized for all simulations. The flow features are examined, and the results for both LES approaches are compared to each other, and with experimental data.
Active Flow Control on Low-Pressure Turbine Blades Using Synthetic Jets
Authors: Poondru Shirdish , Ghia Urmila , Ghia Karman
Published: September 2008

The operating Reynolds numbers (Re) for a low-pressure turbine (LPT) in an aircraft engine can drop below 25,000 during high-altitude cruise conditions. At these low Reynolds numbers, the boundary layer on the LPT blade is largely laminar, and is susceptible to separation on the aft portion of the blade suction surface. This separation is detrimental and causes a significant loss in the engine efficiency. The objective of the current research is to control this separation, and minimize the associated losses by numerically implementing an active flow control strategy. Unlike passive flow control techniques, active flow control (AFC) techniques can be turned on and off depending on the requirement for flow control. In the present paper, we numerically investigate the flow through an LPT cascade at a chord inlet Reynolds number of 25,000 with active separation control using synthetic jets and synthetic vortex-generator jets (VGJ’s). Synthetic jets hold an advantage over steady or pulsed jets in that they require no net mass flow, i.e., synthetic jets are formed entirely from the working fluid of the flow system in which they are deployed and, thus, can transfer linear momentum to the flow system without net mass injection across the flow boundary. In the LPT environment, this means that no compressor bleed air is required. While LPT separation control using steady and pulsed VGJs has been numerically investigated before, AFC on an LPT blade by synthetic jets and synthetic VGJs has not yet been numerically investigated. The geometrical difference between a synthetic jet and synthetic VGJ is the angle at which the jet enters the main flow. A synthetic jet enters the main flow normal to the surface, and on the other hand, a synthetic VGJ enters at a certain angle to the wall (pitch angle) and at a certain angle to the main flow (skew angle). For the present case, the VGJs are oriented at 30° to the surface and 90° to the main flow. In addition to the angle at which these two jets enter the main flow, these flow control mechanisms differ in the way they delay or avoid separation. Synthetic jets generate turbulent spots which energize the flow, whereas synthetic VGJ’s generate streamwise vortices which enhance mixing. The relative magnitudes of the effects of turbulence and streamwise vortices in enhancing mixing are being investigated. The results for both control mechanisms will be compared to each other, and with experimental data. An MPI-based higher-order accurate, Chimera version of the FDL3DI flow solver developed by the Air Force Research Laboratory at Wright Patterson Air Force Base, is extended for the present turbomachinery application.
Sensitivity Analysis of a Three-Dimensional Wind Tunnel Design
Authors: Kirkman Richard , Metzger Meredith , Deaver Mark , Pardyjak Eric
Published: September 2008

The present paper describes the design of the TreadPort Adaptive Wind Tunnel (TPAWT), which is a wind tunnel retrofit to the University of Utah Treadport Virtual Environment (VE). The TPAWT integrates haptic wind sensation with the preexisting VE, which includes a large tilting treadmill and a cave-like frontal visual display. Desired flow patterns at the center of the TPAWT (where the VE user stands) are generated by appropriately steering the inlet airstream from two sets of vents embedded in the side walls of the facility. Hypothetically, the addition of haptic wind sensation in the virtual environment will improve the sense of immersion in the virtual reality. The present study focuses on quantifying the sensitivity of the flow field inside the TPAWT to perturbations in boundary conditions at the vents. Results from three-dimensional and two-dimensional numerical simulations are compared to laboratory experiments in a 1:4 scale model of the TPAWT. The stability of the flow near the VE user is shown to be highly sensitive to the angle of the mean flow at the vent boundary.
Using Ultrasound to Characterize Pulp Slurries With Entrained Air
Authors: Bamberger Judith Ann
Published: September 2008

The development of fast and practical methods for inspecting fiber suspensions is of great interest in the paper making industry. For process control and paper quality prediction, several elements of the refining process during paper making must be accurately monitored, including specific fiber properties, weight percent fiber (composition), degree of refining, amount of solids, and entrained air content. The results of previous ultrasonic studies applied to wood pulp provide guidance that ultrasound attenuation is information rich, and it does potentially provide a tool for consistency measurement. Ultrasound has the ability to penetrate dense suspensions such as wood pulp slurries. It is has been shown, in some studies, that ultrasound is sensitive to degree of refining. The effects of entrained air, additives, the origin and treatment of the fibers do however all influence the measured data. A series of measurements were made with hardwood and softwood slurries to evaluate the ability of measuring pulp consistency, solids, and entrained air. The attenuation through the slurry was measured as the ultrasound travels from one transducer through the slurry to the other. The measurements identified the presence of entrained air in the pulp samples. To better understand the effects of air, measurements were made at increasing pressures to show how increased pressure reduced the amount of air observed in the spectrum.
Transport of Non-Spherical Particles in Turbulence: Application of the LBM
Authors: Ho¨lzer Andreas , Sommerfeld Martin
Published: September 2008

Direct numerical simulations of the motion of volume equivalent single cylindrical particles with axis ratios of 1, 2, 3, and 4 and Stokes numbers of 1, 2, 4, and 40 in a homogeneous isotropic turbulent flow field are presented. The forced turbulent flow is simulated using the Lattice Boltzmann Method (LBM). It is observed that the rms velocity and the rms angular velocity in longitudinal and in radial direction are identical for every particle, even though the rms forces can differ more than 100% and the rms torque more than 1000% in both directions. However, these differences in force and torque result in a different short-time behaviour of the particle in longitudinal and in radial direction. The rms particle velocity is found to decrease with increasing axis ratio and the rms particle angular velocity to have a maximum at an axis ratio of about 2.5. The ratio of the rms velocity of the particle to that of the fluid decreases with increasing Stokes number as well as the ratio between the rms angular velocities, as one could expect.
On a Mechanism of Stabilizing Turbulent Free Shear Layers in Cavity Flows
Authors: Stanek Michael J. , Visbal Miguel R. , Rizzetta Donald P. , Rubin Stanley G. , Khosla Prem K.
Published: September 2008

Turbulent free shear flows are subject to the well-known Kelvin-Helmholtz type [1] instability, and it is well-known that any free shear flow which approximates a thin vorticity layer will be unstable to a wide range of amplitudes and frequencies of disturbance. In fact, much of what constitutes flow control in turbulent free shear layers consists of feeding a prescribed destabilizing disturbance to these layers. The question in the control of free shear flows is not whether the shear layer will be stable, but whether you can influence how the layer becomes unstable. In most cases, since these flows are so receptive to forcing input, and naturally tend toward instability, large changes in flow conditions can be achieved with very small amplitude periodic inputs. Recently, it has been discovered that turbulent free shear flows can also be stabilized using periodic forcing. This is, at first glance, counter-intuitive, considering our long history of considering these flows to be very unstable to forcing input. It is a phenomenon not described in modern fluid dynamic text books. The forcing required to achieve this effect (which we will call turbulent shear layer stabilization) is of a much higher amplitude and frequency than the more traditional type of shear layer flow control effect seen in the literature (which we will call turbulent shear layer destabilization). A numerical study is undertaken to investigate the effect of frequency of pulsed mass injection on the nature of stabilization, destabilization and acoustic suppression in high speed cavity flows. An implicit, 2nd-order in space and time flow solver, coupled with a recently-developed hybrid RANS-LES (Reynolds Averaged Navier Stokes - Large Eddy Simulation) turbulence model by Nichols et. al. [2], is utilized in a Chimera-based parallel format. This tool is used to numerically simulate both an unsuppressed cavity in resonance, as well as the effect of mass-addition pulsed jet flow control on cavity flow physics and ultimately, cavity acoustic levels. Frequency (and in a limited number of cases, amplitude) of pulse is varied, from 0 Hz (steady) up to 5000 Hz. The change in the character of the flow control effect as pulsing frequency is changed is described, and linked to changes in acoustic levels. Limited comparison to 1/10th scale experiments is presented. The observed local stabilization of the cavity turbulent shear layer, when subjected to high frequency pulsed blowing, is shown in simulation to be the result of a violent instability and break-down of a pair of opposite sign vortical structures created with each high frequency “pulse”. This unique shear layer stabilization behavior is only observed in simulation above a certain critical frequency. Below this critical frequency, pulsing is shown in simulation to provide little benefit with respect to suppression of high cavity acoustic levels.
Hot-Dip Galvanization and Jet Wiping Technique
Authors: Gosset Anne , Buchlin Jean-Marie
Published: September 2008

This paper presents an analysis of the jet wiping process in hot-dip galvanization. This technique consists in reducing the liquid film thickness on a moving substrate by applying gas slot jets. A theoretical development allows the computation of the film thickness distribution in the wiping zone. It is further simplified to an engineering model which predicts the final coating thickness, in good agreement with wiping experiments, as well as numerical simulations. The limit of applicability of jet wiping is due to the occurence of a violent film instability, called splashing, which takes the form of a liquid droplet emission just below the nozzle. An experimental investigation of this phenomenon is conducted on a water model facility. Two nozzle designs are tested. The effect of the process parameters such as the strip speed, the nozzle pressure, the standoff distance and the tilt angle of the nozzle on splashing is emphasized. A dimensionless correlation is established to allow the prediction of the operating conditions leading to splashing occurence. It is confronted to observations made on galvanization lines.
Development of Nano-Microtechnology and Biomedical Applications
Authors: Chen Ching-Jen , Haik Yousef , Chatterjee Jhunu
Published: September 2008

Blood, air and water are not only most abundant but also the most important fluids on the earth. Each adult human carries almost a gallon of blood every moment. This paper concerns with the treatment of the blood and discusses in particular the blood cell separation (fluids engineering) and the safe elevation of the body temperature (thermal engineering). Unlike air and water the blood is a biological fluid. Therefore it comes with the complexity of blood composition and disorder of the blood affecting human life and health. This study presents applications of electro-magnetic field on nanomagnetic particles that attach to the blood cells in creating complex fluid dynamic cell separation from the whole blood and creating complex thermal heating, magnetic hyperthermia, for potential use in cancer treatment. In general, biological cells are weak paramagnetic or diamagnetic. Therefore nano-microtechnologies are developed to attach the nanoparticles to the selected cells and to enhance the magnetic susceptibility of the cells to interact with an applied magnetic field. The paper demonstrates that nano to micron size magnetic particles are tagged to the biological cells.
Flows in Rotation Cylinder Filled With Polymer Solutions
Authors: Kim Jae Won , Hyun JaeMin , Ahn Eun Young
Published: September 2008

This investigation deals with the spin-up flows in a circular container of aspect ratio, 2.0. Shear front is generated in the transient spin-up process of the present flow system and it is propagating from the side wall to the central axis in a rotating container. Propagation of the shear front to the axis in a rotating container means the region behind the shear front acquires an angular momentum transfer from the solid walls. Propagating speed of the shear front depends on the apparent viscosity of polymer solution. Two kinds of polymer solutions are considered as a working fluid: one is CMC and the other is CTAB solution. CMC solution has larger apparent viscosity than that of water at the present applied shear stress, and CTAB shows varying apparent viscosities depending on the applied shear rates. Transient and spatial variations of the apparent viscosities of the present polymer solutions (CTAB and CMC) cause different propagating speeds of the shear front. In practice, CMC solution that has larger values of apparent viscosity than that of water always shows rapid approach to the steady state in comparison of the behavior of the flows with water. However, for the CTAB solution, the propagating speed of the shear front changes with the local magnitude of its apparent viscosity. Consequently, the prediction of Wedemeyer’s including viscosity in the propagating speed of the velocity shear front quantitatively agrees with the present experimental results.
Liquid Turbulence Spectra in Two-Phase Bubbly Flow Under Turbulence Augmentation and Suppression Conditions
Authors: Shawkat Mohamed E. , Ching Chan Y. , Shoukri Mamdouh
Published: September 2008

An experimental investigation was performed in air-water bubbly flow to study the liquid turbulence spectra in a 200mm diameter vertical pipe. A dual optical probe was used to measure the local void fraction and bubble diameter while the liquid velocities were measured using hot-film anemometry. Experiments were performed at two liquid superficial velocities of 0.2 and 0.68m/s for gas superficial velocities in the range of 0 to 0.18m/s. Generally, as the void fraction increases there is a turbulence augmentation. However, a turbulence suppression was observed near the pipe wall at the higher liquid flow rate for low void fraction. In the augmentation case, the turbulence spectra showed a significant increase in the energy at the wave number range comparable to the bubble diameter. In the suppression case, the spectra showed that suppression initially occurs at the low wave number range and then extends to higher wave numbers as suppression increased.
Visualization of Flow Regime Transitions in Two-Phase Flow Under High Voltage Electric Fields
Authors: Sadek Hossam S. , Cotton James S. , Ching Chan Y. , Shoukri Mamdouh
Published: September 2008

The effects of applying DC high voltage electric fields on two-phase flow regime transitions for flowing refrigerant HFC-134a were visualized using a high speed camera. The viewing test section was made of 10 mm inner diameter quartz tube with a 3.18 mm diameter charged electrode placed along the center of the tube. The quartz tube was coated with an electrically grounded transparent conductive film of Tin Oxide. The experiments were performed for mass flux (55 kg/m2s < G < 263 kg/m2s), quality (20% < x < 80%) and applied voltage (0 kV < V < 8 kV). The flow regime transitions depend on the flow regime prior to applying the EHD. For stratified flow, EHD increases the interfacial instabilities and causes liquid extraction to the upper section of the tube. When the flow regime is initially annular flow, EHD increases the uniformity of the annular film by extracting liquid from the thicker liquid regions into the vapor core.
The Radial Migration of Bubbles in Two-Phase Bubbly Flow in Vertical Pipes
Authors: Shawkat Mohamed E. , Ching Chan Y. , Shoukri Mamdouh
Published: September 2008

The radial distribution of bubbles in air-water bubbly flow was experimentally investigated using a dual optical probe and hot-film anemometry. The experiments were performed in a 200mm diameter vertical pipe at liquid superficial velocity in the range of 0.2 to 0.68m/s and gas superficial velocity from 0.005 to 0.18m/s. At low void fraction flows, the radial void fraction profiles show a wall peak. As the void fraction increases the profiles tend to peak at the pipe centreline. The distribution of the net radial interfacial forces for both core and wall peak void distributions was obtained using the two-fluid model. The radial direction of the bubble migration in the pipe core was related to the ratio between the turbulent dispersion and the lift forces. The effect of the pipe diameter on this ratio was investigated.
A Study of the Brownian Transport in Straining Flows
Authors: Swailes David , Ammar Yasmine , Reeks Michael
Published: September 2008

The combined effects of Brownian forcing and straining flow on the statistical description of particle dynamics are considered. Using a Fokker-Planck (pdf) model results are obtained for both instantaneous and continuous releases of particles into the flow. The approach shows that continuous sources generate true equilibrium distributions, and highlights important features of these distributions that have implications for the closure modelling of third-order velocity moments.
Wave Interaction With Fixed and Floating Vertical Breakwater Based on Analytical Modelling
Authors: Elchahal G. , Younes R. , Lafon P.
Published: September 2008

Nowadays, modelling and computer simulation are used in structure design to reduce the use of experimental investigations and laboratory tests required in a real layout structure. Using the potential-flow theory, the hydrodynamic pressure deduced from sea wave’s propagation has been computed based on the non linear theory of Stocks. The extension to the vertical breakwater (fixed bottom and floating breakwater) behaviour due to such excitations is indicated in this paper. Analytical expressions for functional performance variables of wave reflection by vertical breakwater, and stress analysis inside the breakwater have been obtained. These expressions have been numerically verified to demonstrate the capability of this analytical model.
Active Control of Vortex Breakdown Phenomenon in the Wake of a Simplified Car Geometry
Authors: Lehugeur Benjamin , Gillie´ron Patrick
Published: September 2008

The breakdown of longitudinal vortices originating from the rear pillars of a simplified geometry of automobile vehicles is obtained with a view to reducing aerodynamic drag. Numerical experiments are conducted on an Ahmed body according to a computation code based on the Lattice Boltzmann Method (LBM). Vortex breakdown is obtained by a continuously and uniformly blowing at the separation line prompting the formation and maintenance of the vortex. The breakdown is characterized by a sudden disintegration of the vortex core and the appearance of a recirculation zone. Numerical results obtained at several blowing velocities reveal the critical impact of the Swirl number on vortex breakdown. Moreover, breaking down the longitudinal vortices induces an increase in the static pressure at the wall of the rear window, which can bring about drag reductions close to 6%.
Comparison of Experimental and Numerical Obtained Velocity Fields in a Single-Blade Centrifugal Pump
Authors: Benra Friedrich-Karl , Dohmen Hans Josef , Zwingenberg Marcel
Published: September 2008

The development of a pressure and a suction surface of a single-blade pump impeller leads to a strong asymmetric pressure distribution at the perimeter of the rotor outlet. The interaction of the impeller flow with the pump casing produces a flow field which is periodic with the impeller turning. In a numerical approach the transient flow in a complete single-blade centrifugal pump has been calculated by solving the 3-dimensional time dependent Reynolds averaged Navier-Stokes equations (URANS) with a commercial CFD code for a wide range of pump operation. A strong dependence from the impeller position has been recognized for all flow parameters. Especially at off-design conditions the flow in the impeller and in the casing showed stall and reverse flow at particular impeller positions. Experiments have been used to validate the numerical investigations of the time dependent flow in the single-blade pump. The submersible pump, completely made of transparent plastic, has been investigated in detail by the Particle Image Velocimetry. The phase averaged 2D-velocity field inside the pump was measured for the same operating points which were investigated by numerical methods in advance. Measurement planes near the hub and the shroud disc and also at mid-span of the blade were chosen to expose the 3D-character of the flow inside the pump. The measured velocities were compared to the results from numerical simulations in detail. The good agreement between measurements and calculations, which was obtained for all investigated operating points, certifies the numerical simulations a high accuracy.
Experimental Study on Particle Behaviour in Simulated Gas-Oil-Sand Multiphase Production and Transfer Operations
Authors: Bello O. O. , Reinicke K. M. , Teodoriu C.
Published: September 2008

A crucial point still to be established in the prediction of oil-gas-sand multiphase production and transfer system performance is the identification of relevant mechanisms describing sand particle transport. To resolve this issue, experimental investigations are made on the behaviour of suspended sand particles in simulated oil-gas-sand multiphase pipe flows paying attention to the time-averaged local and global sand velocity and holdup. Simultaneous measurements of the time-averaged local and global sand velocity are made by digital imaging technique for better understanding of the oil-gas-sand multiphase flow hydrodynamics and sand transport mechanisms. The results show flow regimes of the multiphase flows significantly influence sand transport in the pipeflow. The shape of the local and global sand particle velocity and holdup profiles are also strongly modified by flow regimes. Furthermore, the experimental results indicate that the transport effect of the suspended sand particle can be enhanced by operating the multiphase flows under slug flow conditions. It is concluded that a new mechanism based on bubble-particle interaction needs to be considered in the modelling of sand transport behaviour during oil-gas-sand multiphase production and transfer operations.
Selection of Gas-Based Drag Reduction Technology
Authors: Amromin Eduard , Kovinskaya Svetlana
Published: September 2008

Drag reduction in water has been a goal of numerous efforts based on different technologies. The gas-based drag reduction technologies include supercavitation, partial cavitation and microbubble ejection. The objective of this study is to clarify the vehicle speed and size ranges for the technology effective application. The provided analysis is based on both our results and publications by other authors. Cavitation can reduce drag because a surface under the cavity is practically free of friction. Usually, there is also a significant drag penalty to create a cavity. For supercavitation, this drag becomes smaller than friction reduction only for extremely low cavitation numbers (less than 0.06). Ventilation would be necessary to maintain such cavitation numbers at speed around 100 knots, but there is no confident basis for any forecast: Model test data on air supply to supercavities are affected by flow blockage and a reasonable scaling law for air flux was not found yet. For partial cavitation, there are the possibilities to have no drag penalty and to achieve a total drag reduction in moderate ranges of cavitation number. The penalty-free partially cavitating flow can exist with suppression of cavity pulsation by a pressure gradient downstream of cavity tail. A 25%–30% drag reduction by partial cavitation was measured in model tests with our specially designed hydrofoil (in a water tunnel at the University of Minnesota) and in sea with a 100-ton boat. The friction reduction is proportional to areas covered by cavities. The attainable cavity lengths and covered areas depend on the vehicle speed. Requesting moderate air supply rates at design conditions, partial cavitation looks as the most promising and widely applicable drag reduction technology. Oppositely to supercavitation, microbubble drag reduction decreases with flow speed (the best results were obtained at 4.7m/s) and its effect critically depends on the surface orientation. An opportunity to apply this technology may exist for slow flat-bottom ships.
Lagrangian Statistics of Light-Solid Particle in a Turbulence With Strong Effects of Intermittency: Synthetic Eddy Simulation Approach
Authors: Gorokhovski M. , Sabel’nikov V. , Chtab A.
Published: September 2008

This paper addresses to simulation of a high Reynolds number flow with dispersed light particles. A new numerical approach is proposed in order to get access to the flow structure, which is not resolved by LES approach. Instead of filtered Navier-Stokes equation, the new approach is based on the instantaneous model-equation, where along with resolved acceleration in the gaseous phase, the contribution of subgrid acceleration is modeled stochastically in a way that satisfies the continuity equation. In the limit of zero turbulent viscosity, the model-equation reproduces the instantaneous Navier Stokes equation. The Langevin equation for the subgrid scale velocity increment is used. It is shown that the new approach allows to represent relatively well the velocity spectrum at subgrid scales. This approach is under the development; the first results showed that by accounting for inhomogeneity in the flow at small scales (intermittency), the acceleration of immersed solid particles may be substantially changed.
Experimental Modeling of Air Temperature and Velocity Distribution in an Engine Compartment
Authors: Mozafari A. A. , Saidi M. H. , Neyestani J. , Sany A. E.
Published: September 2008

Investigation of air distribution and wind effect on a vehicle body from the point of view of underhood heat transfer effect and proper positioning of vehicle elements such cooler, condenser and engine configuration is an important area for engine researchers and manufacturers as well. In this research, the effect of air velocity distribution and wind effect around a vehicle is simulated and temperature and velocity distribution around engine block which is influenced by the wind effect is investigated. Thermal investigation of the engine compartment components is performed using results of underhood air temperature and velocity distribution. The heat transfer from engine surface is calculated from the engine energy balance in which their input data are obtained from a comprehensive experimental study on a four cylinder gasoline engine.