bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Investigation of a Cold Turbulent Jet Impinging on a Hot Plate
Authors: Maldonado D. I. , Abrantes J. K. , Azevedo L. F. A. , Nieckele A. O.
Published: July 2013

Impinging jets are an efficient mechanism to enhance wall heat transfer, and are widely used in engineering applications. The flow field of an impinging jet is quite complex and it is a challenging case for turbulence models validation as well as measurements techniques. In the present work, a detailed investigation of a cold jet impinging on a hot plate operating in the turbulent flow regime was conducted. The flow field was characterized by both Laser Doppler Anemometry and Particle Image Velocimetry (PIV) techniques in order to collect 1st and 2nd order velocity statistics to allow a reliable assessment of the numerical simulations. Comparison was performed with two turbulence methodologies: RANS (κ–ω SST model) and LES (Dynamic Smagorinsky model). The comparison was performed to assess LES feasibility and accuracy in capturing the anisotropic structures that several tested RANS models missed. The mean velocity, instantaneous velocity, Reynolds stresses and Nusselt profiles obtained numerically are compared with experimental data. A physical insight about the general flow dynamics was obtained with the extensive amount of information available from the LES.
Entropy Generation in Laminar Flow Junctions
Authors: Sanchez Mauricio , Henderson Andrew W. , Papavassiliou Dimitrios V. , Lemley Evan C.
Published: July 2013

Laminar flow dominates microscale and milliscale applications. This work is focused on laminar energy losses in junctions (bifurcations). Reynolds number plays a dominant role in energy losses for laminar flow. The physical cause of these energy losses is entropy generation. This paper analyzes the energy losses in junctions by considering the entropy generation.

This paper documents results from computational fluid dynamics (CFD) simulations of laminar flow in planar junctions. The junctions studied consisted of circular pipes with two outlets and one inlet tube with Reynolds numbers ranging from one to 1000. A general technique has been developed to produce computer models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. The entropy generation has been determined in junctions from simulation results for the velocity field. Results for entropy generation as a function of geometry and Reynolds are presented. Energy loss coefficients are derived from the simulations and compared to experimental measurements of energy losses in microscale junctions.
Experimental Determination of Hydrodynamic Parameters of Air-Water Two-Phase Slug Flow in Horizontal Pipes
Authors: Romero Carlos H. , Márquez María A. , Vergara Sissi D. , Valecillos María T.
Published: July 2013

Two phase slug flow is the most common flow pattern for horizontal and near-horizontal pipelines. This study is designed to determine experimental velocities of elongated bubbles, lengths of liquid slugs and elongated bubbles, and slug frequencies for twenty flow rates combinations of a two phase air-water system that belong to a slug type pattern in horizontal pipes with a non invasive electronic device made of Photo-diodes (emitter) and photo-transistors (receiver) in a non visible length wave of 940 nanometers. The non intrusive electronic device is validated by simultaneously taking pictures with a high speed camera, (Kodak model Ektapro 4540 mx Imager, at shooting speed of 4500 frames per second, the picture resolution is 256 × 256 pixels), through a visualization cell filled with glycerin. This work is done with acrylic pipes of 0,03175 m inner diameter, to ensure complete flow development, the pictures are taken from a visualization cell located at a x/D = 249, the electronic device is located at x/D = 250. Air superficial velocity ranged between 0.156 and 0.468 m/s while water superficial velocity ranged between 0.159 and 1.264m/s. It is found that the non intrusive electronic device formed by photo diodes and photo transistors is an accurate technique that can be used in the determination of elongated bubble velocities, lengths and slug frequencies.
Computational Estimation of Bubble Gas Velocity for Slug Flow Pattern in Horizontal Pipes Using Image Processing Technique
Authors: Valecillos María T. , Romero Carlos H. , Márquez María A. , Vergara Sissi D.
Published: July 2013

Two-phase slug flow pattern is one of the most common flow patterns present in many industries, therefore its study becomes relevant. The aim of this work was to develop an automated computational program to determine the bubble gas velocity associated to gas-liquid two-phase slug flow by using video digital image processing technique. In order to obtain the images for the analysis, experiments were carried out using a pipe bench for air-water two-phase flow. The experimental facility is located in Simon Bolivar University, in Venezuela. The system has three pipes with different internal diameters and can be rotated around its axis and fixed at any inclination angle from horizontal to vertical flow. The tests were run in a horizontal pipeline of 0.03175m of internal pipe diameter and 8m long. For slug flow visualization a high speed camera Kodak Ektapro 4540mx imager was used. The camera was located in an x/D relation corresponding to 249 from the pipe inlet, ensuring the complete development of the flow. The camera allowed a maximum acquisition velocity of 4500 frames per second. The superficial velocity range was 0.16–1.79m/s and 0.16–1.26m/s for air and water, respectively. To summarize, 165 tests were performed and 1320000 images were analyzed with 20 flow rate combinations. The computational application was validated by comparing it with the velocities measured manually over selected images. Results obtained were compared to several correlations such as Bendiksen [1], Cook & Behnia [2] and Wang et al. [3].
Experimental Study of Evaporator Surface Area Influence on a Closed Loop Pulsating Heat Pipe Performance
Authors: Tabatabaee Mohammad Hadi , Mohammadi Mahshid , Shafii Mohammad Behshad
Published: July 2013

Pulsating Heat Pipes are an effective mean for heat removal with the potential for a widespread application in electronic packaging. An experimental study a Closed Loop Pulsating Heat Pipe (CLPHP) constructed of copper tubes formed into four meandering turns is presented. Once configured in a vertical orientation the lower portion of the CLPHP comes in contact with a heat source (called the evaporator) from which it will remove heat through the pulsating action of the two-phase mixture contained within the initially evacuated copper tubes eventually transfer the heat to a heat sink (known as the condenser). Heat fluxes can be measured using temperature data gathered from experiments. Thermocouples connected to the copper tubes at several locations provide this data. Experiments were conducted using deionized water as the working fluid. The surface area of the tubing which comes in contact with the heat source at the evaporator affects the heat removal rates. This effect was studied by varying the surface area in contact with the heat source while providing the same power input. Experiments were conducted using different filling ratios of working fluid (20–70%) for each case. The heat source (heating elements wound around the tubes) was supplied with different power inputs ranging from 10 to 40 W. Results indicate the surface area affects the pulsating action differently for each configuration because of its dependency on the flow regime. These results are presented for each flow regime. The results can be used to optimize the CLPHP according to the flow regime which it will be working in.
Influence of a Diffuser to the Wake Flow of a Passenger Car
Authors: Marklund Jesper , Lofdahl Lennart
Published: July 2013

To achieve more energy efficient transportation we have to reduce losses and resistance forces all over the vehicle. Aerodynamic drag is one of the primary resistance forces a passenger vehicle has to overcome and the force increases exponentially with increased speed. The under-body and rear-end geometry of a passenger car is a significant contributor to the overall aerodynamic drag and the shape of it is normally a compromise between styling, cost and other properties. To reduce the aerodynamic drag it is very important to have a good pressure recovery at the rear-end; to end up with a base pressure as high as possible. It is not necessarily the case that an optimized lower part of the rear-end for a square-back car has the same performance as a notch-back or fast-back car.

This work investigates the rear-end flow and aerodynamic performance of a sedan and wagon car with varying rear-end under-body design parameters. The study is a numerical analysis using a standard CFD approach commonly used in the automotive industry. A parameter study of under-body covers with varying rear angles, making the rear floor act like a diffuser. The function of the rear floor working as a diffuser is similar regardless of the upper geometry, but its function as a drag reduction device can be very different. Results from this study show a potential to reduce aerodynamic drag of the sedan car approximately 10%, with the best diffuser angle and cover plates over the floor. The best drag reduction for the wagon car was 2–3% and the optimum was at a smaller diffuser angle. Flow analysis of the wake shows how important it is the wake is balanced.
Characteristics of Porescale Vortical Structures in Random and Arranged Packed Beds of Spheres
Authors: Finn Justin R. , Apte Sourabh V. , Wood Brian D.
Published: July 2013

The characteristics of pore scale vortical structures observed in moderate Reynolds number flow through mono-disperse packed beds of spheres are examined. Our results come from direct numerical simulations of flow through (i) a periodic, simple cubic arrangement of 54 spheres, (ii) a wall bounded, close packed arrangement of 216 spheres, and (iii) a realistic randomly packed tube containing 326 spheres with a tube diameter to sphere diameter ratio of 5.96. Pore Reynolds numbers in the steady inertial (10 ≲ Re ≲ 200) and unsteady inertial (Re ≈ 600) regimes are considered. Even at similar Reynolds numbers, the vortical structures observed in flows through these three packings are remarkably different. The interior of the arranged packings are dominated by multi-lobed vortex ring structures which align with the principal axes of the packing. The random packing and the near wall region of the close packed arrangement are dominated by helical vortices, elongated in the mean flow direction. In the simple cubic packing, unsteady flow is marked by periodic vortex shedding which occurs at a single frequency. Conversely, at a similar Reynolds number, the vortical structures in unsteady flow through the random packing oscillate with many characteristic frequencies.
Forces and Flow Structures on a Simplified Car Model Exposed to a Transient Crosswind
Authors: Ferrand Valérie , Grochal Bartlomiej
Published: July 2013

A squareback simplified car model is exposed to a forced oscillating yaw and results are compared to static measurements. Tests are conducted at Reynolds number Re = 3.7×105 and a maximum Strouhal number St=fLrefU0=0.053. Phase average force and moment measurements exhibit a phase shift between static and dynamic tests that increases with oscillating frequency. To gain better understanding of the origin of the phase shift phenomenon, this paper proposes to characterize the flow evolution around the model using PIV measurements. Phase-shift seems to originate from the pressure recovery area where velocity fields exhibit a time delay in their response to dynamic yawing. Moreover, lateral vortical structures appearing on lee side from β = 15° increase this phase-shift and consequently appear to be favourable to the lateral stability of the vehicle.
An Approach on Fluid-Structure Interaction for Hemodynamics of Carotid Arteries
Authors: Lee Sang Hyuk , Kang Seongwon , Hur Nahmkeon
Published: July 2013

In the present study, a problem of the hemodynamic fluid-structure interaction (FSI) in the carotid artery was analyzed using a numerical approach. To predict the blood flow and arterial deformation, a framework for the FSI analysis was developed by coupling computational fluid dynamics (CFD) and solid mechanics (CSM) approaches. Using this framework, the hemodynamics of the carotid artery was simulated with the patient-specific clinical data of the arterial geometry, pulsatile blood flow and blood rheology. It is found that the hemodynamic characteristics of the carotid artery are significantly affected by its geometric factors and flow conditions, and relatively low values of the wall shear stress were observed in the post-plaque dilated region of the carotid bifurcated area. Since these characteristics of the carotid artery are affected by the cerebral circulation system, the effects of the cardiac output and the distal vascular resistance on hemodynamics were also analyzed.
Modeling Wind Flow and Particulate Pollutant Dispersion Around a Realistic Model of a Building Using Large-Eddy Simulation
Authors: Tavakoli Behtash , Ahmadi Goodarz
Published: July 2013

Urban air pollution has been of concern due to its adverse effect on human health. A major portion of urban air pollution is attributed to vehicle emissions. Center of Excellence (CoE) Building was built in Syracuse NY at the intersection of two major highways. The building is fully instrumented for assessing outdoor and indoor air pollutions. In this study the airflow and the dispersion of particulate air pollutants emitted from the highways surrounding the CoE building were analyzed. The wind flow around the model of the CoE building was first simulated using the RANS model. Comparison of the numerical simulations with the available PIV experimental data showed that the RANS turbulence model was not able to capture all features of the flow field due to the complexity of the building’s geometry. While the pressure field on the walls of the building model matched with those measured by the pressure taps, some aspects of the airflow velocity profile were not in agreement with the PIV data. The computational modeling of the wind flow around the building was then performed using the Large-Eddy Simulation (LES) approach. The mean velocity magnitude predicted by the LES showed good agreement with the experimental PIV measurements. The simulated flow field was used to predict the dispersion of the particulate pollutant around the building and the deposition fraction of particles on the walls of the building is studied.
Numerical Modeling of Two-Phase Flow Distribution Inside Evaporator Headers
Authors: Yazdani Miad , Wu Hailing , Alahyari Abbas A. , Radcliff Thomas D.
Published: July 2013

Two-phase flow distribution inside evaporator headers has been a challenging problem for a long time and having a robust predictive tool could substantially alleviate the costs associated with experimentation with different concepts and configurations. The use of a two-phase CFD model to predict flow distribution inside the header and at the discharge ports is demonstrated in this paper. The numerical domain is comprised of an inlet pipe and a distributor tube representing the header with a series of discharge ports. The flow distribution was initially verified using an air-water experiment, where the two-phase modeling approach, mesh requirements, and discretization schemes were defined. Next, the model was used to predict distribution of R134a in a typical heat exchanger distributor. The flow distribution across the discharge ports was provided to a discretized correlation-based heat exchanger model to predict the temperature and quality distribution along the length of the heat exchanger. The resultant temperature distribution is validated against IR imaging results for various operating conditions and header configurations.
A Numerical Investigation of Regional Fiber Deposition in a Realistic Nasal Cavity
Authors: Dastan Alireza , Abouali Omid , Ahmadi Goodarz
Published: July 2013

In this paper, the motion and deposition of micro fibers in different regions of a realistic human nasal airway were studied using a computational modeling approach. The airflow field in the nasal cavity was simulated by solving the Navier-Stokes and continuity equations. The coupled translational and rotation motion of the fibers were analyzed by a Lagrangian approach assuming one-way coupling. The fibers were assumed to be ellipsoids and a computer code was developed for solving the coupled translational and rotational equations of motion of the ellipsoidal fiber. A large number of fibers were injected at the nostril and the deposition pattern and deposition fraction (DF) of the fibers in different regions of the nasal cavity were evaluated for different breathing rates, various fiber diameters and different fiber aspect ratios. The simulation results for ellipsoidal fibers obtained by solving the coupled translational and rotational equations were compared with those obtained by solving only the translational equations of equivalent spherical particles with a shape factor, which were used in some earlier works.
Initiation and Statistical Development of Slug Flow With a High Resolution Two-Fluid Model
Authors: Chucuya R. C. , Carneiro J. N. E. , Nieckele A. O.
Published: July 2013

In the present work, the onset and subsequent development of slug flow in horizontal pipes is investigated by accurately solving the transient one-dimensional version of the Two-Fluid Model using a finite volume technique. Growth of disturbances that eventually bridge the pipe section is an automatic outcome of the solution of the discretized equations in a high resolution mesh, avoiding the need for the commonly used phenomenological models for the stratified to slug transition. Slug dynamics evolve naturally without the need of empirical correlations for slug parameters. This methodology (named “slug-capturing”) was proposed before in the literature and the present work represents a rare confirmation of its applicability in predicting this very complex flow regime. Here, different configurations are analyzed and comparisons are performed against different sets of experimental data. Additionally, statistical analysis of the slug parameters is performed and it is shown through comparisons against experimental measurements that this methodology is able not only to provide mean values of e.g. slug and bubble lengths and their evolution inside the pipe, but also shapes of probability density functions (PDFs), with a good degree of accuracy.
Modelling of Laminar Canonical Flows: Revisit
Authors: Adane Kofi Freeman K. , Tachie Mark F.
Published: July 2013

Three-dimensional laminar lid-driven and wall jet flows of various shear-thinning non-Newtonian and Newtonian fluids were numerically investigated. The complete nonlinear incompressible Navier-Stokes equation was solved using a collocated finite-volume based in-house CFD code. From the results, velocity profiles at several locations, jet spread rates, secondary flows and vorticity distributions were used to provide insight into the characteristics of three-dimensional laminar canonical flows of shear-thinning non-Newtonian and Newtonian fluids.
On the Interaction of Boundary Layer and Mixing Layer in Stratified Pipe Flow
Authors: Merzari Elia , Fischer Paul , Pointer W. David , Pellegrini Marco , Ninokata Hisashi
Published: July 2013

Stratified pipe flow in a pipe has been the subject of several investigations over the years. In fact it is relevant to the operation of thermal energy systems involving significant temperature gradients and low flow conditions. Stratification affects mixing, and is one the key phenomena that need to be addressed in the design of any mixing system of devices involving significant density difference. In order for thermal stratification in a pipe to be correctly modeled the underlying hydrodynamic behavior related to the mixing of two streams in a pipe needs to be fully understood.

The present paper deals with the numerical simulation of the flow in a pipe where the bottom half has a lower velocity compared to the upper half. A turbulent mixing layer develops in the streamwise direction at the interface between low flow region and higher flow region. Since the Reynolds number is low, the boundary layer and the mixing layer are about the same size. This translates in non trivial interactions between the structures in the boundary layer and the mixing layer. The failure of RANS models in accounting for the mixing points in this direction.

An LES of the flow in this geometry has been performed with the spectral code Nek5000. The averaged statistics have been compared with available experimental results. Proper Orthogonal Decomposition has been applied to clarify outstanding issues in RANS modeling.
Numerical Investigation of the Three-Dimensional Flow Structure About a Revolving Wing
Authors: Garmann Daniel J. , Visbal Miguel R. , Orkwis Paul D.
Published: July 2013

A numerical study is conducted to examine the vortex structure about a revolving wing in quiescent flow employing a high-fidelity, implicit large eddy simulation (ILES) technique found to be effective in simulating flows that exhibit interspersed regions of laminar, transitional, and turbulent flows. The revolving wing configuration consists of a single, aspect ratio one rectangular plate extended out a distance of 0.5 chords from the origin. Shortly after the onset of the motion, the rotating wing generates a stable and coherent vortex system across the leading edge and wing root that remains throughout the motion. The aerodynamic loads are also analyzed and found to remain mostly constant during the maneuver. Transitional effects on the vortex system are investigated over a range of Reynolds numbers (3,000 < Re < 15,000). It is found that higher Reynolds numbers promote more breakdown of the leading edge and root vortices, but do not alter the stability of the vortex system. The aerodynamic loads also show little sensitivity to Reynolds number with the higher Reynolds numbers producing only moderately higher forces. Comparisons with recent experimental PIV measurements using a PIV-like data reduction technique applied to the computational solution show very favorable agreement with the mid-span velocity and vorticity contours.
Prediction of Aerodynamic Characteristics of an Elliptic Airfoil at Low Reynolds Number
Authors: Chitta Varun , Walters D. Keith
Published: July 2013

This study focuses on modeling the effects of transitional flow and surface curvature on aerodynamic characteristics of an elliptic airfoil. Numerical simulations have been performed on a 16% thick elliptic airfoil for a range of angle of attack (α) from 0° to 20° and flow Reynolds number (Re) of 3 × 105, using relatively new transition-sensitive and traditional fully turbulent eddy viscosity turbulence models. Test conditions were matched to experiments by Kwon and Park (2005) and numerical results were compared with available experimental data. Results indicate that the transition-sensitive models, namely k-kL-ω and Transition SST, accurately predict the laminar-to-turbulent transition locations and reproduce the laminar separation bubbles on the suction surface of the airfoil in agreement with the experimental data. Also, transition-sensitive models yield improved predictions of lift and drag performance when compared with results from fully turbulent models. The fully turbulent models; including SA and k-ω SST, and a newly developed curvature-sensitive model (SST k-ω-ν2) fail to capture the flow separation and reattachment locations near the leading edge of airfoil. However, the curvature-sensitive SST k-ω-ν2 model predicts the stall point of the airfoil close to experimental results, while all other tested RANS models failed to accurately predict the stall point. Taken as a whole, the results suggest that accurate aerodynamic predictions at both low and high angles of attack might be achieved by using a model that includes the effects of both transition and curvature.
An Eulerian Method for Water Droplet Impingement by Means of an Immersed Boundary Technique
Authors: Capizzano F. , Iuliano E.
Published: July 2013

The estimation of water droplet impingement is the first step for a complete ice-accretion assessment. Basically two different numerical approaches can be found in literature: the Lagrangian and the Eulerian methods. The present paper describes the design and development of a water impingement simulation tool based on Eulerian droplet equations solved on Cartesian meshes by using an immersed boundary (IB) technique.

The robustness of the methodology and the accuracy of the approach are discussed. The method is applying to classical two- and three-dimensional test-cases for which experimental data are available in literature. The results will be discussed by comparing with experimental and body-fitted numerical solutions.
Flow Structure Identification in Unsteady Flow in Porous Media
Authors: Patil Vishal A. , Liburdy James A.
Published: July 2013

This study is an experimental investigation of the turbulent flow structure in randomly packed porous bed made with uniform sized spheres. Results are based on time resolved, two component PIV measurements in individual pore spaces of the bed. Data are presented for pore Reynolds number range of 54–3964. Three different flow regimes are identified, steady laminar, and unsteady transitional and turbulent flows. Small scale coherent vortical structures are visualized, by performing large eddy scale decomposition, for pore Reynolds number of greater than 1000. Quantative analysis of vortical coherent structures was performed using swirl strength analysis. The number density of vortical structures is found to monotonically increase gradually with pore Reynolds number. The rotation rate of these vortical structures is found to increase linearly with pore Reynolds number. The stretching rate (linear deformation) of the eddies were calculated using continuity to determine the out of plane stretching. The ratio of stretching rate to swirl strength (rotation rate) shows a normal distribution which collapsed onto a single curve. The convective velocities of the structures show a symmetric distribution with a peak value close to 0.8 times the average pore velocity.
Investigation on Parametric Design of Centrifugal Pump Impeller and its Optimization With Response Surface Method
Authors: Zhang Renhui , Zheng Kai , Yang Junhu
Published: July 2013

The critical issues of the optimization design of centrifugal pump are introduced in detail, and the main obstacle is the complicated implicit relation between the pump hydraulic performance and its interior passage geometry shape. The parametric design methods of centrifugal impeller proposed previously are introduced, which include the method based on NURBS surface, the method based on free-form deformation (FFD) and the method based on partial differential equation (PDE). To reduce the computational cost, the partial differential equation method is used to parametric design of the centrifugal impeller, and the boundary condition was parameterized. The parameters a(u,v) are consider as constant. The response surface methodology (RSM) is proposed to optimize the design of pump impeller. The objective function can be approximated based on trial results. Analyze the response surface model, and we find that the 2nd order polynomial cannot be used to simulate the complicated relation between the design object and the control variables. So the partial differential equations were proposed to construct the hypersurface response of objective function. The boundary-value problem of hyperspace is numerically solved. According to the optimization analysis, we can get the optimum design of pump impeller. The calculation case shows that the proposed theory and method are rational.
Influence of Bubbles on the Turbulence Anisotropy
Authors: Bolotnov Igor A.
Published: July 2013

Direct numerical simulations (DNS) with interface tracking of turbulent bubbly flows are becoming a major tool in advancing our knowledge in the multiphase modeling research area. Comprehensive analysis of turbulent flow structure allows to evaluate the state-of-the-art computational multiphase fluid dynamics (CMFD) models and to propose new closure laws.

The presented research will demonstrate how the multiphase DNS data can inform the development of computational fluid dynamics (CFD) models. In particular, Reynolds stress distribution will be evaluated for single and two-phase bubbly flows and the level of turbulence anisotropy will be measured in several scenarios. The results will help determine if the isotropic turbulent models are suitable for bubbly flow applications or there is a strong need to apply and develop Reynolds-stress turbulent models for two-phase flow CFD modeling.
Characterization of Liquid Sheet Breakup Using Numerical Experiments
Authors: Sinclair Jarrod , Abanteriba Sylvester
Published: July 2013

For the plain orifice nozzle configuration, breakup mode analysis of the issuing liquid jet has been extensively, over the years, undertaken. The works of Rayleigh, Haenlein, Ohnesorge, Reitz and others have used an Ohnesorge-Reynolds chart to clearly characterize breakup into four distinct modes. These include: (1) Rayleigh, (2) first wind induced, (3) second wind induced, and (4) prompt atomization. Planar liquid sheet flows have not undergone such intensive characterization analysis. In this work a non-expanding (nor thinning) liquid sheet is injected into a quiescent volume of gas from a planar nozzle of constant opening height. The flow has no co-flowing gas stream nor air-assistance to drive the disintegration. The nozzle configuration and subsequent liquid primary breakup is somewhat similar to an outward opening fuel injector having an annular outlet with a large radius to needle lift height ratio.

The numerical experiments in this work use a high fidelity Computational Fluid Dynamics (CFD) modeling approach. This includes the Volume-Of-Fluid (VOF) two-phase method to represent the liquid and gas fluids both considered to be incompressible, coupled with the Large Eddy Simulation (LES) treatment of turbulence modeling. The initial primary breakup of the liquid sheet into large droplets, ligaments and other structures is the main focus of the modeling. As such, secondary breakup and possible evaporation of the liquid is not considered. Due to the configuration of the planar nozzle, upstream cavitation of the liquid within the nozzle is also not considered.

Breakup studies were conducted within the Reynolds number range of 3,000 to 23,400, and Ohnesorge number range of 0.004 to 0.1. Results are extensively validated with the works of Heukelbach and Scholz. In-nozzle velocity profiles are characterized with Reynolds number showing laminar, semi- and fully-turbulent states in the flow boundary layer and core. Velocity profile relaxation is studied as the liquid sheet transitions from a wall-bounded flow within the nozzle to a free shear flow surrounded by gas. Particularly, the axial velocity component is seen to weaken, whilst the sheet normal velocity component strengthens and aids in disintegration of the liquid sheet.
Vibration Characteristics due to Cavitation in Stator Element of Automotive Torque Converter at Stall Condition
Authors: Watanabe Satoshi , Otani Ryosuke , Kunimoto Shun , Hara Yoshinori , Furukawa Akinori , Yamaguchi Takeshi
Published: July 2013

Cavitation behaviors in an automotive torque converter at pump speed of 600, 700 and 800 min−1 at the stall condition are investigated by means of the transparent model. At the same time, the influences of cavitation on mechanical vibration are studied. As a result, at the onset of cavitation, the longitudinal corner vortex cavitation is formed at the corner between outer wall and either suction or pressure surface of stator blades. After the further decrease of charge pressure, the cavitation bubbles are observed in the flow separation region formed at the leading edge on the suction surface of stator blades. Vibration spectrum peaks are found in the wide range of frequency, which increase with the development of cavitation but then decrease with its excessive development. Discussions are made for higher and lower frequency ranges separately to understand the relation between mechanical vibrations and cavitation.
Computational Study of the Dynamics of the Flow in a Gravity-Driven Toilet
Authors: Mahecha J. , López O. , Ardila O.
Published: July 2013

Nowadays, strong efforts are focused in achieving a rational use of water due to the low amount of accessible and available water in the world. Toilets are essential elements that represent a significant percentage of the water consumption in the domestic sector. Any improvement in these devices signifies an important reduction in the water demand. Additionally, regarding the Colombian industry, the toilet design process takes up to one year and it is a totally empirical process. In this document a Computational Fluid Dynamics (CFD) model of a gravity driven toilet flush is presented. First, a base case was implemented with some important assumptions and simplifications, such as the omission of some geometric details and the discharge valve. Then, characterization curves of pressure, mass flow rate and turbulence intensity magnitude in different parts of the toilet are presented. Moreover, a basic experimental comparison of the water mass flow rate at the toilet outlet was done achieving satisfactory results. Finally, the influence of the Coriolis phenomenon in the performance of the toilet was studied.
Flow Characteristics of a Three Dimensional Bluff Body With a Single Rotating Cylinder
Authors: Bell James R. , Burton David , McArthur Damien , Sheridan John
Published: July 2013

This work investigated the application of a rotating cylinder to the upper leeward edge of a three dimensional bluff body in ground proximity.

Aerodynamic drag measurements, base pressure contours and wake velocity profiles were obtained in a closed jet wind tunnel for Reynolds Numbers in the range of approximately 220,000 to 660,000. The cylinder of diameter 0.1H was mounted on the upper edge of the leeward face of the body. The ratio of cylinder surface velocity to freestream velocity was varied from 0 to 2.0. A computational model of the geometry was developed and results are presented for various velocity ratios and cylinder diameters.

The results of this work demonstrated that, even at low velocity ratios, the cylinder rotation has a large effect on the flow structures in the body wake region. A large downwash is observed that creates two large counter-rotating vortices and a resultant significant increase in drag.

The aerodynamic drag changes are presented as a function of velocity ratio and are shown to be Reynolds Number insensitive over the range tested. Aerodynamic drag was shown to increase with increasing velocity ratio over the velocity ratio range 0.25 to 2.0.
A Study of Hydraulic Design of a Ducted Azimuth Thruster
Authors: Park Jong-Hwoo , Chung Kyung-Nam , Chang Bong-Jun , Go Seok-Cheon , Chung Jae-Hoon
Published: July 2013

In order to obtain sufficient towing force, tug boats are usually equipped with high powered engines and special thrusters such as azimuth thrusters. The hydraulic design of a ducted azimuth thruster was carried out for a 2 MW-class tug boat by using CFD. Here, the azimuth thruster consists of a fixed-pitch screw propeller, a duct, a gear casing and a strut. To design the duct propeller, the effects of design parameters of a screw propeller and a nozzle on thruster performance were evaluated. The proper section shape of the strut is also important because it can largely affect inflow velocity distribution on the propeller.

The model of the designed azimuth thruster was manufactured with a scale ratio of 10. Propeller open water and cavitation observation tests were carried out to confirm the performance of the design model.
Investigation of Molten/Oxidized Aluminum Powder Deposition on Stainless Steel 304
Authors: Sanchez Tomas M. , Donaldson A. Burl , Gill Walt
Published: July 2013

Accidents involving solid propellants containing aluminum can be difficult to model due to the additional heat transfer from molten aluminum or aluminum combustion and impingement/deposition of oxide on target objects. A series of tests has been carried out using a commercially available oxy-acetylene torch and powder feeder to investigate the effects of molten/oxidized aluminum on stainless steel 304 substrates. SEM and EDS have been used to determine diffusion/interaction of aluminum with the stainless steel and characterize the constituents of the resulting interfacial layers. These techniques indicated that at the test conditions, aluminum was undetectably oxidized before it deposited on the substrate surface. However, temperature data from thermocouples attached to backside of each substrate detected an increased heat flux to the substrate when aluminum is introduced into the flame spray. Results also indicate that the boundary layers of the aluminum and stainless steel were well defined implying that little diffusion or solution of the aluminum with the stainless steel occurred.
Validated Aerospace Soft Impact Modeling Platform
Authors: Alexander Eric , Carey Ben , DiNardo Michael , Gill Herman , Gonzalez Joey , Harry Mike , Isidro Alex , Judge Scott , Puckett Kevin , Schoepfer George , Song Yangkun , Tilghman Matthew , Siddens Aaron , Satterwhite Matthew , Bayandor Javid
Published: July 2013

The research has been dedicated to developing a virtual crashworthiness platform for large advanced aircraft structures when subjected to water ditching incidents. A numerical design tool, incorporating fluid-structure interaction analysis module, was created to assess damage tolerance in future aerospace design concepts to help with the prognosis of structural failure. To accomplish this, an experimental water impact set up was used to calibrate and validate the developed detailed virtual model. Specific data acquisition techniques implemented allowed for the capture of strain distribution and impact energy dissipation, used to validate the simulation platform.
Simulations of Cyclic Breathing in the Conducting Zone of the Human Lung
Authors: Walters D. Keith , Burgreen Greg W. , Hester Robert L. , Thompson David S. , Lavallee David M. , Pruett William A. , Ford-Green Jason
Published: July 2013

Computational fluid dynamics (CFD) simulations were performed to predict the air flow in the human lung during cyclic breathing. The study employed a morphologically complex computational geometry generated using a combination of patient-specific CT-scan data for the extrathoracic and upper airway regions and a representative branching geometry for the lower airways that is available in the open literature. The geometry extended throughout the entire conducting zone and includes 16 partially resolved airway generations. For each generation beyond the third, only a fraction of the airway branches were retained, resulting in truncated flow outlets (for inspiratory flow) in generations 414. The inhalation and exhalation air flow boundary conditions were prescribed based on a physiologically realistic ventilation pattern, which was obtained using a whole-body model of human physiology. The flow was driven by specifying time-varying volumetric flowrates applied at each of the distal boundaries, while the oral boundary was maintained at constant (atmospheric) pressure. The study investigated the effectiveness of three different mass flow distribution schemes to drive the air flow. It was found that prescribed mass flow distribution fractions based on the square of the airway cross-sectional area produced the best results in terms of a uniform distal pressure distribution, while all methods produced reasonable results in terms of mass flow distribution throughout the lung airway geometry.
Application of Semi-Empirical Probability Distributions in Wave-Structure Interaction Problems
Authors: Izadparast Amir H. , Niedzwecki John M.
Published: July 2013

Ocean engineers are routinely faced with design problems for coastal and deepwater structures that must survive a wide range of environmental conditions. One of the most challenging problems in the field of ocean engineering is the accurate characterization and modeling of the interaction of ocean waves with these offshore structures. The random characteristic of ocean environment requires engineers to consider the effects of random variability of the pertinent variables in their predictive models and design processes. Thus, for ocean engineering purposes, one needs to have accurate estimates of the probability distribution of the key random variables that will be used in sensitivity studies, reliability analysis, and risk assessment in the design process.

In this study, a family of semi-empirical probability distribution is developed based on the quadratic transformation of linear random variable assuming that the linear random variable follows a Rayleigh distribution law. The estimates of model parameters are obtained from two moment based parameter estimation methods, i.e. method of moments and method of linear moments. The studied semi-empirical distribution can be applied to estimate the probability distribution of a wide range of non-linear random variables in the fields of ocean wave mechanics and wave-structure interaction. As examples, the application of the semi-empirical model in estimation of probability distribution of: a) ocean wave power, b) ocean wave crests interacting with an offshore structure is illustrated. For this purpose, numerically generated timeseries and experimentally measured data sets are utilized.
A Numerical Investigation of Internal and External Two-Phase Flows of a Rotating Disk Atomizer
Authors: Lin Cheng-Xian (Charlie) , Phan Long
Published: July 2013

In this paper, a numerical study has been carried out to model and simulate the air-water two-phase flows in and around a rotating disk atomizer, which uses multiple nozzles to breakout the water and forms droplets. The physical problem was simulated with an Eulerian multiphase model. The realizable two-equation turbulence model was used for the turbulent flow. The governing equations were solved with a finite volume based numerical method. The rotary frame approach was used to deal with the spinning disk. Numerical simulation was conducted in a disk rotational speed range of 1000 to 10000 rpm, a liquid feed flow rate range of 100 to 150 gpm. Both uniform and non-uniform liquid distribution conditions were considered. Detailed results about flow velocity and volume fraction fields inside and outside of the atomizer are presented and discussed. It was found that when liquid is nonuniformly distributed through the distributors, some of the nozzles could reach flooding conditions at lower rotational disk speed and liquid feed volume flow rates, as compared to uniform distribution cases.
Fluid Flow Mixing of Turbulent Jets Within a Staggered Rod Bundle
Authors: Amini Noushin , Hassan Yassin A.
Published: July 2013

In this investigation, flow mixing between turbulent jets injecting to a channel containing a rod bundle and the channel flows is studied using Particle Image Velocimetry (PIV) and Matched Index of Refraction (MIR) techniques. A specific case of a single impinging jet with a Reynolds number of 13,400 is considered for this analysis. The time-averaged vorticity fields for three different planes within the measurement volume verify the presence of coherent structures within all three fields, specifically in areas close to the jet impingement area and in the shear layer of the jet within the impingement plane. The cumulative effect of the vorticity patterns observed within all measurement planes is believed to have a significant role in the enhancement of mixing within the test section.

To further analyze the behavior of the large-scale coherent structures observed in the time-averaged vorticity fields, Proper Orthogonal Decomposition (POD) technique was applied to the PIV velocity fields. The results confirm that the jet flow is the most energetic and the dominant feature of the flow field. Therefore, to further analyze the behavior of some of the relatively smaller-scale coherent structures which could play a significant role in the mixing process, a higher number of modes or a different approach needs to be considered.
Noise Prediction in HVAC Squirrel-Cage Fans by Unsteady Reynolds Navier-Stokes Computation
Authors: Velarde-Suárez Sandra , Ballesteros-Tajadura Rafael , Fernández Oro Jesús Manuel , González José
Published: July 2013

Small centrifugal and axial fans are used in automobile applications, as it is the case for HVAC systems for public transport. Typically, these fans are used to work at high speed (over 4000 rpm) and variable operation conditions, even at extreme off-design points. Flow instabilities, low efficiency and high levels of noise and vibrations appear in these machines due to these working characteristics and the need of low fabrication costs. However, lower noise levels are required today to improve the passengers comfort.

Aiming to solve these problems, it is interesting to develop a computer application to predict the generated noise level (especially at the blade passing frequency BPF), which could be used during the design phase of the fans.

In this paper, using Computational Fluid Dynamics (CFD) tools, the three-dimensional (3D) internal flow in a small squirrel-cage fan is computed unsteadily. Based upon the data acquired from the pressure fluctuations at the surfaces of 46 rotating blades and the volute tongue, the Ffowcs Williams-Hawkings analogy, which has been successfully applied in other types of turbomachines, is used to predict noise levels at the BPF.

On the other hand, in order to validate the predicted numerical results, an experimental noise characterization in a semi-anechoic chamber using capacitive microphones and a real-time frequency analyzer is performed.
Carbon Based Electrodes for Upscaling Microfluidic Fuel Cells
Authors: Fuerth D. , Bazylak A.
Published: July 2013

In this work, we present an experimental microfluidic fuel cell with a novel up-scaled porous electrode architecture that provides higher overall power output compared to conventional microfluidic fuel cells and a methodology for electrode material evaluation to inform designs for improved performance. Our proof-of-concept architecture is an up-scaled version of a previously presented flow-through cell with more than nine times the active electrode surface area. We employed 0.04M formic acid and 0.01M potassium permanganate as fuel and oxidant, respectively, dissolved in a 1M sulfuric acid electrolyte. Platinum black was employed as the catalyst for both anode and cathode. Carbon based porous electrodes including felt, cloth, fibre, and foam were compared to traditional Toray carbon paper in order to characterize their respective performances. We also discussed current densities normalized by electrode volume, which is appropriate for comparison of flow-through architectures. The traditional method of current normalization by projected electrode surface area is also presented.