bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Distribution of Air-Water Bubbly Flow in a Vertical Pipe With an Axisymmetric Sudden Expansion
Authors: Kondo Koichi , Yoshida Kenji , Matsumoto Tadayoshi , Okawa Tomio , Kataoka Isao
Published: February 2009

Experimental studies were made on the multi-dimensional behavior of upward gas-liquid two-phase flow through a vertical pipe with an axisymmetric sudden expansion, which is one of the typical multi-dimensional channel geometries. The aims of this study are to clarify the multi-dimensional behavior of bubbly and slug flow affected by the sudden expansion channel geometry and to accumulate the experimental data for two-phase flow analysis, which is applicable to predict appropriate accuracy the multi-dimensional behavior. In this report, the first, the observation using high-speed video camera was performed and revealed the multi-dimensional dynamic flow behavior with bubbles and gas-slug affected by the sudden expansion point. From these results, the flow regime map at the below and above of the sudden expansion point were classified with bubble diameter. The second, the variation of the phase distribution in the sudden expansion was measured at the different axial positions using a point-electrode resistivity probe for various gas and liquid flow conditions. Thirdly, the cross-sectional averaged void fractions along the flow direction were calculated by using the one-dimensional two-fluid model considering the phase distribution parameter to confirm the applicability of the computations. As a result, they concretely pointed out that some multi-dimensional modeling or modifications for numerical simulation would be needed for more accurate prediction of two-phase flow. Such radial phase distributions in this study are significant for the multi-dimensional two-phase flow analysis.
Studies on Gas-Phase Turbulence Modification in Vertical Upward Annular Flow
Authors: Yoshida Kenji , Tanaka Hidenobu , Matsuura Keizo , Kataoka Isao
Published: February 2009

Experimental and numerical studies were made to investigate the effects of wavy interface on the liquid film to gas-phase turbulence modification of air-water annular flow in a vertically arranged round tube. By using the constant temperature hotwire anemometer, time-averaged axial velocity profiles, turbulence fluctuation profiles, energy spectrum and auto-correlation coefficient for fluctuation velocity component of gas-phase axial velocity were precisely measured. The liquid film thickness was also measured by using point-electrode resistivity probe to make clear the time-averaged liquid film thickness and wave height moving on the liquid film. Direct observations using high speed video camera were also added to make clear the dynamic behavior and propergating velocity of ripple or disturbance waves on liquid film flow. Numerical simulations for gas-phase turbulence in annular flow considering the effect of wavy interface of liquid film flow were also carried out. Liquid film flow was modeled to be the wall surface roughness of interfacial wave height moving with the interfacial velocity. The roughness and moving velocity of the modeled liquid film for computational condition were provided by the present experimental results. Time-averaged velocity profiles and fluctuation velocity profiles were calculated with standard k-ε model. Numerical results were generally consistent with the experimental results obtained in the present study.
Two-Phase Flow Through Square and Circular Microchannels: Effect of Channel Geometry
Authors: Chung Peter M.-Y. , Kawaji Masahiro , Kawahara Akimaro , Shibata Yuichi
Published: February 2009

An adiabatic experiment was conducted to investigate the effect of channel geometry on gas-liquid two-phase flow characteristics in microchannels. A mixture of water and nitrogen gas was pumped through a 96 μm × 96 μm square microchannel and the flow pattern, void fraction and pressure drop data were obtained and compared with those previously obtained in a 100 μm circular microchannel. The frictional pressure drop was determined from the measured total pressure drop, and the two-phase flow pattern and void fraction were determined from image analysis of the video recordings. In the square channel, 136 runs were performed over a range of 0.09 ≤ jG,AVG ≤ 62 m/s for the average superficial gas velocity and 0.01 ≤ jL ≤ 4 m/s for the superficial liquid velocity. The frictional pressure drop data showed that the calculations based on a separated–flow model were best at estimating the frictional pressure drop for both microchannels. No particular effect of the channel shape was found for the two-phase frictional pressure drop. The void fraction-to-volumetric quality relationship was also found to be similar for both shapes of microchannels, exhibiting an exponential increase in void fraction with increasing volumetric quality. The empirical correlation that describes the void fraction-to-volumetric quality relationship for the square microchannel was developed earlier from the measured data for the circular microchannel. Observations of the recorded images indicated the two-phase flow patterns to be primarily intermittent with liquid and gas slugs. The liquid film surrounding the gas core displayed a smooth or ring-like structure. The probability of each interfacial structure occurring was examined in detail to develop a novel flow pattern map consisting of four regions named slug-ring flow, ring-slug flow, multiple flow and semiannular flow. Between the square and circular microchannels, the two-phase flow maps exhibited transition boundaries that were shifted depending on the channel shape. The region of ring-slug flow that appears in the circular microchannel collapsed in the square microchannel, possibly due to the suppression of the liquid-ring film in the corners of the square channel.
Rewetting Velocity of High-Temperature Vertical-Narrow-Annular Flow Passages Under Counter-Current Flow Condition
Authors: Koizumi Yasuo , Ohtake Hiroyasu , Tsukudo Masanori , Sakamoto Naoki
Published: February 2009

Quenching of a thin gap annular flow passage by gravitational liquid penetration was examined experimentally by using R-113. The outer wall was made of copper. The inner wall was made of copper or glass. The inner diameter of the outer wall of the annular flow passages was 40 or 41 mm and the annular gap clearance δ was 0.5, 1.0, 2.0 and 5.0 mm. The outer wall was heated initially up to 250 °C and also the inner wall was heated when the copper inner wall was used. The quenching was observed in δ ≥ 1.0 mm. When δ = 0.5 mm, the wall was just gradually cooled down. The relation between the wall superheat and the heat flux during quenching process was similar to the boiling curve of pool boiling. However, the peak heat flux as well as the heat flux in the film and the transition boiling was lower than those in the pool boiling. These heat fluxes became lower as the gap clearance became narrow. The rewetting velocity became slow as the gap clearance became narrow. The rewetting velocity seemed to have a unique relation for the Peclet number Pe = (ρSCSδSU/λS) and the Biot number Bi = hδs/λs ; Pe ∝ Bi which was the same as that of the Yamanouchi correlation. A decrease in the heat flux (the heat transfer coefficient) in the rewetting front region, which corresponds to the peak heat flux, results in a decrease in the rewetting velocity as the gap clearance becomes narrow.
Velocity of a Large Bubble Rising in an Inclined Rectangular Channel
Authors: Hamaguchi Hachiro
Published: February 2009

Velocity of a large single bubble rising in a stationary liquid in an inclined rectangular channel was measured using silicone oil having a kinematic viscosity of 1000mm2/s. The size of cross section of the test channel was 5mm × (5–40)mm, i.e., the aspect ratio was from 1 to 8. Experiments were carried out changing the aspect ratio of cross section of the channel, the inclination angle and “posture angle”, where the “posture angle” is an angel by which the channel is rotated around the channel axis. Movement of a large bubble in an inclined circular tube is determined by the inclination angle. On the other hand, it is shown that movement of a large bubble in an inclined channel is influenced also by the posture angle beside the inclination angel, i.e., the posture angle is an important parameter in an inclined rectangular channel. Relations among the rising velocity, the inclination angle, the posture angle and the aspect ratio were obtained by the experiments.
Study on Two-Phase Flow Through a Micro T-Junction
Authors: Shibata Yuichi , Ikeda Koh , Chung Peter M.-Y. , Hanari Toshihide , Kawaji Masahiro
Published: February 2009

The field of microfluidics is developing rapidly with advances in MEMS (micro electro mechanical system) and μ TAS (micro total analysis system) technologies. In various devices, controlling the flow rate of liquid or gas accurately at micro or nanoliter volume levels is required. In this work, the gas-liquid two-phase flow patterns in a microchannel T-junction have been examined. The two-phase flow patterns were observed in the T-junction under two different gas and liquid injection conditions. The flow patterns of liquid and gas in the microchannel after the T-junction were also observed and classified into three types depending on the flow rate, and a two-phase flow pattern map was constructed. The mechanism of bubble breakup at a micro T-junction was also experimentally and analytically investigated.
Numerical Analysis of Free Surface Deformation in Water Tank
Authors: Shimizu Fumio , Hatakenaka Kiyoshi , Tanaka Kazuhiro , Shigefuji Hiroshi , Shimizu Takeshi
Published: February 2009

A siphon phenomenon is one of gas/liquid two-phase flows including free surface deformation. Since the large-scale deformation of the free surface causes a loud noise, it is important to investigate the motion of the free surface. The purpose of the present study is to reproduce a siphon phenomenon in computer, and to analyze an internal flow field of the siphon phenomenon. An oscillating flow in two-dimensional U-tube was simulated to verify our computational codes, and good agreement compared with the theoretical period was obtained. After that, the numerical reproduction of a siphon phenomenon was succeeded and the behavior of the free surface was captured reasonably.
Experimental Study on Near-Wall Bubble Clustering Behaviors in Bubbly Channel Flow (Keynote)
Authors: So Soo-Hyun , Takagi Shu , Fujiwara Akiko , Matsumoto Yoichiro
Published: February 2009

The turbulence properties of gas-liquid bubbly flows and the near-wall bubble clustering behaviors are investigated for upward flow in a rectangular channel. Bubble size distributions are well-controlled and the flow with mono-dispersed 1mm-diameter and that with 1–4mm diameter bubbles are compared. Bubble size, turbulent properties of liquid phase and the bubble cluster motion were measured using image-processing technique, Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV), respectively. To create the mono-dispersed small bubbles by the bubble generator, being made of stainless steel pipes, a small amount of surfactant (20ppm of 3-pentanol) was added into the flow. In this study, experiments with three different bulk Reynolds numbers (1350, 4100, 8200) were conducted with void fractions less than 0.6% in the fluid with/without the surfactant. In all cases with surfactant, there was a very high accumulation of bubbles near the wall. The local void fraction has a wall-peak distribution and the horizontal bubble clusters are formed near the wall. As a result, the local mean velocity of the liquid phase becomes larger near the wall due to the driving force of buoyant bubbles and the stream-wise turbulent intensity in the vicinity of the wall was enhanced. On the other hand, the turbulent fluctuations and Reynolds stress are remarkably suppressed in the other region. At the Reynolds number of 8200, the bubble cluster was investigated. Experimental observation showed that the bubble cluster changes its shape in time and that the shape change is caused by the difference of the rising velocity between the cluster center and the both ends. The clusters accelerated the mean streamwise velocity near the wall, thus the mean velocity profile of the liquid phase becomes flattened. It is suggested that the highly concentrated bubbles in the vicinity of the wall disturb the transport of turbulence energy produced in the wall shear layer toward the center of channel. Moreover, in the middle of channel, the turbulence structure is governed by pseudo-turbulence induced by present bubbles.
Application of Preconditioning Method to Gas-Liquid Two-Phase Flow Computations
Authors: Shin Byeong Rog , Yamamoto Satoru , Yuan Xin
Published: February 2009

A preconditioned numerical method for gas-liquid two-phase flows is applied to solve cavitating flow. The present method employs a finite-difference method of dual time-stepping integration procedure and Roe’s flux difference splitting approximation with MUSCL-TVD scheme. A homogeneous equilibrium cavitation model is used. The present density based numerical method permits simple treatment of the whole gas-liquid two-phase flow field including wave propagation, large density changes and incompressible flows characteristics at low Mach number. By this method, two-dimensional internal flows through a backward-facing step duct, a venturi tube and decelerating cascades are computed. Comparisons of predicted results with experiments are provided and discussed.
A Computational Methodology for Large-Eddy Simulation of Tip-Clearance Flows
Authors: You Donghyun , Mittal Rajat , Wang Meng , Moin Parviz
Published: February 2009

A large-eddy simulation (LES) solver which combines an immersed-boundary technique with a curvilinear structured grid has been developed to study the temporal and spatial dynamics of an incompressible rotor tip-clearance flow. The overall objective of these simulations is to determine the underlying mechanisms for low-pressure fluctuations downstream of the rotor near the endwall. Salient features of the numerical methodology, including the mesh topology, the immersed boundary method, the treatment of numerical instability for non-dissipative schemes on highly skewed meshes, and the parallelization of the code for shared memory platforms are discussed. The computational approach is shown to be capable of capturing the evolution of the highly complicated flowfield characterized by the interaction of distinct blade-associated vortical structures with the turbulent endwall boundary layer. Simulation results are compared with experiments and qualitative as well as quantitative agreement is observed.
Numerical Model for the Unsteady Flow Behaviour Inside a Double Suction Pump
Authors: Gonza´lez Jose´ , Santolaria Carlos , Castro Francisco , Parra M. Teresa
Published: February 2009

The fluid flow inside a single stage double aspirating pump has been studied using a three-dimensional unsteady numerical model. The main goal is the validation of the numerical procedure proposed and the flow-field analysis at the whole stage. The URANS equations have been solved using a sliding mesh unsteady model, which is able to model the real movement of the impeller inside the volute. The equations have been considered both in the rotating frame for the impeller and in the absolute reference frames, for the inlet and volute sections. Therefore, unsteady effects and dynamic interactions are captured. Mesh independency studies have been carried out and the usual turbomachinery boundary conditions have been imposed. Once the model was validated through performance curve comparison, the flow patterns in the impeller, volute and suction regions have been investigated. Particularly, the suction flow field is of special interest due to induced distortion of the axial and circumferential velocity fields. Besides that, the pressure evolution is also considered in order to study the different patterns at the inlet of the pump, where cavitation is likely to arise. The flow at the suction of this pump is characterized by the existence of a particular geometry that tries to force a uniform flow for nominal flow rate. However, this geometrical configuration produces a strong distortion for off-design conditions. This lack of uniformity produces an unsteady incidence that gives rise to strong loading variations. The study of the evolution of such unsteadiness of the inlet flow throughout the impeller and the volute was also carried out. Even at nominal flow rate, some non uniformities are detected in the pressure distribution at the inlet, that may be caused by the geometrical arrangement of this part of the inlet casing. Instantaneous and averaged pressure fields are studied.
CFD Validation for a Marine Propeller Using an Unstructured Mesh Based RANS Method
Authors: Rhee Shin Hyung , Joshi Shitalkumar
Published: February 2009

Results of computational fluid dynamics validation for flow around a marine propeller are presented. Computations were performed for various advance ratios following experimental conditions. The objectives of the study are to propose and verify a hybrid mesh generation strategy, and to validate computational results against experimental data with advanced computational fluid dynamics tools. Computational results for both global and local flow quantities are discussed and compared with experimental data. The predicted thrust and torque are in good agreement with the measured values. The pressure distribution and pathlines on and around the blade surface well reproduce the physics of highly skewed marine propeller flow with tip vortex. The circumferentially averaged velocity components compare well with the measured values, while the velocity and turbulence quantities in the highly concentrated tip vortex region are under-predicted. The overall results suggest that the present approach is practicable for actual propeller design procedures.
Unsteady Radial Forces on the Impeller of a Centrifugal Pump With Radial Gap Variation
Authors: Gonza´les Jose´ , Santolaria Carlos , Parrondo Jorge Luis , Ferna´ndez Joaqui´n , Blanco Eduardo
Published: February 2009

An experimental and numerical study is presented on the unsteady radial forces produced in a centrifugal pump with volute casing. Two impellers with different outlet diameter were considered, which gave radial gaps between blade and tongue of 10% and 15.8% of the impeller radius, respectively. Firstly, the data from pressure fluctuation measurements was processed to obtain the dynamic forces at the blade-passage frequency, for a number of flow-rates. Afterwards, these results were used to check the predictions from a numerical simulation of the pump with the code Fluent. This paper describes the work carried out and summarizes the experimental and the numerical results, for both radial gaps. The steady and unsteady forces at the blade passing frequency obtained by radial integration of the pressure distributions in the shroud side of the pump volute are analysed in detail and similar trends are obtained.
Fundamental Analysis of the Secondary Flows and Jet-Wake in a Torque Converter Pump: Part 1 — Model and Flow in a Rotating Passage
Authors: Flack R. , Brun K.
Published: February 2009

Previously, experimental results for the velocity field in a torque converter pump showed strong jet/wake characteristics including backflows and circulatory secondary flows. To understand the fundamental flow behavior simplified analytical/numerical Navier-Stokes flow models were developed herein to independently analyze the pump pressure-to-suction side jet/wake flow, the core-to-shell side jet/wake flow, and the secondary flows. Parametric studies were undertaken to evaluate the effect that operating conditions and geometry had on the characteristics. Two relatively simple models were employed: (i) a rotating 2-D straight-walled duct to model the pressure-to-suction side jet/wake flow due to rotational Coriolis forces and (ii) a 180° flow bend to model the core-to-shell side jet/wake flow due to rapid radial/axial flow turning. The formation and development of the pump jet/wake flow was studied in detail. Results showed that the core side wake and the suction side wake, both of which drive the formation of 3-D jet/wake flow in a mixed flow impeller were primarily dependent on two non-dimensional force parameters: the modified Rossby number and the Reynolds number. The suction side wake, which was due to the counter-rotational tangential Coriolis force, was almost only a function of the modified Rossby number and independent of the Reynolds number, while the core side wake, which was due to flow separation caused by rapid radial flow turning, was primarily a function of the Reynolds number. Increasing the modified Rossby number increased the pressure-to-suction side jet/wake flow; similarly, increasing the Reynolds number increased the core-to-shell side jet/wake flow. The geometric parameters that were seen to affect the pump flow were the back-weeping angle for the pressure-to-suction side jet/wake, and the passage length (or curvature) for the core-to-shell jet/wake. Results showed that using backswept blades can completely eliminate the pressure-to-suction side jet/wake flow effect. Other geometrical parameters were tested but only a small to moderate influence on the jet/wake flow phenomena was found. Predicted trends compared favorably with experimental results.
Fundamental Analysis of the Secondary Flows and Jet-Wake in a Torque Converter Pump: Part 2 — Flow in a Curved Stationary Passage and Combined Flows
Authors: Flack R. , Brun K.
Published: February 2009

Previously, experimental results for the velocity field in a torque converter pump showed strong jet/wake characteristics including backflows and circulatory secondary flows. Navier-Stokes flow models were developed herein to independently analyze the pump pressure-to-suction side jet/wake flow, the core-to-shell side jet/wake flow, and the secondary flows. Two relatively simple models were employed: (i) a rotating 2-D straight-walled duct and (ii) a 180° flow bend. Parametric studies were undertaken to evaluate the effect that operating conditions and geometry had on the characteristics. Using the modified equations for the generation of streamwise vorticity and the results from the two-dimensional jet/wake model for the normal and binormal vorticity components, trends for the secondary flows in the torque converter pump were predicted. Predicted secondary flows in the torque converter pump circulated in the counter-clockwise direction (positive streamwise vorticity) in the pump mid-plane and in the clockwise direction (negative streamwise vorticity) in the pump exit plane. These trends agreed with experimental observations. Both the Reynolds number and the modified Rossby number were seen to have a significant influence on the streamwise vorticity and, thus, on the magnitude of the secondary flow velocities. The pump mid-plane counter-clockwise secondary flow circulation was primarily caused by the interaction of the pressure-to-suction side jet/wake non-uniform flow (and the associated normal vorticity component) with the high radial/axial flow turning angle the flow underwent while passing through blade passage. Similarly, the pump exit plane clockwise secondary flow circulation was caused by the core-to-shell side jet/wake non-uniform flow (and the associated binormal vorticity component) being rotated about a fixed centerline (pump shaft). Thus, the pump streamwise vorticity, which was responsible for the generation circulatory secondary flows, was directly related to the pump jet/wake phenomena.
Propeller Cavitation Breakdown Analysis
Authors: Lindau Jules W. , Medvitz Richard B. , Boger David A. , Kunz Robert F.
Published: February 2009

A Reynolds-Averaged Navier-Stokes computational model of homogeneous multiphase flow is presented. Cavitation driven thrust and torque breakdown over a wide range of advance ratios is modeled for an open propeller. Computational results are presented as a form of validation against water tunnel measured thrust and torque breakdown for the propeller. Successful validation of the computational model is achieved. Additional observations are made with regards to cavity size and shape as well as cavitation breakdown behavior.
Generalized Numerical Framework for Cavitation in Inducers
Authors: Hosangadi Ashvin , Ahuja Vineet , Ungewitter Ronald J.
Published: February 2009

In this paper we present a capability to predict pump performance in cavitating flow regimes. Simulations of cavitating flowfields in a single-stage inducer type pump have been carried out. The pump used in this paper is the Simplex inducer geometry that has been extensively tested at NASA Marshall. We follow our turbomachinery simulations up with an extension of our cavitation model to cryogenic flow regimes, where temperature effects begin to play a significant role. Our framework encompasses an acoustically accurate, compressible multiphase model that has been previously validated. The model is implemented within a multi-element unstructured framework that permits efficient grids with locally high resolution near the cavitating zones and in the tip gap region. The pump simulations were performed at a fixed flow rate with different Net Suction Specific Speeds (NSS). The computational analysis indicates a strong correlation between performance loss and the extent of cavitation blockage, and accurately identifies the critical NSS number where breakdown occurs. Predictions of head loss compare well with experimental data. The cryogenic simulations were performed with liquid nitrogen flowing over a cylindrical headform. These simulations capture the essential features of cryogenic cavities such as saturation pressure depression close to the leading edge, and frothy nature of cavitating zones.
Experimental and Numerical Study of Cavitation Breakdown in a Centrifugal Pump
Authors: Nohmi Motohiko , Goto Akira , Iga Yuka , Ikohagi Toshiaki
Published: February 2009

A low specific speed centrifugal pump was constructed to measure cavitation flow characteristics. Pressure distribution over blade surfaces and wall static pressure were measured dynamically and cavitation behavior were photographed by using high speed video and a digital camera. Cavitation flow inside the impeller was computed by commercial CFD code CFX-TASCflow. Head drop characteristics were measured in detail and compared to CFD results. In the case of the best efficiency point flow, bubble cavitation increases along the suction side while decreasing NPSH. When bubble cavitation reaches the throat, another cavity appears on pressure side and the head breakdown occurs steeply. At the high flow rate, cavitation bubbles appear incipiently at the throat on pressure side and head drops gradually. At best efficiency point flow, cavitation phenomena are well captured by CFD.
Acoustic and Hydrodynamic Response of an Annular Cascade to Inflow Disturbances in Swirling Flows
Authors: Elhadidi Basman , Atassi Hafiz M.
Published: February 2009

A model is developed for the interaction of high frequency inflow disturbances with an annular cascade in swirling flows. The computational domain is decomposed into inner and outer subdomains. The outer subdomain scales with the radius of the duct R and the high frequency approximation is used to simplify the governing equations. The inner subdomain scales with the blade chord c << R, and the mean flow variation due to the blade geometry has significant effects on the solution. The numerical results show that for swirling mean flows, as the rotor-stator spacing increases the unsteady blade pressure and the level of acoustic radiation are first reduced. However, further increasing the spacing to more than 2–3 chord lengths produces no significant change. The spanwise variation of the swirl angle (blade twist) has significant effects on the spanwise unsteady lift distribution and propagating acoustic pressure. Spanwise modulation of the incident gust reduces the unsteady lift considerably.
Predicting Skin Friction for Turbulent Flow Over Randomly-Rough Surfaces Using the Discrete-Element Method: Part I — Surface Characterization
Authors: McClain Stephen T. , Hodge B. Keith , Bons Jeffrey P.
Published: February 2009

The discrete-element method for predicting skin friction for turbulent flow over rough surfaces considers the drag on the surface to result from the combination of the skin friction on the flat part of the surface and the drag on the individual roughness elements that protrude into the boundary layer. To adequately analyze flow over a randomly-rough surface using the discrete-element method, the blockage fraction and the roughness element cross-section area distributions as a function of height must be measured. Taylor, in 1983, proposed a method for evaluating the blockage fraction and cross-sectional areas distributions, assuming circular cross sections, using two-dimensional profilometer traces. With the advent of three-dimensional profilometery, the geometry of a randomly-rough surface can be completely characterized. Two randomly-rough surfaces found on high-hour gas-turbine blades were characterized using a Taylor-Hobson Form Talysurf Series 2 profilometer. A method for using the three-dimensional profilometer output to determine the geometry input required in the discrete-element method for randomly-rough surfaces is presented in this paper, Part 1. Part 2 extends the validation of the discrete-element roughness method to closely-packed, randomly-rough surfaces. The procedure for handling randomly-rough surfaces is described, and the characterizations for the surfaces used to validate the discrete element model in Part 2 are presented.
Reconsideration of the Fan Scaling Laws: Part I — Theory
Authors: Sardar Asad M. , George William K.
Published: February 2009

Generalized Fan Scaling Laws (GSFL) are derived for the scaling of fan performance. These follow from first principles using the Navier-Stokes equations appropriate to rotating and swirling flows. Not surprisingly, both Strouhal and Reynolds number similarity must be maintained. Thus for a geometrically similar family of fans, dynamic similarity is only possible if ΩD/U = constandUD/ν = const. If the second relation is solved for U and substituted into the first, it follows that full dynamic similarity is possible only if ΩD2/ν = const. This can be contrasted with the classical fan laws (CFSL) which for the same flow rate coefficient would imply that Q/ΩD3 (or U/ΩD) = const, implying that both fan size ratio and fan speed ratio are independent fan scaling parameters. Clearly for dynamic similarity to be maintained, the velocity and fan speed can not be varied independently (i.e. fan size and fan speed are not independent scaling parameters), contrary to the implications of the classical fan scaling laws. Further implications of the differences between the classical and generalized scaling laws for fan performance testing and design will be explored. Also several examples will be given in Part II as to how the generalized scaling laws can be applied in design practice.
The Design of a Radial Turbine for Microgasturbine Applications
Authors: Cravero Carlo , Marini Martino , Satta Antonio
Published: February 2009

An automatic software procedure, previously developed by the authors, is used for the design of a radial inflow turbine for microgasturbine applications. The procedure is formed by algorithms of different complexity levels ranging from the meanline one-dimensional design tool to the fully three-dimensional Navier-Stokes based analysis. Each code gives complementary information to the designer. The codes have been written and developed by the authors at DIMSET. The present application demonstrate the use of the above procedure and allows for a critical analysis of the tools involved.
An Undergraduate Fluid Mechanics Course for Future Army Officers
Authors: Reed Shad A. , Van Poppel Bret P. , Arnas A. O¨zer
Published: February 2009

The mission of the United States Military Academy (USMA) is “To educate, train, and inspire the Corps of Cadets so that each graduate is a commissioned leader of character committed to the values of Duty, Honor, Country; professional growth throughout a career as an officer in the United States Army; and a lifetime of selfless service to the nation.” [1] The academic program at the USMA is designed to meet the intellectual demands of this mission statement. One very unique aspect of this academic program is the requirement that each cadet take a minimum of five engineering courses regardless of his or her major or field of study. Because of this requirement, nearly one-third of every graduating class take Fluid Mechanics. The Fluid Mechanics course taught in the USMA’s Department of Civil and Mechanical Engineering differs from others throughout the country for two primary reasons: 1) Within every class there is a mixture of cadets majoring in engineering and those who are in other majors, such as languages, history, and political science, 2) Each cadet will be commissioned as a Second Lieutenant in the United States Army immediately upon graduation, [2] and [3]. In this course cadets learn about fluid mechanics and apply the principles to solve problems, with emphasis placed upon those topics of interest to the Army and Army systems that they will encounter as future officers. The course objectives are accomplished through four principal methods. The first is through engaging, interactive classroom instruction. Cadets learn about the principles of fluid statics, conservation laws, dimensional analysis, and external flow; specialized topics, such as compressible flow and open channel flow have also been integrated. The second method is through hands-on laboratory exercises. Pipe friction, wind tunnels, and smoke tunnels are examples of laboratories in which cadets take experimental measurements, analyze data, and reinforce concepts from the classroom. The third method occurs in the “Design of an Experiment” exercise. In groups, cadets design their own experiment—based upon an Army parachutist—that will predict the coefficient of drag of a parachute system. The fourth method is a hands-on design project that culminates in a competition. In teams, cadets build a water turbine to lift a weight on a pulley from ground level to a designated height. Competition categories include the torque competition, in which maximum lifted weight determines the winner and the power competition judged by minimum time to lift a designated weight. This project, implemented within the curriculum prior to formal instruction on the design process, requires cadets to develop their own design process through analysis, experimentation, and trial and error.
Numerical Simulation of Jet Breakup Using Particle Method
Authors: Koshizuka S. , Shibata K. , Oka Y.
Published: February 2009

Numerical analysis of jet breakup is carried out using Moving Particle Semi-implicit (MPS) method in x-y two dimensions. In the MPS method, particle interaction models are prepared for differential operators and the governing equations are discretized without grids. Surface tension is also modeled as particle interactions. Effects of the Weber number and the Froude number on the jet breakup length agree well with experimental data.
Selection of an Appropriate Turbulence Model to Evaluate Performances of Novel Fuel Geometries for the “IRIS” Reactor
Authors: Baglietto Emilio , Ninokata Hisashi
Published: February 2009

A comparative study of different turbulence models is presented to select the most appropriate one for the evaluation of thermo-hydraulic performances of innovative core designs. The standard k-ε and different, linear and non linear, low Reynolds k-ε models are applied to fully developed flow in a triangular lattice rod bundle. Shear stresses and velocity distributions are evaluated using the commercial code Star-CD. The relative performance of the models is assessed indicating different predictions between linear and non linear turbulence closures. The results show that the capability of non linear models to account for anisotropic effects leads to better performances in modeling turbulent flow in tight lattice rod bundles. This capability is clearly shown by the existence of a secondary flow field in the plane normal to the flow direction.
Effect of Damkohler Number and Non-Unity Lewis Number on a Laminar Diffusion Flame
Authors: Ramadan Bassem H.
Published: February 2009

The effect of the Damkohler number (Da) and non-unity Lewis number on a two-dimensional, steady, laminar diffusion flame anchored by a dividing plate in a rectangular channel was considered. The governing equations were solved numerically, using the SIMPLE and ADI schemes. The results for non-unity Lewis number were compared with those for a unity Lewis number, and Da a was also varied in order to determine their effect on the flame structure. The results show that an increase in the Da causes the flame to exist closer to the trailing edge of the divider and to increase the reactivity. A non-unity Lewis number creates a non-symmetrical flame by forcing the flame to exist on the fuel side.
Simulation of Vortex Instability in a Pipe Trifurcation
Authors: Ruprecht Albert , Neubauer Ralf , Helmrich Thomas
Published: February 2009

The vortex instability in a spherical pipe trifurcation is investigated by applying a Very Large Eddy Simulation (VLES). For this approach an new adaptive turbulence model based on an extended version of the k-ε model is used. Applying a classical Reynolds-averaged Navier-Stokes-Simulation with the standard k-ε model is not able to forecast the vortex instability. However the prescribed VLES method is capable to predict this flow phenomenon. The obtained results show a reasonable agreement with measurements in a model test.
Two-Phase Flow Analysis With the Two-Fluid MPS Method: II — Analysis of the Bulk Subcooled Boiling
Authors: Shirakawa Noriyuki , Yamamoto Yuichi , Horie Hideki
Published: February 2009

The most important element in any effective subcooled boiling model is to be able to accurately calculate where significant void fraction appears, that is, the location of the void departure point. The location of the initial void ejection into the subcooled liquid core can be determined fairly well experimentally and conventionally is given in terms of a critical subcooling. We investigated the relation between Stanton and Pe´clet numbers in the calculated results with TF_MPS method, varying the inlet water velocity to change Pe´clet number.
Application of the Vector Finite Element Method to 3D Magnetohydrodynamics
Authors: Matsumoto Masaaki , Tanahashi Takahiko
Published: February 2009

It is well known that the vector finite element method is one of the powerful tools for solving electromagnetic problems. The vector shape functions that are consist of the facet and the edge vector shape functions have a lot of characteristics. One of them is automatic conservation of the magnetic flux density in analyzing the Induction equations without iterative correction. In the present paper the vector finite element method is applied to the problems of magnetohydrodynamics. Three-dimensional natural convection in a cavity under a constant magnetic field is analyzed numerically using the GSMAC finite element method for flow field and temperature field and the vector finite element method for the Induction equations. The computational results are good agreement with those obtained using B method that is one of the iterative methods to satisfy the solenoidal condition for the magnetic flux density of the Induction equations.
Reliability Analysis of CFD Solution Using Sensitivity Theory
Authors: Tanaka Nobuatsu , Motoyama Yasunori
Published: February 2009

In this study, we present a new numerical method to quantitatively analyze the reliability of numerical models by using the sensitivity theory. If a reference case of typical parameters is once calculated with the method, no additional calculation is required to estimate the results of the other numerical parameters such as more detailed solutions. Furthermore, we can estimate the strict solution from the sensitivity analysis results and can quantitatively evaluate the reliability of the numerical solution by calculating the numerical error.
Development of a Virtual Two-Dimensional Wind Tunnel Using a Vortex Element Method
Authors: Shono Hideaki , Ojima Akira , Kamemoto Kyoji
Published: February 2009

This paper describes the work of development of a virtual two-dimensional wind tunnel using a vortex element method carried by the authors group, explaining the mathematical basis of the method and structure of the virtual wind tunnel. Following the development of an advanced vortex element method, the authors proceeded to development of a virtual wind tunnel, which provides a useful tool for researchers, designers and teaching staffs in the field of fluid dynamics. As the first step of the development, construction of a two-dimensional wind tunnel has been studied. The 2-D wind tunnel works on a PC, and it has such attractive features that once a user prepares a set of numerical data of two-dimensional bodies, he or she can begin immediately unsteady calculation of a flow around either an isolated body or multiple bodies in a uniform flow without any grid-generation work. The calculation provides unsteady characteristics of lift and drag coefficients acting on each body and instantaneous flow patters visualized by distribution of vortex elements. In this paper, the numerical procedure of the vortex element method and structure of the virtual wind tunnel are briefly explained. And typical results of two-dimensional and unsteady calculation of flows around bluff bodies will be demonstrated.
Some Experimental Results on Laser Doppler Velocimetry (LDV) and Birefringence (FIB) Studies of Non-Newtonian Fluids Flow Through Rectangular Channels
Authors: Gampert Bernhard , Braemer Thomas , Eich Thomas , Dietmann Torsten
Published: February 2009

In the present study, the turbulence behaviour of polymer solutions is investigated using laser-Doppler velocimetry (LDV). At the same time, an attempt is made to determine a possibly occurring extension and orientation of the macromolecules by flow-induced birefringence (FIB). Flow-dynamic and rheo-optical experiments are presented which were performed in a smooth square channel in the area of the fully developed turbulent flow. The turbulent flow properties of aqueous solutions of PAAM and Xanthan Gum were studied. The Reynolds number was 30000. The concentration of the polymer solutions was varied between 300 wppm and 800 wppm for PR2300 and between 30 wppm and 120 wppm in the case of Xanthan Gum. The obtained experimental data indicate a significant dependence of the turbulent flow properties on the molecular structure of the polymers used. Furthermore, the extension and orientation of the macromolecules on the turbulent flow properties was investigated.
Turbulent Flow Around a Wavy Interface Between a Porous Medium and a Clear Domain
Authors: de Lemos Marcelo J. S. , Silva Renato A.
Published: February 2009

Flow over forests and vegetation can be characterized by some sort of porous structure of irregular surface through which a fluid permeates. Also, in engineering systems one can have components that make use of a working fluid flowing over irregular layers of porous material. This paper presents numerical solutions for such hybrid medium, considering here a channel partially filled with a sinusoidal porous layer saturated by a fluid flowing in turbulent regime. One unique set of transport equations is applied to both regions. Effects of Reynolds number, porosity and permeability on mean and turbulence fields are investigated. Results indicate that around the peaks of the sinusoidal layer values of the turbulent kinetic energy are higher.
Effect of Attack Angle Fluctuation Superimposed on the Cross-Flow Oscillation of a Rectangular Cylinder in Uniform Flow
Authors: Koide Mizuyasu , Takahashi Tsutomu , Shirakashi Masataka , Kubo Yuuki , Baranyi La´szlo´
Published: February 2009

The cross-flow oscillation of a rectangular cylinder supported by a cantilever plate-spring system was investigated using a wind tunnel, in order to reveal the effect of attack angle fluctuation superimposed on cross-flow oscillation. Three kinds of support systems were tested in order to give a different phase-shift between attack angle and cylinder displacement. Three rectangular cylinders with the slenderness of 0.5, 1.0 and 2.0 were used to investigate effect of attack angle both on the Ka´rma´n vortex excitation and the galloping. The effect of attack angle fluctuation on oscillation behavior markedly differed among the three rectangular cylinders of different slenderness. When the slenderness was 0.5, attack angle fluctuation had no influence on the oscillation behavior of the cylinder. When the slenderness was 1.0 and 2.0, the oscillation behavior was quite different compared with pure cross-flow oscillation, depending on the support system and slenderness.
Numerical Investigation on Unstable Oscillations of Two Circular Cylinders in Tandem Arrangement
Authors: Itoh Yoshiaki , Himeno Ryutaro
Published: February 2009

Three-dimensional simulations of incompressible and viscous flow around tandem circular cylinders at Re = 20000 in unstable oscillations can be carried out by means of finite difference method without any turbulence model. The numerical response behaviors are in good agreement with the previous experimental ones. The mechanism of negative damping force in vortex-induced oscillations and wake-galloping is investigated.
Complex Pressure Fluctuations and Vibrations in a Pump-Water Tunnel System
Authors: Guo Shijie , Maruta Yoshiyuki , Okamoto Hidenobu , Kanno Hideki , Sato Kiyonori
Published: February 2009

This paper reports on the complex phenomena of pressure fluctuations and vibrations in a large-capacity drainage pump station. Significant pressure fluctuations were observed in suction water tunnels when an axial flow pump was operated without an actual head at some blade angles. To identify the causes, investigations were done by measuring acoustic natural frequencies and pressure fluctuations in the tunnels, lateral and torsional vibrations of the pump shaft, and pressure fluctuations of the oil in the hydraulic system to control the blade angle. The measurements were taken for different blade angles, rotating speeds, as well as acoustic natural frequencies. The natural frequency was changed by inserting air into the suction tunnels with a compressor and by setting air bags. The results showed that acoustic resonance occurred in the tunnels, but it was not a simple resonance. The dominant frequency, which was neither the blade passing frequency nor its higher harmonics, depended on rotating speed in the reverse way: it decreased when rotating speed increased, and vice versa. Pressure fluctuations in the water tunnels and lateral/torsional vibrations of the pump shaft had a strong relationship. However, they had different dominant frequencies and occurred at different blade angles. Several measurements were made in different seasons and it was found that the phenomena were season-dependent (dependent on quality of water). The causes are discussed. It is believed that the excitation source was vortex shedding from the blades, which locked into the acoustic resonance in the water tunnels via vibration of the blades.