bluuebunny/crossref_metadata_2025 huggingface dataset:
Echo-PIV Measurement Around the Pump System in the Nuclear Reactor
Authors: Tu Xin-Cheng , Cha Jae-Eun , Kim Hyoung-Bum
Published: June 2012

Echo-PIV system was applied to measure the velocity fields of a pump system inside the nuclear reactor model. The scale-downed model of pump system driven by a motor was built for this study. 2D instantaneous velocity vector fields of the downstream region of impeller were obtained. The flow rate was calculated and compared with the result from the flow meter. From this study, the feasibility of echo-PIV for studying the opaque flow in the fluid machinery was shown.
Turbulent Free-Surface Flow Behind a Surface-Piercing Body: Towed PIV Measurements
Authors: Seo Jeong Hwa , Seol Dong Myung , Rhee Shin Hyung
Published: June 2012

Detailed information on the free-surface wave in the turbulent wake of a surface-piercing body is important in various fields of naval architecture and ocean engineering such as designing ship hulls and floating structures. In the present study, a towed underwater particle image velocimetry (PIV) system was used to investigate the free-surface wave effects on the turbulent wake of a simple surface-piercing body. The selected test model was a cylindrical geometry formed by extruding the Wigley hull’s waterplane shape in the vertical direction. The towing speed of the model was set to Froude numbers of 0.2 and 0.4, which represent typical speeds of commercial ships and combatants, respectively. The corresponding Reynolds numbers were 0.541 million and 1.08 million, respectively. Due to the constraints of the two-dimensional PIV system used for the present study, the velocity field measurements were done separately for the vertical and horizontal planes. Using the measured data at several different locations, it was possible to identify the free-surface wave effects on the turbulent wake in terms of the mean velocity components and turbulence quantities. In order to provide the accuracy level of the data, uncertainty assessment was done following the International Towing Tank Conference standard procedure.
Dissolved Oxygen Concentration Field Measurement in Microfluidics Using PtOEP/PS Film Sensor
Authors: Yi Seung Jae , Song Dae Hun , Kim Kyung Chun
Published: June 2012

A planar optode system based on an oxygen quenchable luminophore platinum (II) octaethyporphrin (PtOEP) bound with thin polystyrene (PS) film and UV light-emitting diodes (UV-LEDs) was developed to measure the dissolved oxygen (DO) concentration field in microscale water flows. An intensity-based method adopting a pixel-to-pixel in situ calibration technique was used to visualize DO concentration fields in a Y-shaped microchannel. The achievable spatial resolution of the acquired concentration map could be as high as 2.94 μm. The diffusion process of DO through the interface between two parallel water flows having different DO concentrations was quantitatively analyzed. We found that the thickness of the concentration gradient of DO increased as the Reynolds number decreased. The ratio of diffusion length scales coincided with the ratio of inner scales of viscous shear layers in the microchannel for two different Reynolds numbers.
Stochastic Large Eddy Simulation of Bluff-Body Two-Way-Coupled Gas-Particle Turbulent Flow
Authors: Berrouk Abdallah Sofiane , Laurence Dominique
Published: June 2012

With the steady increase in computing power, there have been numerous efforts to numerically quantify turbulence modulation by inertial particles. However, highly resolving the flow around thousands to millions of particles to get an accurate particle/turbulence interaction has been prohibited by the number of grid points required. Thus, physical models have been developed and “plugged” to well-resolved numerical simulations to render prediction of turbulence modulation tractable. In this work, flow turbulence modulation by dispersed solid particles in a bluff body was studied using two-way-coupled stochastic large eddy simulation. Point-force scheme was used to model the inertial particle back effects on the fluid motion. The fluid velocity field seen by inertial particles was stochastically constructed based on the filtered flow field obtained from well resolved large eddy simulations. For that purpose a Langevin-type stochastic diffusion process was used with the necessary modifications to account for particle inertia, cross-trajectory effects and the two-way coupling. The numerical results regarding mean and turbulence statistics for the fluid phase show a very good agreement with the experimental findings for both low and high mass loadings (22% and 110% respectively). This numerical investigation demonstrates also the ability of the stochastic-LES-particle approach to predict turbulence modification by inertial particles.
Influence of Fluidizing Velocity on Fluidized Powder Conveying in a Horizontal Rectangular Channel
Authors: Ogata Koichiro , Furukawa Tomoya , Yamamoto Yusuke
Published: June 2012

This study experimentally investigated the high dense pneumatic conveying of glass beads in a horizontal rectangular channel using the fluidizing air. The powder used belongs to Geldart A particle, where the mean diameter is 53 μm, the particle density is 2523kg/m3 and the minimum fluidizing velocity is 4.329mm/s. The fluidized powder conveying system consists of a powder supply hopper, a horizontal rectangular channel at the side of hopper and a receiving tank. The powder was fluidized by air through the porous membrane at the bottom of hopper and horizontal channel. Then, this system could be transported the fluidized powder toward the horizontal direction. In this study, the mass of transported powder, the bed height of powder in a hopper and the supply air pressure were measured when the fluidizing velocities at the bottom of hopper and horizontal channel were changed. The mass of transported powder with the fluidizing air to the bottom of hopper multiplied rapidly when the fluidizing velocity at the bottom of horizontal channel was larger than the minimum fluidizing velocity. Therefore, the fluidizing air at the bottom of hopper and horizontal channel was important to obtain smooth powder conveying on this system. Also, the mass flow rate of powder and the solid loading ratio were estimated from the mass of transported powder against the elapsed time. As the result, the solid loading ratio has taken a one peak when the fluidizing velocity at the bottom of channel was larger than the minimum fluidizing velocity. It was found from the analyzed solid loading ratio that the high dense powder conveying was possible in this system.
Motion and Temperature of Individual Particles in Two-Dimensional Fluidized Bed With Heat Transfer
Authors: Miyauchi Takuya , Oh Satoshi , Tsuji Takuya , Tanaka Toshitsugu
Published: June 2012

Fluidized beds are widely used in industrial processes concerned with heat transfer such as combustion, gasification, catalytic reaction and calcination. In recent years, numerical simulation models that predict the heat transfer phenomena in fluidized bed in the framework of DEM-CFD coupling simulation are developed. The heat transfer in fluidized beds is conducted by several mechanisms and its behavior is extremely complex. In order to improve these numerical models, it is important to know the relation between the convective and diffusive motion of particles and heat transfers in the particle-level. In the present study, a measurement technique based on the coupling between particle tracking velocimetry (PTV) and infrared thermography (IT) measurements is proposed. By using the technique, the motion and the temperature of individual particles and its relations with the characteristic flow structures formed in fluidized beds can be investigated simultaneously without disturbing the flow field. After careful preparations, the technique is applied to a two-dimensional gas-fluidized bed under a spouting condition and the motion and the temperature of individual particles largely-influenced by the bubble occurrences are clearly observed. The relations between convective and diffusive behaviors of individual particles and heat transfer in the bed are studied in detail.
Effects of Rough Wall in Fully Developed Turbulent Pipe Flow
Authors: Win Aung Thuyein , Mochizuki Shinsuke , Kameda Takatsugu
Published: June 2012

Hot wire measurement is carried in fully developed turbulent pipe flow which introducing the rough wall sections (containing d- and k-type roughness alternatively) and emphasis on the statistical properties of turbulence for each flows. Sufficient pipe length is provided to ensure for fully recovery after disturbed by rough wall. On comparison, the major differences between d- and k-type rough wall effect could be found in early response region (x/D = 0.1 to 4). The violent ejection from the k-type roughness is found to the large effect to the main flow which turns into larger additional turbulent energy production. The changing of wall friction could increase the local shear stress which leads to the formation of stress bore but depends on the amount of changes. This stress bore is found to propagate from the vicinity of the wall to the pipe center which does not depend on type or length of roughness. The effectiveness of rough wall can also be found in the power spectra of streamwise component. The energy containing region agrees to both undisturbed and disturbed flow but shifting in power spectra appears which primarily depends on strength of disturbances.
Effect of DBD Plasma Jet on the Flow Around a Circular Cylinder
Authors: Kozato Yasuaki , Kikuchi Satoshi , Imao Shigeki
Published: June 2012

This study analyzes the flow around a circular cylinder when a dielectric barrier discharge (DBD) plasma actuator is mounted on the cylinder surface. The experiments are mainly performed at Re = 26500. Flow visualization, surface pressures, and wake velocity measurements are performed for the on and off modes of the plasma (pulse modulated drive). The results indicate that the wake expansion and the length of the cavity region significantly change depending on the actuator location, duty ratio and modulation frequency. When the actuator is located close to the separation point and is driven at the Karman vortex shedding frequency (St = 0.19) with the symmetric actuation mode or at St = 0.38 with the asymmetric actuation mode, the vortex shedding is amplified and the surface pressure behind the cylinder decreases; consequently, the pressure drag increases. On the other hand, at a higher modulation frequency (St ≧1), the vortex shedding process is weakened and the wake turbulence is suppressed; consequently, the drag is reduced to 80% of the non-excited case.
Dependence of Ice Thickness on the Performance of Medicated Water Electrolysis Apparatus
Authors: Lee Sang-Jun , Kim Youn-Jea
Published: June 2012

Medicated water electrolysis apparatus, which electrolyzes water into acidic water and alkaline water, was in the spotlight as the effect of alkaline water was became known. It is known to have a positive effect for health as removing active oxygen in the human’s body and promoting digestion. But, the customers could not get their desired water temperature due to the fact that these apparatuses are directly connected with water pipe. So, the cooling system to control the temperature of the alkaline water was developed. One of the typical way is to store water in water tank and control its temperature. But, in this way, stored water can be polluted by impurities entering from outside. As the protection for this pollution, the cooling system based on indirect heat exchange method through phase change between water and ice was developed. In this study, we have calculated the efficiency of the cooling system with phase change by experiment and commercial CFD (Computational Fluid Dynamics) code, ANSYS CFX. To consider the effect of latent heat generated by the melting ice, we have simulated two phase numerical analyses by using enthalpy method and found the temperature, velocity, and ice mass distribution, which are required to calculate the efficiency of cooling system. From the results, we obtained the relationship between the cooling efficiency and the thickness of ice, which is created by evaporator located in the cooling system.
Drag Reduction Performance due to Repetitive Laser Pulses on the Blunt Body
Authors: Kim Jae-Hyung , Sasoh Akihiro
Published: June 2012

Supersonic wave drag reduction due to the repetitive laser induced energy deposition is performed experimentally in this study. Laser pulses are irradiated through a convex lens installed in side of the in-draft wind tunnel of Mach 1.94. The maximum frequency and power of the energy deposition is limited up to 50kHz and 400W. In order to estimate the drag reduction, time-averaged drag force is measured by a force balance system and stagnation pressure history is synchronized with corresponding sequential schlieren images captured by high-speed camera. Drag reduction performance is linearly increased up to 21% with input laser power. The power gain which only depends on the pulse energy, is realized by approximately 7. Virtual spike formation induced by highrepetitive energy depositions is remarkably discussed in the visualization results.
Fluid Flow Characteristics Around a Pair of Diamond-Shaped Cylinders in Side-by-Side and Tandem Arrangements
Authors: Torii Shuichi , Ueda Noritugu , Lin Zijie
Published: June 2012

The present study deals with unsteady laminar fluid flow phenomena around a pair of diamond-shaped cylinders in free stream. Emphasis is placed on the effects of the Reynolds number, Re, and the ratio of cylinder separation distance to length of diamond-shaped cylinder, s/d, on the flow patterns in side-by-side and tandem arrangements. The Navier-Stokes equations are discretized using finite difference method to determine the time history of velocity vector in the flow field. The Reynolds numbers, Re, is ranged from 30 to 300 and gap spacing, s/d, is varied from 0.0 to 2.5 for side-by-side and 0.0 to 5.0 for tandem, respectively. The results are compared with the experimental results with the aid of flow visualization method. The study discloses that (i) the generations of Karman vortex streets behind the diamond-shaped cylinders are intensified with an increase in the Reynolds number, (ii) the categorized flow patterns in the wake region of the diamond-shaped islands are affected by s/d, and (iii) the vortex shedding frequency in the wake of diamond-shaped cylinders depends on both the gap spacing and the formation of the vortices.
A Functional Scaling Relationship for Laminar to Turbulent Flow Regimes
Authors: Papadopoulos George
Published: June 2012

A dimensional analysis that is based on the scaling of the two-dimensional Navier-Stokes equations is presented for correlating bulk flow characteristics arising from a variety of initial conditions. The analysis yields a functional relationship between the characteristic variable of the flow region and the Reynolds number for each of the two independent flow regimes. A linear relationship is realized for the laminar regime, while a nonlinear relationship is realized for the turbulent regime. Both relationships incorporate mass-flow profile characteristics to fully capture the effects of initial conditions on the variation of the characteristic variables. The union of these two independent relationships is formed utilizing the concept of flow intermittency to further expand into a generic scaling relationship that incorporates transitional flow effects to fully encompass solutions spanning the laminar to turbulent flow regimes. The results of the analysis are discussed within the context of several flow phenomena (e.g. pipe flow, jet flow & separated flow) resulting from various initial and boundary conditions.
Three-Dimensional Vortex Structure in the Wake of an Oscillating Discoid Airfoil
Authors: Nakagawa K. , Hasegawa H.
Published: June 2012

Flow fields around an oscillating airfoil at the low Reynolds number region are extremely unsteady because the change direction of leading edge produces unsteady vortex motions. Studies of unsteady propulsion system of birds, insects, and fish are few and inconclusive. It has been noted that the unsteady fluid force plays an important role in biological flight. To evaluate the force correctly, it is necessary to know the unsteady properties determined from the vortex dynamics. The actual motion of a hand in swimming is obviously unsteady, and time-dependent fluid forces must be considered, because a quasi-steady-state approach towards predicting the fluid forces acting on a hand under unsteady conditions yielded errors. The three-dimensionality and the unsteady effect of a hand must be important to the estimation of the fluid forces acting on a swimmer’s hand. The purpose of this study is to investigate the relationship between unsteady fluid forces and vortex structures for a three-dimensional airfoil during the pitch-oscillating motion. Particle image velocimetry (PIV) was used to aid in understanding the flow field in the near field of the airfoil edge for the wind tunnel test. It is confirmed that the unsteady fluid forces were affected by the vortices shed from the airfoil edge during up-stroke in pitching oscillation. There are two peaks in the fluid force during one pitch-oscillating due to the vortex behavior. The vortex behavior was strongly affected by the reduced frequency, and the fluid force acting on the airfoil model increases with increasing the reduced frequency.
3D Structural Imaging of Porous GDL of a Fuel Cell
Authors: Kim Seung-Gon , Lee Sang-Joon
Published: June 2012

Synchrotron X-ray computed tomography was employed to measure the volume variation of gas diffusion layer (GDL) for polymer electrolyte fuel cell (PEFC). The study was conducted using 3D reconstruction (or a 3D rendering software) of orthoslice images. Especially, the temporal variation of structural parameters such as porosity was measured under freeze and thaw cycles. The freezing and thawing cycle were generated using a CRYO-system and an external light source alternatively. As a result, the structural parameters such varied significantly between the successive freeze/thaw cycles and irreversible change was also observed.
Numerical Investigation of Turbulent Flow in a T-Junction
Authors: Kim Jungwoo , Jeong Jae Jun
Published: June 2012

In the present study, a large eddy simulation, at conditions of experiments by Vattenfall, was performed in order to investigate the phenomenon of turbulent mixing affecting the thermal fatigue in a T-junction. Mean velocity and turbulence intensity from the simulation are compared against those measured in the Vattenfall experiment, and the observed agreement is good. Based on the numerical results from the LES, the energy spectra were examined because they have been regarded as being of primary importance in the study on the thermal fatigue according to previous studies. The energy spectra showed the dominant frequency of around St = 0.5 agrees with the value reported in experiments. Also, near the T-junction the frequency characteristics are shown to depend on the azimuthal angle. However, this dependency of the frequency characteristics on the azimuthal angle is disappeared in downstream because the turbulence in the T-junction eventually approaches the fully-developed turbulent pipe flow. On the other hand, although not shown here, the dominant frequency near the wall is different from that reported at the centerline (St∼1), meaning that the thermal fatigue may not result from the wake structure, and is affected by the vertical structures existing near the wall. This result is consistent with one stated by [1] that the frequency characteristics are closely associated with arched vortices.
Evaluation of Entrance Blockage of Inner Channel in Dual-Cooled Annular Nuclear Fuel
Authors: Shin C. H. , Chun T. H. , Oh D. S. , In W. K.
Published: June 2012

The Korea Atomic Energy Research Institute (KAERI) has been developing a dual-cooled annular fuel for the power uprate of 20% in an optimized pressurized water reactor (PWR) in Korea, OPR1000. The dual-cooled annular fuel is configured to allow the coolant flow through the inner channel as well as the outer channel. Several thermal-hydraulic issues exist for the application of the dual-cooled annular fuel to OPR1000. One of the key issues is the hypothetical event of inner channel blockage because the inner channel is an isolated flow channel without the coolant mixing between the neighboring flow channels. The inner channel blockage could cause the Departure from Nucleate Boiling (DNB) in the inner channel that eventually results in a fuel failure. A long lower end cap for the annular fuel was invented to provide flow holes by perforating the side surface of the end cap body. The side holes in the lower end cap are expected to supply a minimum coolant in the inner channel in order to prevent the DNB occurrence in the event of partial or even complete blockage of the inner channel entrance. But due to very unusual shape of the lower end cap, it is difficult to estimate the flow resistance of the side flow holes using empirical equations available in the open literatures. Experimental and computational fluid dynamics (CFD) study were performed to investigate the bypass flow through the side holes of the end cap in the case of complete entrance blockage of the inner channel. The form loss coefficient in the side holes was also estimated by using the pressure drop along the bypass flow path.
Numerical Simulations of Thermal-Mixing in T-Junction Piping System Using Large Eddy Simulation Approach
Authors: Tanaka Masaaki , Murakami Satoshi , Miyake Yasuhiro , Ohshima Hiroyuki
Published: June 2012

Thermal striping phenomenon caused by mixing of fluids at different temperatures is one of the most important issues in design of fast breeder reactors (FBRs), because it may cause high-cycle thermal fatigue in structure. Authors have been developed a numerical simulation code MUGTHES to investigate thermal striping phenomena in FBRs and to give transient data of temperature in the fluid and the structure for an evaluation method of the high-cycle thermal fatigue problem. MUGTHES employs the boundary fitted coordinate (BFC) system and deals with three-dimensional transient thermal-hydraulic problems by using the large eddy simulation (LES) approach and artificial wall conditions derived by a wall function law. In this paper, numerical simulations of MUGTHES in T-junction piping system appear. Boundary conditions for the simulations are chosen from an existing water experiment in JAEA, named as WATLON experiment. The wall jet condition in which the branch pipe jet flows away touching main pipe wall on the branch pipe side and the impinging jet condition in which the branch pipe jet impinges on the wall surface on the opposite side of the branch pipe are selected, because significant temperature fluctuation may be induced on the wall surfaces by the branch pipe jet behavior. Numerical results by MUGTHES are validated by comparisons with measured velocity and temperature profiles. Three dimensional large-scale eddies are identified behind of the branch pipe jet in the wall jet case and in front of the branch pipe jet in the impinging jet case, respectively. Through these numerical simulations in the T-pipe, generation mechanism of temperature fluctuation in thermal mixing process is revealed in the relation with the large-scale eddy motion.
Direct Simulation of Dense Suspensions of Non-Spherical Particles
Authors: Shardt Orest , Derksen Jos
Published: June 2012

We describe the direct simulation of high-solids-fraction suspensions of non-spherical rigid particles that are slightly denser than the fluid. The lattice-Boltzmann method is used to solve the flow of the interstitial Newtonian fluid, and the immersed boundary method is used to enforce a no-slip boundary condition at the surface of each particle. The surface points for the immersed boundary method are also employed for collision handling by applying repulsive forces between nearby surface points. Due to the finite number of these points, the method simulates rough surface collisions. We also discuss methods for integrating the equations of particle motion at low density ratios and propose a method with improved accuracy. Rigid particles shaped like red blood cells were simulated. Simulations of a single particle showed that the particle settles in its original orientation when the Reynolds number is low (1.2) but flips to a higher drag orientation when the Reynolds number is higher (7.3). A simulation with a 45% solids volume fraction and a low solid over fluid density ratio showed the possibility of simulating blood as it is found in the body. A simulation at a lower solids volume fraction (35%) was used to compare the results with the erythrocyte sedimentation rate (ESR), a common blood test. The sedimentation rate was estimated as 0.2 mm/hr, which is an order of magnitude lower than a typical ESR of about 6 mm/hr for a healthy adult. The most likely reasons for the discrepancy are the omission of agglomeration-inducing inter-cellular forces from the simulations and the treatment of the red blood cells as rigid particles.
Application of the Integrated System of Laser-Induced Heating and the Microfluidic Device for Selecting Cells Treated With Drugs
Authors: Hung Min-Sheng , Lin Chao-Jie
Published: June 2012

The aim of this study is to develop a microfluidic device capable of trapping individual cells that have been treated with drugs, and to analyze and compare the cell capturing efficiency of the series-loop microchannels with the parallel-loop microchannels. The microfluidic device utilized in this project consists of PDMS. Each set of microchannels is composed of a main flow channel and several branch channels with capturing regions. The results indicate that the solution flows with greater resistance in the series-loop microchannels, thereby causing the entrance in the far end of the capturing zones to catch no cell. The cell capturing efficiency of the series-loop microchannels is only about 14% in this study. With regard to the flow resistance, it is greatly reduced in the parallel-loop microchannels; capturing efficiency is thus promoted. Last, due to the difference in flow rates, the cells are inclined to flow towards the branch channels rather than the main channel, thereby promoting successful trapping of cells. Additionally, incubating the cells treated with drugs for 4 hours in microfluidics device consequently causes mitotic arrest due to drug action among 70% of the cells in seven capturing zones. When the laser radiates at the ink in laser heating zone, as an output power of 0.6 W is yielded, the bubbleis formed and the cell is thereby pushed away from the capturing zone.
Fast and Accurate Simulation of Strongly Coupled Fluid-Structure Interaction Using a Direct Forcing Immersed Boundary Method
Authors: Yang Jianming , Stern Frederick
Published: June 2012

In this paper, a direct forcing immersed boundary method is presented for the simple and efficient simulation of strongly coupled fluid-structure interaction. The previous formulation by Yang and Balaras (An embedded-boundary formulation for large-eddy simulation of turbulent flows interacting with moving boundaries, J. Comput. Phys. 215 (2006) 12–40) is greatly simplified without sacrificing the overall accuracy. The fluid-structure coupling scheme of Yang et al. (A strongly-coupled, embedded-boundary method for fluid-structure interactions of elastically mounted rigid bodies, J. Fluids Struct. 24 (2008) 167–182) is also significantly expedited without altering the strong coupling property. Several cases are examined and compared with the results from the previous formulations to demonstrate the accuracy, simplicity and efficiency of the new method.
An Improved Penalty Immersed Boundary Method for Fluid-Flexible Body Interaction
Authors: Huang Wei-Xi , Chang Cheong Bong , Sung Hyung Jin
Published: June 2012

An improved penalty immersed boundary (pIB) method has been proposed for simulation of fluid-flexible body interaction problems. In the proposed method, the fluid motion is defined on the Eulerian domain, while the solid motion is described by the Lagrangian variables. To account for the interaction, the flexible body is assumed to be composed of two parts: massive material points and massless material points, which are assumed to be linked closely by a stiff spring with damping. The massive material points are subjected to the elastic force of solid deformation but do not interact with the fluid directly, while the massless material points interact with the fluid by moving with the local fluid velocity. The flow solver and the solid solver are coupled in this framework and are developed separately by different methods. The fractional step method is adopted to solve the incompressible fluid motion on a staggered Cartesian grid, while the finite element method is developed to simulate the solid motion using an unstructured triangular mesh. The interaction force is just the restoring force of the stiff spring with damping, and is spread from the Lagrangian coordinates to the Eulerian grids by a smoothed approximation of the Dirac delta function. In the numerical simulations, three-dimensional simulations of fluid-flexible body interaction are carried out, including deformation of a spherical capsule in a linear shear flow. A comparison between the numerical results and the theoretical solutions is presented.
Numerical Simulation of Unsteady Flow Through a Two-Dimensional Channel With a Vocal Cord Model
Authors: Miyauchi Suguru , Omori Takeshi , Takeuchi Shintaro , Kajishima Takeo
Published: June 2012

For the understanding of the phonation mechanism and for the design of an artificial vocal cord, we developed a computational method for the fluid-structure interaction, including the elastic walls and membranes. A robust and efficient method is required to deal with large deformation of biological materials and high frequency vibration. To this end, we apply an immersed boundary method. The flow through a two-dimensional channel including a pair of flexible structures, which is a simplification of a vocal cord, is simulated. The elastic solid is modeled by the St. Venant-Kirchhoff constitutive equation and its motion is simulated by a finite-element method, where the contact of the vocal cord is taken into account by a Lagrange multiplier method. The incompressible fluid flow is computed by a finite-difference method. Then the immersed-boundary method of a body-force type developed by the authors is successfully applied for the fluid-structure interaction. In the present results, the deformation of the structure and the frequency of the pulsating flow are reasonably reproduced. The obtained frequency is within the measured range of the data for a human vocal cord. Also, two velocity peaks are observed when the vocal cord is in the opening and closing phases in each period of the vocal cord vibration, and the velocity of the closing phase is larger than that of the opening phase.
Characteristics of the Scalar Field in a Turbulent Liquid Jet and a Fundamental Study on the Micro Scale Concentration Measurements by the Optical Fiber LIF Method
Authors: Kawaguchi Tatsuya , Sakai Yasuhiko , Nagata Kouji , Terashima Osamu , Takaku Shoichi
Published: June 2012

In this study, the characteristics of the scalar field in an axisymmetric turbulent water jet are investigated experimentally. In the experiments, the axial velocity, the concentration of the dye solution and the temperature of the fluid are measured by the hot-film probe, the fiber sensor and the cold-firm probe, respectively. In particular, the difference of statistics between scalars (concentration and temperature) with the different molecular diffusion coefficients is discussed. The Schmidt number of the diffusing matter is 3,800, and the Prandtl number of temperature is 7. As regarding the mean values, the r.m.s values and distribution of PDF, we cannot find any difference between the concentration field and temperature field. However, in the spectrum, it is found that the temperature spectrum shows the −5/3 law almost in the same range as the velocity spectrum, on the other hand, the concentration spectrum shows the −5/3 law in the wider range than the velocity spectrum. This means that the shape of spectrum depends on the diffusion coefficient. In order to make the higher resolution measurement of concentration, a new optical probe based on the LIF method is designed. This probe consists of the two optical fibers, the tip of which is processed like the shape of a lens. By the effect of lens, the laser beam can be focused on the narrower area in comparison with the past LIF measurements. In the present design, the width of focus of laser beam is set to 0.6 micrometers, and the focal length is set to 7.3mm. It is shown that this probe has the resolution less than the Batchelor scale at x / d ≥30 in the condition of present jet diffusion field (d = 4mm, Re = 20,000). Further, a new system to adjust the position of the optic fiber probe exquisitely is developed.
Wake Vortices in Jets in Cross-Flow
Authors: Milanovic Ivana , Zaman Khairul B. M. Q. , Bencic Tim
Published: June 2012

The objective of the current experimental study is to investigate unsteady wake vortices of jets in cross-flow in order to (1) explore the effect of various excitation techniques, their parametric dependence, and impact on the flow field, and (2) provide detailed flow visualizations for a range of velocity ratios. The jet passed through a nozzle and entered the cross-flow with a turbulent boundary layer. While mechanical perturbation did not result in any significant periodic organization of the wake vortices, the database obtained for the unperturbed flow provided an insight into their possible origin and behavior. The key finding was the shedding of wake vortices from the ‘swell’ at the lee side of the jet. The ‘swell’ delineated a region of the flow at the intersection of the jet efflux boundary layer and the cross-flow boundary layer. Separation events released upright vortices and these peeled strands of vorticity convected, twisted and stretched for a few diameters along the wall while still being attached to the bottom of the ‘swell.’ They extended from the tunnel wall and penetrated the jet core where they appeared to burst. In no case were the wake vortices seen to originate either from the wall boundary layer or the jet shear layer at downstream locations. Increasing the jet-to-cross-flow velocity ratio influenced the slope of the wake vortices relative to the jet. The upper part of the vortical strand for VR < 4 was almost perpendicular to the cross-flow. Higher velocity ratios featured a tilt of the vortex structure toward the jet. This angle was particularly pronounced for VR = 8 and 10, and could be observed at all downstream distances. The average convection velocity of the wake vortices for the given cross-flow and all velocity ratios was estimated to be about 0.8 Ucf.
Development of Flow Behind Three-Dimensional Fractal Structure
Authors: Hiramatsu Toshimasa , Kato Yuuki , Ushijima Tatsuo , Kitoh Osami
Published: June 2012

Flow development of wake behind Sierpinski tetrahedron has been investigated. The Sierpinski tetrahedron is a three dimensional object of which fractal dimension is 2. Blockage ratio of the Sierpinski tetrahedron over cross section of wind tunnel is 100%. It is found that the fractal object can has an ability to generate relatively high Reynolds number based on turbulent intensity and Taylor microscale (Reλ = 155) even with the small scale wind tunnel of the present study.
Numerical Study on the Range Enhancement of a Centrifugal Compressor With a Ring Groove System
Authors: Park ChiYong , Choi YoungSeok , Lee KyoungYong , Yoon JoonYong
Published: June 2012

This paper presents a numerical study of casing treatments on a centrifugal compressor in order to improve stability and the surge margin. High efficiency, a high pressure ratio, and a wide operating range are required for a high-performance centrifugal compressor. A ring groove casing treatment is effective for flow range enhancement in centrifugal compressors. In the present study, compressor performance was analyzed according to the ring groove location and the results were compared with the case without a ring groove. The effect of guide vanes in the ring groove was also investigated. Four more variants of grooves were modeled and simulated using computational fluid dynamics (CFD) in order to optimize the groove location. The numerical analysis was carried out using a commercial code ANSYS-CFX program. The simulation results showed that the ring groove increased the operating range of the compressor. The ring groove with guide vanes improved both the compressor’s performance at low flow rates and improved the compressor’s surge margin.
Coupled Design and Optimization for Runner Blades of a Tubular Turbine Based on the Boundary Vorticity Dynamics Theory
Authors: Li Fengchao , Fan Honggang , Wang Zhengwei , Chen Naixiang
Published: June 2012

In this paper the Boundary Vorticity Dynamics Theory is applied to optimize the runner blade shape of a bulb tubular turbine, based on a three-dimensional coupled design model. The initial spatial runner blades and guide vanes are designed together with the simultaneous equations solved in the flow domain involving them. Since the wake flow behavior of guide vanes influencing the inflow condition of runner blades is taken account of, compared with that on separate design method, the static pressure distribution obtained on coupled model is improved near the inlet of the blades. Thus the effective head becomes higher and the runner’s efficiency rises. To improve the performance on the design point, the boundary vorticity flux (BVF) on the runner blade surfaces is simulated to analyze its effect to the unit output emphatically. The runner blade shape is modified by changing the prescribed distribution of swirl according to the diagnosed position where the flow behavior is defective. The static pressure on optimized runner blades varies indistinctly, which is difficult to estimate the flow behavior. Nevertheless the BVF distribution indicates that near the hub of the pressure surface the negative effect on the output becomes weak, and negative region near the leading edge reduces obviously in area, which results in the further rise of runner’s efficiency. The result shows that the BVF distribution on blade surfaces can more potently reflect the performance of tubular turbines and provide reliable solution for shape optimization.
An Experimental Study on the Clutch-Type Water Pump of Diesel Passenger Vehicle for Reducing Fuel Consumption and CO2 Emission
Authors: Jeong Soo-jin , Kim Woo-seung , Oh Chang-boke , Park Jung-kwon , Lee Ho-kil , Oh Se-doo , Chun Hyung-ho
Published: June 2012

A typical cooling system of an engine relies on a water pump that circulates the coolant through the system. The pump is typically driven by the crankshaft through a mechanical link with engine starting. In order to reduce the friction and warm-up time of an engine, the clutch-type water pump (CWP) was applied in 2.0 liter diesel vehicle. The clutch-type water pump can force cooling water to supply into an engine by the operation of an electromagnetic clutch equipped as the inner part of pump system. The operation of CWP is decided by temperature of cooling water and engine oil. And, the control logic for an optimal operation of the clutch-type water pump was developed and applied in engine and vehicle tests. in this study, the warm-up time was measured with the conventional water pump and clutch-type water pump in engine tests. And the emission and the fuel consumption were evaluated under NEDC mode in vehicle tests. Also, tests were carried out at the various temperature conditions starting the operation of CWP. As the results, the application of CWP can improve the fuel consumption and CO2 reduction by about 3%.
Direct Numerical Simulation of Turbulent Friction Drag Reduction by Traveling Wave-Like Blowing Using Plasma Actuators
Authors: Murai Yasuhito , Fukagata Koji
Published: June 2012

We numerically investigated the effects of friction drag reduction and energy gain by traveling wave-like blowing using plasma actuators arrayed on channel walls. Wall-normal flow is induced by opposed arrangement of plasma actuators. We used Shyy et al.’s model [1] to compute the body force of plasma actuators, which is added to the Navier-Stokes equation. With this model, the body force distribution is simplified as compared to the actual one, which is quite complicated. We perform direct numerical simulation under several parameter sets: the wavenumber, the amplitude, and the phasespeed of body forces. The obtained maximum friction drag reduction rate is 37% as compared to the uncontrolled case. Under the same phase speed and amplitude of body force, the friction drag is found to be reduced more with larger wavenumber. Under the same phase speed and wavenumber, the friction drag reduction is found to be larger with stronger body force. In the drag reducing cases, formation of spanwise vortices leads to reduction of the Reynolds sheer stress near the wall as well as the friction drag. Although net energy saving is acheived in some parameter sets, it is not achieved in most cases. This means that the reduced pumping power is generally smaller than the power input of plasma actuators.
Turbulence in Accelerating Boundary Layers
Authors: Joshi Pranav , Liu Xiaofeng , Katz Joseph
Published: June 2012

In this study we focus on the effect of mean flow acceleration on the near wall structures within turbulent boundary layers. 2D PIV measurements in streamwise-wall normal and streamwise-spanwise planes have been performed upstream of and within a sink flow for inlet Reθ of 6326 and 3071, and at constant acceleration parameters of K = 0.6×10−6 and 1.1×10−6, respectively. Due to the imposed favorable pressure gradient (FPG), the Reynolds stresses normalized by the local freestream velocity decrease over the entire boundary layer. However, when scaled by the inlet freestream velocity, stresses increase close to the wall and decrease in the outer part of the boundary layer. This is caused by the confinement of the structures in the near-wall region in the accelerating flow. The weaker normalized strength of the vortical structures and the substantial negative wall-normal mean velocity in the FPG region are identified as the likely contributors to this trend. Data in the wall parallel planes dissecting the large scale structures shows their signatures in the form of “swirling” patterns and low speed streaks. For the higher Reynolds number flow, the high near-wall ∂U/∂y in the accelerating region decreases the angle of inclination of the large eddies. Consequently, their signature in the x-z plane is weaker and elongated in the streamwise direction. In the FPG region, the small scale structures tend to occur in streamwise aligned groups and almost all of them are observed in the low speed streaks, which are the regions of ejection induced by large eddies. Due to the lower turbulence levels in the outer parts, the high momentum regions, indicating sweep events, contain very few small scale structures. This distinction between the low and high momentum regions is much weaker in the zero pressure gradient (ZPG) area which has high turbulence levels in the outer layer.
Correction of Flow Metering Coefficients Using Two-Dimensional Curve Fitting
Authors: Chun Sejong , Yoon Byung-Ro , Lee Duck-Ki , Choi Hae-Man
Published: June 2012

Swirl flows are either tumbling motions of main flows or circulating secondary flows in the cross-section of pipe, which makes accurate flow metering difficult without installing a long straight pipe upstream of a flow meter. However, there are many situations, where such long upstream/downstream pipelines cannot be installed due to limited space in the installation site for flow metering. The relative deviations of flow rates between the testing and the reference flow meters can be reduced by introducing a correction formula. The correction formula considers flow parameters such as curve number, swirl factor, Reynolds number and two non-dimensional numbers regarding installation of flow meters. Nonetheless, there are certain flows where the correction formula is not effective due to strong swirl flows. Two-dimensional curve fitting is introduced in the present study to solve some of difficulties in compensating flow rates due to swirl flows upstream/downstream of flow control elements, i.e., a contraction pipe, an expansion pipe, a single elbow and a butterfly valve. This method minimizes the gap between the measured and the estimated flow rates by applying the Levenberg-Marquardt algorithm. 2nd or 4th order polynomials with two independent variables, i.e., Reynolds number and a non-dimensional location of testing flow meter, are chosen to test their ability to compensate flow rates. From this study, the relative deviations were maintained within ±2% by applying the two-dimensional curve fitting.
Design and Testing of Instrumentation for Multi-Phase Flow Sampling and Local Void Fraction Measurement
Authors: Yang Yihong , Telionis Demetri P.
Published: June 2012

Instrumentation is available to obtain samples and then measure the local void fraction as well as the size and number density of bubbles and/or particles in two and three-phase flow. But in most cases, these methods interfere with the flow and bias the sampling process. We have developed an isokinetic probe that can take accurate samples without changing the sample’s composites. This is achieved by aligning the probe’s intake nozzle with the flow’s local predominant direction and matching its internal pressure with its hydrodynamic environment and hence equalizing the inside and outside velocities. Then the fluid sample’s density is measured to calculate the local void fraction. The calibration procedure and results as well as extensive test data obtained in bubbly-flow tunnel and flotation cells respectively are presented and discussed.
National Measurement Infrastructure for High-Pressure Natural Gas and Traceability Practices
Authors: Shaw Jiunn-Haur , Ho Yi-Lin , Yang Fong-Ruey , Liao Ben-Shen , Huang Tsai-Wang , Chou Ru-Chin
Published: June 2012

Based on the policies of efficient energy utilization, environmental protection, particularly in reduction in CO2 emissions, and stable economical growth, Taiwan government adopted natural gas as a source of clean energy since 1980s. Each year, over 3 million tons of Liquefied Natural Gas is imported from Indonesia and Qatar for electrical power generation from nationally-owned and private industrially-owned companies. It is estimated by the year 2020, the appropriation of natural gas consists of 25% of national energy sources. To safeguard fair trade of energy transactions and validation of gas emission on the effects of global warming, accurate measurement of natural gas consumption and traceability to national primary standards is essential. Roughly, a 1% error in measurement causes 40 million USD unaccounted losses per year for NG supplier. Thus, a project to construct a national measurement infrastructure to serve this purpose was initiated since the 1990s. This paper describes the use of three different flow design principles to construct an unbroken chain of traceability hierarchy and demonstrates calibration with well-proven uncertainties. For each standard facility, ultrasonic meters are used in parallel to cascade up from Dia: 150 mm, 10 bar pressure, 1000 Actual m3/h; to Dia: 600 mm, 55 bar pressure, and 16000 Actual m3/h. For two years of successive on-site measurement for six meters, relative errors are within ±0.1%, with uncertainty less than 0.35%. The daily difference between custody transfer and check meters remains within ±0.2%.