bluuebunny/crossref_metadata_2025 huggingface dataset:
A Turbulence Model of Bi-Component Fuel Droplet for Atomizing Sprays
Authors: Abianeh Omid Samimi , Chen C. P.
Published: June 2012

A new approach to account for simultaneously finite thermal conductivity, finite mass diffusivity and turbulence effects within atomizing liquid sprays is presented in this paper. The main contribution of this paper is to incorporate the liquid turbulence effect in modeling the multi-component droplet liquid jet evaporation. For this study, we consider a binary mixture of heptane and decane liquid fuel injected into a hot gas environment. The finite conductivity model is based on a newly developed two-temperature two-layer film theory of Chen et al. [1], where the turbulence characteristics of the droplet are used to estimate the effective thermal conductivity. Fuel droplets inherit turbulence from high Reynolds number issuing liquid injector flows. The present paper extends the formulation of Chen et al. [1] to estimate effective mass transfer diffusivity within the drop. In this model four regions are considered, interior and the surface of the droplet, the liquid gas interface and the surrounding gas phase. An approximate solution to the quasi-steady energy equation was used to derive an explicit expression for the heat flux from the surrounding gas to the droplet–gas interface, with inter-diffusion of fuel vapor and the surrounding gas taken into account. The thermo-transport properties including their dependence on temperature are considered. Validation studies were carried out by comparison with the experimental results.
Numerical Study of Pressure Drop Oscillations in Parallel Channels
Authors: Chiapero Ezequiel Manavela , Fernandino Mari´a , Dorao Carlos A.
Published: June 2012

Pressure drop oscillations have been modeled and analyzed in the present study. The purpose of the present study is to understand the behavior of the individual channels in a parallel arrangement under different conditions such as balanced and unbalanced heat loads and operation mass flux during pressure drop oscillations. The differential equations have been solved using the least squares method. The cases with two parallel channels with balanced and unbalanced heat loads have been discussed. The modes of oscillations found in both cases are in phase and the unstable region can be divided in two characteristic regions. The so called “Region 1”, where the oscillations themselves take place, and a second region, “Region 2”, dominated by stable maldistributed solutions.
Self Organized Structure of Microbubble Plume in a Thin Fluid Layer
Authors: Miyagishima Yoshihito , Watamura Tomoaki , Tasaka Yuji , Murai Yuichi
Published: June 2012

This study aims to clarify the self-organized structure of microbubble plume as a result of two-way interaction between microbubbles and a flow of the surrounding liquid medium. We observed a sequence on a development of microbubble plumes in a thin fluid layer. Here the microbubbles show accumulation pattern with a different wavenumber depending on the height in the vessel. Variation of spatial wavenumber in the developing process was determined from visualization images, and three areas were distinguished in this process; (1) the area of rising microbubbles with a large wavenumber in a horizontal direction without time dependence; (2) the area of forming a large-scale flow structure, called ‘microbubble plume’ here, which keeps the primary information, horizontal wavenumber of the bubble accumulation with a large wavenumber; (3) the area where the microbubble distribution takes a smaller wavenumber and makes vertical accumulation pattern inside the bubbly flow that is due to the mutual interaction between rising microbubbles and a flow induced by bubbles. To clarify these mutual interactions between liquid and gas phases, we visualized fluid motion of the liquid phase around the microbubble plumes by laser induced fluorescence, LIF. In this way, swaying motions on the tip of rising up bubble plume and liquid phase entrainment into the bubble plumes were visualized. We found the mechanisms for the creation of the self-organized distribution of microbubbles in bubbly flows and its temporal change as the result of the interaction between gas and liquid phase motions in bubbly flows.
Velocity and Concentration Field Measurements in Bubble-Driven Turbulent Liquid Flows
Authors: Jeong Won Taek , Yi Seung Jae , Kim Hyun Dong , Kim Sang Moon , Kim Kyung Chun
Published: June 2012

In this study, simultaneous measurements of velocity and concentration fields using the time-resolved particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) methods have conducted to investigate mixing characteristics in turbulent water flows driven by air bubbles in a cylindrical water tank. The flow rates of compressed air is changed from 1 to 5 L/min at 0.5 MPa and the corresponding range of bubble based Reynolds number is from 8,320 to 22,100. PLIF measurement results demonstrate that the mixing efficiency is enhanced with increase of gas flow rate. The sloshing motion of the free surface is also effective to the scalar mixing process since the vertical motion can be correlated with concentration fluctuation and increase turbulent dispersion process.
Quantitative Measurement of Temperature Gradient in Natural Heat Convection Using Color-Stripe Background Oriented Schlieren (CSBOS) Technique and Computed Tomography (CT) Method
Authors: Zeb Muhammad Falak , Ota Masanori , Maeno Kazuo
Published: June 2012

Quantitative image analysis and measurement of flow fields in convective heat transfer has great importance for the optimum energy consumption problems. In natural and forced convection phenomena of fluids, the complexity of flow field prevents us from detailed three dimensional (3D) experimental analyses of steady/unsteady dynamics in fluids. These flow fields have locally different density and temperature values and yet to be observed quantitatively. Recent development of the Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) techniques lead us to the quantitative investigation of flow fields in experimental researches. On the other hand, in image measurements density and temperature distributions have been grasped only in two-dimensions (2D). These qualitative image analyses of flow fields were obtained by using classical flow visualizing techniques, such as shadowgraph and color schlieren method. This paper describes the quantitative measurement of convective flow field using our originally proposed color striped background oriented schlieren (CSBOS) method. The obtained measured image data is used for CT reconstruction and 3D temperature gradient distributions.
Heat Transfer Enhancement of Natural Convection Along a Vertical Heated Plate by Microbubble Injection
Authors: Yamamoto Kazuaki , Kitagawa Atsuhide , Hagiwara Yoshimichi
Published: June 2012

This paper describes the heat transfer enhancement of natural convection along a vertical heated plate due to injection of microbubbles. Thermocouples are used for the temperature measurement and an image processing technique is used for obtaining the bubble diameter and the bubble layer thickness. The working fluid used is tap water, and hydrogen bubbles generated by electrolysis of the water are used as the microbubbles. The mean bubble diameter dm ranges from 26 to 57 μm. For each of the laminar and transition regions, the significant heat transfer enhancement is caused by the microbubble injection. Under a constant bubble flow rate (Q = 42 mm3/s), in the laminar region, the heat transfer coefficient for dm = 39 μm is higher than that for dm = 57 μm, but it is vice versa at x = 770 mm (transition region). Under a constant bubble size (dm = 39 μm), at each measurement position, the heat transfer coefficient for Q = 42 mm3/s is higher than that for Q = 30 mm3/s. These are deeply related to the fluctuation of the bubble layer thickness and small-scale eddy motions inherent in the flow. Moreover, in the case of dm = 39 μm and Q = 30 mm3/s, the heat transfer gain (which is the ratio of the heat transfer rate obtained with the microbubble injection to the power consumption of the mirobubble generation) is approximately 33. Therefore, microbubble injection is a very highly efficient technique for enhancing the natural convection heat transfer of water along a vertical flat plate.
The Experimental Study of Impinging Interaction of Rarefied Gas Jet With Plane Wall Using LIF Method
Authors: Yamazaki Shunsuke , Yanagi Ai , Tanaka Yusaku , Ota Masanori , Maeno Kazuo
Published: June 2012

Discharging gas jets in low-pressure conditions are interesting and important phenomena from an engineering point of view. For example, in aerospace technology they relate to the gas jet thruster for attitude control of artificial satellite, or in laser technology assist gas behavior for laser material processing under low pressure. The jets, however, deform to the complicated shapes by interacting with solid walls. This paper deals with a visualization experiment on the interacting jet and plane wall by applying LIF (Laser Induced Fluorescence) method using an Ar-ion laser. We have obtained a series of jet-wall interacting images at various distances and clarified the behavior of impinging jet to the plane wall.
Numerical Study on Properties of Interior Ballistics According to Solid Propellant Position in Chamber
Authors: Jang Jin-Sung , Sung Hyung-Gun , Yoo Seung-Young , Roh Tae-Seong , Choi Dong-Whan
Published: June 2012

Analysis of the interior ballistics is essential for the development of gun or propellant configurations. The granular solid propellants with high energy and fast burning rate produce a large thrust in extremely short time intervals. For the study of these, therefore, it is necessary of a numerical code for the two-phase flow of the interior ballistics. Recently, an interior ballistics code (IBcode) for the two-phase flow using the Eulerian-Lagrangian approach has been developed. The SIMPLE algorithm and the SMART scheme have been used for the IBcode. The ghost-cell extrapolation method has been used for the moving boundary with the projectile movement. In this study, a performance of the interior ballistics according to the position of the solid propellant in the chamber has been investigated using the IBcode. In previous researches, propellants had been evenly distributed in the chamber. In this study, however, three cases of the existence of empty space in the chamber at which the propellants are not evenly distributed have been considered; Propellants are located in the region near the base, propellants in the region near the breech, and propellants in the center of the chamber, respectively. The 7-perforated configuration of the solid propellant has been used in this research. The results have shown the performance variations of the interior ballistics according to solid propellant position in the chamber. The cases of the propellants located in the region near the base and breech have shown that the value of the negative differential pressure and the difference between the breech pressure and the base pressure are much higher than those of the propellants located in the center of the chamber. The case of the propellants in the center of the chamber is, therefore, more profitable to improve the performance of the interior ballistics.
DEM-CFD Coupling Simulation of Fluidized Behavior of Geldart’s Group A Particles: A Contact Force Model for Expressing Adhesion Force
Authors: Kobayashi Tomonari , Shimada Naoki , Tanaka Toshitsugu
Published: June 2012

A discrete particle model for flows of Group A particles in Geldart’s classification was studied. In general, Group A particles are fine and light, so that the adhesion force has a strong effect on their fluidization behavior. At first, interparticle adhesion force of Group A particle was measured. The DEM-CFD coupling simulation with the measured adhesion force was performed, and the simulated results were compared with experimental data about a small scale fluidized bed for verification of the simulation. It was found from the results that there were considerable differences between their flow patterns. In order to reveal the cause of the differences, we investigated the effect of the contact force model with adhesion force on the motion of a single particle colliding with a wall. Then, we focused on the critical relative velocity of particle before collision that the particle kept in contact by the adhesion force, and discussed about the correlation of key parameters in the contact force model. From the analysis on the particle-wall collision process, it is found that the spring constant used in the DEM model has a large effect on the particle’s sticking behavior on the wall. The dynamic adhesion force model is proposed based on the present analytical investigation, and it is shown that the present model well expresses the experimental Group A particle bed fluidization behavior.
Effect of Particle Size on Feedback in an Idealized Annular Flow
Authors: Mito Yoichi , Kawamoto Keita
Published: June 2012

The effect of the droplet size and volume fraction on deposition, droplet turbulence and gas turbulence in an idealized gas-liquid annular flow has been examined. Fully-developed disperse flow in a rectangular channel is considered. A direct numerical simulation is used to calculate the gas turbulence seen by the droplets. A point force method is used to calculate the forces exerted by the droplets on the gas turbulence. Inter-droplet collisions are not considered. Gravity is assumed to be zero. Wide range of droplet inertial time constants and of volume fractions are considered. Theories about the momentum transfer in the disperse flow are tested. Correlation between the mean deposition velocity, the particle turbulence and the gas turbulence is shown. The gas turbulence decreases to accommodate the forces exerted by the droplets. Drag reduction is achieved due to the acceleration of the gas by the droplets in the near-wall region.
Numerical Study on Coarse Grain Modeling of the DEM for Industrial Scale Gas-Solid Flow Systems
Authors: Sakai Mikio , Yamada Yoshinori , Shigeto Yusuke , Mizutani Shin , Yang Shao , Shibata Kazuya , Koshizuka Seiichi
Published: June 2012

The Discrete Element Method (DEM) is widely used in various numerical simulations related to granular media. The DEM is a Lagrangian approach where individual particle is calculated based on the Newton’s second law of motion. Therefore, the DEM enables us to investigate the granular flow characteristics at the particle level. On the other side, the DEM has a difficulty to be applied in large-scale powder systems because the calculation cost becomes too expensive when the number of particles is huge. To solve this issue, we have developed a coarse grain modeling as a large scale model of the DEM. The coarse grain particle represents a group of original particles. The coarse grain model was used in typical gas-solid and solid-liquid two phase flows so far, where the particle size was relatively large, namely, cohesive force did not act between the solid particles. In the present study, the coarse grain model is evolved to simulate fine particles by considering the interparticle van der Waals force. The adequacy of the coarse grain model is proved by comparing the simulation results of original particle system. Through this study, the coarse grain model is shown to simulate the cohesive particle behavior precisely.
PIV Experiment on the Gas-Solid Multiphase Flow Relevant to Wind-Blown Sand: Comparison of Velocity Fields of Sand Particles and Air Flow by Simultaneous Measurement
Authors: Otakeguchi Kenji , Aoshima Daisuke , Sakamoto Yusuke , Tsukahara Takahiro , Kawaguchi Yasuo , Yamamoto Makoto
Published: June 2012

We measured simultaneously the air flow velocity and the suspended sand-particles velocity in the turbulent boundary layer, using particle image velocimetry (PIV), to study the wind-blown sand transport. It is important, in the context of the environmental issues, to elucidate the mechanism of the wind-blown sand, which gives rise to serious problems in arid/desert areas, such as the dust storm and the yellow sand. It is also necessary to understand quantitatively the interaction between the gas phase (air) and the solid phase (sand grains) in the multiphase flow. We found that the momentum exchange between the streamwise and the wall-normal velocities might be inhibited by sand grains and that the streamwise velocity of the gas phase in the multiphase flow was decreased by the momentum exchange between the air and the sand grains. It was observed that gas-phase flow was biased by a cluster of sand grains near a wall.
Vortex Simulation for Behavior of Solid Particles Falling in Air
Authors: Yagami Hisanori , Uchiyama Tomomi
Published: June 2012

The behavior of small solid particles falling in an unbounded air is simulated. The particles, initially arranged within a spherical region in a quiescent air, are made to fall, and their fall induces the air flow around them, resulting in the gas-particle two-phase flow. The particle diameter and density are 1 mm and 7.7 kg/m3 respectively. A three-dimensional vortex method proposed by one of the authors is applied. The simulation demonstrates that the particles are accelerated by the induced downward air flow just after the commencement of their fall. It also highlights that the particles are whirled up by a vortex ring produced around the downward air flow after the acceleration. The effect of the particle volume fraction at the commencement of the fall is also explored.
Numerical Study of Horizontal Pneumatic Conveying of Powder in Different Gravitational Environments
Authors: Lai´n Santiago , Sommerfeld Martin , Botina Leonardo
Published: June 2012

This paper evaluates the performance of horizontal pneumatic conveying under different gravity environments. An Euler-Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux and mean conveying velocity in Lunar and micro-gravity conditions. Gravity reduced computations predict an increase of particle-wall collisions with the upper wall of the channel affecting greatly the particle mass flux profile in the case of low wall roughness and small particle mass loading. If gravitational settling is reduced, e.g. by means of higher wall roughness and/or higher particle mass loadings, particle mean conveying velocity is very similar in Earth and micro-gravity conditions.
A PID Control of Flow Over a Circular Cylinder
Authors: Son Donggun , Jeon Seung , Choi Haecheon
Published: June 2012

In the present study, we apply proportional-integral-differential (PID) feedback controls to flow over a circular cylinder for suppression of vortex shedding in the wake. The transverse velocity at a centerline location in the wake is measured and used for the feedback control. The actuation (blowing/suction) is provided to the flow at the upper and lower slots on the cylinder surface near the separation point based on the P, PI or PD control. The sensing location is varied from 1d to 4d from the center of the cylinder. Given each sensing location, the optimal proportional gain in the sense of minimizing the sensing velocity fluctuations is obtained for the P control. The P control significantly reduces the fluctuations of the sensing velocity at certain sensing positions that is called the effective sensing region. The additions of I and D controls to the P control increase the control performance and broaden the effective sensing location. The P, PI and PD controls significantly reduce the velocity fluctuations and attenuate vortex shedding in the wake, resulting in the reductions in the mean drag and lift fluctuations.
Lattice Boltzmann Method Used to Simulate an Unsteady Flow Around an Obstacle in Laminar Regime
Authors: Abassi Wafik , Aloui Fethi , Ben Nasrallah Sassi , Legrand Jack
Published: June 2012

This work deals with the application of the lattice Boltzmann method to simulate the unsteady laminar flow around a confined square obstacle. For this configuration, we can observe some regimes that fluid may occur during its flowing. We have determined numerically the flow behavior for linear and stable regime. The variable aspect of the flow observed depends on the Reynolds number. In this study, we determine the velocity fields for a various Reynolds numbers by resolving the Navier-Stokes equations using the Lattice Boltzmann Method with BGK schema. This method is a recent extension of the LB method which demonstrated its potential for describing incompressible flow around an obstacle. A numerical study of 2D and 3D problem around a square obstacle using the Lattice Boltzmann Method with BGK schema is presented for an unsteady flow in laminar regime. The flow behavior in a horizontal channel with a rectangular cross-section, where a squared obstacle is placed in the middle, is discussed. In the 2D simulation, the obtained numerical results show a good agreement with experimental results [18]. Then we extend the ability of this method to solve the 3D problem. Numerical results behind the obstacle, obtained for various Reynolds numbers, are also analyzed and discussed.
Flow Properties for Several Kinds of Liquid Flows Through Micro-Orifices
Authors: Ushida Akiomi , Hasegawa Tomiichi , Uchiyama Hiroshige , Narumi Takatsune
Published: June 2012

In this paper, the flow properties of several types of liquid passing through various sizes of micro-orifices were investigated. The jet thrust and pressure drops were measured for two polyethylene glycol solutions and four surfactant solutions. Different flow properties were found for the various surfactant solutions depending on the charge of the solute. For an anionic surfactant, the results were similar to those for water, whereas in the case of a cationic surfactant, both the jet thrust and pressure decreased greatly in comparison with the other test liquids. Finally, a nonionic surfactant exhibited a steep rise in the pressure drop at a particular value of the Reynolds number. In explaining this behavior, the liquid-solid interface and alignment of the surfactant molecules are considered, and consequently, it is strongly suggested that the elastic stress on elongational flows is a contributing factor. In addition, the decreases in pressure and thrust for polyethylene glycols are attributed to viscoelastic properties, regardless of the molecular weight of PEG.
Numerical Analysis of Three-Dimensional Flows of Wormlike Micelles Solutions Through Abrupt Contraction Using a Modified Bautista-Manero Model
Authors: Yamamoto Takehiro
Published: June 2012

Startup flows of wormlike micelles solutions in a three-dimensional rectangular abrupt contraction channel are numerically simulated using a modified Bautista-Manero model as a constitutive equation. The numerical scheme applied is based on the finite volume method with the PISO algorithm, and the DEVSS method is employed to stabilize the numerical computation. Temporal changes in micelle network structures are investigated based on the analysis of the fluidity, which represents the structural change in micelle networks. The numerical results indicate that the orientation behavior of micelle networks around the entrance to the contraction remarkably changes with time. Around the entrance, micelle networks undergo strong elongation and shear deformations and hence the deformation of network is accelerated. Furthermore, the velocity distribution in a cross section takes a plug-like profile similarly to that of viscoplastic fluids because the fluidity rapidly changes near channel walls, where the shear rate is high. Three-dimensional patterns in the distribution of the fluidity appear more remarkably at high Weissenberg numbers, while in a conduit downstream of a contraction part they appears in a limited region near the walls where the fluidity rapidly changes.
Numerical Analysis of Two-Phase Flow in Fluidized Bed Reactor With Jet Nozzle for Polysilicon Growth
Authors: Kim Hwang Suk , Lee Hwansung , Song Jiwoon , Moon Hokyu , Cho Hyung Hee , Chung Yoon-sub , Park Yeon-seok
Published: June 2012

The present study has been conducted on three dimensional flow characteristics between poly-silicon particles and gas in a large scale fluidization bed reactor (FBR). This study was mainly performed numerically by commercial code Fluent. The Eulerian multiphase model was used to simulate hydrodynamics of bubbling fluidized bed. The size of silicon particle was 1000 μm and 2000 μm, and density was 2329 kg/m3. The reactor chamber had base gas flow from bottom porous plate and reacting flow from the jet nozzles (single or multi) with high velocity. The base gas and reacting gas were hydrogen (H2) and trichloro-silane (TCS) respectively. The TCS mole fraction was controlled to 13% and 20% of total gas amount. From the simulation, performance and design parameters were evaluated on single and multi nozzles jet related to flow mixing characteristics and a gas-solid contact performance. As a result, considering of the mixing characteristics between the gas and the solid, multi nozzle jets much improved the mixing performance in the reacting zone. In addition, the widespread distribution of TCS which led to better gas-solid contact performance were showed by the multi nozzle jets. This CFD data will provide useful basis to predict fluidization characteristics in the poly-silicon FBR process.
Mechanical Properties of Complex Structure Formed From Electro-Convection State of Smectic Liquid Crystal
Authors: Narumi Takatsune , Hoshi Hideaki , Muraki Tomohiko , Hasegawa Tomiichi
Published: June 2012

In the present study, electro-rheological characteristics of a liquid crystal (8CB) in smectic-A phase were investigated utilizing a parallel-plate type rheometer under a stress control mode. Solid like behaviors of the liquid crystal under DC electric fields were mainly examined. Bingham-like properties were observed and yield stresses measured were affected with the electric field conditions. When the electric field strength was low, the yield stress was almost the same as that obtained under no electric field. Above a threshold of DC electric field strength, the yield stress increased. It was clarified that the increase in the yield stress was caused with the complex structure formed in cooling process from an electro-convection state in nematic phase. Mechanical property changes after deformation of the structure were also examined as changes in dynamic viscoelasticities under condition of very small strain amplitude and the yield stress. The properties were measured before and after the deformation and compared. Moreover, the deformed structure of the liquid crystal was visualized with a polarizing microscope. Since the initial structures formed after the cooling have unevenness, the strength of the structure varied widely. When the small deformation is applied, peculiar changes in the strength were observed, i.e. the G’ measured was increased or decreased after the deformation. Moreover, the values measured after the deformation had reproducibility despite of the scattered initial data. We observed growth of typical optical patterns in the visualization of the structure and it is considered that defects like focal conic domains were generated and developed. After large deformation, the strength of the structure decreased and the deformed structure had almost no elastic properties. The structures were changed to irregular flow structures.
Driving Performance of Liquid Crystalline Actuators
Authors: Zhou Yuan , Tsuji Tomohiro , Chono Shigeomi
Published: June 2012

We have experimentally investigated the driving performance of liquid crystalline actuators, which are recently proposed for micro-actuators. In our experiment, the liquid crystalline material (5CB) is placed between two glass plates with surface orientation treatment. When a pulsed electric field is applied between the plates, the liquid crystalline molecules alternately exhibit clockwise and counterclockwise rotation, inducing the flow of the material. This flow is the source of the actuator drive. For the practical use of the liquid crystalline actuators, one must have the information of the performance of the actuators, such as the motion trajectory, driving speed, driving force, and so on. These performances strongly depend on voltage, frequency and duty ratio of the pulsed electric field. From the results, it is found that the driving speed and driving force can be controlled by these input factors. The maximum driving force is relatively large compare to the other micro-actuators.
Influence of Counter-Ion Concentration on the Impinging Jet of Surfactant Solutions
Authors: Tuan Nguyen Anh , Mizunuma Hiroshi
Published: June 2012

An impinging jet is characterized by high heat transfer and thus is widely used in cooling and heating process in industry. On the other hand, surfactant solutions reduce pipe friction in turbulent flow and at the same time reduce heat transfer. In our past study, it was found that the surfactant solution with higher counter-ion concentration did not reduce the heat transfer in the impinging jet. This phenomenon suggested that the high heat transfer was characterized by high shear rate in impinging jet and not by turbulence. However, it has not yet been determined satisfactorily how the heat transfer is influenced by surfactant solutions in the impinging jet. Especially, the influence of the counter-ion concentration is important, because the counter-ion changes not only the heat transfer but also the rheology of the surfactant solutions. In this study, we visualized the impinging jet of the surfactant solutions, and the influence of the counter-ion was investigated. The results indicated that the wall flow was remarkably influenced by the counter-ion concentration in the impinging jet. In the case of the surfactant solution with equi-molar counter-ion, the induced wall flow was continued only near the stagnation point. By contrast, the solution with higher molar counter-ion induced the radial boundary layer flow on the wall similar to the water flow. This difference in flow would cause the different heat transfer, and the solution with higher molar counter-ion produces normal heat transfer. When comparing the visualized results of the impinging jet with the numerically simulated results, the qualitative agreement was not satisfactory for the surfactant solution with counter-ion of equi-molar concentration. The simulation used a Bingham model as the rheological equation, the constants of which were obtained from a cone and a plate rheometer. It was suggested that the surfactant solution indicated different rheological behavior in these viscometric flow and impinging jet.
Effects of Vibrational Relaxation on Weak Shock Wave Structure in Air
Authors: Sakai Takeharu , Makino Yoshikazu , Naka Yusuke , Murakami Akira
Published: June 2012

A computational fluid dynamic method is developed to calculate the long range propagation of weak shock wave with the vibrational relaxation in air. Vibrational relaxation kinetics among N2, O2, and H2O is accounted for by solving each species conservation equations with total mass, momentum and energy equations. The conservation equations are solved using a moving grid technique to capture the distortion of the wave during propagation. The propagation of the wave with an overpressure value typically observed in sonic boom on the ground is analyzed using the developed method. The computed results are mainly presented to show the ability to capture a dispersed nature in waves under different humidity conditions due to vibrational relaxation. The present result shows that the variation of a converged wave thickness dependent on a wide range of humidity can be recognized clearly by using the present method.
Performance Improvement of an Ejector-Diffuser System Using Shock Generator
Authors: Lijo Vincent , Kim Heuy Dong , Setoguchi Toshiaki
Published: June 2012

Supersonic ejectors are simple mechanical components, which generally perform mixing and recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for high altitude testing (HAT) of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser (SED). This paper aims at the improvement in HAT facility by focusing attention on the vertical firing rocket test stand with shock generators. Shock generators are mounted inside the SED for improving the pressure recovery. The results clearly showed that the performance of the ejector-diffuser system was improved with the addition of shock generators. The improvement comes in the form of reduction of the starting pressure ratio and the vertical height of test stand. It is also shown that shock generators are useful in reducing the total pressure loss in the SED.
Thrust Characteristics of Cycloidal Propeller and Flow Measurement
Authors: Hasegawa Daisuke , Matsuuchi Kazuo , Onda Masahiko , Sekiguchi Yuya
Published: June 2012

Now airships are expected to be used as drones for support services at disasters and global environment monitors. However, such applications have not been successfully attained due to the vehicle’s poor kinetic performances. Our team, then, tries to improve the kinetic performances of airships by installing cycloidal propellers which can instantly change thrusts toward arbitrarily directions by controlling attack angles of the rotor blades. In this study, we report results of static thrust measurement experiment of a cycloidal propeller for 10-meter class airships, and wind tunnel tests and flow measurements around a rotor by the particle image velocimetry (PIV) applying to a miniature cycloidal propeller. The radius of rotor, the chord and the span of blades, the number of blade of the cycloidal propeller for 10-meter class airships are respectively 0.4m, 0.3m, 0.5m, and 3, and those values for the miniature cycloidal propeller are respectively 0.16m, 0.12m, 0.2m, and 3. Firstly it was found that the cycloidal propeller for 10-meter class airships can generate 50N as the maximum thrust at a rotational speed of 8 rps and with attack angle of 25 degrees. Moreover, thrust directions deviate from instructed directions toward the rotational direction by 25 degrees at the maximum. Secondly, from the wind tunnel test, thrust coefficients were found to be decreasing as advance ratios increase, which corresponds to a tendency of general type propellers. In addition, it was clarified that the propeller intakes the air not only from the rotating surface of the propeller but also from the rotor axial direction of the propeller by visualizing the air flow around the rotor by PIV.
Thrust of a Thin Plate Starting Impulsively
Authors: Ichikawa Seiji , Kikuchi Kenji , Mochizuki Osamu
Published: June 2012

We studied on a vortex ring generated by a suddenly accelerated thin plate to understand a relation between the circulation and necessary force to accelerate the thin plate. The motion of thin plate is operated by trust force. We measured velocity fields around a circular disk, using a PIV system and high speed CMOS camera. We showed that the time derivative of the circulation related to the force to drive the disk because the disk gave energy impulsively to the vortex ring. This gives us the way to estimate thrust if we could measure the change in circulation of the starting vortex ring by the disk. We applied it to the estimation of thrust by an accelerated non-circular disk by introducing an equivalent circle that has the same area as the non-circular disk.
Vortex Shedding Suppression for a Circular Cylinder by Attaching Cylindrical Rings (A Consideration of the Mechanism)
Authors: Nakamura Hajime
Published: June 2012

Omnidirectional reductions in drag and fluctuating forces can be achieved for a circular cylinder subjected to cross-flow by attaching cylindrical rings along its span at an interval of several diameters. In this work, the effects of ring configuration, the diameter D, spanwise width W, and spanwise pitch P, on the vortex shedding suppression was investigated. As a result, it was found that the periodicity in the pressure fluctuation on the sides of the cylinder disappeared for Red ≥ 20000 at ring configurations of D/d = 1.3, W/d = 1 and P/d ≈ 3. At this configuration, the fluctuating lift force reduced markedly to about 1/30 of a 2D cylinder due to the suppression of the periodic shedding together with the weakening of the spanwise correlation. The mechanism of this was explored through flow visualizations and PIV measurements, which was considered as follows: A spanwise pressure gradient originated from a stepwise change in the diameter induces a spanwise flow, which brings the corner vortex to the side of the ring. This promotes the turbulent transition in the shear layer separated from the ring for Red ≥ 20000. As a result, the wake behind the ring markedly shrinks, which induces a pair of large transverse circulations just behind the ring edges. Consequently, two-dimensional spanwise vortices are obstructed to form, resulting in the suppression of the periodicity in the vortex shedding.
Characteristics of Impinging Water Jet Discharged From a Central-Body Nozzle
Authors: Kang Can , Zhou Liang , Wang Weifeng , Liu Haixia
Published: June 2012

Submerged water jet discharged from a central-body nozzle was investigated through flow visualization, numerical simulation and impingement experiment. Under jet pressure of 15 MPa, three layout plans of central body were introduced and corresponding water jets were visualized by using high speed photography technique. Cavitating jet flow fields were simulated with commercial computational fluid dynamics (CFD) software Fluent which employs full cavitation model. Sandstone cuboid was used as the sample workpiece exposed to the submerged water jet of 15MPa. It is proved that cavitation tone exist in the wake flow after the central body. When the end cross-section of the central body is parallel with the nozzle outlet section, the largest axial length of cavitation zone is obtained. Compared with round water jet with the same equivalent nozzle outlet area, the central-body nozzle yields stronger impinging effect.
Experimental Extraction of Linear Disturbance in a Two-Dimensional Turbulent Jet and Comparison to a Linear Stability Theory
Authors: Tazoe Shun , Kawanishi Ayako , Matsubara Masaharu
Published: June 2012

In a two-dimensional turbulent jet, there exists a lateral vibration of the high-speed jet core. In the present study, a periodic initial disturbance is introduced into fully developed turbulent jet from a slot mounted at a duct exit in order to control this vibration. The streamwise and lateral velocity fluctuations are measured with an anemometer with an X-type probe, and are filtered using a phase ensemble average technique based on the periodic initial disturbance. This vibration enables extraction of the fluctuation of the synchronized disturbance and restruction of its velocity field. The experimental result shows that the streamwise variation of the extracted amplitude draws a characteristic growth curve that has the exponential growth at the upstream and slow decay parts at the downstream. It is worth noticing that within a certain amplitude of the initial disturbance the growth curves are identical as well as the spatial distribution of the extracted fluctuations. Furthermore the disturbance amplitude is directly proportional to the intensity of the initial disturbance. A linear stability theory with parallel flow assumption well captures futures of the lateral disturbance. This apparent linearity of the disturbance keeps until the average velocity and the total velocity fluctuation starts to vary with sufficient amplitude of the disturbance. The existence of the linear mode in the turbulent jet implies that the large-scale disturbance can be regarded as an incoherent set of the linear modes.
Study on the Flow Characteristics of Synthetic Jets Near a Rigid Plane Boundary
Authors: Tsunoda Ryota , Nishibe Koichi , Fujita Yuki , Sato Kotaro , Yokota Kazuhiko , Koso Toru
Published: June 2012

The jet flows have been applied to various fields to control the flow separation. Over the last decade, several studies have investigated synthetic jets. However, there are still many clarifications needed, including details of the structure and Coanda effect of synthetic jets. The present study clarifies some fundamental flow characteristics of free synthetic jets and synthetic jets near a rigid boundary by conducting an experiment and numerical simulations. As the main results, it is found that the velocity distribution of free synthetic jets depends on K = Re/S2 (the ratio of the Reynolds number to the square of the Stokes number) and can be identified by the maximum velocity at the centerline and the jet half-width. Flow visualization is carried out applying the smoke wire method. In addition, it is confirmed that the flow characteristics of the synthetic jet near a rigid boundary and re-attachment length of the synthetic jet are determined not only by H1/b0 (normalized step heights) but also K.
Simulation of Hydrogen Production by Using Concentrated Solar Energy Through Thermo-Chemical Water Splitting Process: Part II—Simulation of Zinc Hydrolysis Reaction to Generate Hydrogen
Authors: Khan Furqan Ahmad , Siddiqui Kamran
Published: June 2012

This study is focused on the second step of ZnO/Zn thermo-chemical cycle, where zinc (produced in the first step of the cycle) reacts with steam to produce hydrogen and zinc oxide. The simulation of this hydrogen production step was carried out inside a cylindrical reactor using commercial CFD software, FLUENT. A parametric study was conducted based on the zinc particle diameter, reactor wall temperature, and steam/zinc molar ratio. The yield of hydrogen was found to increase with an increase in the reactor wall temperature, and with a decrease in the zinc particle diameter. However, steam/zinc molar ratio was found to have no effect on the hydrogen yield.
Production of Liquid Hydrocarbon Fuel by Catalytic Cracking of Waste Fish Fat in Continuous Pilot System
Authors: Mrad Nadia , Paraschiv Maria , Aloui Fethi , Tazerout Mohand , Ben Nasrallah Sassi
Published: June 2012

Liquid fuels can be produced from triglyceride sources via thermo-catalytic process. In the present work, the production of bio-fuel by catalytic cracking of waste fish fat in a continuous reactor at atmospheric pressure has been studied. Different catalysts were used and maximum bio-oil yield of 66% with the lowest acidity of 4.3 mgKOH/goil was obtained with a controlled reaction temperature of 500°C and Na2CO3 as a catalyst. After chemical treatment of this bio-oil, the acidity decreases to 1.5mgKOH/goil. These bio-fuels were characterized according to their physico-chemical properties, and compared with the diesel fuel. The results show that the catalytic cracking process represents an alternative method to produce bio-fuels with physico-chemical characteristics similar to petroleum fuels from fish oil industrial residues.
Simulation of Liquid Water Evaporation in GDL for PEMFC Under Gas Purge Condition
Authors: Inoue Gen , Ishibe Naoyuki , Matsukuma Yosuke , Minemoto Masaki
Published: June 2012

In automotive Polymer Electrolyte Fuel Cell (PEFC) system, dry gas purge operation is needed at shutdown condition in order to remove the liquid water in gas diffusion layer (GDL) and to reduce the oxygen diffusion inhibition by liquid water in GDL. However, exceed drying operation leads to degradation of electrolyte membrane because of little water content. Therefore, drying process has to be optimized. In this study, various GDL structure with unique fiber orientation were simulated by numerical analysis, and the real GDL structure was reconstructed by X-ray CT image of carbon paper GDL. Next, our past two-phase network model was improved to include phase change effect. The multi-block two-phase network model based on an actual structure was developed by a direct 3D networking porous structure. As results, the evaporation interface area depended on the porous structure of GDL, and the overall evaporation rate of homogeneous GDL which has uniform structure was 1.5 time higher than that of heterogeneous GDL because of the difference of this interface area. In addition, in the case of rib and channel, liquid water under channel evaporated faster than that under Rib. It is very important to control the drying operation in order to prevent the excess membrane drying.
Study of the Pump of a Mosquito
Authors: Kikuchi Kenji , Mochizuki Osamu
Published: June 2012

Structures and functions of a mosquito’s pump system were investigated experimentally to clarify the mechanistic aspects of this optimized bio-pump. The three-dimensional strucure of the pump that was reconstructed by 1500 slices of the mosquito’s head was obtained using a histopathological method. The mosquito’s pump motion is predictable, and the pump volume can be estimated by the three-dimensional structural observations. The pump volume of the pumps, an oral cavity pump and pharynx pump, were estimated as being 7.92×10−4mm3, 63.3×10−4mm3 respectively. The frequency of the mosquito’s pumps was predicted to be 2.09–16.7 Hz, and was estimated using the pump volume and the volumetric blood flow rate. The motion of the mosquito’s pumps was visualized directly by an x-ray phase contrast imaging method using synchrotron radiation. It was found that the mosquito’s pumps (i.e., the oral cavity pump and the pharynx pump) worked alternately with a 4.23 Hz pump frequency. Moreover, the phase difference of each pump was almost 0.5, suggesting that the mosquito’s pumps worked in opposite phases. In addition, the mosquito’s pumps were found to work as a inline pump, which is suitable for increasing the pressure head of pump.
Investigation Into the Acoustic Streaming and Convective Cooling Phenomena During a High-Intensity Focused Ultrasound Thermal Ablation
Authors: Solovchuk Maxim A. , Sheu Tony W. H. , Thiriet Marc
Published: June 2012

The present study is aimed at predicting liver tumor temperature increase during a high-intensity focused ultrasound (HIFU) thermal ablation using the proposed acoustics-heat-fluid coupling model. The linear Westervelt equation is adopted for modeling the incident finite-amplitude wave propagation. The nonlinear hemodynamic equations are also taken into account in the simulation domain that contains a hepatic tissue domain, where homogenization dominates perfusion, and a vascular domain, where blood convective cooling may be essential in determining the success of HIFU. We also consider the energy equation for the modeling thermal conduction heat transfer. Two heat sinks are dealt with to account for tissue perfusion and forced convection-induced cooling. The effect of acoustic streaming is also included in the current HIFU simulation study. Convective cooling in large blood vessel and acoustic streaming were shown to change the temperature near blood vessel. It was shown that the acoustic streaming effect can change the blood flow distribution in hepatic arterial branches and leads to mass flux redistribution. The effect of acoustic streaming can be used to control blood drug delivery. In the current work the realistic geometry for the blood vessel and liver was reconstructed using the MRI images. The presented results may be further used to construct a surgical planning platform for the non-invasive HIFU (High-Intensity Focal Ultrasound) tumor ablating (or cauterizing) therapy in real liver geometry on the basis of the MRI image.