JSME International Journal Series B Fluids and Thermal Engineering
Online ISSN : 1347-5371
Print ISSN : 1340-8054
ISSN-L : 1340-8054
Volume 49 , Issue 3
Special Issue on Environmental Flows
Showing 1-40 articles out of 40 articles from the selected issue
PAPERS
  • Lionel ELLIOTT, Derek Binns INGHAM, Stephen David WRIGHT
    2006 Volume 49 Issue 3 Pages 556-566
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    In this paper, novel mathematical methods are implemented. In particular a mesh refinement technique is developed that allows the larger scale topographical effects on the atmospheric boundary-layer to be taken into account, yet still enabling the fine resolution of the boundary-layer within the smaller scale of the urban environment, as well as a parameterisation for urban effects. In the latter, the surface roughness is included through additional drag terms within the Navier-Stokes equations. A surface energy budget equation is solved using a force-restore method to obtain a ground surface temperature. It is shown that this method allows the diurnal and yearly variation of the structure of the atmospheric boundary-layer to be accounted for within the model. The combined effects of all these features enable the resolution of the atmospheric boundary-layer within the urban canopy and also the surrounding area to be obtained.
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  • Takanori UCHIDA, Yuji OHYA
    2006 Volume 49 Issue 3 Pages 567-575
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    We are developing the numerical model called the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain). The object domain of this numerical model is from several m to several km, and can predict the airflow and the gas diffusion over complex terrain with high precision. The RIAM-COMPACT has already been marketed by certain tie-up companies. The estimation of the annual electrical power output is also possible now based on the field observation data. In the present study, wind simulation of an actual wind farm was executed using the high resolution elevation data. As a result, an appropriate point and an inappropriate point for locating a wind turbine generator were shown based on the numerical results obtained. This cause was found to be a topographical irregularity in front of the wind turbine generator.
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  • Yoichi UTANOHARA, Shigeo KIMURA, Takahiro KIWATA
    2006 Volume 49 Issue 3 Pages 576-582
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    We have studied the effect of ground topography, focusing on mountain waves, on the transport of Yellow Sand by two-dimensional numerical simulation. An advection-diffusion equation for scalar concentration is solved to simulate the transport of Yellow Sand. Two different models are employed: the first is a one-layer model in which the density gradient is constant in the entire domain, and the other is a two-layer model in which the density gradient changes at an altitude of 11km. In the both models stream lines at high altitude descend greatly toward the ground along the lee side of the mountain as the atmospheric stability increases. However, in the two-layer model, trapped mountain waves become stronger than those in the one-layer model, and rotors are also generated on the ground. These become stronger for larger mountain width, and the scalar concentration rapidly diffuses there. It is found that the ground scalar concentrations for the two-layer model are generally much larger, especially in the rotors, compared with those in the one-layer model.
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  • Robert MCKIBBIN
    2006 Volume 49 Issue 3 Pages 583-589
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Pollen released from trees within a forest is transported by the wind through the canopy. Some is trapped by the foliage as it is advected and dispersed while falling under gravity. Taking into account these three mechanical processes, the quantitative model presented here is based on principles of conservation of mass. It is assumed that the pollen particles, being small, quickly reach their terminal velocity with respect to the mean air flow, and are mechanically dispersed by the turbulence generated by the air flow through the foliage. The rate of removal of the pollen from the flow, the so-called “trapping rate”, is assumed proportional to the volumetric concentration of the pollen mass in the air. The aim is to obtain analytic solutions to the resulting advection-dispersion-trapping (convection-diffusion-decay) equations. Some examples are presented to illustrate the effects of various parameters.
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  • Rodney O. WEBER, John W. DOLD
    2006 Volume 49 Issue 3 Pages 590-593
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Fires burning on 18th January 2003 generated a series of cumulonimbus clouds that probably exacerbated a fire that reached suburban Canberra. Powerful whirlwinds were generated, at least one of which might have been a genuine tornado. We briefly review the development of plume theory over the last fifty years and a potential atmospheric stability index that may assist in the identification of conditions that are conducive to extreme fire behaviour in the environment. This information can assist in deciding the location of future monitoring stations.
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  • Yuko KUNIKANE, Nobuyoshi KAWABATA, Takaaki YAMADA, Akifumi SHIMODA
    2006 Volume 49 Issue 3 Pages 594-600
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    This study is a part of an investigation project to examine emergencies in a large cross sectional tunnel, to be constructed on the New Toumei Expressway in Japan. Backlayering characteristics, the most important behavior in tunnel fires, are investigated through large-eddy simulation for various longitudinal air flows and fire sizes. The accuracy of this simulator has been previously confirmed by comparing with experimental results. In this study, specifically, stationary vehicles in a tunnel are considered in the simulation for the first time. Their presence induces turbulence in the longitudinal air flow and greatly affects the backlayering characteristics. However, earlier studies have not yet considered these effects. The results show that the presence of stationary vehicles reduces the backlayering length. Furthermore, the ratio of large-sized vehicles to total traffic is found to have little effect on fire behavior.
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  • Roman N. BARDAKOV, Yuli D. CHASHECHKIN
    2006 Volume 49 Issue 3 Pages 601-604
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Flow field pattern produced by a strip of arbitrary width moving with constant velocity along a horizontal plane in exponentially stratified fluid is calculated analytically in linear approximation. Constructed solution describes upstream transient and attached waves, and a boundary layer. Numerically visualized flow pattern is consistent with Schlieren observations. Drag on the strip is calculated and compared with well-known results following from conventional boundary layer theory. Due to action of edges singularities an inducing torque lift force is formed.
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  • Chengwang LEI, John C. PATTERSON
    2006 Volume 49 Issue 3 Pages 605-615
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    This study is concerned with natural convection in a reservoir with slowly varying topography in response to diurnal heating and cooling due to heat transfer through the water surface. In the daytime phase, heat is transferred into the water body through absorption of solar radiation; and in the night-time phase, heat is transferred out of the water body through heat loss from the water surface. An unsteady model is formed and solved numerically in order to investigate the transient flow response in the reservoir. Two different scenarios with shallow and deep waters respectively, based on the comparison between the maximum water depth and the penetration depth of the solar radiation, are considered. The numerical results reveal that there is a distinct time lag in the response of the overall flow to the switches of the thermal forcing, and the lag time depends on the Grashof number. It is also found that thermal instabilities play an important role in breaking the residual circulation and reversing the flow in deep waters.
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  • Takashi KARASUDANI, Hiromasa UEDA, Yuji OHYA
    2006 Volume 49 Issue 3 Pages 616-620
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    We experimentally studied development and statistical properties of the free convective layer under a water surface. Cooling the gas-liquid interface by water evaporation generated the convective layer. Velocity and temperature fluctuations were simultaneously measured by a laser-Doppler velocimeter and a fine thermocouple. Variances and correlations for the fluctuations were normalized by the heat flux and the thickness of the convective layer, and vertical profiles of those quantities were obtained. Their profiles were compared with those in convection over a solid wall. They had striking differences near the surface, and showed almost the same behavior in the remaining convective layer. From the profile of kurutosis, the velocity fluctuation was expected to become a Gaussin distribution in a region from near the surface to the midst of the convective layer. On the other hand, the distribution of the temperature fluctuation had two peaks near the surface, and wasn’t Gaussin in entire convective layer.
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  • Yasuaki AOTA, Michio KUMAGAI, Kenji KASHIWAYA
    2006 Volume 49 Issue 3 Pages 621-625
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Using continuous monitoring data over last two years in the North Basin of Lake Biwa, we showed the time change of water currents and temperature from May 2003 to May 2005. Two acoustic current meters (ACMs) were deployed at 1.8m and 54m height from lake bottom respectively, at the observation point with the depth of 90m near the deepest place (104m depth). We measured horizontal current velocity, current direction, and water temperature at every 20 minutes, and estimated the bottom stress with horizontal current velocity and water temperature. Average water current velocity near the lake bottom through the observation was weak as reported before, however, maximum current velocity due to strong typhoon in October 2004 reached almost 30cm/s. Moreover, comparatively strong water current velocity was observed from January to February in each winter. The estimation of the bottom stress with current velocity suggested us that strong currents could re-suspend bottom sediments.
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REVIEW
PAPERS
  • Naoki TAKADA, Akio TOMIYAMA
    2006 Volume 49 Issue 3 Pages 636-644
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    For interface-tracking simulation of incompressible two-phase fluids with high density ratios, a new numerical method was proposed by combining Navier-Stokes equations with a phase-field model based on a van der Waals-Cahn-Hilliard free-energy theory. The method was applied to several benchmark problems. Major findings are as follows: (1) The volume flux derived from a local chemical potential gradient in the Cahn-Hilliard equation leads to accurate volume conservation, autonomic reconstruction of gas-liquid interface, and reduction of numerical diffusion and oscillation. (2) The proposed method gave good predictions of pressure increase inside a bubble caused by the surface tension force. (3) A single liquid drop falling in stagnant gas and merging into a stagnant liquid film was successfully simulated.
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  • Yoshifumi OGAMI, Ken NISHIKAWA, Hiroo UKITA
    2006 Volume 49 Issue 3 Pages 645-652
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    The mixing efficiency of an optical micro rotor designed to be used as a part of the Micro Total Analysis Systems has been studied using Computational Fluid Dynamics. It is found that the mixing efficiency due to convection by the rotor depends on the ratio of the circumferential speed of the rotor to the inlet speed of the fluids, and the efficiency due to the diffusion of the fluids depends on the ratio of the diffusion coefficient of the fluids to the inlet speed. A multiplier effect due to convection by the rotor and diffusion of the fluids on the mixing performance is observed. The results obtained in this study can be used for designing more effective optical micro rotor systems.
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  • Takashi YOSHIMOTO, Yosuke MATSUKUMA, Gen INOUE, Masaki MINEMOTO
    2006 Volume 49 Issue 3 Pages 653-659
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Knowing the movement of water in polymer electrolyte fuel cells (PEFCs) is important for deciding the optimum shape of the cell and the optimum operating conditions. It is well known that PEFCs show the best performance under conditions of moderate relative humidity. However, the experimental measurement of water movement is difficult because of the flow through the complex geometry of the diffusion layer. Therefore, to observe the movement of water in a PEFC, microscopic analysis was performed by the lattice gas automata (LGA) method. The influence of prevention of gas diffusion by water was investigated. According to the channel configuration, the distribution of water was observed in the diffusion layer and the distribution of the extent of reaction between oxygen and hydrogen was affected. Moreover, because the influence of prevention of gas diffusion by water on the cathode side was more pronounced than that by water on the anode side, it was determined that the cathode side affects cell performance markedly.
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  • Kazuo MATSUURA, Chisachi KATO
    2006 Volume 49 Issue 3 Pages 660-669
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Large-eddy simulation of compressible transitional flows in a low-pressure turbine cascade is performed by 6th-order compact difference and 10th-order filtering method. Numerical results without free-stream turbulence and those with about 5%free-stream turbulence are compared. In these simulations, separated flows in the turbine cascade accompanied by laminar-turbulent transition are realized, and the present results closely agree with past experimental measurements in terms of the static pressure distribution around the blade. In the case where no free-stream turbulence is taken into account, the unsteady pressure field essentially differs from that with strong free-stream turbulence. In the case of no free-stream turbulence, pressure waves that propagate from the blade’s wake region have appreciable effects on the separated-boundary layer near the trailing edge and on the neighboring blade.
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  • Akinori FURUKAWA, Tomoya TAKANO, Toru SHIGEMITSU, Kusuo OKUMA, Satoshi ...
    2006 Volume 49 Issue 3 Pages 670-677
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump with more compact structure, higher efficiency and higher cavitation performance. The blade rows interaction between front and rear rotors should be taken into account in pump design for stable operation and reduction of unsteady losses. The measurements of static pressure distributions on casing wall with the phase locked sampling method are carried out for two types of the rear rotors. In the present paper the difference of the rear blade interaction and the unsteady pressure fluctuation are clarified. The pressure fluctuations are more remarkable in the front rotor than in the rear rotor and they are caused by rear rotor pressure field. The effects of pressure fluctuations will be discussed in more details toward understanding the blade rows interaction in the contra-rotating axial flow pump.
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  • Souichi SASAKI, Yoshio KODAMA, Makoto HATAKEYAMA
    2006 Volume 49 Issue 3 Pages 678-685
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    In the prediction theory for a broadband frequency noise generated from a multiblade fan, the vortices in Karman vortex street were divided into n pieces. The frequency distribution of the noise was estimated so that the Strouhal number could become constant even if the wake is spread by the diffusion. From the results of the measurement of the internal flow of the fan, it was found that the noise was related to the wake characteristics of the specific location in the scroll casing where the relative flow velocity was high. The noise operating in the vicinity of the maximum efficiency point of the fan was distributed over the domain from 500Hz to 1250Hz. It was experimentally proved that when the distribution of the estimated sound pressure level corresponded to the measured broadband frequency noise, no influence of the vortices on the noise in the domains of high and low frequencies existed.
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  • Hoshio TSUJITA, Shimpei MIZUKI, Atsumasa YAMAMOTO
    2006 Volume 49 Issue 3 Pages 686-694
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    In a series of present studies, the flows within the stationary curved ducts are analyzed numerically with the aerodynamic or the geometrical parameters affecting the loss generation caused by the passage vortex within a passage of a turbomachinery. In the former reports, the inlet boundary layer thickness and the inlet velocity distortion were taken as the aerodynamic parameter and the aspect ratio of the cross-section was chosen as the geometrical parameter. In this report, the effects of the curved angle of the bend on the loss generation caused by the passage vortex are examined by relating the bend of curved duct to the blade-to-blade surface of an axial flow turbine cascade. The curved angle is changed from 90 to 160 degrees by 10 degrees with fixing the length of arc for the mean radius of curvature of the bend or with fixing the mean radius of curvature.
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  • Go-Long TSAI, Tsung-Hsien TU, Tung-Chen LI, Kuang-Hsieng WANG
    2006 Volume 49 Issue 3 Pages 695-704
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    The purpose of this study was investigating the noise emission, flow-style, fan’s performance regarding to cross-fan with three different rotor-skew angle (RSA) rotors. The special flow visualization setups for both vertical and parallel investigation of smoke slice were used to overcome the blind sight of a Laser-Doppler or a particle-tracking velocimeter, and the three-dimensional flow differences were confirmed with streamline images. The experimental results indicated that RSA-5, which is a rotor with a nearly a pitch skew within blade’s two end shrouds, has a lower sound emission and little pressure drops relative to that of no skew angle case, RSA-0. RSA-10, two pitches twisting case, also has a better acoustics quietness than that of RSA-0, but it excited undesired noise in a high frequency components around 2-4kHz. In this work, for a compromise between flow and acoustics performances, RSA-5 shows the most suitable design for cross-flow fan rotor.
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  • Masaki SUGIMOTO, Toshihiko SHAKOUCHI, Kohei HAYAKAWA, Moriyasu IZAWA
    2006 Volume 49 Issue 3 Pages 705-713
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Recently, the micro-blasting process has been widely used to process brittle material, and a conventional circular nozzle has been commonly used. But the cutting performance of a circular nozzle does not process a large area well, so the use of a slot nozzle is considered. In this study, in order to improve the cutting performance of the micro-blasting nozzle, a new slot nozzle with a large aspect ratio is proposed and the flow characteristics and cutting performance are examined precisely by experimental and numerical analyses. The main results show that (1) setting the circular vane in the slot nozzle perpendicular to the stream can diffuse particle flow uniformly at the nozzle exit, making the particle velocity distribution uniform, (2) expanding the nozzle outlet at an angle, uniform air and particle velocity distributions at the nozzle exit can be obtained, (3) in spite of setting obstacles at the nozzle, a fine cutting efficiency is obtained compared to the conventional micro-blasting circular nozzle.
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  • Yasuhiko SAKAI, Nobuhiko TANAKA, Takehiro KUSHIDA
    2006 Volume 49 Issue 3 Pages 714-721
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    The simultaneous measurement of the velocities at two points with X-type hot wire probes has been performed in three different downstream regions of a plane jet (the potential core region, the interaction region and the self-preserving region). By applying Karhunen-Loève (KL) expansion in space and time, the structure development of the plane jet is investigated from a viewpoint of both space and frequency. From the downstream variation of the eigenfunctions, it is found that in the early stage of the interaction region the profiles of the first u (streamwise component of velocity fluctuation) and v (cross-streamwise component of velocity fluctuation) mode in the low frequency range become self-similar, but in high frequency range these continue to change until the self-preserving region. The characteristics of coherent structure can be extracted efficiently by the two-point spatial velocity correlation reconstructed from the first mode of KL expansion.
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  • Yasuhiko SAKAI, Nobuhiko TANAKA, Mutsumi YAMAMOTO, Takehiro KUSHIDA
    2006 Volume 49 Issue 3 Pages 722-730
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    In order to clarify the dynamics of the coherent structure in a turbulent plane jet, the simultaneous measurement of the main streamwise velocity at 21 points in the self-preserving region of a turbulent plane jet has been performed by an array of I-type hot-wire probes. Then the KL (Karhunen-Loève) expansion was applied to extract the coherent structure in the jet. The total number of eigenfunctions (modes) is N=21, which corresponds to the number of probes. The eigenfunctions (modes) are numbered in order of magnitude of their corresponding eigenvalues. From the investigation of the random coefficients and the eigenfunctions (modes), it is found that the low-numbered (energetic) modes represent the large scale (coherent) structure, the middle-numbered modes represent the finer (small-scale) random structure, and the higher-numbered modes contribute mainly to the intermittent structure in the outer edge region. From the spatio-temporal velocity field reconstructed by the first KL mode, it is found that there exist a pair of fluid lumps with the positive and negative streamwise velocity fluctuation on the opposite sides of the jet centerline, and the signs of velocity fluctuation for those fluid lumps change alternately as time proceeds. These characteristics are consistent with the so called “jet flapping” phenomenon.
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  • Takahiro HARADA, Yukihito SUZUKI, Seiichi KOSHIZUKA, Takahiro ARAKAWA, ...
    2006 Volume 49 Issue 3 Pages 731-736
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Micro droplet generation is one of the basic functions in a micro total analysis system (micro TAS). Micro TAS has a lot of advantages and thus has wide range of applications in these days. In this study, a numerical calculation code for micro multi-phase flow is developed using Moving Particle Semi-implicit (MPS) method. Since surface tension is extremely strong and dominant in micro multi-phase flow, a time step is divided to sub-time steps for the surface tension term. This sub-time step algorithm enables us to calculate micro multi-phase flow efficiently with keeping numerical stability. Micro droplet generation in a micro channel is analyzed by the present code in two dimensions. The calculated droplet size, pitch and production rate show good agreement with those of the experiment.
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  • Akira T. TOKUHIRO, Hidekazu NO, Michel CALL, Koichi HISHIDA
    2006 Volume 49 Issue 3 Pages 737-747
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    An experiment to study the near-wake flow structure behind an air bubble attached to a cap and separately, a solid equivalent was conducted. The objective was to elucidate the near-wake characteristics of the “cap-bubble” relative to the solid; in particular, to elucidate the role of the “moving tail”. Experiments were performed in 80 × 80mm2 × 1m tall channel with each object suspended in downward flow of water. Both the cap-bubble and solid had an approximate equivalent diameter, Deq∼ 11.5mm (volume ∼ 0.8mL), The average downward flow velocity (U ∼ 25cm/s ∼ rise velocity of bubble) defined Reynolds number was, 2450 < ReDeq<2890. The Eötvös and Weber numbers were, 17.8<<17.85, 6.04<We<6.06. Particle Image Velocimetry using a cross-correlation method was used to generate velocity data; vorticity, turbulent kinetic energy (TKE) and other parameters we then calculated. Graphic and numerical comparisons between the objects led to the following: 1) for the cap-bubble, the influence on the flow structure due to motion of the tail is relatively minor, 2) tail motion contributes to transverse fluctuations and uniformity in TKE distribution and 3) object deformation, oscillation and gyration localizes the flow structure in contrast to a solid object. Results are discussed.
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  • Ichiro KANO, Ichiro TAKAHASHI
    2006 Volume 49 Issue 3 Pages 748-754
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    A micro-electrohydrodynamic (EHD) pump is experimentally tested. In order to improve the static pressure performance, the EHD pump examined in this paper was fabricated with a series of thin stainless steel wires (the outer diameter is 0.3mm). The overall dimensions of the EHD pump were 30× 30×4.9mm and of the pumping channel were 24× 24× 0.9mm. An electrode pair consisted of one emitter electrode and two collector ones. The five sets of pumps were prepared for experiment. Those pumps were consisting of the number of electrode pairs from 1 to 5. The static pressure is measured with dibutyl-sebacate as a working fluid which has a dielectric constant, ε / ε 0=4.8 and a low electric conductivity, σ=4.7× 10-10S/m. The experimental results are compared with the theoretical results. In the theoretical model, the pressure is generated by Coulomb force which forces to move the unipolar ions in the high electric field. The experimental results indicate that the pressure increase as the number of electrode pairs increases and is generated up to 350Pa at an applied voltage of 1kV with 5 electrode pairs. Also, the experimental results show a good agreement with the theoretical ones. It is found that the theoretical model is useful for design of the high performance EHD pumps.
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  • Ichiro YAMANOI, Masaaki TAMAGAWA
    2006 Volume 49 Issue 3 Pages 755-760
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    This paper describes a fundamental investigation of a new shock wave application in a drug delivery system (DDS) using a microcapsule including a single gas bubble. In this study, to design effective disintegrated microcapsule using a microjet, bubble deformation by shock waves near a curved elastic wall, which is the model of this microcapsule, is observed in an optical shadowgraph system using a high-speed camera and analyzed by image processing. The results show that a bubble compresses after shock wave propagation and the minimum radius of the bubble decreases with its distance to the model wall. During its expansion, a bubble near the wall extends locally and sharply, and then collapses. This deformation speed is estimated of microjet speed. Deformation speed has the peak against the initial bubble position from the wall, and can be controlled by changing the kind of bubble gas, the position of the initial bubble, and the elasticity and curvature of the wall. Therefore, it is found that changing these parameters a microcapsule can control the degree of its disintegration.
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  • Masanobu IIDA, Katsuhiro KIKUCHI, Takashi FUKUDA
    2006 Volume 49 Issue 3 Pages 761-770
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    An analysis and a model experiment are performed on the compression wave generated by a train entering a tunnel with an entrance hood, which is a prevailing countermeasure for reducing the micro-pressure wave emitted from a Shinkansen tunnel portal. The tunnel entrance hood is a structure for extending a tunnel and has openings on its side walls or roof for decreasing the pressure gradient of the compression wave generated by train entry. The hood design has principally been performed through model tests since the three dimensionality of flow field is generally important. Thus, a more efficient design method is required. In this paper, an analytical method based on the aeroacoustic theory developed by Howe is applied to a short “acoustically compact” hood having a window on its side wall. Analytical results are in good agreement with experimental results including the effect of train offset in a double-track tunnel. It is also clarified by analysis that the performance of the entrance hood is greatly affected by the relative length of the train nose to the distance between the window and the hood entrance.
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  • Nobuyuki TSUBOI, Yoichiro MATSUMOTO
    2006 Volume 49 Issue 3 Pages 771-779
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    An experimental study of the interaction between a shock wave and a boundary layer over a flat plate with a sharp leading edge in hypersonic rarefied gas flow is presented. Experiments in a low-density wind tunnel using an electron beam probe were conducted at the Shock Wave Laboratory, RWTH Aachen, Germany. Rotational temperatures for stagnation temperatures of T0=670∼1000 K and Kn=0.024∼0.028 based on a reference length of 0.05m were calculated using Muntz’s method and Robben and Talbot’s method. The domain of quasi two-dimensional flow over the plate was determined from three-dimensional rotational temperature measurements. Nonequilibrium between translational and rotational temperatures was observed near the leading edge, and the experimental rotational relaxation length explains the rotational collision number of 2∼4.
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  • Hiroaki MATSUMOTO
    2006 Volume 49 Issue 3 Pages 780-786
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    The rotational energy gain function for Monte Carlo simulation of an inelastic molecular collision in rarefied gas flow is revised by analysis using a combination of Monte Carlo integration and classical trajectory calculation (CTC) for diatomic molecules. The rotational energy gain function presented here is combined with the statistical inelastic cross-section (SICS) model and applied to evaluation of the transport coefficients of nitrogen gas using the Wang-Chang-Uhlenbeck (WCU) theory. The normal shock wave structures for nitrogen determined by the proposed energy gain function, Parker’s energy gain function, and from experimental data are compared, and it is shown that the transport coefficients and shock wave structures given by the proposed function are in better agreement with the experimental results than Parker’s energy gain function.
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  • Tae-Yoon KIM, Bo-Sung LEE, Yo-Cheon KU, Dong-Ho LEE, Yasuaki KOHAMA
    2006 Volume 49 Issue 3 Pages 787-796
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    In this study, passive control methods for attaching horizontal and vertical fences on the lower surface of the cylinder near a moving ground were adopted to enhance the aerodynamic characteristics with the changes in gap height. The horizontal fences increase the domain where the lower separated shear layer is interfered by viscous effect on the ground. In a moving ground, this viscous effect is only slightly observed due to elimination of shear layer induced by relative ground motion. However, vertical fences diminish the momentum provision intended to roll up to wake region by blocking the gap flow, thereby suppressing the vortex shedding irrespective of ground conditions. Therefore, the horizontal fences in a moving ground have the advantage of reducing averaged lift and drag though cannot suppress the vortex-induced oscillation. Even though vertical fences have an advantage of suppressing vortex shedding past a cylinder, the existence of the vertical fences themselves causes the averaged drag to increase above the critical gap height due to the existence of vertical fences.
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  • Kazuhiko KATO, Hirotaka DAN, Yasuaki MATSUDAIRA
    2006 Volume 49 Issue 3 Pages 797-805
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    The violent cavitation breakdown occurs periodically during vortex cavitation shedding when a sheet cavity elongates near the trailing edge of a hydrofoil. This causes unsteady and nonlinear fluid forces to act on the hydrofoil. This nonlinear behavior, when the breakdown frequency locks at the pitching frequency of the cavitating hydrofoil, has not yet been clarified. The unsteady lift coefficient and the flow structure of a pitching NACA hydrofoil under the lock-in phenomenon were clarified by load cell measurement and particle and bubble image processing for PIV. As the main result, in the Subcavitation region, when the elongation of the sheet cavity cannot follow the variation of the pitching angle at a highly reduced frequency, the pitching lift coefficient is offset similar to that of nonpitching oscillation. In the Transition region where cavitation breakdown frequently occurs, the reduced frequency range for the pitching lift coefficient can be characterized roughly into the Unlock-in, Quasi-lock-in and Lock-in ranges according to whether or not the breakdown frequency is synchronized with the pitching frequency.
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  • Mitsuru SHIMAGAKI, Tomoyuki HASHIMOTO, Mitsuo WATANABE, Satoshi HASEGA ...
    2006 Volume 49 Issue 3 Pages 806-811
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    In this investigation, pressure fluctuations in an inducer were observed in order to examine the characteristics of unsteady cavitation at lower cavitation coefficients. From the spectrum analysis, it was confirmed that the pressure fluctuations occurred with the frequency of 0.6× ωs (ωs, shaft rotational frequency), 1.0×ωs, 1.1∼ 1.3×ωs and also 2.1×ωs. The 0.6×ωs was caused by the rotating phenomena in an inducer rotational direction. The 1.1∼ 1.3×ωs was caused by the super-synchronous rotating cavitation. The 2.1×ωs was caused by rotating cavitation in the counter direction. In addition, the amount of head reduction of the inducer caused by the synchronous cavitation (1.0×ωs) depended on the cavity pattern of the blades.
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  • Keisuke HORIUCHI, Prashanta DUTTA
    2006 Volume 49 Issue 3 Pages 812-819
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    We analyze heat transfer characteristics of steady electroosmotic flows with an arbitrary pressure gradient in two-dimensional straight microchannels considering the effects of Joule heating in electroosmotic pumping. Both the temperature distribution and local Nusselt number are mathematically derived in this study. The thermal analysis takes into consideration of the interaction among advective, diffusive, and Joule heating terms to obtain the thermally developing behavior. Unlike macro-scale pipes, axial conduction in micro-scale cannot be negligible, and the governing energy equation is not separable. Thus, a method that considers an extended Graetz problem is introduced. Analytical results show that the Nusselt number of pure electrooosmotic flow is higher than that of plane Poiseulle flow. Moreover, when the electroosmotic flow and pressure driven flow coexist, it is found that adverse pressure gradient to the electroosmotic flow makes the thermal entrance length smaller and the heat transfer ability stronger than pure electroosmotic flow case.
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  • Kuohsiu David HUANG, Sheng-Chung TZENG, Wei-Ping MA, Tai-Sheng WU
    2006 Volume 49 Issue 3 Pages 820-830
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    This study attempts to improve the local high temperature distributions in rotary-blade-coupling (RBC), which is the source of motive power for sport-utility-vehicles (SUV). The experiment takes RBC with forced convection and circumferential ribs for the research on heat transfer enhancement. During rotation, RBC produces centrifugal fluid flow, convection phenomenon and temperature distributions that differ with rotational speed. Simultaneously, rotation enhances the turbulence intensity of the flow field, promoting heat transfer and destabilizing Taylor vortices. This instability influences the local heat transfer distribution and damages the machine parts because of overheating. To analyze the actual convection of the rotary flow field, the experiment testing section is designed based on the actual size of the RBC. In the experiment, the RBC is cooled via forced exterior oil supply, and ring-shaped turbulence ribs of three aspect ratios (AR=5/3, 2.5, and 10/3) are added to augment the heat transfer area, for discussing the axial temperature distributions at the top and bottom of the RBC. The experiment adopts major physical parameters within 2.856 × 105Ta≤2.031 × 106 and 0.053 ≤Re ≤1.054 to discuss the heat transfer effect in the interior rotary flow distribution groove of RBC in the four-wheel-drive (4WD) vehicle. Finally, based on the relevant experimental results, an empirical correlation is established for the reference of 4WD vehicle designers.
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  • Yi-Hsiang CHENG, Chunkuan SHIH
    2006 Volume 49 Issue 3 Pages 831-838
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    This study presents a new approach that uses a genetic algorithm (GA) to optimize the arrangement of two-stage thermoelectric coolers (TECs). Three practical configurations of two-stage TECs, 1) with two stages electrically connected in series, 2) with two stages electrically separated from each other and 3) with two stages electrically connected in parallel, were studied. Parameters, the applied electrical current and the number of thermocouples in each stage, were optimized to maximize the cooling capacity and the coefficient of performance (COP). The optimal parameters of each two-stage TECs were determined for each target cold-side temperature, and the maximum cooling capacity and the maximum COP were thus reached. The results of the optimization show that the electrically separated two-stage TECs yield the maximum cooling capacity, whereas the two-stage TECs that are electrically connected in series and electrically separated both produce the maximum COP. The optimal design of two-stage TECs can be realized using GA, and this method has considerable potential in designing a complex TEC system.
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  • Itoro Etim AKPAN, Masafumi SASAKI, Noboru ENDOH
    2006 Volume 49 Issue 3 Pages 839-846
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    A simplified double grade meteorological data model for the simulation of the annual performance of a domestic-size renewable energy system is proposed. With the model, only two representative days (clearest and cloudiest) during each season of the year are necessary to estimate annual energy balances, carbon emissions and the running costs. The model was chosen in preference to other simplified models based on the error distributions from the results of the continuous simulations in a test period. Detailed numerical simulation studies show that the carbon emissions from the renewable energy system are about 16%of a comparable conventional system. The thermal energy produced by a solar collector during the winter season, however, is insufficient to meet all the loads so that frequent heat pump operations and the auxiliary boiler are necessary in cold climate regions.
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  • Susumu NODA, Shuhei YAMAMOTO
    2006 Volume 49 Issue 3 Pages 847-855
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    The flame base structures of laminar lifted flames are numerically investigated in order to develop a model of triple flame applicable to the flamelet model. The lifted flames formed in the downstream expanded duct developed by Kioni et al.are calculated systematically in terms of the fuel concentration gradient at the inlet using a variant of the HSMAC method, modified so as to deal with variations of density. The triple flame is formed at the flame base of lifted nonpremixed flame for every case, even the case which does not initially have partial mixing. The diffusion flame appears to be supported by the enhancement of the surrounding premixed flames, resulting in a temperature rise. All scalar quantities along the premixed flames of the triple flame decline along a similar profile in mixture fraction space, and scalar quantities in the region surrounded by the premixed flames are almost completely conserved. On the basis of the results, we developed a model of triple flame that is applicable to the flamelet model. In the model, the region without reaction upstream of the flame base is referred to as the unburned region (frozen flow structure region), followed by the transition region outside the premixed flames, in which the flame changes from the frozen structure to the fully burning diffusion structure. The region surrounded by the premixed flames is referred to as the triple flame structure region. The region following the triple flame structure region is the fully burning diffusion flame structure region.
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  • Atsushi MAKINO, Naohiro SHIBATA
    2006 Volume 49 Issue 3 Pages 856-863
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Relevant to the self-propagating high-temperature synthesis (SHS) process for the Ti-Al system, burning velocity and the range of flammability are examined theoretically. The heterogeneous theory for SHS flame propagation, presented in the literature is used. It is found that the effects of particle size, mixture ratio, degree of dilution, and initial temperature on the burning velocity and/or the range of flammability are the same as those for other representative systems. It has been confirmed that even for the Ti-Al system, a parameter defined as a product of the burning velocity and the particle size can be useful in correlating experimental results for flame propagation. It has also been confirmed that a parameter defined as the square of particle size divided by the compact diameter can be useful in correlating experimental results for flame extinction. In addition, it has been demonstrated that a fair degree of agreement exists between theoretical results and experimental data in the literature, as far as the trend and approximate magnitude are concerned.
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  • Kihyung LEE, Changhee LEE
    2006 Volume 49 Issue 3 Pages 864-868
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    The combustion and emission characteristics of gasoline-fueled stratified-charge compression ignition (SCCI) engine according to intake temperature and compression ratio was examined. The fuel was injected directly to the cylinder under the high temperature condition resulting from heating the intake port. With this injection strategy, the SCCI combustion region was expanded dramatically without any increase in NOx emissions, which were seen in the case of compression stroke injection. Injection timing during the intake temperature was found to be an important parameter that affects the SCCI region width. The mixture stratification and the fuel reformation can be utilized to reduce the required intake temperature for suitable SCCI combustion under each set of engine speed and compression ratio conditions.
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  • Masao YOSHIDA, Soichi ISHIHARA, Yoshio MURAKAMI, Kohei NAKASHIMA, Masa ...
    2006 Volume 49 Issue 3 Pages 869-875
    Published: 2006
    Released: February 15, 2007
    JOURNALS FREE ACCESS
    Effects of the number of fins, fin pitch and wind velocity on air-cooling were investigated using experimental cylinders for an air-cooled engine of a motorcycle. Experimental cylinders that had a various number of fins and fin pitches were tested in a wind tunnel. Then the temperature inside of the cylinder, on the surface of the fins and in the space between the fins was measured. Results indicated that the heat release from the cylinder did not improve when the cylinder had more fins and too narrow a fin pitch at lower wind velocities, because it was difficult for the air to flow into the narrower space between the fins, so the temperature between them increased. We also obtained the expression of average fin surface heat transfer coefficient derived from the fin pitch and the wind velocity. This expression is useful for the fin design of an air-cooled cylinder.
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