JSME International Journal Series B Fluids and Thermal Engineering
Online ISSN : 1347-5371
Print ISSN : 1340-8054
ISSN-L : 1340-8054
Volume 47 , Issue 3
Special Issue on Micro Mechanical Engineering
Showing 1-30 articles out of 30 articles from the selected issue
PAPERS
  • Tadahiro OHMI
    2004 Volume 47 Issue 3 Pages 422-428
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A large size display for entertainment, internet, PC and other information instruments is key tool for coming IT revolutionary era, so that the large size display must be characterized by very low electric power consumption and human friendly performance without tiring user's eyes. Thus, liquid crystal (LC) and electroluminescence (EL) displays are candidates for this target. High quality poly-silicon TFT is essentially required even for LCD displays instead current amorphous Si TFT, because very large current drivability is necessary for TFT due to the increase of LCD cell capacitor with an increase of display size up to 50 inches and beyond. The key issue for this target is a creation of very low temperature poly-Si TFT manufacturing technology without excimer laser annealing and very low cost manufacturing which is characterized by very simplified display structures and very simplified manufacturing steps based on very drastic progress of various relating materials and components such as backlights, polarizer, color filter, and etc.
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  • Masayoshi ESASHI, Takahito ONO, Shuji TANAKA
    2004 Volume 47 Issue 3 Pages 429-438
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    Advanced states of art of MEMS (Micro Electro Mechanical Systems) technology have been applied to micro industry equipments. These are electrostatically levitated ring rotor gyroscope and micro energy source for self moving machines like robots, maintenance systems used in narrow spaces, components for multi-column electron beam lithography and multi-probe data storage, micro gas control systems, micro/nano mold, micro contactor and thermal RF relay for LSI testing and nano-instruments which performs high sensitivity and spatial resolution.
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  • Hiroshi TOSHIYOSHI
    2004 Volume 47 Issue 3 Pages 439-446
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    This paper overviews the MEMS applications to micro optics and focuses onto recent development in the field of fiber optic telecommunication such as optical crossconnects, variable optical attenuators, and general spatial light modulators using microelectromechanical scanning mirrors or lenses. We also discuss common topics in MEMS that await technical solutions such as lower driving voltage, higher mechanical tolerance and better electromechanical stability. As a next target, we present a new perspective to nanophotonic approach of MEMS where photonic crystal waveguides are integrated with micro/nano mechanical devices to realize highly integrated photonic circuits.
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  • Toshio TOMIMURA
    2004 Volume 47 Issue 3 Pages 447-452
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A series of experiments have been performed to investigate the filler insertion effect on the temperature drop at the wavy contact interface ΔT and the mean thermal contact conductance hm, f. Representative behavior of ΔT against the mean nominal contact pressure pm is clarified, and the effect of an interval of time on ΔT is shown for the silicone filler with thickness δfo=2mm. The silicone elastomer is proved effective to increase hm, f despite its low thermal conductivity. Further, it is shown that hm, f of 0.5mm thick silicone filler becomes two to three times higher than that of bare contact under the unloading process. However, it is also shown that hm, f decreases with increasing δfo, therefore filler insertion with improper thickness results in a reverse effect on increase in hm, f. As for metallic filler insertion using an aluminum or a copper foil, only a little improvement in hm, f is obtained in spite of its high thermal conductivity.
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  • Kenji SUZUKI, Masayuki KURITA
    2004 Volume 47 Issue 3 Pages 453-458
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    This paper describes design and fabrication of a MEMS-based active-head slider using a PZT thin film for flying height control in hard disk drives. A piezoelectric cantilever integrated in an air bearing slider is used to adjust the flying height individually. A novel air bearing surface (ABS) geometry that minimizes the aerodynamic lift force generated beneath the head has been designed on the basis of the molecular gas film lubrication (MGL) theory. The slider with PZT actuator was fabricated monolithically by silicon micromachining. Performance of the actuator was tested by using an optical surface profiler. Furthermore, the fabricated slider was mounted on a suspension and flying height of the slider above a spinning disk has been measured by means of interferometry. Change in the head-disk spacing has been successfully confirmed by applying voltage to the PZT actuator.
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  • Kousuke ISOMURA, Shuji TANAKA, Shinichi TOGO, Hideki KANEBAKO, Motohid ...
    2004 Volume 47 Issue 3 Pages 459-464
    Published: 2004
    Released: February 22, 2005
    JOURNALS FREE ACCESS
    Micromachine gas turbine with centrifugal impellers of 10mm diameter fabricated by 5-axis micro-milling is under development at Tohoku University, in conjunction with Ishikawajima-Harima Heavy Industries Co., Ltd. (IHI), Tohoku-Gakuin University, and Sankyo Seiki Mfg. Co., Ltd. The development is currently at the stage of proving the feasibility of the gas turbine cycle by component tests. Micro-combustors have been developed for both hydrogen and methane fuel. Over 99.9% of the combustion efficiency has been realized in both combustors and the baseline configuration of the combustor for the gas turbine is set. A compressor of 10mm diameter has been developed as a micromachined turbocharger. The performance test of the micromachined turbocharger has been started, and ran up to 566000rpm, which is approximately 65% of the design speed. Compressor performance has been successfully measured along a constant speed line at 55% of the design speed.
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  • Hirotaka KAMEYA, Masakazu AOKI, Shigekazu NOZAWA
    2004 Volume 47 Issue 3 Pages 465-469
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A reliability evaluation of meshing rotor surfaces needs contact theory on a micro size area. We propose a method to evaluate whether a screw compressor rotor has enough contact fatigue strength. The method is based on analyses of three dimensional curvatures and the Hertz contact pressure. At a contact point one of the principal curvatures directs the rotor's sealing line and this is calculated as the gap distribution. Another perpendicular curvature is calculated with an approximate arc to the rotor profile. As the contact point is an inflection point, the contact condition is first calculated on each side and then composed. Using our method we found the rotors of a typical screw compressor have enough strength. This is because the rotor contact pressure is calculated to be 0.57 times of a contact fatigue strength of their material.
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  • Tomio IWASAKI
    2004 Volume 47 Issue 3 Pages 470-476
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A molecular-dynamics technique for simulating interface diffusion, which is one of the dominant factors in mechanical failures of thin-film devices, has been developed. This technique was used to find effective methods for suppressing the interface diffusion and for stabilizing interfaces. Barrier-underlayer materials effective for improving the adhesion strength with interconnect films were identified by using this technique. Ruthenium was found to be an effective underlay material for improving the adhesion with Cu interconnects. The crystal orientation of Si substrates effective for reducing atomic diffusion at interfaces between the Si substrates and high-k dielectrics (ZrO2 and HfO2) was determined. The use of Si(111) substrates was found to be effective for suppressing the formation of interfacial layers.
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  • Katsutoshi KOBAYASHI, Hayato SHIMIZU, Masayuki KAIHO
    2004 Volume 47 Issue 3 Pages 477-482
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A fluid analysis system that automatically and quickly generates meshes by the so-called voxel method was developed. This system was applied to calculate the flow characteristics in a magnetic disk drive, an LCD (Liquid Crystal Display) projector, a volute-type mixed-flow pump, and around an elevator. These calculations agreed well with the experimentally measured characteristics; thus it can be concluded that the developed voxel-method-based fluid analysis system can be successfully applied to numerical simulation of the fluid flow for designing turbomachinery and other fluid-engineering devices with complicated boundary forms.
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  • Yoshihiro TAGUCHI, Yukihiro HORIGUCHI, Mikako KOBAYASHI, Toshiharu SAI ...
    2004 Volume 47 Issue 3 Pages 483-489
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    The nanoscale thermal properties are becoming increasingly important for the thermal design of electronic devises as the MEMS technology makes progress. The thermal conductivity of nanoscale thin film is remarkably lower than that of bulk materials because of its various size effects. In addition, the nano-materials will have pointing defects or lattice imperfections during the production process. Therefore, nanoscale thermal properties measurement technique, which can be applied in-situ or in-process, is required. We have developed a new thermal properties measurement technique by using near-field optics, which targets spatial resolution better than 100nm (up to 10nm) and is applicable to measure the thermal properties of nanoscale materials in-situ. In this article, in order to check the validity of the control system, the topographic image of diffraction grating is monitored. Moreover, the temperature change of Al thin film is detected as a thermoreflectance signal. Finally, the capability of our present work, to measure the thermal properties of nanostructures, is discussed.
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  • Masato IKEGAWA, Hitoshi AZUMA
    2004 Volume 47 Issue 3 Pages 490-496
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    Physical phenomena associated with the dynamic spreading and dried shape of droplets on solid surfaces were demonstrated reviewing several models and discussed with regard to designing the most suitable thin-film formation processes using ink-jet printing. After droplets strike a substrate surface and expand for several microseconds, they spread semi-statically for tens of seconds and asymptotically approach the final equilibrium shape determined by droplet volume and contact angle. The contact angle and the volume, number, and impact velocity of droplets for various ink-jet-deposition applications can be designed by using semi-empirical formulas. If the contact angle at the edge of droplet on the substrate is small, a large amount of solute might accumulate there during the drying process because the evaporation rate there is high. The evaporation rate distribution on droplet surfaces should therefore be controlled to be uniform in radial direction during drying.
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  • Masamichi KOHNO, Yoshihiko MATSUOKA
    2004 Volume 47 Issue 3 Pages 497-500
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    Laser microfabrication using a diffraction-free beam (Bessel beam) was performed. Microfabrication with a deep focal depth is possible because a diffraction-free beam has a main lobe with a small diameter, which does not depend on propagation length. The diffraction-free beam was generated using an axicon lens, and the generation was confirmed using an optical microscopy image of a laser-fabricated spot on a silicon wafer. Nevertheless using a nanosecond pulsed Nd:YAG laser, microfabrication with a spot diameter < 1µm was realized. As a result of the deep focal depth of the diffraction-free beam, even if we change the work distance within a range of several millimeters, we are still able to maintain the diameter of the laser- fabricated spots to approximately 1µm. Since an almost straight penetration hole with a diameter of 3µm was drilled into SUS304 foil (20µm thick), it was found that the diffraction-free beam has a high feasibility for the high-aspect-ratio laser drilling of an opaque material due to its deep focal depth.
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  • Atsushi KAZAMA, Yasuhiro ITOU, Masaya HORINO, Kazuyuki FUKUDA, Masatos ...
    2004 Volume 47 Issue 3 Pages 501-507
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A three-dimensional (3D)-type MEMS optical switch with low insertion loss and low assembly cost has been developed. The switch consists of two optical beam scanners placed facing each other. Each scanner consists of a collimator array and two mirror arrays. The scanner controls the direction of each optical beam by means of two single-axis mirrors. The mirror arrays are fabricated by MEMS technology and contain holes through which the beam traverses in each mirror array. The mirror arrays are stacked directly on the collimator array, which is passively aligned using pins and alignment holes. Based on this structure, a prototype 32-port (with three extra ports) optical switch was developed. Measured insertion loss of six arbitrary paths in the switch is in the range of 1.5-1.9dB. It is thus concluded that a 3D-type optical switch assembled by wholly passive alignment with lower insertion loss than 2dB is feasible.
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  • Masahiro OHNO, Kazuhisa IWASAKI, Yoshimichi HAGIWARA
    2004 Volume 47 Issue 3 Pages 508-515
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    We have carried out a molecular dynamics simulation for the mixture of a cubic ice nucleus, supercooled water and a molecule of alanine dipeptide. The dipeptide molecule has been allocated near the nucleus surface. The dipeptide is found to approach the surface by the effect of hydrogen bond between two hydrophilic sites of the dipeptide and water molecules nearest to the liquid region in the ice nucleus. It is also found that the other hydrophilic sites far from the surface change their location with time due to the wobbling motion of the dipeptide molecule. This causes additional fluctuation of water molecules. These two sites and the hydrophobic site attenuate the approach of water molecules to the alanine dipeptide molecule or the ice surfaces.
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  • Hiroshi CHIBA, Tetsuro OGUSHI, Hideo NAKAJIMA, Teruyuki IKEDA
    2004 Volume 47 Issue 3 Pages 516-521
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    Lotus-type porous copper is a form of copper that includes many straight pores, which are produced by the precipitation of supersaturated gas dissolved in the molten metal during solidification. The lotus-type porous copper is attractive as a heat sink because a higher heat transfer capacity is obtained as the pore diameter decreases. We investigate a fin model for predicting the heat transfer capacity of the lotus-type porous copper. Its heat transfer capacity is verified to be predictable via the straight fin model, in which heat conduction in the porous metal and the heat transfer to the fluid in the pores are taken into consideration by comparison with a numerical analysis. We both experimentally and analytically determine the heat transfer capacities of three types of heat sink: with conventional groove fins, with groove fins that have a smaller fin gap (micro-channels) and with lotus-type porous copper fins. The conventional groove fins have a fin gap of 3mm and a fin thickness of 1mm, the micro-channels have a fin gap of 0.5mm and a fin thickness of 0.5mm, and the lotus-type porous copper fins have pores with a diameter of 0.3mm and a porosity of 0.39. The lotus-type porous copper fins were found to have a heat transfer capacity 4 times greater than the conventional groove fins and 1.3 times greater than the micro-channel heat sink under the same pumping power.
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  • Yuji SUZUKI, Joichi SAITO, Nobuhide KASAGI
    2004 Volume 47 Issue 3 Pages 522-527
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    Catalytic combustion of butane in micro-scale conduits is investigated. Nano-porous alumina formed through anodic oxidation of aluminum is employed for the support of platinum catalyst. Combustion starts at 250°C, and a heat release rate up to 710MW/m3 is achieved in a 0.6mm ID tube. It is found that the surface reaction speed is a limiting factor for the overall reaction rate. A prototype silicon-based catalytic combustor is designed and fabricated using MEMS technologies. The Pt/alumina catalyst layer is successfully integrated onto a silicon microchannel, and a Pyrex lid is anodically bonded onto the Si substrate. It is found in a preliminary experiment that the MEMS combustor also works well, but gives somewhat smaller reaction rate due to the thinner catalytic layer.
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  • Sohei MATSUMOTO, Yu-Chong TAI
    2004 Volume 47 Issue 3 Pages 528-533
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A micro flow regulator with a capability of continuous volume flow control of a ultra-small volume flow rate liquid in nL/min scale is reported. A valveless principle based on the temperature dependence of liquid viscosity and the parylene-based freestanding micro channel structure enabled an extremely simple structure of the regulator element. This simplicity and the small footprint are advantageous over other mechanically movable regulation valves as the driving element for integrated chemical devices that require flexible control of liquid flow. A prototype device was fabricated with the surface micromachining technology. The experimantal results using de-ionized (DI) water as working fluid showed that the flow rate was continuously controlled in the range of 100-200% of that in the room temperature regardless of the applied pressure drop, successfully proofing the initial concept.
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  • Akira YABE, Shigeki HIRASAWA, Nobuhide KASAGI, Takayuki KITAMURA, Eiji ...
    2004 Volume 47 Issue 3 Pages 534-540
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A new road map of future trends in micro-engineering and nano-engineering was established from the viewpoints of manufacturing and mechanical engineering. This road map was made by evaluating the results of questionnaires given to the leading engineers including elected trustees of the JSME, and by considering the discussions during the “International Symposium of Micro-Mechanical Engineering (ISMME2003)” held on December 2003 in Tsuchiura and Tsukuba, Japan. The micro- and nano-engineering were categorized from the manufacturing viewpoint. The road map shows the important trends in micro- and nano-engineering, which include new technological areas, as well as technical development, new manufacturing processes, and new kinds of mechanical engineering. The road map also estimates, from the engineering standpoint, the expected time for practical application and technological breakthroughs.
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PAPERS
  • Kazuhiko YOKOTA, Kimihiko MITSUDA, Yoshinobu TSUJIMOTO, Chisachi KATO
    2004 Volume 47 Issue 3 Pages 541-548
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    The present paper describes the vortex structure and the flow field of model experiments simulating the inlet flow of turbomachines at low flow coefficients. A new experimental apparatus was devised to freely set the axial velocity of the main flow and the axial and tangential components of the swirling backflow. The vortex structure was visualized by small air bubbles. It occurs in the shear layer between the main flow and the backflow. The number and the radial location of vortices are determined mainly by the axial and tangential velocities of the backflow normalized by the axial velocity of the main flow. These characteristics agree with those of the backflow vortex structure of real turbomachines. This shows that the vortex structures are caused by the roll-up of the shear layer between the axial main flow and swirling backflow, not associated with the flow interaction with individual blade of the impeller. It was shown that a two-dimensional linear stability analysis can reasonably predict the relation between the number of vortices and their radial location.
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  • Reima IWATSU
    2004 Volume 47 Issue 3 Pages 549-556
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    Numerical study was conducted for steady swirling flows of viscous incompressible fluid confined within cylindrical containers driven by the bottom wall rotating at constant angular velocity with top free surface. The flow axisymmetry is assumed and the top wall is treated as an undeformable flat free surface. The physical parameters to govern the flow field are the Reynolds number Re defined by the angular velocity of the bottom wall and the radius to height container aspect ratio h. In the previous experimental and numerical investigations, richness of meridional flow patterns was observed and these secondary flow patterns are classified into several flow types. Numerically obtained steady solutions are synthetically analyzed by the estimation of major transport mechanism of momentum whose information is disregarded in the topological classification of the flow types for representative physical parameters, and they point to qualitatively different characteristics for the flows with small and large aspect ratio respectively. When h is small i.e., h«1, a substantial portion of the fluid inside the cylinder exhibits a near rigid body rotation and notable meridional fluid motion is limited to a region in the vicinity of the side wall. Richness of meridional flow patterns formed by multiple surface bubbles or cellular zones are shown to be created in the region surrounding the axis of rotation where the Taylor-Proudman theorem prevails. When h is large i.e., h»1 on the other hand, the outcome of the analysis indicates that the reduced quasi-cylindrical equations hold as a fair approximation to describe the momentum balance in the vicinity of the axis of rotation where recirculating axis bubbles are formed.
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  • Tomiichi HASEGAWA, Shinji TOGA, Makoto MORITA, Takatsune NARUMI, Nobuh ...
    2004 Volume 47 Issue 3 Pages 557-563
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    Experiments of micro-flow control and micropump conducted by applying electric fields on the flow through a porous membrane have clarified that only NaCl solution in water is effective for the control of micro-flow among the liquids examined but KCl solution and a colloidal dispersion of polystyrene latex particles in water as well as NaCl solution are good as working fluids for the micropump. Although the applied voltages are less than 10V, performance of the present micropump is found belonging to the highest class in the past methods. Effects of electro-osmosis, electrophoresis and absorption were discussed about whether or not they may become causes of the present phenomena and it is concluded that absorption is most possible as a cause. The colloidal dispersion of polystyrene latex particles is thought to be a good working liquid, because it provides the flow rate proportional to the applied voltage without generating any bubble of by-product.
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  • Hiroshi YAMAGUCHI, Takuya KUWAHARA, Yoichi UENO
    2004 Volume 47 Issue 3 Pages 564-571
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    An investigation was carried out for swirling flow in a rotating pipe with highly viscous fluid containing micro-bubbles experimentally and numerically. In the numerical analysis, bubble trajectory of each bubble was calculated using resultant numerical flow field solutions. From experimental results, with an aid of the numerical simulation, data were obtained for the location of a stagnation point, which moves towards the inlet region as swirl ratio being increased. It was found that the position of the stagnation point had a particular convergence value in relation with Reynolds number and types of the rotating channel. In the bubble behavior, big bubbles fall into the stagnation point, and that the parabolic surface is formed by some smaller bubbles. Critical diameter of bubble, which was to be caught at the stagnation point, was also obtained numerically for the model rotating channels.
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  • Takeshi SETA, Koji KONO
    2004 Volume 47 Issue 3 Pages 572-583
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A lattice Boltzmann method (LBM) for two-phase nonideal fluid flows is proposed based on a particle velocity-dependent forcing scheme. The resulting macroscopic dynamics via the Chapman-Enskog expansion recover the full set of thermohydrodynamic equations for nonideal fluids. Numerical verification of fundamental properties of thermal fluids, including viscosity, thermal conductivity, and surface tension, agrees well with theoretical predictions. Direct numerical simulations of two-phase phenomena, including phase-transition, bubble deformation and droplet falling and bubble rising under gravity are carried out, demonstrating the applicability of the model.
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  • Keisuke NISUGI, Toshiyuki HAYASE, Atsushi SHIRAI
    2004 Volume 47 Issue 3 Pages 584-592
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    The present paper deals with a fundamental study of aerodynamic drag reduction for a vehicle with a feedback flow control. As the first step, two-dimensional calculation was performed for a flow around a simplified vehicle model. The mechanism of unsteady drag was investigated in relation to the vortex shedding from the model. The location of the control flow nozzle was so determined that the control flow influences the drag most effectively. The key in designing the present feedback control is the definition of the output signal. Based on the physical consideration of the drag generation, the location of the output velocity measurement was changed within a limited region near the front windshield. A systematic calculation revealed that the output signal defined in a small region results in a significant drag reduction of 20% with respect to the case without control. The present feedback flow control is generally applicable to the drag reduction of the bluff body for which the drag is generated under the same mechanism of essentially two-dimensional vortex shedding.
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  • Keisuke NISUGI, Toshiyuki HAYASE, Atsushi SHIRAI
    2004 Volume 47 Issue 3 Pages 593-604
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    This paper deals with a new flow analysis system, namely the hybrid wind tunnel, which integrates the experimental measurement with a wind tunnel and a corresponding numerical simulation with a computer. Analysis here is performed for the fundamental flow with the Karman vortex street in a wake of a square cylinder. A specific feature of the hybrid wind tunnel is existence of the feedback signal to compensate the error in the pressure on the side walls of the cylinder and the feed-forward signal to adjust the upstream velocity boundary condition. Investigation is focused on evaluating the hybrid wind tunnel as a flow analysis methodology with respect to the ordinary simulation and the experiment. As compared with the ordinary simulation, the hybrid wind tunnel substantially improves the accuracy and the efficiency in the analysis of the flow. Especially, the oscillation of the flow due to the Karman vortex street reproduced with the hybrid wind tunnel exactly synchronizes with that of the experiment, while that with the ordinary simulation never behave like that. In comparison with the experiment, the hybrid wind tunnel provides more detailed information of the flow than the experiment does.
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  • Md. Tawhidul Islam KHAN, Kunisato SETO, Zhixiang XU
    2004 Volume 47 Issue 3 Pages 605-611
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    The aeroacoustic performances of different perforated tubes were experimentally investigated. The length and the exit diameter of the tubes were fixed at 50mm and 10mm, respectively. Sound pressure level and thrust due to the exerted jet of the perforated tubes were measured and compared with each other. A perforated tube with forward-slanted perforations showed favorable performance. The shock structure of an underexpanded jet was removed using the perforated tube so that the generation of screech tone component was eliminated. However, the perforated tube with forward-slanted perforations suffered a discrete noise component when the jet pressure was very low. When the sharp edges at the inner surface of the perforated tube were removed the discrete component was eliminated. Moreover, the reduction in tube thickness also improved the noise suppression performance of the forward-slanted oblique perforated tube.
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  • Ken-ichi FUNAZAKI, Kazutoyo YAMADA, Yoshiki KATO
    2004 Volume 47 Issue 3 Pages 612-621
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    This paper describes an experimental investigation on aerodynamic interaction between incoming periodic wakes from moving bars and separation bubble on a scaled leading edge model. Numerical simulations are also attempted to grasp an idea how the incoming wakes interact with the separation bubble. The model, which consists of a semi-circular leading edge and two flat-plates, is used to simulate the flow field around a compressor or a turbine blade. Cylindrical bars of the wake generator produce the periodic wakes in front of the test model. The study aims at enriching the knowledge on how and to what extent the periodic wake passing suppresses the leading edge separation bubble. Special attention is paid to emergence of wake-induced turbulent spots and subsequent calmed regions. Hot-wire probe measurements are executed under five different flow conditions to examine effects of Reynolds number, Strouhal number, direction of the bar movement and incidence of the test model against the incoming flow. The measurements reveal that the wake moving over the separation bubble does not directly suppress the separation bubble. Instead, wake-induced turbulence spots and the subsequent calmed regions have dominant impacts on the separation bubble suppression for the all test cases.
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  • Hajime NAKAMURA, Tamotsu IGARASHI
    2004 Volume 47 Issue 3 Pages 622-630
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    This paper describes the unsteady and three-dimensional characteristics of heat transfer from a circular cylinder to the cross-flow of air for Reynolds numbers from 120 to 30000. An infrared camera was used to measure the time-spatial characteristics of heat transfer on the cylinder surface, heated under a condition of constant heat flux. Fluctuating heat transfer was measured using a heat flux sensor. The heat transfer in the separated flow region had a spanwise nonuniformity, the wavelength of which agreed well with that of the streamwise vortices formed in the near-wake. In particular, the streamwise vortices formed at approximately Re=200 due to “mode-A” instability effectively enhanced the heat transfer at the rear of the cylinder. For Reynolds numbers greater than 6000, the heat transfer at the rear face was markedly increased by the alternating reattaching flow, caused by the rolling-up of the separated shear layers.
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  • Kazuhiko KUDO, Hong LI, Bing-XI LI, Jun SAITO, Akira YAMAGUCHI, Takash ...
    2004 Volume 47 Issue 3 Pages 631-636
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    A method to estimate the complex refractive indices of dielectric aerosols is developed. The three-dimensional radiative transfer problem in an absorbing-scattering medium is solved by the Monte Carlo method. Mie scattering theory is used to handle particle scattering and absorption. Magnesium oxide aerosol, with its well-known complex index of refraction, is selected as an example of a dielectric aerosol. Magnesium is burnt to produce MgO aerosol and the transmission of the radiation from a black body furnace through the aerosol layer is measured. The analytical results of the transmitted energy profiles along the wall facing the emission source, a black body furnace, were obtained for a wide range of complex indices of refraction and compared with the experimental results. It is shown that the value of the complex refractive index of an aerosol can be estimated.
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  • Shyy Woei CHANG, Yih Jena JAN, Lo May SU
    2004 Volume 47 Issue 3 Pages 637-646
    Published: 2004
    Released: February 15, 2005
    JOURNALS FREE ACCESS
    This paper describes an experimental study of heat transfer in an axially rotating tube fitted with twin twisted tapes. The manner in which rotation modifies the forced heat convection is considered for the case where the tube rotates about an axis in parallel to the tube's axis of symmetry with particular reference to the design of enhanced cooling channels for rotor windings in a rotating electro-machinery. A selection of experimental results illustrates the individual and interactive effects of Coriolis and centripetal buoyancy forces on heat transfer along the radially outer edge of rotating tube. With the prevailing swirl-flow structures generated by twin twisted tapes, the isolated Coriolis force effect plays a dominant role to initiate the heat transfer reduction form the static-tube scenario that is followed by a subsequent recovery which could lead to heat transfer improvement as the relative strength of Coriolis force increases. The reversed buoyancy impact from improving to impeding heat transfer develops at the higher level of Coriolis force. An empirical correlation, which is physically consistent, has been developed to permit the evaluation of interactive effects of swirling-flows, convective inertial force, Coriolis force and centripetal buoyancy on heat transfer.
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