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Eric J. WHITNEY, Mourad SEFRIOUI, Karkenahalli SRINIVAS, Jacques PERIA ...
2002 Volume 45 Issue 1 Pages
23-28
Published: 2002
Released on J-STAGE: May 11, 2004
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The paper presents the recent developments in Hierarchical Parallel Evolutionary Algorithms to speed up optimisation of aerodynamic shapes. One is the implementation of different models in different layers of a Parallel Genetic Algorithm. The other is Asynchronous Hierarchical Evolution Strategy. These methods are employed to reconstruct a one-dimensional transonic nozzle and a two-dimensional aerofoil shape. Considerable speed up is achieved as a result.
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Jinhao QIU, Junji TANI, Toshiyuki HAYASE, Morio SUZUKI
2002 Volume 45 Issue 1 Pages
29-34
Published: 2002
Released on J-STAGE: May 11, 2004
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In this study, numerical simulation was performed with the SIMPLER method on the amplification of Tollmien-Schlichting (T-S) wave in the boundary layer over a flat plate and its suppression with a wall motion actuator. The T-S wave was induced by the interaction between sound wave introduced by a speaker and a protuberance on the surface of the plate, and amplified in the unstable region of the boundary layer. The vertical vibration of a wall motion actuator was used to control the T-S wave. The influence of the amplitude and phase of actuator vibration on the control effectiveness was investigated in the simulation. The results show that the T-S wave can be effectively suppressed by the motion of the actuator surface if the phase and amplitude of the actuator are appropriately adjusted.
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Mizue MUNEKATA, Eiji SHIBATA, Kazuyoshi MATSUZAKI, Hideki OHBA
2002 Volume 45 Issue 1 Pages
35-40
Published: 2002
Released on J-STAGE: May 11, 2004
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The surfactant used in this study is well known as an additive for drag reduction in straight (non-swirling) pipe flow. This paper deals with swirling flow characteristics of a surfactant solution. We investigated the effects of surfactant concentration and Reynolds number on flow characteristics. It is shown that the drag reducing effect is less than in straight pipe flow, and that the surfactant solution must be highly concentrated with great elasticity in order to produce a drag reduction. As the results of velocity measurement by LDV and wall pressure measurement in the axial direction, it is expected that the swirl intensity of the drag reducing swirling flow with a surfactant decays more quickly as the flow progresses downstream. And we propose that this mechanism helps create the drag reduction in swirling flow. For the velocity profiles of drag reducing swirling flow, only the forced-vortex type is observed in this experiment. This suggests that the velocity profiles of drag reducing swirling flow change more quickly to a forced-vortex type from a Rankin's combined vortex type. It is also reported that turbulence intensity of drag reducing swirling flow is smaller than turbulence intensity of a solvent.
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Takashi SHIMURA, Makoto YOSHIDA, Kenjiro KAMIJO, Masaharu UCHIUMI, Yos ...
2002 Volume 45 Issue 1 Pages
41-46
Published: 2002
Released on J-STAGE: May 11, 2004
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The cause of 350 Hz large-amplitude rotor vibration of the H-2A rocket's LE-7A fuel turbopump was investigated by wideband oscillating-pressure measurement. Measurement was successfully conducted by quartz-type pressure sensors in full-load liquid-hydrogen tests. The phase difference of pressure oscillations between two pressure measurement ports under conditions of pump cavitating operation revealed a phenomenon similar to rotating stall in turbomachinery which had not been previously observed. The rotating speed of a cell was 350 Hz, about a half the rotor speed. This phenomenon is different from rotating cavitation in which the cavitation pattern rotates around the periphery of an impeller faster than shaft rotating speed. Based on these findings, it was concluded that this phenomenon cased the large-amplitude 350 Hz vibration of the LE-7A fuel turbopump. Results of FFT analysis of measured oscillating pressure are presented.
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Akira FUJII, Seiji AZUMA, Yoshiki YOSHIDA, Yoshinobu TSUJIMOTO, St&eac ...
2002 Volume 45 Issue 1 Pages
47-54
Published: 2002
Released on J-STAGE: May 11, 2004
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Unsteady stress-of 4-bladed inducer blades was measured at the blade root near the leading edge with and without inlet flow distortion. The following results were obtained: (1) Without the inlet flow distortion, the mean stress of the blade with shorter cavity is smaller than that with longer cavity under the alternate blade cavitation at intermediate cavitation number. At lower cavitation number, the stress fluctuation occurs caused by the cavitation instability such as rotating cavitation/cavitation surge, which is one of the major causes of stress fluctuations in inducers. (2) The magnitude of the blade stress fluctuation due to the interaction with the inlet flow distortion basically decreases as we decrease cavitation number. With inlet flow distortion, the occurrence ranges of alternate blade cavitation and cavitation instabilities shift toward lower cavitation number. Under the alternate blade cavitation, the fluctuation of longer cavity causes the stress fluctuation of the adjacent blade with shorter cavity. The stress fluctuations caused by the rotating cavitation and acvitation surge are nearly the same level as those in case without inlet flow distortion.
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Jing LIU
2002 Volume 45 Issue 1 Pages
55-60
Published: 2002
Released on J-STAGE: May 11, 2004
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Magnetorheological (MR) fluids are suspensions of magnetizable micrometer particles in a liquid. The rheological properties of the fluids can be changed rapidly, reversibly and repeatedly from that of a liquid to that of a solid when an external magnetic field is applied. This tunability of the fluids comes from the microscopic structure of the particles. Different microscopic structures are observed, quantified and correlated with rheological properties. The yield stress and viscosity of MR fluids depends on the particle size and volume fraction, sample cell geometry, magnetic field strength and application rate. The application of MR fluids in cancer therapy is discussed. In-vitro experiments show the blood flow can be blocked leading to a tumor by injecting a dilute MR fluid in a blood vessel and placing a magnet on top of the tumor. Without blood supply, tumor necrosis occurs shortly.
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Hiroshi YAMAGUCHI, Zhongguo ZHANG, Shigemitsu SHUCHI, Kunio SHIMADA
2002 Volume 45 Issue 1 Pages
61-65
Published: 2002
Released on J-STAGE: May 11, 2004
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Transition phenomena for the natural convection of a magnetic fluid in a square cavity was studied numerically for an externally imposed magnetic field. In the present study, particular attention was focused to verify heat transfer characteristics for non-gravity situation when the magnetic field was imposed. By applying magnetic fields the convection state many be largely affected improving heat transfer characteristics followed by various flow transitions in the non-gravity simulation. It was revealed that magnetic field could enhance the convection and consequently improves heat transfer characteristics, indicating that the magnetic field would be used as a substitute for the gravity in the zero-gravity situation of space.
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Zhihong LIU, Toshihiro KAWAGUCHI, Toshitsugu TANAKA, Yutaka TSUJI
2002 Volume 45 Issue 1 Pages
66-71
Published: 2002
Released on J-STAGE: May 11, 2004
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The effect of ambient air temperature on the minimum fluidization velocity U
mf of glass beads is investigated by Distinct Element Method (DEM). Under different ambient air temperatures, the pressure drop curves are calculated by DEM to determine U
mf. The mean kinetic energy E of particles is defined to judge whether the particles move or not. The fluidization characteristics of fluidized bed are investigated in details. The calculated U
mf is compared with empirical data. The different behavior of Geldart B and D particles against temperature is reproduced numerically. U
mf decreases with increasing ambient temperature for Geldart B particles, while it increases for Geldart D particles.
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Shigefumi NISHIO, Hiroaki TANAKA
2002 Volume 45 Issue 1 Pages
72-78
Published: 2002
Released on J-STAGE: May 11, 2004
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Great efforts have been made to attain a good understanding of boiling heat transfer, but we have a poor understanding for the boiling structures in high heat-flux boiling. For example, there are still opposing opinions for the mechanism of the critical heat flux in saturated boiling and there are no rigorous models for that in subcooled boiling. In the present paper, the nucleation site density (NSD) was measured using high-speed video pictures and an image processing technique. The video pictures were taken from below the boiling surface made of single crystal sapphire with a total reflection technique. Based on the experimental results of NSD, a simplified model predicting the contact-line-length density (CLLD) at CHF is proposed.
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Igor MEN'SHOV, Yoshiaki NAKAMURA
2002 Volume 45 Issue 1 Pages
79-84
Published: 2002
Released on J-STAGE: May 11, 2004
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The propagation of sound waves in a finite vortex is investigated by numerically solving the linearized Euler equations in two dimensions. Two types of vortices are considered: homentropic, when the entropy is uniformly distributed in space, and non-homentropic, or entropy stratified, when it is distributed non-uniformly. In the latter case, the results reveal instability of the perturbation field, which is caused by entropy-rotational waves excited in the vortex region by incident sound waves.
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Guowei YANG, Masahiro KONDO, Shigeru OBAYASHI
2002 Volume 45 Issue 1 Pages
85-90
Published: 2002
Released on J-STAGE: May 11, 2004
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An implicit multiblock Navier-Stokes solver, which contains the LU-SGS subiteration method and the HLLEW scheme, has been developed for numerical simulations on complex are realistic aerodynamic configurations. Two-level halo cells are used to communicate data between abutting blocks. The transfinite interpolation (TFI) and the elliptic method with boundary control are employed to generate the initial multiblock grid and to smooth the grid distribution in each block. A comparison is first done for the AGARD supercritical LANN-wing with single- and multi-block grids. Then the present method is applied to a NASA transport wing/fuselage configuration and the NAL supersonic transport (SST) model. The choice of multiblock grid topology from the view of aeroelastic calculation and the comparison of Euler and Navier-Stokes solutions are investigated.
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Mikiya ARAKI, Jun OSAKA, Shinji NAKAYA, Mitsutoshi OSHITA, Mitsuhiro T ...
2002 Volume 45 Issue 1 Pages
91-96
Published: 2002
Released on J-STAGE: May 11, 2004
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Early stages of transition to turbulence of compressible shear layers were investigated in the viewpoint of a linear stability analysis. The primary stage of the transition is by which instability of a laminar flow (
primary instability), in which disturbances develop into spanwise vortices and form a secondary flow. The secondary stage of the transition is by which instability of the secondary flow (
secondary instability), in which disturbances develop into streamwise vortices. In the present study, the primary and secondary instability problems were formulated as eigenvalue problems and solved numerically using spectral methods. At first, the primary instability problems were solved. From the eigenvectors of the primary instability, we obtain density, velocity, temperature and pressure fields of the secondary flow. Using these quantities, the instability of the secondary flow was calculated. For the secondary instability, it is shown that (1) growth rates of disturbances are larger than those in the primary instability, (2) growth rates of disturbances have a peak when the ratio of wavelength of the primary and secondary instability is approximately 0.8 and (3) growth rates of disturbances are less affected by flow compressibility than those in the primary instability.
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Hironori TAKEDA, Satoru YAMAMOTO
2002 Volume 45 Issue 1 Pages
97-101
Published: 2002
Released on J-STAGE: May 11, 2004
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An implicit time-marching method based on the LU-SGS scheme developed for self-field magneto-plasma dynamic (MPD) fully-ionized viscous flows is extended to the method for self-field MPD viscous flows considering a finite rate of ionization. The axisymmetric compressible Navier-Stokes equations with Lorentz force and Joule heating, the equation of magnetic induction induced from Maxwell's equations with Ohm's law, and the continuity equation of electron are simultaneously solved using the present time-marching method. Partially ionized flows in an experimental MPD thruster are simulated and compared with the experiments. Also the effect of flow conditions such as the inlet temperature, the total current, and the rate of ionization to the flow field is numerically investigated.
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Hiroshi ENOMOTO, Hitoshi NAGATA, Daisuke SEGAWA, Toshikazu KADOTA
2002 Volume 45 Issue 1 Pages
102-107
Published: 2002
Released on J-STAGE: May 11, 2004
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In order to investigate the spray combustion mechanism, a new methodology (Fine Wire Sustaining method) was established. Fine wires of 14µm in diameter were used to sustain the droplets. Any arrangement of the droplets could be performed with this method. In this study, 33 fuel droplets arranged in symmetrically were subjected to the quiescent high temperature air in an electric furnace. The temperature of the environment air was about 1000K. Fuel was n-eicosane and the mean droplet diameter was 0.58mm. The standard deviation of the droplet diameter was 0.02mm. A high-speed video camera of 250ftp was provided to observe the auto-ignition and flames of fuel droplet clouds. The experiments were done at atmospheric pressure using the JAMIC drop shaft that provides 10 seconds of effective period of time for the micro-gravity. As the results, the time histories of the diameter of the particle flames had maximum and that of the diameter of the group flame had the minimum.
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Dirk RIECHELMANN, Soichiro KATO, Toshiro FUJIMORI
2002 Volume 45 Issue 1 Pages
108-111
Published: 2002
Released on J-STAGE: May 11, 2004
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In the present work, the effect of probability density function (PDF) selection and intermittency on the result of the numerical simulation are examined by the simulation of a turbulent methane-air jet diffusion flame, where air is preheated to 1073K. As to the PDFs, beta-function and clipped Gaussian are considered. It is found that intermittency has a large impact on the numerical result, while the choice of PDF has a minor influence. When intermittency is considered, the flame height becomes larger and maximum temperature decreases. Comparison of radial profiles with experimental data shows that it is necessary to consider intermittency also for high temperature air diffusion flames.
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Michael BIEHL, Wolfgang KINZEL
2002 Volume 45 Issue 1 Pages
112-116
Published: 2002
Released on J-STAGE: May 11, 2004
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We investigate a solid-on-solid model of epitaxial crystal growth in 1+1 dimensions. The emerging distribution of terrance sizes and the resulting currents on surfaces with a given inclination angle are calculated analytically. Furthermore, we evaluate the stable
magic slope which is selected due to the compensation of the competing effects. Results of Monte Carlo Simulations are in very good agreement with the theoretical predictions.
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Doosik KIM, Demetre J. ECONOMOU
2002 Volume 45 Issue 1 Pages
117-122
Published: 2002
Released on J-STAGE: May 11, 2004
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A two-dimensional fluid/Monte Carlo simulation model was developed to study plasma “molding" over surface topography. The plasma sheath evolution and potential distribution over the surface were predicted with a self consistent fluid simulation. The trajectories of ions and energetic neutrals were then followed with a Monte Carlo simulation. In this paper, energy and angular distributions of ions and energetic neutrals bombarding an otherwise planar target with a step are reported. As one approaches the step, the ion flux decreases and the ion impact angle increases drastically. For a time invariant sheath (DC case), the ion energy distributions (IED) remain relatively unaffected. When the plasma sheath oscillates at radio frequencies, the IED narrows, while the ion angular distribution becomes broader as one approaches the step. The energetic neutral flux is found to be significant near the vertical step wall. The simulation results are in good agreement with experimental data.
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Fumihiko TANAKA
2002 Volume 45 Issue 1 Pages
123-128
Published: 2002
Released on J-STAGE: May 11, 2004
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A simple transient network model is introduced to describe creation and annihilation of junctions in the networks of associating polymers. Stationary non-linear viscosity is calculated by the theory and by Monte Carlo simulation to study
shear thickening. The dynamic mechanical moduli are calculated as functions of the frequency and the chain disengagement rate. From the peak of the loss modulus, the
lifetime τ
x of the junction is estimated, and from the high frequency plateau of the storage modulus, the
number of elastically effective chains in the network is found. Transient phenomena such as
stress relaxation and
stress overshoot are also theoretically studied. Results are compared with the recent experimental reports on the rheological study of hydrophobically modified water-soluble polymeters.
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Heiner Müller-KRUMBHAAR, Thomas ABEL, Efim BRENER, Miks HARTMANN, ...
2002 Volume 45 Issue 1 Pages
129-132
Published: 2002
Released on J-STAGE: May 11, 2004
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The evolution of interfacial patterns during growth processes is shortly summarized. The analogy between hydrodynamic dewetting patterns and diffusion controlled growth patterns is demonstrated. A phase-field method for the treatment of hydrodynamic flow with free interfaces is presented and illustrated with some examples.
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