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Masahiro KONDO, Rei OKUMA, Jiro FUNAKI, Katsuya HIRATA
Article type: Article
Session ID: 1837
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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In the present study, the authors consider a control of the flow past a semi-infinite plate with a blunt front. The flow is one of the simplest separated-and-reattaching flows, and can be a model such as heat exchangers and flow straighteners commonly seen inside power plants, chemical plants and household appliances. As a control device, a rotating object, which is a small flat plate, is placed in the upstream of the semi-infinite plate. In a wind tunnel, the authors conduct flow-velocity-fluctuation measurements using a hot-wire anemometer for various control-object positions and rotation speeds. As a result, we can classify the controlled flow into four regions. Moreover, in order to clarify the characteristics for each region, the authors carry out (1) flow visualisations with particle-image-velocimetry analyses, and (2) velocity-profile measurements concerning time-mean and turbulence-intensity values.
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Osamu Terashima, Yukinobu Abe, Toshio Kanno, Masayoshi Sakamoto
Article type: Article
Session ID: 1838
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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A new rectifying device is developed that is constructed of octahedral blocks and has a low-pressure loss. The device consists of octahedral blocks and support struts. Experiments are conducted to test the airflow in a nozzle that has this new device in it. The downstream velocity profile is measured using a Pitot tube and a hot-wire anemometer. The experimental results show that the velocity profiles downstream of the rectifier that consist of octahedral blocks are better in uniformity compared to ones with a wire-mesh (8 mesh). The pressure loss coefficient of the new device is about 40% lower than the one with the wire-mesh. Thus, the new device is proven to be a useful rectifier.
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Takefumi Komaki, Taketo mizota, Takeshi Naruo
Article type: Article
Session ID: 1839
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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New wind tunnel balance for steady aerodynamic force measurement of three orthogonal components and one moment around perpendicular axes, which suspended by air bearing has been developed to measure weak air force on highly spinning golf ball. The each table oriented to each direction is balanced with small values of spring constant one. On the top table, one flame is mounted. In the center of this flame, one golf ball is suspended by fine piano wires. As a result, aerodynamic forces acting on the spinning golf ball are well detected on each table's small displacement. These table shifts are well measured using photonic displacement sensor. In this paper, each displacement is under well calibration stage.
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So MATSUMOTO, Hiroyuki HIRAHARA, Kenji HOSOI, Masaaki KAWAHASHI
Article type: Article
Session ID: 1840
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Nasal CPAP is one of the well-known artificial ventilation methods for neonatal breathing care. Different type devices for this method are being widely used in practical care, but some improvements in size, installation method and so on are still required. In order to meet these requirements, a new type of device has been developed and its fundamental characteristic has been investigated. In this report, detailed flow field in the device at each phase of breathing was analyzed by numerical method under the optimal condition confirmed by experiment. The result gives useful knowledge to improve the nasal CPAP device for clinical use.
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Mizuki KITO, Toshihiko SHAKOUCHI, Atsushi MORIE, Chayut NUNTADUSIT, Ko ...
Article type: Article
Session ID: 1901
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The effects of orifice nozzle plate thickness on orifice free jet characteristics were investigated experimentally. Hot-wire measurements of velocity distribution were conducted at Re=1.5×10^4 for different orifice plate thickness t/d_0≒0.01-1.5 (d_0: nozzle diameter). A Comparison with pipe jet having a fully developed turbulent pipe flow was also performed. The effects of vena contracta were apparently observed for small t and flow behavior similar to the pipe jet was seen as increasing t. Sudden increase of the jet center turbulent intensity at the nozzle exit occurred for the jet of t/d_0≒0.5, which has the shortest potential core length and the lowest dominant frequency than the other jets. It is also found that the jet of t/d_0≒0.5 spreads remarkably. This indicates that the jet from the orifice plate thickness t/d_0≒0.5 could fluctuate unsteadily at the nozzle exit.
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Tatsuya HASHIDO, Yasuaki KOZATO, Satoshi KIKUCHI, Shigeki IMAO
Article type: Article
Session ID: 1902
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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This study is concerned with the characteristics of the radial jet flow which reattaches on a rotating disk. The velocity fields near the side wall and in the jet were measured to clarify the variation of the basic characteristics of the mean flow. As the step height becomes high, the reattachment position of the jet moves to the upstream side depending on the increase of the disk rotating speed. The maximum velocity and the jet half-width change like the radial free jet until reattaching on a disk, and they show the change similar to the radial wall jet after the reattachment.
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Yoshihiro INOUE, Takaaki NISHIZUKA, Shintaro YAMASHITA, Haruhisa YANO
Article type: Article
Session ID: 1903
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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This study is to clarify the flow structure of a three-dimensional wall jet discharged on a flat surface from a circular nozzle. Mean velocities and fluctuating velocities in a cross section of a fully-developed flow region were measured by using a rotating single hot-wire probe. The direction of the mean flow in the inner layer is about constant and coincides with the radial lines from a virtual origin of jet. The distributions of the mean velocity in the normal direction to the wall are almost similar to each other in the inner scaling. Skin friction coefficients were estimated by means of the momentum balance analysis.
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Akinori MURAMATSU, On Ishikawa, Tomoya SASAKI
Article type: Article
Session ID: 1904
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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A natural development process of a low-density jet, such as a helium gas, is different from that of a constant-density jet. Side jets, which are radial ejections, are formed at vicinity of the nozzle exit and mixing of fluids between the jet and the ambient is enhanced. Main parameter to distinguish formation of the side jet is density ratio of jet fluid to ambient fluids. The other parameters are the Reynolds number and the shear layer thickness at the nozzle exit. Helium gas, helium-air mixture, and air are discharged from a round nozzle upward and visualized by planar laser Mie scattering (PLMS). The region for formation of the side jets in the density ratio-Reynolds number plane is illustrated. The velocity profile at the nozzle exit is measured by a hot-wire concentration probe and a hot-wire probe, and the momentum thickness at the exit is given. The region of the side jets in the density ratio-momentum thickness domain is shown.
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Koichi TSUJIMOTO, Hidetaka FUJII, Toshihiko SHAKOUCHI, Toshitake ANDO
Article type: Article
Session ID: 1905
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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In order to construct a low dimensional model for a round jet, fundamental properties of low-order mode are investigated. Based on the data of flow field provided with the DNS(direct numerical simulation) of a round jet, the flow field is decomposed into each mode using the snapshot POD(proper orthogonal decomposition) method. The energetic modes, i.e., 1st to 5th mode demonstrates similar spatial structures and intermittently appears accompanying a phase shift with each other. Namely it is suggested that the construction of low dimensional modes needs a certain number of modes compared to the previous-investigated simple flow, e.g., 2D cavity flow or, he flow around a circular cylinder. Further it is found that the energetic mode well represents the large-scale structures existing downstream compared to the instanteneou flow field.
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Kousuke AIZAWA, Hidemasa YAMANO, Nariaki UTO, Shoji KOTAKE, Osamu WATA ...
Article type: Article
Session ID: 1906
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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A conceptual design study of a large-scale sodium-cooled fast reactor adopts a two-loop primary cooling system with large-diameter piping in order to reduce plant construction cost. In this design, one of issues is a flow-induced vibration behavior of the piping under a high Reynolds number of 10^7 order. To evaluate the piping integrity, it is necessary to obtain power spectrum densities of pressure fluctuations on the piping wall by a numerical unsteady flow simulation. In this study, the numerical simulation capability of Reynolds stress model and large-eddy simulation in the STAR-CD code has been investigated using the 1/3-scale hot-leg test data. Through the sensitivity analysis, the Reynolds stress model with appropriate analytical models has shown the best applicability to flow dynamics simulation in the short-elbow pipe.
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Hisayoshi TSUKIKAWA, Hirioshi KANAYAMA, Kazuo MATSUURA, Masahiro INOUE ...
Article type: Article
Session ID: 1907
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Numerical simulation of leaking hydrogen impinges a ceiling in an open air is performed, and hydrogen concentrations are compared with the experimental data.. Fluctuation and oscillation of hydrogen concentrations in the boundary layer on the ceiling are recognized. Periodic expansion occurs at the hydrogen exit nozzle.
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Shohei NAMAITA, Hirotoshi IHARA, Kazuya SUMITA, Akinori MURAMATSU, Tom ...
Article type: Article
Session ID: 1908
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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A two-dimensional jet is a basic, free shear flow. The analytical solution of velocity for a laminar tow-dimensional jet was given by Bickley. The critical Reynolds number of the two-dimensional jet was obtained using linear stability theory and its value is approximately 20. However, it is very difficult to conduct the experiment on the jet flow at very low Reynolds numbers. We deal with the two-dimensional jet within the range of Reynolds number from 10 to 100. A pump was newly made to control the small flow rate accurately by a stepping motor. Flow visualization by smoke and velocity measurement by the hot wire anemometer are tried using the pump. From flow visualization of the jet flows, it is expected that the critical Reynolds number is between 30 and 40. Mean velocity profiles are in agreement with Bickley's profile.
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Yuki KOJIMA, Takaaki KATO, Yasuhiko SAKAI, Kouji NAGATA, Takashi KUBO
Article type: Article
Session ID: 1909
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The fluctuating static pressure plays an important role in the energy balance and anisotropy of turbulence. So, for understanding dynamical characteristics of turbulent flow, the simultaneous measurement of velocity and pressure field is essential. In this study, we attempted to develop the combined probe of X-type hot-wire and static pressure probe, and the measurement was carried out in two dimensional jet flow by this new combined probe. In the velocity spectrum, the κ^<-5/3> power low could be observed and in the pressure spectrum, the κ^<-7/3> power low could be observed.
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Tomoya HOURA, Kenji AMANO, Masato TAGAWA, Yasutaka NAGANO
Article type: Article
Session ID: 1910
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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We have measured temperature and concentration fields over a two-dimensional hill in an attempt to elucidate important characteristics of the complex turbulent flow. On the leeward side of the hill, the turbulent intensities peak along the dividing stream line. In the separation bubble, the mean temperature stays relatively high, and decreases to the free-stream temperature level. Thus, there exists a second maximum intensity of temperature fluctuations aside from the peak in the vicinity of the wall. On the other hand, the mean concentration profiles of ethylene (C_2H_4) show almost uniform in the vertical direction up to the height of the crest of the hill. Thus, the turbulent flow field strongly affects the temperature and concentration fields in a quite different manner.
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Yoshinori FUKUMURA, Takashi KUBO, Yasuhiko SAKAI, Kouji NAGATA
Article type: Article
Session ID: 1911
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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A two-dimensional jet diffusion in liquid-phase has been investigated experimentally in order to clarify an effect of turbulent mixing on chemical reactions. The chemical reaction used in this study is an one-stop, the second-order reaction (A + B→R). The equilibrium limits of concentrations of all the species (A, B, and R) have been estimated by the results on nonreactive diffusion field with the conserved scalar theory. It is found that the mean concentrations of reactants A and B decrease in the downstream direction as compared with the frozen limit by the effect of chemical reaction and the mean concentration of product R increases substantially near the nozzle. The concentration r.m.s. value of reactant B becomes larger than that of frozen limit near the nozzle, whereas that of reactant A becomes larger in the downstream.
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Aogu ONO, Tetsuya SATO, Masaki ENDO, Junjiro IWAMOTO
Article type: Article
Session ID: 1912
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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It is well known that some of sources of noise which radiates from an exhaust pipe of automobile engine exist in the flow field downstream of the pipe end. An unsteady jet issues periodically from the pipe end with shock waves, so that the unsteady jet interacts with them, resulting in the formation of the complicated flow pattern. To clarify the mechanism of noise generation, the flow field downstream of the pipe end is experimentally examined using a shock tube of diaphragmless type. Two shock waves are generated at short intervals of time in the tube. The flow field is visualized by shadowgraph method and different types of density waves are observed. The density wave is considered to be one of the sources of noise.
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Masaki ENDO, Yoko SAKAKIBARA, Eijiro INAMURA, Junjiro IWAMOTO
Article type: Article
Session ID: 1913
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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A supersonic jet issuing from a convergent nozzle impinges on a circular plate. The flow field between the nozzle and the plate is experimentally visualized and the vibration of the plate is measured using 8 strain gauges, which are radially glued to the plate, at different nozzle-to-plate spacings. The outputs of the strain gauges are analyzed using a FFT analyzer. It was found that the plate vibrates at certain natural frequencies and the vibration at each station has different phase differences. The behavior of the impinging jet is inferred from the pattern of the plate vibration, being compared to the structure of the impinging jet obtained from the visualized results in order to seek the causes. As a result, the jet is found to oscillate axisymmetrically at small nozzle plate spacing, while laterally at large spacing.
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Ryouta KOZUKA, Yoko SAKAKIBARA, Masaki ENDO, Junjiro IWAMOTO
Article type: Article
Session ID: 1914
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Three-dimensional oscillatory phenomena of a radial underexpanded jet are discussed in this paper. The jet issues from a small slit between two circular tubes. Flow field is visualized by the shadowgraph method and numerically simulated using TVD scheme. These are compared well to each other. Typical cell structure of the underexpanded jet is found to be formed around the tube and the shock waves in the cells are shown to be of ring shape. The numerical simulation shows that the flow in the downstream region of cells oscillates almost periodically and density contour lines in such region are seen to be swirled, which is caused by the phase difference in the circumferential direction of the radial jet.
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Soichi ITO, Yoko SAKAKIBARA, Masaki ENDO, Junjiro IWAMOTO
Article type: Article
Session ID: 1915
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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In this paper, the oscillation of an impinging jet on a spherical object is discussed. An underexpanded jet issuing from a convergent nozzle collides against a hemisphere which is glued to a flat plate. The flow field is visualized by the shadowgraph method and the numerical simulation is carried out using TVD scheme, and the frequency of the pressure change at the top of spherical object obtained by the computation is analyzed. As a result, it is found that the oscillation mode of the jet mainly depends on the position of the plate shock, and the feedback mechanism of the density disturbances in the flow field is shown by the computational results.
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Tomohiko Aoyama, Seiji Shimizu, Guoyi Peng
Article type: Article
Session ID: 1916
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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An abrasive suspension jet (ASJ) has a greater capacity for drilling and cutting than a conventional abrasive injection jet (AIJ). However, the drilling capability of the ASJ under submerged condition decreases steeply with the increase of the standoff distance. In order to expand the effective standoff distance of the ASJ under submerged condition, a sheathed ASJ nozzle was proposed in the previous paper. In the present paper, observations of the jet issuing from the sheathed nozzle are observed without any abrasive. The injection pressure is set to 5 MPa and the cavitation number is in the range from 0.02 to 0.05. A sheath made of transparent acrylic resin pipe is used and flows in the sheath are observed with high-speed video camera. The results show that a cavity full of vapor is formed in the root part of the sheath. The jet expands fully out to the sheath inner diameter in the region near the sheath exit and a bubbly mixture zone is formed. A cavitation cloud extends from the bubbly mixture zone until to a certain distance of the sheath exit and then break lumps of cavitation bubbles. The bubbly mixture zone in the sheath fluctuates with time and its frequency depends on the cavitation number.
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Toshihiro SAWAMURA, Shingo TSUBOTA
Article type: Article
Session ID: 1917
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The abrasive water jet consists of water and solid tiny particles. The cutting by abrasive water jet mostly progresses by particles. Therefore it is necessary that the particle distributions should be clear to know the cutting ability. This paper describes on the experimental study on the particle distributions in abrasive water jet. The measurements of distributions are carried out by gathering the water and particles in the box with a hole so that a part of the jet is able to go through. As the result, both the water and the particle mass distributions change by the condition of the jet and the nozzle shapes. Moreover, the 2nd peak appears in the particle mass distribution.
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Sota NAKAJO, Takaaki SHIGEMATSU, Gozo TSUJIMOTO, Naoya SAKASHITA
Article type: Article
Session ID: 1918
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Turbulence in pores of porous media in oscillating flow was measured by using a Particle Tracking Velocimetry with the Refraction index matching method. Relationship between turbulent energy and oscillating flow characteristics such as the Reynolds number and KC number is presented. Variation of generated turbulent energy in pores and vicinity of porous media in a phase is presented in detail.
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Toru Iai, Koichi Inose, Masashi Higashiura, Masahiro Motosuke, Shinji ...
Article type: Article
Session ID: 1919
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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A synthetic jet is promising technique to promote mixing and to control flow separation because it introduces flow perturbation without a net mass injection and can downsize the device. The purpose of this study is to investigate the three-dimensional flow behavior and the possibility on the interaction of the synthetic jet with cross flow in low Reynolds number using scanning stereo-PIV. Continuous jet with the same parameter is prepared to compare with the synthetic jet. A pair of longitudinal vortex is observed in both jets. The maximum vorticity of Synthetic Jet in cross flow (SJCF) remains higher than Continuous Jet in cross flow (JICF) at downstreem, although the vorticity of SJCF is similar to JICF near the orifice.
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Shunsuke Yamada, Keita Okamoto, Takashi Nitta, Masahiro Motosuke, Shin ...
Article type: Article
Session ID: 1920
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The objective of this study is to control the reattachment process of the separating and reattaching flow over a backward facing step in a low Reynolds number range by the synthetic jet. The Reynolds number based on the step height ranges from 300 to 900. The synthetic jet has a frequency of 10, 36, 70, and 150Hz. In order to investigate the effect of the periodic disturbance on the reattachment process, Micro Flow Sensor was used for measurement of phase-averaged forward flow fraction. The results show effectiveness of the synthetic jet for flow control. The reattachment process strongly depends on Reynolds number and a vortex motion which is generated at the separating shear layer.
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Shouichiro IIO, Ken HIRASHITA, Yoshiaki HANEDA, Toshihiko IKEDA
Article type: Article
Session ID: 1921
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Effect of acoustic excitation on rectangular jet characteristics, such as spreading, stretching and flapping, is discussed in this study. Sound wave locally irradiated the jet at a nozzle exit enables 'phase-lock' which means synchronization between flow oscillation and external sound. Therefore, hot-wire measurement by means of phase locking directly provides a phase averaged flow field. We especially focused on the effect of excitation modes, amplitude and frequency on jet characteristics. As a result, the jet flapping motion became strongly apparent for asymmetric excitation mode with large amplitude excitation. Then the jet spreading and shrinking in the major and minor plane occurred rapidly. In other words, the axis switching position moved upstream for this excitation condition. In contrast, for the symmetric excitation mode, jet pulsating motion was clearly observed, and there was no change in the jet spread rate. The enhancement of periodic-velocity fluctuation and non-periodic velocity fluctuation was completely different between both excitation modes.
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Fujio AKAGI, Sumio YAMAGUCHI, Youichi ANDO, Yusuke KATO, Masato FURUKA ...
Article type: Article
Session ID: 1922
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The effect of pulsatile flow conditions on the behavior of a wall boundary layer in a nozzle and the formation of a vortex ring induced by pulsatile jet flow is investigated by LES analysis and PIV measurement. The waveform of a pulsatile flow is performed by cosine curves. The result indicates that the amplitude condition of flow influence of the vorticity in a wall boundary layer and the separating time of a wall boundary layer. Separated boundary layer, which is shown negative vorticity area inside a nozzle, is attached vortex core region in the way of forming and is caused the change of a vortex ring diameter or a diffusion process of the vortex core region. The stop period of flow effect on diffuse vorticity in a separated boundary layer and so it doesn't effect on the vortex core region.
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Takashi NAITOH, Yusuke UTSUMI, Osamu SUMITOMO, Nobuyuki OKURA
Article type: Article
Session ID: 1923
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Characteristics of material transportation by using vortex rings with circumferential flow, so-called swirl, was investigated in a water tank. Vortex rings with swirl were generated by a piston-cylinder system that has rotating cylinder mechanism. The density distribution of particle material carried by vortex rings was measured by means of particle counting method. we quantitatively confirmed that the vortex rings with swirl can carry the fluid material farther downstream and the radial density distribution of transported material spreads wider as the strength of swirl increases.
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Hiroyuki TSUNODA
Article type: Article
Session ID: 1924
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Simultaneous measurements of instantaneous velocity and concentration fields were conducted using particle imaging velocimetry (PIV) and planar laser-induced fluorescence (PLIF) for the diffusion field of passive scalar in a round jet discharging into uniform counter-flow. Axial profiles of the concentration statistics along the jet centerline showed that both rms concentration fluctuation and axial turbulent flux of scalar have two certain peaks in the near field of the jet and in the mean stagnant region. It was also suggested that the absolute value of radial turbulent flux has a tendency to increase in the region where the counter flow deflects around the dividing stream surface.
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Yoichi Takahashi, Tomohiro Yamamoto, Nobuo Ogawa
Article type: Article
Session ID: 1925
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Turbulent jet, which is used in many industrial processes like heat transfer, admixture and reaction promotion, is studied to find a method of control. It has been reported that the control of opposed jet has the critical factor in the jet center. And, we try to examine the control method of the fluidic actuator by very small signals, for example, laser radiation pressure in axisymmetric flow fields. In this study, investigate role of thin cylinder around the jet center and discuss shift of the impact position by laser radiation pressure in the jet center in the opposed jets.
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Mizuki KITO, Toshihiko SHAKOUCHI, Koichi TSUJIMOTO, Toshitake ANDO
Article type: Article
Session ID: 1926
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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An orifice impinging jet improves the heat transfer characteristics on an impingement plate due to the vena contracta, but it has the high flow resistance. In order to reduce the flow resistance as well as maintain better heat transfer performance, we suggested a cone orifice nozzle. Effects of the cone angle α on the cone orifice free jet flow and heat transfer characteristics of the impinging jet are examined. The results were demonstrated that the suggested cone orifice nozzle with α=15° enhanced the heat characteristics greater than the common orifice nozzle at Re=1.5×10^4. Under the same operation power, the cone orifice jet of α=15° had better heat transfer performance than the pipe jet in the region near the stagnation point as well as the common orifice jet.
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Yasumitsu MATSUBARA, Shouichiro IIO, Yoshiaki HANEDA, Toshihiko IKEDA
Article type: Article
Session ID: 1927
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The experimental study of flow field and heat transfer characteristics of a rectangular jet impinging normally flat plate is performed. The jet velocity is set equal to 10 m/s which corresponds to Reynolds number of 6700. The excitation frequency is set at F_n=300Hz, F_n/2, 2F_n, where F_n is the natural frequency of the jet. Velocity distributions with two excitation modes are investigated by means of hot-wire measurement. We focused on the influence of forcing frequency and of the excitation mode (symmetric mode and asymmetric mode) on the heat transfer coefficient. As a result, for the short nozzle-to-plate spacing, the heat coefficient is enhanced with the both excitation modes of f_p=2F_n. A non-periodic velocity fluctuation enhanced the heat transfer, but there is little effect of a periodic velocity fluctuation.
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Yoshiaki HANEDA, Hideo KURASAWA, Shoichiro IIO, Toshihiko IKEDA
Article type: Article
Session ID: 1928
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Measurement of pressure and heat transfer on a jet target plate and flow visualization were carried out for mounting two parallel plates near both sides of the nozzle exit. The jet velocity was kept constant at 10m/s for the experiment on the pressure and heat transfer and the Reynolds number based on nozzle width, h=15mm, was about 9500. The distance, H, between the nozzle and the target plate was 2, 3, 4 and 5 times of h. The space, W, between two parallel plates changed from 2.67h to 6.67h or 8h. The flow directions for the presence of the two parallel plates irregularly changed for top and bottom. The root mean square value of fluctuating wall pressure and local Nusselt number on the target plate varied with W/h values. The maximum local Nusselt number were augmented by about 50% compared to the ones for normal impinging jet.
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Koichi Tsujimoto, Takahiko Inden, Taiga Ishikura, Toshihiko Shakouchi, ...
Article type: Article
Session ID: 1929
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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In order to improve the heat transfer on the wall, impinging jets is used in various industrial applications, and has been investigated experimentally and numerically so far. However, it is not enough to make clear the detail of vortical structure contributing to the heat transfer. In the present paper, DNS (direct numerical simulation) of the impinging jet is conducted to investigate the heat transfer through the different Re number flow. The discretization in space are performed with hybrid scheme in which Fourier spectral and 6th order compact scheme are adopted. From the statistical flow properties, it is demonstrated that depending on the Re number, the thinning of viscous layer induces the enhancement of heat transfer on the wall. In addition, from instantaneous view of flow structures, it is found that not depend on the Re number, the large-scale vortex rings are formed on the wall and contribute to the heat transfer enhancement.
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Masaharu ANDOH, Nobuhiro HOMMA, Masahiro MOTOSUKE, Shinji HONAMI
Article type: Article
Session ID: 1930
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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A horseshoe vortex (HV) at a wing-body junction introduces the reduction of wing performance. Vortex Generator (VG) is effective for the performance improvement. However, the loss is increased depending on conditions of flow and VG because of passive scheme for the flow control. Then, in this study Active Vortex Generator (AVG) which can change angle of attack of VG is utilized. The purpose of this study is to clarify the phase-averaged behavior of a HV with a pair of longitudinal vortices (LV) generated by AVG. NACA0024 wing at zero angle of attack was mounted in a wind tunnel. We measured three-components of velocity by the rotating X-probe hot-wire anemometer and total pressure by Pitot probe. In the Common Flow Down case, HV moves away from the wing and merges with LV. In the Common Flow Up case, HV moves toward the symmetry plane (Z/T=0). Dependence of VG angle on the total pressure loss under the vortex interaction is also clarified.
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Yuji OKITA, Katsutaka NAKAMURA, Timothy JUKES, Kwing-So CHOI
Article type: Article
Session ID: 1931
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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An experimental investigation of flow separation control over an airfoil has been carried out using yawed RF glow-discharge surface plasma actuators. Flow visualization using smoke injection and smoke wire techniques, as well as PIV measurements, have been conducted in a wind tunnel to demonstrate the ability of surface plasma in reattaching a separated flow. A short surface plasma electrode with different yaw angles was placed over a NACA 0024 airfoil at x/c=0.3 at 7° of angle of attack, where the flow normally separates without control The Authors were able to show the suppression of global flow separation by surface plasma-induced flow. The mechanism of flow reattachment by surface plasma is quite different from other type of actuators in that large-scale streamwise vortices seem to playa key roll
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Kenichiro Sakumoto, Takaya Kitahora
Article type: Article
Session ID: 1932
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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In this study, flow around an oscillating airfoil, which discrete vortices in accordance with the Kelvin's circulation theorem are included in, is solved by using the discrete vortices method. Then, Unsteady characteristics of airfoil, such as lift force and drag force, are estimated. The result shows that the amplitude of fluctuating lift force decreases than that of quasi steady result. During decrease process of setting angle, the pressure difference between both sides around the leading edge of airfoil is larger, and during increase process of setting angle, the pressure difference around the trailing edge is larger, than the results of quasi-steady solver, by cause of a direction of relative main flow or induced flow by discrete vortices.
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Takashi YASU, Koji MIYAJI
Article type: Article
Session ID: 1933
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Aerodynamic characteristics of a High-Lift-Device (HLD) are investigated by CFD. A two-dimensional configuration with a slat and flap for a taking-off arrangement is simulated. The k-ω SST turbulence model is carefully incorporated with a mean flow to treat complex flows around HLD, which includes the interaction of the separated shear layer from a fore-wing and the boundary layer on the aft-wing. The results are compared with experimental data and a previously reported simulation. The lifts coincide among them before the stall angle and the drag components also agree reasonably with the referred computation.
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Tomoki KURINAMI, Masaki FUCHIWAKI, Kazuhiro TANAKA
Article type: Article
Session ID: 1934
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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An unsteady flow in a low Reynolds number region attracts attention in recent years. The authors measured vortex flow in the wake of the elastic flat plate and elastic NACA0010 with heaving motions. Furthermore, we measured dynamic thrusts acting on these airfoils with heaving motions and clarified their relations with vortex flows. By giving an elasticity to the latter half of the flat plate, thrust-producing vortex streets same as those of the airfoils can be formed in the wake of the elastic flat plate with heaving motions. The dynamic thrusts that act on the elastic flat plate and elastic NACA0010 are strongly dependent on the Strouhal number based on the trailing edge amplitude regardless of heaving amplitudes, heaving frequencies, airfoil shapes and elastic deformations.
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Yoshifumi YOKOI, Keiko HIRAO
Article type: Article
Session ID: 1935
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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In this study, the flow features of vortex shedding from a circular cylinder oscillating along the direction of the flow and its characteristics of fluid force were simulated using a vortex method at the frequency ratios f/f_K=1.6 and f/f_K=3.0. the ranges of amplitude ratio 2a/d=0〜0.75 and Reynolds number Re=530. As a result of calculations, two typical flow patterns of the lock-in were shown, and it was confirmed that the calculated flow patterns were in reasonable agreement with previous experimental results. The fluid force act on the oscillating cylinder was investigated. It is understood that the drag amplitude is increased according to the oscillating condition and there is a part that becomes an impellent in the target momentarily. Moreover, it was clarified that the amplitude of the lift coefficient was larger than the amplitude of the drag coefficient in the lock-in of f_<VK>f=1/2, and the amplitude of the drag coefficient was larger than the amplitude of the lift coefficient in the lock-in of f_VK/f=1/1. When the amplitude ratio 2a/d grows, this tendency becomes remarkable.
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Masatoshi SANO, Ipei SUZUKI
Article type: Article
Session ID: 1936
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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An experimental study has been performed for turbulent channel flow over an inclined backward-facing step. The inclination angle of the step is varied from 30° to 90°. The wall static pressure and local heat transfer coefficient are measured behind the inclined backward-facing step. The velocity profiles and turbulent quantities are measured by PIV. It was found that the pressure drop at the step was reduced and the heat transfer coefficient in the recirculating region was improved by leaning the backward-facing step. Enhancement of the heat transfer coefficient was related to the increase of turbulent energy, Reynolds shear stress and turbulent diffusions.
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Yuki Honda, Hirokazu Hattori, Masahiro Motosuke, Shinji Honami
Article type: Article
Session ID: 1937
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The behavior of longitudinal vortex pair generated by active vortex generators and the interaction between the vortex pair were investigated by the measurement of three components of velocity with a rotating X-type hotwire anemometer. We can obtain the phase-averaged behavior of the vortex pair including the detail of the interaction process from the velocity, vorticity, and circulation data. The interaction between the vortex pair is dependent on the behavior of the VG trailing edge and the magnitude of the interaction affects the vorticity and circulation.
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Koji MUTO, Hiroo OKANAGA, Katsumi AOKI
Article type: Article
Session ID: 1938
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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It is known that the flow characteristics of the three dimensional bluff body such as a sphere depends on the surface structure. The purpose of this study is to clarify the relation of Aerodynamics characteristics and flow pattern for the surface structural change. In this study, the diameter of the test spheres are 42.6 and 100 mm. The number of dimples are 0, 104, 184, 328 and 504. Reynolds number is 1.27×10^5. Spin ratio α(α=V/U, V is rotational speed of the test sphere, U is uniform velocity) is changed from 0.049 to 0.198. The drag and lift are measured using a three components loadcell. The pressure around the test sphere is measured using a pressure transducer. And more, the flow visualization around the test sphere is performed applying the spark tracing method. As the results of these experiments, the drag and lift coefficient for the number of dimple, pressure coefficient, separation point and the flow pattern around the test sphere became clear.
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Hajime NAKAMURA
Article type: Article
Session ID: 1939
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Omnidirectional reductions in drag and fluctuating forces were achieved for a circular cylinder subjected to cross-flow by attaching cylindrical rings along its span at an interval of several diameters. In this work, the ring configuration, the diameter D, spanwise width W, and spanwise pitch P, was systematically varied in order to explore the optimum configuration for the vortex shedding suppression. The Reynolds number based on the cylinder diameter d was Red , 30000. As a result, it was found that the periodic pressure fluctuation on the sides of the cylinder due to the alternating vortex shedding was disappeared for the smaller pitch of P/d ≤ 4 at D/d = 1.3 and W/d = 1. This is likely to be related to the non-existence of the two-dimensional flow field in the near wake between two adjacent rings, due to the smaller axial spacing of the rings.
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Satoshi KAMEO, Takashi OHTA, Takeo KAJISHIMA
Article type: Article
Session ID: 1940
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The flow around solid bodies involves small density changes due to the compressibility of the air even with small Mach number. Since these small density fluctuations cannot be predicted by the incompressible method, the use of the weak compressibility method is proposed. The flow around a cylinder was simulated using the weak compressibility method and the incompressible method. The results obtained by the weak compressibility and the incompressible methods were compared. It was confirmed that the weak compressible method is capable to simulate the flow with low Mach number and take in account the density changes. The use of the weak compressibility method in this case, clarified the relation between the density fluctuation due to complex phenomena such as turbulence transition or separation.
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Yosuke YAMAUCHI, Hitoshi ISHIKAWA, Yasufumi YODA, Shunsuke YAMADA
Article type: Article
Session ID: 1941
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Flow field around a prism with sway motion was experimentally investigated by wind tunnel experiment. The prism, which was made of the polyurethane block, was cantilevered on a flat plate. The swaying motion of the prism involves a flow induced in-line oscillation with small amplitude. PIV measurement was conducted to show the instantaneous and the phase-averaged flow structure around the swaying prism. We discussed differences in flow structure between the curved prism and the pliant prism.
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Masaru SUMIDA, Kazumasa ZOTA, Taro FUJIMOTO
Article type: Article
Session ID: 1942
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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An experimental investigation was performed for the pulp-suspension flow in a duct, which is an extremely simplified model of a hydraulic headbox of paper-making machines. Flow visualization and optical measurements of the fiber concentration were made in the wake region of a flat plate. Characteristics of pulp-suspension flow were examined for five cases of fibers behavior appeared in the passages partitioned by the plate. A discussion is given on the time-averaged and the fluctuating fiber-concentration and on the flocculation and the breakdown of the fiber network.
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Daiji SONE, Masato YAMADA, Manabu YAMAMOTO, Toshiyuki SANADA, Takayuki ...
Article type: Article
Session ID: 1943
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Characteristics of the surrounding liquid motion through the collision of a pair of bubbles were experimentally investigated. Hypodermic needles and a bubble generator utilizing pressure oscillation were employed to exactly extract and highly reproduce the interaction between the liquid-phase motion and bubble motion at the collision. The recursive cross correlation PIV technique made it possible to obtain the accurate velocity field of the surrounding liquid motion of a pair of bubbles. From the PIV results, standard deviation of liquid-phase velocity was calculated as the turbulence intensity of turbulence induced by a pair of bubbles. Comparing the turbulence intensity of liquid-phase velocity at each case, the case of collision and the case of no collision, the turbulence intensity of vertical liquid-phase velocity is obviously different. Especially at the case of collision, the turbulence intensity of vertical liquid-phase velocity around the collision point shows high value.
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Koichi MORIKAWA, Hackho Kim, Masato YAMADA, Toshiyuki SANASDA, Takayuk ...
Article type: Article
Session ID: 1944
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Characteristics of surrounding liquid motion induced by single bubble and bubble swarm were experimentally investigated. Two types of bubble were precisely generated by bubble generator using audio speaker and hypodermic needle. PIV measurement was carried out to capture the liquid motion disturbed by bubbles. The liquid motion was analyzed from turbulence intensity defined by standard deviation of liquid-phase velocity fluctuation and bubble velocity. As a result, as increasing the bubble radius, the area of disturbance region increases in both single bubble and bubble swarm. In addition, horizontal component of turbulence intensity was obviously different.
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Tameo NAKANISHI
Article type: Article
Session ID: 1945
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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Contraction and inversion of a slab liquid jet occur as a result of surface tension forces. Numerical analysis of contraction and inversion of a slab liquid jet was conducted by the VOF method. Computational results qualitatively agree with the experiment measurements. The contraction length, however, is 20% larger than the experimental value. The discrepancy is considered due to the ignorance of the nozzle. Given H the width of the jet, We the Weber number, and L the contraction length, the contraction number is defined by C=L/(H We^∧0.5). A theoretical value of 1/4 is proposed based upon examinations of the flow field.
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Koichi Tsujimoto, Tomoki Wada, Makoto Nagaoka, Toshihiko Shakouchi, To ...
Article type: Article
Session ID: 1946
Published: August 02, 2008
Released on J-STAGE: August 01, 2017
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The improvement of the atomization of liquid jets is required in several engineering applications. Although the breakup process of liquid jets has been studied so far, the mechanism of second breakup contributing to the performance of atomization has not been well explained. Hence, in the present paper the temporal numerical simulation, which is a predictably effective method to analyze the breakup process in detail, is proposed. As remarkable features, the Cahn-Hilliard equation is employed to trace the interface between the gas-liquid two-phase flow. In order to validate and examine the possibilities of the proposed method, we compare the present results with both experimental and DNS results. Finally, the behavior of interface and eddy structures in each phase is investigated.
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