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田部井, 勝稲 ; 春山, 周夏 ; 山口, 修市 ; 白井, 紘行 ; 高草木, 文雄
概要:
application/pdf<br />Journal Article<br />Characteristics of a micro bubble generator using a strong swirl jet were studied experimentally and numerically. Experiments were conducted by changing the nozzle diameter, the inflow pressure
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and the gas flow rate, systematically. For measurements of the bubble distribution function of PDF, a simple method using a light transmission was proposed. Principle of the method was based on changes of the light transmission due to the bubble rising to the surface of water. The bubble distribution measured by the method agreed well with that by a usual backlight method. In this study four non-dimensional parameters governing the micro bubble generation were adopted, that is, Weber number for the average diameter of bubbles, Reynolds number, the ratio of flow rate and the velocity ratio for the swirl jet. It was found that the relationship between Weber number and Reynolds number could be arranged with each velocity ratio as a parameter. An approximate experimental expression for the average diameter showed that the micro bubble diameter strongly depended on the axial flow velocity and the rotational speed of the swirl jet.
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| 2.
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舩津, 賢人 ; 渡辺, 泰夫 ; 白井, 紘行 ; 伊藤, 健 ; 石田, 清道
概要:
application/pdf<br />Journal Article<br />Spectroscopic measurements were made of a shock layer generated by a flat-head body in high-enthalpy air and nitrogen plasma flows of NAL 750kW arc-jet wind tunnel. In the wavelength region of 350nm
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to 450nm, N_2^+ 1- band was predominant in the nitrogen jets and the N_2^+ 1- and CN violet bands in the air jets. These bands were analyzed in detail by using synthetic spectra calculated theoretically. Temperature determination of the shock layer was tried by applying a spectral matching method to these band systems. In case of the nitrogen plasma jet, axial temperature distribution across the shock layer was measured and compared with the flow calculation based upon the modified fully-merged shock layer theory. It was found that the rotational temperature in the shock layer for both the arc jets was about 7000K, and the tempeature of a free stream in the nitrogen plasma jets was much higher than that expected.
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| 3.
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野村, 友和 ; 石間, 経章 ; 小保方, 富夫
概要:
application/pdf<br />Journal Article<br />Spatial correlation measurements of velocity fluctuations in turbulent flow over a rectangular cube are presented. Direct measurement of spatial correlation requires simultaneous measurement of
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velocities at two or multi-points in the flow. Therefore this study is carried out by means of a particle image velocimetry (PIV) or two LDAs (laser Doppler anemometer) composed by He-Ne and Ar^+ lasers. The cube is set on the floor of the wind tunnel. At the inlet, the mean flow velocity and the relative turbulence intensity are 4.0m/s and 1.5%, respectively in both experiments. Under this condition, the flow Reynolds number based on the rectangular cube height and the mean velocity is about 8800. Firstly, comparisons are made for longitudinal and transversal spatial correlation coefficients measured by LDA. Secondly, distributions of integral length scales distributions acquired by LDA and PIV have been discussed. In addition, the validities of integral length scale calculated by Taylor's hypothesis are evaluated in the flow.
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| 4.
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石間, 経章 ; ヨゼフ, イスマイル M ; 小保方, 富夫
概要:
application/pdf<br />Journal Article<br />Particle laden water jet have been analyzed by means of a laser Doppler anemom
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eter (LDA). Glass spheres of 389μm in mean diameter were loaded into the injection water by a particle mixer and after then injected into still water bath. The particle/water jet injectors were made by brass pipes of which diameters were 5 and 8 mm. The mean velocities of the center of the jet were set as 1.8 and 1.5 m/s for 5 and 8 mm pipes, respectively. The initial volume fraction was set as 0.087% in all experiments. The results of vertical relative velocity between particle and water indicate that the particles have same velocity as water at the outlet of the jet however particle velocities are larger than that of water at the expanded jet in downstream. From the results of the transverse relative velocity, it is considered that the particle can get larger velocity than water at a certain downstream from the outlet. These features are well explained by using local Stokes number defined by local time scale of the turbulence and particle time constant as well as Saffman's lift force.
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| 5.
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藤沢, 延行 ; 井上, 智 ; 横田, 正二 ; 田名網, 弘 ; 渡部, 功 ; 高野, 祐二
概要:
application/pdf<br />Journal Article<br />Air flows in a heater unit for automobiles are studied by flow visualization w
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ith tracer injection technique and the visualized images are analyzed by cross correlation method to obtain the velocity distributions in the unit at various mixdoor angles. The results indicate the variations of flow pattern in the heater unit with the mixdoor angles and the appearance of strong interaction between separated main flow and circulating heater flow at relatively large mixdoor angles, which promotes the flow mixing and simultaneously increases the pressure loss inside the unit. The flow fields in the heater unit are calculated numerically based on three dimensional momentum equations combined with κ-ε model of turbulence and with an experimental flow model of heater core. The numerical results reproduce well the experimental flow patterns in the heater unit, but there exits some deviations in the mean velocity and surface pressure distributions at large mixdoor angles.
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| 6.
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藤沢, 延行 ; 堀, 陽一
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application/pdf<br />Journal Article<br />Flow around a Darrieus wind turbine operating at low tip-speed ratios is studied by flow visualization using the dye injection technique and also by measuring the velocity field using a particle
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imaging and conditional sampling technique. The instantaneous flow patterns observed upon the visualization pictures correspond well to the measured velocity distributions, vorticity contours and velocity magnitude maps. It is found that two pairs of mushroom-type vortices are shed from the blade during a rotation of the rotor, which is due to the dynamic stall phenomenon. These stall vortices are produced by the flow separation over the suction side of the blade and the formation of roll-up vortices from the pressure side. The stall vortices at small incidence angles advance to the returning blade side, while those at large incidence angles grow along the moving blade and interact with flow near the blade. The effect of tip-speed ratios on the growth of stall vortices is also examined.
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| 7.
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FUJISAWA, Nobuyuki ; KURIBARA, Toshiaki ; YOKOTA, Masaji ; TANA-AMI, Hiroshi ; WATANABE, Isao
概要:
application/pdf<br />Journal Article<br />Flow mixing in an air conditioning unit for automobiles is studied experimentally in a water tunnel to investigate the mixing mechanisms of flow inside the unit at various mix-door angles. Flow
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visualization is carried out using tracer particles and the fluorescent dyes illuminated by Ar laser sheet, which allows the simultaneous measurement of velocity and diffusion distributions of the flow mixing in the unit by analyzing the captured color images. The measurement of velocity and diffusion distributions indicates enhanced flow mixing at certain mix-door angles, which is caused by the intense mixing of the main flow and the recirculating heater flow downstream of the mix-door. The temperature distribution measured in a prototype unit supports the mixing characteristics observed in the model unit, suggesting the usefulness of the present image analysis.
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| 8.
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藤沢, 延行 ; 栗原, 俊昭 ; 横田, 正二 ; 田名網, 弘 ; 渡部, 功
概要:
application/pdf<br />Journal Article<br />Flow mixing in an air conditioning unit for automobiles is studied experimentally in a water tunnel to investigate the mixing mechanisms of flow inside the unit at various mixdoor angles. Flow
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visualization is carried out using tracer particles and fluorescent dyes illuminated by an Ar laser sheet, which allows the simultaneous measurement of velocity and diffusion distributions of flow mixing in the unit by analyzing the captured color images. The measurement of velocity and diffusion distributions indicates enhanced flow mixing at certain mixdoor angles, which is caused by the intense mixing of the main flow and the recirculating heater flow downstream of the mixdoor. The temperature distribution measured in a full-scale unit supports the mixing characteristics observed in the model unit, suggesting the usefulness of the present image analysis.
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| 9.
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田部井, 勝稲 ; 白井, 紘行 ; 高草木, 文雄
概要:
application/pdf<br />Journal Article<br />Emission experiments on cavitation bubbles in water were performed with circular orifice flows. The region emitting faint light due to the bubbles was visualized with the combined method of photon
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counting and computerized tomography. Emission data obtained from outer-side observation were inverted into internal intensity distributions by means of the modified Abel transformation in which the light-quenching effect by cavitation bubbles was taken into account. It was observed that, under the condition of large pressure difference before and behind the orifice, a large number of photons were emitted from the region downstream of the cavitation flows, and the emission intensity was strongly dependent upon the pressure difference. The effect of an addition of a small amount of luminol to water was examined to demonstrate the effectiveness of the present method.
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| 10.
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藤沢, 延行 ; 田口, 祥和 ; 佐藤, 毅 ; 植村, 知正 ; 長屋, 幸助 ; 井開, 重男
概要:
application/pdf<br />Journal Article<br />Conditional sampling and the point-averaging technique have been introduced to particle-tracking velocimetry using a binary cross-correlation algorithm. This system is applied to the
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measurement of unsteady flow inside a rotating Savonius rotor, and the quantitative nature of the power mechanisms of the rotor at various rotor angles and tip-speed ratios are newly discussed and the usefulness of this techique is demonstrated. It is found that all velocity fields in and around the rotor vary markedly with the tip-speed ratio, and that the separation of Coanda-like flow on the convex side of the advancing blade is delayed by the velocity fields induced by the rotor rotation and also by the production of vortices downstream of the advancing blade.
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