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| 1.
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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 />Light emission properties of xenon-water cavitation in circular orifice flows
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were investigated experimentally and theoretically. The emission was enhanced by dissolving a small amount of Xe gas into water, and its spacial pattern was taken by a chilled CCD camera and an image intensifier. A spectrum of cavitation emission was measured by a spectrometer with a photon counter. Based upon the collisional and radiative theory for plasmas and a two-temperature model, synthetic spectra were calculated for emission of a collapsing xenon bubble at the minimum radius. It was found that the light emission pulsated and was intense around the flow axis a little downstream of the orifice, and the experimental spectrum was predominated by continuum and its intensity distribution was very similar to the theoretical ones with electron temperature of about 12000 K to 14000 K. Mean emission energy per unit pulse was estimated experimentally to be smaller than 5×10^<-9> μJ/nm・sr at the wavelength of 450 nm, which is consistent with the plasma conditions from the emission spectrum.
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| 2.
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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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| 3.
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藤沢, 延行 ; Ronald, J.Adrian
概要:
application/pdf<br />Journal Article<br />A new calibration technique of liquid crystal thermometry has been introduced
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to the quantitative measurement of temperature in a thermal fluid and applied to the study of turbulent thermal convection. The present calibration technique improves the accuracy of temperature measurement in comparison with the classical calibration technique with hue. Three-dimensional temperature measurement of turbulent thermal convection over a horizontal smooth surface is carried out at a flux Rayleigh number of 3×10^9 by scanning a light sheet normal to the image plane and capturing a number of sequential visualized images. The spatial temperature distributions of thermal plumes over a horizontal surface are demonstrated by the reconstruction of isothermal contour surfaces and various cross-sectional views of the plumes. These results indicate the presence of a polygonal cell structure close to the surface and the generation of plumes at the intersections of high-temperature lines.
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| 4.
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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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| 5.
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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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| 6.
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田部井, 勝稲 ; 白井, 紘行
概要:
application/pdf<br />Journal Article<br />Properties of light emission from a cavitation generated by a circular orifice shear flow have been investigated experimentally. In order to enhance the weak emission from clear water
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cavitation, xenon gas and luminol were dissolved in the water. The emission intensity was directly measured by an optical system with a photon counter and a spectrometer. It was seen that the emission could be enhanced by more than 100 times, and that the measured spatial profile of emission and its spectrum for xenon-water cavitation were very similar to those for clear water. The spectrum for luminol-water cavitation was a simple superposition of the spectrum from clear water and that due to luminol. The color temperature of emission from xenon-water cavitation was as high as roughly 20 000K.
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| 7.
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藤沢, 延行 ; 川路, 泰司 ; 池本, 宏一郎
概要:
application/pdf<br />Journal Article<br />The active control mechanisms of vortex shedding from a circular cylinder in a uniform flow by rotary cylinder oscillations are investigated by measuring the pressure distributions and by
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visualizing the flow around the cylinder with sampling the angular velocity of the cylinder simultaneously. Here, the rotary cylinder oscillations are controlled by the reference velocity signal in the wake with some phase lags. A clear reduction in the unsteady lift forces is observed by the active controls. The simultaneous observation of the phase averaged pressure distributions, the visualized flow fields and the cylinder rotations indicates that the rotary cylinder oscillations with the optimum phase control decelerate the accelerated flow on one side of the cylinder and accelerate the decelerated flow on the other side of the cylinder, which results in a reduction in the time-variation of shed circulations and forms the suppressed vortex pattern in the flow visualization pictures.
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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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藤沢, 延行 ; Warui, Mwai Hebron
概要:
application/pdf<br />Journal Article<br />The present paper describes the active method for controlling vortex shedding from a circular cylinder in uniform flow. The cylinder motion in the cross-flow direction is controlled by the reference
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velocity signal in the wake with some phase lag, with the aim of reducing vortex shedding from the circular cylinder. The effectiveness of this method is studied by wind-tunnel experiments with flow measurement and visualization. All the results indicate that the reference velocity in the wake is weakened by active control at the optimum phase lag and is strengthened at the reverse phase lag. A similar reduction and enhancement in the velocity fluctuations in the wake with this control at these phase lags is observed in the flow measurement in the cross section of the wake, and is also cofirmed in the whole flow-field visualization study by the smoke-wire method with a laser-sheet technique. These results suggest the possibility of reduction of vortex shedding from a circular cylinder and modification of the wake by the present active control method.
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| 10.
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藤沢, 延行 ; 川路, 泰司
概要:
application/pdf<br />Journal Article<br />The present paper describes a new active method for controlling vortex shedding from a circular cylinder in a uniform flow, using rotary cylinder oscillations controlled by the reference
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velocity signal in the wake with some phase lag. The effectiveness of this active method is evaluated by measuring the response of mean and fluctuating velocities in the cylinder wake and by visualizing the flow field around the cylinder. It is found that velocity fluctuations are reduced by the control at the optimum phase lag, while they are enhanced at the reverse phase. The maximum reduction of 30 percent in the reference velocity fluctuations is obtained with the optimum control, where the optimum value of phase lag and the feedback coefficient are adopted. The modification of the mean velocity profile and the reduction in the fluctuating velocities in the wake are measured under the optimum control and the corresponding variations in the visualized flow field are recognized, similar to the change observed under the control with cross-flow cylinder oscillations.
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| 11.
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隆, 武強 ; 大塚, 博行 ; 小保方, 富夫
概要:
application/pdf<br />Journal Article<br />To study the characteristics of flow and particle diameters in large-angle con
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ical spray proposed for Diesel engines of premixed combustion, unsteady conical spray in the air has been analyzed using a phase Doppler anemometer (PDA). In experiments, the frequency of injction is 20.8 Hz and the amount of injection fuel is 10.3 mg in each cycle. Axial and radial distributions of bulk velocity and mean diameter of particles are obtained. As a result, it is found that the profile of mean velocity distribution is close to the Goertler distribution, and the Sauter mean diameter of droplets in the conical spray is as small as 30μm. Correlation between particle diameter and velocity in the entire spray is negative and unusual, but is found to be normal if the spray is divided into parts and studied. We also find that particles with small diameter (20μm) which are emitted at high speed (60m/s) at the earliest stage lose velocity rapidly, merge into bigger particles, and are overtaken by bigger but slower particles which are emitted at the later stage. Particles with large diameter (50μm) gather at the tip of the spray as they travel farther from the nozzle exit.
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| 12.
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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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| 13.
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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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| 14.
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細谷, 肇 ; 小保方, 富夫
概要:
application/pdf<br />Journal Article<br />There have been many experiments to characterize Diesel fuel spray under steady-state conditions. However, the appropriate number of holes and the hole position on the sac to be used in the
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experiment are not clear. To address this subject, we investigate Diesel type spray flows using a laser Doppler anemometer (LDA) and a phase Doppler anemometer (PDA). Spray flow characteristics such as mean and fluctuating two-component velocities, two-dimensional distribution of particle diameter and the variation of three parameters at the log-hyperbolic fitting for particle size distribution are given from measured data. Spray jets from four varieties of Diesel nozzle are compared with each other to clarity the differences in spray characteristics between them. The results show that the spray from the single-hole nozzle on top of the sac is distinct from the others.
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| 15.
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TABEI, Katsu'ine ; SHIRAI, Hiroyuki ; TAKAKUSAGI, Fumio
概要:
application/pdf<br />Journal Article<br />Using the moire-schlieren method for symmetric and asymmetric flow fields, density distributions of underexpanded free jets of air from circular and square nozzles have been measured.
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Experimental moire image data of the flows, which show integrated light deflection across the flow, were converted to an internal density distribution by the numerical inverting method. The experiment was performed systematically by changing the pressure ratio across the nozzles from 4 to 13. It was found that the density profiles measured in the expanded free jets from a circular nozzle agreed well with other experimental results, and that those for a square nozzle were much more complex than for a circular nozzle. In spite of the large difference in such profiles, the density variations along the flow axis for both nozzles were very similar to each other.
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| 16.
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藤沢, 延行 ; 池谷, 和昭
概要:
application/pdf<br />Journal Article<br />Effect of an overlap on the power mechanism of a Savonius rotor has been studied by measuring pressure distributions on the blade surfaces and by visualizing the flow field around the
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rotor with and without the overlap. It is found that the presence of the overlap induces a strong negative pressure on the convex side of the advancing blade of the rotating rotor, which produces a positive torque for the rotor rotation. This phenomenon is observd as a strengthened attached flow over the convex side in the visualized pictures, which indicates the reduced separating region by the flow through the overlap. These results together with the flow control effect inside the rotor show an improved mechanism of the rotor performance by the presence of the overlap.
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| 17.
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藤沢, 延行 ; 白川, 昌和
概要:
application/pdf<br />Journal Article<br />The flow in and around two-dimensional right-angled intake has been studied bo
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th experimentally and numerically. Pressure distributions on the intake surfaces are measured at various velocity ratios of the intake flow to the main flow, and the basic intake performances, such as the total pressure loss, the cavitation and the drag, are evaluated. It is shown that they are reproduced well by the numerical results with a standard k-ε model of turbulence, while the agreement becomes poorer as the velocity ratio becomes large. It is also demonstrated by the smoke-wire visualization study that the recirculating region formed upstream of the intake flow is reduced as the velocity ratio increases, contributing to the relative decrease in the total pressure loss at large velocity ratios.
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| 18.
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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 />By using the moire-schlieren method for symmetrical and asymmetrical flow fields, density distributions of underexpanded free jets of air from circular and square nozzles have been
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measured. Experimental moire image data of the flows, which show the integrated light deflection across the flow, were inverted to an internal density distribution by the numerical inverting method. The experiment was performed systematically by changing the pressure ratio across the nozzles from 4 to 13. It was found that the density profiles measured in the expanded free jets from a circular nozzle agreed with other experimental results on the whole, and that the results for a square nozzle showed complex flow configurations caused by the nozzle figure, nevertheless, the density distribution on the flow axis was very similar to that for a circular nozzle.
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| 19.
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藤沢, 延行 ; 小川, 芳弘 ; 白井, 紘行
概要:
application/pdf<br />Journal Article<br />Unsteady flow field inside a Savonius rotor at various overlap ratios has been investigated by flow visualization with a smoke-wire method. The experiment is performed for rotors with 4 different
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overlap ratios (OL=0-0.5) and for various rotor angles and
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| 20.
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TABEI, Katsu'ine ; SHIRAI, Hiroyuki
概要:
application/pdf<br />Journal Article<br />A mathematical method for transforming moire-schlieren data into internal density (and/or temperature) distributions has been presented. The method of transformation, which is applicable to both
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symmetrical and asymmetrical flow fields, has been deduced by modifying the Maldonado-Olsen's series. The accuracy of the present method was examined with a mathematical model of a density function of the truncated pyramid type. In order to demonstrate its usefulness for asymmetrical flows, temperature distributions in a combustion flame have been measured for a square nozzle. Experimental moire images of the flame were recorded by a video camera, and the integrated light refraction was converted into an internal temperature distribution. The results showed that the temperature profiles in the flame are distinctive owing to the rectangular nozzle, and that the present method is very effective.
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| 21.
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藤沢, 延行 ; 白井, 紘行 ; 齋川, 雄司
概要:
application/pdf<br />Journal Article<br />Unsteady flow fields around a Savonius rotor and its power mechanism are studied by a flow visualization experiment for various rotor angles and tip-speed ratios. For small tip-speed ratios, the rotor
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receives a corotating torque mainly due to the difference of the drag on both the blades. As the tip-speed ratio increases, a Coanda-like flow pattern is formed on the convex side of an advancing blade, and the corotaing torque is expected by the induced lift, though the torque due to the difference of the drag decreases. The power performance of a Savonius rotor can be explained reasonably by the flow visualization results.
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