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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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藤沢, 延行 ; 堀, 陽一
概要:
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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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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論文
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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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