There are a lot of studies on biofouling until now. However, few studies focused on the method that controlled the photosynthetic organism growth on outdoor triangle weirs in a sewage treatment plant. We investigated the growth of photosynthetic organisms on the triangle weir of a second sedimentation basin in a sewage treatment plant. In addition, the growth suppression of photosynthetic organisms was investigated through the surface treatment and shape of the triangular weir.

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We experimentally investigate effects of effective interfacial tension (EIT) on miscible viscous fingering (VF). To do so, we prepare two liquid systems in which the viscosity contrast is the same but EIT is different. We confirm that the viscosity contrast is the same in the both system but EIT is different by means of the measurement of viscosity and EIT. We also conduct diffusion experiment to confirm the Peclet number has no effect on the experiments. We perform VF experiment by using a Hele-Shaw cell. We find that the typical width of the fingers is larger for larger EIT system. This experimental result has a good agreement with recent numerical studies of the related issue.

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Influence of polymer additive and surface roughness on liquid transfer phenomena was investigated utilizing two flat plates. Test fluids of water or polymer (PEO, SPA) aqueous solutions were transferred from an acrylic plate to aluminum plates with different surface roughness. In the cases with rough surface, similar transfer ratios were obtained regardless of test fluids, i.e. Newtonian or polymer solutions. On the other hand, only the PEO solution keeps higher transfer ratio even when relatively smooth surface was utilized, and water and the SPA solution were slightly transferred to the aluminum plate. In order to verify the effect of molecular weight to the transfer phenomena with relatively smooth surface, an aqueous solution of PEG having same molecular chain structure with the PEO was also examined. But short chain of polymer (PEG) additive did not show such kind of advantage in transfer phenomena.

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The Drying process is very important in making aggregates orientation film by application of chromonic liquid crystals; Biebrich Scarlet Sodium Salt 6wt%(BSS6) and Sunset Yellow FCF 36wt%(SY36). The effect of drying process was investigated by using polarimetry. We measured the extinction distribution of the whole application film and distribution of drying time at each local point, and evaluated the correlation of extinction and drying time. In the case of BSS6, the extinction increases a little for the low value of drying time and keeps constant range between 0.05 and 0.2 when drying time is larger than 10 seconds. In the case of SY36, the extinction increases with increasing drying times by effect of crystallization. The extinction distribution on Drying film of BSS is uneven. We consider that this unevenness is not of degree of aggregates orientation but of film thickness. Because, the extinction distribution correlate strongly with distribution of intensity of transmitted light.

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We have performed the numerical simulation of liquid crystalline molecular orientation field between eccentric cylinders. The liquid crystal is confined between the outer and the inner cylinders on which a homeotropic anchoring layer is treated. While the radial molecular orientation field is obtained for the case that the centers of the inner and the outer cylinders are coincident, the field is distorted for the case that the centers are deviated, causing the force on the inner cylinder toward the center of the outer cylinder. The force increases with the increase of the deviation, and is found to be of tens of nN. Finally, we propose the novel force sensor utilizing the relation between the force and the distortion of the molecular orientation field of the liquid crystal.

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Power consumption of large paddle impellers was measured for shear thinning fluids. The large paddle impellers are MAXBLEND, FULLZONE, Super Mix MR203 and Super Mix MR205. The test fluids were 3.5wt%, 4.0wt%, 4.5wt% carboxymethylcellulose(CMC) solutions. The shear stress of CMC solutions was correlated with the power law model. The correlation of power consumption was conducted by the use of Metzner-Otto method. As a result, this method was valid for estimating power consumption of large paddle impeller. The Metzner-Otto constant increased with increasing the impeller diameter.

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In order to realize the high-efficiency of a process in which milk was filled into a gable top carton with the volume of 1000 mL, the effect of the value of surface tension coefficient on flow dynamics of milk were computationally considered using the Volume-of-Fluid (VOF) method. From numerical results, it was shown that the value of surface tension coefficient largely influenced fluid flows inside the carton in a filing operation process. When a lower surface tension coefficient was used, the dynamic motion of milk became more complicated than that for a higher surface tension coefficient.

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The flow around a sphere falling through viscoelastic wormlike micelle solutions is investigated by using a particle image velocimetry (PIV) when the falling velocity of the sphere is high compared to the shear wave speed of the fluid. The speed of the shear waves generated by the impulsive excitation of a plate is measured with a PIV. Mach waves due to the passage of the sphere are observed at viscoelastic Mach numbers greater than 1. In relatively dilute cases, Mach waves are accompanied by small vortices generated by the sudden drop of falling velocity of the sphere.

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Control of aggregation/dispersion behavior of fine particles in a suspension is important to improve characteristics of complex materials. The dispersion behavior of fine particles in a suspension was observed and analyzed in a flow across sudden contraction in a microchannel. The dispersed particle and media of the suspension were polystyrene (diameter: 3:5 μm) and 27:0 wt% aqueous glycerol solution. The volume fraction was 0.02. The suspension was introduced to the microchannel using syringe pump. The velocity and dispersion behavior of fine particles of the suspension were determined in the PIV and image analysis. As a result, the velocity profile was fully developed at x/H = 0:23. The profile of the mean number of particles in a cluster at x/H = 0:24 was equal to the profile at upper stream. At x/H = 0:74, the mean cluster size was smaller than that at x/H = 0:24 It indicates a difference in the entrance region of the velocity field and aggregation/dispersion characteristics.

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Instability characteristics observed in a micro-cavity swept by a visco-elastic fluid has been investigated. Surfactant solution used as a viscoelastic fluid was inserted in a micro-cavity whose length, depth and wide low path were set constant at 1, 0.2 and 0.4 mm, respectively. The time variation of the tonguing motion of the separation bubble formed in the downstream region in the cavity was measured when the Reynolds number defined with water viscosity, cavity depth and the mean velocity in a narrow flow path was change in three steps: 1, 5 and 20. From the results, it was found that the fluctuation time scale is from 1.9 to 4.5 s, which is located between the middle and longest relaxation times. It was also found that the time scale does not depend on the Reynolds number.

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We investigated influence of viscoelasticity on turbulent backward-facing step flow at low Reynolds number using direct numerical simulation (DNS). In this study, Newtonian fluid and viscoelastic fluids (Wi_<τ0>=10, 20) were calculated at a friction Reynolds number Re_<τ0>=100. The geometry of the flow channel is that having an upper wall and a step with the expansion ratio of ER=1.5. The reattachment length X_r/h (h: step height) from the step is 6.80, 7.82 and 8.82 for Newtonian, Wi_<τ0>=10 and Wi_<τ0>=20, respectively. For instantaneous fields, the amount of vortices emerging at separated shares layer decreases with the increasing Wi_<τ0>. For averaged fields, while u'rms near the separated share layer decreases as Wi_<τ0> increases, that near the upper wall increases as Wi_<τ0> increases. This result may be caused by the separating of mainstream from the upper wall.

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Dynamic surface tension is one of the most important physical properties for interfacial phenomena of many applications. A proposal on the measurement method of dynamic surface tension was found in previous research, which uses local deformations in the droplet surface. To clarify the local flow in the tiny droplet, we investigated the deformation of shell liquid of the droplet on the vibrating plate using 2D finite element method. The gas-liquid droplet surface area was calculated locally in each section of radial angle under given apparent gravity. We found that the interface of the local droplet deformation can be related to the local surface tension.

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The shear banding in Large Amplitude Oscillatory Shear flow, LAOS, of the wormlike micellar solution is examined. The shear banding is visualized by the crossed Nicol observation system that is built in a remote. A concentric cylinder flow cell is used to apply the LAOS flow and birefringence distribution in the whole area of the flow cell can be observed by 60fps. At the small strain amplitude, the birefringence appears monotonically. The shear banding is generated in the larger strain range in the first period when the maximum strain amplitude exceeds 1 at frequency 1 Hz. but it does not appear when the shear stress achieves on the periodic state. Increasing strain amplitude or frequency, the shear banding keeps in whole phase. Therefore, it is found that the non-linear behavior of the wormlike micellar solution in LAOS is affected the shear banding strongly.

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We have proposed a new defoaming method by applying pressure-oscillation in the continuous flow channel. Due to the bubble expansion and contraction, there are complex flow structures in the vicinity of an air bubble in the fluid. To clarify the flow structures, we tried measuring the retardation profile around the bubble by the high speed polarization camera. As a result, strong retardation can be observed in the opposite side of the movement direction of the contracting bubble. There exists fine bubbles in the both side of the bubble. We observed the motion of fine bubbles as tracers. It turned out that a uniaxial extension is observed in the opposite side of the movement direction of the contracting bubble. It's consistent that a uniaxial extension, strong retardation and the motion of fine bubbles are caused by negative wake in the opposite side of the movement direction of the contracting bubble.

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Experimental study on the turbulent flow in a circular pipe with a semi-circular orifice has been conducted. The velocity was measured by a stereo PIV system that provided the three components of mean velocity as well as streamwise vorticity on the cross section of the pipe at different streamwise locations. The distributions of mean vorticity exhibited symmetry about y-axis. Wall pressure measurement has been conducted along the pipe wall. The profiles of pressure fluctuations and cross correlation was obtained.

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In this study, the characteristics of the swirling flow type micro-bubble generating jet device has been developed for the purpose of cleaning of oil stains such as industrial products was demonstrated. Further, the impingement pressure of the micro-bubble jet was visualized. From these results, the bubble size distribution for the flow ratio of the microbubbles, chlorine concentration, PH distribution, etc. were shown. Moreover, the impingement pressure of the micro-bubble jet than impingement pressure of the water jet was a pressure value of about 1000-25000 times from visualization results using the pressure-sensitive paper

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In this study, we fabricated a hot-film sensor to measure the wall shear stress fluctuation in turbulent flows. The heated element of the sensor, which acts as a sensing part is 10 μm wide and 1 mm long. The substrate of the sensor is made of oxidized silicon wafer of 1 μm thickness for increasing the sensor's temporal resolution. The calibration test shows that the sensor can measure the time-averaged wall shear stress accurately. The result of wall shear stress fluctuation measurement shows a good agreement with that of previous study.

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This study used three-dimensional particle tracking velocimetry (3D-PTV) to measure the water jet flow inside two parallel flat plates. The gap in the walls 2h was 4mm, the nozzle height D was 4mm, and the jet Reynolds number was varied from Re=1150 to 3840. The velocity profile of z=0 had top-hat profile at the nozzle exit and the profile agreed with theoretical solution of two-dimensional free jet by Goertler in the lower reaches of stream. The growth rate of the jet width was approximately db/dx=0.08, which is slightly lower than the value of planar free jet of 0.1. The velocity profile of y=0 became similar to the profile of turbulent channel flow in accordance with reaching downstream. The downstream evolution of UCL exhibited more decay than planar jet and The RMS u'_<CL> was lower than that of planer jet. Streamwise decay of momentum was consistent with a theory involving friction factor of approximately C_f=0.015.

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We have studied the effects of the moving wall and contraction ratio on turbulence statistics and separation bubble appearing in turbulent Couette and Poiseuille flows over a forward-facing step. The turbulence statistics are obtained by PIV measurements, and are used to specify the difference of the Couette and Poiseuille flows. The experiments were carried out at the contraction ratio of CR = 0.250, 0.375, 0.500 and the Reynolds number of Re_<c0> = 10000 based on the upstream centerline velocity U_<c0> and channel height 2h_1. As a result, separation bubble of Couette flow is smaller than that of Poiseuille flow. The separation bubble grows larger with decreasing the contraction ratio in both flow types.

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This research deals with the oscillation frequency of a flip-fop jet nozzle on the measurements of pressure and velocity in a connecting tube. The trace of pressure difference between both the ends of the connecting tube is simply modeled by a triangular wave, and the velocity in the connecting tube is calculated by the method of characteristics and the Runge-Kutta method. The authors assume that a jet switches when the integral JM, JK or JP reaches a threshold value, where JM, JK and JP are the accumulations of momentum, kinetic energy and mass which are transported through the connecting tube from a side wall with higher pressure into another side wall with lower pressure, respectively. As a result, JP is the most adequate among the three. The Strouhal number calculated on the basis of JP agrees well with experimental one.

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In low Reynolds numbers region, a laminar separation and laminar separation bubble was observed on upper surface of airfoil. This flow field could be realized over a backward-facing step. The numerical calculation over a backward-facing step was carried out to examine both separation and reattachment of shear layer at Reynolds number of 2,000 based on the step height. The flow after the separation reattached of being instability of separated share layer by amplifying the disturbance. In reattachment region, the time change of reattachment position indicated that the dominant spectrum was the high and frequency components. The reattachment position was locally increased by this high frequency component. As a result, we confirmed that the reattachment position of span-wise direction was three-dimensional.

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Side jets are generated in round jets by causing self-excited oscillations when the density of issuing fluid is sufficiently lower than that of the ambient fluid. The side jets in a helium gas jet rotate slowly in the azimuthal direction. In this case, both the varicose and spiral modes are unstable. While, self-excited oscillations are produced in a two-dimensional jet with low-density fluid. However, the side-jet formation in the plane jet not has been confirmed until now. An aim of this study is that the side-jet formation in two-dimensional jets is examined using flow visualization. When the self-excited oscillations are generated in the initial region of the plane jet, the side jets are formed. In this case, the spiral mode does not appears.

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It has been known that the side jets are formed in a round jet when the density of the jet fluid is lower than that of the ambient fluid. The density ratio between the jet fluid and the ambient fluid for the side-jet formation is generally lower than 0.7. However, it is found out that flow structure similar to the side jets in a round helium gas jet exists in a round air jet, namely uniform-density jet, by the flow visualization in the jet shear layer and the three-dimensional imaging of the jet. In this experiment, the flow structure similar to the side jets is generated in the air jet when the jet Reynolds number is from 2,000 to 3,000, although the density ratio is 1.

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This study is concerned with the numerical simulation of the jet issued into two-layer density-stratified fluid in a cylindrical tank. Vortex in cell (VIC) method combined with an Immersed Boundary (IB) method is applied to the simulation. The upper and lower fluids are water and a NaCl-water solution, respectively, and the lower fluid is issued vertically upward from a nozzle on the bottom of the tank. The Reynolds number Re defined by the jet velocity and the nozzle diameter ranges from 95 to 1188, and the mass concentration of the NaCl-water solution is set at 0.02. The simulation highlights that the jet behavior relative to the density interface and the resultant mixing phenomena depend on Re. Such simulated results are confirmed to agree well with the experimentally visualized ones, demonstrating the validity of the present simulation method.

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The Kutta condition applied in the potential flow is the used for explanation of the lift mechanism. The present research experimentally and numerically investigated the transition process from the flow with the zero circulation to the flow satisfied with the Kutta condition. For visualization, glycerin solution with aluminum powder is used as the working fluid. In the numerical and experimental results, the downstream stagnation point is located at the upstream of the blade trailing edge, which is similar to the zero circulation flow. As the Reynolds number is increased, the stagnation point is moved to the blade trailing edge, finally the flow is satisfied with the Kutta condition.

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The present research investigated unsteady characteristics of a swirling jet. The experimental facility was designed to control the swirl ratio adjusted by varying the angle of the guide vanes. For visualization, the swirling jet with a smoke was illuminated by a laser sheet. The circumferential velocities were measured by hot wire probes. By the computational fluid dynamics (CFD), the swirling jet was simulated at the same conditions as the experiment. The CFD and experimental results show that the swirling jet for the 0 degree of the guide vanes flows along the outside wall. By the FFT, one peak with the four rotating cells observed in the pictures taken for the swirling jet is found in the experiment and the CFD results.

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This study investigated the effect of turbulence properties of main flow on turbulent diffusion phenomena. Turbulence including longitudinal vortices was generated by several turbulence generators and was stretched by a contraction unit of a wind tunnel. CO_2 gas was injected continuously from a point source into main flow controlled turbulence properties by several turbulence generators, and then the concentration of CO_2 was measured in the downstream region. As a result, it was found that the diffusion coefficient is increased by not only turbulence intensity but stretched turbulence. Finally, it was found the effect of several turbulence properties on turbulent diffusion phenomena.

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Three-dimention structures in the vortex street wake of a two-dimention bluff body mean two types of structures. One is three-dimensionality for a lateral vortex shed from a two-dimensional body, another is three-dimensionality structure wound around a lateral vortex, such as longitudinal vortex. The purpose of this study was to investigate these two types of three-dimensional structures in detail by flow visualization. As the results, these two types of three-dimensional structures were classified based on Reynolds number and aspect ratio of body, three-dimensionality for a lateral vortex was shown quantitatively.

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ToThe stability of high-speed liquid lithium film flows on a wall was analytically studied for the neutron source in Boron Neutron Capture Therapy (BNCT), which makes cancers and tumors curable with cell-level selections and hence high QOL. The object of our research is to materialize the thin and high-speed wall film flows of liquid lithium in a high-vacuum as an accelerator target. Linear analysis approach is made to the stability on thin film flows of liquid lithium in a high-vacuum. We experimentally observed the splitting phenomena of film flows on a wall with 0.5 mm in film thickness and over 10.0 m/s in flow velocity, caused by the slit-nozzle was stopped up with the contaminant particulate of nitrous lithium. We also obtained the knowledge to materialize the desired wall film flows.

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The effect of the disturbance on the laminar-turbulent transition of the mixing layer is experimentally investigated. So far, two kinds of experiments were conducted with the Reynolds number of 5000; in one, the plates at the nozzle exit do not protrude into the nozzle section and remain in a 'stationary state' and in the other, 'anti-symmetrical oscillating state', the plates oscillate perpendicularly to the flow and anti-symmetrically with each other in relation to the flow. In the present study, the Reynolds number was decreased to 3000. The effect of the Reynolds number was examined.

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In the decay of turbulence generated by passing through Sierpinski tetrahedron, there exists a region in accordance with the exponetial law, without obeying the power law. In this study, mechanism of exponential decay is investigated by measuring the profile of velocity statistics over the cross section. Mean velocity profiles are similar to each other amongst the structures with different number of iteration (N=2, 3, 4) and so are turbulence intensities except the case for the least number (N=2).

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The flow field around an elastic body is treated as a fluid-structure interaction problem and has been investigated by experimental and numerical approaches. Many researchers have already reported the characteristic of dynamic thrust acting on an elastic moving airfoil at 0 degree of angle of attack and their wake structures. In this study, we investigate the characteristics of dynamic forces acting on elastic heaving airfoil in a separation region, at 16 degree of attack angle, and the dynamic behavior of the vortices rolled up from the leading edge by fluid structure interaction simulation using ANSYS 16.1/ANSYS CFX 16.1. The generation and the growth of the leading edge vortex in the elastic airfoil delay slightly than that in the rigid airfoil due to the effective angle of attack.

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Studies of synthetic jets generated by compact actuators have been conducted for various applications such as drag reduction, boundary layer separation control, and multi-flow mixing. This study represents fundamental research on jet fan development using a synthetic jet. The fan performance characteristics are discussed. In particular, this work is an attempt to experimentally clarify the effects of the jet oscillation characteristics and the height of duct (duct geometry) on the fan performance, the pressure rise mechanism inside the fan duct, and fan efficiency.

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Several studies have been carried out on the behavior of synthetic jets as a substitute of continuous jets. In addition, studies have also begun to control the fluid machine using the synthetic jets. The present study attempts to clarify the flow characteristics around a rectangular cylinder with symmetric/asymmetric slot for synthetic jets in a duct. The relation between flow characteristics of two-dimensional synthetic jets and the geometry of slots is investigated to apply the posture control of jet thruster. The influences of a beak-shaped slot on the behavior of synthetic jets are evaluated through experimental flow visualization using the smoke wire method and numerical simulations.

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As a part of study on the diffusion control of jet flow, the purpose of this study is to control the jet diffusion by using the deforming nozzle. The shape of polypropylene nozzle can change from square shape into cruciform one smoothly. The velocity measurement of the jet flow was carried out by using a hot-wire probes, by changing the shape of nozzle exit variously. The basic characteristics of the jet flow, such as velocity distributions and half value widths have been obtained. As a result, it has been found that the jet width of the deforming nozzle is suppressed in the downstream location from the nozzle exit to the 8 times the characteristic length. And the jet width of the deforming nozzle in xOy'-plane is small, comparing with that in xOz-plane. Moreover it has been also clarified that the diffusion of the deforming nozzle is same level in both planes in the downstream location more than 10 times of the characteristic length. Furthermore, in the downstream location more than 13 times of the characteristic length, in the case of the shape of the nozzle is a square, the diffusion of the jet is suppressed and the jet diffusion in the case of changing the shape of the nozzle continually periodically is promoted.

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Numerous studies on the fundamental flow characteristics of the synthetic jets and the control of the separation flows using the synthetic jets have been conducted actively. However, to use the synthetic jets as an actuator for the fluid machinery, many issues need to be clarified, including the optimum relation between the synthetic jet oscillation and the mechanical configuration. In this paper, a jet pump (fan) using the synthetic jets produced by a piston actuator is proposed. The time variation of the jet centerline velocity inside the pump and the performance curves from the experiment have been discussed the optimum condition for the operation.

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A plasma actuator has been extensively investigated as a flow control device for separated flow in recent years. A burst wave induced plasma actuator (BWPA) is highly expected for the separation control in low Reynolds number flow. In this study, spatiotemporal flow characteristics induced by BWPA in a parallel plate laminar channel flow was investigated by particle image velocimetry. Furthermore, the BWPA was applied to a backward facing step flow to control the flow separation and reattachment. The experimental result shows that the velocity amplitude defined as the magnitude of velocity oscillation generated by BWPA strongly influences the decrease of reattachment length.

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In recent past, a wide variety of applications have been found for the use jets in fields of study of flow control and many researchers have worked on jet flow control to enhance mixing and/or reduce noise. In order to develop a new mixing procedure, a direct numerical simulation (DNS) of dynamic controlled free jets was conducted. To achieve a high accurate computation, space discretisation method was performed using the hybrid scheme consisting sine or cosine series and 6th order compact scheme. The dynamic control proposed here are single and multiple rotating jets which are rotated unidirectionally around streamwise direction. According to the instantaneous vortex structures and , it is found that the flow pattern changes considerably with the rotating frequency. From the contour of streamwise velocity, in both cases, it is clear that the radial jet expansion of controlled jets are significantly enhanced compared to the uncontrolled one. We also concluded that, using the statistical entropy and the entrainment rate, it is clear that the mixing performance is significantly improved compared to the uncontrolled jet and under the same rotating frequency, the mixing performance of single rotating jet control is superior than multiple one.

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In the present paper in order to investigate the possibility of flow control using elastic body, we conduct a simulation of a finite-length flexible cantilever installed in turbulent channel flow. For a flexible cantilever, the rigorous equation of motion for elastic continuum is solved with a finite volume method; the effect of existence of cylinder in the flow computation is taken into account using the immersed boundary method.From time averaged quantities, we demonstrate that the flexible cantilever markedly modulates the wake structure and heat transfer characteristic.

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The current understanding of flow separation and the control technologies by new generation actuators are reviewed. In particular, recent developments of the flow control devices such as synthetic jets and plasma jet are discussed, since the actuator induced flow structure has been well understood by the advanced sensing technologies. Emphasis is placed on the flow behavior around the actuator in the separated flow field. Finally, the review examines the passive and active flow control in the recent application where a backward facing step flow is selected as one of the most typical examples of flow separation and reattachment.

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Micro plasma actuator designed under a millimeter in the electrode size was developed. In this study, the power consumption of the micro plasma actuator was measured by Q-V Lissajous method. Micro plasma actuator archived lower power consumption as compared to a conventional type plasma actuator. Wave type micro plasma actuator which electrode form has a curvature in span direction was applied for flow control. The induced vortex structure by wave type micro plasma actuator was visualized in quiescent air. Also wake profiles behind NACA0012 airfoil under the curved type plasma actuator control were measured by using X-type hot-wire anemometer.

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Mass transfer from a bubble to the surrounding liquid plays an important role in engineering processes. To improve the efficiency of the processes, a deep understanding of the mass transfer mechanism from bubbles to the surrounding liquid is essential. In our study, we consider the influences of bubble surface contamination (1-pentanol) on mass transfer through discussion of the relationship between bubble motions, bubble-induced surrounding liquid motions and mass transfer. We visualized the CO_2 dissolution process via LIF/HPTS (a fluorescent substance) method from the front view (zigzag plane) and side view. Moreover, we measured the surrounding liquid motions by using PIV method. According to these experimental results, horse-shoe-like vortices were observed in the bubble wake in purified water. Mass transfer was promoted by convective transportation induced by the horse-shoe-like vortices. In contrast, mass transfer in contaminated water reduced as the vortex structure changed in the bubble wake.

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When a single bubble goes up in liquid, a bubble moves three-dimensionally and meanderingly. Its trajectory changes from straight to straight by zigzag and spiral as the diameter of bubble increases. But the detail of bubble's behavior has not been clear yet because a bubble shape shows a very complex change. It was shown by previous researches that behavior of rising single bubble of sub-mm size had reproducibility. In this study, Improving equipment for the experiment is carried out in order to obtain the knowledge of the detail of reproducibility. Moreover, images of bubbles of various size are taken multilaterally and it is attempted that constructing of three-dimensional shapes of a bubble.

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The motion of single bubbles rising in a hydrophobically modified alkali-soluble associative (HASE) polymer solution is experimentally examined. The polymeric liquid is made up of 1.6 wt% HASE polymer solution, which are adjusted to pH &ap; 7.0 by adding a sodium hydroxide solution. In this study, we focus on unique threadlike shapes formed at the bottom of the bubble. Trailing edges with threadlike branches are observed in detail for the Eotvos number. Consideration for trailing edges with threadlike branches is made based on enlarged pictures taken with a high-speed video camera. As the Eotvos number is increased, it is shown that the number of threadlike branch is increased.

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For clarifying detail structure of bubbly flows which have multi-scale structure, it is necessary to understand bubble-bubble interaction phenomena. Some theoretical models of interaction between two spherical bubbles located in-line rising in a viscous liquid have been proposed, however experimental verifications are insufficient. In this study, we observed motion of a pair of spherical bubbles initially located in-line rising in quiescent ultrapure water or aqueous surfactant solutions. The bubble Reynolds number is ranged from 50 to 300. The results indicate that the slight difference between bubbles radius greatly affects the relative motion. When radius of the trailing bubble is larger than that of the reading bubble, the trailing bubble approaches to the reading bubble. Otherwise the trailing bubble separates from the reading bubble. Also the lift force acts on the trailing bubble when bubbles located in-line, and bubbles attract in the transverse direction when bubbles located about side by side.

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Numerical simulations of gas-liquid flows in a thin microchannel are performed to gain insight into the dynamics in microbubble generation. In consideration of liquid inertia, the basic equations consist of the Laplace law and the two-dimensional Euler-Darcy equation under the assumption of Hele-Shaw's flow owing to a large width-to-thickness aspect ratio of the channel cross-section, and are numerically solved by means of a boundary element method. The simulated results of the interface motion in a T-shaped channel (composed of two inlets for gas and liquid and an outlet for liquid) well capture the experimentally observed behaviors that the interface pinches off at the channel junction and then a bubble forms, and imply the significance of the liquid inertia in the microbubble generation process.

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System analysis of bubble oscillations in an elastic tube is important for medical applications using nano/microbubbles such as ultrasonic contrast agents and high intensity focused ultrasound. In order to investigate inuences of the bubble-bubble interaction on the natural frequencies of two bubbles, a simple bubble model combined with the springmass system for the tube wall is proposed. In this model, the bubbles are represented by point sources for volume oscillations. The natural frequencies of the system are derived by linearizing the governing equations. Two bubble resonance frequency modes are obtained from the eigenvalue analysis. The eigenvector analysis shows that the lower resonance frequency of the bubble corresponds to the mode in which both bubbles oscillate with the same phase; the tube wall also oscillates with the same phase. The higher corresponds to the mode in which one bubble oscillates with inverse phase to the other; the left-hand side of the tube wall oscillates with the inverse phase to the right-hand side of the tube wall while either side of the tube oscillates with the same phase as each nearby bubble.

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We have been investigating particle flocculation using ultrasound in water. Irradiating kHz-band ultrasound, sub-mm-order/mm-order particles were flocculated in spherical form at a fixed position. This flocculation was caused by Acoustic Cavitation-Oriented Bubbles (ACOBs). The ACOBs were generated by the acoustic pressure amplitude. In this study, changing the component ratio of the dissolved gases (air/CO_2) in water, we evaluated the relationship between the particle flocculation patterns and the ACOBs. In air-dissolved water, the spherical flocculation was formed. On the other hand, in CO_2-dissolved water, the line-like flocculation was formed. The difference arose from the differences in motion between air bubble and CO_2 bubble. In this report, we explained the relationship between the particle flocculation patterns and the component ratio of dissolved gases in water.

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Ultrasound techniques are applied in various fields such as washing, fine particle manipulation and solid-liquid separation. In the fine particle manipulation, ultrasonic ranging in MHz band is usually employed. Fine particles with μm order in diameter are treated because of limitations of the wavelength. In contrast, we discovered phenomena that mm-order particles dispersed in water are flocculated spherically by irradiating 20-kHz-band-ultrasound. In order to clarify the mechanism of this flocculation, we investigated the sound pressure profiles in the vessel, and the positions and diameters of the flocculated particle swarm, varying the water depth, ultrasound frequency and particle diameter. From these results, the particle swarm was trapped in the anti-node of the standing wave. The diameter of the particle swarm was dramatically changed by subtle control of the frequency. Based on these results, we will propose a new technique capturing and separating sub mm- or mm-order particles by their diameter.

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In this study, we control the velocity of a narrow liquid jet and the condition of cavitation occurrence. A liquid filled test tube impacts a rigid floor and the jet is induced from curved meniscus. Its velocity is strongly related to the volume of bubbles if the cavitation is occurred by the water hammer. In order to control its velocity, we investigate the condition for cavitation occurrence. We change the material of the floor and hence the impact duration. As floor materials, a metal and a resin are used. We found that the jet velocity linearly increases with the impact velocity for both materials. On the other hand, the condition for cavitation occurrence depends on the oor material. These findings suggests that the cavitation occurrence can be suppressed and the jet velocity can be well controlled by changing the material of the floor.

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