Jet flow phenomenon is one of the basic flows in the fluid mechanics because it includes the free and wall bounded turbulent shear flows and large-scale vortex structure, and so on. It is used widely in the field of industry for the operations of heating, cooling, mixing and diffusion. In order to improve the mixing and diffusion characteristics between the jet and surrounding various non-circular nozzles have been tried. In this research, the flow characteristic, mixing and diffusion properties, of free jet from the petal-shaped special nozzle with six petal-shaped protrusions are made clear experimentally. It is expected that petal-shaped free jet will have a good mixing and diffusion characteristics because of a large wet length, perimeter, and large vortex structure.

View full abstract

The purpose of this work is to control the diffusion and the direction of the jet flow issuing from the pentagonal duct. The velocity measurements of the jet flow issuing from the pentagonal duct with and without the synthetic jet were performed by means of hot wire sensors and the constant temperature anemometer. In order to catch the flow feature the flow visualization was also conducted by the LIF method. And decays of the maximum velocity and the jet half value widths were investigated by analyzing the velocity distributions. As a result, it has been clarified that the jet width with synthetic jet becomes large, comparing with that of the jet without one. Moreover it has been also found that the jet is induced by the synthetic jet.

View full abstract

Abrasive water jet being excellent cutting performance, the cutting, perforating and chipping of several construction material such concrete and metal were applied. However, more effective method measured perforation and cut depth in real time have not been developed yet. In order to estimate a perforation depth on concrete material in real time using abrasive water jet, the resonance propagation model in perforating hole and the model of frequency vortex generation due to inverse jet on the hole edge were analyzed and investigated in experiments. Measuring the sound pressure level around the water jet and perforated depth by water jet exactly, the resonance frequency of acoustic impedance in perforation depth and that of vortex generation concerned with Strouhal number was found to correspond to the peak frequency of sound pressure. From those results, these two analysis model was related interactively, and analyzing the resonance frequency of measured sound only, the perforation depth on the concrete material was able to estimate in real time.

View full abstract

The flow characteristics of a plane air jet have been investigated experimentally. Two deflectors were installed inside of plane nozzle and their slant angles were 6°. Serried isosceles triangle tabs were placed on the upper and lower side of the nozzle exit. The effects of serrated tabs and deflectors on the mean and fluctuating velocities were examined by means of hot-wire measurements. The operating velocity of the jet was fixed at 7.4 m/s. The half width of the plane jet with serrated tabs was smaller than that without serrated tabs due to the contracted flow. The half widths of the jet with divergent or convergent deflectors and serrated tabs were also smaller than that without serrated tabs near the nozzle exit. The plane jet with serrated tabs was observed the predominant frequency as well as that without serrated tabs. The jet with divergent or convergent deflectors and serrated tabs was not observed apparent predominant frequency.

View full abstract

The present paper describes the flow characteristics of round and plane air jets with deflectors. The divergent or convergent deflector was installed symmetrically inside of the nozzle. The effects of the slant angle and length of deflectors on the mean and fluctuating velocities, and the velocity ratio of the inner jet to outer jet at the nozzle exit were examined by the hot-wire measurement. In the case of the jets with the divergent deflector, the outer jet was accelerated and the inner jet was decelerated. The spread of jet with the divergent deflector increased in the near field of the jet. In the case of the jets with convergent deflectors, the outer jet was decelerated and the inner jet was accelerated. The spreads of plane jet with the convergent deflector was smaller than the other jet. We found the relation between the velocity ratio of the nozzle exit and the area ratio of the entrance to exit cross section of deflector.

View full abstract

Large-scale vortical structures and associated flow development in an axisymmetric jet are actively controlled by manipulating the initial shear layer with arrayed miniature jet actuators. The periodic radial miniature jet injections are realized by using a rapid-response pneumatic servovalve, and sinusoidal/pulsed flowing are employed in the present study. The spatio-temporal primary jet structures are investigated through phase-locked particle image verocimetry (PIV). In the pulsed configuration, it is found that intense vortex rings are produced in phase with the periodic control input regardless of the valve-driven frequency f_v examined. When the Strouhal number Stv, which is defined with f_v, is larger than unity, the vortex rings are shed continuously and thus the jet flow development is prompted with low periodic velocity fluctuation. The diameter of the vortices becomes small as Stv is increased, so that the transport range of the jet and ambient fluids can be controlled by changing Stv. In addition, the evolution of counter-rotating streamwise vortices is also confirmed. These streamwise vortices are formed as a result of tilting of the primary jet azimuthal vorticity by the miniature jet impinging on the primary jet shear layer. It is conjectured that they contribute the mixing enhancement in the azimuthal direction.

View full abstract

Turbulent diffusion phenomena are of practical importance with many engineering and environmental field (e.g., in the reactor design and the prediction of pollutant diffusion). In order to clarify turbulent diffusion field experimentally, it is useful to measure instantaneous concentrations of multiple species simultaneously in a turbulent flow. In the present study, measurement system for concentrations of two species using absorption method has been developed, and instantaneous concentrations of two species in a turbulent jet were measured. Two laser diodes (LDs) with different wavelength are used as light sources; red LD (635 nm) and green LD (532 nm). It is confirmed that the instantaneous concentrations of two species in a turbulent jet can be measured by the present measurement system.

View full abstract

Dispersion of exhaust gas from an automobile model is studied experimentally by gas sampling method and smoke visualization in a wind tunnel. Exhaust emission is simulated using CO_2 and the gas concentration in the automobile wake is sampled by sampling probe and measured by a NDIR gas analyzer. The gas dispersion from an Ahmed body with 0°, 25° and 35° slanted back is measured. The measured concentration profiles show that gas dispersion behind the model depends strongly on the slant angle. In case of a 25° slanted model, the high concentration area is observed at roadside and it travels outward. This gas dispersion can be caused by the large-scale longitudinal vortex formed in the wake of the 25° slanted model. The concentration profiles behind the 35° slanted model also show large lateral dispersion that is attributed to the weaker longitudinal vortex in the wake. The smoke visualization using small aerosol agrees well with the measured concentration profiles.

View full abstract

In automobile exhaust systems, catalytic converters have become essential to reduce environmental pollutions and contaminations. The goal of our research is to reduce the pressure loss and to improve the flow distribution under spatial constraint, simultaneously. In our past studies, we have proposed a flow deflector, which can reduce the pressure loss and improve the flow distribution in both steady flow and pulsating flow. So, in the present research, we try to estimate the more practical performance of the flow deflector, using the exhaust-gas flow from a gasolin engine.

View full abstract

In a planar liquid jet with a second-order reaction (A + B →R), the concentrations of reactive species and the streamwise velocity are simultaneously measured by an I-type hot-film probe and an optical fiber probe based on the light absorption spectrometry. The eddy diffusivity of reactive species is obtained from the mean concentration gradient and the turbulent mass flux. The results show that the eddy diffusivity of species A becomes small due to the chemical reaction, and the effects of the chemical reaction on the eddy diffusivity depend on the Damkoler number. These results imply that the gradient diffusion model should be used with considerations of the effects of chemical reactions on eddy diffusivity.

View full abstract

Authors reported that flip-flop flows having the self-excited oscillations are induced by the rotation of the vortex in the concavities constructed on both sidewalls inside the diamond-shaped cylinder bundle. Experiments of the flow visualization are performed for flip-flop flows exiting from diamond-shaped cylinder bundles. Comparison is carried out using the measured results in the absence or presence of the concavities constructed on both sidewalls inside the diamond-shaped cylinder bundle. It is found from the study that (i) flip-flop flows are mutually spread on left or right direction at the angle of 30°, that is the diverging angle of the jet-stream from the bundle becomes 60°, and (ii) the diffusion phenomenon in the jet-stream is quantitatively disclosed by different bundle shapes.

View full abstract

For obtaining the verification data of the numerical analysis of an unsteady flow, the wall surface pressures of an elliptic cylinder were measured under different rotational speeds.The elliptic cylinder, which rotated around the center of the cylinder, was placed in a uniform flow so that the flow separation points moved periodically.The experiments were performed with the Reynolds number equal to or less than 1.26xl05, and a peripheral speed coefficient equal to or less than 0.0443.The pressure fluctuation due to Karman vortices remained even after the periodical averaging operation of the measured data at every rotation.Therefore, it could be elucidated that the discharging vortices were synchronized with the rotation angle of the elliptic cylinder. In addition, hysteresis phenomena, wherein the flow separation point near the leading edge differed according to the rotational direction, occurred even if the rotating speed was low.

View full abstract

Vortex structure and drag characteristic of a circular cylinder accelerated from a rest were investigated by drag measurement and flow visualization techniques. The circular cylinder installed in a linear-motor actuator system moves with a constant acceleration in a water tank. The drag measurement of the circular cylinder was conducted by the measurement equipment using the expansion of coil. The wake flow of a circular cylinder is visualized by using the dye. The formation and the collapse process of the twin vortex and shedding vortices were observed during accelerated motion of the circular cylinder. From the results of flow visualization, the drag was increased after the formation of twin vortex. The drag gradually increased after the collapse of twin vortex. Then the drag increased rapidly after the formation of shedding vortices.

View full abstract

The effects of laminar boundary layer thickness and aspect ratio on the aerodynamics of a circular cylinder supported by two large end-walls is studied by the measurements of surface pressure, turbulent intensity and velocity spectrum. As the results, it is found that the base pressure coefficient on the circular cylinder increases remarkably when laminar boundary layer is thick and aspect ratio is small. And, a new Strouhal number is observed in the wake region close to the end-wall where the contribution of Karman vortex decreases.

View full abstract

Vortex induced vibration is caused by the fluidic interaction in a circular cylinder. This phenomenon is influenced by the flow around the circular cylinder and vortex motions in this wake. In order to control this phenomenon, the suppression of the vortex shedding generated from a circular cylinder is conducted by the attaching spherical rings. In this paper, the flow behavior in the wake and the drag coefficients is measured using X type hotwire anemometer and three-components balance. As these results, the wake width and the drag coefficients decrease due to the flow toward the center of the cylinder behind these rings.

View full abstract

The purpose of this study is to know differences between steady and unsteady drag coefficients of a sphere. Though we often have to estimate unsteady drag-forces acting on a moving obstacle, we are obliged to use the well-known steady drag coefficient for the first estimation because of lack of information about effects of unsteadiness on the drag coefficient. The usual way to take account of unsteadiness is an added mass. However, its application is restricted within the simple shape of an obstacle. We propose a way based on the equation of motion to obtain the unsteady drag coefficient. To confirm validity of the way, we measured and analyzed the motion of the falling sphere in water by using a high-speed camera and a motion capture method. The drag coefficients as a function of time were obtained by substituting measured values of velocity and acceleration into the equation of motion. The drag coefficient was 0.52 when the sphere attains the terminal velocity, being quite large at the beginning of motion. Comparing with the values obtained by the other previous studies, our result is reasonable.

View full abstract

Recently, the mechanism of butterfly flight has attracted significant attentions in bio- hydrodynamics. Especially, a number of recent studies have examined the flow field around an insect wing. However, the detailed flow structure around insect wing and its growth process have not been understood. The purpose of the present study is to clarify the dynamic behavior of the vortices around the flapping butterfly wing. Moreover, we estimated the dynamic lift produced by the butterfly wing using the circulation of the vortex ring. A vortex ring is formed over the butterfly wings when the wings flap downward to the bottom dead position, and then passes through the butterfly completely and grows until reaching the wake at the bottom dead position. The dynamic lift produced by the butterfly wing in flapping downward estimated using the circulation of the vortex ring. The dynamic lift becomes large rapidly as the vortex ring develops over the wing sufficiently. Maximum lift becomes about four times larger than the gravity of the butterfly at -30deg.

View full abstract

Bending stiffness EI, which is defined as cube of a material thickness, corresponds to the resistance to cross-sectional deformation. Hyperelastic materials, such as gel and rubber materials, have an extremely small bending stiffness because of small body stiffness. The hyperelastic materials deform nonlinearity and it is not easy to treat surrounding vortex structures. These flow fields around a moving elastic body is treated as a fluid-structure interaction (FSI), and these phenomena have been continued a series of moving body, elastic deformation, vortex generation, growing and development. In the present paper, we simulate the fluid structure interaction simulation of flow field around an elastic moving body using ANSYS/ANSYS CFX. The purpose of this study is to clarify the effect of bending stiffiiess to the elastic deformation, the vortex flow structure and dynamic forces of the elastic moving body.

View full abstract

The purpose of this study is to compare aerodynamic characteristics of flight motion between rigid and elastic wing. Especially, in Elastic wing we investigate about wing of partially different Young ' s modulus. In order to this investigation, we used Fluid-structure interaction (FSI) analysis. In FSI anaiysis , fluid analysis employ finite difference method (FDM) and structure analysis employ finite element method (FEM). Computation of flapping wing motion are performed for various Young ' s modulus condition, we survey relationship between lift coefficient, thrust coefficient and displacement.

View full abstract

This paper describes the experimental study of the characteristics of a new non-contact type suction device. The present study has been carried out for handling technology in various environments. The main aim was to obtain high suction force in non-contact. We propose a new non-contact type suction device. The jet of nozzle ring flows along surface of device by coanda effect. Eject effect caused by the coanda effect decreases pressure in inside area of nozzle ring. The pressure brings strong suction force. The force distribution vs. parts alignment refers optimal size and condition. This time, we confirmed the suction force by the new method. However, the improvement is depended on suitable alignment. That is suggested that we have to consider relation between coanda and eject effect in thin space put between device and object.

View full abstract

AIST discovered that Coanda phenomenon occurred to an non-contact type suction device. A specification for the switching mechanism which extinguishes the Coanda phenomenon is decided. A structure of a device which added a switching mechanism is clarified, and the prototype is made. A switching effect of produced device is verified. A suction force of produced device is evaluated.

View full abstract

The separated-reattaching flow between the two-dimensional blades is investigated experimentally and numerically In the experiment, a tandem-type probe which consists of two I-type hot-wire probes and a small elliptical cylinder is used to measure the velocity field because a separated flow involves a reverse flow which can not be measured by means of a general hot-wire probes. The experimental results show that the RMS value of the velocity fluctuation in the region of the separated shear layer approaching to the reattachment point is high and this is considered to be caused by the spatio-temporal fluctuation of the reattachment point. Further, numerical results show that the dissipation rate of the turbulent energy becomes high in the region where the Q-value and the RMS value of the velocity fluctuation are also high. These results indicate that the dissipation of the turbulent energy is caused by the separated vortex at the leading edge and the fluctuation of the reattachment point.

View full abstract

A separation control system using a flap, tufts, and image processor is developed and its control performance is evaluated against strongly unsteady separating flows. The flap-control system only works when a separation is detected from the movement of the tufts. The results show that the control system can successfully delay the flow separation.

View full abstract

Basic flow characteristics were investigated for a circular wind tunnel with a 3/4 open-type test section. Its characteristics were exceptionally good; the uniformity of mean velocity is ±0.4%, turbulence intensity is 0.16% at the exit of its contraction nozzle and a statics pressure coefficient is 0.001/m along the center line of the test section. Meanwhile, since the final goal of the present research is to investigate the mechanism of pulsation flows generated in the test section, strong pulsation flows were generated and observed by the change of a streamwise distance between the contraction nozzle and the collector, a collector size and an inducement ratio into the collector.

View full abstract

Flow separation is mostly an undesirable phenomenon and boundary layer control is an important technique for the separation problems on airfoils. The vortex generator jet method is an active control technique which provides a time-varying control action to optimize performance under a wide range of flow conditions because the strength of longitudinal vortices can be adjusted by varying the jet speed. In this study, wind tunnel tests for an airfoil installed active boundary layer control system using VGJs were performed. The experimental results indicate that the maximum lift coefficient increases 10%, and the stall angle is to rise by 2 deg in contrast to the case under no control. It was confirmed that our proposed system can suppress stall on the NACA0012 airfoil and the aerodynamic performance of the airfoil can be enhanced.

View full abstract

An active dimple with oscillating bottom surface is developed for flow separation control of low Reynolds number diffuser flow. This device can provide a periodic disturbance into the flow by means of an amplified piezoelectric actuator. In the present study, basic characteristics of the active dimple were obtained by measuring an induced flow around the dimple using dynamic PIV. The influences on separated flow were also evaluated based on the pressure recovery in a diffuser. The dimple dimension was 5 mm in diameter and 0.1 〜 0.5 mm in amplitude. Reynolds number of the main flow based on the channel height is 650. As the oscillating amplitude increases, the induced flow velocity is changed and the flow structure as well. The strength of the induced flow has a great effect on the pressure recovery at the diffuser.

View full abstract

Effects of the cylinder wake in a freestream on statistical properties of a turbulent boundary layer over a flat plate are experimentally investigated in a wind tunnel. The cylinder is set horizontally over the flat plate. We investigated 3 types of interactions between the wake and the zero-pressure-gradient turbulent boundary layer. Instantaneous velocity is measured by using the hot wire anemometry. We used the variable interval time average (VITA) technique to detect the bursting event. The results show that the time-averaged mean velocity in the inner layer for the case with the cylinder wake coincides with that for the case without the cylinder wake. However, turbulence intensities and Reynolds stress normalized by the inner parameters are suppressed in the outer layer by the cylinder wake. It is found that the velocity fluctuation during the sweep phase in the bursting event is increased by the cylinder wake.

View full abstract

This study is about the heat transfer enhancement in a backward-facing step flow with a little amount of mist.In the forced convection place which used the air flow, a little amount of mist is made to mix to the separated-shear-layer and the spatial temperature in the channel is decreased by using the evaporation latent heat of the mist. Therefore, a thermal boundary layer can be changed without changing a velocity profile and it does not cause pressure loss. The experiments were conducted to examine the effects of thermal and flow field in the channel by changing amount of mist using Infrared Camera and High-speed camera. It is concluded that changing amount of mist supply is effective to enhance the heat transfer.

View full abstract

The technique for measuring the wall shear stress accurately is developed with two types of micro-scale sensor fabricated with MEMS technique. One of the sensors is a thermal type sensor which is based on the quantity of heat diffusion from thin hot film (hereafter called "HF sensor"). The other is a floating type sensor which is based on the electric capacity variety by displacement of the floating element (hereafter called "FE sensor"). To calibrate these sensors, two types of calibration instruments are manufactured. One is an instrument which generates the flow by rotating the cylinder above the flat plate (hereafter called "Cylinder instrument"). Another is an instrument which generates the wall shear stress by Stokes Layer using plane acoustic wave is used (hereafter called "Stokes Layer instrument"). The result of HF sensor calibration shows that the sensor output increases with wall shear stress. Moreover, the square of the sensor output voltage is proportional to 1/3 power of wall shear stress on the hot film, which is consistent with the heat transfer theory. The preliminary experiment results of FE sensor indicates that sensor output voltage seems to increase with the wall shear stress.

View full abstract

In the present study, to evaluate the effect of local flow field on flow accelerated corrosion (FAC), the distributions of time-averaged and root mean square (RMS) of wall shear stresses downstream from an orifice were measured using a flow vector sensor of micro electro mechanical system (MEMS). The air flow was supplied to a circular pipe from a blow-down wind tunnel. The diameter of the pipe is D = 194 mm and the diameter of the orifice is d = 97 mm, yielding a diameter ratio of 0.5. The measured RMS of wall shear stress was found to qualitatively agree with the numerical results obtained previously by Large-eddy simulation. Experimental data of FAC thinning rates, mass transfer coefficients, and the RMS of wall shear stress were compared and the shape of distributions of them relatively agreed well each other. It indicated that an analogy between momentum and mass transfer is still useful downstream from the orifice.

View full abstract

Direct numerical simulations are performed in order to investigate the development of flow field and the friction drag in a subsonic plane boundary layer with a back-step. The boundary layer is forced by normal velocity disturbance of various frequencies at the end of the back-step. The numerical results for no-disturbance case show that the profile of mean streamwise velocity with inflection point is formed behind the back-step and velocity fluctuations are amplified in this region. The rollup of vortexes caused by the growth of the fluctuations are observed around the re-attachment point. In the downstream region of this re-attachment point, irregular vortex street is formed. It is found that the disturbance imposed at the end of the back-step influence the re-attachment point and the vortex street formed downstream of the point. The disturbance with the frequency of about St=0.016 moves the re-attachment point toward the back-step most and is yielded regular distance of vortex street. Although the total drag is larger than laminar boundary layer without back- step, lower total drag compared to turbulent boundary layer is observed in all disturbance cases.

View full abstract

The behavior of necklace vortices around a square flat plate in the laminar boundary layer on the floor wall was investigated by using visualization and PIV measurement. It was found that the relative stagnation height s/h gradually decreased with increasing the plate height compared with the boundary layer thickness. The main vortex center position and the maximum vorticity normalized by using the stagnation height were almost constant in the range of Re>700.

View full abstract

The behavior of star polymer in shear flow was investigated using Multi-Particle Collision Dynamics (MPCD),which is particle-based mesoscale hydrodynamic algorithm. MPCD is a suitable tool for the simulation of complex fluids because it can express both hydrodynamic interaction and Brownian motion, which are not negligible in the simulation of complex fluids. The present study considered the behavior of a star polymer under flow. A star polymer has many brunches interacting each other. In the present simulation a star polymer chain is consist of beads and elastic spring. The simulation was carried out by changing the number of brunches. The numerical results showed that the deformation behavior and conformation of star polymers depended on the number of branches.

View full abstract

Three-dimensional extrudate swell simulation is a basic calculation technique for the consideration of die shape on a profile extrusion. In this study, we simulated the three-dimensional extrudate swell simulation of polymer melts by the finite element method. The Phan-Thien Tanner model was employed as the constitutive equation for calculation of viscoelastic flow simulation. We carried out the three-dimensional extrudate swell simulation through the straight die having the square cross-section. The extruded fluid swelled at once near the die exit because of elastic recovery. The degree of swelling phenomena near the die exit depends on the elasticity of polymer fluid. The profile of the extruded fluid in the draw region from the profile of the die exit is almost independent of fluid elasticity. However, this profile would depend on the swelling phenomena near the die exit. The comparison between the experimental data and simulation result is needed as the future works.

View full abstract

Little amount of flexible polymer induces drag reduction (DR) to suppress turbulent flow. While this phenomenon is well known and has been studied for long years, the mechanism is not understood so far. We assume that the origin of the DR is related extensional viscosity due to the elongation of polymer under extensional strain in the turbulence flow. It is possible that the steep increase of the extensional viscosity in the high rate region of the strain effectively suppress the growth of turbulence. Here we study whether the DR is induced by the addition of a rigid polymer, hydroxypropyl cellulose (HPC), in comparison with a flexible polymer, polyethylene oxide (PEO). We use our original visualization method of 2-dimentional turbulent flow, named Film Interference Flow Imaging (FIFI), to analyze the difference between the cases of the HPC and PEO. The FIFI succeeds to observe that while the PEO obviously induces the DR, the HPC hardly induces the DR. We discuss the different behaviors of the extensional vi scosity toward the strain rate in the cases of flexible and rigid polymers and their different effects on the DR.

View full abstract

In this paper, Ion strength conditioning system which can control a rheological property of Polymeric electrolyte solution is reported. Polyelectrolytes dissociate in aqueous solutions, making the polymers charged. The rheological properties of polyelectrolyte solutions are strongly affected by counter ion concentration. The newly developed Ion strength conditioning system consists of a colloidal particle in water providing hydrogen ions to the target solution, a membrane filter which separates the target solution and the colloidal dispersion, and electrode. In the experiment, the viscosity of a PAANa 200ppm solution treated with the ionic strength conditioner was measured by capillary rheometer. As a result, we can see a reduction of a viscosity for a supply of the hydrogen ions by the conditioner. And further more, we can increase the viscosity of the solution by a collection of the hydrogen ions from solution.

View full abstract

The velocity profiles of dilute polymer solutions, surfactant solution and distilled water near the wall surface in a microchannel was clarified by using evanescent wave illumination. Fluorescent particles with the diameter of 20 nm and 100 nm were used as tracer particles. Polymer solutions were aqueous solutions of polyethylene-glycol (PEG8000 and PEG20000) and polyethylene-oxide (SE15 and SE70) at 5 ppm. Surfactant solution was aqueous solution of Oleyl bis-(2-hydroxyethyl) methyl ammonium chloride (trade name : Ethoquad 0/12) at 500 ppm with sodium salicylate. The results obtained for the velocity profiles basically fitted with plane Poisuille flow, except for surfactant solution whose velocity profile significantly decreased compared with that of distilled water. The resolution of the velocity profile near the wall surface was improved from the conventional result.

View full abstract

In this study, we have investigated the mixing property of water and polymer solution in micro-channels. We have utilized T-shaped micro-channels which have contraction-expansion parts with five asymmetric rectangular block gates and observed the mixing procedure. Dyed water and a dilute aquaus solution of polyethylenoxide (PEO) of 100 ppm by weight were mixed in the tests. In the micro-channels, the polymer solution caused unstable vortexes before the rectangular gates and the instability of the flow grew at the later part of the contraction-expansion region. The unstable flow with the vortex due to the elastic property of the polymer solusion leaded the efficient mixing.

View full abstract

When strong pressure-oscillation was applied to the two vertically aligned air bubbles in viscoelastic fluids from the bottom side, the lower-bubble rose faster than the upper-bubble. It is thought that a hydrodynamic interaction may be occurred in the fluid between air bubbles. To clarify the stress contribution on the interaction, we tried measuring the retardation profile near and between the vertically aligned small air bubbles under pressure-oscillating fields, by using the flow birefringence technique with CTAB / NaSal solution. In the case of near the bubbles (2μL for each), it was found that the stronger retardations were observed as approaches to the bubble surface under pressure-oscillating field, as well as the higher frequency. The higher uniaxial strain rate (about the order of 10) was obtained in vicinity of small air bubbles. However, in the case at the bubbles center, the moderate elongational velocity was observed. As for the between the two bubbles, the relatively flat retardation profile was also obtained.

View full abstract

Flow properties of water, microbubble/water mixture, and complex fluids (anionic surfactant solution and dilute polymers solutions) were observed in the flows through porous membranes which had micron sizes pores. Pressure drops of water agreed with the predictions of Navier-Stokes equation. The resultant pressure drops of microbubble/water mixture and surfactant solution were lower than water ones in a range of Reynolds number >10^1,and so-called drag reduction effect was confirmed. In addition, much lower pressure drops compared with the water results was obtained for dilute polymer solutions. Size effect, elasticity, and electric interaction as contributing factor were discussed. Whereat, electric interaction between solid wall and microbubble (anionic surfactant micelle) was strongly suggested. Furthermore, surface tension was measured and corresponding to the discussions.

View full abstract

Axisymmetric flow of surfactant solutions past a sphere moving at constant velocity is experimentally investigated. Test fluids used are entangled wormlike micelle solutions of 30mM cetyletrimethylammonium bromide and sodium salicylate at various molar ratios. To obtain full-field flow birefringence image of transient flows behind an impulsively started sphere, a division of focal plane type polarization image sensor is utilized. Left circularly polarized light is used as incident light and the degree of linear polarization (DOLP) and the angle of polarization (AOP) of transmitted light are measured, from which distributions of spatially averaged values of the retardation and the angle of fast axis of the fluid are obtained. Distributions of the retardation along the centerline of the sphere are investigated at various Deborah numbers. At a critical Deborah number, the retardation distributions become propagate at a constant speed away from the sphere. The measurements also show the abrupt change in the wake accompanied by the necking of the cross section when Deborah number exceeds a critical value.

View full abstract

Influence of pre-shear on the shear-hardening behavior of a wormlike micelles solution in step shear flow is experimentally examined. The peak stress during the shear-hardening decreases with increasing the shear rate of the pre-shear. A component of the contribution of shear- hardening in the shear stress is evaluated by deducting the shear stress of the steady state from shear stress. When integration of the shear stress component of the shear-hardening by shear strain is defined as a shear energy caused by the shear-hardening, the maximum value of it decreases with increasing the shear rate of the pre-shear. By introducing non-dimensional shear rate, which is defined as shear rate in the product of the relaxation time, the maximum shear energy for the shear rate in the first step shear can be plotted on a curve but it depends on the micelles conformation.

View full abstract

This paper is concerned with plant hydrodynamics. The water disappearance process from the cut dandelion petal was observed by a Color 3D Laser Scanning Microscope. Some morphological parameters and cell shape profiles of the petal surface of the dandelion, Taraxacum officinale, was measured. The time change in the surface-roughness of the petal surface was obtained. The stoma surface shape on the involucral scale was also measured. Processes to the cell death of a plant were discussed using the time change of the petal surface shape of dandelion.

View full abstract

Basic flow behavior of supercritical CO_2 in solar water heater using supercritical CO_2 is studied for a flow of supercritical CO_2, a small change in temperature or pressure can result in a large change in density and specific heat capacity, especially in the state close to the critical point. Natural convective flow of the supercritical CO_2 can be easily induced by solar heating in the system,when flow characteristics and heat transfer of supercritical CO_2 natural convection are important.Considering thermophysical properties of CO_2 near the critical point, phase change from liquid to supercritical state have significant effects on the CO_2 local heat transfer behaviors.

View full abstract

MCF is one of the intelligent magnetic responsive fluids developed. It is compounded by magnetic fluid (MF) and magneto-rheological fluid (MRP). The MCF is defined by the suspensions conducted from micro to nano ordered metal particles in MF, and is responsive to a magnetic field. Since the particles aggregate in the fluid by the application of the magnetic field, the fluid become to involve many magnetic clusters. By the effect of the existence of the clusters in the fluid, the properties of viscosity, magnetism and magnetic pressure change according to the kinds of the particles and solvent, and the fraction of the particles. The cause can be explained by the magnetic cluster model.

View full abstract

We proposed a new type of finishing with fluid. It was utilized of non-attachment the finishing surface to the finished surface of a material under a steady magnetic field. We used the fluid as an intelligent fluid which reacts upon the magnetic field, MCF (magnetic compound fluid). We can deal with larger clearance between the finishing surface and the finished surface by utilizing the MCF than magnetic fluid (MF) and magneto-rheological fluid (MRF). Not only without polishing pad but also with buffer material in the fluid, we can obtain nano-finishing surface.

View full abstract

At the fields of robotics, sensing for artificial arm and leg, and investigating surface property, the sensor that is applicable to response for shear force as well as normal force should be developed. Our developed haptic sensor by combining metal particles in balloon crude rubber has high quality of sensing for 0.01 N ordered force and has the ability of responding at the case of rubbing any bodies. The rubber involves MCF as one of intelligent fluid, and then it is called MCF rubber. Because of making the rubber more sensitive to the shear force, the fingerprint is also attached on its surface. The MCF rubber is applicable for sensing at various fields: paper, clothes, human skin and so on. The present study also clarifies the effect of the fingerprint on the electric current flowing inner the MCF rubber.

View full abstract

We have investigated the behavior of interface between liquid crystal and isotropic phases to establish its control method. In our experiment two thermo modules are attached on the liquid crystal cell and the temperature of the cell is controlled to obtain both the liquid crystal and isotropic phases. By changing the temperature of the thermo modules, the area of the phases changes causing the movement of the interface between the phases. The moving velocity of the interface is measured as a function of the temperature of the thermo module, and the velocity increases with increasing temperature. The theoretical result with the Landau-deGennes free energy agreed with the experimental result.

View full abstract

In this study, we have investigated the changes in flow property and electric characteristic of carbon nanotube (CNT) suspensions under steady simple shear flows applied. The CNT was dispersed in polybutene of an insulating carrier liquid. A parallel plate type rheometer was utilized, and shear thinning viscosities and normal forces were measured. Moreover,electrical resistances of the liquid film between the two plates were also obtained. The flow curve of shear viscosity shows two step shear thinning property and a typical shear rate was estimated between the two shear thinning regions. The normal forces and the electric resistances were rapidly increased in high shear rate region. The increase in the normal force was normalized well with the typical shear rate obtained with the viscosity flow curve. However the deviating point of the electric resistance from the constant value in a low shear rate region was almost same as that of the normal force, the increase in the resistance after the deviation were dependent on the volume fraction of CNT.

View full abstract

We examined the shear flow of dilatant fluids with a cone-plate rheometer. The dilatant fluids used in this experiment were mixtures of potato starch and water with three different concentrations. In transitional response of shear stress at a constant shear rate, it was found that the stress after beginning of flow increases abruptly. Moreover, the gap between cone and plate became small with increase of time. These results were considered due to a dilatancy of fluids and suggested the occurrence of a squeeze effect in a shear flow. However, the shear viscosity of dilatant fluids in the range of shear rate applied in this experiment showed the shear-thinning property, apparently.

View full abstract