In this study, numerical calculations were performed using blade models with different thicknesses in order to reduce the noise caused by the separated/reattachment flow between the blades of a sirocco fan used in a blower of a car air conditioner. The blade model is a fixed model that reproduced three sirocco fan blades. Reynolds number of the flow into the blade was fixed at the maximum of the actual machine, and the flow field and pressure field were visualized to clarify the relationship between the blade thickness and the flow field. As the blade thickness increased, the following three points have been found. (1)The separation position changes, (2)The blade surface fluctuation pressure becomes large when separation occurs at the blade surface compared to the leading edge separation, (3)The variation in force applied to the blade surface decreases. Furthermore, the noise generated from the blade surface was estimated using Curl's theory assuming that the blade surface is smaller than the wavelength of the sound wave, and the relationship between the blade thickness and the generated noise was examined. It was found that as the blade thickness increases the fluctuation of the force applied to the blade surface decreases, From this result, the noise generated by the interference with the blade surface is expected to decrease.

The experimental prediction methodology of the broadband noise as the first step to organize the blade elementary momentum theory for a cooling fan is proposed. For the prediction equation of the broadband noise, the theory on the acoustic radiation from airfoil with turbulent boundary layer is applied. The broadband noise of the cooling fan is predicted experimentally by using the measured flow regime in the wake of the actual fan based on the results of wind tunnel test on the aerodynamic noise of a flat plate. The prediction by the suggested methodology could explain that the broadband noise in the low frequency domain in the operation point of the cooling fan is influenced by the wake vortex noise in the pressure side separation.

In order to reduce the aerodynamic noise generated from bogies in high-speed trains, deflectors attached at the leading and trailing edge of the bogie cavity are expected to be one of the effective mitigation measures. In past studies, the deflectors reduced the aerodynamic bogie noise, but the reduction mechanism still remains unclear. Then, we measured the flow field around a bogie with deflectors by using PIV technique. It was found that the deflectors deflect the air flow downward to the ground and the flow velocity at the bottom line of the vehicle decreased to 50% compared with the baseline condition without the deflectors. This effect of the deflectors could be the reduction mechanism of the aerodynamic bogie noise. As another mitigation measure, based on the physical understanding that a free shear layer develops along the bottom line of the vehicle in the bogie, we proposed a new design guideline for the vertical location of main motors and gear boxes in the bogie. From a wind tunnel test, it was found this bogie components arrangement could reduce the aerodynamic bogie noise by more than 2dB by avoiding the free shear layer.

Aerodynamic noise generated from the bogie section is one of main sources when high speed trains run above 300km/h. Therefore, it is important to reduce the aerodynamic bogie noise appropriately. In this paper, the countermeasures to control the noise are investigated. In order to examine the effect of the countermeasures on the aerodynamic noise, a wind tunnel test was carried out by using a two-dimensional microphone array and Pitot tube rake. Two countermeasures to control flow at the bogie, i.e. deflector and concaved bottom section, were developed. It is found that the flow speed was reduced by these countermeasures, and that the aerodynamic bogie noise was properly reduced by the deflector, however, the reduction by the concaved bottom section was seen only in lower frequencies.

To clarify the effects of jet angle on the radiated sound from the flute, the radiated sound and jet fluctuations were experimentally investigated. An artificial blowing device with an artificial oral cavity was used to change the jet angle and the geometric edge offset (the relative height of edge from the jet oscillation center) independently. The actual jet offset was estimated based on the velocity profile measured by a hot-wire anemometer. Although the geometric edge offset was set to zero, the actual edge offset increased with the jet angle since the jet deflects toward inside the resonator. The radiated sound pressure of the first mode remained almost at the same level, while the sound of the second mode radiated more intensely with the increase of the jet angle in the range of 15 degrees from the measured angle for a human player. With the increase of the jet angle beyond this range, the sound of the third mode radiated less intensely. These results indicate that jet deflects toward inside the resonator influenced by the acoustic resonance and that the variation of the jet angle affects the actual jet offset, which affects the harmonic structure.

The possibility of production of sibilant fricative /s/ in chimpanzee is investigated by aeroacoustic experiments and simulations. The upper and lower jaw, tongue and lip geometries were extracted from CT images of a 9-yr-old chimpanzee. Then, each geometry was printed out with 3D printer and assembled to form the vocal tract with sibilant groove. The flow was inserted to the replica of chimpanzee and the far-field sound was measured by a microphone. In addition, the large eddy simulation of compressible flow was conducted on the same geometry to clarify the flow configuration inside the vocal tract geometry. Results of the experiments showed that frequency of the sound generated by the replica of chimpanzee was lower than that of /s/ pronounced by humans. The simulation showed that the sound source emerged mainly near the upper incisor surface, indicating that the difference of flow configuration and acoustic resonance in the lip cavity is the cause of the difference of sound between the chimpanzee and humans.

In this experimental study, fluid dynamic response characteristics of wake galloping between two square prisms of same size in tandem and staggered arrangement to their relative position and free stream velocity were investigated. An immovable square prism of size d was fixed at upstream side and another vibratile square prism was placed at downstream side. The relative position of the vibratile downstream prism to the upstream prism was varied in the range from 1.6 d to 3.1 d in stream-wise direction, and in the range from 0.0 d to 2.1 d in cross flow direction. The vibratile prism at downstream side is elastically supported at it's both end and is restricted to vibrate in only cross-flow direction. Instantaneous displacement of vibratile prism was measured by means of Laser Displacement Anemometer, and degree of vibration was evaluated by rms value of the fluctuating displacement. In addition, the temporal displacement of vibratile prism was evaluated by time variation of the local rms value of the fluctuating displacement. From the experiments, it was found that the local rms value of the fluctuating displacement in quasi-instantaneous is more than twice the rms value of the fluctuating displacement. Also, the classification map with unstable vibration to their relative position at two square prisms was obtained.

Multi-articulated flat plate which consists of some flat plates connected with smooth articulates is self-oscillated in a mean-flow. To clarify the oscillation mechanism analytically, the equation of motion on the multiple-pendulum was derived. The two-dimensional numerical simulations of fluid-structure interaction were conducted. In order to calculate the flow around the oscillating flat plate, moving overlap meshes were applied. In the results of the simulation, Multi-articulated flat plate started oscillation itself. At first the vorticity layer was formed behind the static plate and Kármán vortex street was appeared far from the trailing edge. Then the shear layer became wavy with longer wavelength than Kármán vortex. The flat plate was swayed and started fluttering. The three-dimensional simulation was also conducted, and Kármán vortex street was also appeared. However the wavy motion of the shear layer was not appeared and the flat plate did not fluttering.

Large aeroacoustic noise is generated by the vortex shedding from a circular cylinder. The suppression of the vortex shedding is one of the important issues in engineering. The instullation of cylindrical rings on a circular cylinder has been proposed as a method to suppress the vortex shedding. In this study, the effect of the configration of cylinderical rings attached to a circular cylinder was investigated on reduction of the aeroacoustic noise by using the low-noise wind tunnel in Reynolds number range from (1.9 to 3.9) × 10⁴. Also, the flow fields in the wake was mesured by using Stereo-PIV. As a result of this study, the sound pressure level decreased by 15 dB compared to a 2Dcylinder due to an appearance of the three-dimensional flow structure in the wake by attaching the cylindrical rings.

It has been confirmed that the taper cylinder has an effect of reducing the Aeolian tone radiated as compared with the circular cylinder. In this paper, static pressure fluctuations and velocity fluctuations in the wake of a tapered cylinder were measured using a conical tip type static pressure tube probe and an x-type hot wire probe, and the flow structure and static pressure fluctuations in the wake of a tapered cylinder were clarified. The static pressure fluctuation power spectral density was also clarified. The Reynolds number based on the diameter of the mid span of the tapered cylinder and the uniform flow velocity is 2.65×10⁴. At the position of x'/D = 2.0 to 5.0, the static pressure shows a smaller value as the taper ratio increases. It was found that in the tapered cylinder, the dead water region was long and the rolling up of the shear layer was on the downstream side, and the static pressure fluctuation decreased. Also, it was considered that the von Karman vortices did not occur in the wake of the tapered cylinder and it was observed of decreasing of the peak level in the sound spectra. Comparing the peaks level, it was confirmed that TC1 was reduced by 24.7 dB, TC2 by 15.6 dB, and TC3 by 9.7 dB compared to the circular cylinder.

Galloping is induced on a circular cylinder driven by a necklace vortex generated in the gap between the cylinder and a wake plate. The lift force caused by the necklace vortex is evaluated by a rotary circular cylinder turbine with a wake ring plate system to predict the condition of the galloping based on the quasi-stationary theory of galloping. The rotational oscillation system of the circular cylinder blade with an arc-shaped wake plate is designed to induce the galloping of circular cylinder. From the experiments, the large amplitude of the oscillation was induced and we confirmed that it was different from the longitudinal vortex-induced vibration.

Multi-blade fan can achieve high pressure and flow rate despite of its small size. However, the fun has still has drawback on the noisegeneration. Although it is required to understand the cause of noise, it is difficult to understand the internal flow of a multi-blade fan because of its complexity. From the experimental results and analysis results, the multiblade fan in the present study was noisy around 1 kHz. The static pressure data obtained by CFD is filtered with narrow band pass filter, and only the frequency around 1kHz is extracted and analyzed. As a result of visualization, the change in static pressure is small at a location shifted by about 90 ° from the tongue rotation span of the blade, the positive / negative pressure changes at a location shifted by 270 °, and the static pressure change is large at other locations. Since the length of the scroll casing is close to the wavelength of the sound wave, it is assumed that the noise around 1kHz is due to the resonance phenomenon. The visualized result is similar to the behavior that assuming a resonance phenomenon. In the future, it will be important to conduct detailed acoustic analysis to clarify that 1kHz noise is a resonance phenomenon.

To clarify the aerodynamic noise characteristics of an NACA0012 airfoil with a blunt wingtip by means of Large Eddy Simulation and Computational Aeroacoustics, we calculated the characteristic St numbers, which were 0.1, 0.3, and 0.5 for the angles of attack of 10° and 12° ± 2°. The Reynolds number based on the chord length of the airfoil and uniform flow velocity was 3.0 × 10⁵ for the constant angle of attack and 2.0 × 10⁵ for the oscillating airfoil. The flow field and the acoustic field around the airfoil were calculated using hexahedral meshes. As a result, the tip vortices were found to merge at x/C = 0.75 and form the main noise source. The directional characteristics of acoustic radiation showed a dominant quadrupole at St = 10. Pressure fluctuation on the wingtip at St = 0.1 was the same as that in case of constant angle of attack. At St = 0.5, the vortex structure disappeared because of increased pressure fluctuation, which reached 15% of chord length. Therefore, we concluded that the noise generated due to tip vortex formation is dependent on St.

An underexpanded jet is often used as an assist gas to eliminate molten material during laser processing and as a cooling jet of glass tempering process. When the jet impinges on a flat plate to be processed, a plate shock wave is generated in front of the plate and the jet strongly oscillates depending on the nozzle-plate spacing and the nozzle pressure ratio. Oscillation of jet affects the stagnation point on the plate and, in addition, high-frequency noise called screech is radiated in the flow field, which cause the working efficiency and the processing quality to be worse. In this study, an underexpanded jet issuing from a circular tconverging nozzle and impinging on a flat plate perpendicularly is examined experimentally. The flow field is visualized using schlieren method and the sound radiated from jet is measured to examine the relation between the oscillation of jet and the frequency of noise. As a result, a dominant frequency that seems to be a screech tone appears in the high frequency region. Furthermore, the arrangement of vortices surrounding the jet under such condition is found to be different from that of the free jet. Therefore, these high-frequency sound is shown to be caused by the impingement on the flat plate.

The interaction between the supersonic jet and an obstacle is one of the fundamental problems of the compressible fluid dynamics, and causes the various problems of the aeronautical and other engineering, such as the design of a rocket launcher system. It seems that the characteristic of the interaction between the rectangular jet and an obstacle is necessary to control the interacting jet, but it is not conducted in past papers for the characteristic of a rectangular jet. This paper aims to clarify the characteristics of the interaction between the rectangular jet and an obstacle by the experiment and the numerical analysis.

The supersonic jet is used on engineering devices and is one of the fundamental problems of the compressible fluid dynamics, and causes the various problems of the aeronautical and other engineering, such as: the design of a rocket: launcher system. It seems that the characteristic of supersonic jets is necessary to control the engineering devices, but the effect of nozzle diameter does not conducted in past papers. This paper aims to clarify the effect of nozzle diameter for characteristic of supersonic jets by the numerical analysis.

In a small cooling fan with contra-rotating impellers, it is necessary to clarify the influence of the tip leakage vortex on the flow field of the rear impeller because the tip leakage vortex generated by the front impeller enters the rear impeller. However, RANS, which is generally used in the design and development of turbomachines, can not solve the flow phenomena related to the small vortex. Therefore, in this research, LES analysis is performed for the contra-rotating small cooling fan that are commercially available for server cooling, and the flow phenomena such as tip leakage vortex is investigated. We aim to elucidate the complex internal flow. If complex flow phenomena such as tip leakage vortices can be predicted with high accuracy, it may lead to the elucidation of fan noise sources, and it may be possible to establish a design method of the contra-rotating small sized fan for noise reduction. In this report, LES analysis is performed on a small cooling fan with contra-rotating impellers, and the internal flow is considered focusing on the behavior of tip leakage vortex from the calculation results. As a result, it was confirmed that the tip leakage vortex had a large influence on the low velocity area in tip clearance.

Cavitation in torque converters causes negative effects such as noise, vibration, and performance degradation. In actual machines, the occurrence of cavitation is suppressed by sufficiently pressurizing the working fluid with the oil pump, but the power required for it hinders improvement of fuel consumption. In this study, experiments were conducted under dynamic conditions assuming an accelerated operation of automobile, and the effects of acceleration on the cavitation appearance and torque performance of a torque converter were investigated. As a result, the cavitation development was delayed as the acceleration was larger, that is, as the acceleration time was smaller. It is considered that the growth of cavitation is delayed in the smaller acceleration because the diffusion of the air dissolved in the oil is insufficient. As for torque performance, the smaller the acceleration was , the lower the torque was. This is considered to be due to the fact that cavitation is more developed with the sufficient diffusion of dissolved air in the smaller the acceleration case.

Under the specific angle of attack on NACA16-012 hydrofoil, generated cavitation suddenly disappears even in low cavitation number, in which cavitation is normally generated. This cavitation disappearance phenomenon was confirmed by previous research to be unique to NACA16-012 hydrofoil. It was experimentally confirmed that this phenomenon occurred when the sheet cavity generated on the hydrofoil was periodically broken and the cloud cavity was released. In this study, the break-off frequency before and after cavitation disappearance phenomenon was measured experimentally. NACA16-012 with the cord length of 30 mm and high-temperature and high-pressure water tunnel installed at Institute of Fluid Science, Tohoku University were used. Since the compressor and vacuum pump were connected to this tunnel, the pressure can be controlled independently of the flow velocity. The experimental conditions were flow rate of 13.4 m/s, water temperature of 30 ℃ and dissolved oxygen of about 30 %. Under these conditions, cavitation disappearance phenomenon was confirmed at angles of attack of 6° and 7°. The fluctuation of pressure was measured with a pressure transducer 80 mm downstream from the center of the hydrofoil and the characteristics frequency was evaluated by the frequency analysis. In general, the break-off frequency of cloud cavity releasing tends to decrease with decreasing cavitation number. However, NACA16-012 hydrofoil showed different results. The peak of the break-off frequency increased to a certain frequency when the cavitation number decreased. In addition, no strong peaks were observed before and after this break-off frequency, it is assumed that the frequencies before and after the break-off frequency were related to the cavitation disappearance phenomenon.

Cavitation is a phase change phenomenon from liquid to gas phase that occurs in low-pressure regions of high-speed fluid machinery such as rocket turbopumps. In particular, the phenomenon that a cavity rotates faster than rotational speed of the pump in the direction of rotation is called super-synchronous rotating cavitation (super-S RC). Cavitation are known to cause vibration, noise and decrease of efficiency. Therefore, understanding characteristics of occurrence of cavitation is significant. It is known that super-S RC is often observed in rocket turbopumps, but that in industrial pumps it is not observed. For this reason, it is estimated that its occurrence is related to rotational frequency of pumps. In this study, experiments of an inducer were conducted at two types of rotating speed at Kakuda Space Center in the Japan Aerospace Exploration Agency. By the rotating speed of the motor and the mean flow rate is held constant and the inlet pressure decline, pressure fluctuation was measured, and the ranges of cavitation number where super-S RC occurred were compared. As a result, super-S RC is observed at higher range of cavitation number when rotating speed is low.

To improve the launch capability of rocket, which is the only means for putting man-made objects such as artificial satellites into space, rocket engine turbines are required to have high efficiency and high reliability. In this study, unsteady calculation using Transient Blade Row (TBR) method was performed on the original blade and the optimized blade obtained by blade shape optimization so as to compare the flow fields of the two types of blades and to investigate the resonance caused by the unsteady fluid force. Then, frequency response analysis is performed using unsteady fluid force, and the structural analysis is made using two types of materials (Inconel 718 and Ti-6Al-4V) to determine maximum von Mises stress occurred in the tested blades. It is found that the optimized blade exhibited 4% higher turbine efficiency than the original blade, which is because the exit Mach number from the nozzle is reduced in the optimized blade, weakening the shock wave in the first stage blade so that the generation of entropy of the entire turbine is suppressed. Frequency response analysis was performed using the secondary blade passage frequency (56 EO) component of the nozzle. It is found that there is low risk of the resonance due to the 56EO component because there is no vibration mode excited near the design point in the first stage blade of the optimized blade.

Turbine stages for rocket engine usually operate in a supersonic regime, causing some serious troubles in turbine efficiency and vibration. Therefore, highly efficient and reliable turbines driven with a small amount of mass flow rate are strongly required. In addition, it is important to reduce manufacturing costs. This study accordingly have dealt with numerical investigation on scarfed nozzle, which is composed of axisymmetric and non-axisymmetric parts and relatively easy to manufacture as a supersonic turbine nozzle for rocket engine, calculating its aerodynamic performance in comparison with conventional turbine nozzles. Six test cases are examined, where three types of first stage nozzles, that is conventonial turbine nozzle and two scarfed nozzles, are used along with two sets of the first stage turbine blade and second stage turbine vanes and blades. As for computational grid used in the three-dimensional steady simulation, wall function treatment is applied to the flow field near the solid wall to reduce the computational cost. According to the numerical results, due to first rotor load ratio, clear differences are observed in turbine efficiency among the test cases, which can be attributed to loading balance between the first and second stages. Also, turbine efficiency using scarfed nozzle is improved by 0.3% through the decrement in the design outlet Mach number at the exit of the axisymmetric part of the scarfed nozzle.

In this research, insertion effects of hot-wire probe (HWP) upon the velocity measurement of boundary layer with separation and reattachment are investigated. Constant-temperature anemometry (CTA) and PIV measurements are performed on the suction side of an airfoil in the low-pressure turbine cascade. In the past research, we found flow may change due to insertion of the HWP in separation and reattachment region. Therefore, the aim of this paper is to find the insertion angle (θ_HWP) which is the angle between wall-normal direction and HWP to enable to reduce the insertion effects by means of particle image velocimetry (PIV). Especially, we focused on the survey in separation area because the separated shear layer is significantly affected by the external disturbance. The tip of the HWP was fixed at y/p=0.0125 in separation area, and changes in the flow field when the θ_HWP was changed were investigated. Time-averaged velocity distributions obtained in the case of HWP inserted compared with those in the case of HWP ejected. As a result, θ_HWP= 65°was the best insertion angle to reduce the effects in this research. Furthermore, CTA measurement was conducted with the insertion angle. Finally, the velocity distributions of both PIV and CTA were good agreement.

We developed a tornado-type remote suction device. That is, a generation method of tornado-like swirling flow using a rotating disk was proposed. Visualization experiments with dry ice mist are conducted to investigate the characteristics of tornado-like swirling flow. The experimental parameters controlled in this study are configuration of the rotating disk, installation height, and suction flow rate. Swirling flow with fins attached on the rotating disk is stronger than that without fins. Various shapes of fin are tested to intensify the swirling flow. The simplest fin shape like a straight board aligned with radial direction is sufficient to enforce the swirling flow. Installation height is limited for the generation of tornado-like swirling flow under a certain operation condition. The diameter of the rotating disk is very important parameter for generating swirling flow. Proper balance of suction flow rate and swirling flow is required to generate stable tornado-like swirling flow.

In the operation of hydro turbines and pump, self-excited vibration can occur due to fluid force which is generated as a response to the vibration and is called rotordynamic fluid force. The tangential component of rotordynamic fluid force has large impact on the stability of rotors. Characteristics of the tangential fluid force acting on a whirling columnar rotor which is modelled on the front shroud of a Francis turbine during self-excited vibration were investigated in computation in the present study. The angular velocity of the whirling motion of the rotor and the tangential force could be normalized by the axial velocity of axial leakage flow through the clearance between the rotor and the casing and the square of it, respectively. In the range of large whirling velocity, the tangential force was caused by a pressure distribution in the case without axial leakage flow. In the range of small whirling velocity, it is known that the tangential force is generated by the inertia of axial leakage flow. In the range of middle whirling velocity, the tangential force was found to be caused by both effects of whirling motion of the rotor in static fluid and the inertia of axial leakage flow. The pressure distribution without axial leakage flow was due to pressure loss in the wake of the rotor in addition to effects of shear stress and discharge from /suction into the clearance.

The final goal of this study is to suppress hub-corner separation in a first stator cascade of a transonic 2-stage axial compressor. This study used an inverse design method based on meridional viscous flow analysis for designing first stator vane, and used large-scale detached eddy simulation (DES) in order to evaluate the flow field and the performance of the full stage of this axial compressor. The flow field in this compressor was analyzed by data mining techniques, which include a vortex identification based on the critical point theory and limiting streamlines visualized by the line integral convolution (LIC) method. In this study, chordwise blade loading distribution was modified to shift the peak load position from the front part to mid-chord, and give gently-sloping distribution profile at each span in order to suppress the hub-corner separation. As a result of modifying the chordwise blade loading distribution and redesigning the first stator vane, the hub-corner separation has been suppressed and the flow field in a first stator cascade has been also improved. For these reasons, total pressure loss coefficient in first stator has been decreased and the performance of full stage of the redesigned compressor has been enhanced by 0.53% in adiabatic efficiency compared with that of the original compressor. This paper describes how to suppress hub-corner separation and shows the flow field in a stator cascade in details.

This paper describes experimental and computational studies to investigate an Effect of Upstream Bent Pipe on Performance characteristics of a Transonic Centrifugal Compressor. To get compressor performances effected by upstream form, static pressure gages and orifice flow meter were applied to a pipeline including a Transonic Centrifugal Compressor for vehicles. Inlet tube of this compressor is exchangeable between straight and bent which have two kind of curvature, 43mm and 49mm. The experiment was carried out from choke flow rate to nearby surge at 140,000rpm. Computationally, RANS was used to study internal flow in straight and bent in detail. About the simulation of bent pipe, all over Computational grid were 62,820300 in straight and 100,510010 in bend. The following aspects were clarified by the experiment: (a) Total pressure ratio declines in the order of decreasing curvature radius, straight, 49mm and 43mm; (b)the declines are remarkable in high flow rate. In contrast, the gap gets small from peak flow point to choke. The computational results show the following: (c) When inlet pipe is bent, compared with straight pipe, total pressure ratio decreases because of pressure loss caused by a bent part. These result suggests that compressor with bent pipe have a wide surge margin because secondary flow restrains a stall and improves aerodynamics performance.

An experimental study was performed to investigate the relationship between the extensional rheological properties of drag reducing string-like micelle solutions and turbulent statistics in two-dimensional (2D) flow. Cationic surfactant and counter ion supplier were added to 2D turbulent flow, and the flow field and vortex shedding in the flow were visualized using interference patterns and particle image velocimetry (PIV). We considered the relationship between vortex shedding and drag reduction properties of the fluid.

The flow of viscoelastic fluids in an annular space between a rotating corrugated inner cylinder and a stationary outer cylinder, in which shear waves propagate, is studied. The fluids used are aqueous cetyltrimethylammonium bromide (CTAB) solution with sodium salicylate (NaSal) as added salt. The velocity fields are measured using a particle image velocimetry (PIV). Three different types of mean flow profiles are observed between the cylinders with a radius ratio of 0.178, depending on the rotational speeds of the inner cylinder. The different types include (a) Couette flow like profiles, (b) profiles having the maximum between the cylinders, and (c) profiles with small slopes. Type (a) profiles appear at lower rotational speeds, and type (c) profiles appear at higher rotational speeds. The results show that the high-speed streaks appear on the surface of the inner cylinder, and the radial extent of these high-speed streaks can be seen to determine the mean flow profiles between the cylinders. The experimental results with different concentrations of CTAB/NaSal suggest that the critical values of the rotational speed at which the flow type changes depending on the shear wave speed of the fluid.

We have attempted to control the rotational and translational motions of cholesteric liquid crystal droplet using electric fields. The cholesteric liquid crystal (4-Cyano-4'-pentylbiphenyl with chiral dopant) material is sandwiched between glass plates, and two types of electrode patterns treated on the glass plates: (1) homogeneous electrode pattern and (2) interdigitated array electrode. The cholesteric liquid crystal droplets are suspended in the isotropic phase, and thus the density of the droplet and surrounding liquid is almost same. From the experimental results, it is found that the helical axis of the chiral structure of the molecular orientation field tends to align perpendicular to the field inducing the rotational motion of the droplets. On the other hand, the pulsed electric fields cause the translational motion of the droplet perpendicular to the helical axis and the electric field. Thus, the three dimensional motion control of the cholesteric liquid crystal droplet might be achieved by the proper choice of the electric fields and the electrode patterns.

In this study, a new magnetic material was made by microencapsulating the Temperature-sensitive magnetic fluid. Microcapsules are made by dissolving the organic solvent, polymer, Temperature-sensitive magnetic fluid, dropping it into pure water and stirring with a homomixer. Fluorescence observation of particles and visualization of flow field are performed by mixing fluorescent dye in microcapsules. As the results it was confirmed that microcapsules formed clusters by supplying a magnetic field. It was shown that the flow of microcapsule solution can be visualized by using self - made magnetic capsule containing fluorescent dye. The forced convection flow characteristics were investigated using a 1mm×1mm micro channel.

We measured pressure drops and jet thrusts of dilute (100 ppm and 10 ppm) or ultra-dilute (1 ppm) aqueous solutions of polymer in flows through slits with width of 1.0 mm, 480 μm, and 122 μm owing to investigation of flow properties of dilute polymer solution passing through a small slit. Good agreement between the experimental results of water alone and the predictions was obtained within the experimental errors. However, the dilute and ultra-dilute polymer solutions exhibited lower values. To understanding the experimental results, we estimated mean elastic stresses via jet thrust method. Moreover, we clarified that power-law relationship between mean elastic stress and mean velocity, and it corresponded to the flow properties via the pressure drops.

Drying of colloidal particle dispersion film is important for technical applications such as inkjet printing. There is a problem of the occurrence of cracks in drying process. One of the important factors related to this problem is the non-uniformity of volume fraction distribution in film, but, there is no efficient simple measurement method for it. In this study, we demonstrate a very simple technique to evaluate volume fraction during drying process of the liquid film. Red dye and nano-size particles disperse in the sample and measure the magnitude of the blue and the green components of the transmitting light. The transmittance ratio increases with increasing the volume fraction or decreasing the dye concentration. In dispersion film, not only volume fraction distribution also dye concentration distribution exists near the drying-front.

In this study, we have focused on the relationship between the transient response generated with concentrated suspension of non-Brownian particles after shear-reversal and the individual particle velocity growths measured in the flow. The shear flows between two parallel plates were tested utilizing a suspension with volume fraction of 50 vol%. A pre-shear flow was applied for 30 seconds and then a rest time of 10 seconds was taken before the subsequent forward or backward flows. The motion of tracer particles were photographed and the particle velocities were estimated. The particle velocities had large fluctuations. Even under such conditions, it was concluded that the velocity growths measured in the subsequent backward flows were delayed in particular near the stationary plate even in the higher shear rate.

A system in which oil phase droplets containing water phase droplets are dispersed in the water phase is called W/O/W double emulsion (DE). DE is an indispensable material used in many industries, but it is difficult to obtain a uniform controlled DE. The flow focusing technique is used to generate uniform size bubbles and particles using only the fluid force. This method is useful in many industrial and medical applications, such as encapsulating biological molecules or drugs, and conducting chemical or biological analysis in micro scale. However, conditions for stable production of DE have not been fully established. In particular, the use of three phases to produce double emulsion droplets is more complicated than when two phases are used to produce an emulsion. In this study, a double emulsion formation system in microfluidic flow-focusing devices is discussed. In order to obtain size-controlled stable double emulsions, the effects of flow rates of each phase, and the effects of interface tension of each interface have been studied. The results obtained by changing the flow rate and the physicochemical properties of the solution were arranged in a dimensionless capillary number. We studied the conditions under which a monodispersed DE can be generated stably.

The dynamic motion of single bubbles rising in hydrophobically modified alkali-soluble emulsion polymer (HASE) solutions with pH = 9 is experimentally examined. In this study, HASE material is neutralized with sodium carbonate (Na2Co3) and with sodium hydroxide (NaOH), and HASE solutions with almost the same rheological properties are prepared. In the experiment, we focus on the bubble shape and microstructures at interfaces depending on high viscous HASE solutions neutralized by these alkaline materials. As a whole, it is observed that the morphology of trailing edges with threadlike branches is sensitive to the bubble size for both the HASE solutions as reported in previous studies. But, from detailed comparison of experimental results between both the HASE solutions, it is found that the global bubble shape and microstructures emerged from interfaces are similar but slightly different depending on the HASE solutions, even if HASE solutions have almost the same rheological properties.

We use machine-learning-based super-resolution analysis to reconstruct high-resolution flow field data from grossly coarse low-resolution data, for three-dimensional fully developed turbulent channel flow at Re_τ = 180. The training data is obtained by three-dimensional direct numerical simulation (DNS). We use an average pooling operation used commonly in image tasks, to prepare the coarse input data set. As a machine learning model, the hybrid downsampled skip-connection multi-scale (DSC/MS) model based on convolutional neural network is utilized in this study. Remarkable about this model are its robustness against rotation/translation of the flow images and its ability to consider multi-scale property of turbulence. The super-resolved flow fields recovered through the proposed machine learning model are in agreement with the reference DNS data in terms of velocity color distributions, root mean squared values of velocity fluctuations and L₂ error norm defined as the difference between the reference DNS data and super-resolved flow field. The maximum wavenumbers of streamwise and spanwise energy spectrum recovered by machine learning are increased by the super-resolution reconstruction. The proposed method holds great potential for various applications in experimental and numerical situations to handle the fluid big data efficiently, e.g., PIV measurements and subgrid-scale modeling of large-eddy simulation.

Planar particle image velocimetry (PIV) measurements are performed for turbulent channel flows over porous media with structural surface roughness. The roughness elements are mounted on the porous media and their spacing is controlled to reproduce so-called k- and d-type roughness. For comparison, flows over solid impermeable rough walls of both types are also measured. It is found that, in the k-type roughness case, time and space averaged turbulent intensities over the solid wall is higher than those over the porous wall, while an opposite tend occurs in the d-type roughness case. By the discussion on logarithmic mean velocity profiles, it is confirmed that the parameters show different trends between solid and porous cases regardless of the roughness types, and there is a characteristic roughness scale which is larger than the porous scales.