Microbubbles are very small air bubbles with diameters on the order of less than several tens of micrometers. A crucial characteristic of microbubbles is that they are electrically charged on their surface (ζ-potential). In the previous study, we conducted an experiment of the effect of microbubble bathing on organisms by mouse and it was confirmed that microbubbles have an effect on recovering vitality. However, the relationship between restoring vitality and the electrical potential of microbubbles still has not been clarified. The purpose of this study is to investigate the relationship between restoring vitality and the electrical potential of microbubbles. It is assumed that the dynamics behavior of microbubbles can be varies by ζ-potential and the dynamics of microbubbles under ultrasound irradiation was investigated using a high speed microscope.

View full abstract

In this study, molecular dynamics simulation of a nanoscale argon bubble is performed to confirm the validity of Stokes-Einstein equation. The center of bubble is found to move randomly as well as Brownian motion of solid particle and its radius is evaluated by density profile. Negative pressure of liquid is supposed to keep the bubble because liquid density is lower than natural saturated liquid density. Moreover, Kelvin effect seems to decrease vapor density in the bubble.

View full abstract

We investigate the collapsing mechanisms of a lipid coated nanobubble and the subsequent lipid vesicle formation by coarse grained molecular dynamics (CGMD) simulations. A preformed nanobubble coated by lipid monolayer in water is a model of an aqueous dispersion of phospholipids under negative pressure in sonication. Relaxing to a positive pressure, the spherical bubble shape deforms into irregular prolate ellipsoidal shape and the monolayer starts to fold from an apsis of the ellipsoid. The local folding is rapidly propagated in the ellipsoid, pushing gas core, and a discoidal membrane forms. The discoidal membrane develops into a unilamellar vesicle via bowl shape.

View full abstract

In the present study, Microbubbles are used as a contrast agent for ultrasound diagnosis. It is also expected to be use for the treatment. One of the possible applications is microbubble DDS. For that purpose, microbubbles need to be well-controlled for the generating process and manipulation. In this talk, Non-contact manipulation techniques of microbubbles are developed by controlling the ultrasound filed. A plane standing wave-type, a ring-type and the focused-type ultrasound are used to manipulate microbubbles. It is shown that Primary Bjarknes force is well-utilized to control the position of microbubble. Microbubble clusters are observed in the experiments and they show the complicated behaviors as bubble clusters. These behaviors are discussed through the comparison between the experimental observation and theoretical estimation.

View full abstract

We propose an experimental technique for forming a spherical gaseous bubble in highly viscous liquids and observing subsequent free oscillation of the bubble. A nanosecond laser pulse of wavelength 532 nm and energy up to 1.5 mJ is focused into glycerin-water mixtures to create plasma that recombines and deposits heat locally in the focal spot. The subsequent vaporization leads to the growth of a spherical vapor bubble, while gases dissolved in the liquid come into the bubble. When the bubble reaches its maximum size, the bubble temperature decreases so that vapor condenses back into the liquid. The subsequent free oscillation of the micron-sized gas bubble is visualized using a high-speed camera. To quantify damping mechanisms in the bubble dynamics, we compare the measurements to nonlinear Rayleigh-Plesset-type calculations that account for dissipation effects (liquid viscosity, heat conduction and acoustic radiation).

View full abstract

Erosion due to high-speed droplet impact is caused by the water-hammer loading on the material surface and possibly by the reloading from collapsing cavitation bubbles that appear within the droplet. Here, we simulate the dynamics of cavitation bubbles accompanied by high-speed droplet impact in order to see whether the bubble collapse is violent enough to account for cavitation erosion on the surface. The evolution of pressure waves in the water droplet to collide with a deformable wall is inferred from simulations of multicomponent Euler flow where phase changes are not permitted. For simplicity, we perform Rayleigh-Plesset-type calculations in one-way-coupling manner; namely, the bubble dynamics are determined according to the pressure variation obtained from the Euler flow simulation. In the simulation, the preexisting, submicron-sized nucleus show bubble growth because tention in the liquid is obtained through interaction of the pressure waves and the droplet interface; this supports the possibility of having cavitation due to the droplet impact. It is also found that radiated pressure from collapse of the cavitation bubble is comparable to the water-hammer pressure created by the initial impact of the droplet. Hence, cavitation may need to be accounted for when it comes to discussing erosion in the droplet impact problem.

View full abstract

Droplet impact on a solid surface is essential phenomenon for industry applications such as semiconductor cleaning. We present experimental observation of droplet impact on a solid surface. Using the curvature of droplet surface as a lens to intensify the illumination, we can observe the development of lamella at early stage after the impact. We apply plasma treatment to change wettability of the solid surface. In case of high-speed droplet impact on non-plasma-treated surface, fingers are formed from the edge of lamella, and then splash is ejected at the tip of finger. On the other hand, lamella spreads with a circle shape and no finger and splash are observed when droplet collides with plasma-treated surface in high-speed impact.

View full abstract

In this study, we experimentally observed the high-speed water droplet impact on acrylic surfaces in a vacuum chamber with a high-speed photography, in order to clarify the effects of both the ambient gas pressure around the droplet and the impact velocity. The results show that the splash does not occur under the reduced ambient gas pressure even when the impact velocity becomes much higher than in the conventional experiments. This result agreed with our previous experiments of ethanol droplet impacts. Furthermore, we observed that generation processes of splash in low ambient and atmospheric gas pressures are different.

View full abstract

Liquid micro-jets are applied to many devices such as inkjet printing and automotive engines. For example, for engine applications, liquid atomization is an important process to improve fuel consumption. High-speed jet tip behavior is important to understand the liquid atomization. However, physical mechanisms of the atomization process have still not been clarified. Hence, in this study, we observed the liquid jet flow using the high-speed video camera. Especially we focus on the jet flow just after the injection from the nozzle. In this paper, we developed high-speed droplet injector using syringe. Furthermore, we discussed a shape of the jet tip by changing velocities and diameters of liquid jet.

View full abstract

A liquid jet is used in ink-jet printers, needle-free injections and other important devices. However, it is difficult to generate high-viscous jets using present methods. We propose a generation system for high-viscous liquid jets. We verify the performance of this system and find that this system can generate a high-viscous (1,000 mm^2/s) jets. We present a physical model based on pressure impulse, which can describe all experimental results. In this paper, we reproduce a liquid jet using numerical calculation. The calculated jet velocity agrees with experimental results and the proposed model. The pressure field in a liquid using numerical calculation also agrees with the physical model.

View full abstract

We investigated the interfacial behavior and atomization of an acoustically levitated droplet. It is vital to understand quantitatively the non-linear dynamic behavior of such the interface deformation and translational motion of the acoustically levitated droplet in order to apply acoustic levitation method to the various scientific fields. The purpose of our study is to investigate experimentally the interfacial behavior and atomization of droplet. In this paper, we recorded its time evolution from the interfacial deformation to atomization by high speed video camera. We estimated the dynamics of the droplet quantitatively with three different levitated liquid samples and compared with the experimental correlation by Danilov. et al.. It is shown that the mechanism of the atomization of the levitated droplet is more complicated than the existing model indicated by the theory.

View full abstract

We investigate capillary oscillations of a sessile drop experimentally. Following Suzuki et al., we put a hemispherical drop on a small horizontal stage and excited capillary oscillations by vibrating the stage at resonant frequencies, and recorded its shape evolution by a high-speed video camera. From the videos, we quantitative time evolution of the drop deformation, and obtained its power spectrum. In the spectrum, we found several discrete spectrum peaks, corresponding to the eigen-frequency and its higher harmonics, and broad band spectrum at smaller frequencies.

View full abstract

The purposes of this study are to demonstrate numerically the droplet manipulation utilizing the Marangoni effect and to investigate the acting force magnitude and the flow relevant to the droplet movement. The analysis object is an oil droplet suspended in water (liquid-liquid two-phase flow). The liquid-liquid interface is captured by the volume-offluid method, and the surface tension model we used here is the continuum-surface-force method with considering the temperature dependency. We confirmed a quantitative agreement with experimental and theoretical results with respect to the manipulation force exerted on the droplet. The pressure and velocity fields in/around the droplet, and their dependencies on temperature and diameter were investigated.

View full abstract

Icing is a phenomenon that super-cooled droplets impinge on a solid surface and accrete on it. Many studies on ice accretion have been conducted because the icing phenomenon causes serious problems in various places. Because there are many unknown physical properties of the super-cooled droplet, the detailed freezing process of super-cooled droplets has not been clarified yet. In the previous study, we reproduced static freezing process of super-cooled droplet by the numerical simulation. Therefore, in this study, we simulate dynamic freezing process when it impinges on the flat plate. The obtained results indicate that the simulation code which has been developed in the present study can reasonably reproduce the behavior of the droplet freezing up along the interface between the water and the air.

View full abstract

Capacitance type void fraction sensors for cryogenic fluid has been developed by our research group. The sensors are roughly categorized into three types; arc type, small-sized arc type, and asymmetric type. In this paper, the three type sensors are compared, and each sensor's merits and demerits are indicated. The arc type sensor was first developed. The sensor is simple, but S/N ration is low and influence of "temperature drift" is large. The small-sized arc type sensor was developed for the sounding rocket S310 test No.43, so the sensor was needed to make as small as possible. The sensor succeeded to measure the void fraction of the liquid nitrogen flow even under microgravity. The asymmetric type sensor was deviced to improve the measurement accuracy. Inaccuracy of the sensor between true void fraction and measured void fraction was only 3% for stratified flow, whereas that of the arc type sensor 30%.

View full abstract

Needle-injection system is widely utilized for medical treatments. However, the system has various problems such as strong pain and infection. The usage of a highly-focused high-speed microjet as needle-free injection system is expected to solve these problems. For its safe and robust application it is necessary to understand injection performance such as ejected volume of the jet, which is one of the important indicators for drug injection system. We conduct experiments and find that the maximum volume of a laser induced bubble is about equal to the ejected volume.

View full abstract

When a wave-breaking jet plunges onto the forward wave trough, three-dimensional organized free-surface flows with longitudinal counter-rotating vortices are organized at the plunging location. The finger jets are induced through free-surface entrainment by the vortices beneath the surface. The surface tension destabilize the jets to form multiple droplets. Fundamental features of the series of free-surface deformation during the wave breaking process are studied on the basis of numerical computations and laboratory experiments.

View full abstract

The effect of electrolytes on the drainage and the rupture of the thin liquid film formed between the bubble and the flat solid surface approaching at a constant velocity has been investigated experimentally. The transient thickness distributions are measured by the interferometer with high-speed observation. 0.05 M MgSO_4 solution and 0.05 M CH_3COONa solution are used as electrolyte solutions. The surface shape changed from pimple shape to dimple shape as 3 mm bubble approaches to the flat surface, and the effect of the electrolytes on the drainage process was negligible in the present cases. On the other hand, in 0.05 M MgSO_4 solution, the timing of the rupture retarded compared to that in the case with purified water.

View full abstract

Foam is encountered in many industrial fields, and influences safety and efficiency of plants such as floatation, wastewater treatment. However, conventional foam measurement techniques measure only an average foam diameter near a transparent wall. Hence, we propose a new technique to measure the dense foam by using a single-tip optical fiber probe (S-TOP). A problem is that foam cells are broken by contact of the S-TOP. In this study, the surface of the S-TOP was changed to hydrophilic by the surface treatment in order to prevent the foam burst. First, we elucidated the mechanisms of an output signal piercing a thin liquid film through experiments and computations. Second, we measured a small foam cluster in a glass cell using the S-TOP system. Based on these results, we established a new measurement system to measure foam-cell chord lengths. The differences between the S-TOP measurement and the visualization were ±10 %.

View full abstract

For shortening of surface cleaning time in semiconductor device fabrication, it is necessary to understand the liquid infiltration characteristics into tip-closed microstructures. In this study, we observed the liquid infiltration characteristics on miri- and micro-scale closed end by applying pressure under two conditions, i.e. quasi-static, and stepwise changes. As a result, we found that the effect of wettability of the tubes are limited, and the amount of dissolved air was very small. In addition, we confirmed that the time change of water level by applying pressure could be well expected to model by using the expression of isothermal process.

View full abstract

To obtain the specific values of uncertainty of flowrate measurement using the ultrasonic Doppler velocity profile (UVP) method under disturbed flow conditions, experimental measurements are carried out. To generate the disturbed flow, obstacle plates are installed upstream of the test section. In order to estimate which experimental parameter is a dominant factor of the uncertainty, the parametric examinations are carried out for the obstacle plate layout, the distance between them and measurement section, the incident angle of the ultrasonic beam, and flowrate. Since several uncertainty factors are cross-correlated each other in this examination, uncertainties of these factors are evaluated independently using an analysis of variance, namely ANOVA. The total uncertainty is 7.98% at 8D, 1.97% at 16D and 1.14% at 25D, respectively.

View full abstract

Ultrasonic pulsed Doppler method (UDM) can obtain velocity profile along the ultrasonic beam path. However, the UDM has the limitation of the detectable velocity based on the measurement volume size. This problem was apparent when higher velocity were measured by using a velocity extension method. In order to investigate the accuracy of the velocity extension method, velocity distributions in a rotating cylinder were measured with changing of the measurement volume, and the relation between the maximum velocity required for the reflector to remain in the same measurement volume during the pulse interval, ν_<allow>, and the measured velocity was investigated. It was found that if measured velocities were higher than the ν_<allow>, the velocity accuracy dramatically decreased. Further, the tendency was more apparent with going away from the transducer.

View full abstract

Ultrasound-based flow measurement methods can be easily applied to many two-phase flows. Ultrasonic Velocity Profiler (UVP) is well established measurement technique based on Doppler frequency shift of ultrasound reflected by moving bubbles. In order to improve the degree of information obtained by UVP, the bubble separation algorithm has been developed. Separating bubble data allows easy comparison of results with other measurement methods (such as cameras) even in the time domain (not only time-averaged values). Also, separated data might be more useful for numerical codes validation. Finally, separating data allows to recognize measured bubbles from each other and track the trajectory of their reflecting interface. This allows to measure bubble diameters, average velocities. Separation was used for air bubbles rising in the water column and the velocity of bubbles in the radial direction was compared with results from high speed camera measurement.

View full abstract

Stopping contaminated water leaking is required for reactor decommissioning of Fukushima 1 nuclear power plant. Using Ultrasonic velocity profile measurement (UVP) is proposed to find leak points. However hard environment prevents us from getting in and finding leak points. Therefore it is expected that robot with UVP system gets in and measures flow field there. As a basic research of making robot with UVP system, making two dimensional vector map of the flow field which was made by measuring four different points of flow fields in the tank which water came out from an outlet with fan shaped array transducers. Hence, vector of the map shows the place of outlet.

View full abstract

A Taylor-Couette Vortex Flow has a mild mixing effect even in high rotating speed with the inner cylinder. This effect is expected to be applied new bio-reactor system where the micro cells are damaged by strong share flows. Furthermore, in the case of small aspect ratio, this vortex has characteristics such as the different vortex structure, because of the Ekman effect in the top and bottom boundary layers and the acceleration of the inner cylinder. However, this vortex flow mechanism like a chaotic flow has not been investigated much. The purpose of this study is to understand the flow mechanism from a numerical analysis. In this report we mainly analyzed the process of transition to turbulent flow by direct numerical simulation.

View full abstract

Cross-flow wind turbine has a characteristic of high torque coefficient at low tip speed ratio, good self-starting, low noise and high stability. Therefore, it attracts attention as the city type small-sized wind turbine for urban district. However it is serious problem that the maximum power coefficient is extremely low as 10% compared with other smallsized wind turbines. In this research, in order to improve the performance of a cross-flow wind turbine, a symmetrical casing is installed to it. Then the internal flow is investigated, and the effect of the symmetrical casing on the performance of the turbine is clarified by CFD simulation.

View full abstract

The performance of the orthopter-type wind turbine in a shear flow was investigated. The orthopter-type wind turbine is one of the vertical-axis wind turbines (VAWT) which each blade combines a rotating movement around its own axis and a rotating movement around turbine's axis. The diameter and height of wind turbine were 510mm and 400mm, respectively. The number of flat plate blade was three. The experiments were carried out in an open circuit wind tunnel. The effects of the location of wind turbine and the strength of shear flow on the performances of the orthopter-type wind turbine were found. The power of the wind turbine increased when porous plate installed the backward side.

View full abstract

In this study, the influence of the relative ratio between the duct width W and the wind turbine diameter D on the duct-flow power generation as well as the relationship of the power generation with the wind turbine relative position to the duct exit are investigated by two-dimensional CFD. The tendency of power coefficient regarding the Y direction (normal to main flow) is reversed as the rotor goes downwind, when W/D is 1 or more. However, the reverse does not take place when W/D is 0.5. The energy recovery rate is highest when the rotor diameter is two times as large as the duct width (W/D = 0.5). In this case, the rotor gives little influence on the duct.

View full abstract

Three-dimensional computational fluid dynamics (CFD) has been carried out in order to investigate the effects of endplates on the performance of straight-bladed vertical axis wind turbine. The computational wind turbine model has two blades; the rotor diameter is 0.75m; the blade span length is 0.5m; the blade chord length c is 0.08m. The endplate is assumed to be an airfoil-like shape, which outline is larger than the blade section by length of s. The results of the CFD showed that the endplates with s/c = 6.25% give almost no influence on the condition of tip vortex shedding. However, the power coefficient increases about 8.1 % due to the endplates.

View full abstract

DDWFTTW (Dead-DownWind Faster Than The Wind) refers to a wind powered car using rotary wings that runs faster than the wind in tailwind. It was found experimentally by Jack Goodman and was experimentally demonstrated in a nearly perfect form by Rick Cavallaro. A full scale model called Blackbird with weight 200kg and propeller diameter 5m has run at the 2.8 times faster speed than tailwind. On the other hand, the theoretical verification was given by Mark Drela. The absorbed energy through rotation of wheel or water turbine is transferred to air propeller, and the thrust is generated by the air propeller. If the running resistance of the car or ship is sufficiently smaller than the thrust, the car or the ship can advance faster than the tailwind speed. The present paper clarified the problem and direction when applied to a wave powered ship. A reasonable application would bring us a big energy saving effect.

View full abstract

A wind turbine operates in turbulent natural wind. In particular, the unsteadiness and turbulence of wind in japan are stronger than one of western countries - Europe, America and others in general. Therefore, we should take account of the unsteadiness of natural wind in installed open-air location for designing a rotor blade in order to make higher performance. The present paper describes the effects of sinusoidally velocity fluctuation, turbulent intensity and vortex scale of simulated natural wind on performance of a horizontal axis wind turbine (HAWT). Using five wind turbine rotors on the basis of NACA and MEL blades, experimental results are mainly presented to demonstrate the dependency of wind frequency, turbulent intensity of the wind. As the results, we succeed that one of our designed MEL-type rotors indicates 130% power coefficient as large as one of steady wind in simulated natural wind.

View full abstract

In recent years, size of wind turbines has been increasing in order to reduce energy costs. However 3-bladed wind turbines are common as commercial wind turbines at the present time, 2-bladed wind turbines may be a better choice instead of 3-bladed ones with increase of size in the future. It is because of some advantages of 2-bladed ones such as reduction of manufacture cost for blades, reduction of rotor shaft torque by faster rotational speed and simplification of installation and maintenance. At the same time, aerodynamic forces exerted on 2 blades could cause unstable motion or load fluctuation. In this study, fluctuation of load on tower root is calculated for 2-bladed and 3-bladed wind turbines by fluid-structure coupled analysis.

View full abstract

In recent years, many wind farms, which mean groups of wind turbines installed in each site, are introduced globally. In wind farms, energy deficit occurs when the downstream wind turbine operates in wakes generated by upstream wind turbines. Especially in large wind farms, it may occur that the overlap of some wakes and it forms complex flow field due to the wake interference. Therefore, it is important to propose the wake model that can consider the overlap of the wake in order to arrange wind turbines optimally in wind farms. In this study, overlapped wakes are simulated by consideration of viscous diffusion and compared with the experimental results to clarify the wake interference effect.

View full abstract

This paper presents the results of coupled analysis of CFD simulation of a two blade rigid wind turbine with an Independent Pitch Control (IPC) system in stable atmospheric boundary layer (ABL) condition. A CFD analysis code rFlow3D is applied to this computation. The IPC system is a load-based feedback type, which can control the pitch angle of the blades in a rated rotational frequency. The purpose of this study is to verify the applicability of the IPC system and its effect on load mitigation to wind turbine in stable condition. The results indicate that the IPC system is capable to reduce fluctuation for tilt moment. Furthermore, it is observed that the system is capable to lower fatigue load of yaw and tilt moment on rotor and thrust on a blade.

View full abstract

To reduce both the power output fluctuation and the platform motion, a feedback control algorithm based on blade pitch and generator torque manipulations for a spar-type floating offshore wind turbine-generator system was developed through numerical analysis using the aeroelastic simulation model (FAST), observed high wind speed data, and irregular sea waves. The blade pitch is collectively manipulated to maintain the generator power at a rated value, and the generator torque is manipulated to dampen the nacelle fore-aft motion. The concept of this control approach is to increase the generator torque in response to the platform motion to the leeward side and to provide a positive damping effect immediately to the platform motion. The numerical simulation showed the effectiveness of the generator torque manipulation and the filter of the nacelle fore-aft speed for the reduction in the platform motion. This feedback control approach had an advantage in not only the power output fluctuation and platform motion but also damage equivalent fatigue load characteristics over previous control approaches.

View full abstract

The turbine used for a wave-power-generating system is driven by the oscillating airflow produced by the water wave motion. The Wells turbine has the simple vane-less structure using no-twist and symmetrical blades, which drives its unidirectional rotational motion even though the turbine is driven in the oscillating airflow. In this paper, the important basic characteristics of the turbine are derived by the 2D-CFD and the potential theory of cascade. The lift coefficients solved by the CFD become much less than the potential calculation with increase of the solidity.

View full abstract

In the present paper the attention is focused on the characteristics of tonal noise at a discrete frequency radiated from Wells turbine for wave power conversion. We measured the sound pressure level (SPL) of aerodynamic sound radiated from Wells turbine which operated at the low attack angle. The experimental investigations have been performed under steady flow condition. The effects of rotational speed, blade profile, blade number and attack angle on the tonal noise at discrete frequency were investigated experimentally. The overall level of SPL increased as the rotational speed of Wells turbine increased. The noise proportional to the rotational speed and its overtone components increased. The overall level of SPL increased also at NACA0012 and low attack angle. The tonal noise at a discrete frequency was generated from Wells turbine of NACA0012 and low attack angle.

View full abstract

In the optimum design of a fixed oscillating water column (OWC) type wave energy converter, it is necessary to develop a design method which can consider the characteristics of incident wave motion, the motion of the internal free surface affected in the structure such as a partly submerged wall, the fluctuation of air pressure in an air chamber, the rotation of the air turbine. In this paper, the 2-D wave tank tests for the fixed OWC type wave energy converter with an impulse turbine were conducted to obtain the experimental data needed to make this design method. As the results, the effects of the turbine diameter and the air chamber length on the generating efficiency corresponding to product of the primary and secondary conversion efficiencies are clarified.

View full abstract

As a system using a conventional unidirectional air turbine in oscillating water column (OWC) based on a wave energy plant, a twin unidirectional impulse turbine topology has been suggested in previous studies. However, the average efficiency of the suggested twin turbine is considerably lower than that of a conventional unidirectional turbine in this topology because reciprocating air flow can't be rectified adequately by a unidirectional turbine. In order to improve the efficiency, using fluidic diode is discussed. The fluidic diode characteristics under steady flow conditions were investigated numerically by computational fluid dynamics. The effect of fluidic diode geometry on the performance were discussed in this study.

View full abstract

A straight-bladed vertical axis turbine for wave energy conversion has been proposed in order to develop a novel air turbine suitable for OWC based on wave energy plant. The objective of this study is to clarify the effects of guide vane number and solidity on the performance of the straight-bladed vertical axis turbine. Performances of the proposed turbine under steady flow conditions have been investigated experimentally by using a wind tunnel. The tested rotor has some straight blades with a profile of NACA0018, a pitch diameter of 460 mm and a width of 490mm. It is found that the guide vane number n suitable for the proposed turbine is obtained in the case of n = 2.

View full abstract

Cross flow turbines for the Oscillating water column were simulated by LES analysis. The equations are discretized by Finite volume method for space and Fractional step method for time. In this study, blade number is 24 and chord length is 15% of diameter. Shapes of duct are point symmetry. Important parameters of ducts are curvature and position of tongue. The following are results of analysis. Gentle curvature of tongue decrease pressure drop and improve turbine efficiency. Maximum efficiency in steady flow was 72%. Starting torque performances were very good in every case.

View full abstract

Using reactive control and tuning the control parameters for wave conditions are effective for the oscillating-body wave energy converter, but there are many difficulty for operating such a system. In this study, unifying the control parameters into a function and evaluating the performance of the new control function are discussed. Although the suggested unified control parameter functions are a constant value or a simple linear function, the performance of the suggested control is close to that of the former control in which the optimal parameters for wave conditions are used.

View full abstract

The bi-directional impulse turbine and the bi-directional diffuser for tidal energy conversion is investigated in this paper. The bi-directional impulse turbine with fixed guide vanes is adopted because the turbine has a large efficiency and an advantage of maintenance. The turbine characteristics is obtained experimentally by the air turbine test rig. As a bi-directional diffuser suitable for the bi-directional impulse turbine, the diffuser geometry is proposed, which has a straight part and a semicircular brim part. By using a CFD analysis, the diffuser geometries are selected for the water flow turbine. Numerical results showed that the install of the brim can reduce the flow resistance.

View full abstract

To develop the power generation system using iron-gallium alloy, we focus on transverse galloping for a rectangular prism with a critical depth section of less than the side ratio of 0.6, and a D-section (semi-circle) prism at a flow velocity lower than the resonant velocity. The purpose of the present study is to investigate the effects of the attack of angle on the transverse galloping vibration of a cantilevered prism and the performance of a power generator using an irongallium alloy as a magnetostrictive material and a cantilevered prism in a water tunnel. The effect of the attack of angle on the transverse vibration of D-section prism with the side ratio of 0.23 was smaller than the other prisms. The maximum electric power using iron-gallium alloy and a D-section prism with the side ratio of 0.23 was 26 mW at the reduced velocity of V_r = 4.15.

View full abstract

A new small-lot renewable energy supply system has been proposed from view point of increasing its use by a large number of users. It is composed of a lead battery and an accessory part with a inverter to change to AC from DC. It was shown by a performance testing that the battery remaining amount is about 10% when a load current of 1.8A was given for continuation eight hours.

View full abstract

Small hydropower generation is one of important alternative energy, and potential of small hydropower is great. Efficiency of small hydro turbines is lower than that of large one, and these small hydro turbine's common problems are out of operation by foreign materials. Then, there are demands for small hydro turbines to keep high performance and wide flow passage. Therefore, we adopted contra-rotating rotors which can be expected to achieve high performance and low-solidity rotors with wide flow passage in order to accomplish high performance and stable operation. Spokes needs to support rotors, and influence on the performance of the small hydro turbine. The performance of the contra-rotating small hydro turbine is investigated when the spokes shapes are changed. The performance of test small hydro turbine is improved by the spoke shape modification, and the internal flow of it is clarified by the numerical analysis results

View full abstract

We have developed water turbines appropriately for low head open channels to effectively utilize the hydro power energy. To improve the performance of the turbine, it is necessary to determine the free surface flow patterns around the turbine. We introduced the new equipment system and the more precise computational grid of numerical analysis, it was possible to specify more precise flow patterns than old ones. Time-averaged velocity distribution at inner or outer circumference of runner was almost consistent. The flow direction at the second stage outlet had rapidly changed against the mainstream. At the inner circumference of runner at the first stage outlet, the small scale vertical flow toward the same rotational direction of runner occurred. In addition, we investigated the transient flow patterns at outer circumference of the runner.

View full abstract

An undershot cross-flow water turbine does not require a casing for open channels and hence considerable simplification is attained. We proved that shock loss at first-stage and second-stage inlet areas has a considerable influence on turbine performance in previous study. So, in this study, we changed the blades angle of straight turbine and investigated the effect of shock loss on its performance. Then, we changed the inlet and outlet blades angle of curved turbine appropriately and tried to performance improvement of this turbine. As a result, shock loss of curved turbine could be reduced and turbine performance was also improved. In addition, we found that flow field became better by changing inlet and outlet blades angle of curved turbine and flow field also has a considerable influence on turbine performance.

View full abstract

We have proposed an axial flow hydraulic turbine with a collection device, using water flow energy of open channel. In this study, we investigate the flow field around the hydraulic turbine by numerical analysis in consideration of free surface and PIV measurement with water tunnel. As the result, it showed the validity of the analysis because the calculated values and experimental values were in good agreement. There are the formations of large-scale vortex behind the brim of hydraulic turbine. In addition, there are separation vortex regions near the inner wall of the collection device. The separation vortex regions become larger with increasing rotational speed. Therefore, the diffuser pressure recovery decreases and inlet velocity ratio becomes lower with increasing rotational speed.

View full abstract

We carried out large-scale towing tank experiments as an open flow system to elucidate spatial development of quasi-uniformly injected bubbles. Measurement results by a shear stress sensor indicated drag reduction by injecting bubbles into turbulent boundary layer developing on a flat plate, and visualized pictures showed spontaneous development of quasi-periodic distribution of bubbles at the corresponding parameters.

View full abstract