The mechanisms of reducing the turbulent frictional drag are discussed with regard to the bubble flow and the influence of bubble injection and turbulent shear stress on the wall. Research focusing on bubble deformation and effective viscosity has been actively conducted. In order to verify the influence of bubbles on the shear stress field, it is important to verify bubble deformation and effective viscosity in a simplified field such as a single bubble. Therefore, in this report, in order to carry out continuous verification of bubble deformation, an experimental apparatus capable of tracking and photographing bubbles was manufactured and basic data on bubble deformation in the turbulent boundary layer was acquired.

We studied a measurement using UVP (Ultrasonic Velocity Profiler) for the milk products flowing in pipe line; here, whole milk, low-fat milk and water-coffee cream were employed as samples of the milk products. Those milk products all include fat as emulsion. Although the diameter of fat particles is much smaller than suitable size of UVP tracer particles, UVP can measure velocity in the whole milk in short distance; Sufficiently large number of fat particles in the milk, however, also cause strong attenuation of ultrasonic wave. Wedge-shape wave guide was thus designed to have sufficiently strong ultrasonic wave with considering measurement in thick stainless-steel pipes, where further strong attenuation is expected.

We have developed novel rheometry using a cylindrical vessel in periodic oscillations and ultrasonic velocimetry (UVP) to overcome critical problems in conventional torque-type rheometry caused by influences of shear-banding, slips, non-homogeneous distribution of rheological properties, etc. The rheometry, termed “ultrasonic spinning rheometry”, evaluates quantitatively different rheological properties, representative “local” Newtonian viscosity, shear modulus, linear viscoelasticity, through fundamental mechanical relations utilizing spatio-temporal velocity information measured by UVP. In this report, basic concept of the rheometry and its applicability and measurement limitations are summarized. Further, application of frequency-domain algorithm on linear viscoelastic analysis was described in detail.

We have been developed the ultrasonic positioning system in order to realize high precision positioning with real time, with a simple and inexpensive system. Demonstration of prototype system proved that it is possible to actually measure accuracy of several centimeters. At present, we are studying to expand the positioning space by using array speaker transmitter. In this research, we report the transmission characteristics of array speakers by FDTD method acoustic wave simulation.

This paper reports the investigations of the transient flow rate of the several flow meters and the ultrasonic flowmeter based on the pulsed Doppler method. The reference flow rate is given by the gravimetric method which is newly established in NMIJ. The flow rates are investigated for pulsation flow with 0.5 Hz – 8 Hz frequency. The fluctuations of flow rate by ultrasonic pulsed Doppler method and Coriolis flowmeter are agreed well each other and with the reference flow rate. The influence of the fluctuation of flow rate is less than 2% for the pulsed Doppler method. The result gives new advantage, which is high response for transient flow, for the ultrasonic flowmeter based on the pulsed Doppler method.

Sonoluminescence with a specific wavelength emitted from the cavitation bubble produced by a sufficient acoustic energy irradiated into the liquid solution. The specific wavelength depends on the element in water solution. In this paper, as a fundamental study on sonoluminescence for elemental analysis, strontium sonoluminescence characteristics of different parameters were investigated. The experiment was conducted with 3 working frequencies (26, 78 and 137 kHz) in the power range from 0-50 W in 4 different concentrations of strontium (0.05 M – 3 M). The results were analyzed using MATLAB code for image processing with HSV based color identification technique. As the final results in the form of a percentage of sonoluminescence relative intensity show that higher sonoluminescence intensity emitted at higher ultrasound frequency, highest sonoluminescence intensity emitted at highest ultrasound power and higher intensity emitted at higher solution concentration. In addition, the HSV technique can be used for analyzing the sonoluminescence relative intensity for elemental analysis.

Stirring is necessary when culturing photosynthetic microorganisms. In this study, we focused on TVF stirring which enables uniform stirring with low shear, and cultured experiment was conducted. There are few studies focusing on algal body behavior in the Taylor vortex. In this study, we focused on the algal body behavior in the Taylor vortex and measured the influence of photosynthetic microorganisms on Taylor vortex using UVP. In order to confirm the possibility of ultrasonic measurement for Spirulina, comparison with nylon particles. As a result, the Spirulina follows the flow and has a periodic vibration component.

We have been developed in ultrasonic positioning system that can get the position of target object in real time measurement. In the distance measurement experiment, it includes the measurement error by receiver signal attenuation for speaker’s directivity. To aim for improvement of measurement accuracy, this study introduces a correction formula for the receiver signal arrival time measurement.

Clamp-on type ultrasonic flowmeter has a potential to measure steam flow rate. However, the steam wetness fraction increases with the heat loss, and the liquid film and the droplets may disturb the ultrasonic propagation. In this study, ultrasonic propagation experiments were carried out in air-water two-phase and wet steam flows. Two ultrasonic sensors located at up- and down-stream positions were used for the measuring ultrasonic time-of-flight that depends on the flow rate. It was shown that the accuracy of the flow rate measurement strongly depended on the flow regime. In wavy flow, the time-difference of ultrasonic propagation were good agreement with the reference values. However, the signals were time-dependent in annular mist flow resulting in the difficulty of the flow rate measurement.

At Fukushima Daiichi Nuclear Power Station, leaking water from PCVs is disturbing the removal of fuel debris. Therefore, investigating the leakage locations of the PCVs is required. In this research, we developed a system to investigate leakage locations remotely. We applied the flow vector mapping by Phased Array UVP method as a method of investigating leakage locations, and we considered that this method is possible to estimate leakage locations by measuring the flow pattern in the PCVs. In order to measure remotely using this method, we have developed a self-localization method using particle filter to estimate sensor position under water. After that, we experimented a leakage location estimation by remotely using the developed robot system, and we confirmed that it is possible to estimate leakage positions from the flow vector map we measured.

Fuel debris removal on decommissioning of Fukushima Daiichi nuclear power plants requires the investigation inside Primary Containment Vessel (PCV) to obtain clear status of fuel debris. Although the camera investigation was conducted inside the PCV recently, further high radiation and longtime measurement environment approaching fuel debris may cause camera to malfunction. Therefore, ultrasonic imaging measurement was proposed in this research. In particular, the air-coupled ultrasonic imaging system has been developed for fuel debris investigation in air. However, in case that the fuel debris come out of the water surface, the influence of liquid surface flow should be considered. In this paper, the identification method of liquid surface and debris shape was proposed. The method was validated by analyzing vibration of the liquid surface experimentally. The results showed the method identified frequency of liquid surface vibration using air-coupled ultrasound. In conclusion, the proposed method has possibility to apply for identification of liquid surface and debris shape.

Multiple jets are used in the industrial processes such as combustion, ventilation and so on, and their improvement of mixing and diffusion is demanded. Unlike single jet, since the jets issuing from nozzles will coalescence, merge or combine with each other, it is necessarily to reduce mixing performance such as entrainment from surroundings and spreading into surroundings. It is well known that the characteristics such as mixing and diffusion of the jet is strongly dependent on the large-scale vortex structures being formed near the nozzles. Therefore, as giving appropriate inflow conditions at a nozzle, it is capable of controlling the large vortex structures near field around nozzle and is expected to improve the mixing performance. In this study, we examine an intermittent control of jets varying the control freqency and the jet spacing so as to reduce the interaction between each jet. We conduct the DNS (direct numerical simulation) of intermittently-controlled two round jets. In order to quantify the mixing efficiency of the intermittent control, an entrainment rate is examined. Compared to the uncontrolled jet, it is confirmed that the mixing efficiency is markedly improved, suggesting that the intermittent control can be expected to be useful for the improvement of mixing performance of multiple jets.

In order to analysis the performance of heat transfer with multiple impinging jets, we investigate the DNS (direct numerical simulation) of two round impinging jets arranged at an inflow of flow field. In addition we introduce the intermittent control of inflow velocity. And a parameter, distance between jets is varied. From the view of time-averaged velocity distribution of multiple impinging jets, it reveals that the generation of flow phenomenon such as up-wash due to the interaction between two jets are reduced through the intermittent control. In the case that distance between jets is small, heat transfer performance is improved compared to when distance is large.

A wide variety of applications of jets enhancing mixing, difusing, heating and cooling efficiency have been studied. Mixing and diffusing characteristics markedly depend on outlet conditions of jet. In particular, blooming jets occur with a appropriate superimposition of axial and helical exicitations on an inlet velocity profile. Blooming phenomenon of jets is characterised by vortex rings moving along branches of separate streams. The present study evaluates the mixing performance of blooming jet using direct numerical simulation (DNS). It reveals that the statistical entropy and entrainment rate are obviously greater than that of unexcited jet as well as the momentum transfer of blooming jet is significantly enhanced.

Buzzing sound generated by lips is studied to understand a biological sound. This is known as a sound which is generated when the trumpet player blows breath to a mouth piece. The dominant frequency of the pulsatile jet related to the vibration of the opening and shutting of lips model made by konjak jelly must be obtained by the force balance of the pressure and closing force of lips. The sound and vibration of the lips are observed experimentally by using a microphone with a high directivity and a high-speed CCD camera. In this experiment, the relationship between open-close cycle of lips and frequency of buzzing sound was focused on. The open-close cycle determines the frequency of emission of pulsatile jet from the model, and the possibility of that the open-close cycle of the model depends on its natural frequency was shown by calculations. The sound sources are discussed in this paper.

In order to suppress separated flow by turbulent transition in initial region of the separated shear layer, we introduced induced flow opposite to uniform flow by using plasma actuator. We carried out flow visualization tests on a NACA0012 airfoil at Reynolds number of 30,000. By results of the flow visualization, in continuous mode, the separated flow could not be suppressed and flow field make separated flow encouragement. In addition, by changing of applied voltage, changing of induced flow velocity influenced on flow state near separation position. On the other hand, in burst driving mode, in inverse direction of induced flow, flow field with vortex structure was confirmed on wing surface like flow field of forward direction. Therefore, it is considered that the separated flow can be suppressed by injecting the induced flow by operating plasma actuator in inverse direction in burst driving mode.

Eddy viscosity and mixing length in the wake behind the Sierpinski tetrahedral structure have been investigated. The Sierpinski tetrahedron is considered the model of a crown tree. Two cases are examined. One is the case where the Sierpinski structure completely covered the cross-section of the test duct (internal flow). The other is the case where the wall of the test duct is away from the Sierpinski strcture (external flow). In both cases, the turbulence generated weakened with the interation number of the structure. It is found that the mixing length scale is maily determined by the size of the smallest tetrahedron in the Sierpinski structure.

Wake flow control was experimentally conducted with a pair of a dielectric barrier discharge plasma actuator (DBD-PA), attached to both sides of a long flat plate near its trailing edge. The strength of the double-jet was controlled by varying plasma excitation voltage and frequency applied to the PA. The discharge voltage shows nonlinearity for the setting voltage to the PA. The value of the input voltage with maximum output peak corresponds to that with the fastest double-jet flow with strong radiated light of ionized air. Power consumption of the PA was proportional to the second power of the applied voltage. It is shown by experiments with Pitot tube and hot-wire probe that the actuator can strongly modify the mean velocity distribution of the wake flow, depending on the direction of the double-jet. The PA recovers velocity defect in the wake flow and narrows the wake width with double-jet towards upstream or downstream.

Side jets are radial ejections of the jet fluid in the initial region and enhance the mixing between the jet and the ambient fluids. Helium gas and air were vertically discharged from a round nozzle into the still air. The velocity and vorticity fields in the initial region of the helium gas and air jets with side-jets formation were measured using a PIV in order to investigate a relationship between the process of side-jet formation and the vortex structures.

Side jets are radial ejections formed at the initial region of a jet. It is known that the side jets are generated in a sufficiently low density jet. However, it was recently found that the side jets are formed in the initial region of a round jet when the density ratio is unity. A relationship between the side-jets formation and the non-dimensional velocity gradient is experimentally examined in isothermal air jets. The value of non-dimensional velocity gradient at the nozzle exit has lower and upper limits for the side-jets formation. Also, there is hysteresis in the values of the lower and upper limits.

Vortex rings are periodically formed in the initial region of a round jet. Many researchers and engineers have done studies focusing on the vortex structure for clarification and control of the jet. It is necessary to locally give the jet the disturbance to control the local structure of the jet. In this study, a round jet is locally excited by a local sound wave radiated from a loudspeaker inputting a sine wave. it is found that the acoustic excitation produces azimuthod deformation of vortex ring. So that the spatial development is different from that of an unexcited jet. The relationship between the input signal to the speaker and the spatial structure of the jet was investigated using visualization using PLMS.

Vortex rings are periodically formed in the initial region of a round jet and they change to a wavy shape in the azimuthal direction. It is suggested that this azimuthal deformation is related to streamwise vortexes. In order to investigate the relation between the azimuthal deformation of the vortex ring and the formation of the streamwise vortexes, we attempted to artificially deform the vortex ring in the azimuthal direction by an acoustic excitation. The vortex rings azimuthally deform by introducing a sound wave through the small holes at a nozzle exit, so that the streamwise vortices are constantly generated in the round jet.

The effects of velocity fluctuations of upper flow on turbulent structure of atmospheric boundary layer were experimentally investigated. The atmospheric boundary layer was reproduced in a wind tunnel. In order to produce various velocity fluctuations in the upper flow, three kinds of turbulence grids were set to the entrance of the test section. The streamwise and spanwise velocities were simultaneously measured by using hot-wires anemometer. Turbulence statistics were estimated. The ratio of the Reynolds stress, Ruw, decreases as z/L increases and this tendency weaken according to the increase of the grid spacing. It is suggested that the effects on the turbulent structure of the atmospheric boundary layer depends on the scale of velocity fluctuations of the upper flow.

Three-dimensional structures such as longitudinal vortex appeared in the two-dimensional vortex street wake of a columnar body are very complex structures. It is very important to understand the origin and growth process of the three-dimensional structure in the two-dimensional vortex street wake. The purpose of this study is to investigate the three-dimensional structures in the two-dimensional vortex street wake by flow visualization. As the results, the details of the three-dimensional structures depending on the Reynolds number and the separation angle from a body were clarified.

A wake without reverse flow like a flat plate wake is a very unstable flow, and the vortex structure in such a wake is affected by various disturbances in main flow. In this study, the vortex formation process in the wake of the flat parallel plates with periodic disturbance was shown by using flow visualization technique in order to control the wake structures by disturbance frequency. As a result, it was found that the lock-in phenomenon of the vortex shedding frequency occurs when the disturbance frequency is close to the natural vortex shedding frequency, but the flow pattern changes sensitively depending on the disturbance frequency even the lock-in occurs.

The three-dimensional compressible Navier-Stokes equations are numerically solved to study suppress Mach wave emission in a supersonic round jet at high Mach number using high-order compact upwind schemes. Two cases of inlet disturbance for Mach number M_j=2.0 are presented. The first case is the jet flow forced randomly. The second case is the jet forced by random disturbances and a pair of unstable helical modes (m=±3，m=±3) with a subsonic phase speed. The numerical results show that the jet potential core region is reduced in the jet forced by a pair of the helical modes with a subsonic phase speed. In the relatively high amplitude case, the helical modes with high frequency tends to have a high suppression effect of Mach wave.

In this study, the frequency f_n at which the initial vortex train generated in the jet ejected by the converging nozzle with the entrance pipe was measured, and it was to clarify the determinants of f_n. The f_n at the Reynolds number Re = 1400 to 5600 was measured. As a result, the f_n was changed by changing the length of the entrance pipe, regardless of the same nozzle, the same flow velocity and measurement environment. Also, the f_n doesn’t increase linearly with Re, but it rises stepwise. In the simulation, organ pipe resonance inside the nozzle was evaluated. As a result, the resonance frequency was observed at a frequency that the f_n was became almost flat of rising stepwise with increasing Re. Therefore, it was found that the frequency of the organ pipe resonance determined by the shape of inside of the nozzle, dominates the f_n.

It was investigated the change of the jet flow by using plasma actuator by changing the direction of the plasma induced flow. It was using nozzles equipped with two types of PA with forward flow (Type A) and back flow (Type B). When the duty ratio was 50%, for Type A and Type B, the fluctuation due to plasma induced flow was able to give the most stable fluctuation near the nozzle exit. In Type B, when the duty ratio = 10%, the velocity fluctuation due to the induced flow is weak. In the case of duty ratio = 90% the amplitude of the fluctuation was unstable. When duty ratio = 50%, the most stable fluctuation could be given.

Velocity fields of air circular jets issued from circular holes arrayed in a line on a flat plate and a half round tube were investigated experimentally with a central focus on the effect of curved surface with the circular holes exist. The circular holes were arrayed at regular intervals in a line, and ratios of the interval s to the jet exit diameter d was 1.5. The Reynolds number based on the jet exit diameter d and the jet exit velocity Ue was 2000 for the experiments. Velocities were measured with a single normal hot wire probe, and fundamental properties of the jet diffusion were discussed. The experimental results have suggested that the jet width was increased in an initial region by the effect of the curved surface of jet outlets, which leads to non-uniform curvature effects of the shear layer and vortex ring.

The multi-articulated flat plate oscillates itself in a mean flow, and it has steady oscillating mode. The flow structures around an articulated plate were attracted interests. These were visualized by using the smoke wire method. From the results, it was found that the separated flow region formed on the concave side of the articles of the plate and behind the plates. Also, the tip vortices were formed from both side edges of the plate. These separated regions and tip vortices were released into downstream and the new vortices with the opposite sign were formed synchronized with the periodic movement of the plate. Furthermore, the results of the visualization showed that the separated region formed behind the plates was disappeared when the third plate inclined perpendicular to the mean-flow. It is because that the tip vortices induce the flow behind the plate to the surface of the flat plate.

This study conducts experimental exploration on the motion of a solid spherical particle falling in a microbubble plume and the bubble behavior around the particle. Bubbles with a mean diameter of 0.037 mm, released into a rectangular conduit using the electrolysis of water, rise by the buoyant force and induce a bubble plume. A spherical particle with a diameter 11.1 mm and density 1130 kg/m³ is released from the top of the conduit. The experiment clarifies that the particle falls meandering through the plume and that the terminal velocity is almost the same as that for a particle falling in quiescent water. The experiment also makes clear that the bubbles separate from the particle surface and that the separation induces a stagnation area just behind the particle. A wake still exists at a location with a distance of three times of the particle diameter from the particle.

This study numerically investigates the mixing of a two-layer density-stratified fluid caused by two vortex rings. Initially, the density-stratified fluid is in a static condition in a rectangular tank. The upper and lower fluids are glycerol aqueous solution and an aqueous solution of potassium dihydrogen phosphate, respectively. The density ratio is 1.015. Two vortex rings are arranged on a vertical line in the lower fluid. The Reynolds number, based on the circulation, ranges from 4000 to 8000. The vortex rings are launched simultaneously in the vertically upward direction. The simulation explores the collision of the vortex rings with the density interface, the entrainment of the fluids into the vortex rings, and the resulting mixing between the fluids. It also clarifies the behavior of each vortex ring, such as the deformation and the collapse.

The flow characteristics of a rectangular jet with deflectors were investigated experimentally. Two flat deflector plates were installed symmetrically inside of a 2.17:1 rectangular nozzle to passively control the rectangular jet. The angle between the deflectors was set to α = 6° (Divergent deflectors), 0° (Parallel plates) and −6° (Convergent deflectors), and the effect of this change on the mean and fluctuating velocities was examined. The experiment was carried out at a Reynolds number of 9,000. In the case of the rectangular jet with the divergent deflectors, the minor axis spread was more promoted than the major axis spread, and the axis-switching phenomenon occurred closer to the nozzle exit than in the case with no deflectors. On the other hand, in the case of the rectangular jet with the convergent deflectors, the minor axis spread was more suppressed than the major axis spread, and axis-switching occurred farther from the nozzle exit than in the case with no deflectors. Therefore, the axis-switching location of the rectangular jet is significantly affected by the angle between the deflectors.

The present paper describes the results of the passive flow control of a plane jet by rectangular tabs at relatively low Reynolds numbers (Re = 2000). The effect of width of rectangular tabs at the nozzle exit on the flow characteristics and vortical structures of a plane jet are investigated. The flow visualization and velocity measurements were carried out using particle image velocimetry (PIV). In addition, three-dimensional plane jet numerical simulations were performed using ANSYS Fluent to investigate the vorticity and the vortical structures. Good agreement was found between the experimental and numerical simulation velocity profiles when large eddy simulation (LES) was employed in near field region. We found that a plane jet with small width tab had the smallest jet spread downstream, and the jet’s centerline velocity was larger than that with large width tab. The preservation of streamwise vortices in the downstream relates to the location and intensity of the four streamwise vortices behind a rectangular tab.

Cavitation jet is one of the way to improve the processing performance of water jet. Cavitation jet emits ultrasonic sound, and its sound pressure is known to increase the effect of cutting or washing processing. The purpose of this study is to increase the sound pressure by using a narrow tube attached to the front of the nozzle. As a result, we clarified the conditions that the sound pressure becomes larger than in the case of without a tube.

A synthetic jet device is a useful tool for active flow control. The vortex ring released from the synthetic jet traverses boundary layer at self-induced velocity and gives momentum in the flow. Synthetic jet actuators require low operating power, however, they can give zero-net-mass-flux and the device can compact. Therefore, a synthetic jet is expected as a new method of boundary layer control. For the synthetic jet, the effect of the orifice depth on the vortex ring behavior has not been completely clarified yet. In this paper vortex ring structure was visualized that was released in cross flow or into quiescent flow for two types of orifice depth and the difference of their structures were compared. The breakdown of the vortex ring in quiescent flow was affected by the orifice depth. The small vortex structures were observed around the collapsed ring. Orifice depth could change the rolling up of the rings and the momentum in the cross flow.

In this paper, the turbulence intensity of flow passing through the wire mesh and the nozzle have been investigated. The base flow after the wire mesh is keep at 3 m/s. The wire mesh used in the experiment, the wire diameter is 0.23 mm to 1.0 mm and the open area ratio is 49.6 % to 76.4 %. The wire diameter Reynolds number with respect to the wire diameter of the wire mesh is 43 to 185. As the result, the turbulence intensity of flow passing through the wire mesh is more influenced by the wire diameter than the open area ratio. The turbulence intensity of flow through the nozzle is homogenized independent of the wire diameter and the open area ratio.

The increasing of the aerodynamic force and aeroacoustic noise are caused by the vortex shedding generated from a circular cylinder. The suppression of the vortex shedding is one of the important issues in engineering. In order to reduce the aerodynamic force and aeroacoustic noise, the drag coefficients and sound pressure level of the cylinder attached with the cylindrical rings was experimentally measured. In this study, the reduction effect of the aerodynamic force and aeroacoustic noise generated from the cylindrical rings is investigated by using the low-Noise wind tunnel in the Reynolds number ranged from (1.9 to 5.0) × 10⁴. As a result of this study, the drag coefficients and sound pressure level reduction was confirmed. These ring pitches of 4 decrease the drag coefficients and sound pressure level by 15 % and 16 %, compared with the no rings.

In this research, the influence on the flow field around the horizontal axis wind turbine when applying the plasma air flow control is examined. The flow field around the wind turbine is measured by Laser Doppler Velocimetery in wind tunnel at the tip speed ratio where the plasma air flow control effect has the most remarkable on the wind turbine performance.

The cylinder blade wind turbine is driven and rotated by that the longitudinal vortex is formed steadily between the cylinder blade and ring-plate placed behind the cylinder blade. In this report, the influence of form factors such as the width of ring-plate and the diameter of the cylinder blade on the blade length for the most effective forming of the longitudinal vortex has been examined. The flanges are attached on a cylinder blade to place the inside and outside of the ring-plate and the effective blade length is controlled by changing their distance. The effective blade length increases as the width of ring-plate increases at a constant diameter of cylinder blade. On the other hand, even if the diameter of cylinder blade is changed, the blade length scarcely changes at a constant width of ring-plate.

When the upstream cylinder with the rotating shaft moves parallel along the ring-shaped flat plate placed the downstream side, the steady lift force acts on the cylinder as the driving force of the wind turbine by the longitudinal vortex statically generated behind the cylinder. In this study, we examined that the occurrence of the time change of torque in the new wind turbine driven by longitudinal vortex predicted by numerical analysis. Furthermore, the relation between the operating condition of the wind turbine and its vibration was experimentally clarified.

In this study, we found that the torque fluctuation becomes very large at the tip speed ratio λ = 0.1. Since torque fluctuation reduces power efficiency, it was found that it is necessary to avoid this tip speed ratio in actual operation.

Various wind power generators such as propeller, Darrius and Savonius types have been used. The present study proposed the new screw-type wind turbine. As compared to other power generators, the present one become simpler and more portable. By these advantages, the new applications of the wind power systems such as disaster areas and outdoor activities will be expected. The power characteristics of the screw-type wind turbine were clarified by using a Computational Fluid Dynamics (CFD) and a wind tunnel experiment. The CFD and experimental results show that the maximum-efficiency wind speed is about two times of the tip velocity. The angular momentum flow rates in a control planes surrounding the screw-type wind turbine were examined by the CFD. The results show that the angular momentum flow rate to the axial direction contributes to mainly the power coefficient in the wind speeds larger than the tip speed. On the other hands, the angular momentum flow rate to the radial direction becomes negative when the ratio of the tip speed to the wind velocity is high. That is, the energy of the flow to the radial direction was inversely supplied by the wind turbine. It was confirmed that the low velocity on the blade suction surface caused the negative angular momentum flow rate.

The wake of an upstream wind turbine decreases the output power of, and increases the fatigue load on the downstream wind turbines. It is therefore important to accurately evaluate the influence of the wake of the upstream turbines on the downstream turbines for considering an arrangement of wind turbines in a wind farm. The ultimate goals of this research are to identify the essential features of the near and far wakes of a wind turbine, which originates from the boundary layers on the blade surfaces and is subjected to the approaching atmospheric boundary layers, and to understand the interferential effects of two off-shore wind turbines in tandem arrangement in a much more detailed manner than it has been done in previous research. To this end, large scale LES analysis is carried out for an NREL 5MW wind turbine by using K computer. Then, by comparing LES results with reference data, the accuracy of the prediction of the wake and the power performance has been evaluated.

Computational Fluid Dynamics (CFD) has been performed regarding the twist moment of a blade of a vertical axis type Butterfly Wind Turbine (7m diameter), whose blades were slanted around each blade axis to control the rotor speed. In the CFD analysis, wind speed and rotor rotational speed were assumed to be 1 m/s and 79 rpm, respectively, in accordance with the previous forcible rotation experiments using an induction motor. Predictions based on the Blade Element Momentum theory (BEM) agreed roughly with the CFD results. Averaged twist moment was almost proportional to the twist angle when it was less than 10 degrees. As the results of the additional CFD analyses, vertical displacement of a blade did not influence on the twist moment.

Several models have been proposed to predict the shaft output characteristics of the vertical axis wind turbine from the aerodynamic characteristics of the blade. However, it has not predict the output characteristics of the small wind turbine even the multiple stream tube model included effect of the momentum reduction. Therefore, the purpose of this study was to find out a similarity parameter of the shaft output characteristics based on blade wake interference to establish a prediction model for the small wind turbine. From the measurement of the blade wake using the turbine model with single blade, the scale of the blade wake depends on the ratio of the rotational speed to the free stream velocity, and the advection velocity of it depends on the free stream velocity. The shaft output characteristics of the small wind turbine indicate good similarity for the parameter, λ³σn/D , based on interference of blade wake.

Savonius type wind turbines are suitable for installation in urban areas because of their advantages in less wind-direction dependences and small-sized constructions. One of the major problems is its poor and unstable power coefficient mainly due to negative torques on returning blade in a cycle. These periodic fluctuations of the output power coefficient should be improved by decreasing rotation-angle dependences of the turbine blades. In this study, in order to assess the effects of new additional blades on the power coefficient, numerical simulations were carried out, and flow around the rotor was considered by using the regularized lattice Boltzmann method (RLBM). The virtual flux method was used to express the shape of the rotor on a Cartesian grid. As a results, the new shape improved the output power coefficient by 21.6% compared to the classical type owing to the additional ellipsoidal blades.

A wind turbine blade with a Magatama-type section is examined. This blade specialize exclusively for vertical axis wind turbine. In this report, Lift that a Magatama-type section blade produced of ideal fluid is experimentally investigated using Hele-Shaw cell. At first, by this experiment, Pressure distribution from the flow around a Zhukovsky blade is calculated. This is compared with the theoretical pressure distribution. Pressure distributions around a Magatama-type section and the NACA0018 blades are experimentally examined from Hele-Shaw cell. From there pressure distributions, Lift is calculated. Using this technique, a new Magatama-type section to produce higher lift is examined. The lift of this a new Magatama-type section blade was increased than that of before.

In this study, a new blade which has a Magatama-type section for VAWT is proposed. This blade can be operated under low wind speed and low tip speed ratio circumstances. It is found from the numerical analysis and the wind tunnel experiment that the double blade turbine generates 4 times larger power coefficient as compared with the former blade wind turbine. It is found from the field experiment that high power coefficient is obtained at a relatively low tip speed ratio that is around 1.0. The blade which has a Magatama-type section for VAWT is suitable for VAWT that can be operated under low wind speed and low tip speed ratio circumstances.

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 high performance is required. Therefore, we adopted contra-rotating rotors, which can be expected to achieve small size and high performance. However, when the rotors become smaller, the output power of conventional contra-rotating rotors, which is composed of axial flow rotors, is very low. In order to achieve small size and high output power, we propose new type contra-rotating rotors, which are composed of a hybrid rotor and a centrifugal rotor. In this research, we investigate performance of the new type contra-rotating small hydroturbine model by the numerical analysis. In this report, we investigated of the influence of the deflection angle and blade number related to the load of rotor.

A contra-rotating turbine system is theoretically torque free, since the second blade counters the first blade torque. In this study the contra-rotating turbines are adopted as an ocean current power generator. In this paper computational study is performed to investigate the wake flow characteristics of contra-rotating configuration. In additional to calculating the hydrodynamic forces and power outputs by using Computational Fluid Dynamics (ANSYS Fluent 18.0).

In this study the flow generated by the ocean current turbine has been calculated. The purpose is to study how a contra-rotating ocean current turbine design. This method is validated by comparing with experimental results.