Perfluoroalkoxy (PFA) is a type of fluoropolymer with properties similar to polytetrafluoroethlene (PTFE). It is a kind of perfect self-lubncating material due to its very low friction coefficient, good high-temperature stability and chemical stability. Yet, it cannot be used as anti-wear materials alone because of its poor mechanical properties, bad thermal conductivity and high wear rate. Multiwall carbon nano-fiber (MWCNF) is expected to be a new functional material having high electrical conductivity, thermal conductivity, chemical stability and mechanical strength. It is widely used as fillers in composite materials, particularly lightweight polymer-matrix composites. PFA reinforced MWCNF composite coating is expected to be used in applications requiring low friction and wear situations. In this study, mechanical alloying technique using mechanochemical reaction was applied to prepare the thermal spraying powder of PFA resin matrix composite covered with MWCNF. The composite powder containing 0, 1, 3 and 5 mass% MWCNF was deposited on mild steel substrate by the powder flame spraying. Influence of the MWCNF content and difference of the powder flame spraying conditions, such as preheating temperature of substrate, on the microstructure and friction coefficients are examined. Experimental results revealed that reduced wear of the MWCNF-PFA composite coating compered to PFA coating.

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The thermo-mechanical fatigue tests of a protective coated Ni-base superalloy were carried out. The substrate of Ni-base superalloy, IN738LC, was coated with CoNiCrAlY protective coatings sprayed by cold spray process. In this paper, the influence of thermo-mechanical loading on fatigue strength was discussed. In addition, the fatigue strength of Cold sprayed specimen was comparison with that of conventional low-pressured plasma sprayed one.

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Coating adhesion is a critical factor on coating technology. However, the adhesion mechanism of cold sprayed metallic coating on ceramic substrate has not understood sufficiently yet Therefore, there is a limitation to apply cold sprayed coating to industrial products, such as power electronic components. Generally, shear localization that occurs at the interface between a particle and a substrate during particle impact has a notable effect on adhesion strength of cold sprayed coatings. In this study, spray angle is focused to improve the shearing area and force. And also, the effects of spray angle, substrate hardness and surface roughness on adhesion strength of aluminum coatings were investigated. The spray angle was varied to two different levels: 60 and 90 degree. Used substrate materials were ceramics Al_2O_3 and Si_3N_4 and soda glasses. In addition, morphologies of individual aluminum particles was observed. As a result, the adhesion strength of the aluminum coating on Al_2O_3 and Si_3N_4 substrates increased in case of the spray angle of 60 degree. Then, it is shown that the adhesion strength of the aluminum coating on the Al_2O_3 substrate is higher than that on the Si_3N_4 substrate. The morphologies of a single aluminum particle varied depending on the spray angle.

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Cold spray is a promising process to produce high quality metallic coatings without oxidation and phase transformation. In this process, feedstock particles are accelerated by a super-sonic gas flow, then the particles collide and deposit on a substrate surface with solid phase. The super-sonic gas flow forms plate shock wave in front of the substrate, and it affects in-flight behaviors of the particles. This study investigates the influences of plate shock wave on the in-flight behaviors of the particles and coating deposition. The spray distances between the nozzle and the substrate was changed to change the plate shock wave occurence. The gas flow was analyzed by the computational fluid dynamics. The results of the deposition efficiency of the coatings corresponded to the spray distance. From the simulation results, Mach number distributions increased as the nozzle got close to the substrate. On the other hand, the plate shock wave did not occur when the spray distance increased beyond a certain distance. The plate shock wave formation and particle velocity distribution in the gas flow were strongly affected particle flight and deposition behaviors.

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Currently, graphite is used for anodes of the lithium ion battery. The higher capacity of a battery with the lithium alloy anode requires the development of a larger theoretical electrochemical capacity than graphite. Tin is a promising anode material, having a theoretical capacity more than 10 times that of the graphite used in these lithium alloy batteries. In this study, numerical simulation and experiments investigated influence of nitrogen gas stagnation pressure and temperature on behavior of particle and coating properties of tin in cold spraying. The deposition efficiency of tin coating reached a peak of 90% with gas stagnation pressure of 0.8MPa and gas temperature of 350 ℃. But the deposition efficiency fell from 90% to 20% rapidly and many fine particle with 1 μm were observed at coating surface when the gas pressure exceeded 0.8MPa.

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In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. There is a rectangular and round cross-sectional shape on the cold spray nozzle. It has been reported that spray pattern of the rectangular spray nozzle is wider than that of the round spray nozzle. Accordingly, rectangular nozzle is better efficiency than round nozzle at spray a constant width. However, cold spray nozzle on the market is mostly round nozzle. Therefore, the purpose of this study is the uniformity of the spray pattern of coatings. We made two different rectangular nozzles to compare with the round nozzle. As a result, spray pattern were fabricated by converging-diverging rectangular nozzle has become more uniform and wider than that of round nozzle. However, in the converging-diverging-barrel rectangular nozzle coating was deposit to end on spray pattern of coatings. According to the numerical simulation, N^2 gas velocity that vertical to spray and width direction is quite different comparing the converging-diverging-barrel rectangular nozzle and converging-diverging rectangular nozzle at divergent section. Converging-diverging-barrel rectangular nozzle velocity is 150m/s and Converging-diverging rectangular nozzle velocity is 30m/s. In addition, in velocity of the spray direction end portion is 50m/s larger than nozzle center in the converging-diverging-barrel rectangular nozzle barrel section.

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A cold-spray (CS) method is a new technology which collides fine particles with a solid surface and make a deposit on it. The CS method can produce a thick deposit with little heat affect. Although the strength of this thick deposit is high comparing with bulk material, it often shows brittle fracture. The brittle fracture was found to occur at the interface between the deposited particles. The authors, therefore, observed the difference in the micro texture around the grain boundaries in each particle and that around the interface between the deposited particles in the cold-sprayed copper deposit by an EBSD (Electron backscatter diffraction) method. It was found that the average grain size in the deposited particles was much smaller than that in the particles before deposition. This fine grain size is the reason for the high strength of the deposit. However, there is no difference in the misorientation angle distribution between them. Thus, the microstructure around the interface between the deposited particles should be analyzed more in detail.

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Thermal barrier coatings (TBCs) for blades of gas turbines are an indispensable technology for improvement of the turbine efficiency. During service, a thermally grown oxide (TGO), which has harmful influence on delamination of the TBC, grows at the interface between the TBC and a bond coat (BC). In this study, the influence of bond coating process for the TBC on the TGO growth was investigated The BCs were sprayed by different spray techniques, namely the low pressure plasma spraying (LPPS) and the cold spraying (CS). Yttria Stabilized Zirconia (YSZ) top coat was subsequently fabricated on the BC layer by air plasma spraying (APS). The coatings were oxidized isothermally at 1273K for different time periods up to 1000h and their TGO growth were compared and fully discussed by measuring their TGO thickness, and impedance measurement of their TGOs. As a result, it can be found that the TGO growth of the TBC with CS-BC was less than that of the TBC with LPPS one. And also, in the case of the TBC with CS-BC, formation of mixed oxides, which are porous and crack initiation site, was less than LPPS one. And it was found that CS-BC impedance was much higher than LPPS-BC one from the results of impedance measurements. It concluded that the TBC with CS-BC can be generated and grew much higher quality TGO than that of the LPPS-BC.

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We investigate numerically the dynamical behavior of an axial flow hydraulic turbine model with a collection device in an open channel. To study the effect of the collection device, we first introduce a model impeller and investigate its performance and flow field. We then explore the performance and flow field of the collection device, and the impeller with the collection device. We find the introduction of the collection device accelerates and enhances the velocity of collective flow. Finally, to confirm the effectiveness of the simulations, a real scale model is developed and tested in a river. We obtain reasonable agreement between the numerical calculations and experiment.

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The aim of this investigation was to develop an environmentally friendly nano-hydraulic turbine utilizing extreme low head waterfall. The relative distance between a runner and a waterfall is one of the important factors for stable generation. It is often necessary to adjust precisely the relative position every time flow rate change, because that flow rate always change. So, changing the runner position or controlling the waterfall direction is needed. But the former is very difficult from the viewpoint of generation cost. We, therefore, focused on the flow direction control method via a curved channel. Open cross-flow runner was selected, and the runner performance was evaluated for several types of curved channel. As a result, turbine performance has the biggest impact on fast water velocity made by small radius of curvature.

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Membrane module that is currently being used in osmotic power generation is less osmotic flux, cannot remain current for practical use. Osmotic flux must be improved by confirming internal flow of membrane module because there is a need to improve the efficiency of osmotic power generation. But research on the internal flow of membrane module has not been so far. So concentration distribution and flow conditions are unknown. Therefore, visualize the flow by flowing dyes, investigate the flow properties and change in concentration by change in color due to concentration.

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The concentration difference power is power generation which use osmotic pressure generated when having carried out sea water and fresh water by the semi-permeable membrane and turn the turbine In this power generation, the amount of osmosis of fresh water is important. By this research, it is proposed a model of the feed water flow and the osmosis from a hollow fiber into the sea water in pressure retarded osmosis (PRO). The influence of the diameter and the internal pressure of the hollow fiber are examined for osmotic flux and power of PRO. It is clear of the existence of the maximum flux for internal pressure.

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This paper describes the performance of a drag-type vertical axis wind turbine with variable-pitch simple flat plate blades. The pitch of the blades was controlled using a chain and sprockets arrangement to ensure that the blades rotated around their own longitudinal axes by only 180° during the each full revolution of the main rotor. To improve the performance of this wind turbine, the effects of the end plates and the ribs of the blades were investigated. The power coefficient of the wind turbine with variable-pitch blades depends on the turbine solidity, and that with the end plates increased more than that without end plates. However, the power coefficient of the wind turbine with the ribs decreased more than that without the ribs.

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Darius type wind turbine with straight blades has many advantages of high performance, the wind direction independency, and easy productivity of the blade. Moreover, practical use in urban areas can be expected by the improvement of the performance because it is suitable for downsizing, and low cost due to simple mechanism. In this paper, the relationship between the fluid force of blade and flow field around blade was analyzed by using CFD method. Moreover in order to improve the wind turbine performance, the relationship between cylindrical guide mounted inside the wind turbine and chord length were examined by wind tunnel test. It was clarified that the cylindrical guide with the diameter of r_c/l_r=0.5 and chord length l_c=60〜120[mm] and number of blades N=2〜4 could increase the efficiency of the wind turbine because of improvement of flow around the blades.

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The influence of solidity on performance of a stand-alone system using a straight-wing vertical axis wind turbine is analyzed through a numerical simulation. The specifications of the straight-wing vertical axis wind turbine based on the solidity and rated electric power are determined through a strength calculation employing an aerodynamic load analysis. This is because the consideration of not only output characteristics of wind turbines but also strength to extremely high winds are indispensable for the appropriate design. The numerical simulation on the system performance under an annual wind condition shows that with the decrease in the solidity, the capacity factor expressing a power generation capability is improved; however the damage equivalent fatigue load is also increased. As a result, a trade-off between the power generation performance and the fatigue load that are influenced by the solidity is revealed.

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Flow fields around an airfoil of a straight-wing vertical-axis wind turbine are measured using a PIV method to obtain a design guide for a more efficient wind turbine. The result shows that the flow field changes dramatically along with the tip speed ratio. High speed regions are generated near the airfoil because the flow must go around the airfoil, and the flow separation causes a part of fluid to accelerate and move with the airfoil. The timing of vortex shedding related to the flow separation is delayed when the tip speed ratio is high.

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This study investigated the influence of a wind turbine tower on the wind velocity distribution in the wake of a wind turbine. Large-eddy simulation (LES) of the wind flow around the wind turbine was performed using an actuator disk model for the rotor and by explicitly resolving the tower and nacelle. In addition, LES with no tower was performed. With regard to the streamwise component of the wind velocity in the wind turbine wake, the LES with tower reproduced the asymmetric distribution in the lateral direction, which was observed in a wind tunnel experiment, while the LES with no tower produced symmetric distribution.

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Performance of a pair of tandem arranged close Cross Flow Wind Turbines (Twin Rotor Cross Flow Wind Turbine, TRCFWT), and of Cross Flow Wind Turbine (Single Rotor Cross Flow Wind Turbine, SRCFWT) investigate by OpenFOAM CFD software. Rotation of the rotors at TRCFWT has forward and backward mode and complex mode. Forward mode is that the rotor peripheral velocity direction and the main flow direction is the same at the minimum clearance between the rotors. In contrast to this, backward mode is that the direction of these is reverse. Complex mode is that a pair of rotors rotates in the same direction. Calculation of the TRCFWT at forward and backward mode and the SRCFWT are conducted under the conditions of the rotors of the same form, uniform flow velocity of 4 m/s, flow angle of 0 degree, and G/D of 0.230(G: the distance between the rotors, D: the rotor diameter, except for the SRCFWT). The calculation result suggests that the maximum power coefficient of forward and backward mode is 1.16 times and 1.05 times that of the SRCFWT, respectively. Furthermore, operating tip speed ratio of forward and backward mode is 1.10 times that of the SRCFWT.

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Offshore floating-type wind turbines are less affected by water depth and are expected to be an effective power source for sustainable development. An experimental study was begun to realize a practical offshore floating-type wind turbine in the ocean near the Goto Islands, Nagasaki. The most striking characteristic of offshore floating-type wind turbines compared with traditional foundation-mounted wind turbines is that they pitch and roll with the waves. Research on the sea current and wave forces acting on an offshore floating-type wind turbine is important for launching the development of this wind turbine technology in the waters of Japan. The result of this study is important for installation and actual operation. The forces acting on the wind turbine were estimated through a model experiment and numerical simulation. Thirty-seven observation points from the Nationwide Ocean Wave Information Network for Ports and Harbours in Japan were taken as estimation sites.

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Some foil sections of cross flow wind turbines were simulated by Laminar Flow analysis. The equations are discretized by Finite volume method for space and Fractional step method for time. In this study, blade number is 16 and chord length is 15% of diameter. Blade set angle is 45degree and its camber is 15% of chord. Important parameters are thickness and the edge shape of blade. The following are results of analysis Best shape was outer- wedge type and round edge was not good in the standpoint of maximum power. Thickness of blade decrease maximum power.

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The purpose of this study is to research the effect of Silent Disrupter Blade (SD-Blade) on numerical analysis. It is one of noise reduction technologies for small wind turbines and has protrusions made by painting along the wing chord like a riblet. The effect of SD-Blade is known in experiments, but its detail mechanism doesn't become clear. In this research, the flow field is simulated using compressible Large-Eddy Simulation (LES) and the acoustic field is evaluated by BPM model. The study compares SD-Blade with normal blade using LES and BPM. The results of SD-Blade shows decreasing Sound Pressure Level (SPL) and increasing lift-drag ratio compared to normal blade. Besides, from the looking of the flow field, we can confirm that the protrusions reduce flows of span-wise direction in boundary layer.

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The small wind turbines have not become widely used due to their pour power generation efficiency. They are operated at low Reynolds number (Re≦2.0×10^5) because the rotor size is small. In general, wind turbine performance becomes low due to the blade surface boundary layer separation at low Reynolds number. In urban areas where small wind turbines are operated, the blade elements are subjected to significant variation of angle of attack. This variation causes the fluctuation of power output and loads. In this study, by using blade surface boundary layer control, M01-26 airfoil which has shown superior performance at high Reynolds number (2.0×10^5≦Re≦4.5x10^5)was applied to small wind turbines operated at low Reynolds number. Static and dynamic characteristics of 2D airfoil were evaluated, and the validity of boundary layer control on wind turbine rotor was verified by wind tunnel experiment. As a result, wind turbine performance has improved significantly in low wind speed with stall.

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Applied pitch control usually used in onshore wind turbine to Floating Offshore Wind Turbine, some property such as Tower vibration, produced power were negative damped. We call it negative damping. When using Floating Wind Turbine, rated power is to be reduced to avoid negative damping. In this paper, we reproduce negative damping of Floating Offshore Wind Turbine by tank test, based on it, devise and evaluate a pitch control system to suppress negative damping. According to tank test, tower pitch motion was amplified by pitch control. We propose a new pitch control system to control turbine rotation and tower movement, and evaluate this control by tank test of scale model wind turbine and numerical simulation of NREL 5MW Wind Turbine using FAST that made by NREL. This research shows that we should not use pitch control only but combine other control such as torque control to suppress negative damping.

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In this study, a new type of vertical axis wind turbine (VAWT) named as Butterfly Wind Turbine had been proposed, which has armless blades consisting of a closed curve. Since a part of flow intersects the Butterfly Wind Turbine rotor four times, a new flow-field model used in BEM (Blade-Element Momentum) theory was proposed. The model was named as Quadruple-Multiple Streamtube (QMS) model, which nests the Double-Multiple Streamtube (DMS) model. Power characteristics of three kinds of VAWTs, that is, general single-straight-blade VAWT, double-straight-blade VAWT, and Butterfly VAWT, were simulated based on the BEM theory using the QMS model. The results show that, under the condition of a constant chord length, the Butterfly Wind Turbines improve the starting performance of general VAWT as well as double-straight-blade VAWTs. Furthermore, a Butterfly VAWT equipped with tapered blades shows higher power coefficient at low rotational speed condition, without significant decrease in maximum power coefficient.

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In wind farms which mean many wind turbines constructed in a site, the wind passed through an upstream wind turbine (i.e., wind turbine wake) flows in a downstream wind turbine. As a result, the wake causes power reduction and fatigue load on the downstream wind turbine. Therefore, it is important to clarify the characteristics of wind turbine wake. In this study, by using a test wind turbine and wind speed measurement systems, the wind speed distribution in the wake were measured in non-yawed and yawed conditions in field and the effects of yawed inflow on the wake characteristics were clarified. A gaussian wake model for non-yawed and yawed conditions was investigated and compared with the experimental results.

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This paper aims to simulate the motion of wind turbine and the swing rudder under wind direction change. Swing rudder is a rudder pivoted on the nacelle. The turbine with it shows good performance on yaw alignment under sudden wind direction change. However the efficiency of swing rudder is only evaluated by field operation that wind condition is hard to measure precisely. Thus the detailed mechanism of swing rudder is not sufficiently revealed. In order to evaluate the efficiency of Swing rudder, we simulated both the turbine model with swing rudder and with fixed rudder. The yawing motion is simulated using aeroelastic simulation code FAST developed by National Renewable Energy Laboratory. Numerical model of wind turbine is based on Zephyr Airdolphin GTO. In order to evaluate the efficiency of swing rudder, Simulation condition is set to be one wind direction change with steady wind speed. As a result, it is revealed that swing rudder reduces maximum yaw error when wind direction change is fast. Moreover, that characteristic is not dependent on magnitude of wind direction change. In addition, from the simulation with turbulent condition, the performance between swing rudder and fixed rudder is observed.

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A parallel-variable speed operation system using multiple large-scale wind turbines is proposed in order to reduce fluctuations in the generated power output. In this operation, the electric power outputs of load induction generators are connected to one large-capacity PWM converter. The rotational speeds of the wind turbines can be controlled by only one converter because they are restrained by a converter-impressed frequency. This operation aims not only to reduce power output fluctuations by using large moment of inertia of the multiple rotors but also to improve the generating performance by adequately controlling the rotational speed in response to variations in inflow wind speeds. As the first feasibility study for this system, this study analyzes the target operating point of the system, which means the maximum power output point under different wind speed to each wind turbine, through a numerical simulation.

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Evaluating power generation of a small wind turbine is becoming more important because the certification and feed-in law will be systematized in our country. However, the behavior of a grid-connected small wind turbine is not analyzed adequately and difficult to simulate only with the numerical analysis. On the other hand, experiments and measurements in the field are expensive and cost too much time. In this study, we calculated the torque of the rotor axis of the wind turbine under specific wind condition using numerical analysis called FAST provided by NREL, and produced the calculated torque on the shaft connecting a motor and a generator to simulate the real wind. The generator is connected to a grid simulator. Therefore the simulator we developed enabled the generator to produce power like the wind turbine in the field. We measured the torque on the shaft, rotational speed and power generated. Through some experiments and numerical analysis, and comparing the experiments on the field, we could simulate dynamic behavior which is not considered using FAST and found out problems to improve.

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The aim of this study is to design and propose the size and layout of buildings which provide the better wind distribution for the higher power generation of wind turbine. At first, this study performed the numerical simulation on wind velocity distribution around a building model to investigate the wind acceleration blowing through buildings. Based on the simulated wind velocity distribution around the building model, the power output of wind turbine was calculated for the assumed wind turbine installation points. In addition, the annual power energy of wind turbine was also calculated by data base of local wind conditions for the sample location to verify the proposed model. As a result, it was confirmed that the wind was accelerated blowing through buildings due to contracted flow between buildings. The ratio of power energy to energy demand which was calculated for the proposed building model was about 12 - 13 %.

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The purpose of this study is developing the wind turbine acoustic model considered operating condition by microphone array measurement and operating data acquisition at the same time. This paper reports the result of preliminary measurements and the design concept of microphone array. The Preliminary measurements were operated with sound-level meter at two field wind turbines to characterize wind turbine noise. The measurements show that wind turbine noise in these measurements has broadband characteristic whose peak exists at about 600Hz. In addition, we identified Characteristic sound in wind turbine noise through both measurements by A-weight sound pressure level fluctuation whose period correspond with the number of blade rotation period divided by the three. The fluctuation of one-third octave band spectrum suggested that the frequency of Characteristic sound ranged higher than about 600Hz. Based on the result, we designed the microphone array which is able to analyze at sufficient spatial resolution in higher than 600Hz.

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In recent years, various countries worldwide have developed wind power as a clean energy source. In offshore regions, wind turbines other than the seabed-mounted type can also be developed; the floating-type wind turbine has been studied for expansion into deeper waters. Because offshore floating-type wind turbines are vibrated by wind, ocean currents, and waves-which varies the efficiency-the mechanical system is affected. This can be important for predicting sway. In this study, a spar-type floating offshore wind turbine was evaluated; likened to a pendulum in water, the angle is detected by a rotary encoder. The ratio of the period of the pendulum in air and in water and the sway of the pendulum were investigated in a water channel subjected to waves. The period ratio of the pendulum was found to increase in proportion to the aspect ratio of the immersed part of the weight. The period of the pendulum in the water was dependent on the moving speed, weight diameter, and pendulum mass. The ratio of the angular frequency of free vibration in water and the angular frequency of water waves in the vicinity of 1.05 was most upset.

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The purpose of this paper is the numerical prediction of the wind on the complex terrain and its turbulence characteristics. This paper shows the LES analysis of the complex terrain site and the power spectrum analysis of the turbulent wind. Because of the simplification of the flow condition at the inlet boundary, the LES analysis was applied for the sea wind case of the site and the results agreed with the 10 minutes averaged observations. This means the turbulence in the sea wind is generated mainly by the geographical features. Then, the turbulence characteristics of wind were shown by the power spectrum analysis of the wind speed data. The parameters for the power spectrum density model were derived by fitting the power spectrum at the measuring points into the model. The parameters showed the very turbulent characteristics of the wind on the complex terrain. Simultaneously, the length scale in the model could become the guideline for the resolution in the numerical simulation of the complex terrain.

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A relation between the vorticity disturbances and the leading edge receptivity is investigated numerically. Freestream disturbances are given as a two-dimensional periodic vorticity fluctuation at the upstream boundary. Three cases changing the height of the impinging vortices are tested. The result shows that location of the impinging vorticity pattern influence the vorticity pattern near the wall of the boundary layer, changing the receptivity.

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In this study, a numerical simulation using a vortex method was performed in order to investigate the aspect of flow and the fluid force around a symmetrical airfoil NACA0012 with relative velocity fluctuation in the direction of flow against main flow velocity. An airfoil with three kinds of fixed attack angle was forced oscillating in ranges of the oscillation amplitude ratio 2a/c=0.5, 1.0, 1.5 and 2.0 and the oscillation frequency ratio f/f_K=0.25, 0.5, 1.0 and 2.0 (here, a :half-amplitude of oscillation, c :chord-length, f :oscillation frequency,f_K :natural Karman vortex shedding frequency from a stationary aerofoil with the attack angle of 90 degrees) at the Reynolds number Re=4.05×10^5 based on the main flow velocity U=20m/s. In results, at the airfoil with attack angle which does not produce the separation on the surface of airfoil in stationary condition, the flow separation was produced even if the movement speed of airfoil does not exceed main flow velocity. At the airfoil with attack angle which can recognize the flow separation clearly in stationary condition, the aspect of flow around airfoil became more complicated without becoming calm. And the variations of fluid forces according to oscillation were obtained in all cases. The relationship between the variation of relative flow velocity and producing the separation including reattachment was investigated in each attack angle. And the separation in stationary condition was observed at smaller attack angle which observed the static stall in the experiment of Maresca et al (1979).

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The corelation between the influence of the shape of wavy channel and pressure loss in the channel are investigated in this paper. The need for lightweight and spacesavig has driven the development of advanced heat exchanger. Among them, wavy passages are characterized by extended surface area/volum ratios that are often configured in plate-fin heat exchanger. However,optimum configulation is not found that formed the minimum recirculation regio at curved passage. In this research, the vortex structure of the secondary flow for two type of the passage was investigated.

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In this paper, we study Lagrangian Coherent Structures (LCS) and Lagrangian Chaos in Rayleigh-Benard Convection. The notion of LCS denotes stable and unstable manifolds of time-dependent mechanical systems, which is defined as a ridge of Finite-Time Lyapunov Exponent (FTLE) fields. It is shown how fluid particles are to be transported and mixed by the Lagrangian advection in the LCS.

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In this study, a grid-free vortex method was developed and applied to various turbulent flows in order to validate the method. The grid-free redistribution model proposed by Fukuda and Kamemoto^<[1,2]> and newly developed vortex elements reconnection model were introduced and the spatial resolution was improved for high strain regions. The calculation was accelerated by using Graphics processing Units (GPUs). From the results, it was confirmed that the unsteady feature of the vorticity region and its development were successfully captured. Furthermore, comparisons of the calculated data with experimental data showed that the method provided an accurate velocity profile of turbulent internal flow and accurate energy spectra of vortex ring interaction.

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This study concerns conservative properties of the kinetic energy in two-dimensional incompressible flow simulations using the vorticity equation. A procedure which derives the conservation equation for the kinetic energy from the inviscid vorticity equation is analytically considered and then the procedure is formulated discretely. In the procedure, the vorticity equation multiplied by stream-function is integrated (or summed discretely) over the computational domain under the periodic boundary condition and the Green's second identity and the Gauss's divergence theorem are applied to deform the equation. When the identity and the theorem are formed discretely, the total amount of kinetic energy is conserved discretely in time. Hence formulations of fully consistent discretized forms (referred to as "appropriate" form) for the identity and the theorem are necessary. In this study, the appropriate forms for the identity and theorem are proposed and then the discretized conservation equation for the total amount of kinetic energy is appropriately formulated.

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Vortex array in circular synthetic jets is investigated experimentally by instantaneous velocity measurements using a hot-wire anemometer. The ensemble averaged velocities are derived by referencing the oscillatory flow in the orifice. The contours of the ensemble averaged velocity indicate that a vortex ring is generated per a cycle of oscillatory flow. The structures of vortex array are compared for seven strokes of oscillatory flow range from L/d = 0.712 to 7.10. It is found that vortex rings with nearly equal interval along the jet axis travel to downstream and collapse in further downstream. For strokes larger than L/d= 3.6, it is observed the vortex ring accompanies a weaker trailing vortex ring. It is also found that dimensionless convection velocities of vortex ring are independent of stroke. As the stroke is increased, the spatial interval of vortex rings is increased and the location of vortex collapse is moved to downstream that can delay the jet growth in mean jet flow distribution.

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The behavior of a vortex ring convecting in a rotating fluid is investigated by the numerical simulation. The convection direction is parallel to the rotation axis of the fluid. The simulation highlights the flow and vorticity fields induced by the Coriolis force around the vortex ring. An axial vorticity appears along the central axis of the vortex ring, and secondary vortex rings occur at the front and rear of the vortex ring. The simulation also demonstrates that the decay of vortex ring is enhanced by the secondary vortex ring.

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Flow fields around an oscillating airfoil at low Reynolds numbers are extremely unsteady. In particular, the pitching oscillation at the high angle of attack encourages vortex dynamics in the separated shear layer near wake of the airfoil and produces unsteady vortex motions. To evaluate the force correctly, it is necessary to know the unsteady properties determined from the vortex dynamics because that unsteadiness is known to make the force greater. The purpose of the present study is to investigate the relationship between unsteady fluid forces and vortex structures for a discoid airfoil during the pitching and heaving motions. Furthermore, the effect of phase difference θ between pitching and heaving motions on vortex dynamics is also observed. It is confirmed that the unsteady fluid forces were affected by the vortices shed from the airfoil edge during upstroke in pitching oscillation. There are two peaks in the fluid force during one pitch-oscillating due to the vortex behavior. The vortex behavior was strongly affected by the reduced frequency due to pitching oscillation, and the fluid force acting on the airfoil model increases with increasing the reduced frequency. During coupled heaving and pitching motions, phase difference between pitching and heaving motions affects the vortex behaviour in the wake of the airfoil.

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Unsteady airfoils develop a vortex flow in the vicinity of these walls and induce a delay in separation and the generation of reverse Karman-vortex streets by unsteady motions. These phenomena have attracted attention in industry due to the effect of the fluid force acting directly on objects. Moreover, elastic moving parts (wings or tail flukes) of flying and swimming animals have attracted a great deal of attention. We believe that the "elastic deformation" and "unsteady motion" strongly affect the generation and development of the fine vortex structure, which is origin of wake structure in the vicinity of a wall. However, the behaviors of vortices on the surface of unsteady airfoil have not been clarified in detail. The authors performed the PIV measurement for vortex flow in the vicinity of a wall of the elastic NACA0010. We focused on the relative angle of attack generated by heaving motion and elastic deformation and clarified the effect of relative angle of attack to the developing process of vortices generated in the vicinity of a wall.

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In this study, the flow features of vortex shedding from a pair of tandem arranged circular cylinders oscillating along the direction of the flow were observed by visualizing water flow experiment at the ranges of the frequency ratio f/f_K=0〜7 (28 steps), the amplitude ratio 2a/d=0.0625〜1.0(12 steps), the distance ratio L/d=1.5, 2.5 and 5.5 and Reynolds number Re=640. The variations of mean vortex shedding frequency were investigated. Although the cylinder oscillation frequency f is lower than the natural Karman vortex's frequency f_K, the lock-in phenomenon can be seen even in tandem arrangement case. The lock-in ranges have been shown in each distance ratio L/d. It is found that the lock-in ranges become wide when comparing with the single cylinder case. The typical flow patterns of the lock-in or un-lock-in states were shown every distance ratio L/d. In distance ratios L/d=2.5 and 5.5, the twin vortex street from the 2nd cylinder (rear set cylinder) was not seen. The 2nd circular cylinder has more flow patterns than the 1st circular cylinder. The flow pattern of the 2nd circular cylinder was complicated, and various.

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In semiconductor manufacturing, a new pneumatic non-contact handling device is developed. This device named Vortex Cup makes use of a negative pressure at a central area of swirling flow in order to hold the wafer and to prevent significant wafer damage and foreign material contamination. The Cup provides lower-cost, higher-performance than other pneumatic type devices, but has a problem that periodic pressure fluctuation is caused when the gap height between the work and the Cup becomes large. This problem causes the work falling or the work collision against the cup. In this report, we proposed simple method for suppression of the pressure fluctuation by using cylinders set into the cup. As a result, it was revealed that the cylinder diameter has great effect on the fluctuation suppression, but the height has little influence on it. PIV measurement clarified that the meandering motion of swirling flow in a cup was disappeared when the pressure fluctuation was suppressed.

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The laminar-turbulent transition of a mixing layer induced by oscillating flat plates at an exit of a two-dimensional nozzle was experimentally investigated. The mixing layer was formed between the jet which issued from the nozzle and the surrounding quiescent fluid. The plates oscillated vertically in relation to the mean flow. The disturbance was introduced by oscillating the plates at two vibrational modes. The one is due to symmetrical oscillating plates with respect to the nozzle center line, and the another is due to antisymmetrical oscillating plates with respect to the nozzle center line. The oscillation frequency was two orders of magnitude smaller than the fundamental frequency of the velocity fluctuation. The mixing layer was more expanded due to the disturbance introduced by the oscillating plates. The growth of turbulence was promoted due to the plate oscillation. The difference of oscillating motion did not affect the mixing layer downstream. The velocity fluctuation in the antisymmetrical oscillating mode was larger than that in the symmetrical oscillating mode.

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In order to develop a new mixing procedure, we conduct DNS (direct numerical simulation) of vector control for free jet. A nozzle is rotating around the streamwise axis of jet. From view of instantaneous vortex structures, it is found that the structures are modulate, compared with the case of the free jet. In contours of ensemble averaged streamwise velocity, the jet diffuses largely in the radial direction. In addition, in order to estimate the mixing performance, the statistical entropy is calculated. It is found that the mixing efficiency are improved than that of uncontrolled case. Further for a candidate case of vector control, a structural mode analysis is conducted with both POD(proper orthogonal decomposition) and DMD(dynamic mode decomposition). It reveals that a dominant mode structure which is governed with the rotating frequency of vector control, seems to contribute to the mixing enhancement downstream.

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Active control of a rectangular jet has been attempted to manipulate the vortex shedding interval in the major shear layer. It is considered essential that the vortex distribution along the each major shear layers plays an important role to characterize a rectangular jet behavior. In the present investigation, it was remarkably observed that the jet spreads more widely in the minor direction and contracts more greatly in major direction by the asymmetric excitation than that of the non-excited jet. The measurement results showed that the coherent vortices are generated in synchronization with the excitation frequency and the pattern. In addition, it was revealed that the inclined vortex rings are formed and interacted with each other only when the jet was excited by asymmetric mode.The jet spreading is attributed to the tilting alignment of the vortex ring, and the jet contracting in minor direction is due to the self-induced deformation of the rectangular vortex ring.

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The spatial development of vortices in a subsonic mixing layer which have wake components is investigated numerically using two-dimensional direct numerical simulations (DNS). The mixing layer is formed by a thin flat plate and forced by normal velocity disturbances of various frequencies at the lower region of the flat plate trailing edge. The numerical results show that the growth of the disturbance induces the counter-rotating vortices in the wake like region of the mixing layer. It is found that the vortices caused by the disturbance of the frequency St=0.042 uppress development of the mixing layer. This frequency corresponds the dominant vortices period in the near downstream region of the trailing edge for non-disturbance case. This result suggests that the emission noise caused by vortex rollup or pairing in the mixing layer can be reduced by forcing with a disturbance at the lower region of the flat plate trailing edge.

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In the present numerical study, we investigate the oscillatory control on a two-dimensional bi-stable jet discharged from a flip-flop nozzle. Oscillating jet can be used to flow control actuators but the oscillatory frequency of the nozzle has a significant dependence on the geometric configurations of the nozzle such as the length and volume of the feedback tube and the entrance pressure. On utilizing this jet as flow control actuators, it would be desirable to be capable of switching the oscillatory frequency of the jet without modifying the nozzle configuration. We conducted DNS of the oscillating jet at Re=100. At first, the pressure difference across the deflected jet and the oscillatory frequency f_0 which is proper to a given nozzle configuration were investigated using the periodic boundary condition on the control ports of the nozzle. Then we computed the jet using pressure boundary conditions instead of the periodic one. Depending on the input pressure ratio, when the ratio of the input pressure frequency f_<in> into f_0 was less than unity (f_<in>f_0=0.48), it was found that the oscillatory frequency of the jet could be rocked in f_<in>.

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A synthetic jet is one of flow control devices that can topologically disturb flow field. It can be applied to downsized fluid machinery without a net mass injection for its simplified structure. The study provides quantitative classification of vortex regimes of synthetic jet in quiescent fluid. The vortex structure was measured by scanning stereoscopic PIV. The Stokes number S and non-dimensional length of strokes L were used as evaluation parameters. According to the vorticity distribution, vortex rolls more neighboring fluid when S and L are large. No jet regime is defined as the case that a ratio of maximum velocity at suction phase to maximum velocity at njection phase is smaller than 0.05. Vortex roll up regime is defined as the case that the distance between the vortex centers of ring vortex by jet orifice diameter D (= 1.0 mm) is larger than 1.1. Without vortex roll up regime is middle region between No jet and Vortex roll up. Consequently, a parameter map of vortex regimes of synthetic jet as functions of S (= 6.3 〜 12.7) and L(= 0.25 〜 10) is obtained.

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