We performed direct numerical simulations (DNSs) of turbulent boundary layer flows with the wall injection of Newtonian and viscoelastic (FENE-P) fluids in order to distinguish the effects of drag reduction due to the high-speed wall injection and viscoelastic effect. The high-speed wall injection within the viscous sublayer parallel to the wall was simulated by imposing uniform velocities, which were 1, 2, and 3 times larger than the free stream velocity. We clarified the effect of wall injection of Newtonian and viscoelastic fluids via the investigation of streamwise variations in the drag reduction ratio and mean velocity profiles.

We present two-dimensional incompressible direct numerical simulation of the suppression of open cavity flow oscillation by using leading-edge microjet blowing. The cavity aspect ratio L/D is 2.0, where D is the cavity depth and L is the cavity length. The width of microjet that is located at just below the cavity leading edge is 0.01D . The velocity of microjet is varied from 0.0 to 1.0 at 0.1 intervals. As increasing microjet velocity from 0.0 to 0.2, the amplitude of selfsustained oscillation decreases. The self-sustained oscillation is completely suppressed when the microjet velocity is from 0.3 to 0.5. The cavity shear layer oscillates again when the microjet velocity is 0.6 or higher.

For energy efficiency, flow control techniques for the skin-friction drag and the heat transfer in a wall-turbulence are essential issues. Due to the strong analogy between momentum and heat transfers, it is difficult to obtain the simultaneous achievement of the skin-friction drag reduction and heat transfer enhancement. The control, which achieves simultaneous reduction of frictional resistance and enhancement of heat transfer, is called as dissimilarity control. In this study, we perform direct numerical simulations of the turbulent channel flows controlled by the traveling wave-like body force. The traveling wave control mimics the self-excited thin film in the corresponding experimental study. When the wave travels slower than the mean bulk velocity in the downstream direction, we found increase of the skin-friction drag, the heat transfer, and the analogy factor. The vortical structures are significantly promoted and increased. In addition, the results of the parametric study imply that the upstream traveling wave has a potential to induce the dissimilar control effect, i.e., reduction of the skin-friction drag and enhancement of the heat transfer.

Drag reduction effect of travelling wave control for turbulent boundary layer flow is measured by laser doppler velocimetry (LDV). Travelling waves are generated on a rubber sheet by oscillation of a piezoelectric actuator. Experiment apparatus is consist of 1.5 m of run up section and 1 m of testing section where the rubber sheet is installed. Experiment is carried out in the condition of mainstream velocity U_∞ = 3m/s, and momentum thickness-based Reynolds number Re_θ ~ 1500 at the center of the testing section. Friction drag coefficient C_f is calculated by integrated velocity distribution within 3% of uncertainty.

Performance of bubbly drag reduction (BDR) can be improved by repetitive bubble injection (RBI) which provides spatiotemporal fluctuation of local void fraction, termed void waves, to enhance momentum exchange between turbulence and bubbles. The interaction has a variety of time scale as multiphase turbulent flow, and the optimal frequency for RBI has not been clarified to date. We measured temporal change of Reynolds shear stress profile in a horizontal turbulent channel flow when bubble injection was suddenly stopped, i.e., the step response of BDR. The results obtained by particle tracking velocimetry revealed a significant overshoot of the stress before returning to the state of single-phase flow.

Experimental investigation was conducted on heat transfer enhancement in a vibrating pipe flow with blades. The test section is located at the end of a larger pipe to simulate a transition from turbulent to laminar flow as a consequence of a sudden change of the diameter. The friction drag coefficient C_f, which correlates with the heat transfer, is estimated by differential pressure measurement. The test section has blades inside the pipe to induce the secondary flow by the vibration control. The parametric study of the present experiment focused on blade angle. As a result, the rate of increase in C_f increased by decreasing blade angle.

It is well known that fine bubbles have excellent washing properties. Although this property has been applied to a variety of products and technologies, the mechanism has not been clarified. To clarify it, we conducted a washing experiment using a solution containing microbubbles. The size of the bubbles was 100 nm in average particle diameter. an ultrasonic washer was used for washing. The washing target was beef tallow, which is an oily dirt. To compare the amount of dirt before and after washing, fluorescent particles were mixed into the beef tallow. By irradiating the dirt with UV light, the amount of contamination can be evaluated. The results before and after washing were compared, as well as the size and number density of the bubbles. The experimental results showed that the solution containing fine bubbles had better washing performance than purified water. This improvement was noticeable in the early stages of cleaning.

In ball games, a changing ball is one of the factors that determine a game, and in soccer, a knuckling ball in which the ball changes irregularly is attracting attention. Research has been conducted on the surface structures of the sphere and the ball, but the aerodynamic characteristics at low rotation and the aerodynamic characteristics of the sphere and the surface structure, which are irregular orbits, have not yet been clarified. Therefore, the purpose of this study is to clarify the relationship between the surface structure of a soccer ball and a knuckling ball. First, the groove volume is measured using various official balls. After that, a drag measurement experiment at no rotation and low rotation by a wind tunnel experiment and a flight trajectory simulation were performed.

We investigate the drag reduction effect of uniform blowing (UB) on the pressure surface of the airfoil by wind-tunnel experiments. The experiments are performed using a Clark-Y airfoil model. The UB is conducted by supplying air to a chamber in the airfoil model covered with porous material using an external compressor. The blowing region is installed near the leading edge of the pressure surface of the airfoil. To investigate the effect of UB on the friction drag, the velocity distribution in the boundary layer is measured using a hot-wire anemometer, and it is confirmed that the distribution shifted away from the airfoil surface by UB. Quantitative evaluation using the wall law shows that the local friction drag is reduced up to about 51% under the experimental conditions of the angle of attack α = 0° and the Reynolds number based on the chord length Re_c = 0.65 × 10⁶ and UB at 0.33% of the free-stream velocity. In addition, pressure measurements performed in the wake of the airfoil qualitatively confirm that the velocity deficit is reduced by UB on the pressure side of the airfoil, qualitatively resulting in up to 5.4% reduction in the total drag, although, the measurement uncertainty is found to be on the same order as the total drag reduction rate.

The feedback flow control has the potential to significantly improve the performance of fluid machinery. However, due to the nonlinearity of the flow, it is difficult to construct the control law analytically. In previous studies, the feedback flow control system utilizing Deep Reinforcement Learning is successfully applied to the flow separation control over an airfoil in wind tunnel experiment to suppress the detached flow. In this study, the effect of penalty proportional to the applied voltage in the reward for the learning is investigated, and the control policy achieving higher energy efficiency is successfully obtained. The results show that variation of the penalty amplitude changes the control policy obtained in the learning. In the case of small penalty, the system successfully achieves the suppression of flow separation by lower voltage continuously. On the other hand, when the penalty is increased, the system periodically turns the Plasma Actuator on and off for reducing the consumption power.

Recently, plasma actuators have been attracting attention as devices for controlling fluids such as water and air. This device generates a fluid flow by electricity. The purpose of this study is to develop a fluid control device with a simple structure and versatility. In this study, the focus is on a corona discharge plasma actuator, which has high durability. The flow field and current values were investigated by experiments, and the flow field and electric field were investigated by numerical analyses. A flat plate and a wire electrodes were used as cathode to investigate the effect of electrode shape. A wedge electrode is used as anode. In the experiments, the induced flow is measured by PIV (Particle Image Velocimetry), and current value is also measured by a digital multimeter. PIV was performed on several cross sections to obtain the spatial velocity distribution. In the experiment, it was found that the flow velocity was faster for the flat electrode than for the line electrode. From the numerical analysis, the maximum electric field strength was obtained at the tip of the wedge electrode. On the other hand, the strong electric field was not concentrated at the flat and wire electrodes. Moreover, it was found that the flow spread from the tip of the wedge electrode.

The objective of this study is to numerically investigate the effect of multiple encapsulated electrode configurations on the body force generation in plasma actuator. As a result, the amount of body force generation and the efficiency are improved by providing gaps in the encapsulated electrode. It is considered that the change in the surface charge causes local enhancement of electric field and that leads to the enhancement of the body force generation.

Weakly nonlinear propagation of focused ultrasound in liquids containing many spherical microbubbles is theoretically and numerically investigated, especially focusing on the thermal conductivity of gas inside bubbles toward medical applications such as HIFU treatment. A Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation for the weakly nonlinear propagation of quasi-plane waves in pure liquid has been widely used as the mathematical model for HIFU treatment. Our previous study [Kagami & Kanagawa, Jpn. J. Multiphase Flow, 35(2) (2021), 346] derived a KZK equation for bubbly liquids incorporating the thermal conductivity of gas inside bubbles by utilizing the energy equation for gas inside bubbles and then we found that the thermal conductivity strongly contributes the dissipation effect, however, basic equations based on the mixture model of bubbly liquids were used. In the present study, a KZK equation incorporating the thermal conductivity of gas inside bubbles is re-derived by using basic equations based on the two-fluid model of bubbly liquids. Furthermore, we numerically solve the newly obtained KZK equation, and we then found temperature rise near the focus.

Bubble ring is a well-known phenomenon such as a belga can produce a single bubble ring and, also, separate it to two rings, etc. To clarify the cause of stable durability, we studied on the flow structure of bubble and ordinal vortex ring. An axisymmetric two-dimensional numerical simulation was conducted in terms of ordinal vortex ring and three kinds of bubble rings in the conditions of same initial flow field. As a result, the flow filed of bubble ring transit to free vortex structure from the arbitral initial condition immediately. It was deduced that bubble played a role of a singularity, and it leads to stable movements of bubble ring. Afterwards, the temporal circulation was estimated to evaluate viscous loss. The circulations of bubble rings were higher than vortex ring. This result is attributed to the dissipation near the bubble-water interface.

In this paper, control of the motion of oil droplets in an O/W (Oil-in-Water) emulsion by electric field is attempted. To move the oil droplets by electric field, the surface of oil droplets was negatively charged by anionic surfactant (sodium dodecyl sulfate). The emulsion with these oil droplets flows in an acrylic channel. Electric field (3V) was applied from electrodes placed on both side of the channel. Accordingly, the oil droplets were attracted to the anode side by the electric field and flowed in the channel. As a result, the droplets flow in the region close to the anode. Anode direction velocity of oil droplet is measured by PTV. The channel bifurcates at downstream of the electrodes. These oil droplets flowed evenly through the branch when no electric field was applied from electrodes. Number of oil droplets guided through one side (anode side) of the branch were increased when electric field was applied from electrodes. On the other hand, it decreased when Reynolds number (flow velocity) increased. Anode direction velocity was independent of the Reynolds number.

In manufacturing processes using liquids, such as cleaning, painting, and gluing require to fill the inside of the pores on the product surface with liquid. However, the surface tension prevents interface deformation and causes difficulty filling the liquid for small pores closed at one end. In this study, we observed the gas discharging process from the pores by irradiating acoustic waves. First, we found a correlation between the amplitude of the interfacial oscillation and the gas discharging, suggesting the importance of the volume oscillation of the gas column. The three important factors for gas discharging were the bubble and droplet generation from the gas-liquid interface and liquid film formation along the wall. Besides, these phenomena easily occurred in the ethanol, where the surface tension was small. Finally, we found enhancement of the coalescence and ejection of the bubble by irradiating the natural frequency of the bubble when a breakup bubble remained in the pore.

Various industrial processes use droplet impingement phenomena, for example, two-phase flow jet in semiconductor cleaning, inkjet method in producing organic EL display, and more. For that, researchers extensively study droplet impingement onto a solid surface. Although a general experimental method is a time-resolved visualization with cameras, long-time and high-speed recording are incompatible. Therefore, we newly developed a droplet detection method with a Film-based Optical Waveguide (OWF). The OWF is a thin and flexible film that has multi-microsensors for gas-liquid phase detection. In this study, we investigated the OWF signals delivered during the measurement of the droplet (d=2.9mm) impact. Time delays for liquid phase detection among the sensors appear, which we can use to estimate radial velocity during the droplet impact with deformation. Moreover, a characteristic peak emerges when the sensor detected a vicinity of the droplet center. These results imply that the OWF can measure the extremely high-speed local surface motion of the impacting droplet.

The flow past an archery bare-shaft arrow was numerically studied for the angle of attack, α, in a range of 0-3.0 degrees. The Reynolds number, Re, based on the arrow diameter was varied as 10000, 15000 and 20000, and the length of the shaft was fixed at about 120. Two kinds of arrow point, S-type and B-type, were adopted. The numerical result showed that the boundary layer flow on the shaft was steady for Re=10000 and 15000 at α=0 degrees for both types of arrow point. For S-type point at Re=15000, it was steady up to α=0.6 degrees and unsteady for α ≧ 0.8 degrees. Within this range of α, the drag and lift of the arrow was found to be in good agreement with wind tunnel experiment.

Flow visualization experiments with smoke and particle image velocimetry are conducted to investigate the characteristics of tornado-like swirling flow generated by a tornado-type remote suction device. The experimental parameters controlled in this flow are configuration of the rotating disk and rotation number. The results obtained are as follows. Swirling flow with cap-shaped rotating disk is stronger than that with flat rotating disk. In addition, outer fins attached on cap-shaped rotating disk strengthen the flow generated by rotating disk. The larger the degree from horizontal plane of cap-shaped rotating disk is, the stronger the swirling flow generated by the disk becomes. Proper balance of upflow and swirling flow is required to generate stable tornado-like swirling flow. Under the condition of tornado generation, the tangential velocity component of tornado becomes larger for smaller disk angle from horizontal plane.

Demand for corrugated cardboard boxes has been increasing in recent years due to the expansion of the logistics market and restrictions on outings associated with global measures against infectious diseases. Our company is developing a carton making machine that can make corrugated cardboard faster than before. The flow field in the box making machine was reproduced by CFD, and the motion of the corrugated board was modeled by MBD (Multi Body Dynamics), and the Two-way coupled analysis model was constructed. The flight behavior of the corrugated fiberboard sheet can be predicted without trial manufacture using the construction model. In addition, it became possible to study the operation method and derive the optimum set value by parameter study.

Due to global COVID-19 pandemic, environmental control system design for building and mobility products would be increasingly demanded to ensure comfortable indoor environments, and to ensure the effective biological contamination control. In this paper, 3D simulation tool is introduced to address such brand-new needs by coupling CFD with epidemiological model. The characteristics of anti-activation function was mathematically modeled and incorporated into the coupled analysis. A trial analysis in an office with air-conditioning system showed that 92% infection risk reduction was realized before and after the anti-activation on the air-conditioning. With the developed tool, space design such as HVAC system layout can be proposed to satisfy contamination safety as well as thermal comfort by quantifying and visualizing the change of contamination propagation and infection risk distribution.

A design concept for suppressing the leading edge separation and tip leakage flow is introduced in order to improve aerodynamic performance of a transonic centrifugal compressor. The aerodynamic design method used in the present study is an inverse design method based on a meridional viscous flow analysis. As the design concept, the blade loading distributions at the leading edge are reduced to decrease the incidence angles. In addition, the peak of the blade load at the mid-chord of the full blade causes the second tip leakage vortex and tip leakage flow at mid-chord. On the other hand, tip leakage flow around the trailing edge is suppressed and aerodynamic performance is improved. The effectiveness of the design concept was evaluated by three-dimensional Reynolds Averaged Navier-Stokes simulations. The performance improvement was observed in the redesigned impeller compared with the conventional design impeller.

Centrifugal compressors for automotive turbochargers are operated under conditions with unsteady cyclic pressure pulsations caused by intake and exhaust of the engine. Because of its complexed unsteadiness, it is not fully revealed how internal flow fluctuates under such conditions, especially in stall or surge condition.

In this paper, the time variation of the internal flow angle was quantified by unsteady analysis which utilized a measured pressure pulsation of as a boundary condition. As a result, it was found that the 0 ~ 60% span at the leading edge of the impeller shows little time variation, but that remarkable unsteadiness appeared at 60 ~ 100% span, and it leads the tip stall.

The ensemble kalman filter(Enkf) is combined with one dimensional surge model in order to improve accuracy of one dimensional surge model. In addition, flow estimation of surge is tried by this method. The analysis object of this research is a centrifugal compressor for turbocharger, which is composed of unshrouded impeller, vaneless diffuser, scroll. Experimental setup consists of a screw compressor as a power source, a turbocharger, variable capacity plenums, measurement pipes, other pipe systems. Data assimilation use unsteady pressure data measured upstream and downstream of the compressor was assimilated. The compressor performance curve for one dimensional surge model is obtained from steady measurements and three dimensional Reynolds Averaged Navier-Stokes simulations. As a result of the application of Enkf to one dimensional surge model, maximum pressure rise at surge quantitatively agrees with experimental results. However, the experimental results were not reflected in the velocity upstream of the compressor. It is possible to improve the accuracy of one dimensional surge model by applying Enkf.

In the radial turbine used for marine turbocharger, the collision of combustion residue particle contained in engine exhaust gas causes turbine blades erosion. However, there are many unclear points in the flow mechanism. In this paper, we evaluate the particle behaviour in the radial turbine based on lagrangian particle tracking method. As a result, the possibility of explaining the turbine erosion phenomenon by the particle adhesion rate of each part was obtained. At the leading edge of the turbine blade, the impact of particles with large inertia which are difficult to follow the air flow was found to be the cause of erosion, and it was confirmed that turbine design including particle behaviour was possible.

The energy loss of the airflow generated by forced convection in the cooling system included in heavy construction machinery is due to friction and turbulence in its ventilation path, and its behavior is three-dimensional. Therefore, computational fluid dynamics (CFD) is effective in clarifying the three-dimensional energy loss mechanism, but there are few reports that three-dimensionally capture the flow field in the cooling system of construction machinery, especially including some components around the axial fan. In this study, the flow field of the entire cooling system was visualized by numerical simulation using ANSYS-CFX17.0, and the effect of the three-dimensional flow field formed around the blades of the axial flow fan on the fan performance was investigated. From the results of CFD analysis, the fan performance is inferior in the case of the axial fan only than in the case of the entire cooling system, which is consistent with the blockage effect of the wing tip leakage vortex limiting the air flowing into the impeller. The wing tip leakage vortex is large-scale and has a high vorticity, and is divided into leading edge of adjacent blade because it flows in the tangential direction while maintaining the same height as the wing tip.

A ship's side thruster is a device that can provide thrust to the left or right in relation to the ship's direction of travel through the rotation of a propeller installed in the device, enabling a significant increase in the degree of freedom in ship operation. While most propellers are used for rotation in only one direction, the thruster is a device that can be used for both forward and reverse propeller rotation. And it has a shaft case that supports the propeller cantilevered inside the device. Therefore, it is important to improve the thruster performance based on its internal flow. However, there are few studies that focus on the internal shape of the propeller and other components of the thruster, and the relationship between the internal shape and performance has not been fully clarified. In this study, we focused on propeller solidity and the blade number, which are parameters that greatly affect the performance of thrusters, and investigated their performance characteristics and internal flow using computational fluid dynamics analysis. The performance characteristics and internal flow of the thruster were investigated by numerical fluid dynamics analysis. From the performance characteristics during forward and reverse rotation, the optimum solidities and number of blades were clarified.

The diffuser rotating stall(DRS) is one of the biggest problems in pumps because unstable flow and pressure fluctuations are induced and the pump operating range is severely limited. However, it is difficult to quickly predict the flow rate of the DRS onset. The authors had already confirmed that the flow rate of DRS onset is shifted to lower flow rate by slitting the diffuser vanes in the experiment of previous research work. However, the optimized slit shape has not been sufficiently studied yet. In the previous study, the effect of the slit on the internal flow and the qualitative mechanism for suppressing the DRS were verified by unsteady RANS(Reynolds Averaged Navier Stokes) calculations. We also suggested a simple prediction method of diffuser rotating stall onset using steady state numerical simulation, and examined the evaluation function effectiveness for optimizing the slit shape. In this study, a multi-objective optimization with a simple prediction method of DRS onset using steady state numerical simulation was conducted for the slit width as a single design parameter. The effect of the slit on the pump performance and internal flow was investigated in order to refine the DRS suppression method.

Generally, cavitation develops as the cavitation number decreases. However, on NACA16-012 hydrofoil, once occurred cavitation disappears despite of in low cavitation number condition. This phenomenon was called as cavitation disappearance phenomenon. In previous study, Franc and Michel reported that cavitation disappears at the angle of attack where the laminar separation point and transition region move from the rear to the front of the hydrofoil. Between two consecutive turbulent spots, the boundary layer is laminar, and a sheet cavity can develop locally for a short time, before being swept out by the next turbulent spot. Our research group confirmed that cavitation disappearance phenomenon was unique to NACA16-012 hydrofoil, the pressure distribution was different under disappearance condition from under non-cavitation condition despite of the same single-phase flow, and the short bubble was instability at the angle of attack where cavitation disappearance phenomenon occurs. It was considered that the boundary layer changed to one which cavitation did not occur due to some effect. In this study, for the purpose of investigating the relationship between cavitation disappearance phenomenon and the boundary layer, the boundary layer was experimentally investigated. As the experimental apparatus, low-turbulence heat-transfer wind tunnel installed at Tohoku University was used. Normally, the cavitation tunnel should be used, however the size of hydrofoil was too small to accurate measure, therefore the wind tunnel was used. NACA16-012 airfoil with the chord length of 200 mm and the span length of 1400 mm was used. The experimental conditions were set to mainstream velocity of 36 m/s, temperature of 16 ℃. Oil film method was used to visualize the boundary layer. As the results, the angle of attack where cavitation disappearance phenomenon occurs corresponds to onset of the short bubble. This tendency is consistent with the results of Franc and Michel in 1985. Therefore, it was suggested that onset of the short bubble related to cavitation disappearance phenomenon.

In this study, targeting the cavitating flow around a Clark Y-11.7% hydrofoil, the unsteady RANS simulation using Multi-process model which is a homogeneous model considering the main elementary processes of cavitation bubbles was carried out. Besides, simulations using Singhal’s full cavitation model were also conducted. As a result, there existed no remarkable difference in the time-averaged lift between the two cavitation models; the lift was under-estimated similarly as other homogeneous models. However, the time-averaged pressure distribution on hydrofoil surface computed by Multi-process model showed better qualitative agreement with experiment than Singhal model. This is probably because the unsteady behavior of cavity was simulated quite differently by each cavitation model.

Cavitation in fluid machinery can cause several problems such as degradation of performance, damage by erosion, structural vibration and noise. Therefore, the development of prediction methods for cavitation flow is an important research topic, and several cavitation models for CFD have been proposed. The multi-process model used in this study is a homogeneous bubbly flow model that can take account of main elementary processes in cavitation using the moment method. In addition, the model can indirectly represent information of the size distribution of bubbles. In this paper, unsteady RANS simulation using the multi-process model was carried out on final stage model of multi-stage centrifugal pump. As a result, it was possible to qualitatively simulate the change in pump suction performance under cavitation. Additionally, it was indicated that the model can represent the polydispersity of bubble in the pump. Thus, it was confirmed that the model can be applied to fluid machinery as the prediction method although the quantitative validation has been under consideration.

Pumps are widely used in the industrial field and are expected to be applied to the fuel cells, medical devices and electrical devices in recent years. The two types of centrifugal pumps that are the subject of this research have the same specific speed as general centrifugal pumps. Conventionally, the disc friction loss is not important in the centrifugal pump in this specific speed range, but this pump is characterized by its small size and open type. Therefore, it is expected that the effect of disc friction loss on performance will change compared to the conventional centrifugal pump in the same specific speed range. Then, the purpose of this research is to focus on the disc friction loss of these two types of centrifugal pumps and to seek a method for reducing them. Eventually, I would like to establish the method for reducing disc friction loss that can be used for centrifugal pumps in the low specific speed region with a specific speed of 100 or less. In this paper, for two types of centrifugal pumps, I created the model of only the back shroud without blades of each pump. For the model, I performed Computational Fluid Dynamics to calculate the ratio of disk friction loss power to shaft power and to investigate the internal flow.

The friction loss acting on a rotating disk for flows in a narrow clearance was investigated by the experimental and computational method. We used the experiment apparatus simulating a clearance flow between a rotating impeller and a stationary casing in centrifugal pumps. The CFD analyses were carried out to evaluate the adequacy of experimental results. The friction torque could be evaluated by the Reynolds number considering not only the disk rotational speed, but also physical property due to temperature change of working fluids. Additionally, it was noted we could minimize the friction torque by choosing optimum value of disk clearance width which differed depending on the flow direction.

In this study, flow field which caused by temperature-sensitive magnetic microcapsules with temperature difference and magnetic field investigated. The temperature-sensitive magnetic microcapsules containing the temperature-sensitive ferrofluid and fluorescent dye were created by the in-liquid drying method. In this experiment, temperature-sensitive magnetic microcapsules were dispersed in water and injected into the visualization channel to visualize the flow caused by the magnetic field. The visualization channel is made of aluminum alloy and glass, and a temperature difference was formed by heating and cooling with a Perche element installed in the channel. Capturing a fluorescence image of the microcapsules when irradiated with laser in the channel, the velocity field of the flow field of two types with and without the temperature difference was visualized by PIV software. When a magnetic field was applied so that there was a difference in magnetic field strength in the channel, magnetic convection was observed. The magnetic convection also observed when there is a temperature difference, an increase in flow velocity due to thermal magnetic convection was confirmed. In addition, clusters were formed near the wall surface of the flow path, and it was observed that they moved along the wall surface. The moving speed of this cluster also increased due to thermomagnetic convection.

Cellulose Nano-fibrils (CNFs) are the fundamental building blocks extracted from wood fibers and have gained great attentions as a novel biological material. It is known that the outstanding mechanical properties of cellulose filament made of CNFs can be obtained with their orientation inside the filament. In this study, the effect of CNF pre-aligning by electric field and the flow rate ratios of the two sheath flows on the orientation of CNFs during flow focusing process are clarified with correlating to the enhancement of mechanical properties. Results clearly show that the CNF orientation can be controlled both by the flow rate ratio and the electric field with enhancing the mechanical properties of the fabricated filaments. The improvement of their ultimate tensile strength and elastic modulus can be obtained by increasing the flow rate of one of the sheath flows under the fixed total flow rate. The electric field assisted alignment effectively enhances the mechanical characteristics of the filament for any flow rate conditions.

Cellulose Nano-fibrils (CNFs) are the fundamental building blocks of wood and paid special attentions because of their outstanding mechanical and thermal propeties. The mechanical properties of cellulose filament made from CNFs can be improved by their orientation control. In this study, the complex behavior of CNFs in the elongational flow and electric field were clarified by solving the equation of motion for indivisual CNFs. When the electric field of 700 V/cm is applied for 1 μm CNF in the upstream of flow focusing point, the CNF order parameter increases from 0.15 to 0.33 between the electrodes and then decreases to 0.26 by Brownian rotation at 5 mm downstream of the electrode. The CNF order parameter increases by injection of sheath flow and separation of CNF dispersion from the wall. The maximum order parameter of 1 μm CNF increases from 0.45 to 0.52 in the elongation flow with upstream electrostatic alignment.

In the wind turbine performance test, a meteorological mast about the height of the hub is installed 2.5 times the rotor diameter upstream from the wind turbine. However, in recent years, wind turbines have become larger and the construction cost of Meteorological mast has increased. Therefore, we devised a technology to estimate the inflow wind speed by measuring the pressure with a pressure sensor mounted on the spinner of the wind turbine and converting it to the wind speed. This technology has the advantage that it can be performed at a lower cost than the existing inflow observation technology. The purpose of this paper is to clarify the pressure field on the surface of the spinner by CFD analysis and to propose an accurate inflow wind observation technique by proposing an appropriate sensor arrangement. The analysis target was a 3-blade upwind horizontal axis wind turbine with a rotor radius of 0.8 m, and the analysis software was OpenFOAMv1912. As a result, with the proposed sensor arrangement, the wind speed estimation error was less than 1% when the yaw angle was within 15 degrees. In addition, the wind speed estimation error was less than 2%, even considering the temporal pressure fluctuation due to the electrical noise of the sensor.

In this study, field experiments were conducted with the aim of clarifying the range of influence of the wake of a straight-blade vertical axis wind turbine under unsteady natural wind conditions. In the experiment, a test vertical axis wind turbine with a rotor diameter of 2 m and a bladespan of 1.2 m was operated and the wake of the wind turbine was observed up to 3 times the diameter of the rotor. The wind direction and the wind speed distributions in the wake was investigated using three-dimensional ultrasonic anemometers installed in the downstream area. The spatially discrete wind directions and wind speeds obtained in this field experiment were quantitatively evaluated by a wake model expressed in a Cartesian coordinate system. In addition, each parameter value of the wake model was expressed as a function with the wake position, and the range of influence of the wake of the vertical axis wind turbine was estimated. As a result of the experiment, the asymmetry of the wake of the vertical axis wind turbine was confirmed, and the wake recovery distance for each peripheral speed ratio could be obtained.

A performance of a gyro-mill wind turbine whose rotating blades with deformable flaps is experimentally clarified. Main blade part is made by an aluminum thin plate and blade shaped foamed styrol. Experiments are performed not using wind tunnel but using 6 fans in a room. The effect of deformable flaps and shapes of the main blades are clarified.

The effect of the lift force of an upstream airfoil used in the horizontal axis wind turbine in set of a cruciform downstream flat plate was examined by using experiments and numerical simulations. In the wind tunnel experiments, it was clarified that the lift force acting on the airfoil increases depending on the angle of attack of the airfoil and the distance from the flat plate. The analysis of the flow field revealed that at the angle of attack of the airfoil where separating occurs from the leading edge, reattachment is induced by sucking the flow separated by the Necklace vortex formed on the upper surface of the airfoil. In an experiment in which the ring plate was installed behind the small horizontal axis wind turbine, it was confirmed that the power coefficient increased when tip speed ratio was small.

The blade-install-position of a lift-type vertical-axis wind turbine (VAWT) is theoretically set at the aerodynamic center (25%c). However, some practical VAWTs often select the center of mass of a blade cross section as the install-position or the other position. This study analyzes the effects of the blade-install-position on the performance of two-bladed VAWTs by two-dimensional computational fluid dynamics (CFD). Two turbine rotors with the diameter D = 10 and 2 m are selected as the numerical models. The blade-install-positon defined by x_install / c ×100 (x_install is a distance from the leading edge) is set at five values of 0, 25, 50, 75, 100%c for each rotor (chord length : c = 0.4 or 0.2 m) under the condition holding a constant pitch-angle of 0°. In the case of a large rotor (D = 10 m), the optimum tip speed ratio (TSR) is about 4.5; and the blade-install-position does not affect the output performance greatly at the optimum TSR or more. In the case of a small rotor (D = 2 m), the optimum TSR is about 3; and the blade-install-position gives a great influence on the turbine performance around the optimum TSR. The change in the blade-install-position gives rise to the effective pitch-angle even when keeping a constant geometrical pitch-angle. The difference of the influence of the blade-install-position on the performance between the large and small rotors can be attribute to the difference in the ratios of the chord-length to the rotor diameter of both turbines (c/D = 0.04 and 0.1).

When a circular cylinder is used as the blade of a horizontal axis wind turbine and a ring-shaped flat plate is installed in the wake, the longitudinal vortex shedding from near the intersection generates a steady lift force on the cylinder. In this study, the relationship between the flow field around the blade and the power characteristics of a longitudinal vortex wind turbine is discussed based on the results of numerical simulation. The relative angle of attack of the main flow to the cylindrical blade was adjusted according to the rotational speed of the blade. It was confirmed that the torque obtained by the cylindrical blade increased in a specific range of the relative angle of attack by controlling the separation point.

For both a Butterfly Wind Turbine (BWT) and a straight-bladed vertical-axis wind turbine (SB-VAWT, i.e. H-Darrieus wind turbine) assumed having two blades, the same rotor-diameter (D = 750 mm), and the same rotor-height (H = 500 mm), the three-dimensional computational fluid dynamics (CFD) analysis was carried out mainly focusing on the wake recovery. This study shows that the wake recovery of the BWT rotor tends to be faster than that of the H-Darrieus rotor and that the power of the former can be higher than that of the latter. In addition, the positive effects of the blade inclination (twist angle) of the BWT rotor and the rotation-axis inclination of the H-Darrieus rotor on the wake recovery are illustrated.

Previous studies have shown that installation of a symmetrical casing that is adapted to the prevailing wind with two wind directions for a crossflow wind turbine improves performance. The symmetric casing utilizes the depressurization effect of the separating vortex to increase the flow rate into the impeller, and the flow field is extremely complex, so capturing the flow in a numerical analysis is necessary to improve performance and clarify mechanisms such as loss generation. However, quantitative evaluation of performance characteristics using RANS has not been possible at present. In this study, the numerical conditions were investigated to reproduce the flow around the wind turbine accurately by making the best use of the experimental results, because the improvement of the accuracy of numerical analysis is considered to be the key to reproduce the complicated flow. As a result, it was found that the velocity difference at the inlet of the impeller was expressed as the power difference of the cross-flow wind turbine, and the performance did not match between the experiment and the analysis. It is considered that the strong shear between the main flow from the wind tunnel outlet and the surrounding fluid has a significant effect on the flow field from the wind tunnel outlet to the impeller.

In an offshore wind turbine of the floating type, when the floater tilts due to waves, the axis of rotation of the wind turbine is also inclined to the wind. The inclination of axis may decrease the output because the effective flow velocity is reduced. On the other hand, the inclination may increase the output because a part of the downstream blade passes through a region that is not affected by the upstream it. Therefore, the purpose of this study is to clarify the effect of inclination of axis on the output characteristics of a small wind turbine. From the results in the case of low solidity turbine, the output characteristic shifts to the high tip speed ratio and the maximum value of it decreases, but it does not depend on the inclination direction. From the velocity profiles, it was observed that either the upper or lower part of the wake has a characteristic of low solidity turbine. Since this feature is symmetrical with respect to the inclination direction, the output characteristics does not depend on the inclination direction.

Recently, renewable energy attracts attention due to the concern about the global warming. Among them, small hydropower is expected because it has an extremely large amount of energy and a high operating rate. Although small hydropower is already widespread, there is a problem that there is a limit to the installation place and the environment load is relatively large for the small hydropower over 10kW. Therefore, we focused on pico hydropower generation less than 1 kW, which can be applied to pipelines of agricultural water and fish farm and has a low environmental load. However, pico hydropower generation has problems of lower efficiency than large one. In this research, we use a contra-rotating rotor that can generate electricity efficiently by rotating two rotors in opposite directions for high performance. In previous research, suitable design parameters for contra-rotating small hydroturbines were investigated, and the possibility of higher performance was shown. Therefore, this research is on the verification stage in field experiments. First, we investigated the head, flow rate, and water quality of the field and obtained the potential. Next, we determined the design parameters, designed the turbines, and examined the feasibility by unsteady numerical analysis. Furthermore, we made a generating equipment and conducted power generation experiment in the field. As a result, it was analyzed that this hydroturbine has sufficient power generation performance, and 689 W power generation was realized in the field experiment.

Cross-flow turbine is widely used in run-of river type small hydropower stations because of its excellent partial load characteristics with cheap manufacturing cost. The authors proposed the cross-flow turbine with a guide wall and cylindrical cavity that controls the outflow direction from the runner. The outflow separates locally at the guide wall top in a partial load operation, and vibration and noise generate due to the pressure fluctuation around the nozzle tip. Blade number is one of the critical factors that affect the turbine performance. Especially for the outflow from our developed cross-flow turbine, it seems that blade number has a significant effect on them, So, this study focused on the effect of the blade number on the turbine performance and vibration characteristics. As a result, flow separation from the top edge of the guide wall disappears by increasing blade number. The turbine efficiency does not change because of the decrease in the runner torque with the flow rate. Pressure fluctuation between the tip clearance around the outer casing wall tip becomes small by increasing the blade number.

Cross-flow turbines are utilized in many run-off river types and small hydropower stations because of their excellent partial load characteristics and low manufacturing cost. But the maximum turbine efficiency is not high, so there have been many studies to improve the performance. The authors have been developing a new shape cross-flow turbine with a cylindrical cavity and a guide wall to enhance the performance by controlling the runner outflow and making the turbine small. The outflow situation will depend on the shape of a draft tube. This study focused on the influence of the wall shape in a part of a draft tube on the turbine performance experimentally. Results under various guide vane openings show that the efficiency is degraded for overload and improved for the partial load without draft tube throat. Also, the flow separation, captured with PIV measurement, from the outer casing tip changes with the change of the draft tube shape.

The condition to cavitation occurring and the effects of cavitation on the performance of a cross-flow turbine were investigated using an experimental apparatus placed high above the water surface of storage tank while changing the effective head and the runner chamber pressure. The results confirmed that cavitation occurred in four regions around the runner and in one region on the wall surface of the guide vane. The influence of the net head on the occurrence of cavitation was considerable for high NPSH. It was cleared that the occurrence of cavitation inside the runner or in a region of water reentering would have a positive effect on the efficiency. The cavitation in the region, where cavitation occurring confirmed by experiment, could be recreated using CFD.

Recently, renewable energy has been attracting attention as a clean energy due to concerns about global warming. Among them, we focused on pico hydroelectric power generation, which can generate 1kW-100W. We aim to realize an in-line compact hydroturbine capable of generating 100 [W] with a flow rate of about 3 [l / s]. It is requested that the hydroturbine be a small size and have high performance. Therefore, we adopted contra-rotating rotors, which can be expected to achieve miniaturization and high performance. However, when the rotors become smaller, the output power of conventional contra rotating rotors, which are composed of axial flow rotors, is low. In order to achieve small size, high performance and high output power simultaneously, we propose a new type of contra-rotating rotors, which are composed of a hybrid rotor and a centrifugal rotor. The hybrid rotor consisted of an axial flow rotor and a mixed flow rotor. However, the performance of hybrid rotors tended to be low. Therefore, we focused on the deflection angle and the number of blades of each rotor. In this study, the feasibility of an in-line compact hydroturbine capable of generating 100 [W] at a flow rate of 3 [l / s] was examined from the results obtained from numerical fluid analysis.