The drainage and rupture of the thin liquid film formed between a bubble and a flat mica plate have been investigated. It is known that the bubble coalescence can be prevented in electrolyte aqueous solution, and its effects strongly depends on the type of electrolyte. In this study, by using two types of electrolyte aqueous solutions (0.05 M MgSO₄ aqueous solution and 0.05 M CH₃COONa aqueous solution) and surfactant aqueous solution (10 ppm Triton X-100 aqueous solution), evaluate the effects of impurities on the behavior of the liquid thin film. The effect of the approach velocity also is also evaluated. By using an optical interferometer and a high-speed video camera, interference fringe images are taken, and the shape of the liquid thin film formed between a bubble and a flat mica plate can be obtained. The effect of solute in transition on the thin film process in the center of the liquid film is investigated. Under conditions of 2 mm bubble diameter and the approach velocity of 50 μm/s or less, the thickness of the central film increases, and the spreading of the liquid film is suppressed when electrolytes are added into water.

In a compressor, shock waves are generated when the impeller blade velocity reaches supersonic speed relative to the air drawn in from the air inlet. The shock interacts with the tip-leakage vortex and the boundary layer on the impeller blade surface. The interaction causes the pressure rise and the reverse flow. Thus, it is important to predict the formation of shock on the blades in compressor design. This study focused on a position of the shock in a centrifugal compressor. In general, simultaneous measurement by multiple pressure sensors is necessary to measure the angle of the shock formed near the leading edge of the impeller blade. In this study, a pressure history was measured at a single point near the leading edge of the blade using a semiconductor pressure transducer. The semiconductor pressure transducer has a diaphragm onto which a semiconductor strain gauge is glued. The pressure acting on the diaphragm is proportional to the strain at the center of the diaphragm. The direction of maximum principal strain of the diaphragm corresponds to the shock direction or its perpendicular direction. The strains in three different directions on the diaphragm were obtained and the direction of maximum principal strain was calculated using Rosette analysis. As a result, the angle of formation of the shock wave generated in the centrifugal compressor impeller was estimated.

In axial flow compressors, it is important to understand the detailed behavior because the tip leakage flow may leads to performance degradation and surge generation. However, since the tip clearance is very narrow with only a few millimeters of clearance, it is difficult to insert a probe and the flow angle cannot be measured by actuation point change in oil flow visualization.

In this paper, a flexible MEMS sensor with a thickness of several hundred micrometers was developed by applying the thermal tufting method, and flow angle measurements were performed on the blade end casing surface of a 1.5 stage axial flow compressor test rig. As a result, it was shown that the flow angle change due to the leakage flow with the change of the working point of the compressor could be measured in the clearance section of less than 3 mm.

Aircraft icing is the phenomenon that forms an ice layer on the solid surface by impingement of supercooled water droplets in the atmosphere. In icing on rotor blades, ice is shed from the blade surface by centrifugal force as the accumulated ice grows. Therefore, it’s necessary to establish an ice shedding model for icing simulations. In this study, the authors proposed an ice shedding model in which the condition for ice shedding is that the centrifugal force exceeds both the adhesion strength and the tensile strength. A numerical analysis was performed to validate the model, and the ice shedding conditions were investigated through comparison with the experimental results. The progress of icing on the rotor blade was predicted by UPACS. We simulated the change of centrifugal, adhesion, and tensile force over time in the icing process. The results showed that the present model is able to predict both the shedding timing and location with reasonable accuracy.

In this study, a numerical analysis using the Lattice Boltzmann Method was performed on a Multi-Slotted Wing that mimics a Bird's Wing Tip, for which experimental results have been published. The aim of this study is to investigate the feasibility of the application of a Multi-Slotted Wing mimicking a Bird's Wing Tip to an axial compressor. In prior experiments, multiple slots in the wing tip mimic a Bird Wing Tip. The results of the analysis showed that the change in swirl velocity around the wing tip vortex with and without slots could be captured with sufficient accuracy, confirming the validity of this method. In the downstream, a Multi-Slotted Wing shows a 10% decrease in circulation compared to the base model. Further detailed analysis revealed that the wing tip slots promote the subdivision of the wing tip vortex and allow the wing tip vortex to decay faster than without the slots, which can contribute to the reduction of induced drag.

A compressor for turbochargers is commonly required improving efficiency and expanding the operating flow rate range. Though an aerofoil type diffuser shows better pressure recovery than conventional vaneless diffuser, it is difficult to design the aerofoil type diffuser under conditions of wide change of the flow angle. An innovative design of a Low Solidity circular cascade Diffuser (LSD) was proposed for flow range enhancement of cascade diffuser¸ and an interesting function of the LSD is introduced. At small flow rate conditions, low energy fluid near the diffuser side wall spread between the diffuser blade, and low energy fluid moves to the leading edge of the adjacent blade, then low energy fluid merged with main flow and suppress the flow separation. The phenomena spread to circumferential direction, and whole of the LSD blades show high stability for separation under a large angle of attack. In this study, LSD is designed for compressors of turbocharger by using a Genetic Algorithms (GA) with meta-model of an Artificial Neural Networks (ANN). The final goal of this study is to optimize the LSD with having secondary flow effect under low flow rate conditions.

The target mixed flow blowers are required to have high efficiency, low noise, compact size and light weight. The target mixed-flow opentype impeller under consideration deforms due to centrifugal stress, and the blade tip clearance changes. This study investigated the effect of centrifugal stress deformation on fan efficiency using fluid structure interaction analysis. Using the results of fluid analysis, the authors compared the static pressure change in the flow direction inside the impeller with and without centrifugal stress deformation. The centrifugal stress deformation of the impeller has the effect of reducing the loss at the impeller outletside by increasing the impeller outer diameter and decreasing the blade tip clearance. However, deformation due to centrifugal stress increases the tip leakage vortex loss due to the enlarged tip clearance near the leading edge.

This study deals with experimental and numerical investigations on aerodynamic loss of two different types of low-pressure turbine (LPT) cascades. A special focus is placed on additional loss mechanism due to mixing of incoming wakes from the moving bars because there is still neither established consensus about the bar-mixing process nor any prediction method of incoming wake mixing loss. Two loss models developed by Denson as well as Coull and Hodson are employed to estimate steady-state (no wake condition) turbine cascade loss, which can be used to determine the mixing loss by comparing the steady-state and unsteady (wake condition) cascade losses. It is turned out that the aerodynamic loading of LPT cascade has some impact on the bar-wake mixing loss.

Large Eddy Simulation (LES) for compressible flow was conducted to analyze the pressure fluctuation at 17% of the impeller rotation frequency, which was confirmed at the impeller inlet and diffuser inlet under the operation condition on the lower flow rate in centrifugal blower with peripheral Mach number of 0.48. It was found that the pressure field in the diffuser generally decreases when the region of large radial flow caused by the diffuser rotating stall passes through the scroll tongue. As the pressure decrease in the diffuser, the pressure upstream of the impeller also decrease.

In this paper, turbulent flow fields in a multi-stage transonic axial compressor have been investigated using large-scale detached eddy simulation (DES) analysis. The flow field was analyzed by data mining techniques including vortex identification based on the critical point theory and topological data analysis of the limiting streamline pattern visualized by the line integral convolution (LIC) method. Ensemble averaging was performed on the obtained numerical results using the phase-locked averaging method to quantitatively investigate the unsteady state of the interaction between the inlet guide vane (IGV) and the first-stage rotor blade. As a result, the wake interference was confirmed. Periodic fluctuations of the flow field around the IGV occurred with the same period as the blade passing of the first-stage rotor, indicating that the flow field fluctuates due to the potential interference with the first-stage rotor blade.

W Suppressing the pressure fluctuations distributed on the blade surface of an axial fan is applied as one of the means to reduce the noise generated in the cooling system of construction machinery. For that purpose, it is effective to use computational fluid dynamics (CFD) to capture the 3D vortex structure around a fan blade. However, while there have been many reports on the flow field formed around the blades of a fan alone or an axial fan with a duct-shaped shroud, the influence of the vortex structure formed at the actual operating point of the axial fan on the pressure fluctuation on the blade surface has not been sufficiently discussed. In this study, the three-dimensional vortex structure around the fan blade installed in the cooling system is investigated, and in particular, the influence of the wing tip leakage vortex on the pressure fluctuation on the fan blade surface is clarified. Wing tip leakage vortex that flow from forward in the direction of rotation of the fan interfere with a blade while oscillating periodically in the y-axis direction. The oscillation of the forward wing tip leakage vortex causes the separation position of the newly formed wing tip leakage vortex to change, and as a result, the pressure fluctuation increases at the tip of the blade suction surface near the separation position.

The tone noise is known as an aerodynamic noise generated from a two-dimensional airfoil placed in a flow, which is said to be attributed to vortices shedded from the trailing edge of the airfoil. Commonly, the trailing edge shape of an airfoil is uniform in the span direction from the viewpoint of manifacturing and structural strength, but the vortex shedding becomes coherent in the spanwise direction, resulting in the increase in the tone noise. In this study, simultaneous calculations of the flow field and sound field were performed using the lattice Boltzmann method for the tone noise generated from the NACA0012 airfoil. We investigated the influence of the spanwise trailing edge shape on the vortex shedding causing the tone noise.

Centrifugal pumps, which are widely used in industry for transporting liquids in plants and in water purification systems, and it is necessary to improve the instability characteristics at extremely low flow rate conditions. The negative slope of the characteristic curve is the evidence of instability of the flow, and it must be based on the local reverse flow zone and pre-whirl at impeller inlet. It is possible to predict the negative slope of the characteristics by unsteady numerical analysis at low flow rate, however, optimization design search requires many numerical analysis of individuals, it is not realistic solution to use the unsteady numerical analysis for the optimization.

In this study, a meta-model assisted genetic algorithms are used for design search. A neural networks is applied as the meta-model for accelerate the ranking solution in the genetic algorithms. Moreover, a characteristic of the flow field at low flow rate that can be obtained by steady-state analysis, and incorporated the characteristic of the flow field as a constraints for the optimization system. After conducting an optimization geometry search using steady analysis to improve the characteristic flow field, unsteady numerical analysis was conducted on the optimal geometry to investigate the improvement of the negative slope characteristics and the design parameters that have a significant impact on the improvement of the instability characteristics.

Industrial centrifugal pumps that require low NPSHR over a wide flow range, such as when pumping liquefied natural gas from storage tanks, are equipped with low solidity fan type inducers. Further improvement of pump suction performance is industrially expected because the lowest liquid level height that can be pumped directly affects the economic efficiency. In this study, several inducers made by a 3D printer were attached to an industrial centrifugal pump and investigated experimentally and using computational fluid dynamics to analyze the effect of the blade angle of the fan-type inducer on pump suction performance. The experimental results showed that the blade angle has no significant effect on the pump performance curve but has a clear influence on the pump suction performance, and CFD was used to investigate the cause of this for a flow rate with φ = 0.099, the design flow coefficient of the attached centrifugal pump. From the calculation results, the vapor volume was visualized and flow blockage due to cavitation in the internal flow path of the pump was analyzed. It was confirmed that the tendency of cavitation generation differs depending on the inducer vane angle even at the same cavitation number. Further analysis of the CFD results revealed that the influence of the swirling flow generated by the inducer on the flow field at the impeller inlet changed the occurrence of cavitation at the impeller inlet, leading to the occurrence of cavitation at the impeller inlet. As a result, the authors considered that there is a clear influence on the breakdown performance of the centrifugal pump.

In the present study, the gas-liquid two-phase flow performance of a turbopump equipped with an inducer was experimentally investigated. The almost homogeneous bubbly two-phase flow condition was successively set by the uniform aeration of gas dissolved in water upstream of the test pump, which was realized by a sudden pressure decrease with the valve closure. The gas-liquid volumetric flow rate ratio was estimated from the pump inlet pressure and the initial amount of dissolved oxygen under the assumption of mass equilibrium condition of the local dissolved oxygen. The effect of dissolved oxygen content on the gas-liquid two-phase flow performance of a turbopump was investigated. The results showed that low DO conditions are not suitable for evaluating gas-liquid two-phase flow performance because of in-negligible effect of vaporous cavitation. In addition, the effects of a reduced-diameter suction pipe and a swirl brake on the gas-liquid two-phase flow performance of a turbopump were investigated. The results showed that the effect on the gas-liquid two-phase flow performance was small under high DO condition, but the performance deteriorated under low DO condition.

Flow conditions near the casing tongue have a significant impact on the performance and stable operation of the centrifugal pump, so the internal flow conditions have been measured by the experiment and PIV measurement. The internal flow conditions of mini centrifugal pumps especially smaller than 100mm are less measured by PIV measurement and its flow conditions near the casing tongue are not clarified yet. Therefore, PIV measurement was conducted near the casing tongue for the mini centrifugal pump having 55mm impeller diameter. The two-dimensional open impeller with the large blade outlet angle β₂=60° was selected as the test impeller. FlowMaster Stereo-PIV by LaVision was used for the PIV measurement and the whole test section was made of the acrylic resin including the test impeller. Two CCD cameras with its resolution 2048×2048 pixels were used and velocity vector and contour were calculated by the PIV measurement software DaVis(Lavision). The internal flow conditions near the casing tongue were focused in this research. The PIV measurement results at different flow rates were shown and the tongue flow angle was defined to clarify the flow condition near the casing tongue with the impeller rotation. With the increase of the flow rate, the tongue flow angle increases which means the flow near the casing tongue is discharged to the casing throat. In the present paper, the internal flow near the casing tongue is clarified by PIV measurement results and the flow conditions with the impeller rotation are discussed.

Cavitation in fluid machinery can cause several problems such as degradation of performance, erosion, and so on. Therefore, the development of prediction methods for cavitation flow is an important research topic, and several cavitation models have been proposed. Multi-Process (MP) model, which is a homogenous one composed of multiple equations, can take account of main elementary processes in cavitation using the moment method for a size distribution function of cavitation bubbles. It is necessary to formulate the transport equations for each state variable based on appropriate assumptions. In this study, unsteady RANS simulation of the final stage model of a three-stage centrifugal pump using MP model was carried out to investigate the influence of the formulation of two kinds (types) of transport equations, i.e., advection-type and conservation-type. As a result, both types showed agreement with experiments in terms of head degradation curves, although differences were observed for cavity growth. In the conservation-type, bubble number density decreases in contrast to the increase in void fraction. It was confirmed that this suppresses the growth of cavities.

A Francis turbine runner was optimized by a combination of means of the 3D Inverse Design Method and Computational Fluid Dynamics (CFD). An experiment of the directly optimized conventional turbine confirms the validation of CFD calculation. A new meridional shape was designed by Design of Experiments with CFD and the database of meridional shape factors. Angular momentum at the runner inlet was corrected to cover the effects of the boundary layer from runner upstream domains such as stay vanes and guide vanes. Using the meridional shape and the corrected angular momentum and considering the secondary flow mechanism, blade loading distribution and stacking condition were optimized. It led to the decrease of secondary flow energy near the runner inlet and of the runner loss. The full-domain CFD calculation confirms that the total loss of the new turbine at the design point is 4[%] lower than that of the conventional one. This result shows the 3D Inverse Design Method is practical to control the secondary flow in the Francis turbine runners and optimize the shape.

The investigation of turbulence model in CFD using RANS model was carried out to improve the stall prediction accuracy. Decreasing the coefficient of eddy viscosity in k-ω SST turbulence model improved the prediction accuracy of the separating flow on a NACA631-012 blade, but it made the prediction accuracy of the non-separating flow worse. Thus, the modified turbulence model that decrease the eddy viscosity based on the adverse pressure gradient and GEKO turbulence model were applied to analysis of a NACA631-012 blade. As a result, both of these turbulence model improved the predection accuracy of the lift characteristic in a wide range of angles of attack. In addition, it was clarified that the separating flow on the blade simulating the hydro turbine runner can be predicted with high accuracy by using these turbulence model. It is expected that the modified turbulence model based on the pressure gradient and GEKO model will improve the performance prediction accuracy at off design operationg points in the analysis of hydro turbine runner.

The authors focus on a small propeller turbine fabricating additive manufacturing technology represented by 3D printers. 3D printer runner fabrication is faster and cheaper than conventional manufacturing, but resin runner strength is not enough for utilization as it is. The authors proposed a ring runner integrated with a ring around the blade tip circumference to improve the strength of the runner vane and suppress blade tip leakage. This study conducted, CFD analyses for both the normal without ring and ring runner models to clarify the internal flow of the turbine and to elucidate the cause of the lower turbine efficiency in the ring runner model. As a result, it is found that the ring runner does not significantly improve the turbine efficiency compared to the normal one. Still, runner-only efficiency increased by approximately 2% because of increasing blade loading at the runner tip. Also, the circumference velocity downstream of the runner becomes larger near the shroud, so the ring runner model increases the loss downstream of the runner.

This study examined the effect of pressure recovery on the underside of multi-winglets due to changing the main wing airfoil of an aircraft. Winglets play a role in suppressing the generation of the wingtip vortex and reducing induced drag. Previous research has shown that changing to multiple winglets disperses the wingtip vortex and decreases the induced drag compared to the conventional single winglet. In addition, multi-winglets reduce drag by scattering the wingtip vortices and gain lift by narrowing the gaps between winglets. It seems to be because air flowing through the gaps accelerates and reduces the pressure on the upper surfaces of the following winglets. However, if the winglet’s lower surface pressure decreases due to the shock-wave expansion on the winglet’s underside, the flow rate through the gap would decline; the effect must not emerge. Thus, we applied a main wing airfoil design, which did not generate shock waves on the lower surface, to compare the aerodynamic characteristics and the pressure distribution before and after the airfoil change using numerical analysis. The comparison employed a single wing without winglets in the same way. Consequently, the negative pressure region narrowed on the winglet’s lower surface; the pressure recovered. Accordingly, this contributed to an increase in the lift coefficient of the winglets.

We have conducted laboratory experiments on air entrainment and bubble generation by rotating ventilated hydrofoils aimed at reducing power consumption by subsurface aerator. The negative pressure generated on the hydrofoil drives the atmospheric air into water, which enables the subsurface aeration without air compression. Small air bubbles with the diameter from sub-mm to mm order were generated by the turbulent shear flow around the rotating hydrofoils. We experimentally obtained threshold of air entrainment, air volume flux, and power consumption by the hydrofoil bubble generators, which depend on the rotating speed, water depth, and angle of attack of the hydrofoil.

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. We added skirt structure to the conventional flat rotating disk. In this research, several rotating disks with the skirt structures were used in the tornado generator to examine the effect of the skirt structure. The experimental parameters controlled in this flow are configuration of the rotating disk and installation height. The results obtained are as follows: When the device is installed in the higher position, the rotating disk with the skirt structure stabilize the tornado compared with the flat rotating disk. This may be due to the approaching and vertical transformation of the vortex ring surrounding the tornado-like swirling flow. When installed in the lower position, the skirt structure causes the vortex ring to disturb the bottom wall flow and weaken the vortex. It was found that a balance between the size of the vortex ring and the installation height is important to enhance the swirling flow. In addition, when installed in the higher position, the skirt structure with an outward angle enhances the swirling flow more as the skirt height increases. However, the inward skirt structure weakens the swirling flow as the skirt height increases. This seems to be due to the vortex ring being too close to the tornado-like swirling flow.

Journal bearings have the advantage of being damped. However, at high rotational speeds, self-excited oscillations called oil whip occur, leading to damage of bearing and shafts. Tilting Pad Journal Bearings are used in high-speed rotating machinery as they are effective against oil whip. The Reynolds equation has been used as a typical calculation method to investigate bearing characteristics, but it is difficult to apply when the bearing is complex. In this paper, a prediction method of bearing characteristics of Tilting Pad Journal Bearing using CFD was constructed. To simulate the motion of the pad as it oscillates against the fluid force, Dynamic Fluid Body Intersection was studied. In order to compare with the calculation results, an active oscillating rotor using magnetic bearings was constructed. As a result, the calculation results were roughly consistent with the experimental results, and a prediction method by CFD was constructed.

In this study, the effect of the flow by the force of temperature-sensitive magnetic microcapsules caused when supplied magnetic field investigated. The multifunctional working fluid used this experiment was the water contained temperature-sensitive magnetic fluid were microencapsulated. The temperature-sensitive magnetic microcapsules containing the temperature-sensitive ferrofluid and fluorescent dye were created by the in-liquid drying method. The temperature-sensitive magnetic microcapsule dispersion flowed through a flow path to which a magnetic field was supplied by a syringe pump. A microscope and a CMOS camera were used for observation, and particle images were taken. The velocity was calculated with PIV software using the captured image and the velocity field was visualized. The effect of temperature-sensitive magnetic microcapsules on forced convection was observed when a magnetic field was applied. Clusters were observed to form on the walls and be attracted to the direction of the strong magnetic field, facilitating the flow. By changing the position where the magnetic field is applied, there was a tendency for the flow promotion to weaken. Also, increasing the temperature of the channel decreased the effect of the magnetic field on the flow. This response to temperature is due to the decrease in magnetization with temperature that is characteristic of thermosensitive magnetic fluids. This suggests the possibility that temperature-sensitive magnetic microcapsules can promote heat transport in the same way as temperature-sensitive magnetic fluids.

Recently, ionic current responses in mico- and nanofluidic channels have attracted significant attention from both fundamental and application perspectives in various research fields. For single particle analysis, ionic current responses are often caused by interactions between electrolyte ions and target particles as well as the volume exclusion effect due to the transport of target particles. Therefore, the behavior of ions in narrow confined spaces is required to measure more precisely to obtain detailed information of particles. In this study, we propose a novel method to identify ion species in electrolyte solutions, using the ion selectivity of nanochannels. Applying an external potential on an electrolyte solution for a probe, which is separated from a sample solution by a nanochannel, ion concentrations are separately determined. As a result, it is found that electroosmotic flows have an important role to distinguish ion species, breaking a symmetry of ion transport phenomena that are dominated by diffusion and electrophoretic transport.

Poly(3,4-ethylenedioxythiophene)(PEDOT) is known as one of the best conducting polymers and has been applied to various electronic devices. The dopants are typically used to enhance the solubility of synthesized PEDOT, however the dopants lower the conductivity of PEDOT. Then, we developed an innovative plasma enveloped bubble process to enable PEDOT synthesis with high water dispersion without introducing any dopants. The plasma polymerization process is realized in the emulsion of 3,4-ethylenedioxythiophene (EDOT) in water by plasma generated radicals inside bubbles of oxygen and argon mixture. In this study, the characteristics of plasma inside the bubbles and processed samples prepared by this innovative method were experimentally clarified. The FT-IR analysis of the synthesized sample clearly indicated the foot print of EDOT polymerization. The conductivities of the synthesized PEDOT films increased with the processing time.

Many run-off river types and small hydropower stations use Cross-flow turbines 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 turbine 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. Previous research has shown that the cavity effectively reduces pressure fluctuation at the nozzle's bottom tip and improves turbine efficiency. However, the mechanism is not fully understood. Therefore, the purpose of this study is to elucidate the mechanism of the cavity. The authors investigate how the flow pattern and turbine performance change with the flow pattern inside the cavity. It is clarified that the swirling flow in the cavity improves the turbine efficiency and suppresses pressure fluctuations at the lower end of the nozzle.

Many small hydropower stations, which are run-off river types, use a cross-flow turbine because of its excellent partial load characteristics and low manufacturing cost. So far, there have been various studies to improve turbine performance. On the other hand, the flow field pattern is expected to be different with the variable effective head condition. Therefore, understanding the characteristics of flow field patterns and obtaining design guidelines for cross-flow turbines will improve the turbine performance and enlarge operating conditions. This study investigates the influence of the head on cross-flow turbine performance. This study used CFD analysis to evaluate the flow field pattern in the turbine with several head conditions. As a result, it is confirmed that the turbine shows a low degree of reaction. The first stage generates much torque by velocity head variation. The energy recovery rate at the second stage is changed with the head, which is a major reason for the change in turbine efficiency. The flow pattern around blades at the first stage varies with the head.

Small-scale hydropower is one of the important alternative energy and is expected because of its large amount of energy and high capacity factor. Pico hydropower generation less than 1 kW can be applied in many locations, such as agricultural pipelines and small rivers, and has a low environmental load. Since, pico hydropower generation has the problem of low efficiency, we adopt contra-rotating rotors that can be expected to achieve high performance. In previous research, performance characteristics for contra-rotating small hydroturbines were investigated by experiments and numerical analysis, and the possibility of higher performance was shown. As the next step, our research is on the verification stage in field experiments. First, we investigated the theoretical power from the head and flow rate of the field and designed a small hydroturbine having a 76mm rotor diameter which was suitable for the field. Next, we constructed an experimental apparatus and conducted field tests to investigate the power generation performance of the hydroturbine. In addition, there was concern that the bearings connecting the rotors and spacer would wear out due to long-term operation. Therefore, we evaluated the effects of the spacer presence on the thrust and performance of the hydroturbine by numerical analysis, and examined operation without spacers for long-term operation.

In recent years, growing concern over global warming caused by the use of fossil fuels has led to a demand for clean power generation that can be used semi-permanently and is environmentally friendly. Wind power generation is expected as the development of new energy sources accelerates. Propeller wind turbines are widespread for large wind turbines. On the other hand, a wide variety exists for small wind turbines. Among them, the authors consider that 1kW wind power generation is important for the spread of small wind turbines, and are focusing on contra-rotating propeller wind turbines, which are expected to achieve high power. In this research, we aim to increase the power of a small wind turbine by installing a wind collecting device suitable for a contra-rotating propeller. However, the aerodynamic characteristics of a contra-rotating propeller inside a hollow structure have not been clarified. In addition, small wind turbines are operated under low Reynolds number conditions, and change in Reynolds number due to fluctuation in wind speed are expected to have a significant effect on performance. In this paper, the effect of Reynolds number on the performance of a contra-rotating propeller wind turbine is investigated by numerical flow analysis using a model with a contra-rotating propeller installed in the pipe.

Numerical investigation of the effect of winglets on NREL Phase VI wind turbine blade is performed. In this research, two different winglet configurations upstream winglet and downstream winglet are compared to see which configuration has the benefit to improve the blade performance. The thickness of winglet tip with the blade shape varied from 100% to 85% and 70% of tip blade thickness to see the effect on blade performance. Moving reference frame method was chosen to perform the blade rotating motion. Computational results were compared with experimental data and it was found that upstream winglet able to increase torque production compared to normal blade up to 1.6%. While downstream winglet decreases. Reducing winglet thickness tends to increase the torque.

We examined the feasibility on the stall-control of a horizontal axis wind turbines combined with a camber blade and symmetrical blade. The measured lift and drag force could be evaluated by Xfoil analysis and the momentum of the incoming flow. Although the maximum lift of the cambered blade is 175% than that of the symmetrical blade, there is no significant difference in the drag. The output of the wind turbine consisted by the camber blade with the setting angle 12° becomes larger than the symmetrical blade; however, the blade could not stall-control the output. The wind turbine of the symmetrical blade with the setting angle 60° made the stall-control possible at the main flow velocity around 25m/s. Moreover, the wind turbine combined with the camber and symmetrical blade could control the rated power and the cutout speed aerodynamically.

Tidal stream power generation as renewable energy is one of the energy-source candidates for realizing sustainable society. Counter-rotating-type propellers are utilized in the conversion of tidal stream kinetic energy to electric energy. In this type of propeller, the rotational torques of the front and rear propeller are counter-balanced, thus they have no reaction force. This feature enables to moor a power unit with a cable from a floating or sea-bed base. The posture and performance of a moored power unit is easily affected by tidal stream condition. To evaluate precisely the performance in such power unit, unsteady flow simulation using a propeller rotating model is studied. As a first step, the flow simulations were carried out under the condition that the power unit axis was aligned with the flow direction. Moving element model was employed as a propeller rotating model. At first, the grid convergence in the simulations was confirmed. Second, the rotational speeds of the front and rear propeller under the torque equilibrium were examined. Finally, the power coefficient was evaluated at various rotational speeds. The output ratios were calculated from the obtained power coefficients and were compared with Lee’s wind tunnel test results. The numerical output ratios almost agreed with the experimental ones.

The studies on the oscillating water column (OWC) type wave energy converter has to be special geometry so that it can always rotate in the same direction in a bi-directional airflow, which makes it difficult to increase the efficiency and select a turbine geometry compared to the turbines for uni-directional flows. In order to overcome these difficulties, the use of a new air turbine for wave energy conversion, a sail wing turbine for bi-directional flow has been proposed by the authors. This turbine is operated in a bi-directional airflow by using some rotating sails made of a thin, flexible material such as cloth that changes shape in response to the airflow direction. The advantages of this turbine are that the rotor is lightweight, the turbine structure is simple, and it does not suffer from the stalling as seen in Wells turbine. However, it has been pointed out that the efficiency of this type of turbine is lower than that of the Wells turbine. In this study, in order to improve the performance of the sail wing turbine, the effect of the guide vane solidity on the performance was conducted through a wind tunnel test under steady flow condition.

For the wind assessment at the wind turbine performance test, a meteorological mast at the hub height is installed around 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 also increased. Therefore, in this study, devised a technology to estimate the inflow wind speed is developed by measuring the surface pressure with a pressure sensor mounted on the spinner of the wind turbine rotor and converting it to the inflow 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 application of spinner-mounted pressure sensors in natural environments through field experiments. The obtained wind speed by the pressure on the spinner was compared to the inflow wind speed measured by an ultrasonic anemometer located upstream of the wind turbine. As a result, the spinner sensor wind speed estimation error may exceed the nominal error range equivalent to ±10 Pa of pressure sensor accuracy. However, the spinner sensor wind speed can generally estimate the inflow wind speed.

Recently novel artificial heart valves, which are made by using tissue regeneration techniques or the latest biocompatible materials, are actively developing. The purpose of this study is to clarify the effects of mechanical anisotropy of valve leaflet on valve functions because the new materials and human native heart valves are anisotropic. We fabricated the human aortic valve model made of polyurethane with mechanical anisotropy in valve leaflet by adding spatially periodical surface asperities. Furthermore, to determine the optimal anisotropic property of the valve leaflet, the amount of sheet thickness and the spacing of surface asperities were varied as experimental parameters. Using our fabricated in-vitro simulator, experiments were conducted under the physiological conditions of healthy adults to compare valve function between isotropic and anisotropic models. The valve function was evaluated on basis of the ISO 5840-1 and ISO 5840-2 international standards for artificial valves. The obtained results indicate that anisotropic models with 3 mm spacing were found to have the best valve function, and isotropic models and anisotropic models with 1 mm spacing were found to have similar performance. Furthermore, comparison with data from clinically used prosthetic valves showed that among anisotropic models with 3 mm spacing, the valve leaflet thickness of 280 μm was superior in both opening and closing performance.

Swallowing disorder has been becoming a serious issue with increasing in elderly people. Disorder sometimes appears with a decrease in saliva, because saliva has an important role in lubrication over the oral cavity and throat. Though the structure of biological mucosa has been studied physiologically, there are only few studies that examined the influence of its oral and throat mucosa on fluid lubrication. Therefore, we investigated the friction reduction effect on the oral cavity and pharynx. There is a thin liquid phase with a thickness of about 0.1 mm called saliva layer on oral and throat mucosa. It is necessary to evaluate the rheological properties of mucus with low viscosity and high spinnability like saliva layer using a PEO solution, because of the viscosity characteristics different from the shear viscosity. The PEO solution concentration was determined from the measurement of the viscous characteristic by the rotational viscometer to set the same viscosity as that of saliva. Therefore, we investigated the rheological characteristics by measuring the extensional viscosity to make a mucus using a PVA coating. We measured friction torque on the artificial mucosa lubricated by PEO solution. The effect of torque reduction of friction by high-viscosity liquids (100% glycerin solution) on the artificial mucosa was clarified in this study. We considered apparent slip occurs in the saliva layer. However, there was no effect of friction reduction on the low viscosity (40% glycerin aqueous solution). Even if apparent slip occurs in the artificial mucosa, the viscosity on the artificial mucosa is the same as that of the liquids.

Abnormal outbreaks of aquatic cyanobacteria have severely impacted water quality in many coastal areas and lakes worldwide. Cyanobacteria can increase significantly when nutritional, temperature, climatic, and light conditions are favorable and appear in a high-density accumulation state at the water's surface. Such a state is comparable to a limitation of the natural vertical migration function of cyanobacteria. It is thought to cause physical effects not seen in everyday physiological phenomena of aquatic cyanobacteria. In this study, we investigate the forces that act on cyanobacteria to maintain high-density accumulation at the water surface by conducting tank experiments.

In recent years, the regenerative medicine has been being developed due to the improvement of tissue engineering, e.g. autologous regenerative tissue by three-dimensional culture. In this study, Ultrasound-assisted Doppler Velocigraphy (UA-OCDV) is constructed to measure the tissue displacement and the inerstitial fluid flow, tomographically, non-contactly and non-invasively at the micrometer resolution. This is based on Doppler OCT, which can visualize Doppler velocity inside tissue by applying phase analysis to low coherence interference signals. Furthermore, a High Intensity Focused Ultrasound (HIFU) transducer is introduced into Doppler OCT as a non-contact loading device of periodical acoustic radiation pressure. UA-OCDV was experimentally applied to flow field around scaffold. As a result, UA-OCDV was able to provide the tomographic visualization of periodical flow velocity field. Flow velocity through fibers of hydrophilic scaffold was observed to increase 140% compared to that of hydrophobic one. The nano-scale water film generated around hydrophilic surface is considered to reduce the flow resistance. In conclusion, it was therefore suggested that UA-OCDV had a potential of diagnosing tissue permeability non-contactly and non-inasively.

It is well-known that aging and photoaging causes tissue degeneration of collagen and elastin in the upper dermis. As a result, the change in rheological properties of skin, i.e. viscoelasticity, develop wrinkles and sagging. In this study, a hybridded system with suction pressure device and Optical Coherence Tomography (OCT) can visualize rheological properties as strain rate distribution as well as capillary blood flow information tomographically at the micrometer scale. In this experiment, the dynamic viscoelastic analyzing (DMA) test was applied to human forearm skin by sinusoidal pressure loading, with simultaneously taking OCT images. As a result, DMA-OCSA can reveal rheological distribution from epidermis to upper dermis as the tomographic phase difference map of strain rate. Consequently, it is suggested that DMA-OCSA has good potential of diagnosing rheological properties inside skin tissue.

A wing vein network of a fore wing of a Drosophila fly has asymmetry. One vein breaking symmetry of the wing vein network was found via application of our topological transformation. This asymmetry-creating wing vein can be a strategy to improve functionality of the wing veins. As one of multiple functions of the wing veins, they are pipes to transport blood according to the entomological knowledge. However, there have been no engineering attention to the function of vein network as pipe network for blood transportation and are no understandings of how blood circulation is achieved in such a network consisting of extremely narrow pipes based on physics. In this study, we revealed the effect of the asymmetric vein network structure on the blood circulation via comparison with symmetric vein network without the asymmetry-creating vein. A numerical simulation based on the Hardy-Cross method allowed us to demonstrate how addition of this vein influences blood circulation in the wing. The result of that showed the asymmetrical structure improves blood flow distribution in the posterior region of the wing and energy consumption by pumping organ for circulation. Our results interpreted importance of the asymmetry caused by one irregularly positioned vein for the efficient maintenance of the wing via circulation.

A numerical calculation method for detonation transition process using an experimental-scale grid was proposed in this study. This method consists of multicomponent diffusion model. Detonation transition experiments were conducted to investigate the usefulness of the proposed method. A detonation was generated in rectangular tube with a square cross section of 30 mm per side. The tube was filled with an oxyhydrogen mixture with an initial pressure of 100 kPa, and an equivalent ratio of 1.0. The time history of the flame front position was obtained by observation with a high-speed camera. The time history of flame front position by the proposed numerical method were compared with one by the experimental results. As a result, the results obtained by the proposed numerical model are in good agreement with the experimental results. It was also found that the effect of thermal diffusion can be neglected in the simulation of the detonation transition process.

This study investigates the atomization and evaporation process of liquid fuel jets in crossflow by considering the evaporation from not only Lagrangian droplets but also the liquid column and Eulerian droplets which are generated from the primary breakup of the column. The evaporations from the liquid column and Eulerian droplets are calculated using the heat and mass transfer model, while the evaporation of Lagrangian droplets is calculated by a non-equilibrium Langmuir-Knudsen model. The results show that the evaporation occurs actively at the gas-liquid interface of the liquid column tip and droplets torn from the jet. In addition, in comparison to the evaporation of Lagrangian droplets, the Eulerian part of the evaporation is marked. Moreover, regarding fuel vapor distributions on a downstream plane, fuel vapor from the gas-liquid interface is greatly influenced by the liquid column trajectory and is distributed mostly at the same height as the column tip. In contrast, fuel vapor from Lagrangian droplets is also highly distributed near the wall.

Metal additive manufacturing (AM) is a promising digital manufacturing technology that can produce parts of complicated shapes. Fluid flow dynamics in melting and solidification determines the final shape accuracy and mechanical properties. Here, detailed numerical simulation is used for in-situ alloying to elucidate the processes of heating, melting, mixing, vaporization and solidification. The solidification process by the phase field method is coupled with the fluid flow dynamics. The laser heat input melts the powders of each element and a melt pool is formed. Here, entrainment and stirring of each element can enhance mixing in the melt pool, but complete mixing is not achieved in a single track. Grain growth is mostly governed by the thermal gradient and columnar grain growth is dominantly observed. The inhomogeneity of the chemical species induces a difference in the timing of grain growth, which may lead to collision of nearby growing grains. The second track melting induces remelting and further mixing occurs due to the stirring effect of the keyhole. It is suggested that controlling the keyhole dynamics by the heat input can control the species mixing and the grain growth. Optimization of such processes is our next future issue to be pursued.

LiCl-KCl binary mixture consists of two phases between liquidus temperature and eutectic point temperature. Our objective is to detect 1) its solid-liquid phase change and 2) the volume fraction of the solid phase. We have measured its resistance, which comes from impedance measurement using alternating current, and referred to the reported LiCl-KCl phase diagram. As a result, 1) the conductance is capable of detecting liquidus temperature and eutectic point temperature, and 2) it has a linear relation with the volume fraction by measurement using the current of 10kHz~100kHz.

From the end of 2019, COVID-19 prevails. Wearing a facial mask was effective in preventing COVID-19 infection. However, there are two problems with facial masks. First, there is gaps between the face and facial masks around the nose and cheeks, through which virus droplets can enter. Second, wearing a facial mask makes breathing difficult. Therefore, the purpose of this study is to establish an evaluation method for the virus droplet invasion ratio and suffocation magnitude. Furthermore, using the established evaluation method, we aim to develop a new facial mask for medical and general use that eliminates the gaps between face and facial mask and releases the suffocation. We measured the invasion ratio of three types of facial masks, when the facial mask is worn normally or when the facial mask is taped to the face to eliminate the gap. We proposed a two-variable index for the mask development that combines the two invasion ratios. When the two invasion ratios are equal, the filter performance of the facial mask might be at its maximum, and such a facial mask is defined as an optimized mask. Finally, we succeeded in developing a new optimized facial mask that solves the problem of commercial products.