Owing to investigation of generation for flow-induced structure (FIS) of micellar solutions in an abrupt contraction and expansion flow, we observed the FIS of a rod-like micellar solution passing through a rectangular channel with a symmetric or asymmetric slit. Furthermore, liquid-temperature was changed as experimental conditions (relatively high-, room-, and low-temperature). For relatively high-temperature, a weak FIS exhibited in a symmetric slit-flow. For roomtemperature, agreement between the resultant FIS and the reported FIS was obtained. For relatively low-temperature, drastic FIS in upstream and slit section. In case of an asymmetric slit flow, the same tendency was obtained. However, profile of retardation was asymmetric in slit section. Moreover, degree of spatial constraint was discussed.

Drag forces on a circular cylinder placed in a rotating cylindrical annulus filled with a viscoelastic wormlike micellar fluid are measured using a load cell. The flow patterns are extracted from the PIV (particle image velocimetry) measurements of the flow fields around the circular cylinder. In viscoelastic fluids, shear waves can be propagated, and the viscoelastic Mach number M is defined as the ratio of the speed of an object in a fluid to the speed of shear waves in the fluid. In this study, the effect of viscoelastic Mach number on the drag characteristics of the circular cylinder is investigated. The results show that when the viscoelastic Mach number M > 1, an increase of drag over that expected from the growth rate at viscoelastic Mach numbers M < 1 is observed. From the results of PIV measurements, a dead water region is observed, which is formed symmetrically around the circular cylinder when M < 1 and behind the circular cylinder when M > 1. It plays an important role in the drag increase on a circular cylinder.

In this study, the suspension flows in a Hele-Shaw cell were experimentally examined. We focused on the free surface of suspension in a Hele-Shaw radial flow and discussed the effect of particle behaviors on the change in surface shape. The test fluids used were two kinds of suspension with a different particle size. The volumetric fraction of each fluid was 40 vol.%. In the observation of free surface in the Hele-Shaw flow, it was found that concave and convex parts appeared on the free surface with a time. Furthermore, at the inside region of surface undulation, the occurrence of the particle-induced viscous fingering was confirmed. Measuring velocity profiles inside the viscous fingering using the particle imaging velocimeter (PIV), we found that the velocity in the fingering region became higher than those of entire suspension. The difference between the particle velocity inside fingering and that of entire suspension suggested that the shear flow in the Hele-Shaw cell affected the particle behaviors. Furthermore, since the temporal changes in the fingering shape was different between both fluids, the particle behaviors inside the viscous fingering might relate to the particle migration in the perpendicular direction to flow direction due to the local change in the shear deformation.

This study investigates graphene oxide (GO) nanosheets with excellent thermal conductivity and water dispersibility as additives to achieve a trade-off between heat-transfer performance and drag reduction. We experimentally examine the pressure loss characteristics of GO nanosheet suspensions in ethylene glycol aqueous solution flowing through a recirculating pipeline system. The GO nanosheets have a size of 0.8 nm × 3 μm × 3 μm, and the test suspension concentration is 0.1%. When the base fluid is ethylene glycol, the results show that the suspension containing 0.1% graphene oxide nanosheet delays the transition to turbulence, and drag reduction occurs in this Reynolds number range.

This drag reduction rate is found to be lower than that when the base fluid is water.

In this study, visualization of the reaction in partially miscible solvents has been conducted using the Schlieren method, an indicator addition method and PIV method. The CH₃COOH in C₄H₁₀O was set on the NaOH in water against the vertical downward direction of the Hele-Shaw cell. It was found that various convection phenomena could be induced by the generation of H₂O and CH₃COONa during chemical reaction, which were depended on the ratio of initial concentration, R = C_CH3COOH,0/C_NaOH,0. For R = 1, the horizontal travelling wave was observed from the left-hand side to the right-hand side in the HS, which could be caused by Marangoni convection due to the locally H₂O concentration. After that vertical convections were also observed on the interface of the C₄H₁₀O and water and below the interface. They could be caused by Rayleigh Tayler instability and the salt finger, respectively. It was found that the time change of the reaction front from the interface was largely divided by R. For R <1, the change in the reaction front position gradually approaches a constant value in a few seconds. On the other hand, for R≧1, the reaction front increased proportionally t^0.5.

The flow characteristics of wall-impinging diesel spray near the wall were investigated in a constant volume vessel which can simulate diesel-engine condition. The wall-flow of a vaporized spray was visualized from the downstream point of view by using laser scattering from tracer particle, and velocity distributions were analyzed based on PIV. As the result, it is observed that the intermittent structure of fuel-air distribution appears near the wall occasionally. And, PIV result suggests that the vortex of which rotation axis is parallel with mainstream direction produces the intermittent structure.

This study examined diurnal variation in metabolic functions of Cyanobacteria bloom. Cyanobacteria bloom showed distinct patterns of metabolic compounds between samples collected in surface water and middle water (water depth 0.3m). Nucleic acids, metabolic compounds related to glycolysis and gluconeogenesis, and dipeptides were found abundantly on surface water, and amino acids and metabolic compounds associated with the citric acid cycle were found abundantly in middle water. These metabolic fluctuations suggest that the fluid phenomena seen in the Cyanobacteria bloom field to function as a field that activates ATP synthesis at surface water, providing abundant energy sources for Cyanobacteria.

In recent years, it has been confirmed that micro bubbles are effective in various industries such as aquaculture and hydroponics. It is expected that the required micro bubble diameter distribution and void fraction of micro bubble water are different in each industry. Therefore, we focused on micro bubble generated by pressurized dissolution method and an experimental study on how micro bubble diameter distribution and void fraction of micro bubble water was affected by a change of a shape of a micro bubble generating nozzle was carried out. One of the important elements that make up the nozzle is clearance part. We conducted experiments using several nozzles with various clearance widths. (clearance widths x = 0.135, 0165, 0.180, 0.210, 0.260, 0.310, 0.365 mm) As a result, we found that changes in the nozzle clearance width affect the micro bubble diameter distribution and void fraction of micro bubble water.

Gas flow measurement is indispensable for social activities. Critical flow nozzles used for flow standards have been improved in ISO 9300 in 1990 and 2005. However, there are still issues regarding their rational shape. The main reason is that it is difficult to measure the flow velocity in the nozzle with low disturbance and high accuracy, although various velocity measurement methods have been proposed.

In this paper, we developed a recovery temperature anemometry (RTA) to measure the flow velocity from micrometer-order temperature sensors. The validity of RTA was verified through experiments and numerical simulations. It was confirmed from the experimental results that the difference between RTA and the reference was within 5% in the velocity range from 60 to 95 m/s. The supersonic flow in the critical flow nozzle measured using RTA agrees with the numerical simulations. In addition, the sensor part of the thermometer has a small heat capacity, and a test to confirm the temperature response was also conducted. As a result, a temperature response of about 30 Hz was confirmed.

The present study developed a wind tunnel with eight multi-fans and a shutter mechanism and evaluate the performance by measuring outlet velocity. The fan was always driven, and the shutter mechanism located right downstream the fan was quickly opened to rapidly accelerate the flow at the test section of the wind tunnel. As a result, we obtain unsteady flow in which the velocity change 2 m/s to 10 m/s within 0.3 seconds. We tried to generate a uniform shear flow, with the top two horizontal rows of shutters open and the bottom two shutters closed. And we obtain shear layer which has the vorticity of 6.6 s^-1.

The current study designed and fabricated multi-fin active turbulence generators (ATGs) and evaluated their wind speed characteristics with the long term aim of reproducing atmospheric flow in a lab environment. Two ATGs designed for the study are: (1) upwind ATG which consists of 24 square and triangular fins and is installed upwind from the test section and (2) downwind ATG which consists of 3 rectangular fins and is installed downwind from the test section. Experiments are conducted for several combinations of rotational speed and rotational angle and the amplitude of wind speed variation (u_A) which is the difference between minimum and maximum wind speeds for each cycle is used to describe the characteristic of the ATGs. For the upwind ATG, values of u_A decrease significantly with downstream distance. u_A is large for larger rotational angle, but the effect of rotational speed is not very significant. For the ATG downwind, magnitude of u_A is smaller compared to upwind ATG. However, u_A does not vary significantly with streamwise location and maintains strong correlation with the cyclic motion of the ATG fins.

One solution to reduce the cooling system noise generated by construction machinery is to drive the fan at low speed while ensuring the flow rate required for the cooling system. An approach to achieve this is to reduce the pressure drop that occurs in the flow path in the cooling system. Using CFD is effective for estimating the three-dimensional spatial pressure drop characteristics of the system, but the mechanism of pressure drop that occurs in the three-dimensional flow field has not been clarified. In this study, the flow field around the axial flow fan placed in the cooling system enclosure is visualized, and the mechanism of pressure drop that occurs in the three-dimensional flow field considering the actual configuration is clarified. With the default exhaust port, we found that portions of the fan outlet flow divert significantly inside the enclosure and are exhausted at exhaust port outlets located some distance away from the fan. With the optimized exhaust port, there are few diverting flow and the flow in the enclosure is discharged in a shorter route than the default exhaust port, so the pressure drop is reduced and the flow rate is increased. Hence, by expelling the flow at the exhaust port via the shortest path without allowing it to mix chaotically inside the enclosure, the flow rate can be increased using the same fan speed.

A method for predicting the coefficient of friction of pipes with smooth walls in turbulent flow was investigated without using the knowledge from experiments. As a result, the following was found. (1) It was necessary to secure a sufficient amount of turbulence that naturally occurred from the wall surface. For a shape such as a square cross section in which no unevenness existed on the wall surface of the calculation model, it was effective to rotate around the central axis to increase unevenness on the wall of the calculation model and to occur turbulence. (2) A method to control the strength of the turbulence was clarified. The coefficient of friction of pipes with smooth walls could be calculated by controlling the strength of the turbulence to minimize the pressure loss.

Synthetic jets are expected as an effective method of active boundary layer control. A synthetic jet device generates jets by vibrating the diaphragm of a speaker or a piezoelectric actuator by using a method of suction and blowing. The actuators are low power, zero-net-mass-flux and compact devices. Mixing enhancement is one of the key technologies in boundary layer control and it is necessary to control the behavior of vortex rings to promote mixing the crossflow and the boundary layer. The purpose of this study is to investigate the effect of vortex ring interaction due to differences in orifice distance (S=1.5D, 1.7D, 2.0D) on the behavior of vortex rings. In this experiment, the smoke flow visualization was used to describe the interaction process by changing the distance between adjacent orifices. It was confirmed that the height where two vortex rings collapse that in the case of S=2.0D was lower that in the case of S=1.5D.

To provide stable operation over a wide flow range, centrifugal pumps should have high pump efficiency at a low flow rates and high total head. A new impeller with radial and annular flow channels that has higher pumping performance than conventional design impellers with the same specific speed and flow rate at a low specific speed was proposed. however, a high unsteady flow was observed inside the pump. In this study, to predict performance, unsteady CFD was used to investigate pump performance, including different hydraulic losses. The results show that pump performance can be estimated more accurately using unsteady CFD than using steady CFD. The constant drop in total head with flow rate is owing to the hydraulic losses in the impeller, which exclude friction, growing in proportion to flow rate.

In this study, we investigate the flows around two Savonius turbines that rotate independently by numerical simulation considering the application to ocean current power generation. In general, when analyzing the flow around a rotating object, a rotational coordinate system is often used. However, it is difficult to calculate with such coordinate system when two objects rotate in the reverse direction independently. Therefore, we use the overset grid that consists of two rotational coordinates for each turbine immersed in a steady coordinate to calculate this turbines’ system. The basic equations are the incompressible Navier-Stokes equations expressed by the both rotational and steady coordinate systems. The nonlinear terms of the basic equations are approximated by the third order upwind difference in order to perform stable calculations even at high Reynolds number. The fractional step method is employed to solve the basic equations. In this study, the torque acting on the device is calculated from the flow field, and the equation of motion of rotation is solved using the torque, and the flow is simulated even when the rotation speed changes with time.

Because ships are exposed to severe corrosive and fouling environments, painting is an important factor in determining the service life of a ship. However, in most situations, the details of hull coating operations are left to the field, and basic information for production and process management, such as the amount of paint used and working hours, is not yet available. In this study, we investigated a simple method for measuring such basic information on coating operations. In this study, we investigated a method for monitoring paint consumption and work time based on the operating principle of a coating machine. Experiments were conducted to simulate spray coating operations. The amount of paint used could be estimated from the number of piston strokes and the supply air pressure of the coating machine.

The shock wave mitigation technique by using the electromagnetic energy is one of the promising methods. The baroclinic effect has the important role in this method. This effect has the possibility to apply to the generation the vortex phenomena in the compressible flow field. Therefore, the comprehension of the effect is inevitable for exploring the further vortex control- ing application in the supersonic flow field. Until now, the temperature distribution measurement has been conducted in order to the comprehension of the baroclinic effect by the interaction between the shock wave and the temperature modulated field due to the electric discharge energy, based on the shock wave velocity. However, the conventional method depends on the Mach number at the down stream region of the discharged field. This Mach number has a large impact on the temperature determination.Based on this background, in this study, we tried to improve the temperature determination method. As a result, the determination accuracy improved.

An information analysis of a relaminarizing turbulent boundary layer was investigated. It has been shown by the present authors that in the free-shear turbulent transition processes, the information analysis using Shannon entropy, which focuses on the complexity of the fluctuations, was effective for a measure of the transition progress. The present study applied this information analysis to the relaminarization process of the turbulent boundary layer. The turbulent boundary layer was relaminarized by an acceleration due to flow convergence. Velocity fluctuations were measured by a hot-wire anemometer. From the probabilities of the fluctuations, the Shannon entropy was obtained. It was large near the wall, then decreased away from the wall. In addition, they rapidly decreased just after the start of the flow convergence. The rapid decrease did not appear in the turbulent statistics, e. g., the fluctuating velocity and the intermittency factor. Thus, it was found that the Shannon entropy could be a measure of the progress of relaminarization.

With the accelerating global adoption of electric vehicles, the automotive industry is about to reach a major turning point. In this context, we focused on centrifugal force and agitation for stable lubrication and delivery of oil inside the drive unit, which is indispensable to achieve the compact and high-speed motor technology that is so important. We quantitatively measured the ratio of the oil supply to the oil discharge by placing three discharge holes at each point of the circular tube. Based on the experiments, Ansys Fluent was used to reproduce the gas-liquid two-phase flow using the VOF method, and the rotational expression was analyzed numerically on a periodic boundary using MRF with fixed mesh and considering centrifugal and Coriolis forces. The percentage of discharge flow rate at each hole was evaluated for every 1000 [rpm] of rotation at different temperatures and different number of discharge holes. As a result, the results could not be perfectly reproduced because it was not clear whether the oil temperature in the high-temperature range was strictly controlled under the experimental environment, but the trend could be captured as the discharge from the first discharge hole became dominant at high rpm for both the 2-hole and 4-hole models. The trend could be captured.

There are oil bath lubrication and shaft core lubrication as methods for appropriately supplying transmission oil, but this time we focused on shaft core lubrication. In shaft core lubrication, due to the structure in which oil flows through the rotating lubrication path, centrifugal force becomes dominant and agitation occurs, making it impossible to supply the desired lubrication. In order to solve this problem, the effects of supply flow rate, rotation speed, and TP shape on the lubrication flow rate were investigated.At present, it has been found that the lubrication flow rate becomes uniform by increasing the supply flow rate. As for the TP shape, it was obtained that the lubrication as intended was possible by increasing the number of holes rather than increasing the hole diameter.Furthermore, by visualizing and measuring the oil film distribution, the relationship between the lubrication flow rate and the influencing factors was clarified.

Venturi tube fine bubble generator has been focused in the recent studies due to its simple structure, high generation efficiency and low power consumption. The generated fine bubbles with the properties such as cleaning, sterilization, disinfection, and deodorization, have been applied in many fields including the environment, agriculture, food, medical fields, etc. In this work, an oral irrigator utilizing fine bubble technology for oral purification is developed. The venturi tube is embedded in irrigator for fine bubble generation. We design venturi tubes with different geometrical combinations to improve the performance of fine bubble generation including bubble size and volume by experiment and numerical simulation. In the experiment, the flow states in the nozzle are photographed with a high-speed camera, and the area ratios of the bubbles in the tank are calculated to analyze the production volume of the bubbles. In numerical simulation, the models with the same geometrical parameters are made and Ansys Fluent is used to implement 3D CFD simulation to analyze the internal flow state and evaluate the generation performance. Both the experimental results and simulation results show that the generation performance is dependent on the geometrical parameters of venturi tube, and the venturi tubes with divergent angle of 1.2°, divergent length of 40 mm, and the one with divergent angle of 5°, divergent length of 20 mm demonstrate the best performance compared with others.

Bubbles with a diameter of 100 μm or less are called fine bubbles, which have been applied widely in the industrial fields due to its strong detergent, bactericidal effect, and bioactivity. Ballast water is the seawater to stabilize the center of gravity of a ship. In water purification, a technology has been developed to reduce the dissolved oxygen (D.O.) concentration and pH by mixing water with gas to deaerate D.O. and dissolving CO2, but gas is mixed with such water. When purifying water quality, it is important to reduce the bubble diameter when gas is mixed with water, and to improve the efficiency of dissolving CO2 by degassing D.O.. In this research, a method to improve the mixing efficiency of ballast water treatment equipment by improving the fine bubble generation efficiency of the venturi tube is investigated by experiment and simulation analysis. We design venturi tubes with different divergent angles and investigate the optimized geometric combination by experiment and numerical simulation for improving the fine bubble size and volume. From the experimental results, we find that in the nozzles with small divergent angles the low pressure region becomes longer and the pressure recovery slows down, which promote the breakup of bubbles. The simulation results show that in the nozzles with the divergent angles of 15°and 20°, the affection region of gas-liquid two-phase flow becomes larger, and the concentration of bubbles near the wall or near the center of the nozzle will promote the breakup process of bubbles.

Ozone is superior to conventional disinfectants such as alcohol and chlorine as it is highly effective, environmentally friendly, and non-carcinogenic. However, ozone is not commonly used because of its short concentration lifespan. In this research, ozone ultrafine bubbles (UFB) were created, and experiments were conducted with the aim of obtaining ozone water with a long lifespan. The effect of the particle size distribution of ozone UFB on the concentration and the lifespan was measured. The ozone concentration increased by up to 75% with an increase in the number of bubbles. The lifespan of ozone concentration was partially increased, while the lifespan of ozone concentration decreased as the circulation time increased. The ozone UFB water was effective in killing Escherichia coli bacteria, and the effect lasted for one day. This may be due to the increase in the concentration of ozone in UFB water.

3D motion mixer is designed for mixing by rotating a sealed vessel without inserting any blades or other parts into the stirring tank, so that no foreign objects can be mixed inside the container during stirring. However, as the process and state of stirring of the sample inside the container was unknown, therefore, operating conditions such as rotation speed and filling rate were dependent on experience. In this study, a transparent container was used to reveal the flow state of the powder interface inside the rotating container. Spatial analysis methods were applied to the positional information in the recorded images of fluorescent particles distributed near the transparent vessel wall through visualization experiments using UV fluorescent particles to clear the stirring process and to evaluate the dispersion state.

The interaction between impeller stall and diffuser stall in a centrifugal compressor with a vaneless diffuser is investigated both experimentally and numerically. The numerical results showed that an impeller stall rotated at approximately 60% of the impeller rotational speed and diffuser stall cells rotated at approximately 25% of the impeller rotational speed. The experimental results showed that an impeller stall is generated intermittently, and one or two stall cells exists in the diffuser region and the number changes over time. In addition, it was found that the number of diffuser stall cells tended to be switched from one to two when an impeller stall was generated. This phenomenon was also observed by numerical analysis. Therefore, it is indicated that an impeller stall has effects on the formation of diffuser stalls. The low-velocity region discharged from impeller exit of the passage with impeller stall propagated in radial direction and merged into low-velocity region at diffuser exit. Thus, impeller stall effects diffuser stall.

For a baffled vessel agitated by turbine type impellers with six flat blades, the liquid flows discharged by the impellers were measured using the particle tracking velocimetry (PTV). The impellers were used in the two configurations for the blades to be open and closed. For the the two configurations of impellers, the time-averaged flow with induction of a secondary flow and the turbulence in the flow were evaluated and the discharge flow characteristics were compared. The external flow of the closed impeller has an increased inflow from the surrounding of discharge region and a decreased turbulence downstream near the baffles.

This study investigated the effects of crosswind and shroud mounting heights on the thrust characteristics of a shroud and a propeller for a drone using wind tunnel experiments. The shroud mounting height h_t/h_r was varied from 0 to 0.75 (with h_t being the distance between the height of the top of a shroud and the height of the tips of the propeller and h_r being the length of the inlet part of the shroud). Three kinds of shrouds were tested, and crosswind speeds of 0, 2, and 5 m/s were set in the wind tunnel. All required aerodynamic data were obtained using a 6-component balance. The results showed using an elliptical inlet shroud at a crosswind speed of 2 m/s provided the highest thrust at each shroud mounting height compared to other combinations of shrouds and crosswind speeds. In all shroud cases, as the h_t/h_r increased, the total thrust on the shroud and the propeller, the power output of the motor, and the efficiency of the propeller with a shroud generally increased. In contrast, the thrust on a propeller was independent of the h_t/h_r. Therefore, the thrust improvement from the shroud mounting is considered to be due to the increase in thrust on the shroud, which is caused by a decrease in pressure in the vicinity of the shroud inlet part.

In order to investigate whether the branch shaft can be used as an evacuation route or a smoke exhaust route in tunnel fire, an experiment was conducted using a tunnel model with a scale of approximately 1/10. The ceiling jet thickness was measured using the temperature rise distribution in the vertical direction. Under the condition of the branch height ratio of 1.0, which is the height ratio of the branch shaft to the main tunnel, the ceiling jet thickness in the main tunnel is larger than that in the branch shaft, on the other hand, under the condition of the branch height ratio of 0.8, the ceiling jet thickness in the branch shaft is larger than that in the main tunnel one. Under the condition of branch height of 0.6, the temperature rise was too little to calculate the ceiling jet thickness in the branch shaft. As a results, it is considered that the branch shaft can be used as a smoke exhaust route when the branch height ratio is 0.8 or more, and can be used as an evacuation route when the branch height ratio is 0.6 or less.

This study focused on impulse turbines that generate hydraulic power using excess pressure from the water supply. For hydropower generation in water supply systems, it is necessary to operate the turbine submerged in water for sanitary reasons. However, impulse turbines are generally designed to operate in the air. We have developed an impulse turbine suitable for submerged operation. In previous research, we have studied runner shapes suitable for submerged operation and methods to reduce lost torque. The shape of the nozzles used to supply the jet stream has also been studied. The authors aimed to evaluate the effect of the number of nozzles on the turbine performance of a submerged operating impulse turbine. The results show that the maximum efficiency increased with the number, and the operating speed range widened. Increasing the number of nozzles enhances the turbine performance due to increased input energy against power loss and the change of relative velocity angle. Increasing the number of nozzles enhances the turbine performance due to increased input energy against power loss and the change of relative velocity angle.

The development of a nano-hydro turbine that can effectively utilize the wasted hydro energy in infrastructure such as agricultural and industrial channels and irrigation waterways, will expand the available area as small hydro energy. Up to this time, the utilization of such a small hydropower has not progressed owing to economic reasons. Therefore, we focus on the Savonius type, which has the advantages of low manufacturing cost and excellent maintainability because of its simple structure. Conventionally, the Savonius type has been developed and researched as a vertical axis wind turbine. To effectively utilize the water surface flow, which is particular to open channels, we place the turbine runner perpendicular to the water flow and horizontally on the channel bottom. In our previous study, we experimentally investigated the effect of the turbine installation condition, which specifies the distance between a runner and the water surface, on the performance at each water level. As a result, it was clarified that there is a suitable turbine installation height for each water flow condition such as water level. Therefore, in this study, we visualized the flow fields paticular to Savonius type runners such as attached flow and dragging flow by PIV measurement and investigated the mechanism by which the turbine installation height brings about a difference in torque characteristics.

LES analysis was performed using OpenFOAM to investigate the characteristics of vortices in the separated-andreattachment flow between the blades of a sirocco fan. Five models with different blade thicknesses were used. The results showed the followings. (1) As the blade thickness increases, the position of the separation point changes from the leading edge of the blade to the middle of the suction surface. (2) The spectrum of pressure fluctuation between the blades changes along the separated shear layer as vortices merge and reattach when the separation occurs at the leading edge, but almost the same when separation occurs at the middle of the suction surface. (3) The size of the vortex continues to grow at the almost same rate from roll-up to reattachment. Its growing rate is independent of the blade thickness.

One of the methods to improve the thrust of a drone rotor is to attach an external guide composed of a bottom plate and cylindrical side plates around the outer circumference of the rotor blades. Although its thrust force has been studied in previous research, its efficiency as a thrust system is still unknown. In this study, the efficiency of the thrust system is evaluated from the thrust force and power consumption of the thrust system. Experimental results show that the thrust increases by 15% and the power consumption per rotor power decreases by 7%. The “figure of merit” (FM) also increases by 0.1 with the addition of the external guide.

This study focused on the nature of a cavitating jet issuing from a small rectangular orifice the same size as a control port in a water hydraulic spool valve. The aspect ratio of the jet exit was varied to investigate the cavitation jet behavior. The flow characteristics for each aspect ratio were measured, and the jet behavior was observed with a high-speed camera. The flow characteristics of cavitating jets are changed with the aspect ratio and cavitation number. The larger aspect ratio orifice shows a higher flow rate and larger cavitation number of inception. Visualization of a cavitating jet shows that the behavior of cavitation bubbles depends on the aspect ratio. The cavitating jet region is maintained to the same dimensionless position for all aspect ratios. In addition, the distribution and time history of luminance of the visualized images for each aspect ratio shows that the cavitation generates stably in the jet shear layer.

The effect of the nozzle spacing on the flow characteristics of twin rectangular jets was studied experimentally. The rectangular nozzle has a height of 10 mm and a width of 20 mm. The nozzle spacing between the center of twin rectangular jets was varied from S = 44 mm to 110 mm. Measurements of mean and fluctuating velocities were made with cross-wire probes for Reynolds number = 1.5 × 10⁴ based on the equivalent diameter d_e of 16 mm. In case of S/d_e = 2.75, the merging and combined points of the twin jets become closer to the nozzle exit than that of the other spacing ratio S/d_e because of the increment of mixing between the twin jets. In case of S/d_e = 6.875, the spread of mean velocity and turbulence increase at x/d_e ≥ 30 than that of the other spacing ratio S/d_e. Also, at x/S > 4.36, the mean velocity u /u_max and turbulence u^'rms/u_max has similarity for the dimensionless parameters of y/S.

The purpose of this study is to control the jet diffusion by using the deforming nozzle. The shape of polypropylene nozzle can change from square shape into the cruciform shape or the octagonal shape smoothly. The velocity measurement of the jet flow was performed using X-type hot wire sensors and the constant temperature anemometer. The basic characteristics of the jet flow, such as the velocity distribution and the half value width were obtained. Moreover, to catch the flow feature of the jet near the nozzle the flow visualization was conducted by using the Laser Light Sheet and the high speed video camera. As a result, it has been found that the diffusion of the jet issuing from the deforming nozzle is promoted, comparing with the case of the square nozzle jet.

The present paper describes the flow characteristics of air injected from a slit nozzle into a cylindrical container. The effect of the slit nozzle offset distance on the flow in the container were experimentally investigated. The velocity distributions were measured using the particle image velocimetry (PIV). The Reynolds number of the jet flow, Re = U₀b/ν (U₀: nozzle exit velocity (≈ 6 m/s), ν: air kinematic viscosity), was held constant (2000). The non-dimensional nozzle offset distance was changed from y_n/D = 0 to 0.4, where D is the diameter of the cylindrical container. When the nozzle is located at the center of the container i.e., y_n/D = 0, the jet oscillates with a large amplitude in the container and does not reach the bottom of the container as the same as the rectangular container. However, when the nozzle is offset close to the cylindrical container wall at y_n/D ≥ 0.2, the jet flows along the wall surface and reaches the bottom of container due to the Coanda effect. This non-dimensional nozzle offset distance is smaller than that of the compared rectangular container.

A desktop-type air curtain device capable of being installed on a desk to protect healthcare workers from infectious diseases was developed. Pseudo-exhaled air containing aerosol particles emitted from a mannequin was blown toward the air curtain generated by the air curtain device. The aerosol blocking effect of the air curtain device was investigated using particle image velocimetry measurements. Air curtain flow was maintained inside the gate of the air curtain device. The aerosol particles approaching the air curtain device were observed to abruptly bend towards the suction port without passing through the gate, signifying that the aerosol particles were blocked by the air curtain flow.

A virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The flow characteristics of virus particles inside the virus inactivation unit were investigated using numerical simulations. The percentage of particles colliding on the inner wall of the virus inactivation unit is 56 %. Especially, many particles collide with the partition plates behind the sharp-turn parts.

Washing with water jets has been used effectively in various areas in recent years. In this study, a coaxial fan-shaped jet combined with a high-pressure jet is being investigated to improve the washing effect using a fan-shaped jet nozzle. The combination of nozzles and jetting pressure have been studied as washing conditions, and effective jetting conditions are now being shown. In this report, we evaluate the washing effect of a relatively small object coated with a starch-derived thin film on a flat plate, focusing on the feed rate as a washing condition. As a result, we found that increasing the number of washes is more effective than slowing down the feed rate (lengthening the washing time per cycle) for the same washing time (jet impingement duration).

Sweeping jet is a jet that oscillates at high velocity and is known to have a higher mixing effect. Therefore, it is attracting attention especially from the viewpoint of flow control. In fact, although reports have been made that contribute to control, the flow characteristics that directly contribute to control have not been clarified, and optimization and practical application have not progressed. Moreover, it has been shown that the flow splits in the wake and that a vortex structure similar to a single Jet in cross flow is emitted to the left and right near the exit of the sweeping jet, but the formation and decay processes that link them have not yet been clarified. In this study, we focus on the temporal changes of the flow structure generated near the exit of the inclined sweeping jet and elucidate them. In addition, numerical simulations are used to capture changes in spatial and temporal phenomena in detail.

In order to investigate the dependability of the circular cylinder span length of a lock-in phenomenon, closed circuit water channel experimental apparatus was used, and the visualization experiment was performed. In the visualization experiment, the aspect of the vortex shedding from the circular cylinder which is carrying out the in-line forced oscillation was observed by varying the water level of a test section. In the experiment, adjustment was carried out so that flow velocity might constitute about 0.06 m/s every water level. Main experiment parameters are a circular cylinder diameter (6 mm, 10 mm and 16 mm), amplitude ratio (2a/d=0.5 and 1.0),oscillation frequency ratio (range of f/f_K is from 0 to 6), and circular cylinder span length (200 mm, 150 mm and 100 mm). As a result, although changes of the configuration of the lock-in corresponding to the variation of circular cylinder oscillating frequency were the same, it was found that the appearance ranges differ. Distribution of the lock-in range was classified into three groups by the aspect ratio. In the closed circuit water channel experiment, sunken span length was required 150 mm or more, and the aspect ratio L/d obtained the indicator in which the circular cylinder diameter which becomes 15 or more was selected.

Characteristics of hair-pin vortex shedding from axisymmetric bodies, such as a sphere and a circular disk, were investigated by flow visualization. The wakes behind a sphere and a circular disk at Re = 650, 800 were visualized by water tunnel experiment with fluorescence dye. The hair-pin vortex was continuously separated from the axisymmetric bodies. However, the orientation of hair-pin vortex shedding in various mode was depended on the Reynolds number. In this study, the azimuthal angle of the head of hair-pin vortex were observed from downstream direction. In the case of the sphere wake, the azimuthal angle of the hair-pin vortex was almost constant direction of 270 degree at Re = 650. The angle was gradually scattered at Re = 650. For the circular disk, it was found that the shedding angle of the hairpin vortex was more unstable as the Reynolds number increased than the case of sphere.

The wire mesh has a rectifying effect, and the parallel two-sided grid has a turbulent effect. This each effect is a fully developed area, and the transition process to that region has not been clarified. The purpose of this experiment is to clarify the transition process of the wire mesh wake. As the result, it was shown that there is a locally fast secondary flow in the wire mesh wake with the large open area ratio and that the direction of the secondary flow is different. It is considered that the structure of this secondary flow affects the rectification effect.

We have been developing a local air conditioning system which supplies airflow locally to users. This system directs a composite jet to users, created by colliding jets from nozzles on either side of a wall. However, Coanda effect near the nozzle caused instability at the collision point of the two jets, resulting in the composite jet not being delivered to the user. This research aims to control passively the suppression of Coanda effect by changing the wall shapes near the nozzle to convex type or concave type. The effects of convex thickness and concave groove width on the suppression of Coanda effect were examined by numerical simulation and flow visualization. As a result, Coanda effect becomes larger as the jet velocity slows down, and as a result, the two jet collision points oscillate greatly to the left and right. Moreover, Coanda effect can be suppressed if the thickness and groove width were larger, and consequently the composite jet was centered. On the other hand, the jet was influenced by the wall in the smaller sizes, and the composite jet was shifted to the left and right.

The flow characteristics in water in the tank under impinging air jets was experimentally investigated using the technique of flow visualization. The water surface depression was observed and velocities in water were measured with a particle image velocimetry (PIV) by varying the velocity of a jet and the distance between the nozzle and the impinging surface. From the experiments, it was confirmed that convective flows were formed in the flow inside the water tank by the impinging jets. The results of the experiment showed that from no concavity at the water surface, the concavity began to form from the impinging area, followed by a wave, and then, depending on the conditions, either a large wave formed over the entire water surface or the concavity oscillated, which could be classified into five states. It was also found that there is a suitable combination of conditions for the velocity of a jet and nozzle-to-water surface distance under which convective flow is enhanced.

Since the heat transfer performance of the impinging jets decreases rapidly away from the stagnant region, it is necessary to eliminate the non-uniform heat transfer distribution and to increase the heat transfer area. It has been shown that the combination of inclined and rotating control of the jet and axial excitation produces a bifurcation structure of the jet characteristic of blooming jets, resulting in high mixing performance. In addition, the DNS of this blooming jet when it is impinged on a wall reveals that the Nu number distribution and the heat transfer distribution change significantly depending on the impinging distance. Therefore, this study investigates the flow characteristics and heat transfer performance when the frequency ratio is varied in addition to the impingement distance.

Thermocouple and infrared thermography have been widely used to measure a temperature. However, thermocouple is only one point measurement, and infrared thermography cannot use through infrared impermeable material such as water or acrylic board. To solve these problems, we have developed a real-time temperature measurement system by using temperature sensitive paint (TSP). TSP is a kind of luminescent paint and its luminescent intensity decreases with increasing temperature. Using temperature dependency of TSP, planar temperature distribution can be measured from an image of luminescent intensity taken by digital camera. TSP is composed of luminescent molecule, binder, and solvent. In the present study, Ru(phen)₃²⁺ is adopted as luminescent molecule, and blue LED is used to excite the molecule. To evaluate the present measurement system, the temperature of the side plate in a two-dimensional jet was measured.

A sweeping jet produced by a fluidic oscillator has recently been examined from the viewpoint of flow separation control. A sweeping jet, which is an oscillating jet with high frequency and large amplitude, is generated by the internal structure of the oscillator, which eliminates the need for a drive unit. Sweeping jets have attracted attention as an active flow control device. Studies have proposed active flow control techniques for an airfoil based on sweeping jets. Most of these studies focused on the characteristics of the dynamic forces acting on the airfoil. However, the flow fields formed by the interaction between the sweeping jet and the main flow and their flow mechanisms are poorly understood, especially for the case where a sweeping jet is ejected into a main flow when a flow field is used to control flow separation. In this study, the detailed vortex structure generated by the interaction between the sweeping jet and the main flow was quantitatively examined using stereo PIV. The stream tube generated by the interaction between the sweeping jet and the main flow consists of two vortex tubes near the outlet of the sweeping jet at a location of 2.0d to 6.0d. At the wake over 10.0d, a pair of vortex tubes gradually separates.

We experimentally and numerically study the cavity oscillation of a compound jet in narrow parallel plates. Particle Image Velocimetry (PIV) obtains the time series velocity distribution with four jets. To perform the mode decomposition of the flow field, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are applied to the PIV data. The POD analysis reveals that the cavity oscillation involves two hierarchical structures: one corresponds to the cavity-scale oscillating of the jet, and the other to the advecting multiple smaller vortices. The DMD analysis classifies the oscillation modes into three categories: (i) oscillation mode on the container scale, (ii) pulsating mode on the container scale, and (iii) oscillation modes of individual jets. The results suggest that the superposition of these oscillation modes at the high flow rate is observed as cavity oscillation.