Small heavy solid particles can form clusters even in statistically homogeneous turbulence. To investigate the effect of particle size on the clustering, we have developed a direct numberical simulation code using the immersed boundary method.

The Japanese cedar pollinosis is a very serious problem in Japan. In particular, in the Tokyo metropolitan area, a survey reports that the prevalence rate in the 0 - 14 years age group became more than 10 times during the recent 20 years. We are concerned that the urban environment promotes the pollen re-transport and exposure. Therefore, we discuss the possibility that the re-transport of fallen pollen from building roofs increases the concentration of atmospheric pollen. We measured the amount of the cedar pollen on each height of the urban canopy layer by using Durham samplers, and calculated under the conditions with and without pollen re-transport. These measured and calculated results are compared to confirm the influence of the re-transport in the urban environment.

The pressure field data based on PIV contributes understanding flow field although PIV based pressure field has uncertain because of its boundary condition and assumption of two dimensional flow. Thus we did direct pressure measurement experiment and compared with PIV based pressure field in vortex ring impinging flow field. Focusing on the time span between vortex ring impinging and rebounding, PIV based pressure is match with direct measurement pressure. But focusing on the value of pressure coefficient, PIV based pressure is not match with direct measurement pressure. So if the PIV based pressure is used as quantitative data, it needs more consideration.

Low-temperature gas sterilization methods are needed to sterilize heat-sensitive equipment. These methods put sterilization gasses having oxidizing properties into a sealed space to destroy microorganisms attached to equipment by chemical reaction. Although Ethylene oxide gas (EOG) or formalin has been used as sterilizing gas, their strong toxicity adversely affects the people and the environment. Therefore, this study investigates a new method that improves sterilization performance by using ozone as sterilizing gas in addition to hydrogen peroxide. We model physical phenomena during the sterilization process and perform its numerical analysis. Finally, the concentration of sterilization gas is investigated using the developed simulation tool.

In this research, in order to improve prediction accuracy of numerical analysis of turbulent non-premixed combustion field, numerical analysis is performed by applying an improved combustion model to a turbulent combustion field by a coaxial methane burner, and A comparison was made with experimental result. We calculated with LES as turbulence model and modified 2 scalar framelet approach with level set function considering flame thickness and flame surface curvature as combustion model. As a result, it turned out that the model improves the prediction accuracy of the temperature compared with conventional model in the fuel lean region and the fuel rich region.

This study investigate the effect of Solidification process of thick-walled spheroidal graphite cast iron when controlling the cooling rate. The solidification analysis was done by Direct-Finite-Difference-Method using software for casting simulation, ADSTEFAN. The analytical model assumed a casting and had a sector of the outside diameter is 530 mm, the inside is 200 mm and the height is 300 mm (with five chills / without a chill). Casting the specimen based on the analysis model, compare the temperature measurement of the specimen with the result of the analysis. As a result, the cooling rate improved the model using chills. It's considering that chill affected the cooling rate.

The differential case is a part drive system of car, and a casting product. In order to lightweight car, it is required to thin the wall of motor part. Therefore, this study analyzed a molten metal flow, solidification for the purpose of the close nest defect prediction of the differential case using casting simulation “JSCAST”. As a result, the close nest defect outbreak position of the differential case were predicted by matching a temperature change when the molten metal of analysis and the experiment are solidified. We added feeder to the center of the product. As a result, the occurrence of shrinkage cavity could be eased.

A high-performance heat exchanger was developed. This heat exchanger has a form of double tube type, and the inner tube spins around its axis. Additionally, fixed blades are settled to touch the surfaces of the heat transfer tube. With this mechanism, the boundary layers on the heat transfer tube are scraped and the heat transfer rate is drastically improved. The heat transfer characteristics of this heat exchanger were experimentally measured in the previous study and it was suggested that the fluid flow in the heat exchanger contributes to improve the characteristics. In this study, the thermal fluid flow in the heat exchanger is numerically analyzed and its characteristics are discussed.

In recent years in Japan, there has been a change required in the generation of electricity with a focus on renewable energy. The aim of this study is to analyze CFD around the micro-hydro turbine. The final aim is to generate electricity by unutilized hydraulic energy in water supply facilities. As a result of the analysis, the flow velocity at the time of passing through the turbine increased, and the validity of the analysis was confirmed by the continuous equation. In addition, it was speculated that the torque acting from the fluid is affecting the change of the rotational angular velocity of the turbine.

A phenomenon in which a flow occurs without external force is known as the electrohydrodynamics (EHD) phenomenon, when a high voltage is applied a dielectric liquid. A micropump using the EHD phenomenon has several advantages. For example, no mechanical parts are require, noise and vibrations are almost completely absent. The purpose of this study is to analyze the flow inside the micropump using the EHD phenomenon. Thus, two 4mm diameter circular tubes with electrodes on the inner wall were modeled as an EHD micropump. This study explored the effects on flow as analysis parameters to which the voltage was applied. As a result, it was found that a rotational movement occurred between the electrodes, and flow in one direction occurred from the anode to the cathode side.

Liquid jet is used in industries. However, the relationship between pressurization and jet speed have never been established, because the jet phenomenon contains a lot of fluid dynamics factors, for example, physical property, container shape and profile of pressurization. The purpose of this study is, therefore, to develop the physical model for liquid jet ejection. We performed experiment and numerical simulation using ANSYS/FLUENT and MATLAB. We found high correlation between outlet velocity and pressure. Also, we found that the liquid jet is ejected as compressible liquid in the beginning but the behavior changes from compressible liquid to incompressible liquid over time.

2-D numerical simulation of the flames propagating through a periodic array of cylindrical obstacles with a diameter of 0.12 mm was performed to investigate the quenching phenomena of laminar hydrogen-air flames by a metal-mesh flame arrester. The reactive Navier-Stokes equations with the detailed chemistry were solved by using the OpenFOAM. The critical obstacle spacing, L*, was determined for three equivalence ratios, 0.4, 1.0 and 1.6. We have identified three regimes that characterized the interaction between the flames and the obstacles. The near critical regime with the obstacle spacing L ≈ L* is of particular interest and showed that reestablishment of a propagating flame can occur downstream even when the flame is locally quenched near the obstacles.

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 cruciform one smoothly and periodically. The velocity measurement of the jet flow was conducted using a PIV method, by changing the nozzle shape variously. The basic characteristics of the jet flow, such as the velocity distribution and the half value width have been obtained.

In hydraulic equipment, cavitation erosion is occurred on the surfaces at oil-jet impingement and the walls near the jet flow. Effects of a hole of a jet-impingement surface on erosion was investigated experimentally using hollow and solid cylindrical specimens. The stainless steel chamber with an inner diameter of 170 mm was utilized, including a long-orifice nozzle. The aluminum and acrylic specimens with a length of 20 mm, an outer diameter of 20 mm, and inner diameters of 0-5 mm were prepared. The test fluid was hydraulic oil with a viscosity grade of 32. The upstream and downstream absolute pressure were set at 10.1 MPa and 0.2 MPa, respectively. The standoff distance was set at 27.5 mm. The hole of the specimens contributed to reduce the erosion of the jet-impingement surfaces. However, the upstream-side inner wall of the flow passage was damaged for the small hole specimens and the downstream-side wall was damaged for the large hole specimens. The cavitating jet was visualized using a high speed video camera and the pictures were compared with the eroded specimens.

We investigated the free surface fluctuation of liquid in a rotating cylindrical container which receives horizontal vibration in the horizontal direction. In the experiments, we changed the oscillation frequency f and the rotation frequency Ω. We measured time dependent pressure fluctuation instead of free surface fluctuation. By performing FFT analysis, two significant frequencies f − Ω and f + Ω are obtained, which correspond to wave rotation in the same and in the opposite directions of the container, respectively. We also examined these results using linear wave theory.

It is important to use a wind-wave tank for investigating the mechanism of the wind-wave development. Although the wind-wave tank is generally used for investigating the mechanism, the maximum fetch in the wind-wave tank is limited by the length of the wind-wave tank, where fetch means the length of the water surface by air blowing. Therefore, the purpose of this study is to develop the fetch extension method, which we called the air-side loop method. In this method, the vertical distribution of streamwise mean wind speeds at the air outlet is reproduced at the air inlet by the shutter. The results show that the air flow in long fetch condition can be reproduced by the method.

Temperature-sensitive magnetic fluids are a kind of magnetic nanofluids, in which magnetic nanoparticles with the low Curie temperature are stably dispersed in a proper carrier liquid. Owing to the low Curie temperature, the magnetization of the magnetic fluid strongly depends on its temperature. This temperature-dependent magnetization realizes a magnetically-driven heat transport device, which does not need a mechanical pump, with energy conversion from thermal to kinetic energy. In the present study, a magnetically-driven heat transport device using the temperature-sensitive magnetic fluid was fabricated and its properties relating the long distance heat transfer was investigated. As the obtained results, the temperature-sensitive magnetic fluid could be driven by applying heat and a magnetic field. Under the conditions of the magnetic field intensity of 136 kA/m and the heat flux of 5 kW/m², the fluid was found to show the mobility and transfer the heat with a long distance of 6,000 mm.

Magnetic fluids are stable suspensions of ferromagnetic particles in a solvent such as water and kerosene. In the presence of magnetic field, it is well known that ferromagnetic particles form chain-like clusters in the field direction. When chain-like clusters of the ferromagnetic particles are formed in the fluid, anisotropic properties of thermal conductivity appear. From the visualization experiment using a microscope, it was found that a silver nanowire in the magnetic fluid orients its axial direction in the direction of the magnetic field in the presence of uniform magnetic field. It was also found that by adding silver nanowires to the magnetic fluid, it is possible to enhance the thermal conduction anisotropy caused by applying the magnetic field.

To develop a new firefighting method with an extinguishing capsule, the extinguishing experiments were performed using a rubber balloon filled with a physically-acting gaseous extinguishing agent (N2 and Ar gases). The rubber balloons were carried at an arbitrary speed to the extinguishing target by an electric linear slide actuator. A methane-air diffusion flame was used as the extinguishing target and formed on a porous burner. The extinguishing probability was measured by varying the inert-gas volume in and the transporting speed of the rubber balloon. From the experimental results, we have clarified the optimal speed range to extinguish the flame for each inert-gas volume.

To investigate the physical flame-retardant effect of origami structure on a thermally thin flammable solid material, the flame-spread experiments have been performed. The aluminum hydroxide paper folded to an accordion shape was used. Upward flame spread was formed. From the experiments, the extinction limits and the flame spreading rate at near extinction limits were clarified.

Currently, instead of the popular injection system which is administered through the needle, a needleless injector has been developed all over the world aiming at reduction of pain, safety, and further convenience. A powder injection device driven by a shock tube was fabricated for the development of a system in which minute drug particles are injected at high speed and administered to living bodies. In this study, in order to investigate the influence of size, density, number and flight velocity of drug particles on penetration into the living body, and the optimum particle condition for powder injection device, visualization experiments were carried out under a few kinds of conditions. Further, numerical analysis was carried out and comparison between the experiment and numerical results was performed.

Particle diffusion experiments were conducted in a short-time diffusion field where the meandering diffusion is dominant using a wind tunnel with active grid. Relative diffusion and meandering diffusion were separately measured by visualization line measurement using laser and line scan camera. Each diffusion scales, total diffusion, relative diffusion, and meandering diffusion were obtained, and it was confirmed that they almost agreed with the Gifford's theorem. The intermittency shows a different tendency in the total diffusion and relative diffusion in the downstream direction and the relationship with the meandering ratio which is the scale of the diffusion field was obtained.

Solid-liquid two-phase flow was studied in an inclined settling rectangular tube. Three kinds of inclined settling rectangular tube was used this experiment where distance between inclined side plates is 53, 83 and 114 mm. The upward flow velocity and downward flow velocity were measured, and inclined rate effect in an inclined settling rectangular tube was studied experimentally. Moreover, the velocity ratio of each component was calculated. At the equipment of height 300mm, the optimum distance between inclined side plates was proved to be 83 mm.

The purpose of this study is to develop the sensor to measure the wall shear stress due to the flow by using MCF rubber. MCF is the name of Magnetic Compound Fluid. MCF rubber is combining the metal particle in a natural rubber (NR) latex. The MCF rubber can be measured the force normal to the rubber and shearing force. The force acting on MCF rubber causes the change of electric conductivity of rubber. This is caused by the deformation of MCF rubber. The experiments are carried out with the mechanism of rotational viscometer. The results show that the MCF rubber has the good time response as the sensor.

Calcium carbonate has been studied more than 100 years as the subject of basic chemistry, materials science, chemical engineering, and so on. In the natural world, this is often found in seashells and bones of sea creatures, and when these settle on the ocean floor for millions of years it forms limestone. Specific surface area defined as the total surface area of a material per unit of mass (with units of m²/g) is one of the key physical properties to evaluate powder or porous solids. Here we report our original crystallization method to obtain nanoparticles of calcium carbonate with huge specific surface area (~200 m²/g). We show the effect of process parameter, especially fluid properties; viscosity, temperature, and concentration on calcium carbonate microstructure.

The precession of a rotating vessel drives strong turbulence, and therefore strong mixing, of a confined fluid. We aim at applying this technique to the mixing of granular materials and conduct the numerical simulation by using the discrete element method to evaluate the mixing efficiency of this system. However, the precessing spherical vessel cannot drive effective mixing of granular particles regardless of the packing rate. In particular, when the rate is high, we need agitation to fluidize and mix the material.

In this paper, we measure the flow around a stirring object revolving inside a circular casing by using a derotator and the Rotational-Invariant-PTV. We experimentally evaluate the performance of the Rotational-Invariant-PTV with a derotator in three different states of the rotational flow in a circular casing, which are rigidly rotating flow, unsteady flow and stationary flow. As a result, it is confirmed that we can stably observe the rotating flow as a stationary state through a derotator, and easily measure the unsteady velocity field around a stirring object. In addition, we show the robustness of the Rotational-Invariant-PTV against strong rotation by comparing the particle tracking results of the Rotational-Invariant-PTV with those of the Cross-Correlation-PTV.

In this study, we aimed to compare and examine each stirring blade from the mixing behavior of the Taylor vortex mixer, the mass transfer between the vortex, and the energy aspect. In order to compare and examine each stirring blade, we used a mixed stirring experiment using Taylor vortex rhodamine solution and stirring using a torque meter. We conducted experiments to determine the power number of the stirring blade. As a result, it was revealed that the energy required for industrial stirring blades was large, although high mixing efficiency (80%) could be maintained by using cylinders with protrusions.

Ironmaking blast furnace is a reactor to produce molten iron. In the furnace, iron ore and coke particles are packed in layer-by-layer structure. Iron ore is heated up, reduced, softened, and then melted. During these processes, ore layer deforms and its permeability is deteriorated. It is known that excessively high pressure drop causes in instability of blast furnace operation. Recently, a technique to mix coke particles into the ore layer is attracting interests. Thus, it is important to understand the deformation characteristics of iron ore layer that contains coke particles. In this study, the deforming ore layer was modeled by using Discrete Element Method, and the deformation behavior of coke mixed ore layer was discussed through numerical analysis.

Settling enhancement effect in a inclined tube was studied experimentally with calcium carbonate slurries. The model proposed in this study, which has a wedge-shaped layer of clear liquid developed at the upper surface of the inclined plate, can explain the difference between vertical and inclined settling velocities. It was shown that the inclined settling rate increases with increasing inclined settling enhancement factor in consideration of inclined tube cross-section shape.

The Buoyancy Weighting-bar Method can estimate particle size distribution and velocity mean particle sizes of solid particles. In this study, W/O emulsion mixed with ion-exchanged water and n-dodecane was prepared, and then droplet size was measured by Buoyancy Weighting-bar Method. The droplet size distribution observed by Buoyancy Weighting-bar Method was almost agree with that by microscopy.

A conventional disk turbine impeller with 6 flat blades was modified for the blade geometries, namely, the number and the axial width of the blade. An impeller with the 12 flat blades of standard width (12-STD) and an impeller with 6 flat blades of small width (6-Small) were employed to produce a nearly uniform liquid flow in a narrower flow path between the neighboring blades of the rotating impeller. The internal flows of such impellers in a baffled vessel were examined by means of PTV and their power characteristics were evaluated, in comparison with that of the 6-standardly bladed turbine type impeller (6-STD). With both 12-STD and 6-Small impellers, the head characteristic rather than the flow one was improved because of the flow patterns reformed in the intensity and directionality leading to the uniformity. The resultant power transmission differed among the impellers but the efficiency was unchanged, which suggested viscous losses corresponding to the powers.

As demands for the reduction of energy consumption in steam heating system increased, it is very important to measure accuracy of mass flowrate in steam flow. Particularly, it is essential to confirm the measurement accuracy and uncertainty of the steam flowmeter that can be installed afterwards in existing piping. In this paper, at first, we described the procedure for realizing steam flowmeter calibration by general-purpose steam facility. And we conducted the calibration of tested steam flowmeter to be attached the outside of a tube using a circumferential heater in only dry steam flow. Finally, we discussed the uncertainty analysis of tested flowmeter.

In hydraulic systems such as construction machinery, many pipe fittings including a tee, an elbow, a bushing, a nipple, and a socket are used. Pressure loss occurs when a hydraulic oil passes through these fittings. It is requested that the losses should be estimated precisely and reduced efficiently. In this report, the pressure losses through a hydraulic pipe with many fittings are measured using a hydraulic oil and the flow loss is estimated experimentally.

Nowadays, fast-response pressure sensitive paints (PSP) with high pressure sensitivity and application methods for internal flows are developed, and it is expected that the development enables application of PSP to EFD analysis of internal flows of turbomachinery. However, temperature sensitivity of PSP is still a serious source of measurement error. In this study, we apply PSP and TSP to inner surface of a turbofan casing, to examine the non-uniformity of temperature distribution on the surface when the turbofan is operated, and its effect on pressure measurement by PSP. As a result, temperature distribution on the inner surface of the turbofan casing in operation showed non-uniformity as large as 4K, causing serious error of 26kPa in the result of PSP. By applying temperature compensation, the error has decreased drastically as small as 0.29kPa.

In this research, we are aiming to develop the measurement method which can be detected surface pressure on a freeflight projectile at supersonic to hypersonic speed by using unsteady pressure measurement technique based on PSP. For this purpose, we improved the “ultrafast-response PSP” with 90% rise time t_90% = 0.81 μs, which had the fastest response time, and developed “ultrafast-response bi-luminophore PSP”. In this study, by conducting the calibration test, the basic characteristics of the developed bi-luminophore PSP were evaluated.

This research aims to analyze the reproducibility of wind tunnel tests using windbreak fence models. To achieve the objectives, wind velocity distribution and turbulence intensity distribution measurement in wind tunnel using PIV and hot wire anemometer are carried out with model and prototype of panels respectively. Corrugated perforated panels are adopted as test pieces which are commonly used for windbreak fences in railway in Japan. Scaling ratio is 1/5 and 1/10, but that of panels’ thickness is 5/8. As a result, wind velocity distribution and turbulence intensity behind the 1/5 scaling model and the prototype shows similar tendency. However, the results behind the 1/10 scaling model and the prototype shows different trend. There is a possibility that the results are caused by the “apparent” solidity ratio (taken account of thickness) difference between 1/5 and 1/10, and better reproducibility testing model can be made with consideration of the “apparent” solidity ratio.

An underexpanded jet is one of supersonic jets. The jet becomes underexpanded when the pressure ratio exceeds the critical value across the convergent nozzle discharging it. The jet is not uniform because of the presence of the expansion wave, the compression wave and the shock wave formed in it. In the jet boundary, many vortices are generated by the shearing stress between the supersonic flow of jet and still atmosphere The interaction of vortices and jet is closely related to the strong acoustic noise radiating from such flow field. In this study, the acoustic characteristic of flow field of underexpanded jet was experimentally examined. The flow field was visualized using shadowgraph methods. And the acoustic noise emitted from the flow field is measured using a microphone.

In order to understand the aspect of flow around two circular cylinders, the pressure on the circular cylinder surface was measured. The single tube manometer was used for measurement of the pressure, and image processing in a computer was introduced into reading of the scale. The pressure measurement experiment was performed by the low flow velocity which is performed by flow visualization. The Reynolds number based on the circular cylinder diameter D and the flow velocity U was Re=2500. Surface pressure distribution of the circular cylinder was investigated for every arrangement pattern of two circular cylinders, and the flow characteristic was obtained. The drag coefficient C_D was calculated from distribution of the measured pressure coefficient C_P.

Since high chromium cast iron forms high hardness Cr7C3 carbide, it has high wear resistance and it is used for heavy equipment parts and hot working rollers. Hot working rollers are manufactured by casting. However, the problem is nonuniformity of solidification structure and macro / micro segregation due to convection phenomenon of cast iron. In this study, we observed high temperature samples and the flow field of high chromium cast iron using CLSM. As a result, the formation of solidification structure influences in flow direction and moving speed of sample surface. In addition, it is possible to capture micro segregation formation process of high chromium cast iron from in situ observation by CLSM and average slag moving.

Currently, small hydropower generators using unutilized hydropower energy are receiving much attention in Japan. As one method using unutilized renewable energy, it focus on power generation through a small hydropower generator. The aim of this study is the development of a highly efficient turbine. This study is to visualize the flow field of a pipe with a small, axial hydro turbine in pipes of small internal diameters, like are present in city water services. In particular, it is an analysis of the flow field around a small, axial hydro turbine focusing on the difference in the number of blades as imaged by a high-speed camera.

The influence of surface tension of extinguishant on the flame blowout probability of indirect fire extinguising method which the fire extinguishant droplet was impinged on heated solid surface was investigated experimentally. The surface tension was controlled by mixing a small amount of a surfactant in pure water. The droplet collision behavior onto the heated plate was captured with high-speed camera. We especially focused on the spreading behavior, liquid film evaporation behavior, and secondary atomization of the droplet. It was found that the fire extinguishing ability was reduced by increasing the surfactant concentration in pure water. It was also found that the indirect fire extinguishing ability depends on the amount of vapor generated after the collision of droplet.

Baton wheel is known as a bicycle-wheel aerodynamic drag reduction equipment. The bicycle wheels fitted with a Wells turbine is effectively a baton wheel, and have the similar effects. In the cross flow condition, not only the aerodynamic drag is reduced but also the driving torque can be generated. The aerodynamic characteristics of a bicycle wheel with the Wells turbine is studied in this report. A few Watts power could be available, but even higher power can be generated depending on wind conditions.

The purpose of this study is to realize the pump driven by the traveling waves which is generated by two standing sine waves, and to improve the performance of the pump. We compared the flow rate waveform of experiment with that of theory, and we investigated the cause of difference between experiment and theory. As a result, it was confirmed that the pump tested in this study did not generate a sine wave but generated a triangular wave and a gap created between two plate makes flow rate waveform intermittent. As its measure, we clarified that it is effective to add to the intermediate driven point between the nodes and the anti-nodes.

Cylindrical wings with longitudinal grooves, streamwise grooves and spiral fins are used to clarify the performance of the magnus windmill. Windmill number of revolutions was measured using a wind tunnel at wind speed of 4~20 m/s and a cylinder rotation at 400~1600 rpm. As a result, it was revealed that a spiral fin has a windmill rotation with the lowest wind velocity and a longitudinal groove cylinder has a highest rotation number of windmill.

Biodiesel and biogas as the renewable energy will give the advantages for reducing fossil fuel dependency. In addition, biogas is easy to adjust as dual fuel in the diesel engine without major modification. However, the biogas mainly contents are methane (CH₄) and carbon dioxide (CO₂). The effect of methane content ratio on combustion pressure, thermal efficiency, specific fuel consumption and biodiesel fuel replacement investigated under varied torque with constant engine speed. The maximum 2.1% thermal efficiency improvement with 27.4% biodiesel fuel replacement has achieved. Overall the adjustment of biogas in the absence of knocking was possible for all load variation and methane content ratio, considering the thermal efficiency using dual fuel mode recommended in the high load condition.

The effect of pyramid type hood for reducing tunnel micro-pressure waves are experimentally studied. The cross sectional shape of hood is square, and cross-sectional area ratio of hood and tunnel changes 1.27-2.5 in longitudinal direction. The hoods have some adjustable windows. Model experiment is performed for various hood length and opening height h, and the pressure gradient in the tunnel is measured. The experimental result shows that the optimization method of adjusting h can be applied to pyramid type hood. Besides that, if h is optimized, the pressure gradient for pyramid type hood is smaller than that for hoods with constant cross-sectional area.

The tunnel-hood effect should be improved to increase the maximum speed of the Shinkansen, while avoiding the serious noise and vibration due to micro-pressure waves (MPWs) from the tunnel portals. The longitudinal positions of windows on conventional hoods are usually optimized. This study used model experiments to investigate the optimal height of windows on the tunnel hoods. The obtained results showed that the hoods with optimized-height windows can reduce the MPWs to the same value as conventional hoods. In addition, the height-optimizing procedure is very simple, compared to the position-optimizing procedure, and the optimized-height can be easily and certainly obtained.

Scale model launching experiments and numerical calculations were carried out to evaluate the aerodynamic drag of the middle part of a train in the open air and in tunnels. Scale model launching experiments were performed by projecting two types of cylindrical trains with smooth and concave-convex surfaces into three types of circular tube tunnels with different diameters to measure pressure variations in the tunnels. Friction factors of the middle part of the trains in the tunnels were determined by comparing pressure variations of the numerical calculations to those of the experiments. Friction factors in the open air were estimated from the factors in the tunnels by extrapolation method in certain conditions. Based on the obtained friction factors, it is demonstrated that the aerodynamic drag of a Shinkansen train estimated from the friction factors in the tunnels is approximately 4 to 8 percent greater than that in the open air.

The tunnel hood is one of the countermeasures for reducing the micro-pressure waves emitted from high-speed railway tunnels. The experiments using the axisymmetric models were conducted for investigating the effect of the conventional vented hood and the cross-sectional area of the unvented hoods. The ratios of the cross-sectional area of the unvented hoods to that of the tunnel were set to 1, 1.4, 2, 2.5, and 3. The results show that the optimum ratio of the cross-sectional area of the unvented hood is 2.5, and the effect of the unvented hood of the optimum crosssectional area with the length of 30 m is equivalent to that of the vented hood of the length of 50 m in the case where the train nose length and its speed are 15 m and 360 km/h, respectively.