In the flow around a circular cylinder, a sudden decrease in the drag force occurs at a high Reynolds number, but the same phenomenon occurs at a lower Reynolds number in the case where there exist grooves or roughness on the circular cylinder surface. In previous study of authors, in order to investigate the effect of the depth and number of grooves on a circular cylinder for both arc and triangular grooves, the drag coefficient, pressure, turbulence intensity and velocity distribution were measured. Moreover, the flow around circular cylinders was analyzed by applying the RNG k-ε turbulent model. From these studies, it was found that in order to reduce a drag in a wide range of Reynolds number, the depth and number of grooves is increased and the circular cylinder surface is made to change to a turbulent boundary layer in a low Reynolds number. Furthermore, it was clarified that in order to prevent generating of a separating bubble, capacity of groove is made small and separation is retarded. In this paper, new shape of grooves was developed on the basis of the factor of above-mentioned drag reduction. As a result, the separation point of the circular cylinder with grooves of curved sectional shape shifts to the most downstream side and the drag coefficient becomes the smallest.

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To understand the mechanism of the turbulence transport in porous media, large eddy simulations have been performed by a multiple-relaxation time lattice Boltzmann method. The porous media presently considered are square rod arrays. Changing the square rod size, five different cases of the porous media are analysed. Using the simulation data, the budget terms of the volume averaged Reynolds stress equations are investigated in detail. It is found that the behaviour of the production, redistribution and dissipation terms drastically changes when the porosity of the porous media becomes higher than 0.75. When the porosity becomes higher, it is observed that a perturbation by the Kármán vortex shedding propagates in the whole domain. This perturbation is the source of the the cross-streamwise component of the Reynolds stress. It is confirmed that there is a relation between the porous characteristic scales and the turbulent length scale and one of the production terms of the transport equation of the volume averaged Reynolds stress can be modelled by the Darcy-Forchheimer form.

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Spatial distributions of flow reattachment position on the bottom wall downstream of a backward-facing step in a duct have been measured by 2D PIV method. Investigations have been done for changing the flow Reynolds number, ranging from steady (Re=200) to unsteady (Re=1000) flow regimes for the stepped duct having an aspect ratio of 16 and expansion ratio of 2. It was found that non-uniform spanwise distribution of the reattachment length was observed in each case. Within the steady state, the reattachment length shows a unique distribution in the spanwise direction being protruded like a tongue over a channel, that is, having the maximum at the center of the duct but the minimum near the side wall. Its short length near the side wall reaches only 60% of that of the center of the duct. Generally, the reattachment length increases rapidly as the Reynolds number is increased and has the maximum at the center of the duct at Re=400. It should be noted that in this paper, as the Reynolds number is further increased Re>400, the reattachment length conversely decreases due to the flow unsteadiness occurring near the center of the duct. This flow unsteadiness expands to the side wall with the further increase of the Reynolds number, therefore, it makes the spanwise distribution of the flow reattachment position more complicated.

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Thermal management of industrial vehicles is severe due to heavy load and low traveling speed under operation. And amount of noise exposure tends to increase compared to passenger cars because the industrial vehicles often stay in an area for a long time. Speed-up of a cooling fan and enlarging open area on an engine compartment enhance cooling performance but noise exposure rises. Therefore means to satisfy both of the thermal management and the low noise are required in design of industrial vehicles. In this study, non-parametric sensitivity analysis has been applied to an engine compartment of an agricultural tractor to obtain sensitivity on design variables to coolant temperature. The non-parametric sensitivity analysis has brought in less computational load compared to conventional parametric approach regarding the engine compartment design.

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In order to improve the efficiency and decrease the noise level of centrifugal blowers at the same time, we have developed a “slit diffuser” which has a slit structure that connects the flow passages of neighboring diffuser vanes. We investigated the influence of slit structure in terms of performance, internal flow field, as well as noise level. We obtained the following conclusions. Compared with non-slitted diffusers, for the diffusers with slits, the stagnation area generated from the diffusers decreases near the slits and there is less diversion of the mainstream flow. Owing to the flow that goes through the slits from the pressure side to the suction side, the stagnation inside the diffuser is improved and the adiabatic efficiency increases by 0.8%. Compared with non-slitted diffusers, it is possible with slit diffusers to reduce the blade-passing frequency noise and to suppress the acoustic resonance.

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Homogeneous heat conduction analysis can be easily solved by means of the boundary-element method. However, domain integrals are generally necessary to solve the heat conduction problem in non-homogeneous and functionally gradient materials. This paper shows that the three-dimensional heat conduction problem in non-homogeneous and the functionally gradient materials can be solved approximately without a domain integral by the triple-reciprocity boundary element method. In this method, the distribution of domain effects is interpolated by integral equations. In this paper, heat conduction analysis is carried out for laminated materials and a particle-dispersed composite as special cases of functionally gradient materials. The same triple-reciprocity method is used for the analysis of functionally gradient materials, the laminated materials and the particle-dispersed composite. A new computer program is developed and applied to several problems.

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A novel rotational internal combustion engine has been investigated in this study. No eccentric rotational component is used in this engine, resulting in vibration-free operation. The engine consists of rotor casing and two types of rotor; cycloid rotor and trochoid rotor. The shape of the cycloid rotor is characterized by epicycloid surface, and the trochoid rotor also superior-epitrochoid surface. In this paper, first, the typical configuration was shown. Next, a procedure for designing the rotors were described in detail. Furthermore the design drawing and appearance of the prototype engine were given. Its cyclic behavior, the time variations of the chamber volume and the estimated pressure were also indicated. Additionally the flame behavior in the working volume of the prototype engine driven in motoring condition, was presented. Finally the compactness and S/V ratio of the engine was investigated.

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A Mist flow, an air flow with mixed water droplets, is suitable for rapid cooling by the latent heat of vaporizing water droplets. The technique using a small amount of fine mist is promising to partially cool the local region. The air flow which contains fine mist promotes heat transfer in some area. The cooled air by means of the evaporating mist augments the heat transfer on the duct wall. All the mist evaporates, and does not remain in the air flow. Therefore, this technique can be useful as well as the usual single phase air flow with heat transfer enhancement of a forced convection. This paper attempts to figure out how the heat transfer coefficient in the mist flow is affected by Reynolds number and heat flux on the duct wall. Experiments of heat transfer enhancement using the mist flow were carried out. It was found that the heat transfer coefficient increases when the mist is added, Reynolds number becomes larger and the added heat flux becomes smaller. The experimental results show that this technique is very promising to heat transfer enhancement.

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The aim of this study is to clarify the characteristics of the heat transfer enhancement in the downstream region of a backward-facing step flow using a small amount of mist. The effects of the diameter and the amount of mist upon the heat transfer enhancement were investigated analytically and experimentally. The images of the flow field and the behavior of the mist were taken using a high-speed video camera. The distributions of spatial temperature and the heat transfer coefficient were measured. The evaporation position of the mist in the main flow was calculated with the changing parameters of the relative humidity and the particle diameter of the mist. The results of the visualization experiment and the theoretical calculation revealed that the mist almost evaporated in a relatively small region of the channel. The experimental results show that the heat transfer coefficient becomes maximum near the reattachment position irrespective of the amount of mist, and that the maximum and the average Nusselt numbers increase linearly as the amount of mist increases.

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Spark ignition of premixed gases was experimentally studied. Minimum ignition energy and initial burning velocity, which is a burning velocity at an initial stage of flame propagation, were measured and their dependences on equivalence ratio were discussed. Minimum ignition energy takes a minimum value when equivalence ratio is around 0.9 for methane/air mixtures, and around 1.5 for n-butane/air mixtures, which corresponds with the study of Lewis and von Elbe. A shadowgraph technique was used to observe the growth of the flame kernels. A burning velocity was measured from the images of the flame kernel, and initial burning velocity was defined as a burning velocity at the moment when the equivalent radius of the flame kernel is approximately 3.0mm. Initial burning velocity takes a maximum value when equivalence ratio is around 0.9 for methane/air mixtures, and around 1.5 for n-butane/air mixtures, while laminar burning velocity of well-grown flame takes a maximum value when equivalence ratio is around 1.1 for both mixtures as known well. This is caused by the curvature of flame surface at the initial stage. It is suggested that the equivalence-ratio dependence of minimum ignition energy is derived from that of initial burning velocity.

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In this paper, we conducted analysis of p-V-T relation of cryogenic hydrogen using classical Molecular Dynamics (MD) and path integral Centroid MD (CMD) method to understand an effect of quantum nature of hydrogen molecules. We performed NVE constant MD simulation across a wide density-temperature region to obtain an Equation Of State (EOS). Simulation results were compared with experimental data. As a result, it was confirmed that classical MD cannot reproduce the experimental data at the high density region. On the other hand, CMD well reproduces the thermodynamic properties of liquid hydrogen. Moreover, it was clarified that taking the quantum effect into account makes repulsion force larger and the potential well smaller. Because of this mechanism, the intermolecular interaction of hydrogen diminishes and the virial pressure increases.

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Concentrated Solar Power, or CSP, is a system that concentrates and converts sunlight into thermal energy by tracking the sun. University of Miyazaki set up a beam-down solar concentrator, one of CSPs, on August 2012. Gardon gauge is a heat flux sensor which is generally used for measuring the heat flux on the light condensing part of CSP. Gardon gauge needs a water-cooling system, and it is impossible to measure heat flux on the sunlight condensing part where equipment is running. In this study, the thin-film heat flux sensor which can measure the heat flux by non-cooling during the equipment operation was developed. Furthermore the calibration system for the heat flux sensor was developed, and the advantages of the sensor were confirmed.

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Polymer electrolyte fuel cell (PEFC) is expected to be used with the power sources for the automobile and the cogeneration power source for home and so forth. At the cathode-side of a PEFC, oxygen is transported as the reactant gas from gas channel through gas diffusion layer (GDL) to the catalyst layer. However, the large quantity of moisture is generated under the situation of the high power generation. Since, as a result, the moisture blocks transporting oxygen, the cell voltage falls off drastically. The objective of this study is to improve the management of moisture from GDL in gas channels of separator for PEFC. The oblique micro-grooves are manufactured inside gas channel walls. Water from GDL is discharged through the micro-grooves to upper-side of gas channel by surface tension and shearing force generated by air flow. Velocity of water flowing in the micro-grooves was measured by using the laser induced fluorescence method. It was confirmed experimentally that micro-grooves manufactured inside gas channel worked properly, that is, water discharge from GDL to upper-side of channel was succeeded. The water velocity and effective length of micro-grooves to remove water from GDL surface increased with the decrease in inclination angle θ of micro-grooves in this experimental range of θ=20～40°. It was shown that the effective length of approximately 200mm, which was overall length of experimental apparatus, was attained.

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