The ventilation technology for road tunnels has been developing for these 30 years. The author always has been involved in this field, and describes various notable aspects of its development. They include 1) the ventilation planning for the Kan-etsu Tunnel, in which ordinary and emergency ventilation for longitudinal tunnel was studied, 2) the emergency strategy for transversely ventilated tunnels, 3) the emergency ventilation simulation for the Yamate Tunnel, which has a complex ventilation structure, etc. The Author describes at the last part of the paper the importance of establishing a safety standard of road tunnels facility in an early stage.

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This paper aims to simulate motions of wind turbine with free yaw and the rudder under wind direction change. Rudder's contribution to yaw alignment under operating condition is presented in this paper using simulation of traditional fixed rudder wind turbine model. Related to this, swing rudder system is also modeled in this paper. Swing rudder is a rudder pivoted on the nacelle. The yawing motion is simulated using aeroelastic simulation code FAST developed by National Renewable Energy Laboratory. Models of wind turbine are based on Zephyr Airdolphin GTO. In order to evaluate the efficiency of swing rudder, Simulation condition is set to be one wind direction change with steady wind speed. As a result, it is revealed that aerodynamic force on the rudder is far lower contribution compared with rotor aerodynamic force. Moreover rudder's inertia acts as obstacle on yawing. In the same condition, swing rudder contributes more than fixed rudder and reduces maximum yaw error when wind direction change is fast.

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The direct numerical simulation of a spectral method is performed to study the flow structure of a turbulent channel flow at low Reynolds number, where the turbulent and quasi-laminar regions alternatively appear in the streamwise direction. The turbulent region is punctuated by the high-speed and low-speed fluids at the upstream and downstream sides, respectively. As a result, both the bulk and friction Reynolds numbers decrease from upstream to downstream regions, which makes the low Reynolds number effects pronounced at the downstream turbulent region; attenuation of turbulent diffusion into the wall vicinity and decrease in dissipation rate there. Differences between streamwise vortical structures in upstream and downstream turbulent regions are also investigated, which elucidates the effects of local mean flow on the vortices even in the wall vicinity as well as low Reynolds number effects.

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The aim of this study is to address the essential features of experimental decaying grid-generated turbulence. Specifically, this study has focused on invariants of grid turbulence in the downstream region and Rotta model by means of direct numerical simulation based on the finite difference method. The mesh Reynolds number defined by the mesh size of the grid M, streamwise mean velocity and kinematic viscosity is 2; 500. Streamwise computational domain size is 112 M. The result shows that u²_oL⁴ is nearly constant such that u²_oL⁴ ∝ X^0:08 in the far downstream region, where X = x/M - x_o/M, x is the streamwise distance from the grid and x_o is the virtual origin. Rotta model is applicable in the region holding u²_oL⁴ = constant, and value of the Rotta constant is almost 1. The value can be well estimated by an estimation method introduced by previous experiments.

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The effects of the applied voltage and electrode dimensions on the backward jet induced by a dielectric barrier discharge plasma actuator (DBD-PA) are investigated experimentally. The applied voltage waveform used in this study is a pulse waveform with an amplitude V_PP = 8 kV (-8 kV ≤ V ≤ 0 kV) and a frequency f = 5 kHz. With respect to duty ratio D of the applied voltage waveform, it is found that the backward jet induced by the DBD-PA is only generated for 93% ≤ D ≤ 93.5%. On the other hand, the forward jet is only generated for 10% ≤ D ≤ 92%, and the velocity and direction of the jet are significantly dependent on the duty ratio. These jets do not occur when D < 10% and D > 93.5%. With respect to the electrode width, the backward jet is generated for an upper electrode of sufficient width (10 mm in this study), even if the lower electrode width is short. In contrast, the forward jet is generated when the upper electrode width is short (5 mm or less), and the velocity of the jet increases as the upper electrode width decreases.

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Large-scale vortical structures and associated mixing in a methane-air coaxial jet are actively controlled by manipulating the initial jet shear layer with miniature jet actuators installed on the inner surface of the annular nozzle. The periodic radial miniature jet injections are realized by using a rapid-response pneumatic servovalve, and sinusoidal/pulsed flowing are employed in the present study. The spatio-temporal primary jet structures are investigated through phase-locked 2C-PIV (2 Component Particle Image Velocimetry) and Stereoscopic-PIV. In the pulsed configuration, it is found that intense vortex rings are produced in phase with the periodic control input regardless of the valve-driven frequency f_v examined. When the Strouhal number St_v, which is defined with f_v, is larger than unity, the vortex rings are densely-shed and thus methane/air mixing is prompted with low periodic fluctuation. The diameter of the vortices becomes small as St_v is increased, so that the transport range of the inner methane and outer air fluids can be controlled by changing St_v. In addition, the evolution of counter-rotating streamwise vortex pair is also confirmed. These streamwise vortices are formed as a result of the radial injection of the miniature jet, which leads to entrainment of the ambient fluid near the primary jet shear layer. They contribute the mixing enhancement in the downstream, where the vortex rings are broken down. Moreover, it is demonstrated that the coaxial jet flame characteristics such as flame holding are drastically improved by the present jet control scheme.

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The objective of the present study is to clarify macroscopic behavior of microbubble (MB) and acrylic particles in tap water under ultrasonic waves. Ultrasonic waves (in a traveling-wave field) at frequencies of 485 kHz and 3.493 MHz were irradiated on a microbubble-water mixture or an acrylic particles-water mixture in a vertical closed cylinder from the bottom with a disk transducer and ultrasonic waves at a frequencies of 96.3 kHz from the side wall in a rectangular vessel. The following results were obtained; (a) Macroscopic behavior of MB was affected by a directivity function while an effect of the function on behavior of acrylic particles was small. (b) Most MB were transported along radial lines from the center of the disk transducer at the frequency of 3.493 MHz, however, a few MB were transported in different directions. (c) Magnitudes of MB velocity were greater than those of acrylic particles. (e) The frequency became higher, MB was transported in the region of smaller deviation angle, i.e., near the irradiation axis.

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Aiming to the study on large-scale structures in high-Reynolds number turbulent channel flows, the direct numerical simulation (DNS) code based on high-order accurate finite difference methods has been developed on both vector- and scalar types massively parallel-processing supercomputer systems. In this DNS code, fully conservative 6th and 12th order accurate finite difference methods proposed by Morinishi et al. (Journal of Computational Physics, Vol.143, 1998, pp.90-124) are adapted to compute the spatial discretization in the stream and spanwise directions, and the derivative in the wall normal direction is computed by a second-order method. The present DNS code has been applied for a fully-developed turbulent channel flow at Reynolds number of 1000 based on the friction velocity, channel half-length, and kinetic viscosity. Present DNS results of not only mean and turbulent statistics but also several kinds of spectral profiles such as a pre-multiplied spectrum, were validated compared with the results by means of the spectral method in the same spatial resolution condition. And the maximum computational speed was measured up 7.7 Tera flops and the sufficiently parallelization efficiency was achieved by using the Message Passing Interface (MPI) for a distributed memory parallel programing tool. Definitely, the present DNS code based on the high-order accurate finite difference method has the advantages in numerical costs in the study on large-scale structures in high-Reynolds number flows.

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Eddy diffusivity D_tα and turbulent Schmidt number Sc_tα (α = A,B,R) in a planar liquid jet with a second-order chemical reaction (A+B → R) are experimentally investigated. Species A is premixed in the jet flow and species B is premixed in the main flow. The concentrations of reactive species and the streamwise velocity are simultaneously measured by combining I-type hot-film anemometry with an optical fiber probe based on the light absorption spectrometry. Eddy diffusivity and turbulent Schmidt number on the jet centerline are estimated from the results of the simultaneous measurements of concentration and velocity. The results show that the chemical reaction makes Sc_tA large, and Sc_tB has a negative value in the region where the mean concentration of species B decreases in the downstream direction whereas Sc_tB for the nonreactive case has a positive value in the whole region on the jet centerline. It is also shown that Sc_tR has a positive value in the upstream region whereas it has a negative value in the downstream region. The difference in Sc_tB between the reactive and nonreactive cases becomes small in the downstream region. These results imply that the gradient diffusion model using the global constant turbulent Schmidt number poorly predicts the turbulent mass flux for reactive flows.

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Direct numerical simulation (DNS) is combined with probability density function (PDF) methods to simulate turbulent reactive flows. DNS is performed to predict an instantaneous velocity field and an instantaneous mixture fraction, whereas reactive scalars are predicted by the PDF method, in which a transport equation of joint PDF of reactive scalars is solved by using a large number of particles. We develop a new model for a mixing timescale of mixing model, which is used in the PDF method. In the present model, the mixing timescale is estimated from the mixture fraction predicted by the DNS. The numerical simulation based on the DNS and the PDF method is applied to a reactive planar jet. The results show that the PDF method can accurately predict the statistics of mixture fraction, and the present model for the mixing timescale can implicitly take into account the effect of distance between two particles without adjusting any model parameters. It is also found that the PDF method can accurately predict the statistics of reactive scalars.

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We have performed an atomistic analysis of the vehicular transport of hydronium ions and water molecules in the nanostructure of hydrated Nafion membrane using classical molecular dynamics simulations with a model of Nafion membrane based on DREIDING force field, which is newly modified and validated by comparing the density, water diffusivity, and morphology of the membrane with those obtained experimentally. In addition to determination of radial distribution function of solvent molecules vicinity of sulfonate groups as a function of hydration level, we have also calculated mean residence time of solvent molecules in the solvation shells which were classified into three types, overlapped shell, single shell, and second solvation shell. The mean residence time of solvent molecules explicitly showed different behaviors in each region, and they provided insights into the correlation between the nanoscopic structure of ion clusters and the dynamics of hydronium ions and water molecules in the membrane.

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Almost stirring devices used blades to stir materials, by the existence of which some efforts were necessary to wash stirring tanks or to exchange materials. So the purpose of this study was to develop devices to stir materials by Coriolis force with no blade. A cylinder rotating around horizontal axis was put on the turntable rotating around vertical axis. The vortex in the rotating cylinder was inclined in the directions upper right or lower right by the effects of Coriolis force. As the speed of turntable was increased, the vortex was collapsed. The phenomena were expected applicable to stirring process and washing process. To examine the effects of stirring process, two types of material were used, that is, undiluted solution of the aqueous paint and washing paste (polyvinyl alcohol). As a result, successful conditions of stirring process became clear with the relations among rotation numbers of capsule, rotation numbers of turntable and diameters of capsule. As an application to cooking, milk shake was cooked at various rotation numbers, and it became clear that it was cooked well when successful conditions were satisfied. As an application to washing, small pieces of the cotton cloth were colored with red ink, and they were washed in a capsule at various rotation numbers, and it became clear that they were washed well, when successful conditions were satisfied.

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The objective of this study is to extend the HCCI operational range while maintaining high thermal efficiency of a HCCI engine using the blowdown supercharge (BDSC) system. Two different compression ratios of 11.7 and 14.1 were tested by replacing the piston. The effect of compression ratio on both the HCCI operational range and thermal efficiency were investigated. The experimental results showed that the HCCI operational limit and the fuel consumption at the low load operation were successfully improved by increasing compression ratio. On the other hand, high load operational limit was hardly affected by compression ratio. Also, it was found that the BDSC-HCCI engine with higher compression ratio improves thermal efficiency of the whole HCCI operation range.

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Utilization of bio-ethanol as an alternative fuel for diesel engines is one of the effective strategy for suppression of global warming because of its high thermal efficiency. In order to realize a premixed compression ignition (PCI) engine by utilizing the ethanol blend fuel, the effects of ethanol blend ratio and exhaust gas recirculation (EGR) ratio on combustion and exhaust emission were investigated experimentally in a direct injection diesel engine. According to the experimental results, in the case of ethanol blend fuel with the blend ratio larger than 40%, smoke density could be reduced in spite of increase in EGR ratio without deterioration of thermal efficiency. The combustion of two components fuel blended with ethanol and tetradecane instead of gas oil were simulated by means of the numerical code KIVA-3V in order to elucidate the reason for reduction in smoke density by EGR. It is shown that if the smoke density reduces by increase in EGR ratio, the mass fraction of the local unburned mixture having high equivalence ratio decreases in the combustion region with increase in EGR ratio by promotion of the premixed condition based on the longer ignition delay due to ethanol blend and EGR.

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This paper describes about dominant parameters for fuel lean hydrogen-air premixed flame with curvature. The numerical simulations considering detailed chemical kinetics are conducted to elucidate the dominant parameters for a steady positively or negatively curved counterflow flame. The positive or negative of flame curvature and its amplitude are changed by the spouted velocity of the mixture with the fixed equivalence ratio, φ = 0.4, and ambient pressure. As candidates for dominant parameters, progress variables defined by mass fraction of oxygen, C_o,q, and hydrogen, C_f,q temperature, T_q, and their gradients, ∇_n,qC_o, ∇_n,qC_f and ∇_n,qT at flame front are investigated. As a result, for maximum heat release rate, it is found that the most proper dominant parameters are ∇_n,qC_f and ∇_n,qT. On the other hand, maximum mass production rates of various species cannot be arranged by the above-mentioned two parameters. However, that for many species (i.e., H₂O, OH, etc.) can be arranged by separating out the spouted velocity conditions into positive or negative curvatures.

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In the present study, a combined system of particle image velocimetry (PIV) and a high-speed infrared thermography (IRT) was employed to investigate turbulent flow in the unsteady thermal and flow fields. Simultaneous measurements of the velocity near a wall and the temperature on a heated thin-foil were conducted. The heat transfer coefficient was obtained from the temporal and spatial temperature data recorded at the thin-foil surface. Reynolds numbers based on main flow velocity and momentum thickness were 630, 1,050, 1,540, 2,290 at 10mm upstream from the heating start point. Uncertainties at the 95% confidence interval of the measured heat transfer coefficient and velocity are 2.8% and 2.4%, respectively. In the thermal and flow fields, the spatial distribution of heat transfer coefficient on the heated foil is similar to that of the streamwise velocity near the wall-region. It is concluded that there is the strong positive correlation between the fluctuations of the heat transfer coefficient and the streamwise velocity by the statistical procedure.

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Atomization of spray and spray characteristics of an air-blast atomizer for aero-engine are affected to improve combustion characteristics, that is, combustion efficiency, emission performance and flame stability. Air-blast atomizer is widely used as atomizers for aero-engine due to the benefits such as high-dispersion of spray, generation of smoke is little under high-load condition. However, droplet size of spray increases with decreasing in atomizing air flow rate. The purpose of this study is to develop the air-blast atomizer, which excellent spray with uniform and small droplets are obtained under small pressure differences. Hence, the air-blast atomizer was designed by the following configuration. Eight liquid supplying holes were installed at center and tip of the air-blast atomizer. Moreover, two atomizing air flow passes, that is, swirling parts with same and different swirl direction were installed at inner and outer of the air-blast atomizer in order to study about effects of swirling flow and supply methods of atomizing air on atomization of spray, were designed. As the results, high-dispersion and uniform spray, which spray spreads widely toward radial direction of spray, was obtained under wide ranges of atomizing air flow rate. Moreover, Sauter mean diameter of about 20 μm order was obtained under relatively low atomizing air flow rate.

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In this study, the authors numerically investigate the frequency response on the three-dimensional thermal convection in a cubic cavity heated from below in the gravitational field, concerning flow characteristics such as flow structure and a global quantity the spatially-averaged kinetic energy K. The authors assume incompressible fluid with a Prandtl number Pr = 7.1 (water) and with a Rayleigh number Ra = 1.0×10⁴ or 4.0×10⁴. The direction of a forced sinusoidal oscillation is parallel to the terrestrial gravity. The authors especially focus upon the influences of both the forced-oscillation amplitude η and frequency ω in non-dimensional forms, whose test ranges are 1.5 ≤ η ≤ 15 and 10 ≤ ω ≤ 10³. The obtained results are as follows. For Ra = 4.0×10⁴, as well as Ra = 1.0×10⁴ (Tanigawa et al., 2009), we can observe the optimum frequency ω_|K|max where the amplitude of K attains the maximum for each η. And, for both Ra's, ω_|K|max becomes the minimum at η = 1.5 - 2.0. Especially for Ra = 4.0×10⁴, ω_|K|max is affected by the initial conditions. For both Ra's, the maximum of the K amplitude uniquely exists at ω = ω_|K|max each η, when η < 1.5. On the other hand, we can observe not single but plural peak frequencies with locally-maximum |K|'s for each η, when η ≥ 1.5. It is confirmed that such plural frequencies are related with the appearances of various flow structures. Especially for Ra = 4.0×10⁴, this relation is also affected by the initial conditions. In addition, the details of a new flow structure are reported.

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