Direct numerical simulation of turbulent heat transfer in a channel flow through high spatial resolution has been carried out for Re_τ =180, which is based on the friction velocity and the channel half width. The configuration is a fully developed turbulent channel flow with uniform heat flux heating from both walls. Molecular Prandtl numbers are set to be 0.71, 1.0, 2.0 and 10.0. The Prandtl number effect on the turbulence quantities such as turbulent Prandtl number, skewness and flatness factors of temperature derivatives are examined. Moreover, the resulting one-dimensional pre-multiplied energy spectra of temperature fluctuations at large wavenumbers are investigated to confirm the accuracy of the calculation.

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Direct numerical simulations of a turbulent channel flow under spanwise system rotation are performed. When the system rotation is imposed on the turbulent Poiseuille flow, the Reynolds number decreases in one side of a channel, while it increases in the other side. Hence, the effects of the Reynolds number as well as spanwise system rotation cannot be negligible in the turbulent Poiseuille flow. To exclude the Reynolds-number effects, we performed the numerical simulations of the open channel flow where the free-slip-boundary condition is imposed on a wall, and the Reynolds number can be set constant. When the spanwise system rotation is imposed to enhance mean spanwise vorticity associated with the mean shear, turbulence at the large scale is attenuated and the mean velocity gradient increases over the entire channel. In contrast, when the system rotation is imposed in the opposite sense to the mean spanwise vorticity, the mean velocity is leveled and turbulence at the higher wavenumbers is markedly decreased. We also investigate the effects of spanwise system rotation on the longitudinal vortical structure typically observed in the near-wall turbulence.

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Recently found unstable time-periodic solutions to the incompressible Navier-Stokes equation are reviewed to discuss their relevance to plane Couette turbulence and isotropic turbulence. It is shown that the periodic motion embedded in the Couette turbulence exhibits a regeneration cycle of near-wall coherent structures, which consists of formation and breakdown of streamwise vortices and low-velocity streaks. In phase space a turbulent state wanders around the corresponding periodic orbit for most of the time, so that the root-mean-squares of velocity fluctuations of the Couette turbulence agree very well with the temporal averages of those along the periodic orbit. The Kolmogorov universal-range energy spectrum is observed for the periodic motion embedded in high-symmetric turbulence at the Taylor-microscale Reynolds number Re_λ=67. A laminarization strategy inspired by investigation of the phase-space structure in the vicinity of the unstable periodic orbit is presented for a drag reduction of the Couette turbulence. The periodic orbit to be used for laminarization is on the separatrix between the basin of attraction of turbulent and laminar flows. During natural or forced approaches of the turbulent state to the periodic orbit weak spanwise rotation is imposed on the fluid so that the state can go beyond the separatrix toward the laminar flow.

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The three-dimensional time dependent compressible Navier-Stokes equations are numerically solved to study acoustic emission mechanism in a supersonic plane jet at high convective Mach numbers using high-order compact upwind schemes. High-order compact schemes of 5th order developed by Deng and Maekawa (1996, 1997) ⁽¹⁾⁽²⁾ are used for spatial derivatives and a 4th order Runge-Kutta scheme is employed for time advancement. Navier-Stokes characteristic boundary conditions are used in the streamwise and vertical directions and periodic boundary conditions in the spanwise direction. Two cases for convective Mach number Mc=1.17 are presented. The first case is the jet flow forced randomly. The second case is the jet forced by random disturbances and a pair of linear unstable oblique modes with a subsonic phase speed. The numerical results provide new physical insights into three-dimensional structures and acoustic wave generation mechanisms in a plane turbulent jet. Intense Mach waves radiating at low-frequencies are attributable to the growth of two-dimensional radiating mode with a supersonic phase speed in the jet shear layers. Upstream disturbance conditions play an important role for the evolution of the jet shear layers. The growth of a pair of oblique modes is responsible for the Λ structure in the jet shear layers, which yields sooner decay of the centerline velocity due to the shear layer rapid evolution. Therefore, the intense sound radiation observed in the randomly forced jet can be reduced by forcing with a pair of oblique modes.

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To analyze a cooling performance of air-cooled motorcycle's engines, we used the Karman'sanalogy between the fluid friction and the heat transportation. The Partial Cells in Cartesian coordinate method were employed as a CFD calculation. The calculated heat transfer coefficients at the flow in a straight pipe were compared with the Colburn's empirical formula. As a result, in Pr=0.7 and 10⁴<Re<1.2×10⁵, the values were almost agreed within±10% errors. Furthermore, as an application example, distributions of local heat transfer coefficients of an air-cooled motorcycle's engine were analyzed. It was helpful to examine the characteristic of heat radiation.

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With improving a computer hardware and CFD software, the problems treated in industries tend to be more complex, physically and geometrically. The turbulent flow with strong unsteadiness is one of physically complex examples. Since Large Eddy Simulation (LES) is still too time-consuming, a great number of unsteady Reynolds-Averaged Navier-Stokes (RANS) computations have been employed in such engineering applications. However, the applicability of RANS to unsteady flows has not been clear. In the present study, RANS computations for two-dimensional turbulent flow with periodic perturbation over a backward-facing step are performed to verify the performance of a low-Reynolds-number type k-ε turbulence model. Visualizing and investigating the temporal change of the flow pattern and the instantaneous term-by-term budget of the governing equations, it is clarified that the RANS computation can reproduce the unsteady nature satisfactorily, and why the RANS model captures the unsteady turbulent flow reasonably.

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Large-eddy simulation of compressible transitional flows in a low-pressure turbine cascade is performed by using 6th-order compact finite-difference and 10th-order filtering method. Numerical results without free-stream turbulence and those with about 5% of free-stream turbulence are compared. Based on the computed results detailed investigations are presented on the effects of the free-stream turbulence on the boundary layer transition, and behavior of the pressure waves that originate near the trailing-edge along with its effects on the separation/transition of the boundary layer. Also, based on Snapshot Proper Orthogonal Decomposition (POD) Analysis, dominant behaviors of the transitional boundary layers are investigated.

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Our main purpose is to study the structures of the large (comparable to the boundary-layer thicknessc δ) and very large (more than 10 times larger than δ) scale motions observed at or above the logarithmic layer of fully developed wall-turbulence, using Large Eddy Simulation (LES). In the second report of the continued research, we impose stable thermal stratification at different Richard-son-number conditions on the fully developed open channel flow to investigate the interactions among the very small structures near the wall (typically sublayer streaks), the large, and very large scale motions. It was fond that the large scales are strongly affected by thermal stratification and the very large scales are suppressed at a certain weakly stable condition, contrary to the sublayer streaks that appear to be rather insensitive to thermal stratification. As a result of their suppression in the outer layer, the peak wavelengths of the streamwise velocity's premultiplied spectra recovers linear growth with the wall distance above the buffer layer, which implies that the very large scales are the main reason for the lack of self-similarity of the streamwise velocity in wall-turbulence.

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Slit nozzles are used in some gasoline direct injection engines and make fan shaped spray. Spray injecting flows to turbulent flows from a slit nozzle have been analyzed numerically using combination of Large Eddy Simulation (LES) and lagrangian Discrete Droplet Method (DDM). As a result, LES can resolve the internal structure of the spray and irregular droplet distribution made by small eddies that momentum of spray itself induced. In conventional Reynolds Averaged Navier-Stokes (RANS) combined DDM calculation such eddies cannot be resolved, and also the internal spray structure or irregularity doesn't appear since all effects of turbulence are averaged. But such structure or irregularity is important for stable combustion in gasoline direct injection engines. Therefore the combination of LES and DDM method will play essential role for developing more robust and high efficient engines under wide operating conditions. We also proposed the way of constructing pseudo particle image in order to compare calculation results with sliced spray pictures obtained by experiments. We show time changes of the shape of brightness Probability Density Function (PDF) can be used to evaluate variance of spray droplets.

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This paper describes an experimental investigation of the transition mechanism of a wake generated behind a thin airfoil with a small angle of attack in a towing wind tunnel. A linear stability analysis shows that the wake is characterized by a change in the instability from locally absolute to locally convective at a downstream location (30 mm) of the airfoil trailing-edge. When the airfoil is towed in the tunnel, boundary layers develop on the upper/lower airfoil surfaces with different thicknesses. Since the asymmetric wake is generated, starting vortices of a single row are observed first in the wake, which is different from the wake Karman vortex street. The experimental result shows that time-harmonic fluctuations of the starting vortex sustain in the natural transition process due to a self sustained resonance in the absolutely unstable region behind the trailing edge. The wake profile in the saturation steady state yields the vortex street structure, where the fluctuation frequency is defined as the fundamental unstable mode by the final saturation steady state. The growth of the fundamental unstable mode in the convectively unstable region suppresses the high frequency fluctuations associated with the staring vortex generation. On the other hand, low-frequency fluctuations in the quasi-steady state sustaining in the saturation state grow gradually during the vortex street formation, which lead to the vortex street deformation downstream.

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The direct numerical simulations of turbulent flow in a rotating channel are executed, with the attention on a transient state after an onset of the rotation. Some different rotation numbers which contain 0, 0.5, 1, 2.5 and 5 are tested. To clarify a relationship between rotation numbers and the alteration of turbulence structures, we paid notice to temporal evolutions of wall friction velocities on both sides, volume-averaged velocity, kinetic energy and its production and dissipation. We found that the time evolutions of flow rates indicate non-monotonic behaviors due to the system rotation. The major reason of it is the difference in response of wall friction velocities on both walls. Moreover, we applied an analysis based on the theory of the invariants of Reynolds stress tensor to associate the status of turbulence with turbulence structures. From the result of the analysis, the three-dimensionality of turbulence is emphasized by the system rotation except for the vicinity of the wall on the pressure side. On the suction side, however, flow field indicates the feature of two-dimensionality.

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This study is to clarify the flow structure of a three-dimensional wall jet discharged tangentially on a flat surface from a circular nozzle. Distributions of the mean velocities and fluctuating velocities in a cross section of a fully-developed flow region were measured by using a single hot-wire probe and cross-wire probes. It is confirmed in any position of the lateral direction that the distributions of the mean velocities U and W in the direction normal to the wall are made similar to each other when they are made dimensionless by the maximum local velocity while the jet height remains almost invariable in the spanwise direction. The direction of the mean flow vector in the inner layer is remained constant while the direction of the mean flow vectors outside the half-value height is coincided with the direction of the jet axis. The distributions of the turbulent statistics in the direction normal to the wall are almost similar to each other outside the half-value height due to the scaling by the maximum local velocity, and on the other hand, the magnitude of the turbulent energy and Reynolds stress in the wall-side region becomes larger at the position farther from the jet axis.

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A fluctuating static pressure is closely related with a fluctuating velocity in turbulent flow, and it plays an important role in the energy balance and anisotropy of turbulence. Thus, the measurement of fluctuating static pressure is very effective for clarification of the organized structure of the turbulent flow. In this study, the yaw-insensitive static pressure probe with a good frequency response was developed, and the simultaneous mesurement of velocity and pressure field was carried out in two dimensional jet flow by the combined probe of I-type hot-wire and static pressure probe. In the pressure spectrum, the κ^-7/3 power low could be clearly observed, and the distribution of cross-correlation between streamwise velocity and static pressure is shown to be consistent with the past model of coherent vortex structure.

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An experimental study has been made on the management of a two-dimensional turbulent channel flow with a pair of streamwise vortices. A common-flow down type streamwise vortex pair, which was generated by a pair of half-delta wings mounted on the wall, was introduced into the fully developed turbulent channel flow. The half-delta wings were as high as inner layer thickness of the channel flow. The mean velocity and Reynolds shear stress distributions were measured and some properties were obtained to find meanings of the vortex generator for management of turbulent channel flow. Convective motion of the secondary current is responsible for most of the streamwise momentum transfer toward the wall in the interaction between the vortices and the shear layer. In the velocity profile averaged over spanwise extent, velocity is accelerated below the vortex center and decelerated above the vortex center. Deformation of the mean velocity profile is remained over remarkable long downstream distance of 250 times wing height which corresponds to 50 times channel half-width H.

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The wind tunnel used is equipped with an array of fans, each of which is independently controlled via a personal computer. To establish an efficient driving mode for generating high-Reynolds number isotropic turbulence, a new driving mode (“active grid mode”) is attempted where the active and inactive fans are grid-like arranged. The characteristics of turbulence are investigated for two kinds of external fluctuated signals. A flow structure of the turbulence generated by the active grid mode is proposed.

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Mechanical-drive steam turbines have the heavy deposition of fouling materials on blade and nozzle path surfaces due to contamination. As a result, turbine performance tends to be deteriorated gradually. The first paper introduced this fouling phenomena and actual conventional washing procedure in order to prevent the fouling problem and its practical disadvantage. In this second report, regarding new washing method to resolve above disadvantage, the results of detail analysis for erosion damage, thermal stress evaluation of internal parts due to injected water and heat balance of steam/water mixture are introduced in comparing online washing test results.

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Transparent PEFC (Polymer Electrolyte Fuel Cell) to visualize and to analyze microscopic image of product water in gas channel and GDL (Gas Diffusion Layer) has been developed by three times trial and error design improvement. To obtain electrical contact and gas seal, MEA (Membrane Electrode Assembly), a pair of GDLs, polar plates, glass windows and gaskets are independently clamped by each bolts and nuts, which are effective to avoid performance decrease with running time and periodical change of output voltage caused by gas channel plugging. Cutting slits around gas channel in polar plates make out-plane rigidity lower and electrical contact resistance between GDL and MEA lower. This transparent PEFC enables us to observe micro scale product water exhaust from porous GDL, which could be effective to improve gas permeability and product water exhaustibility of GDL.

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In this study, we aim to convert heavy fuels or solid fuels into lighter liquid fuel with high quality and propose fuel reformulation approach through sonochemistry and fuel design approach. Fuel design approach is to design fuel properties to suit engines by mixing fuels. Concept of fuel design originates chemical-thermodynamics. By this method, mixing fuel can control fuel transportation properties and phase change characteristics : evaporation and freezing characteristics. The origin of sonochemistry is acoustic cavitation : the nucleation, growth, and implosive collapse. Sonochemical effects on organic liquid are carbon bond cleavage of saturated component and polymerization of nitrogen containing component and aromatic component. In this study, chemical effects of 20 kHz high-intensity ultrasound on n-alkanes and cavitation behavior under ultrasound field are reported. N-alkanes were sonicated under Ar or N₂ atmosphere and cavitation behavior was photographed and calculated by bubble dynamics model.

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Hydrocarbon refrigerant isobutane (R600a) began to be carried in household refrigerator. The proper processing technology of isobutane is required in order to prepare for recycling of the refrigerator. Isobutane below the inflammable range is oxidized to CO₂ and H₂O by usin a palladium catalyst. The catalyst temperature conditions for isobutane completely oxidation were clarified. Oxidation reaction starts at the catalyst temperature of about 570 K, the complete oxidation temperature becomes higher with isobutane concentration and premixture space velocity. The temperature distribution of catalyst showed that 60% or more of isobutane had oxidized near the catalyst inlet. Isobutane oxidation characteristics are mostly in agreement with propane on the condition of the same combustion rate.

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In this paper, we presented two simulation results by the finite volume lattice Boltzmann method and unstructured grids. Incompressible flow in a square cavity shows good agreement with the standard solution based on the Navier-Stokes equations, and the proposed boundary condition is shown to be satisfactory. A direct simulation of the Aeolian tone is also performed and the sound pressure is compared with the Navier-Stokes based accurate solution. It is shown that the pressure is about 20% smaller than the N-S based result, and it is considered to be due to coarseness of the grid and using a second order accurate scheme. However, it is shown that the sound waves emitted from complex shaped bodies can be easily simulated by proposed technique.

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In this paper, we simulated directly the Aeolian tones emitted from a circular cylinder by the Finite Volume Lattice Boltzmann Method (FVLBM) using a two-dimensional thermal compressible lattice BGK model with the internal degrees of freedom proposed by Takada and Tsutahara, on unstructured grids. We also proposed a new scheme of higher accuracy, and, by this method, we obtained accurate results of the acoustic waves that agree well with those by highly accurate calculation based on the Navier-Stokes equation. We showed that the acoustic waves from complex objects can be calculated directly by this FVLBM model on unstructured grids.

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We present a new numerical method to simulate unsteady compressible flows under arbitrary Mach number condition. A hybrid explicit / fractional-step temporal discretization for Euler equation on strictly conservative formulation has been developed. The explicit method is adopted when the flow speed is high so that strong shocks as well as sound waves are accurately captured; while the fractional-step pressure-iteration method is adopted when the flow speed is low so that the CFL condition as a constraint on the time step can be avoided. We selected as the base scheme Jiang et al.'s nonstaggered version of the high-resolution central scheme by Nessyahu and Tadmor for hyperbolic conservation law since the scheme is well-suited to construct the fractional-step algorithm. An additional pressure correction procedure (GCUP) is implemented to deal with general equation of state. Riemann problems in one dimension are solved for a gas and a liquid to show high accuracy and robustness of the present scheme. A flow transition calculation from subsonic to supersonic due to a heat source is also successful.

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This study has investigated the nature and source of the vibrating and scattering behavior of roof tiles with the aim of providing a better insight to the mechanism. The 100 roof tiles were set up on 10 lines and 10 lows on the pitched roof in the downstream of the flow from the wind tunnel. These experiments were followed by series of tests where the slope angle of the roof tiles was changed. The vibrations of the roof tiles were simultaneously measured by the two accelerometers, and the motions of the vibration and scattering were observed by the high-speed video camera. The frequency response function and coherence function of roof tile were measured by impact hammer test under no flow condition. Just before scattering of the roof tiles, both vibrations of higher frequency mode and vibrations of lower frequency mode appeared simultaneously in roof tiles. The values of the higher frequencies were corresponding to the values of resonant frequencies of the roof tiles. It was thought that the scattering of roof tiles was influenced by the vibration of the lower frequency mode. The frequencies of the vibration were measured by the high-speed video camera system. The values of the lower frequencies were 10 Hz-20 Hz. The mechanism of scattering of roof tiles could be understood by means of the information from the accelerations and the images of roof tiles.

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This paper presents an investigation of PWM control with plasma synthetic jet actuator (PSJA). PSJA is an electric device designed for flow control using electrohydroninamic (EHD) effect. PWM control (ON-OFF control to glow discharge periodically) was proposed to induct waves which are subjected to lower frequencies than the frequency to drive the PSJA. The results show that the decrease of drag such as maximum velocity deficit and RMS has dropped by selecting a proper frequency in an angle of attack 15°, where the decrease of drag wasn't observed without PWM control. The result has indicated that the most effective frequency exists for separation control with PWM.

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Numerical simulations of flow around a smooth sphere and a sphere with temporally deforming dimples (active dimples) in critical Reynolds number regime, have been conducted in order to investigate the influence of deformation of active dimples on surrounding boundary layer. It is observed that the drag coefficient is decreased when the Reynolds number is greater than Re> 10⁵ by the transition of the boundary layer for the smooth sphere, as is reported by many experiments in the literature. It is shown the drag coefficient is decreased up to 40% when appropriate dimple scales and period of deformation are given. The active dimple promotes transition of boundary layer in the vicinity of the sphere, and restraints the detachment of flow. It is expected the applicability of active dimples displayed to a flow control device which is attached the surface of transportation body such as an airplane, a ship and so on.

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The attachment of an inducer upstream of the main impeller is a powerful method to improve the cavitation performance. It is known, however, that the cavitation surge oscillation, which is focused in the present paper, occurs under operation condition of partial flow rate and low suction pressure. The attempts to suppress the cavitation surge were made by installing a ring-shaped obstacle plate just upstream of inducer. The ring-shaped inlet plates with various blockage rates of 14%, 27% and 39% were tested to examine the effect of blockage rates on the suppression of cavitation surge for two kinds of inducers having two blades with the solidity of 2.0 and the different blade angle of 14° and 8°at the blade tip. In the present paper, the changes of the onset region of cavitation surge are clarified and the mechanism of cavitation surge suppression is discussed with casing wall pressure distribution and inlet velocity distribution.

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In this paper, some preliminary experiments and the calculations were performed to clarify the flow field, in which the rods surrounded by a porous cavity were normally inserted into the main supersonic flow. As a result, it is found that the starting shock wave severely interacts with the rods, the bow shock wave, its reflections, and the porous wall, which are numerically well predicted under some conditions. In case of the single rod, the main supersonic flow is sucked in front of the rod and blown downstream of the rod. Furthermore, the suction mass flux through the porous holes depends on the number and the locations of the rods. On the other hand, the three rods aligned parallel to the flow make favorable suction area downstream of the rods and also generate as less total pressure loss as that for a single rod. In addition, the spanwised three rods cause the strongest bow shock wave making the large mass flux through the porous wall and also large total pressure loss downstream of the rods. The calculation also suggests that interaction between the bow shock wave and boundary layer along the upper wall results in the boundary layer separation.

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Coherent vortical structures in a high-Reynolds number turbulent jet indicating edgetone oscillations were extracted from velocity and pressure data. Three quantities were chosen as candidate indicators of the coherent structures : (i) phase-averaged vorticity, (ii) phase-averaged pressure, and (iii) the phase-averaged velocity gradient tensor. All these quantities worked well in extracting coherent structures in a test case of a low-Reynolds number wake of a cylinder. However, when applied to the high-Reynolds number edgetone flow, (ii) and (iii) indicated much better performance than (i), since (i) was affected by the background time-averaged vorticity field. The advection of the coherent structures was well captured by using (ii) and (iii).

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We investigate flow between co-rotating disks with a narrow gap, enclosed by a stationary shroud at the circumference, using the flow visualization with aluminum flakes, PIV analysis and the measurement by a laser-Doppler velocimetry. Experiments are conducted methodically concerning three system parameters, that is, disk-tip Reynolds number, gap aspect ratio and dimensionless peripheral radius. As a result, time-averaged flow fields are characterized as roughly two-dimensional. Stability diagrams are specified in terms of the three governing parameters. The rotational speed of a central core configuration obviously depends upon flow modes, which approximately coincides with the Kirchhoff's potential theory, while the radius of the configuration does not. Furthermore, we propose a theoretical modeling for flow modes.

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The transition process of pulsatile flow in a grooved channel is studied both numerically and experimentally for five different groove-lengths at intermediate Reynolds number. The effects of the pulsating flow frequency upon the transition process are also examined for fixed Reynolds number and pulsation amplitude. The numerical simulation reveals the occurrence of multi-period oscillations and the transition process from periodic to chaotic flow follows the Feigenbaum scenario, where the period-doubling occurs by increasing the groove length. The double-period oscillation was also observed experimentally. However, the experimental results show that the pulsatile flow is more unstable than predicted by numerical simulation.

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Gasification and power generation from biomass such as livestock wastes has possibility to contribute to solve energy and environmental problems. But some biomass has high fuel nitrogen content, which may cause the emission of fuel-NO_x. There are few reports on the behavior of nitrogen contained in biomass during the pyrolysis and reforming process. In this study, we investigated the behavior of nitrogen content in chicken manure and meat-and-bone meal during the gasification and reforming processes. The release behaviors of gas-N such as NH₃, HCN and N₂ and Tar-N and Char-N during the pyrolysis process within the temperature range from 873 K to 1173 K were examined using an up-draft fixed bed gasifier. In the pyrolysis process, more NH₃ was observed from chicken manure and more HCN was observed from meat-and-bone meal, which is due to the difference of nitrogen composition in those fuels and of the conversion from tar-N or char-N to gas-N. We also investigated the nitrogen behavior in the reforming process within the temperature range from 973 K to 1173 K. In the reforming process, NH₃ was decomposed to N₂, but HCN was not. And tar-N produced from meat-and-bone meal was converted to HCN during the reforming process. From these results, to decrease the harmful nitrogen compounds such as NH₃ or HCN, higher temperature reforming is desirable in the case of chicken manure, and lower temperature gasification to leave nitrogen in the char is desirable in the case of meat-and-bone meal.

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The characteristics of TBAB (tetra-n-butyl ammonium bromide) clathrate hydrate slurries were investigated experimentally. Phase change temperature of TBAB hydrate slurry is from 5 to 10°C, and it is suitable as a thermal storage material for air-conditioning. TBAB hydrate forms two types of hydrate, and solid fraction, hydration number and enthalpy of hydrate slurries were measured in each hydrate. Moreover, observations of adhesion of hydrate slurries to vessel wall as a heat transfer surface were carried out in order to confirm the temperature and concentration range to keep the slurry state. As the result, it was found that appropriate range of temperature of the slurries and initial concentration of the solution for thermal energy storage differ in each hydrate. Moreover, it was found that adhesion of hydrate slurries to the wall occurs in the condition of solid fraction of more than 25 wt.%.

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The melting of two vertical parallel ice plates into a binary aqueous solution is considered experimentally and numerically. When the aspect ratio of liquid region is 1.0, the numerical results are compared with experimental ones and also quantitatively predicted the velocity in the liquid melt, mean melting mass, ice plate temperature. The influence of melting system sizes on melting mass, flow field, isotherms, and concentration isopleths are considered numerically, and the relation between the corrected melting mass change ratio and aspect ratio is presented for various liquid layer heights with dimensionless ice plate thickness as a parameter.

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Experimental and numerical analysis of methanol steam reforming for fuel cell have been carried out. The reforming catalyst was supported by metal honeycomb to decrease the heat capacity. Conversion performances were improved by segmenting the catalyst into several blocks due to the enhancement of mixing of gases and heat transfer at the front edges of the segmenting catalyst. Numerical simulation model for methanol steam reforming catalyst was developed by changing chemical reactions in the model for exhaust catalyst of internal combustion engine and using a smaller mass transfer coefficient for methanol steam reforming. The calculated results for plate type methanol steam reformer which generates hydrogen of 7 kW (LHV) were also in good agreement with the measurements. It was found that the pattern of heat supply to catalyst and the reformer configuration affected the steam reforming performance. It was predicted that the optimized methanol steam reformer for 50 kW size fuel cell vehicle had a sufficient compactness.

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Authors have developed a spray model for multicomponent fuel and reported the successful model which represents batch-distillation in multicomponent fuel by employing chemical thermo dynamics analysis including liquid-vapor equilibrium. However, the model considers the aerodynamic interaction as a breakup force by employing Taylor Analogy Breakup but ignored internal nozzle flow characteristics inspite of their importance. Nozzle flow is one of the major mechanisms for atomization of liquid jet. Therefore, this paper deals with a new breakup model for multicomponent fuel spray. The model takes account of the energy induced by cavitation bubble collapse or shrinkage. In addition, the model is implemented into KIVA-3 V code in order to validate the effect of energy generated by cavitation on the primary breakup of the discharging jet.

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Particulate Matter (PM) formation is still one of the most significant problems of diesel engines. PM having a diameter of less than 100 nm is usually called nano-PM which is considered being serious hazardous for human health. The objective of this paper was to obtain knowledge of PM from diffusion flame which was a base of diesel combustion process. For the purpose of it, a fundamental pool combustion flame was used to clarify the nano-PM exhaust behavior from the flame. Diesel fuel and lubricant added diesel fuel were used to clarify the formation process of nano-PM. Number concentration of the PM was measured using a scanning mobility particle sizer (SMPS-3034 TSI), and PM composition was quantitatively analyzed using a combustion type exhaust gas analyzer (MEXA-1370 PM HORIBA). As the result, the number concentration measurement showed that nano-PM number concentration in a diffusion flame increased with increasing lubricant content. The PM component analysis clarified that the nano-PM constituent substances were consist of soot, soluble organic fraction (SOF) and sulfate. The main component of nano-PM exhausted from a small pool flame which had closed flame tail was SOF, however dry soot was the main component of a large flame with sooty flame tail.

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To burn PET-resin powder as an alternative fuel and to realize the effective thermal recycling of a great deal of recycled PET-resin, a series of experimental investigations has been made on the physical aspect of PET-powder combustion in the industrial burner. The results showed that a large amount of PET-powder of up to about 80% is exhausted without burn-up in the open atmospheric operation, whereas it is perfectly consumed in the high temperature in-furnace operation. Understanding of the relationship between the heating time and the unburnt rate of PET-powder is therefore necessary for getting an important knowledge to reduce the amount of unburnt PET-powder. In this paper, the behavior of particle diameter is first modeled according to those experimentally measured, a particle-size histogram of PET-powder is transformed to a particle-number distribution by stepping the particle diameter at 0.01 μm intervals, and finally a numerical prediction of the unburnt rate in the PET-powder combustion is attempted by introducing the parcel approximation. The results give good quantitative agreement between the unburnt rates of PET-powder measured experimentally and those predicted numerically.

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Carbon combustion has been studied in the stagnation flow field, which can be specified uniquely by the velocity gradient. Use has been made of a rod of high-density graphite and/or carbon/carbon-composite as a test specimen. It has succeeded in conducting combustion experiments under conditions with high velocity gradients, up to 6000 s^-1. It is observed even for the high-density graphite that the combustion rate increases monotonically and reaches the diffusion-limited value with increasing surface temperature at high velocity gradients, while there appears a discontinuous change in the combustion rate, related to the establishment of CO flame, at relatively low velocity gradients. It is also observed that the combustion rate is nearly independent of graphite density, which can even hold for the carbon/carbon-composite. In addition, a discontinuous change in the combustion rate can even be observed for the carbon/carbon-composite when the velocity gradient is relatively low. As for the effect of airflow temperature, it is found that the combustion rate in high-temperature airflow is suppressed, compared to that in room-temperature airflow, because of a reduced mass transfer rate through the thickened boundary layer, when the velocity gradient is the same. Theoretical works have also been conducted and it has been found that the “Frozen” mode without CO flame and the “Flame sheet” mode with infinitely fast gas-phase reaction can fairly represent combustion behavior before and after the establishment of the CO flame, respectively, as far as the trend and the approximate magnitude are concerned. Since the high-density graphite and/or carbon/carbon-composite are expected to be used as heat-shielding structural materials in various aerospace applications, knowledge for their combustion mechanisms is considered to give useful information in preventing their oxidation at high temperatures.

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Effects of the velocity and the air ratio of the mixture and the air supplied into the boundary region between the rich and lean flames on the characteristics of the rich-lean combustion were investigated in order to develop a new type of a domestic boiling water heater and a warm heater with low emission of NO_x and high TDR. The characteristics of flame stabilization of the rich-lean combustion are improved even under the condition of the practical combustion when the stoichiometric, lean mixture and the air are supplied into the boundary region between the rich and lean flames. The stable combustion is achieved under the condition of 1.34 times of the normal load combustion by ontrolling the boundary region. The emission of NO_x is decreased when the air is suplied into the boundary region between the rich and lean flames. Especially, the effects of NO_x reduction are noticeable under the conditions of low load combustion. Therefore, it is possible to prevent combustion oscillation and combustion noise with low frequencies from occurring, and to develop the new type of burners with high performance of high TDR and further low emission of NO_x by supplying the mixture and the air into the boundary region between the rich and lean flames in the rich-lean combustion.

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Stabilization of oscillatory flames caused by strong pressure and hest release fluctuations has been investigated for a methane/air mixture, and effects of secondary injection system on suppressing pressure and heat release fluctuations have been discussed.Furthermore, characteristics of the NO_x emissions have been also discussed. Especially, in this study, outer secondary injection nozzle array which is arranged around a swirl-type flame holder is provided to stabilize the oscillatory flame. Methane, hydrogen and air are used for a working mixture of the secondary, respectively. Results show that with appreciate flow rate condition of the secondary injection ; (1) the oscillatory flame is stabilized with the outer secondary jets, where the configuration of secondary nozzle array is optimized, (2) the outer secondary injection has a performance to reduce the pressure fluctuation despite the kind of injected gas as the secondary, and (3) air injection as the secondary is more effective to suppress the pressure oscillation and NO_x emissions due to the momentum effect.

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Experiments were conducted in order to investigate behaviors of a detonation wave propagating into two pieces of slit, since the detonation wave might be quenched behind a slit-plate by expansion waves generated at a corner of the plate and this technique might be applicable to a detonation arrestor. The detonation wave produced in a stoichiometric mixture of hydrogen and oxygen was propagated through the slits and behaviors of the detonation wave were experimentally investigated by using a technique of pressure measurement, soot track record and high-speed schlieren photography. As a result, when the detonation wave propagated through the slits, it was quenched and a schock wave was decoupled with a reaction front. Two shock waves diffracted from the slits interacted each other at centre of the tube, then this shock wave interaction induced a hot-spot enough to cause local explosions behind the slit-plate. Since the shock wave was reflected from the wall and interacted at centre of the tube, the detonation wave was re-initiated behind the slits.

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Comprehension of the burning velocity for micro-scale flames is inevitable in the improved design of micro-combustors for miniaturized power supplies, and also useful for modeling local burning characteristics of turbulent flames. The present study is performed to examine experimentally the burning velocity characteristics of lean hydrogen-premixed micro-scale spherical laminar flames in the range of flame radius γ_f approximately from 1 to 5 mm, and also macro-scale laminar flames with γ_f>7 mm for comparison. The mixtures have nearly the same laminar burning velocity at socalled unstretched flames and different equivalence ratio φ which is varied from. 0.3 to 0.9. The radius and the burning velocity of micro-scale flames are obtained by using sequential schlieren images recorded under appropriate ignition conditions. The results show that the burning velocity of micro-scale flames with φ=0.3 and 0.5 has a tendency to decrease with increasing γ_f and approach that of macro-scale flames, but such a trend can not be seen for φ 0.9 micro-scale flames. This suggests that burning velocity characteristics of micro-scale flames can not be always explained based on that of macro-scale flames. In the micro-scale flames, the optimum size and stretch of flames to improve the burning velocity are also found to exist, depending on φ.

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The depletion mechanism of polycyclic aromatic hydrocarbons (PAHs) in a partially-premixed methane-air counterflow flame is investigated. The oxygen added to fuel flow is varied in the range from 0.0% to 5.0%, corresponding equivalence ratio is from ∞ to 30, respectively. 1-D structures of PAHs and C3, C4 hydrocarbon species are analyzed by a gas chromatograph mass spectrometer (GC/ MS). Numerical analysis (based on GRI-mech 3.0) for corresponding 1-D flames is performed to obtain detail flame structure up to C2 class of hydrocarbons. As partial premixing proceeded, most of PAHs except for cyclopentadiene (C₅H₆) in the flame are decreased, while C3, C4 species remains as nearly constant value. In order to elucidate major PAHs depletion pathways, possible mass production rate is calculated by using experimentally-measured PAHs concentrations and numerically-predicted radical concentration. It is indicated that benzene (C₆H₆) is oxidized mainly by O₂ and HO₂ and decreased as the partial premixing proceeded, then subsequent PAHs formation is decreased according to the benzene depletion. In addition, higher-class of PAHs could be decomposed by way of benzene and cyclopentadiene.

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