A new idea is proposed in this work to convert an original rough surface of irregularly indented complex geometry to a simplified model surface. The purpose is to provide a substitutive simple solid boundary surface that allows us to perform a RANS by a practical computer of ordinary memory size and computational speed. As tall and comparatively large roughness peaks are expected to affect dominantly the flow over an irregularly indented surface, it is intended here to pick up those peaks adequately and substitute them by equivalent hemispheres. The first task is to coarsen the original surface to remove surface indentation of high frequency. In place of filtering the surface by a filtering function as is common in LES, wavelet multi-resolution analysis is introduced. Specifying a threshold height on the coarsened surface, we obtain a map of islands of peaks taller than the threshold plane. These peaks are converted to hemispheres of same volume. Hemispheres are least sensitive with respect to interference with surrounding elements and individual hydrodynamic performance is most easily evaluated. Wall drag of channel flows having original and model surfaces are compared by RANS simulation and has been confirmed to be coincident with reasonable accuracy.

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A model for an irregularly indented rough surface has been proposed by the authors in which tall peaks are picked up and represented by hemispheres having equal volume to corresponding peak. In practical application, drag of a hemisphere is substituted by plane shear stress on a flat plate. This simplified model surface is used to simulate flow over the original rough surface. The model requires drag of a hemisphere on a flat plate. In this work, unique drag formula which is simple and acceptably accurate in balance with the compactness of the model, is investigated by numerical simulations. The formula for a hemisphere on a flat plate is deduced on the basis of simulations by RANS, of channel flows having periodically arranged hemispheres on both plates. Obtained formula is confirmed to compare reasonably to those realized by hemispheres of different size in different ambient situation, in a rough wall channel flow, though drag largely scatters. The form is applied also to pipe flows having periodic hemispheres on the wall and is found to reproduce measured friction, satisfactorily. Although the proposed idea must be examined farther carfully and should be improved in details, promising step has been set up to make proposed model a useful method in practical application.

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An experimental study was performed for the flow in a modeled hydraulic headbox of paper making machines. The turbulent boundary layer generated on the partition plate in the dispartion part and the wakes formed downstream of the plates were investigated by using the flow visualization technique of a smoke wire method and by hot-wire measurements. Those controls were explored for several kinds of test channels and the plates that differ in convergence and trailing edge shape, respectively. As a result, the rectification by contracting the channel is effective in making the distribution of the average velocity uniform and in attenuating and unifying the turbulence intensity. Furthermore, the uniformalization of the average velocity is high for the trailing edges of a tapered and a wavy shape, while the homogeneity of the turbulence intensity is excellent for the tapered edge.

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An experimental investigation has been made on the vortex structure behind a long flat plate with a blunt trailing edge. The flow was controlled by an additional splitter plate attached to the trailing edge along the wake center line. The length of the splitter plate, l, was varied from a half to five times the trailing edge thickness, h. Measurements of vortex shedding frequency and of fluctuating velocity and pressure distributions were made in the vortex formation region under the freestream zero pressure gradient. Without splitter plate (l/h=0), the remarkable difference of Strouhal number, S, between for the long flat plate and for the short flat plate, has arisen. A maximum value of the Strouhal number was achieved at the splitter plate length of l/h=1.5, which is the same size for the short flat plate, attached to the long flat plate. The vortex strength expressed by the minimum pressure value on the wake center line, showed a tendency for vortex formation to be suppressed with the splitter plate of l/h≥1, which gave the same trend for the base pressure distribution. The vortex formation length, shear layer thickness, and the reattachment length have been discussed in connection with the vortex shedding.

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Local clear water scour around a cylindrical pier have been studied in a wind tunnel. Characteristics of fluid flow and fluid force acting on the pier standing in a scour were investigated with a pier and five different depth scours (scour depth/pier diameter=0, 0.5, 0.7, 1.0 and 1.5). The diameter of the pier is 40mm and free stream velocity is 16m/s, so that the Reynolds number is 4.2×10⁴. The flow visualization was carried out by the surface oil-flow pattern and smoke-wire methods. The surface pressure distributions on the pier and scour were measured and the drag coefficient of the pier was determined by integration of surface pressure distribution on the pier. Characteristics of the horseshoe vortex and drag acting on the pier in the scour are clarified. The results show that the two horseshoe vortices are observed in near the root the pier as the scour grows deeper and the stagnant area is formed in the bottom of the scour for the deepest depth.

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The aim of this study is to control pressure and flow rate in a circulating pipeline system to conform to various target cyclic waveforms by operating a pump at rotational speed n and valve opening θ. In a first step, the pipeline system is operated at arbitrarily selected cyclic waveforms n and θ. Then, a recurrent neural-network (RNN) computer program learns the response characteristics of the system from the input and output data. At the next step, suitable values of n and θ are obtained by using the two-dimensional steepest descent method so that the sum of root-mean-square residuals between target values and the respective outputs of the RNN is minimized. Thereby, the RNN can generate values of n and θ that can produce a pressure and flow rate that conform to the target waveforms. This method was investigated by numerical simulation of the pipeline system as a preliminary step toward applying it to a real experimental apparatus. By using the RNN which has learned the response characteristics obtained by measuring the controlled variable time-series of the system without investigating the individual characteristics of each device, it was possible to derive operating variables time-series that produced pressure and flow rate conforming to target waveforms with high accuracy.

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Perforations caused by a laminar-turbulent transition of a radial liquid sheet are described. A liquid film produced by an impingement of liquid to a disk center spreads out radially on the disk and forms a radial liquid sheet outside the disk edge. The radial liquid sheet is unstable because of an internal velocity profile with an inflexion point. The instability causes a laminar-turbulent transition just outside the disk edge and the transition leads to strong turbulence. Flow patterns completely depend on the frequency of perforations produced by the strong turbulence. The countless perforations lead to atomization of the liquid sheet and no perforation results in a smooth liquid sheet. The perforation frequency relies on the configurations of aggregations produced by fine waves after the transition. The wavy short aggregations induce the countless perforations and atomization immediately after the transition. The perforation frequency also relies on liquid properties and temperature of ambient air flow. Chemical properties of the liquid sustaining a very thin liquid sheet of a bubble suppress the perforation and hot ambient air flow promotes the perforation.

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To study the enhancement and degradation mechanism of impinging two-phase heat transfer, air/water two-phase jet was applied on the cooling of copper surface of 30 mm in diameter. The two-phase jet impinged vertically on the horizontal heat transfer surface from capillary nozzle holes of2, 4 and 6 mm in inner diameter. The larger heat transfer and stagnation pressure fluctuation were observed with the nozzle of larger diameter. The larger nozzle could provide the more significant enhancement of heat transfer and pressure fluctuation with an addition of air. It was considered that the enhancement of heat transfer was due to the stimulation of thermal boundary layer with an addition of air. Furthermore for the actual application, the two-phase jet was generated with the auto air-bleeding nozzle of 8 mm in the outlet inner diameter. Air could be automatically supplied into the nozzle inside with the low pressure generated with the converging water flow. Significant enhancement of heat transfer could be also provided with the auto air-bleeding nozzle.Key Words : Impinging Heat Transfer, Stimulation of Thermal Boundary, Layer, Two-phase Jet, Auto Air-bleeding

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Forced convection heat transfer in a non-Newtonian fluid flow between parallel plates subjected to heat convection on the external surfaces is investigated analytically. Fully developed laminar velocity distributions obtained by a power law fluid rheology model are used, and viscous dissipation is taken into account. The effect of heat conduction in the direction of fluid flow is considered to be negligble. The physical properties are assumed to be constant. The theoretical analysis of the heat transfer is performed using an integral transform technique-Vodicka's method on the assumption that the velocity distribution is piecewise constant in the channel cross section. An important feature of the approach is that an arbitrary variation of surrounding medium temperatures in the direction of fluid flow and an arbitrary velocity distribution can be permitted. A comparison with the existing results provides a verification of this technique. The effects of the Brinkman number, outside heat transfer coefficients and rheological property on the distributions of the fluid temperature and the local Nusselt number are illustrated. Moreover, the effects of the parameters on the length of freeze-free zone are discussed in the case where the surrounding medium temperatures are below the solidification temperature of the fluid.

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For a natural convection turbulent boundary layer in water along a vertical flat plate, measurements such as mean velocities, mean temperature, velocity and temperature fluctuation intensities. Reynolds shear stress and turbulent heat fluxes are obtained with a particle image velocimetry and a thermocouple rake. To confirm measurement accuracies, a direct numerical simulation for a time-developing natural convection boundary layer is also conducted. The measured results coincide relatively well with those obtained from the direct numerical simulation and, consequently, it is found that the turbulence characteristics of the boundary layer in water are similar to those in air, although the turbulent heat fluxes become fairly smaller than those for air due to the effect of high Prandtl number.

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High pressure metal hydride tank system is a key technology for hydrogen powered fuel cell vehicles to get practical driving range. Both high storage capacity and good charge-discharge performance can be achieved by this system, however, mass reduction of the hydrogen-absorbing alloy is necessary. Ti₂₅Cr₅₀V₂₀Mo₅ alloy with BCC single phase structure, has been developed for this system and it shows 2.5 mass% of effective hydrogen capacity, 40% larger capacity than previous Ti₃₅Cr₃₄Mn₃₁ system. It also shows high dissociation pressure and can release hydrogen from 233 K. Estimated hydrogen storage capacity by this alloy is 9.5 kg in 180 L tank. It enables over 900 km driving range of fuel cell vehicles. Hydrogen storage density in weight is 2.0 mass% and volumetric storage density is 5.3 kg hydrogen per 100 L as on-board tank system. Although higher storage capacity has obtained, this system gives that 72% of hydrogen can be stored within 5 minutes. This rapid charging capability is due to its small absolute value of ΔH, -25kJ/molH₂. And further improvement in rapid charging is indicated by a simulation if the hysteresis of equilibrium pressure between absorbing and desorbing could be reduced.

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A numerical simulation of single droplet combustion in uniform electrical fields is carried out. Ethanol is adopted as fuel and two flat plate electrodes are set on the both sides of droplet. The distance of electrodes is 10 cm and applied voltage is 4 kV. The profiles of temperature, electrical potential, electrical field and some ion species are obtained in 3 cases, including (a) no electrical field is considered, (b) electrical fields is independent from charge density profile and (c) electrical field is given as the function of electrical potential which can be changed by the formation of ion species in the droplet flame. The numerical results show that the flame shape is deformed to the direction of electrical fields. The change in electrical potential which is caused by bias of charge results in the local spike of electrical fields. It is considered that the flame deformation is caused not only by Coulomb force but by the electrical field spike. The numerical results are compared with the experimental results and the agreement is good when the effect of charge density in the flame at the electrical field is considered.

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In order to use palm oil methyl ester (PME) as an alternative diesel fuel at relatively low temperature condition (-15 to 0°C), the pour points at cold condition and the diesel combustion of PME blend fuels with various gas oils are investigated. The JIS No. 2 gas oil (GO2), No. 3 gas oil (GO3) and special No. 3 gas oil (GO3S) are used as base fuels. To make the pour point of blend fuel to be below that of GO2 (-12.5°C), the upper limit of PME content is about 5 vol% for GO3 blend and about 20 vol% for GO3S blend. Moreover, three PME 20 vol% blend fuels (GO2/PME 20, GO3/ PME 20 and GO3S/PME 20) are tested using a DI diesel engine, and compared with the base gas oils. Thermal efficiency of the blend fuels are almost the same as that of GO2. The blend fuels have shorter ignition delay and lower HC and Smoke emissions compared with the base gas oils because of the higher cetane number of PME.

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Biomass resource is one of the attractive alternative fuels. It is efficient method to use it in distributed power generation system with gas engine because it disperses. However, its calorie is low, and gas composition is affected by resource, gasification method and gasifying conditions, it will change momentarily during engine operation. Gas engine is needed to be stable and high thermal efficiency operation under these fluctations. The objective of this study is to develop a small size gas engine system for biomass gaseous fuel. In this paper, effect of fuel composition on combustion was clarified by engine experiment with low calorific gaseous fuel. Diluted fuel made longer combustion duration and lower thermal efficiency, but it was not necessarily in lower calorie fuel. It was also confirmed that spark timing control against fuel composition fluctuation was efficient method to keep high thermal efficiency.

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In order to reduce the friction of the piston system, it is important to understand the friction and lubrication at the skirt and ring. In gasoline engines, the friction of the skirt is often equal to or larger than that of the ring pack, then the reduction of the friction at the skirt is indispensable. In this study, the piston skirt friction was measured by the floating liner engine which consists of independent measuring devices for skirt and ring pack friction. In addition, the skirt friction was calculated by a simulation model considered surface roughness, boundary lubrication, skirt profile and skirt stiffness. The calculated skirt friction compared with experimental data measured by floating liner method. As a result, the calculated skirt friction showed good agreement with the measured results, thus it was confirmed that the calculation accuracy of the skirt friction was sufficient. Furthermore, calculations of the skirt friction were carried out to clarify the influence of friction factors. It was also found that the skirt friction was affected by the skirt stiffness, skirt profile and skirt bearing area at the case of gasoline engines.

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