Turbulence structure and friction and pressure forces acting on two dimensional wavy walls with and without swell were numerically investigated. A three dimensional direct numerical simulation (DNS) based on a finite difference method was applied to turbulent boundary layer over the wavy walls. Two conventional methods for estimating the friction velocity from the loglaw of the mean velocity and the Reynolds stress in the vicinity of the wall were also examined by applying the results of the DNS. The results show that the turbulence intensities, turbulence kinetic energy and the Reynolds stress over the wavy walls are promoted by the swell on the wavy walls. The larger swell makes the friction drag smaller and the pressure drag larger. The total drag increases with the increase of the swell amplitude because of the rapid increase of pressure drag. The results suggest that the reduction on the friction drag by the swell causes the decrease of the mass transfer across the air-water interface with swell as reported in the previous measurements. The friction velocities estimate by the conventional methods increase with the increase of the swell amplitude, whereas the net friction velocity calculated directly from the friction drag is decreased by the swell. This suggests that the friction velocities estimated by the conventional methods do not reflect the friction drag and they are not appropriate parameters for correlating the mass transfer coefficient across the air-water interface with swell.

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Collisions of monodisperse particles in turbulent flows are important phenomena appearing in both the mechanical engineering and cloud microphysics. Although many researchers investigated the phenomena, they neglected the gravity effects in order to use a simple assumption of isotropic particle motions. In this study, we therefore investigated the gravity effects on the collision frequency and proposed a model that can predict the effects. We confirmed the reliability of the proposed model with the data obtained by direct numerical simulations (DNS). Furthermore, we clarified that, although the gravity effects are significant for moderately small Re number flows, they are negligibly small in typical convective clouds.

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Drag and lift forces acting on a spherical droplet in a homogeneous linear shear flow were numerically studied by means of a three dimensional direct numerical simulation based on a marker and cell (MAC) method. The effects of fluid shear rate and particle Reynolds number on drag and lift forces acting on a spherical droplet were compared with those on a rigid sphere. The results show that the drag force acting on a spherical droplet in a linear shear flow increases with shear. The lift force acts on a droplet from high-speed side to low-speed side in the linear shear flow with high particle Reynolds number of Re_p≥100. The direction of the lift force is different between low and high particle Reynolds number flows. The behavior of the lift force on a droplet is quite similar to that on a rigid sphere, but the effects of fluid shear rate on the lift force acting on a spherical droplet in the linear shear flow become smaller than that acting on a rigid sphere in the low Reynolds number region of Re_p<10.

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Whether a critical orifice with a diffuser worked well as a superior flow meter for low gas flow measurement were examined experimentally. The results show that their discharge coefficients is not almost affected by influences of a boundary layer, and their critical pressure ratios are larger than those of ISO type nozzles in the Reynolds number range of less than 900. Furthermore, a sonic plane appearing in a contraction of a jet flow is stable due to an existence of a diffuser wall even when the Reynolds number changes. It is found from these results that a critical orifice with a diffuser, if an orifice diameter is less than 20μm, is applicable to gas flow measurement of lower than 1 mg/min where can not be measured by ISO type critical nozzles.

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The mechanisms of energy transport by solid particles in a turbulent water channel flow were investigated by particle image velocimetry. A filtering technique, which is used in large eddy simulation, was applied to the fluid flow amongst particles to extract a characteristic length scale that governs the energy transfer from particles to fluid turbulence. The turbulence intensity in the streamwise direction, which is identical to the gravity direction, was strongly augmented by particles whose size is slightly greater than the Kolmogorov length scale. The directional scale-dependency structure was observed, i.e., large eddies were dissipated in front of particles and particle wake generated eddies, which is emphasized when particles aligned perpendicular to the gravity direction.The subgrid scale turbulence energy is increased until Δ/η≈10 (Δ : filter width, η : kolmogorov length scale), which means that particles generate eddies whose size is less than 10η. The energy backscatter in the presence of particles was observed at Δ/d_p≈5 (d_p : particle diameter), indicating that particles affect the eddy motion whose size is approximately five times particle diameter.

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Skin frictional drag of bubbly two-phase mixture in a horizontal turbulent channel is investigated experimentally using a shear stress sensor and a high-speed video camera. We choose non micro bubbles having a size of 1 to 10 mm intentionally to confirm that the drag reduction still works with relatively large bubbles to the channel height. The measurement results have shown that the drag reduction realized in case of a void fraction higher than a critical value that depends on liquid flow velocity. Also, significant bubble size dependence was found in the region near bubble injector. A synchronized measurement of local shear stress and interfacial structure has newly shown that the instantaneous friction factor decreased in rear part of individual bubble.

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The frictional drag reduction provided with small bubbles is investigated experimentally using vertical concentric cylinders. The friction reduction ratio is measured using a torque meter mounted on the inner cylinder for a wide range in Reynolds number from wavy vortex flow (WVF) to turbulent Taylor vortex flow (TTV). The present data show around 36% drag reduction in the case of WVF regime at Re =600 and the reduction maintains until Re =4 000. The friction reduction ratioη defined by the unit void fraction obeyed in a linear relation with inverse values of Froude number, and reached up to 10 in the best case, that implies the highest sensitivity for the drag reduction. The bubble distribution measured in the gap showed a peak near the inner cylinder surface resulting in high local shear stress reduction.

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Breakdown process of the Klebanoff mode and origin of turbulence are experimentally investigated in detail. An acoustic excitation using a 2D roughness attached on the wall are used for T S wave generation. Piezo-ceramic actuators are used to introduce the Klebanoff mode fluctuation. It is shown that the turbulence region starts from two locations, one is beneath the head of a A vortex and the other is the high-shear layer accompanying by the A vortex.

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This paper describes a new monolithic approach based on the Pressure Poisson Equation (PPE) to solve interaction problems of incompressible viscous fluid and an elastic body. The PPE is derived so as to be consistent with the coupled equation system for the fluid-structure interaction (FSI). Based on this approach, we develop two efficient monolithic methods. In both methods, the fluid pressure is derived implicitly so as to satisfy the incompressibility constraint and all the other unknown variables are derived fully explicitly or partially explicitly. The coefficient matrix of the PPE for the FSI has characteristics of (a) symmetric and positive definite feature, (b) reduction of degrees of freedoms to be solved, and (c) less dependence of the condition on material properties. The arbitrary Lagrangian Eulerian method is employed for the fluid to take into account the deformable fluid structure interface. To demonstrate fundamental performances of the proposed approach, the developed two monolithic methods are applied to simulate the vibration of a rectangular cylinder induced by vortex shedding.

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In the present paper, the distribution of the wall shear stress around the apex of the anterior communicating artery with the initial, progressive, and developed aneurysms has been studied in laminar steady flow. The anterior communicating artery composing of the circle of Willis is one of the predilection sites where the cerebral aneurysm is prone to appear frequently. Once the small aneurysm initiates at the apex in one confluent tube with much flow rate, the distribution of the wall shear stress abruptly changes around the initial aneurysm. Accompanying with the progress of the aneurysm, the wall shear stress distinctly changes along the concaved surface of the aneurysm. The effect of the wall shear stress change on the progress of the aneurysm is physiologically examined from the viewpoint of hemodynamics.

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A procedure of a nozzle design for a low density wind tunnel is presented. Numerical method to estimate the flow in the nozzle is governed by the Navier-Stokes equations with the non-slip boundary condition. The design process has two step : first step is to optimize for the half angle at the nozzle exit, and second step is to select the nozzle expansion ratio. Selected half angle at the nozzle exit and expansion ratio are 15 degrees and 53.18, respectively. The performance of the nozzle on the experiments has Mach number of 4.8, an Kn based on 5 cm of 0.024-0.026. The core diameter at the nozzle exit is 4 cm with water cooling on the nozzle wall. The numerical results for the Navier Stokes simulations agree well with the experimental results, and the present procedure for the nozzle design was confirmed to he adequate.

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The rotational energy gain function for inelastic collision models in the Monte Carlo simulation of rarefied gas flow is calcuated by the Monte Carlo integration technique with the classical trajectory calculation (CTC) of diatomic molecule. The rotational energy gain function presented in this study is combined with the statistical inelastic cross section (SICS) model and then applied to the evaluation of transport coefficients of nitrogen gas using the Wang Chang Uhlenbeck (WCU) theory, and the comparative simulation of nitrogen normal shock wave structure among the presented energy gain function, Parker's energy gain function, and experimental data. This study demonstrated that the transport coefficients and shock wave structures of present energy gain function are in better agreement with those of experimental results than Parker's energy gain function.

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Aerodynamic force measurement technique was developed for large scramjet models within short test time. The technique was based on direct acceleration measurement with miniature accelerometers mounted on a test model, which was suspended with stainless steel wires to make the restorative force negligible. In order to cancel the natural mode of vibrations of the test model, sum averaging signal processing technique was proposed. The technique was applied on drag force measurement of a 3 m length rectangular duct scramjet in the high enthalpy shock tunnel HIEST. Measurement result was evaluated with a three-dimensional Navier-Stokes numerical simulation. The evaluation with numerical simulation showed that the difference between measurement and numerical simulation is less than 5%. It is demonstrated that the technique has sufficient reliability to measure aerodynamic force with time resolution of 350μs, which is equivalent to frequency response of 2.88 kHz.

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The pressure fluctuations and the radial fluid forces induced by rotor-stator interaction in a centrifugal pump were measured and their relations were investigated. Experiments were done for different diffuser vanes, flow rates, and rotating speeds. It was demonstrated that both the blade pressure fluctuations and the volute static pressures are non-uniform circumferentially (not axisymmetric) under off design operating conditions and that the two have a strong relation. At high flow rates, the interaction induced blade pressure fluctuations are large in areas where the volute static pressure is low. The propagating directions of the rotating pressure fluctuations, the whirling directions of the radial fluid forces acting on the impeller, and the dominant frequency components of both the fluctuations and the fluid forces are discussed. When measuring fluid forces in the rotating frame, other frequency components, in addition to those related to the products of the diffuser vane number and the rotating frequency, may occur due to the circumferential unevenness of the pressure fluctuations.

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We have developed a sewage treatment system using a superconducting magnetic separation that combines high gradient magnetic separation using a continuously rotating magnetic filter with a superconducting magnet. We tested the magnetic separator to remove ferromagnetic floc, when ferromagnetic powder and coagulant are added to the influent water. The experiment showed that the magnetic filter can be practically used in this treatment system and that when the separator operates at a high speed (i.e. about 50 times faster than normal speed of conventional technology), its performance improved 90%.

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A feedback control upon nonlinear thermocapillary convections in a half-zone liquid bridge of a high Prandtl number fluid was conducted. In the liquid bridge, the convection changes from two-dimensional steady flow to three-dimensional oscillatory one at a critical temperature difference. The feedback control was realized by locally modifying the free surface temperature using local temperature measured at different positions. The present study aims to develop a new control scheme by taking spatiotemporal azimuthal distribution of temperature fluctuation into account. The performance of the control was evaluated with amplitude of the surface temperature with and without control. The behavior of the present controlled system was compared with that of our previous one on the spectral analysis. The new control scheme achieved significant attenuation of the temperature oscillation compared with the previous one for high Marangoni number region.

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Natural air cooling technologies of electronic equipment have important advantages of no fan and high reliability. However, natural air cooling has lower cooling capability than fan air cooling, so the cooling capability enhancement has been required. In this paper are presented the results of the experimental casings on the chimney effect in natural air-cooled electronic equipment. The system box is inclined for the purpose to enhance the capability of natural air-cooling. Experiments have been carried out using a model of thin laptop PC. The influence of the box inclination, outlet positions and numbers, and the porosity coefficient of outlet openings on the cooling capability was investigated. The results show that the temperature values inside casing and heater surface are gently diminished by the effect of increase in inclination and porosity coefficient of outlet openings. Moreover, the increase in natural circulation flux in the box is quantitatively proven by experiments. The experimental data were reduced to a Nusselt number-Rayleigh number correlation by using modified the reference length.

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We propose an analysis technique to support the layout optimization of the vacuum insulation panels (VIPs) for refrigerators. We used a one-dimensional calculation technique to simulate the heat loss caused by VIP envelope materials. The VIP thermal characteristics were shown by approximated system efficiency by using the panel's average length (L_p). We compared this simplified method to three dimensional numerical analysis on 1-6 micrometer thick, vacuum-packed aluminum foil and 1.5 6 mW/mK of thermally conductive heat-insulated core materials. The heat loss generated by the proposed method was verified to with a 1% error margin.

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An experiment study has been conducted to elucidate characteristics of transient heat transfer during quenching a hot cylindrical block with an impinging water jet. The experiment was done at atmospheric pressure for the following condition : an initial block temperature of 250 to 400°C, a subcooling of 5-80 K, a jet velocity of 3 15 m/s, and a nozzle diameter of 2 mm. It is observed that in a certain case the hot surface is hardly wetted immediately after the water jet impinges on it. After some times named resident time, the wetting of the surface starts and the position of wetting moves forwards. The quench of the hot block also starts with the movement of the wetting position. The resident time when the wetting location starts spreading after the jet impingement is one of the most importance and can be predicted by a proposed correlation. In addition, a correlation to predict the surface temperature at the resident time is proposed.

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In order to investigate the humidity recovery from the exhaust gas of the fuel cell vehicle by using micro porous plate, experimental apparatus to examine the performance in the heat and mass transfer between water and air through the micro porous plate was established. The effects of experimental method and property of materials, such as impregnation, hydrophilicity treatment and pore diameter etc., on mass transport were measured. It was shown that the effects of impregnation and pore diameter on mass transport vary with the thickness and pore diameter of porous plate. Further, the variation of mass transport caused by hydrophilic treatment for porous plate is not observed in the conditions of the experiment.

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The Capillary Pumped Deployable radiator (CPDR) is the mission equipment to verify the radiator deployment in the space and to transfer the heat from the equipment inside the CPDR to the deployable radiator by the Capillary Pumped Loop (CPL). It was installed on the Unmanned Space Experimental Recovery System (USERS) that was launched at the Tanegashima Space Center by the H-II launch vehicle on September 10th in 2003. In this paper we describe the summary of CPDR and on-orbit experimental result of CPL that was used in the CPDR.

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Theoretical analysis of the frequency response of a fine-wire temperature sensor such as a thermocouple or a cold wire was performed, and the strict solution of the response was derived by treating rigorously a boundary condition of heat transport between a temperature sensing part and its adjoining support. The solution obtained is highly universal and can express the frequency response of both a fine wire thermocouple and a cold-wire with a single equation. The validity of the theoretical solution was examined experimentally, and a response-compensation technique widely applicable to fine wire temperature sensors was developed based on the theoretical results. In this technique, any special apparatus for calibrating the dynamic response is unnecessary. The present response compensation technique can make fluctuating temperature measurement by a 3.2μ m tungsten wire well comparable to that by a 0.63μm platinum-wire which is regarded as one of the fastest temperature sensors commercially available.

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This paper presents general characteristics of cogeneration system (CGS) for the reduction of carbon dioxide emission and economy compared to the conventional systems. Applying the method reported previously, the paper compares the CGS characteristics for types of cooling systems, building types, and locations in Japan. The result shows that absorption coolers are superior to electric coolers for the reduction of carbon dioxide, but the extent is not significant and it is reversed when the power plant efficiency becomes greater than 45%. The result also shows that when the systems and operation patterns are selected from economic points of view, CGS sometimes increase carbon dioxide more than the conventional systems without CGS. This tendency is most apparent in offices among different types of buildings. The CO₂ reduction rate with CGS is higher in northern cities with larger heat demand than southern cities in Japan, but the tendency is reversed in the case of stores, whose cooling demand is significantly high.

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Transient response characteristics of electric power supply of small-scale fuel-cell co-generation systems constituted from a reformer, a fuel cell stack, an inverter, inter connection device system with a changeover switch, and auxiliary heat sources were investigated. Furthermore, numerical analyses of the relation of settling time, time constant of reformer and fuel cell, setting values of parameter in PT control were carried out. By changing PI control parameters according to the load of reforming, it turns out that setting time is shortened. Moreover, operating cost of the system was estimated using electric power demand and heat power demand pattern of the average individual houses in Sapporo-city and Tokyo. Consequently, annual balance of payment by installing heat pump systems with COP=3.0 into the fuel cell system serves as favorable balance in Tokyo, and become passive balance of about zero or a some in Sapporo-city.

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A performance analysis is carried out for Kalina cycle power generation utilizes warm waste-water as a heat source. The Kalina cycle utilizes ammonia/water mixtures as the working fluid. The factors in the performance analysis consists of the inlet and outlet temperatures of warm wastewater, the inlet and outlet temperatures of cooling water, the mass fraction of ammonia and each heat transfer performance of the evaporator, condenser and regenerator. In this analysis, the thermal efficiency of Kalina cycle utilizes warm wastewater is compared with that of the Rankine cycle. Also, effects of these heat transfer performances on the thermal efficiency of Kalina cycle are clarified. The optimum mass fraction which is the highest thermal efficiency for Kalina cycle i found out from heat transfer performance of each heat exchangers.

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A computational fluid dynamics (CFD) code with partial cells in Cartesian coordinate (PCC) method has been developed. The merit of this method is that input data preparation time is extremely short because computational mesh data are separated from geometry data. However, a general Cartesian coordinate method has a big subject in calculation accuracy. One of the factors is precision in geometry expression around the complicated shape, and another is a turbulence model near the wall because mesh is independent from the boundary and not fitted with it. Therefore, discretization equations were derived based on Finite Volumetric Method, and a combination of the wall function and a low Reynolds number k-ε turbulence model was proposed here. This paper describes implementation of this method and shows the results compared with experimental data by particle image velocimetry (PIV) at the steady flow in the cylinder of a 4-valves S.I. engine. The comparison results of velocity vector maps show good agreement between CFD and PIV.

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Laser-induced breakdown spectroscopy (LIBS) with atomic emission excited with a focused high-energy ND : YAG laser was applied to quantify the concentration and the vapor fraction of liquid-gas mixtures. LIBS can exactly quantify local concentration even in liquid-gas mixtures as the ratio of the number of fuel-borne hydrogen atoms to nitrogen or oxygen atoms in the ambient gas has a strong linear relation with the ratio of their peak emission intensities regardless of phase of the fuel. The full width half maximum (FWHM) of the emission peak from the fuel-borne hydrogen linearly increases with an increase in liquid fraction due to doppler shift with micro explosion, and the FWHM yields the fuel vapor fraction. Simultaneous, high-resolution measurements of equivalence ratio and vapor fraction in an intermittent fuel spray in a pressurized atmosphere were obtained with this method. The results showed that the tip of an intermittent spray has a richer mixture with lower vapor fraction.

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In order to investigate early soot formation process in a diesel spray flame, 2 D imaging and spectral measurements of laser-induced emission from soot precursors and soot particles in a transient spray flame achieved in a rapid compression machine (2.8 MPa, 710 K) were conducted. 3rd harmonic (355 nm) and 4th harmonic (266 nm) Nd : YAG laser pulses were used as the light source for laser-induced fluorescence (LIF) from soot precursors and laser induced incandescence (LII) from soot particles in the spray flame. The 2-D imaging covered an area between 30 mm and 55 mm downstream from the nozzle orifice. The results of 2-D imaging showed that strong laser induced emission excited at 266 nm appears only on the laser incident side of the spray flame, in contrast to an entire cross-sectional distribution of the emission excited at 355 nm, indicating that 266 nm-excited emitters are stronger absorbers and more abundant than 355 mil excited emitters in the spray flame. The spectral measurments were conducted at three different positions, 35, 45 and 55 mm downstream from the nozzle orifice, along the central axis of the spray, where LIF from soot precursors was observed in a previous 2-D imaging study. The spectra measured in upstream positions showed broad emission peaked around 400 to 500 nm, which is attributable to LIF from polycyclic aromatic hydrocarbons (PAHs). The spectra measured in downstream positions appeared very much like grey-body emission from soot particles.

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Effects of ethanol blending on performance and emissions of a direct injection diesel engine equipped with common rail injection and cold EGR systems were investigated under various ethanol blending conditions. The results indicate that ethanol blending with high injection pressure offers smoke-free combustion under high engine loading. However, this gives an increase in combustion noise and NO_x emissions. In such a condition, employing pilot injection and cold-EGR lowers the combustion noise and greatly improves the NO_x-PM trade-off. Under low engine loading, usage of pilot injection with proper timing and amount improves combustion stability and lowers emissions of unburned species. The overall results indicate that maximum acceptable ethanol blending does not exceed 20%.

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The effects of the Helmholtz resonator on combustion oscillation stabilization have been investigated for gas turbine combustor, and mechanism of Helmholtz oscillation control has been discussed. Numerical model, based on compressible Euler equation including combustion chamber and resonator, is proposed in order to describe the behavior of acoustic wave excited by dynamic heat release of flame in combustor. Relaxations of acoustic oscillation amplitude corresponding to resonator parameters, such as throat diameter, are calculated and compared by atmospheric combustion experiments. In case resonator is resonant to combustor, it is shown that oscillation amplitude can be minimized. However, effectiveness of resonator is lessened with decrease of throat diameter, while throat diameter is tuning parameter of resonator. Resonator parameters must be optimized in terms of attenuation characteristics as well as resonant frequency.

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