Today an inch-size flying robot so-called Micro Air Vehicle (MAV) has been attracting much attention. In such a small size, flapping wing is known to have higher flight performance than conventional fixed or rotational wing. However the mechanism of force generation by flapping wing is so complicated that it has not been understood well. In this research using finite element simulation, we precisely evaluate force generations for several wing motions and clarify the relationship between wing motion and flight performance. By interpreting the simulation results with the multi-dimensional interactive visualization tool named ADVENTURE_DecisionMaker, we perform multi-objective design of the wing motion for flapping MAV.

抄録全体を表示

A theoretical analysis for pulse wave in a blood vessel with an inhomogeneous part has been conducted by using a one-dimensional lattice model associated with the material nonlinearity of the arterial vessel wall. In the present study, from the viewpoint of mechanics, a certain part of blood vessel, which has the different configuration and mechanical properties of the arterial vessel wall, is regarded as the inhomogeneous part by a generalization. The pulse wave is modeled by the solitary wave. The integrability of the solitary wave is applied in order to analyze the behaviors of the pulse wave. As a result, the behaviors of the pulse wave which propagates through the inhomogeneous part in the blood vessel are shown analytically. The factor which has the effects on the propagation of the pulse wave is revealed clearly. Moreover, the relations between the behaviors of the pulse wave and the properties of the inhomogeneous part are clarified theoretically.

抄録全体を表示

The lattice Boltzmann method based on the Diffuse-Interface Model for the simulation of the flow of multiphase fluids is extended to allow the fluid components to have different viscosities. A convective Cahn-Hilliard equation for capturing interface is resolved by an additional lattice Boltzmann equation. To allow the different phases to have different viscosities, the relaxation time depends only on the sign of the order parameter. Numerical surface tension obtained from the Laplace's law agrees very well with the respective analytical solution for any viscosity ratio. The velocity profiles of the LBM show good agreement with those of the analytical solutions for the Poiseuille flow and Couette flow in channels filled with different phase viscosities without pseudo velocity on the interface. In the simulation of evolution of a single finger in a Hele-Shaw cell, the finger widths and terminal velocities show good agreements with the results of the previous studies.

抄録全体を表示

In the present paper, the pessure performance of a screw-type viscous micropump is investigated by mean of a experiment, a numerical simulation and a theoretical analysis. The several conditions of Reynolds numbers and numbers of turns of a screw groove, or a screw thread, are examined. In experiments, a centimeter-scale, i.e. not micrometer-scale, pumps are used and the low Reynolds numbers corresponding to micrometer-scale flow are realized by using glycerin as working fluid and rotating the screw at quite low speed. The experimental pressure performance shows straight lines with negative slopes. In the numerical simulations, the continuity equation and the three dimensional Navier-Stokes equations are numerically integrated by using the SIMPLE. The numerical pressure performance shows good agreements with the experimental one with respect to the qualitative and quantitative aspects. In the theoretical analysis, the quite simple formula of the pressure performance is derived from the two-dimensional Navier-Stokes equation in the flow direction based on the analytical integrations by using the low Reynolds number approximation, similarly to the two-dimensional lubrication theory. The theoretical pressure performance shows the adequate agreements with numerical and theoretical ones. Therefore, the formula can be used in the parametric survey in the design process.

抄録全体を表示

We have investigated aggregation phenomena of a colloidal dispersion composed of magnetic plate-like particles by means of Monte Carlo method. Such plate-like particles have been modeled as disk-like particles with a magnetic moment normal to the particle axis at the particle center, with the side section shape of a spherocylinder. The main objective of the present study is to clarify the influences of the magnetic field strength and magnetic interactions between particles on particle aggregation phenomena. We have concentrated our attention on a quasi-2D system from an application point of view such as development of surface changing technology using such magnetic plate-like particles. Internal structures of particle aggregates have been discussed quantitatively in terms of radial distribution and orientational pair correlation functions. The main results obtained here are summarised as follows. For the case of strong magnetic interactions between particles, particles form long cookie-like clusters and alternate between magnetic moments. This tendency appears under circumstances of a weak applied magnetic field. However, as the magnetic field strength becomes significant, particle inclines toward the magnetic field direction, so that the particles do not form the clusters.

抄録全体を表示

The experimental results of the choking pressure ratio and the choked flow rate in a converging nozzle are compared with three theoretical values calculated by the Fanno flow theory, the compound flow model, and the average flow model. The experimental values are in qualitative agreement with the calculated values in any of these cases, and agree best with the values by the average flow model. Based upon these comparisons, the mechanism of the choking of the flow where the velocity distribution is not uniform due to the boundary layer is made clear.

抄録全体を表示

In vehicle development, it is generally said that a vehicle with lower aerodynamic lift coefficient C_L has better straight-ahead stability at high-speed. However, in some cases, straight-ahead stability differs between two vehicles with similar low C_L. On the other hand, a moving vehicle shows complex behaviors due to unsteady aerodynamic forces caused by unsteady flow around the vehicle and unsteady vibration induced by undulated road. As C_L simply indicates time-average, it could be considered that C_L may not fully describe such complex vehicle behaviors during high speed driving. Therefore. in this study, an attempt was made to clarify the relationship between unsteady flow around a moving vehicle and straight-ahead stability by investigating aerodynamic forces generated from unsteady flow. As a result, it is clarified in wind tunnel experiments and on-road driving experiments that vehicle straight-ahead stability is greatly influenced by a distinctive unsteady vortex structure above the trunk deck.

抄録全体を表示

The purpose of this study is to evaluate the diameter of small bubbles separated from an air jet injected into a turbulent boundary layer from a hole on the wall. There exist three patterns of bubble separation dependent on the jet velocity, i.e., single bubble, coalesced bubbles, and continuous air jet. The mechanism of bubble separation from the jet is theoretically considered for the single bubble region. First, the bubble volume is calculated when the force separating the bubble such as drag or lift from the free stream overcomes the surface tension acting on the wall. The total volume of separating bubble is estimated from the sum of the volume stated above and that supplied to the bubble during the separation process influenced by the surface tension. The diameter of single bubble was measured for various experimental conditions. The results are approximated well by those obtained from the theoretical consideration proposed in this study.

抄録全体を表示

The swirl decay mechanisms are described for a wide range of swirl strengths in a straight pipe made of Plexiglass and 154.5mm in inner diameter and 9500mm long. Flow measurements using a cylindrical Pitot tube and a hot-wire anemometer are performed at a Reynolds number of 10^5, which is based on the inner diameter of the tube and the axial mean velocity. A guide-vane swirl generator, with guide-vane angles of 60, 45, 30, 5 and 0 degrees, is employed. As a result, the swirl number and the swirling angle neighboring the pipe wall exponentially decrease downstream. Axial velocity, which decreases in the central domain at a high swirl strength, gradually recovers downstream simultaneously with the swirl decay. The combined vortex formed upstream changes to a forced vortex far downstream. It is confirmed that the local angular momentum, which gradually changes in the central domain, exponentially decreases downstream neighboring the pipe wall. The conjectured swirl decay mechanisms in a straight pipe are as follows. First, the swirl decay mainly occurs in an annular region at a high swirl strength. Second, it occurs in the central domain at a medium swirl strength. Third, it occurs in the whole pipe cross-sectional area at a very low swirl strength.

抄録全体を表示

Standing waves excited by the periodic deformation of meniscus are investigated for the interface between two immiscible fluids confined in a vertical cylindrical container. When meniscus is subject to vertical oscillation, it can be deformed due to the time-dependent change of the capillary length, which is the horizontal scale of the meniscus, and the periodic deformation excites interface waves. The resonance characteristics of the excited wave is experimentally and numerically investigated under pinned-edge contact line condition and it is found that the resonant wave height grows with increase in the absolute deviation of the static contact angle from 90 degrees. A linear analysis model is derived under the assumption of quasi-static deformation of the meniscus with respect to the change in the vertical acceleration. The model shows that the magnitude of the excitation term is in proportion to tan|π/2-θ_0| with θ_0 the static contact angle, and to the fourth power of the exciting frequency. With appropriate decay factor, the linear model well reproduces the resonance curve of the wave height and the dependence of the resonant wave height on the static contact angle observed in the experiments and the numerical simulations.

抄録全体を表示

For the development of an active control of a turbulent jet, measurements of an axisymmetric turbulent jet are performed with multiple prominences: 90° and 45° delta tabs and vortex generators. Six computer-controlled prominences, which can be driven independently, are installed at the skimmer. First, effects of the shape and number of stationary prominence on turbulent jet are investigated. Then, the prominence that is most effective in the 'stationary mode' is used for the 'moving mode'. Three modes are tested; in the first mode, the prominences are oscillated in phase (axisymmetric mode), in the second mode, single prominence is inserted alternately along the circumference direction (rotational mode), and in the third mode, three adjacent prominences are inserted alternately (alternative mode). Instantaneous streamwise velocities are measured by using hot wire anemometry with an I-type probe. The results show the significant influence of moving prominences on turbulent jet field.

抄録全体を表示

Galloping of a square cylinder can be suppressed by the downstream strip-plate set in cruciform arrangement with a gap s. In addition, another strong vibration is generated at certain conditions of the flow velocity and gap s. The specific aim of this work is to confirm generality of these phenomena for various dimension systems and nondimensional parameters by the wind tunnel experiment. When the width of the downstream strip-plate w is equal to the side length of the square cylinder d, the suppression of galloping and the strong vibration are observed for all the square cylinders. The effective region of suppression is affected by w. The strong vibration is confirmed to be the longitudinal vortex excitation from measurement of the dominant frequency of the velocity fluctuation near the cross and flow visualization.

抄録全体を表示

For centrifugal pumps for artificial hearts, a magnetic drive and lightly loaded journal bearing system are often used to avoid leakage and to minimize the damage on blood cells. The rotor bearing rotates in a concentric casing without mechanical contact and Taylor vortices were observed in the clearance flow. The flow into the clearance has both axial and tangential components and exhibits a whirling motion. An experiment was carried out to investigate the effects of the inlet velocity components and the whirling motion of the rotor on the vortex structure. The present stydy reports about the results of numerical study on the vortex structure.

抄録全体を表示

The sewage pump are demanded a high pump efficiency and a performance in passing foreign bodies. Therefore, the impeller used by these usages demands the large passing particle size (minimum particle size in the pump). However, because conventional design method of pump impeller calculates impeller exit width small, it is difficult to apply to single-blade centrifugal pump impeller which is used as a sewage pump. This paper proposes design method for single-blade centrifugal pump impeller. As a result, the head curve of the impeller by this design method satisfied a design point, and pump efficiency was over 62% more than conventional single-blade centrifugal pump impeller. Having compared design values and CFD analysis values, the suction velocity ratio of the design parameter accorded well, but the relative velocity ratio did not agree by the influence of the backflow of the impeller entrance.

抄録全体を表示

A new spectrophotometer system is developed for the study of thermal radiation characteristics of surfaces in thermal engineering environments. The system measures spectra of normal-incidence hemispherical reflectance R_<NH> and normal emittance ε_N in a near-ultraviolet through infrared region of wavelength of 0.30〜11μm simultaneously and repeatedly with a cycle time of 4s. The system enables us to evaluate the normal-incidence absorptance A_N in this wide spectral region. Spectrum transition of specular-finished and rough-finished nickel surfaces in a high-temperature air-oxidation process is measured to demonstrate the performance of the system. Clear interference behaviors are found even in the spectra of hemispherical reflectance R_<NH> and emittance ε_N of the rough-finished surface.

抄録全体を表示

Direct numerical simulation was performed for a spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel, where one wall was heated at the constant temperature and another wall was cooled similarly. In the simulation, fully developed flow and temperature computed by the straight-channel driver was given to the inlet of curved channel domain. The frictional Reynolds number was assigned 150, and the Prandtl number was given 0.71. Since the flow field was examined in the previous paper, thermal features are mainly targeted in the present paper. Turbulent heat flux showed trends consistent with growing process of large-scale vortices. In the curved part, the wall-normal component of the turbulent heat flux was twice as large as the counterpart in the straight part, suggesting active heat transport of large-scale vortices. In the inner side of the same part, temperature fluctuation was abnormally large when compared with modest fluctuation of wall-normal velocity. This was caused by the combined effect of the large-scale motion of the vortices and the monotonous variation of the mean temperature; in such a temperature distribution, large-scale ejection of the hot fluid near the outer, which is transported into the near inner-wall region, should made large impact on thermal boundary layer near the inner wall. Wave number decomposition was made for various statistics, and such effort showed that contribution of the large-scale vortex to the total turbulent heat flux normal to the wall was roughly 80 percent at the channel center of 130° downstream from the curved-channel inlet.

抄録全体を表示

Mixing process in a high-speed unsteady hydrogen jet is investigated by using large eddy simulation (LES) with the pseudo nozzle concept at inlet boundary. The results show that a jet shape of LES is similar to that of visualization image and the development of jet is well described in various injection coditions. Furthermore, the effects of injection condition such as injection pressure and nozzle diameter on mixture formation are investigated. As a result, low-injection pressure and small nozzle diameter promote mixing quickly, because the core region become small. And the effect of jet-fluid on mixing process is also investigated. As a result, the volume of entrainment is less and mixing inside jet is suppressed in case of hydrogen compared with methane in the same injection condition, because the density of hydrogen is much lower than the ambient air so the flow motion which promotes mixing inside jet quickly decreases when the air is entrained.

抄録全体を表示

Experimental study of the design optimization of a traveling-wave thermoacoustic refrigerator is described. The thermoacoustic refrigerator is composed of a looped tube and regenerator; the regenerator is located in the looped tube. The looped tube is connected to an acoustic driver via a connecting tube. The regenerator is composed of many narrow flow channels and works as an energy conversion component. The coefficient of performance (COP) of the traveling-wave thermoacoustic refrigerator was measured with varying the position of the regenerator and the radius of the narrow flow channels in the regenerator. It was found that the measured COP depends on both regenerator's position and radius and both of them have the optimum values for high COP. The reasons of the existence of the optimum regenerator's position and radius for high COP were addressed.

抄録全体を表示

In this paper, numerical modeling methods for a fuel cell are explained. The aim of this study is to make an analysis system to perform investigation on the whole behavior of a fuel cell with higher precision. Through numerical analysis, the effects of changing the structure and the control will be able to be made clear. Liquid water distribution and temperature distribution inside the fuel cell are analyzed and evaluated in general under various situations. This paper describes through a two-phase two-dimensional analysis effects of pressure and temperature for liquid water distribution in fuel cells.

抄録全体を表示

Nano meter size particulate matter (nano-PM) and polycyclic aromatic hydrocarbons (PAHs) have harmful effects for human health. It was thought that PAHs were a precursor of nano-PM. Then fundamental information of PAHs behavior in combustion process has been required to establish reduction technologies for nano-PM emission. In this paper, PAHs concentration, PM composition, and number concentration of PM in diffusion flames of methane (CH_4) and propane (C_3H_8) were investigated. As the result, benzene and toluene formed from fuel (methane or propane) had the two peaks at upstream and at downstream of PAHs-soot transition region in the flames. Moreover, concentration of PAHs formed from propane was higher than that formed from methane. In addition, both of soot and SOF compositions in PM formed from propane flame showed higher concentrations than those in methane flame.

抄録全体を表示

Six-stroke diesel engine proposed here has six processes in one cycle, i.e. intake, 1st compression, 1st combustion, 2nd compression, 2nd combustion and exhaust. By the direct EGR in the 2nd combustion process, NO emission could be expected to decrease. However, much Soot was exhausted by a weak mixing in the 2nd combustion process. A high pressure injection with a common rail was introduced into the engine to improve the mixing in the second combustion process. As a result, more NO was exhausted while Soot was decreased due to better mixing. In this study, to decrease NO and Soot simultaneously, two stage fuel injection was applied to the 1st combustion. When the main injection timing for the 1st combustion process was extremely delayed, NO and Soot were decreased. It was considered that NO reduction was due to the 1st combustion of low temperature and EGR effect in the 2nd combustion. Also, Soot reduction was due to a relatively long ignition delay for the 2nd combustion

抄録全体を表示