In the present study, we treat the dirty (small) and the adsorbing (large) particles as charged and anti-charged spheres and investigate the behavior of these particles under the gravity field by means of Brownian dynamics simulations. As an interaction potential between these charged particles, we have employed the electrical interaction energy based on the electrical double layers formed around the particles. Although putting a numerous number of large particles enhances the adsorption rate, the number of inefficient large particles that do not contribute to the adsorption performance increases. If it is necessary to remove the dirty particles during a short period, adsorbing particles with larger diameter may be used. If it is desirable to obtain a significant adsorption performance even if a long time period is necessitated, adsorbing particles with smaller diameter may be adopted.

View full abstract

We have discussed the feasibility of a hybrid-type method of Brownian dynamics and lattice Boltzmann for activating the Brownian motion of magnetic particles in a suspension composed of these particles. In this hybrid-type method, the random forces are added to the equations of motion of magnetic particles as in the usual Brownian dynamics. In order to activate the Brownian motion at a physically reasonable level, a viscosity-modifying method is introduced in adjusting the random displacements of the particles. This hybrid-type method with viscosity-modifying procedure is verified by comparing the present results with those of the Monte Carlo simulations.

View full abstract

We have investigated aggregation phenomena in a suspension composed of disk-like hematite particles by means of Brownian dynamics simulations. We have investigated the influence of the magnetic particle-field and the particleparticle interactions, shear rate and the volumetric fraction of particles on particle aggregation phenomena. The significant column-like clusters are formed at a magnetic particle-particle interaction much larger than in the case of a magnetic spherical particle suspension. This is because the rotational Brownian motion has a significant influence on the formation of clusters for a suspension composed of disk-like particles with large aspect ratio. An applied magnetic field is found to decrease the formation of column-like clusters. A shear flow is found not to have a significant influence on the internal structures of clusters, but it does influence on the cluster size distribution of the column-like clusters.

View full abstract

Superfluid helium has peculiar turbulence structure, superfluid turbulence, which is dominated by quantized vortex. Particle seeding visualization method is applied to this flow. The point of issue in this study field is that the particles motion mode difference. It is considered that the mode difference depends on the condition of particle-quantized vortex interaction and some particles motion models are introduced and experimental verification is required. In our study solid hydrogen is selected as tracer particles. We built fine hydrogen particles seeding system. This paper introduces our seeding method and image of hydrogen particles in HeII.

View full abstract

In this paper, we investigate the boiling phenomena in superfluid helium of 4He(HeII). It has been found that the four film boiling modes exist in HeII. They are named as silent, noisy, weakly subcooled and strongly subcooled film boilings. These modes occur depending on pressure, temperature, heat flux and experimental setup. We observed that the noisy film boiling occurred in the rectangular duct and the periodic oscillation of temperature and sound were generated. We present here the noisy film boiling model by measuring temperature and sound pressure. From the temperature spectrum, we specify that there is peak frequency fd. Defining the effective heat flux qα as the difference between the provided heat flux and critical heat flux, we discuss the relationship between fd and qα.

View full abstract

Large-eddy simulation was conducted to investigate the mechanism of pollutant removal from the there-dimensional street canyon. A tracer gas was released as a ground-level continuous gas line source at the center between three dimensional blocks. The results show that at least 75% of total emissions from the three-dimensional street canyon were attributable to turbulent motions. Pollutant removal by turbulent motions was related to the coherent structures of low-momentum fluid above the canyons. Though the coherent structure size of the low-momentum fluid differed, the positions of low-momentum fluid largely corresponded to instantaneous high concentrations of pollutant above the target canyon, irrespective of canyon geometry.

View full abstract

A three-dimensional direct numerical simulation (DNS) is applied to a wind-driven turbulence, and the effects of the water turbulence and Langmuir circulations on scalar transfer across the air-water interface are investigated. In order to capture the deformable interface, an arbitrary Lagrangian-Eulerian formulation (ALE) method is applied. The results suggest that Langmuir circulations emerge on the water side but that the scalar transfer across the air-water interface is mainly controlled by the water turbulence and the effect of the Langmuir circulations is relatively small.

View full abstract

In this study, the dependence of the scalar statistics on the Schmidt number is investigated experimentally in a liquid axisymmetric jet. In this experiment, the concentration of two diffusing dyes is measured by means of the light absorption method. As diffusing dyes, Acid Blue 9 and Direct Blue 86 are chosen whose Schmidt numbers are about 600 and 3,800, respectively. Experimental results show that the slope of the power spectrum of the concentration fluctuation of Direct Blue 86 is gentler than that of Acid Blue 9 in the high frequency region. Moreover, the probability density function of the concentration fluctuation is skewed more negatively as Schmidt number becomes higher.

View full abstract

This study investigated the effect of anisotropy of turbulence on the turbulent diffusion. Anisotropic turbulence was made by vortex stretching, and diffusion condition of CO2 were investigated. As a result, it was found that turbulence diffusion is proportional to total velocity fluctuation energy. It seems that the stretched longitudinal vortex and the anisotropy of turbulence cause this result.

View full abstract

The purpose of this study is to investigate the characteristic of the thrust for the propulsive nozzle driven by the high-pressure air compressed by the self-excited vibration in the blower piping system. In order to increase the performance, two valves were arranged in the piping system. The pressure and the thrust were measured for various parameters such as the number of revolution for the blower, the period of the opening and closing action of the two valves, and the water depth. The following conclusions were obtained. The peak of thrust for the nozzle with valve moved to the side of the deep depth. In the range of the present experiment the value of the thrust increased in comparison with that of original nozzle without valve. The finite difference lattice Boltzmann method is helpful to investigate the characteristics of the flow in the nozzle.

View full abstract

The present study focuses on the AA-PSP response to a periodic change in pressure. The periodic change in pressure is produced by mounting a rectangular cavity on the duct in which air flows at a Mach number of 〜0.8. The pressure oscillation frequency is ranged from 4 to 14 kHz by changing the cavity length. The phase delay in the pressure measured by the AA-PSP is estimated by calculating the cross-correlation between two pressure signals measured by the AA-PSP and semiconductor-type pressure transducer. The effect of coating thickness is investigated by testing two AA-PSPs having different coating thicknesses of 4 μm and 29 μm. As a result, the phase delay is close to zero over the entire range of frequency tested for the AA-PSP with the 4 μm coating, while the phase delay increases with frequency for that with the 29 μm coating.

View full abstract

We developed the critical nozzle flow meter used at high-pressure and high-flow-rate hydrogen gas for the practical application of fuel cell vehicles and their infrastructure. This paper describes the results of characteristic evaluation of the flow meter in high Reynolds number area for nitrogen gas. The results show that the critical back pressure ratio is 0.92-0.93 and its discharge coefficient decreases with increasing the Reynolds number. These results are similar to the results for hydrogen gas qualitatively.

View full abstract

Fatigue failure of the pipe system has become a critical problem in the petrochemical plant and is caused by the acoustic-induced vibration and the fluid-induced vibration.These vibrations simultaneously occur and so,complicated phenomena are established in the pipe system.This paper focuses on the AIV separated from the FIV and the effect of sound waves propagating in pipe on vibration of the pipe wall is discussed.The sound pressure wave at fixed frequency is generated using a pulsating-flow generator and its acoustic energy is emitted into the pipe.The pipe vibration is measured using strain gages and the vibration mode is analyzed.The expermimental result is compared with the computational one by FEM and a good agreement is obtained between them.

View full abstract

Flow and acoustic fields of a transitional supersonic free jet with the moderate Reynolds number are investigated. Compressible Navier-Stokes equations are solved by a high-order compact scheme, and the effects of inflow shear layer characteristics are investigated. The Mach and Reynolds numbers are set to 2.1 and 70,000, respectively. Five different jets with different shear layer thicknesses without disturbances, and the effects of the shear layer thickness and the disturbance are discussed. With decreasing the shear layer thickness or adding the disturbance, the transition position and the turbulence growth rate after the transition are significantly affected, and the turbulent fluctuation along the shear layer and the intensity of resulting Mach waves becomes smaller.

View full abstract

An air suspended load cell, which is available to measure steady aerodynamic forces on the spinning golf ball in the wind tunnel flow, has been developing during these five years. The characteristic to measure two components of forces as drag and side ones had already been accomplished with sufficient accuracy. However, the performances of the lift force direction had not been achieved by the influences of atmospheric pressure changes. The sufficient accuracy has accomplished, in this study, mainly by two improvements of the light-weight of ball supporting unit and the cancellation mechanism of atmospheric pressure variations. The lift force on highly spinning golf ball in the wind tunnel flow are measured and compared with the results of gauge type load cell.

View full abstract

It is known that low rotating or no-rotating balls have the erratic ball path especially in the new different panels of soccer balls. Velocity distributions of the balls wake wake were measured by Dynamic PIV on five balls of the different panels. Three dimensional twin vortices and jets between them were found in each wake of the ball. The velocities of the jet cores were different according to the difference of the ball panel. Especially, large velocity vectors were found in the ball wake which was heard to be big erratic path.

View full abstract

In a long-distance bicycle road game, in order to make the main rider win, an entire team makes a formation and assigns the main rider in an advantageous position for less drag. This study verified the effects from the formation consisted of multiple riders, usually called "train," with replicas aerodynamically. Four replicas were used as a train in drag force measurement and flow visualization. Bicycle replicas were fixed onto a ground plate, and the spacing of each replica was kept constant. Drag force of each replica was measured with three component load cell. Flow visualization in a smoke wind tunnel was also carried out in a horizontal plane at the riders' height. Several train formations expected to reduce drag including crosswinds were attempted. As a result, the least drag on the replica of the main rider was obtained when it was placed at the end of the train in a linear arrangement. The results of the flow visualization also explain these phenomena well.

View full abstract

A flying disc can fly through the air because of the combination of the lift and drag forces by the oncoming air flow. Actual fight conditions were confirmed to perform the wind tunnel experiment beforehand. In order to clarify the mechanism of flight of flying discs, the flow field structure and the fluid force were investigated on non-spinning and spinning conditions. In the fluid force measurement, lift and drag forces were taken by varying wind speeds, spin speeds, and angle of attack. Drag and lift forces were found to increase as spin increased. The angle of attack on the maximum range of lift-drag ratio or glide ratio was found to be wide from 6 to 13 degrees which was suitable for a long distance throwing. Using a smoke wind tunnel, flow visualization around the disc was performed in order to understand the effect of disc spin. It was found that spin enhances lift force by attracting the Coanda effect on the trailing edge.

View full abstract

Investigations on the definition and randomness of turbulence was reviewed at first. Then, the Kolmogorov complexity which measures the randomness were introduced. Numerical data in the mixing layer which was formed downstream of two-dimensional nozzle exit were compressed with the aid of a compression program. Approximated Kolmogorov complexity, AK, and normalized compression distance, NCD, were obtained. The AK indicated the regularity of the laminar flow and the randomness of the turbulent flow quantitatively. The NCD of the numerical value in the natural transition process in the mixing layer increased monotonically downstream. Thus the NCD appears to be the measure of the transition process.

View full abstract

Signal analysis methods to educe organized vortex structures from random signal in turbulence are introduced here. Continuous wavelet was applied to detect flow separation from the velocity fluctuations on the surface of aerofoil with increase of attack angle. Continuous wavelet, Morlet wavelet, has the advantage to detect unsteady fluctuation over other signal analysis method. Organized vortex structures from numerical data of the supersonic mixing layer (Watanabe and Maekawa, 2004) were investigated using Proper Orthogonal Decomposition (POD). Lambda-shaped vortices were reconstructed as organized structure with high energy contribution in supersonic mixing layer by POD.

View full abstract