A cyclone separator separates particles by using centrifugal force that acts on the particles in a swirl flow and the separated particles finally fall to the bottom part of the separator by the gravity force. For a gas cyclone separator, the Reynolds number of the bulk flow is typically in the order of 10⁴ to 10⁵, and complicated vortical structures are generated. The particle behaviors in such vortical flows have not yet been fully understood. The final goal of the present study is to clarify the mechanism of particle separation in a cyclone separator and to improve the separation efficiency. To achieve this goal, the unsteady flow in cyclone separators is firstly computed by large-eddy simulation. The computed flow velocities will then be fed to the subsequent analysis of particle tracking. This first report describes results of validations for the large-eddy simulation, where we compared the computed velocity profiles with the experimental data. We also compared the precession frequency of the vortex rope with that reported in the literature. Regarding the vortical structures in the cyclone separator, we identified longitudinal vortices which are generated in the periphery of the large vortex rope. These vortices have one end attached to the inner wall and their strength is stronger than the longitudinal vortices in the boundary layer on the wall. The identified vortices are most likely to play an important role in the particle separation, which will be proven in the second report that describes particle motion in the cyclone separator.

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Mechanism of particle separation in a cylindrical cyclone separator has been fully clarified by a combined numerical method of large eddy simulation and a particle tracking method. The former resolves all the important vortical structures in the separator while the latter inputs the instantaneous flow fields computed by the LES and computes trajectory of each particle by considering Stokes drag as well as gravity force. Particle collection efficiency predicted by the proposed method has been compared with the experimental data measured for two cylindrical cyclone separators with several sets of particle diameters. The results showed that the collection efficiency has been quantitatively predicted by the proposed method, which confirms that the method can be used for the engineering design of such a cyclone separator. Detailed investigation of the particle trajectories predicted by the present method has clarified the mechanism of particle separation of a cylindrical cyclone separator. Those particles that are successfully collected by the separator move outward in the swirl flow and are collected when the swirl flow changes its direction at the bottom of the separator. The essential mechanism of this particle separation is due to the centrifugal forces acting on the particles. Three types of particle trajectories have been identified for those particles that are exhausted from the cyclone separator together with the swirl flow. More than half of the uncollected particles are trapped by longitudinal vortexes. The unsteady longitudinal vortexes and vortex rope drastically decrease collection efficiency.

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In the previous paper, the effect of angle and length of the inlet guide vane on the performance of the cross-flow fan was examined. By installing guide vane of one sheet in tongue division side in the suction region, the performance of the cross-flow fan becomes more high pressure and high efficient than the case without the guide vane. In this study, it is examined that the guide vane of several sheet is installed as a more convenient method in the suction region of the cross-flow fan. To begin with, the cause of generation of inlet prerotation flow of the cross-flow fan is investigated. Next, it is examined that the prerotation is controlled by the inlet guide vane. As the result, following fact became clear. (1) The prerotation is being generated by drawing in the inlet flow for eccentric vortex of the rotor inside, and therefore, the inlet velocity becomes non-uniform in the circumferential direction. (2) The cross-flow fan becomes a high-efficient and high pressure by controlling the prerotation using the inlet guide vane.

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Decaying characteristics of grid turbulence are investigated by means of the laboratory experiments using a wind tunnel. Turbulence-generating grids are installed at the entrance to the test section to generate nearly isotropic turbulence. Four grids (mesh size M = 10, 15, 25 and 50 mm) are used. Instantaneous streamwise velocity is measured by a hot wire anemometer. The mesh Reynolds numbers are adjusted to Re_M = 6,700, 9,600, 16,000 and 33,000. In this study, decaying characteristics and invariants of grid turbulence for four grid sizes and Re_M are mainly investigated. The result for each case shows that the decay exponent of turbulent intensity is close to a theoretical value of -6/5 for Saffman turbulence. Each case also shows that streamwise variation of integral length scale L_uu and Taylor microscale λ grow as L_uu ∝ (x/M - x₀/M)^2/5 and λ ∝(x/M - x₀/M)^1/2 at (x/M - x₀/M) > 50, where x₀ is the virtual origin. Consequently, it is concluded that in the decaying region of grid turbulence, u²_r.m.sL³_uu, which corresponds to Saffman's integral, are constant for all grids and Re_M examined. However, u²_r.m.sL⁵_uu, which corresponds to Loitsianskii's integral, is not constant.

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A mathematical model on the frequency response of pressure-sensitive paints (PSP) is derived. Frequency response of PSPs is usually dominated by the diffusion timescale of gas permeation into the paint layer. However, recent fast-response PSPs have a very short response time close to 1 μs. This short response time is occasionally equivalent to the emission lifetime of luminophores used as the sensing molecules of PSP. In the model, the unsteady light emission process of the luminophores is taken into account with the gas diffusion in the paint layer. Then the effect of two characteristic timescales, the luminescence lifetime and the diffusion timescale, was evaluated using Bode plot. The result indicates that the luminescence lifetime alters the response dominated by the diffusion when the lifetime is close to the diffusion timescale. The gain and phase difference due to each timescale are linearly decomposed in the Bode plot.

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Direct Numerical Simulations (DNS) resolved Kolmogolov scales were employed to investigate large-scale structure in fully developed turbulent channel flows. Quadrant and probability density function analyses were conducted over a decoupled range of Reynolds numbers (Re_τ), 150, 400, 1000, and 2000, based on the friction velocity and channel half-width. The quadrant analysis has proved a larger contribution of sweep event to the Reynolds shear stress with increasing Reynolds number at each location from the wall to the channel center. This suggests that energy transfer increased on large-scale structure from outer region to inner region. In contrast, at each location from the wall, the PDF profiles of turbulent velocities and pressure have the analogous them uninfluenced by increasing Reynolds number. In near log-law region, Kullaback-Leibler divergence profiles of the streamwise turbulent velocity have the V-shaped them in cases of Re_τ> 400.

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An LDV system was employed to measure three components of velocity at a mid-flame point on the centerline of a propane-air flame of equivalence ratio 1.10 on a 26 mm-diameter Bunsen burner with fully developed turbulent pipe flow upstream at a Reynolds number of 6700. The LDV measurement volume was 1 mm below the leading electrode of a four-element electrostatic probe that provided the velocity and direction of motion of flamelets in the turbulent flame brush. It was found that when the coordinate system was rotated about a vertical axis to the plane of the flamelet velocity vector, most of the burnt-gas motion following flamelet passage remained largely in this plane. Moreover, within the accuracy of the LDV measurements, profiles of changes of the component of gas velocity normal to the flamelet agreed with velocity profiles calculated for steady, planar, unstrained, premixed laminar flames. These results indicate relatively little distortion of laminar flamelet structures in the turbulent flame brush at these turbulent intensities of about 5 %.

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As heat generation in satellites increases, ensuring that they are provided with sufficient radiator panel area is an important problem. Deployable radiators, with radiator panels that are deployed post-launch in space to increase the satellite's effective radiator panel area, are becoming an important thermal control technology. For the deployable radiator mounted in KIKU-8 satellite, we previously developed a reservoir embedded loop heat pipe (RELHP). RELHP is made to operate more reliably by incorporating a fluid-filled reservoir into the evaporator and forming axial grooves in the interior surface of the wick so that the wick remains wet under any microgravity condition. This paper presents temperature oscillations phenomena of the RELHP for use on the deployable radiator under a geostationary orbital environment by experiments and calculations. Firstly, a transient calculation model which can predict the deployable radiator's heat characteristics on the orbit was developed. Next, calculated results were compared with experimental results. It was found that the sub-cooling region is shorter, in a microgravity environment than in a terrestrial gravity environment, because there is less heat leakage into the reservoir in a microgravity environment. And that is cause of temperature oscillations.

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Impinging atomization, which has been widely utilized in liquid rocket propulsion systems, is able to produce fine drops at a rated operation. In contrast, however, the atomization characteristics deteriorate under off design conditions when injection velocity comes to be slower. In the present study, for improving atomization characteristics at off design operation, an effective technique is verified utilizing small amount of gas injection. The gas jet is supplied from a pressurized reservoir independent of the liquid supply system, and it is injected from the center of the liquid nozzles toward the impingement point. To clarify the flow field and the mechanism of the effectivity, experimental visualizations, drop size measurements and corresponding numerical analyses are carried out. It is elucidated that atomization is drastically promoted when the dynamic pressure of gas overcomes that of liquid at the impingement point. By the gas injection with the amount of only 1% of liquid mass flow rate, Sauter Mean Diameter (SMD) becomes one-tenth of the original SMD. In addition, the optimized atomization efficiency is achieved when the gas dynamic pressure is twice as much as the liquid at the impingement point.

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Ignition by using a laser-induced breakdown (Laser-induced ignition) is considered as a new approach to control the ignition phenomena. It is known that the laser-induced ignition is affected by characteristics of the laser source. In this study, effects of the pico-second order pulse duration of laser source on laser induced ignition phenomena of methane-air lean premixed gas are examined experimentally. Plus durations of laser and conditions of initial gaseous pressure are varied for investigating the effects of laser duration time on Laser-induced ignition. Results clearly show that the minimum ignition energy decreases with increasing the initial pressure. This tendency is same as the previously reported results by using the laser which has nano-second order pulse duration. On the other hand, there is little difference in the minimum pulse energy for ignition with the difference of laser pulse duration time.

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Objective of this study is to propose a new method to predict liftoff heights of turbulent non-premixed flames in combustion furnaces. At the first stage of this study, we investigated effects of the burned gas dilution of fuel jet on the liftoff height. The burner used consists of co-axial nozzles from which fuel, oxidizer and co-flow gas are issued, respectively. The co-flow gas surrounding the fuel jet simulates burned gases with low oxygen concentration in combustion furnaces. The fuel jet entrains the co-flow gas in the unburned mixing region of the base of lifted flame. The entrainment of co-flow gas decreases the oxygen concentration of mixtures, and hence the laminar burning velocity of premixed flame formed at the flame base decreases. The lower burning velocity lifts up the flame base. Edge flame model and premixed flame model fail to reproduce this phenomenon of liftoff height due to the dilution through co-flow gas entrainment. A dilution ratio is introduced to quantify the magnitude of the dilution. It has found that the dilution ratio can generalize liftoff heights of the turbulent flames diluted through co-flow gas.

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We have developed a loop thermosyphon for cooling electronics devices. Non-condensable gases (NCG) in a loop thermosyphon increase by leakage from outside, release of the gas dissolved in the refrigerant, and chemical reaction in the inside. Hence, it is necessary to know how the heat transfer performance changes when the amount of NCG in a loop thermosyphon increases. The effect of NCG's amount was measured for each component of the loop thermosyphon while changing the amount of heat input. The overall thermal resistance of a loop thermosyphon increased with the amount of NCG. The thermal resistance of the condensing part particularly increased with the NCG. The effect of NCG on the boiling part should be considered only by steam temperature which was raised by increase in the amount of NCG. The thermal resistance of the air cooling part is not affected by NCG, but the temperature difference of the air cooling part becomes smaller because heat-leakage increases with steam temperature.

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The purpose of this research is to clarify the requirements for the length of the SMA belt for a SMA engine. In order to put the SMA engine in practical use, maximizing the output power density is most important from the viewpoint of economic efficiency. In the former paper we showed that the output power of the SMA engine highly depends on the diameter of the SMA belt , the radius of the high-temperature wheel and the radius of the low-temperature wheel. In this study we will change the diameter of the SMA belt and theoretically explain whether there is a relational expression between the diameter and the length. If the length of the SMA belt is determined, the height of the SMA engine is also determined. Since the output of the SMA engine can be calculated by the already derived theoretical formula, we can divide it by the volume of the SMA engine and thus, calculate the output power density of the SMA engine. As the result, changing the diameter of the SMA belt, we can calculate the most appropriate value, at which the output power density of the SMA engine is maximal.

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