In order to address recent environmental problems such as global warming due to CO₂, emissions, continuous efforts are required to improve the performance of the steam turbine, which supports the base of energy conversion. Although the aerodynamic design technologies of steam turbine have been developed remarkably by applying the computational fluid dynamics (CFD), it is not easy to reduce the losses within a low aspect ratio cascade in the control stage and high-pressure stages even if the latest three-dimensional design are used. Then, the authors investigated the loss generation mechanism in a low aspect ratio cascade using the smoke visualization and detailed internal flow measurement with a micro pitot probe to develop the new technologies for reducing the secondary loss. This paper describes the evolution of horse-shoe vortex and passage vortex through a turbine blade in experimental studies, theoretical approach to explain the motion of the vortex and the effects of inlet boundary layer on passage vortex interaction analyzed by three-dimensional viscous flow analysis.

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In order to develop the performance improving technology for low aspect ratio cascade of the steam turbine, mechanism of the secondary loss generation has been investigated using the smoke visualization and detailed internal flow measurement in phase I. Next in phase 2, flow control technologies such as the blade fillet, endwall convergence and negative curving are introduced. This paper presents the loss reduction mechanism of these flow control technologies by applying the computational fluid dynamics (CFD) and the test results of air model turbine to verify the effects of endwall convergence and negative curving in rotating flow field. In conclusion, the technologies greatly contribute to improving the performance of the actual steam turbine with low aspect ratio cascade.

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A numerical method for simulating compressible thermal convections of arbitrary substance is presented. The numerical method is based on the preconditioning method proposed by the authors. This method is coupled with a database of thermochemical properties, PROPATH, developed by Kyushu University. Since PROPATH has accurate thermochemical models for 48 substances, the present method can calculate flows of such substances accurately. Also PROPATH can be used for not only substances in a gas state but also those in liquid and supercritical states. In this paper as numerical examples, natural convections in a square cavity for several substances, such as carbon-dioxide, water, nitrogen, methane and helium are calculated assuming gas and liquid conditions and the calculated results are compared with the existing numerical results and with each other. Especially, the natural convection of water liquid near CC is calculated and the anomalous convection is captured and the results are compared with the existing numerical and experimental results.

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Rotating cavitation in inducers is known as one type of cavitation instability, in which an uneven cavity pattern propagates in the same direction as the rotor with a propagating speed ratio of 1.0-1.2. On the other hand, cavitation in cryogenic fluids has a thermodynamic effect because of the thermal imbalance around the cavity. To investigate the influence of the thermodynamic effect on rotating cavitation, we conducted experiments in which liquid nitrogen was set at different temperatures (74 K, 78 K and 83 K) with a focus on the cavity length. At higher cavitation numbers, super-synchronous rotating cavitation occurred at the critical cavity length of Lc/h≅0.5 with a weak thermodynamic effect in terms of the fluctuation of cavity length. In contrast, synchronous rotating cavitation occurred at the critical cavity length of Lc/h≅0.9-1.0 with a strong thermodynamic effect in terms of the unevenness of cavity length. Furthermore, we confirmed that the amplitude of the shaft vibration depended on the degree of the unevenness of the cavity length through the thermodynamic effect.

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In this study, the flow features of vortex shedding from a circular cylinder oscillating along the direction of the flow were observed by visualizing water flow experiment at the ranges of the frequency ratio f/f_K=0-6.2, amplitude ratio 2a/d=0.0625-1.0, and Reynolds number Re=570-1700. The variations of mean vortex shedding frequency were investigated and the existence range of the lock-in was shown. It was obtained that although the cylinder oscillation frequency is lower than the natural Karman vortex's frequency; the lock-in phenomenon arises. It was found that the distribution of the lock-in form in the lock-in region was shown and that it became the tendency where the range with the frequency which becomes the lock-in form of f_VK/f=1/1 with the increase of amplitude ratio expands. The flow patterns were classified into five kinds by the configuration of vortex shedding and the direction of vortex shedding. The structure of the vortex flow which depends on the frequency ratio was clarified by observing flow from both to the axial direction and the direction of span. In the case of lock-in state f_VK/f=1/1, two kinds of vortex structure were obtained. One of which was three-dimensional characteristic on the side of low oscillation frequency, and the other was two-dimensional characteristic on the side of high oscillation frequency. In the case of lock-in state f_VKf=1/2, even if the lock-in had occurred, it was shown that the phase difference sometimes occurred to the direction of the span in vortex shedding.

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In general, cavitation is an undesirable phenomenon in many cases. In order to prevent from cavitation which produces great damage in the valves and piping system of power plants, it is necessary to detect the occurrence of cavitation. In order to determine the initial stage of cavitation process, an accelerometer was used to establish the technique of estimating the incipient cavitation number by impact signals. On the other hand, in many cases, cavitation number in orifice part is defined with the average flow velocity, however, the definition with upstream and downstream pressure of flow is more useful. Therefore, the incipient cavitation number defined in general way by using a cavitating jet method was clarified and was extended to regular orifice cavitation.

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We developed a numerical simulation code and an estimation method for predicting the cavitation erosion in pumps. The cavitation erosion is closely related to the cavitation intensity based on the bubble dynamics. A 'bubble flow model' simulates the detailed bubble behavior in a cavitating flow. The cavitation intensity was estimated by analyzing the bubble pressure and the bubble nuclei distribution in a centrifugal pump. We simulated impulsive bubble pressure that varied in microseconds. The impulsive pressure is considered to be related to actual bubble collapse, which causes the cavitation erosion. The erosion area was experimentally detected using a paint method. The predicted high cavitation intensity area agreed well with the experimental erosion area, since the predicted and experimental areas were both located between the shroud and mid-point of the blade near the leading edge. Our code is thus effective for estimating the cavitation intensity and predicting the erosion area around the impeller of a centrifugal pump.

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A lattice Boltzmann method for one-phase incompressible flows is proposed. The conventional lattice Boltzmann equation leads to the compressible Navier-Stokes equations through the Chapman-Enskog expansion. The compressible error is eliminated by applying the Fractional Step method to the conventional LB method. Two particle velocity distribution functions are used in this method : one calculates the momentum, and the other does the pressure in numerical computations. This method is able to compute the fluid flows as the density is constant, that is, the sound velocity is infinity. This method is validated by simulations of the Taylor vortex flow, of the Poiseuille flow, and of the cavity flow. The proposed model eliminates the pressure oscillation observed in the simulations of the Taylor vortex flow. The simulations show that the both errors of the continuity equation and of the fluid velocity reduce to about one-tenth. The numerical results of the proposed model are more accurate than those of the conventional LB method.

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We propose the Spectral Lattice Boltzmann Method (SLBM) that is the numerical calculation method of fluids based on the lattice BGK (Bathnagar-Gross-Krook) model discretized with spectral method. Two-dimensional homogeneous isotropic turbulence are simulated by the SLBM. Numerical results agree with another calculation results i.e. the energy spectra proportional to the wave number to -4 and backward cascade of energy is observed. As a result, we obtain the conclusion that homogeneous isotropic turbulence can be simulated by the SLBM, and it is confirmed that this method is useful for numerical simulations of turbulent flows.

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In this paper, the propulsion performance of a nozzle for a ship directly driven by ejecting a high-pressure gas was investigated about the characteristics of the velocity of the surrounding water, the shape of the nozzle and the frequency of the high pressure gas ejection. In the combustion frequencies 2-4 Hz, the thrust of the nozzle was smaller but the specific impulse was higher than the higher frequencies in each surrounding velocity. Even if the surrounding velocity increased, the thrusts of each combustion frequency in the rear wall angle 15 degrees of the nozzle were almost same. However, the thrusts in the angle 30 degrees became small by increasing the surrounding velocity. The gas-water unsteady flow in the nozzle was also clarified by the observation with a high speed video camera.

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In view of developing an efficient artificial kidney module, the shape effect of hollow fibers was studied in terms of the dialysate flow. Two different fiber shapes : straight and wave-shaped ones, showed different dialysate flow distribution. We adopted a porous media model for the bundle of thousands of hollow fibers and studied axial and radial permeability for two kinds of fiber shapes from low to high fiber density. Present experimental results showed that the straight and wave-shaped fibers had anisotropic permeability. Wave-shaped fiber shows larger permeability in radial direction than the straight-shape fiber. Due to this higher radial permeability, the pressure drop was lower for the wave-shaped fiber in the artificial kidney module.

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The effect of inlet and outlet blade angles on the performance of a micro regenerative pump was examined. The head of the regenerative pump was little increased by changing the blade angles compared with the original pump with the inlet and outlet blade angles of 0 degree. The effect of the axial clearance on the performance was also examined. The head was increased largely by decreasing the axial clearance. The computation of the internal flow was performed to clarify the cause of the increase of the head due to the decrease of the clearance. The local flow rate in the casing decreased as the leakage flow rate through the axial clearance decreased due to the decrease of the clearance. By offsetting the performance curve with the local flow rate, the effect of the clearance did not appear and it was found that the larger head in the smaller clearance was just caused by the smaller local flow rate in the casing. In the case of the smaller clearance, the smaller local flow rate caused the smaller circumferential velocity near the front and rear sides of the impeller, and the angular momentum in the casing and the head increased.

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An improved construction of air separator was investigated with respect to stall prevention effect on a low-speed single-stage axial-flow fan. The fan is a rather lightly-loaded one. For directly scooping and rectifying the near-stalling flows, the device incorporates radial vanes embedded within its inlet circumferential cavity with their leading edges facing the moving tips of the fan rotor blades. Stall-prevention effects by the separator layout, relative location of the separator to the rotor-blades, and the effect of widths of the openings of the air separator inlet and exit were parametrically investigated. Those factors were observed to affect the fan performance characteristics, particularly the stalling points and curve configurations. As far as the particular fan is concerned, the device together with the best relative location has proved to be able to eliminate effectively the stall zone having existed in the original solid-wall characteristics, which has confirmed the promising potential of the device. This study has provided information for maximizing the stall prevention effect of the device and for minimizing the axial size of the device at least on lightly-loaded fans. With respect to simplifying the radial vanes and minimizing the radial extent of the device, the readers are asked to refer the second report of this investigation.

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Stall prevention effect of air separators incorporating radial vanes was investigated on a low-speed single-stage axial-flow fan. The survey results have clarified a possibility of effective and compact air separators of simplified structure equipped with radial vanes. To develop air separators of the kind having a simplified structure and reduced size, and for optimum layout and manufacturing simplicity, effects of several geometrical dimensions of the device on the stall prevention were experimentally surveyed. The conclusions are as follows; (1) Simplified radial vanes made of flat plates in place of curved vanes have shown strong stall-prevention effect comparable to those of the curved-vane type one. The most favorable ones showed no stall up to the fan shut-off conditions. (2) Radial heights of the recirculation passage within the air separator were found to show significant influences on the stall improvement. It should be larger than some critical value experimentally given in the study. (3) The whole axial length of the device, if reduced too much down below some value, gave rise to an abrupt loss in the effect. The axial length of the device should be larger than some critical value given experimentally in the study. (4) The optimum axial locations of the rotor-tip blade leading-edge within the device inlet opening were found to lie near the center of the width of the inlet opening, from both aspects of stall improvement and fan efficiency.

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Experiments have been carried out for combined convective flows of air adjacent to the vertical heated plates in the uniform horizontal forced flows to investigate relationships between the flow and the heat transfer. The experiments cover the ranges of the Reynolds and modified Rayleigh numbers as; Re_L=160-2300 and Ra_*L=4.3×10⁵-2.0×10⁸. The flow fields over plates are visualized with particles and smoke. The results show that the stagnation point moves downward away from the center of the plates when the surface heat flux is beyond a critical value. The condition where the stagnation point begins to move is expressed with the non-dimensional parameters as; Gr_*L/Re^2.5_L=0.15. Profiles of measured local heat transfer coefficients are smooth even at the stagnation points in all cases examined. When the buoyancy effect is sufficiently weak, the coefficients agree well with those of the wedge flow. With increasing the surface heat flux, the coefficients are augmented to approach asymptotically the boundary layer solution of natural convection along a vertical heated plate. Finally, forced, natural and combined convective flow regimes are classified by the nondimensional parameter (Gr_*L/Re^2.5_L).

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A micro-grooved evaporator is composed of μm-order width grooves on a heat transfer plate, in which the inter-line regions at the liquid-vapor meniscus of coolant become specific. The high heat performance are realized by this inter-line region where the liquid thin film reduces thermal resistance on the heat transfer surface. In this report, we proposed a numerical simulation model of heat and mass transfer in a single groove to predict the capillary force and the heat flux in a single groove. In addition, the capillary force performances (capillary-rise length in a groove) for a single groove of various width, superheat and inclination was measured. The measured capillary-rise length became maximum at a specific groove width of 200-400μm, which is in good agreement with the predicted results calculated by the proposed model. For the better prediction of capillary-rise length, effective capillary force and, especially, effective flow resistance were considered.

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We have proposed a novel method of non-contact thermal type measurement for low flow rates using radiation heating and spectroscopy of water in the near-infrared wavelength range. We made a simulation for studying the performance of the flowmeter, and based on the simulation we conducted experiments using a prototype flowmeter. We obtained calibration curves between the estimated and true flow rates. From the experimental results, we can measure the flow rates from 0.3 to 9 ml/ min with the accuracy of about 10% of the flow rate. We also obtained agreement between the simulation and measurement results. Discussions are made to improve the measurement accuracy.

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An application of variable mechanisms and novel combustion technologies to a gasoline engine will be a solution to improve its thermal efficiency. The authors performed an experimental study to improve indicated thermal efficiency using an experimental engine with variable valve trains and high compression ratio. High efficiency SI (Spark Ignition) operation was achieved by reducing pumping loss as much as possible and using a high geometric compression ratio. High efficiency SI operation enabled about 10% improvement of indicated thermal efficiency to a conventional SI engine in a range of IMEP_n 300-650 kPa. However, the improvement ratio fell with decreasing the engine load. HCCI (Homogeneous Charge Compression Ignition) is a promising operation and possible for this engine utilizing these variable mechanisms effectively. HCCI enabled about 30% improvement of thermal efficiency in a range of IMEP_n 200-400 kPa. Furthermore, the improvement ratio was kept high even in the low load. These two operations have quite low pumping loss, but it was revealed that HCCI is a superior cycle in thermal efficiency thermodynamically. The reasons were examined by 0-D cycle simulations.

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Droplet size and spray dispersion characteristics of an impingement-jet type jet engine fuel injector are investigated experimentally. The fuel injector is consisted of a pintle, intermediate ring, and outer ring, forming co-axial air flow channels with co-swirlers. Compressed air at room temperature is supplied with a blower, and is injected into the atmosphere through the co-axial channels. Distilled water is supplied with a liquid pump, and is injected from hole nozzles mounted in the pintle. The number of nozzles is 8 and 16. The liquid jets impinge onto impingement walls mounted on the intermediate ring, forming a free liquid film. From the tip of the liquid film, fine droplets are formed. The droplet size is measured using an LDSA, and the spray cross section is visualized using time-average Mie scattering method. It is shown that the droplet size is almost the same as the atomization of a simple wall-impingement jet, which is much smaller than that for a conventional air-blast fuel injector, and it is observed that a relatively uniform spray is formed using the fuel injector.

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In-plane air permeance of gas diffusion layers (GDLs) was measured under compression conditions typical of polymer electrolyte fuel cells (PEFCs). When the compression pressure increases, maximum and mean flow pore diameters of GDLs decrease, causing the permeability to be deteriorated. In the case of the GDL coated with a micro porous layer (MPL), through-plane permeance measured using the conventional Gurley method decreases significantly, however, in-plane permeance decreases slightly when compared to the GDL without MPL. The MPL thickness penetrated in the carbon paper substrate can be estimated by the comparison of in-plane permeances with and without MPL. The permeance increases in proportion to the value of porosity multiplied by squired mean flow pore diameter. This relationship provides effective means to evaluate the porosity of GDLs with MPL. Increasing thickness and porosity of the GDL substrate enhances in-plane permeability of GDLs with MPL. This is effective in reducing flooding, thereby improving the PEFC performance under high-humidity conditions.

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This study is made to attempt to establish a prediction model of tubulent burning velocity for hydrogen mixtures based on the local burning velocity of turbulent flames instead of laminar burning velocity. The turbulent burning velocity characteristics of the specific mixtures having the same laminar burning velocity S_L0 with different equivalence ratio φ are examined experimentally at a constant volume vessel (φ=0.3-3.6 at the maximum, S_L0=10-50cm/s). The mean local burning velocity S_L of turbulent flames is also determined by using our proposed method which takes the preferential diffusion effect into consideration. It is found that the lower the equivalence ratio is, the higher the turbulent burning velocity becomes and the more extended the quenching limit is. S_L/S_L0 for each φ of hydrogen mixture has a tendency to increase or decrease with u'/S_L0, as compared with hydrocarbon mixtures. Therefore, the S_L for hydrogen mixtures needs to take account of u' as well as φ and S_L0. The quantitative accuracy of our proposed model for hydrogen mixtures is improved by using S_L based on φ and u'/S_L0.

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Recently many issues related to automotive engineering, such as the environment and energy problems have gained attention. These social-related issues are giving impetus to the adoption of urgent measures such as alternative fuels and new combustion techniques for the internal combustion engines. In this context, dimethyl ether is thought to be a potential alternative to diesel fuel, as it has lower overall pollutant emissions and better economy. On the other hand, oxygen-enriched combustion has been gaining acceptance as an environmental friendly combustion, because this can reduce soot and NOx emission. The purposes of this paper are to examine the extinction properties of DME flames and the feasibility concerning the application of oxygen-enriched combustion to DME flames using a counterflow burner. Firstly, the strain rate at extinction is measured for dimethyl ether and propane flames as a function of equilibrium flame temperature under the same flame structure. Secondly, the strain rate at extinction is also measured under the condition that the flame structures are changed, but the equilibrium flame temperatures are not varied. In addition, numerical calculations are also performed using detailed chemical-kinetic mechanism to obtain value for extinction and compared with measurements.

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We have investigated jet engines, in which hydrogen fuel is injected from turbine blade surface and combusted within turbine blade passages. Although these hydrogen-fueled propulsion systems are expected to have higher power, lighter weight and lower emissions, it still has many problems to be solved. In the previous studies, it was found that blade surface temperature exceeds the allowable temperature limit. Therefore, it is necessary to investigate the flow field with hydrogen combustion and the cooling method which prevents structure materials from melting down. The objective of this study is to clarify the influence of the injector-hole layout on the characteristics of the 3-dimensional flow field with hydrogen-fueled combustion within a turbine blade passage. Reynolds-averaged compressible Navier-Stokes equations are solved with incorporating a turbulence and a reduced chemical mechanism models. Using the computational results, the 3-dimensional turbulent flow field with chemical reactions is visualized and investigated. Additionally, the film cooling effect and the aerodynamic performance of the blade are estimated.

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Because of NO_x, SO_x and CO₂ exhausted by fossil-fuel combustion, air pollution is one of critical issues in our environment. To overcome these environmental problems, we have investigated jet engines, in which hydrogen fuel is injected from turbine blade surface and combusted within turbine blade passages. In the previous studies, endwall effects on the turbine performance have not been considered. However, it is expected that secondary flows due to the endwall have substantial effects on the engine performance. Therefore, it is necessary to clarify the influence of the endwall on the characteristics of the 3-dimensional flow field with hydrogen-fueled combustion. Reynolds-averaged compressible Navier-Stokes equations are solved with incorporating a turbulence and a reduced chemical mechanism models. Using the computational results, the engine performance is evaluated from the standpoints of combustor and turbine.

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