Conditional averaged patterns on the outer layer of a turbulent boundary layer have been investigated in order to understand the development process of a boundary layer interacting with spanwise periodic longitudinal vortex arrays which is artificially generated in a free stream. Two parameters, nemely, the spanwise periodicity of the longitudinal vortex arrays L/S and the arrangement height of airfoil arrays, were independently varied for five cases. Intermittency factor profiles revealed the effect of pairs of counterrotating secondary flows which showed the downwash flow for the midspan of the airfoil, and conversely, the upwash flow for the center slice of neighbouring airfoils. Intermittency factors are strongly affected by the spacing between neigbouring airfoils. The value of the intermittency factor decreases in the inner layer with increasing L/S at the midspan of the airfoil.

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A plume released into a turbulent flow shows an intermittent structure owing to the transport process definitely regulated by the flow field. Conditional statistics for a wall point source plume released into a turbulent pipe flow will be discussed. The distributions of the intermittency factor, conditional mean and r. m. s. fluctuation concentration show self-similarity. In particular, the slope of the distribution of the intermittency factor is more moderate than the one in the turbulent boundary layer on a flat plate. Spectra of intermittency functions reveal the property of detection Patterns of concentration in a wall point source plume. The KL-divergence between PDFs of the fluctuating concentration and a log-normal distribution is almost zero in the near wall region, and the distributions of the KL-divergence value are also self-similar in the downstream direction.

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In this paper we describe the flow around two-dimensional circular cylinder bundles supported by wires. The experiment was carried out in an N. P. L. blow-down wind-tunnel with a 500mm×500mm×2000mm working section, and with Reynolds number 9.4×10³. The displacement of a vibrating circular cylinder, and the time mean surface pressure distributions on the circular cylinder were measured. The results were compared with those for the cases of a fixed test cylinder and a flexible test cylinder only which is supported by elastic wires, in fixed circular cylinder bundles. It was found that (i) the critical value of the fluid elastic vibration is obtained as the spacing ratio D/S for a single row, two rows and three rows, and (ii) the lift coefficient becomes nearly zero for a vibrating cylinder mentioned in (i), while it increases for the case of a fixed cylinder.

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In this paper we describe the flow around two-dimensional circular cylinder bundles supported by wires. The experiment was carried out in an N. P. L. blow-down wind-tunnel with a 500mm X 500mm X 2000mm working section, and with Reynolds number 9.4 X 10³. The displacement of a vibrating circular cylinder, and the fluctuating pressure distributions on the surface of the circular cylinder were measured. It was found that (i) the critical value of the fluid elastic vibration occuring is obtained as the spacing ratio D/S for a single row, two rows and three rows, (ii) the fluctuating pressure distribution on the surface, fluctuating drag and fluctuating lift by natural frequency increase rapidly beyond the critical value mentioned in (i), and (iii) the variation of fluctuating drag and fluctuating lift corresponds to that of the displacement of a vibrating cylinder.

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The fundamental problem of the impulsively started, unsteady boundary layer at a rear stagnation point has been analyzed theoretically. Our previously published, original phenomenological viscous diffusion theory and the numerical analysis with a rational nondimensionalizing scaling technique based on the said phenomenological theory are further expanded, and a new numerical method of double-layer matching is developed for the present flow of a double-layered structure. This method can give highly accurate solutions over an extremely long nondimensional time T of up to 16, while Dommelen-Shen [JFM, 157 (1985), 1-16]'s Lagrangean numerical method, which is so far considered to be the best method for the present problem, cannot give a solution beyond T=7. Furthermore, it has been proven mathematically that Proudman-Johnson [JFM, 12 (1962), 161-168]'s and Robins-Howarth [JFM, 56 (1972), 161-171]'s asymptotic solution exists, to be sure, but does isolated only at T=Q, and the correct solution starting from T=0 does not approach their solution as T→∞.

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The reflection of planar shock waves over a compressive corner is one of the most important problems that must be resolved in order to clarify the structure of shock-wave reflections. This kind of problem has been investigated both experimentally and theoretically in the past few decades. In spite of many approaches, there remain some problems to be solved with respect to the generative factors or structures of Mach reflection. A numerical simulation, which can examine the flow fields quantitatively and in detail, has become very important recently. However, a numerical method, which provide results that agree well with the experimental results, has never been established, and occasionally the numerical results show an unphysical phenomenon which does not appear in the experimental results. This is due to the lack of resolution of the complicated flow patterns containing many shocks. A high-order accuracy scheme has been developed recently. The piecewise parabolic method (PPM) is important as the high-order accuracy scheme which can examine fluid flow with strong shocks. The PPM scheme is a high-Order extension of Godunov's method and simulates the physical phenomenon accurately.

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When electromagnetic fields are applied to thermoelectrically conducting fluids such as melted metals, the velocity, electromagnetic and temperature distributions are interrelated. Therefore the behavior of thermoelectrically conducting fluids is complicated under electromagnetic fields. In this work, we propose coupling GSMAC (generalized simplified marker and cell) finite element method with the φ-method, and discuss the natural convection of a thermoelectrically conducting fluid in a cubic cavity under a constant magnetic field. In the case of mercury (Prandtl number Pr=0.025, Grashof number Gr=3.75×10⁷) under a magnetic field, the temperature distributions obtained using the present numerical method agree qualitatively with the visualized experimental results, obtained using a thermosensitive liquid crystal sheet.

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Chord Reynolds numbers of turbine blades in the 300kW Industrial Ceramic Gas Turbine (CGT) Project are between 104 and 105. Although a few studies on the characteristics of airfoils at low-Reynolds-numbers have been reported, it is not clear how turbulence of the main flow affects the characteristics of airfoils. Some wind tunnel tests for determining the characteristics of an airfoil have been conducted using a wind tunnel with a specially designed turbulence generator. We summarize the designed turbulence generator, in which the turbulence intensity can be controlled continuously, and the performances of the wind tunnel with the turbulence generator, and describes some results of airfoil characteristics and flow visualization obtained by the oil flow method at the Reynolds numbers of 0.5×10⁵, 1.0×10⁵ and 2.0×10⁵.

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We discuss the dynamics of a two-joint bending mechanism composed of a streamlined body and a rectangular caudal fin. An analysis method in which the slender body theory and the linearized wing theory are combined was described in the preceding paper. In this work, the characteristics of the cosumed power and the propulsive efficiency are examined for one specific body form, and the optimum motion parameters for maximum propulsive efficiency are estimated. Furthermore, the dynamic characteristics of the body motion and the force acting on the body are investigated for the optimum motion parameters. It is found that the body moves like a travelling wave in the anguilli form mode although there is only one joint within the body.

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In this paper we discuss the dynamics and efficiency of the two-joint bending mechanism composed of a streamlined body and a rectangular caudal fin. As the next topic to the analysis method and the performance of a typical body form in the previous papers, in this paper, we investigate the effect of variation of the body form parameter on the characteristics of the propulsive efficiency, and compare the results with dolphin observation data. It is found that two joints should be located at posterior position of the body to obtain high propulsive efficiency. It is also found that the reduced frequency of the motion for the dolphin observation data is somewhat larger than the optimum reduced frequency for maximum propulsive efficiency in the present analysis.

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A durable gas flow sensor applicable to hot and dusty gas has been developed based on the measured cooling time constant of a heated probe in the flow. This sensor, consisting of double concentric cylindrically coiled heaters (similar to double concentric cylindrical shells), can reduce the radiative heat transfer, which may cause serious error during use at temperatures higher than 400°C, to a negligible amount. The outer temperature-controlled shell of the sensor functions as a radiation shield for the inner shell which acts as the flow sensing probe. This sensor can achieve an accuracy of ±10% in the velocity range of 0.7m/s∼7m/s with gas temperature ranging from room temperature to 600°C. The concept structure and experimental results for the sensor are described and discussed.

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A direct-imaging technique for measuring size and velocity of solid/liquid particles dispersed in two-phase flows was developed. The depth-of-focus effect that had imposed a serious limitation on the accuracy of the previous methods was resolved here through the use of a stereoimaging technique. Three-dimensional information provided by stereoimaging has made it possible to obtain simultaneously the size, location and velocity of each particle in the flow. The measurement procedures were fully automated with an on-line system consisting of such devices as two CCD cameras, strobe lamps, and a digital image processor. Particles were identified with a newly devised algorithm which was shown to be robust against the out-of-focus effect. The performance of this algorithm was verified by sizing stationary particles. As a comprehensive test of the present technique, transparent glass beads falling through a vertical pipe were measured.

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A magnetically suspended centrifugal blood pump has no mechanical friction, so its shaft torque is stable and almost linear to its motor current. Using this characteristic, the pump head and flow rate can be evaluated from motor current and rotating speed. However, pump characteristics depend on blood viscosity. Therefore, it is important that the change of blood viscosity can be calibrated. Reynolds number is defined using Casson's viscosity and rotating speed of the motor. Then the relationships of pump head versus flow rate and motor current versus flow rate indicate a slightly different Reynolds number dependence between blood and glycerol aqueous solutions. The indirect measurement of the pump head and flow rate from observed motor current and rotating speed was confirmed to have good accuracy and response.

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The authors developed a method to estimate nozzle-wake exciting forces (NEF) using Fourier series development of angular momentum flux (AMF) at the blade inlet of radial turbines. The NEF is strongly affected by the nozzle profiles. Application of this method to the evaluation of the NEF and AMF resulted in fundamental standards for selection of the number of nozzle blades and the profiles. The values of each order of NEF are obtained from Fourier series development of AMF. There is an increasing region of NEF to the distance from a nozzle trailing edge. The maximum estimation error of the blade vibration stress, which is calculated using the values of the first order of NEF and the coefficients of effective exciting force, is 10%. The coefficient of effective exciting force is 1/3 in the first and second modes, and 1/2 in third mode. Those coefficients are evaluated as the ratio of NEF and equivalent exiting forces calculated using the measured data of vibration stresses at two different points on the blade.

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Characteristics of fluid dynamics and noise of a multiblade radial fan have been experimentally investigated with respect to the effects of two parameters: inner diameter and the number of blades. The inner diameter D_i of 58mm gave the highest fan efficiency and pressure coefficient. Up to the critical number of blades B of 120, the greater the number of blades used the higher the fan efficiency and pressure coefficient. The optimal number of blades was found to be around 120 since the characteristics of fluid dynamics remain at a maximum even if a higher number of blades is used. Blade passage frequency tone decreases as the number of blades is increased. Sound pressure level and specific noise level are reduced as the number of blades is increased up to the critical number of blades but do not decrease further when a higher number of blades are used.

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An experimental study was conducted to improve the performance of a vibration pump using a vibrating pipe for conveying the molten salt at 784K. A new system to measure the pump performance safely at such a high temperature was developed, which was characterized by simplicity in construction and ease of operation. All parts of the system, including a pump, valves and a volume tank to measure the volumetric flow rate, were placed in a cylindrical tank. The pump was driven by an air actuator. Experimental results indicated that the measuring system fulfilled the intended function: the pump worked effectively and its performance was safely evaluated at a high temperature. A few possible improvements related to the construction of the pump were suggested based on the results.

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In this paper, the velocity distributions around the impeller of a multiblade blower and noise reduction by the silencer within the scroll are investigated. It is shown that the region of small meridian velocity C_m2 at the outlet of the impeller is about 40% of the blade width b₂ due to the inclination of the main flow to thce hub. It is also shown that the velocity fluctuations at the trailing edge of a blade are about 30% of the maximum velocity and that a silencer composed of sound-absorbing fiber and an air chamber within the scroll can reduce the specific sound level SLs by 2.5dB.

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An experimental study of natural convection heat transfer in a differentially heated semicircular enclosure was carried out. The flat surface was heated and the radial surface was cooled isothermally. The effects of angle of enclosure inclination on the heat transfer across semicircular regions of several radii were measured for Rayleigh number Ra_R ranging from 6.72×10⁶ to 2.33×10⁸, using water as a working fluid. The angle of inclination varied from -90deg to 90deg with radii R of 50, 40 and 30mm. The flow patterns were sketched from the results of a visualization experiment using aluminum powder. The temperature measurements in the enclosure were carried out using liquid crystal and thermocouples. The results indicate that different flow patterns were encountered as the angle of inclination varied, and the heat transfer rate was largely dependent on the flow pattern. In particular, enhanced heat transfer rates can be obtained when plume-like flow occurs along both hot and cold walls in the case of an upward facing hot wall. Heat transfer for the inclined enclosure can be predicted using the equation for a vertical enclosure presented in this paper.

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The experimental analysis of flow and heat transfer around a rectangular cylinder with width/height ratio of 4/6 set in the near wake generated by an elastically vibrating flat plate was performed under low Reynolds number conditions. Measurement of the unsteady velocity field was measured using a laser-Doppler anemometer, and the unsteady temperature field was measured by a Mach-Zehnder interferometer. We found that the time-averaged heat transfer around the cylinder increased compared with the case in which it was setting in an uniform velocity field, and that the flow beehind the cylinder with a vibrating plate was similar to the jet/wake velocity pattern.

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Three-dimensional numerical computation was performed for the developing region of flow and thermal fields in finned channels. The channel studied here has a heated region of finite length to which plate fin arrays are attached in order to improve its heat transfer performance. The performance was evaluated using Nu_L^^*, an apparent Nusselt number corresponding to the heat transfer rate per unit heated area. The effect of fin height, fin pitch, fin length and Reynolds number on Nusselt number was examined parametrically. As the fin height increases with the fin pitch kept constant, Nu_L^^* increases monotonically. The maximum value of Nu_L^^* was obtained when the top of the fin reached the top wall of the channel. When the fin pitch was changed with the fin height kept constant, the numerical results demonstrated two tendencies. In the case with clearance between the fin top and the wall, there existed the optimal fin pitch leading to maximum Nu_L^^*. In the case without clearance, Nu_L^^* increases with decrease of fin pitch. The optimal fin pitch gradually decreased with decrease of fin length and/or with increase of Reynolds number. The ratio of the j-factor to the f-factor was also obtained to evaluate the performance of the fins.

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A methanol-fueled direct-injection diesel engine with a glow-assisted ignition system tends to suffer from poor ignitability under low load conditions. Chemical delay phenomena associated with methanol mixture ignition were investigated to improve ignitability. Effects of vaporization heat of liquid methanol, surface temperature of the glow-plug, heat provided from the glow-plug and the effect of O₂ excess ratio of methanol-air mixtures on ignition characteristics were examined. Our numerical model accounted for these parameters and detailed chemical kinetic schemes, including 39 chemical species and 157 elementary reactions, were used to predict the delay of methanol mixture ignition.

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Ammonia (NH₃) contained in coal gasified fuel is converted to NO_x in the combustion process in gas turbine combustors. Low fuel NO_x combustion technology is very important. The present numerical computations are carried out for laminar jet diffusion combustion taking detailed chemical kinetics and multicomponent diffusion into consideration. Attention is focused on the effect of pressure on NO_x formation. By distinguishing the reaction paths of the fuel NO and thermal NO reaction processes, the interaction between fuel and thermal NO is clarified and the conversion rate of NH₃ to fuel NO can be computed directly. The result shows that high pressure induces an increase in thermal NO formation and a decrease in fuel NO formation and the conversion rate of NH₃ to fuel NO during combustion.

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Coal gasification performances of the entrained-flow coal gasifiers tend to be the lower for coal with higher ash fusion temperature because of higher air ratio required to elevate the combustor gas temperature in order to get the stable slag discharging state. Addition of flux and blending of coals with different characters, known effective to reduce the ash fusion temperature, have been investigated with a gasification test fasility (2t/d Process Development Unit) to confirm them in actual gasifiers. This paper reports the proposition of a correlation to predict the ash fluid temperature on the ash acid rate and presents a procedure to decide the suitable rate of flux addition and coal blending. This report also presents the proper selection guidelines of these methods based on the difference in the effects on gasification performance improvements when these methods are applied.

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This paper deals with the cold latent heat energy release characteristics of direct-contact heat exchange between the solidified oil droplets [tetradecane, CH₃(CH₂)₁₂CH₃, melting point5.8°C] and hot air. Hot air is injected into the solidified oil droplet-water mixture layer from the distributor with a number of small circular nozzles. The solidified oil droplet-water mixture layer is fluidized by the air bubbles ascending in the layer, and the air bubbles are cooled from the layer by the direct-contact heat exchange. This paper deals with the characteristics of temperature and humidity of the outlet air from the layer, and time history of the cold heat energy release. The experiments were performed with respect to several experimental parameters, i. e., air flow rate, air temperature and humidity, and the amount of oil droplets and water in the mixture layer. Finally, some empirical correlations for the outlet air temperature and humidity and the finishing time of cold latent heat release were derived in terms of various nondimensional parameters.

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Sintering behavior of flying slag particles in entrained bed coal gasifiers was examined using various amorphous and crystallized coal slags and deposits. The amorphous slag was water-quenched slag obtained by coal gasification at a pilot plant. This plant was designed to gasify 50 tons of coal per day. The crystallized slag was produced by heating the amorphous slag at 800, 850 and 900°C for one hour. Sintering temperatures of the amorphous slags for four coals tested were all approximately 800°C. Those of the crystallized slags were higher than 800°C and the sintering temperature increased with increasing heat treatment temperature. Those of the crystallized slags obtained by heating at 900°C were between 950 and 1050°C. The sintering temperature of the amorphous slags was the lowest among the various flying slags, and deposits sintered by flying slag particles in the pilot plant were found at approximately 800°C, the sintering temperature of the amorphous slags. It is suggested that the sintering temperature of the amorphous slags should be considered in the design of entrained bed gasifiers from the viewpoint of safety.

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In our previous study, it was found that amorphous slag had the lowest sintering temperature among the flying slag particles in entrained bed gasifiers, and this temperature should be of great importance for designing a gasifier without slag sintering problems. In this paper we describe how to produce amorphous slag not in pilot scale tests but in a laboratory. Ash in a graphite crucible with a plug was heated and melted at between 1400 and 1700°C, and then the molten slag was quenched in a water bath. The amorphous slag can be made by heating at approximately 100°C above the ash fluid temperature. The sintering temperature was almost the same as that of the amorphous slag obtained from a gasification pilot plant. This plant was designed to gasify 50 tons of coal per day. Although Fe in the ash heated to over 1650°C was reduced and separated from the slag, XPS (X-ray photoelectron spectroscopy) analysis showed that oxidized Fe existed at the surface, while a mixture of oxidized Fe and metallic Fe existed approximately 60nm below from the surface of the laboratory slag. The Fe distribution in the slag was confirmed to be the same as that for the amorphous slag obtained by coal gasification.

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A high-speed gas sampling method was used to analyze the local gas composition within the main combustion chamber of a lean burn gas engine with a 260mm bore. The spatial distribution of the gas composition and changes every crank angle were studied. The optimum design of a jet hole in the pre-combustion chamber was then investigated based on these results, with the aim of reducing CO and THC concentration and increasing the thermal efficiency. The engineering findings were evaluated by means of a performance test on a 6 cylinder engine.

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Exhaust HCs from spark ignition engines are considered a main source of photochemical air pollution. In this study the behavior of unburned HCs on the surface of the combustion chamber wall was investigated by a high-speed gas sampling technique during the expansion and exhaust processes. The mass of HCs near the surface of combustion chamber and that desorbed from oil on the combustion chamber wall were estimated with the models in which HC concentration profiles were assumed. When the engine was operated with ignition timing retardation and EGR, the quenching distances were lengthened and the mass of HC in the quenching layer was increased more than that of the operation of MBT and without EGR. It seemed that fuel absorption and desorption in oil could contribute to mass of unburned HCs in the combustion chamber in these operating conditions. The mass of HCs on the surface of the combustion chamber was not affected by the induction swirl that could increase the burning velocity and shorten the combustion duration.

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In order to reduce fuel consumption, smoke, noise and NO_x emission of the IDI diesel engine, the discharge coefficients of the jet passage and the jet in the main chamber were investigated, and a new combustion system for improving these characteristics was devised. As a result, the new combustion chamber with a refined jet passage, in which the jet passage angle inside the main chamber is smaller than that inside the prechamber, was very effective in improving the discharge coefficient of the jet passage, as well as the diffusion and penetration of the jet in the main chamber. Installed in the diesel engine of a utility vehicle and a passenger car, and tested, the new combustion system was proven to reduce the engine fuel consumption, smoke, noise and NO_x emission.

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Characteristics of combustion and exhaust emissions of a D. I. Diesel engine were investigated under various spatial arrangements of fuel sprays. The cylinder liner was elongated and a flat-too piston was installed in the engine to obtain a relatively large pancake-type combustion chamber. Six to twelve fuel injection nozzles with a single hole were installed in the elongated cylinder liner parallel to each other, and one injection nozzle with six holes was installed in the cylinder head. Such modification of the engine made it possible to obtain radial arrangement of six fuel sprays and parallel arrangement of six to twelve sprays in the combustion chamber. The parallel arrangement of six to ten sprays showed shorter ignition delay than the radial arrangement of six sprays. Changing from the radial arrangement of six sprays to the parallel arrangement of six sprays reduced NO_x and smoke emissions simultaneously and resulted in an increase in indicated mean effective pressure.

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