An experimental study of the turbulent flow due to a rotating disk in an infinite quiescent fluid was conducted. Using a single normal- and an inclined-type hot wire, the mean velocity distributions and all six components of Reynolds stress were obtained for various local Reynolds numbers Re_L(=γ²ω/ν). A log-law region, where the circumferential velocity profile shows a linear variation in a semilogarithmic plot, was observed at Re_L≥4×10⁵. The profile in the log-law region at Re_L=1.0×10⁶ was in close agreement with that for the flat-plate boundary layer. All components of the turbulence intensity, normalized by the friction velocity, were found to be considerably smaller than those for the flat-plate boundary layer, except very near the wall. The values of the structure parameter a₁ are smaller than those for the flat-plate boundary layer.

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A mathematical model is presented for numerical simulation of the fluid transients in the return line during the decompression operation of a hydraulic system. Particular attention has been paid to clarification of the influence of gas diffusion on the fluid transients because in such a system, part of the separation cavity consists of a gas-liquid two-phase flow containing a number of minute gas (air) bubbles. Experiments using sump oil and deaerated oil as a test fluid showed that the generation mechanism of the separation cavity and the fluid transients are significantly affected by the gas diffusion. Values calculated from the proposed "bubble-diffusion model", which takes into consideration the effects of gas diffusion as well as the amount of gas bubbles released from the oil flowing out of the valve before column separation occurs, the change of state of gas and the surface tension applied to the gas bubble, agreed well with the measured values over a wide range of tests.

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Development of planar mixing layers confined to expanding and reducing ducts was studied by a visualization system which enabled time-resolving two-dimensional concentration measurement. Water mist was used as a tracer and a laser sheet was passed through the planar mixing layers confined to expanding, parallel, and reducing ducts. The scattered light was detected by a high-speed framing image sensor, and analyzed to obtain instantaneous pictures and statistical quantities of concentration, such as mean value, fluctuation intensity, spatial correlation, and frequency spectra. It was found that a planar mixing layer in the expanding duct developed faster than in parallel and reducing ducts because the distance between roll-up vortices was reduced by decrease of the flow velocity and thus the interaction of the vortices became stronger. On the other hand, a planar mixing layer in the reducing duct developed more slowly due to the increased distance between the vortices and their weaker interaction.

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Constitutive equations regarding the drift flux model for a multiphase flow consisting of molten material and its solidified particles were thermodynamically derived under a condition of local quasiequilibrium. The basic equations, including the conservation equations and the constitutive equations for the multiphase flow, were expressed in dimensionless forms. The theory developed here confirmed that the temperature fields closely depended on the Lagrangian derivative of the solid fraction accompanying the latent heat effect, and was characterized by the Stefan number. It was also suggested that the simplified basic equations corresponding to the phase equilibrium diagram were useful in the analysis of multiphase flow with solid-liquid phase change.

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A numerical simulation of coarse particles of different sizes in a horizontal pneumatic pipe is carried out by considering particle-particle collision and particle rotation. A regular bouncing model is applied for both particle-particle collision and particle-wall collision. The pipe diameter is 40 mm and its length is 20 m. The mean air velocity is 20 m/s, and solid/air ratio is about 0.5. The particle floating mechanism due to particle-particle collision is examined based on the simulation.

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In the previous study, top flooding in thin rectangular channels could be characterized by using the wider span W as a characteristic length in the Wallis nondimensional velocity. To further study the flooding characteristics related to the span W, top flooding experiments in thin rectangular channels of different spans W were conduct-ed. When liquid penetration into the channels was small, the span W was the most important characteristic length. However, when the liquid penetration was large, the span W was not an appropriate scale. The nonuniform distributions of void fraction and velocity in the spanwise direction can be represented by the span W in the low liquid penetration region. However, in the high liquid penetration region, random penetration of liquid along the spanwise direction mitigated the role of W.

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Shock wave propagation over a perforated wall and the wall discharge coefficient through the perforation were studied experimentally and numerically. The experiment was conducted in a shock tube equipped with double-exposure holographic interferometry. The shock Mach number was 1.54 in air and the wall perforation ratio was 0.4. The numerical simulation was conducted by means of an upwind finite difference scheme using the TVD scheme. To determine the wall discharge coefficient through the perforation, the numerical result was compared with the experimental one. The wall discharge coefficient through the perforation was obtained as 0.54, and this value can be extended to the perforation ratio ranging from 0.1 to 0.5, a shock wave Mach number of 1.5 to 5.5 and a corresponding Reynolds number of 1.24×10⁵ to 9.78×10⁵.

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In order to measure the transient density distribution of the exchange process caused by a negatively buoyant jet, an automatic and high-reliability system has been developed. The upward jet of air into a box with helium was visualized using the Mach-Zehnder interferogram. The VTR images of the Mach-Zehnder interferogram are automatically analyzed by an engineering work station, resulting in the desired two-dimensional transient density distribution. The stratification of air and helium was clarified from the measured density distributions.

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This paper reports the injection of a supersonic diesel fuel jet by a compact gas gun. The diesel fuel was contained in a titanium alloy nozzle and sealed by a 1-mm-thick rubber diaphragm. A high-speed polyethylene projectile hit a brass piston located at the back end of the nozzle, and consequently, the fuel was pushed through a small nozzle hole to form a supersonic jet in air. The supersonic jets were visualized by double-exposure holographic interferometry. The influences of the nozzle diameter D, the ratio of nozzle length to nozzle diameter L/D, and injection volume on the diesel fuel injection were examined separately. A pressure chamber was designed for measuring the injection pressure. It was found that the rubber sealing diaphragm did not affect the amplitude and width of the pressure pulse caused by compression of the brass piston. The interaction between a supersonic diesel fuel jet and a solid wall was also studied. Photographs show that the reflection of the precursor shock wave of the supersonic jet from the wall surface may play an important role in mixing diesel fuel with surrounding gas, and producing a high concentration of fuel vapor.

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This paper describes measurements of pressure distribution around a semicone with a delta wing traveling at the hypersonic speed of Mach 10. The semiapex angles of the delta wing and semicone are 30 deg and 15 deg, respectively. The measurements are carried out under the conditions in which the angles of attack are 0 deg, 10 deg, and 20 deg. In this study, the pressure distribution measuring method using magnetic tape has been improved to be suitable for measuring pressure distribution around hyper-sonic vehicles. The pressure distributions are measured by utilizing the improved method.

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The purpose of the present paper is to investigate the steady and unsteady flows through subsonic and transonic turbine cascades using the Euler and Navier-Stokes (N-S) solvers developed by the authors. Use of the fundamental equations of contravariant velocity components also proposed by the authors is very convenient for treating several kinds of boundary conditions. Some efficient numerical schemes for the unsteady calculation, shock capturing and turbulent quantities are also developed. As numerical examples, we show the numerical results of some turbine cascade flows by assuming the flows to be inviscid or viscous (turbulent) and steady or unsteady. The results are compared with each other and with the experimental data. Finally, the reliability and the limitation of the present numerical solvers for the turbine cascade cases are discussed.

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A numerical method using a finite element approach is proposed to analyze the unsteady three-dimensional flow of power-law fluids with moving free surfaces. Based on the fractional step method and Rational Runge-Kutta (RRK) method for mass and momentum equations, this method is a semi-explicit scheme with unconditional numerical stability for pseudoplastic fluids. The transfer equation for the volume fraction of molten polymer is solved to calculate the moving free surface. The energy equation is divided into the transfer and diffusion equations. These equations are solved by a modified characteristic curve method and the RRK method, respectively. The calculation results are obtained by the present method for two box-shaped cavity flows. These are compared with the experimental results using a short-shot injection technique. Experimental and computational findings agree within 5% regarding location of the meltfronts.

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The integro-differential equation for a thin jet-flapped aerofoil was derived by Spence (Proc. Roy. Soc., London A-238 (1956), p.46). Its numerical and asymptotic solutions have been obtained, but the existence of solutions has not been discussed yet, since the governing equation is singular. In the present paper, we derive an integral equation of the Fredholm type of the second kind which is not singular from the original integro-differential equation. We further prove the existence and uniqueness of the solution and derive the asymptotic solutions. Comparing with earlier works, we show that earlier asymptotic solutions obtained by the method of matched asymptotic expansions are reasonable.

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Full measurements of the temperature field have been made in a turbulent flow of air through the entrance section of a two-dimensional curved channel. According to the experimental results, the wall heat flux develops more rapidly than the time-mean temperature distribution, decreasing and increasing on the inner and outer walls, respectively. Since radial locations at which the time-mean temperature gradient and the radial turbulent heat flux become zero do not coincide, the eddy diffusivity of heat becomes negative in a wide region extending about 20% of the channel width. In the vicinity of the wall, the temperature fluctuation intensity normalized by the friction temperature is not affected by the wall curvature, whereas the cross-correlation coefficients, the skewness and the flatness of velocity and temperature fluctuations are appreciably affected. The triple correlations relating to the transverse diffusion decrease and increase markedly on the inner- and outer-wall sides, respectively.

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Fully developed forced-convection heat transfer in a cylindrical packed bed is examined theoretically based on a two-dimensional, distributed parameter model incorporating the effects of non-Darcy, variable porosity and radial thermal dispersion. The validity of the present heat-transfer model is addressed in comparison with available experimental data. Several system parameters such as the Prandtl number Pγ, the ratio of the thermal conductivity of solid to that of fluidκ, the bed radius to particle diameter ratio Γ and the particle Reynolds number Re_p are varied systematically in the theoretical computations. It is found that the Nusselt number Nu_p at Re_pPγ→ 0 takes a constant value depending on bothκ and Γ, while Nu_p for large Re_pPγ depends on both Re_pPγ and Pγ, but scarcely onκ.

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The Wettability of a heated surface plays an important role in nucleate and transition boiling. In most previous research on boiling, the contact angle has been a common measure of surface wettability. However, because of hysteresis, measuring it from the shape of a liquid droplet on a solid surface has little meaning. In this research, the hysteresis of contact angle is studied theoretically, and effects of surface roughness, energetics and temperature on wettability are investigated experimentally by measuring contact angles of water on copper, aluminum, glass and Teflon surfaces under various conditions. As a result, a new method for evaluating surface wettability is proposed.

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Monochromatic radiative properties of anisotropically scattering fly-ash polydispersions in combustion gas, such as an extinction coefficient, a scattering coefficient, a scattering albedo and Legendre expansion coefficients for a phase function, are calculated by the Mie scattering computer code with the monochromatic complex refractive index measured and arranged in a wavelength region of 0.7∼13μm and with a measured or an estimated bimodal particle distribution of fly-ash. Extinction and absorption coefficients calculated for fly-ash polydispersions closely agree with the results obtained by a small-particle (x«1) approximation when the Sauter diameter D₃₂ for polydispersions is much smaller than the incident wavelength (x₃₂<0.1). They also agree with the approximations of the complex refractive index near 1(|m-1|«1) when D₃₂ is much larger than the wavelength (x₃₂>10) ; in the intermediate region (0.1<x₃₂<10), however, exact Mie scattering calculations are required.

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Flame-front propagation in a matrix of compacted Ti and C particles is studied experimentally, in relation to fundamental research on self-propagating high-temperature synthesis (SHS). The effects of mixture ratio, diameters of particles, relative density, and degree of dilution on burning velocity are investigated. Burning velocity has been defined as the flame-front velocity normal to its surface through the adjacent unburned condensed medium. Results show that there exist flammability limits, over which flame-front propagation occurs, and outside of which the flame cannot be self-sustained. The diameter of carbon particles is found to exert great influence on the burning velocity, while that of Ti particles presents no marked effects when particle sizes are smaller than the thickness of the reaction zone. Dilution with the combustion product is also shown to be effective in controlling the burning velocity although there exists a dilution limit beyond which the flame front ceases to propagate.

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The pressure dependence of the laser-induced fluorescence (LIF) spectrum of NO molecules has been investigated when NO molecues are excited by ArF excimer laser light of 193 nm. The fluorescence intensity of NO increases with increase of gas pressure, which originates from the collisional condition between the buffer gas molecules (N₂) and NO molecules in the B²Π(ν'=7) state. It is pointed out that characteristics of the pressure dependence of LIF and Rayleigh scattering can be used for pressure detection.

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An optical fiber thermometer (OFT) having a sapphire tip of 1.27 mm diameter sputtered with platinum as a sensor and heated to 1000°C was rapidly inserted into an air jet by using pendulum motion. The time constant, the heat-transfer coefficient of OFT, and the correlation of Nu=(3.07+0.529Re^0.5)Pγ^0.38 for Re=380∼1800 were obtained. OFT output shows a very slow response in the quasi-steady period but a considerably quick response in the transient period. Frequency response of OFT was investigated by Fourier analysis and analytical simulation was carried out to obtain the gas temperature from the temperature variation indicated by OFT. Such a high resolution of OFT in a commercially available size such as 0.1°C is found to be necessary for the measurement of gas temperature in an engine. The output signal of OFT should be cut off at the 30th harmonic by a low-pass filter, since the large error in obtaining the gas temperature is caused by the higher-frequency noise. A reduction error constant is proposed as a reduction error index.

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High-speed tomography for simultaneous measurement of a series of two-dimensional distributions of both temperature and density of species in the medium in a turbulent burnt gas is developed. The optical system consists of four sets of projections which simultaneously measure all the projection data by four photodiode arrays with each installed in respective projections for the acquisition of 35 sampling datums. The validity of the method is checked by simulations and by reconstructing the distributions of temperature and density of a pulsed flame jet. The temporal resolution is 1 ms and it yields a spatial resolution of 6.8 mm for a flame jet with a velocity of 3.5 m/s.

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Sauter mean diameter and air-entrainment characteristics of nonevaporating unsteady dense sprays are measured by means of an image analysis technique which uses an instantaneous shadow picture of the spray and amount of injected fuel. Influences of injection pressure and ambient gas density on Sauter mean diameter and air entrainment are investigated parametrically. An empirical equation for the Sauter mean diameter is proposed based on a dimensionless analysis of the experimental results in which Sauter mean diameter decreases with an increase in injection pressure and a decrease in ambient gas density. It is also shown that the air-entrainment characteristics can be predicted from the quasi-steady jet theory.

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Spark ignition properties of combustible mixtures under high-turbulence-intensity conditions were studied using an ignition device which was able to vary the energy of capacitance and subsequent inductance sparks, independently. The high-intensity turbulence field was generated by mutual collision of injected mixtures at the center of a cylindrical combustion chamber. From observation of schlieren photographs of flame kernel development, it was found that the turbulence had little effect on the flame kernel shape in the incipient stage of ignition process. The experimental results showed that addition of the subsequent spark to the capacitance one improved ignition ability especially under high-turbulence-intensity conditions, and that high ignition ability appeared with an increase in the ratio of the subsequent spark energy to the total spark energy.

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A method was proposed to represent the model-predicted burning velocities and flame structure parameters diagrammatically in three coordinates (Re-Da, η_K/η₀-u'/S_L0and L/η₀-u'/S_L0) so far used to illustrate turbulent flame structure phase diagrams ; this method was applied to three models by different researchers. By showing the same model in different planes, the model responses to turbulence characteristics and mixture properties were elucidated from different viewpoints, and by showing the turbulent burning velocities and flame structure parameters by the same model in the same plane, their respective relationships implied by the model were clarified.

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Microscopic structures in turbulent diffusion flames are studied by time-resolved temperature distributions measured by a laser-sheet-illuminated Rayleigh scattering (LRS) method recorded by a high-speed VTR system, and one-point LRS measurement. The microscopic structures of temperature distribution are measured by analyzing the two-dimensional LRS pictures by image processing. Coaxial turbulent diffusion flames at moderate Reynolds numbers, which exhibit typical diffusion flame structures, are formed on laboratory-scale burners. It is found that the flame can be divided into four characteristic regions based on the distributions of macroscale temperature fluctuations. These four regions are visualized by the two-dimensional LRS images. The turbulent heat-transfer mechanisms in these four regions are discussed in terms of the two-dimensional LRS and the power spectral density of temperature fluctuations measured by one-point LRS. Clusters of temperature inhomogeneity are observed by the image analyses in Regions I and III. It is found that different structures of microscopic temperature inhomogeneity exist within Taylor's dissipation length scale defined by velocity fluctuations.

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In the present study, a flow field developed in an opposed jet burner and its turbulence characteristics were measured in detail using a hot-wire anemometer. The flame structure was clarified by schlieren photographs and instantaneous temperature measurements with a thermocouple. Extremely strong turbulence of small scale is generated by impingement of two mixture flows. For the case of a low mixture supply velocity, a flame within the transition regime from a wrinkled laminar flame to a distributed reaction zone is produced in the opposed jet burner. With increasing the mixture supply velocity, the structure of the flame zone changes to the distributed reaction zone. These two types of structure correspond to those of region 2 and region 3 of the 3-region model of the turbulent premixed flame structure.

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High-intensity premixed combustion (0.71-1.12×10⁹ kJ/m³h) was achieved using an opposed jet burner. The NO_x emission was measured by an NO/NO_x chemiluminescence analyzer. Maximum NO_x formation measured was extremely low and varied from 20 ppm to 40 ppm, depending on the combustion intensity. Such a low NO_x formation is attributed to the short residence time and the structure of the distributed reaction zone. The equivalence ratio at which NO_x is maximized was found to be 1.3. The temperature dependence of NO_x concentration can be given empirically by an Arrhenius expression, and the apparent activation energy is small compared with that of the Zel'dovich mechanism. On the basis of these results, we can conclude that the contribution from the Zel'dovich mechanism is suppressed in the distributed reaction zone and that the NO_x originating from prompt NO is predominant.

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The postflame reaction zone structure of a lean-burn flame was studied by two-dimensional consecutive imaging of flame chemiluminescence using an image intensifier with short-decay phosphor. Quantitative and statistical analyses were performed to elucidate the effect of tumble and charge stratification on the flame behavior. It was found that in the early stage of combustion, significant air entrainment enhancement was realized by tumble but its effect on eddy burning was small. After the completion of flame propagation, however, tumble activated the eddy burning process. Charge stratification activated both air entrainment and eddy burning. These phenomena could be related to the flow field structure after the collapse of tumble. A procedure to derive the tomographic image of the reaction zone was proposed. It was found that under a uniform mixing condition, no reaction-zone structure was observed. When charge was stratified, however, an annular postflame reaction zone was observed behind the flame front.

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In this paper a numerical technique is presented to predict the image of a free flame in the visible spectrum range from the computational results obtained with a fluid flow and combustion code. The numerical technique is composed of two sub-models. The first one is a mathematical model based on the solution of the time-averaged form of the conservation equations for mass, momentum and energy. The output results are used as input data for the second submodel which is able to predict the flame image/brightness. This submodel is based on the integration of the radiative heat transfer equation along selected directions. The basic assumption of this submodel is that radiation is mainly due to soot in the visible range of the spectrum. The model was applied to a turbulent propane free flame for which experimental temperature measurements and digitized flame images were available. The predicted temperatures are in reasonable agreement with the experimental data, and the shape of the predicted flame image is qualitatively similar to that of the digitized flame image. Overall, the model proved to be a useful engineering predictive tool for numerical visualization of sooty flames.

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Knocking in internal combustion engines causes various problems such as increase in thermal loads, abnormal wear and the deterioration of performance. Even the mechanism of thermal loads alone has not been clarified yet. In this study, therefore, instantaneous temperatures on piston top surfaces of a four-stroke gasoline engine during knocking, caused by changing the spark timing and octane number, have been measured using highly accurate thin-film thermocouples. Conditions of heat losses dependent on the knock intensity have been clarified from the instantaneous heat fluxes and coefficients of heat transfer determined from measurements.

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The characteristics of prechamber lean burn were researched by using a high-speed, small single-cylinder engine. The prechamber system can run on a leaner mixture than the open chamber because the ignition lag of the prechamber and combustion period are very short and remain constant in spite of changing A/F. When no gas is supplied to the prechamber, the effect of the shape of the main chamber is relatively large. However, when gas is supplied to the prechamber, the effect of the main chamber on the combustion period is relatively small. The strong squish decreases the combustion period, but NO_x is reduced. Then, THC is increased by the large squish area and the high swirl.

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